# Refining of Gold from Mines



## ashapura refinery (Apr 23, 2015)

Hi.

I have received gold from mines. The weight is 10 Kgs and I want to refine this mining gold. 

The Contents are:
Gold - 92.45%
Silver 7.25%
copper 0.15%
iron 0.11%
other metals 0.04%

Now I want to remove only silver, copper and iron without using the aqua regia process. Can we use the nitric acid in this or is there any other process other than aqua regia and the electrolyte process which I can use for the refining??


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## 4metals (Apr 23, 2015)

Generally this type of material comes to a refinery in bar form. It has already been through the process of concentrating and the resultant material is usually referred to as mining doré bars. 

Your quantity of material is relatively small, is it something you will see a lot of or something you will process this time and do not know if it will be a continuous feed?

Why do you want to avoid the aqua regia process?

We know relatively little about what your refining capabilities are at your refinery and what you normally process. If we knew what you are currently capable of refining and how you are equipped, likely we can give you some scenarios for processing this material. 

I see a lot of this material and have many paths you can follow to process it, however the best fit for your refinery depends on how your refinery is currently equipped.

So answer these questions and we can get a dialogue started here and a good number of our members can benefit from the discussions.


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## ashapura refinery (Apr 24, 2015)

@ 4 metals:

Our main activity is to refine the gold which we get in the form of dore bars or scrap gold and also silver. We have a refining capacity of 30 Kgs Gold and 100 Kgs Silver this can reach up to 75 Kgs Gold a day. We have started this refinery few months back.

And we have done refining of some batches using the aqua regia process but we have incurred losses. The first batch was of 11 Kgs and we lost 280 gms, second batch 12.5 Kgs, we lost 400 gms, third batch was of 9 Kgs we lost 160 gms and the fourth batch was 12.4 Kgs and we lost 100 gms - The total loss is 940 gms. Now we have kept all the solutions and added stannous chloride to it along with caustic soda (lye form) and recovered 500 gms but we still have a loss of 440 gms. 

We still have all the solutions which is approx 5000 Ltrs. 

We have hired experienced chemists who have worked on these processes and they are also very much confused as to what is going wrong. Due to these losses we now fear re-doing the aqua regia process and want to try some other method. 

We are listing down our steps of refining just to be more clear. 
Our steps for Refining 12.4 Kgs of Gold Dore:

1) Melting the Dore bar in the induction melting machines.
2) Assaying of the gold through fire assay method and the X-ray method
3) The bars are then re melted for making the grains in the induction melting machines. (Picture attached)
4) The grains are then put in the mixing reactor ( Picture attached)
5) We then added Nitric Acid (72% CP Grade )- 12.5 Ltrs and HCL - 36 Ltrs (33% CP Grade)
6) After the completion of the aqua regia process, we had undissolved grains of approx. 70 gms. 
7 ) Then we filtered the aqua regia solution and removed the silver chloride and in the chemical we added soda ash to get a PH level of 7. Then we added sodium metabisulfite and filtered the fine gold powder. We received 11.287 Kgs Fine gold after melting, the purity of this gold is 999.22 
8 ) The solution is then stored in the glass beakers (Glass beakers of capacity of 200 Ltrs)
9) After 2 days we added stannous chloride and caustic soda to the solution and recovered 20gms

In this batch we have lost approx. 100 gms. 

I am attaching pictures of the following:
1) The refinery structure
2) The Gold Dore Bar
3) The gold grains formed after the melting for the refining process
4) The mixing reactor
5) The fine gold bars

Now we have one more batch coming in but this time we don't want to use aqua regia process and want to try some other method apart from aqua regia and electrolyte process.


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## Barren Realms 007 (Apr 24, 2015)

What is the average purity of your starting gold?

Have you processed your silver chloride into metallic silver and then processed this through a silver cell?

You did not mention anything about inquarting your gold so my guess is you started your process directly with AR?


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## ashapura refinery (Apr 24, 2015)

@ Barren Realms:

When the gold is sent to us an assay test is done and the assay test report is sent along with the gold and after we receive it also we do an assay test before starting the process so this generally gives us an idea of what is the percentage of gold content and what other metals are present in it. Generally the purity of the gold we receive ranges between 920 to 930. 

And yes we process our silver chloride further. We use zinc powder to recover the silver but we are not 100% satisfied with this process as well because we get a purity of 996 or 997 and we require a purity of 999.


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## butcher (Apr 24, 2015)

1) Melting the Dore bar in the induction melting machines.
2) Assaying of the gold through fire assay method and the X-ray method
3) The bars are then re melted for making the grains in the induction melting machines. (Picture attached)
I would look into adding silver to the melt quarter the gold with silver, and parting the gold with nitric acid
4) The grains are then put in the mixing reactor ( Picture attached)


5) We then added Nitric Acid (72% CP Grade )- 12.5 Ltrs and HCL - 36 Ltrs (33% CP Grade)

For 1240g gold (pure) it should take about 4.7liters of HCl and about 1.18 liter of HNO3.
Looks to me you're using much more acid than needed, you do have impure gold, and are not parting it but even with that, it seems such a waste of acid causing trouble in later procedures...

6) After the completion of the aqua regia process, we had undissolved grains of approx. 70 gms.

Have you tested this material for some of your loss in values? 

7 ) Then we filtered the aqua regia solution and removed the silver chloride and in the chemical we added soda ash to get a PH level of 7. Then we added sodium metabisulfite and filtered the fine gold powder. We received 11.287 Kgs Fine gold after melting, the purity of this gold is 999.22 

Why use soda ash Na2CO3 to try to neutralize the acid, it will make salts of the acid, like sodium nitrate and sodium chlorides.
2HNO3 + Na2CO3 --> 2NaNO3 + CO2 + H2O
2HCl + Na2CO3 --> 2NaCl + CO2 + H2O
These salts would again make a form of aqua regia to keep gold in solution if acid was added. 

I do not see the need to get the pH to neutral (you just need to get rid of excess nitric acid), you can do that by several means, not using more acid than needed, evaporation with added gold, sulfamic acid...


8 ) The solution is then stored in the glass beakers (Glass beakers of capacity of 200 Ltrs)
9) After 2 days we added stannous chloride and caustic soda to the solution and recovered 20gms

Why would you add stannous chloride and caustic soda?
You stated above you lowered the pH to neutral, are you trying to make this solution caustic? trying to precipitate base metals? Stannous chloride if gold was involved can form colloidal gold, making recovery of that gold from solution harder to recover...


In this batch we have lost approx. 100 gms. 

I am surprised with the methods above your losses were not much higher.
How do you know for sure how much gold was in the dore bar to begin with, are you using testing of the insoluble, and solutions to find where you are losing the gold? With the method your using even testing the solutions for gold would be hard to do.
I see so much I would do differently, in your process.

I believe if you study Hoke's book and the forum, you can come up with a much better solution, and process to recover your gold from the dore bars.


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## 4metals (Apr 24, 2015)

Considering your equipment setup, the process you should use is aqua regia. The QVF glassware you have is nice equipment but I have concerns. 

First off let me say I would not be inquarting the material in silver. The gold assay and the existing percentage of silver in the feedstock should allow for good recovery. 

I am not a fan of the bottom drain in the glass reactor because the shot you digest often gets hung up in the drain section which minimizes its exposure to acid and can result in incomplete digestion. The 70 grams of undissolved metal you referenced likely was in the neck of the drain and could not take full advantage of the acid in the reaction due to limited circulation in the tight space.

You do not include pictures of your condenser setup. There is always an exhaust on these reactors and you are using aqua regia at 3:1 so you get an aggressive reaction. It is possible from seeing the level of solution in the vessel that an aggressive reaction combined with non condensed exhaust or excessive exhaust will result in sucking values out with your exhaust. Please provide photos of your condenser setup and some figures of airflow exhausting the system. 
I would immediately drop the acid to a 5:1 ratio if you are using a condensed reactor. 

Typically solution after precipitation holds about 2 PPM as gold. Your solutions are holding greatly in excess of 2 PPM. You will enjoy much greater success if you do not add too much nitric acid. I do not like your precipitation methods either. I would be neutralizing any extra nitric acid by adding sulfamic acid and gassing the gold out with sulfur dioxide. It will produce a cleaner gold. Gold is normally precipitated until it tests negative to the stannous chloride, the amount of gold you are carrying over into waste should be indicated with a normal stannous test. What formulation of stannous chloride do you use? 



> After 2 days we added stannous chloride and caustic soda to the solution and recovered 20gms



This is another technique I do not like. For one stannous chloride is not a means of recovery. You add it to recover gold? 

I notice in your photos of the tall cylindrical reactors a light blue liquid in the reactors in the background. Is that the result of your addition of caustic soda? If so, you have formed a copper hydroxide slurry which will only allow the recovery of the gold if it is dried and crushed and sifted and processed by a copper smelter. What is the source of the light blue liquid?

So in summary, there are a few places we can look for the gold. 

One is up the stack with the exhaust. Your reactors need condensers and you need to allow the fume to escape by the ambient pressure of the vessel not be sucked out. 

Two is in the copper hydroxide stannous chloride combo you are using for recovering waste liquids. The cementation metal of choice is copper but given the minimal base metals in the feedstock zinc dust will suffice. Do not attempt neutralization with caustic until all of the metals have been recovered by cementation. 

Three is in the silver chlorides. Reduce the metal and fire assay for gold, it is easy to figure out if it is in there. 

Finally four is employee theft. Nobody likes to think about this but I have seen it in refineries all over the world. After your gold is produced into grain for dissolution do you dry and re-weigh it? Are you absolutely sure all of the metal actually entered the reactor? 

I can assure you with the equipment you have you can achieve 99.9 % recovery with aqua regia using the right methodology and addressing the 4 areas mentioned above. 

Get back with answers to the questions I have asked and we can continue.


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## Lou (Apr 24, 2015)

I think most of it is probably in the AgCl; the rest in the exhaust lines, presuming we have no theft issues.

Without actually being there to play Sherlock Holmes and audit the whole process, my thoughts:

Been to several refineries on accountability mass balance audits that were losing values to the waste solution b/c of poor instrumentation/analytical. 


@ashapura refinery:

--Do you have AA or ICP spectroscopy to check your filtrates? You need one! What about the PGMs left in the mix and any gold?! You need to at least put in a resin recovery system (think purolite S920 thiouronium-functionalized chelating resin for Pd/Pt/Au)
--Also, be sure to rinse the silver chloride residue after discharging the reactor; rinse with 0.5M HCl. Regarding the bottom drain hold up 4metals mentioned, if you ordered the right QVF stuff, it should have a zero dead space PTFE valve in there which doesn't hold the grain.
--DeNOx the solution with sulfamic acid before filtering; it generates sulfuric acid as the nitric oxidizes it to N2O and the sulfate precipitates lead as its sulfate, improving the assay on your gold.
--Also, be sure to dilute your chloroauric acid with water to decrease the solubility of [AgCl2-] complex in the reactors and consider adding a cationic flocculant after the nitrates are gone and it is diluted; it will help get the fine particulate silver chloride to agglomerate and aid in rinsing. All of that solution should go through staged 30 micron, 10 micron and 0.5 micron polypropylene filter cartridges. When the gold is rinsed off of those, they can be cleaned periodically with ammonia or thiosulfate solution and then* well rinsed with water*. That will declog them. 
--Precipitate the gold with SO2 gas, checking with stannous for completion. That gold should be rinsed with 6M HCl, then c. ammonia water, deionized water at a minimum. Tumbling with hot 70% sulfuric, or batch sonicating, will improve the purity over 4N unless you have Se/Te in your feed (which you can blow out mostly in the melt).
--Also, have a dedicated cell for the AgCl material--don't convert with carbonate, much better to get a plastic tumbler and use iron rods or clippings and 10% sulfuric. When it looks all good, then take a 10 g sample to melt to ensure conversion. Mix with some borax and look for the telltale metallic slag that AgCl gives. If it's good to melt, remove the iron magnetically, rinse the silver cement powder with water, then a solution of carbonate/borax, suck it dry on a filter (or filter press it if you're doing 5-10K ounces batches). That can then get melted, well stirred and sampled with a vacuum pin tube. Roll that flat and analyze the silver by titration and the gold content gravimetrically. Off to the cell house to get the last gold.


I see no reason why you shouldn't be making a consistent 99,993+ pure gold out of your refining circuit with your equipment. But if you don't have ICP and a good analyst, you'll have issues hitting the ASTM or ISO specs for that product. Doubt it makes much of a premium, but it's always better to be above spec on your metals than just barely hitting them!


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## 4metals (Apr 24, 2015)

Lou said;



> Regarding the bottom drain hold up 4metals mentioned, if you ordered the right QVF stuff, it should have a zero dead space PTFE valve in there which doesn't hold the grain.



In the picture shown, the stub above the valve, below the vessel, gives quite a bit more than zero dead space. It will fill up with shot and pack even tighter with chlorides as the reaction progresses. I believe the white teflon center shaft is for a stirrer, although I have seen plugs made that look like this specifically to prevent material accumulating in the void we are discussing. Can't really see but based on the top connections outside the reactor I'll bet a stirrer. 

This is what a Deadspace free bottom valve looks like. They close from the bottom and opening the valve unplugs the bottom drain and allows flow out the side outlet. 




The pictures submitted by Ashapura refinery show a case of right equipment and wrong chemistry. Although the chemistry works, there are more efficient ways. 

High purity and excellent accountability is attainable with this setup.


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## ashapura refinery (Apr 25, 2015)

Thank you all for replying to the post. 

We have attached some more pictures of the setup including the condenser unit maybe this will give a clearer idea of the setup.

And we looked around for sulfamic acid in the area where we are but its not available. Now in this case instead of sulfamic acid and sulphur dioxide gas can we go for some other alternate? Would sulfuric acid help?

Stannous chloride - We generally use 30 gms of stannous chloride powder and mix it with water to make approx. 1 ltr of the solution and then add it to the leftover solutions for recovery of the metal.

@4Metals - Sir, the unit you saw with the blue color is the scrubber unit with the raschig rings. We have attached a picture of it. 

And as far as theft is concerned ... we thought about it too and maybe this time when we process our material we will keep all our eyes open so that we can rule out this one factor for the losses 

EDIT : We forgot to mention a few details in the previous posts:

1) As mentioned in the replies - the possibility of the grains being stuck at the neck of the reactor - we generally cover the bottom neck of the mixing reactor with borax and the mixing reactor has a continuous stirring mechanism in it. When the mixing happens the borax does not get dissolved or mixed with the solution. And when the process is done and we open the drain valve the borax comes out with the rest.

2) We do not heat the HCl or the Nitric Acid before adding to the reactor or when the process is happening.


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## goldsilverpro (Apr 25, 2015)

Sulfamic acid should be available from any supplier of electroplating chemicals and equipment.


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## 4metals (Apr 25, 2015)

My first impression, after seeing your setup and going back and reading your previous posts leads to a question.

Why did you set up such a process specific piece of equipment? (which likely cost you quite a sum of money) And please tell me whomever sold you the equipment did not provide the methods of refining you are using. 

If you have a refinery where you are seeing one type of feedstock, day in, day out without significant variation, I would not have issues with the equipment you have. I would have issues with the chemistry.

These units are made to completely eliminate the handling of the acids and set up to transfer between units or process modules by vacuum. By doing that, you limit yourself by not having versatile equipment. In today's refining environment a refiner needs versatility, sadly your equipment is single purpose. 

That said, it is what it is. Now we have to come up with a procedure you can follow to get the most from this equipment. 

From your pictures, I see your bars are stamped .995. That is good gold delivery purity, and quite easy to attain with a single pass in your system. 

Lets address the potential for losses first. In the fume coming off the reaction the condensate from the condenser is collected before the packed towers. The photos do not show this collection vessel but it should be there. I see it now in the smaller photos when I blow them up, the condensate is collected in this vessel. Do you collect a lot of liquid in there? Have you ever tested it with stannous chloride?  This is where I would look first for gold in solution. The second liquid I would check is the sump where the fluid pumped over the tower packing is held. Check both with an AA for gold. This system is a low air flow design so the retention time in the fume scrubber is high, that is good for pollution control and likely you are not over drawing fume from the reaction vessel. 

In your photo you show an elevated vessel for storage of nitric acid and hydrochloric acid. Do you mix the acids in this single chamber before adding it to the reaction vessel or do you add all of the required hydrochloric first and then refill with nitric and add as needed? From what you said earlier, this is likely where you mix the two acids before adding it to the vessel. This allows for no variation in nitric additions and contributes to your problems. You are definitely over adding nitric and causing issues down the line. 

Suggestion, fill the reservoir with all of the required hydrochloric acid and add it all to the reaction chamber. Then draw up the entire quantity of Nitric calculated for the batch and add about 1/4 of it by eye to kick off the reaction. As the reaction slows, add additional fractions of nitric until additions no longer cause a reaction. This requires an operator to be able to see the reaction taking place and make adjustments based on what he has learned about the process. This equipment, QVF glassware, is ideal for observation. (QVF stands for Quick visible fit.) Less nitric added here means less problems later. Ideally you will not use all of the nitric, the setup as I see it has no drain to remove unused chemical from the reservoir. You need the ability to do so. A water rinse into the reservoir to facilitate rinsing between chemicals would be nice too. (This becomes critical if you do silver dissolves for silver refining.)

When the reaction is complete you will add the sulfamic acid. If you were not in a tightly closed vessel I would suggest (reluctantly) urea as an alternative (as you have not mentioned recoverable platinum group metals in the material) but it is not an option in a closed vessel, potentially too violent a reaction. I would scour the industry for sulfamic acid. It has a wide variety of uses and it must be available in India. It goes by other names as well or just use the formula H3NSO3. A tip that Harold uses is to add refined gold which will react and consume the remaining nitric acid. Considering you are having issues with accountability, adding gold may not be wise at this point so you could substitute copper. The goal here is to react all of the nitric out of the solution. If you add copper (or gold) allow it to react but do not add any additional nitric. Sulfamic acid is the best approach, everything else is a band aid fix. 

Note; Harold's method of adding gold involved suspending a weighed quantity of refined gold in bar form in the solution and removing it and re-weighing when the acid no longer reacts with the gold. By weighing the bar before and after, you can figure how much additional gold was added so your accountability isn't screwed up. You will have trouble suspending a bar in these vessels to do this so I would be adding small increments of copper metal powder until they no longer react. The excess copper will come out with the insolubles. Just be careful not to add too much copper as to displace gold from solution. Again the less excess nitric added, the less you have to mess with this. 

After adding the sulfamic acid (or reacting with added copper) you will filter out the chlorides. Reduce them as Lou suggested in sulfuric with iron and melt into bars and check for gold by gravimetry. If you added a substantial excess copper to the reaction to kill the extra nitric it will lower the purity of the iron reduced silver.

Finally on to precipitation. The filtered solution is in another vessel where you can ideally gas with SO2. Sodium metabisulfite is an acceptable second choice but I would strive to do it with SO2. If you could, please post a photo close up of the precipitation vessel you are using. If you have removed all of the nitric acid, the SO2 or metabisulfite is all you need to precipitate the gold. Experience will teach you to look at the solution and know when all of the gold is out, then even an experienced operator should always check with stannous chloride to be certain. The precipitation vessels you have need access ports for additions and testing so photos would help.

You should have all of your gold precipitated now with the exception of a few PPM which remains in the waste. Allow it to settle and collect the gold, wash it well as Lou described above.

That is it for gold recovery. Your treatment of gold in the wastes with stannous chloride will likely wake me from a sound sleep in a sweat! That is insanity from a recovery standpoint, a refining standpoint, and where that method came from I would like to know. 

I will continue with this later this evening, I am still kind of in shock having seen your equipment and read your methods. I assure you if you continue to detail your process, we will get you on the proper path. We can't help you with what we do not know. For instance, who would ever assume you recover gold from waste with tin? Had you not told us, we could not help you get it right.


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## 4metals (Apr 25, 2015)

I just looked again at the tanks you have for settling the solutions after precipitation. The sight of them, and the knowledge of what they cost, makes me cringe! Whom ever sold you these tanks for the express purpose you are using them deserves to be castrated! And I'm being nice! 

Let me explain what you are trying to do and how it is normally done. The solution needs to go into a holding tank where any small quantity of gold that passed through the filtration can settle and further cementation of values can take place. To do that, you need a vessel that can hold the quantity of solution and ideally it is covered. You also need a means of getting the solution into that tank. I assume you either pump or use a vacuum to fill these tanks with the spent acids. Then you need the ability to suspend copper in the vessel and agitate the solution. I do not see an access port to put the copper into the vessel or any means of agitation. Then, after the cementation is complete, and you have tested the liquid to see if there is any stain indicative of values in solution, (again using the access port to draw the sample to test) the solution needs to settle. Usually after a day of settling it is advantageous to not have to filter the entire volume, for that reason most have a drain valve on the side just above a conical bottom so the clear liquids can be drained off without filtration. Then the bottom drain can be opened and all of the metals which have come out of solution can be filtered. Your equipment only has the bottom drain. Typically a tank for this purpose would look like this;


These tanks are typically not very expensive and I would say you would pay substantially less than what you spent on one of your tanks for one of these big enough to hold the same volume as all of yours. 

Now let's address the combination of what you did and the equipment you did it in and how it likely is the result of your lost gold. 

To start with you likely added an insufficient quantity of metabisulfite to drop the gold in the precipitation vessel. Before the solution is discharged from the precipitation process, it needs to be agitated for two reasons. First it is very possible that when gold starts dropping it traps solution saturated with gold under the precipitated gold and this solution can be holding gold even as the solution above it tests negative. Always agitate to assure the gold solution trapped on the bottom is free of gold in solution. Second reason for agitating is you want the solution you sample for stannous chloride testing to be representative of all of the solution in the tank. When you think all of the gold is dropped, open the sample port and take a small beaker full of solution and add a drop of it on to a paper towel or wet a Q Tip with it and add a drop of stannous chloride to the wetted towel or Q tip. If the test indicates the solution is barren of gold, you have added enough metabisulfite and the solution you pump out of the tank should only contain a few PPM of gold in solution. 

I suspect you added insufficient metabisulfite and allowed your gold to move on to the holding tanks. Testing as described above will eliminate this problem in the future. 

Let's talk about your method of recovering the gold from the waste tanks. First off we need to talk about Purple of Cassius. It has been around since God was a boy, it was used to make dye by the ancients and it is made by reacting gold chloride with tin chloride to form a colloid of gold made of elemental gold and tin oxide. Great for indicating the presence of minute quantities of gold in solution but not great for recovering it. You formed a colloid which does not like to settle, which does not like to filter, and which loves to clog your filter media. You formed that compound and eliminated any potential of complete gravity settling, meaning you had to pump the entire volume of liquid through some sort of filtration device which you have not shown us yet. Any gold that was caught in your filter media is the gold you have reported finding, undoubtedly you passed a substantial quantity through your filter media and it now resides in your waste. Your waste (as a metal hydroxide) likely contains the remaining colloidal gold.

Please send us a photo of your filters for collecting the gold precipitated from the concentrated solution as well as your filtering mechanism for the recovery of solids from the waste holding tanks. In addition if you detail your waste treatment process we can see if the remaining gold is recoverable.


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## g_axelsson (Apr 25, 2015)

This reply was written a coupe of hours ago, before the two last replies of 4metals, and I wrote some that now is a repetition but I post it in full anyhow. There might be a few points that 4metals haven't taken up

Göran



This was one of the most interesting threads in a long time. To actually see how a big refinery is doing it is fascinating and then reading Lou and 4metals comments about the equipment. Pure gold!

ashapura refinery, I can only remember once before in the history of the forum that someone used tin chloride to precipitate gold and if I remember correctly it was agreed that it was a bad idea. What we all use tin chloride for is to test for gold dissolved in solution. When added to a gold chloride solution it is creating a colloidal gold solution with a very specific purple colour. 

Some recommended reading :
http://www.goldnscrap.com/index.php?option=com_content&view=article&id=63:stannous-chloride-test-for-gold-platinum-and-palladium-presence&catid=25:scrap-gold-9k-24k&Itemid=20
Point 10 in http://goldrefiningforum.com/phpBB3/viewtopic.php?t=562#p4766
Chapter 9 in Hoke : Identifying metals in solution : http://goldrefiningwiki.com/mediawiki/index.php/Hoke:Refining-Page-088

When testing you take a small sample (spot plate, q-tip or a drop on filter paper) and test, you don't add the tin chloride to your batch as it could create a colloidal solution that will never settle and doesn't show up when testing with stannous. Maybe your gold is held up as a colloidal solution.

Since you don't denox your solution (removing nitrates, not only nitric acid) but only adjust the pH to neutral the SMB precipitates the gold but a byproduct of SMB is sulfuric acid which lowers the pH and creates an environment where nitrate and chloride salts yet again can dissolve gold. That is probably the reason you can't get all the gold to precipitate at the first instance.
What we teach on the forum is one or several of these methods work:
- Do not use too much nitric acid, add nitric incrementally until most of the gold is dissolved
- Remove excess nitric by denoxing (ie repeated evaporation and addition of hydrochloric acid or addition of sulfamic acid)
- Addition of extra gold to use up any excess nitric acid

I have measured the amount of nitric acid I needed to dissolve 54g gold once and only needed 150 ml HCl and 28 ml HNO3 and only used a watch glass as reflow to capture and return acid vapours. Converted into your numbers it would mean 12.5 kg would take 17 liters of HCl and 6.5 liters of nitric acid.
Maybe it doesn't scale up that well but to me it sounds you are using too much acid for the work and get problems down the line.

I'm just an amateur and have never worked with larger batches so read my comments with that in mind. 4metals and Lou on the other hand is well seen professionals with a lot of experience so I advise you to listen to their advices, something they usually charge people for but here on the forum you get their advice for free. That's quite amazing.

Where are you located? Sulfamic acid shouldn't be hard to find. For example from your name I would suspect India and 30 seconds after googling for it I ended up at
http://www.ravirajchemicals.com/products-sulphamic-acid.aspx
If you put your general location in your profile then you might get better advice from local members.

Göran


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## Anonymous (Apr 25, 2015)

Guys I am stunned reading this thread. More than stunned I am humbled. The advice and help the OP is getting here is brilliant.

The pictures are brilliant, I nearly fell off my chair looking at them.

OP if you are not already aware you have at least 2 professional refiners helping you here who have a wealth of experience and knowledge far beyond anything I will ever achieve. You're a genuinely fortunate guy. Good luck with this.

Jon


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## Palladium (Apr 25, 2015)

ashapura refinery said:


> We have hired experienced chemists who have worked on these processes and they are also very much confused as to what is going wrong.



Well there's your problem right there! Chemist don't know how to refine gold! :twisted: :twisted: :twisted: 
Using smb are they diluting before the drop?


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## Anonymous (Apr 25, 2015)

Palladium said:


> Using smb are they diluting before the drop?



There's more than school of thought on that mate. Some prefer to drop very dilute whilst others have stated they prefer highly concentrated.

Regards

Jon


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## Palladium (Apr 25, 2015)

It was meant because more water with smb = more room for gas absorption. You don't always get a complete drop at one time from a concentrated solution. You need water to grease the wheels. First drop diluted to filter the chlorides, 2nd refining concentrated for the drop. Here he's only doing one filter before the drop so I'm betting some chlorides are rolling over to the drop. In the 2nd refining it shouldn't matter that much from a concentrated solution, but I think he's doing a one drop process so to me it makes sense. He might get it in the clean up of the gold afterwards, but an efficient process should will remove it before it ever get down stream where it has to be handled.


I would like to hear more about the silver side once they get on track with their gold. The silver cell is going to be important in this environment not only for the silver, but for the gold residues.


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## Lou (Apr 25, 2015)

Palladium said:


> ashapura refinery said:
> 
> 
> > We have hired experienced chemists who have worked on these processes and they are also very much confused as to what is going wrong.
> ...




Hey! I resemble that remark! I'm a chemist and darn proud of it but I only know a little bit about gold refining :mrgreen: 

Too bad I didn't get hired; I'd have _loved_ to visit India


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## 4metals (Apr 25, 2015)

For some reason, refiners have been a closed mouthed group for a very long time. The concept of refiners helping refiners that is exhibited in the spirit of this forum is rather unique. 

A degree in chemistry did not teach me refining. It prepared me to learn the science of refining, and as I said it is not something often spoken about. Successful refiners don't want competition. It comes as no surprise that an experienced chemist could miss some of the points we have discussed, refining is a science combined with a hands on experience where an operator learns by seeing, and doing. Not necessarily from reading. In my mind a good experienced refiner is also an artist. 

As Göran pointed out, sulfamic acid is available in India and it is worth finding a source. Sulfur dioxide gas would also be good to find. The difference in your end results will make the search and acquisition of both of these chemicals worth the effort. 

I have been thinking why Ashapura would have as many 200 liter vessels for holding the solution after precipitation and I believe it is to maintain batch accountability through to waste cementation. The cost of the individual vessels and the support stands and connecting plumbing is considerable. By keeping every lot separate they have the ability to re-check the waste liquors for values. I feel that implementing the methods we already discussed along with assays of outturn, the long term holding of individual waste batches will not be necessary. 

I also believe in batch accountability, but after assay of the outturn of fine gold, and the assay of the silver bar for gold, an allowable loss as high as .15% for a small refiner is acceptable and these values are usually recoverable in the residues at a later date. So I believe that after a preliminary short term holding of waste liquors, they can be combined with waste liquors of previous lots all of which have met the accountability standard. (99.85% of assay) Then the wastes can be cemented and harvested in economical sized batches. 

One issue in maintaining tight accountability standards is the ability to assay to the required precision with proof corrected fire assays. This is critical, as some alloys have high proof correction factors and if they are not determined and applied properly you may be looking for gold that was never there. We can go over this if you have questions. I like to see labs that I work with participate in the ASTM round robin fire assay program to learn, and monitor, how precise your assayers are. In addition the LMB runs a proactive monitoring program (PAM) for all refiners certified to produce good gold delivery bars. Good analytics is the foundation of good accountability. 

I would like to hear the waste treatment process used at Ashapura to figure out how the metals already lost to waste may be recovered. Do you have pictures of your neutralization process and filter press for retaining the solid hydroxides from waste treatment?


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## Lou (Apr 26, 2015)

I've made a simple flow chart to demonstrate the process steps. Note that it is not fully complete, but is a general conceptual example of what needs done and where material must flow. The Devil remains in the details. 


Note that much of this is similar to if the Miller chlorination process were used. The silver chloride slag bail off is dumped into water, leached with HCl/NaClO3, centrifuged, and then converted and run through cells. I'm not a fan of Miller for the most part.


Lou


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## 4metals (Apr 26, 2015)

Excellent flow chart Lou.

One thing Ashapura should note. They are stamping their bars .995 from the photo early on in the thread. The procedures we are outlining will produce gold in excess of .999 and if he does the sulfuric pulping process he will attain .9999. (Barring the presence of Selenium or Tellurium in the feedstock) That means for every kilo bar they produce, they will be giving away 0.5% of gold. 

0.005 X 32.15 = .160 ounces of gold at $1200 an ounce that's $192 extra value with every kilo out the door. 

They have to be careful to either alloy down their .9999 product or get a new stamp and charge for .9999.

Considering large refineries don't even charge 0.5% for refining these days, that can be a make or break deal!


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## ashapura refinery (Apr 27, 2015)

We are definitely very fortunate for having such great people out there helping us through this entire process. We sat down yesterday and took note of all the points listed out.

To begin with:
This is a completely new setup. And we had a chemical engineer who had previously worked in one of the gold refineries in the Middle East. And the practice of using Soda ash after the silver chloride removal is very common there. What they do is after the aqua regia process (ratio being kept at 3:1), they remove the silver chloride, add the soda ash to the solution and Sodium Metabisulfite to precipitate the gold. Once this is done they further add caustic soda in order to recover any left over material. Now this is being followed in refineries who refine 200 Kgs to 800 Kgs of gold on a daily basis and our chemists who work here had been previously working in one of these refineries.
Our chemical engineer who helped do the setup was the one who had suggested that we use stannous chloride for the recovery part. Anyway now due to some reasons we no more contact him.

*But now we understand the following (Hope we have understood it well enough):*

1) Soda ash will only neutralize but give a problem of creating the salts as mentioned by Butcher.
2) We have to remove the excess nitric acid from the solution as the most important process before we go ahead for the precipitation.
3) Stannous chloride is not a method of recovery as it forms colloidal form of gold and this makes recovery difficult.

*Keeping these points in mind we have done the following:*

1) Sulfamic Acid : Finally we did track down a dealer and got it in the powder form. The place which Goran had mentioned is actually another state all together. That state is pretty famous for chemical manufacturing. And the problem with things being in other states is that you will get the goods but nothing less than 10 working days. But it is okay we did manage to find a dealer locally and have got it with us now.

2) Condenser : We have a batch of fresh stannous chloride coming in today so today we will be testing the condensers and other places for the presence of the metal as suggested in the thread.

3) The storage of Nitric Acid and Hydrochloric Acid - We generally fill the tank with Hydrochloric Acid first and transfer that to the mixing reactor and then fill it up with Nitric and transfer to the Mixing reactor. But we now understand as per your advice and the other advice by others is that Nitric acid should be added lot by lot so that we do not add excess of nitric.

4) The Storage Tanks - We are considering getting small conical tanks now instead of using these glass cylinders. Hopefully we can use these glass cylinders for some other purpose.

*Apart from this:*

1) Sodium Metabisulfite - Earlier in one of our batches, we had a problem of precipitating gold using SMB, it was just not settling down and we contacted our engineer he asked us to get Food Grade SMB and use that. As per his advice we did that and are now using food grade SMB. We generally dilute the powder in water and then add it to the solution.

2) The Gold Bars - Sir (4metals) When we complete the refining and get the pure gold in hand we do an assay test. For the last batch we had got the purity of 999.22. We generally get a purity of 999 in all the batches. But the local market where we sell our bars require the product to be of purity 995.0. So for this we do the following conversion:

995.80 gms Pure Gold of purity 999.22 + 4.20 gms Silver = 1000 gms weight of Gold Kilobar of purity 995.0
In this case we sell the gold at the price of 995.

3) The filters used - We have been using 2 layers of Polypropylene filter cloths - first layer is of 1-2 microns and the layer below this is 4-5 microns. (We are not 100% sure of the microns as this is India and we learned a lot of things after starting this setup that you will get all kinds of stuff but guarantee of the quality is given by very few). 

4) Filtration Plant - We transfer the solution from the cylindrical vessels to two tanks of 2000 Ltrs each, we store the solution in these tanks for few days then transfer the solution to the Filter press and from the filter press we transfer to another tank of 4000 Ltrs. Picture attached

(Lou) Sir thank you very much for the flow chart, this now gives a much more better clarity in what we should be doing (definitely better than the way I have scribbled all over my book ) 

We will get back with more information on our past workings which might help you all in guiding us further.


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## Palladium (Apr 27, 2015)

I love air assisted double diaphragm pumps. I have one myself and I've seen two in your pictures. I use filter socks though and not a filter press.


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## 4metals (Apr 27, 2015)

Let me start out by saying that a process which is good for one feedstock is not necessarily good for another. When I evaluate a process, the first thing I consider is what equipment is available for the refining. This can eliminate some processes immediately. No one likes to spend more money than they have to and no refiner likes to turn away work because they are not set up to process it. For this reason I favor versatile equipment. Once a refinery starts to see a consistent quantity of a certain material then it is fine to set up to maximize efficiency and yield with dedicated setups. 

I would never build a refinery without a process hood where individual lots of varied material could be processed if required. 

Now the material at hand. The preliminary assays indicate 99.5% precious metals to start with. Wow, pinch me! What an ideal feedstock to start with! You have not indicated if there are any traces of Platinum Group metals in the material so I have assumed not. This becomes important because the flow chart Lou provided and his descriptions include a resin system to catch these values before waste treatment. In your original post you stated 0.04% other metals. Even if that was all platinum, in a 10 kilo lot you are talking about $4.50 worth of platinum (less recovery cost). But even at that level, your refinery is set up to process 100 Kg a day and $45 a day can add up to real money over time. Plus lots of higher PGM value can sneak in. Anyway, it is good to track its presence. A good fire assayer, and some good fresh stannous chloride can determine its presence qualitatively and allow you to separate your waste streams, one holding tank set aside for PGM trace recovery, and another for Gold and silver traces. 

This is a resin system which solutions are pumped through to recover values before waste treatment.





If you have been reading about refining on this forum you have surely noticed that in the best case you want to clean up your material as much as possible before using aqua regia, the reason being you do not want to affect your final purity by dragging down other metals in solution. That is why some members suggested inquartation for this material. In reality, the quantity of base metals you will have in solution will be exceptionally low for this material almost as if you had done an inquartation with the exception being an inquartation and treatment will have removed the silver as well. In this case the cost of acids and extra handling does not justify inquartation. 

So what does this mean about the refineries in the Mid East where your methods came from? We do not know what the purity of the material they are adding to the aqua regia is. If they pre treat by inquartation or other processes before aqua regia then the relatively high purity of the material going into aqua regia will allow for the chemistry you have outlined. I am not saying I like the method, I am saying it can work (obviously it does). But the reason it works is how clean the material is going into the aqua regia. The picture you posted of your digestion vessel full of beautiful red acid tells me your feedstock has very little base metals without even looking at the preliminary assay. (That could be a centerfold in a refining magazine!) 

Let's for a moment say you were refining karat gold in your system. No pretreatment, no inquartation, just straight melted and granulated karat. In the industry, karat gold can be refined on a large scale by melting all of the metal for a particular lot together and making sure the cumulative silver content is under 9%. With that silver content or less, a straight aqua regia dissolve will give you a good dissolve and leave you with silver chloride as an insoluble. The acid however will be a green color, not even close to the pretty red acid you have shown us. If you were to proceed to neutralize to pH 7 the excess nitric with soda ash as you described, you would be bringing down metals as hydroxides which would mix with your gold dropped with metabisulfite. In short you would have a mess.

The soda ash can have an unintended consequence adversely affecting your gold purity. Remember your primary goal is to eliminate excess nitric acid from the dissolve process. You can add soda ash and have problems with some of the other metals dissolved in the acid, or you can add sulfamic acid and not cause any unwanted precipitation save the dropping of the lead as lead sulfate. In the karat gold refining scenario, the sulfamic choice will allow you to drop only the gold leaving the base metals in solution. Note you add the sulfamic before filtering out the silver chlorides. 

Continuing on in your process following the Mid East method. After filtering out your precipitated gold, you continue to add Caustic soda to recover any other materials. Here we call that waste treatment. The problem being you have not attempted to cement out remaining values, you have dropped all of the metals as hydroxides and co-mingled your values with any base metals. Not to mention the fact that any Platinum will remain in solution and go out with your waste water. 

On to waste treatment. Classic waste treatment is done after you have recovered all of the values by cementation or resin column. The remaining metals will be base metals and we raise the pH to drop them as metal hydroxides. The base metal hydroxides are collected in a filter press and the water from the filter press is neutralized and checked for metals to meet discharge standards and if it passes, discharged to sewer. The photo you attached shows the filter press feeding off the tank where normally the pH is raised with good agitation so the hydroxides remain suspended in solution and can be pumped through the press. I do not see any mixing motors on the tank. Is this where you raise the pH or does the liquid come into these tanks alkaline as per the Mid East recipe?

This is what a typical mixing tank feeding a filter press would look like.



And this is the hydroxides that come out. These particular hydroxides are very high in copper due to the cementation process used. They are dried and shipped to a copper smelter who pays on copper and any precious metals contained. 



I notice your filter press, and the one in the photo I attached are both European design. The difference is American made presses pass the liquid through the plates and discharge out the end of the press into a pipe all using the power of the double diaphragm pump to move the liquid. European models allow each plate to drain into a trough which has to be collected and transferred to the next process. I have used both and both work well. 



> 3) The filters used - We have been using 2 layers of Polypropylene filter cloths - first layer is of 1-2 microns and the layer below this is 4-5 microns. (We are not 100% sure of the microns as this is India and we learned a lot of things after starting this setup that you will get all kinds of stuff but guarantee of the quality is given by very few).



The paper of the most coarse porosity, in this case the 4-5 micron, should be the first layer to contact the liquid being filtered, followed by the least coarse 1-2 micron. Your goal is to filter out the larger particles first and allow the smaller particles to pass and be collected by the finer paper. It will not clog as fast if you do coarser first. 



> 2) The Gold Bars - Sir (4metals) When we complete the refining and get the pure gold in hand we do an assay test. For the last batch we had got the purity of 999.22. We generally get a purity of 999 in all the batches. But the local market where we sell our bars require the product to be of purity 995.0. So for this we do the following conversion:
> 
> 995.80 gms Pure Gold of purity 999.22 + 4.20 gms Silver = 1000 gms weight of Gold Kilobar of purity 995.0
> In this case we sell the gold at the price of 995.



Excellent, no sense giving gold away!


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## 4metals (Apr 27, 2015)

I am still a little confused as to where you recovered some gold after the losses. If you can detail the steps you followed and what and where in the process you found the gold that was missing along with how much remains missing. Maybe we can piece together the whereabouts of the missing gold.


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## ashapura refinery (Apr 28, 2015)

@4metals:

We do not have any platinum group metals present in the material we receive. The main contents in the material is gold, silver, copper, iron. 

As for the recovery we have done so far:
1) We had used cpvc pipes earlier and we found fine gold particles in the pipes, we then removed these pipes and cleaned them out.

2) We had added caustic soda and stannous chloride to the left over solutions and we recovered a small amount of gold from the material that settled. It was not a 100% recovery but a small part.

3) Apart from this the used gloves, filter cloths, etc was washed out carefully as well.


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## ashapura refinery (Apr 28, 2015)

Hello. We noted down the points mentioned in the previous posts. And started a new fresh batch of refining.

The weight of the Gold Dore Bar - 7.8 Kgs (Actual weight - 7812.20 Gms)

We did the assay of the Dore Bar to know the exact contents. 
The content of the dore bar are:
1) Gold - 92.96%
2) Silver - 06.55
3) Copper - 00.20
4) Iron - 00.24

We started off with the aqua regia process:

1) We added HCl - 24 Ltrs.
2) Then started adding nitric acid - total added - 7.5 Ltrs
3) This time very few grains remained undissolved.
4) Then we added about 1.8 Kgs of Sulfamic Acid powder in the solution ( lot by lot).
5) Then we filtered the aqua regia solution and removed the silver chloride.
6) After the filtration of the silver chloride, we were left with total solution of 45Ltrs including the water used for the washing. 
7) We then took the first batch of 20 Ltrs of the solution into the other mixing reactor and added about 3 Kgs of Sodium Metabisulfite diluted in water for the precipitation. The reaction happened immediately. The gold started settling but after a few minutes the gold got dissolved in the solution again i.e., it turned back to the aqua regia solution.

The Color of the solution is exactly same as the Aqua Regia process. I have attached two pictures of this solution.

Can someone please explain where have we gone wrong this time?


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## Barren Realms 007 (Apr 28, 2015)

You said you added 1.8 Kgs of sulfamic acid.

Was this as a crystal dry form of dissolved in water?

When using sulfamic acid I have had best results with dissolving it in hot water and then adding it to the solution. You need to be able to stir your solution when adding the sulfamic acid to get to mix well with your solution. When the violent reaction stops from adding the sulfamic acid I usually add 15%-20% more of the solution to make sure I have removed all of the nitric.


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## ashapura refinery (Apr 28, 2015)

We have sulfamic acid in the powder form. We mixed this in water (at normal temperature) and added it to the solution of aqua regia before the filtration of the silver chloride. While adding the sulfamic acid liquid the stirring was also going on. 

We checked for the PH level and it is 3 right now. 



Barren Realms 007 said:


> You said you added 1.8 Kgs of sulfamic acid.
> 
> Was this as a crystal dry form of dissolved in water?
> 
> When using sulfamic acid I have had best results with dissolving it in hot water and then adding it to the solution. You need to be able to stir your solution when adding the sulfamic acid to get to mix well with your solution. When the violent reaction stops from adding the sulfamic acid I usually add 15%-20% more of the solution to make sure I have removed all of the nitric.



Does it mean that we still have some nitric acid left over in the solution? Is this why the entire solution is reacting back and forming aqua regia? I thought about this as a possibility but I am not very sure if this is the reason. Also what is the best way to know if Nitric acid is still present in the solution or not? Is there any test for this?


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## Lou (Apr 28, 2015)

Barren is right!

If you want the sulfamic to work correctly, here's the gig:

Take boiling hot water and dissolve the sulfamic. The dissolution is endothermic and the solution will get cold. Hence the use of boiling water. Do not boil it on a hot plate--the heat from the hot plate on the crystals on the bottom will decompose the sulfamic acid in ammonium cation amongst other things (more important if you deNOX PGM solutions).

Add the hot sulfamic solution to the HOT gold solution, and stir. Add until the production of nitrous oxide gas stops. Add slowly to avoid foam over.

*If you use an ORP meter (get a titanium probe!) you can see the ORP fall from typical >950 mV+ to around 650-700 mV+.* <--this tells you the speciation of the gold and how much nitrate is available. Every ORP meter is different--make up an aqua regia solution and check that ORP. Then dissolve gold, and check again. This is calibration. You will soon be able to tell. ORP varies with temperature too, so make sure to keep meticulous notes. You are almost there. 

Regarding incomplete precipitation--obviously all the gold was not out of the solution. Keep treating with sulfite and you'll eventually get it all. If you don't want to deal with that and want it all out pretty much instantly, use hydrazine hydrochloride salt solution. Produces nitrogen gas as the by product. 

Do NOT overuse the sulfamic or you will get plating upon the exposed surfaces in the reduction kettle. 

@ 45 L total gold solution with 7.8 kg (say 12 g grains remained) X 0.9296 = 161.13 g/L, over 5 oz/L. That's a good concentration. 
24L HCl means total chloride content (you should have rinsed chloride with 1M HCl! telling you it helps to get the gold off the AgCl and prevents peptization of the AgCl), assuming 12 M conc HCl is 6.4 M in [Cl-]. This is a good strength to precip. Maybe a bit high on the chloride content.

It's important to get the chloride out of the gold sponge with ammonia rinse b/c if you don't, and you melt the gold sponge with AgCl, some of the AgCl decomposes to chlorine and the gold volatilizes. 

*just saw your post: 3 kg of metabisulfite should NOT bring the pH up high enough to make it pH 3. Adjust the pH down to 0 with fresh HCl. If the pH isn't low enough, the metabisulfite will not form the SO2 in situ which is what's doing the reduction. Add 10 L concentrated HCl and try again*

Lou


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## nickvc (Apr 28, 2015)

I'd say you still have nitric left to redissolve your gold.
The one good use of urea prills is for testing whether you have nitric left in your solutions, simply add a couple of pieces and see the reaction, if it fizzes and dissolves you have nitric left.


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## ashapura refinery (Apr 28, 2015)

Okay understood. So our first step should be to remove the excess nitric acid. Now in this batch of refining we have used 7.5 Ltrs of Nitric Acid and have added 1.8 Kg Sulfamic Acid. 

Can anyone suggest how much more should we add - like 3 Kgs more or 5 Kgs more?


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## Lou (Apr 28, 2015)

Don't add anymore sulfamic. If anything heat the solution and it'll get it.

Failing that, add more muriatic acid and try the sulfite again. I think that'll get it.

EDIT:

You all need to start doing your maths. The math is less critical on the digestion side because aqua regia decomposes in use so the stoichiometry is never right.

If your assay is 
1) Gold - 92.96%
2) Silver - 06.55
3) Copper - 00.20
4) Iron - 00.24


Now, you should also do your math on the metabisulfite. I'm not going to run through the stoichiometry because this is something that your chemist, if he's worth anything, should be able to do.

Take the weight of the charge in grams X purity of gold and divide by molar mass of gold 196.97 g/mol, then use the stoichiometric coefficients to get the minimum amount of acids to do the job. In practice, you'll probably end up using a 25-30% excess of HCl, and a 5-10% excess of nitric acid because of side reactions of decomposing nitroysl chloride and the small amounts of copper. 

Given the grade of your feed, this is an ideal candidate for Miller chlorination--you should hit 995 no problem, and that's what would be made into anodes to go into the Wohlwill cell, or else put into aqua regia. Cell is the cheapest but requires extensive gold inventory and accounting, something which your refinery might struggle with at this point. 

Lou


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## ashapura refinery (Apr 28, 2015)

@ Lou:

We started this process today morning. We did the assay, the granulating and then went on with the chemical process. This time we told our chemist that we are not going to use the Soda Ash procedure and will be using Sulfamic Acid and then precipitate by using only SMB. Apparently he was not very happy with this idea. Later in the evening he gave up saying I cannot do this process anymore and left. (This is India employees leave whenever they want :roll: ) So right now we are on our own and working with the help of our refinery department helpers who generally help around. So calculating the stoichiometry part would be difficult for now.

So as per your suggestion we went ahead with the Sulfamic Acid addition and also added some HCl and the pH level right now is near 1. We have now added SMB and are checking for the precipitation reaction.

A question on a general basis, is there any method/test on testing the presence of Nitric Acid in any solution?


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## 4metals (Apr 28, 2015)

Part of the challenge in refining is the chemical equations for all of the reactions can be done on paper but then they have to be applied to the real world. 

For example sulfamic acid's reaction with Nitric acid is pretty straightforward. For every 3 1/3 pounds (1.5 Kg) of sulfamic acid you add, you will convert one liter of nitric acid. That's the easy part.

You said you ran the reaction by adding a total of 7.5 liters of nitric acid. (With only 24 liters of Hydrochloric it is only a 3.2:1 ratio, still too much nitric.) The variable is how much of the nitric acid remained after the reaction. Every system is different, heat, no heat, agitation, pressure, condensate return, and a few other factors all play in determining this. And the type of material is critical, your nitric consumption for a high gold alloy like you are running will be different with karat gold for example. 

Lou said, 


> so make sure to keep meticulous notes. You are almost there.



Once you determine the proper quantities of reagent for each scrap type write it down and keep copies of the notebook. (You never know when an employee decides to open up his own refinery down the street and takes all of his knowledge, both written and learned, with him. Don't ask me how I know this!)

So from what you said you can see you did not add enough sulfamic to kill the excess nitric, and the sulfamic that you did add, 1.8 Kg, is enough to kill 1.2 liters. The presence of free nitric acid in your solution after you dropped the gold is what caused the gold to re-dissolve. The thing to take from this is LESS NITRIC. 

Doing the math thus far 7.5 liters to start, less 1.2 liters neutralized is 6.3 liters. Had you started with 6.3 liters of nitric and used the same 24 liters of Hydrochloric you now are at a 3.8:1 ratio. Since you had enough nitric to re-dissolve the gold there was obviously more in there. I would suggest at a minimum (a starting point which can likely be decreased further) start with 24 liters HCl and 6 liters of Nitric. DO NOT add all of the nitric at once, be patient and you will learn to observe when the reaction is complete and stop adding nitric. 

Lou's suggestion to use ORP to determine when the nitric has been converted is sound advice. However it has been my experience that the analytical capabilities of intermediate sized refiners would never live up to Lou's expectations. Another trick an analytically poor refiner can use was mentioned by NickVC. A few, one or two prills, not a handfull, dropped into the solution after you have added your first dose of nitric will fizz and dissolve quickly if there is free nitric in solution and float up and barely react when you are close. 

From here on out, start out with a 4:1 nitric ratio but only add as much nitric as needed. I am thinking you will find a ratio of 1:5 will work. Keep notes! 
Test for free nitric with urea prills
Add 1.5 Kg of sulfamic acid dissolved in HOT water. An excess of sulfamic acid will not hurt but do not get carried away. 
RE test with urea prills
Add ever decreasing quantities of sulfamic acid.
Never add more than 4.5Kg for a 6 liter nitric addition, this quantity allows for 50% of the nitric to be un-consumed and you can do better than that by adding the nitric conservatively. 

If I were running this process, I would add ice to the reactor after the sulfamic additions, the ice lowers the temperature of the solution as well as the solubility of silver chloride so it makes for less silver carry over into the next step.

If you get the technique down of not using too much nitric it is common to use SO2 gas (I didn't give up on you finding that yet) which will drop the gold only to have the gold re-dissolve and emit a red fume until all of the free nitric is consumed. If you can have a minimal quantity of free nitric you can skip sulfamic acid altogether and use SO2 to burn off the excess free nitric acid and then the SO2 will continue to drop the gold until the solution is barren of values. Sodium metabisulfite will also drop the gold and consume the free nitric just like SO2 but I have always preferred the gas for this.


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## Lou (Apr 28, 2015)

Given that sulfamic is about $2/kg in bulk (at least for me it is), they need to be cognizant about chemical costs.

Take home message is PATIENCE and LESS NITRIC ACID. Either make smaller grain so it dissolves faster or else wait longer on the material to get full digestion of the gold. Get a flashlight to look into the reactor. 

Another thing, if the digestion starts to stall, you might consider adding some more muriatic acid FIRST then small additions of nitric acid.

You're lucky to have such a great material to refine. 


As for your chemist, if he is unhappy about expert advice and is giving up despite having worked at a refinery in the Middle East (Kuloti?), find a new chemist. This process isn't hard. Gold refining should be one of the simple pleasures of life, and if your process/equipment is right, your feed material consistent, it should run the same every time all the time and print you money so long as you can feed the machine. One thing I did not see, is how you are heating your digestion reactor?

I'd tell him to get on here and come talk to us, he'll either start making you money, or start looking for a job. Did you show him the flow chart I made?


To recap, step by step for this chemist of yours:

1. Weigh incoming dore bars after visual inspection.
2. Melt the gold at 1115C, stir it well and take a vacuum pin tube sample. Have your melt operator clip off 2 g or so for fire assay (centimeter length is plenty!); return the rest of the sample to the molten gold. De slag the gold with a graphite rod. If your slag is too thin to stick to the rod, add some sand or broken glass so it doesn't report in the granules. Alternatively, cast a bar at this stage, peen off the slag, and melt the rest of the inbound refining lots together after sampling individual heats. 
3. Granulate the gold as small as possible into cold, circulating water.
4. Pump off the water from the granulation tank and put the granules into a flat stainless steel pan that is tared and dry them until no more steam comes off and no water drips off of a cold piece of glass held over it. Or until they weigh the same (constant mass).
5. Mass up the charge, doing the math based off of preliminary X-ray, add in all of the 12M muriatic acid, then 90% of theoretical 16M nitric acid to get the reaction going. Stir very well. Bring to 80C. Add small 100 mL amounts of nitric acid followed by 400 mL amounts of muriatic until all dissolves and no more red NOx gas is seen. Use flashlight to check the chlorides for granules and fizzing.
6. When all the gold is dissolved, add in hot saturated sulfamic acid to destroy nitric acid. When fizzing with sulfamic stops, test with a few prills of urea to be sure it is all gone; if not, urea will leave trail of bubbles. Check the ORP with ORP probe before and after to see the decrease in potential indicating nitric acid is gone.
7. Add clean ice to reactor to dilute the acids down to 4-5 M concentration and help precipitate the silver chloride by lowering its solubility. Sulfamic makes sulfuric when reacting with nitric acid, so any lead is going to precipitate as its sulfate.
8. Discharge reactor carefully, wash the silver chloride in a dedicated Buchner funnel with 1 M HCl until the washings are colorless._ Go convert the AgCl into metal in a large plastic concrete mixer with clean scrap iron and 10% sulfuric, pull test samples and take to lab, rinse well with water til not acidic and melt up in cupel with small amount of borax and carbonate. If good, melt all of it and make anodes. Take sample for parting to determine gold content and find the silver content via titration. Silver should be 995 or so. Run the anodes through the silver cell to make crystal silver that is 9995 or better. Black residue is gold mixed with lead and other insolubles._
9. Return to your gold solution that should be cool due to the ice. If it was filtered right, should be a clear red solution no haze. If there is haze, no big deal, it's just silver chloride that you can remove later. ORP should be as mentioned above. This is then treated with either sulfur dioxide gas, or metabisulfite (do the math, you'll need probably 5-10% excess). Again, hydrazine hydrochloride is terrifically good at this operation and gives much nicer precipitate. 
10. Stir the gold solution well as it is reducing, and when done, test with stannous chloride on Q-tip to be sure no gold remains.
11. Allow to settle, siphon off the barren gold solution, discharge reactor into an 18" buchner funnel with a 1 um polypropylene felt filter. Wash the gold with 6M acid that you can re-use until no color leaves, then with cold water, then ammonia to remove any silver chloride (keep this ammonia separate from other waste liquids). When rinsing with ammonia, rinse until no blue color is seen (tetrammine copper complex) and the silver chloride is surely removed. The final rinse is with hot DI water.
12. Dry and melt the gold sponge, weigh it, sample, and it should assay at 9999 given your feed. Alloy down to 99.5 with copper (cheaper than silver). 








Some points to be made:
1. test your acids for their strength via titration and have the manufacturer/supplier send you the analysis of the batch
2. If you don't yield the right gold following our explicit instructions, then the problem is your assayer.


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## 4metals (Apr 28, 2015)

Lou,

What I see more often than not is refiners wanting to kick off a reaction and let it work over night. These guys dose up the nitric acid based on their best guess calculations and deal with any excess nitric in the morning. For them sulfamic is a necessary evil and they find a 20% excess does no harm. 

As far as heat, I believe they do not heat the reaction. I don't see a mantle on the vessel so unless they have an internal heat probe it is running on whatever heat the reaction provides.


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## Lou (Apr 28, 2015)

That's part of their problem. Heat is really required to drive the reaction without excessive amounts of aqua regia.


Mole for mole, sulfur dioxide is probably much cheaper at NOx removal, but it is less effective and the gold precipitate loses quality towards the end.


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## 4metals (Apr 28, 2015)

Well QVF does sell a strap on soft mantle for the bottom of that vessel. Maybe they can trade in some of the taller vessels they are using for holding spent solution for a mantle. 

Without going back and reading everything, said I do believe they said there is no additional heat. I have used Italimpianti tumbler plants without heat successfully but a blade stirrer is not the same as tumbling the shot. Tumblers actually allow for higher silver content in the feed due to the abrasion of the tumble.

The use of chemistry to kill off excess nitric is higher in the tumbler plants than in the closed reaction vessels like the QVF that have heat to drive the reaction.


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## ashapura refinery (Apr 28, 2015)

@ 4Metal
The calculation for the sulfamic acid addition gives a clear idea thank you so much for that. I have noted it down. And what you said about employees well yes we just got a slight taste of it. And definitely learnt - Less Nitric Always.

Now the Sulphur Dioxide (No we have not given up either  ) - In order to use sulphur dioxide gas we cannot use it right away here in the place where we are located. We need to inform The Pollution Control Board Department of our State that we will be using sulphur dioxide gas and they have to come and inspect our premises for this, to make sure that all the safety measures have been taken and that the entire process would be carried out properly provided that the neutralization of the fumes is done well before it is let out in open air. We have already informed the department. Once we get the green signal we will use this method. 

@ Lou

Yes we did learn that patience is always important and in this particular process, to carry it out properly, less nitric is one of the keys.
As for the chemist no he has not worked at Kaloti, it was another refinery.


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## Palladium (Apr 28, 2015)

I'm not a chemist by any means and don't understand all the chemistry involved, but I do think more water is your friend with smb.

Pull a 1 lt sample and dilute it by half after filtering and see if that helps. It won't take but a min to see! I'm a firm believer in water and smb. I used to have problems with my solutions wanting to redissolve when I added smb even though the nitric was neutralized. It was like when the nitrate ion left the gold for precipitation it would act with the smb to redissolve the gold because it didn't have a place to go. Not sure in chemistry terms how that would work, but I figured it was because there wasn't enough water to buffer the reaction. With more water I've learned I have less problems.


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## Barren Realms 007 (Apr 28, 2015)

Something that might you might want to consider adding to your process is a heating mantel for your reaction vessel to be used during your primary reaction. A warm or hot solution will utilize your nitric more and allow you to get closer to completely using all of the nitric in your solution. This would also aid in having a warm solution when adding the sulfamic acid to denox the solution. 

I am not sure if this would help him or not in his process but I have been guilty at times of adding 32% hydrogen peroxide to my reaction vessel to give the nitric acid some added oxygen for the process and allow a more complete use of the nitric acid that is added. This should be commented on by Lou and the others before it is added because it might cause some problem that I am not aware of.

Another train of thought is that after he has added the sulfamic acid and the endothermic reaction has dropped the temperature of the solution. Not being sure of how much ice he is using at this point in his process to cool the solution to help remove the silver chloride from the solution, I will generally add enough ice to bring the temperature down in the solution to where the outside of the reaction vessel starts condensing the water vapor from the surrounding ambient air and sometimes even creates frost on the side of the vessel.

Another trick to consider that I use is I add crushed ice to my filtering vessel to keep the solution cold during filtering and I have found that I have better success at removing the silver chloride from the solution when doing this. I have found that sometimes but not always this will also trap the silver chloride in the ice and not allow it to clog the filter during the filtering process, but he has not stated he has a problem with this aspect of the procedure.

Another note to be added here is after that filtering is if he uses ice in the filtering vessel is that it gives him a super cooled solution in his precipitation vessel. This is an aid in one part in that when he adds his sodium metabisulphate to the solution is that it will allow more of the SO2 gas to stay in the cold solution to precipitate the gold, and prevent some gassing off of the SO2 gas out of the solution during the exothermic reaction that takes place from the precipitation of the gold out of solution. There is a drawback to doing this with a cold solution as well, if he reads enough on the forum he will find that ice is recommended by some in the precipitation vessel to counter react the exothermic reaction during the precipitation of the gold to allow better usage of the SO2 gas created, if he gets over confident in doing this he can set up a scenario where he adds a lot of sodium metabisulphite solution to the vessel and as the temperature raises quickly that the SO2 gas can try to gas off and cause a boil over reaction in the precipitation vessel.

Another point that needs to be addressed is that if he uses a large excess of sodium metabisuphite in the solution is that as the gold drops out of the solution it will trap SO2 bubbles in the powder and as the solution warms up these bubbles will try to escape the powder and bring some of the gold up into the solution with them. I will generally boil my gold powder in water a couple of times to remove any excess SO2 gas.

Another point to make is that during the denoxing of the gold chloride is that if he has not denoxed all of the excess nitric out of the solution he will have some minor carry over of nitric to his precipitation vessel and after he removes his precipitated gold from the vessel and then tries to wash it with hot HCl that he will have some of the gold go back into his washing solution. One way to counter react this is after the boils in water as mentioned in the paragraph above is to make sure the gold is in fine particles after the water boils and instead of going to an HCl wash is to go to an ammonia wash a couple of times to remove any traces of silver chloride and copper that might have gotten through the procedure.

Another tool he might want to consider putting in his arsenal is an infrared temperature reader to keep up with judging the temperatures of his reactions since glass is a good thermal conductor of temperature.


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## Lou (Apr 28, 2015)

Frank, if the gold is gone out of the solution with sulfur dioxide and no more red NOx is fumed off, the nitrates are gone. 

One can safely wash the gold precipitate with muriatic if one has a quantitative precipitation and negative stannous. 

Should mention that after stirring and the first negative stannous, give it some time to settle and when it's settled, then check again with stannous just to be sure. 


Lou


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## Barren Realms 007 (Apr 28, 2015)

Yes I agree. About the only time I have had the gold go back into the solution is when I have left the gold powder on the hot plate in HCl over night. So I have learned not to leave it on the hot plate over night. 8)


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## ashapura refinery (Apr 28, 2015)

We did the process again properly this time. I am sending the pictures of the left over solution after the precipitation. 

Now we took a bit of the solution in a beaker and tested it with a little stannous chloride and this is what it looks like. There is some left over gold in the solution. Now how should we go about this? Should we be adding more SMB?

The drying of the fine gold powder, the melting and the assaying is still pending though so we yet do not know the exact amount pending. 

And we have understood the need of a heating device for the mixing reactor. Will get it done as well so that next time we work with Sulfamic Acid we get the proper result.


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## Palladium (Apr 28, 2015)

You should test before you filter the gold powder to make sure the drop is complete. That way you don't have to filter and drop it twice. You should test with stannous using a spot plate or a piece of paper. If it still tests positive add more smb until you get a negative reaction with stannous.


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## Palladium (Apr 28, 2015)

[youtube]http://www.youtube.com/watch?v=Hz8odRIqtuQ[/youtube]


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## Palladium (Apr 28, 2015)

Every time I see you add SnCl to liquid I cringe!

[youtube]http://www.youtube.com/watch?v=CGBrsfn0ouM[/youtube]


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## 4metals (Apr 28, 2015)

Ralph is right. Putting stannous chloride into your acid forms the colloid we spoke of earlier. It is so fine that in low concentrations it is difficult to even see. Using a spot plate, paper towel, or Q Tip wet with a few drops of solution and applying a single drop of stannous chloride test solution will detect less gold in solution. I prefer paper towels because they go with the burnable recoverable materials and you get your gold back down the line. 

Please remember that stannous chloride goes bad. Faster if you do not add tin metal to the solution. Always keep a small volume of solution you know contains gold to test the solution when you get a negative test. It is an easy way to screw up and lose gold. Take a few milliliters (maybe 2) of gold dissolved in your reactor with the next lot and add about 20 ml of water and keep it in a vial so you have a sample to compare to. 

Your acid after the drop is as clean as the Hydrochloric often is before we start refining! If this mining doré is the type of material you set up to refine, why did you buy a filter press? At the concentration of metals in the waste you have shown us, it will take thousands of treated gallons to fill the press with hydroxides. What other gold or silver material do you process?


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## Palladium (Apr 28, 2015)

Silver Silver Silver !!! You're right 4metals with that waste stream after recovery of the silver he could use an evaporator in his waste process to concentrate the solutions. He could run a long time between waste treatments with a lot less trouble!


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## Palladium (Apr 28, 2015)

http://www.chemteksys.com/Evaporators.html


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## Palladium (Apr 28, 2015)

ashapura refinery said:


> As for the recovery we have done so far:
> 1) We had used cpvc pipes earlier and we found fine gold particles in the pipes, we then removed these pipes and cleaned them out.



Where were these pipes located? Was it between precipitating vessels and settling vessels or after the settling vessels and before waste disposal?


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## g_axelsson (Apr 28, 2015)

ashapura refinery said:


> We did the process again properly this time. I am sending the pictures of the left over solution after the precipitation.
> 
> Now we took a bit of the solution in a beaker and tested it with a little stannous chloride and this is what it looks like. There is some left over gold in the solution. Now how should we go about this? Should we be adding more SMB?


That could be a false positive due to an excess of SMB. Correct me if I'm wrong as I've only worked with smaller lots, but the pale liquid after the drop and the brown color of the colloid after adding stannous to the liquid looks like a complete drop to me. Stannous reacts with a brown color on excess SO2 or SMB.

And I agree with the others, your 100 ml test sample for stannous is as big as my larger lots. You only need drops of the liquid to do a test with stannous.

It will be nice to see the final yield of this lot, both in purity and quantity. I'm eagerly awaiting the results.

Göran


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## 4metals (Apr 28, 2015)

Ralph,

Waste treatment from acid refining never benefits much from atmospheric evaporators. The most concentrated you can get the acid is down to its azeotrope concentration so there is still a lot of volume you will not evaporate easily. 

The other option is break the acid with caustic. In this case there is a lot of chloride in the waste and caustic adds a lot of sodium so the salt concentration is very high. The salt will clog the evaporator quickly. 

As much as Shawn from Chem Tec would love to sell you an evaporator, they are made for electroplaters rinse waters where the majority of the waste is water. Chem Tec also makes a line of scrubbers, hoods and vacuum equipment specifically for refining http://www.goldrefiningequipment.com/Index.html


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## kurtak (Apr 29, 2015)

ashapura refinery said:


> This time we told our chemist that we are not going to use the Soda Ash procedure and will be using Sulfamic Acid and then precipitate by using only SMB. Apparently he was not very happy with this idea. Later in the evening he gave up saying I cannot do this process anymore and left.



ashapura

If your chemist was unable to understand &/or follow the instructions being passed on to you by Lou & 4metals you are better off with out him --- He was clearly taught wrong methods when it comes to refining ( I could not believe what I was reading when I first read the methods you were using they were so wrong) & does not want to accept that his methods are wrong & therefore is not open to learning what is right & what works

You are currently being advised by 2 of the very best in the world when it comes to large volume refining of PMs - about the only thing I can think of that would be better then getting this advise from them here on the forum - would be to actually "hire" 4metals to come over & do an actual on sight walk through of your operation (if he is willing to do so as that is what he does/did but I believe he is now retired &/or semi retired) 

A heating mantle on your reaction vessel would be a good thing as that will help to drive the reaction of the acids to completion especially as the reaction nears the end which means you will use less nitric which in turn means less free nitric to de-NOx

I have been following this thread with much interest & you are being "very well advised" by those commenting on your problems & if you follow what is being said you should start seeing much better results

Kurt


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## justinhcase (Apr 29, 2015)

I agree, You may just find you precious metal leak has just walked out your door.
Big alarm bells when an employee throws his toys out of the pram for you improving your system.
Make a good offer to a refiner with a good reputation who you like and get on.
I can not take any one who suggests you try to run a lab with out heating vessels seriously.
Just


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## Anonymous (Apr 29, 2015)

I agree with Kurt.

You'd be well advised to engage Lou or 4metals professionally, they really do understand what this is about and their fees would likely be recouped in short order. As others have mentioned I think you may have the wrong team around you and that is a road to nowhere. As a point of reference for you I also run a company which is over 18 years old and employ many people so I do understand business, and from my perspective you need to stop the problems right now or you could lose a lot of money and possibly all the investment.

Good luck, and take the good advice that has previously been given. 

Jon


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## 4metals (Apr 29, 2015)

Gentlemen, 

While there is appeal in visiting far off exotic places all in the name of employment, there would be little to gain on the part of forum members who rarely see this degree of detail in an operation like Ashapura's refinery. 

I applaud Ashapura's willingness to share the details of his operation in order to get valuable advice to aid his company. Hopefully others will learn to give detailed descriptions and photos of their operations in order to get meaningful and helpful advice. Then the true spirit of the forum, *Refiners helping refiners*, can show through.


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## ashapura refinery (Apr 29, 2015)

Firstly saying thank you will never be enough when it comes to the amount of help we have received. After reading everything and understanding things we have learnt a lot. As for the amount of money we have lost - we have no idea where to begin from. Today in the afternoon we were calculating on how much money we could have saved in doing the entire setup. 

*Coming to the process* - we completed the batch how much ever we could. The washing of the refined powder was done well as per the instructions of Lou in our filtration vessel itself. There was no problem with that at all. Sadly everyone was so tired from working for hours continuously that we forgot to take pictures (Sorry about that.) 
Now for the leftover solution - the pictures of which we had put up in our last post - we added SMB to a small batch of it but there was no reaction in that. Then we collected another small part of the solution in a beaker and added zinc to it and got black color. 

For now we have kept that solution aside as it is. ( Pictures of the solution with SMB and with Zinc addition have been put up.)
Now for the purity - we dried the fine gold powder, melted a sample and did an assay and got the purity of 9992, the same as the previous batch. So yes the purity of the gold did come out to be good.

We next moved on to making a large bar and then making the grains of the bar and started the melting process for the Kilobars. This time we are moving on with 999.0 and not converting it to 995.0 as this was the request of the client. 

Well the Bars are coming out to be good on the back (picture attached) but on the front (picture attached) we have these reddish spots which generally get removed by Hand Buffing and cleaning with sulphuric acid.

Tomorrow morning we will be marking these bars. Once done we will post pictures of the bars immediately.

*Coming to the advice given for improvising:*
Heating of the mixing reactor - As 4metal suggested - we will be contacting the company who supplied the glass equipments and check with them if they can take back the cylindrical vessels and provide us with a heating device for the mixing reactor. We will make arrangements for this at the earliest.

*Other problems faced:*
One small problem we faced during the Aqua regia process was that we had undissolved grains of approx. 302.00 gms. We had the stirring in the mixing reactor going on for nearly 4 hours. What we have noticed during the stirring process is that in the beginning the material starts dissolving very quickly but, like almost 80-85% gets dissolved easily but later the process slows down - is this because of too much of silver chloride being formed?

*What other material we process:*
We are getting the entire batch of dore gold from West Africa. We get it from one particular supplier in batches of 7-13 Kgs each batch and this dore generally contains gold, silver, copper and iron. Apart from this we do not process any other material at the refinery.

*Apart from all this* - one thing which is bothering us is that there are bigger refineries than ours in U.A.E wherein they follow the process which we had mentioned in the very beginning. And they say that their losses are way less as compared to ours. It's not like we do not want to go ahead with the method we followed now or anything of that sort. It is just something which we have been wondering about because the place from where they receive their material is also the same place from where we are receiving.

We talked about asking for consultancy by Lou or 4Metals today morning when we completed the process. So yes we will be contacting them to know their fees and the way to go about the entire thing. 

And as 4metal said about sharing details, we can share every single detail we have no problems with that because we believe that learning has no end and as he mentioned that our details maybe helpful to the members of the forum – trust us we will be way more happy if anyone else can benefit from all the advice being given in this post. 

*Some more details about us:*

When we decided on setting up this refinery in India (This is our first business in India) we consulted with our friend who is a chemical engineer and had previously helped in the setup of another refinery. We didn’t have 100% knowledge in the topic of refining but we did have some idea on how to go about it because we have previously worked with our friend and seen the process. 

Our aim when setting this refinery was to make it one of India’s best refineries and also to reach the acceptance level of LBMA. India is a large consumer of gold and on a daily basis a lot of gold is being imported into the country. We had set this entire unit keeping large quantities in mind. Which is one of the reasons of having so many cylindrical vessels, a big tank for collection, a filter press etc.

But sometimes things do not work as planned, we had a lot of issues in setting up. A lot of delays took place and a lot of problems came as well but we worked our way through and then imported our very first batch. Now in the very first batch we had our friend who took care of the entire process with ease but there was a big loss, along with him we had an assayer who was excellent in assaying and did have some knowledge about refining but again not completely. 

The losses remained unexplained and after that we did not get in touch with him, the assayer also left after a month because he was not able to adjust with the environment and also his knowledge in refining was less. We had done two batches of refining before he left. 
We kept our search for a good chemist on and waited for sometime till we got somebody better. Upon recommendation we hired another chemist who was earlier in a good refinery. Based on his past experiences we hired him but had the same problem of losses which even he failed to explain. 

Well this is just a part of the chemist. Apart from this we faced problems with the chemicals in the beginning. The acids were easy to find but none of them were of good quality, we had to then find a manufacturer in another state whose chemicals are much better percentage and grade wise. 

Also the governmental policies changed due to which our importing licenses were cancelled and we had to wait for nearly 2 months without any work going on. So yes we have invested a lot of money in this setup and we have also incurred losses. 

Anyhow this was our last big batch. Now we will not be processing big quantities and will instead process with a small quantity to make sure we are getting on the right path. 

A small background info on us:
The person managing the entire process now is my father, who has experience in Gold Jewellery manufacturing. He has been in the field for almost about 35 years now. And he loves advancing with the technology and also never says no to learning something new. This refinery was something he wanted to do long time ago and that is how we have started off by getting the support from his friend and everything. 
Even though things did not work as planned nor did we become one of the best refineries in India, but we are still glad we got to learn so much  . 

Tomorrow morning we will be stamping our bars and we will definitely put up the pictures of the final finished goods. Hopefully the finishing would be good. Once we are done with our delivery we will be back on the recovery of the left over gold.


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## nickvc (Apr 29, 2015)

I hate to say this but the fact your chemist walked out and also your assayer is rather suspicious, this business is full of crooks and thieves I just hope the losses you incurred are not down to them!
Not fully understanding the processes you have left yourselves open to be robbed and have no comeback, how do you prove it?
Your aims are admirable but your ability to achieve them is low, sorry but the truth is often unpleasant.
You need to fully understand the whole process and methodology of refining to be able to see what's happening or not, this unfortunately you do not, if money isn't the problem I suggest employing a competent refining chemist or even just a competent refiner but you really need to know what they are doing and why.


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## Palladium (Apr 29, 2015)

Cameras !!! Cheap and easy! Cameras everywhere! It might not catch them, but it sure keeps an honest man honest when he thinks someone is watching and keeping a record. It's also good to have to look back on if there's an accident or questions about anything.


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## justinhcase (Apr 29, 2015)

nickvc said:


> I hate to say this but the fact your chemist walked out and also your assayer is rather suspicious, this business is full of crooks and thieves I just hope the losses you incurred are not down to them!
> Not fully understanding the processes you have left yourselves open to be robbed and have no comeback, how do you prove it?
> Your aims are admirable but your ability to achieve them is low, sorry but the truth is often unpleasant.
> You need to fully understand the whole process and methodology of refining to be able to see what's happening or not, this unfortunately you do not, if money isn't the problem I suggest employing a competent refining chemist or even just a competent refiner but you really need to know what they are doing and why.


Not actually as difficult as you might think.
A simple credit check and a little field work to see if there has been any out of character purchase will yield wonders.
I have spent twenty years in the security and investigative services and I have to say the idiots always expose themselves


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## 4metals (Apr 29, 2015)

The key to profitability in the refining industry is your analytical chemistry. Knowing how much gold you start with is critical as you can imagine. 

Before you beat yourself up about yields and how much gold you lost, let's discuss how you determined how much was there to begin with. 

So if you will, let's discuss your assay lab and review a few things that may help you to determine how good your lab is. 

I assume you do both classical fire assay and have some sort of XRF device for quick assays, is this correct? Then, based on the fact that you said your purity of the most recently refined lot was .9992, are you using either an AA or an ICP for checking your purity? 

Starting with some basic analytical concepts. A good analyst will always run multiple samples of the same material, using whatever method your lab has available. So to start with let's talk about accuracy and precision. A common mistake is people thinking they are the same thing. Accuracy is how close your result comes to the actual number. This is often difficult to pinpoint because human nature has us exaggerating these things or understating them depending on which scenario best serves our position. But a good assay is very close to the real number. Precision, on the other hand is how close your results are to each other. Remember I said a good assayer runs multiple samples? I prefer at least 3 samples and if the results are very close to each other, there is a high degree of precision. If I can get 3 samples to assay within .0001 of each other, I see that as a high precision assay and I would take the result to the bank and assume high accuracy. By looking at the spreads between analyses your assayer performs on the same sample, you can see how precise he or she is. Also submitting the same sample under a different lot number a few days later and seeing the result is a fair test as well. Sneaky.....maybe, but helpful!

I think it is critical for you to determine how good your own starting numbers are. It is also critical to do a proof corrected fire assay as results can vary by 1/2 to 1/3 of 1 percent based on the correction factor calculated. All of this leads to attaining the right starting numbers. If you would like we can discuss the techniques for a corrected fire assay here. We have a good number of members who have hands on fire assay experience here, it wouldn't be an exaggeration to say easily tens of thousands of individual assays if we added them all up, so detailing this process for you can come from others as well as me if I become a little too long winded! And I heartily encourage discussion here. 

I would also like to know how you attain your silver assay. Is it by difference from running a doré bead? And how does your assayed result compare to your fine silver recovery? 

Moving on, assuming you started a lot with 10 Kg of assayed material with an assay of 92%. You are confident the assay is good because you have reviewed the assayers notebook and the precision was acceptable. That means you expect (32.15 x 10) X .92 = 295.78 ounces to come out at a 100% yield. We know because you found values in downstream liquids and ducting that 100% is not attainable, don't lose sleep over it, nobody attains 100% accountability. 

So you shot all of the gold recovered and it weighs 294.89 ounces. It assays at .9992 so your actual recovery was (.9992 X 294.89) = 294.65. The difference between what you started with and ended with is what you lost (temporarily hopefully).... (295.78 - 294.65) = 1.13 ounces. 

Dividing what you lost 1.13 ounces by what you expected 295.79 equals .382% lost.
Subtracting that from 100% you get 99.618% which is your lot accountability. 

These were numbers I made up for example, most refiners running decent sized lots are coming up with in house accountability of 99.85 to 99.9% or better. And the losses do turn up in ducts or spills or in the silver chloride which in this case was not even calculated. 

Now that you know how this is calculated, you can calculate your refining lot accountability for every lot (a very effective management tool!) and in discussions with your Middle East refining buddies find out their actual refining lot accountability numbers. Tracking these numbers routinely is critical to loss control and continual improvement. There is nothing that workers notice more than the boss coming out the day after a lot and letting them know that he knows EXACTLY how good or bad they performed. I always reward good performance and also let them know when there are issues. It is quite possible that a lot high in silver can hang up excessive gold which is not reduced and assayed for a few days, but when your workers know you have that under watchful eye they respect that. 

Cameras can only go so far.....the workers knowing you know what is happening gives you better control. 

If you can get back to us with a discussion of your analytical abilities in the refinery we may be able to help you fine tune this operation further.


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## 4metals (Apr 30, 2015)

Glowing hot gold bars, now that's a picture you don't see often. I assume you weigh out your shot and melt and pour while using a torch to prevent it from cooling too quickly? You should consider "toughening" your bars with a pinch of niter, it may be all you need to solve the copper color on the bar. 



> One small problem we faced during the Aqua regia process was that we had undissolved grains of approx. 302.00 gms.



For now I would attribute that to lack of heat driving the reaction. If the buildup of silver chloride buries the gold shot it will slow down the reaction so the agitation needs to keep the silver chloride moving. In any event, when you have undissolved material mixed with silver chlorides you need to separate the two.

For simplicity sake you can screen the silver chloride / undissolved shot in a polypropylene mesh screen. The screens I like (because they work well, are inexpensive, and last for a long time) look like this:



The screen sits perfectly in a 5 gallon plastic pail and you place the chlorides and undissolved on top and wash through the majority of the fine silver chloride particles. Remaining on the screen will be the undissolved, often crusted over with silver chloride. These can be put in a 4 liter beaker and heated in ammonium hydroxide. This must be done in a laboratory hood. The silver chloride will dissolve and the gold color of the shot will be apparent. 

Rinse the undissolved material, dry the undissolved and melt it into a bar. Assay the bar and subtract the gold content from your expected yield as discussed in the previous post. It can be added to the next lot for refining. The ammonia solution now needs to be addressed. You should add Hydrochloric acid to it slowly after it has cooled and you will generate silver chloride as all of the silver chloride that was encrusting the undissolved shot which the ammonia dissolved, will drop out again as silver chloride. Filter this chloride and add it to the silver chloride you collected with the screen and all of your silver will be together for reduction.

While there are other ways of going about this, this is direct and pretty quick, and it doesn't cause you to end up with an alloy high in silver to deal with.



> For now we have kept that solution aside as it is. ( Pictures of the solution with SMB and with Zinc addition have been put up.)



I do not understand why you added additional metabisulfite to the solution and then zinc. Your friend in a refinery is stannous chloride. (although it was not your friend the way you were using it) You should be testing the solution as you are dropping the gold from solution. When it tests negative to the stannous chloride test, all of the gold is down. 

What did adding the extra metabisulfite do for you? And the zinc, did you add it to recover values from stannous testing? It does not warrant adding zinc, and producing waste treatment issues down the line, if your testing shows no values to be recovered. 

It is encouraging to actually hear someone received bars from Africa that had gold in them. Here in the US refiners get calls daily by sellers of African gold and it is always a scam. I have melted quite a bit of "African gold sponge" which looked like the real thing, only to be an alloy containing no precious metals. We quickly learned to give the sponge a quick nitric test before wasting time melting.


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## 4metals (Apr 30, 2015)

I made a spreadsheet while on the train this morning. 

Fill in the yellow boxes with assays and weights and it gives you the accountability. 
As you add in values from the silver bar and undissolved the accountability goes up
Make one of these for each lot you run and fill in the blanks

View attachment Gold refining lot accountability.xlsx


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## g_axelsson (Apr 30, 2015)

That's great!

I made it even greater... :mrgreen: 

There is a pale yellow field after the unaccounted gold holding the unit. Now you can change it in grams, kilos, grains or even elephants. :shock: Just write your unit of choice there and it will change all the other places on the spreadsheet.

Göran


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## ashapura refinery (Apr 30, 2015)

Details of our assaying:

We have our own assayer in the refinery who has some good experience and has worked in assaying labs for more than 6 years. (The new person we hired after the old one left.)

Now generally we take 3 samples of the dore bar - 2 back from back side and one from the front. These samples are both taken for the fire assay test which takes place in our refinery itself. And we divide the three samples before we take it for the fire assay so that we can also get an xrf test done on this (XRF testing is done outside our premises as we do not have the equipment for that.
Dore pictures with sample taken - 


For the fire assay test we have muffle furnaces and also the 6 digit scale for proper weighing of the samples. Most of the time fire assay and xrf result have a difference of 0.0005 (example 0.9296 and 0.9291), we calculate the average and then proceed ahead.

Today we did the accounts of the process we have done and here it is: 



The silver chloride process and the checking of the drain valves, the filter cloths, the pipelines is pending.

Also here is a picture of the gold bar:



During the melting though we faced a problem. As you can see in the picture below, after the melting we cut a part of the bar and inside there is a shape which looks similar to a honeycomb. Generally when a bar is cut this kind of a shape does not come.


Also after the pouring of the gold in the mold, there is a small point where it gets sucked inside and then there are some spots on the bars. Probably this is because of the presence of some other material.


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## goldsilverpro (Apr 30, 2015)

I've worked in many refineries and internal theft occurred in most all of them, especially the small to medium sized ones, most of which had lax internal security. In some cases, the thieves rationalized that since the refinery was stealing from the customer, it was OK to steal from them. In most cases, they just fired the employee. Too hard to prove anything, legally.

When I had my own refineries, a method I used to help avoid theft (at least in my mind) was to know exactly what all the in-house scrap materials were worth and I also kept track of scrap inventory and weights. Thank God for fire assay, AAs, a good lab, and a variety of good balances and scales. I let the employees know I was doing all that. They always saw me pulling samples and running assays. They had no doubt that I had the ability to evaluate anything.

At a big plating shop where I once worked, they caught a guy that had been stealing nickel (primarily) and copper anodes daily for about 7 years in his lunch box. Adds up. A gram or two of gold per day also adds up fast.

When I worked at a big refinery in Hong Kong, all the employees wore fairly skin tight overalls with no pockets. There was also a metal detector when they left for the day.


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## 4metals (Apr 30, 2015)

Generally a refiner does not accept a melt done outside of their facility. I have seen all sorts of games played with gold coated steel and other devious methods used by sellers who want to be paid quickly. When you get a bar in from an outside source, you should melt the bar, sample with a vacuum pin dip, and pour back into a bar. This will help you to avoid some potential issues. 

One issue is anything foreign in the melt will show up and you will know the bar was not homogeneous. Another benefit is any melt loss will be on the new bar and as a refiner you should pay exclusively on after melt weight. 

Once you know a customer, it is possible to melt the bar, take a dip sample, and then pour the shot to granulate the metal for digestion. I always like to dry it and weigh it after granulation. This way you can avoid one melt. 

Vacuum dip samples are better than drillings, they are more homogeneous. This is a website of a manufacturer of the sampling tubes. http://pintubes.com/bur139/

I believe the honeycomb you mention is just the mark from the blade cutting the section, I do not usually cut fine gold bars to see the insides so I would seek a second opinion on this question.

The caved in section you mention is normal and can be prevented by playing a hot torch over the bar immediately after the pour to slow down the cooling off process. If you were to not use a torch at all it is likely on high grade gold to get that caving in, which we refer to as a pipe, along the entire center of the top of the bar. Slowing the cooling with a torch will eliminate it completely if done properly. From the looks of your bar, you do some torching after the melt and this bar was not torched long enough. 

I think you can eliminate the spots on the bar by toughening with niter. 

Using the spreadsheet posted above, fill in the numbers from an actual lot and let us know your accountability.


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## Lou (Apr 30, 2015)

That is the formation of a pipe. This happens more and more prominently with higher and higher purity gold.
Watch this video carefully:
https://www.youtube.com/watch?v=nQ37SFKahc0
You heat the mold hot, and you bathe it in a reducing fan flame of methane or hydrogen gas to keep the gold surface shiny and control the solidification rate. 

You need to bring XRF in house, even if it's a handheld thermofisher Niton gun. It's close enough for ball parking.

Also, if you're drilling the bars, sometimes iron from the drill bit will add iron to sample, decreasing the purity.


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## goldsilverpro (Apr 30, 2015)

A fairly standard way (I've seen it in several old mining books) of drilling bars is to drill 3 holes on the top side and 2 on the bottom. The 3 on top formed a diagonal line - 1 at the center and 2 at the 2 corners forming the diagonal with the center. The 2 on the bottom were at the 2 corners not drilled on top. All 4 corner holes are brought in from the corners somewhat. On a 1 kilo bar with the same proportions as yours, I would bring the holes in at least 1/4", both horizontally and vertically, from the corner. On larger bars, bring them in proportionally. All holes are drilled only half way through the bar. If roughness is present on the top, which often happens with, say, 14K, I first drill very, very shallow holes on the drill press, just barely enough to clean up the surface. I remove those drillings and then drill the same holes as normal.

Since I don't want a ton of drillings, I prefer about an 1/8" drill bit for gold alloys. I put the ingot inside a small PVC tote box about 3" deep when I drilled. I then collected all the drillings and used a pair of jeweler's shears to cut them up into in small pieces. After blending the pieces together, I pulled at least 3 separate samples for assay. This method was proven to consistently give very good correlation with the triplicate assays.

With an induction furnace, though, I would give it a good stir and then take pin samples.


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## Palladium (Apr 30, 2015)

I'm way out my league on them size bars, but I can speak of what I see from the experience side. The honeycomb you speak off I've seen before. Though not quiet that bad. I pour smaller bars so it less pronounced for me. That usually occurs between what I call a cooling ridge . Your bar didn't lay flat so where that rise or loaf is indicates a cooling rift. The outside of the bar cooled and formed the ridge or loaf before the middle solidified. The middle solidified as a mass at a later point than the ridge because of the thermal mass that the middle holds. The outer regions towards the edge radiates heat at a faster rate. Looks like you were almost there but not quiet hot enough, long enough. This can be caused by a cold pour, or a cold mold. You need a ox void environment, a pre heated mold, and enough btu heat to allow a controlled cooling effect. Do that with what 4metals recommended with a pinch of niter. Cool it slowly and it will make a holographic crystal pattern that will blow your mind. I would then clean them up with a 15-25% nitric bath and never have to touch them with a brush. The brush marks present a negative to me. The nitric will remove the flux and any oxides and do them more justice than that brush. Stamp them just the way they are. I've made the crystal pattern a trade mark in my gold bars for clients and they fall all over themselves for it. I assume with the money you've spent you're using induction?


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## ashapura refinery (May 2, 2015)

@4Metals:In Africa, we have our own business setup there. We buy the dore gold directly from the miners. We get the gold in small nuggets so after the collection and checking the purity we melt it at our own office (we have a small induction melting furnace for melting all the collected gold). This way we avoid a problem of melting at someone else's place. 

Now when we receive the gold dore at our refinery, the entire process right from the 1st melting to the final production of the gold bars is done here itself. For this we have Induction Melting Furnaces ( 20 Kg Melting, 8kg Melting, 5kg Melting and 1 Kg Melting Machines ). The only time the gold goes out of the doors of the refinery is when we need an XRF test and after the xrf test is done the gold weight is checked at our premises to make sure we have not lost anything.

@4Metals and @Goran - Thank you very much for this spreadsheet, it makes calculating even more easy. Hopefully this will benefit not just us but more refiners on this forum :lol:

@Lou and @ Palladium : We generally melt the bar, and make sure the gas torch is on when we are about to pour the gold in the mold. But we do not keep the torch flame on for a long time. So as per what you have said we should try keeping the flame on for a bit more longer than usual and reduce it slowly. Hopefully this will not result in the pipe formation and also help in getting a much more better finishing. But we must say that the finishing of the gold bar is way more better than the last few batches.

@Palladium : Yes we use induction melting machines. We have tilting induction melting machines(20 Kgs and 8Kgs) and also the normal induction melting machines (1kg and 5 Kg). We are using tilting for bigger quantities to make it easy for the staff to pour out the gold instead of risking carrying it out by hand.

@Goldsilverpro : we make holes of about 1/4" deep. But as per your suggestion of 5 samples - 3 in the front diagonally and 2 on the back - this will give a good coverage so next time we test we will make 5 samples instead of 3. 

We are almost done with the cleaning of the drain valves, the pipes and everything. Once it is 100% complete we will definitely get back with the actual accountability to know how better we have done this time. 
And this time we had our eyes on the staff - there were 4 staff members who were working for the entire batch and three of us keeping a watch. So this time we have ruled out the problem of theft. Hopefully our recovery is better than the before batches. We will keep you all posted on this.


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## nickvc (May 2, 2015)

When commercially melting, recovering and refining the profits can be from the residues rather than the actual refined gold. If you are using flux in your melting make sure to keep it, there are posts here about how to recover any values within it most from the experts. The flues over your melting will need cleaning again keep the dust, sweep and keep everything off the floors especially in the melting room, basically anywhere you have had values think if there may be anything to recover.
As an aside I had a good friend whose family were jewellery manufactures in India and the only scales in the factory were kept in the owner's office, gold makes people do very odd things, I'm not saying your staff are thieves but put security in and point out that it's for their safety as if anything does go missing you can prove it wasn't them but as pointed out the best security is in you knowing exactly where your values are in what form and how to recover them, if you don't the old smoke and mirrors trick is easy to pull.


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## 4metals (May 3, 2015)

A few more questions for Ashapura,

So I gather from the response that their refinery has a fire assay lab, no XRF on site, and apparently no instrumentation, either ICP or AA. Is this correct?

Do you correct your fire assays? If so what result does this purity of feedstock average for a correction factor? 

How is it possible then for you to state the purity of your fine gold bars for sale? XRF?


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## 4metals (May 3, 2015)

> When commercially melting, recovering and refining the profits can be from the residues rather than the actual refined gold.



This is very true. Fortunately Ashapura is refining gold they have purchased at another location so their margins are not subject to the cut throat price wars happening between refiners these days. But when a refiner's margins are tight, often the profits are found in the residues. 

The accountability we spoke of earlier usually comes out showing a loss of values. There are exceptions though. Sometimes the difference between individual assays is sufficient and if your result comes out on the high side of the average, you can actually exceed 100%. That doesn't mean that you made gold, but it does mean your results exceeded your average assay result. 

I can be pretty anal when it comes to recordkeeping in a refinery so I track all of my losses due to accountability on a spreadsheet. Then when I ship out slags for recovery, burn all the burnables and assay for values, clean out ductwork, or process stock pots from cementation, I add these numbers back in to my running totals and keep track of how much metal was "lost" to individual lot processing, versus how much metal was recovered in the facility from processing residues. If the gold retention is low enough in the silver recovery, the gold from the slimes recovery process is added in here too. (Just don't add it twice, it either goes back into the lot it came from or in when you clean up the silver cells) 

In the long run, with good assaying and good housekeeping, you can get back almost all of what you expected to get from the individual lots. Unfortunately, you usually have to end up waiting for that last 0.15% until you clean up all of the drips and settles and other unscheduled events that yield values to your operation.


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## nickvc (May 3, 2015)

4metals I agree about the OP been in a fairly lucky position with their materials but I would still want to know every last trace of values were been recovered and that the incoming weight and the final weight recovered were within the correct expectations. 
Running a successful refinery needs constant attention and professional attitude letting anything slip will allow discrepancies to be made by employees if they so decide.


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## 4metals (May 3, 2015)

Nick,

Not sure I would call it luck that they are in the position they are in, they set up a buying operation, managed it well, and obviously were able to set up a refinery to process the material themselves based on their profitability. 

But I agree, every refiner needs to be certain that their operation is running within their own defined and acceptable parameters. The numbers don't lie, and if you see the numbers slipping, the ability to go into the plant and start asking questions from an informed perspective will generate respect from your employees. Being aware of your losses and sharing that awareness with your staff makes anyone thinking of stealing think twice. (Share the awareness, not your techniques!)

As many people smarter than me have noticed, gold makes people do weird things!


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## 4metals (May 9, 2015)

The moderators would like to thank all of the members that contributed to the original thread upon which this thread was based, as well as those that asked questions showing what was missing. Because of the extra length and interest in this thread we have created the above consolidated version making for an easier read. We encourage all members to read, comment, and ask questions in the original thread, Refining of Gold from Mines

The Library threads should not be considered to constitute a complete education. Instead, they're more like reading a single book on the subject of recovery and refining. There is so much more information on the forum, and it is impossible to include it all in these condensed threads. Members are strongly encouraged to read the rest of the forum to round out their education.

For those who prefer a printed copy, a pdf file of this thread is provided below.


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