Refining of Gold from Mines

[ashapura refinery]

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??

 

[4metals]

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 scenario's 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.

 

[ashapura refinery]

@ 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 upto 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 loses. 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 chlroide 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.

 

[Barren Realms 007]

What is the average purity of your starting gold?

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

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

 

[ashapura refinery]

@ 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.

 

[butcher]

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 your 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 procedure's...

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 chlroide 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.

 

[4metals]

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 processes 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.

 

[Lou]

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!

 

[4metals]

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.

 

[ashapura refinery]

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.

 

[goldsilverpro]

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

 

[4metals]

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 photo's do not show this collection vessel but it should be there.I see it now in the smaller photo's 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 definately 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; Harolds 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 photo's 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.

 

[Palladium]

4metals lives for this kind of thread and i love reading and learning from his replies.

 

[4metals]

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 lets 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.

Lets 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 reocvery 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.

 

[g_axelsson]

This reply was written a coupe of hours ago, before the two last replies of 4metals, and I wrote some that now is a repitition 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 don'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 mthods 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 advice 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 shouldnt 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

 

[Anonymous]

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 of 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

 

[Palladium]

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

 

[Anonymous]

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

 

[Palladium]

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.

 

[Lou]

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

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