consolidation of Loss Gold thread

[4metals]

I set up a refining system, but I have little experience. To know if I was on the right track, I wanted to report one of Refine operations.
Please help me about losing gold in this operation.


We performed refining operation using the AR method. Our input was 2610 grams; Analysis includes: 765 gold, 68 silver, 148 copper, 8 zinc, 4 nickel, 6 cadmium and some others.

We calculated the acid values to digest 7.5 ounces per liter of solution. Hydrochloric acid 32%, 9.3 liters and 2.3 liters of nitric acid 64%. We flaked the gold as much as possible. Then we poured it in Tumblr.

We added 7 liters of hydrochloric acid along with 1.3 liter of nitric acid.

We also added some hydrogen peroxide during the slow reaction. After one hour, the reaction was somewhat balanced, we added 3.5 liters of hydrochloric acid again and slowly we added 1.1 liters of nitric acid.

After four hours, the reaction was very low. I added about one kilogram of 46% white urea to neutralize nitric. About Urea , I have little experience with urea. I added until the bubbles on the surface of the solution diminished. I added a little water. Then I did not see a quick reaction by adding urea.



After a while, I added 12 liters of 4 C cold water. We waited for a while, then filtered the solution, left the silver chloride, and transferred the solution with water until the transfer path became clear. At the end of the Tumbler wash we had 111.38 gr unresolved gold.

In the case of solid gold residue, I did not notice washing it with ammonia. Because they were not covered with anything. I first tested them with XRF and then melted them, their assay was 771 Au.


I Approximately 1.8 liters of 55% hydrazine is dissolved in 2.2 liters of water and Slowly add to solution in half an hour.

Add the flocculate , leave the solution for 12 hours.



The liquid became green and clear, we filtered the liquid into a secondary tank(with Fabric polypropylene), took all the pure gold. Then we washed the gold powder with hot water. Then we dried the gold powder in a steel container.

We filtered the solution with two polypropylene cloth filters. We did not use a paper filter, of course I like the paper filter because it does not absorb. We took more than 98% of the solid particles from the first fabric filter and the rest from the second filter. We thoroughly washed the filters. Some gold precipitated, we took it and sent the remaining liquid to the second tank.



Stannous test, when the gold was sitting on the bottom of the solution, I tested the solution on top of that gold. The answer was negative.

Unfortunately, after filtering the solution, I did not try again.

Also, all the water has been added to them while washing, now it may be close to 200 liters.

I added some aluminum to the solution and mixed it and let people do it.



I need to learn more about Stannous testing, it's very important. I have never had a positive Stannous test.



After melting and XRF test, the purity of gold was 999.6 Au and it was shown in the analysis 0.4 cu cu and no silver Ag. (But it seems not enough washing) because the surface of gold bullion was not best quality, Their surface is star-shaped impurities.



We dried the gold powder in a steel container, then melted it in an induction furnace with a new plant.



After accounting, we do not have 12.6 grams of gold. I'm surprised, all the steps went well, no errors, and I'm sure of the scrap analysis. There may be some during the initial dubbing and gold powder, but we were careful and definitely not a lot. We have two places still left, silver chloride, the second bunker deposit.



I added two sheets of aluminum to the second bunker.



Then we mixed well every few hours. We added flocculate and left for another day.



we filtered the place, the amount of jelly powder had accumulated on the bottom of the bunker.



We took it and heated it in a steel pan and it was almost dry.



We tested with XRF. Showed 30/1000 gold.


We transferred the rest of the solution to the third bunker and added the aluminum again.

So far, 12.6 grams of that lost gold, 3.6 grams in the second bunker have been deposited in the sludge, so our lost gold is about 9 grams.



How to get the gold in this purple powder?



My friend told me ,that powder put in reactor for next part refining. Is it ok?



So far there is some gold in silver chloride and maybe in the third bunker solution.



Dried silver chloride is about 170 grams, but I know the silver get is much less, right?

XRF testing of silver chloride showed that 98/1000 of it contained gold.



In the third bunker, after filtering, sludge containing 2/1000 gold was taken.(Almost very little)



Here I want the best way to recover the silver chloride to get the gold trapped in it and recover the silver.



Where do you think gold has gone?



This is important for any refiner.



It will not be economical to continue with these calculations.



Can you help find the deficit and control the various steps for possible corrections?

 

[4metals]

These are the photo's of the system shared by the OP.

 

[4metals]

We can best serve the needs of the OP by starting at the top of his descriptions and both clarifying his process and making suggestions for discussion. Any additional photo's can further benefit this thread.

I'll invite others to start and do my best to keep this on the rails and work towards a successful resolution of the OP's problems.

I realize there are questions we may have which can only be answered by the OP, by example what was the flocculant used and quantity. His participation is necessary for a successful resolution.

 

[nickvc]

It’s possible with the cloth filter that with fine particles the loss may well be there , he could pour a weak AR solution through the filter and see what is actually there.

 

[4metals]

There are questions I have based on the terminology he has used. for example what is a gold sedimentation bunker and at what phase of the operation is it used. I am familiar with the italian systems called tumbler plants which are quite similar and they look like this;

In much the same way the solution drains from the drum and is filtered through a filter media. I would expect the manufacturer to have supplied or sourced proper filter media for both the aqua regia filtration before precipitation and after.
There are also in line filter canisters used which are notoriously difficult to rinse free of values. where in the line are these filters? More details will be both informative for our members and helpful for the OP.

 

[4metals]

"We calculated the acid values to digest 7.5 ounces per liter of solution. Hydrochloric acid 32%, 9.3 liters and 2.3 liters of nitric acid 64%. We flaked the gold as much as possible. Then we poured it in Tumblr.

We added 7 liters of hydrochloric acid along with 1.3 liter of nitric acid.

We also added some hydrogen peroxide during the slow reaction. After one hour, the reaction was somewhat balanced, we added 3.5 liters of hydrochloric acid again and slowly we added 1.1 liters of nitric acid.

After four hours, the reaction was very low. I added about one kilogram of 46% white urea to neutralize nitric. About Urea , I have little experience with urea. I added until the bubbles on the surface of the solution diminished. I added a little water. Then I did not see a quick reaction by adding urea."

Let's start step by step to review what was done here. First off as a rule of thumb for every liter of aqua regia you will dissolve 7.5 ounces of metal.

starting with 2,610 grams. 2610/31.103 = 83.9 ounces. let's call it 84

84/7.5 = 11.2 liters of aqua regia.

since you have a chilled condensed vessel some of the nitric will recondense back into the reactor so you can get by with a 4:1 aqua regia mix. 4 parts Hydrochloric Acid one part Nitric Acid

Thats 5 parts total. so...... 11.2 liters total divided by 5 is 2.24

This means you add 4 times 2.24 liters of Hydrochloric Acid which we round up to 9 liters. This should be all the aqua regia you require. Your total Nitric Acid addition should be 2.24 liters which should be roughly divided into 3 equal portions.

All of the hydrochloric can be added from the start, along with 1/3 of the calculated nitric. The reaction will begin and once the reaction has risen and begins to subside, the second third of nitric should be slowly added.
In a production environment (with the equipment you have) generally the full complement of acid is added to assure complete digestion. When the reaction again subsides, the last third can be added. Allow the reaction to go to completion at which time it should not be blowing any red fumes.

Is this a heated vessel? Some manufacturers have heaters for tumbler plants. If you do it will assist with the rate of the reaction.

I do not think it wise to add urea while it is in the tumbler plant. A better choice would be sulfamic acid. There are. many posts on the forum concerning its use and it will cause less issues down the line should your scrap contain any platinum group metals you wish to recover later.

Once the reaction is complete I would cool it by throwing in ice. Ice has the benefit of chilling the solution and diluting it at the same time. Silver is much less soluble in cold solutions and is more likely to be eliminated as it will be captured by filtration when you filter the solution out of your reactor and transfer it to where you will precipitate the gold.

What filtration is employed between the filter it drops into to be transferred to the precipitation tank. I believe it to be what you call the Silver Chloride filter and also the cylindrical filter. Please verify if this is correct.

On the silver chloride filter will remain all of your undissolved gold and all of your silver chlorides. The best method here is to rinse the chlorides and insolubles into a pail of water and store them in water until you are ready to process them.

Please let's comment and question on the process up to this point before moving forward.

 

[Martijn]

I got that same message in a private message and advised him to post it public. He only took part of it to the public forum as far as i know.
I have way to many questions from that first long post.
Hat's off for diving in

 

[Gold.refinery]

Hi guys ;

I was finally able to convince my partners to share refining operation information.
I am here to gain experience from gold refining specialists, I am ready to answer your questions step by step. Then I will ask my questions.
We did another operation in the last few days. Some ambiguities remain for us, but I like not to raise issues sporadically.
I would like to ask Dear 4metal to take these issues step by step.
We have little experience, but we will succeed with you.

 

[Elemental]

@Gold.refinery,

We are all here to learn and share knowledge. While I understand you came here looking for the help of our specialists, a major part of this forum is the free exchange of information and knowledge of refining from the hobby to industrial level. While I can appreciate your desire to keep you refining operations information as a cooperate secret, please understand that to ask questions here requires transparency so others may learn.

If you seek the freely given information here, then please share freely as well. I have no doubt that many of our specialists would have no issues with contracting themselves out as consulting specialists, thus allowing for NDA's and the what-not at an expense to your business.

That's my two-cents on that, I'll get off my soapbox and see if I can't put some math to your process and help out on the chemistry side as well.

Elemental

 

[4metals]

Is this a heated vessel? Some manufacturers have heaters for tumbler plants. If you do it will assist with the rate of the reaction.

What filtration is employed between the filter it drops into to be transferred to the precipitation tank. I believe it to be what you call the Silver Chloride filter and also the cylindrical filter. Please verify if this is correct.

Start with answering these 2 questions

 

[Gold.refinery]

1)
In the last operation, all the feed was dissolved in 4 hours, except for 22 gr of 2900 gr.
No, Tumblr does not have a heating system. Just to help better reactivity at the beginning and end of the AR reaction, we add some hydrogen peroxide with Dosing pomp.

2)
The solution to exit the Tumbler first reaches a polypropylene cloth filter (sucked by a diaphragm pump), then passes through it through a short path with a hose to a vertical cylindrical filter (as shown). And then pours into the tank for sedimentation operations.

 

[4metals]

The tumbler plants I am most familiar with are made by Italimpianti. The newer ones do have a heat option but it is a luxury and not necessary for karat gold refining. I have never found it necessary to add peroxide to get a good vigorous reaction in a tumbler plant.

When you filtered the solution out of the reactor, sitting on the filter paper was what? Silver chloride and 22 grams of undissolved karat? Above you also said 111 grams. To avoid confusion here let's discuss one lot with all of the specifics. I am sure there is language translation going on here and I want to minimize confusion. The gold recovered as undissolved shot in your filter is not gold you lost as you accounted for it, it just needs to be refined.

What we are looking for here from one of your original questions is gold that does not emerge from the system at the end. Gold that is lost to the process. For this lot that you have mentioned last, how much gold that was expected based on assay did not come out of the system?

When gold containing silver dissolves in aqua regia, it is not uncommon to have a small percentage of the gold mixed in with the silver chlorides. With a tumbler plant that number should be less than with a static motionless reaction. Generally silver below 7.5% will be low enough for an effective dissolve. Tumbler plant manufacturers say you can push that number up to 10% because of the mechanical contact breaking away silver chloride crusts. I have found this to be true in practice. If the size of the shot you dissolve is too large you will leave more values undissolved.

When the solution is drained into your filter from the reactor, the solution contains most of the gold. I mentioned in an earlier post that a single drop of gold at today's prices is worth around 41¢ so it becomes critical to get as much of that liquid to the tank you will be precipitating the gold in. Based on your original alloy composition you were looking at green aqua regia. When you filtered everything through the filter, how did you assure yourself you got all of the liquid rinsed from the reactor? And once you pulled all of the liquid through the filter paper, what color was the paper? If it's green it is holding gold that will show up in the loss column. Until you are comfortable with the process you should learn the simple stannous chloride test well documented on this forum. The pumps and base of the filters also can trap liquids which hold gold. You need to open up the filter and check out the bottom to assure you are not leaving values behind.

This is the inside of a typical filter, you can see it is easy to leave values behind without complete rinsing. And the smaller the lot, the larger the losses are.

The filter path you showed also has a cylindrical filter in the line. These are difficult to rinse free of values. Here you should also test the filter with stannous chloride to make sure it isn't trapping solution. If you can, provide a photo of the system so we can see the path the loaded acid follows to your precipitation tank. it is critical that you can be sure you are rinsing that pathway clear of values.

Before you drop your gold from solution, the volume of solution you lose can be as small as half of a small diners coffee cup and it will be all of the gold you are looking for. This is an area worth looking at.

Please respond to these, and other questions you may be asked, before we move on the the chemistry of gold recovery.

I would like to ask Dear 4metal to take these issues step by step.
We have little experience, but we will succeed with you.

One more thing, those who know me certainly know I am no dear! And I fully expect to hear from other members with hands on experience so we get a wider perspective on your system.

And more photo's will help us to help you with your precipitation process as well as your cementation process you mentioned when looking for lost values.

 

[snoman701]

Rinse your AgCl with very dilute HCl until you get a negative stannous test. I cannot imagine running the above system without stannous. 4metals post should put it in perspective for a lot of people...a little bit of liquid is significant amount of money. Go get yourself a roll of 95% tin solder at the local hardware and make some.

 

[Gold.refinery]

I never calculated the unresolved gold in the reactor as lost gold.
I did 3 experimental refining operations in the last few days to gain experience. In the second operation, 111 grams of gold was not dissolved, in the third operation, 22 grams remained unresolved.

In the second operation, 12.8 grams of gold was not obtained. As mentioned, by dissolving some aluminum in the mother solution, I obtained 120 grams of sludge, which contained 30/1000 gold (approximately 3.5 grams gold), this sludge. I added to the feed in the third operation.

To ensure complete washing of the reactor, we have the possibility to open the door completely from the top of the reactor. And the reactor is thoroughly washed. We also take out the unresolved gold.
When all the solution came out of the primary silver chloride filter, it was gray, there was yellow liquid in some places, it was washed with water flow and suction pump, to make the hose route colorless.
The bottom of the filters, the way of the hoses, the valves, are washed together after each operation.

I will send the solution way from the reactor to the gold sedimentation tank.

I will also answer your other questions about the calculation of chemical quantities (especially the amount of sediment),
we do a lot of this experimentally and See reactions with eyes , not computationally, this is not desirable. Because it pollutes the gold and adds the next steps.


We have a Stannous test , but we do not know when to use it exactly .
We have not seen a positive test so far.
After filtering the solution, we wash silver chloride with hot water. We have never done washing with hcl. Maybe it's better to test the solution left in the hose with stannous,
you mean?

I have many questions, but I'll answer your questions right now.

 

[nickvc]

I think we should start right at the beginning of the whole process so
1 I’m assuming you are taking your numbers from an xrf reading hopefully from several areas at least top and bottom of the bar ? Is that correct ?
2 once you have your reading you then melt the bar into flake ?
Do you dry and weigh that flake ?
Im asking these questions because melting areas can be a major contributor to loses or put it another way if the gold doesn’t reach your reactor you can’t recover it.

 

[Gold.refinery]

Hi nickvc
Yes of course , I test scrap gold bars from different areas, top and bottom,
Some of them I both XRF and Fire Assaying.

After melting the bars and flaking them, I will test again. The average is confirmed.
Also, out of three operations, I dried in two operations after flaking.It was acceptable.

 

[nickvc]

Thank you , that’s the first steps confirmed as minimal loses or possible causes of loses.
Next you load your reaction vessel with your flake and add your acids so where do any fumes go? I’ll assume you vent them off but what to?
If the reaction is fairly violent then any piping and the end recipient vessel could have gold solution in them , have you tested them ? A simple stannous test will confirm if you have small amounts there or larger amounts that could be some of your loses.
4metals will have a better understanding of any potential loses here rather than me as I have never used this sort of system but I think closed systems certainly have more chances of hidden loses, in pipes , filters etc , than an open one .

 

[Gold.refinery]

The vapors from the reaction are transferred to a titanium condenser condensed with gas to less than 0 ° C and returned to the reactor. I can test the circulating water in scrubbers with stannous , right?

Large-scale refining, for example, 20 kg in a shift work, is done with similar devices, of course, 4 metal must confirm !!!

 

[4metals]

Large-scale refining, for example, 20 kg in a shift work, is done with similar devices, of course, 4 metal must confirm !!!

The capacity of the system you purchased is based on the volume the reactor can hold. The manufacturer can tell you the volume in liters the reaction vessel can safely process. That reactor needs to hold approximately 86 liters of acid to process 20 kg per cycle. Some manufacturers are pretty slick and they realize you can push the system and process 2 runs a day so they rate the system as processing 2 lots. It is hard to tell from your system the volume the reaction vessel holds. That is something you need to ask the manufacturer. Ask them specifically what the working capacity aqua regia is in liters.

Their volume calculation should leave room for a reaction to rise without the solution level getting too close to the exit point of the fumes because it will suck out values (as Nick cautioned) if it gets too close.

Please post a photo of your system standing in front so I can see the distance relationship between the condenser and the exhaust port.

I have noticed that when anyone covers multiple points in a single post, especially if they get long, some questions are not answered. To assure we get all of your issues addressed, I will use a separate post for each important issue covered.

 

[4metals]

We have a Stannous test , but we do not know when to use it exactly .
We have not seen a positive test so far.

Stannous chloride goes bad. And it's not the kind of thing that you can predict based on shelf life. Since you have not seen a positive test for gold thus far, alarm bells go off in my head!

What I always teach new refiners is when you test gold solutions with stannous chloride, if the first test of the day produces a negative result, you have to test the test. This is simple to do. Get a small dropping bottle that holds perhaps 50 ml and use it to store acid which will test positive. To a small beaker add a half a gram of gold and dissolve it in a small quantity of aqua regia. When it dissolves, transfer it to the dropping bottle and fill it with water. You now have a solution that will keep very long that will test positive for gold with your stannous chloride solution.

I always like to see that dropping bottle stored right next to your stannous chloride testing solution so you will use it. What successful refiners know is that you CAN NOT tell if a solution has gold in it by looking at it. Stannous chloride is your eyes! And just like humans, you need to routinely have your eyes checked!

Please make up the test solution and test your stannous chloride. It is a small step but an important one.