Major gold losses in new gold refinery plant... Help!

[Yggdrasil]

First of thank you for refering to the previous thread, I have used it as a reference before my third attempt.
1- Fire assay was used and samples from different locations from the alloy were taken.
2- The composition of the feed were gold of 760 purity ( a mixture of 700-800 purity alloys)
3- for the silver chloride sludge we used iron and H2SO4 to recover and the silver from the first two attempts contained around 3 grams, so i did not count them in my losses.
4- for the liquids we only added caustic soda nothing else. I saw suggestions of Tin, and others of just letting it sit for days. I'm not sure which method should I use. If I'm considering the aluminum is there a standard procedure or specific amount to be added?

Her is something to study:
Pay special attention to safety and dealing with waste.

We ask our new members to do 3 things.
1. Read C.M. Hokes book on refining jewelers scrap, it gives an easy introduction to the most important chemistry regarding refining.
It is free here on the forum: https://goldrefiningforum.com/phpBB3/viewtopic.php?f=54&t=19798
2. Then read the safety section of the forum: https://goldrefiningforum.com/forums/safety.47/
3. And then read about "Dealing with waste" in the forum: https://goldrefiningforum.com/threads/dealing-with-waste.10539/

Suggested reading:
https://goldrefiningforum.com/forums/the-library.101/
https://goldrefiningforum.com/threads/when-in-doubt-cement-it-out.30236/
https://goldrefiningforum.com/threa...le-read-this-before-you-post-about-ore.33333/


Forum rules is here.
https://goldrefiningforum.com/threads/gold-refining-forum-rules.31182/

 

[goldandsilver123]

SMB isn't added in a specific amount, you will add as much as is needed, you will use a LOT if you had excess nitric.

How did you measured urea ? Or it was an fixed amount too?

 

[orvi]

First of thank you for refering to the previous thread, I have used it as a reference before my third attempt.
1- Fire assay was used and samples from different locations from the alloy were taken.
2- The composition of the feed were gold of 760 purity ( a mixture of 700-800 purity alloys)
3- for the silver chloride sludge we used iron and H2SO4 to recover and the silver from the first two attempts contained around 3 grams, so i did not count them in my losses.
4- for the liquids we only added caustic soda nothing else. I saw suggestions of Tin, and others of just letting it sit for days. I'm not sure which method should I use. If I'm considering the aluminum is there a standard procedure or specific amount to be added?

So this means that you never tested your waste liquid if it contains gold ? Or correct me if I am wrong.

Similar question as Yggdrasil, what is the purpose of NaOH ? Just waste treatment, or anything else ?

For aluminium cementation, you just add some clean aluminium scrap to the waste liquid and do it in small pieces, as the reaction is strongly exothermic. For this "test" purposes, it is not necessary to remove all metals, as gold will be reduced first. Aim for the moment where there is significant cement present in the mixture and it does not react with liquid. In that moment you can filter the sludge and measure it with XRF to see if there is some gold.

 

[orvi]

SMB isn't added in a specific amount, you will add as much as is needed, you will use a LOT if you had excess nitric.

How did you measured urea ? Or it was an fixed amount too?

Yup. I was gonna write this same thing

When it comes to chemistry, I never liked "manual with everything lined up precisely" Some ballpark numbers to start, but then, if it isn´t same case scenario (which with scrap gold never is), it can be very misleading to people who don´t completely understand the subject. And they can take it as some holy numbers, not paying attention to actual important leads, tests and signs.

 

[4metals]

I have been away for a few days and missed this thread but before I start I would like to apologize on behalf of the forum. Badman's comments do not speak for this forum, and he has no right to speak to you that way. From my perspective he should be banned for his behavior, personally I will never contribute to any threads where he is the OP.

Now to the problem at hand.

First off, I have a lot of first hand experience with Italimpianti tumbler plants of various sizes and they do not hang up gold to any appreciable amounts.

To start off please describe how you arrived at the assay on the starting material? Was it by fire assay or XRF?

What percentage of the starting alloy was Silver?

Was the entire lot melted together and poured into shot before digesting or were separate bars shotted individually?

The key to successful refining is to know what questions to ask when evaluating your technique. I know for a fact the equipment you have is capable of refining the gold you have so your issue comes down to technique. We can help you if you simply give us the details we ask for.

Also, I see no mention of stannous chloride. Do you have it and do you use it?
There is also no mention of silver chloride. Did you recover it and reduce it and assay it?

Finally, welcome to the forum Nouran. If you answer these questions we can get you up and running with good returns quickly.

 

[4metals]

These are some different size Italimpianti tumbler plants I have worked with. What model or capacity do you have?

 

[Nouran Alaa]

One company that we were consulting were using +10kg of urea per batch of 8 kg of gold. It was with an Italian reactor too, but not from Italimpianti.

Nouran, when you filter the solution, it's only the movable filter (big Polypropilene filter that looks very similar to a buchner funnel)? There's an filter cartridge in line on the output of this filter?

yes, we do use a lot of urea. and regarding the filter its a filter trolley made of polypropylene attached to it a diaphragm pump

 

[4metals]

 

[Nouran Alaa]

I have been away for a few days and missed this thread but before I start I would like to apologize on behalf of the forum. Badman's comments do not speak for this forum, and he has no right to speak to you that way. From my perspective he should be banned for his behavior, personally I will never contribute to any threads where he is the OP.

Now to the problem at hand.

First off, I have a lot of first hand experience with Italimpianti tumbler plants of various sizes and they do not hang up gold to any appreciable amounts.

To start off please describe how you arrived at the assay on the starting material? Was it by fire assay or XRF?

We used fire assay.

What percentage of the starting alloy was Silver?

unfortunately we did not measure the amount of silver before hand. But in the first and second attempt we recovered 430 grams of silver by treating the AgCl with iron and H2SO4 and we found 3 grams of gold entrapped in the AgCl.

Was the entire lot melted together and poured into shot before digesting or were separate bars shotted individually?

The entire lot was melted and thoroughly mixed and then added to the tumbler.

The key to successful refining is to know what questions to ask when evaluating your technique. I know for a fact the equipment you have is capable of refining the gold you have so your issue comes down to technique. We can help you if you simply give us the details we ask for.

Also, I see no mention of stannous chloride. Do you have it and do you use it?

We do not use it. The technicians where I live are not familiar with it. I have seen you explaining its importance in a different thread before and have researched how its made and willing to use it the next time.

There is also no mention of silver chloride. Did you recover it and reduce it and assay it?

We recovered it for the first 2 attempts and assayed it. as for the third attempt its still in the AgCl sludge form and to be treated.

Finally, welcome to the forum Nouran. If you answer these questions we can get you up and running with good returns quickly.

Thank you 4metals for your help, its very much appreciated.

 

[Nouran Alaa]

These are some different size Italimpianti tumbler plants I have worked with. What model or capacity do you have?
View attachment 62644
like this one
View attachment 62645
View attachment 62646View attachment 62647

its exactly like the first picture. It was sold to us second hand as 8kg capacity but with multiple use i would say it can only hold up to 5kg.

 

[FrugalRefiner]

Nouran, as 4metals posted, badman's opinions do not represent those of our forum. Badman has been banned for his disrespectful, racist posts.

Dave

 

[Nouran Alaa]

SMB isn't added in a specific amount, you will add as much as is needed, you will use a LOT if you had excess nitric.

How did you measured urea ? Or it was an fixed amount too?

We added around 900grams of urea to each kg of gold

 

[Nouran Alaa]

And of course... "Urea" obsession Why people in middle east and close countries use it everywhere, hard to say

2 kg of urea... Oh my

I can see people on this forum are not fans of Urea but you said very well its an essential in the middle east. I'll check the cost of sulfaminic acid where I live. It might be expensive here, I'm not sure though

 

[Nouran Alaa]

So this means that you never tested your waste liquid if it contains gold ? Or correct me if I am wrong.

Similar question as Yggdrasil, what is the purpose of NaOH ? Just waste treatment, or anything else ?

For aluminium cementation, you just add some clean aluminium scrap to the waste liquid and do it in small pieces, as the reaction is strongly exothermic. For this "test" purposes, it is not necessary to remove all metals, as gold will be reduced first. Aim for the moment where there is significant cement present in the mixture and it does not react with liquid. In that moment you can filter the sludge and measure it with XRF to see if there is some gold.

We did not test it. We filtered it after it stayed for a few days. Yes Naoh just for neutralization.

For the aluminum -correct me if im wrong- its only to test if there is gold and not a method of recovery is that correct?

 

[4metals]

Unfortunately, acid that contains gold looks the same to the human eye and working without any indication of how much gold, if any, is in solution will undoubtedly cause losses. Working with stannous chloride the refiner has an instantaneous indication of gold in solution while using only a single drop. And it is sensitive down to parts per million. So if nothing else, make some stannous chloride solution and do some familiarization tests to see how it works.

My guess what happened is you are using too much nitric acid, right off, I would lower the nitric ratio from 3 parts Hydrochloric Acid to 1 part Nitric Acid
down to 4 parts Hydrochloric Acid to 1 part Nitric Acid. This is effective because the reaction is condensed which essentially recycles a percentage of your nitric acid.

The urea is not consuming any free nitric acid, so using more nitric than necessary tends to leave the solution active after urea additions and can re-dissolve gold after you drop it with metabisulfite. If you use stannous chloride you can detect this instantly. Sulfamic is a better option but many people worldwide use urea effectively.

The tumbler plants also do not heat the solution. A heated dissolve allows free nitric to "burn off" and you can heat it until it stops blowing red fumes as an indication. You do not have this option.

You will have to rely on slow additions which allow the urea to work. Too much can cause excessive crystallization and hold up gold in the crystals. I assume you are adding the urea and dropping the gold in one of these?
you should slowly add urea and allow it to mix in. It will foam up violently with excessive additions. Add a little and wait for a reaction to subside. Then add a little more and wait. When you have added enough you will see the prills of urea start to float. That is when you stop.

Next you add the metabisulfite, again slowly with mixing. If the solution starts to blow red fumes that is only the excess free nitric acid burning off as the gold you just dropped re-dissolves. Not a problem, these slow additions will consume all of the free nitric and then the gold will drop and stay dropped.

If the gold alloy was from jewelry or had a percentage of copper in it the acid will be a green color. When there is gold in solution it affects the color and it starts out a brighter green and when the gold is out it is a dull green. Seeing this is something you learn and observe from doing it often enough, it never takes the place of testing with stannous chloride. When all of the gold is dropped, and your stannous chloride test is negative, the solution is dropped out the bottom of the vessel into the filter trolley to separate the gold from the spent acid.



When the filter removes all of the liquid the gold should look like this.

 

[galenrog]

Badman has been banned for his disrespectful, racist posts.

Dave

Saw this coming five days ago. Thank you for bringing the hammer down.

Time for more coffee.

 

[4metals]

A caution when using the filter trolley.

When the filter pulls the solution through the paper and under the plate, the pump transfers the solution to the next step. But you need to be sure all of the solution containing gold is out of the filter. You cannot see it. This is a filter trolley without the plate.

The pump can effectively remove most of the liquid but sometimes a little remains. If this is liquid from the dissolve in the tumbler, it contains gold. If you don't check and make sure it is clear of any liquid, when you move the filter to the next operation and pump the waste liquid through, you take that gold that may have been under the plate with it and can lose gold.

It is easy to check and it should be standard procedure. The perforated plate has 2 oval holes that are bigger than the rest of the holes. They are made for 2 keys that you should have to allow for easy removal. These are the keys.

And these are the keys in the plate allowing you to pick up the perforated plate to make sure all of the liquid is rinsed on to the next step.

I assume you have been using the proper filter paper and installing it properly with the rubber tubing to assure the paper seals and no solids suck around the edges and out of the filter. If you are not doing this let me know and I will explain how it is done.

If you bought this unit used, you may not have gotten all of the proper instructions. If you have questions we can answer them for you.

 

[Edlin]

Unfortunately, acid that contains gold looks the same to the human eye and working without any indication of how much gold, if any, is in solution will undoubtedly cause losses. Working with stannous chloride the refiner has an instantaneous indication of gold in solution while using only a single drop. And it is sensitive down to parts per million. So if nothing else, make some stannous chloride solution and do some familiarization tests to see how it works.

My guess what happened is you are using too much nitric acid, right off, I would lower the nitric ratio from 3 parts Hydrochloric Acid to 1 part Nitric Acid
down to 4 parts Hydrochloric Acid to 1 part Nitric Acid. This is effective because the reaction is condensed which essentially recycles a percentage of your nitric acid.

The urea is not consuming any free nitric acid, so using more nitric than necessary tends to leave the solution active after urea additions and can re-dissolve gold after you drop it with metabisulfite. If you use stannous chloride you can detect this instantly. Sulfamic is a better option but many people worldwide use urea effectively.

The tumbler plants also do not heat the solution. A heated dissolve allows free nitric to "burn off" and you can heat it until it stops blowing red fumes as an indication. You do not have this option.

You will have to rely on slow additions which allow the urea to work. Too much can cause excessive crystallization and hold up gold in the crystals. I assume you are adding the urea and dropping the gold in one of these?View attachment 62649
you should slowly add urea and allow it to mix in. It will foam up violently with excessive additions. Add a little and wait for a reaction to subside. Then add a little more and wait. When you have added enough you will see the prills of urea start to float. That is when you stop.

Next you add the metabisulfite, again slowly with mixing. If the solution starts to blow red fumes that is only the excess free nitric acid burning off as the gold you just dropped re-dissolves. Not a problem, these slow additions will consume all of the free nitric and then the gold will drop and stay dropped.

If the gold alloy was from jewelry or had a percentage of copper in it the acid will be a green color. When there is gold in solution it affects the color and it starts out a brighter green and when the gold is out it is a dull green. Seeing this is something you learn and observe from doing it often enough, it never takes the place of testing with stannous chloride. When all of the gold is dropped, and your stannous chloride test is negative, the solution is dropped out the bottom of the vessel into the filter trolley to separate the gold from the spent acid.

View attachment 62651

When the filter removes all of the liquid the gold should look like this.

I am a raw newbie to the gold refining world, but I have a lot of experience with various chemical batch processing methods.

Looking at her actual vs theoretical yields, they are at around 99.5% which seems extremely good to me.

4metals, what is a realistic yield for this process? To me expectations of 100% seem unrealistic .

Great information by the way.

Ed

 

[4metals]

unfortunately we did not measure the amount of silver before hand. But in the first and second attempt we recovered 430 grams of silver by treating the AgCl with iron and H2SO4 and we found 3 grams of gold entrapped in the AgCl.

I did the math on the silver because you gave the start weights of the first 2 lots and the recovered Silver weight. The silver assay was about 5.3%. That is well within the limits for aqua regia and the tumbler plant is effective with higher Silver (they claim 10%)

When you said you recovered 3 grams. I assume you came to that number by fire assay of the Silver bar from reducing the chlorides. I wrote, and since edited, that it is not uncommon for these chlorides to assay 1/2% gold when assayed. Yours assay a slight bit higher.

But this is acceptable and proves the effectiveness of the tumbling action. A static digestion usually leaves a bit more in the chlorides.

 

[4metals]

4metals, what is a realistic yield for this process? To me expectations of 100% seem unrealistic .

It is not out of the realm of refining to recover 99.85% and after accounting for metal hung up in the Silver Chloride and on filter papers and test papers to get that up to 99.95. Then there is the fact that when a refinery does a cleanup or replaces ductwork, there is always gold in the duct. So all in, it's never 100% but it can come close.

Remember that pesky little law of physics called the Law of Conservation of Mass. Matter can never be created or destroyed. So that gold in the duct didn't come out of thin air!