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

[Nouran Alaa]

We built a refinery gold small factory scale, 4kg per day in an italian impianti closed tumbler attached to it a precipitator. Aqua regia was used to recover the gold.

First Time:
Our first time I had zero experience and throughout the process the technician lead us blind. We put 4102 grams of unrefined gold and we were expecting 3494.57 grams, we only recovered 3478.90 grams with a loss of 15.67 grams.

The technician insisted that the machines normally "eat" the gold in their first run.

All machine parts were thoroughly washed, no water was thrown out and we let the water sit for 3 days with 3kg of caustic soda and the refiltered the water to see if there is still any water inside.

Second time:

3976.58 grams of gold entered the tumbler.

3027.88 grams of gold were expected to be recovered after the full process. only 3015.57 grams were recovered with 12.31 grams losses

In both times the gold purity ranged between 999.1 to 999.5 which pretty satisfactory but the losses were unbearable.
After doing some research here are some mistakes, I think our technician did:
1- He added all the urea all at once and then he directly added the SMB and waited for the bubbles to settle and then filtered directly.
2- The addition to caustic soda was unnecessary to the resting water after all the process was done.
3- He let the gold in the tumbler for 3.5 hours only which might be low time but the purity was of 999.1 was not bad.
4-He did not measure very accurately the amounts of chemicals
for each Kilo of gold he used:
3Liters of HCL
1 Liter of HNO3
900 grams of urea dissolved in 2L/kg of water
670 grams of SMB dissolved in 3L/kg of water
he added all the HCL at once and the titrated the HNO3 till it was fully poured into the tumbler (approximately 20 mins)


We tried to recover these losses:
we collected all the gold in all the waters
we burned any gloves or cotton used throughout the process
we burned the filter papers used
We recovered the silver and did fire assay analysis on it
At the end: 12.75 grams were fully recovered and 17 grams remained lost.



We suspected that the issue might be the technician or the fire assay performed in the beginning. to fix this issue:
1- We hired a different experienced technician
2- we used gold that was analyzed by our fire assay lab and another external lab were both gave the same values.



Third Time:
4992.62 grams of gold were admitted to the tumbler and 3796.14 grams were expected but only 3774.64 were recovered.
21.51 grams losses the highest so far.

we ran into some operational issues where:
1- the precipitator's capacity was so small it couldnt hold all the amount of gold so we had to empty some of it into 2 buckets using a rubber pipe which was thoroughly washed after.
2- The Precipitator was leaking but the leak was instantly noticed and any leakage was collected (not yet recovered but the leakage was around 10mls of fluid so it wont be holding 21 grams of gold that's for sure)
3- I did not like the washing technique of the technician as i I felt there was a lot of splashing drops everywhere but where then all wiped with cotton and also yet to be recovered.

Chemicals used and technique:
1-15 liters of HCl added all at once and 5 liters of HNO3 were then titrated for 30 mins.
2-The tumbler was operated for 6 hours and then the gold was recovered.
3-in the precipitator tank the urea was added whilst the filter was pumping the gold solution from the tumbler (2.5 kg of urea was used)
4- The SMB was then added (3kg of SMB) and the gold in the buckets (from the issue we rand into was also readded again to the precipitator and filtered.

We are planning on doing a recovery cycle were all waters are refiltered and materials (gloves, cotton, ... etc) are burned and refined to see how much we will recover.

I still cant put my hand on where all the losses are coming from. I will be glad to clarify any issues and please excuse my English and terminology as they are not my first language.

 

[Yggdrasil]

We built a refinery gold small factory scale, 4kg per day in an italian impianti closed tumbler attached to it a precipitator. Aqua regia was used to recover the gold.

First Time:
Our first time I had zero experience and throughout the process the technician lead us blind. We put 4102 grams of unrefined gold and we were expecting 3494.57 grams, we only recovered 3478.90 grams with a loss of 15.67 grams.

The technician insisted that the machines normally "eat" the gold in their first run.

All machine parts were thoroughly washed, no water was thrown out and we let the water sit for 3 days with 3kg of caustic soda and the refiltered the water to see if there is still any water inside.

Second time:

3976.58 grams of gold entered the tumbler.

3027.88 grams of gold were expected to be recovered after the full process. only 3015.57 grams were recovered with 12.31 grams losses

In both times the gold purity ranged between 999.1 to 999.5 which pretty satisfactory but the losses were unbearable.
After doing some research here are some mistakes, I think our technician did:
1- He added all the urea all at once and then he directly added the SMB and waited for the bubbles to settle and then filtered directly.
We usually do not recommend the use of Urea, better to use Sulfamic acid or even better not use too much Nitric.
2- The addition to caustic soda was unnecessary to the resting water after all the process was done.
There is no upsides of using NaOH, why neutralize until you are treating the waste?
3- He let the gold in the tumbler for 3.5 hours only which might be low time but the purity was of 999.1 was not bad.
The Gold need to be there until no more Gold is present or there is no more reaction.
4-He did not measure very accurately the amounts of chemicals
There is no set amount to use so no need to be very accurate, better to adjust during the reaction.
for each Kilo of gold he used:
3Liters of HCL
1 Liter of HNO3 This will dissolve more or less 4000g of Gold give or take.
900 grams of urea dissolved in 2L/kg of water Use Sulfamic
670 grams of SMB dissolved in 3L/kg of water This will drop more or less 670g of Gold give or take
he added all the HCL at once and the titrated the HNO3 till it was fully poured into the tumbler (approximately 20 mins)


We tried to recover these losses:
we collected all the gold in all the waters
we burned any gloves or cotton used throughout the process
we burned the filter papers used
We recovered the silver and did fire assay analysis on it
At the end: 12.75 grams were fully recovered and 17 grams remained lost.



We suspected that the issue might be the technician or the fire assay performed in the beginning. to fix this issue:
1- We hired a different experienced technician
2- we used gold that was analyzed by our fire assay lab and another external lab were both gave the same values.



Third Time:
4992.62 grams of gold were admitted to the tumbler and 3796.14 grams were expected but only 3774.64 were recovered.
21.51 grams losses the highest so far.

we ran into some operational issues where:
1- the precipitator's capacity was so small it couldnt hold all the amount of gold so we had to empty some of it into 2 buckets using a rubber pipe which was thoroughly washed after.
2- The Precipitator was leaking but the leak was instantly noticed and any leakage was collected (not yet recovered but the leakage was around 10mls of fluid so it wont be holding 21 grams of gold that's for sure)
3- I did not like the washing technique of the technician as i I felt there was a lot of splashing drops everywhere but where then all wiped with cotton and also yet to be recovered.

Chemicals used and technique:
1-15 liters of HCl added all at once and 5 liters of HNO3 were then titrated for 30 mins.
2-The tumbler was operated for 6 hours and then the gold was recovered.
3-in the precipitator tank the urea was added whilst the filter was pumping the gold solution from the tumbler (2.5 kg of urea was used)
4- The SMB was then added (3kg of SMB) and the gold in the buckets (from the issue we rand into was also readded again to the precipitator and filtered.

We are planning on doing a recovery cycle were all waters are refiltered and materials (gloves, cotton, ... etc) are burned and refined to see how much we will recover.

I still cant put my hand on where all the losses are coming from. I will be glad to clarify any issues and please excuse my English and terminology as they are not my first language.

I'll reply in bold inside the quote.
You do not say the karat of the Gold and what you do with the Silver Chloride.

After the Gold is precipitated was the liquor tested and if so how?
After it is done it may be wise to put the liquor in holding tanks and add a slab of copper to cement out what ever values are left i there.
Remember agitation.

 

[SRM]

Can you describe the tumbler? If it is anything like a ball mill, metallic gold can and will get caught between the liners and the shell.

SRM

 

[Yggdrasil]

Can you describe the tumbler? If it is anything like a ball mill, metallic gold can and will get caught between the liners and the shell.

SRM

This is a different kind of tumbler I guess.
It is actually a rotating reactor so you can digest karat Gold without inquarting.
The tumbling rubs off the Silver Chloride so new Gold are exposed.
If I'm not mistaken.

 

[orvi]

We built a refinery gold small factory scale, 4kg per day in an italian impianti closed tumbler attached to it a precipitator. Aqua regia was used to recover the gold.

First Time:
Our first time I had zero experience and throughout the process the technician lead us blind. We put 4102 grams of unrefined gold and we were expecting 3494.57 grams, we only recovered 3478.90 grams with a loss of 15.67 grams.

The technician insisted that the machines normally "eat" the gold in their first run.

All machine parts were thoroughly washed, no water was thrown out and we let the water sit for 3 days with 3kg of caustic soda and the refiltered the water to see if there is still any water inside.

Second time:

3976.58 grams of gold entered the tumbler.

3027.88 grams of gold were expected to be recovered after the full process. only 3015.57 grams were recovered with 12.31 grams losses

In both times the gold purity ranged between 999.1 to 999.5 which pretty satisfactory but the losses were unbearable.
After doing some research here are some mistakes, I think our technician did:
1- He added all the urea all at once and then he directly added the SMB and waited for the bubbles to settle and then filtered directly.
2- The addition to caustic soda was unnecessary to the resting water after all the process was done.
3- He let the gold in the tumbler for 3.5 hours only which might be low time but the purity was of 999.1 was not bad.
4-He did not measure very accurately the amounts of chemicals
for each Kilo of gold he used:
3Liters of HCL
1 Liter of HNO3
900 grams of urea dissolved in 2L/kg of water
670 grams of SMB dissolved in 3L/kg of water
he added all the HCL at once and the titrated the HNO3 till it was fully poured into the tumbler (approximately 20 mins)


We tried to recover these losses:
we collected all the gold in all the waters
we burned any gloves or cotton used throughout the process
we burned the filter papers used
We recovered the silver and did fire assay analysis on it
At the end: 12.75 grams were fully recovered and 17 grams remained lost.



We suspected that the issue might be the technician or the fire assay performed in the beginning. to fix this issue:
1- We hired a different experienced technician
2- we used gold that was analyzed by our fire assay lab and another external lab were both gave the same values.



Third Time:
4992.62 grams of gold were admitted to the tumbler and 3796.14 grams were expected but only 3774.64 were recovered.
21.51 grams losses the highest so far.

we ran into some operational issues where:
1- the precipitator's capacity was so small it couldnt hold all the amount of gold so we had to empty some of it into 2 buckets using a rubber pipe which was thoroughly washed after.
2- The Precipitator was leaking but the leak was instantly noticed and any leakage was collected (not yet recovered but the leakage was around 10mls of fluid so it wont be holding 21 grams of gold that's for sure)
3- I did not like the washing technique of the technician as i I felt there was a lot of splashing drops everywhere but where then all wiped with cotton and also yet to be recovered.

Chemicals used and technique:
1-15 liters of HCl added all at once and 5 liters of HNO3 were then titrated for 30 mins.
2-The tumbler was operated for 6 hours and then the gold was recovered.
3-in the precipitator tank the urea was added whilst the filter was pumping the gold solution from the tumbler (2.5 kg of urea was used)
4- The SMB was then added (3kg of SMB) and the gold in the buckets (from the issue we rand into was also readded again to the precipitator and filtered.

We are planning on doing a recovery cycle were all waters are refiltered and materials (gloves, cotton, ... etc) are burned and refined to see how much we will recover.

I still cant put my hand on where all the losses are coming from. I will be glad to clarify any issues and please excuse my English and terminology as they are not my first language.

This problem was very thoroughly discussed here in one thread, where very experienced refiners like 4metals helped to elucidate the problem. It is many many pages of reading, and I am pretty confident the problem causing you to lose gold is discussed there.

https://goldrefiningforum.com/threads/consolidation-of-loss-gold-thread.31119/

My suggestions in order of probability:

1. How the Au content is measured and what is the sigma value/statistical error of the measurement ? Did you re-checked by another assay house ? Was it only XRF-ed ? Is material completely homogenous ?

This is my first bet. 10-20g represent relatively small fraction of the bulk, less than 1%. It is quite a bit of money, but if you are using uncallibrated XRF, this can be the case.

2. What is the composition of the feed ? You do not specify this and it is very very important thing to know for us. As the method of digestion is AR treatment, my second bet would be undissolved gold in the silver chloride sludge. This is well known thing and can be easily found out. Take a homogenous sample of silver chloride from filter, wash it well with water and dissolve it in ammonia. If there is gold encased in AgCl, you will surely see it.

3. You post exact measures of this and that chemical for each step of refining - which is really good (tracking what you did can help you find errors and problems in the future, if you will have good database of what you did previously and how it worked out). But rely only on numbers isn´t good. What testing do you use ? Stannous chloride, XRF of the liquid, ferrous sulfate...
Third most probable reason can be you are losing gold in the liquids - either in form of soluble gold (incomplete precipitation or re-dissolution after gold drop/washing) or as microscopic particles, which cannot be filtered on your filters.

For first possibility, take 100 mL´s or so of waste liquid and evaporate it down to crust. Then measure it with XRF to see if you have some gold in it. Or you can completely cement all metals from the solution on aluminium and measure the resulting sludge - this is maybe better approach since you will be measuring metal not compound.

For second, take 1L of waste solution and pour it into tall graduated cylinder or any similar suitable glass vessel, and let it settle for at least 24 h. Then look at the bottom (you can help yourself by aiming some LED torch from the bottom to see better) of the jar. If there is precipitate, you can be losing gold this way.

 

[Nouran Alaa]

The guy is sniveling over a few grams of gold,

Moderators note a since banned member posted some rather nasty comments about the OP, all of those comments and responses related to those comments have been deleted.

I'm not a guy. Also I did not fire him he was a part time technician and not a refiner.

 

[Nouran Alaa]

This problem was very thoroughly discussed here in one thread, where very experienced refiners like 4metals helped to elucidate the problem. It is many many pages of reading, and I am pretty confident the problem causing you to lose gold is discussed there.

https://goldrefiningforum.com/threads/consolidation-of-loss-gold-thread.31119/

My suggestions in order of probability:

1. How the Au content is measured and what is the sigma value/statistical error of the measurement ? Did you re-checked by another assay house ? Was it only XRF-ed ? Is material completely homogenous ?

This is my first bet. 10-20g represent relatively small fraction of the bulk, less than 1%. It is quite a bit of money, but if you are using uncallibrated XRF, this can be the case.

2. What is the composition of the feed ? You do not specify this and it is very very important thing to know for us. As the method of digestion is AR treatment, my second bet would be undissolved gold in the silver chloride sludge. This is well known thing and can be easily found out. Take a homogenous sample of silver chloride from filter, wash it well with water and dissolve it in ammonia. If there is gold encased in AgCl, you will surely see it.

3. You post exact measures of this and that chemical for each step of refining - which is really good (tracking what you did can help you find errors and problems in the future, if you will have good database of what you did previously and how it worked out). But rely only on numbers isn´t good. What testing do you use ? Stannous chloride, XRF of the liquid, ferrous sulfate...
Third most probable reason can be you are losing gold in the liquids - either in form of soluble gold (incomplete precipitation or re-dissolution after gold drop/washing) or as microscopic particles, which cannot be filtered on your filters.

For first possibility, take 100 mL´s or so of waste liquid and evaporate it down to crust. Then measure it with XRF to see if you have some gold in it. Or you can completely cement all metals from the solution on aluminium and measure the resulting sludge - this is maybe better approach since you will be measuring metal not compound.

For second, take 1L of waste solution and pour it into tall graduated cylinder or any similar suitable glass vessel, and let it settle for at least 24 h. Then look at the bottom (you can help yourself by aiming some LED torch from the bottom to see better) of the jar. If there is precipitate, you can be losing gold this way.

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?

 

[Nouran Alaa]

This is a different kind of tumbler I guess.
It is actually a rotating reactor so you can digest karat Gold without inquarting.
The tumbling rubs off the Silver Chloride so new Gold are exposed.
If I'm not mistaken.

yes you're right.

 

[orvi]

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

 

[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?

What is the purpose of the NaOH!
Neutralize before disposal?

 

[goldandsilver123]

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?

 

[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]

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]

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.