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

[4metals]

I'll start with stannous chloride for testing, but i'm not sure of the method of collection from the solutions

I think the best way to explain this is to give you a numbered step by step procedure to follow the you can ask for more detail based on which step is causing questions to arise. I'll start at the beginning when the bars originally enter your facility.

1. Melt and sample the bars for assay, a vacuum dip sample is the best way to do this.
2. Assay the bars for Gold and for Silver. As silver may vary we want to assure the silver content is not exceeding the level where gold entrapment causes excessive Gold hung up in the chlorides.
3. With both Gold and Silver assays it is easier to mix the bars together for a process lot by "diluting" the high Silver bars with bars of lower Silver content, keeping the Silver as low as possible will make for more consistent and predictable results.
4. Melt the bars you select for a refining lot together and draw a sample before pouring the gold into water to make shot for refining. The sample need not be assayed but in the event of a shortage, it is nice to have a sample of what you started with. This is more of a measure to detect employee theft issues but it is good to have.
5. Dry the shot and verify the start weight for this refining lot.
6. Open up the large charging port on the tumbler and add all of the shot to be refined. Close the charging port tightly and start the tumbler rotating.
7. Turn on the cold water flow to the condenser.
8. Add the required Hydrochloric Acid from the overhead Hydrochloric Acid reservoir.
9. Add about 1/3 of the total required Nitric Acid and wait about 20 minutes for the reaction to die down.
10. Add the second 1/3 of the nitric and continue rotation for 20 more minutes.
11. Finally add the balance of the Nitric Acid and let the rotation to continue for a total of 3 1/2 to 4 hours.
12. If at all possible allow the reaction to cool overnight before the next step. Cooler acid fumes less and makes for a more pleasant work environment.
13. Cold acid holds less Silver Chloride in solution and will make your final product of a higher purity. To make this as efficient as possible, stop the tumbler, open the charging cover, and add about 2 kg of ice. This will help by causing the majority of Silver Chloride to come out of solution and allow you to catch it on the filter paper in the next step.
14. Replace the charging hole port and tumble for about 20 minutes. It doesn't matter if all of the ice melts, it will remain on the filter paper if it hasn't melted completely.
15. Stop the tumbler
16. Clean the filter trolley and put a new paper on the plate and seal it with the tubing to prevent solution from going around the filter paper rather than through it.
17. connect the discharge hose to the filter trolley to the precipitation tank
18. Remove the cover from the discharge port and attach the ball valve. The valve needs to be directly over the filter trolley which should be positioned to receive the flow from the valve and pointing straight down. The valve is to slow or stop the flow from the tumbler if needed. (HINT, it is possible the flow will tear the filter paper, placing a small porcelain plate, a pie plate works perfectly, where the stream hits the paper will prevent this)
19. Start the airflow to the filter trolley, the pump can run dry and it will develop suction under the plate.
20. Allow all of the contents to drain onto the filter trolley. As the liquid drains it will fill the trolley. If it is filtering slowly, adjust the flow with the valve.
21. Open the charging port and look inside to be sure everything has rinse out onto the filter.
22. When the filter trolley has pulled all of the liquid through the perforated plate you will see all of the silver chlorides on top of the filter paper and any chunks of Silver Chloride encrusted Gold that may not have dissolved. Using a hose with a gentle spray, rinse the silver chlorides until they are white and the paper is not still stained green.
23. The solution now has been transferred to the next step. Remove the filter paper to collect the chlorides and pull up the perforated plate to make sure the liquor under the plate has all rinsed on to the next step. If needed, turn on the trolley pump and spray water to clean out any residue which is liquid containing gold.
24. Replace the plate on the filter trolley and add new filter paper to filter the liquid generated in the next step.
25. Start the mixer on the tank (which Italimpianti calls a cementation tank) and slowly begin to add urea prills. Add small increments and allow the reaction to stop before adding more. (Urea is used here in keeping with the way it is done in Europe and Asia we can debate options later but this will work.)
26. When the additions of urea no longer react, shut the mixer off and add a few prills of urea. If they float, you are done with the urea additions. Note, if the mixer is not shut they will not float so this test depends on the mixer having been shut off.
27. You are now ready to add your precipitant. Most use sodium metabisulfite but if possible I prefer Sulfur dioxide gas. But these instructions are for powdered sodium metabisulfite.
28. The mixer should be on now.
29. It is entirely possible that free nitric acid still exists in solution. if this is the case, metabisulfite additions will be followed by red gas coming from the solution. This is because the metabisulfite did reduce the gold to metallic gold and the free nitric acid caused it to be re-dissolved. When the red cloud stops again add a small scoop of metabisulfite and wait for the reaction. When it stops, add another small scoop.
30. Rule of thumb. Expect to add 1 gram of sodium metabisulfite for every gram of gold you expect to recover.
31. After a few additions, take a drop of solution from the tank and check it with stannous chloride. A quick dark color change says you still have a ways to go. As you add more metabisulfite you will develop a feel for how long to wait between tests. When you get a negative test, all of the gold is dropped. allow it to continue mixing for a minute or two and test again. If negative, shut the mixer and prepare to filter the solution.
32. Position the filter trolley under the cementation tank and direct the discharge hose to your waste holding tank.
33. turn on the pump on the trolley and open the valve to drain the liquid from the cementation tank above it.
34. I prefer to drain the tank without the mixer running, when all of the liquid is drained, open the top of the cementation tank and a lot of the gold will be on the bottom. The bottom is tapered so some of the gold is already on the paper. Using a flow of water from a hose, rinse the gold sponge through the bottom drain onto the filter below.
35. Using the same rinse hose rinse the gold sponge in the filter and allow the filter to suck it dry.
36. The gold sponge layer, if it thick enough, will crack apart telling you it is dry enough to handle.
37. Clean the gold from the filter trolley and, depending on purity, either melt it as is or perform some chemical rinses to improve the purity.

 

[4metals]

sorry, didn't mean to hit post!

38. As a precaution test the discharge liquid with stannous chloride. This will assure you that all of the recoverable gold is in the filter and the few PPM remaining will be recoverable by cementation.
39. You will now be able to see any stains from Platinum group metals that may have been in the alloy. while there is gold in the acid the gold stain masks the PGM stains, which are only visible after the gold is dropped.
40. The waste acid sitting in your tank should be air agitated and using a copper slab and, as described in many threads on the forum, recover any remaining PGM's.

This is the tank Italimpianti usually ships with the unit you have. It is good for recovery of small quantities of PM's from the waste.

 

[4metals]

Nouran,
All of the photo's posted here are from a system which is the same as the system you reported as purchasing used. But they are from installs I was involved with.

If you would post photo's from your setup we can be assured that the instructions above work for your setup as well.

Also, do you have a laboratory hood in your refinery where you could clean up the refined gold if desired or where you could perform small test lots?

 

[Nouran Alaa]

sorry, didn't mean to hit post!

38. As a precaution test the discharge liquid with stannous chloride. This will assure you that all of the recoverable gold is in the filter and the few PPM remaining will be recoverable by cementation.
39. You will now be able to see any stains from Platinum group metals that may have been in the alloy. while there is gold in the acid the gold stain masks the PGM stains, which are only visible after the gold is dropped.
40. The waste acid sitting in your tank should be air agitated and using a copper slab and, as described in many threads on the forum, recover any remaining PGM's.

This is the tank Italimpianti usually ships with the unit you have. It is good for recovery of small quantities of PM's from the waste.
View attachment 62683

Thank you very much 4Metals, I'll use this as a guide for our next time.
I'm currently working on making my own stannous chloride stock to use for next time. I'll make sure to check other threads detailing the proper method of preparation.

 

[Nouran Alaa]

Nouran,
All of the photo's posted here are from a system which is the same as the system you reported as purchasing used. But they are from installs I was involved with.

If you would post photo's from your setup we can be assured that the instructions above work for your setup as well.

Also, do you have a laboratory hood in your refinery where you could clean up the refined gold if desired or where you could perform small test lots?

I'll take some pictures tomorrow and post them. I have a lab hood for the fire assay but it was never used for small test lots.

 

[Yggdrasil]

Thank you very much 4Metals, I'll use this as a guide for our next time.
I'm currently working on making my own stannous chloride stock to use for next time. I'll make sure to check other threads detailing the proper method of preparation.

Be aware that the Stannous go bad over time.
So it makes no sense to make too much at a time.
It is very quick and easy to make anyway.

 

[Nouran Alaa]

I think the best way to explain this is to give you a numbered step by step procedure to follow the you can ask for more detail based on which step is causing questions to arise. I'll start at the beginning when the bars originally enter your facility.

1. Melt and sample the bars for assay, a vacuum dip sample is the best way to do this.
2. Assay the bars for Gold and for Silver. As silver may vary we want to assure the silver content is not exceeding the level where gold entrapment causes excessive Gold hung up in the chlorides.
3. With both Gold and Silver assays it is easier to mix the bars together for a process lot by "diluting" the high Silver bars with bars of lower Silver content, keeping the Silver as low as possible will make for more consistent and predictable results.
4. Melt the bars you select for a refining lot together and draw a sample before pouring the gold into water to make shot for refining. The sample need not be assayed but in the event of a shortage, it is nice to have a sample of what you started with. This is more of a measure to detect employee theft issues but it is good to have.
5. Dry the shot and verify the start weight for this refining lot.

When preparing the shot, we weighed before the melting and then melted and granulated the gold. We did not weigh after granulation? do you think this might have caused us to overestimate our losses? also is there a proper method for drying the granules?

1. Open up the large charging port on the tumbler and add all of the shot to be refined. Close the charging port tightly and start the tumbler rotating.
2. Turn on the cold water flow to the condenser.
3. Add the required Hydrochloric Acid from the overhead Hydrochloric Acid reservoir.
4. Add about 1/3 of the total required Nitric Acid and wait about 20 minutes for the reaction to die down.
5. Add the second 1/3 of the nitric and continue rotation for 20 more minutes.
6. Finally add the balance of the Nitric Acid and let the rotation to continue for a total of 3 1/2 to 4 hours.
7. If at all possible allow the reaction to cool overnight before the next step. Cooler acid fumes less and makes for a more pleasant work environment.
8. Cold acid holds less Silver Chloride in solution and will make your final product of a higher purity. To make this as efficient as possible, stop the tumbler, open the charging cover, and add about 2 kg of ice. This will help by causing the majority of Silver Chloride to come out of solution and allow you to catch it on the filter paper in the next step.
9. Replace the charging hole port and tumble for about 20 minutes. It doesn't matter if all of the ice melts, it will remain on the filter paper if it hasn't melted completely.
10. Stop the tumbler
11. Clean the filter trolley and put a new paper on the plate and seal it with the tubing to prevent solution from going around the filter paper rather than through it.
12. connect the discharge hose to the filter trolley to the precipitation tank
13. Remove the cover from the discharge port and attach the ball valve. The valve needs to be directly over the filter trolley which should be positioned to receive the flow from the valve and pointing straight down. The valve is to slow or stop the flow from the tumbler if needed. (HINT, it is possible the flow will tear the filter paper, placing a small porcelain plate, a pie plate works perfectly, where the stream hits the paper will prevent this)
14. Start the airflow to the filter trolley, the pump can run dry and it will develop suction under the plate.
15. Allow all of the contents to drain onto the filter trolley. As the liquid drains it will fill the trolley. If it is filtering slowly, adjust the flow with the valve.
16. Open the charging port and look inside to be sure everything has rinse out onto the filter.
17. When the filter trolley has pulled all of the liquid through the perforated plate you will see all of the silver chlorides on top of the filter paper and any chunks of Silver Chloride encrusted Gold that may not have dissolved. Using a hose with a gentle spray, rinse the silver chlorides until they are white and the paper is not still stained green.
18. The solution now has been transferred to the next step. Remove the filter paper to collect the chlorides and pull up the perforated plate to make sure the liquor under the plate has all rinsed on to the next step. If needed, turn on the trolley pump and spray water to clean out any residue which is liquid containing gold.
19. Replace the plate on the filter trolley and add new filter paper to filter the liquid generated in the next step.
20. Start the mixer on the tank (which Italimpianti calls a cementation tank) and slowly begin to add urea prills. Add small increments and allow the reaction to stop before adding more. (Urea is used here in keeping with the way it is done in Europe and Asia we can debate options later but this will work.)
21. When the additions of urea no longer react, shut the mixer off and add a few prills of urea. If they float, you are done with the urea additions. Note, if the mixer is not shut they will not float so this test depends on the mixer having been shut off.
22. You are now ready to add your precipitant. Most use sodium metabisulfite but if possible I prefer Sulfur dioxide gas. But these instructions are for powdered sodium metabisulfite.
23. The mixer should be on now.
24. It is entirely possible that free nitric acid still exists in solution. if this is the case, metabisulfite additions will be followed by red gas coming from the solution. This is because the metabisulfite did reduce the gold to metallic gold and the free nitric acid caused it to be re-dissolved. When the red cloud stops again add a small scoop of metabisulfite and wait for the reaction. When it stops, add another small scoop.
25. Rule of thumb. Expect to add 1 gram of sodium metabisulfite for every gram of gold you expect to recover.
26. After a few additions, take a drop of solution from the tank and check it with stannous chloride. A quick dark color change says you still have a ways to go. As you add more metabisulfite you will develop a feel for how long to wait between tests. When you get a negative test, all of the gold is dropped. allow it to continue mixing for a minute or two and test again. If negative, shut the mixer and prepare to filter the solution.
27. Position the filter trolley under the cementation tank and direct the discharge hose to your waste holding tank.
28. turn on the pump on the trolley and open the valve to drain the liquid from the cementation tank above it.
29. I prefer to drain the tank without the mixer running, when all of the liquid is drained, open the top of the cementation tank and a lot of the gold will be on the bottom. The bottom is tapered so some of the gold is already on the paper. Using a flow of water from a hose, rinse the gold sponge through the bottom drain onto the filter below.
30. Using the same rinse hose rinse the gold sponge in the filter and allow the filter to suck it dry.
31. The gold sponge layer, if it thick enough, will crack apart telling you it is dry enough to handle.
32. Clean the gold from the filter trolley and, depending on purity, either melt it as is or perform some chemical rinses to improve the purity.

 

[4metals]

We did not weigh after granulation? do you think this might have caused us to overestimate our losses? also is there a proper method for drying the granules?

The only reason to weigh after granulation is because the shot is now transported between the melt shop and the refining room. It is always good, when tracking down losses, to be sure all of the material actually went into the reactor. Shot is generally dried in a stainless steel tray on a hot plate.

In larger shops with a lot of employees it is weighed before leaving the melt shop and weighed into the refinery. Just a little extra security because when something is as compact and valuable as gold it tends to disappear when visited by humans. An unfortunate but true reality of the business.

 

[4metals]

I'm currently working on making my own stannous chloride stock to use for next time. I'll make sure to check other threads detailing the proper method of preparation.

 

[Nouran Alaa]

Hi everyone!
on April I posted this thread
Major Gold Losses in New Gold Refinery
https://goldrefiningforum.com/threads/major-gold-losses-in-new-gold-refinery-plant-help.34317/

and in August I posted this thread
Cementing with Zinc didn't go as planned
https://goldrefiningforum.com/threads/cementing-with-zinc-didnt-go-as-planned.34839/post-375418


Everyone on this forum was very helpful and specially 4Metals who did not hesitate to explain thoroughly what could have gone wrong.

I'm updating you now in December when my refinery now has recovered from the major losses it had.
The Gold losses are now highly controlled and within the normal accepted range.

I hired a much more experienced technician and followed every advice here religiously. Whenever I find myself facing a new issue I get back to these threads and usually find an answer.

I wanted to wait until things were under control to celebrate with you the minor success we had in our refinery.


Thank you all for your support!


Best Regards
Nouran

 

[Lou]

Glad to hear!!

 

[kurtak]

I'm updating you now in December when my refinery now has recovered from the major losses it had.
The Gold losses are now highly controlled and within the normal accepted range.

Very good to hear

Thank you for updating us

Kurt

 

[Yggdrasil]

Hi everyone!
on April I posted this thread
Major Gold Losses in New Gold Refinery
https://goldrefiningforum.com/threads/major-gold-losses-in-new-gold-refinery-plant-help.34317/

and in August I posted this thread
Cementing with Zinc didn't go as planned
https://goldrefiningforum.com/threads/cementing-with-zinc-didnt-go-as-planned.34839/post-375418


Everyone on this forum was very helpful and specially 4Metals who did not hesitate to explain thoroughly what could have gone wrong.

I'm updating you now in December when my refinery now has recovered from the major losses it had.
The Gold losses are now highly controlled and within the normal accepted range.

I hired a much more experienced technician and followed every advice here religiously. Whenever I find myself facing a new issue I get back to these threads and usually find an answer.

I wanted to wait until things were under control to celebrate with you the minor success we had in our refinery.


Thank you all for your support!


Best Regards
Nouran

Excellent news

 

[nickvc]

It’s always good to hear a success story.

 

[Shark]

I agree, hearing the success stories help to give credit to the forum and it's members.

Thanks for the update.

 

[4metals]

This thread puts a happy face on my day, thank you for posting your progress, and don't be a stranger, we can be useful with anything refinery related.

 

[goldshark]

Hi everyone!
on April I posted this thread
Major Gold Losses in New Gold Refinery
https://goldrefiningforum.com/threads/major-gold-losses-in-new-gold-refinery-plant-help.34317/

and in August I posted this thread
Cementing with Zinc didn't go as planned
https://goldrefiningforum.com/threads/cementing-with-zinc-didnt-go-as-planned.34839/post-375418


Everyone on this forum was very helpful and specially 4Metals who did not hesitate to explain thoroughly what could have gone wrong.

I'm updating you now in December when my refinery now has recovered from the major losses it had.
The Gold losses are now highly controlled and within the normal accepted range.

I hired a much more experienced technician and followed every advice here religiously. Whenever I find myself facing a new issue I get back to these threads and usually find an answer.

I wanted to wait until things were under control to celebrate with you the minor success we had in our refinery.


Thank you all for your support!


Best Regards
Nouran

So we would like to know the reasons for getting losses under control. It is part of the learning on this forum, be it good or bad. If you would care to share, we would appreciate it.

 

[4metals]

we would like to know the reasons for getting losses under control. It is part of the learning on this forum

Truth of the matter is they may never know. Kind of like closing the barn door after the horse has gone.

If I were to guess, literally from the other side of the world, there is the obvious culprit of theft. If your staff knows you don't know what is happening small losses can pile up. Once they got it figured out, and their help knew it, the party was over. Sad to say this scenario plays out all over the world. The only refiners insulated from it are the ones that spend big on security, metal detectors, and cameras. A lot of overhead for a small shop.

The second and a high probability cause was the filter trolley. The particular filter they have is an excellent filter, it is self powered with a pump to suck and discharge through the filter media and deposit into the tank for the next process, very efficient, but if the operator is not aware solution laden with gold is trapped beneath the filter plate. If they simply moved the filter for the post precipitation rinses without emptying the filter entirely, they could easily lose a liter or more of pregnant acid. It would be pumped with the waste liquids and possibly totally overlooked. When I explained to her how to use the system I pointed this out with photo's from the exact same system I had installed in 3 American Refineries. So she had good images to learn from and prevent future losses. Losing as many as 3 ounces of fine gold trapped in a poorly rinsed filter per lot can add up. The acid filtered from the tumbler is loaded pregnant acid running around 7 ounces of karat gold per liter. This is strictly operator error and not theft. But losses nonetheless. They would have noticed the difference immediately.

The possibility of the silver chlorides holding gold is real too. Bars of Silver Chloride reduced from this process can contain as much as 1% Gold. She never discussed setting up a Silver cell to make fine Silver and recover the Gold from the slimes.

I would still like to hear her story but these are my 3 best bets to account for losses.

 

[nickvc]

I think one point for all to remember is that losses do occur however careful you are , if we can discount negligence and theft from the system all losses should be mostly recovered at a later date but knowing where to look and how to ensure you do recover those losses is part of the art , not science , of refining.
The one thing that makes you learn is to have your own money on the line it truly fuels that need to improve.

 

[Shark]

The one thing that makes you learn is to have your own money on the line it truly fuels that need to improve.

Yes, that is a huge motivation. Even the small, home refiner knows this and is why many use a stockpot to recover those losses. Money is a great motivator.