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

[Nouran Alaa]

Why would you start trying to process significant quantities of material before successfully running small lots first?
The margin if you run a reasonably efficient system is quite small in the first place, so clocking up lost value in the thousands of pounds seems imprudent.
Maybe you should stop what you are doing until you have acquainted yourself properly with the process.
The mention of Urea is enough for me to think you are working out of a faulty cookbook, not a recommended methodology.

Although Justin you're comment is a bit on the "not very nice" spectrum. The Tumbler has a capacity and we refined accordingly.

The urea is not the issue here, I have been to multiple refineries in Turkey, Dubai, Egypt and the urea was very common practice.
I'll admit my inexperience but there is always room for improvement and learning.

 

[Justincase]

Although Justin you're comment is a bit on the "not very nice" spectrum. The Tumbler has a capacity and we refined accordingly.

The urea is not the issue here, I have been to multiple refineries in Turkey, Dubai, Egypt and the urea was very common practice.
I'll admit my inexperience but there is always room for improvement and learning.

I smoke, but I would not recommend it to other people.
Urea has no real value in refining and may even produce unintended energetic compounds if improperly disposed of.
In ten years, I have never found it useful or necessary in any way.
And if you are losing thousands of pounds worth of value at a time, you need someone to be blunt and truthful with you.
Not help, you dig yourself into a deeper hole.
The fundamental operations should be the same as whatever reaction chamber you are using.
I prefer the round-bottomed flange vessels as you can run anything from 100ml to 20,000ml, all with the same reflux condensers.
They let you wash and flush material very effectively.
Simply buying a large system does not mitigate the need to understand each step in the process properly.
Even once you are up to the point of confidently being able to process material, you will spend the next ten years improving your process incrementally with each run.

 

[Yggdrasil]

I smoke, but I would not recommend it to other people.
Urea has no real value in refining and may even produce unintended energetic compounds if improperly disposed of.
In ten years, I have never found it useful or necessary in any way.
And if you are losing thousands of pounds worth of value at a time, you need someone to be blunt and truthful with you.
Not help, you dig yourself into a deeper hole.
The fundamental operations should be the same as whatever reaction chamber you are using.
I prefer the round-bottomed flange vessels as you can run anything from 100ml to 20,000ml, all with the same reflux condensers.
They let you wash and flush material very effectively.
Simply buying a large system does not mitigate the need to understand each step in the process properly.
Even once you are up to the point of confidently being able to process material, you will spend the next ten years improving your process incrementally with each run.

Did you follow the latest discussion where Deano chimed in on this use?

 

[Justincase]

Did you follow the latest discussion where Deano chimed in on this use?

No, I did not catch that.
But seeing as he mostly deals with larger volumes of naturally occurring gold materials, I suppose there might be a need not found in basic scrap alloy processing.

 

[Yggdrasil]

No, I did not catch that.
But seeing as he mostly deals with larger volumes of naturally occurring gold materials, I suppose there might be a need not found in basic scrap alloy processing.

It was regarding the tendency of base metal nitrates to redissolve Gold.
Which is what we can see in scrap and low karat Golds.
There is however a established practice among the Gold refiners especially in the Middle East to rely on Urea rather than other methods.
This is partly due to lack of knowledge of other possibilities and
the resistance to adapt new techniques when they have a system they are happy with.
The OP is however open to new techniques so I hope we can help streamlining the processes fitting her gear.

 

[FrugalRefiner]

I use a cementing tank that is around 100 Liters capacity and I let the solution sit for 3 days. The NaOh was just for better disposable and was of no value to ppt the gold.

The tanks however do not have a circulation inside. I might add them if it helps the process.

by contacting copper, you mean add a piece of copper in the tank and then collect the sludge around?

Nouran, for some information on cementing, see When In Doubt, Cement It Out.

Dave

 

[goldandsilver123]

You could use an ORP meter to measure how much SMB to add. I find it much better than the stannous chloride test, it also prevents you to over add SMB.



Don't know how is your environmental regulations, but here the maximum sulfate permited is 1 g/L so we need to remove it from the waste water

 

[4metals]

You could use an ORP meter to measure how much SMB to add. I find it much better than the stannous chloride test, it also prevents you to over add SMB.

The O.R.P. probe will be useful to find the actual point in the reaction where the Oxidation, reduction, potential point is reached. But it is no substitute for the definitive indication that stannous chloride provides.

 

[4metals]

Regarding the underlined part, I should first add urea gradually then the SMB, I'll test the water coming out of the filter with stannous chloride.

When adding the reagents to drop the gold the liquid is tested before you ever open the valve to discharge the liquid. The stannous chloride is usually tested on small strips of filter paper. I prefer to cut up a sheet of filter paper into strips about 1 cm wide and 4-5 cm long. Then, using a glass stir rod, reach down into the well mixed solution and deposit a single drop on one end of a piece of the cut up filter paper and then add a drop of stannous chloride. The results are instantaneous.

Only when you get a negative test a few minutes after your last addition of the metabisulfite should the solution be discharged through the clean rinsed filter trolley to collect the precipitated gold.

Testing the discharge once the liquid is filtered is the equivalent of what we call here in the USA closing the barn door after the horse is gone.

 

[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?

 

[Justincase]

It was regarding the tendency of base metal nitrates to redissolve Gold.
Which is what we can see in scrap and low karat Golds.
There is however a established practice among the Gold refiners especially in the Middle East to rely on Urea rather than other methods.
This is partly due to lack of knowledge of other possibilities and
the resistance to adapt new techniques when they have a system they are happy with.
The OP is however open to new techniques so I hope we can help streamlining the processes fitting her gear.

I have had a look at that thread now.
Very interesting how Urea acts on Nitrate salts and sulfamic acid for free nitric acid respectively.
That would probably be of great use to someone using poor-man's AR.
Nitrate contamination is an issue I have noted mostly with AgNO3, but I simply improved my washing stages to minimize that carryover.
Unfortunately, no matter how much you wash you will eventually come to a place where the return for effort is too low to be practical, so have to live with some level of contamination.
It is very hard for the wash water to reach deep inside the individual clumps of gold, both after base metal leaching and once a fine gold is precipitated and clumping.
If it is hard for a compound to be leached out, it will be equally hard for a chemical to penetrate.
I will experiment with attenuating my solution's PH as he suggests, to see if that helps with my final refining purity and the high amount of value I have been recovering from my Hydrochloric acid washes.
Would love to buy Deano and 4metals a pint for all the extra help they provide.

 

[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.

 

[Nouran Alaa]

I smoke, but I would not recommend it to other people.
Urea has no real value in refining and may even produce unintended energetic compounds if improperly disposed of.
In ten years, I have never found it useful or necessary in any way.
And if you are losing thousands of pounds worth of value at a time, you need someone to be blunt and truthful with you.
Not help, you dig yourself into a deeper hole.
The fundamental operations should be the same as whatever reaction chamber you are using.
I prefer the round-bottomed flange vessels as you can run anything from 100ml to 20,000ml, all with the same reflux condensers.
They let you wash and flush material very effectively.
Simply buying a large system does not mitigate the need to understand each step in the process properly.
Even once you are up to the point of confidently being able to process material, you will spend the next ten years improving your process incrementally with each run.

you're completely right Justinhcase
I was here searching for the cause of losses not realizing my techniques had some major flaws. Unfortunately as Yggdrasil mentioned here in the Middle east, people are a bit stuck on old methods, I came across this forum recently while searching for some questions and I'm trying to learn from everyone expertise as much as I can and hopefully update my techniques to what is new and recent.

​

 

[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.