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

[4metals]

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.

That is the model IAO/BR25. The Italians have a peculiar habit of rating everything as daily production capacity. So you are correct, you can push it to 8kg but that is running 2 batches in a workday. Each batch is max at 4 kg based on the fill level of the tumbler.

edit to correct model number

 

[Alondro]

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

Urea does NOT de-nox aqua regia-based gold solutions. It does pretty much nothing but raise the pH slightly.

You would need sulfamic acid to de-nox. It reacts with the remaining nitric acid and creates sulfuric acid and nitrous oxide (laughing gas) or, at low concentrations, mostly nitrogen gas.
The sulfuric acid formed in the reaction will help drop any residual lead in the solution as fine light grey lead sulfate.

 

[Yggdrasil]

Good Morning Nouran.
Now when 4metals has chimed in, you will be well guided in the the equipment end.

I'm how ever a bit puzzled on the process you use, especially the lack of testing.
So you should immediately make some Stannous Chloride so you can get control of the status on the liquors after precipitating.
Next I'm also a bit confused on your use of NaOH, can you please tell us a bit detail on how and why it is used?

A cementing tank for the after precipitation liquors should take care of any remaining values.
It need to big enough and either have an air-bubbler, a circulation pump or an impeller to create sufficient stirring
to let all the liquid contact a Copper bar suspended in the liquid.

 

[Nouran Alaa]

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.

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. If it happens to have gold, should i refilter the solution? or should i treat the solution? and if it should be treated, what method do you suggest?

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.

 

[Nouran Alaa]

Good Morning Nouran.
Now when 4metals has chimed in, you will be well guided in the the equipment end.

I'm how ever a bit puzzled on the process you use, especially the lack of testing.
So you should immediately make some Stannous Chloride so you can get control of the status on the liquors after precipitating.
Next I'm also a bit confused on your use of NaOH, can you please tell us a bit detail on how and why it is used?

A cementing tank for the after precipitation liquors should take care of any remaining values.
It need to big enough and either have an air-bubbler, a circulation pump or an impeller to create sufficient stirring
to let all the liquid contact a Copper bar suspended in the liquid.

Good Morning Yggdrasil,
I'm very new to the field and I have to admit the technicians were taking the lead in some aspects. You can learn the manual but not the tricks from the book.
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?

excuse my lack of knowledge and my inexperienced questions

 

[Nouran Alaa]

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.

After reading your analysis to the situation and the others as well, I do not suspect the silver. I guess its most probably in the solutions
I'm still not sure which method from the suggested I should use and how to apply effectively without causing more losses.
I'll start with stannous chloride for testing, but i'm not sure of the method of collection from the solutions
your help is very much appreciated, thank you

 

[Yggdrasil]

Good Morning Yggdrasil,
I'm very new to the field and I have to admit the technicians were taking the lead in some aspects. You can learn the manual but not the tricks from the book.
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?

excuse my lack of knowledge and my inexperienced questions

Yes.
And what you refer to seem to just be used as a settling tank if I understand you correct?
In a cementing tank you need to have a piece of less precious metal, Copper is preferred because it will only cement precious metals.
Iron and Zinc can also be used but they will drop other metals as well if present.
And the circulation is to make sure all the liquid will be in contact with the Copper.
How many days a week do you plan to have production?

Regarding the waste treatment it is important to have good protocols in place.
The thread "Dealing with waste" goes through this.

Simplified it will be more like this.
1 A "stock pot"/cementing tank to drop any residual PMs with Copper.
2 The barren liquid is then cemented with Iron to drop out the Copper.

The liquid is then treated by rising the pH to drop out the Hydroxides,
this is best done in steps since the solubility of the Hydroxides change over the pH range.
After each drop the solids are either filtered or settled.
When all the Hydroxides is dropped from the liquid it is the brought to neutral.
The waste is now barren and can be discarded or evaporated depending on the regulations in your area.
The solids can be dried and discarded as solid waste usually, of course depending on the regulations.

 

[Justincase]

After reading your analysis to the situation and the others as well, I do not suspect the silver. I guess its most probably in the solutions
I'm still not sure which method from the suggested I should use and how to apply effectively without causing more losses.
I'll start with stannous chloride for testing, but i'm not sure of the method of collection from the solutions
your help is very much appreciated, thank you

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.

 

[Yggdrasil]

Additionally as have been mentioned.

Do not rely on pre-planned/list amounts of Chemicals.

This is live reactions and there is many reactions going on at the same time.
This means that some reactions need more and others less reagents.
One has to use as much as needed and know how to judge this.
Often we allow a bit of excess to ensure the reaction is properly finished.
The only real issue regarding this is the Nitric which may create a bit of hassle
but with careful deNOxing and proper use of a cement tank this can be mediated.

As an example to dissolve one gram of Gold, the text books say you need 1ml of Nitric in the Aqua Regia.
But in real life you may need only 0.5 ml or if it is heavy on Copper in the alloy maybe as much as 1.5 ml.

So basically it needs as much as it needs, do not rely on a set amount.
It is useful to have it as a guideline though.

 

[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.