Nouran Alaa
Well-known member
We added around 900grams of urea to each kg of gold
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Major gold losses in new gold refinery plant... Help!
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Nouran Alaa
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I can see people on this forum are not fans of UreaAnd of course... "Urea" obsessionWhy people in middle east and close countries use it everywhere, hard to say
2 kg of urea... Oh my
but you said very well its an essential in the middle east. I'll check the cost of sulfaminic acid where I live. It might be expensive here, I'm not sure though
Nouran Alaa
Well-known member
We did not test it. We filtered it after it stayed for a few days. Yes Naoh just for neutralization.
For the aluminum -correct me if im wrong- its only to test if there is gold and not a method of recovery is that correct?
Unfortunately, acid that contains gold looks the same to the human eye and working without any indication of how much gold, if any, is in solution will undoubtedly cause losses. Working with stannous chloride the refiner has an instantaneous indication of gold in solution while using only a single drop. And it is sensitive down to parts per million. So if nothing else, make some stannous chloride solution and do some familiarization tests to see how it works.
My guess what happened is you are using too much nitric acid, right off, I would lower the nitric ratio from 3 parts Hydrochloric Acid to 1 part Nitric Acid
down to 4 parts Hydrochloric Acid to 1 part Nitric Acid. This is effective because the reaction is condensed which essentially recycles a percentage of your nitric acid.
The urea is not consuming any free nitric acid, so using more nitric than necessary tends to leave the solution active after urea additions and can re-dissolve gold after you drop it with metabisulfite. If you use stannous chloride you can detect this instantly. Sulfamic is a better option but many people worldwide use urea effectively.
The tumbler plants also do not heat the solution. A heated dissolve allows free nitric to "burn off" and you can heat it until it stops blowing red fumes as an indication. You do not have this option.
You will have to rely on slow additions which allow the urea to work. Too much can cause excessive crystallization and hold up gold in the crystals. I assume you are adding the urea and dropping the gold in one of these?
you should slowly add urea and allow it to mix in. It will foam up violently with excessive additions. Add a little and wait for a reaction to subside. Then add a little more and wait. When you have added enough you will see the prills of urea start to float. That is when you stop.
Next you add the metabisulfite, again slowly with mixing. If the solution starts to blow red fumes that is only the excess free nitric acid burning off as the gold you just dropped re-dissolves. Not a problem, these slow additions will consume all of the free nitric and then the gold will drop and stay dropped.
If the gold alloy was from jewelry or had a percentage of copper in it the acid will be a green color. When there is gold in solution it affects the color and it starts out a brighter green and when the gold is out it is a dull green. Seeing this is something you learn and observe from doing it often enough, it never takes the place of testing with stannous chloride. When all of the gold is dropped, and your stannous chloride test is negative, the solution is dropped out the bottom of the vessel into the filter trolley to separate the gold from the spent acid.
When the filter removes all of the liquid the gold should look like this.
My guess what happened is you are using too much nitric acid, right off, I would lower the nitric ratio from 3 parts Hydrochloric Acid to 1 part Nitric Acid
down to 4 parts Hydrochloric Acid to 1 part Nitric Acid. This is effective because the reaction is condensed which essentially recycles a percentage of your nitric acid.
The urea is not consuming any free nitric acid, so using more nitric than necessary tends to leave the solution active after urea additions and can re-dissolve gold after you drop it with metabisulfite. If you use stannous chloride you can detect this instantly. Sulfamic is a better option but many people worldwide use urea effectively.
The tumbler plants also do not heat the solution. A heated dissolve allows free nitric to "burn off" and you can heat it until it stops blowing red fumes as an indication. You do not have this option.
You will have to rely on slow additions which allow the urea to work. Too much can cause excessive crystallization and hold up gold in the crystals. I assume you are adding the urea and dropping the gold in one of these?
you should slowly add urea and allow it to mix in. It will foam up violently with excessive additions. Add a little and wait for a reaction to subside. Then add a little more and wait. When you have added enough you will see the prills of urea start to float. That is when you stop.
Next you add the metabisulfite, again slowly with mixing. If the solution starts to blow red fumes that is only the excess free nitric acid burning off as the gold you just dropped re-dissolves. Not a problem, these slow additions will consume all of the free nitric and then the gold will drop and stay dropped.
If the gold alloy was from jewelry or had a percentage of copper in it the acid will be a green color. When there is gold in solution it affects the color and it starts out a brighter green and when the gold is out it is a dull green. Seeing this is something you learn and observe from doing it often enough, it never takes the place of testing with stannous chloride. When all of the gold is dropped, and your stannous chloride test is negative, the solution is dropped out the bottom of the vessel into the filter trolley to separate the gold from the spent acid.
When the filter removes all of the liquid the gold should look like this.
A caution when using the filter trolley.
When the filter pulls the solution through the paper and under the plate, the pump transfers the solution to the next step. But you need to be sure all of the solution containing gold is out of the filter. You cannot see it. This is a filter trolley without the plate.
The pump can effectively remove most of the liquid but sometimes a little remains. If this is liquid from the dissolve in the tumbler, it contains gold. If you don't check and make sure it is clear of any liquid, when you move the filter to the next operation and pump the waste liquid through, you take that gold that may have been under the plate with it and can lose gold.
It is easy to check and it should be standard procedure. The perforated plate has 2 oval holes that are bigger than the rest of the holes. They are made for 2 keys that you should have to allow for easy removal. These are the keys.
And these are the keys in the plate allowing you to pick up the perforated plate to make sure all of the liquid is rinsed on to the next step.
I assume you have been using the proper filter paper and installing it properly with the rubber tubing to assure the paper seals and no solids suck around the edges and out of the filter. If you are not doing this let me know and I will explain how it is done.
If you bought this unit used, you may not have gotten all of the proper instructions. If you have questions we can answer them for you.
When the filter pulls the solution through the paper and under the plate, the pump transfers the solution to the next step. But you need to be sure all of the solution containing gold is out of the filter. You cannot see it. This is a filter trolley without the plate.
The pump can effectively remove most of the liquid but sometimes a little remains. If this is liquid from the dissolve in the tumbler, it contains gold. If you don't check and make sure it is clear of any liquid, when you move the filter to the next operation and pump the waste liquid through, you take that gold that may have been under the plate with it and can lose gold.
It is easy to check and it should be standard procedure. The perforated plate has 2 oval holes that are bigger than the rest of the holes. They are made for 2 keys that you should have to allow for easy removal. These are the keys.
And these are the keys in the plate allowing you to pick up the perforated plate to make sure all of the liquid is rinsed on to the next step.
I assume you have been using the proper filter paper and installing it properly with the rubber tubing to assure the paper seals and no solids suck around the edges and out of the filter. If you are not doing this let me know and I will explain how it is done.
If you bought this unit used, you may not have gotten all of the proper instructions. If you have questions we can answer them for you.
I am a raw newbie to the gold refining world, but I have a lot of experience with various chemical batch processing methods.
Looking at her actual vs theoretical yields, they are at around 99.5% which seems extremely good to me.
4metals, what is a realistic yield for this process? To me expectations of 100% seem unrealistic .
Great information by the way.
Ed
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.
It is not out of the realm of refining to recover 99.85% and after accounting for metal hung up in the Silver Chloride and on filter papers and test papers to get that up to 99.95. Then there is the fact that when a refinery does a cleanup or replaces ductwork, there is always gold in the duct. So all in, it's never 100% but it can come close.
Remember that pesky little law of physics called the Law of Conservation of Mass. Matter can never be created or destroyed. So that gold in the duct didn't come out of thin air!
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
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.
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.
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
Well-known member
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?
Nouran Alaa
Well-known member
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
Well-known member
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
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.
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.
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
Well-known member
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.
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.
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.
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