consolidation of Loss Gold thread

[orvi]

I made the standard gold solution. Dissolve 0.1 grams of pure gold in AR , Then add about 100 ml liters of water.
Then I tested with different concentrations with stannous chloride.
Different colors were created.

But the question is whether the solution we want to test during the refining operation is opaque green, and combines with the colors shown Below.
How to recognize?

I agree with 4metals, drop testing on filter paper would be more accurate to distinguish. You are looking for violet-dark-black colour. You have an advantae, that your solutions are highly concentrated, and as you have seen, 1g/L gold produce completely black test - so you can be testing even the greenest liquid, that flip to completely opaque black colour you cannot miss.

This show your stannous work, but I am curious about all of the colours from 0,25g down. Maybe it is just a photo, but they seem to be still orange (impurity ?) and precipitate or opalescence is rather brownish than violet/black.

 

[silver1]

 

[4metals]

I've re-read what amounts to 6 full pages of this thread and realize that gold Refinery has equipment issues which he appears to be working through, and then there are chemistry issues which to this point have been untouched beyond dissolving of the gold scrap. So let's try to keep this organized by working thru step by step. We will start with chemistry of refining gold and move on later to fume scrubbing, cementation, waste treatment and any other pertinent topics in an orderly (hopefully) fashion.

It is time to discuss chemistry options to button up the actual refining process. To make things easier it will help to know the OP's access to chemicals. Is sulfamic acid available to you? How about sodium metabisulfite?

For the next day or so we will be assuming the well filtered solution is sitting in the precipitation tank awaiting processing. Please Gold Refinery detail what steps come next in your current process. Don't be shy with photos, we have seen how actual photos so far in this thread have revealed much in helping us help you.

 

[4metals]

Not part of this discussion, but based on the same concept that i built mine out of. Powered by a Shop Vac. I took the cheap route! Wonder what's the price on that thing?

Ralph,

I love listening to your video's, I also enjoy listening to your (slightly) southern accent. A bit different than my New York accent!

I think your filter might offer Gold Refinery a solution here. The pump he has to draw vacuum in his filter could do the same here and transfer the solution downstream just as it does with his current filter. My concerns are the seal between the inner bucket and the outer bucket but possibly a strip of rubber cut from a tire tube stretched around the inner bucket may solve that. Also it may be necessary to cut a third bucket to make a ring to go inside the inner bucket and seal the paper down.

But all things considered, considering he has the pump, the price is right and the removable bucket is easily emptied because it isn't too heavy to lift out.

 

[Gold.refinery]

It is time to discuss chemistry options to button up the actual refining process. To make things easier it will help to know the OP's access to chemicals. Is sulfamic acid available to you? How about sodium metabisulfite?

I did not follow sulfamic acid until now in the market, but we have SMB available in the workshop.
We also have hydrazine 55%.

 

[4metals]

Most of the suppliers of tumbler plant refining systems recommend urea to burn off excess Nitric Acid and sodium metabisulfite to drop the gold. Personally I would be staying away from the hydrazine.
The metabisulfite is quick and efficient at dropping gold once the nitric has been consumed. The urea is not my favorite because it will cause waste treatment issues down the line as it will decompose into ammonia which will redissolve copper into your waste stream. That is why you should investigate sulfamic acid.
Discussing the various options of dropping the gold is where the various methods used by members will help present Gold Refinery with all of the potential options. So I invite other opinions for sure.

 

[Gold.refinery]

Yes right, I did the final Final purification of the solution, after adding the caustic soda, the smell of ammonia filled completely in the workshop space. So I will definitely follow sulfamic acid. I just heard that it is expensive. I also do not know the ratio of its use.

As for the precipitate, from there we are in a busy commercial area, the manufacturer of machine suggested hydrazine. (I hate it).
We predicted that SO2 gas could cause irritation to neighbors's eyes and noses.
Of course, after discussing the capacity of scrubbers and their chemistry, this issue may become clear.

 

[4metals]

the manufacturer of machine suggested hydrazine. (I hate it).

Is this the same guy who said use 58cm paper to fill a 60cm diameter plate? Or mixed you up a liter of Stannous chloride so you have enough for years of refining?

I have used hydrazine extensively to reduce platinum group salts to metal but not ever to drop gold. Hydrazine will drop gold with free nitric so I do not know why you were instructed to add so much urea. If there is Platinum or Palladium in the jewelry you melt and refine, I do not know if the long standing (overnight) exposure to hydrazine will reduce them along with the gold. As I said I never used hydrazine to drop gold, possibly Lou will know the answer to this. Here in the US it is heavily regulated so options are often considered to limit its use.

 

[Gold.refinery]

Unfortunately, this is the same person who made the 2 liter tin chloride solution !!!!

Did I get what you mean? Do you believe that if hydrazine is used to precipitate gold, there is no need to kill nitric with urea ????

The platinum and palladium in our scrap are very very small, so we are not going to take the platinum group right now,
assuming, is not hydrazine suitable?
Also, what is your opinion about so2 gas from smb?

 

[4metals]

Also, what is your opinion about so2 gas from smb?

The Sulfur Dioxide fume is much more water soluble than a NOx fume and European standard fume scrubbing usually can accommodate Sulfur Dioxide, it's NOx where there is a retention time issue, which we can discuss later.
Another option for dropping the gold is Sulfur Dioxide gas cylinders. It can drive off the excess Nitric by dropping gold and allowing the nitric to burn off by re-dissolving gold until the gold drops and stays dropped because the nitric is gone. And gaseous Sulfur Dioxide drops gold very clean.

A last option which has very low odor is Vitamin C or Ascorbic Acid. I know some smaller scale refiners using it and maybe someone with first hand experience with it will chime in here.

 

[orvi]

Yes right, I did the final Final purification of the solution, after adding the caustic soda, the smell of ammonia filled completely in the workshop space. So I will definitely follow sulfamic acid. I just heard that it is expensive. I also do not know the ratio of its use.

As for the precipitate, from there we are in a busy commercial area, the manufacturer of machine suggested hydrazine. (I hate it).
We predicted that SO2 gas could cause irritation to neighbors's eyes and noses.
Of course, after discussing the capacity of scrubbers and their chemistry, this issue may become clear.

I do not know from what perspective you judge the "expensiveness" of chemicals, but here I purchase it for about 5euro/kg. If you do not overshoot with nitric that much, you won´t need more than one or two cups to neutralize the solution. Not even half a kilo. For me, if I would refine 2,9 kilograms of gold, some 2 euros extra money will be practically nothing And I am purchasing kilo packages, not in bulk. It will get even cheaper in bulk.
Sulfamic acid is industrial chemical, often used for de-scaling.

I do not know to choose what is better - to slightly smell severly poisonous and carcinogenic hydrazine, or strong smelling probably less toxic SO2 (just in my view, poisonong with SO2 is much more difficult because unbearable smell in very low concentrations).
If you do not overadd the metabisulfite, not that much SO2 will escape the vessel. You have very concentrated gold solution, so majority of SO2 will be consumed to reduce gold. So sulfur will in turn oxidize to S(VI) - forming sulfate ions, which do not smell and are practically harmless.

As it ws said, if you ever stumble across PGMs in your solution, hydrazine will reduce them to metals, too. Maybe you do not have the PGMs in your feed now, but if they emerge in the future, you won´t have the means to get rid of them from your gold.

Other possibilities for reducing gold are all quite impractical in my eyes. Ferrous sulfate is overkill - too much waste weight, lots of it for reducing this large batches, and subsequently enlarged waste stream.
Ascorbic acid is expensive, oxalic acid is quite impractical with need for prolonged boiling...
SMB is winner for me.

 

[Gold.refinery]

Our scrubs can purify NOx gases completely, so, do you think they will purify so2 gases as well?

If we use so2 gas, there is no need for the free nitric killing step, right?

If we use so2 gas, will all the solutions have an annoying smell until they reach the end and treat the wastewater? Also smb?

 

[4metals]

The platinum and palladium in our scrap are very very small, so we are not going to take the platinum group right now,

Stannous chloride will also indicate Platinum and Palladium in your acid after the gold has dropped. The intensity of the positive gold test on your solution will mask the PGM's so you will not see it until the gold is out.

If it is even a few grams in solution the stannous will indicate it. for this reason you need to learn what the color changes are for the Platinum group metals. This is part of the learned art of refining that experience brings.

 

[4metals]

If we use so2 gas, there is no need for the free nitric killing step, right?

If we use so2 gas, will all the solutions have an annoying smell until they reach the end and treat the wastewater? Also smb?

Sulfur Dioxide will eliminate the need for sulfamic acid or urea, but is likely more costly than sulfamic. It works by burning off the excess nitric because it drops gold, which re-dissolves to be dropped again based on how much free nitric remains. By killing off with sulfamic, you will use substantially less Sulfur Dioxide gas. Either way you have to kill off excess nitric acid unless you choose hydrazine which is not my first choice. And with hydrazine, if there are PGM's in solution they will be in with your gold as Orvi confirmed. Then the only way to get them out is to re-refine the gold.

The annoying smell is probably from the urea in a caustic solution becoming ammonia. Not an issue with Sulfur Dioxide or metabisulfite. In either event, you should consider a general exhaust to get those fumes out of your shop. Waste treatment over an unvented tank isn't conducive to the best of working conditions.

 

[orvi]

The Sulfur Dioxide fume is much more water soluble than a NOx fume and European standard fume scrubbing usually can accommodate Sulfur Dioxide, it's NOx where there is a retention time issue, which we can discuss later.
Another option for dropping the gold is Sulfur Dioxide gas cylinders. It can drive off the excess Nitric by dropping gold and allowing the nitric to burn off by re-dissolving gold until the gold drops and stays dropped because the nitric is gone. And gaseous Sulfur Dioxide drops gold very clean.

A last option which has very low odor is Vitamin C or Ascorbic Acid. I know some smaller scale refiners using it and maybe someone with first hand experience with it will chime in here.

Well explained. Nox is much difficult to scrubb or destroy. SO2 is acidic, so very simple "basic" absorber with NaOH is usually enough to catch vast majority to acceptable levels.

I just add that with good fitting and fritted glass on the end of the SO2 delivery tube, you can very easily adsorb majority of the gas without significant escape to the air.

Vitamin C is fine, produce good precipitate I think. But I only used it for gram scale drop. Not for production scale.

 

[Gold.refinery]

I just add that with good fitting and fritted glass on the end of the SO2 delivery tube, you can very easily adsorb majority of the gas without significant escape to the air.

Would you please explaine more , I didn’t understand.

 

[4metals]

Sulfur Dioxide is typically delivered through a tube which reaches down low into the tank and forces the gas to contact more solution as it rises. Much like an airstone in an aquarium which makes more surface area by making smaller bubbles, a glass frit is the all glass "airstone" which allows more bubble surface area to utilize the Sulfur Dioxide more efficiency to react more completely before it passes out of the solution.

 

[Gold.refinery]

I know so2 creates the best gold Sediment.
Is the smell of sulfur created by so2 gas Sedimentation more or by SMB?

Now, We have food grade SMB available.
If we want to use SMB to deposit gold in the next operation, what points should we follow?

For example, what is the ratio of adding smb to gold? (Helps for less gas and less pollution of gold dust).

Do we have to dissolve it with water and add it or can it be added solid?

In terms of time, how long does smb deposition take (compared to hydrazine)?

 

[Shark]

How well would sodium nitrite work at this scale?

 

[Geo]

A very good alternative for removing overages of nitric acid from solution before dropping the gold is sulfamic acid. Sulfamic acid is sold as grout cleaner for cleaning the cement that holds the stone tiles in kitchens and bath rooms. The formula is (H3NSO3). I suggest you incorporate this chemical to your process. The use of this chemical is fairly simple. Heat the solution to 93°-94°C. It is the best to use this chemical dry, if possible. Or, it can be added in a concentrated solution. The first amount added should be relative to amount of solution you are adding to, and, available room for gas expansion. I add 1 gram per 1,000ml's. It will produce a vigorous reaction if there is free nitric acid available in solution. After the initial addition, the next addition will be more subdued. The subsequent additions will be even more subdued. Make additions until there is no more reaction. This does not mean that the solution is nitric acid free. The solution should stay at heat and checked every thirty minutes. If the solution is generating N2O, which is a clear gas, do not add more. If the solution is producing NO2, which is a red gas that is noxious and corrosive and you need to add more sulfamic acid. Begin the additions the same as before. Small amounts until the initial gaseous outburst and then you can add bigger amounts at a time. While on heat, after thirty minutes, if the solution is not creating tiny reaction bubbles, the reaction is complete. The reaction generates a small amount of sulfuric acid in solution. This may cause some sulfate salts to form in solution, so it is best to filter after this stage.