The less you know about chemistry, the better inquartation looks!
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Aqua Regia method with 12-13% Ag _inquart_
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giahylxag
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Well that is my worst fear when thinking about refining gold. At the end of the day when I gather all the stuff and add to calculation then some gold is lost and I don't know why. I just made a lost.
giahylxag
Well-known member
That's how my friend told me *laugh*
Soda ash, carbon powder, and a borax cap if you go the melt route.
But the resultant silver metal will have gold in it, maybe 1 or 2%, and you won't see that back until you clean up the anode slimes. That can be weeks to months!
giahylxag
Well-known member
It seems getting gold to 99+% even to 99.95+% consistently at a home refining is not hard at all. But it seem really hard to get 99.99% Why? Is this the limitation of AR and one can only get 99.99% by electrolysis?
No, but there are impurities in the water, acids and precipitants.
giahylxag
Well-known member
Distilled water, tech grade acid, and SO2 as recipitant is good?
Most of the refined bars in my market come up with silver (0.005%) as impurity
Should be good, but needs plenty washing after precipitation.
There are procedures from Harold_V to get 59 by these means.
Search the forum.
Filtering plays a large part in purity as well. Poor technique or some make do filter papers can allow tiny amounts of various impurities through, and it will show up in your gold when melting. Even something as simple as a dirty torch or burner in the furnace can bring about small impurities.
Another question is why to do it?
It won't pay much better than 99.5 and its cost are way higher.
giahylxag
Well-known member
Given the market price here they pay 0.5% more from 9995 to 9999. 9999 can make coins and bars. Quality under that can make jewelry
In my case, just to know if I can do it. I want the best I can produce, to satisfy myself. If the buyers like, it is even better.
giahylxag
Well-known member
Me too.
I just want to reach the limit
giahylxag
Well-known member
Most of the time I see there is silver impurity in bars that I got. As low as 0.003%.
Filtering the solution diluted with Ice cold water will remove most of the Silver Chloride.
Washes the powders with Ammonia will too even though I seem to recollect there were reasons not to do it.
giahylxag
Well-known member
Here are a couple of posts/threads that may help.
Lou's Washing Procedure
Method for Ultra High Purity Gold
Dave
Lou's Washing Procedure
Method for Ultra High Purity Gold
Dave
giahylxag
Well-known member
Wow really appreciate your help. The Library thread is not so big and many knowlegde (beside Hook's book) are scattered around, some threads are acient.
Getting gold to .9999 is a challenge, but actually getting anything to .9999 pure, whether it's gold or borax or peanut butter is difficult. The reason with gold is some of the metals like to stay together. With gold the major impurities of 9999 metal are copper and silver when run on an ICP. That is if the feedstock is karat gold, as your feed is. Truth be told all of the refining machines out there that claim .9999 gold with single pass aqua regia really aren't telling you the whole truth. But there are some tricks you can add to your standard processing that will get you very close to if not past 9999. But as others have noted, it comes at a cost.
There are some tricks mentioned here like cold acid, which is very effective for removing Silver from the gold. I believe if you know why that is true, it will make more sense to you and you will incorporate it into your process.
First off, silver chloride is soluble in water, very slightly, but still some is soluble. If you have ever filtered a hot or warm solution of aqua regia that dissolved an alloy which had silver in it, and after you filtered it, you let it stay overnight, you will likely see a fine white precipitate sitting on the bottom of the flask. You know you did the filtration properly and used a good grade of filter paper yet that layer of white Silver Chloride is there. It is there because when you filtered it some of that Silver Chloride was dissolved in the acid and when it cooled down it came out of solution. So no matter how well it was filtered, if it was dissolved in the acid it will pass the filter paper.
It turns out that, according to the handbook of chemistry and physics, the solubility of Silver Chloride in hot water is 0.0021 g/100 cc. The solubility of Silver Chloride in cold water is 0.000089 g100 cc. This tells us that the colder the acid is before you filter it, the more of the Silver Chloride is insoluble and will be caught on your filter paper.
For this very reason I tell mid sized refiners I set up to purchase an ice maker. Before they filter the acid after a digestion, it is best to add ice to drop the temperature as cool as you can get it. This step will assure you that any silver carried over from the dissolution in aqua regia will have as much Silver filtered out as possible and it will be reflected in the purity of your gold at the end.
In this particular application the OP has high Silver in the alloy. The debate has been whether to try direct aqua regia and deal with the chlorides and the gold contained, or inquart in nitric first to remove the base metals and silver. If the scrap is inquarted and only the insoluble gold is put up in aqua regia, this will be very similar to doing a second aqua regia refine to raise the purity. You should end up with a beautiful red solution which has a lot of gold and very little else in terms of metal impurities. Usually these are copper and Silver.
The gold from the parting also has the benefit of having been etched out of an alloy and having a lot of surface area and it is a powder like material. This will dissolve quickly in aqua regia and slow nitric additions will result in almost no free nitric when you are done.
The OP said he is able to get SO2 gas for precipitation. This is probably the best way to drop the gold in as pure a form as possible. Careful attention to the gassing process will assure no copper (as copper 1 chloride) is dropped with the gold at the end of the reaction. It is visible as a white crystal mixed with the gold sponge if there is any dropped and it can be cleaned up by dissolving it away with a strong solution of Hydrochloric Acid which will dissolve out the copper chloride. (this rinse acid can be reused for future aqua regia solutions)
These steps, after inquartation and parting, will get you a long way towards your goal of 9999 gold. And they are easy to implement in your process. There are other steps you can incorporate to get your purity where you need it but these steps should be first.
I assume (and assuming is often dangerous) that your potential buyers will be using an XRF to determine the purity of what they buy from you. Gold processed the way described above usually reads 9999 on these machines. The only true way to determine purity is by ICP which is a long process (compared to the XRF) and it is costly.
In the days before XRF kilo bars were cooled without a torch, when they cooled the surface would cleave and you could see gold crystal structure in the bar. Back then any bars cooled with a torch were not purchased by knowledgeable buyers, only bars with the bars showing the surface cleavage were bought because bars with impurities did not show the crystalline structure. This is still a good way for you to test your own purity for your own knowledge.
Other posts about this cleaving of the bar were posted by both Harold_V and GSP but they called the cleavage a pipe. so if you search for this concept use the word pipe.
Are there any PGM's in the normal lots sent out to the refiner? Not enough to be paid on by the refiner but enough to pick up on XRF of your bars shipped out? We should know if PGM's are there if you want to recover them eventually.
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