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.
Aqua Regia method with 12-13% Ag
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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.
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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.
giahylxag
Well-known member
Most of the stock I have, I can say 90% of the stock don't have any PGM's.
PGM's mostly come from white gold and there are some particular lots (white gold 18k 14k 10k) that has PGM's but they come separated.
Yes I want to recover them eventually but i think it is out of scope right now, I will bring them later.
If you were to process bars with just a few percent of the alloy as Platinum or Palladium, inquarting will take the PGM's with it into the silver and parting that silver will put those metals into the silver nitrate. Generally, as old assaying books say, if you add 10 times the weight of Platinum as Silver (which you will do when you inquart) the Platinum will be parted and dissolve in nitric. Palladium will always dissolve in nitric anyway.
But the good news is when you cement the values (mostly Silver) from the parting liquids with copper. all PGM's in with the Silver will come down as metals and when cast into anodes for your Silver cell, you will get that Platinum in the anode slimes and some of the Palladium will be in the slimes, and some in the electrolyte, recoverable with Dimethylglyoxime.
If you were to do the first digestion in aqua regia, the PGM's would be in the acid after the gold drops and for 6 kilo's that will be about 25 liters plus rinse waters. This will have to be cemented on Copper to collect the PGM's. So in your debate about aqua regia first or inquartation first, choose cementing small amounts of PGM's out of 25 plus liters or concentrating them in anode slimes in your Silver cell.
giahylxag
Well-known member
Given the market I can get 0.25 to 0.5% more if i can get from 9995 to 9999. 9999s are sourced for coins and bars, 9995 and below are for jewelry making.
Beside I just want to push further. I have read many infomation about AR process, (on the internet and on this forum, and from many source can't remember) most of them claim 9995 is the standard, but I don't think it is the limit.
So to be clear if you produce 99.95% gold they discount it by .25 to .5% and if you produce 99.99% gold they pay spot? The difference can be as much as $10.50 per ounce!
giahylxag
Well-known member
The difference between 9999 and 9995 is $5~7/ounce and yes it can be high to $10 as demand for coins and bars rise.
Physical market right now here is around $40/ounce higher than spot
Well then, that represents some serious money on a weekly basis. I would start out with the precautions defined above and see where your purity ends up.
From there there are options such as chelation which will hold the impurities in solution as the gold drops, resulting in high purity. And then there is cleaning up the gold sponge by tumbling in hot acids depending on the impurities you are eliminating.
So either way you can cost effectively get the gold to 9999 and we can discuss the pro’s and cons of these methods when you get closer to production. Be warned, as your pro chemistry associate may love, these methods delve deeper into chemistry!
From there there are options such as chelation which will hold the impurities in solution as the gold drops, resulting in high purity. And then there is cleaning up the gold sponge by tumbling in hot acids depending on the impurities you are eliminating.
So either way you can cost effectively get the gold to 9999 and we can discuss the pro’s and cons of these methods when you get closer to production. Be warned, as your pro chemistry associate may love, these methods delve deeper into chemistry!
The pros and cons of producing higher quality product have to be considered carefully and can depend on your cash in hand as refining to a higher quality takes longer and uses more chemicals against the increased value placed on it.
If you can afford to have stock bullion on hand you can sell as you buy so you are not risking price movements and if you have enough you can produce the higher quality as the time element will not be so important in your costs.
giahylxag
Well-known member
Most of the time I move the gold as soon as possible. I have stock bullions. But for me I "feel" it risky when I sell my stock bullion as I refine the scrap later.
As a middleman, I can move the gold without risk and take a little profit. But as a refiner I can make much more but sure there will be some risk involved.
Really appreciate this forum when there are people can help me when some "wtf" moments happen.
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What a wonderful post Thank you so much. I have 40 grams of scrap 14K gold and would like to attempt this process. Still digesting all the procedures listed here. I was thinking of creating a spreadsheet to calculate the amounts of everything needed for processing. What are your thoughts on this.. Maybe you have something created already? I see your calculations are with 4.5 kilograms. a few questions.
1. Is it ok to use my little furnace for the inquarting? I see many people just using a torch to melt and inquart. I think the furnace would be better, Maybe not as cost-effective, But Im learning so Im not concerned about this.
2. I also saw sreetips use copper for inquarting instead of silver and it came out very nice. I did read in your post that there is already copper in the 14k gold material so that's why you use silver if I am correct. Just curious about why or if it's not a good decision to just use copper. Should silver always be the inquarting material?
3. I am confused about using the stainless steel vessel with the nitric once you have melted and inquarted. I was going to use my 2000ml beaker to do the separation with nitric. and then the rest of the processes with 2000ml beakers as a vessel.
I am sure you have probably covered all of this somewhere. I appreciate the post and look forward to trying this, but not until I am comfortable with all the processes and amounts of material for each process. I think 40 grams of 14K is a good amount for a first try... Any guidance on the amounts of materials for the processes would be greatly appreciated. Thanks in advance.
You need 4 times as much Nitric for the Copper than the Silver, that is why one use Silver to inquart if you can.
If there is little Silver one might go directly to AR.
Most Stainless steels is passified in Nitric and can be used for Nitric digestions.
40g of 14 k is 40 x 14/24 which is 40x 0.583 equals 23.3 grams pure Au.
You want the Gold to be 25% so 23.3 times 4 is 93 grams total.
you need to add 70 grams of Silver or Copper.
And then part it in Nitric.
A second reason for using silver to inquart is that if there are any PGMs present in the gold, especially platinum, they will "follow" the silver into solution during the nitric leach, leaving your gold a little cleaner for the AR digest.
You do want a total weight of around 93 grams, but there are already about 17 grams of base metals present in the 14K alloy. Take the 93 gram final weight minus the 40 gram starting weight and you need to add about 53 grams of silver.
Dave
Oops forgot what was there already
Some of the details in this thread are detailed to the OP’s rather unique situation. However inquartation with Silver is a viable method for smaller (even 1.25 ounce lots). Keeps all of your Silver together.
Kadriver or sreetips on you tube, has an excellent video on doing this entire process and if I wasn’t on my phone posting this I would find the link and post it. We rarely suggest you tube video’s but sreetips video’s are excellent.
Thank you 4metals, I am in no rush, so if you can post those videos in the thread when you can, that would be greatly appreciated.
thank you!!
