refining using borax, soda ash, etc

im trying to make the switch to fire assaying but one of my suppliers recommended just using borax
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basically im clueless

Your supplier is showing his lack of knowledge, at least in my opinion. No one can make a blanket statement about what fluxing is required for an assay without knowing what is being assayed. You may need litharge-----or not. You may need soda ash------or not.

I never worked as an assayer, and had all my assays run by an assaying lab. I did, however, recover values from waste materials that required good and proper fluxing to be successful. It worked. I was.

Harold

could you elucidate?

Your objective, please? I may not have the knowledge you seek.

Are you trying to refine via the cupelling process? If so, you need to study the AR process instead. Cupelling won't accomplish a separation of the precious metals, although, properly applied, it will dispose of base metals. Am I on the right track? I fear I'm not sure what your desire may be.

Harold

just to refine gold... i already smelt it but i heard i can refine it as well by adding borax and soda ash and some other compounds

would you know why you have to add silver and lead to cupel gold?

My honest opinion? Forget it. As I said, you can not make a separation of precious metals via the cupellation process.

Lead is generally added as litharge, which oxidizes the ore samples and then collects values with the resulting lead. That would be in the first process after crushing the ore. It would not likely be used when assaying extracted metals, but more so when extracting from ores. That may or may not be true in all cases. It's possible that the litharge that comes from the cupellation process (the lead that collected the values is converted back to litharge in cupellation) acts as a carrier for the base metal oxides and allows them to be absorbed by the cupel, along with the litharge. Please note that I said I paid to have any assays run by an assay lab, so I'm not up to speed on assays, although I have a basic understanding of how they work.

Silver is used for the inquartation process, so gold can be parted with nitric acid, removing traces of base metals and all the silver. The percentage of added silver is critical in that it's very desirable for the coronet to not break in to pieces or fine particles. It is hoped that all base metal and silver can be dissolved, leaving behind a barren honeycombed representative of the coronet, which would be gold and other precious metals.

Assuming you have to inquart your gold to get to the point of purification, the only thing lacking at that point is actually dissolving the gold in AR, then going through a proper precipitation. By that method, you can separate the platinum group metals from your gold. That may not sound like a problem, but if you get involved with dental gold, or even jewelry wastes, platinum and palladium are a fact of life, and can add appreciably to your stores of precious metals when handled properly. Further, you don't really want to leave them in gold, for each of them toughen gold considerably. That's why they're used in dental gold. Once alloyed with gold, the gold is not very desirable for use in jewelry.

In order to process platinum group metals, you almost have to get involved in silver refining----assuming your source is dental or jewelry. Both will contain silver, which becomes the carrier of the majority of the platinum group, like it or not. Even platinum will dissolve in nitric to some degree---when in the presence of silver. You recover values from the sludge from the silver parting cell. They're difficult to recover otherwise.

One thing to consider. If, by chance, you want to improve gold by absorbing oxides with flux, DO NOT USE SODA ASH. It is a reducer, and will put oxides right back in the alloy as clean metals. It's used in recovering values from waste material routinely. I posted on that subject tonight, a recipe for flux. Please follow this link to read my opinion if you're interested. http://goldrefiningforum.com/phpBB3/viewtopic.php?p=1844#1844


Harold

I'm sure you're right about the soda ash, Harold. I know it reduces AgCl to metal. I probably started using it because someone else was using it. I do like the consistency of the flux a little bit gives. I never used more than one small pinch in a torch melt and always finished off the melt with niter and borax, if necessary. I finally built a small #4 pot furnace just for puring gold. It's easier and faster and more efficient to pure gold in a crucible than in a melting dish. When I had my refinery, I shipped 9999 pure about once a week and never had a lot rejected. I remember only having to do redos on a couple of lots during a 5 year span. My success probably had more to do with my aqua regia technique than anything. Also, before filtering the original aqua regia, I always diluted the solution with 3 or 4 times water to drop most of the silver and used sulfuric to drop the lead.

My gold was always clean and slag free and had no staining. I always avoided fingerprinting or scratching the top surface. I kept it wrapped in a tissue. The crystals were well pronounced. The sink(s) was deep. All of these things are proof of high purity. They are what an educated buyer looks for as, they are about the only ways he has to determine 4 nine purity. For example, on a 999 or less bar, there might not be any crystals or sink. Only pure gold exudes enough gas to get a sink. Fire assay, wet chemistry, instruments, and any other method that I can think of, won't measure gold at this high level. You have to send it to a spectro lab, who will run it for everything except gold. You get a readout of impurity percentages, add them up, and subtract from 100.

I think my biggest improvement in purity was in the way I rinsed the final gold mud. I always went with hot tap water except on the final distilled water rinses. I did the following, in order: about 5 hot rinses; weak nitric (maybe 10 to 20%) leach; 8 hot rinses; ammonia (household ammonia without perfume or soap in it - full strength) leach; 5 hot rinses; 5 hot distilled water rinses. The nitric gets rid of any reduced metals and the ammonia gets rid of any silver chloride. I did everything in the same filter without removing the gold between steps. I applied the rinses and leaches with a beaker or lab squirt bottle around the top edge of the filter paper. This sounds like a lot of work but, the whole thing probably didn't take over 45 minutes and, most of time, you're doing something else while waiting for it to drip dry. Gold mud, when of the lighter colored variety, which I always tried to achieve, filters very fast. Darker mud, sometimes nearly black, is more finely divided, filters slower and is harder to get clean. It's more efficient and faster to do a lot of small rinses (cover just the gold with water) than a few big rinses (fill the water to the brim). For the leaches, I filled the funnel to the top of the paper and let it drain through. I let every rinse and leach drain through until there was only an occasional drip at the tip of the funnel.

You can do a great job on the rest of the steps and fail on filtering. If the gold is more than a few tenths of a point off purity, you can't clean it in the melt.