PhillipJ said:
Ok now. So if a guy has gold in AR solution, and suspects platinum, the spot plate will always show gold. Right?
Yes. But it's important that your stannous chloride solution be fresh. It loses it's ability as it oxidizes. Even with a heavy concentration of platinum, you will still get a purple stain, even if the gold content is low. In that case, it may be masked to some degree and you might not see the reaction in the spot, but the stain will remain when you rinse the spot plate. Platinum, in concentration, yields a reaction that looks much like dark coffee.
Just having palladium and gold together can be confusing. Adding platinum makes it somewhat worse----but as I said, each of them have a distinctive reaction, so you have to get used to what they look like, especially when they're mixed----and maybe even do further testing (using DMG, for example) to help sort what you're seeing. I don't recall ever having gold present and not being able to identify it, although if you had your solution down to just a few parts per million, that might be a case where you could overlook traces. Not much to worry about considering the value would border on nothing. The stannous chloride test for gold is VERY sensitive, and will detect amounts that are hardly worth recovering.
Aside from dropping either the gold or platinum one wouldn't know for sure if there was platinum?
That's entirely possible when working with a solution that contains a serious amount of gold, but you can do a test with ferrous sulfate to eliminate the gold, then test the solution for values if there's any question about content. Here's what you do: Place a drop of your solution in a spot plate cavity, then apply a crystal of ferrous sulfate. The crystal will precipitate the gold as a very thin sheet, or fine powder, leaving behind any other values. You can then test the cavity with stannous chloride to see if there is any reaction. If you get a purple reaction, you know the gold is not yet all down. If so, start another test, and stir the tiny sample with a glass rod, exposing all of it to the ferrous sulfate. The sample will change color as the gold precipitates. It's a good idea to have a tiny amount of ferrous sulfate left, which will indicate that the gold is all down. When there is no further action or color change, apply a drop of stannous chloride. With the gold gone from the solution, you can now see if there are other values present.
Also. Can any platinum be dropped after the gold has settled out?
Absolutely. That's how you effectively separate the two. You won't get a perfect separation when you have them mixed, for the first thing to be precipitated will always drag down a trace of everything that's in solution with it. When you wash what ever comes down first, you'll remove some of the dragged down values, which can be recycled for later recovery. My choice was always to precipitate gold first, but I worked with, primarily, gold solutions. The Pt group metals were often in such low levels of concentration that they could not be recovered without evaporating the solutions to concentrate them. I've mentioned time and again that the Pt group metals do not precipitate from dilute solutions. They don't. Not at all. Armed with this knowledge, and a future plan of processing everything through my reduction furnace, I simply poured all my solutions (that bore traces of values) in my stock pot, where they were precipitated on scrap steel. Residues from the stock pot were th
en combined with all my other waste materials and furnace reduced to recover the values. You need not do the furnace work, the residues can be chemically processed just as well, so recovering traces of values on scrap steel to concentrate them is not a bad idea. All depends on how badly you want to get your hands on the values. I was willing to wait for years-----and it turned out to be about 20 of them before I recovered mine. It was a wonderful savings plan. Remember-----I've told readers I retired at age 54. Couldn't have done it without refining
Harold
Edit: changed word "than" to "then"
(this was my first "successful" attempt with AR). Would I be correct?
