andyman
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nickel/gold separation
any suggestions on how to separate gold from nickel matte?
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Fleaker
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Well I know for a fact that nickel doesn't dissolve well in concentrated nitric (very little hydrogen released). I suggest you dissolve it all in
aqua regia (1 part nitric to 3 hydrochloric) and then use sulphur dioxide gas to precipitate the gold. You'd probably want to repeat the aqua
regia treatment and SO2 precipitation for higher purity gold.
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praseodym
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Separating using a magnet? If I have not remembered wrongly, nickel is ferromagnetic while gold is not. Since nickel is a magnetic material while gold
is not, you can just simply wave your magnet to remove the nickel from the Ni/Au mixture.
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neutrino
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That won't work if the Ni/Au is an alloy.
What exactly are you dealing with, andy? Alloy, mixture, coarse, fine, etc.? A little background would help.
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Fleaker
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Pure nickel is fairly magnetic and it would work if it's merely a mixture of powders.
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BromicAcid
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Fleaker, my nickel dissolves in nitric fairly rapidly, much more so then simply hydrochloric or hydrochloric/peroxide mixes. It is interesting to
note nitric acids tendency to oxidize, only very reactive metals will actually produce hydrogen gas and then usually for only short periods of time.
For example, I dropped some magnesium into a test tube of nitric, for a few moments it fizzed up with white bubbles but then suddenly turned red and
started spewing out NO<sub>x</sub> this is the most classical example and I had to see it with my own eyes.
Incidently I found electrolysis puts nickel into solution well, there is likely some electrolytic technique that could be taken advantage of here.
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praseodym
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But by using electrolysis wouldnt it mean that we have to either melt the mixture of Ni/Au or form an aqueous solution of the mixture? Separation by
electrolysis will only work when either of these methods are used, if I am not wrong...
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Mephisto
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| Quote: | Originally posted by praseodym
But by using electrolysis wouldnt it mean that we have to either melt the mixture of Ni/Au or form an aqueous solution of the mixture? Separation by
electrolysis will only work when either of these methods are used, if I am not wrong... |
Similarly to the electrolytic refining of copper you can separate a Ni/Au alloy. The alloy itself is used as anode and dissolves during the
electrolysis, while the gold sinks as fine powder to ground. On the cathode the nickel precipitates again as pure metal.
~Mephisto
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Fleaker
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Metaphisto is right, electrochemically speaking, it's a good method to dissolve nickel.
And Bromic, I meant very little hydrogen released initially. As I'm sure you've noticed, heat hastens the production of NOx fumes (it's
actually a method of destroying nitric, heating it.)
Your nickel goes in to solution quickly because it is thin and has more surface area than mine. Believe me, I tried to flatten it out on the anvil,
but the material is really tough and I had limited success. This chunk is over a 1\3 of a cm thick by 2 cm square which explains why it is still
dissolving days later.
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