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Separating gold and platinum alloy


#1

dear friends,

this is sathish from dubai. accidentally one of my friend mixed
platinum and gold while melting. is there any technique where i can
seperate both metals without loosing both of them. both the metals
are in almost equal quantity.

warm regards
sathish chellen


#2

Hello Satish. The best way for separating the gold and platinum
depends on how much you have. It would be best from an economic
standpoint to send it to a refiner if you have close to an ounce or
more. Whether it would pay for you to do a small quantity yourself
depends on the availability of technical help, proper facilities and
your cost of the reagents required.

The time honored method of separating precious metals is by wet
chemical and electrochemical procedures. Someone else will probably
respond if there are other more modern efficient methods available
of which I am unaware. An excellent description of the procedures
used to separate (“part”) precious metals is in a book by C. W.
Ammen, “Recovery and Refining of Precious Metals.” This book was
published in 1984 by van Nostrand Reinhold, New York City. The ISBN
is 0-442-20934-7. There is an excellent description of the
practical procedures used for the recovery of precious metals from
every conceivable type of scrap. The author is conscientious in
pointing out the many hazards involved, and he is outspoken in his
instructions for avoiding problems. Discussion of the chemistry
needed to understand what is occurring is adequate, but he does not
hold your hand regarding the proper way to do standard laboratory
procedures. I cannot recommend this book too highly. It would have
been of great value to me some 55 years ago when I was a chemistry
student. I was parting precious metals for a San Francisco
manufacturing jeweler friend of mine as a means of making additional
income. At present, I process only low grade material about once a
year. It does not pay from a financial standpoint, but it is fun,
and I feel better about not discarding values. The volume I work
with is small enough (a few pennyweight of metal recovered) it does
not need to be reported. Waste cyanide is easily decomposed to
harmless materials. Heavy metals are saved as dry salts for future
disposal at a certified facility. I don’t know what the regulations
and laws regarding toxic waste are in your country. It would be
wise to find out what they are.

Recovery of the gold and platinum from your alloy would involve the
following general procedures:

  1. Physical preparation of the material for digestion in aqua
    regia. Any solids remaining after digestion is salts of iridium,
    ruthenium, rhodium, osmium and silver, if any of those metals were
    present in your alloy. These solids are filtered out. Recovery of
    any values in the filtered solids is more complicated than is the
    recovery of gold and platinum. The clear filtrate contains gold and
    platinum along with palladium if it were present in the alloy.

  2. Nitric acid is eliminated from the filtrate after which gold is
    recovered by precipitation with ferrous sulfate or sulfur dioxide.
    The gold is a very fine powder. Serious loss can occur if an
    attempt is made to torch melt it without following proper procedure.

  3. Platinum is precipitated from the filtrate of (2) as the
    chloroplatinate with ammonium chloride. The chloroplatinate is
    decomposed by heating to give sponge platinum.

  4. If palladium were present in the original alloy, the filtrate
    from (3) is treated with sodium hypochlorite. This precipitates
    palladium ammonium chloride which is decomposed by heating to give
    sponge palladium.

I hope this is a help in deciding what to do with your accidental
alloy.

Captain Blood
"Marlinespike Seamanship in Precious Metals"
@Alden_Glenda_Blood


#3
Waste cyanide is easily decomposed to harmless materials. 

Captain Blood: Please describe the proper method to this. thank
you