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Re: [Orchid] Separating gold and platinum alloy
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Alden & Glenda Blood Sunday, September 14, 2003
   
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    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"
mariner AT tgtel.com




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