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| Updated 9/9/09 |
An ordinary spoon is convenient to transfer the gold into the crucible and working over a smooth clean surface so any spilled
particles are not lost. When the filter is quite empty of gold the paper and the last of the gold are transferred into the crucible.
The paper should be pressed down firmly.
When the gold is being melted the filter paper will burn and leave any adhering gold in the crucible. It usually burns quite slowly
because the furnace flame at gold melting temperature does not have excess oxygen. With time it will burn away.
Fluxes are not usually needed, but if a surface film appears on the melt a very little borax may be added. However, the filter
paper can be burned out very quickly by adding a small amount (say ~ teaspoonful or less) of sodium nitrate. When this is
added to a hot crucible the paper burns with an eye-dazzling flame.
Slag from such fluxes are often very liquid and cannot be easily skimmed off. If it is necessary to skim, a graphite rod is used to
dip out the slag as adhering lumps on the end of the rod. When the gold is well molten and 'quick' it can be poured into the mold.
The mold should be smoked with a sooty flame,` or sprayed with a silicone parting fluid. Mineral oil coatings are sometimes
recommended but they may discolor the gold. The mold must be warm and dry. If cold, it may have traces of moisture. Molten
metal poured onto traces of moisture can create the most amazing, costly and potentially painful eruptions.
particles are not lost. When the filter is quite empty of gold the paper and the last of the gold are transferred into the crucible.
The paper should be pressed down firmly.
When the gold is being melted the filter paper will burn and leave any adhering gold in the crucible. It usually burns quite slowly
because the furnace flame at gold melting temperature does not have excess oxygen. With time it will burn away.
Fluxes are not usually needed, but if a surface film appears on the melt a very little borax may be added. However, the filter
paper can be burned out very quickly by adding a small amount (say ~ teaspoonful or less) of sodium nitrate. When this is
added to a hot crucible the paper burns with an eye-dazzling flame.
Slag from such fluxes are often very liquid and cannot be easily skimmed off. If it is necessary to skim, a graphite rod is used to
dip out the slag as adhering lumps on the end of the rod. When the gold is well molten and 'quick' it can be poured into the mold.
The mold should be smoked with a sooty flame,` or sprayed with a silicone parting fluid. Mineral oil coatings are sometimes
recommended but they may discolor the gold. The mold must be warm and dry. If cold, it may have traces of moisture. Molten
metal poured onto traces of moisture can create the most amazing, costly and potentially painful eruptions.
Melting the Gold
Any gas or electric furnace normally used for gold melting or alloy production may be used for melting the precipitated gold.
Crucible material is not critical and may be selected to suit the melting furnace. Crucibles, however, should be clean and kept
solely for melting pure gold.
Any gas or electric furnace normally used for gold melting or alloy production may be used for melting the precipitated gold.
Crucible material is not critical and may be selected to suit the melting furnace. Crucibles, however, should be clean and kept
solely for melting pure gold.
| Aqua Regia Information: |
| Instructions for Large Scale Gold Refining By the Aqua Regia Acid Method* Page 6 |
* Posted with Permission from Shor International
Bibliography
"Refining Precious Metal Wastes" by C.M. Hoke. Metallurgical Publishing Co., 123 William Street, New York, U.S.A. 1940
University Microfilms International, 300 N. Zeeb Road, Ann Arbor, Michigan 48106, U.S.A.
and 18 Bedford Row, London WC1R 4EJ, England.
This is probably the best of available literature on this subject.
"Methods for the Recovery of Platinum, Iridium, Palladium, Gold and Silver from Jewelers Waste" by C.W. Davis. Technical Paper No. 342, U.S.
Bureau of Mines, U.S. Government Printing Office, Washington D.C., U.S.A. 1924.
Now out of print.
"Recovering Precious Metals from Waste Liquid Residues" by Geo. M. Gee. E. & F.N. Spon Ltd., 57 Haymarket, London SW1. 1920
"Gold Refining" by Geo. Gajda. CA 90406, U.S.A. 1976.
For electrolytic methods general descriptions of silver and gold cells may be found in various texts on electrochemistry, electrorefining, etc. These
methods are not new, having been devised at the turn of the Centur or earlier.
Geo. Gajda, P.O. Box 1846, Santa Monica, Appendix No. l
"Refining Precious Metal Wastes" by C.M. Hoke. Metallurgical Publishing Co., 123 William Street, New York, U.S.A. 1940
University Microfilms International, 300 N. Zeeb Road, Ann Arbor, Michigan 48106, U.S.A.
and 18 Bedford Row, London WC1R 4EJ, England.
This is probably the best of available literature on this subject.
"Methods for the Recovery of Platinum, Iridium, Palladium, Gold and Silver from Jewelers Waste" by C.W. Davis. Technical Paper No. 342, U.S.
Bureau of Mines, U.S. Government Printing Office, Washington D.C., U.S.A. 1924.
Now out of print.
"Recovering Precious Metals from Waste Liquid Residues" by Geo. M. Gee. E. & F.N. Spon Ltd., 57 Haymarket, London SW1. 1920
"Gold Refining" by Geo. Gajda. CA 90406, U.S.A. 1976.
For electrolytic methods general descriptions of silver and gold cells may be found in various texts on electrochemistry, electrorefining, etc. These
methods are not new, having been devised at the turn of the Centur or earlier.
Geo. Gajda, P.O. Box 1846, Santa Monica, Appendix No. l
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