MadSci Network: Chemistry

Re: How do you extract gold that is dissolved in mercury.

Area: Chemistry
Posted By: Greg Dries, Senior Research Engineer,U. S. Steel Technical Center
Date: Mon Aug 11 20:36:12 1997
Area of science: Chemistry
ID: 870643793.Ch

In response to your question regarding how to extract gold dissolved in mercury, there are two methods which can probably do the job, however one is extremely hazardous and the other may be only marginally safer. Therefore neither are methods that you could try. Both would not be something you could do without proper equipment for safety concerns. But for your informationand if your goal is to end up with metallic gold and metallic mercury, a distillation approach will do the separation. Because mercury boils at a temperature of 356 C, you could conceivably heat the amalgam (the alloy of gold in mercury) to the boiling temperature under a vacuum to draw off the vapors through a cold condensing coil. This will condense out the mercury. As the mercury vapor is drawn off however, the melting temperature of the remaining mixture will increase and the remaining alloy will eventually become solid unless the temperature is continuously increased. Therefore it would be necessary to continue heating the melt to higher temperatures as the process continues. Eventually the temperature of the melt will need to be about 1100 C (slightly above the melting temperature of the gold, to boil off the remainder of the mercury. In the distillation section the mercury will condense out as liquid metallic mercury, and the gold will remain in the crucible the original amalgam was placed into. Obviously this is not something you can do at home. THIS APPROACH WOULD BE VERY DANGEROUS!!, MERCURY IS A HIGHLY TOXIC METAL AND IS MOST HAZARDOUS IN ITS VAPOR STATE. DO NOT HEAT THIS MIXTURE AT HOME AND DO NOT TRY THIS ANYWHERE EXCEPT IN A PROPERLY CONFIGURED LABORATORY WITH KNOWLEDGEABLE PROFESSIONALS.

A second method would involve solution chemistry, an area where I am not an very knowledgeable. Although gold and mercury are chemically similar, I suspect that the amalgam could be dissolved in a special acid, and under the right conditions of pH, mercuric salts and/or other compounds of each constituent could be selectively precipitated from the solution. It would then be necessary to chemically reduce the compounds to their metallic state, which would depend upon what the compounds actually were. Solutions containing cyanide are usually used to remove gold from finely ground ore in mining operations. CYANIDE COMPOUNDS ARE DEADLY and must be handled carefully. Again this is nothing you can do at home!

From the foregoing, it should be obvious to you that what you wish to do can be done only with extreme care and under appropriate conditions and safeguards. I would encourage you to take your vial of mercury containing dissolved gold to someone who could ensure that it is disposed of properly. Mercury is not something that should be played around with. Mercury is a poison, and should be treated accordingly.

Greg Dries.

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