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How to Remove Gold from Black Sand with Nitric Acid

Recreational prospectors typically end up with a lot of black sand in the bottom of their gold pans or in the sluice box. Gold dust often appears with the mineral sand and dirt that remains after the removal of the larger pieces and nuggets. Processing the black sand can recover more gold, yielding a bigger profit for the prospector. Physical methods are available but are labor intensive. Chemical methods of removal are easier but you must take care when using the hazardous chemicals the separation requires.

Things You'll Need

Pan
Mercury
250 ml beaker
Dilute nitric acid
Alcohol
Porcelain parting cup
Hot plate

Instructions

- 1
  Place a small pile of black sand into a pan. Make a small depression in the center of the sand and place a small amount of mercury in the center. Mercury aids in removing the gold from the black sand by forming an amalgam with the gold.
- 2
  Work the mercury back and forth through the black sand until it has formed an amalgam and no gold colored flecks remain in the sample of black sand.
- 3
  Transfer the mercury to a 250 ml beaker and add 40 to 50 ml of dilute nitric acid. The nitric acid will dissolve the mercury into solution but leave the gold.
- 4
  Transfer the glob of amalgam to a porcelain parting cup and heat slowly on a hot plate until the bottom of the cup is red hot. Add fresh acid and allow the digestion to complete. If necessary, heat the sample on low heat. Do not boil the sample.
- 5
  Pour off the remaining acid and wash the remaining gold with warm water three times.
- 6
  Add a few drops of alcohol and dry on low heat.
- 7
  Heat the bottom of the cup to a low red to anneal the gold. This will drive off any remaining mercury before you weigh the gold.

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