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How does mercury amalgamation recover fine particles of gold?

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A diagram showing the periodic table entry for gold, with the symbol Au, atomic number 79, atomic weight 196.96657, electron configuration, and labels for its properties as a solid transition metal with a face-centered cubic crystal structure. — gold The precious metal gold is a chemical element with the symbol Au. Its square on the periodic table details some of its properties, including its atomic weight, atomic number, and crystal structure.

Mercury amalgamation recovers fine particles of gold by exploiting the metal's solubility in mercury. When fine gold particles contact a fresh mercury surface, they are wetted and dissolved, forming an amalgam—a metallic alloy.21

This process is typically achieved by:
* Passing ore slurry over mercury-coated copper plates.2
* Mixing ore and mercury in specialized vessels, such as an amalgam barrel.2
* Grinding ore in a mill with added mercury until the gold dissolves.2

Because the resulting amalgam is denser than the remaining ore, it can be separated from the barren material. The gold is then isolated by heating the amalgam in a sealed retort; this distills off the mercury, which is recovered for reuse, leaving the precious metal as a residue.21

While effective, this method presents significant ethical and safety concerns. The use of mercury poses severe risks of mercury poisoning to operators and the environment, necessitating the use of strictly controlled, well-designed equipment to prevent contamination.23