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How did the cyanide process make low-grade gold ores more useful?

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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.

The cyanide process revolutionized the mining industry by enabling the profitable extraction of gold from low-grade ores that were previously considered uneconomical to process.1

The primary method used for these low-grade ores is heap leaching. In this technique, large piles of crushed ore are sprayed with a dilute solution of sodium cyanide. As the solution percolates through the heap, it dissolves the gold.1

To manage the high costs associated with processing the large volumes of material required for low-grade ores, engineers developed methods to avoid expensive solids-liquids separation equipment. A key innovation involves adding granular activated carbon to the ore slurry. The dissolved gold is adsorbed onto the carbon, which is then easily separated from the barren ore using screens. The gold is subsequently recovered from the carbon through further chemical treatment or electrowinning.1

These advancements allow for the efficient recovery of gold from deposits where the metal concentration is too low for traditional vat leaching methods.1