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How does froth flotation help concentrate gold-bearing sulfide minerals?

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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.

Froth flotation is a critical process for concentrating gold that is finely disseminated within base metal sulfide minerals, such as pyrite, pyrrhotite, or arsenopyrite.12

The process works by exploiting the differences in the surface wettability of minerals. After the ore is crushed and ground, it is mixed with water and specific chemical reagents to create an agitated suspension. These reagents alter the surface properties of the sulfide particles, making them hydrophobic (water-repelling).3415

When air is bubbled through the mixture, the hydrophobic sulfide particles—which contain the gold—attach to the air bubbles and rise to the surface to form a froth. This mineral-rich froth is then skimmed off the top of the flotation cell, effectively separating the gold-bearing sulfides from the hydrophilic (water-attracting) waste rock, or gangue, which remains in the pulp and sinks to the bottom. Once concentrated, these sulfide minerals can be further treated through oxidation methods, such as roasting or autoclaving, to release the gold for final extraction via cyanidation.352