Driven by gold’s inherent value and relative rarity, mining technology has continuously evolved to use ore more efficiently and extract every molecule of gold possible. One of the earliest methods for extracting gold, salt cementation, was perfected by the Lydian Empire during the Iron Age. Pre-19th century placer mining operations used mercury to dissolve the gold in crushed ore, making it easier to recover. Later innovations include the MacArthur-Forrest Process and borax flux extraction. However, one of the most interesting methods is froth flotation.
Froth flotation works by exploiting the hydrophobic properties of gold molecules. First, ore is ground into an extremely fine powder. The powdered ore is mixed with water to create a slurry, which is mixed with surfactants to increase the gold’s hydrophobicity. This mixture is placed into a large tank filled with distilled water. Air bubbles are pumped into the tank and the water is agitated.
Aided by the surfactant, the water repels the gold into the air bubbles, which rise to the top – creating a bubbly golden froth. The froth is skimmed from the surface and collected and later condensed into metallic gold. Meanwhile, the tailings and waste material sink to the bottom of the tank.
Along with mechanized mining equipment, froth flotation dramatically improved the efficiency of gold mines. Thanks to this process, miners and refiners are able to extract quality minerals from ore at lower grades than has been previously possible – making it perhaps the most important mining industry innovation of the 20th century.