Cyanide compounds: Sodium cyanide (NaCN) and potassium cyanide (KCN) were once classic gold leaching components. Cyanides can form stable complexes with gold, allowing the gold to dissolve from the ore crystal lattice and enter the solution. Subsequent processes such as zinc powder replacement can then extract the gold from the cyanide solution. For example, in heap leaching, a low-concentration cyanide solution is prepared and sprayed onto the ore heap to slowly leach gold. However, cyanides are highly toxic and pose significant risks to the environment and human health, and their use is now strictly controlled.
Thiourea compounds: Thiourea (CS(NH₂)₂) is gradually emerging. Under acidic conditions, it can form stable complex cations with gold ions, making it more environmentally friendly than cyanides. Furthermore, thiourea leaching is faster and applicable to a wide range of ore types. It also performs well in some difficult-to-process gold ores containing carbon or arsenic. Combining it with oxidants such as ferric sulfate can enhance the gold leaching effect.
Lime-sulfur mixture: This is a composite mineral processing agent, mainly composed of calcium polysulfide, made from lime and sulfur in a specific ratio. It combines gold leaching with impurity suppression, has low production costs, and is frequently used in small-scale gold mines or for the secondary recycling of gold mine tailings. Its alkaline properties reduce corrosion to equipment, although its leaching efficiency is slightly lower.
