Oxidized gold ore processing: Crushing, grinding and key steps in beneficiation

Oxidized gold ores, unlike gold oxides, are ores that are formed during the natural oxidation process and contain gold and other metal oxides. These ores are mainly composed of minerals such as limonite and pyrite, usually without sulfides, but contain secondary gold-bearing minerals such as iron hydroxide or hydrated iron oxide and quartz. Oxidized gold ores range in color from yellow to brown due to weathering, with gold embedded in hematite, goethite or limonite, and are usually loose in texture. 

There are various methods to extract gold from oxidized gold ores, which first require reducing the size of the ore through crushing and grinding to release the gold in the ore. The crushing process usually includes primary, secondary and tertiary crushing, using jaw crushers and cone crushers. Subsequently, vibrating screens classify the ore to ensure that the ore reaches a particle size suitable for further processing.

The grinding process uses ball mills or wet disc mills to grind the ore to a finer particle size to facilitate the release of gold. Ball mills are suitable for long-term large-scale processing, while wet disc mills are suitable for small and medium-sized beneficiation plants, with cost and maintenance advantages. 

The beneficiation process can adopt different methods according to the occurrence state of gold and the properties of the ore. Common beneficiation methods include:

Gravity separation: physical separation using the difference in specific gravity between gold and gangue minerals, using equipment such as shaking tables, spiral chutes or jigs.

Cyanidation method: gold is dissolved by mixing cyanide solution with the ground ore, and then recovered by activated carbon adsorption or zinc precipitation. The cyanidation method is suitable for fine-grained and high-grade ores, but attention should be paid to the treatment of cyanide waste.

Heap leaching: suitable for low-grade or large-block oxidized gold ores, by stacking the ore on a leak-proof heap leaching pad and spraying cyanide solution to dissolve the gold and then recover it. The heap leaching method has low investment cost, simple operation, and is suitable for large-scale operations.

For partially oxidized ores, gravity separation and cyanidation are often used in combination; while in completely oxidized ores, coarse gold is mostly recovered by gravity separation, while fine gold is treated by agitation cyanidation.