Understanding the Ore Washing Process

Key takeaway: Ore washing is the process of using hydraulic or mechanical force to scrub ore that is cemented by clay or contains a large amount of mud, causing the ore to break apart, washing away the fine mud from the ore surface, and separating the ore from the mud.

For placer deposits of gold, platinum, tungsten, tin, and oxidized and deeply weathered ores of lead, copper, iron, and manganese, ore washing is often a necessary preparatory step before crushing or beneficiation.

High-grade iron and manganese ores sometimes only need to have the mud washed away before they can be directly used for smelting. Construction sand and gravel and clay used in light industry often require washing for purification. The washability of the ore indicates the ease with which mud can be removed from the ore. It is mainly related to the nature, content, and state of the clay in the ore.

Common ore washing equipment includes hydraulic washing screens, cylindrical washing machines, trough washing machines, flat screens, and spiral classifiers. Sluice boxes can also be used for ore washing. Hydraulic washing screens utilize water jets to wash ore on a fixed bar screen and are used in China for washing difficult-to-wash ores. Cylindrical washing machines include rotary screens and rotary scrubbers. The former has a higher rotation speed, and the inner wall of the screen cylinder is equipped with longitudinal lifting plates, annular baffles, and high-pressure water spraying devices to improve crushing and dispersion capabilities, and is used for easily washable ores. The latter has a cylinder divided into two sections: the front section is unperforated and used for soaking and breaking up the ore, while the rear section is perforated and used for mud-ore separation.

Rotary scrubbers are mostly double-layered, and the cylinder also has lifting plates and high-pressure water spraying devices. Trough washing machines are often used for difficult-to-wash ores. They consist of an inclined semi-circular metal trough and two sets of intermeshing, counter-rotating spiral blades, providing a strong scrubbing action. Pre-soaking the ore, using high-pressure water spraying during the washing process, applying vibration, and adding a small amount of reagents (such as 1% concentration of NaOH) can all improve washing efficiency. Washing efficiency has a significant impact on subsequent processes and should be given due attention.