This kind of plant is oriented to reject non-valuable material and reduce the problems produced by fine material, specifically when the clay content is high. In general, washing plants are able to perform classification, concentration and Recovery of gold minerals from Placer/Alluvial Fields and hard rock. They can be combined with other concentration plants.
Washing plants have an important advantage, they are easily moved and some of them were designed with water tanks for use in places where the water source can be a problem. Small designs can treat 150 to 180 cubic meters per hour at 20% solids.
A point very important is the screening due to is the first separation operation and the screen surface must be designed considering the apertures for the passage of fine material. The screening area must be enough to support the weight of material being screened, also have to be flexible to promote vibrating forces and light to avoid obstructions so that the throughput can not be affected. Typically, a grizzly is included at the beginning of the washing plant. The oversize material can be rejected is the gold is present in fine particles and can fed the crushing circuit when there are interesting amounts of free gold (nuggets). A gravimetric device such as a jig can be included in the design of the equipment. The flowsheet must consider several options so that the operations can be able to treat different gold ores.
Some design includes a scrubbing trommel. In this case during the treatment, the ore enters through the screen where it is washed. Minus one quarter material passes through the screen in to the sluice. The last one vibrates during the processing in order to promote the recovery of fine gold particles and preventing the formation of agglomerates. Heavy minerals are collected in the riffles and the gangue is discharged.
Washing Plant with trommel and sluices