If the concentration tests have to be performed in the same field and the water is not abundant, the Dry Washer is an interesting alternative in order to prospect and evaluate preliminary a deposit. Basically the equipment is a rocker or sluice without water addition and the particles are fluidized by adding air under certain pressure and flow. The equipment has a screen that classify the material to be concentrated, coarse particles are separated and the fine particles pass to the riffled section, which received a pneumatic action to separate light and heavy particles. The riffled section is equipped with bellows. Basically the equipment receives a shaking and classification action that separates the particles according to their specific gravity and shape. Dry washer separates gold from sand by pulsations of air through a porous medium.
One condition very important at the moment of employing this equipment is to be sure that the material is totally dry and there are not lumps. If the material does not present both conditions, it is necessary to prepare the sample. The bellows are a very important part and the operator must assure the appropriate addition of air. Approximately, the bellows operate at 200-250 strokes per minute and the final value is obtained during the test because all the materials have different minerals and the separation parameters are not the same.
When all the material was processed, the heavy particles deposited on the riffles must be removed and cleaned by using a panning dish. It is a good idea to pan each riffle separately in order to compare the concentration action on the riffled area.
Schematic view of Dry Washer