Soil washing involves mixing material with water and agitating it to release pollution from the surface of larger particles.
The technique works best on soils with a high granular content, with fines making up 30% or less. After oversize material - rocks and stones - are screened out, the gravel fraction goes to a water-wash soil scrubbing unit to remove organics and heavy chemicals.
Clean, coarse fraction gravels are separated and the remaining mixture of water, sand and fines is pumped through sieves, mixing blades, two hydrocyclones and water sprays. Clean sand is taken out and the fines are passed over a dewatering table where flocculent is added to bind the solids into lumps which sink. Water is drawn out by passing the mixture over a fine mesh sieve. A belt press then squeezes out the remaining water leaving a highly contaminated 'cake' which is usually sent to landfill.