Recycling. Soil Recycling from Heavy Metal Contaminated Soil by Soil Washing Treatment.

Soil washing treatment is a water based process for mechanically scrubbing soils ex situ to remove undesirable contaminants. The process remove contaminants by dissolving or suspending them in wash solution or by concentrating them into a smaller volume of soil through particle size separation techniques. This process together with biological treatment is relatively mild to soil nature compared thermal treatment, so adequate for recycling of soil.The concept of reducing contamination through the use of particle size separation is based on the finding that most inorganic or organic contaminants tend to bind to clay and silt soil particles. Washing processes that separate the clay and silt particles from sand and gravel soil particles effectively separate and concentrate the contaminants into a smaller volume of soil that can be further treated or disposed. The clean, larger fraction can be recycled.In this paper, we demonstrate our trials with four types of heavy metal contaminated soil by three methods. Those method are a laboratory size separation experiment, a pilot plant experiment and a full scale plant treatment.For one type of soil the results of the laboratory experiment were shown to be different from those of the pilot plant experiment. It was suggested that a laboratory test with small volume of soil would make a incorrect estimation for treatability caused by heterogeneity of soil.Another type of soil showed a result that heavy metals exist at higher concentration in coarse particles than fine ones. It was suggested that for this type of soil, simple soil washing treatments are not applicable.A full scale treatment process were shown, and practical quality control were emphasized.