Patent ID: 7361283

Claim:
A method of decontaminating heavy metal contaminated soil or sludge which includes a) treating soil or sludge with an acid at a pH below 2 in a first treatment stage to form a liquid and a solid phase with a solids content from 5 to 30% b) separating the liquid and solid phases from the first treatment stage c) mixing the solid phase from the first treatment stage with a fresh acid liquid at a pH below 2 in a second treatment stage to form a liquid and a solid phase with a solids content from 5 to 30% d) separating the liquid and solid phases from the second treatment stage e) treating the liquid separated in step b) from the first treatment stage to precipitate heavy metals f) separating the precipitated heavy metals from the liquid of step e) and recycling the liquid to step c) g) treating the solids from step d) to adjust the pH to a level acceptable for a soil conditioner or fertilizer h) using the liquid from step d) as the acidic liquid in the first treatment stage for fresh batches of soil or sludge.