Décontamination à l'échelle pilote de sols pollués en métaux toxiques par des procédés miniers et lixiviation chimique

A pilot plant study permitted to demonstrate the scale up of a process using screening, spiral, hydrocyclone, and chemical leaching to decontaminate a soil. Thirty tons of a soil were treated. Screening allowed to separate a clean coarse fraction (>2 mm) of sand and gravel representing 70.9% of the total mass of soil. The <2 mm fraction of untreated soil contained 2200 mg Pb/kg, 350 mg Cu/kg, and 956 mg Zn/kg. The spiral treatment removed 10.2% Pb, 22.7% Cu, and 4.3% Zn, but it produced a small proportion of concentrate (0.53% of the whole soil). The spiral was more effective for Cu removal, because the 1–2 mm fraction of the soil contained more Cu than the smaller size fractions. The spirals are not usually efficient for the <75 µm fraction. This process was then not efficient for Pb removal, this metal being particularly concentrated in the <20 µm fraction. The <20 µm fraction, representing 6.48% of the total mass of soil and containing 5150 mg Pb/kg, was removed using a hydrocyclone. The chemical leaching process was used to treat 20.4% of the whole soil. This method has allowed to decrease the Pb concentration by approximately 57%, thus reducing the Pb content below the C criteria (1000 mg/kg) for commercial or industrial use in the province of Quebec. Overall, the process produced 91.1% of a noncontaminated soil and 8.9% of metallic residue and heavily contaminated soil. Key words: metals, soil, treatment, leaching, decontamination, mineral processing technology.