Removal of Metals from Contaminated Soils by Mineral Processing Techniques Followed by Chemical Leaching

Abstract

A contaminated soil was exhaustively sampled at various depthson a rectangular sampling grid of 12 by 15 m (107 samples).Four metal contaminated soil samples were submitted to physicaltreatment methods followed by chemical leaching. The treatmentflowsheet consisted of crushing the 2–10 mm contaminatedfraction, various sieving and use of a wet magnetic separatorprocess for the >63 μm size fraction (SF). Subsequently theWilfley shaking table was applied to the 63-850 μm SF while ajig gravimetric separator was used on the SF >850 μm. Themagnetic separator had a small removal efficiency. Out of fourSF, one was successfully decontaminated by the Wilfley table andtwo other SF were successfully decontaminated by the jig; bothtreatments removed a significant part of metals from all soils.Chemical leaching using hydrochloric and acetic acids at atemperature of 37 °C was performed on 9 SF out of 12. After completion of the treatment, soils were recombined and tested with the Toxicity characteristics leaching procedure (TCLP) of the United States Environmental Protection Agency anda gastric juice simulation test (GJST). Untreated small size particles leach more metals with the GJST than coarse particles.Decreases in Pb concentrations varied from 33.9 to 82.5%, thehighest values corresponding to the most heavily contaminated soils. Decreases in Pb TCLP between 54.1 and 99.5% were observedand the maximal value for a treated soil was 1.53 mg Pb L-1.The GJST decrease varied from 48.5 and 92.5% (highest leachingpotential before treatment). No problematic levels of leachingoccurred, as leaching of Pb, Cu, Zn and Sn after treatment wasrelatively low. The amount of soil to be treated was estimated from a micro and macro characterization. For an heterogeneous soil like the one studied here, the estimated cost for a 100 000 metric tons project on a 2 year span is relatively low at nearly 60 $CDN/mt.