Abstract. Biological solubilization of metals in highly contaminated sediments (Lachine Canal, Montreal, P.Q., Canada) was tested in 500 mL batches. The biological process uses the leaching capacity of Thiobacilli. Batch experiments were performed to determine the influence of initial pH, the percentage of inoculum, and the addition of nitrogen and phosphate on the efficiency of the process. Similar metal recoveries were obtained at either of the initial pH values (pH 4.0 and pH 4.5). The addition of 20% inoculum (v/v) appears to result in acceptable yields over a short time period (24-48 hours). Solubilization of Cu is strongly correlated with the presence of bacteria (r 2 increase with time up to 0.90 after 53h). In the case of Zn (within first 6 hours) and Pb Cat the beginning), the chemical environment appears to be the main factor controlling solubilization of these elements (r 2 up to 0.99). The addition of nutrients had no affect on the production of Thiobacilli, but the addition of NH4 reduced the solubilization of Zn, Pb (r 2 up to 0.90) and at the beginning, the solubilization of Cu (r2=0.67). While the addition of PO43-diminished the solubilization of Zn, Pb and Cu (r 2 up to 0.96). Upon addition of substrate (FeSO4.7H20), the growth of Thiobacilli already present in the sediments is favored. The application of this process to sediments appears feasible, as Zn and Cu levels were at acceptable levels following treatment. Further studies are necessary to improve the removal of Pb.

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Recently, an efficient and promising process was developed to allow the removal of As, Cr, Cu, pentachlorophenol (PCP), and 7 polychlorodibenzo-dioxins and furans (PCDDF) from soil using alkaline leaching. The present study evaluates the performance and the 8 robustness of this decontamination process for the treatment of four different polluted soils by attrition and alkaline leaching at a pilot scale. 9The attrition process carried out on the coarse fraction (>0.125 mm) allowed the removal of 24-42% of As, 0-13% of Cr, 23-46% of Cu, 0-10 85% of PCP, and 17-64% of PCDDF from the different contaminated soils. Removal yields of 87-95% of As, 50-72% of Cr, 73-84% of Cu, 11 52-100% of PCP, and 27-73% of PCDDF were obtained after three leaching steps (½NaOH ¼ 1 M; ½Cocamydopropylbetaine-BW ¼ 3% 12(w/w); t ¼ 2 h; pulp density ½PD ¼ 10% [w/v]) conducted on the fine fraction (<0.125 mm). The performance of both attrition and alkaline 13 leaching processes seemed to be influenced by the nature of the soil and the type and initial level of contaminants present in the soils.14 However, the entire leaching process seemed to be highly efficient, allowing the simultaneous reduction of concentrations of inorganic 15 and organic contaminants. The cost, including direct and indirect costs, were estimated between US$214 and 454 per ton of treated soil, 16 depending on the nature of the soil and the initial level of contamination.