Treatment of contaminated soil leachate by precipitation, adsorption and ion exchange

• Alkaline leachate containing metals, PCP and dioxins was treated by various methods.
• Precipitation is the most efficient method to remove simultaneously metals and PCP.
• Activated carbon and resins are not efficient to remove As and Cr in alkaline media.
• Anion exchange in alkaline media is the most efficient to remove Cu, PCP and DF.

The alkaline washing of soil polluted by organic (pentachlorophenol (PCP) and polychlorinated dioxins and furans (DF)) and inorganic (As, Cr, and Cu) compounds generates large volumes of effluents with high concentrations of contaminants. The objective of the present study is the treatment of leachate produced by a soil decontamination process under alkaline conditions. The alkaline leachate (pH0 13.1) initially contains [As]0 = 14.5 mg L−1, [Cr]0 = 2.41 mg L−1, [Cu]0 = 8.22 mg L−1, [PCP]0 = 6.42 mg L−1 and [DF]0 = 127 ng TEF L−1. Precipitation allows the reduction of the concentrations to below 5 mg/L for Cu and below 1 mg/L for PCP and As to comply with regulations for effluent discharge in sewer in Quebec City and Montreal. The concentration of Cr was taken into consideration in this study even if it is below the legal limit (5 mg/L) without any treatment. Precipitation is the most efficient technique investigated here for the simultaneous removal of metals and PCP but does not eliminate DF beyond 17%. None of the activated carbons and resins tested can effectively remove As and Cr in strong alkaline media. The anionic resin Lewatit SR7 developed for anion exchange in strong alkaline media is the most effective for the simultaneous removal of Cu, PCP and DF, with recovery yields of 83, 99 and 97%, respectively.