Chemical leaching of metals from wastewater sludge: comparative study by use of three oxidizing agents [H2O2, FeCl3, and Fe2(SO4)3].

Chemical leaching of the toxic metals (cadmium, chromium, copper, nickel, lead, and zinc) and behavior of other elements (aluminum, calcium, iron, potassium, magnesium, manganese, sodium, phosphorus, and sulfur) in the wastewater sludge of the Montreal Urban Community wastewater treatment plant (Montreal, Quebec, Canada) were studied in 2-L beakers using sulfuric acid and three oxidants [H2O2, FeCl3, and Fe2(SO4)3] and their association. Metal removal efficiencies of these oxidants were evaluated under different conditions of pH (2.0 and 2.5) and oxidation-reduction potential (ORP) (350 to 500 mV). The solubilization of the different elements was linked to pH and/or ORP, and a period of 2 to 4 hours was required to obtain satisfactory metals removal yields. Sludge-fertilizing properties generally were little affected by the decontamination process, especially for processes using a ferric salt. Finally, optimal conditions, for best metals solubilization, were established at pH 2.5 and ORP = 450 mV in a 4-hour period.