Metals removal from soil, fly ash and sewage sludge leachates by precipitation and dewatering properties of the generated sludge

This study concerns the treatment by precipitation of three acidic and metal-rich leachates by using various reagents. Two treatment modes (simple and combined precipitation) have been performed to evaluate the metals removal efficiency and the dewatering ability of the generated sludge. It appears that for the three leachates used, the Ca(OH)(2) addition gave better metals removal at pH 10.0 than the use of NaOH at the same pH. Moreover, the combination of NaOH and Na2S allows better removal for Pb2+ Zn2+, Cu2+ and Mn2+ ions than with NaOH/Na2CO3 or NaOH/Na2HPO4. The dewaterability (vacuum filtration) of precipitates produced during the treatment of soil leachate was established as follows on the basis of the specific resistance to filtration (SRF) values: sulphides (4.3 x 10(12) m kg(-1))< phosphates (6.4 x 10(12) m kg(-1))