[Comparative studies on the characteristics for Cu2+ or Zn2+ adsorption onto different landfilled sludge]

In this paper, it was comparatively studied about the adsorption or desorption behaviour for Cu2+ or Zn2+ ion onto different landfilled sludge. The results showed that Cu2+ or Zn2+ adsorption isotherm could significantly conform to Freundlich and Henry equations both for the directly landfilled sludge (SSA) and the solidifying landfilled sludge (SSB). Moreover, much higher adsorption capacities were found for Cu2+ on SSA but for Zn2+ on SSB, and the removal efficiency could reach 95% for Cu2+ by SSA with dosage being 10-20 g/L or Zn2+ by SSB with dosage being 5 g/L when the initial CU2+ or Zn2+ concentration was 128 mg/L. However, the desorption ratio of Cu2+, Zn2+ decreased with their increasing adsorption amount, with the same initial concentration, it was much more difficult for Cu2+ to release from SSA while for Zn2+ to release from SSB. Relatively, first-order dynamic equation was the optimal model to describe the kinetics of Cu2+, Zn2+ adsorption by the two sludges, the rates for Cu2+ adsorbed onto SSA and for Zn2+ adsorbed onto SSB were much higher at the same adsorption time. FTIR analysis showed that, the site for Cu2+ adsorption onto SSA is the Si-O group from silicate and carboxy groups from aromatic acids or fatty acids which making stable complex compound with CU2+, while it was specific adsorption by Me--O group from metal oxide and hydroxyl group or carboxy groups from fatty acids for Zn2+ adsorption onto SSB.