Sorption of Cd(II), Cr(VI), Ni(II), and Pb(II) onto unmodified sludge from a pond treating woolen processing industry wastewater

Efficiencies in metal removal (Cd(II), Cr(VI), Ni(II),and Pb(II)) using as sorbent an unmodified sludge generated in the wastewater treatment pond from the wool industry in the city of Trelew (Patagonia, Argentina) were evaluated through batch sorption experiments. Optimal sorption conditions regarding mass of sorbent, contact time, pH, and metal initial concentrations were assessed. Sludge was characterized by a low porosity and scarce organic matter content. In addition, the sorbent presented an important variety of functional groups, necessary for the metal sorption. Kinetic studies revealed that the metal retention onto woolen sludge had better fit of experimental data to the pseudo-second-order model ( R 2 between 0.956 and 1.000), indicating that the process was jointly controlled by multiple mechanisms dominated by chemisorption. Sorption equilibrium data for Pb and Cd fitted to both Langmuir and Freundlich models, while Ni adjusted better to Langmuir model and Cr to Freundlich model. The maximum sorption capacities of the woolen sludge were 14.16 mg Pb g −1 , 29.33 mg Cd g −1 , 15.77 mg Ni −1 , and 1.10 mg Cr g −1 .