Paper sludge as a feasible soil amendment for the immobilization of Pb2+.

The possibility of amending Pb2+ contaminated soil (S) with paper sludge (P) was investigated through adsorption and desorption experiments. The adsorption process of Pb2+ in soil containing paper sludge (SP) could be well described by pseudo second-order kinetic model and the Langmuir isotherm model. After P addition, the equilibrium time decreased greatly (from 28 to 8 hr) and the Pb2+ maximum adsorbed amount (Qmax) increased by a factor of more than three to 102.04 mg/g. Qmax reached its maximum as S:P was 9:1 (m/m) after 10 days contact between S and P. Moreover, Pb2+ adsorbed amount increased with the rise of pH during the adsorption process. Desorption experiments indicated that Pb2+ adsorption in SP was irreversible. The metal ion fraction was analyzed with Energy Dispersive Spectrometer and Environmental Scan Electron Microscope. As a result, the addition of P to soil was found to induce a decrease in the mobile forms. The Pb2+ complexes formation in the presence of carbonates was the main adsorption mechanism. Overall, the paper sludge could be one of the promising soil amendments for the remediation of soil with Pb2+ contamination.