Heavy metals immobilization in contaminated soil by grape-pruning-residue biochar

Abstract

ABSTRACTTo investigate the influence of grape-pruning-residue (GPR) biochar on cadmium (Cd), lead (Pb), copper (Cu) and zinc (Zn) immobilization in a contaminated soil, a laboratory study was conducted with different rates of GPR biochar (0, 2, 5 and 10% w/w) at 25°C. After 1, 2, 4, and 8 weeks of incubation, the Tessier sequential extraction procedure was performed and metal mobility factor (MF) and metal stability index (IR) were calculated. The exchangeable (EX) and carbonate (CAR) fractions of the metals decreased significantly (p ≤ 0.05) with the biochar addition. The EX metal fractions decreased by 23 to 72%, and the CAR fractions decreased by 51 to 67% in the 10% biochar treatment after 8-week incubation. The MF values of Cd, Pb, Cu and Zn decreased by 47, 62, 70 and 49%, respectively, with addition %10 of the biochar. Biochar addition favored the metal redistribution into more stable fractions and resulted in an increase in IR values. The results demonstrated that the GPR biochar, especially at high application rate (10%), can effectively immobilize the heavy metals, thereby reducing their mobility in contaminated soils.