The aging effects of biochar and Zn2+ on adsorption and desorption kinetics of Pb2+ in a calcareous sandy soil

Abstract

ABSTRACT Adsorption and desorption rates play an important role in the availability and mobility of Lead (Pb2+) in soils treated with biochar. However, information is still limited about the effects of pyrolysis temperature, presence of Zn and incubation times on these processes. This study was performed to investigate the effects of 1% (w/w) walnut leaves biochars produced at different temperatures (200 °C (B200), 400 °C (B400) and 600 °C (B600)) on adsorption and desorption kinetics of Pb2+ in the presence of Zn2+ at two incubation times (30 and 90 d). Results explained that the adsorption rate of Pb2+ was decreased with increasing the pyrolysis temperature, whereas the desorption rate of Pb2+ was increased. In the presence of Zn2+, there was a decrease in the adsorption sites for Pb2+, while there was an increase in the available desorption sites for Pb2+. The rate of Pb2+ adsorption in 90 d of incubation was higher than 30 d of incubation, whereas the rate of Pb2+ desorption in 90 d of incubation was slower than 30 d of incubation. It can be concluded that 1% (w/w) walnut leaves biochar could not immobilize Pb2+ in the soil because more than 74% adsorbed Pb2+ desorbed in DTPA-TEA solution.