The Effects of Biochar on Sorption - Desorption Characteristics of Pb (II) in a Calcareous Clay Loam Soil: Isotherm and Kinetic Studies

Abstract

ABSTRACT Lead (Pb2+) sorption and desorption rates are the most important processes controlling the mobility and availability of this metal in soil. However, information about biochar addition on amounts and rates of Pb2+ sorption and desorption in calcareous soils is limited. In this study, the effect of application of 1% (w/w) walnut leaf biochar produced at 200 (B200), 400 (B400), and 600°C (B600) was investigated on the adsorption and desorption characteristics (isotherm and kinetics) of Pb2+ in a calcareous clay loam soil at two incubation times (30 and 90 days). Results of the isotherm study showed that the maximum adsorption capacity (qm) (2–277 mg kg−1) and the strength of adsorption (KL) (0.010–0.230 l mg−1) increased significantly (P < .05) with an increase in the pyrolysis temperature. The qm and KL decreased significantly (P < .05) in the soils incubated for 90 days compared to the soils incubated for 30 days (except B600). Moreover, rate of Pb2+ adsorption increased significantly (P < .05) with an increase in the pyrolysis temperature, while, available sites and rate of Pb2+ desorption decreased significantly (P < .05) with an increase in the pyrolysis temperature. The rate of Pb2+ adsorption decreased (P < .05) during incubation, while rate of Pb2+ desorption increased (P < .05). Significant correlations (P < .05) were found between isotherm and kinetics coefficients and surface area and P of the biochars. It can be concluded that the application of biochars produced at high temperature contain high P and surface area are suitable for improve Pb-contaminated calcareous soils.