Kinetics and adsorption isotherm of cadmium and lead on waste- agricultural derived biochar and their stabilization in two different polluted soils

Abstract

The current study evaluated sugarcane bagasse biochar (SCBB) as an adsorbent for cadmium (Cd²⁺ ) and lead ( Pb²⁺). By using the stirred-batch technique, a kinetic experiment was conducted at two concentrations, while an adsorption isotherm experiment was performed at five concentrations. Furthermore, the role of SCBB at doses (0%, 0.5%, 1%, 2%) for stabilization of Cd2+ and Pb2+ in two polluted soils (S(I), S(II)) and decreasing their bioavailability was assessed through pot experiment. Results showed that equilibrium was achieved after 2 h for Cd2+ and after 1 h for Pb2+. Pseudo second-order model was more fitted for kinetic data (R²= 0.99) for Cd²⁺ and Pb²⁺ at two concentrations; thus, chemisorption may controladsorption process. Adsorption isotherm results were better represented by the Langmuir model (R²= 0.99). Consequently, monolayer adsorption may be the main mechanism in Cd²⁺ and Pb²⁺ adsorption. The efficiency of Pb²⁺ removal by SCBB was higher than that of Cd²⁺, where it was 60%, while for Cd²⁺ it was 50% at the same initial concentration. Cultivation experiment demonstrated that SCBB could significantly decrease Cd²⁺ and Pb²⁺ uptake by radish plants. The percentage of decrease in Cd²⁺ content in shoot was 49% and 54%, while it was 57% and 45% for Pb2+ at SCBB 2% in S(I) and S(II), respectively. A positive correlation between DTPA- extracted Cd2+ and Pb2+ in soil and their content in plant was obtained. An increase in CEC, OM of the agricultural environment, and dry biomass of shoot and root was observed. Therefore, resourceful utilization of SCBB is a beneficial method for removing lead and cadmium from aqueous solutions and stabilizing them in polluted soil.