Competitive removal of Cd(ii) and Pb(ii) by biochars produced from water hyacinths: performance and mechanism

Abstract

Three biochars converted from water hyacinth biomass at 300, 450, and 600 °C were used to investigate the adsorption properties of Cd²⁺ and Pb²⁺. In addition, the competitive adsorption mechanisms between Cd²⁺ and Pb²⁺ were also conducted. Adsorption kinetics and isotherms indicated that the maximum adsorption capacity of Pb²⁺ was larger than that of Cd²⁺, and the adsorption process in the mixed solutions of two heavy metals (Cd²⁺ and Pb²⁺) was more favorable for Pb²⁺. Further investigation about the characterization of biochars demonstrated that cation exchange, surface complexation, cation–π interaction and precipitation were the main mechanisms responsible for the heavy metal removal. In this study, competitive adsorption may also be explained by these mechanisms. These results are useful for the application of biochars in selective adsorption and in practical wastewater treatment.