High-efficiency removal capacities and quantitative sorption mechanisms of Pb by oxidized rape straw biochars

Chemical oxidation is an effective method to improve the ability of biochars for metals removal, but there are too few studies on screening of high-efficiency oxidants and quantitative analysis of sorption mechanisms. In this study, rape straw biochars (BC) were oxidized with HNO3, H2O2, and KMnO4, and noted as BC-HNO3, BC-H2O2, and BC-Mn, respectively. The Pb removal capacities and quantitative sorption mechanisms of biochars were explored through batch sorption experiments. Compared with that of BC (175 mmol kg-1), the maximum Pb sorption capacities of BC-HNO3 and BC-H2O2 increased to 526 and 917 mmol kg-1, in which contribution of surface complexation accounted for 55.1% and 39.0%, respectively. Due to the large surface area and abundant newly formed MnO2, BC-Mn showed the maximum Pb sorption capacity of 1343 mmol kg-1, and its high removal efficiency appeared even at low pH value (pH = 2) and high initial Pb concentration (1.0 mol L-1). The contribution of cation exchange accounted for 97.4% of the Pb sorption by BC-Mn. These results suggested BC-Mn had great potential for Pb removal from aqueous solution, and the quantitative analyses of sorption mechanisms revealed the contribution of each mechanism and provided a basis for evaluating application prospects of biochars.