Quantitative contribution of minerals and organics in biochar to Pb(Ⅱ) adsorption: Considering the increase of oxygen-containing functional groups

An accurate method for understanding the contribution of minerals and organics in biochar to lead adsorption was proposed, while considering the effect of increased oxygen-containing functional groups (OFG). Biochar derived from cotton stalk was prepared by slow pyrolysis at 350 °C and 550 °C, and then the water-soluble matter (WM), acid-soluble matter (AM) and organic matter (OM) of biochar were separated by washing and pickling. Physicochemical properties and Pb2+ adsorption performance of pristine biochar (BC), water-washed biochar (WB) and acid-washed biochar (AB) have been investigated in detail. The order of the content of separated components in biochar was: OM>AM>WM, and the sequence of Pb2+ sorption capacity of biochar was: BC>WB>AB. The OFG content of all biochar before and after adsorption were quantified by Boehm titration, and the veracious sorption capacity of each fraction of biochar were acquired. The contribution of each component of biochar to Pb2+ sorption was ranked as: AM (69.49–72.69%)>OM (23.93–27.51%)>WM (3.00–3.39%). Furthermore, SEM-EDS, FTIR, XRD and other advanced technologies were used to characterize and analyze all biochar before and after adsorption, indicating that in the adsorption mechanism, minerals were related to ion exchange and precipitation, while organics were relevant to complexation and Pb2+-π interaction.