Oxalic Acid Modification Improves the Removal Effect of Cr(VI) by Biochar through Three Important Means: Adsorption, Reduction and MineralizationFangfang Min, Haoming Chen and Dehua MaE3S Web Conf., 350 (2022) 03003DOI: https://doi.org/10.1051/e3sconf/202235003003