Exploring different modification methods of biochar for Se(IV) removal from water: Synergistic effect of adsorption...

Selenium (Se) is a vital micronutrient for humans health; however, elevated concentrations can result in numerous health problems and negatively impact ecosystems. This study examines the influence of two distinct modification approaches (pre- and post-treatment) on the physicochemical properties of biochar and its efficacy in removing selenite (Se(IV)) from water. A comprehensive characterization of unmodified biochar (BC), pre-treated biochar (Fe/Mn-impregnated biochar, F-Fe/Mn-BC), and post-treated biochar (Fe/Mn-oxide-loaded biochar, A-Fe/Mn-BC) was carried out using a suite of advanced analytical techniques. To determine the optimal parameters, a systematic key parameters affecting adsorption performance was conducted by varying the initial pH, contact time, initial Se(IV) concentration, and the presence of coexisting ions. The findings indicate that A-Fe/Mn-BC has a higher adsorption capacity for Se(IV). A-Fe/Mn-BC achieved a maximum adsorption capacity of 248.8 mg∙g^-1, which is roughly threefold higher than that of both BC and F-Fe/Mn-BC. The removal mechanism involves surface adsorption accompanied by the reduction of Se(IV) to elemental selenium (Se(0)), with Fe(II) and Mn(II) species on the biochar surface acting as electron donors. Furthermore, the presence of common coexisting ions in solution had negligible effects on Se(IV) removal efficiency. These findings indicate that post-treatment modification enhances biochar performance more effectively than pre-treatment, and suggest that A-Fe/Mn-BC nanomaterial demonstrated remarkable potential for use in the treatment of Se(IV) contamination.