Comparison of biochar- and activated carbon-supported zerovalent iron for the removal of Se(IV) and Se(VI): influence of pH, ionic strength, and natural organic matter

Biochar (BC) and activated carbon (AC) were both produced from corn straw. Biochar-supported zerovalent iron (BC-ZVI) and activated carbon-supported zerovalent iron (AC-ZVI) were synthesized and applied for Se(IV)/Se(VI) removal. The sorption capacity of BC-ZVI for Se(IV) and Se(VI) was reported at 62.52 and 35.39 mg g −1 , higher than that of AC-ZVI (56.02 and 33.24 mg g −1 ), respectively, due to its higher iron content and more positive charges. The spectroscopic analyses showed that Se(IV)/Se(VI) were reduced to Se(0)/Se(-II) of less toxicity and solubility. The effects of various factors such as pH, ionic strength, co-existing cations and anions, and natural organic matter (NOM) were also investigated. Ionic strength showed no significant effect on Se(IV)/Se(VI) removal, but pH was critical. The presence of NO 3 − and SO 4 2− did not cause obvious inhibition to the removal, while PO 4 3− inhibited the sorption capacity of BC-ZVI and AC-ZVI for Se(IV)/Se(VI) significantly. Common cations (K + , Ca 2+ , and Mg 2+ ) were found to slightly enhance the removal, while NOM significantly decreased the sorption capacity of BC-ZVI and AC-ZVI for Se(IV)/Se(VI). Besides, NOM showed stronger inhibition effect on AC-ZVI than that on BC-ZVI. These results indicated that BC-ZVI, compared with AC-ZVI, could be a promising sorbent to remove Se(IV)/Se(VI) due to its low cost and high efficiency.