Co-effects from inorganic and organic fractions in dissolved components of biochar on its adsorption behavior: Taking uranium adsorption as an example

Abstract

Biochar could release water-soluble fraction (WSF), including intrinsic dissolved organic matter (BDOM) and soluble minerals simultaneously. However, the co-effects from the inorganic and organic fractions in the WSF of biochar are always overlooked during its environmental application. Herein, this study specified the direct roles of BDOM and soluble minerals in the WSF from biochar on uranium (U(VI)) adsorption, and the indirect roles of WSF on the evolution of interfacial behavior of biochar toward U(VI) after the release of WSF. The results show that BDOM and soluble minerals (e.g., phosphate) in WSF contribute directly to U(VI) precipitation, which accounted for 8.94 % - 34.12 % of the U(VI) removals by the bulk biochars. Specifically, U(VI) precipitation by the WSF from the low temperature biochar prepared at 300 °C (B300) is presumably dominated by BDOM, while the U(VI) precipitation by the WSF from the high temperature biochar prepared at 600 °C (B600 and OB600) is presumably governed by leached phosphate. Furthermore, the dissolution of WSF indirectly changes the adsorption behavior toward U(VI) through the change of surface functionality and exposure of insoluble U(VI)-binding minerals. Finally, this study provides new insights into co-effects of inorganic and organic fractions in biochar WSF on its adsorption behavior, suggesting that the WSF (including BDOM and soluble minerals) in biochar deserves more attention when the biochar is designed for environmental applications.