Retention of oxyanions on biochar surface

Biochar integrated reactive filtration of wastewater for P removal and recovery, micropollutant catalytic oxidation, and negative CO2e: Process operation and mechanism

“…The increase in P loading of the biochars can be determined by their physical and chemical properties. Biochar removes phosphate from a solution by adsorption or precipitation processes, which are influenced by properties such as specific surface area, cation composition, and amount and types of surface functional groups (Bakshi et al, 2022; Leng et al, 2021; Li et al, 2019). At pH levels from 4 to 9, phosphate is a negatively charged oxyanion and attaches to positively charged surfaces by electrostatic attraction and covalent bonds, by formation of cation bridges, or by formation of either bidentate or monodentate coordinated inner‐sphere bonds (Arai & Sparks, 2001; Gypser et al, 2018; Parfitt et al, 1975).…”

“…At pH levels from 4 to 9, phosphate is a negatively charged oxyanion and attaches to positively charged surfaces by electrostatic attraction and covalent bonds, by formation of cation bridges, or by formation of either bidentate or monodentate coordinated inner‐sphere bonds (Arai & Sparks, 2001; Gypser et al, 2018; Parfitt et al, 1975). Because biochar's surface charge is dominated by functional groups that are negatively charged weak acids (Bakshi et al, 2022; Wang, Bakshi, et al, 2020; Yang et al, 2021), it repels the negatively charged phosphate anions. Thus, most of the phosphate anion adsorption likely occurs through cationic bridging (Deng et al, 2021).…”