Removal of arsenic using Fe-modified biochar and Carbo-Iron® materials

Arsenic (As) mobilization in aquifers poses potential threats to global human health and ecosystems. The adsorption performance and stability of pristine biochar, Fe-modified biochars, and Carbo-Iron for As removal from water were evaluated to investigate feasibility for potential remediation applications. The Fe-modified biochars included ferrihydrite-containing biochar (FH+BC; 155 mg/g Fe) and magnetite-containing biochar (M+BC; 86 mg/g Fe). SEM and XRD indicated aggregated Fe phases in FH+BC and partially crystallized Fe with readily soluble Fe in M+BC. Adsorption over 24 hours (initial As 100 μg/L, dosage 5 g/L) showed that all Fe-containing materials achieved substantially higher As(V) removal than pristine biochar. The pH dependence was biochar-specific: FH+BC favoured As adsorption under acidic conditions, M+BC displayed largely pH-dependent adsorption, and Carbo-Iron demonstrated consistently high adsorption with limited sensitivity to equilibrium pH range of 3.5 – 7.4. Under circumneutral conditions, the three materials showed broadly comparable performance, while Carbo-Iron demonstrated a significantly higher adsorption than M+BC, consistent with Carbo-Iron > M+BC in adsorption isotherm modelling. Performance of adsorption extended over six months (initial As 100 μg/L, initial pH 5.0 – 8.0) showed marked differences in long-term As retention. Pristine biochar supported negligible As(V) removal, while FH+BC exhibited declining performance with aqueous As(III/V) exceeding 30 μg/L. In contrast, both M+BC and Carbo-Iron maintained aqueous As(V) and As(III) concentrations below 1.4 μg/L after 27 days, with Carbo-Iron achieving this level within 24 hours. These findings highlight the role of biochar- or activated carbon-supported Fe phases in remediating As and identify M+BC and Carbo-Iron as potentially effective materials for mitigating low As contaminated waters over timescales of up to six months.