Adsorption analysis of Cr(VI) by ZnCl₂-bentonite-comodified cyanobacterial bloom-derived biochar

Biochar has been utilized to treat industrial wastewater containing high Cr concentrations. The collection of large amounts of nauseous algae sludge from lakes where cyanobacterial blooms frequently occur and the conversion of this sludge into biochar is a valuable strategy for optimizing resource utilization. In this study, the copyrolysis of bentonite and ZnCl₂ with waste cyanobacterial bloom biomass produced biochar (ZBMC) with a high cation exchange capacity (CEC) and specific surface area (SSA), enabling the effective remediation of high Cr concentrations in industrial wastewater. The morphological properties of ZBMC were characterized via several methods (XRD, FTIR, XPS, etc.). The cation exchange capacity of ZBMC was 57.82 cmol/kg, and the specific surface area was 396.20 m²/g. Single-factor experiments (pH, dosage and initial concentration) based on the Box-Behnken design method demonstrated that the pH significantly influenced the adsorption process of ZBMC. This adsorption process was well fitted by the pseudo-second-order kinetic model and Langmuir model, and the maximum adsorption capacity for Cr(VI) was 93.86 mg/g. Quantitative experiments to elucidate the adsorption mechanism indicated that Cr-π coordination and mineral precipitation accounted for more than 83 %.