Effectiveness of different biochar in aqueous zinc removal: Correlation with physicochemical characteristics

Bochar from typical Vietnamese biomass residues (acacia wood chip, rice husk, bamboo) were assessed for application in remediation of metal-contaminated water. The biochar physical (e.g., surface area, morphology) and chemical (e.g. surface functional groups, proximate and elemental analysis) characteristics were correlated with their effectiveness in removing zinc (Zn2+). The impact of biochar dose, contact time, and initial adsorbate concentration were investigated to determine the adsorption capacity of the biochar for Zn2+. All three effectively remove Zn2+ from aqueous solution, with bamboo biochar especially efficient (removal of 96–98% Zn2+ from 40 to 80 mg/L). Maximum adsorptions were 7.62, 4.02, and 3.82 mg Zn2+/L for bamboo, wood, and rice husk biochar, respectively. The Freundlich model fit the adsorption of Zn2+, and a pseudo-second order model described the adsorption kinetics. Adsorption was governed by chelation with biochar organic groups (-COOH, -OH−) and precipitation onto inorganic groups (CO32−, PO42−), not ion exchange.