Mechanism of enhanced Sb(V) removal from aqueous solution using chemically modified aerobic granules

•Ionic strength significantly inhibits Sb(V) removal efficiency.•Fe-modified granules almost have almost no affinity for cations.•The maximum adsorption quantity is calculated to be 125mg/g.•Adsorption of antimony was spontaneous and endothermic.•Outer and inner-sphere complexes could be formed stepwise during adsorption. Sb(V) removal using Fe-modified aerobic granules was investigated. Increasing the biomass dosage improved the Sb(V) removal rate, but lowered the adsorption quantity; the optimal biomass concentration was 20g/L (wet basis). Adsorption equilibrium was obtained at 2h at 175rpm; the adsorption quantity was 36.6mg/g. NaCl and other salts inhibited Sb(V) adsorption on Fe-modified granules, and the mechanism possibly lied more with the anions. The adsorption isotherms were evaluated using the Langmuir, Freundlich, and Temkin models. The Langmuir model best described the adsorption process, and gave a maximum monolayer adsorption quantity of 125mg/g. The ΔH value for adsorption was 16.1kJ/mol, indicating endothermicity, and the negative ΔG values at various temperatures suggested spontaneous adsorption. Outer-sphere and inner-sphere complexations were involved in Sb(V) adsorption.