Adsorption Performance of Chitosan and Glutaraldehyde Modified Biochars for Trivalent Antimony in Acidic Wastewater

Acidic wastewater from mining activities contains a large amount of Sb(III). Biochar can provide with an economical and efficacious method for removing of Sb(III). However, highly efficient removal was still challenging under acidic environment. In this study, bamboo charcoal biochar and rice straw biochar were modified with glutaraldehyde and chitosan to examine their Sb(III) adsorption performances in terms of adsorption isotherms, adsorption kinetics and thermodynamics under different treatment conditions, i.e. biochar dosages, pH values, adsorption durations, coexisting substances and temperatures. Characterizations including Brunauer–Emmett–Teller surface area analysis, Fourier transform infrared spectrometry, scanning electron microscope coupled with energy dispersive X-ray spectrometry as well as X-ray photoelectron spectroscopy were employed to further reveal the mechanisms. Results showed that the modified bamboo biochar and modified rice straw biochar showed excellent Sb(III) adsorption efficiency of 94.29% and 93.36%, respectively, under strongly acidic environment. The maximum Sb(III) adsorption capacities of the modified bamboo biochar and modified rice straw biochar reached to 81.16 mg/g and 72.92 mg/g, respectively. Langmuir adsorption isotherm model and quasi-secondary kinetic model best described the adsorption processes. Thermodynamic studies showed that the adsorption of Sb(III) by modified biochar was a spontaneous, exothermic and irreversible process. It was proposed that electrostatic attraction, complexation with functional groups (e.g., C = O, -NH₂, -OH), as well as oxidation of Sb(III) were involved in the adsorption processes. The modified biochar has greater removal capacity for Sb(III) than pristine one, suggesting its potential applications for the wastewater treatment.