Removal of sulphate from aqueous solution using modified rice straw: Preparation, characterization and adsorption performance

Rice straw as a lignocellulosic agricultural residue was chemically converted into a strong basic anion exchanger (RS-AE). Epoxy and amino groups were introduced into raw rice straw by reaction with epichlorohydrin and trimethylamine after it was treated in sodium hydroxide solution. The exchangers were characterized by element analysis, Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The results showed that total exchanger capacity of rice straw was increased by 1.32 mEq/g, and quaternary amino groups were formed on its new fibrous surface after modification. Batch adsorption experiments suggested RS-AE exhibits a much higher sulphate maximum adsorption capacity (74.76 mg/g) in contrast to that of raw straw (11.68 mg/g). The equilibrium data were described by Langmuir and Freundlich isotherm models, respectively, and were found to agree very well with the former. RS-AE also showed a good performance in regeneration cycles and a high selectivity for sulphate ions.