Sulphate Removal from Aqueous Solution Using Modified Bentonite

Sulphate ion is a naturally occurring substance present in various mineral salts that are found in soil and various water supplies. Sulphate ions are generally considered to be non-toxic and therefore not strictly regulated, however, the consumption of drinking water containing high amounts of magnesium or sodium sulphates may result in intestinal discomfort, diarrhoea and consequently dehydration. Although there are numerous traditional adsorbents for sulphate ions removal, it is imperative to develop a cheap, easily accessible, and ecological-friendly adsorbents for the treatment of sulphates in water. This research investigated sulphate ions removal by the synthesized modified bentonite (MB) and acid-digested bentonite (ADB) as an alternative for traditional adsorbents. The modified bentonite was prepared through microwave acid digestion of raw bentonite (RB) and was subsequently coated with cationic polyelectrolytes polydiallyl dimethyl ammonium chloride (poly-DADMAC). The RB, ADB and MB were characterized using scanning electron microscopy/energy dispersive X-ray (SEM/EDX), X-ray diffraction spectroscopy (XRD) and Fourier transform infrared ray (FTIR) spectrometer. The effects of solution pH, contact time, agitation speed, the dosage of the adsorbents and initial concentration of sulphate ions on the removal from synthesized wastewater were investigated in batch adsorption studies. The characterization results showed successful impregnation of poly-DADMAC and changes in the chemical composition of the synthesized adsorbents. Results of the study showed that as high as 65% of 10 ppm sulphates were removed using 20 g/L MB dosage at pH 6, agitation speed 50 rpm within 30 min of treatment time. However, only 16% of sulphates were removed with ADB under the same conditions. The results also showed that the sulphates removal by modified bentonite followed pseudo-first-order kinetics. It can be concluded that the Poly-DADMAC-modified bentonite has a very good removal capacity for sulphate ions in aqueous solution.