Abstract
In this study, the performance of thermally activated and vibratory ball milled South African bentonite clay for the removal of chromium ions from aqueous solution was evaluated. A batch experimental approach was used to fulfil the goals of this study. The one-factor-at-a-time (OFAAT) approach was the key principle in optimizing operational parameters. The optimized parameters include contact time, adsorbent dosage, concentration, and pH. Characterization of feed and product materials were done using Brunnet–Emmett–Teller (BET), High-resolution scanning electron microscopy coupled with electron dispersion spectroscopy (HR-SEM-EDS), and X-ray diffraction (XRD). Optimum conditions were observed to be 60 min of mixing, 0.8 g of the adsorbent dosage (0.8 g: 500 mL – S:L ratio), 100 mg/L of chromium concentration, and acidic pH (pH ≤ 5). Greater than 99% removal efficacy was achieved from different water matrix except for AMD and fortified water. Furthermore, the adsorption capacity was observed to be 62.5 mg/g, which was observed to be superior to other families of bentonite clays. Adsorption kinetics followed the pseudo-second-order (PSO) than the pseudo-first-order (PFO) kinetics hence indication that adsorption process is a rate-limiting step. Adsorption isotherm followed the Langmuir adsorption isotherm model than the Freundlich adsorption isotherm. This was based on the regression analysis (R2), which gave 100% fit for pseudo-second-order (PSO) kinetics and the Langmuir adsorption isotherm. HR-SEM-EDS confirmed that the pre-treated bentonite clay is acting as a sink of chromium ions from aqueous solution and it can serve as the best candidate for depollution of chromium ions from wastewaters.
Published Version
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