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The Recovery of Rare Earth Elements (REEs) from Aqueous Solutions Using Natural Zeolite and Bentonite
- Mosai, Alseno K., Chimuka, Luke, Cukrowska, Ewa M., Kotzé, Izak A., Tutu, Hlanganani
- Water, air, and soil pollution 2019 v.230 no.8 pp. 188
- adsorbents, adsorption, ammonium sulfate, aqueous solutions, bentonite, cost effectiveness, desorption, industry, ions, models, pH, rare earth elements, surface area, wastewater, zeolites
- Increasing applications of rare earth elements (REEs) and improving technologies have led to increased demand. Because of their limited availability and depletion of most resources, the recovery of these elements from waste has become important. The use of cost-effective materials for this purpose and the high value that can potentially be recovered would be beneficial and attractive to many industries using REEs. In this study, natural zeolite and bentonite were used in batch studies to recover REEs (La, Y, Lu, Sm, Pr, Tm, Ce, Nd, Yb, Gd, Eu, Er, Ho, Dy, and Sc) from aqueous solutions. The effect of adsorbent dosage, pH, concentration, contact time, and competing ions on recovery was investigated. Desorption studies were conducted using ammonium sulphate. Adsorption onto zeolite was found to increase with pH, whereas uniform adsorption was observed for bentonite, except at pH 2 (16% less efficiency). The pH values of 6.2 and 3.2 were selected as the optimum for zeolite and bentonite, respectively. For zeolite, the average adsorption efficiencies for REEs at 0.5, 1.0, 2.0, 5.0, and 10 mg L⁻¹ were found to be 91, 96, 89, 40, and 20% respectively but, > 98% adsorption efficiencies were achieved with bentonite at all concentrations. The zeolite and bentonite adsorption data were better described by Langmuir though, for bentonite, the coefficients of determination (R² values) for the Freundlich and Dubinin-Radushkevich isotherm models were also significant. There was no significant difference (p > 0.05) on the adsorption of the elements in the presence of competing ions. Bentonite proved to perform better, most likely as a result of its higher surface area. Generally, the good adsorption performance of both adsorbents in their natural forms makes them an attractive and potential cheap option for the recovery of REEs from wastewaters.