Enhanced U(VI) Removal from Groundwater Using Amide-Functionalized Biopolymer-Based Adsorbent for a Practical Solution
Sampan Seth, Md Rabiul Islam, Tanmayaa Nayak, Amoghavarsha Ramachandra Kini, Sujan Manna, Bijesh K. Malla, Ankit Nagar, Thalappil Pradeep
Abstract
Uranium (U(VI)) contamination poses a serious threat to groundwater, which is the primary source of drinking water in many regions across the world. Removal of the predominant UO 2 2+ species present in environmental water samples at affordable cost in resource-limited settings is challenging, particularly in the presence of competing ions. In this work, we introduced a sustainable approach for developing a biopolymer-based carboxymethyl cellulose (CMC)-chitosan (CH) adsorbent, free of metals, for selective removal of U(VI) from water. Amide functionalities, which serve as active sites for U(VI) capture, have been introduced by cross-linking CMC and CH with 4-aminobenzoic acid via 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide (EDC) coupling. The adsorbent demonstrated excellent U(VI) removal efficiency in the presence of counterions such as transition metals, alkaline earth metals, and pentavalent vanadium (V(V)), which interfere strongly with many adsorbents. The composite showed 99.5% removal efficiency when tested on a field water sample containing 102 μg/L of U(VI). Mechanistic insights into U(VI) adsorption on the composite were obtained through infrared spectroscopy and X-ray photoelectron spectroscopy, which revealed that nitrogen in the amide functionalities facilitates interaction with U(VI). Raman measurements were performed to understand the speciation of U(VI) in solution at pH 7, which confirmed no change in the charge state of uranium in solution upon interaction with the composite. The adsorbed U(VI) can be easily removed by 10 mM HCl (10 mL) within 90 min of reaction, and the adsorbent can be reused. The adsorbent maintained a removal efficiency of more than 92% over three reactivation cycles. Cost of the composite was estimated to be around $10 for treating 1 KL of contaminated water at a U(VI) concentration of 1000 μg/L. However, as N -hydroxysuccinimide and EDC reagents, used for the synthesis, are contributing more than >90% of the overall cost, further optimization or substitution of these reagents by industrial chemicals will ensure economic viability of the process.