Nucleotide-grafted coal for high-efficiency removal of uranium: performance, optimisation, and insight into the adsorption mechanism.

Abstract

Removal of radioactive waste from aqueous medium using cost-effective material is an utmost priority to manage the radioactive waste toxicity. Here we present a novel approach for uranium removal from aqueous system by chemically modifying low-grade coal (low-carbon and high silicate content) with adenosine 5'-monophosphate (AMP) nucleotide and adsorbent referred here as coal@AMP. Functionalisation of coal was carried out by incorporating amide and phosphate functional groups via oxidation and reduction phenomenon. Chemical make-up and structural morphology of coal@AMP was explored using FT-IR and SEM-EDX analysis. Under the optimised pH 6 and adsorbent dose (10 mg per 100 mL), the coal@AMP exhibited 92.2% removal of uranium from aqueous medium in 300 s, following pseudo-second-order kinetics and Langmuir adsorption isotherm. It corresponded to a maximum adsorption capacity (q_max) of 624.6 mg/g. The fast and efficient adsorption of uranium by coal@AMP is favoured by the strong interaction or chelation of uranium species with the amide and phosphate groups. Coal@AMP exhibited excellent selectivity towards adsorption of uranium against interfering ions, e.g. Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Hg²⁺, Pb²⁺, Mn²⁺, Zn²⁺, and Ni²⁺. The thermodynamic studies favour spontaneous and endothermic nature of adsorption.