Polyphosphazene-based hyper crosslinked polymer for efficient uranium ion removal from nuclear wastewater

Abstract

This study focuses on the removal of uranium ions from nuclear wastewater by fabricating an inorganic-organic hybrid cyclic and linear polyphosphazenes based polymer. Synthesized HCP-A and HCP-B had BET surface areas of 497.06 m2/g and 410.75 m2/g, respectively, while pore size distribution (PSD) was under 1 to 20 nm. Maximum removal efficiency of uranium by HCP-A and HCP-B for lab prepared sample was found 97.6 % and 95.2 % respectively at pH 6, contact period of 80 minutes, an adsorbent weight of 0.6 g, and temperature of 25 °C, while for lab prepared nuclear wastewater sample it was 83.9 % and 79.8 %, respectively. Lone pair-cation interactions, metal ligand complexation, hydrogen bonding, cation-pi interactions and electrostatic interactions are responsible for adsorption. The point of zero charge (PZC) of both HCPs is at pH 4.6. The optimal uranium uptake capacities of HCP-A and HCP-B were found to be 714.28 mg/g and 555.56 mg/g, respectively. Freundlich model is the best match for uranium adsorption by both HCPs, with R2 values of 0.9775 and 0.9931, respectively. The adsorption kinetics study exhibits that it fits a pseudo 2nd order kinetic model with R2 values of 0.9446 for HCP-A and 0.9882 for HCP-B. The uranium uptake process was found to be spontaneous and exothermic in nature. For HCP-A and HCP-B, Gibbs free energy (ΔG) was found -1.516 kJ ¬mol−1 and -0.27 kJ -mol−1, enthalpy change (ΔH) −41.59 kJ ¬mol−1 and −40.65 kJ ¬mol−1, and entropy change (ΔS) –0.134 kJ ¬mol−1 ¬K−1 and −0.136 kJ ¬mol−1 ¬K−1, respectively. The reusability of HCPs with minor decrease (2 % and 1 %) in their adsorption capability suggests that they can be used in industrial level applications.