Uranium and thorium adsorption from aqueous solution using a novel polyhydroxyethylmethacrylate-pumice composite

Poly(hydroxyethylmethacrylate-pumice), [P(HEMA-Pum)], composite was synthesized by free radical polymerization in aqueous solution. The adsorptive features of P(HEMA-Pum) composite were investigated for UO2(2+) and Th(4+) using a range of pH, concentration, time (kinetics), temperature (thermodynamics), ionic strength and selectivity, and the related parameters were derived from the obtained results. These results indicated that all adsorbents had high affinity to the uranium and thorium ions. The parameters obtained from Langmuir, Freundlich and Dubinin-Radsushkevich models fit the data well. The values of enthalpy and entropy changes showed that the overall adsorption process was endothermic (ΔH > 0) and increasing entropy (ΔS > 0), and it was spontaneous (ΔG < 0) as expected. The adsorption kinetics following the pseudo-second order model indicated that the rate-controlling step was chemical adsorption that occurred by ion exchange process. Reusability of P(HEMA-Pum) was also investigated, and it was found that the composite could be used at least 5 times.