Sequestering of thorium ions from aqueous media on rice husk: Equilibrium, kinetic and thermodynamic studies

Abstract

Abstract The adsorption behaviour of thorium on rice husk has been studied by optimizing different parameters like nature of electrolyte, amount of adsorbent, equilibration time, metal concentration, and temperature, employing batch method and radiotracer technique. Maximum adsorption was observed at 0.0001 mol L –1 HNO3, using 0.1 g of adsorbent for 4 cm3 of 5.19 · 10 –5 mol L –1 of Th+4 solution in fifteen minutes equilibration time. The adsorption phenomenon was verified by FTIR, SEM and EDX techniques. The adsorption data was well fitted to Freundlich, Langmuir and Dubinin-Radushkevich isotherm equations. The characteristic Freundlich constants i.e. 1/n = 0.528 ± 0.019 and K = 4.88 × 10−4 ± 1.29 · 10 –5 mol g –1 whereas the Langmuir constants Q m = (4.159 ± 0.234) × 10 –6 mol g –1 and K L = (3.627 ± 0.328) × 104 dm3 mol –1 have been computed for the sorption system. The sorption free energy was found to be 11.24 ± 0.211 kJ mol –1 showing chemisorption nature of interaction between thorium and rice husk. The results showed that thorium adsorption on rice husk follows pseudo 2nd order with rate constant = 1.448 g mg –1 min –1. The determined negative values of ΔG indicated spontaneity of the process, whereas the positive values of ΔH and ΔS confirmed endothermic nature and increased randomness during the adsorption process respectively. The removal of Th+4 ions from spiked tap water was checked by employing the optimized experimental parameters which indicated that rice husk is a good adsorbent for thorium ions and may be used for waste management of radionuclides.