Desorption studies for the recovery of radionuclides (Th and Zr) and optimization using Taguchi mixed design L18(2132) - A regeneration step for loaded biosorbent, general mathematical model for multistage operation

Thorium and zirconium are the most stable radionuclides used in various nuclear operations and the removal of them from aqueous industrial streams is essential. Biosorption is one of the most effective removal processes and it will be more attractive if loaded biomass can be regenerated for reuse. Reported studies on the desorption of metal ions from loaded biomass is limited in the literature. The present study aims to investigate the desorption of Th and Zr from loaded deoiled Karanja seed cake (DKSC) and study the efficiency of desorption process. All desorption experiments were carried out under batch mode using different eluents by varying liquid to solid (L/S) ratio, eluent type and concentration. Taguchi mixed level design L18(2132) was used to optimize the process and achieve the maximum desorption efficiency (D%). The eluent concentration was found to be the major factor that affects desorption. The optimum conditions for maximum D% inlcude 1 M HCl at L/S ratio of 7 with a recovery of 96% and 0.1 M NaHCO3 at L/S ratio of 3 with a recovery of 69% for thorium and zirconium, respectively. It was also shown that desorption kinetics follows pseudo-second order for both thorium and zirconium at optimal conditions. The regenerated DKSC was found to possess properties similar to those of native DKSC. A simple mathematical model was developed for computing the concentration of metal ions in the eluent in a counter-current multi-stage desorption system and validated using thorium desorption kinetic data.