Utilization of bentonite as a low-cost adsorbent for removal of ⁹⁵Zr(IV), ¹⁸¹Hf(IV) and ⁹⁵Nb(V) radionuclides from aqueous solutions

Adsorption behaviour of ⁹⁵Zr(IV), ¹⁸¹Hf(IV) and ⁹⁵Nb(V) radionuclides onto bentonite is investigated in this study. Optimization of parameters is governed by conducting the adsorption experiments at different pHs, contact time, adsorbent mass and temperature. Distribution coefficient values of 21,388, 19,869 and 12,866 mL/g for ⁹⁵Zr(IV), ¹⁸¹Hf(IV) and ⁹⁵Nb(V) radionuclides, respectively, are achieved at pH 2.5. Contact time of 120 min was sufficient to reach equilibrium and the Lagergren kinetic model was appropriate to describe the kinetic data of zirconium. Of the studied adsorption isotherms, Redlich-Peterson was the best model to fit the adsorption equilibrium data of zirconium onto bentonite. The maximum adsorption capacity of bentonite toward zirconium is found to be 63.35 mg/g. The obtained values of enthalpy change and free energy change showed that adsorption of radionuclides onto bentonite was endothermic and spontaneous processes. Bentonite succeeded to efficiently remove the studied radionuclides even in presence of high concentrations of foreign ions. Bentonite succeeded to adsorb ⁹⁵Zr(IV), ¹⁸¹Hf(IV) and ⁹⁵Nb(V) radionuclides from radioactive process wastewater with distribution coefficient values of 10,422, 15,453 and 9774 mL/g, respectively. (author)