Sorption study of long-lived ⁹⁴Nb on laterite: Effects of physicochemical parameters on sorption

Zr-Nb alloy is used as the pressure tube in pressurized heavy water reactors (PHWR). Prolonged neutron irradiation of the pressure tubes leads to the formation of a long-lived radioisotope ⁹⁴Nb. Thus, the discharged pressure tubes possess huge ⁹⁴Nb activity which persists for a prolonged period.If these discharged pressure tubes come in contact with ground water, ⁹⁴Nb isotope may leach and migrate and this can lead to a long-term radiological impact in the environment.In the present study, we have explored the capability of laterite as a filler material for the containment and retarding the migration of ⁹⁴Nb. In this regard, detailed characterization of the laterite soil was carried out using energy dispersive X-ray fluorescence (EDXRF), X-ray diffraction (XRD), fourier transform infra-red spectrometry (FTIR), total cation exchange capacity determination, zeta potential measurement and thermogravimetric analysis (TGA). The sorption study of ⁹⁴Nb on laterite was carried and the effects of different physico-chemical parameters like pH, ionic strength, temperature and equilibration time were evaluated. Ionic strength, temperature and time dependent sorption studies assist to explore the probable sorption mechanism of ⁹⁴Nb on laterite, which helps in understanding the migration behaviour of ⁹⁴Nb in natural aquatic environment. This study suggests that laterite is a promising material in containment of ⁹⁴Nb isotope owing to its good cation exchange behaviour in the acidic medium and ability to form surface complex in the neutral medium.