Kinetics of ⁹⁹Мо sorption onto a sorbent based on hydrated titanium dioxide

Abstract

The kinetics of ⁹⁹Мо sorption onto T-5 sorbent in the batch mode at different values of the stirring rate, temperature, and sorbent granule size was studied. All the experimental kinetic curves are described by a sum of two exponents. In the first time interval of phase contact, from 0 to 5–10 min, the sorption is controlled by external diffusion, and in the interval from 10 to 40 min the step of transformation of unsorbable Mo species into sorbable hydroxo species also becomes a rate-determining step (external kinetic control). In the final stage (time interval from 40 min to 2–3 h), the sorption occurs at the lowest rate, and the Mo diffusion in micropores and overcoming of electrostatic hindrance on the surface of titanium hydroxide pores become the most probable limiting steps. In sulfate solutions, the Mo sorption rate considerably decreases already in the first stage, and the external kinetic control becomes prevalent because of hindered redistribution of unsorbable sulfate complexes into sorbable hydroxo complexes. The controlling factor in the sulfate and nitrate solutions in the second stage is presumably the same.