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The kinetics of the 99Mo sorption onto T-5 sorbent at different pH values of the nitric acid solution was studied. The previously suggested limiting steps of the 99Mo sorption onto T-5 sorbent were confirmed. The effective rate constant of the molybdenum sorption onto titanium hydroxide (fast step) as a function of pH passes through a maximum at pH from 4.5 to 5.5, which does not correspond to the maximum of the pH dependence of the distribution coefficient but correlates with the maximal content of one of the sorbable species, HMoO4-, in the solution. Thus, the rate of Mo sorption onto titanium hydroxide as a function of pH passes through a maximum at a minimal negative charge of the sorbate near pH of the isoelectric point of the sorbent. The kinetic studies confirm the scheme of the sorption of molybdenum hydroxo complexes onto titanium hydroxide, suggested previously on the basis of the logkd-pH and log e-log[m] sorption isotherms. According to this scheme, simultaneous redistribution and sorption of sorbable molybdenum species, MoO2OH+, H2MoO4, and HMoO4-, are possible. [ABSTRACT FROM AUTHOR]

The kinetics of Мо 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. [ABSTRACT FROM AUTHOR]