Influence of pH of Nitric Acid Solution on the Kinetics of the ⁹⁹Мо Sorption onto Titanium Hydroxide

Abstract

The kinetics of the ⁹⁹Мо sorption onto T-5 sorbent at different pH values of the nitric acid solution was studied. The previously suggested limiting steps of the ⁹⁹Мо sorption onto Т-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, НМоО₄^–, 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 logk_d–рН and log ε–log[m] sorption isotherms. According to this scheme, simultaneous redistribution and sorption of sorbable molybdenum species, МоО₂ОН⁺, Н₂МоО₄, and НМоО₄^–, are possible.