REACTION-KINETICS OF POLYSTYRENE-BASED PHOSPHINIC ACID ION-EXCHANGE REDOX RESINS WITH METAL-IONS

The ion exchange/redox kinetics displayed by the phosphinic acid polymer with aqueous solutions of silver and mercury is presented as a function of reaction temperature (6-degrees to 45-degrees-C) and solution pH (0 to 5). The network variables studied include the crosslink level and macroporosity. At each pH, increasing the temperature leads to a more rapid approach to equilibrium. The amount complexed at equilibrium is lowest at pH 0 relative to the higher pH solutions due to increased H+ competition for ligating sites. Metal ion reduction, rather than ion exchange, is the dominant component at equilibrium. Matrix rigidity and macroporosity do not affect Ag(I) kinetics. The rate of Hg(II) sorption is much faster than for Ag(I). Macroporosity is an important variable with mercury: macroporous resins complex more than -twice the amount found with gels at 15 minutes contact. It is proposed that Ag kinetics are limited by a slow redox reaction while the Hg kinetics are diffusion-limited due to a fast redox reaction. Differences in reactivity arise from the reaction stoichiometry.