Multicomponent anion exchange with a resin having weakly and strongly basic groups

Multicomponent anion exchange with a resin having both weakly and strongly basic groups was investigated by means of modelling and column experiments. Our objective was to develop a model able to predict the evolution of the composition of a water treated by such a resin. The studied resin was Purolite S108, used for boron removal from water, on which ternary and quaternary amines were attached (additionally to boron complexing groups). Column dynamics were modelled with the computer code IMPACT, devoted to reactive transport in porous media. A reaction scheme was proposed to represent anion exchange on the two types of groups, with a quaternary anionic system including hydroxide, chloride, sulphate and nitrate at a given ionic concentration. This reaction scheme needed eight parameters: concentrations of weak and strong-base groups and the anion exchange selectivities. These parameters were measured through binary anion exchange, without or with pH step. The breakthrough curves of the binary experiments were in very good agreement with the experimental one. The model was then used to predict the results of a more complex experiment in which the column had been fed by a mixture of acids. The main features of the experimental behaviour were fairly well predicted, even if the agreement was not perfect. These discrepancies were attributed to the model assumptions, mainly to the expressions of anion exchange selectivities. These results enabled us to predict almost quantitatively the evolution of the water composition during its treatment. This point is an improvement in the prediction of the dynamics of an anion exchange with two types of groups. In the future, the model would have to be extended to take into account different expressions of the exchange selectivities, and nonequilibrium conditions. (c) 2005 Elsevier Ltd. All rights reserved.