The role of hydrophobic properties in ion exchange removal of organic compounds from water

Abstract

The removal of organic compounds by ion exchange resins is a complex process due to the involvement of several interacting phenomena during the course of removal. The objective of this research is to clarify the contribution of these interactions to the removal of different organic compounds under various solution conditions. This study investigates the sorption of three ionizable organic compounds, which are identical in terms of ionic charges and different in their non‐polar moieties, in order to better evaluate the contribution of solute‐solvent interactions to the affinity of these compounds for ion exchange. The higher uptake of hydrophobic compounds and lower competition effect from inorganic anions on the removal of these compounds provide evidence for the importance of the hydrophobic effect. The hydrophobic characteristics of organic compounds and the favourable entropy change that they impose during de‐solvation contribute greatly to the ion exchange selectivity of these compounds. Furthermore, increasing the ionic strength of solution by adding high charge density anions, such as sulphate, to the water diminishes the contribution of electrostatic interaction, and hence the potential physical adsorption between resin and organic molecule predominates the removal mechanism. No change in removal mechanism is observed in the presence of inorganic anions with low charge density such as nitrate.