Clay minerals for the removal of pharmaceuticals: Initial investigations of their adsorption properties in real wastewater effluents

Abstract

The adsorption of pharmaceutical products (PPs) onto kaolinite and raw and sodium-exchanged montmorillonite was investigated in real wastewater effluents (WWE). The important role of the charge state of the PPs in controlling the adsorption extent was highlighted. Whereas cationic PPs were mostly adsorbed through cation exchange, the adsorption of neutral and anionic PPs appeared to be controlled by the nature of compensating inorganic cations and/or the simultaneous adsorption of organic moieties onto clay minerals. In raw WWE, the concentration of PPs is indeed far lower than the concentration of other organic molecules. Among the adsorbents tested, kaolinite displayed the lowest adsorption capacity of both PPs and other organic molecules, compared to raw montmorillonite which presented the highest adsorption capacity. The sodium-exchanged montmorillonite displayed intermediate adsorption properties, highlighting the key role of divalent inorganic cations in the adsorption of non-cationic PPs and other organic molecules. Hence, raw montmorillonite appears to be the most promising adsorbent for further investigations aiming to test the practicability of a clay-based adsorbent for the removal of organic contaminants, such as PPs, in WWE.