Clay–magnetite co-aggregates for efficient magnetic removal of organic and inorganic pollutants

Abstract

This work reports the behavior of montmorillonite magnetite mixtures of varying composition in aqueous dispersions and evaluates their adsorbing properties using a cationic organicpollutant, methylene blue (MB+), and an anionic inorganic pollutant, arsenate (As(V)), as the adsorbing species. The effects of the presence of montmorillonite on the As(V) adsorption by magnetite andthe effects of magnetite on the MB+ adsorption by the clay were specially addressed. The simple mixture of a montmorillonite dispersion with a magnetite dispersion led to the spontaneous formation ofmontmorillonite?magnetite co-aggregates. These co-aggregates showed a unimodal electrophoreticmobility distribution, with no evidence of the presence of separate populations of montmorilloniteor magnetite. The application of a magnetic field confirmed the formation of co-aggregates andshowed that their separation rate increased as the magnetite content increased. Adsorption studiesas a function of the aggregate composition demonstrated that MB+ uptake was mainly controlledby the content of montmorillonite, while As(V) adsorption was mainly controlled by the content ofFe3O4. This permits an easy tuning of the adsorbing properties of cations and anions by controllingthe composition of the system.