Mercury Removal from Aqueous Solution by Mixed Mineral Systems I. Reactivity and Removal Kinetics

This study investigates the reactivity and removal kinetics of arsenite on mixed mineral systems from aqueous solution related to contaminated waters. The sorbents used were kaolinite, montmorillonite, goethite, and their mixtures. The effects of, proton coefficient, and sorption kinetics were studied at room temperature (23 ± 2 ◦C). Reactivity studies demonstrate enhancement of proton coefficient and the acidity of reactive sites by mixed mineral systems except for kaolinite-montmorillonite, thus increasing mercury removal by proton exchange. Kinetic studies demonstrate two- phase reactions attributed to outer sphere complexation and inner sphere complexation. In the first-phase reaction, mineral mixing based on our empirical model decrease the mass transfer rates for kaolinite-montmorillonite and montmorillonite-goethite, not affecting kaolinite-goethite. For the second-phase reaction, mineral mixing did not change the mass transfer rates for the mixed mineral systems except for montmorillonite-goethite. The behaviors of the mixed mineral systems in mercury sorption suggest that different reactive sites were involved at the onset of sorption, with reactions and sorption ending with inner-sphere complexation. Differences between actual and theoretical % sorption progressed from negative to positive for all mixed minerals as contact time was increased. This means that increase in contact time during Hg-sorbent interaction could help increase mercury removal based on mineral mixing.