Copper and zinc removal from aqueous solution by mixed mineral systems I. Reactivity and removal kinetics

This study investigates the reactivity and removal kinetics of Cu and Zn onto mixed mineral systems from aqueous solution related to acid mine drainage impacted areas. The sorbents used were kaolinite, Al-montmorillonite, goethite, and their mixtures. The effects of surface charge, proton coefficient, and sorption kinetics were studied at room temperature (23+/-2 degrees C). Using an empirical model, mineral mixing reduced the exchange of protons for sorbing ions and the acidity of the reactive sites, thus impeding Cu and Zn removal by proton exchange. Based on the amount of Cu and Zn sorbed on the mixed mineral suspensions at ionic strength 0.01 to 0.1 M and pH 4, it is suggested that Cu and Zn removal from aqueous solution was by both inner and outer sphere complexation. Mineral mixing reduced the transfer rate of Cu relative to the single mineral suspensions in both slow and fast reaction phases. The behavior of the mixed suspensions in Cu and Zn sorption suggest that different reactive sites were involved at the onset of sorption, becoming similar to those of the single mineral components over time.