CHARACTERIZATION OF SORPTION AND QUANTITATIVE ANALYSIS OF HYDROXYL COMPLEXES OF CU AND ZN IN AQUEOUS SOLUTION: THE INTERACTIVE EFFECTS OF MINE WASTEWATER-MIXED MINERAL SYSTEMS

This study investigates sorption of Cu and Zn onto binary mixed mineral systems from natural mine wastewater obtained from disused mine workings at Parys Mountain and Cwmrheidol in Wales, United Kingdom. These contaminants flow into water courses such as River Lledr in North Wales and River Rheidol in Mid Wales where commercial and local fishing activities exist. In an attempt to reduce the levels of Cu-Zn intake by fish in the watercourses, mixed mineral systems of kaolinite/montmorillonite, kaolinite/goethite and montmorillonite/goethite are characterized for sorption at variable pH. In addition, levels of saturation of hydroxyl complexes were analyzed using quantitative techniques. Batch reactions conducted at constant ionic strength and constant solute concentration reveal significant behavioral differences in Cu and Zn sorption by mixed mineral systems. With the Cwmrheidol mine wastewater more Zn is removed than Cu by the mineral systems. This may be attributed to the inability of Cu to compete effectively with Zn for sorption sites. With Parys Mountain mine wastewater more Cu is sorbed than Zn. Comparatively, the water quality of leachate from Parys Mountain mine wastewater could be remediated more effectively than the Cwmrheidol mine wastewater after treatment, because equal amounts of Cu and Zn are removed in Parys Mountain mine wastewater using single minerals of kaolinite and montmorillonite under similar pH ranges. In all cases, Cu and Zn metals demonstrate under-saturation of potential hydroxyl complexes. The study indicates progressive increase in saturation indices of Cu-Zn hydroxyl complexes with increase in pH. There is no evidence of stable hydroxylation of Cu and Zn species that could significantly contribute to the sorption of these metals by mixed mineral systems.