REMOVING INORGANIC CONTAMINANTS FROM HUMAN DRINKING WATER USING MODIFIED RED MUD

At previous Alumina Quality Workshops, we have shown that red mud can be chemically and physically treated to form Bauxsol™ materials, which have a near-neutral pH, a good acid neutralisation capacity, an excellent metal binding capacity and a very high reactive surface area. In this paper we show how further chemical treatment and pelletisation can produce materials that can remove several hazardous contaminants from drinking water. The pellets meet NSF standards for direct contact with drinking water and are currently being used in several water treatment plants. One pelletised reagent (Radium ProActive™) is being used to lower radium concentrations in potable water from well above the regulatory limit of 5 pg/L to < 0.5 pg/L. These pellets also remove common trace metals (e.g. copper, zinc and cadmium), some less common elements (e.g. uranium), and lower gross alpha counts for the water to well below regulatory limits. If the Bauxsol™ reagent is acid treated then water washed before pelletisation, the pellets can be used to lower arsenic concentrations in water to < 1 μg/L. However, the arsenic must be present in the more oxidised arsenate form (arsenite can be converted to arsenate using an oxidant such as during chlorination) and the pH of the water should be kept below 6.5 for optimum performance and above 6.0 to meet regulatory limits. In this paper we describe the preparation of these new materials and present data for several water treatment applications in North America.