The removal of arsenic from water using natural iron oxide minerals

Abstract

The contamination of groundwater with arsenic is a serious health issue in many parts of the world. Although iron has been shown to be effective at removal of arsenic from water, there has been no research to assess the feasibility of using natural iron oxide minerals for water treatment. The successful treatment of water to remove arsenic requires an understanding of arsenic chemistry and the physical–chemical interactions between arsenic and iron oxide minerals. A study was conducted to evaluate hematite, magnetite, goethite and iron rich laterite soil as arsenic adsorbents. Electroacoustic measurements were conducted to assess the nature of arsenic adsorption. Results showed that arsenic adsorption occurred over the entire pH range tested (pH 4–11). The isoelectric point shifted due to arsenic adsorption and this is a strong evidence of specific ion adsorption. This was supported by leaching tests that indicated strong attachment of arsenic to the surface of iron oxide minerals. Adsorption tests showed that iron rich laterite was most effective for arsenic removal, followed by goethite, magnetite and hematite. This was attributed to the higher specific surface area of the respective minerals. The study also demonstrates a simple water treatment method involving the use of low cost natural ironoxide minerals for arsenic removal to meet drinking water standards. Treatment of 100 mL of water containing 20 ppm arsenic with 5 g of laterite reduced the arsenic level down to 10 ppb within a period of 10 min.