Arsenic removal by iron oxides

Abstract

Arsenic has long been recognized as a toxin and carcinogen. Arsenic contaminated drinking water probably poses the greatest threat to human health. A successful treatment for removing arsenic from drinking water requires an understanding of arsenic chemistry and the physical-chemical processes that occur during each treatment step. Iron oxide (Fe-Ox) minerals showed good efficiency for arsenic removal (Simeonova 2000, Matis et.al., 1999). Additionally, naturally occurring iron oxides are more attractive for arsenic removal from contaminated water than the synthetic oxides because they are more cost effective. However, few studies have been carried out on the feasibility of their use as adsorbents for arsenic removal. Hematite, magnetite, goethite and laterite have been studied in their role as arsenic adsorbents. Results showed that all of them are suitable as arsenic adsorbents. Electroacoustic Tests (ET) tests showed that arsenic adsorption occurs over the whole pH range considered (4-11) and also that the Fe-Ox have IEP at pH between 6.5 and 8.5. Their surface charge is negative at pHpzc. The presence of inner sphere complex, which implies stability of the arsenic adsorbed onto Fe-Ox because of covalent bonding, was shown by ET and leaching tests. Leaching tests by MgCl₂ were performed to study the stability of the adsorption products and results expressed on a weight percentage basis showed that hematite had 60.2%, magnetite 75.4%, goethite 78.0% and laterite 86.2% of arsenic strongly fixed. While these results expressed on a surface area basis showed that hematite had 0.16mg/m² , magnetite 0.11mg/m² , goethite 0.065 mg/m² and laterite 0.011 mg/m² of arsenic strongly fixed. In addition, this study presents a simple method developed to remove arsenic from water using natural iron oxides (Fe-Ox) minerals. The method involves mixing natural iron mineral bearing soils (lateritic soils) with arsenic contaminated water for ten minutes and then filtering (coffee filter). The aadsorption capacity of laterite was estimated at 0.1 lmg/m². After addition, arsenic levels in the treated water were below drinking water standards. The treatment method is inexpensive and simple, making it suitable for house hold use.Applied Science, Faculty ofMining Engineering, Keevil Institute ofGraduat

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