Studies on the electrochemical decontamination of wastewater containing arsenic

Abstract

The arsenic removal from aqueous solutions by electrocoagulation (EC) using mild steel electrodes was studied. Effect of electrolytes such as NaCl, NaNO 3 and Na 2SO 4 on anodic dissolution of iron and in turn the arsenic removal was deliberated. The arsenic removal was observed to be 98% in the presence of NaCl whereas it is around 75% in the presence of Na 2SO 4 and NaNO 3. The removal of arsenic by EC process was found to be almost similar irrespective of its oxidation state. Almost 95% of the total arsenic was removed within 5 min from its initial concentration of 10 mg L −1. The precipitates formed during EC were characterized using FT-IR, SEM-EDAX, XRD, XPS and magnetometer. The iron oxy-hydroxide precipitate formed during EC was identified as maghemite and lepidocrocite. The magnetic property, particle size and surface properties of the iron oxy-hydroxide precipitate were found to be influenced by arsenic adsorption. The oxidation state of arsenic and iron in EC products was ascertained by XPS. It was observed that some amount of As 3+ was converted to As 5+ during EC. The electrokinetic and FT-IR measurements revealed the co-precipitation of arsenic by specific chemical interaction between arsenic species and iron oxide precipitate. The effect of initial As 3+concentration and current density on arsenic removal was also discussed. The TCLP test (USEPA method-1311) was conducted on EC products to assess their toxicity. It was confirmed that the solid waste generated during EC process is non-hazardous and can be safely disposed.