Concurrent elimination of arsenic and hydrated silica from natural groundwater by electrocoagulation using iron electrodes

Abstract

This paper concerns the removal of arsenic and hydrated silica (HS) from groundwater (32.45 µg L−1 As, 5.70 mg L−1F−, 155.5 mg L−1 HS, 30.0 mg L−1 SO42-, 0.77 mg L−1 PO43-, pH 8.36, and conductivity of 533 µS cm−1) by electrocoagulation (EC) using an up-flow continuous reactor. Iron electrodes were used as sacrificial anodes. The EC efficiency on pollutants removal at current densities from 4 to 8 mA cm−2 and mean linear flow velocities ranging from 1.1 to 4.5 cm s−1 were analyzed. The best EC trial was obtained at 8 mA cm−2 and 1.1 cm s−1, where the residual concentrations of As and HS were 1.1 µg L−1, and 33 mg L−1, respectively, giving values of electrolytic energy consumption (Econs) and overall costs (OC) of 1.96 kWh m−3 and 0.28 USD m−3. The proposed EC process agrees with the WHO guideline for the concentration of As (<10 μg L−1). XRF, SEM-EDS, XRD, FTIR, and Raman analyzes indicate that HS reacts with coagulant forming iron silicates. Arsenic was removed by adsorption on iron hydroxides, iron oxyhydroxides, and iron silicates flocs. Sulfate and phosphate are trapped and swept within the sedimentation of the flocs. The removal of fluorides (17%) is attributed to weak adsorption on the iron agglomerates.