Removal of hydrated silica, fluoride and arsenic from groundwater by electrocoagulation using a continuous reactor with a twelve-cell stack

The simultaneous removal of hydrated silica, fluoride and arsenic from deep well water (hydrated silica 72 mg L-1, fluoride 4.4 mg L-1, arsenic 106.2 mu g L-1, sulfate 50 mg L-1, phosphate 0.99 mg L-1, pH = 8.2 and conductivity 659 mu S cm(-1)) by electrocoagulation (EC) was investigated. The EC was performed in a continuous electrochemical reactor using aluminum plates as sacrificial anodes coupled directly to a jar test device. The effect of current density (4 <= j <= 8 mA cm(-2)) and mean linear flow rates in the EC reactor (0.057 <= u <= 0.57 cm s(-1)) on the hydrated silica, fluoride, and arsenic removal efficiencies was analyzed. The abatement of hydrated silica was obtained at 8 mA cm(-2) and 0.057 cm s(-1), while the residual concentrations of F- and As after the same electrolysis were 0.19 mg L-1 and 9.8 mu g L-1, satisfying the WHO guidelines for F- (<= 1.5 mg L-1) and As (<= 10 mu g L-1). Spectroscopic analyses on aluminum flocs revealed that they are predominantly composed of aluminum silicates. Arsenates adsorb on aluminum flocs and fluoride replaces a hydroxyl group from aluminum aggregates. (C) 2018 Elsevier Ltd. All rights reserved.