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 mgL-1, fluoride 4.4 mgL-1, arsenic 106.2 µgL-1, sulfate 50 mgL-1, phosphate 0.99 mgL-1, pH = 8.2 and conductivity 659 µScm-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 µg L-1, satisfying the WHO guidelines for F- (≤1.5 mg L-1) and As (≤10 µg 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.