Removal of fluoride and hydrated silica from underground water by electrocoagulation in a flow channel reactor.

This paper concerns simultaneous removal of fluoride and hydrated silica from groundwater (4.08 mg L ^-1 fluoride, 90 mg L ^-1 hydrated silica, 50 mg L ^-1 sulfate, 0.23 mg L ^-1 phosphate, pH 7.38 and 450 μS cm ^-1 conductivity) by electrocoagulation (EC), using an up-flow EC reactor, with a six-cell stack in a serpentine array, opened at the top of the cell to favor gas release. Aluminum plates were used as sacrificial electrodes. The effect of current density (4 ≤ j ≤ 7 mA cm ^-2 ) and mean linear flow rate (1.2 ≤ u ≤ 4.8 cm s ^-1 ), applied to the EC reactor, on the elimination of fluoride and hydrated silica was analyzed. The removal of fluoride followed the WHO guideline (<1.5 mg L ^-1 ), while the hydrated silica was abated at 7 mA cm ^-2 and 1.2 cm s ^-1 , with energy consumption of 2.48 kWh m ^-3 and an overall operational cost of 0.441 USD m ^-3 . Spectroscopic analyses of the flocs by XRD, XRF-EDS, SEM-EDS, and FTIR indicated that hydrated silica reacted with the coagulant forming aluminosilicates, and fluoride replaced a hydroxide from aluminum aggregates, while sulfates and phosphates were removed by adsorption process onto the flocs. The well-engineered EC reactor allowed the simultaneous removal of fluoride and hydrated silica.
Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest regarding the publication of this paper.
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