Fluoride Action Network

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

Source: Chemosphere 244: 125417 | January 24th, 2020 | By L.F. Castaneda, O. Coreno, J.L. Nava, G. Carreno
Location: International
Industry type: Water Treatment

Highlights

  • Abatement of fluoride and silica from underground water by electrocoagulation.
  • Flow channel cell with aluminum electrodes open to the atmosphere to favor H2 exit.
  • Significant aluminum dosages were produced at current densities >6 mA cm2.
  • Hydrated silica reacted with the coagulant forming aluminosilicates as flocs.
  • The removal of fluoride followed the WHO recommendation, while silica was abated.

Abstract

This paper concerns simultaneous removal of fluoride and hydrated silica from groundwater (4.08 mg L1 fluoride, 90 mg L1 hydrated silica, 50 mg L-1 sulfate, 0.23 mg L1 phosphate, pH 7.38 and 450 uS cm1 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 cm2) and mean linear flow rate (1.2 ? u ? 4.8 cm s1), 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 L1), while the hydrated silica was abated at 7 mA cm2 and 1.2 cm s1, with energy consumption of 2.48 kWh m3 and an overall operational cost of 0.441 USD m3. 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.

*Original abstract online at https://www.sciencedirect.com/science/article/pii/S0045653519326578