Electrocoagulation with Fe-Al hybrid electrodes for the removal of arsenic, fluoride, and silica from natural groundwater

This communication is about the removal of arsenic (As), fluoride (F-) and hydrated silica (HS) from real un-derground water (initial concentration: 28 & mu;g L-1 arsenic, 1.55 mg L-1 F-, 155 mg L-1 HS, 35 mg L-1 sulfate, pH 7.4, and 470 & mu;S cm-1 conductivity) by electrocoagulation (EC). The novel EC reactor consists of eight hori-zontally stacked cells using Fe and Al plates as sacrificial anodes with an upward flow. The abatement of As and the elimination at the same time of F- and HS was performed by analyzing the influence of the mean linear flow velocity (1.2 < u < 4.8 cm s- 1) at different current densities (3 < j < 7 mA cm-2) imposed on the EC system. The best condition was carried out atj = 7 mA cm-2 and u = 1.2 cm s- 1, achieving complete arsenic elimination, and a remaining F- concentration of 0.45 mg L-1, fulfilling the World Health Organization (WHO) guideline for arsenic (< 10 & mu;g L-1) and fluoride (< 1.5 mg L-1). The remaining HS reached a value of 10 mg L-1. Spectroscopic techniques applied to the Fe-Al flocs evidenced the generation of iron oxides and hydroxides, as well as the formation of aluminosilicates.

Automated summary

This study investigates the application of electrocoagulation technology for the removal of arsenic, fluoride, and hydrated silica from underground water. By analyzing the influence of the mean linear flow velocity and current density in the electrocoagulation system, it was found that complete arsenic elimination and fluoride concentration of 0.45 mg L-1 can be achieved under a current density of 7 mA cm-2 and linear flow velocity of 1.2 cm s-1, meeting the World Health Organization guidelines. The remaining hydrated silica reached a concentration of 10 mg L-1.