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

• Arsenic abatement and removal of fluoride and silica from groundwater. • Al-Fe hybris electrodes are stacked in continuous electrocoagulation (EC) reactor. • World Health Organization recommendations for arsenic and fluoride were fulfilled. • Al and Fe react with silica producing flocs of aluminosilicates and iron silicates. • Arsenic adsorbs on aggregates, and fluoride substitutes a OH from aluminum flocs. This communication is about the removal of arsenic (As), fluoride (F −) and hydrated silica (HS) from real underground water (initial concentration: 28 µg L−1 arsenic, 1.55 mg L−1 F − , 155 mg L−1 HS, 35 mg L−1 sulfate, pH 7.4, and 470 µS cm−1 conductivity) by electrocoagulation (EC). The novel EC reactor consists of eight horizontally 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 at j = 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 μg 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. [Display omitted] [ABSTRACT FROM AUTHOR]