Concurrent arsenic, fluoride, and hydrated silica removal from deep well water by electrocoagulation: Comparison of sacrificial anodes (Al, Fe, and Al-Fe).

Some studies have reported the removal of As (As) and fluoride (F ^- ) using different sacrificial anodes; however, they have been tested with a synthetic solution in a batch system without hydrated silica (SiO ₂ ) interaction. Due to the above, concurrent removal of As, F ^- , and SiO ₂ from natural deep well water was evaluated (initial concentration: 35.5 μg L ^-1 As, 1.1 mg L ^-1 F ^- , 147 mg L ^-1 SiO ₂ , pH 8.6, and conductivity 1024 μS cm ^-1 ), by electrocoagulation (EC) process in continuous mode comparing three different configurations of sacrificial anodes (Al, Fe, and Al-Fe). EC was performed in a new reactor equipped with a small flow distributor and turbulence promoter at the entrance of the first channel to homogenize the flow. The best removal was found at j = 5 mA cm ^-2 and u = 1.3 cm s ^-1 , obtaining arsenic residual concentrations (C _As ) of 1.33, 0.45, and 0.77 μg L ^-1 , fluoride residual concentration ( [Formula: see text] ) of 0.221, 0.495, and 0.622 mg L ^{-1 ,} and hydrated silica residual concentration ( [Formula: see text] ) of 21, 34, and 56 mg L ^-1 , with costs of approximately 0.304, 0.198, and 0.228 USD m ^-3 for the Al, Fe and Al-Fe anodes, respectively. Al anode outperforms Fe and Al-Fe anodes in concurrently removing As, F ^- and SiO ₂ . The residual concentrations of As and F ^- complied with the recommendations of the World Health Organization (WHO) (As < 10 μg L ^-1 and F ^-  < 1 mg L ^-1 ). The spectroscopic analyses of the Al, Fe, and Al-Fe aggregates showed the formation of aluminosilicates, iron oxyhydroxides and oxides, and calcium and sodium silicates involved in removing As, F ^- , and SiO ₂ . It is concluded that Al would serve as the most suitable sacrificial anode.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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