Electrocoagulation of boron by electrochemically co-precipitated spinel ferrites

Magnetically separable spinel ferrites were created in an electrocoagulation (EC) process for removing boron from aqueous solution. Coprecipitates of NiFe2O4, CoFe2O4 and CuFe2O4 were obtained using sacrificial iron anodes (EC-Fe) in an electrolyte that contained transition metal salts (Ni, Co, Cu). The use of nickel chloride (NiCl2) as the supporting electrolyte yielded the highest boron removal since the maximum adsorption capacity of the resulting sludge was 28.9 mg-B/g. An EC that used iron and nickel as anodes (EC-Fe/Ni) in NaCl electrolyte was then employed to form nickel ferrite by electrochemical dissolution of ferrous (Fe(II)) and nickel (Ni (II)) ions, providing comparable removal efficiency but minimizing the residual level of Ni(II) in the treated water. The saturation magnetization of the precipitate that was produced in the EC-Fe/Ni system was 50.3 emu/g which exceeded that in the EC-Fe system with nickel chloride -21.8 emu/g, indicating its outstanding magnetic separability. EC-Fe/Ni was optimized to remove 95% of boron from solution in 60 min with an initial boron concentration of 10 ppm at pH 8 and a current density of 3.75 mA/cm(2).