Electro-oxidation and characterization of nickel foam electrode for removing boron

The electrocoagulation (EC) using metallic Ni foam as electrodes was studied for the removal of boron from solution. The electrolytic parameters were pH (4-12), current density (0.6-2.5 mA cm^-2), and initial concentration of boron (10-100 mg L^-1). Experimental results revealed that removal efficiency was maximized at pH 8-9, and decreased as the pH increased beyond that range. At particular onset potentials (0.5-0.8 V vs. Hg/HgO), the micro-granular nickel oxide that was created on the surface of the nickel metal substrate depended on pH, as determined by cyclic voltammetry. Most of the crystallites of the precipitates comprised a mixed phase of β-Ni(OH)₂, a theophrastite phase, and NiOOH, as revealed by XRD and SEM analyses. A current density of 1.25 mA cm^-2 was effective in the EC of boron, and increasing the concentration of boric acid from 10 to 100 mg L^-1 did not greatly impair removal efficiency. A kinetic investigation revealed that the reaction followed a pseudo-second order rate model. The optimal conditions under which 99.2% of boron was removed from treated wastewater with 10 mg L^-1-B, leaving less than 0.1 mg L^-1-B in the electrolyte, were pH 8 and 1.25 mA cm^-2 for 120 min.