Synthesis of Ferrate(VI) in Two Cathodes and One Anode Cell: Enhanced Efficiency and Treatment of Thiocyanate in Wastewater

Ferrate(VI) (FeO42-) is a greener oxidant in the treatment of wastewater. This paper presents electrochemical synthesis using two titanium ruthenium sheets as cathodes and a gray cast iron sheet as anode (two cathodes/one anode cell configuration). This electrolytic cell was demonstrated to produce more Fe(VI) than a one cathode/one anode cell configuration (approximate to 1.6mmol/L versus 0.4mmol/L). In the cell, hydroxide ion concentration ([OH-]), current density (Id), distance between cathodes and anode (d), and electrolyte NaCl concentration were varied to obtain optimum conditions to generate Fe(VI) efficiently. The optimum NaOH concentration was determined to be 6.2mol/L in using applied voltage=2.8V, I=10.0A, Id=31.2mA/cm2, d=2cm, and [NaCl]=100g/L. The efficiency of Fe(VI) to remove SCN- in petroleum wastewater was tested in the pH range from 7.0 to 12.0. Additions of coagulants, polyaluminum chloride (PAC), and polyacrylamide (PAM) to petroleum wastewater under alkaline conditions eliminated the large particles present in the wastewater. Fe(VI) treatment of particle-free wastewater showed almost complete removal of SCN- at pH 7.0-9.0 using [Fe(VI)]:[SCN-]=4.7. At pH>9.0 of the reaction mixture of Fe(VI) and wastewater, incomplete removal of SCN- in wastewater was observed.