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Iron(VI) and Iron(V) Oxidation of Thiocyanate

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journal contribution
posted on 22.08.2002, 00:00 by Virender K. Sharma, Christopher R. Burnett, Donald B. O'Connor, Diane Cabelli
Thiocyanate (SCN-) is used in many industrial processes and is commonly found in industrial and mining wastewaters. The removal of SCN- is required because of its toxic effects. The oxidation of thiocyanate (SCN-) by environmentally friendly oxidants, Fe(VI) and Fe(V), has been studied anaerobically using stopped-flow and premix pulse radiolysis techniques. The stoichiometry with Fe(VI) was determined to be 4HFeO4- + SCN- + 5H2O → 4Fe(OH)3 + SO42- + CNO- + O2 + 2OH-. The rate law for the oxidation of SCN- by Fe(VI) was found to be −d[Fe(VI)]/dt = k11{[H+]/([H+] + Ka,HFeO4)} [Fe(VI)][SCN-] where k11 = 2.04 ± 0.04 × 103 M-1 s-1 and pKa,HFeO4 = 7.33. A mechanism is proposed that agrees with the observed reaction stoichiometry and rate law. The rate of oxidation of SCN- by Fe(V) was approximately 3 orders of magnitude faster than Fe(VI). The higher reactivity of Fe(V) with SCN- indicates that oxidations by Fe(VI) may be enhanced in the presence of appropriate one-electron-reducing agents. The results suggest that the effective removal of SCN- can be achieved by Fe(VI) and Fe(V).