Thiocyanate (SCN{sup}-) is used in many industrial processes and is commonly found in industrial and mining wastewaters. The removal of SCN{sup}- is required because of its toxic effects. The oxidation of thiocyanate (SCN{sup}-) 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 4HFeO{sub}4{sup}- + SCN{sup}- + 5H{sub}2O → 4Fe(OH){sub}3 + SO{sub}4{sup}(2-) + CNO{sup}- + O{sub}2 + 2OH{sup}-. The rate law for the oxidation of SCN{sup}- by Fe(VI) was found to be -dFe(VI)/ dt = k{sub}11{H{sup}+/(H{sup}+ + K{sub}(a,HFeO{sub}4)} Fe(VI)SCN{sup}- where k{sub}11 = 2.04±0.04 × 10{sup}3 M{sup}(-1) s{sup}(-1) and pK{sub}(a,HFeO{sub}4) = 7.33. A mechanism is proposed that agrees with the observed reaction stoichiometry and rate law. The rate of oxidation of SCN{sup}- 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{sup}- can be achieved by Fe(VI) and Fe(V).
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