Minerals Engineering, Vol.81, 88-95, 2015
Degradation of thiocyanate in aqueous solution by persulfate activated ferric ion
Thiocyanate formation from cyanidation of gold bearing ores is becoming a more common problem during gold processing. In this work, the application of an advanced oxidation process based on the use of persulfate (S2O82-) as an environmentally friendly oxidant in the presence of ferric ion for destruction of a persistent and non-volatile inorganic contaminant, such as thiocyanate, in aqueous solutions is reported for the first time. The influence of various reaction parameters like ferric ion and persulfate dosage, initial thiocyanate concentration and the influence of radical scavenger are examined. An accelerated reaction using S2O82- to destroy thiocyanate can be achieved via chemical activation with Fe3+ to generate highly reactive sulfate anion-radicals (SO4 is approximately equal to). The results showed that degradation efficiency was negligible when persulfate was used alone, ferric ions significantly improved the degradation efficiency of thiocyanate at ambient temperature. Under the optimum molar ratios ([S2O82-]:[SCN-] = 5:1 and [S2O82-]:[Fe3+] = 1:0.2), 99% of thiocyanate present in aqueous solution at the initial concentration range of 1.72-17.2 mM was degraded within 60 min of reaction time. To evaluate the contribution of reactive free radicals generated through Fe(III)-mediated activation of persulfate to thiocyanate degradation, quenching experiments using methanol as the radical quenching agent were carried out. The obvious decrease in thiocyanate oxidation efficiency in the presence of methanol confirmed that the radical-based pathway was the dominant mechanism in Fe3+/S2O82- system. The degradation of thiocyanate was accompanied by the formation of cyanide as the main final product of the reaction. Thus the catalytic oxidation of thiocyanate makes it possible to return NaCN into the production process for leaching of precious metals. The work presents an efficient and environmentally acceptable wastewater treatment process applicable in mining facilities utilizing cyanidation of sulfide ores and/or concentrates. (C) 2015 Elsevier Ltd. All rights reserved.