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Ferrate [Fe(VI)] is increasingly used for the treatment of several contaminants in drinking water and municipal/industrial waste water. Recent findings also show that Fe(VI) is a promising alternative for the treatment of gold mine effluents contaminated by cyanides (CN − ), thiocyanates (SCN − ), and ammonia nitrogen (NH 3 -N). However, the ferric [Fe(III)] salt used in Fe(VI) synthesis could affect this alternative’s efficiency and costs, as well as residual contaminants in the treated effluent. The objective of this study was to evaluate the influence of three Fe(III) salts on the performance of Fe(VI) in the treatment of gold mine effluents and the residual contaminants produced in the process. To do so, the performance of wet Fe(VI) synthesized with ferric nitrate [Fe(NO 3 ) 3 ], ferric chloride (FeCl 3 ), or ferric sulfate [Fe 2 (SO 4 ) 3 ] was evaluated for the treatment of a real gold mine effluent, with final adjustment of pH at ∼7. The results showed that for the effluents treated with Fe(VI) synthesized in the presence of Fe(NO 3 ) 3 , the final NO 3 − concentrations were 4 times higher relative to those in the treated effluents with Fe(VI) synthesized from either FeCl 3 or Fe 2 (SO 4 ) 3 . The use of Fe 2 (SO 4 ) 3 in the wet Fe(VI) preparation did not entail a significant increase of the final SO 4 2− concentrations, which were very similar to initial ones (1220 vs. 1012 mg/L). At the same time, Fe(VI) synthesized from Fe 2 (SO 4 ) 3 was the only one to remove the CN − and NH 3 -N almost totally (∼99%). Finally, the production yield of Fe(VI) with FeCl 3 was lower than Fe 2 (SO 4 ) 3 or Fe(NO 3 ) 3 (3400 vs. 5500 and 5635 mg/L, respectively). This low yield production of Fe(VI) from FeCl 3 entails more costly production costs. Thus, Fe 2 (SO 4 ) 3 is potentially the most appropriate Fe(III) salt source for Fe(VI) synthesis for use in the treatment of contaminated mine effluents. [ABSTRACT FROM AUTHOR]

Available technologies for cyanides (CN − ) treatment in gold mine effluents marginally degrade the thiocyanates (SCN − ). Commonly, they convert the CN − into a less toxic compound, such as cyanates (OCN − ), which afterwards are oxidized and generate ammonia nitrogen (NH 3 -N). Thus, the pretreated effluents require additional steps for complete degradation of SCN − and NH 3 -N. Recent research shows that ferrates [Fe(VI)] might represent a sustainable option for the efficient treatment of gold mine effluents. In this context, the objective of the present study was to assess the performance of Fe(VI) in SCN − and/or NH 3 -N treatment, as well as in their by-products degradation. The performance of Fe(VI) was evaluated using three different synthetic effluents (solutions) and two gold mine effluents contaminated by SCN − and/or NH 3 -N. Results indicated that more than 97% of SCN − were degraded with Fe(VI), while the NH 3 -N increased up to 50%, after SCN − oxidation of the presence of NH 3 -N, within one hour of reaction time. Consequently, for effluents that contain SCN − and NH 3 -N, longer reaction time is required or complementary treatment technologies, such as nitrification – denitrification, should be evaluated for complete degradation of N-compounds. [ABSTRACT FROM AUTHOR]