Ferrates performance in thiocyanates and ammonia degradation in gold mine effluents

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 (NH₃-N). Thus, the pretreated effluents require additional steps for complete degradation of SCN⁻ and NH₃-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 NH₃-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 NH₃-N. Results indicated that more than 97% of SCN⁻ were degraded with Fe(VI), while the NH₃-N increased up to 50%, after SCN⁻ oxidation of the presence of NH₃-N, within one hour of reaction time. Consequently, for effluents that contain SCN⁻ and NH₃-N, longer reaction time is required or complementary treatment technologies, such as nitrification – denitrification, should be evaluated for complete degradation of N-compounds.