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Cyanidation is the most commonly used method for leaching and recovering Au and Ag from ores. In the process, some copper species may dissolve and react with cyanide to form cyanide–copper complexes in a cyanide solution. Waste cyanide solutions must be treated to reduce their cyanide concentrations before they may be safely discharged into tailing storage facilities. In this preliminary work, precipitate flotation techniques were used to remove cyanide–copper complexes from synthetic solutions similar to those found in gold cyanidation plants. Cetyltrimethylammonium bromide (CTAB) and octadecyltrimethylammonium bromide (OTAB) were both employed as precipitants and frothers. Multiple parameters, including reaction time, bubbling time, pH, and surfactant dosage, were investigated. The results show that it is possible to remove up to 84.51% of the cyanide and 81.62% of the copper with a 7.60% water loss when adding 3.75 mg/mg Cu CTAB at a pH of 6. While further decreasing the pH may increase removal efficiencies, the contribution of hydrogen cyanide (HCN) volatilization and stripping will also be greatly increased. Tests performed with an industrial solution corroborated the results obtained using synthetic solutions. This study reveals that precipitation flotation can be used in the gold mining industry as a treatment for cyanidation solutions with high cyanide concentrations discharged into tailings facilities. [ABSTRACT FROM AUTHOR]

• An advanced method for zinc cyanide removal based on precipitation. • 92.17% of cyanide and 88.86% of zinc could be removed using OTAB. • The process is effective when non-polar organic contaminants and <50 mmol/L salt are present. • Co-existed copper can be simultaneously treated. In gold-processing plants, the final tailing containing metal cyanide species is typically treated using various oxidation methods to produce the main source of process water, which is subsequently recycled to the upstream units, such as flotation units. In some gold-processing plants, a considerable amount of metal cyanide species such as zinc cyanide remains in process water, despite the cyanide destruction process. Because residual zinc cyanide complexes can depress gold flotation, the amount of process water must be decreased such that it can be recycled to a flotation circuit. Previous studies report that the critical concentration of zinc cyanide, measured based on the total cyanide concentration during flotation depression, is 0.4 mmol/L. In the present study, the feasibility of using quaternary ammonium salts to precipitate zinc cyanide complexes to less than the critical concentration was studied. The results showed that 92.17% of 60 mg/L of cyanide and 88.86% of 50 mg/L of zinc (molar ratio Zn/CN = 1:3) can be removed using 0.4 g/L of octadecyl trimethyl ammonium bromide at a pH of 10. The concentration of the residual CN cyanide was less than the critical concentration. This indicates that the abovementioned process is effective when nonpolar organic contaminants and moderate amounts of salt (<50 mmol/L) are present. This work revealed that the precipitation process can be used as an advanced treatment method for process water subjected to oxidation treatment. [ABSTRACT FROM AUTHOR]

• Cyanide adsorption onto CTAB-PSS aggregates. • Copper cyanide complexes removed from effluents containing Cu and CN by precipitation and filtration. • Conductivity plot of the solution as a tool for optimization of substrate dosage and ratio. • Thiocyanate ions significantly reduced the removal efficiency of Cu and T CN. Precipitation of metal cyanide complexes using quaternary ammonium salts has been used in cyanidation solutions after gold leaching. Due to the high residual load of metal cyanide complexes and ammonium salts, this method does not apply to effluents containing moderate or low cyanide concentrations. To overcome these limitations, in this study, we introduce poly(sodium 4-styrenesulfonate) (PSS) into a solution containing cetyltrimethylammonium bromide Sinpharm (CTAB), to form polymer-surfactant aggregates (PSAs) and enhance the removal efficiency of Cu and T CN. 93.8% and 97.0% of Cu and T CN , respectively, were removed from the synthetic solution (Cu 0.5 mM and CN 1.5 mM) under optimum dosage of 150 ppm PSS and 0.8 mM CTAB, resulting in 92.2% of substrate usage. The addition of 3.0 mM CTAB without PSS resulted in only 46.3% of substrate usage, even though the removals of Cu and T CN were 92.2 and 93.6%, respectively. The presence of thiocyanate ions significantly reduced the removal efficiency due to the competitive interaction with PSAs, whereas the pH of the solution and the temperature did not have any noticeable impact. Tests performed with an industrial effluent corroborated the results obtained with synthetic solutions: PSAs react with copper cyanide to form a precipitate that can be separated from the solution. [ABSTRACT FROM AUTHOR]