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Other Leaching Processes
Published in C. K. Gupta, T. K. Mukherjee, Hydrometallurgy in Extraction Processes, 2017
Like gold and silver, copper minerals can also be dissolved in cyanide solutions by forming cuprous cyanide complexes. There has been much speculation regarding the exact nature of the cyanide complexes, and a large number of papers18–30 on this subject were published. Shantz and co-workers51,52 had reviewed these investigations and commented that complexes like Cu(CN)2−, Cu(CN)32−, and Cu(CN)43− coexist in cyanide solutions and the relative dominance of any particular specie is a function of the cyanide-to-copper ratio, pH, and the equilibrium constants values. The generally accepted explanations are that in dilute copper cyanide solution, tricyanide Cu(CN)32− is the predominant specie, and any Cu(II) present oxidizes cyanide to cyanogen or cyanate. Accordingly, at least 2.32 kg NaCN equivalent is required to dissolve 1 kg of copper provided no side reaction occurs.
Hydrometallurgical Waste Production and Utilization
Published in Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde, Waste Production and Utilization in the Metal Extraction Industry, 2017
Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde
The cyanide associated with the copper cyanide complexes is released by Sodium hydrogen sulphide (NaHS) dosing to precipitate copper and zinc and convert cyanide to hydrogen cyanide (HCN) gas under weak acidic conditions, thus allowing it to be recycled back to the leaching process as free cyanide. However, the chemical sulphide (NAHS) can be replaced by biogenically produced hydrogen sulphide (H2S), which has the added advantage of lowering the acid demand for copper and zinc cyanide treatment. In addition, the overall process cost is lower as the cost of production of H2S through the bioprocess is much lower. Metals such as copper and zinc are converted to high-grade sulphides, the solids are thickened and filtered and the liquor is neutralized and recycled to the leaching step (Fleming, 2003; Adams et al., 2008). Cyanide recycling allows the leaching circuit to be operated at higher cyanide levels thus, maximizing the leaching efficiency and minimizing the copper and zinc deportment to the gold EW stage.
INCO Cyanide destruction insights from plant reviews and laboratory evaluations
Published in Mineral Processing and Extractive Metallurgy, 2020
Fundamental studies by CSIRO Mineral Resources (Breuer et al. 2010; Breuer et al. 2011) have shown that: Upsets to the process (e.g. the loss of sulfite or oxygen addition into the reactor, which results in the presence of undestroyed, free cyanide – CN− – in the reactor) stops the destruction of cyanide (Equation 2 becomes hindered and Equation 3 dominates).To restart the destruction process, the addition of copper sulfate is required (so as to eliminate the presence of free cyanide in the reactor, through the formation of copper cyanide complexes, e.g. Cu(CN)2− and Cu(CN)32−).The dissolved oxygen (DO) concentration provides an indicator of the residual oxygen capacity available to the INCO process; zero DO in the reactor indicates insufficient oxygen addition for the rate of WAD CN and sulfite addition.The addition of hydrogen peroxide to the INCO process may not be beneficial as sulfite can be preferential oxidised (to sulfate) rather than reacting with WAD CN.In treating a slurry, the solids (particularly the surface of sulfide minerals) can catalyse Reaction 3, thereby requiring higher SMBS addition.
A review of Preg-robbing and the impact of chloride ions in the pressure oxidation of double refractory ores
Published in Mineral Processing and Extractive Metallurgy Review, 2022
Wei Sung ng, Qiankun wang, Miao chen
In contrast to pyrite, chalcopyrite has been noted to be a stronger preg-robber (Quach, Koch and Lawson 1993; Rees 2000), and gold uptake proceeds through a different pathway. Using Mössbauer spectroscopy, a highly sensitive technique for observing nuclear interactions, Adams, Swaney and Wagner (1996) demonstrated that gold is reduced on the surface of chalcopyrite and arsenopyrite, particularly on edges and defect sites, and it was suggested that there might be an interaction with the oxidized copper phases. Rees and van Deventer (2000) observed that the reduction of gold on chalcopyrite coincided with an increase in soluble copper cyanide species, and suggested the following reaction:
Stope depth effect on field behaviour and performance of cemented paste backfills
Published in International Journal of Mining, Reclamation and Environment, 2018
The two types of mixing water: namely, as-received tailings interstitial water and added tap water were chemically analysed through the ICP-AES method. Table 3 lists the results of chemical and geochemical testing. It is apparent that the tailings interstitial water is aggressive in terms of sulphate content (SO42– content around 4880 ppm). However, it also contains calcium (Ca content about 560 ppm). The origin of sulphate ions was likely ferrous and/or copper sulphate added for cyanide removal (tailings are treated before mine backfilling), precipitating as iron/copper cyanide complexes. Besides, the origin of calcium was likely the lime added during mineral processing (often used as pH modifier).