Chalcopyrite dissolution in cupric chloride solutions
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Doctoral thesis (article-based)
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2009
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en
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Abstract
Hydrometallurgical technology offers the possibility of processing low-grade or small copper ore bodies and concentrates economically. Chloride solutions have become of great interest, having high leaching kinetics and no passivation of sulfide minerals. This thesis presents an investigation of chalcopyrite (CuFeS2) dissolution in cupric chloride solutions. Firstly, the formation and composition of reaction product layers formed on chalcopyrite were studied. Secondly, the rate-controlling step in chalcopyrite dissolution was defined and thirdly, the prevailing cupric and cuprous species were observed. Electrochemical methods, such as anodic and cathodic polarization, potentiostatic measurements, redox measurements, and electrochemical impedance spectroscopy (EIS) were applied. In addition, stereo-optical microscopy and scanning electron microscopy (SEM) as well as thermodynamic software HSC 5.11/6.1 were used. The solution used had sodium chloride concentrations in the range 250 - 280 g/l, cupric ion concentrations were 0.9 - 40 g/l. The temperature was set to be 70 - 95 °C and the pH values were in the range of 1 - 3. The thesis focuses on studying the reaction product layer on chalcopyrite. Color, thickness and the resistance of reaction product layers in the solid - solution interface were determined as a function of time from 0 to 22 hours at pHs 1, 2 and 3. The results suggested that sulfur was present at all times and pHs in the reaction product layers. At pH 1, elemental sulfur was the main phase forming the reaction product layer. This gray colored, porous, and easily removable layer grew to a thickness of 9 µm within 22 hours. The elemental sulfur layer appeared to decrease the rate of the chemical dissolution reaction. By increasing the pH from 1 to 3 and by increasing the dissolution time, the formation of FeOOH became more dominant. At pH 2, the formation of FeOOH was observed after 3 hours and at pH 3 at all leaching times. The co-precipitation of FeOOH was favorable for chalcopyrite dissolution, shifting the dissolution equilibrium to the right. It was determined that the dissolution of a stationary chalcopyrite sample was controlled by diffusion in the reaction product layer at pH 3, changing to chemical rate control at pH 1. FeOOH formation, in addition to the elemental sulfur, favored chalcopyrite dissolution. In concentrated cupric chloride solutions, cupric ions were assumed to be at least partially not in a chloro-complex form, whereas cuprous ions readily form complexes in chloride solutions. However, cuprous ions were determined not to be chloro-complexed at significantly low cuprous concentrations, in the order of 10-13 - 10-17 mol/m³. This was based on the determined Eo value of 0.158 V ± 0.121 V vs. SHE, which is typical for redox couples having cuprous ion not in a chloro-complex form.Description
Keywords
chalcopyrite, dissolution, leaching, cupric chloride solutions, hydrometallurgy, copper ores, reaction product layers, cuprous ions, cupric ions, redox measurements, redox potentials
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Parts
- [Publication 1]: Mari Lundström, Jari Aromaa, Olof Forsén, Olli Hyvärinen, and Michael H. Barker. 2005. Leaching of chalcopyrite in cupric chloride solution. Hydrometallurgy, volume 77, numbers 1-2, pages 89-95.
- [Publication 2]: Mari Lundström, Jari Aromaa, Olof Forsén, Olli Hyvärinen, and Michael H. Barker. 2007. Cathodic reactions of Cu2+ in cupric chloride solution. Hydrometallurgy, volume 85, number 1, pages 9-16.
- [Publication 3]: M. Lundström, J. Aromaa, O. Forsén, and M. H. Barker. 2008. Reaction product layer on chalcopyrite in cupric chloride leaching. Canadian Metallurgical Quarterly, volume 47, number 3, pages 245-252.
- [Publication 4]: M. Lundström, J. Aromaa, and O. Forsén. 2009. Redox potential characteristics of cupric chloride solutions. Hydrometallurgy, volume 95, numbers 3-4, pages 285-289.
- [Publication 5]: M. Lundström, J. Aromaa, and O. Forsén. 2009. Transient surface analysis of dissolving chalcopyrite in cupric chloride solution. Canadian Metallurgical Quarterly, volume 48, number 1, pages 53-60.