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Chalcopyrite Dissolution in Sulphate-Based Leaching and Bioleaching Systems

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Chalcopyrite Dissolution in Sulphate-Based Leaching and Bioleaching Systems ISSN: 1402-1757 ISBN 978-91-7439-XXX-X Se i listan och fyll i siffror där kryssen är LICENTIATE T H E SIS Department of Civil, Environmental and Natural Resources Engineering Mohammad Khoshkhoo Chalcopyrite Dissolution in Sulphate-Based Leaching and Bioleaching Systems Division of Minerals and Metallurgical Engineering ISSN 1402-1757 Chalcopyrite Dissolution in Sulphate-Based ISBN 978-91-7439-921-9 (print) ISBN 978-91-7439-922-6 (pdf) Leaching and Bioleaching Systems Luleå University of Technology 2014 Mohammad Khoshkhoo Chalcopyrite dissolution in sulphate-based leaching and bioleaching systems Mohammad Khoshkhoo Minerals and Metals Research Laboratory Department of Civil, Environmental and Natural Resources Engineering Luleå University of Technology SE- 971 87 Luleå Sweden June 2014 Printed by Luleå University of Technology, Graphic Production 2014 ISSN 1402-1757 ISBN 978-91-7439-921-9 (print) ISBN 978-91-7439-922-6 (pdf) Luleå 2014 www.ltu.se Abstract Chalcopyrite (CuFeS2) is the most abundant and the most economically important copper mineral. Increasing worldwide demand for copper accompanied by exhaustion of copper resources necessitate the development of new processes for treating lower-grade copper ores. Heap (bio)leaching of copper oxides and secondary sulphides (covellite (CuS) and chalcocite (Cu2S)) is a proven technology and a convenient process due to its simplicity and relatively low capital investment requirement. As a result, the technology appears to be an attractive process option for treatment of low-grade chalcopyrite ores as well. However, chalcopyrite is recalcitrant to leaching and bioleaching in conventional heaps: its dissolution is slow and it halts on a low level of copper extraction usually unacceptable for a commercial practice. Slow dissolution of chalcopyrite is attributed to the formation of compounds on the surface of the mineral during its oxidative dissolution, often termed “passivation”. There is still no consensus about the nature of the passivation layer. There are, however, four proposed candidates suggested in the literature: metal deficient sulphides, polysulphides, jarosite and elemental sulphur. This project was aimed to further investigate the chalcopyrite dissolution and its passivation. In this thesis, dissolution of a pyritic and a pure chalcopyrite concentrate was studied in stirred tank reactors in the absence and presence of moderately thermophilic microorganisms. The abiotic experiments were performed under accurately controlled redox potential conditions to reproduce the same oxidising conditions recorded during the bioleaching experiments. The results showed that the microorganisms did not have any effect in the copper leaching efficiency other than oxidation of ferrous ions to ferric ions. Comparing the copper dissolution rates in the experiments where bulk elemental sulphur was formed with those experiments where the elemental sulphur was oxidised to sulphate due to microbial activity showed that the bulk elemental sulphur did not hinder the dissolution. The same phenomenon was observed in case of bulk jarosite. Under otherwise identical leaching conditions, the presence of bulk jarosite did not decrease the leaching efficiency compared to those experiments were bulk jarosite was not formed. It was also shown that surface spectroscopic methodologies such as X-ray photoelectron spectroscopy (XPS) cannot be applied on powder leached samples due to interfering data from the bulk precipitated species. As a result, massive natural chalcopyrite samples were I prepared and used in the leaching experiments for XPS measurements. Different samples in different stages of leaching were extracted from the biotic and abiotic experiments and analysed by XPS. Results indicated that the surface elemental sulphur was not oxidised by bacterial activity. The data revealed that the common phases on the surface of the samples leached biotically and abiotically for different durations were elemental sulphur and iron- (oxy)hydroxides. The surface elemental sulphur was rigidly bound to the surface and did not volatise in the room temperature XPS measurements. Jarosite was observed in only one sample from the abiotic experiment, but no correlation between its presence and the slow dissolution could be made. Other minor surface compounds such as iron-sulphate was also observed in some samples with no contribution to the leaching behaviour. It was concluded that a multi-component surface phase consisting of mainly sulphur and iron-hydroxides were responsible for the slow chalcopyrite dissolution. II Acknowledgments I wish to express my gratitude for the financial support from the Swedish Research Council Formas (contract number 229-2009-657). Boliden Mineral AB is highly appreciated for providing financial support, the mineral samples and the automatic redox potential control system. Prof. Åke Sandström has spent much time than what he had to on supervising me during this project, both professionally and personally. He had showed that he is not only a great supervisor, but also a very good friend whose office door is always open for a chat. I will never be able to thank him properly. His support made it all much easier than it should be. My co-supervisor Assoc. Prof. Mark Dopson is appreciated for his professionalism and perspective. He has an extraordinary ability in making my amateur writings to something looking professional. Andrei Shchukarev hosts me very kindly when I am at Umeå University. He is also extremely efficient in running the XPS. Lots of credits for this work should go to him. Lic. Andreas Lennartsson and Dr. Fredrick Engström had helped me a lot to run the SEM. They are great colleagues and friends whose presence in the corridor (as we call our division) makes a real difference. I am sincerely grateful to Dr. Nils-Johan Bolin and Jan- Eric Sundkvist for the fruitful discussions I had with them time to time. Rolf Danielsson and his team in pilotverket (Boliden) are acknowledged for the construction of the electrochemical cell. I have to also appreciate their hospitality for the period I was working there. On the personal front, I have a long list of people to thank. My present and former colleagues in the division are only some of them. We had great “fikas” together and I have learnt a lot from all of them, in one way or another. Ehsan, Roland, Saeid and many other friends who I cannot list here, simply due to lack of space, will always be a part of my memories for the great moments we had spent with each other during last few years. You all mean a lot to me. And above all my family whom without I could not stand where I am standing today. This thesis is dedicated to them. III IV List of papers I. Mohammad Khoshkhoo, Mark Dopson, Andrey Shchukarev and Åke Sandström, “Electrochemical simulation of redox potential development in bioleaching of a pyritic chalcopyrite concentrate”, Hydrometallurgy 144-145 (2014), p 7-14. II. Mohammad Khoshkhoo, Mark Dopson, Andrey Shchukarev and Åke Sandström, “Chalcopyrite leaching and bioleaching: An X-ray photoelectron spectroscopic (XPS) investigation on the nature of hindered dissolution”, Submitted to Hydrometallurgy. Contributions to the papers: Running the leaching experiments, analyses, interpretation of data and writing of papers I and II was carried out by M. Khoshkhoo. XPS analyses and peak fitting were performed by A. Shchukarev. XPS data interpretation was done by M. Khoshkhoo with assistance of A. Shchukarev. Å. Sandström and M. Dopson have contributed in a supervisory capacity and assisted with revision of the manuscripts. Published conference papers (not included in this thesis): Mohammad Khoshkhoo, Mark Dopson and Åke Sandström, “Bioleaching and electrochemical leaching of a pyritic chalcopyrite concentrate”, Advanced Materials Research 825 (2013), p 254-257. Presented at International Biohydrometallurgy Symposium (IBS) 2013, Antofagasta, Chile. V Conference papers (not included in this thesis): Mohammad Khoshkhoo and Åke Sandström, “An investigation on the role of microorganisms on chalcopyrite leaching efficiency”, Presented at Mineralteknikkonferens 2014, Luleå, Sweden. Other peer-reviewed journal papers (not included in this thesis): Awe, S.A., Khoshkhoo, M., Kruger, P. and Sandström, Å., “Modelling and process optimisation of antimony removal from a complex copper concentrate”, Nonferrous Metals Society of China Transactions 22 (2012), p 675-685 Nathalie Pérez Rodríguez, Mohammad Khoshkhoo, Åke Sandström, Ilia Rodushkin, Lena Alakangas and Björn Öhlander, “Isotopic signature of Cu and Fe during bioleaching and electrochemical leaching of a chalcopyrite concentrate”, Submitted to International Journal of Mineral Processing. VI Table of contents: Abstract...................................................................................................................................................................I Acknowledgments ...............................................................................................................................................III List of papers .........................................................................................................................................................V 1. Introduction ................................................................................................................................................. 1 1.1. Copper ..................................................................................................................................................
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