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Improved Process Development for Complex Silver Ores Through Systematic, Advanced Mineral Characterisation

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Improved Process Development for Complex Silver Ores Through Systematic, Advanced Mineral Characterisation Improved process development for complex silver ores through systematic, advanced mineral characterisation Jocelyn Andrea Quinteros Riquelme B. Eng (Mineral Processing) and Metallurgical Engineer A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in December 2014 Sustainable Minerals Institute Abstract With the general trend across all commodities towards the treatment of lower grade ores, it is becoming increasingly important to develop robust protocols for comprehensive mineralogical characterisation. The tendency for the complexity of the mineral assemblages in the ore to increase requires the use of more sophisticated tools in order to characterise the ore in the context of the implications of the mineralogy on its process response. Some of the key mineralogical attributes that are used to inform process selection and infer process response include: which minerals host the valuable element (elemental deportment); the type and relative proportions of the minerals present (modal mineralogy); and the grain size, association and liberation characteristics of the valuable minerals. Silver ores are typically complex in terms of their mineralogical characterisation. There are a wide range of minerals that contain silver in different proportions which can make it difficult to identify them. Additional challenges include the relatively low concentrations of silver (ppm) within an ore, the large number of silver-bearing minerals that can occur in a single deposit and the potential for silver to occur in solid solution in wide range of sulphide minerals. Therefore, understanding the mineralogical attributes of an ore, particularly the deportment of the silver within the ore, is critical in developing an effective flotation processing strategy. Automated SEM-based systems are a commonly used tool to quantify these attributes for an ore, but the low-grade together with the large number of minerals that are potential hosts for silver means that often, complementary analytical tools must be used in order to properly account for the valuable element. This thesis aims to develop an appropriate methodology to characterise complex low-grade silver ores for the purpose of developing the most appropriate flotation strategy. As result of this investigation a novel methodology is proposed for the mineralogical characterisation and it consists of three different levels of characterisation using sophisticated analytical techniques. Level 1, the simplest (which included chemical assays, XRD, oxide characterisation of lead and zinc, optical microscopy and MLA), was applied to Toldos ore (oxide ore) and successfully characterised the mineralogy. Level 2, which included laser ablation inductively coupled plasma mass spectroscopy, was needed for Tesorera ore (sulphide ore). Jayula ore (supergene oxide ore) required the added sophistication of Level 3. In addition to the techniques of Level 1 and Level 2, Level 3 included the use of electron micro probe and synchrotron XRD, XRF and XANES methods to estimate the mineralogical attributes of this ore. The insights from the mineralogical characterisation were then Jocelyn Quinteros Riquelme ii used to inform the metallurgical testing that was undertaken, for example, selective or bulk flotation. The ore characterisation for Toldos identified the presence of at least eight silver-bearing minerals including coarse grained chlorargyrite and acanthite. Mineralogical analysis of preflotation test samples indicated that acanthite exhibited natural hydrophobicity. These results, together with the mineralogical characterisation, indicated that selective flotation would be an appropriate processing route for this ore. The coarse grained silver minerals required a P80 of 100 m and a specific dosage of a mix of collectors. The final flow sheet produced a rougher concentrate that contained 4404 ppm of Ag, at a recovery of 83.8%. In the Tesorera ore, the majority of the silver (>99%) was contained in pyrite, which itself represented approximately 4% of the ore. A bulk flotation strategy using sulphidisation agents and the introduction of mainstream inert grinding (MIG) to generate a P80 of 56 m, was necessary to recover pyrite minerals to achieve a rougher concentrate of 485 ppm Ag at a recovery of 87.2%. The mineralogical characterisation of Jayula, during which a previously unreported association was found between silver and barite, accounting for more than 20% of silver in this ore with most of the remainder occurring as fine grained acanthite helped to guide the metallurgical characterisation. The fine grind required a final flow sheet with a P80 of 25 m and a produced concentrate for which the silver recovery was 80.8% at a grade of 1709 ppm Ag. Again, as with the previous ores, the mineralogical characterisation guided the metallurgical test work. The outcomes of this research include: A systematic method that enables the development of flotation strategies to achieve >80% silver recovery in laboratory rougher separation. Analyses of flotation products were performed on unsized, size-by-size and size-by-liberation bases, opening a broad understanding of the behavior of complex low-grade silver ores. The identification of a unique chemical association between silver and barite, which has not been previously reported in the literature and was shown to account for up to 20% of the silver in one of the ores studied. A framework for assessing the ‘refractoriness’ of silver ores based on the mineralogical characteristics of the ore and the metallurgical performance. In summary this work provides a clear demonstration of how powerful a detailed mineralogical study at the onset of a project can be to guide the metallurgical test work for improved recoveries. Jocelyn Quinteros Riquelme iii Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, experimental design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the General Award Rules of The University of Queensland, immediately made available for research and study in accordance with the Copyright Act 1968. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. Jocelyn Quinteros Riquelme iv Publications during candidature Peer-reviewed journal paper Quinteros J., Wightman E., Johnson N.W. and Bradshaw D., 2015. Evaluation of the response of valuable and gangue minerals on a recovery, size and liberation basis for a low grade silver ore. Minerals Engineering Journal, Vol. 74, 150-155. Peer-reviewed conference papers J Quinteros-Riquelme, E Wightman, N W Johnson and D Bradshaw., 2014. Applying process mineralogy to complex low-grade silver ores. IMPC 14, Santiago Chile, October 2014. J Quinteros-Riquelme, N W Johnson, D Bradshaw and E Wightman., 2012. Study of flotation performance in a complex silver ore at laboratory scale. IMPC 12, New Delhi, India, September 2012. Conference paper Quinteros-Riquelme J, Wightman E, Johnson NW and Bradshaw D., 2013. Evaluation of the response of valuable and gangue minerals on a recovery, size and liberation basis for a low grade silver ore. Flotation ’13, Cape Town, South Africa, November 2013. Jocelyn Quinteros Riquelme v Publications included in this thesis Quinteros J., Wightman E., Johnson N.W. and Bradshaw D., 2014 – Incorporated in Chapter 5. Contributor Statement of contribution Quinteros J Conception and design (50%) Analysis and interpretation of data (70%) Wrote the paper (60%) Wightman E Conception and design (30%) Analysis and interpretation of data (20%) Wrote and edited paper (20%) Johnson NW Conception and design (15%) Analysis and interpretation of data (10%) Wrote and edited paper (15%) Bradshaw D Conception and design (5%) Analysis and interpretation of data (0%) Wrote and edited paper (5%) J Quinteros-Riquelme, E Wightman, N W Johnson and D Bradshaw., 2014 – Incorporated in Chapter 7. Contributor Statement of contribution Quinteros J Conception and design (60%) Analysis and interpretation of data (80%) Wrote the paper (70%) Wightman E Conception and design (40%) Analysis and interpretation of data (20%) Wrote and edited paper (20%) Johnson NW Conception and design (0%) Analysis and interpretation of data (0%) Wrote and edited paper (5%) Bradshaw D Conception and design (0%) Analysis and interpretation of data (0%) Wrote and edited paper (5%) Jocelyn Quinteros Riquelme vi J Quinteros-Riquelme, N W Johnson, D Bradshaw and E
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