Interaction of milling media and water chemistry in the flotation of selected base metal sulfides
| dc.contributor.advisor | Corin, Kirsten | |
| dc.contributor.advisor | O'connor, Cyril | |
| dc.contributor.author | Nyoni, Sancho | |
| dc.date.accessioned | 2026-10-06T10:06:26Z | |
| dc.date.available | 2026-10-06T10:06:26Z | |
| dc.date.issued | 2026 | |
| dc.date.updated | 2026-09-29T12:24:15Z | |
| dc.description.abstract | As the mineral processing industry advances toward more sustainable operations, many factors must be considered, extending beyond the primary goals of ore beneficiation. Notable chemical and operational considerations include process water recycling and the choice of milling media, which can significantly affect metallurgical performance. A primary consideration of the study was how the pulp phase changes during milling, focusing on the chemical interactions of dissolved species common in recycled water with milling media, minerals, and xanthates, and then using flotation as a diagnostic tool to examine the effects on metallurgical performance. Most studies focus on particle size and liberation, with limited attention to the chemical changes occurring during milling. Therefore, this study specifically investigated the chemical effects of milling, including considerations of pulp and mineral surface chemistry. The research was conducted in three distinct phases, examining changes in the pulp phase without any mineral present (the control phase) and during the processing of single sulfide mineral and mixed sulfide mineral ores. Pyrite (Py) and Galena (Gn) were selected for the study. Py is an iron (Fe)-bearing sulfide mineral, often regarded as problematic in flotation operations, while Gn contains no Fe. Each phase involved testing three milling media options: forged steel (FS), 21% high chrome (HiCr), and ceramic (Cer).In the case of FS, milling media are the main producers of Fe ions, which can form complexes capable of modifying pulp chemistry and mineral surface interactions, in ways that complicate ore metallurgy. Synthetic plant water (SPW) was used in each phase to mimic plant water recycling at four progressively higher ionic strengths, and the effects of pH were compared between natural pH and controlled pHs of 4 and 10. Decoupling the effects of the milling media type, mill shell construction, and water type from that of the ore in Phase 1 provided an understanding of the baseline electrochemical properties of the pulp entering flotation and how the behaviour of xanthate collectors was affected by the water type used and the presence of Fe ions and complexes arising from milling media galvanic contact with the aqueous phase during milling. The oxidation state of the iron species present was found to significantly affect collector availability in free form for attachment to the mineral surface, with the Fe(III) state having a more significant impact on the pH and mixed or redox potential (Eh) of the pulp phase than the Fe(II) state. Furthermore, a more oxidising Eh was found to be important in retaining the xanthate collector in dixanthogen form. The water type was also found to have had significant effects on the galvanic activity of the pulp, despite the absence of minerals, thus influencing the extent of milling media dissolution, particularly in the case of FS media. Analysis of how Py and Gn independently respond to changes in water type, milling media, and pH conditions in Phase 2 revealed different behaviours for each mineral. The extent to which each mineral affected milling media dissolution and the chemical properties of the pulp phase entering flotation was compared with Phase 1 results. Milling media type and pH were found to have a greater impact on metallurgical performance than water type. However, it was noted that water type had a more significant effect on the flotation of Gn compared to Py. Besides insights gained from milling and flotation data, several analytical techniques were employed to examine changes in mineral and water composition across different process streams in milling and flotation. The impact of the investigated conditions on mineral surface chemistry was assessed using X-ray photoelectron spectroscopy. Phase 3 was a mixed ore study focused on identifying suitable milling media, water type, and pH conditions that aid in separating Gn from Py and gangue. The dissolution of Gn and FS milling media was higher in the mixed ore case, while the dissolution of Py, the mineral with the higher rest potential, did not change significantly, as was shown by comparisons between FS and Cer milling results. Compared to the single mineral cases, the residual SIBX concentrations in the mixed ore case were higher than those for Gn, but lower and less influenced by water type than in the Py case. Gn recovery was higher at pH 10 compared to Py recovery across all milling media and water type conditions. On the other hand, Py recoveries were notably lower when FS was employed, regardless of water type. This could be due to the depression of quartz and talc, which comprised the gangue, by dissolved Fe species. Therefore, flotation separation of Gn from Py was most effective using FS milling media at high pH levels, and this outcome could be sustained under high ionic strength water conditions. To optimise milling media costs and efficiently operate in regions with high water demand and limited water catchment areas, it is often preferable to use FS media and recycle process water. This study demonstrates that the concerns about the negative metallurgical impacts of their use can be mitigated by combined pH and water ionic strength control. Overall, the research offers a scientific understanding of the effect of the chemical characteristics of the mill pulp phase on flotation performance. It highlights factors influencing the choice of milling media and addresses issues related to process water recycling in flotation operations. | |
| dc.identifier.apacitation | Nyoni, S. (2026). <i>Interaction of milling media and water chemistry in the flotation of selected base metal sulfides</i>. (). University of Cape Town ,Faculty of Engineering and the Built Environment ,Department of Chemical Engineering. Retrieved from http://hdl.handle.net/11427/43852 | en_ZA |
| dc.identifier.chicagocitation | Nyoni, Sancho. <i>"Interaction of milling media and water chemistry in the flotation of selected base metal sulfides."</i> ., University of Cape Town ,Faculty of Engineering and the Built Environment ,Department of Chemical Engineering, 2026. http://hdl.handle.net/11427/43852 | en_ZA |
| dc.identifier.citation | Nyoni, S. 2026. Interaction of milling media and water chemistry in the flotation of selected base metal sulfides. . University of Cape Town ,Faculty of Engineering and the Built Environment ,Department of Chemical Engineering. http://hdl.handle.net/11427/43852 | en_ZA |
| dc.identifier.ris | TY - Thesis / Dissertation AU - Nyoni, Sancho AB - As the mineral processing industry advances toward more sustainable operations, many factors must be considered, extending beyond the primary goals of ore beneficiation. Notable chemical and operational considerations include process water recycling and the choice of milling media, which can significantly affect metallurgical performance. A primary consideration of the study was how the pulp phase changes during milling, focusing on the chemical interactions of dissolved species common in recycled water with milling media, minerals, and xanthates, and then using flotation as a diagnostic tool to examine the effects on metallurgical performance. Most studies focus on particle size and liberation, with limited attention to the chemical changes occurring during milling. Therefore, this study specifically investigated the chemical effects of milling, including considerations of pulp and mineral surface chemistry. The research was conducted in three distinct phases, examining changes in the pulp phase without any mineral present (the control phase) and during the processing of single sulfide mineral and mixed sulfide mineral ores. Pyrite (Py) and Galena (Gn) were selected for the study. Py is an iron (Fe)-bearing sulfide mineral, often regarded as problematic in flotation operations, while Gn contains no Fe. Each phase involved testing three milling media options: forged steel (FS), 21% high chrome (HiCr), and ceramic (Cer).In the case of FS, milling media are the main producers of Fe ions, which can form complexes capable of modifying pulp chemistry and mineral surface interactions, in ways that complicate ore metallurgy. Synthetic plant water (SPW) was used in each phase to mimic plant water recycling at four progressively higher ionic strengths, and the effects of pH were compared between natural pH and controlled pHs of 4 and 10. Decoupling the effects of the milling media type, mill shell construction, and water type from that of the ore in Phase 1 provided an understanding of the baseline electrochemical properties of the pulp entering flotation and how the behaviour of xanthate collectors was affected by the water type used and the presence of Fe ions and complexes arising from milling media galvanic contact with the aqueous phase during milling. The oxidation state of the iron species present was found to significantly affect collector availability in free form for attachment to the mineral surface, with the Fe(III) state having a more significant impact on the pH and mixed or redox potential (Eh) of the pulp phase than the Fe(II) state. Furthermore, a more oxidising Eh was found to be important in retaining the xanthate collector in dixanthogen form. The water type was also found to have had significant effects on the galvanic activity of the pulp, despite the absence of minerals, thus influencing the extent of milling media dissolution, particularly in the case of FS media. Analysis of how Py and Gn independently respond to changes in water type, milling media, and pH conditions in Phase 2 revealed different behaviours for each mineral. The extent to which each mineral affected milling media dissolution and the chemical properties of the pulp phase entering flotation was compared with Phase 1 results. Milling media type and pH were found to have a greater impact on metallurgical performance than water type. However, it was noted that water type had a more significant effect on the flotation of Gn compared to Py. Besides insights gained from milling and flotation data, several analytical techniques were employed to examine changes in mineral and water composition across different process streams in milling and flotation. The impact of the investigated conditions on mineral surface chemistry was assessed using X-ray photoelectron spectroscopy. Phase 3 was a mixed ore study focused on identifying suitable milling media, water type, and pH conditions that aid in separating Gn from Py and gangue. The dissolution of Gn and FS milling media was higher in the mixed ore case, while the dissolution of Py, the mineral with the higher rest potential, did not change significantly, as was shown by comparisons between FS and Cer milling results. Compared to the single mineral cases, the residual SIBX concentrations in the mixed ore case were higher than those for Gn, but lower and less influenced by water type than in the Py case. Gn recovery was higher at pH 10 compared to Py recovery across all milling media and water type conditions. On the other hand, Py recoveries were notably lower when FS was employed, regardless of water type. This could be due to the depression of quartz and talc, which comprised the gangue, by dissolved Fe species. Therefore, flotation separation of Gn from Py was most effective using FS milling media at high pH levels, and this outcome could be sustained under high ionic strength water conditions. To optimise milling media costs and efficiently operate in regions with high water demand and limited water catchment areas, it is often preferable to use FS media and recycle process water. This study demonstrates that the concerns about the negative metallurgical impacts of their use can be mitigated by combined pH and water ionic strength control. Overall, the research offers a scientific understanding of the effect of the chemical characteristics of the mill pulp phase on flotation performance. It highlights factors influencing the choice of milling media and addresses issues related to process water recycling in flotation operations. DA - 2026 DB - OpenUCT DP - University of Cape Town KW - Milling & KW - Grinding KW - Water Chemistry KW - Mineralogy & KW - Sulfides LK - https://open.uct.ac.za PB - University of Cape Town PY - 2026 T1 - Interaction of milling media and water chemistry in the flotation of selected base metal sulfides TI - Interaction of milling media and water chemistry in the flotation of selected base metal sulfides UR - http://hdl.handle.net/11427/43852 ER - | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11427/43852 | |
| dc.identifier.vancouvercitation | Nyoni S. Interaction of milling media and water chemistry in the flotation of selected base metal sulfides. []. University of Cape Town ,Faculty of Engineering and the Built Environment ,Department of Chemical Engineering, 2026 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/43852 | en_ZA |
| dc.language.iso | en | |
| dc.language.rfc3066 | eng | |
| dc.publisher.department | Department of Chemical Engineering | |
| dc.publisher.faculty | Faculty of Engineering and the Built Environment | |
| dc.publisher.institution | University of Cape Town | |
| dc.subject | Milling & | |
| dc.subject | Grinding | |
| dc.subject | Water Chemistry | |
| dc.subject | Mineralogy & | |
| dc.subject | Sulfides | |
| dc.title | Interaction of milling media and water chemistry in the flotation of selected base metal sulfides | |
| dc.type | Thesis / Dissertation | |
| dc.type.qualificationlevel | Doctoral | |
| dc.type.qualificationlevel | PhD |