Selo NDLOVU

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• Ndlovu, S. (2025). Environmental Considerations. In Treatise in Process Metallurgy. Elsevier. doi:10.1016/b978-0-443-40294-4.00046-3
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  Hydrometallurgy plays a key role in the production of metals necessary for the rapid industrial, technological, and digital advancements in the global economy. However, the hydrometallurgical process steps involved in the extraction of these metals from their natural resources tend to go hand in hand with the generation of a large amount of solid, liquid, and gaseous waste. Such waste streams have been increasingly associated with a negative impact on the ecosystem and the health of the people living in the locality of the mining and metal extraction operations. It therefore becomes imperative that the extraction of these resources is not divorced from the associated environmental impact if mining is to do more good than harm. This section highlights some of the strategies being undertaken by metal extraction operations to ensure that meeting the demand for metals does not happen at the expense of environmental destruction. Environmental impact assessment, processing for environmental compliance, and environmental compliant processing are some of the approaches discussed.

Journals/Publications

• Baleti, C. W., Shemi, A., & Ndlovu, S. (2025). Cloud Point Extraction of Platinum Group Metal solutions: Key factors in metal extraction and selective elution at low concentrations. Microchemical Journal, 216(Issue). doi:10.1016/j.microc.2025.114683
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  Platinum group metals are leached from spent autocatalytic converters and other end-of-life products, producing Platinum group metal concentrations below 500 ppm compared to 15,000 ppm from commercial concentrates. Conventional solvent extraction and precipitation methods are inefficient for processing end-of-life leachates, but Cloud Point Extraction shows promise for recovering trace Platinum group metals with minimal environmental impact. However, literature on Platinum group metal Cloud Point Extraction is limited, particularly regarding methods to elute Platinum group metals or remove co-extracted impurities from the surfactant phase. This study used design of experiments to investigate how initial solution pH, surfactant volume (10 % w/v Triton X − 100), complexing agent volume (1 % w/v 2-mercaptobenzothiazole, 2-MBT), metal ion concentration, and contact time affect Platinum Group Metal extraction from spent autocatalytic converters chloride leachate. Leach solutions contained 82–165 ppm PGMs and 2153–4348 ppm matrix elements. Key factors were identified to be the initial solution pH, metal ion concentration, and complexing agent volume. Interactions between initial solution pH and metal ion concentration, as well as 2-MBT and metal ion concentration, enhanced Pt, Pd, and Rh recovery, while initial solution pH–2-MBT interactions reduced Pd and Rh recovery. An increase in metal ion concentration resulted in all matrix elements being extracted to the surfactant phase. Elution of Pt and Pd from the surfactant phase with 1.0 M thiourea in 0.5 M HCl achieved 66 % and 62 % recovery, respectively, while 6.0 M HCl eluted 68 % of Rh. Attempts to achieve selective Platinum group metal elution were unsuccessful, prompting impurity scrubbing tests. Aluminium and magnesium were removed, but iron remained. These findings highlight key factors influencing Cloud Point Extraction performance and offer insights for optimizing Platinum group metal recovery by Cloud Point Extraction.
• Kumar, A., Shemi, A., Chipise, L., Yah, C. S., Moodley, S., & Ndlovu, S. (2025). Optimizing Biogenic Cyanide Production Using Indigenous Cyanogenic Microorganisms for Bioleaching of Precious Metals. Journal of Sustainable Metallurgy. doi:10.1007/s40831-025-01110-6
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  The present study investigated and optimized biogenic cyanide (bio-CN) production by using mine indigenous bacterial strains with the aim of extracting precious metals from Upper Group Two (UG-2) platinum group metals (PGM) ore. Among all the bacterial strains tested, under optimized conditions, Pseudomonas brassicacearum produced the highest bio-CN (14.1 ± 1 mg/L) and was therefore used in subsequent experiments. The study examined glycine consumption during cyanogenesis, as well as the stability and speciation of bio-CN. The findings confirmed that while glycine was consumed during cyanogenesis, the produced bio-CN was not stable and decreased over time, transforming into different cyanide species. The dose–response analysis for P. brassicacearum showed EC50 of 1785 g/L and 107.9 g/L against untreated and pre-treated PGM concentrate, respectively, suggesting higher toxicity for the latter. Two-step bioleaching of the pre-treated PGM concentrate showed extractions of 75.7, 18.7, 9.4, and 0.3% for Au, Pd, Rh, and Pt, respectively, at 10 g/L pulp density. The findings on bio-cyanide stability and bio-CN speciation presented in this paper are novel contributions. This study has established a foundation for developing a complete bio-based approach to PGM bioprocessing from UG-2 ores.
• Notole, V., Nwaila, G. T., Safari, M., & Ndlovu, S. (2025). Investigating mineral composition of PGE low-grade ore in Bushveld igneous complex, South Africa. Minerals Engineering, 234(Issue). doi:10.1016/j.mineng.2025.109682
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  The mineralogically complex and low-grade ores from the 2.055 Ga Bushveld Igneous Complex (BIC) require extensive characterisation prior to beneficiation. This study integrates multi-complementary mineralogical instruments to systematically characterise Merensky Reef drill core; validates hyperspectral imaging (HSI) and portable X-ray Fluorescence (pXRF) data against reputable methods for real-time, high-throughput ore characterisation. We further evaluate the potential of pXRF in identifying high-grade platinum group elements (PGEs) zones using base metals as geochemical proxies. The HSI results using long-wave infrared, indicate that the ore predominantly comprises pyroxene (i.e., with orthopyroxene dominant over clinopyroxene), plagioclase (i.e., anorthite), olivine, and minor quartz, along with alteration minerals such as serpentine, prehnite, amphibole, talc, chlorite, and epidote. The pXRF geochemical data reveal variations in base metals with drill core depth; with higher base metal concentrations in noritic rocks compared to anorthosite. The results suggest that pXRF can be used as a tool to predict PGE high-grade zones within the drill core (with base metals as proxies). X-ray diffraction (XRD) and TESCAN Integrated Mineral Analyzer (TIMA) results confirm that the ore primarily comprises pyroxene, plagioclase, alteration minerals and base metal sulphides (BMS). The dominant BMS phases in the core samples are pentlandite, chalcopyrite, and pyrrhotite, with similar bulk mineralogical assemblages. These BMS minerals are well liberated and fine-grained, with over 40 wt% having equivalent circular diameters (ECD) between 10–38 µm. Mineral Liberation Analyzer analysis further supports these results. PGEs are primarily associated with BMS attached to silicates. The primary modes of occurrence for PGEs in the ore include PtBiTe, PtFe, PtS, and PtPdS. Most identified PGEs are fine grained with ECDs ranging between 0.6–10.97 µm. Very few PGE grains are >10.97 µm. The integration of rapid data acquisition techniques (HSI and pXRF) with automated mineralogy provides a reliable, near real-time approach for ore characterisation enabling strategic ore blending and selection of suitable processing routes. This multi-technique approach holds significant potential for improving mineral characterisation accuracy, advancing geometallurgical applications, beneficiation processes and ultimately offering a low-cost efficient pathway for selective mining.
• Shemi, A., Ndlovu, S., & Sacks, N. (2025). An optimized recovery of cobalt and tungsten carbide (WC) from a binary-phase WC-6 wt%Co cemented tungsten carbide hardmetal using design of experiments. Minerals Engineering, 233(Issue). doi:10.1016/j.mineng.2025.109597
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  Tungsten extraction from scheelite and wolframite ores is a well-established process. However, continuous exploitation has led to more complex ore compositions and lower WO3 concentrations in tungsten concentrates, posing significant challenges for sustainable extraction. Primary and secondary tungsten sources often contain valuable metals such as Sn, Ta, Nb, Mo, Sc, and Co; however, current industrial processes focus predominantly on tungsten recovery, neglecting other metals and compromising sustainability. This study aimed to develop a process for the co-recovery of tungsten carbide (WC), cobalt (Co), and tungsten (W) from cemented carbide scrap using a sulphate-based leaching system. A statistical Design Of Experiments (DOE) approach was employed to screen and optimize process variables, including acid concentration, leaching time, solid-to-liquid ratio, temperature, and agitation rate. Characterization revealed the material contained 85.95 wt% W, 8.77 wt% C, and 5.28 wt% Co. Optimal leaching occurred with 2 M H2SO4, a 1:10 S/L ratio, at 82 °C, and 750 rpm agitation, achieving 25.13 % Co extraction in 10 h and 97.6 % after 4.2 days. Increasing the temperature to 92 °C improved extraction, reaching 31.7 % in 10 h. Temperature was identified as the primary factor influencing cobalt dissolution kinetics. The recovered WC powder consisted of well-defined, fine particles comparable in quality to ‘virgin’ WC. Electroplated cobalt achieved 91.9 % current efficiency over 3 h, producing metal with 98.0 wt% purity and good morphological integrity. Synthetic tests confirmed that tungsten recovery as scheelite (CaWO4) is highly feasible.
• Vilakazi, A. Q., Shemi, A., & Ndlovu, S. (2025). Dry Magnetic Separation and the Leaching Behaviour of Aluminium, Iron, Titanium, and Selected Rare Earth Elements (REEs) from Coal Fly Ash. Minerals, 15(Issue 2). doi:10.3390/min15020119
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  Coal fly ash (CFA) is a commercially viable source of alumina comparable to traditional bauxite deposits. Due to its high silica content and alumina in the refractory mullite phase, the most suitable processing technique is the sinter-H2SO4 leach process. However, this process is energy-intensive, has low selectivity for Al, and generates a secondary solid waste residue. To develop a sustainable process that is economically attractive, Al can be extracted with REEs, Ti, and Fe as saleable products, while secondary solid waste is regenerated for further applications to achieve high-value and high-volume utilisation of CFA. This study focused on the potential extraction of selected REEs (Ce, La, Nd, Y, and Sc), Al, Ti, and Fe, using dry magnetic separation and the sinter-H2SO4 leach process. XRD analysis showed that CFA is predominantly amorphous with crystalline mullite, quartz, and magnetite/hematite. Further analysis using SEM-EDS and TIMA showed Al-Si-rich grains as the predominant phase, with discrete REE-bearing grains (phosphates and silicates) and Fe-oxide (magnetite/hematite) grains. Traces of REEs, Ti, Ca, Si, and Fe were also found in the Al-Si-rich grains. Discrete Fe-oxide was recovered using dry magnetic separation, and up to 65.9% Fe was recovered at 1.05 T as the magnetic fraction (MF). The non-magnetic fraction (non-MF) containing quartz, mullite, and amorphous phase was further processed for preliminary leaching studies. The leaching behaviour of Al, Ti, Fe, and the selected REEs was investigated using the direct H2SO4 and sinter-H2SO4 leaching processes. The maximum extraction efficiency was observed using the sinter-H2SO4 leach process at 6 M H2SO4, a 1:5 solid-to-liquid ratio, 70 °C, and a residence time of 10 h, yielding 77.9% Al, 62.1% Fe, 52.3% Ti, and 56.7% Sc extractions. The extraction efficiencies for Ce, La, Nd, and Y were relatively lower at 23.2%, 27.6%, 11.3%, and 11.2%, respectively. Overall, the results demonstrate that the extraction of REEs using the sinter-H2SO4 leach process is strongly influenced by the complex CFA phase composition and the possible formation of insoluble calcium sulphates. Appreciable extraction of Al, Fe, Ti, and Sc was also observed, suggesting a potential two-step leaching process for the extraction of REEs as a feasible option for the industrial recovery of multiple saleable products.