A Predictive Geometallurgical Framework for Flotation Kinetics in Complexes Platinum Group Metal Orebodies: Mode of Occurrence-Based Modification of the Kelsall Model Using Particle Swarm Optimization Alain M. Kabemba, Kalenda Mutombo, Kristian E. Waters Minerals, 2025 Mineralogical variability exerts a profound influence on the flotation performance of Platinum Group Metal (PGM) ores, particularly those from the Platreef deposit, where complex associations and textures influence recovery, grade, and kinetics. This study integrates the Mode of Occurrence (MOC) and mineral associations into a modified Kelsall flotation kinetics model, optimized using a Particle Swarm Optimization (PSO) algorithm, to improve prediction accuracy. Batch flotation tests were conducted on eight samples from two lithologies—Pegmatoidal Feldspathic Pyroxenite (P-FPX) and Feldspathic Pyroxenite (FPX)—with mineralogical characterization performed using MLA, QEMSCAN, and XRD. PGMs in liberated (L) and sulfide-associated (SL) forms accounted for up to 90.6% (FPX1), exhibiting high fast-floating fractions (θf = 0.77–0.84) and fast flotation rate constants (Kf = 1.45–1.78 min−1). In contrast, PGMs locked in silicates (G class) showed suppressed kinetics (Kf < 0.09 min−1, Ks anomalies up to 8.67 min−1) and were associated with lower recovery (P-FPX3 = 83.25%) and increased model error (P-FPX4 = 57.3). FPX lithologies achieved the highest cumulative recovery (FPX4 = 90.35%) and the best concentrate grades (FPX3 = 116.5 g/t at 1 min), while P-FPX1 had the highest gold content (10.45%) and peak recovery (94.37%). Grade-recovery profiles showed steep declines after 7 min, particularly in slow-floating types (e.g., P-FPX2, FPX2), with fast-floating lithologies stabilizing above 85% recovery at 20 min. The model yielded R2 values above 0.97 across all samples. This validates the predictive power of MOC-integrated flotation kinetics for complex PGM ores and supports its application in geometallurgical plant design. Model limitations in capturing complex locked ore textures (SAG, G classes) highlight the need for reclassification based on floatability indices and further integration of machine learning methods.
Towards a Dynamic Optimisation of Comminution Circuit Under Geological Uncertainties Alain M. Kabemba, Kalenda Mutombo, Kristian E. Waters Processes, 2025 Geometallurgical programmes are crucial for designing mineral processing plants that maximise comminution throughput. However, the variability of complex ore bodies, such as platinum group element (PGE) deposits, poses challenges in developing these programmes into profitable mine-to-mill production. This paper investigates the geological characteristics of different lithologies hosting the complex PGE orebody located in the Northern Limb of the Bushveld igneous complex in South Africa and assessed their impact on metallurgical efficiency in comminution circuits. Regression machine learning techniques were employed to analyse the ore mineralogical dataset from two lithologies (feldspathic pyroxenite and pegmatoidal feldspathic pyroxenite) and predict the Bond Work Index (BWI), a key comminution parameter for calculating processing plant throughput. The results indicated that BWI is strongly influenced by Chlorite, silicates, iron oxides, and the relative density of the PGE deposit. Using both simulated and laboratory-measured throughput values, a particle swarm optimisation (PSO) algorithm was applied to maximise the plant’s comminution throughput through tactical blending of low-grade and high-grade ore stockpiles. The PSO algorithm was shown to be an effective tool for stockpile management and tactical mine-to-mill operation in response to feed mineralogical variability. This first-time innovative approach addresses complex geological uncertainties and lays the groundwork for future geometallurgical studies. Potential areas for further research include incorporating additional lithologies for tactical ore stockpile blending and optimising parameters critical for ore mineral flotation.
Comparative investigation and optimization of cutting tools performance during milling machining of titanium alloy (Ti6Al4V) using response surface methodology Solomon Ntshiniki Phokobye, Dawood Ahmed Desai, Isaac Tlhabadira, Emmanuel Rotimi Sadiku, Kalenda Mutombo International Journal of Advanced Manufacturing Technology, 2024 The purpose of this paper is to study the optimization of the cutting performance of three different cutting inserts, during the machining operation of titanium alloy (Ti6Al4V) by making use of the response surface methodology (RSM) on a computer numerical control (CNC) milling. The cutting tools employed for the optimisation of the cutting performance during machining operation are silicon, aluminium, oxygen, nitrogen (SiAlON), cubic-boron nitride and carbide cutting inserts. Scanning electron microscope (SEM) was used for the determination of the tool wear for the cutting inserts being compared during machining of Ti6Al4V, and the cutting parameters, which are cutting speed (Vc), feed per tooth (fz) and depth-of-cut that were evaluated from the cutting tools as per the manufacturer’s design specifications. The determination of the tool wear on the cutting inserts was achieved by using the SEM, while the machining operation for the experimental trails was performed from the CNC milling machine, where face milling operation was executed. The optimization process showed that carbide cutting inserts yielded the best performing results and were considered the most significant choice of cutting insert in machining Ti6Al4V when compared to SiAlON and CBN cutting inserts. This choice was from the cutting tool life obtained where a cutting tool life of 29 min was obtained from a use of carbide cutting inserts; 28 min resulted from a use SiAlON cutting inserts and 26 min from a use of CBN cutting inserts. This work finds appropriate value in assisting the machinists in the selection of the best most performing and cost-effective cutting tool.
Tensile properties and microstructural characterization of additive manufactured, investment cast and wrought Ti6Al4V alloy K Beyl, K Mutombo, C P Kloppers Iop Conference Series Materials Science and Engineering, 2019 This paper presents an evaluation of the tensile properties and microstructural characterization of Ti6Al4V alloy manufactured with three different processing routes; traditional wrought processing, investment cast and Laser Engineered Net Shaping (LENS). Tensile specimens were machined from each process and tensile tested at room temperature. Fractured specimens were characterized using light optical microscopy, stereo microscopy, microhardness and Scanning Electron Microscopy (SEM) to investigate the microstructural morphology and the structural hardness variation. The investment cast Ti6Al4V alloy microstructure revealed large equiaxed grains containing various orientated lamellar colonies. The additive manufactured microstructure revealed long columnar grains with Widmanstatten α’ martensite laths and retained β grain boundaries. While the wrought Ti6Al4V microstructure was observed as smaller equiaxed grains with large colonies of fine lamellar and transformed β. Additive manufactured specimens had higher yield strength, ultimate tensile strength and hardness compared to the investment cast and wrought manufactured specimens.
Preparation and microstructural characterization of the 60Al-40V master alloy T O Mapoli, K A Annan, C W Siyasiya, Kalenda Mutombo Iop Conference Series Materials Science and Engineering, 2019 The present study focused on preparation and characterization of 60Al-40V master alloy which was produced via aluminothermic process. The study assessed the production in order to provide the optimum Al requirement for maximum recovery of the V. V2O5(Vanadium pentoxide) and Al metal were mixed in the proportion of producing 60Al-40V and Al2O3(slag) through an exothermic reaction. Microstructural analysis and phase identification were done using Optical Microscopy (OM), Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDX) and X-Ray Diffraction (XRD) analyses. The XRD revealed diffraction peaks mainly of the Al3V phase and some peaks of slightly homogenized Al8V5intermetallic compounds. The chemical composition was found to be 65 ± 0.03 and 35 ± 0.03 wt. % Al and V respectively. Good agreement between the experimental results and the predicted phases using Thermo-Calc. Software was observed.
Development of a biocompatible Ti-Nb alloy for orthopaedic applications L Fikeni, K A Annan, M Seerane, K Mutombo, R Machaka Iop Conference Series Materials Science and Engineering, 2019 Metallic biomedical implants such as titanium-based alloys are very useful for orthopaedic applications due to their excellent properties which responds to changes in temperature and other conditions. However, biological toxicity due to alloying elements and relatively high Young’s modulus or mechanical incompatibilities of previously used Ti alloys have necessitated the development of biocompatible alloys with compatible mechanical properties such as beta-titanium alloys. This study aims at production of beta-titanium alloy with enhanced properties by varying milling speeds. Ti and Nb powders were mechanically alloyed using the high energy ball-mill Zoz-Simoloyer® to produce Ti-7Nb alloys by varying the milling speed. The milling process produced irregular shaped powders with increasing particles sizes as the milling speed increased due to fragmentation and cold welding during agglomeration. The mechanical alloying process had good yield. The predominant phases of the inhomogeneously milled alloy were alpha and beta phases.
Alpha case formation mechanism in Ti-6Al-4V alloy investment castings using YFSZ shell moulds Journal of the Southern African Institute of Mining and Metallurgy, 2013
