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By M. I. Mabala, B. P. Watson, M. J. Kanda

A failed and stable Upper Group 2 chromitite pillar database was collected in 2007 as part of the PlatMine 1.2 pillar strength project. The database consisted of 177 pillars, of which 33 had failed. Most of the data were collected from various intermediate-depth mines near the town of Thabazimbi. Spans between rows of chain pillars were about 30 m. Pillar loads were estimated using pseudo-3D, elastic, boundary element modelling software. The pillar-load data were evaluated using a maximum likelihood regression analysis to determine strength parameters, following a similar approach to historically acceptable practice. The original formula was named the PlatMine Formula. This paper describes re-evaluations of the database, using a linear formula and several variations of the power formula. The formula providing the lowest standard deviation to the data in the database was considered the best representation of the pillars in the database. Through this rigorous process, a new formula for peak pillar strength was developed for Upper Group 2 chromitite pillars, which is unaffected by volume. The small standard deviation provided by this formula suggests a reliable relationship between strength and w/h ratio, in the w/h ratio range between 1.5 and 4.7. Accuracy, precision, and recall analysis confirmed the efficacy of this equation to the data in the database. Importantly, the new formula provided in the paper does not predict a significantly different strength to the current PlatMine formula, within the confines of the database.

Nov 27, 2024

By J. Hadjigeorgiou, G. Knox

Since their introduction in 2010, paddled energy-absorbing rockbolts have been widely used in seismically active hard rock mines. This paper provides new data and reviews previous work to quantify the performance of paddled energy-absorbing rockbolts under controlled laboratory conditions. Of significance is the realization that the typical split location in impact tests, at the centre between two paddle anchor points can at best provide an upper limit value. This inherent variability in performance under different testing configurations should be acknowledged and taken into consideration in the design of ground support in seismic conditions. This paper discusses the reduction in capacity of paddled rockbolts as a function of loading angle from a maximum value during axial tests (0° loading angle) to the lowest value during pure shear (loading angle of 90°). A significant reduction in displacement capacity is observed as the loading angle changes between axial (0°) and 40°. Beyond a 40° loading angle up to shear (90°) loading the reduction in displacement capacity is less significant. Due to the variances in the capacity observed through the variance of the testing configuration: loading mechanism, direction of loading, location / presence of a discontinuity, it must be recognized that results from laboratory-based testing are not independent of the testing configuration. This should be acknowledged when extrapolating anticipated performance in the field.

Oct 9, 2024

By R. P. King

Held on the 22nd March 1972 at Kelvin House. Four papers were presented at this colloquium, which was attended by approximately 120 people. The first paper, 'Flotation Research Work at the N.I.M. research group, University of Natal on the modelling of a Flotation Process' was presented by Dr R. P. King, the leader of the N.I.M. Research Group in the Department of Chemical Engineering at the University of Natal. A discussion panel, under the chairmanship of Dr R. E. Robinson with Mr M. Dawson (PMC), Mr E. Roux (FOSKOR), and Dr B. K. Loveday (NIM), discussed the potential application of the theoretical work on flotation modelling to industrial processes, and alternative approaches to providing a way of control of flotation plants. The second paper, 'Fundamental Studies of the Flotation Process the Work of the National Institute) for Metallurgy', was presented by Dr N. P. Finkelstein. The discussion panel for this paper was under the chairmanship of Professor D. D. Howat,and had as its members Mr H. P. Carlisle (JCI), Professor D. le Roux (University of Pretoria), and Mr E. Rudolph (Anglo American Research Laboratories). A lively discussion on this paper ensued, with several contributions from the floor. After lunch, Mr S. K. de Kok, Assistant Consulting Metallurgist, Anglo Vaal, presented a paper on 'The Flotation of Copper and Zinc Sulphide from Prieska Ore'. The paper was discussed by a panel comprising Dr V. C. Lovell (NIM), Mr A. Gilbert (General Mining), and Dr D. Legge (Anglo Vaal), under the chairmanship of Dr L. Bushell. This discussion, in which many members of the audience participated, revolved around the difficulties associated with the production of copper and zinc concentrates and the lack of fundamental information on the behaviour of copper and zinc sulphides in flotation. The final presentati0n was a paper, 'The Recovery by Flotation of Cassiterite contained in Gravity Concentration Plant Tailings', presented by Mr E. B. Viljoen (Metallurgy Department, Goldfields South Africa Limited). The discussion, led by a panel consisting of Mr O. Tant (Goldfields Laboratories), Mr J. Levin (NIM), and Mr R. I. Shanks (NIM), under the chairmanship of Mr H. Cross (Goldfields South Africa Limited) referred particularly to the use of new reagents for the flotation of tin, with particular emphasis on the fundamental relationship between reagent composition and its ability to float this type of mineral.

Jan 4, 1972

By K. Naidoo, M. Pelser, J. Hagemann, K. C. Sole

The copper tankhouse at Rustenburg Base Metals Refinery is an essential component of the Anglo American Platinum value chain. The tankhouse uses starter-sheet technology that was adopted in the 1980s, so dependence on manually intensive labour and overall operational excellence has a significant impact on process performance. An efficient, stable, and sustainable electrowinning process contributes to minimising energy consumption and reducing operational costs, and enables improved product quality and increased throughput. Historic performance of this tankhouse has often been suboptimum over prolonged periods. An in-depth operational review of performance from 2018–2024 was carried out to understand challenges, risks, and high-impact factors that contribute to poor performance. Implementation of adherence to fundamental operational basics identified from global best practice, such as the frequency and quality of cell cleaning and maintenance, preventing backlogged harvesting or maintenance, preserving cell-top furniture conditions and integrity of electrodes, preventing short circuits and poor current distribution, and maintaining a high level of operational discipline, has since contributed to an era of exceptional performance. Root-cause analysis fault trees pertaining to poor current efficiency and high scrap rate are summarised. Current efficiency has significantly improved since 2021, now consistently exceeding 88%. The copper scrap rate, previously believed to be limited to a minimum of 4%, achieved a historic monthly low record of 2.06% in 2023. Chemical and physical quality has considerably improved, and cathodes exhibit minimal morphological defects.

Jun 27, 2025

By A. Mainza, I. Govender, Elbasher M. E. Ahmed

A mechanistic description of axial segregation in rotating drum flows remains an open question. Consequently, optimal mixing of grinding balls and rocks for efficient breakage, maximum production of fines, and slurry transport is seldom achieved. Experimental and numerical studies of granular mixtures in rotating drums identify alternating axial bands that eventually coarsen in the long-term limit. Most models of axial segregation are limited to binary mixtures and cannot always predict the logarithmic coarsening effects observed experimentally. A key missing factor is a robust description of the axial free surface profile that is valid across a wide range of flow regimes. We present a practical model of the axial free surface profile by linking it to readily-derived geometric features of the cross-sectional S-shaped free surface profile. A parametric study shows good agreement with experimental measurements reported in the literature and heuristically valid trends.

May 1, 2021

By B. Mbuya, A. F. Mulaba-Bafubianda, J. M. Mvita

The paper explains the main effects of input leaching parameters, such as addition of a reducing agent, acidity, agitation, temperature, and leaching system potential, in relation to observed and predicted yields of sought-after cobalt. An artificial neural network coupled with graphical probability networks was developed wherein the abovementioned input parameters were used to predict the percentage of dissolved cobalt. Furthermore, similarities and differences between the Bayesian and neural network approaches in terms of their key outcomes are compared with respect to study of the dissolution of cobalt in sulfuric acid. Key results indicate that there is a need to use neural network results to predict conditions for dissolution of cobalt, while using Bayesian network to explain inferences about conditions of the input parameters, thereby achieving realistic predictions.

Jan 1, 2023

VERSLAG- REPORT No. 1365 STUDIES OF INCIPIENT FUSION IN THE SYSTEM CHROMITE- MgO- Al2O3-SiO2-C 5th January, 1972 Investigator: N. A. Barcza SYNOPSIS A fundamental study was made of twelve chromite ores by use of a thermobalance under atmospheric and reducing conditions. It was found that their thermal behaviour under atmospheric conditions can be related to the mineralogical composition of the chromite spinel and the gangue. The overall mechanism of reduction with solid carbon over the temperature range of 1 200 to 1 500°C was shown to be diffusion of carbon through the reaction product. The effects of additions of fluxes and variations in particle size on the kinetics and mechanism of reduction were determined. It was shown that carbon monoxide does not reduce chromite ore up to temperatures of 1 550 °C, and it can therefore be eliminated as the diffusing reducing species. However, the reaction product of reduction, namely a mixed carbide of iron and chromium, was shown to be an effective reducing agent for chromitc ore, while also facilitating the transport of carbon. VERSLAG - REPORT No. 1380 AN ELECTROCHEMICAL MODEL FOR THE LEACHING OF URANIUM DIOXIDE 10th January, 1972 Investigators: C. R. S. Needes, M. J. Nicol SYNOPSIS A correlation between the rate of leaching of UO2 and the electrochemical properties of the oxidant concerned has been derived. This correlation is found to be borne out by experimental results. Certain effects observed in UO2 leaching and hitherto unexplained have been clarified in terms of an electrochemical mechanism. Experiments have shown that the mixed potential of a UO2 electrode gives a measure of the rate of dissolution of UO2. Its significance to commercial practice is discussed. CONCLUSIONS (I) The dissolution of UO2 in the presence of a number of oxidants can be explained in terms of an electrochemical mechanism. (2) The mixed potential of the UO2 electrode is a measure of the rate of UO2 leaching. This principle could be used in the control of industrial leaching operations. (3) A simple treatment has provided a mathematical basis for a fundamental correlation between the rate of U02 dissolution and the chemical properties of the oxidants concerned. This relation has been found to agree well with experimental results. (4) A number of phenomena occurring during the leaching of UO2, hitherto not explained in a satisfactory manner, have now been clarified in terms of an electrochemical mechanism.

By D. R. Young

Drilling exploration over the Wesizwe Platinum Limited?s Pilanesberg Project has identified the Merensky Reef at depths varying from 594 m to 1 552 m depth. Merensky Reef thickness varies from 0.05 m to 3.63 m and contains PGE(4) mineralization above a cut-off grade of 1.0 g/t over intersection widths of 0.95 m to 2.63 m. Four distinct facies types have been identified over the property, viz.1) Normal Merensky Reef, generally 1.2 m thick, bounded by thin top and basal chromitite layers and composed of upper feldspathic pyroxenite and lower feldspathic olivine pegmatoids containing base metal sulphide mineralization overlying poikilitic anorthosites. 2) Single chromitite Merensky Reef, generally0.15 m thick and usually devoid of internal silicate material, overlying variable stratigraphy containing significant base metal sulphide mineralization. 3) Detached Merensky Reef, generally1.0 m thick, bounded by thin top and basal chromitite layers and composed of feldspathic pyroxenite or pyroxenite containing base metal sulphide mineralization overlying Merensky Pyroxenite. 4) Normal footwall Merensky Reef, generally 1.8 m thick, bounded by thin top and basal chromitite layers and composed of feldspathic pyroxenite containing base metal sulphide mineralization overlying norites also containing significant base metal sulphide mineralization. The PGE(4) content?s (g/m2) distribution for the global intersection data appears to be lognormal, and conversion to lognormal space produces a near normal distribution which could be interpreted as a compound lognormal distribution. The mean PGE(4) contents estimated by these three different distributions are the same, and thus do not impact on the contained metal. Data for the Normal Merensky Reef facies type are sufficient to indicate that a normal distribution is followed for this facies type, and therefore does not need to be transformed to log space for estimation of the mean and the 90% confidence limits. A global evaluation based on all of the data is compared with a facies-weighted evaluation. The latter method is noted to provide a better definition of the associated estimation errors and thus potential classification of Mineral Resources. A valuation of $20.95 for Inferred and $41.90 for Indicated PGE(4) ounces is applied to both of the evaluations and compared. The global evaluation is considered to over-value the project by approximately 40%, thus indicating that valuations based on global summary sampling data that have a compound distribution may be materially flawed, and that cognizance of the underlying geology is crucial for unbiased valuation.

Jan 1, 2006

By L. Kühnel, H. Lieberwirth

Confined bed comminution in High Pressure Grinding Rollers (HPGR) and Vertical Roller Mills (VRM) is gaining substantial attention in many applications. Previously used mainly for milling coal or construction materials, HPGR and VRM have started to complement or even replace tumbling mills in ore beneficiation. Materials like coal or clinker are relatively homogenous, however, in comparison to metal ores and wall rocks. This characteristic poses a new challenge to the confined bed comminution but also an opportunity. Fuerstenau and Abouzeid have investigated the selectivity in comminution of a mixture of particles of different strength in a particle bed. The median particle size and particle size distribution (PSD) of the two constituents used were kept constant. Only the proportion of the two constituents was modified. The competence of a material is, however, also a function of particle size. Smaller particles tend to be more competent than larger ones of the same material. If selective comminution is applied on ores, this size influence has to be understood. The paper presents research results on this topic based on experimental investigations with model materials as well as with natural particles, which were stressed in a piston-die press. It appeared that the comminution result depends substantially on the material characteristics and the composition of the mixture. Conclusions will be drawn for the application in future applications of selective comminution in mineral processing. Keywords: Confined bed comminution, HPGR, VRM, piston die press, particle size

Jan 1, 2020

By V. Moodley

Strict implementation of International Standards for representative sampling of coal is difficult for routine monitoring, due to time, technical, and economic constraints. A large percentage of the total sampling variance arises from errors accumulated during the earliest stages of sample collection. Modified procedures on the precision of the final result leads to controversies between the sellers and customers for coal. Manual collection of coal samples violates the principle of correct sampling, that all fragments must have an equiprobable chance of being in the sample. In addition, manual size reduction of large numbers of samples is time consuming and involves human errors. A coal quality management procedure in alignment with the relevant ISO standards that describes the sampling protocol has been implemented, and current sampling and laboratory analysis of coal from base load mines (mines situated at the mouth of the power station) are well established. For import coal, sampling is performed during unloading by auto-mechanical sampling (AMS). Due to logistical and safety issues associated with multiple suppliers, Eskom opted for the coal to be sampled at source on a pre-certification basis. Online analysers provide a fast, accurate, real-time method of determining the total moisture and elemental composition of coal and is important to the coal industry for pricing, quality control, and reduction of SO2 emissions. Elemental analyses include S, Si, Al, Fe, Ca, Na, Mg, Mn, Ti, K and Cl. Measurement of S is dictated by the control of SO2 emissions from coal-fired power plants. Elements such as Na and Cl have adverse effects on boilers, causing fouling and slagging. Available online elemental analyser technologies include prompt gamma neutron activation analyses (PGNAA), recommended for major element determination, and pulsed fast and thermal neutron analysis(PFTNA), that is capable of measuring the major and minor chemical elements contained in coal. These systems utilize nuclear reactions to produce characteristic gamma rays that are used for identifying various chemical elements. By acquiring the gamma rays in three different time windows, there is a significant reduction of the background as compared with the spectra taken with a radio isotopic source.

Jan 1, 2009

By M. Weir, J. R. Cutland, L A. J. Pronk van Hoogeveen

"A computer system for the design of open pits to mine stratiform orebodies has been developed for use at Nchanga Consolidated Copper Mines, Ltd. The particular requirements of such a system, for example, the accuracy of representation of geological detail and the ability to follow footwalls, arc described in this paper, together with the methods that have been adopted to satisfy them.A modified version of the Open Pit Design Program of Rio Tinto Zinc Consultants, Ltd. is incorporated in the system and the geological data are converted into a form usable by the computer by means of a pencil follower. Some of the uses which have been made of the system are described, with reference to the long- and medium-term planning of the Nchanga Open Pit, the major producing pit at Chingola Division."

Jan 1, 2014

By J. Pelders, F. Magweregwede, S. M. Rupprecht

Increased depths of conventional gold and platinum mines, longer travelling times as working places move further from the shaft, and ancillary activities taking place in the mining cycle reduce the useable time spent at them workface. Current shift lengths of 8 hours 20 minutes may no longer be adequate ton complete required mining activities.The impact of mineworker commuting times on shift work is also not well understood. The aim of this research was to draft a framework to optimize shift cycles in order to maximize productivity, health, safety, and wellness in the South African mining sector. The framework was informed by a review of the literature, case studies at a local gold mine and platinum mine, and a workshop with industry experts. The findings indicate potential advantages of extended shift lengths and continuous operations, such as improved productivity, asset utilization, and employee morale. However, concerns included fatigue and the associated safety hazards, particularly when working longer shifts, night shifts, and numerous consecutive shifts. Job demands, personal factors, and commuting times are further considerations when scheduling shifts. The ideal shift system for the mining sector should holistically consider and balance operational requirements, health and safety, and employees’ and their families’ requirements, and suit the unique needs of each operation. Changes in shift cycles will require a structured change management process, which involves all stakeholders, and could help to enhance the viability of the South African mining sector.

Aug 1, 2021

By J. Bullón, A. Pérez

Some years ago, Ferroatlantica developed a new type of electrode known as the ELSA electrode. In this electrode there is a central graphite core that provides support, surrounded by an annulus of Søderberg paste that gets baked during operation. This technology has been implemented on several silicon furnaces around the world, and was reported on during the previous Infacon conference. In all electrodes, but particularly in the ELSA electrode, the quality and consistency of the paste are important for correct operation. As the type of paste varies between customers and between countries, Ferroatlantica has developed a quality control procedure for their customers of this technology. This procedure is geared to the point of view of the customer rather than the paste producer. The analysis is based on the desired flow pattern of the raw paste and on the desired mechanical and electrical properties of the baked paste, as experience has shown that these are the most important parameters to monitor in order to avoid having problems with the resulting electrodes. This paper discusses these methods of paste analysis in the light of complementary studies that have been done when there has been an electrode breakage in the different plants.

Jan 1, 2007

By M. Asghari, R. Amiri, A. Haratian, S. Haji

The aim of this investigation is the evaluation of optimising the Shahroud copper ore beneficiation plant near the Iranian city of Shahroud, by means of a sensor-based ore sorter applying X-ray transmission technology. Currently, this plant’s feed capacity of 52t/h produces 0.5t/h copper concentrate with a grade of 30% and copper recovery of 85% from a feed grade of 0.36%. By applying an X-ray transmission-based (XRT) sorter, it is possible to preconcentrate the feed and remove the gangue materials before entering the plant, enabling the production rate of concentrate to be increased. In this study, the obtained representative sample from the plant was preconcentrated in particle size of - 75+10mm by using the X-ray sorter, thus the concentrate with Cu grade of 0.85% was obtained. Therefore, by using of X-ray sorter the Cu grade of plant feed was increased to 0.48%. By increasing the feed grade from 0.36% to 0.48%, and considering a Cu recovery of 85%, the production rate will be increased from 0.48t/h to 0.61t/h. Therefore, the preconcentration by using the XRT sorter increases the production rate by 27%. Keywords: Optimisation, preconcentration, copper, X-ray, sensor-based ore sorting

Jan 1, 2020

By D. Orynbassar, N. Madani

This work addresses the problem of geostatistical simulation of cross-correlated variables by factorization approaches in the case when the sampling pattern is unequal. A solution is presented, based on a Co-Gibbs sampler algorithm, by which the missing values can be imputed. In this algorithm, a heterotopic simple cokriging approach is introduced to take into account the cross-dependency of the undersampled variable with the secondary variable that is more available over the entire region. A real gold deposit is employed to test the algorithm. The imputation results are compared with other Gibbs sampler techniques for which simple cokriging and simple kriging are used. The results show that heterotopic simple cokriging outperforms the other two techniques. The imputed values are then employed for the purpose of resource estimation by using principal component analysis (PCA) as a factorization technique, and the output compared with traditional factorization approaches where the heterotopic part of the data is removed. Comparison of the results of these two techniques shows that the latter leads to substantial losses of important information in the case of an unequal sampling pattern, while the former is capable of reproducing better recovery functions.

Aug 1, 2021

By K. Muchima, C. Siame, L. Little, B. Kaputula, Q. Mclennan

"The variability of copper mineralization at Kansanshi mine significantly affects the efficiencies of the processes used to recover copper. Quantifying this variability is therefore essential for monitoring and optimizing the performance of the concentrator, which comprises three different flotation circuits (sulphide, mixed, and oxide) and an atmospheric leach circuit. Onsite automated scanning electron microscopy with energy-dispersive X-ray spectrometry (Auto-SEM-EDS) is used to analyse routine weekly composite samples for each circuit, providing detailed analyses of bulk mineralogy, copper deportment to different minerals, mineral liberation, and associations. Weekly mineralogical trends are used to assess changes in process performance, and characterization of the copper losses has inspired a number of projects to target the specific particle types responsible for the main losses. In this paper we describe the relationship between mineralogy and plant performance at Kansanshi, and discus IntroductionKansanshi is a copper and gold mine located in the Northwestern Province of Zambia, with an annual production in the region of 250 000 t of copper and 160 000 ounces of gold. Ore mined from the epigenetic vein-hosted deposit is classified into three ore types based on the extent of oxidation and supergene enrichment. Sulphide, oxide, and mixed ore are fed to separate mineral processing circuits tailored for recovery of the dominant copper minerals in each. After comminution to a target grind size of 80% passing 150 µm, each ore type is subjected to flotation to recover the copper sulphide minerals (chalcopyrite, bornite, chalcocite, covellite). The oxide float tails and a large proportion of the mixed float tails are then treated by atmospheric leaching to extract copper from the remaining copper-hosting minerals, which include cuprite, malachite, chrysocolla, and delafossite. Some native copper is recovered by flotation and some of it is recovered by leaching. A small portion of the combined concentrate from all circuits is subjected to high-pressure leaching and the rest is sent to the smelter. Sulphuric acid produced during smelting is used for the atmospheric leach."

Nov 1, 2018

The compilation of the sampling nomogram is an essential tool in the optimization of a sampling protocol and allows the operator to track the change in relative variance of the sampling error (the Fundamental Sampling Error) during steps of comminution and mass reduction in the process of recovery of the aliquot for analysis. The data required for the compilation of the nomogram are centered on the sampling constant K and the exponent, alpha (a), of the nominal fragment size. Five methods for establishing K have been identified, but two of them, the duplicate sampling analysis (DSA) method and the heterogeneity test (HT) method purport to provide such a constant. The step by step procedure for each of these two methods was examined using broken ores from three mines, Mponeng mine, Kloof mine and Lily mine. Two of these mines (Mponengand Kloof) are typical Witwatersrand-type gold mines, while the third is an Archaean-type, shear related gold deposit situated in the Barberton Greenstone belt. The results suggest that the factor K derived using the heterogeneity test is very accurate, but applies only to a single size fraction in the spectrum of comminuted materials. The calculation of gold grain sizes using this method appears to be too small and does not conform with the results from detailed mineralogical studies. The factors K and alpha derived using the duplicate series analysis, are appropriate for use across a wide spectrum of comminution sizes and also provide realistic gold grain sizes, comparable with the equivalent circular diameter of gold grains identified in mineralogical studies of the ores.

Jan 1, 2009

By K. C. Naidoo

There are two main types of densifying cyclones currently available in the market, namely polyeurethane (PU) and ceramic. The PU densifying cyclones are currently used throughout the Grootegeluk complex and coal beneficiation in general. It has been identified that PU densifiers wear relatively fast depending on the operating pressure and need to be replaced frequently as a result. The motivation for this paper is to achieve an increase in the densifying cyclone lifetime through less wear and an increase in efficiency resulting in the ability to build higher relative densities (RD) more quickly. This will allow for a reduction in downtimes due to replacing densifying cyclones as well as building RD and a reduction in the operating costs associated with replacing worn densifying cyclones. Some of the major findings of the study indicated that the ceramic cyclone theoretically undergoes less wear than the PU cyclone, but since wear is application-specific and was evaluated, the wear on the polyurethane cyclone was found to be minimal. The RD differential is higher on the PU cyclones than the ceramic cyclones, showing that the PU cyclones perform better in a densifying application. This is the first test conducted on this application and type of cyclones. It should therefore be noted that having the PU cyclone significantly outperform the ceramic cyclone was not expected, due to the only change being the material of construction. This is an indication to take the material of construction into account when selecting cyclones as it can have a significant impact on the cyclone performance in specific applications. Keywords: Ceramic, cyclone, densifying, density, dense medium, polyurethane, wear

Jan 1, 2020

By A. Drumond, J. F. C. L. Costa, M. G. Lemos, A. L. Rodrigues, F. G. Niquini

The past decade has seen a renewed possibility of using machine learning algorithms to solve a large collection of problems in several fields. Data acquisition for mining operations has increased with the growth in sensor-based technologies, and therefore the amount of information available for mining applications has dramatically increased. Ore sorting equipment is available for separating ore from waste based on differences in physical properties detected by a real-time analyser. The separation efficiency depends on the contrast in these properties. In this study we investigate the application of machine learning models trained using data from the output of a dual-energy X-ray ore sorting apparatus at a gold mine. The particles were first hand-sorted into ore and gangue classes based on their mineralogical composition. Classification models were then used to help decide the balance between the number of true and false positives for ore in the concentrate, with a view to economic parameters, using their receiver operator characteristic (ROC) curves. The results showed AUC (area under the ROC curve) scores of up to 0.85 for the classification models and a maximum reward condition Fpr/Tpr around 0.5/0.9 for a simplified economic model.

Aug 8, 2024

By B. S. Agbenuvor, R. Morrison, V. Jokovic, C. Antonio

Body breakage usually involves breakage of particles by compression between two surfaces or impacted against a rigid surface, with the latter of interest in this current study. This mode of breakage has been identified to be the most elementary size reduction process and the most effective breakage process in comminution devices. It has been found in the literature that the progenies produced from this form of breakage possess a residual velocity at which they move, after the breakage event. In the pursuit of efficiently utilising applied comminution energy, a laboratory-scale breakage device has been developed to deliver precise specific impact breakage using the concept of a fast-moving hammer and a slow-moving particle to effect breakage. The residual velocities of the progenies from the breakage event may be used to generate secondary breakage without further addition of energy if the particle encounters a stiff obstacle such as a steel plate at right angles to its path. To measure the extent of secondary breakage, the steel wall of the device was lined with a rubber material to suppress the second set of breakage events. The performance of the new device is analysed, based on calculated t10 values and measured residual velocities of the moving daughter particles. Testing involving anvils showed a much finer PSD and higher t10 compared to the test involving rubber lining. This finding is corroborated by the measured residual velocities of the progenies. The resulting energies calculated from the measured residual velocities of the progeny were found to be approximately 42-88% of the primary specific impact energy. This retained energy was found to be sufficient for secondary breakage. Keywords: Impact breakage, residual velocity, secondary breakage, energy utilisation

Jan 1, 2020