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By C. Dorfling, M. Tadie, S. Grobbelaar

The physicochemical properties of the complex electrolytes used in direct copper electrowinning are an important consideration for the development of a high-fidelity model of the process. Direct electrowinning electrolytes typically contain a high background of metallic impurities. The effect of metallic ions on the properties and accompanying change in the limiting-current density for copper reduction have been the subject of several studies. Although various empirical correlations have been published for describing the physicochemical properties of electrowinning electrolytes, the correlations are only applicable to a limited range of conditions and cannot be extrapolated without further validation. Consequently, in this paper we validated existing physicochemical property correlations for the full range of operating conditions applicable to direct copper electrowinning and developed a new correlation for predicting the associated limitingcurrent density for copper deposition. Following, we evaluated the benefit of using the validated correlations as a component of a dynamic electrowinning model.

Jan 1, 2023

By L. Uotinen, M. Rinne, R. Mishra

Underground mining gives rise to geotechnical hazards. A formal geotechnical risk assessment can help to forecast and mitigate these hazards. Frequentist probability methods can be used when the hazard does not have many variables and a lot of data is available. However, often there is not enough data for probability distributions, such as in the case of new projects. The risk assessment is often subjective and qualitative, based on expert judgement. The purpose of this research is to present the use of Bayesian networks (BNs) as an alternative to existing risk assessment methods in underground mines by combining expert knowledge with data as it becomes available. Roof fall frequency forecasting using parameter learning is demonstrated with 1141 sets of roof fall data across 12 coal mines in the USA. The prediction is nearly identical for individual mines, but when multiple mines are evaluated it is difficult to find a single best fit distribution for annual roof fall frequency. The BN approach with TNormal distribution was twice as likely to fit the observed data compared to the Poisson distribution assumed in the past. A hybrid approach using BN combining multiple probability distribution curves from historical data to predict annual roof fall is proposed. The BN models can account for variability for multiple parameters without increasing the complexity of the calculation. BNs can work with varying amounts of data, which makes them a good tool for real-time risk assessment in mines.

Jun 1, 2021

By D. Kumar, B. Rai, S. G. Srinivasan, V. Jain

Chalcopyrite and pyrite are among the major gold bearing minerals in the world. The gold content in chalcopyrite and pyrite varies from 0.02 to 200 ppm and 0.01 to 20 ppm, respectively. Apart from gold, chalcopyrite is also the primary source of copper. Thus, the recovery of gold and copper are often associated with the recovery of chalcopyrite and pyrite. Flotation is one of the most successful methods applied to beneficiate chalcopyrite and pyrite. The success of a flotation process depends on an appropriate choice of the flotation collector used to achieve the desired selectivity. A thorough understanding of the atomic structure of the predominantly exposed mineral surfaces can immensely aid in developing highly selective collectors that can exploit both the physical and chemical characteristics of these surfaces. In the present study, density functional theory calculations within the plane wave framework are used to understand the surface structure and reconstruction of the most stable chalcopyrite (001), (100), (110) and (112) and most stable pyrite (100) surfaces. The chalcopyrite (001) and (100) metal-terminated surfaces undergo significant reconstruction and result in metal-metal bond formation in the sub-surface layer while the surface layer is replaced by S-atoms. On the other hand, the (001) and (100) S-terminated surfaces show S—S disulfide bond formation upon relaxation, which are consistent with literature reports. The chalcopyrite (110), (112) surfaces and pyrite (100) surface undergo rearrangement, but no reconstructions in terms of metal-metal or disulfide bond formation are observed on these surfaces. Keywords: DFT, surface reconstruction, pyrite, chalcopyrite, adsorption

Jan 1, 2020

By A. E. Lewis, J. Du Plessis, J. Chivavava

Current metallurgical processes lack selective and efficient REE recovery from aqueous leach liquors. Antisolvent crystallisation is used to selectively recover pure inorganic salts from aqueous solutions without excessive chemical use in ambient conditions. Yttrium sulfate octahydrate (Y2(SO4)3.8H2O) was used as a representative rare earth salt to investigate the effect of antisolvent selection on the crystal morphology and size distribution of the final crystalline product produced through antisolvent crystallisation. The antisolvents of choice were short length alcohols that are water miscible i.e. methanol, ethanol, 2-propanol and t-butanol. All experimental parameters except the type of antisolvent were kept constant under isothermal conditions. The large reduction in solubility of the salt by the antisolvent creates high supersaturations. This leads to high product yields as observed in this study at > 91%. In general, a variety of morphologies were successfully formed in each individual alcohol including; rods, plates, prismatic cubes and starburst clusters. The powder X-ray diffraction (XRD) analysis indicated that Y2(SO4)3.8H2O was the only species present for all final products. There was a change observed from the starburst and rod structures for the shorter alcohols towards prismatic cubes for the longer alcohols due to different strengths in the solute-antisolvent interaction at the crystal growth faces. The crystal sizes increased with an increase in the alcohol chain length because of the lower supersaturation conditions due to a limit in the mass transfer induced by the bulkier alcohol structure. In conclusion, it has been shown that the particle morphology and size can be greatly affected by the selection of antisolvent even under high supersaturation conditions, contributing to understanding the effect of different antisolvents on the final particle characteristics. The engineering of favoured product characteristics can therefore be achieved by antisolvent crystallisation, presenting a viable alternative process for the recovery of REE. Keywords: Antisolvent crystallisation, rare earth elements, morphology, particle size

Jan 1, 2020

By H. S. Sichel

This study deals with the development of some new theory concerning the bias which will result from the employment of the t-estimator if in fact the underlying distribution of ore values is not lognormal. It is found that the t-estimator is robust as long as the logarithmic variance is small and the shape factors of the transformed distribution are not unduly large. The choice of the threshold parameter [t] for the t-estimator is important, and some hints are given how to estimate it if the sample size is small, as en- countered in borehole valuation problems.

Jan 1, 1987

By A. Adeli, A. V. Metcalfe, E. Addo, E. Sepulveda

"The accurate modelling of geometallurgical data can significantly improve decision-making and help optimize mining operations. This case study compares models for predicting copper recovery from three indirect test measurements that are typically available, to avoid the cost of direct measurement of recovery. Geometallurgical data from 930 drill core samples, with an average length of 19 m, from an orebody in South America have been analysed. The data includes copper recovery and the results of three other tests: Bond mill index test; resistance to abrasion and breakage index; and semi-autogenous grinding power index test. A genetic algorithm is used to impute missing data at some locations so as to make use of all 930 samples. The distribution of the variables is modelled with D-vine copula and predictions of copper recovery are compared with those from regressions fitted by ordinary least squares and generalized least squares. The D-vine copula model had the least mean absolute error. IntroductionIn this paper we compare the use of D-vine copula, generalized least squares (GLS), and ordinary least squares (OLS) for modelling geometallurgical data from an orebody in South America. The first objective is to construct models for predicting copper recovery (Rec) from the Bond mill index test (BWi); resistance to abrasion and breakage index (A*b); and semi-autogenous grinding (SAG) power index test (Spi). This involves fitting a D-vine copula and regression models fitted by OLS and GLS. The second objective is to investigate the performance of the fitted models for predicting Rec (Willmott and Matsuura 2005).Traditional resource model approaches either ignore the mineral processing characteristics of extracted tonnages or treat processing as an independent component of a mining operation. The net present value (or any other objective) can be truly optimized only by considering the mining operation as an integrated system in which net value is defined as the end-product that the company sells. This approach requires the resource model to be extended to include all relevant rock properties and processing responses."

Mar 1, 2019

A manual on mines rescue, safety and gas detection, by J. Strang and P. Mackenzie-Wood. Australia, Austcue, US$25. (Available through Hampo Systems (Pty) Ltd. Reviewer: W. Holding. The book had its origins in a set of notes used by one of the authors for training purposes at the Southern Mines Rescue Station in New South Wales

Jan 1, 1987

By K. Barani, S. M. S. Ganji

Creatine was used as a lixiviant for gold dissolution from gold ore. The effects of creatine concentration, temperature, leach time, and pH were examined for their influence on extent of gold dissolution. The results show that at a temperature of 75°C and pH 11.5, gold dissolution increased from 51% to 88% on increasing creatine concentration from 25 to 50 g/t. Further increase in creatine concentration showed a negative effect on the gold dissolution. Gold dissolution increased from 47% to 87% by increasing the temperature from 25°C to 55°C, and from 61% to 89% by increasing pH from 10 to 11.5. Under the optimum conditions of solids’ content of 30%, pH 11.5, creatine concentration of 100 g/t, temperature of 75°C, and hydrogen peroxide addition of 2%, about 90% of the gold could be dissolved from the ore after 24 h. A comparison between creatine and cyanide leaching showed that 90% gold dissolution was achieved at a cyanide concentration of 300 g/t, which is three times higher than the creatine concentration under optimal conditions.

Apr 14, 2024

By Huanhuan SU, Jianqiang Zhang, Zhongyuan Liu, Junwei Ma

The high-sulfur bauxite in Henan Province was used as raw material. The grinding fineness, pH value and collector dosage on its desulfurization performance, and industrial flotation desulfurization process were studied. The best flotation desulfurization conditions were grinding fineness of 75%, pH of 8.5, and collector of 600 g/t. “One coarse, one cleaning and one sweep” closed-circuit flotation was established as the industrial flotation desulfurization process. After the closed circuit test, the sulfur content of aluminum concentrate with the yield of 93% was 0.23%, and the sulfur removal rate was 83.16%, and the sulfur content of tailings (sulfur concentrate) was 15.09%. Keywords：High-sulfur bauxite under coal mines, flotation, desulfurization

Jan 1, 2020

By Y. Yang, M. Zhang, X. Xia, S Shi, Z. Shen

A stepwise arrangement of flotation cells is the most common layout of a flotation circuit in the mineral processing industry. In such a design, slurry flows from upstream to downstream by means of gravity, and the middling products are returned to previous stages by pumps. This paper will introduce an alternative solution in which the forced-air and slurry-induced flotation cells are adopted so that all the flotation cells can be placed on the same horizontal platform and no pumps will be needed for middling product transferring. The technology of the forced-air and slurry-induced flotation cell will be described in detail, including unique features, the working principle and the related fundamental problems. The comparison of capital investment, operating cost and metallurgical performance will be made between the conventional stepwise arrangement and the samelevel arrangement technology based on industrial practice. Keywords: Forced-air and slurry-induced flotation cell, same-level arrangement, stepwise

Jan 1, 2020

By Q. Cui, B. Z. Zhou, Z. G. Song, Y. G. Zhu, G. B. Zheng

The complex refractory Cu-Pb-Zn polymetallic ore in Xinjiang, China is a massive sulphide ore with complex mineral components. In the past two years, the ore mineralogy has changed, resulting in a decline in metallurgy, with too much zinc reporting to the lead and copper concentrates. A detailed mineralogical study indicating the presence of secondary copper minerals, which could be activating the sphalerite early in the present circuit, was used to develop a novel reagent and flotation flowsheet termed “Pb-Cu co-flotation, Cu intensified flotation, Zn flotation”. It was tested and found to significantly contribute to improving the flotation performance of the ore. In the Pb-Cu co-flotation circuit, successful depression of pyrite and sphalerite was achieved using a BK612- Na2S based depressant system. Most of the galena and some of the Cu bearing minerals with excellent floatability were collected with the use of the selective collector BK906. The rest of Cu bearing minerals were floated in a copper Z200 circuit using a BK537-lime-zinc sulphate based depressant scheme. Zinc flotation from the copper tailing was performed in a SIBX circuit using lime as a pyrite depressant. Using the proposed flowsheet, overall Pb, Cu, and Zn recovery increased significantly to 88%, 87%, and 90% respectively. Keywords: Complex polymetallic ore, Cu-Pb-Zn, Pb-Cu co-flotation, particle size

Jan 1, 2020

By G. Chitiyo

Prediction of pothole characteristics is a challenging task, confronting production geologists at the platinum mines of the Bushveld Complex. The frequency, distribution, size, shape, severity and relationship (FDS3R) of potholes has a huge impact on mine planning and scheduling, and consequently cost. It is with this in mind that this study was initiated. Quantitative analysis of potholes indicates that pothole size (area covered) can be described by two partly overlapping lognormal distributions. These are referred to as Populations A (smaller) and B (larger). The range of observed pothole sizes conforms to a simple double exponential growth model based on Newton's Cooling Curve. A third size range of very large potholes (Population C) that could not be modelled properly within the proposed growth model is interpreted as to represent a very early phase of aggressive regional thermo-chemical erosion and potholing. In general, potholes are dominantly quasi circular with only a subordinate tendency of elongation. In the UG2, potholes with elongated forms are more prevalent in the size range between 20 and 500 m diameter. In the Merensky Reef elongated potholes are more common in the size range above 50 m in diameter. Although not distinctly visible, elongation of potholes in both the UG2 and the Merensky Reef show a net north/south orientation. Using shapes of pothole rims and floor areas, documented for the UG2 in the Waterval Shaft area, it is demonstrated that the northern, down-dip edges of potholes have steeper dips than the southern, up-dip edges. Spatial distribution studies using a uniform quadrant method suggest that in both the UG2 and the Merensky Reef, the potholes are randomly distributed, with a tendency towards clustering. Clustering appears to be more prevalent in the smaller Population A potholes. Bearing all findings in mind, it is found that the model of thermo-chemical erosion of the cumulus floor by new influxes of superheated magma best explains the observed data. Partial to complete melting of the cumulate floor occurred in three phases. The first represents the emplacement of hot magma. This magma, due to turbulent flow and high chemical and physical potential, aggressively attacks the existing floor (crystal mush on the magma/floor interface). Regional erosion is manifested by large, often coalescing potholes. During the second phase, when the magma emplacement process ceased and cooling in situ started, two distinct periods of pothole formation ensued. The first is related to rapid cooling along the relatively steep part of the Newton Cooling Curve, when Population B potholes nucleated randomly and grew rapidly with concurrent convective overturn and largely laminar flow condition. The second period of cooling occurred on the shallow-dipping part of the Newton Cooling Curve. Population A pothole growth became more subdued and nucleation appears to have been, at least locally, clustered. The final phase of this proposed 'super magma cycle' was introduced when chromitite crystallization and precipitation terminated pothole formation. This was followed sequentially by pyroxene and plagioclase crystallization to form the typical cyclic units of the Critical Zone. No suitable proxy could be found for the prediction of pothole density of potholes associated with the UG2 (likely due to limited spatial data coverage), and these are best predicted by extrapolation. The Merensky Reef slope index, in contrast, provides a proxy for pothole density, enabling prediction with reasonable confidence. This predictive model has been verified using underground information. The findings made during the course of this investigation have, when implemented, significant impact. Successful implementation will not only allow enhanced resource and reserve definition, but also better mine planning and scheduling.

Jan 1, 2008

By F. Hörtkorn, Y. Narainsamy

Rather quietly, a new generation of European norms dealing with earthworks has been developed over the past few years, in particular a part of EN 16907 pertaining to extractive waste. Whereas the majority of the parts deal with routine geotechnical aspects, one part deals specifically with tailings dams. The standard is currently in draft form but if this becomes a European Standard, members of the European Union are bound to comply with the regulations. As such, the standard has the capacity to influence mining in Europe and potentially in South Africa. In this paper we review the standard and compare it to the South African standard on mine residues and the recently published Global Industry Standard on Tailings Management (GISTM). We conclude found that although the European norm makes great strides towards increasing tailings dam safety, there is room for improvement. The current South African standard has served well since its inception, but can be improved by using concepts from the European and global tailings standards.

Jun 2, 2022

By P. F. Dicks, N. J. Shackleton, E. H. W. Theron, V. Malysiak

Flotation is a complex physical chemical process in which flotation reagents play a vital role in valuable minerals recovery and concentrate grades. This study examines the performance of new generation AECI Mining Chemicals (previously named Senmin) collectors. They were developed to enhance the valuable minerals recovery and flotation selectivity by tailoring the collectors to target specific valuable mineral species present in an ore and thus create added value for concentrators treating PGM ores. The case study was conducted on a Platreef ore, where batch flotation tests were performed and the concentrates were mineralogically characterised for PGE and BMS using QEMSCAN. Further batch flotation testwork was conducted on Merensky and UG2 ores from various localities in South Africa to confirm the trends observed for Platreef ore. The results have shown that there is a strong correlation between PGE mineral type and AECI Mining Chemicals collector type - clearly demonstrating that one reagent type does not fit all flotation applications. Keywords: Batch flotation, QEMSCAN, collectors, PGE and BMS

Jan 1, 2020

By M. Gomo, L. S. Mokhahlane

"Underground coal gasification (UCG) is an unconventional mining method that converts coal in situ into a fuel gas that can be used for electricity generation. Residue products from UCG have the potential to leach into surrounding groundwaters. The geochemistry and leaching dynamics of these products are explored in this study. The products include char, ash, and the heat-affected zone in the surrounding rocks. Core samples from the pilot plant at Majuba are the first ever to be recovered from a UCG cavity in Africa, and they give key insights into the geochemistry of the gasification zone. Mineralogical and chemical analyses were performed on the samples, and acid-base accounting (ABA) was used to predict the acid-producing capacity of the gasification zone, particularly for char samples. Some of the char contained pyrite, although not all samples were acid-producing as determined by the ABA analysis. The ABA results showed that some of the unburned coal has moderate levels of sulphur, which could be the driving medium for acidic conditions. The ABA analysis indicated that water in contact with the gasification zone would eventually have a pH lower than 7, which could lead to acid rock drainage. These results form part of a preliminary investigation into the geochemistry of the reaction zone, post gasification. IntroductionUnderground coal gasification (UCG) is an unconventional mining method that converts coal in situ into a fuel gas that can be used for industrial purposes, including electricity generation. The gasification process leads to the formation of a cavity composed of char, rubble, and void space (Bhutto, Bazmi, and Zahedi, 2013). Residue products from UCG have the potential to leach into groundwater. These products include char (devolatilized coal), which can generate acid rock drainage (ARD). ARD is caused by the oxidation of sulphide minerals, which acidifies the leachate, thus increasing the solubility of some environmentally toxic metals (As, Cd, Hg, Pb, Zn, etc.) (Bouzahzah et al., 2015).The main source of ARD is oxidation of sulphide-bearing minerals due to interactions with oxygen, water, and microorganisms (Simate and Ndlovu, 2014; Kefeni, Msagati, and Mamba, 2017; Bouzahzah et al., 2015). Although ARD occurs naturally, it can be enhanced by mining activities that escalate exposure of sulphide minerals to water, air, and bacteria (Simate and Ndlovu, 2014). At the Majuba pilot plant, the unburned coal remaining in the cavity has been in contact with groundwater since the gasifier was shut down in 2013. It is possible that in a commercial UCG plant, most of the coal will be consumed and no unburnt coal will be left in the cavity. Most of the sulphur will be converted to H2S during the gasification process and transported with the syngas to surface, where it can be removed and captured as elemental sulphur."

Oct 1, 2018

By C. B. Espag de Klerk, J. de Goede, M. Le Roux, Q. P. Campbell

"Excessive amounts of moisture in product coal can influence the efficiency of downstream utilization processes due to a decreased calorific value and handling problems. Stockpiles can be used to decrease the moisture content of coal by means of gravity drainage and evaporation. This paper is focused on the evaporation of moisture from a coal stockpile surface with the aim of investigating the effect of particle size on the rate of evaporation as well as the depth to which evaporation extends.It was observed that moisture initially evaporates at a higher rate from a stockpile consisting of fine particles (-6.7 mm) than from coarser particles (-13.2 mm +6.7 mm). This high rate of evaporation is restricted to the outer shell of the fine coal stockpile. However, for coarse coal, the porous nature increases the depth at which evaporation occurs. Evaporation of moisture was observed up to the fourth day of each experimental run, after which steady state was obtained. It was shown the water can evaporate from the surface into the body of the stockpile, depending on the coal particle size and void spacing. An experimental reclaim depth of 0.4 m was achieved after 4 days. IntroductionCoal stockpiles serve as surge capacity for downstream utilization processes and can also be used for moisture reduction by means of gravity drainage and evaporation. Excessive amounts of moisture in coal can cause handling problems and, most importantly, will decrease the calorific value, leading to inefficient combustion.Research has shown that evaporation by means of wind and solar action is considerably more effective than gravity drainage(Williams, D.J. 2006), but the effect is limited to a restricted depth from the exterior of the stockpile (Boyapati, E. and Oates, A. 1994; CSEM-UAE, 2010). The effectiveness of wind and solar action can be improved by orienting the stockpile perpendicular to the predominant wind direction, maximizing the surface area of the pile, and reclaiming the coal from the pile gradually in shallow cuts over a large area (Williams, D.J. 2006)."

Jan 1, 2016

By N. T. Beukes

An engineering house?s perspective of required inputs in designing a copper electrowinning tank house and ancillary equipment calls for both understanding of the key fundamental controlling mechanisms and the practical requirements to optimize cost, schedule and product quality. For direct or post solvent extraction copper electrowinning design, key theoretical considerations include current density and efficiency, electrolyte ion concentrations, cell voltages and electrode over potentials, physical cell dimensions, cell flow rates and electrode face velocities, and electrolyte temperature. Practical considerations for optimal project goals are location of plant, layout of tank house and ancillary equipment, elevations, type of cell furniture, required cathode quality, number and type of cells, material of construction of cells, structure and interconnecting equipment, production cycles, anode and cathode material of construction and dimensions, cathode stripping philosophy, plating aids, acid mist management, piping layouts, standard electrical equipment sizes, electrolyte filtration, impurity concentrations, bus bar and rectifier/transformer design, electrical isolation protection, crane management, sampling and quality control management, staffing skills and client expectations. All of the above are required to produce an engineered product that can be designed easily, constructed quickly and operated with flexibility.

Jan 1, 2009

By C. Massola, E. E. M. N. de Guzmán, M. G. Bergermana

The abrasiveness of a mineral or rock is an extremely important topic in the mining industry and is generally measured by the Bond abrasion index (AI). However, to determine such an index by the Bond test requires 1,600 g of sample with particle sizes ranging from ½” to ¾”, which are not available in certain situations, such as ore prospecting, drilling, and geometallurgical studies. In order to investigate the abrasiveness of smaller-sized sample materials, a modified LCPC test was developed, which allows testing fine materials (i.e., 1.0 mm or smaller) to predict wear in ore processing circuits and anticipate possible failures resulting from changes in abrasive characteristics of the ore being processed. The results for 16 different materials indicated a good correlation with the AI and the modified LCPC, resulting in a reliable alternative for the AI. Keywords: Bond Abrasion Index (AI), LCPC, abrasiveness

Jan 1, 2020

By N. Hadebe, A. Mampuru, F. Jantjies

Mintek conducted test work to study the effect of media wear when using Mintek’s Milling-in-raffinate technology. The grinding media consisted of high-chrome and ceramic balls. The tests were conducted using a laboratory 5L 316 stainless-steel rubber-lined mill. Magotteaux supplied the high-chrome and ceramic balls. The raffinate was synthetically prepared using a typical Cu/Co (2.2 g/L Cu, 3 g/L Co) composition. The milling rate, media wear, mill, leach extraction efficiencies, gangue acid consumption, and residence time were studied. The tests indicated that the high-chrome balls had a higher corrosion rate than the ceramic balls. The ceramic corrosion rate was lower than 0.1 mm/y. The highchrome balls performed better during the leach stages with faster milling time, higher leaching efficiencies for both Cu and Co, lower gangue-acid consumption, and lower residence time

Jan 1, 2023

By E. Vascotto, S. M. Rupprecht, H. C. Grobler

Shaft sinking survey practices in Southern African mining operations have been refined over many decades to meet the stringent accuracy, safety, and productivity demands of deep vertical excavation. However, much of this specialised knowledge remains poorly documented, and the decline in new shaft sinking projects presents a risk that these proven practices may be lost to future generations of mine surveyors. This paper reviews and synthesises current survey control methodologies employed during shaft sinking operations, with particular emphasis on the establishment and maintenance of surface and underground control networks, shaft verticality control, and elevation transfer. Traditional techniques, such as plumb-wire plumbing systems, steady brackets, and calibrated steel shaft tapes, are discussed in detail, alongside quality control principles and common sources of error affecting coordinate transfer. The paper further examines the integration of modern technologies, including total station resections and LiDARbased laser scanning, highlighting their benefits, limitations, and practical constraints in active shaft environments. By documenting both established and emerging practices, this review aimsto preserve critical institutional knowledge, support consistent survey standards, and provide guidance for accurate spatial control throughout the shaft sinking lifecycle.

Mar 30, 2026