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By S. Sekhar, S. Bhargava, A. K. Godugu, J. L. Porathur

Cemented backfilling has enabled underground hard rock mines to extract orebodies more safely with improved ore recovery. It is important to estimate the minimum required strength parameters for a backfill mix by optimizing the binder percentage to enable cost-effective and safe stoping operations. We conducted three-dimensional numerical modelling to study the effect of various stoping parameters on the stability of a free-standing backfill wall. A Mohr-Coulomb material model was used for the backfill material and the rock-fill interface. A strength reduction technique, excluding friction angle, was employed to arrive at a minimum stable strength value for the backfill. For a given combination of strength values, the stability state of the backfill wall could be demarcated using a displacement and yield zone tracking method. The numerical modelling results are compared to some earlier theoretical models. From the simulations, a predictive equation is developed to predict the required strength parameters for a backfill mix to ensure a stable free-standing wall. Examples are given of the successful use of the predictive equation at some underground hard rock mine sites in India.

May 2, 2022

By H. Mulder, M. C. Bekker

The principal objective of this investigation was to conduct a thorough literature review on the status of project readiness mechanisms, tools, techniques, and frameworks for mining projects. The review aimed at identifying common readiness evaluation criteria as well as potential shortcomings that prevent the establishment of a generalizable project readiness index. The literature review included a general overview of capital project performances and the importance of project readiness assessments to improve project delivery success. The study then progressed towards literature involving mining projects and how this differs from infrastructure and industrial project assessments. The paper concludes by summarizing the current state of mining project readiness assessments, the unique and differentiating factors to be considered, and suggests recommendations towards the development of generalizable readiness assessment criteria for mining projects.

Sep 1, 2022

By N. Naude, W. P. Roux

Fine particle beneficiation plays an ever-increasing role in mineral processing plants and it seems that technology can’t keep up with the challenges involved in the treating of these fines. The REFLUX™ classifier has proven itself able to treat high tonnages of fine material, especially in the coal industry. There are various fine ore applications that can benefit from such a process, yet laboratory and pilot-scale tests on many of these ores show poor efficiencies and recoveries. A better understanding of the design, operation and mechanisms of the REFLUX™ classifier is required to determine if and how it fits into these applications. The mechanisms in gravity separators are very complex due to the complex hydrodynamics, and the REFLUX™ classifier is no exception. The mechanisms of these systems are usually described through theoretical single particle-models that are hard to verify through analysing the feeds and products of these processes. To verify these models the movement of individual particles must be measured, which is not an easy task. In this paper the separation mechanisms in the incline channels of the REFLUX™ classifier were investigated with high-speed videography. A small lab scale model of the incline channel was constructed for this purpose. It was possible to capture and track the trajectories of particles under certain conditions and match these trajectories with theoretical models. The resuspension of particles, clustering and streaking was also observed and captured. Keywords: REFLUX™ classifier, particle trajectory, beneficiation, high-speed videography

Jan 1, 2020

By G. Chisakuta, P. Bwando, G. Mitshabu

By the end of 2022, the south-eastern Copper Belt region of the Democratic Republic of Congo was host to more than 40 small, medium, and relatively large sized copper solvent extraction sites. To date, solvent extraction reagents supplied in this region have never exceeded 50% of ketoxime content. We generated laboratory extraction and strip isotherms and used these with the BASF IsocalcTM modelling software to assess the benefit of using higher ketoxime blends on the main metallurgical performance indicators such as copper recovery and net transfer. Pure ketoxime extractants combine a relatively low strip point and a decent loading capacity, which are most effective as the pH of the pregnant leach solution gets closer to 2.

Jan 1, 2023

By F. S. Hoseinian, B. Rezai, E. Kowsari, M. Safari

In order to remove heavy metal ions from a large volume of wastewater with a low ion concentration, ion flotation appears to be promisingly effective. In the ion flotation process, because of the high ion removal percentage, the amount of water recovery percentage is a very important factor which determines the process efficiency. However, ion flotation suffers from relatively high collector concentration to achieve the high removal percentage to the desired limit, which subsequently increases the water recovery. In this study, functionalised graphene oxide (FGO) was synthesised, using a chemical method in the ion flotation process, applied as a collector for increasing process efficiency by reducing the collector consumption and water recovery. The high ion removal was achieved with both collectors of sodium dodecyl sulfate (SDS) and FGO, while the water recovery with a collector of SDS was 3.4% higher than that with a collector of FGO. The results indicated that the FGO could be effectively used for high ion removal and low water recovery in the ion flotation process. Keywords: Ion flotation, synthesised collector, ion removal, wastewater, water recovery

Jan 1, 2020

Exxaro installed their first ultra fines treatment plant at Leeuwpan Coal mine. The plant is now fully operational and results already show that the plant has great potential. The plant was designed and installed by DRA. Several challenges were faced during the installation due to the space constraints in the Leeuwpan plant. Efficiency tests were conducted on both modules after commissioning and showed very promising results. A lower ash product with a higher yield can be produced with the fine coal dense medium cyclones compared to the spirals previously employed.

Jan 1, 2010

By D. Bessinger, J. Rabe, J. Zietsman, C. Coetzee, P. H. Lamont, J. Muller

The UCAR® CHILL-KOTE? freeze lining concept combines wall cooling with carbon and graphite refractories of higher thermal conductivities to ?chill? the refractory lining by transferring heat from the refractory lining. Effective sidewall water cooling, together with the efficiency of the heat dissipating conductive refractories, lowers the temperature of the lining to below that of the molten process materials. This causes a layer of slag and process metal to solidify or ?freeze? and form a protective ?skull? which completely coats the refractory hot face. Once formed, the slag skull insulates the refractories, reducing heat loss and protect the lining from erosion, chemical attack, thermal shock, and other stresses. The result: extended life and greatly improved refractory performance. The Ilmenite smelting process depends on the presence of a solidified slag skull to protect sidewall refractory material from chemical attach by molten slag. No known refractory material is able to withstand this corrosive material. To date, UCAR has not applied their Chill Kote ? technology in the ilmenite smelting industry. This paper revolves around the results obtained from conducting an ilmenite smelting campaign on a 500kW DC open-arc furnace with a UCAR designed refractory system. The purpose of this test was to establish the effects such a lining has on refractory wear and the reduction-smelting process. Proper thermo-couple management enabled the authors to monitor lining wear for the duration of the campaign. Prior to the pilot-scale campaign, modeling work was completed to evaluate the feasibility of applying UCAR® CHILL-KOTE? technology to ilmenite smelting furnaces. The successful operation of a pilot-scale furnace equipped with the UCAR® CHILL-KOTE? lining as well as concise modeling suggest that it should be a viable option to consider for an industrial-scale furnace.

Jan 1, 2007

By S. Kok, D. Delport, J. Calitz

Altering the microstructure in order to improve the tensile properties of bow shackles resulted in inconsistency in the fatigue performance. This raises the question whether the inconsistency in fatigue life can be attributed to microstructural changes along the profile of the shackle or to decarburization at the surface. Bow shackles forged from 080M40 (EN8) material were subjected to different heat treatments in order to alter the microstructure. The shackles were subjected to five different fatigue load cases, which represented typical loads experienced at termination points for an overhead power line with a span length of 400 m, with changes in conductor type, configuration, wind, and ice loading. Although the change in microstructure does improve both the tensile and fatigue performance, we found that the depth of the decarburization layer has a greater effect on the high cycle fatigue life of bow shackles than the non-homogeneous microstructure.

Oct 1, 2021

By J. A. Theron

"This paper provides guidelines on performing mass and energy balance modelling involving coal and coal derivatives. Usually, the inputs to a pyrometallurgical process would be specified in terms of elements and compounds. Reliable thermochemical data is more widely available for species involving uniquely defined, relatively smaller molecules. However, in the case of coal, the molecules are extremely large and not uniquely defined. Consequently, modelling processes involving coal and its derivatives have several potential pitfalls. These are outlined in the present paper. The main findings are as follows:•,Coal proximate analysis should not be regarded as absolute; it could vary with several parameters, including heating rate •,For modelling, the use of ultimate analyses should be considered a preferable option to proximate analyses, where, ‘fixed carbon’ and ‘volatiles’ are not defined in terms of chemical composition •,Significant errors could be made if the larger molecules are neglected during calculation of the calorific value (CV) of coal gas (the gas liberated when coal is heated in the absence of oxygen) •,For elemental analyses, the oxygen content (which is calculated by balance) should be checked to ensure it is within the expected range •,For representation of sulphur in coal, double-counting due to SO3 in the ash analysis should be avoided •,Potentially, oxygen in coal could be represented as O2, H2O, CO, or CO2; however, use of some of these species without considering the experimentally determined gross CV results in significant errors in the energy balance. If coal enthalpy is calculated from elemental analyses without correction, representation of coal oxygen as H2O(l) gives reasonable accuracy (up to 6.9% error for a set of South African coals). Coal volatiles could be represented by a complex mixture of compounds, even using different oxygen-containing species than the abovementioned four, provided the enthalpy is corrected •,It is recommended that an ‘enthalpy correction value’ is incorporated in energy balances involving combustion, devolatilization, or conversion of coal and coal derivatives, e.g. coke, char, or tar. That would imply that proximate analysis, elemental analysis, as well as the gross CV would be required for all solid or liquid coal-derived substances being modelled. No other correction due to the form of carbon being different than graphite should be used, as that would imply doublecounting some effects."

Jan 1, 2014

By W. E. Stumpf

"SynopsisSouth Africa recently announced a resurgence in its commercial nuclear power programme. The implications for the development of the necessary high-level manpower within South Africa’s tertiary educational system and its national research and development (R&D) capacity in materials science and engineering, as well as in other engineering disciplines, are placed into perspective. An organized national process of developing this manpower by moving away from the previously high-risk and costly ’large programmes’ to rather a selection of ‘small and better’ research projects and a redefinition of what constitutes ‘nuclear materials’ are proposed as parts of this strategy.IntroductionSince 2008, and more particularly in 2014/2015, South Africa has woken up to the fact that significant steps need to be taken to ensure sufficient electricity generating capacity for the future, even beyond the coal-fired stations at Medupi and Kusile currently under construction. It is, therefore, encouraging to see some active large-scale wind farms in the Eastern Cape near Jeffrey’s Bay, in the Couga area, and others in the Western Cape already in operation. In addition, many solar energy projects are also progressing from the small localized scale to larger programmes in the Northern Cape, which may contribute some capacity on a national basis. South Africa needs to tap into its renewable resources of wind and solar much more, but will these projects solve the country’s long-term industrial needs? Unfortunately not. One cannot run mines and trains on solar cells. Industry needs reliable baseload capacity, and with very limited easily accessible hydrocapacity this leaves really only coal, possibly natural gas, and nuclear power as options. South Africa’s current over-reliance of about 90% on coal–fired power, however, places it in an internationally vulnerable position, and diversification into a more equitable energy mix should be a national priority for the medium to long term. South Africa cannot significant climate change confronting the human race, as the IPCC cautioned in 2013, and will have to adjust its future energy reliance to a more balanced combination of sources."

Jan 1, 2015

By S. D. Dladla, S. Ramsamy

The majority of the tailings dam operations in South Africa will be required to comply with the new Global Industry Standard on Tailings Management (GISTM) within the next one to three years, depending on the dam classification and the requirements of the respective investors and insurers. With up to 72 auditable requirements, the implementation of the Standard needs careful planning and prioritization. This paper focuses on the practical steps to GISTM compliance for tailings facilities in operation in South Africa. The discussions are based on current practices, South African regulations, and industry standards requirements. The possible changes in dam classifications and the associated requirements are presented.

Jun 2, 2022

By W. C. Joughin

The science of soil mechanics is 100 years old, and rock mechanics is about 80 years old. While methods of analysis and design have been developed and have evolved over time, these are relatively young sciences. The rapid increases in computing power and new technologies have enabled more sophisticated modelling and monitoring. However, there are still many aspects of soil and rock mechanics that are not well understood. Geotechnical failures, which have major consequences, still occur. These consequences may include environmental damage, major production holdups and associated loss of revenue, damage to infrastructure, and loss of life. High-consequence events, which are rare, are more difficult to anticipate and to design for, because by their nature they involve extraordinary circumstances or conditions, often geological in nature. The risks are usually mitigated by conservative designs and monitoring. Detailed geotechnical investigations help us to understand the natural variability of soil and rock masses and identify unusual or unexpected conditions. Investigating and researching major geotechnical failures is essential to enable these unusual circumstances to be anticipated. In the past, severe unanticipated events may have been treated as natural events or ‘acts of God’. However, society now has much greater expectations and it is essential to have policies and procedures in place that enable appropriate management of these rare, high-consequence risks. A good example is the Global Industry Standard on Tailings Management (GISTM), which was introduced after the catastrophic dam collapse at Vale’s Corrego de Feijao mine in Brumadinho, Brazil. The address will explain the concepts of uncertainty and variability, and how they should be taken into account in geotechnical design. The challenges facing geotechnical engineers, mine owners, and managers will be discussed. referencing a number of real case studies.

Sep 6, 2023

By Ronald J. Roman

All mining and milling complexes can, within limits, operate at a variety of production rates. Factors of economic importance that are affected by production rates are costs per unit production, recovery and product grade. Once the relationship between the production rate and cost is established, dynamic programming techniques can be used to define the optimum production schedule (that is, the production schedule that maximizes the present worth of the operation) for the life of the deposit. In general, assuming that the capacity and efficiency of the physical plant remain unchanged throughout the life of the deposit, the optimum production rate is not constant for the life of the deposit, but declines gradually as the deposit is being exhausted.

Jan 1, 2014

By P. Cowx, L. Els, P. Smith, R. Nordhagen

"Tapping operations at ferroalloy smelters generate a significant amount of fume. Effective capture of fumes is required to meet the obligations of environmental, as well as occupational, legislation.A study was completed on an existing fume extraction system at a ferromanganese furnace tapping area. The area under consideration included the tap-hole, launder, and ladle area. The study consisted of site test work as well as computational fluid dynamics (CFD) modelling to identify and evaluate solutions.Site test work and observations during furnace operation provided a baseline of system performance as well as input parameters for CFD modelling. Gas flow rates and energy contents from each extraction area were measured. Photographs and video footage were taken to evaluate areas of fume leakage.The CFD study was firstly validated against site observations to ensure the accuracy of input parameters. Thereafter several modification concepts were modelled and suitable combinations were investigated to ensure robust solutions. The following concepts were considered:•,Air curtains•,Ladle hood aspect ratio and position•,Increase of ladle extraction volume•,Extension of the length of the tapping garage structureThe paper presents the results of a performance test on a working ferromanganese tapping area fume extraction system and the results of CFD modelling as compared to site test results. Upgrade options are evaluated and an integrated robust upgrade of the system described."

Jan 1, 2014

By M. P. Brandt, T. P. Knoetze, I. I. M. Kessler

It has generally been accepted that the volatile mater in a coal is the factor that determines whether or not a specific coal dust is an explosion risk. This paper presents the results of an attempt to relate the explosibility index (Kex) of South African coals, as determined in a AD-litre explosion vessel, to the volatile mater content of the coal and the calorific value of the volatiles. A good relationship between the calorific value of the volatiles and the explosibility index was established, which makes it possible to calculate the violence of an explosion, as expressed by Kex, for South African coals. The Kex value is but one of a number of parameters that influence the explosion hazard in a specific colliery and cannot be used as the sole predictor of the propagation of an explosion underground. Other parameters include the ignitability of the coal, temperature, humidity, dispersibility of the dust, methane concentration, amount of incombustibles present, and ventilation.

Jan 1, 1993

By P. van der Steen

This paper examines the historical developments in diamond beneficiation technology and the impacts on the industry. The art of diamond beneficiation has given way to the application of scientific process, but at considerable capital expenditure. The shift in beneficiation methodologies has been disruptive to the traditional skills set of the industry, but evolutionary change continues and has been beneficial to the quality of the final product.

Jan 1, 2010

By W. J. Whiten

"Models of cone crushers and vibrating screens are described. These models have been constructed from actual plant data using a systematic model-building technique. Included in this technique is regression analysis using multi-dimensional spline functions.The models have been used to simulate complete crushing plants and hence to design and evaluate a control system for crushing plants."

Jan 1, 2014

By N. Naudé, J. de Villiers, C. P. Bergmann

It is proposed that the physical and chemical composition of individual mineral particles are an appropriate basis from which to model the performance of minerals processing equipment. Such a particle-based approach enables modelling across disciplines such as comminution, classification and flotation and automatically generates the traditional mass and chemistry balances. The general approach followed is to generate full grade-recovery curves for a separator by sampling product and tailings at varying mass yields. AutoSEM characterisation of each sample provides particle data that is used to reconcile mineral deportment and liberation to the measured size and assay data. In this way, partition surfaces can be generated and modelled. In this paper, an empirical model for the performance of a gravity spiral concentrator treating fine chromite ore is proposed. The model is based on the combination of two partition surfaces and is able to accommodate both forward and reverse gravity concentration effects per size fraction. The results show that this approach is well suited to represent spiral performance for the cases evaluated. The effect of two feed particle size distributions on the performance of the Multotec SC21 and SC25 spirals is demonstrated. Simulations are run in an Excel environment, linked to Python-enabled routines for enhanced data management and calculation speed. Keywords: Spiral concentrator, gravity separation, particle-based modelling

Jan 1, 2020

By L. Morin, S. Mortazavi, K. Volchek, A. Demers, A. Di Feo

The objective of this paper was to investigate the possibility of reducing process (fresh) water and increasing recycled water (thickener tank overflow water). As part of the investigation, rougher flotation tests were done with the two water types and a mixture of the two (50%/50%). The effect of recycled water on the grade-recovery response and rougher recoveries was investigated. When thickener tank overflow was used (50% and 100%), the nickel+copper grade versus nickel recovery decreased. The decrease in the grade-recovery was due to higher pyrrhotite recovery. Also, there were no effects on nickel and copper recoveries, which was confirmed using multivariate statistical analysis at the 95% significance level. Keywords: Flotation, nickel, copper, water recycling, multivariate statistical analysis, MANOVA, reverse osmosis

Jan 1, 2020

By A. Lebedev

Application of dynamic simulation for a base metal processing plant is discussed. The plant receives ore of variable quality from two pits and blending had to be applied to maximise recovery. The plant employs multiple stage crushing, screening, dense media separation, two-stage milling, flotation and further filtration. Stockpiles and bunkers are used in the plant to cater for breakdowns and operating delays, the latter being appropriately incorporated in the model. A detail dynamic simulation model was constructed from the rock face to the filtration plant to assist the plant design, notably with definition of the ore blending method, sizing storage capacity and in-plant conveyors. The plant model was broken down to capital equipment items and various feed types and mass balances were tested to ensure that the production target is met. The dynamic simulation tested the proposed blending method, identified bottlenecks, produced risk profiles for all strategic storage facilities and overall helped minimise the project risks and improve confidence in the plant design. Keywords: Dynamic simulation, ore grade, blending, capacity, risk profile, throughput, utilisation

Jan 1, 2020