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By J. D. Steenkamp

"In July of 2016 and June 2017, major tap-hole repairs were carried out during the annual shutdown of two 63 MVA submerged arc furnaces producing ferrochromium in South Africa. The hot excavations of the tap-holes allowed for a study of the wear profiles. Subsequent thermodynamic calculations allowed for the quantification of the potential for chemical reaction between refractory and slag or alloy contributing to wear in the tap-hole area. Results from both wear profiling and thermodynamic calculations are reported here. IntroductionFerrochrome (FeCr) is an essential alloy in the production of stainless steel (Gasik, 2013). In 2017, 11.7 Mt of FeCr was produced (Pariser et al., 2018.). The main producers were China (39%), South Africa (29%), Kazakstan (12%), and India (8%).A number of grades of FeCr are available to producers of stainless steel, including high-carbon ferrochrome (HCFeCr) (Gasik, 2013). HCFeCr typically contains 60–70% Cr and 4–6% C (Basson and Daavittila, 2013). When the chromium content is lower (50–55% Cr) and the carbon content higher (6–8% C), it is referred to as charge chrome. Charge chrome is typically produced in South Africa due to the grades of ore available.FeCr is produced in submerged arc furnaces (SAFs) and in open arc furnaces (Mc Dougall, 2013) by carbothermic reduction of oxide raw materials. In a SAF the electrode tips are submerged in a porous charge mix. In FeCr production, the electrical energy is mainly liberated by resistive heating of the wet coke bed (Barker et al., 2007; Steenkamp et al., 2017). Thermally conductive lining design philosophies are typically applied in SAFs producing FeCr (Steenkamp, Denton, and Hayman, 2017; Coetzee, Duncanson, and Sylven, 2010; Coetzee et al., 2010).In July of 2016 and June of 2017, major tap-hole repairs were carried out during the annual shutdown of two 63 MVA SAFs producing FeCr in South Africa. The hot excavations of the tap-holes allowed for a study of the wear profiles. Both SAFs were operated on the same site, by two different operating crews, using the same raw materials. The major difference between them was that the SAF excavated in 2016 was an open SAF (referred to as Furnace A) and the one excavated in 2017 was a closed SAF (referred to as Furnace B). In an open SAF, a gap exists between the top of the steel shell and the roof, with the top of the burden being open to the atmosphere and the CO-rich off-gas being combusted as it escapes. In a closed SAF, the roof is attached to the steel shell and the CO-rich off-gas is collected from an offtake on the roof for further treatment and used in downstream processes.The paper presented here reports the macro-scale observations on refractory wear for the two SAFs, and studies the potential for chemical wear of refractory by slag and alloy as a potential contributing factor to the tap-hole wear observed."

Jun 1, 2019

By M. K. Roberts

The approximately 2800 Ma old Ventersdorp Contact Reef is a unique Witwatersrand orebody, from which about 6% of the world?s gold production is derived. A major portion of this production is mined at depths exceeding 2500 m and deepest levels of mining are at about 3600 m. The orebody?s hangingwall consists of volcanic rocks. This differs from the older Witwatersrand orebodies, which have quartzitic hangingwalls. The thickness of the Ventersdorp Contact Reef is generally about 1.20 m, but is highly variable, at an average dip of about 18°. A pronounced unconformity beneath this orebody is also expressed by varying footwall rock type characteristics and frequent rolling of the reef plane. These rolls follow topographic variations of the palaeo-surface. More geological than rock mechanics studies were performed on the Ventersdorp Contact Reef prior to 1992. Recently, however, a multidisciplinary team comprising various rock engineering and geological disciplines has delineated geotechnical areas by a novel technique. Geotechnical areas are defined by distinct footwall/hangingwall rock assemblages. The presence of three footwall and two hangingwall rock types results in the definition of six geotechnical areas across a distance exceeding 60 km, including about 10 gold mines. Distinct rock mass behaviour has been documented in three of the six geotechnically defined areas. Different rock mass behaviour is expressed by features such as mining-induced fracturing, closure rates, fall of ground characteristics and seismic character. Some geological features override the rock mass behaviour as defined for the individual geotechnical areas. These are undulations of the orebody or the frequency, characteristics and attitude of major discontinuities. It is concluded that the concept of geotechnically subdividing orebodies is not only important for facies delineation and the associated grade, but also needs to be considered for safety aspects, in determining factors such as the appropriate support to be employed.

Jan 1, 1999

By M. Suzuki, T. Shiomi, M. Nakada, K. Tsutsumi

Mold powder plays an important role in the continuous casting process for high quality steel production. It is well known that mold powder entrapment causes surface defects in steel sheet and the high viscosity of mold powder prevents the entrapment of mold powder in molten steel in ultra low carbon steel. This paper deals with the entrapment of mold powder caused by suction by Karman?s vortex in a laboratory experiment. At first the effect of the viscosity of oil and interfacial tension between water and oil was investigated in a water model experiment. Then hot model experiments were carried out by mold powder and molten steel. The amount of mold powder entrapment was affected by the viscosity and the interfacial tension between molten steel and mold powder. As a result, the following equation of the mold powder entrapment was obtained. m=1.06*107?-0.255?m-s-2.18 The amount of mold powder entrapment decreased when the viscosity and interfacial tension increased. But the effect of viscosity was larger than that of interfacial tension in the case of the industrial mold powder when the viscosity was under 0.5 Pa.s, interfacial tension was from 1200to 1300 mN/m.

Jan 1, 2004

By G. E. Blight

Wind erosion can be a major cause of the loss and dispersion of tailings material from a tailings dam into its surrounding environment. Such dust dispersion can be a serious nuisance, as well as a health hazard to inhabitants in nearby settlements, and can also damage the health of animals, degrade crops, making them less marketable, and cause soil and water pollution. The problem of wind erosion can affect tailings dams in all types of climate, but becomes worse as climatic aridity increases. Because clouds of dust are often observed billowing across the top surfaces of tailings dams in dry windy weather, there is a common misconception that the dust arises from wind erosion of the top surface. As a result, much effort and money is vainly spent on treating the tops of tailings dams to prevent dust generation, whereas the slopes of the dams are the true major dust source. This paper briefly reviews what is known of erosion of tailings dams and then proceeds to describe the mechanics of wind erosion in general, and how it affects tailings dams in particular. Finally, recommendations are made for mitigating wind erosion of tailings dams and the resulting blowing dust.

Jan 1, 2007

Standards And Laboratory Monitoring In Gold Assay Key Components Of Best Practice

Jan 1, 2005

By A. M. Neale

Kriel Colliery has experienced some sub-standard blast results on the overburden. Blast results are considered poor when the fragmentation is too big, back break into the new highwall, capping is experienced and/or excess overburden material is thrown into the void. Poor blasting leads to lower productivity, equipment breakdowns, and poor drilling and blasting results on the adjacent blast, contamination of coal or loss of coal. A simulation was developed in Microsoft Excel to model blasting results while changing various parameters. From the simulation results, it could be seen that a change of blast design could be beneficial. As an example, smaller drilling patterns were simulated (10 m x10 m to 8 m x8 m, and 8 m x8 m to 7 m x7 m in Pit 5 and Pit 6 respectively) in combination with changes in explosives (P700 emulsion vs. ANFO) and drill bit diameter (311 mm vs. 251 mm). The results show that each of the options has a specific scenario that will be most beneficial to the mine. These results are quite specific and subject to variable inputs. The purpose of the example is to demonstrate how the simulation can be used as a tool to asses blast design variations.

Jan 1, 2010

By L. Hansen

Sulphuric acid plants now and then see unexpected increases in SO2 emissions. Our experience is that it is not always easy for the acid plants to pinpoint the exact reason for the SO2 increase. Sometimes a catalyst bed is sacrificed even though reliable temperature readings and gas analyses could have verified satisfactory activity. Hence the leaking heat exchanger is never discovered and after the shutdown the SO2 emissions are still too high. This paper will look into some basic catalyst management tools: good record keeping is a necessity for collection of representative catalyst samples; reliable operating data is an inevitable starting point for all analysis; and trending of operating data is a must for plant optimization and troubleshooting. In addition, these catalyst management tools will give continuous updated knowledge of the catalyst status in each bed, providing the basis for a more effective replacement strategy. The most typical reasons for increasing SO2 emissions will be presented together with easy guidelines for cross-checking operating data, temperature optimization and good record keeping.

Jan 1, 2009

By John Freer

On 25th November, 1983, nearly forty members of The South African Institute of Mining and Metallurgy, together with Doris Gardner and Judith Money from Kelvin House, travelled by luxury motor coach to Secunda, there to visit the coal-mining and conversion operations of Sasol Limited.

Jan 1, 1984

There has been disappointingly little development in the analysis of rock slopes in open pit mines over the past 30 years. A brief review of literature shows that the application of numerical stress analysis methods to open pit mine slope stability has become only relatively common in recent times, and that there are as yet no standardized approaches. The lack of development in general, and of robust, standardized approaches in particular, is surprising in view of the ?ultra? deep open pit mines that are being developed to depths in excess of 1000 m. In this paper, the results of a substantial programme of two dimensional and axisymmetric analyses of open pit slopes are described. Variations in the following parameters were taken into account in this programme: slope angle, slope height and horizontal to vertical in situ stress ratio. The evaluation of the data has concentrated on the tensile stresses and the extension strains in the slopes. This is believed to be the first publication dealing with strain distributions in slopes. The occurrence of zones of tensile stress was very limited. These zones occur in the crests of slopes, except in the case of low horizontal to vertical stress ratios, in which case the tensile zone is in the floor of the pit. In contrast, very large zones of extension strain can occur, and this finding represents a significant new aspect in slope stability that has not been considered before. The greatest magnitudes of extension strain occur near the toe of the slope, either in the slope itself, or in the floor of the pit. The magnitudes of the strains are considered to be large enough to result in fracturing of intact rock, and the fracture orientations predicted are adverse for slope stability. The large zone in which such extension failure could potentially occur in a 1200 m deep pit is typically more than 100 m horizontally behind the toe and about 400 m up the face from the toe. Fracturing that is extension in nature is common in competent, brittle rocks and often develops with some violence and little or no warning. Such ?strain bursting? produces easily measurable seismicity, events often being audible as well. In the slope situation, the expected physical manifestation of this behaviour would be popping off of rock slabs and plates of rock from slope surfaces and popping up of the pit floor, as well as the formation of new fractures within the rock mass. Such behaviour may cause overall slope failure, or may initiate failure, which may then be driven to overall slope failure by other influencing factors or combinations of factors. In addition to instability resulting from the fracture surfaces themselves, all induced fracture surfaces could interact with natural geological structures to facilitate formation of a significant failure surface. With suitably orientated joints, extension strains are likely to manifest themselves in the opening up of such joints and hence in the loosening of the rock mass in a preferential orientation, with potential effects on groundwater flow patterns.

Jan 1, 2003

By A. Tor, M. Borowski, N. Szlazak, D. Obracaj

This article presents possibilities of reducing methane emission to the atmosphere in working mines in Jastrzebie Coal Company by means of proecological solution. They form a new approach towards the problem of rational and effective use of natural resources both in economical and environmental respect. Power and thermal energy for underground air conditioning in mining excavations are produced from the methane, which is drained out of the mine for safety reasons.

Jan 1, 2003

Slope stability is a fundamental part of a successful mining operation. It impacts directly on the safety of personnel and the economics of the mine. The Jwaneng Mine in Botswana is planning a push back of 644m depth in the south east wall. Mining will commence in 2010 and be completed in 2024. This will put the mine in the deep pit category. The mine has invested in extensive geotechnical data gathering and design programs that started as far back as 2003 for the south east wall. The south east wail of Jwaneng Mine is characterized by foliation that dips adversely into the mining faces. The orienta1ion of the foliation is variable due to intense tectonic movements that have also caused the occurrence of faults that are sub-vertical. A considerable amount of information on the characteristics of structural patterns and the rock mass has been collected. This paper presents an overview of the feasibility level geotechnical design that is about to be concluded.

Jan 1, 2010

By I. Alp

Application of magnetic separation was investigated for the enrichment of colemanite ores by removing the magnetic gangue fraction. The detailed XRD analysis of the ore has indicated that the gangue fraction is composed predominantly of the iron-bearing silicates such as smectite and, to a lesser extent, illite. Magnetic susceptibility measurements of the colemanite and gangue samples have proved that colemanite is diamagnetic in character whereas gangue fraction is weakly paramagnetic to allow the removal of this fraction by magnetic separation. Magnetic separation of the crushed and sized ore samples (-5 mm +75 µm) was performed using a high intensity permanent magnetic separator. Under the test conditions a colemanite concentrate (41.29 wt.% B2O3) was found to be produced from the crushed ore (30.76 wt.% B2O3) at a recovery of 96.76%. These findings suggest that magnetic separation has great potential as an alternative process for the production of a concentrate of commercially sufficient grade.

Jan 1, 2009

Heavy mineral deposits are becoming more complex in terms of their compositional variation, particle mineralogy and size distributions, and present challenges for the operation of separation equipment to achieve the required grades and recoveries. Changes in equipment design and concepts potentially provide new opportunities for the beneficiation of heavy mineral sands deposits. The development of a framework for the fundamental understanding of separator performance issues is a first step to develop new machines. This paper will present a first step analysis of electro-static and magnetic separation machines with their application to real separation scenarios.

Jan 1, 2010

By N. J. Wagner, D. G. Modiba

There is currently limited knowledge concerning South African coal deposits as hosts for rare earth elements (REE). This project aims to determine the concentration of REE, including yttrium and scandium (REY+Sc) in various coal seams and adjacent sediments in borehole cores from the Ermelo, Witbank, and Waterberg coalfields in South Africa. Coal petrography (maceral count and vitrinite reflectance), XRD, XRF, sequential chemical extraction procedure (SCEP) before ICPMS, and mineral liberation analysis (MLA) were conducted on the coal and associated sediment samples. The coals were inertinite-rich, medium-rank bituminous coal, with moderate to high ash content. The two dominant minerals in all the coalfields are kaolinite and quartz, except for sample ZBS2M, where dolomite was dominant. The dominant major oxides are Al2O3, SiO2, Fe2O3, and CaO, which concur with the XRD results. The ICP-MS results following SCEP indicated that both coal and the associated sediments were light REY+Sc dominant. There was also an elevation of medium REY+Sc in the Witbank coal’s associated sediment samples. Notably, the samples with the highest REY+Sc results were the sediment samples. The Waterberg samples had the lowest REY+Sc from both the coal (less than 2 μg/g to 7 μg/g) and associated sediments (2 μg/g to 15 μg/g). While the highest REY+Sc was yielded from the Witbank-associated sediments (500 μg/g to 2,500 μg/g). The carbonate fraction step proved to be the most successful leaching step, as most REY+Sc was recovered in that step for all coalfields. In addition to the carbonate fraction, the silicates and sulfide fraction in the Witbank samples, and the ion-exchangeable fraction for the Waterbergassociated sediments samples proved successful in leaching out the REY+Sc. MLA determined that monazite and xenotime in all the coal samples were the REY+Sc-bearing minerals.

Nov 6, 2024

By J. A. Bakken, M. Tangstad, P. A. Eidem

In the submerged arc production of ferromanganese, sillicomanganese and ferrochromium, the coke bed characteristics play an important role. The basic mechanisms of electric current conduction in the coke be dare not yet fully understood, but important parameters are the material resistivity of coke and the contact resistance between the coke particles. Preliminary tests indicate that the contact resistance is of great importance to the bulk resistance of the coke bed. An apparatus measuring the material resistivity and contact resistance of carbon materials has been developed. Both graphite and industrial coke have been tested. The material resistivity tests were performed on single particles to ensure that the effects of pores and cracks were included and the contact resistances were excluded. Two geometries were tested to obtain the contribution of the contact resistance to the total resistance of two connecting particles. The tests were performed in an inert atmosphere at temperatures and current levels found in industrial submerged arc furnaces. The results show that the method has a satisfactory reproducibility. It was found that the contact resistance is about 10 times higher than the resistance of the material when two particles are in perfect contact and that the resistivity of SSAB coke is more than 10 times higher than that of the graphite at room temperature, but with increasing temperature the difference decreases. For SSAB coke the general trend is that both the resistivity and the contact resistance decrease with increasing temperature.

Jan 1, 2007

By M. Dworzanowski

The physical beneficiation of iron ore that has a wide particle-size distribution is problematic, regardless of the process applied, whether dense medium separation, gravity concentration, magnetic separation, or flotation. The problem of particle size is further compounded when there is a significant -10 µm fraction. Generally the approach to a wide particle-size distribution is to split into narrower size ranges and treat each separately. More often than not the -10 µm fraction is not treated but discarded. This approach results in a more complicated and expensive flow sheet and the loss of any potential value in the -10 µm fraction. Wet high-intensity magnetic separation (WHIMS) bench-scale test work was conducted on a haematite-rich material with a particle size of -200 µm. What made this material different was that it contained a 60% -10 µm fraction, hence discarding the -10 µm material was not an option. The objective of the test work was to determine how to maximize the recovery of the haematite across the full particle size range. Given the unusual particle size distribution, it was concluded that WHIMS would be the only practical beneficiation route. The -200 +10 µm and -10 µm fractions were treated separately and together under varying WHIMS conditions. For a given concentrate grade, the mass yield obtained was greater when the total particle-size distribution was treated. The inferred optimum conditions, using the same material, were tested on a pilot-scale WHIMS and similar results were obtained.

Jan 1, 2014

By A. Ochieng

Solids suspension influences the quality of mixing and energy requirement in a solid-liquid system, both of which determine the efficiency of industrial processes such as nickel precipitation. Nickel solids concentration distribution in a stirred tank was investigated using computational fluid dynamics (CFD) and experimental methods. The concentration distribution of the nickel solids was compared with that of sand and glass. The laser Doppler velocimetry (LDV) method was used to measure the velocity field for the liquid-only system and an optical technique was employed to determine the axial solids concentration distribution. Regions of in homogeneity in the tank were identified. It was found that, for a given solids loading, the solids concentration distribution depended on both particle size and particle size distribution. High solids loadings were investigated and a difference in the concentration distribution pattern was obtained with nickel, flint glass and sand particles. The CFD simulation results highlighted problems that could be associated with some conventional experimental methods of determining solids concentration distribution in a stirred tank. Keywords: nickel; CFD; simulation; mixing; solids suspension.

Jan 1, 2010

By M. Syamujulu

In 1994, Nkana smelter commissioned a multimillion US Dollar Chilean Teniente converter (CT) in its operations in order to improve its smelting technological base. The main objective was to reduce the overall smelting energy costs and increase the sulphur capture for sulphuric acid production to support the company?s leaching operations at Nchanga tailings leach plant. A decade of CT operations have since ensued following its installation and start-up. This paper provides a technical and operational audit of the performance of the CT in the first 10 years of its operations at Nkana smelter.

Jan 1, 2005

By D. Vogt

South African underground hard rock mines are typically managed using measurements made daily, weekly or even monthly of key parameters such as face advance, readiness to blast, blast success, temperature or dust levels. Health, safety and productivity can all be greatly improved if a real-time measurement system can inform decision making. To enable this vision of widespread sensing, communication and decision support, CSIR has developed an open standard architecture for communication of sensor data, and a reference implementation using that standard. The standard, called AziSA, meaning ?to inform? in isiZulu, will allow any device that complies with it to join any network that supports it. The standard is designed for South African gold and platinum mines. To be practical in a typical Bushveld platinum mine, a real-time sensor system needs to be robust, reliable and cheap: ?Sensors are equipped with power sources that will last as long as the sensor is required. In effect, sensors need to be disposable: cheap enough not to warrant repair if they break. ?Communication in the stope is wireless, to avoid there liability problems associated with wire connections. For example, wires to sensors in the face area are unlikely to survive blasting. ?To get information out of the stope, the power line to the scraper winch is used as a communications link. Unlike a separate communications link, the power line will be repaired if damaged, because of its importance to production. ?Outside the stope, communications are transferred onto the mine communication infrastructure. To succeed as a management system, the next key element is the use of software decision support tools that will analyse masses of real-time data to extract key parameters and trends for decision makers. A range of sensors has been developed, including commercial sensors that have had wireless adapters added to make them AziSA compliant, and bespoke sensors that provide low cost sensing of typical mining parameters. An important parameter in any sensor network is the location of the sensor. This has to be easy and cheap to establish, so a tool has been developed to locate sensors in the confines of a stope, using ultrasonic and radio techniques. Once sensors are installed and located, they associate their location to all data that they produce. All the data from the system are captured at surface in a flexible database that can be queried by any application that requires data of any kind. It is simple to program alerts, and for actions to be associated with alerts. The use of wireless in stope also allows for communication from surface to the stope, or from stope to stope. The first implementation of an AziSA compliant system is being installed as part of the Mine Health and Safety Council funded rockfall elimination project. The design is discussed, and a future application for a platinum mine is considered.

Jan 1, 2009

By T. Celik, B. Genc, C. Musingwini

"This paper discusses a new methodology for defining and measuring mine planning software utilization in the South African gold mining sector within an evolving data-set framework. An initial data-set showing the mine planning software providers, their corresponding software solutions, as well as the software capabilities and information on the number of licences was collected and compiled in 2012 in an online database for software utilized in the South African mining industry. Details of the database development and implementation were published in the Journal of the Southern African Institute of Mining and Metallurgyin 2013. In 2014 the data-set was updated with additional and new information. Using the 2012 and 2014 timestamps, a methodology for estimating the software utilization was developed. In this methodology, the three variables of commodity, functionality, and time factor were used to define and measure the software utilization in order to ultimately inform decision-making strategies for optimal software utilization. Using six different functionalities, namely Geological Data Management, Geological Modelling and Resource Estimation, Design and Layout, Scheduling, Financial Valuation, and Optimization, utilization in the gold sector was measured. This paper presents the methodology employed for measuring the mine planning software utilization. The methodology is useful for stakeholders reviewing existing software combinations or intending to purchase new software in the near future and who want to estimate the comparative attractiveness of a certain software package. These stakeholders include mining companies, consulting companies, educational institutions, and software providers. The work presented in this paper is part of a PhD research study in the School of Mining Engineering at the University of the Witwatersrand."

Jan 1, 2015