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By V. Tathavadkar

Worldwide TiO2is extracted from natural ilmenite, rutile, and anatase minerals via the sulphateand chloride processes. The sulphate process generates large volumes of less toxic wastes, whereas the chloride process, including the ilmenite-chloride process of DuPont, yields much lower volume of wastes, which are highly toxic and hazardous. The treatment and disposal of such hazardous chloride wastes is both expensive and difficult in terms of long-term monitoring. Besides the waste management and disposal, there is also a shortage of high-grade titanium dioxide minerals in nature, which consequently yields much larger tonnages of sulphate and chloride wastes. In the present investigation we report the results of an alternative titaniferous mineral beneficiation process based on soda ash roasting of minerals. Compared to the conventional processes for beneficiation of TiO2- ores, the alkali roasting of titaniferous offers several advantages including the zero process wastes. In the soda ash roasting process, the mineral is mixed with sodium carbonate and heated above 1023 K in air. The oxidative roasting of ores yields several complex alkali compounds, some of which produce a liquid mixture above 1123 K. In this paper, we have attempted to characterize the composition and physical chemistry of alkali-rich liquid phase. The phase equilibria in the Ti-(M:Fe)-Na-O system are evaluated and compared with the phases formed as a result of roasting reaction. The experimental results revealed that the composition of complex alkali liquid at the reaction interface plays an important role in determining the transport of O2-ions and decomposition of ilmenite. The roles of the crystal structure of mineral phases and their energetics are also emphasized in controlling their decomposition during alkali roasting. The presence of molten alkali in controlling the partitioning of water-soluble alkali salts and insoluble sodium titanate is also explained. Keywords: ilmenite, anatase, alkali roasting, phase equilibria.

Jan 1, 2004

By K. C. Mills, R. Thackray

A test has been devised that can predict accurately the % crystallinity developed in a slag film formed between the steel strand and the mould. The % crystallinity in the test samples was determined and compared with that for slag films formed in the mould when casting with that flux. There was good agreement between the % crystallinity in the test samples and the slag films. It was found that additions of TiO2and ZrO2had little effect on the amount of crystalline phase formed, but additions of CaO caused a dramatic increase in the amount of crystalline phase formed. Various parameters (which can be calculated from chemical composition of the flux) have been plotted against % crystallinty in the test samples. It was found that the modified (NBO/T) ratio provided the best relation with % crystallinity for the various parameters tested. There commended relation is % crystallinity=141.1(NBO/T)-284.0. Keywords: continuous casting, mould flux, slag film, crystallinity, chemical composition

Jan 1, 2004

By K. M. Li, Y. D. Zhang

The selection of stripping dragline is a complicated problem. Several factors, such as the deposit buried conditions, the demand of mine production rate, cast blasting result, the mining/stripping operation method and parameters, etc. may comprehensively influence the optimal selection of technical specifications of the dragline. Under these circumstances, the basic thinking and procedures for dragline selection are put forward as follows. •Step 1—Initially estimate the dragline annual stripping rate and stripping bench height according to the annual coal production rate and advancing speed of mining front. Then the feasible alternatives of dragline sizes can be calculated and selected from the existing dragline series. •Step 2—A computer simulation model is developed to simulate the dragline stripping operation, to obtain a series of working face parameters, then to select the best dragline alternative. This step can be interactively iterated until the satisfactory results are obtained. •Step 3— Sensitivity analysis can be done with the systems simulation model by changing the stripping bench parameters, e.g. stripping bench height and cut width, etc. to verify and modify the selection results if necessary. The mathematical model for dragline stripping simulation has been set up. The flowchart of the model is shown. A case study for a large surface coal mine with annual production rate of 16 Mt/a is followed. The dragline bucket capacity and operation radius, stripping bench height and cut width as well as other parameters are comprehensively optimized and selected. Keywords: Open cast, dragline, specification, selection, cast blasting

Jan 1, 2003

By S. Ndlovu

To investigate the influence of orientation of crystal lattice on the bacterial leaching of pyrite crystals, single crystals of 100, 111 and110 plane orientations were used for the study. Experiments were carried out in the presence of a Thiobacillus ferrooxidans culture. The different corrosion patterns observed on the surfaces of the bioleached samples suggests a variation in cell-surface interaction from one crystal plane to the other. The surface corrosion patterns generally reflected the influence of the symmetrical arrangement of the atomic planes in the lattice on which they formed. The results indicate that the surface properties of mineral sulphides may control the evolution of corrosion patterns and consequently the initial oxidation process in acid bacterial leaching.

Jan 1, 2004

By M. Sanchez, I. Imris, G. Achurra

The Smelting and Converting El Teniente Process for copper concentrates as well as Slag Cleaning Furnace Technologies to treat slags coming out from the El Teniente Furnaces are widely applied today in Chile and around the world. Several industrial applications of this process have shown their capability to treat copper concentrates in a wide range of chemical and mineralogical compositions. Main operational parameters determining performance of the process are: oxygen enriched air flow rate, degree of oxygen enrichment, moisture content of the solid materials processed, molten material levels inside the vessel, frequency of molten materials tapping, bath temperature and copper losses in slags. In this work, the copper losses in the slags from El Teniente pyrometallurgical process are predicted by calculation from thermodynamic data and compared with those determined by microscopic examination and slag industrial data. Results obtained show that the main part of copper losses in the slag from El Teniente Furnace are mechanically entrapped or floated unsettled droplets of the coexisting matte phase. by the contrary the very low copper losses in the slag from slag cleaning furnace are limited by the physico-chemical form.

Jan 1, 2004

By R. J. Hundermark, S. Sun

The oxidation state dependence of the electrical conductivity of a calcium ferrite slag with 25 wt% CaO was measured at 1300°C using a shallow slag layer and two-electrode technique. The experiments were started in air and the slag was sequentially reduced by means of a controlled gas atmosphere using CO2and CO. The electrical conductivity in air was approximately 300 S/m and increased with reduction to approximately 1900 S/m at a pO2of 10-10atm. The interest in the oxidation state dependence of the conductivity of calcium ferrite slags was to provide a comparison with the conductivity of iron silicate slags and to establish the effect of slag basicity on the electrical conductivity and its oxidation state dependence. The results obtained are discussed in terms of the slag structural information available in the literature. The co-ordination of the ferric ions appears to play a large role in determining the electrical conductivity. Keywords: calcium ferrite, slags, electrical conductivity.

Jan 1, 2004

By Y. He

The nature of the density distribution in a gas-solid phase fluidized bed for dry coal separation is an important factor in influencing the performance. However, during coal processing, fine slime would mix with dense medium of magnetite powder and accumulate in the bed, and its influence will affect the density of the bed. The mathematical model of the density distribution with fine slime behaviour was studied in an experimental laboratory system. The functional relationship between the density of the air dense medium fluidized bed and the coal slime content were fitted, applying the principle of least-squares method with damping factors. With the model, by analysing the trial testing data, the mechanism of the density distribution of the bed was studied and applied to a coal separation test with a pilot scale separator. Keywords: dry coal separation, gas-solid phase, model fitting.

Jan 1, 2002

By C. Birch

"A ‘geologically constrained’ orebody model has long been hailed as vital for a Mineral Resource statement that is compliant with the South African Code for Reporting of Exploration Results, Mineral Resources and Mineral Reserves (SAMREC Code). In this paper, the requirements for geological modelling as contained in the outline for the SAMREC Code are considered, and whether the new modelling software available on the market is a ‘black box’ or is better for modelling than traditional methods of wireframe creation.Implicit geological modelling is a technique that uses a radial basis function to establish and update geological models relatively quickly and efficiently from borehole data, outcrop data, manually interpreted vertical or horizontal sections, and structural data. Assays and any coded drill-hole data, such as lithology and alteration, can be interpolated.Leapfrog Geo software is an example of this new approach to geological modelling. A case study of a short training course in geological modelling for non-geologists at the University of Witwatersrand, as part of the Higher Certificate in Mineral Resource Management, is presented. The benefits of this type of geological modelling software are considered for this type of assignment as well as for mining industry applications.The use of geological models in mine planning is reviewed and a case study is presented comparing the variations in mine plan design and financial output of 13 final-year Mine Design projects from the University of the Witwatersrand School of Mining Engineering. These designs were all based on the same geological model created in the traditional way, and yet the resultant mine designs were significantly different, with very different resulting financial outlooks for the project. This raises questions as to how significant a very detailed model in the pre-feasibility and feasibility phases of projects really is, considering the huge costs involved in gathering the required data to build a SAMREC-compliant geological model."

Jan 1, 2014

By M. Dworzanowski

Beneficiation, in the context of this paper, has two distinct definitions. From an economic perspective, beneficiation relates to adding value to a mined raw material. From a metallurgy perspective, beneficiation relates to processes used to upgrade the mined raw material. Clearly then, ?economic beneficiation? is dependent on ?metallurgical beneficiation?. South Africa possesses the world?s largest mineral resources by value and is a significant global producer of many mined commodities. Significant metallurgical beneficiation of ores does occur in South Africa. The role of metallurgy in economic beneficiation will be examined in terms of current practice and the potential for expansion. South Africa?s main mining commodities will be covered ? namely gold, platinum, coal, iron ore, manganese, chromium, vanadium, copper, nickel, titanium, zirconium, uranium, and diamonds.

Sep 1, 2013

By H. Ogasawara

To study the preparation process of an earthquake, we should get closer to the hypocentre. In co-operation with ISS International, we had an experimental field (~200 m x~200 m) without dykes and faults in a South African deep gold mine. We have monitored more than 20,000 seismic events (M<2) with borehole tri-axial accelerometers. We used a data acquisition system with 15 kHz sampling and 120-dB dynamic range. In a remnant area at a distance of 100?200 m, an earthquake sequence associated with an M~2 event occurred. Significant changes in seismic parameters such as stress drop, b-value, energy index were observed associated with the sequence. We installed Ishii?s borehole strain meters and could monitor as large a strain change as 10-4associated with mining. However, sampling was only 4 times per hour and 12 bit A/D. A distance from the M2 sequence was ~100 m, being not close enough. Therefore, we found another field with several crosscut tunnels excavated across a fault where an M=2-3 event is expected. We installed the strain meter within several metres of the fault to monitor both shear and normal strains on the fault. The strains are continuously digitized with a 24-bit 25-Hz A/D conversion. The Earth Tide (10-8)is clearly detected. Seismicity induced by longwall mining can be compared to earthquake swarm induced by fluid intrusion to vertical dykes. We also found a decrease in energy index in the source area of M>5events a few days before the major events. Keywords: seismic monitoring, strain monitoring, seismic parameters, preparation process of an earthquake, South African gold mine.

Jan 1, 2002

By Dziurzyn&apos, W. ski

This article outlines the results of a computer simulation reproducing the transport of a mixture of air and methane following the outburst on 25 November, 2005 in transport gallery D-6, bed 409/4, at the ?Zofiówka? hard coal mine. Based on a mathematical model, numerical method and boundary conditions from the disturbance caused by the outburst, the Ventgraph system of computer simulation programs was adopted for the study. We performed a computer simulation of the influence exerted by the outburst on the propagation of the air and methane mixture, and compared the results of this simulation with those of the actual event as registered by sensors of the mine monitoring system. A validation of the model allowed us to present temporal changes in the concentration of methane and air along flow routes. Keywords: mine ventilation, outburst of methane, numerical simulation, monitoring system.

Jan 1, 2008

By M. van Biljon

The possible closure and subsequent flooding of South Deep Gold Mine?s neighbouring Randfontein Estates Limited No. 4 Shaft (REL 4) necessitated the construction of five concrete plugs in the connecting tunnels to prevent the ingress of groundwater into REL4 from flooding South Deep mine. Several technical investigations had been carried out before and during construction of the plugs in order to reduce the probability of groundwater flow through the boundary pillar between the two mines or through the rock mass immediately around the plugs. This paper describes the geological, hydrogeological and stability investigations carried out to evaluate the structural competence of the boundary pillar.

Jan 1, 2006

By J. Martinovic

The large proportion of gangue minerals present in platinum bearing ores in South Africa provides challenges to the flotation and downstream processes. In order to take effective measures to reduce their recovery in flotation, an understanding of the mechanisms and factors influencing their behaviour is needed. Typical gangue minerals are pyroxene, feldspar, quartz, chromite and talc. Of these, talc is a naturally hydrophobic mineral and although it is present in relatively small quantities, it has a disproportionate effect as it has a strong froth stabilizing effect, increasing the recovery of other gangue minerals by entrainment. Talc recovery is effectively reduced with the addition of polymeric depressants. Although the other gangue minerals are assumed to be hydrophilic and their recovery by entrainment is expected to follow the water recovery, there is some evidence that they may be activated by the typical reagent suites used. Reagents such as copper sulphate, added as an activator, and collectors are used to selectively induce hydrophobicity on the sulphides. It has been shown that some of these gangue minerals can be activated. This research work investigates whether inadvertent copper activation is mineral specific and evaluates the mechanisms and factors affecting the reversal of activation with the addition of the depressants using electrokinetic measurements, adsorption and microflotation tests. Results are presented that show that the selected minerals do respond differently and that the reversal of activation is dependent on mineral type, depressant type, dosage and ionic strength of the electrolyte.

Jan 1, 2005

By M. Moys

The use of temperature measurements for unusual applications in the analysis and control of column flotation and milling is discussed. This is followed by a review of some of the authors current research in the application of the discrete element method to the modelling of particulate processes, specifically milling, fluidized beds and chute flow.

Jan 1, 2005

?Longhole blast hole drilling? techniques are not new to the mining industry. Appropriate mechanization and improvement of the techniques and application has evolved from the industry requirements. Today safety and economics play a larger role in the excavation of ore passes, ventilation passes, and relatively small inclined excavations in the conventional gold and platinum industry. The application of dropraise drilling from the top or from the bottom is discussed investigating the current techniques available, DTH application, advantages and disadvantages, limiting factors, typical layouts and proposals, the drop raising technique and future applications. Similarly, the application of longhole blast hole drilling in tabular and massive orebodies is discussed with emphasis on the DTH application, advantages and disadvantages, limiting factors, typical layouts, the long hole stoping techniques and future applications.

Jan 1, 2003

By M. F. Dlamini

The hydrodynamics of a hydrocyclone present a complex internal flow structure, the numerical simulation of which remains a non-trivial task. We report on three-dimensional water-only computational fluid dynamics (CFD) hydrocyclone flow field predictions and highlight some of the issues concerned with the development of a CFD model incorporating an air core. The potential for the application of CFD as a hydrocyclone design tool is also discussed. Physically realistic velocity profile predictions were obtained, which challenge the classical account of the hydrocyclone radial particle classification mechanism. A pressure field distribution consistent with literature reports was also predicted. Keywords: hydrocyclone, computational fluid dynamics (CFD),classification mechanism

Jan 1, 2005

By G. Denton, P. den Hoed, A. Luckos

The potential application of fluidized beds in several sectors of the ferroalloy industry is promising. They can be used in the direct reduction of iron ores to produce a feed for steelmaking, in the reduction of manganese dioxide to produce a lesser oxide for feeding to smelters, in the preheating of chromite for the production of ferrochrome, and in the calcining and pre-reduction of nickel laterites for the production of ferronickel. This paper discusses the potential of fluidized beds in theses processes and highlights the advantages of the technology over other technologies, such as rotary kilns. Two primary advantages?(1) that fluidized beds can treat fine materials and (2) that fluidized beds can be integrated with smelters in a way that allows for more efficient use of energy?may well see the technology gain prominence as more deposits of lower grade are mined and industries strive to use their resources more efficiently. In discussing the potential of the technology in the ferroalloy industry, this paper focuses on the application of fluidized beds in the smelting of chromite, nickel laterites, and manganese ores. Central to the successful operation of this technology is a knowledge of how particle properties influence the behaviour and design of fluidized beds.

Jan 1, 2007

By J. A. Kromhout, J. Trouw, A. A. Kamperman, M. Kick

Mould powders play an important role in the stability of the continuous casting process. The main functions of mould powders are to provide sufficient lubrication and to control the horizontal heat transfer. Because process control of thin slab casting is more stringent, it is generally assumed that mould powder properties become more critical as well. In 2000, the Direct Sheet Plant at Corus IJmuiden (DSP) was commissioned, incorporating a thin slab caster designed for casting speeds up to 6 m/min. During commissioning, several operational problems with mould powders were encountered i.e. insufficient liquid pool depth and the formation of rims/lumps. To investigate the operational mould powder problems, some of the mould powders were characterized using physical and mineralogical methods. The results were linked to operational experiences. It was concluded that for thin slab casting, a stable slag formation is obtained with a proper choice of free carbon and an even distribution of the carbon particles within the granules. The physical properties of mould powders are not as critical as expected when the additional mineralogical requirements are taken into account. Keywords: mould powder, characterization methods, thin slab casting.

Jan 1, 2004

By M. Shapiro, L. A. le Grange, B. Henning

Effective pyrometallurgical process vessel design requires accurate assessment of the heat fluxes through the walls of the furnace. This is particularly important for freeze lining operation which is designed to protect refractory materials exposed to chemically corrosive molten contents, or facilitate high temperature operation when the refractory materials are used at conditions close to their service limits. Numerical modelling of fluid flow and heat transfer in process vessels is often used to aid in the design of process vessels. Sophisticated models are used to analyse the three dimensional flow and heat transfer predicting the effects of electrical heating, magnetic stirring, buoyancy, shear forces, various cooling effects and ultimately heat fluxes at the walls of the furnace and refractory. Traditionally these models are applied to the separate single fluid systems in a vessel such as the freeboard region including the arc, the slag region and the metal bath. Boundary conditions such as shear forces and heat fluxes between connecting regions such as the slag and metal bath are either estimated or carried over from separate solutions. Shortcomings in these traditional approaches include the estimation of sometimes critical boundary conditions leading to unreliable heat flux calculations. Also when boundary conditions are carried over between solutions, the process is difficult to set up, time-consuming and finally not fully coupled. In this paper the definition and results of a fully integrated numerical model of a complete arc furnace are presented. The most important mechanisms acting in an arc furnace were considered, including the fields of electrical potential, current, magnetism, momentum, heat transfer and radiation. Temperature dependant properties included electrical conductivity, density, viscosity, and thermal conductivity. The geometry consists of the freeboard, the arc, slag, metal baths and different refractory regions. Although the combined model of air, slag and metal would be defined as a multi-phase problem it is not solved as such. Instead the different fluids are separated by sets of special solid baffles. These baffles allow the implicit transfer of current, magnetism, heat transfer and shear forces between the different fluids and disallow mixing of the separate fluids. The strengths of the integrated model are threefold: Firstly, it provides robustness in defining the geometry and boundary conditions for the overall model. Secondly, it provides the capability to switch on and off individual mechanisms such as buoyancy, magnetic stirring and shear forces in order to observe their individual importance. Finally, it provides a useful tool in the design process through its ability to obtain results of parameter changes in short time scales.

Jan 1, 2004

By SDN Wessels, WA Naismith

On 16 July 2004, at 07:10 a collapse of about 1.8 million m3 (about 4 ½ million tonnes) took place on the north wall on Nchanga Open Pit This collapse was the result of a developing instability that was first identified when the benches in this area were exposed during September 2002. The NOP Geotechnical and Survey Departments closely monitored the development of the failure. Control measures were implemented to reduce risk to men and equipment. These measures were continually improved and adjusted in reaction to observations and changing conditions. The purpose of this paper is to describe in detail the monitoring results that were obtained both by traditional methods and the novel Slope Stability Radar System (SSR). Difficulties encountered in establishing critical deformation levels and deformation rates that can be used to predict the onset of collapse are described. Details of the monitoring and control measures, which led to the successful completion of mining in the area, are also described in this paper.

Jan 1, 2005