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By J. A. L. Napier

Computer programs which rely on the assumption of linear, elastic rockmass behaviour have been used routinely for many years in the South African mining industry to determine the stresses arising in the vicinity of mining excavations. A description is given of the theoretical background and novel solution techniques used in the recently developed MINSIM-D boundary element program. Features of the program include the ability to analyse multiple interacting reef planes at arbitrary orientation to one another, slippage on fault planes and the effects of backfill placement in mined areas. Incremental mining sequences can be modelled, and digitizer and front-end routines have been written to assist in the capture of mining outlines and general problem specifications. A brief indication is given of design problems for which MINSIM-D is appropriate, as well as some future extensions of the system.

Jan 1, 1987

By L. A. Vermeulen, D. D. Howat

New distribution functions are derived to describe the size distribution of grinding elements in ball mils. The formulations are based on the assumption that abrasive as well as impactive interactions occur during bal milling-an assumption that is supported by a large body of experimental evidence. It is shown that the functions can be used in the estimation of the magnitudes of abrasive and impactive components in the total rate of bal wear. The relative magnitudes of the wear components provide a basis for optimization of the chemical and metallurgical properties of the balls in a given milling situation. However, it is contended that these quantities are also useful indicators of the relative intensities of the abrasive and impactive interactions that are operative in the size reduction of mineral particles within ball mils. These quantities can be determined for any industrial ball mil, and their magnitudes provide practical guidelines for mil operation. The theory is used in an analysis of samples of ball charges from two industrial ball mils, and it is also applied to al the data on bal-size distributions found in the literature. The qualitative correlation between the calculated values of the wear components and the reported operating conditions is good for a variety of industrial ball mils, in conformity with the hypothesis that the relative magnitudes of the wear components are related to the milling conditions.

Jan 1, 1986

By George Kayesa

[ ] A multiple-bench slope failure occurred at Letlhakane mine on 14th July 2005. No injuries or damage to equipment was suffered and mining production was not affected. Slope failure was preceded by the precursors of tension crack formation, crack widening and extension as well as slope monitoring targets movement. It was predicted that slope failure was imminent using the Geomos slope monitoring system, though the timing was not certain. The area to be affected by the slope failure was also known before hand as was the slope failure mode. As a result, measures were taken to avoid exposing personnel and mining equipment to the slope failure risk. This paper discusses how the prediction of the slope failure of 14th July 2005 using the Geomos slope monitoring system resulted into avoiding potentially fatal injury, damage to mining equipment and loss of mining production.

Jan 1, 2006

By F. Trabzuni

Elutriation of solid reactants from fluidized bed reactors can affect their process performance and efficiency greatly. Chlorination fluidized bed reactors for selective conversion of solid metal oxides to metal chlorides are used widely these days. This study provides a platform for a proper understanding of reactant solid characteristics and solid shrinkage interaction with elutriation rate constants using multi-sized particles, sand-like, ?Geldart B? chloridable materials. The study has found that actual elutriation rates of the reactive system are influenced by complex parameters? interaction including bed diameter, reactor freeboard height, bed minimum fluidization velocity, and reactant?s physical properties.

Jan 1, 2009

By R. Guest

Reichert cone concentrators are used successfully in many applications, but have as yet not found favour in the gold mining industry on the Witwatersrand, because, for optimum operation, the cones need to have specially designed feed-preparation and circuit details. In addition, good liberation of the valuable minerals is essential. Gravity tests, in which a pilot plant was used on refractory gold ore, showed that 94 per cent of the gold could be extracted after gravity concentration and preferential grinding, roasting, and cyanidation of the concentrate, whereas 96 per cent could be extracted by flotation followed by the same preferential treatment. However, the capital and operating costs for gravity separation are expected to be considerably lower than those for flotation.

Jan 1, 1982

By H. C. Voges

An account is given of the tests being conducted by Iscor on the following processes for the beneficiation of coal fines: froth flotation, gravity separation, heavy-medium separation, and pneumatic and column flotation. The coals used in the tests came from the Durnacol, Tshikondeni, Grootegeluk, and Hlobane collieries. The problems involved in the dewatering of fine products are stressed. From a theoretical study of the efficiencies that should be possible for a hypothetical South African coal, it is concluded that future fines-beneficiation plants in South Africa may use standard heavy-medium cyclones for coal down to 1 mm in size, fines heavy-medium separation for the 1 mm to 450 µm fraction, and column or pneumatic flotation for the minus 450 µm fines.

Jan 1, 1991

By M. Splaine, C. E. Dohm, S. J. Browner

As the grade of the gold (head grade) in the ore supplied to a reduction plants falls, the efficiency of recovery of the metal drops. This is not simply due to a fixed grade lost in the residue, since the residue grade is itself a function of the head grade. A multi-disciplinary approach was used in the construction of a model to represent the relationship between head grade and recovery efficiency. The model is a physicochemical one based on (i) the reaction characteristics of cyanidation, (ii) the milled-ore selection characteristics of gravity concentration, and (iii) the nearly log normal distribution of gold grades and particle sizes in ore reserves. The model was used to set sound target levels for recovery efficiency for a given head grade at a given plant, against which the performances of the plant equipment can be judged for control purposes.

Jan 1, 1982

By P. R. Jochens, D. D. Howat, C. W. Wolhuter

Prof D. D. Howat (Member): I am a man with a grievance this afternoon. The other authors of the paper entered into a conspiracy to ensure that I presented the paper, and finally even had the audacity to say that this was the least that could be expected from me as I had done so little of the other work. Looking at the distinguished audience here that includes some figures who have forgotten more about cement that some of us have ever learned, I realise how right the other authors were. I feel very much cast in the role of the fool who was pushed in where angels fear to tread. I hesitate to say, Sir, that I would not use the word angels in any definition of the authors of this paper. In presenting the paper, may I try to put forward a few simple points about cement that are probably as little known to the majority of the audience as they were to me-at least until very recently. Concrete, made by mixing Portland cement, sand, crushed rock and water is the most widely used constructional material in the world. Generally the production of actual Portland Cement is about two-thirds that of steel and by the time this is formed into concrete the total is about five times the world tonnage of steel produced. A very rough approximation suggests that world consumption of concrete is about one ton per person per annum. Apart from fresh water mankind consumes no other material in such quantities. What mankind originally required was a mortar to be used for joining blocks of stone or bricks. Such mortar was originally made from limestone burned in a kiln and then mixed with water. Production of mortar of this type began over 5,000 years ago. Some samples from pyramids in Egypt have shown this mortar to be in good condition although over 4,500 years old. The progress of technological development was very slow until 1824 when an English bricklayer, Joseph Aspidin, patented a new mortar material which he made by burning limestone and clay together in his kitchen stove. Aspdin called his product 'Portland Cement' because, in colour, it resembled a well-known building stone quarried in the Isle of Portland on the south coast of England. Aspid's same types of raw materials are used today in modern cement production and the product is still referred to as Portland cement. A lime-containing material such as chalk or shell and a clay-type material such as shale, slate or clay itself, are mixed in the required proportions, ground and fed to a kiln where the minimum burning temperature is about 1,500°C. The raw materials react to form hard chunks of a material known as 'clinker'. About 5 per cent of gypsum is added to the clinker and the mixture is then ground to a very fine powder, the function of the gypsum being to control the rate of setting of the concrete. The key oxides in cement production are lime, silica, alumina and iron oxide. The possible reactions occurring during and the products of the burning process are shown in Table I.

Jan 12, 1968

By J. Gholamnejad

Determination of the optimum cut-off grades is one of the most important aspects of mine production planning. A cut-off is a grade below which we choose not to process material. This material is treated as waste and dumped. Dumping waste is accompanied by the rehabilitation cost which will affect the overall cost of final production and also the optimum cut-off grade. Rehabilitation cost is the cost per ton of rehabilitating material of a particular type of rock after it has been dumped as waste. One of the most popular algorithms for determination of the optimum cut-off grade is Lane?s method. Lane formulated the cut-off grade optimization, but he did not consider rehabilitation cost during the optimization process. This cost item should be evaluated first, and then considered during the cut-off grade optimization process. In this paper the rehabilitation cost is inserted directly into the cut-off grade optimization process using Lane?s theory. The cut-off grades obtained using the suggested method will be more realistic than ones using the original form of Lane?s formulations.

Jan 1, 2009

By Y. -L. Chiang

Paper written on project work carried out in partial fulfilment of BSc (Eng) (Chemical) The generation and control of manganese sulphide particle size distribution using various mixing configurations were investigated. Specifically, this paper discusses how varying mixing intensities on a macro and micro scale affect the resultant manganese sulphide particle size distribution (PSD) at a constant concentration. The mixing variations were achieved using various Y- and T-mixers as premixing devices into a jacketed, agitated vessel. The reagents used to generate the seeds were aqueous manganese sulphate and sodium sulphide solutions. The results showed that the absence of micromixing resulted in very poor control of the particle size distribution, the particle size and the number of particles produced. This was due to the fact that the macromixing time is much greater than the corresponding precipitation time, resulting in different mixing regions existing within the reactor. From the micromixing experiments, the T?mixer was found to be the most effective mixing device at lower concentrations due to the T-mixer providing a faster mixing time than the other mixing configurations, thereby effectively localizing the supersaturation and hence controlling the precipitation. The results obtained from the direct addition without the extension pipe (i.e. short mixing time) indicated a general increase in mean particle size and decrease in total particle number at reagent concentration of 0.007 mol.dm-3as compared to the corresponding micromixing experiments. The phenomenon may be due to incomplete crystallization at the immediate exit of the mixing device. Further experiments need to be conducted before any conclusions can be drawn about the precipitation mechanisms.

Jan 1, 2007

By G. D. Schena

The issue of evaluating the economic impact of large mineral projects in developing countries was studied by the use of econometric models. The evaluating system is demonstrated by its application to an example from Namibia. Three-dimensional graphics are used to illustrate the procedures leading to an assessment of the economic effects of the mineral development. The analysis allows the assessment of the overall economic consequences of mineral developments where there is a need to incorporate in the evaluation issues that are broader in scope than the pure financial objectives. Sets of technical coefficients are exploited for the development of input-output models of the productive structure of an economy. The models are refined to incorporate country-specific behaviours. The increased flexibility of the enhanced semi-input-output model permits a more confident investigation of the economy wide effects associated with a new project in the mineral sector of a developing country. Synthetic measures of profitability at market and shadow prices are introduced, and the cost/benefit ratio is used to rank mineral projects according to their economic profitability. The cost is the capital mobilized for the development of the project and for increasing the productive capacity of the related satellite industries. The benefits are identified with the economy-wide increase in value added induced by the project. 80th costs and benefits are initially valued at market prices. Their ratio is likely to be an index of economic profitability superior to measures that concentrate exclusively on the benefit side of projects. To allow for market distortions, the concept of shadow prices is introduced, and accordingly project-related costs and benefits are re-evaluated. A new cost/benefit ratio at shadow prices is recalculated, which is more meaningful to the policy-maker than decision-making based on socio-economic issues.

Jan 1, 1993

By M. Gershon

During the exploration phase of mine development, drilling location is in the hands of the geologist, and drilling is spread over the entire domain of the property or deposit boundary. During the mine planning and production phases, however, the mining engineer also needs to use the information obtained from the drilling program. Thus it is important that he/she have some input into the selection of the drillhole locations. Usually, when exploitation will center on one portion of the property for the immediate future, the mine engineer will want to have more of the drilling performed in this area. In the early stages, the purpose of the drilling was to make a decision concerning whether or not to develop a mine. Once the decision is made to proceed with this development, the mine engineer needs to know, with as much confidence as possible, the estimate of the ore grade at each location where mining will occur. This paper addresses the problem of drillhole location for the needs of the mining engineer. The goal is to compare a variety of approaches to drillhole location with a new approach developed by the author. This approach is based on the theory of geostatistics, with the estimation variance used as the quantitative measure of the confidence attained. The goal of the algorithm is to select those locations that minimize the estimation variance subject to constraints on the number of drillholes and the total cost of the drilling program. The kriging equations are used as another set of constraints. The resulting nonlinear optimization model is expressed in terms of binary (0 - 1) decision variables leading to a solution by the branch-and-bound procedure. The algorithm has been applied at a number of operating properties, and practical results and suggestions for implementation are provided.

Jan 1, 1987

A brief overview is given of the issues regarding the processing of waste electrical and electronic equipment (WEEE). The printed circuit board component of WEEE is an exceptionally complex feed to possible recycling processes. Scrap printed circuit boards were selectively smelted at 1 200°C to produce a metallic alloy. Iron and aluminium were found not to be part of the alloy. The alloy was characterized by SEM-EDS, and three phases were identified: alpha and delta bronzes, and a lead-rich phase. Calculations show that about 56 mass per cent of the alloy is the alpha phase, 35 per cent delta phase and 9 per cent lead phase. A simplified approach using appropriate binary phase diagrams was used to derive a phase composition for the alloy. This was further backed by FactSage calculations, which showed that the simplified approach was appropriate for this alloy. The experimental findings and theory were found to agree well.

Jan 1, 2009

By P. F. Sorensen

A simple mathematical model is presented that relates the 'head' developed at the surface of pulp in a tank to the power dissipated by the air in producing it. The value for the head is then used in the calculation of the superficial circulating velocity of the pulp and the area of the overflow, and the product of these two values gives the pumping rate of the pulp. Thus, the superficial circulating velocity, and hence pumping rate of the pulp, are related directly to the flow-rate of the air. This hypothesis was tested with good results in an air-agitated pachuca tank (of 1 m in diameter) fitted with a draught tube. The method can also be used for the prediction of the pumping rates in production-scale vessels.

Jan 1, 1985

By S. Budavari

The effects of shaft pillars left in deep-level hard-rock mines during the extraction of tabular deposits were studied some time ago, resulting in the formulation of design principles and procedures, which have been used with success in the design of shaft pillars in the deep-level gold mines of South Africa. The method has not yet been utilized in the design of shaft pillars in shallow and moderately deep hard-rock mines. The purpose of the present study was to remedy the situation since a great number of deposits are worked at those depths. The object of this paper is to present governing equations for the components of stress and differential movement as derived by use of an elastic model. The pillar is taken to be circular in the plane of a horizontal deposit. On the basis of the numerical results obtained, a study was made of the distribution of the vertical strain and tilt along the axis of the shaft, and of the vertical stress along the shaft and across the pillar. In every case investigated, the most adverse geometry was taken into consideration. By use of an empirical criterion and the results of some in situ observations, the determination of pillar dimensions and differential displacement components for South African gold-mining conditions is demonstrated. Pillar dimensions for shallow and moderate depths are compared with those accepted for deep-level conditions.

Jan 1, 1986

By M. Dobbins

Magnetic separation has long been used to upgrade and beneficiate a wide variety of industrial minerals. Advances in both wet and dry magnetic separators over the years has broadened their use, and questions are often raised about which separation technique or equipment type is most appropriate for a particular operation. This paper will provide a brief look at existing magnetic separation technologies, and discuss their potential advantages and disadvantages when applied to heavy mineral applications. Relevant case studies for the separation of ilmenite and chromite are then presented. The process development efforts undertaken for each case are described, and the rationale for selecting appropriate magnetic separation technology is explained. The nature of the material being treated must clearly be understood, knowledge and access to testing the best separation technologies is required, and careful process development and economic evaluations are a must. As is shown in the case study discussions, it is imperative that these principles drive the separation technology selection and placement, rather than looking at typical or existing similar flowsheets as rules. As examples, the ilmenite tailings case study presented in this paper shows how advances in technology have allowed for increased recovery of -45 µm ilmenite by utilizing a multi-stage SLon® wet magnetic separator circuit equating to an additional 30 000 tons of ilmenite produced per year. The virgin chromite case study presented shows that through careful testing and circuit design efforts using RED technology, a 20% increase in overall chromite recovery was achieved over previous demonstration work.

Jan 1, 2007

By A. Hinde, M. H. Moys

Tailings from metallurgical plants, when deslimed with hydrocyclones, provide a valuable source of material for the backfilling of mines. The effectiveness of this material as a support medium is a sensitive function of its particle- size distribution and water content. It is therefore important that the hydrocyclone-classification plants used to prepare the backfill are operated efficiently, and that the effects of feed disturbances on the composition of the backfil are minimized. This paper addresses the problem of the design, control, and optimization of classification plants to satisfy this need. The development of a computer program to simulate the dynamic behaviour of a hydrocyclone circuit of any given configuration is described. The use of the simulator to investigate the relative performance of conventional and innovative control strategies for single-stage and two-stage circuits is discussed in depth. The results of simulation studies are presented that indicate there is considerable scope for improving the performance and cost-effectiveness of backfill-classification plants.

Jan 1, 1991

By E. Cetin

Orebodies that contain more than one economically important mineral are generally evaluated by parametric cut-off grades. This approach often leads to mis-valuation of mineral deposits because cut-off grades are not based on the grades of each individual mineral and, because of the parametric formulation, are only indirectly related to the individual grade distributions. The only realistic approach is a formulation that accounts separately for each component mineral. The grid search method can be used as a means of multi-mineral cut-off grade optimization in this context. This paper describes the use of the grid search method in cut-off grade optimization for multi-mineral deposits. The authors introduce the general concepts of the method and formulate its application to cut-off grade optimization; they describe a software implementation of the method that can accommodate cut-off grade optimization for mineral deposits that contain up to three economic minerals. Keywords cut-off grade, optimization, grid search, multi-mineral deposits.

Aug 1, 2013

By D. F. Malan

This paper describes the development and implementation of amine-wide continuous stability monitoring system at the Declines Section, Anglo Platinum Union JV. The Declines Section at Union JV experienced a number of large panel collapses during 2005 and 2006. As well as posing a major safety risk, the panel collapses had a major effect on production since the Declines Section is a semi-mechanized operation. The collapses would often extend into the mechanized strike roadways, resulting in a loss of access to both current and future production faces. The collapses have been largely overcome owing to a change in support design and the implementation of a mine-wide stability monitoring programme. This paper describes the precursors to collapses, which were identified using continuous closure measurements and the remedial measures taken. It also outlines the design and introduction of a robust and reliable monitoring tool, which is now used on a mine-wide basis to provide early warning of large-scale collapses.

Jan 1, 2010

By M. C. J. van der Merwe

"Carboxymethyl cellulose is an organic binder used in the iron ore pelletizing industry. The basic principles of how carboxymethyl cellulose (CMC) solutions behave during the pelletizing process and how these principles affect the drop and compression strengths of the pellets are poorly understood. The aim of the investigation was therefore to gain knowledge on the behaviour of CMC during the pelletizing of haematite concentrate.Haematite pellets with different additions of CMC (0.1–0.4 wt%), were subjected to drop tests, compression tests, and free moisture content analysis. The relationship between the drop strength, compression strength, free moisture content, elapsed time, and CMC concentration was analysed.The drop strength had a strong correlation with the free moisture content of the haematite pellets, with a correlation coefficient of 0.94. The compression strength of the CMC-bonded haematite pellets increased as the free moisture content decreased, reaching a maximum upon depletion of the free moisture content. Haematite pellets with CMC concentrations of 0.1 and 0.2 wt% developed most of their strength within the first day after pelletizing, whereas pellets with concentrations of 0.3 and 0.4 wt% developed most of their strength between one and two days after pelletizing. The time within which CMC-bonded haematite pellets develop most of their strength is therefore dependent on the CMC concentration. IntroductionFines are produced during the beneficiation of iron ore. These fines are separated from the lump ore and can be upgraded to produce a concentrate, which is used as a raw material for the production of pellets. Pellets in turn form a key burden material for direct reduction processes as well as the blast furnace (Zhu et al., 2015).Inorganic binders such as bentonite have been used predominantly in the iron ore pelletizing process to obtain pellets with suitable properties (Eisele and Kawatra, 2003). These binders, however, have the disadvantage of introducing impurities into the pellets. This has resulted in organic binders being pursued as suitable replacements for inorganic binders, of which carboxymethyl cellulose (CMC) shows good potential. Although CMC has been used as an organic binder in iron ore pelletizing, the fundamental principles of how it behaves during pelletizing and how these impact on pellet properties are poorly understood."

Jan 1, 2017