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By H. W. J. P. Neomagus, J. R. Bunt, T. S. Mthombo, C. A. Strydom

"Low-cost calcium lignosulphonate (CL), which is a byproduct of the wood pulping industry, was investigated as a potential binder during laboratoryscale pelletization of inertinite-rich high-ash coal fines from the Highveld Coalfield of South Africa. Coal-binder mixtures containing between 1 and 15% calcium lignosulphonate were prepared, pressed, and ultimate, proximate, porosity, XRD, and XRF analyses obtained. It was found that increased pressure during pelletization results in increased attractive forces, due to increased interparticle contact areas. FTIR analysis showed that chemical interactions occur between coal fines and the binder, as evidenced by the formation of new C-O ether-type bonds. The presence of moisture during pelletization enhanced surfactant activity of the binder. Chemical interactions between the coal and the binder seem to be mainly electrostatic, driven by Ca2+ from the calcium lignosulphonate, which may act as a bridge between the anionic parts of the binder and the surface of the coal. IntroductionCoal has over the years remained South Africa’s major energy source, with over 90% of the country’s electricity being produced via coal-fired processes (Arndt et al., 2016). Sasol’s coal conversion technology alone provides more than 40% of South Africa’s liquid fuel requirements (van Dyk, Keyser, and Coertzen, 2006). The production of high-grade coal requires the processing of run-of-mine (ROM) resources by a combination of processes which include crushing, screening, and washing (Radloff, Kirsten, and Anderson, 2003). These processes result in the generation of coal fines (< 0.5 mm) which, until recently, have been discarded into slimes dams (le Roux, Campbell, and Smit, 2012). Several issues are associated with slimes dams, among which are the costs of transportation of these fines from the place of origin to the discard point (often a considerable distance), and the potential environmental effects due to seepage of toxic materials into surrounding ecosystems (Clausen, 1973).Consequently, utilization of these coal fines is an area of great interest. Mechanical densification of fine coal by means of pelletization and/or briquetting to larger sizes for use in technologies that require lump coal, such as chain-grate stokers and fixed-bed gasifiers, has been shown not only to reduce environmental risks (Mangena et al., 2004), but also to significantly reduce storage and transportation costs (Mani et al., 2001). Pelletization is the process by which solid particles are consolidated into uniform, usually hard, impact-resistant agglomerates, rendering them useful as a fuel with sufficient calorific value for domestic and industrial utilization (Finney, Sharifi, and Swithenbank, 2009)."

Dec 1, 2018

By Y. J. F. Haven, G. H. J. Kitson, D. G. Beadle

I have read this paper with considerable interest. By using an automatic instrument to assess the dust samples taken in South African collieries, the authors are ahead of the gold mining industry, which still uses the laborious method of microscopic assessment, with its limited accuracy, of the half-a-million dust samples taken each year. As the authors state, the result obtained from the photoelectric assessment of the samples is approximately proportional to the surface area of the respirable dust. However, modern theory is that, in assessing coal dust, it is the respirable mass which is important in determining the danger to health. Thus Table II of their paper is of considerable value in showing the relationship between the P.E.R. value and the mass concentration measurement. Unfortunately this table only gives the mean relationship. The important point is to know the scatter around this mean. If the scatter is small, then this mean value (for different operations) would have considerable value in converting from respirable surface area to respirable mass, but if the scatter is large, then such a conversion, using a fixed factor, will have little value. In the text the authors mention the range of values as being between 3 to 24, but without a statement on the number of samples used to determine this range and their distribution, this is a rather nebulous statement. I hope, in their reply, that the authors will give, in statistical terms, some statement on the overall correlation between these two parameters. I might add that at present a member of my staff is working on similar relationships for dust samples taken in gold mines. Another factor which may well be most important in determining the danger of dust levels in coal mines is the composition of the dust, specifically its quartz content. I understand that the authors have some information on this point, and to make their results of greater value in International comparisons of dust levels and the concomitant development of pneumoconiosis, it will be extremely useful if they could place this information on record. Even though, as I have said above, modern theory postulates that respirable mass is a better parameter to use than respirable surface area, the problem remains of how to measure this parameter with short time sampling, which, as the authors point out, is their preferred strategy for dust sampling and dust control. I know of no easily portable instrument, independent of external power supplies, which can, in 5 to 10 minutes, collect sufficient dust to enable it to be weighed accurately. Thus the authors&apos; implied intention of continuing to sample by their present techniques and using their present parameter to report the results is, in my opinion, an entirely valid decision.

Jan 10, 1968

By C. J. Alberts

The perception exists in many organizations that, once an energy management system is employed, there need not be any further adjustments to such a system. This is not true, as the field of energy management is a dynamic field, and constant feedback and adjustments are needed to enhance the efficiency of a system to the point that substantial pay-back can be obtained. It is stressed that for any energy management system to be successful, careful planning should permeate through the organization, from the top level decision-makers to the workplace. This paper describes a dynamic technique by which energy management strategies can be evaluated by viewing the effects of the strategies on the organization as a whole.

Jan 1, 1997

By E. P. Gush

Diamonds, an enigma in a mineral resource sense. Chemically, diamonds are no more than carbon crystals in a cubic system-formed one might add under conditions of great pressure and temperature. They have certain physical properties which are fairly unique. They are very hard, they have a high refractive index, they luminesce, some of them fluoresce, they have a high specific gravity, they don&apos;t wet and they are a good conductor of heat. In a way, a rather clinical set of qualities. Of course, these qualities are what give diamonds their use and their beauty. It is on the emotional side that they get complex and stir memories of legends, of beauty, of wealth and romance, of war, happiness, bad luck and curses. It is on the emotional side that the value of a diamond is established, if such a thing is possible. Diamonds are extremely varied, there are more than 5000 categories into which they are sorted, so there is room at each point across the spectrum for their individualities to emerge, and accordingly their attractiveness to each buyer is unique.

Jan 1, 1994

By A. Miller, M. Bétournay

The main objectives of the Mine Mechanisation and Automation program (MMAP) are to enhance health and safety in underground mining operations, facilitate mechanization and automation in narrow- vein and deep mines, provide sound science to regulatory agencies and improve mine profitability. The program, which has a unique underground and surface industrial scale facility, is involved in many multi-partner projects, like hydrogen fuel cell applications, electrification and hydraulification of underground mines, reduction of noise and vibration, miner location device, explosive-free blasting and hoisting. The paper presents an overview of the Mine Mechanisation and Automation Program of Natural Resources Canada and some of the main projects.

Sep 1, 2001

In many practical situations, calculation of the point semivariogram is not necessary. Such a case is analysed in this chapter. The purpose of this analysis is to give a better understanding of the meaning of the mathematical formulae developed in the previous chapters. A similar problem will be studied in Chapter 11, using the point semivariogram.

Jan 1, 1978

By A. A. Hazell

Mine management by objectives by A. A. Hazel The procedure of setting production targets is illustrated in Appendix I of the paper. This procedure is intended only as a guide although the standards on which it is based were established by work studies and found subsequently to be well within the limits of a trained crew.

Scientific and technical research is becoming an expensive business, and needs to be managed as well as directed. Regardless of whether it operates under public or private auspices, a research-and development organization should not tolerate inefficiency or irrelevance. Its true worth is ultimately decided by the impact it makes on its environment. Doing the right things is preferable to merely doing things in the right way. Clear definition and the setting of goals form the crux of the Management by Objectives (MBO) system. This system provides the research establishment with a profound sense of purpose and direction, which is essential for effective planning and control. Performance standards, in association with costs and manpower, value assessment, feedback, and improvement, tend to follow naturally once the principle of a results-oriented management system is adopted. MBO is a participative management system, leading to decentralization and self-control of the individual rather than imposed control. If wisely implemented with the necessary respect for creative work, it can enhance the job satisfaction of the research worker as well as the overall productivity ofthe research establishment.

Jan 1, 1982

By Hannweg L. A.

In a first for the diamond industry, Koffiefontein Mine in the Free State, South Africa, opted for the front cave mining method to extract a 90 metre high block of kimberlite ore. Block caving, because of its high initial capital requirements, resulting in a negative internal rate of return (IRR),was ruled out as a feasible mining method for Koffiefontein Mine. Front caving is essentially a combination of the traditional block cave and sub-level cave mining methods, but uses two or more levels of retreating drawpoints. Two extraction levels, in the case of Koffiefontein Mine, are spaced 12 m apart vertically, with the upper 478 m level (48Level) acting as the undercut/extraction level, and the lower 490 m level (49 Level) as the extraction level. Caving is achieved by undercutting a small column of ore, which is then drawn, on both the 48 and 49 Levels, until the planned extraction percentage is achieved. The next column of ore is then mined by advancing the undercut (48 Level), and the process is repeated until the entire ore block is depleted to the contact. Caving-by-gravity techniques of mining rely on closely controlled draw of the caved ore to ensure proper caving action and to minimize the dilution of ore with waste material from the open pit. This paper discusses the need for, and implementation of, a draw control system at Koffiefontein Mine — a computerized production management system, and a draw control system based on linear programming, to allow control over the draw rate and mining sequence — a major factor in all production planning to optimize production efficiency, ore recovery and cave management. Keywords: Draw control, Koffiefontein Mine, Front cave, Caving

Sep 1, 2001

Ladies and gentlemen, it is a privilege to be able personally to welcome you to the opening of this Symposium. It is particularly pleasant to be able to extend a warm South African welcome to al our visitors from foreign shores. We trust you will enjoy your stay in our country. It is a singular honour for me to be present here today, and to have been asked to open this international Symposium. MINING IN SOUTH AFRICA Mining is the single most important contributor to this country&apos;s foreign-exchange earnings. Minerals and processed mineral products together account for about 70 per cent of South Africa&apos;s total foreign exchange earnings. The mining sector employs in excess of 670 000 people, and is one of the largest employers in the country. The construction and development of cities and towns like Johannesburg, Welkom, Orkney, Springs, Benoni, Witbank, and Klerksdorp is a direct result of the contributions of the mining industry to economic activity in these areas, as well as of the multiplier effect of secondary industries.

Jan 1, 1993

Solvent loading: It is agreed that it is advantageous, as far as reagent cost is concerned, to operate at maximum solvent loading. However, owing to the fact that no reliable automatic solvent flow controller is yet available, control tends to be erratic with the result that there is risk of losing uranium. As can be seen from Mr Tunley&apos;s plot, the graph representing total ammonia cost is fairly flat between loadings of 3.5 and 4.0 gpl, while the graph representing uranium loss in the raffinate is steep. It is, therefore, safer to operate slightly below optimum loading in the absence of absolute control. Should the purity of the final product gain importance, operation at optimum loading or even slightly above, may be advantageous. Solvent losses and clarification of pregnant solution: The cost of replacing solvent, as indicated by Mr Carman, represents a high percentage of the overall Purlex costs. It is, therefore, agreed that, amongst other factors, efficient clarification of the pregnant solution and mixer-settler design have an important bearing on the cost. However, as at Blyvooruitzicht, the Buffelsfontein plant can tolerate a suspended solids content of 50 ppm without serious deterioration in efficiency. An increase in the suspended solids content from 15 to 50 ppm normally accounts for an increase of approximately 1 ppm in amine loss. Clarification of acidic pregnant solutions is much more difficult than that of alkaline solutions. Sand clarifiers are being used at Buffelsfontein with moderate success. Clarified solutions containing less than 20 ppm of solids in suspension can be produced, depending on the quantity and type of flocculant used in the filtration process, the thickness and the grading analysis of the sand beds and the quality of supervision. An on-stream duty of approximately 0.15 gallon per sq ft of surface area is obtained. Hydraulic handling of clarifier sand, while cleaning, may effect the efficiency of a clarifier, as size segregation of sand particles may lead to inefficient "pockets" in a sand bed. Control of the solution level in the sand clarifier also affects the quality of the effluent. Exposure of the sand bed invariably causes a cloudy effluent. Recycling of the final and initial solution discharged before and after skimming the clarifier sand improves the clarification efficiency significantly. Post-precipitation of silica and possibly sulphate salts, after clarification, may give a false impression of inefficient clarification. This phenomenon is more pronounced when treating hot supersaturated solutions. Ageing and cooling of the solution before clarification assist in stabilising the solution and reduce precipitation after clarification. The maintenance cost of sand clarifiers at Buffelsfontein is in the order of 0.35 cent per metric ton of solution treated. A redundant ion-exchange column has been tested successfully, either as a primary or a secondary clarifier, depending on the quality of the filtrate treated. The conventional pebble and sand beds in the column have been retained. Operation was enhanced by the addition of a two-foot deep resin bed as a filtering medium. The suspended solids content was reduced to less than 5 ppm. Mixer-settlers: Mixer-settler design is a controversial subject but, in view of the high costs of solvent compared to relatively low pumping costs, it is believed that mixing and pumping functions should be separated. Separate facilities for pumping and mixing not only give greater operational flexibility but also permit eventual changes in the flow circuit as technology develops. Scrub technique: Unlike the pilot plant, where the crud was carried away in the aqueous phase, crud is carried over with the organic phase in the full-scale plant. This carry-over of crud into the strip bank aggravates crud formation in the first strip stage. This phenomenon may result from a slight difference in settler design and/or a variation in the relative phase depths in the two plants. Bypassing of the scrub aqueous solution from the fourth to the second stage was introduced in order to avoid dilution and partial neutralisation of the acid added to the third stage, as it is known that a low pH value enhances the transfer of iron into the aqueous phase. The low aqueous flowrate in the third scrubbing stage was overcome by introducing an aqueous phase recycle. Gleaning: Mr MacDonald&apos;s contribution on "gleaning" was most informative. This process for recovering solvent from raffinate seems to show at least as much promise as coalescers and other methods employed to date. Similar tests conducted at Buffelsfontein pilot plant gave 60 per cent amine recovery from raffinate containing 10 ppm amine. However, the circuit was not operated at equilibrium and recovery may be expected to drop as the amine concentration of the "Gleaner" circuit increases.

By I. J. A. Brackley

An investigation of the slope stability of a pit and failures of spoil dumps, carried out at Silicon Smelters quartz mine, Pietersburg, South Africa, is described. The major geological feature of the mine is the intensely foliated schist in the footwall, with exceptionally Iow strengths upon extensive discontinuities, and the similarly unusual strength properties of the dumped schist spoil. The selection of slope angles for the pit is described, and a proposal for the stabilization of the failing spoil dump by segregated dumping is explained.

Jan 1, 1985

By J. D. Austin, D. G. Kringe

Rates of return realized on investments in the gold mines of the newer goldfields outside the Witwatersrand were calculated and analysed over various time intervals and on various bases. It is shown that these rates of return are strongly correlated with changes in the gold price and cannot be equated with the returns that are expected when investments are made, and that the changes in gold price also affect the rates of return on the Johannesburg Stock Exchange as a whole. These correlations are used, together with a limited application of the Capital Asset Pricing Model, to suggest the expected levels of threshold returns in real terms for new mining projects, for projects on existing mines, and for share valuations.

Jan 1, 1980

By E. H. R. Schümann, H. Wagner

SYNOPSIS The paper gives a detailed overview of the history of subsidence engineering on South African collieries. Surface displacements resulting from total-seam extraction are discussed, and the important role of local geology is highlighted. It is shown that the differences in subsidence behaviour between South African and European collieries can be attributed to the presence of competent strata in the overburden of South African coal seams. Criteria are given for the prediction of the most important subsidence parameters, and a new model for the simulation of surface subsidence above total-extraction panels is introduced. The final section of the paper deals with the damage to surface structures caused by total-seam extraction. A brief summary of the most important undermining experiments on South African collieries is given, and it is concluded that local experiences of damage compare with those in Europe.

Jan 1, 1991

By R. A. Plumbridge

I am deeply honoured by your invitation to address your great Institute on this centenary occasion. Mining is a cyclic industry that continuously faces enormous challenges as it wrests the treasures of the earth from an often reluctant mother nature. Throughout the ages, those challenges have demanded great skill from mining men and women, who are required to blend a mixture of robust determination with art and science. Pioneer Miners and Scientists It is not surprising therefore that the first blush of euphoria surrounding the discovery of gold on the Witwatersrand quickly gave way to consternation about the need to increase the metallurgical recovery of gold from the then readily identifiable conglomerate. The rugged pioneer miners had to turn to scientists for their salvation.

Jan 1, 1994

By K. I. Afewu, L. C. Woollacott

Little is reported in the literature that is directly useful for the interpolation film coefficients for the in-pulp adsorption circuits used in gold metallurgy. This can create a problem if the design or operation of these circuits is to be optimized by the use of simulation techniques. To address this problem, a study was undertaken on the influence of mixing intensity, scale, and geometry on the film coefficient in adsorption systems typical of the carbon-in pulp plants used for gold extraction. This, the first paper deals with the influence of these factors on the film coefficient and shows that the specific power to just disperse the carbon in the slurry is an important variable. This variable is also strongly dependent on mixing intensity, scale, and geometry-a dependence that is dealt with in the second paper in the series. From the informatlon obtained, practical scale-up procedures were developed. These procedures are considered to be applicable to resin-in-pulp as well as to carbon-In-pulp plants.

Jan 1, 1995

By M. C. Mulligan

Counter current decantation (CCD) thickener circuits are used to recover soluble metal as pregnant liquor solution from ore leach residue. The basis of CCD operation is to concentrate suspended solids thereby minimizing liquor content in underflow slurry that flow in one direction. Then the underflow slurry liquor is diluted with wash liquor that flows in the opposite direction and the suspended solids are concentrated again and again. The amount of liquor in the thickener underflow contributes to determining the number of CCD stages required to recover the desired amount of soluble metal. Furthermore, similar results could be achieved at a lower wash quantity, reducing the size of downstream equipment. High density thickeners (HDT) are designed to use gravity and compression, and minimize the amount of liquor in the underflow thus minimizing the number of CCD stages. This paper reviews the process used to select HDTs rather than high rate thickeners (HRT) for the Ruashi II copper-cobalt hydrometallurgical process in the Democratic Republic of Congo (DRC), using laboratory HDT simulations, to CCD simulations and thickener design details.

Jan 1, 2009

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

Written contribution by J.F. Curtist The paper is an interesting exercise in the application of mathematics to a theoretical situation presumed to oc¬cur underground. However, some of the assumptions on which the calculations are based are unlikely to occur in any actual mining situation. Assumptions made in the paper Objections to these assumptions are noted seriatim. (1) `it is assumed that any loading-rate effect will be small and can be ignored&apos; (p. 3). A loading rate of the order of 50 kN-12 per cent of the maximum load-is customary to prevent the props being dislodged by the blast. (2) `it is unlikely that all the props will be installed with their full stroke available, but for the purpose of this analysis, it is assumed that this is the case&apos; (p. 3). A more reasonable assumption would be that, with the most careful selection of prop length and the most rigid control of stope width, the available stroke length would on average be reduced by the order of 70 mm on installation-20 per cent of full stroke. (3) `each support unit supports a block of 3,3 m2 bound¬ed by vertical fractures with zero cohesion that are parallel and at right-angles to the stope face respec¬tively&apos; (p. 5). Joughin and Jager have shown this to be an unwar¬ranted assumption in respect of the positioning, the direction, and the dip of the fractures present in a stope in rockburst conditions. If, as assumed, there was `zero cohesion&apos; between such blocks, the removal of a hydraulic prop in row 3 supporting such a block would ensure that it fell out before a profile prop could be installed in the same position. (4) `the height of each of these blocks is 3,0 m, the volume of each block is 9,9M3, the mass of each block is 27 225 kg&apos; (p. 5). The concept of individual props being affected by dis¬crete blocks of known and uniform dimensions of relatively low ground velocities (less than or equal to 2,16 m/s) acting in line with the axis of the prop is one that lends itself to neat mathematical calcula¬tions. It does not, however, bear much similarity to the actual conditions that are exposed underground in excavations where rockbursts occur. Ortlepp and co-workers concluded that `the impulse of the shockwave can cause the displacement of the

Jan 1, 1991

By P. J. Barton, N. F. Peverett

A brief review of the development and ultimate design of the Model 16 Photometric Sorter is given, including the differences between it and its predecessor, the Model 13, which is currently in operation at Doornfontein. A description of the West Driefontein sorting plant is given, together with the rationale of its design. The installation programme for the sorters is described, and current operating and maintenance procedures are discussed. Operating results are tabulated and compared with the original test results. Operating costs are also discussed.

Jan 1, 1980