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By D. Savile Davis

D. Savile Davis* (Member): The members of the Chamber of Mines Research Laboratories, headed by Dr Cook, indeed deserve all the plaudits that have been given for the original conception of the rock-cutter, and for the research work that has gone into designing the equipment now being tested. Underground trials with the rock-cutting machines at the Doornfontein Gold Mining Company Limited have been encouraging to the extent that 29 square fathoms of rock have been cut in the past three months with two modified prototype machines. Both the hangingwalI condition of the stope and the control of stoping width have been excellent. So far, however, the rate of production has been too slow and does not compare with conventional stoping methods, due firstly to the time-consuming operation of moving the machine forward and resetting it in its next cutting section and secondly to mechanical defects. Although great strides have been made in improving the tungsten carbide cutting tool, further progress is dependent upon engineering development in the design of a more reliable and versatile machine within economic limits. Commenting briefly on the experiments that have been carried out on the Gold Fields mines, the rock-cutter, when used at the Luipaards Vlei mine, some 600 ft below surface, cut very nearly perfect slots above and below the reef on a stope face but was unable to cut slots in the reef itself. At the Doornfontein mine, however, where the tests are currently being carried out at a depth of 8,000 ft below surface and where there is a much greater pressure acting on the rock face, vertical fracture planes can be clearly seen in the hangingwall running parallel to the face. Owing to the presence of these fracture planes it has been found impossible to cut slots of any depth and the action of the machine is more one of spalling than of cutting, resulting in slabs of combined reef and waste falling from the face as the cutting tool advances. This is accentuated by the existence of a well-defined hangingwall parting plane. Most of the slabbing takes place from the slot cut below the reef to the hangingwalI of the stope. Since waste sorting in narrow conditions and poor lighting is not an efficient operation, the reef together with a proportion of waste rock, has to be removed from the stope. The ripping action of the machine as opposed to slot cutting under these particular conditions may not be a great disadvantage, as the volume of waste which can be packed depends on the ratio of reef width to stope width and with a narrow reef body some waste has to be removed to the surface. In these circumstances mining at depth with this type of machine should not be viewed as selective mining but more correctly mining without explosives. Another type of rock-cutter is being tested by the Gold Fields Group, consisting of a diamond studded rotating disc, which has, to date, cut slots 10 ft in length and averaging 7 1/2 in. in depth. It is, however, too early to comment on the practicability and economics of such a cutter. The great interest that is at present being shown in breaking rock without the use of explosives warrants comment on the Robins raise-borer, recently introduced into South Africa, and used for the first time with great success at the Doornfontein mine.

The quality of life in many countries of both the developed and the developing world is strongly affected by the products and processes of mining industries. The first Issue in this new series brings together a set of review articles by leading authorities in the field which, taken together, provide a thorough and detailed survey of many of the key topics of current concern relating to the environmental impact of mining. The level of treatment of most topics is at first introductory but evolves through to the advanced level of current research, backed up by extensive citations of relevant primary literature and other sources. Thus the Issue as a whole will be found equally valuable by students of environmental science and those actively engaged in research related to this theme.

Jan 1, 1995

By A. Marek

The safe and optimal installation of roof support remains one of the biggest challenges in underground mining today. Traditional hand-held, roofbolt installation in conventional mining has been replaced, in a lot of mining operations, by mechanized equipment. This was a first step to moving the operators out of the unsafe working environment and a start on the trend toward a changed support regime in mechanized mining. However, the challenge of handling of the drill steel itself, as well as inserting resin cartridges and bolts, remains a major hazard and the cause of many lost-time injuries. The paper describes and discusses developments in this area, of mechanized bolting and on-board automation, presenting solutions to known problems, achievements to date, and future developments. The solutions presented will identify with addressing customer needs while touching on possibilities for further technology changes, keeping focus on the safety aspect for operators and the need to bring the operators even further away from the unsafe working environment. The-state-of-the-art technology in mechanized bolting equipment is presented and a brief outlook on the past, current, and future developments is given.

Jan 1, 2012

By Z-B. Cheng, X-J. Liu

"Intensive mining of shallow coal seams tends to result in severe subsidence of the ground surface. Surface subsidence is a complex dynamic spatiotemporal process that constantly changes as mining advances. With Liangshuijing coal mine as a case study, 3DEC numerical software was used to simulate the development of the moving subsidence field from open-off cut to full subsidence on the working face. The results demonstrate that the formation of a subsidence field is directly related to the coal seam depth H and the extent of the mine workings. Taking the advance distance of the working face as the unit of scale, the process of surface subsidence can be divided into four stages: micro-change (H/ p), the development of surface subsidence (2H/ p), the formation of a movement subsidence field (3H/ p), and dynamic balance (4H/ p). The changing movement of a subsidence field can be fully described by the characteristics of surface subsidence value, curve slope, and the inflection position. The results provide important technical support for predicting surface subsidence and the temporal–spatial evolution features of mining subsidence. IntroductionChina’s coal output was about 3.52 Gt in 2017 (China National Coal Association, 2018), making it the largest coal producer in the world, accounting for almost half of total world coal production. Coal production and distribution play a vital role in the energy industry of China. However, entire overlying strata, from coal seam to surface, are disturbed as a result of long-term, high-intensity and large-scale mining, causing surface subsidence. This results in groundwater loss, surface desertification, vegetation loss, and mud-rock flows. These issues have become topics of common concern throughout society. According to related research results (Liu 2008), the area of surface subsidence caused by coal mining in China has reached about 600 000 ha, some 0.2 ha (and up to 0.42 ha) of surface subsidence for every 10 000 t of coal produced. Surface subsidence disasters not only damage buildings, water conservancy, transportation infrastructure, and farmland, but also cause adverse effects on individual and community lifestyles, environmental hygiene, and economic development. Deterioration of the ecological environment in mining areas has a long history and is very harmful (Lu, 2015)."

Feb 1, 2019

By J P. van Dyk

The dramatic strengthening of the rand against the dollar as well as a decline in quantity and quality of locally available concentrates have had a dramatic impact on Zincor?s operations during the previous two years. Zincor has responded with the implementation of a number of technical improvements to the process to decrease cost and increase revenue and plant flexibility. Among the initiatives is the pre-leaching and pelletising of the zinc concentrate, de-bottlenecking and process improvements in the leach and purification circuits, the introduction of cathode washing and automated cathode stacking in the cell house and the installation of a new furnace to produce pre-alloyed jumbos. This paper will describe these initiatives and others that Zincor have recently taken to stay competitive in changing global base metals market.

Jan 1, 2005

By F. Nakhaei, Z. Pourkarimi

Tailings produced from the iron ore industry present many challenges due to the high economic and environmental impacts involved with their disposal. However, the relative scarcity of high-grade iron ores has driven manufacturers to recover and recycle these valuable tailings (secondary sources). This study aimed at the purification of ultrafine tailings with high sulphur content from an iron ore concentrator via reverse flotation to produce pellet feed fines. A specially designed flotation column featured with a nano bubble generator and a conventional bubble generator were employed to assess the effects of nano bubbles on the desulfurisation performance of iron ore concentrate under different operating conditions. Results obtained from this study indicated that the sulphur content of iron concentrate could be reduced from 1.2% to 0.22% in the presence of nano bubbles. Also, the results showed that use of nano-micro bubbles increased sulphur recovery 20% more, in comparison to micro bubbles. Keywords: Column flotation, iron ore, tailings, slime, nano bubbles, desulphurisation

Jan 1, 2020

By S. G. Mgenge, J. D. Steenkamp

Tronox Namakwa Sands operates two ilmenite smelters for the production of high-titania slag and low-manganese pig iron. Slag or metal is tapped from one of two product-specific, bi-level tap-holes. In this paper the refractory design specific to the tap-hole refractory layout is described, as well as practices for slag and metal tapping and refractory maintenance. Further developments planned are briefly described.

Jan 1, 2014

By L. Forbes, G. Forbes, J. Wang

Bubble size measurement is a vital part of flotation system analysis and diagnostics. Over the years, a great many different bubble size analysis tools have been developed. However, all of them rely on ex-situ measurement and in-pulp sampling techniques. This paper evaluates the Mettler Toledo ParticleView™ Measurement probe as a novel method for in-situ bubble size measurement. This device is then compared to the conventional Anglo Platinum Bubble Sizer (StoneThree). It was found that the in-situ bubble size analysis technology appears to be a more user-friendly and reliable option for determining bubble size in flotation. However, the current instrument design is not suited to industrial applications. Keywords: Bubble size measurement, bubble coalescence, PVM probe

Jan 1, 2020

The following notes have been compiled to assist authors in the preparation of papers for presentation to the Institute and for publication in the Journal. All papers must meet the standards set by the Council of the Institute, and for this purpose all papers are referred to at least two referees appointed by the Council. Although the worldwide readership of the Journal results in a preference for papers in English, the Council treats papers in Afrikaans on an equal basis, but, to meet the needs of the majority of readers, an English summary of some 5OO to 750 words should be provided.

Jan 1, 1984

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

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

Jan 1, 2020

This volume, which was advertised in the December, 1968, issue of the Journal at a pre-publication price of £4, is edited by W. Ryan of Warren Spring Laboratory and published by the Institute of Mining and Metallurgy, London. It is an up-to-date review of the operations of some 50 or so companies whose activities embrace the extraction and refinement of metals in the United Kingdom. Thirty-four metals are discussed, ranging from aluminium to zirconium and also there are chapters on ferro-alloys, non-ferrous alloys, high purity metals and metalloids, the platinum group metals and the rare earths. The sources of the various metals are given, followed generally by a brief description of the primary recovery process. Thereafter the operations of specific companies that deal in a particular metal are described in some detail. Certain metals such as barium, bismuth, gallium, thallium and zirconium are perforce covered very briefly as their commercial application is limited but in other cases, especially aluminium, copper lead and zinc, fairly detailed descriptions and illustrations are provided. This publication should be of considerable value to students as it presents modern procedures with regard to the refining and uses of the particular metals under review. This information may not be available from text books which in any case tend towards obsolescence. The book should also prove a valuable addition to the bookshelves of practising metallurgists providing, as it does, a schedule of most of the metallurgical companies operating in the United Kingdom. The quality of the paper and binding, the clarity of printing and illustrations and the arrangement of the subject matter are excellent and are subjects for which the editor and publishers are to be commended. R.J.A.

By M. A. Roberts

Oebswana's Jwaneng Mine (south-central Botswana) is the richest diamond mine? in the world and has been contributing substantial revenue to Botswana since the mine started operating in 1982. The resource consists of 3 separate volcanic pipes/vents namely North, South and Centre pipes (2 additional small kimberlite bodies have also been intersected within the mining pit) which erupted through Transvaal strata and the overlying Karoo sediments -245 million years ago. Although earlier drilling and geophysical surveys suggest that the 3 pipes extend to depths greater than 1 km below the surface, the resource is only at an indicated level of confidence to a depth of 400m, and mining activities will start exploiting the inferred resource material below 400m in 2014.

Jan 1, 2010

By D. Clement

A comparison between hydraulic and pneumatic rockdrills by D. CLEMENT The regulation of compressed-air reticulation systems is very poor compared with that of electrical systems; this means that electrohydraulic rockdrill systems offer greater flexibility, additional power being readily available at the working face. Hydrometallurgy A new journal devoted to all aspects of the aqueous processing of metals is scheduled to appear this year. Entitled Hydrometallurgy, the journal will be published in quarterly issues, one volume per year. Mineral dressing Contributions are invited for the Symposium on Recent Progress in Mineral Dressing in South Africa, which is to be arranged jointly by the South African Institute of Mining and Metallurgy and the National Institute for Metallurgy. Mineraalbereiding Bydraes word verlang tot die Simposium oor Onlangse Vordering met Mineraalbereiding in Suid-Afrika wat gesamentlik deur die Suid- Afrikaanse Instituut vir Mynbou en Metallurgie en die Nasionale Instituut vir Metallurgie gereel gaan word. Rock mechanics The Sixteenth Symposium on Rock Mechanics is to be held at the University of Minnesota from 22nd to 24th September, 1975. The Symposium is the official Symposium for 1975 of the International Society for Rock Mechanics (I.S.R.M.), and the Council for I.S.R.M., consisting of members from 25 countries, will meet during the Symposium. Powder metallurgy The annual meeting on powder metallurgy organized by The Metals Society is this year to be held at the Stratford Hilton Hotel, Stratford-upon-Avon (the notification did not include the date of the meeting). Vacation School The South African Institute of Mining and Metallurgy has great pleasure in announcing its intention of holding a vacation school on the topic of electric-furnace melting. NIM reports Report no. 1681 The determination of sulphur and phosphorus in chromite. Report no. 1687 The viscosities and electrical conductivities of slags associated with the production of high-carbon ferromanganese alloys.

Jan 3, 1975

By Oaitse Medupe

The feed to the BCL concentrator is made of the ore from Phikwe No3 shaft, Selebi shaft and Selebi North shaft. The receiving bin of the concentrator has daily throughput of 7869mt live capacity of ore with feed grade from underground operation of 0.70%Ni, 0.75% Cu and 0.05% Co. The valuable minerals in the ore are Pentlandite, Chalcopyrite. Cobalt is present mainly in the solid solution in pentlandite. The common non-sulphides minerals are Amphibolites, quartz, micas, and Feldspar while pyrite and pyrrhotite are the major gangue sulphides. Pyrrhotite contains between 0.1% and 1% Ni in solid solution. From the mineralogical investigation, it was found that approximately 65% of the pentlandite in the ore occurs as exsolutions in the pyrrhotite and the grain sizes ranges from 8 to 38µm. about 25% of the nickel bearing pentlandite is medium grained and subhedral. This kind of pentlandite occurs along the cracks of pyrrhotite or as inclusions in pyrrhotite. The rest of pentlandite present is disseminated in the gangue matrix. Because of the fine occurrence of pentlandite, fine grinding was conducted in order to improve the recovery as well as the concentrate quality. A series of subsequent flotation test were performed in order to evaluate grinds of 35, 40, 45, 50, 60 and 80% passing 75µm. It was observed that ? The mass pull increased together with increasing fineness of grind ? Similar nickel recoveries were obtained at 35 and 40% passing 75µm but from 50% and 60% the grind was seen to adversely affect the nickel recovery. At 80% passing 75µm the recovery increased by small amount. ? Flotation kinetics showed higher initial nickel recoveries but these did not translate into higher final recoveries. ? Grinding finer than 80% passing 75µm yield very high grades of the concentrate in the first minute of the flotation test, and the grade is dramatically reduced in the fifth minute of the test. It was concluded that the current grind of approximately 48% passing 75µm is close to the optimum and no significant benefit were found to be associated with finer primary grinds. The inconsistence of the grade and recovery as well as the pentlandite losses will be discussed. Keywords: Pentlandite, Nickel losses, Grain size, Flotation

Jan 1, 2007

By F. Pinto, J. V. Lemos, A. Sousa, L. Ribeiro e Sousa

The Rossio railway tunnel was built in 1890 crossing several formations involving limestones, basalts and also sandy and clayey formations. Due to the fact that it is an old underground structure rehabilitation and repair works were performed, namely at Km 0,900 and in a zone crossed by a new tunnel from the Lisbon Metro. Reinforcement support systems were designed in the Rossio tunnel in order to prevent its stability. In this paper, repair works and anchor tests performed at km 0,900 are presented, as well as the monitoring system implemented in order to observe the structural effects induced by the construction of the works. For the interpretation of the obtained information complex 3D models was built, permitting the simulation of the sequential excavation scheme used, non-linear behaviour of the different formations, and the support systems used. Der 1890 erbaute Rossio Eisenbahntunnel durchoertert mehrere Formationen, einschliesslich einer Kalkstein-, Basalt- sowie einer sandigen und tonigen Formation. Auf Grund des Alters des unterirdischen Bauwerks wurden Instandsetzungs- und Reparaturarbeiten im Bereich km 0,900 sowie im Kreuzungsbereich mit einem neuen Tunnel der Lissabonner U-Bahn durchgeführt. Aussteifungssysteme wurden entworfen, um die Stabilität des Rossio Tunnels zu gewährleisten. Im Folgenden werden die Instandsetzungsarbeiten und Anker Tests im Bereich km 0,900 sowie das Messystem zur Ueberwachung der strukturellen Auswirkungen der Bauarbeiten dargestellt. Zur Interpretation der gewonnenen Informationen wurden komplexe 3D Modelle entwickelt, die eine Simulation des Bauablaufs und die Anwendung nichtlinearer Stoffgesetze fuer die verschiedenen Formationen und Aussteifungssysteme ermöglichten. Le Tunnel ferroviaire du Rossio a été construit en 1890, traversant des différents terrains comme des calcaires, des basaltes et aussi des formations limoneuses et sableuses. Dû à l’ancienneté de l’ouvrage, des travaux de réhabilitation et réparation ont été faits, nomment au km 0,900 et dans la zone traversée par le nouveau tunnel du Metro de Lisbonne. Des systèmes de support renforcé ont été conçus pour le Tunnel du Rossio de façon à rassurer sa stabilité. Dans ce papier, on présente les travaux de réparation et les essais d’ancrage réalisés au km 0,900, et aussi, le système d’auscultation mise au point pour l’observation des effets structuraux induits par les travaux. De façon à interpréter l’information résultant de l’observation, des modèles 3D complexes ont été utilisés, permettant la simulation de la méthode séquentielle de l’excavation, du comportement non - linéaire du terrain et, aussi les systèmes de support utilisés.

Jan 1, 2003

"Chairman: Dr DeV. HarrisRapporteur: Mr A.H. MunroPapers:Corporate exploration strategies by MacKenzie, B.W.The Engel Simulator and the search for uranium by Griffiths, J.C. and Singer, D.A.The Chairman opened the session by tracing the changes which have taken place in the exploration field since the days of the lone prospector who relied upon his individual skills and to a large extent on luck. The deposits which now remain to be discovered are better covered and are of lower grade. A much greater team effort, involving geoscientists and engineers, is required. The gamble is thus much greater -not only are the probabilities of failure still significant but the consequences are more severe. A recent Canadian survey indicated that expenditures of between two and nine million dollars on regional exploration programs are required to locate one significant deposit.The Chairman went on to say that these facts have led companies to regard exploration as another form of investment and to treat it accordingly. This had placed exploration in the context of corporate strategics and structures, which was the subject of the first paper of the session.In introducing his paper, Dr B. W. MacKenzie said that the paper suggested a decision framework for exploration planning. Initially the environment is analyzed to define observable and relevant economic characteristics. The terms of reference for exploration planning and the appropriate allocation of capital and skills are then established in the light of corporate objectives and growth alternatives. With the aid of this information and in the light of profit and corporate risk criteria, exploration strategies can be selected.Dr MacKenzie went on to say that the usefulness of the concept and criteria outlined in his paper depended critically upon three characteristics of any particular economic environment, namely, the return resulting from an economic discovery, the unit discovery Cost and the probability of making an economic discovery. He then showed by means of a case history relative to the Canadian Shield and Cordilleran areas that these three characteristics could, in fact, be evaluated for regions with reasonable histories of mineral activity.The first contributor to the discussion of the paper, Mr Alfred Weiss, mentioned that his group had been involved in exploration modelling for some ten years and were thus particularly interested in the paper. He went on to say that they had experienced greatest difficulty with reconnaissance programs and that he sensed that these difficulties were also present with the methodology which had been outlined. Mr Weiss asked Dr MacKenzie how he would deal with such situations when no information was available but where there was the potential for both exploration and discovery. Dr Mackenzie agreed that the lack of information was a very severe limitation and said that at the present time his methodology probably did not provide a basis for breaking down the broad geological regions he considered into areas for further assessment."

Jan 1, 2014

By E. B. Viljoen

I. R. M. Chaston* As a gravity concentration man in the midst of so many eminent flotation experts I feel like Daniel. However, I would respectifully disagree with the opening remarks by Mr Viljoen. First, he suggested that gravity concentration of cassiterite was not effective in sizes below 30 microns. In a paper to the Institution of Mining and Metallurgy in 19621, I gave some figures for gravity concentration of deslimed material both for cassiterite and for wolfram which indicated that careful shaking table concentration of fine deslimed material could give recoveries of 75 to 90 percent in the size ranges above 13 micron. These were figures obtained from normal plant operation. It would be interesting to know if any tests were carried out on gravity concentration of the efficiently deslimed feed to this flotation plant to see what the recovery would be. Secondly, Mr Viljoen suggested that gravity concentration plants were expensive. He gives the cost of a flotation plant at R300 000 to treat a feed of 400 t.p.d. to the desliming section or 160 t.p.d. to the flotation cells. From his operating cost figures it would appear that the flotation cost is approximately R2 to R4 per ton of feed to flotation and the total operating cost about R2 per ton of feed. A table plant to treat this tonnage of deslimed feed would consist of about 30 tables and should cost considerably less to install and very much less to operate than the flotation plant. Third, Mr. Viljoen suggests that the concentrate grade from a gravity concentration operation would be unacceptably low. The paper quoted abovel showed that once a primary fine concentrate had been made, giving a suitably deslimed material, further gravity concentration could give concentrates of over 40 per cent Sn with high recoveries. Tailing from this dressing stage was naturally returned to the feed. To give these high grades, sulphides had been removed by flotation but this necessary flotation step is simple and cheap to operate and could be restricted to the final stage when the quantities involved are small. I would agree that flotation has a part to play in fine tin recovery but this role would only seem to become fully effective at sizes below 10 micron and would seem to require, as Mr. Viljoen has suggested, a mechanism for sizing which is effective down to, say, 1 micron. In the meantime it would be interesting to try tabling the flotation tailing to see if it was possible to recover the plus 20 micron cassiterite which is not recovered well by flotation. One point which has been made during discussion is the suggestion that cassiterite particles have a fully hydrated surface at normal pH. I wonder if this layer could materially affect the overall specific gravity of a very small cassiterite particle and, if so, whether gravity concentration of the very fine cassiterite would be improved if carried out in acid conditions, which would inhibit the formation of this hydrated surface. REFERENCES 1. CHASTON, I. R. M. 'Gravity concentration of fine cassiterite'. Trans. Inst. Min. and Met. Vol. 71, p. 4, 1961 and 1962, and discussion of this paper. Dr. R. P. King Mr Viljoen has drawn attention to the difficulties associated with the presence of very fine particles in the flotation pulp and he has indicated that, on the Union Tin plant, they must sacrifice 30 percent of the cassiterite in the minus 7 /Lm material which they separate and lose. He has also indicated that the rate of flotation of cassiterite remained high at these small sizes. The problem arises because the very small particles stabilize the froth making it impossible to handle. These stable froths cannot be easily broken and therefore cannot be pumped and processed. It seems that further fundamental research work on the properties of stabilized froths is urgently required. We have found another difficulty associated with the presence of very fine particles in phoscorite slurries; these particles can be easily floated but with very poor selectivity. We believe that it is possible that a purely physical mechanism such as entrainment is responsible for the collection of fine particles in the froth. We have also demonstrated that the presence of fine particles in the pulp adversely affects the rate of flotation of the larger particles. For esample, we have found an increase in recovery of + 100 um material from 2 percent to 17 percent in a standard laboratory batch flotation test on phoscorite when the - 37 um was removed from the feed. Such interactions between particles are not universally recognised as an important aspect of the complex flotation mechanism. They should appear in any quantitative formulation of the flotation rate process.

By N. Sinclair

"In open pit dozer bulk push operations, the material left resting against the highwall after blasting poses an issue. This is because dozers cannot physically get in behind the waste to begin the bulk pushing process. Instead, an excavator can be used to side-cast this waste for the dozers to access. An alternative technique is to have the dozers ‘side-cut’ the material, which involves the dozers running parallel to the wall, digging out the material, and eventually rotating their blades to begin bulk pushing. Industry practices suggest the latter technique is less productive and economical than using an excavator. However, such excavator sidecasting ‘economic viability’ assumes that smaller/ancillary type excavators are used (i.e. less than 23 m3 bucket capacity). So, what happens if some mine sites are restricted to using relatively larger excavators (> 23 m3 bucket) that are preferred for higher priority digging tasks? When can they avoid using their excavator? This paper explores multiple scenarios that have been designed and developed to simulate data results, which identify conditions in which the dozer side-cutting technique becomes more economically viable than excavator side-casting in terms of decreased unit cost per loose cubic metre. IntroductionOptimizing the cost of waste removal operations is important for the profitability of opencast coal mines. In the past decade, dozer bulk pushing has emerged and taken over from traditional waste removal operations such as dragline and truck-and-shovel methods at various sites around the world (Beatty, 1994). In a typical bulk push operation, once the bench has been blasted, waste is left resting against the highwall, which can either be cleared using a loading unit or by having the dozers ‘side-cut’ the highwall.Dozers perform most effectively when slot dozing side-by-side, perpendicular to the highwall. However, when dozers are required to remove material off the highwall, they must push parallel to the highwall, rather than perpendicular, hence ‘side-cutting’ the material to ensure a clean face. While dozer sidecutting is possible, it has been found that the majority of mine sites use a loading unit in this situation to avoid dozer inefficiency. Other perceived issues with dozer side-cutting include higher maintenance requirements and safety risks to dozer operators working in close proximity to the highwall."

Jan 1, 2019

By D. Mjonono, S. T. L. Harrison, N. Maliela, A. Kotsiopoulos

The improvement of coal waste management practices, through the co-disposal of waste rock with sulphur-lean fine waste tailings (<1 mm in size), can potentially mitigate acid rock drainage (ARD). On exposure to natural oxidants, the sulphide compounds present in mine discards generate acidity, creating a cyclical oxidation process intensified by iron and sulphur oxidising microorganisms. To inhibit the emergence of ARD, a stable mine dump may be constructed that is structurally stable and incompressible through the mixing of complementary waste fractions that reduce voids and access to acid generating surfaces. However, large voids manifest as scale increases, due to decreased particle interlock, enabling the unrestricted access of oxidants leading to the early onset of ARD. To avoid this phenomenon, enhanced packing approaches based on geochemical and geotechnical characterisation tests were employed to improve bed stability. These were assessed for long-term prevention using aggressive oxidative conditions typical of heap leaching applications. Favourable results were obtained for both blended and multi-layered systems. However, long-term success was most notable in beds with alternating layers of waste rock and fine waste tailings with co-mingled systems being more susceptible to failure. Deconstructed co-disposed beds provided valuable insight into post-leach structural transformations. Results indicated that relative changes in initial coarse discards to fine waste ratios were most notable in blended systems. Mass fractions of the comparatively more mobile fine wastes increased axially down these test columns that ultimately resulted in increased contact of oxidants with the acid generating waste discards. Conversely, more consistent ratios were observed in multi-layered configurations. In these systems, near impervious hardpans were created by the moisture retaining fine tailings, forming stable structures with neutralising barriers sustained at each alternating layer. Consistent with post-leach geotechnical characteristics, static acid-base accounting tests showed that the uppermost sections of blended systems were more susceptible to oxidation due to structural failure with fine particles migration, while the more stable multi-layered configuration evenly maintained neutralising capacity. Keywords: Acid rock drainage (ARD), bed structure, mobility of fine particles

Jan 1, 2020

By A. Cambitsis

We show that the prioritization of business improvement and performance management decisions may be significantly improved by taking into account the systemic effects of changes made in a single process area. To do so we build a model of a mining value chain, taking into account consequential downtime that arises from downstream and upstream starvation and choking effects of each activity. Introducing the concept of internal capacity, this approach yields insight into the relative importance of key metrics such as loading and hauling rates. We suggest that a holistic view of this type should be a core component of business improvement and performance management decisions.

Jan 1, 2012