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By N. Z. Fotoyi

Keywords: MgO-MgR2O3 refractory, SO2-containing gases, chemical attack The reaction mechanisms occurring when MgO-MgR2O3 refractories are exposed to SO2-containing gas atmospheres were examined. The study examined the characteristic structures of magnesite-chrome, chrome-magnesite and magnesite refractories exposed to SO2-O2 gas mixture at temperatures of 700°C to 1350°C. The phase characterization was conducted with scanning electron microscopy (SEM) and powder X-ray diffractometry (XRD). The results show that the physical characteristics of the refractory matrix along the grain boundaries are important refractory features during chemical attack from SO2-containing gas. Upon heating in SO2-containing gas, the changes in phase-chemical compositions and accompanying grain growth causes loosening of the structure and the pore volume promotes gas diffusion. The chemical reactions that occur form stable sulfate compounds identified as MgSO4, CaSO4 and CaMg3(SO4)4, and lead to disintegration of various phase structures and consequently erosion of the refractory. In conclusion, the reaction mechanisms in MgO-MgR2O3 refractories exposed to SO2-containing gases progress through a combination of structural disintegration and chemical attack.

Jan 1, 2011

By W. J. Schlitt

The Namibian Copper Joint Venture has been formed to undertake development of the Haib copper deposit, one of the largest undeveloped copper resources in Africa. The development programme includes extensive hydrometallurgical testwork that is being managed by Kvaerner Metals (formerly Davy International).Various parts of the programme have been contracted to four third-party laboratories. The testwork involves sample selection and characterization, amenability tests, and a parametric study on the leaching variables. All portions of the programme are described and the results a represented. The ores selected for testing are quartz feldspar porphyries. The amenability tests include ?mapping? studies to assess optimum leach conditions, tests at high oxidation potentials, oxidation with various bacterial strains, and heap leach modelling. The parametric programme includes such variables as ore grade, leach temperature, crush size, pH, and ferric iron content of the lixiviant. Testing was done on both whole ore and concentrate. Results show that bacterial leaching is effective and that ore grade and temperature are key variables. Crush size and pH have less impact on copper extraction. For mid-grade ore, about 0.25 per cent copper, extraction is projected to reach 50 per cent after two years when heap leaching tertiary crushed ore at 60°C and pH 1.5. The heap leach operation would fit well with the proposed roast-leach operation used to treat higher grade ores. The latter could supply the low cost heat and acid needed in the heap leach.

Jan 1, 1999

By D. Grobbelaar, A. Cichowicz, D. J. Birch

The Q-coda method for estimating the quality factor Q(f)= Qo(f)n was used to characterize seismic wave attenuation in a region of the Kaapvaal Craton that includes the mining areas of the Bushveld Complex and Witwatersrand Basin. Seismic waveform data, collected by locally distant stations of the South African National Seismograph Network (SANSN), consisted of mining-related events with magnitudes ranging from ML 1.8 to ML 4. Q was calculated for nine different source-receiver pairs spanning the study region. A weighted average Q based on the number of available data gave an estimated attenuation relation for the study region of Q(f) = 327 f 0.81.

Jan 1, 2015

By Haiping Sun, Samir Ganguly, Oleg Ostrovski, M. Yaser Lone

Wettability of graphite by synthetic SiO2-Al2O3-CaO-MnO slags with varied MnO content and by industrial slags was studied at 1350-1600 °C using sessile drop method under argon atmosphere. Initial contact angle was the lowest (110-115o) for the MnO-free slag. For slags with 10-40 wt% MnO, the initial contact angle was in the range 125-135o. The contact angle decreased with the contact time. The change in the contact angle with slag mass was found insignificant. The surface tension of slags obtained from the drop shape analyses was 500-800 mN/m and varied in a narrow range with temperature and MnO concentration. The reduction rate increased with increasing MnO content in the synthetic slag from 20 wt% to 40wt% and temperature. Increasing temperature also increased the rate of reduction. No correlation was observed between the reduction rate and MnO content in the synthetic slags in the range 0-20 wt% and in the industrial slags. The rate of SiO2 reduction from the molten slag was close to the rate of MnO reduction. The MnO-free slag had the largest contact area with graphite substrate. Keywords: reduction, wettability, graphite, slag, manganese, surface tension.

Jan 1, 2007

By B. McCosker

The choice of the appropriate delivery process for a project is often not adequately thought about. The industry needs to be prepared to break its preconceived mind-sets on delivery procedures. Industry should also be prepared, on a project by project basis, to commit to a critical review as to how the assessment and then selection of the best procurement method can best optimize the project outcome for both client and contractor. Conventional standards and biased reliances and experienced based preferences should be challenged. To achieve this requires a paradigm shift in attitude to both the process of tendering and the evaluation of tenders. Tender and contracting practices are dynamic and have moved away from solely cost based assessments. Tendering contracts arise imposing changed duties upon owners. Traditional contract delivery models have shifted, reflected in part by the trend towards relationship contracting. The categories of contract options are not closed. Many are but hybrids of other time-tested models. This paper considers options available for any brownfield or greenfield project. The principles outlined are translatable to supply, upgrade, operation and maintenance arrangements.

Jan 1, 2002

By J. du Plooy

Mintek has implemented a training scheme that provides students with the experiential training requirement for the National Diplomas in Chemical Engineering and Extraction Metallurgy. This note describes the main features of the scheme and the course content, and our view of future developments in this area.

Jan 1, 1998

By M. G. Maruma

The effect of the amount of cold reduction and annealing temperature on the evolution of the texture of AISI 441 steel is reported. The steel was cold rolled by 62%, 78%, and 82%, followed by isothermal annealing of each sample at 900°C, 950°C, and 1025°C for 3 minutes. The crystallographic texture was determined by Phillips X?Pert PROMPD texture diffractrometer. Microstructures were characterized using optical microscopy and scanning electron microscopy (SEM).The results show that sample that received 78% cold reduction and annealing at 1025°C presented the highest Rm-value and lowest ?R-value, which would enhance its deep-drawing capability. In addition, this sample showed the highest intensity of shifted ?-fibre, notably {554}<225> and {334}<483>. It can therefore be concluded that the ?-fibre, which favours deep drawing, is optimal after 78% cold reduction and annealing at 1025°C.

Jan 1, 2013

By R. Abela

Heavy mineral sands are usually beneficiated in a spiral concentrator circuit prior to separation of heavy minerals into streams of zircon, rutile and ilmenite. The performance of the spiral concentrators is heavily affected by the presence of slimes in the rougher feed. The paper quantifies the effect of slimes content and discusses the beneficial effect of spiral feed de-sliming. The net effect of inefficient slimes removal can cause significant recovery losses of the heavy minerals present in the feed.

Jan 1, 2003

By F. M. G. Egerton

Mechanisation of mining operations is not a new concept in the world of mining. Machinery has been developed, manufactured and used for many decades in massive orebodies and coal mines, both locally and abroad. Because of their size and the huge tonnages available, massive ore bodies lend themselves very easily to mechanisation. However, little progress in mechanisation has been made in narrow tabular orebodies in South Africa. The equipment available for narrow tabular orebodies requires excavations of a size that introduce large volumes of waste dilution. Nevertheless, it is essential for South African miners to experiment with mechanisation and to find a solution to the problem. This address looks at current conventional mining methods and compares them to bord-and-pillar type mining methods. Off-reef mechanisation is also touched on. It then looks at different hybridised mining methods that are being used, i.e. a mixture of conventional mining and mechanisation. It finally looks at future prospects for mechanisation in narrow tabular orebodies.

Jan 1, 2004

Mine wide, underground wireless communications are possible with the use of Ultra Low Frequency (ULF) technology. Due to the propagation through rock of ULF radio signals a relatively small antenna can provide communications coverage over a complete mining operation. Starting as a Personal Emergency Device (PED) for emergency messaging to miners under all circumstances, the ULF communications system has grown to include capabilities of remote control of underground equipment such as pumps and fans and centralised blasting initiation. This technology is now in use on 5 continents having lately made it onto the African mining scene. The paper and presentation will provide the audience with the benefit from international mining know-how in this technology as well as local African experiences. A recent commissioning exercise for example, is expected to pay for itself in electricity savings within a few months. These and other results from practical demonstrations and usage will be covered. This novel technology becomes an integral part of the daily operating infrastructure of a mine with immediate safety and business benefits. It is able to reduce capital expenditure and is designed for ease of routine operational use. The paper will conclude with insights into current R&D for further development of this technology.

Jan 1, 2007

By R. G. Cawthorn

The earliest authenticated scientific report of the occurrence of platinum in rocks from the Bushveld Complex appears to be by William Bettel on 10 November 1906. Thereafter, prospecting of the chromite-rich rocks for platinum proved frustrating. I suggest that the resurgence of interest shown by Dr Hans Merensky in 1924 resulted from his realization that newly panned platinum had a different grain size from that in the chromite layers and indicated a different source rock, which he located, and it became known as the Merensky Reef.

Jan 1, 2007

By J. Bakken, M. Th. Jonsson, G. Sævarsdottir

A typical three-phase submerged-arc furnace for production of silicon metal and ferrosilicon has arc currents ~100 kA, phase voltages ~100 V and total furnace power ~10 - 60 MW. The arcs burn in gas filled cavities or "craters", where the main atomic components of the plasma mixture are silicon, oxygen and carbon. Two quite different simulation models for high-current AC arcs have been developed: the simple Channel Arc Model (CAM), and the more sophisticated Magneto-Fluid-Dynamic Model (MFD). These models have been described extensively and results reported at INFACON-8 and INFACON-9, respectively. The coupling between the arcs and the AC power source is described by a complete three-phase Electric Circuit Model. Recent numerical modelling studies of industrial AC arcs show that the boundary conditions at the cathode and anode are critical for the simulation results. A novel Cathode/Anode Sub-Model for high-current AC arcs that treats both cathode and anode indicates a completely different cathode behaviour than previously assumed. A cathode spot which serves a high-current electric arc is shown to be dominated by the energy impact from the arc. This leads to lower cathode fall voltage than obtained from previously developed models. The anode fall voltage is negative, as the main function of the potential barrier is to repel plasma electrons. The cathode spot is diffuse in the sense that the arc in fact contracts away from the cathode. Simulation results are compared to measurements on both industrial furnaces and smaller scale pilot furnaces. An important conclusion, supported by our arc studies, is that the arc length in silicon metal and ferrosilicon furnaces does not exceed 15 cm and the arc may burn anywhere on the electrode, not necessarily beneath the electrode tip.

Jan 1, 2004

By R. P. Jensen

This is a sampling of the papers presented at the conference, the proceedings can be bought from the SAIMM Arbitrary Lagrangian Eulerian (ALE) computational techniques allow treatment of gases, liquids and solids in the same simulation. ALE methods include the ability to treat shock waves in gases, liquids and solids and the interaction of shock waves with each other and with media from one of the other categories. ALE codes can also treat explosive detonation and the expansion of the explosive gases and their interaction with air and solids. ALEGRA is a 3-D ALE code that has been developed at Sandia National Laboratories over the past few years. ALEGRA has been applied to a 2-D simulation of presplitting using decoupled explosives in rock blasting with very interesting results. The detonation of the explosive at the bottom of the hole sends a shock wave up the borehole driven by the explosive gas expanding into air. The explosive gas compresses the air against the stemming column where it rebounds and recompresses at the bottom of the borehole. This type of ringing takes several cycles to damp out. The explosively induced expansion of the borehole is also treated by ALEGRA as well as the shock wave imparted to the rock. The presentation of this paper will include several computer animations to aid in understanding this complex phenomenon.

Jan 1, 2000

By Noel C. Joughin

In making judgements on tolerable levels of risk in industry, and in all spheres of life, it needs to be understood that every action gives rise to risk. Without risk, nothing can be done. Without risk, no economy could be advanced. There is a strong tendency to emphasize the risk at work, but persons who are not working are exposed to a different set of risks. Often persons who are not working face greater risks than persons who are working. Simply, in being alive, one is exposed to the risk of an accident, the risk of contracting a disease, and an extremely diverse variety of other risks. According to the Health and Safety Executive of the UK, it is not possible to have a state of zero risk, because ?a state of zero risk does not exist?. Because zero risk is a physical impossibility, it is not possible to design for a state of zero risk in all engineering design. While the strategic target of achieving zero risk is laudable it does not provide any practical guidance to engineers as to what acceptable limits of risk should be. This causes a significant and real problem in the design for and the management of risk. Without meaningful guidelines, engineers, managers and the authorities often find themselves in disagreement. Thus, it has become essential to establish criteria for tolerable levels of risk and unacceptable levels of risk in order to design and manage engineering systems properly.

Jan 1, 2011

By J. M. Schaekers

In the first part of the article, the authors give a broad overview of the chemistry and some engineering aspects of bioleach processes, eventually leading to the important and critical issue of the stability of arsenic-containing residues, especially those derived from bioleaching of sulphidic gold ores. In the section ?Factors affecting arsenic stability? they give an excellent summary of the factors normally affecting the stability of such residues. This is followed by some valid comments on the suitability of a single leach test to evaluate the long-term stability of solid waste streams. However, they fail to mention that, up till now, no tests procedure has been accepted by either environmentalists or the mining/processing industry as a valid method to test the long-term stability of solid wastes. Their own method is no exception, although, like many others, it is useful to identify potential problems with solid wastes considered for disposal.

Jan 1, 2001

By S. Mundike

A scraper-based block cave method has been successfully applied to extract the Lower orebody at Nchanga since the 1950s. Since inception, scraper drifts and service ways have been supported using steel arch sets fabricated to a specific design from high strength manganese steel To reduce costs and to improve productivity, trials commenced in 2002 using fibre reinforced shotcrete as an alternative support method. One of the areas, the 2420 8E 1C trial drift, was subjected to abutment loading for several months prior to undercutting and cave mining. Shotcrete installed exhibited minor cracking shortly after application but very little deterioration thereafter. Following the success of the trial, the application of fibre-reinforced shotcrete was extended to other drifts. This paper describes the application of fibre-reinforced shotcreteat Nchanga and outlines design and quality assurance methods employed.

Jan 1, 2005

The Gordonsville Operation of Pasminco US Inc. along with the Center for Advanced Mineral and Metallurgical Processing (CAMP) at Montana Tech studied, developed and implemented a pilot scale hydrometallurgical facility for the industrial recovery of germanium and gallium. This paper describes the joint testing and engineering program that culminated in this successful process. 1. Introduction The Pasminco US Inc. (PAS), Gordonsville Operation, has been producing zinc concentrate continuously since 1975. Within the zinc concentrate, several byproduct elements were found to be significantly concentrated including gallium and germanium. The gallium and germanium replace zinc and other metals within the crystal lattice structure of the zinc mineral (sphalerite) and are concentrated in the same manner as the zinc mineral. This concentrate is then sent to the Pasminco Clarksville Zinc Refinery for further processing. Within the hydrometallurgical zinc-processing plant at Clarksville, a residue is formed that contains a majority of the impurities that would otherwise contaminate or hinder the zinc process. Approximately 5,000 tons of residue is formed annually containing approximately 0.80% gallium and 0.60% germanium along with significant quantities of iron, zinc, silica, and lead. Pasminco currently sells this residue for the germanium value. Until recently, no revenue for the gallium was obtained from the sale of the residue.

Jan 1, 2008

By O. A. Olaseinde

The 2101 lean duplex stainless steel has wide potential application in storage, heat exchangers, and in the oil and gas industries. This work investigates the electrochemical behaviour of 2101 duplex stainless steel with an addition of 0.15 wt% ruthenium, using potentiodynamic techniques in 1M H2SO4 at 25º, 40º, 60º, and 80ºC. The microstructures of samples were characterized using optical metallography and scanning electron microscopy. The results showed that the ruthenium addition moved the corrosion potential of alloy 2101 to a more positive potential. All samples containing ruthenium displayed longer passive regions at 25°C and 80°C compared to those without ruthenium. Alloys without ruthenium had higher critical current density (icrit) values when compared to the alloys with ruthenium. Ruthenium additions decreased the passive current densities and inhibited anodic dissolution. At room temperature the corrosion rate of alloys with ruthenium was lower than these without ruthenium.

Jan 1, 2012

The Modified Zincex® Process, developed by Técnicas Reunidas, is highly flexible dealing with a wide range of pregnant leach solutions. No matter if those solutions are produced from primary or secondary raw materials, and/or are based on conventional leaching, pressure leaching, heap leaching or bio leaching the result is always high-purity zinc product. The zinc solvent extraction unit within the process is a very effective barrier for impurities and a buffer for the composition of the pregnant liquor. This unit achieves an extremely pure aqueous extract that can be converted into different final products. All of them are characterized by fulfilling the highest purity standards. Also, there is the possibility to adapt the global process to a wide range of pregnant liquor compositions and various production capacities up to a zinc production limit over 150 000 t/a with a single solvent extraction plant.

Jan 1, 2002

By T. Marin, J. E. Seccatore, M. Cardu

The most energy-intensive process in the mining industry is particle size reduction – comminution. The first phase of this process is blasting to fragment the rock from the initial Boussinesq’s halfspace size. Scientific literature demonstrates that the output of a blast in terms of fragment size distribution can be manipulated by varying the specific charge (powder factor) and charge distribution. This study focuses on the influence of blasting on the internal resistance of the blasted fragments; in particular the influence of the spatial distribution of charges. Small-scale blasts were performed on 14 marble blocks using different powder factors and charge distributions. Three control blocks were fragmented by mechanical means for comparison. The results show the correlations between charge distributions and the specific energy of mechanical comminution. Opportunities for adjusting charge diameter and distribution in opencast blasts to improve the performancet of comminution circuits are discussed.

Aug 8, 2024