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By M. Le Roux

Fine coal (-500 µm) is notoriously difficult to dewater. It is not uncommon for a dewatered product to have a moisture content as high as 30 per cent after vacuum filtration. This poses several handling and financial problems to such an extent that a lot of fine coal is discarded onto slurry waste ponds. A novel way of dewatering fine coal was developed at North-West University. It entails deliberately damaging the filter cake during dewatering to allow for an increased flow of air through the cake at the expense of the applied pressure differential. This method resulted in an average improvement in final cake moisture of between 3 per cent and 5 percent when executed in the laboratory under controlled conditions. A device was designed that could be fitted onto existing belt filters that would damage the filter cake as it passes by. This device was tested on a vacuum belt filter installation at a coal beneficiation operation in the Waterberg coal field in South Africa. The results showed a 3 per cent reduction in final moisture of the cake, proving the validity of the method at full industrial scale.

Jan 1, 2012

By M. Le Roux

Fine coal (-500 µm) is notoriously difficult to dewater. It is not uncommon for a dewatered product to have a moisture content as high as 30 per cent after vacuum filtration. This poses several handling and financial problems to such an extent that a lot of fine coal is discarded onto slurry waste ponds. A novel way of dewatering fine coal was developed at North-West University. It entails deliberately damaging the filter cake during dewatering to allow for an increased flow of air through the cake at the expense of the applied pressure differential. This method resulted in an average improvement in final cake moisture of between 3 per cent and 5 percent when executed in the laboratory under controlled conditions. A device was designed that could be fitted onto existing belt filters that would damage the filter cake as it passes by. This device was tested on a vacuum belt filter installation at a coal beneficiation operation in the Waterberg coal field in South Africa. The results showed a 3 per cent reduction in final moisture of the cake, proving the validity of the method at full industrial scale.

Jan 1, 2012

By W. Wittke

SUMMARY: Geotechnical problems often lead to an increase of construction time and costs for large highway and railway projects. Some reasons, which have led to failures and thus to a delay of construction works as well as to increasing costs, are demonstrated by means of case histories, in which the author was involved as expert or planner. Proposals are made how to identify the reasons and to avoid repetitions. ZUSAMMENFASSUNG: Bei Großprojekten der Verkehrsinfrastruktur stehen häufig geotechnische Aufgabenstellungen im Vordergrund. Wegen geotechnischer Probleme kam und kommt es häufig zu Termin- und Kostenüberschreitungen. Anhand einiger Beispiele, bei denen der Autor als Gutachter und Planer beteiligt war, wird gezeigt, welche Ursachen zu Schadensfällen und damit auch zu Termin- und Kostenüberschreitungen geführt haben. Es werden Hinweise und Anregungen gegeben, wie die Ursachen erkannt und Wiederholungen von Schadensfällen vermieden werden können. RÉSUMÉ: À grands projets de l'infrastructure de la circulation, souvent des tâches géotechniques sont au premier plan. Par suite de problèmes géotechniques, souvent des dates et frais ont été dépassés. Au moyen de quelques exemples, à lesquels l'auteur participait comme expert et planificateur, les causes sont mises en vue qui menaient à des cas de dommage et par cela aussi à des dépassements de dates et frais. Des indications et suggestions sont données pour s'apercevoir des causes et éviter des répétitions de cas de dommages.

Jan 1, 2003

By R Kroukamp

Horizontal belt filters are typically used for separation of relatively free filtering solids where good post treatment is required. He horizontal belt filter is a continuous filter with an endless cloth supported on a grooved carrier belt. The belt and cloth are driven around two rollers across a series of evacuated suction boxes. The feed suspension is introduced at one end of the filter and deliquored to produce a cake at the other end. The benefits of using horizontal belt filters are good cake washing, continuous and visible processing, fully automatic operation, flexibility, high capacity and relative high speeds of operation. If required, horizontal belt filters enable efficient counter-current washings to minimize the usage of wash liquid. The horizontal belt filter has applications in the following: [? Metal concentrates ? Mineral sands ? Tailings ? Coal ? Iron ore ? Alumina ? Chloride processing ? Nickel and Cobalt refining ? Platinum group metals ? Zinc processing ? Many other applications in the Mining and Metallurgy industries ] 2. Operating Principle of a Horizontal Vacuum Belt Filter 2.1 Cake Forming The slurry to be dewatered is evenly distributed onto the filtering surface. Gravity assists the cake formation and the feed can be introduced in multiple stages. 2.2 Cake Washing Once the cake is formed, wash liquor/water can be introduced onto the top of the cake via a wash launder or sprays. Multiple wash stages, co-current, counter-current or direct washing can be added by increasing the length of the filter.

Jan 1, 2007

By K. J. Kruger

Aluminium alloys have gained popularity in many industries due to their high strength and low weight. One shortcoming of aluminium alloys is their poor resistance to abrasion and erosion wear compared to materials such as stainless steels. In this project, aluminium alloy 2014 (AA2014) was coated with a 1.5 mm thick laser-deposited layer composed of silicon, copper, and aluminium with the aim of increasing the wear resistance. The amount of silicon, copper, and aluminium added to each sample was determined by a mixtures model. It was discovered that the Al-Cu system is very sensitive to silicon additions and that wear resistance depends on the primary phase to solidify as well as on the final phase distribution. Two primary phases were identified; alpha aluminium and theta intermetallic. It was observed that the clad layer increases both the hardness and wear resistance of AA2014, and that the material solidifying as primary alpha aluminium displayed a lower hardness but higher wear resistance than the samples containing primary theta phase. All clad layers performed better in terms of wear resistance than the unclad samples. The knowledge gained and principles used in this project could be applied to many other aluminium alloys.

Jan 1, 2014

By S. T. Camagu, J. Dutta Majumdar, S. L. Pityana

Laser surface alloying was used to develop copper and molybdenum aluminides by injecting premixed copper and molybdenum powder particles into a laser-generated melt pool on an aluminium substrate. Different laser processing parameters were used to produce the composite thin layers on the substrate material. The microstructure and phase constituents of the composite layer were studied by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) techniques. Experimental results show that the matrix structure of the metal matrix composite layer consists of ?-CuAl2and MoAl5. Surface hardness was increased by a factor of 3.

Jan 1, 2015

By N. Baloyi, P. Popoola, M. Tlotleng, S. L. Pityana

"The advantages of using Nb and Ti-Nb coatings for improving the hardness and corrosion resistance of Ti6Al4V were investigated. It has been reported that Ti6Al4V used in orthopaedic implants tends to release toxic Al and V ions into the surrounding tissue. Thin layers of Nb and Ti-Nb were deposited on Ti6Al4V substrates using a laser metal deposition technique. The deposited material was analysed using optical microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy, and X-ray diffraction. The corrosion behaviour of the deposited layers was investigated using a Metrohm Autolab PG Stat101 compact potentiostat at 25°C in simulated body fluid. A Vickers hardness system was used to study the mechanical properties. Both Nb and Ti-Nb coatings exhibited good metallurgical bonding with the substrate. The microstructure and the XRD analyses for the Nb system showed that the ??-Nb phase was most dominant, while the Ti-Nb system comprised a mixture of the ?? and ?? phases. The average hardness of the Ti6Al4V substrate was 350 HV0.3, with a slight increase for the Nb coating (363 HV0.3) and a much higher hardness from the Ti-Nb coating at 423 HV0.3. The corrosion results show that the deposited Nb was more corrosion-resistant in the solution than either the Ti6Al4V substrate or the Ti-Nb coating. IntroductionMetals such as CoCrMo, 316L stainless steel, and NiTi alloy are used for manufacturing biomedical implants because of their distinct properties, including low Young’s modulus and resistance to corrosion (Ryan, Pandit, and Apatsidis, 2006). These implants are required to remain in the body of the patient for many years. Due to a favourable combination of mechanical and corrosion properties, titanium (Ti) and its alloys have emerged as the material of choice for biomedical implants. Nevertheless, their use is not entirely without challenges. For example, in total hip replacement, surface degradation and release of metal debris from metal erosion caused by friction limit the service life of the implant (Oldani and Dominguez, 2012; Manivasagam, Dhinasekaran, and Rajamanickam, 2010). Ti6Al4V is generally regarded as the material of choice, but it has been found that over extended periods of time, the combination of surface corrosion and erosion releases toxic aluminium (Al) and vanadium (V) ions into the body (Khan, Williams, and Williams, 1996). This has led to the investigation of titanium alloys containing niobium (Nb), zirconium (Zr), tantalum (Ta), and molybdenum (Mo) as substitutes for the aluminium- and vanadium-containing Ti6Al4V (Okazaki et al., 1997)."

Apr 1, 2019

By T. S. Seleka

Laser surface melting has been conducted on a 304 stainless steel (SS) with the aim of enhancing pitting corrosion resistance of the material. This process involves rapid melting of the material?s surface followed by rapid solidification to refine the microstructure. This includes the dissolution of inclusions such as MnS, FeS, CrxCy, and other minor constituents. The microstructures as a result of laser treatment were observed by means of optical microscope and also confirmed by the XRD. The glow discharge optical emission spectroscopy (GDOES) was utilized for chemical analysis. Changes in hardness were observed by using a Vickers microhardness tester. Pitting corrosion tests on laser treated and untreated samples were conducted according to ASTM G48-92 to evaluate mass loss and pitting morphology. Laser surface melting improved the pitting corrosion resistance of this material in a chloride-containing environment.

Jan 1, 2007

By H. J. Ilgner

The paper reviews the results to date of an integrated research programme currently being conducted by CSIR Mining Technology, aimed at impacting significantly on concentrated mining with face advance rates of up to 20 times faster than presently achieved. Consideration is given to the interplay between innovative technologies for continuous non-explosive mining or rock comminution underground and lateral hydraulic transportation in cross cuts, haulages and eventually hydro hoisting. Novel technologies for underground comminution of reef and development waste and an innovative pumping system suitable for the hydraulic transportation of coarse comminuted rock are reviewed. Emphasis is placed on South African gold mine reef and waste samples comminuted by electric shock wave comminution technology. The innovative TORE® pump system appears to be well suited for the successful hydraulic transportation of rock, produced by electric shock wave comminution, at solids concentrations between 45 % and 67 % by mass.

Jan 1, 1997

By Henk van der Bijl, Sean Rogers, Eugene Sidorski, Alan Carpenter

The electrode column is the heart of the submerged arc furnace. Superior electrode performance provides improved furnace performance. This paper describes the main features of the electrode column that delivers superior performance in furnaces worldwide, developed by Pyromet. Pyromet?s electrode comprises the compact slipping device, lower electrode assembly, upper and lower mantles, self-adjusting electrode seal, paste heaters, and Pyromet?s patented innovative electrode breakage detection and length determination system. Pyromet?s slipping device features compact interlocking clamping rings, incorporating fail-safe spring-loaded design. The interlocked clamping rings distribute the clamping force over a larger area of the electrode casing, preventing damage. The slipping device assembly features a low maintenance modular design that allows rapid slipping cycle times, back slipping, and compatibility with Pyromet?s electrode breakage detection and length determination system. Pyromet?s lower electrode assembly consists of the contact shoes, pressure bellows, pressure ring and heat shields. The contact shoes and pressure ring are designed for long, trouble free operation whilst the pressure bellow configuration equalise contact pressure and current distribution. Furthermore, the contact shoes incorporate a self cleaning feature, ensuring optimum electrical contact. The segmented design offers easy maintenance. Pyromet?s clients experience less down time due to longer component life. Pyromet?s remote adjusted electrode seal assembly reduces the rope seal working temperature, increasing rope life. The self compensating rope seal clamping force ensures an effective seal as the rope wears. Pyromet?s electrode breakage detection and length determination system detects electrode breaks utilising Pyromet?s electrode holder and data processing system. The length measurement system controls electrode length, eliminating the occurrence of short electrodes. The length measurement system furthermore eliminates the need for manual electrode length measurement, reducing associated production losses during furnace burn downs.

Jan 1, 2007

By J. J. Swanepoel

Titanium nitride in upgraded nitrided ilmenite (bulk of iron removed) can selectively be chlorinated to produce titanium tetrachloride. Except for iron, most other components present during this low temperature (ca. 200°C) chlorination reaction will not react with chlorine. It is therefore necessary to remove as much iron as possible from the nitrided ilmenite. Hydrochloric acid leaching is a possible process route to remove metallic iron from nitrided ilmenite without excessive dissolution of species like titanium nitride and calcium oxide. Calcium oxide dissolution results in unrecoverable acid consumption. The leachability of nitrided ilmenite in hydrochloric acid was evaluated by determining the dissolution of species like aluminium, calcium, titanium and magnesium in a batch leach reactor for 60 minutes at 90°C under reflux conditions. The hydrochloric acid concentration (11%, 18% and 25%), initial acid-to-iron mole ratio (2:1, 2.5:1 and 3.3:1), and solid-to-liquid mass ratio (1:8.33 to 1:2.13) were varied. The results indicate that a hydrochloric acid concentration of 25 wt% supplied in a 2:1 acid-to-iron mole ratio would produce the most favourable upgraded nitrided ilmenite product. The dissolution of iron in this solution reached 97 per cent after only 60 minutes. The total dissolution of calcium and titanium species was 0.01 and 0.11 wt% respectively. Hydrochloric acid can therefore be used as lixiviant to remove metallic iron from nitrided ilmenite. Keywords Titanium nitride, upgraded nitrided ilmenite, hydrochloric acid leaching, metallic iron dissolution.

Jan 1, 2011

Existing processes for the recovery of platinum group metals (PGM) from UG-2 ores place stringent requirements with regard to chromite content upon feed material to the plant. An alternative hydrometallurgical process for which this is not an issue is proposed that involves reductive roasting of the ore followed by leaching with HCl/chlorine, ion exchange, and recovery of PGM from the ion exchange eluate by reduction. Problems associated with leaching of PGM are discussed and results of laboratory testwork for each of the process steps are given.

Jan 1, 2004

By H. Manurung, I. M. Bendiayasa, W. Astuti, and H. T. B. M. Petrus, F Anggara, K. C. Wanta

The leaching kinetics of cerium (Ce) and yttrium (Y) in sodium-hydroxide-digested non-magnetic coal fly ash using acetic acid were investigated. The variables analysed were pH, solid-to-liquid ratio (S/L), and temperature. The results show that cerium and yttrium's maximum recovery was 57.33% and 58.36%, respectively, under leaching temperature of 90°C for Ce and 60°C for Y at pH of 1,74 and 10 g/mL solid-liquid ratio in 240 minutes. Increasing the leaching time to more than 120 minutes did not significantly improve the results. After the magnetic separation process, the ICP-OES analysis shows a slight increase in the concentration of cerium and yttrium on nonmagnetic components. The XRD and ICP-OES analysis for the sample before and after silicate digestion shows that 40% silicate was dissolved. The calculation of apparent activation energies of leaching using the Arrhenius law for the leaching of cerium and yttrium gives 22.72 kJ/mol and 35.84 kJ/mol, respectively. The kinetic leaching model of cerium and yttrium all fit Dickinson's new shrinking core model. The calculation results show that the leaching reaction is controlled by combining interface transfer and diffusion across the product layer.

Nov 6, 2024

By Marko Lampi, Marc Nicolle, Janne Karonen, Kari Valkama

"In the ten years from 2003 to 2013 global mine production of copper has increased by over 23% to meet demand while the weighted average head grade has dropped from 0.9 to 0.7% Cu. These divergent trends of increasing demand and declining economic grades will extend the life of many existing mines and improve the viability of marginal and/or complex copper deposits. Against that context this paper outlines hydrometallurgical copper sulphide leaching options as alternatives to the more conventional pyrometallurgical processing route of copper sulphides. Three copper sulphide leaching and refining processes are discussed: total pressure oxidation, ferric sulphate leaching and copper chloride leaching. The effect of mineralogy on the choice of processing technology is discussed as well as some of the unit processes used. Additionally, possible benefits that a hydrometallurgical process may offer over an existing pyrometallurgical route are discussed. Subsequently, two very important aspects to the development of projects involving the leaching of copper sulphides are discussed. Finally, a number of conclusions are presented that will be useful to keep in mind when considering projects involving the leaching of copper sulphides. INTRODUCTION In the ten years from 2003 to 2013 global mine production of copper has increased by over 23% to meet demand while the weighted average head grade has dropped from 0.9 to 0.73% Cu (Murphy, 2014). If these divergent trends of increasing demand and declining economic grades continue, they will contribute to the extension in life of many existing mines and improve the viability of marginal and/or complex copper deposits. Against that context, this paper outlines hydrometallurgical copper sulphide leaching options as alternatives to the more conventional pyrometallurgical processing route for copper sulphides. Three copper sulphide leaching and refining processes are discussed: total pressure oxidation, ferric sulphate leaching and copper chloride leaching. Ferric sulphate leaching and copper chloride leaching are carried out at atmospheric pressure while total pressure oxidation takes place at elevated pressures."

Jan 1, 2015

By K. Barani, S. M. S. Ganji

Creatine was used as a lixiviant for gold dissolution from gold ore. The effects of creatine concentration, temperature, leach time, and pH were examined for their influence on extent of gold dissolution. The results show that at a temperature of 75°C and pH 11.5, gold dissolution increased from 51% to 88% on increasing creatine concentration from 25 to 50 g/t. Further increase in creatine concentration showed a negative effect on the gold dissolution. Gold dissolution increased from 47% to 87% by increasing the temperature from 25°C to 55°C, and from 61% to 89% by increasing pH from 10 to 11.5. Under the optimum conditions of solids’ content of 30%, pH 11.5, creatine concentration of 100 g/t, temperature of 75°C, and hydrogen peroxide addition of 2%, about 90% of the gold could be dissolved from the ore after 24 h. A comparison between creatine and cyanide leaching showed that 90% gold dissolution was achieved at a cyanide concentration of 300 g/t, which is three times higher than the creatine concentration under optimal conditions.

Apr 14, 2024

By J. G. van der Watt

Due to increasing concerns of global rare earth element shortfalls in the near future, possible alternative sources of rare earth elements have recently become of economic interest. One such alternative is decanting acid mine water originating primarily from abandoned old mines in the Witwatersrand region of the Republic of South Africa. In this study, a novel way of rare earth element removal from the acid mine drainage was employed, making use of bentonite clay, which has very good adsorbent properties, as a rare earth element carrier material. The process can be economically viable only, if the elements can be selectively removed from the bentonite clay carrier material so as to yield reusable clay. Acid leaching was proposed to liberate the adsorbed rare earth elements from the bentonite clay. Accordingly, acid leaching experiments were performed to study the desorption of three commonly-found rare earth elements, namely neodymium, samarium, and dysprosium, from bentonite clay in the presence of sulphuric and hydrochloric acid. It was established that the three rare earth element species could be selectively removed as a group from iron, magnesium, and manganese metals through the careful manipulation of the pH. An investigation into the kinetic aspects of the rare earth element desorption process from the bentonite clay was also undertaken. The applicability of various kinetic models such as zero-order, pseudo first-order, pseudo second-order, elovich, parabolic diffusion, and power function were tested to describe the time-dependent desorption of rare earth elements from bentonite clay. It was determined that the pseudo second-order kinetic model represented the dissolution processes for neodymium, samarium, and dysprosium from bentonite clay the most accurately.

Jan 1, 2012

This paper describes experimental investigations into the reductive decomposition of arsenopyrite/pyrite (FeAsS/FeS2), a gold and silver bearing iron/arsenic sulphide using metallic iron powder. The main objective was to establish and experimentally confirm the thermodynamic and kinetic feasibility of reductively decomposing the sulphide matrix for precious metals recovery. In this context, cyanidation leach tests were conducted on the reductive leach residues. The arsenopyrite/pyrite flotation concentrate, mainly studied in the hydrochloric acid medium, decomposed through the non?oxidative chemical dissolution reaction and the reductive decomposition reaction for the arsenopyrite and pyrite components, respectively. Desulphurization levels below 65% were achieved at pH values below 0.15 and iron to concentrate ratios above 1, and the system was characterized by overall very slow kinetics. The reaction system had a direct linear relationship with iron to concentrate ratio and an inverse relationship with pH. An analysis of the pyrite/iron galvanic system showed that pyrite forms a partially inert cathodic surface on which the anodic dissolution of iron occurs, supported by the hydrogen evolution reaction. This phenomenon explained the low desulphurization levels and the mineral decomposition seemed to be restricted to the non?oxidative chemical dissolution reaction for the arsenopyrite component. The cyanide leach of the reductive leach residues showed very little improvement in gold recovery. The reductive leach process for arsenopyrite/pyrite has considerable limitations in terms of both desulphurization and precious metals liberation. Keywords: Pyrite, arsenopyrite reductive leaching, hydrogen sulphide, invisible gold

Jan 1, 2009

By A. A. Snodgaass

This paper reviews lead as a commodity, starting with a brief historical outline and dealing with the various uses of lead in some detail. It then goes on to discuss some statistics in relation to the production and reserves of lead, before sketching its mode of occurence. The topics are approached in regard both to the world and to South Africa, with the emphasis on the later. The mining and concentration of lead at Black Mountain Mine at Aggeneys in the north-western Cape Province are detailed, before a general account is given of the smelting, hydrometalurgical extraction, and refining of lead, together with the processes used in these activities. The paper concludes with a discussion of safety and health in regard to lead and a brief look at the commodity's future.

Jan 1, 1986

By Wei Sun, Ruolin Wang, Wenjuan Sun, Junhao Fu, Haisheng Han, Zhao Wei

Pb–benzohydroxamic acid (BHA) (lead complexes of benzohydroxamic acid) exhibits high selectivity but low collecting efficiency in scheelite flotation. This paper reports the manner in which BHA and sodium dodecyl sulfate (SDS) were employed as ligands to coordinate with the lead ions to obtain a colloidal lead-group multiple ligand complex, i.e., the Pb–BHA–SDS, for improving the collecting efficiency of Pb–BHA. The flotation mechanism of Pb–BHA–SDS with respect to scheelite was investigated from the viewpoint of interface science based on the pure mineral flotation, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. The results showed that the BHA and SDS coordinated with Pb2+ to form novel leadgroup multiple ligand complexes, which are different from the traditional understanding associated with the mixed collectors. Pb–BHA–SDS was a better collector with stronger collecting ability and excellent selectivity in regard to a scheelite flotation than Pb–BHA. The addition of SDS to Pb–BHA enhanced the latter’s adsorption ability on the scheelite surface and improved the hydrophobicity of the collector’s nonpolar groups, rendering Pb–BHA–SDS as a more efficient collector at a low dosage. Keywords: Scheelite; Pb-BHA complexes; sodium dodecyl sulfate; multiple ligands; Pb–BHA–SDS

Jan 1, 2020

By M. C. Bekker, T. Govindasamy

The potential benefits of implementing the Last Planner System (LPS) on mining infrastructure projects were explored through two case studies in the South African mining industry. The first part of the study involved measurement of the impact of LPS through earned value techniques on secondary project data. The second part sought to establish the lean construction success factors leading to improvements in construction performance. This was done by means of a research questionnaire distributed to the project owner’s teams, contracted parties, and the LPS facilitators. The results revealed a positive correlation between LPS application and planned percentage complete. However, the performance achieved during the LPS pilot was not sustained. The success factors and benefits considered most evident in the case study pilot differed among the three stakeholder groups. The findings are expected to guide construction stakeholders to better define performance measures and focus on factors required to make LPS implementation more effective in the South African mining sector.

Feb 12, 2024