Search Documents

By R. Kumar, N. R. Mandre

"The beneficiation of iron ore slimes by selective flocculation was studied. Polyacrylamide (PAM) and guar gum were used as flocculant, along with sodium hexametaphosphate (SHMP) as a dispersant. The samples collected were initially subjected for chemical and mineralogical studies. The mineralogical studies indicated the presence of haematite and goethite as the principal iron-bearing minerals, with quartz and kaolinite as gangue minerals. The selective flocculation tests showed that the Fe grade can be enhanced from 58.24% to 64.60% Fe at a recovery of 66.33% using polyacrylamide as the flocculant. A Fe grade of 63.20% at a recovery of 68.04% was obtained using guar gum as flocculant. The efficacy of the studies was analysed using a separation index, which indicated that the higher separation index was obtained with the tests employing polyacrylamide as the flocculant. IntroductionIndia is endowed with huge reserves of highgrade iron ore and is one of the prominent producers in the world. As the high-grade iron ores have been exhaustively mined, it has become imperative to use low-grade iron ores, fines, and slimes to meet the growing demand. Also, generation of fines and slimes during mining and processing contributes to loss of minerals to the extent of 30% of the total value (Mandre and Panigrahi, 1997). These fines/slimes are often discarded as waste into tailing ponds, containing considerable amounts of iron. Therefore beneficiation of tailings/slimes has become necessary for optimal utilization of the resources.In recent years, interest in recovery of valuable minerals from low-grade ores, slimes, and tailings has increased worldwide. These activities are initiated not only to recover minerals but also to address various environmental issues associated with fine particle treatment. The literature reveals that several technologies have been employed in this regard, including flotation, advanced gravity separation, and high-intensity magnetic separation. However, these processes are found to be ineffective for fine particle treatment due to lower collision probability in flotation, decreased gravitational effect in gravity separation, and reduced drag force in magnetic separation, among other factors (Batisteli and Peres, 2008; Das et al., 2007; Dworzanowski, 2012; Rocha, Caneado, and Peres, 2010). Therefore, it is in this regard that selective flocculation has gained importance in treating slimes in recent years."

Jan 1, 2017

By Y. Qin, L. Han, P. Gao, Y. Han, Y. Lia

In the present study, an innovative comminution technology of high-voltage pulse discharge was proposed for galena to weaken the mechanical property. The results of pre-treatment experiments indicated that the optimal operating conditions of spherical gap spacing 25 mm, pulse numbers 120, and loading voltage 25 kV were obtained, where the relative grindability of pretreated products was improved significantly, although with the prolonging of grinding time, the superiority of high-voltage electric pulses was gradually weakened. The galena ores were subjected to a high-voltage pulse discharge, and then the crack generating along the boundary between galena and gangue was observed under an optical microscope, and the surface burning which appeared in the ores. The scanning electron microscope (SEM) results indicated that the pretreated products were in a state of melting and then condensation, accompanied by some pore formation. Pulsed discharge pre-treatment not only produced more micro-cracks and cracks in the sample but also extended the original crack. Keywords: High-voltage pulse discharge; galena; relative grindability; micro-crack

Jan 1, 2020

By C. O’Donova, E. Adam, L. A. Torres-Cruz

High-profile failures of tailings dams illustrate the significant safety challenge they pose. The decant pond of such facilities plays an important role in their mechanical stability. This study investigates the feasibility of using public multispectral data collected by the Sentinel-2 satellite mission to monitor the area of the decant pond. The Sentinel-2 mission has a revisit time of 5 days and the data used herein has a spatial resolution of 10 m/pixel. We considered two water-detection metrics: the normalized difference water index (NDWI) and the near-infrared (NIR) reflectance. Implementation of the method at a South African platinum tailings dam illustrates the capabilities and limitations. Public, sub-metre resolution true-colour imagery served as validation data. There is good agreement between pond area measurements based on Sentinel-2 and the validation imagery. These results suggest the feasibility of using Sentinel-2 data to supplement the monitoring of the decant pond.

Apr 2, 2022

By S. Stuurman

Inorganic acids such as sulphuric acid have found use together with certain reducing agents in leaching of copper-cobalt oxide ores. These reagents are not ideal due to the adverse effect the inorganic acids generally have on the environment and the high costs of the reducing agents. In this study a copper-cobalt oxide ore from the Central African Copperbelt was leached in two different environments; sulphuric acid in conjunction with hydrogen peroxide as a reducing agent and tartaric acid. The effects of acid concentration, reducing agent concentration, and temperature were independently determined for both leaching environments. The sulphuric acid concentration was varied between 0.4 M and 1.2 M and the concentration of hydrogen peroxide between 4.0 M and 6.5 M, while the tartaric acid concentration was varied between 0.15 M and 0.35 M. The temperature was varied between 20°C and 50°C. The results showed that the extraction of both copper and cobalt increased with sulphuric acid concentration, reaching a peak at approximately 0.8 M and then decreasing at higher acid concentrations. A similar increase and decrease in metal extraction was observed when the reducing agent was increased. In leaching with tartaric acid, the extraction of cobalt was much higher than that of copper, although extraction of both metals increased with acid concentration. Additions of small amounts of hydrogen peroxide were found to increase cobalt extraction in tartaric acid but had a minimal effect on copper. An increase in the solution temperature had a significant effect in the organic acid environment, with the effect on cobalt extraction being much more pronounced than on copper.

Jan 1, 2014

By M. Rudolph, A. D. Renno, H. Wu

In this study, synthetic pure cassiterite and cassiterite doped with Fe were successfully produced by sintering. Their crystal structure and chemical compositions are characterised by optical microscopy, X-ray powder diffraction (XRD) as well as scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) based chemical composition analysis. The electrostatic behaviour of synthetic and natural cassiterite was studied by electrophoretic measurements. Their floatability was studied by microflotation with two types of anionic collectors. Results show that the cassiterite floatability with these collectors behaves differently and lead to two opposite results: Natural cassiterite (enriched with Fe) > undoped pure SnO2 by using sulfosuccinamate (Aerosol® 22) Undoped pure SnO2 > Fe3+ doped > natural cassiterite (enriched with Fe) by using styrene phosphonic acid (SPA). Keywords: Synthetic cassiterite, lattice impurities, flotation, zeta potential, Aerosol® 22, styrene phosphonic acid

Jan 1, 2020

By N. Sacks, N. B. S. Magagula, I. Botef

"Low-pressure cold gas dynamic spraying was used to deposit WC-4wt%Ni and WC-4wt%Ni-1wt%Mo coatings onto mild steel. Dense coatings with very low porosities were produced. No decarburization occurred during deposition and no deleterious phases were formed. The coatings were subjected to standardized material characterization tests, as well as slurry abrasion testing to assess their wear behaviour. The wear tests were conducted in synthetic minewater-silica slurries, while distilled watersilica slurries were used as a control. The hardness of the coatings, 512HV0.3 and 458HV0.3 for WC-4wt%Ni and WC-4wt%Ni-1wt%Mo respectively, are comparable to those achieved using high-temperature coating processes. The abrasion wear rates for both coatings were less than 5 mg/min and 10 mg/min in the distilled water-silica and synthetic mine water-silica slurries respectively. The approximately 50% increase in wear rate in the synthetic minewater slurry is attributed to a synergistic corrosive wear mechanism. The predominant wear mechanisms were identified as binder smearing and delamination, with carbide grain fracture and pull-out. IntroductionSlurry abrasion is a common phenomenon in mining operations, particularly in pipelines transporting, for example, sand-water slurries. This type of wear can cause pipeline fracture, shortened operational lifetimes, and impede pipeline efficiency. To reduce or limit abrasion, thermally sprayed tungsten-carbide-based coatings are often used as pipe linings (Kanchan et al., 2010). This is due to their attractive mechanical properties, which include high wear resistance, stiffness, hardness, compressive strength, and tensile strength. These properties are provided by the coating microstructure and composition, which is a blend of hard, wear-resistant tungsten carbide (WC) particles embedded in a fracture-tough metallic binder phase (Brookes, 1997). Cobalt (Co) is the most commonly used binder due to its excellent wetting of the WC phase and moderate mechanical properties; however, its application is limited to non-corrosive environments as it has a low corrosion and oxidation resistance (Andren, 2001). Nickel (Ni) may also be used as a binder, and has been shown to have superior oxidation and corrosion resistance, but in some applications may not have the required mechanical properties (Kim et al., 2006)."

Jan 1, 2016

By R. T. Rudd

DISCUSSION R. T. RUDD I have the following comments on Mr Bosman's paper. Before giving the company permission to discharge neutralized mine drainage containing 1800 mg/l of dissolved solids into a public stream, my Department had to consider the matter from both the legal and the practical viewpoint.

Jan 4, 1974

The Annual General Meeting of the Institute was held in Kelvin House, Johannesburg, on Wednesday, August 14th, 1974. Mr P. W. J. van Rensburg (President) was in the Chair. There were present 56 Fellows, 21 Members, 2 Graduates, 5 Associates, 16 Students, and 58 Visitors, making a total of 158. The President declared the Meeting open at 4.08 p.m. OBITUARIES The President: Ladies and gentlemen, before we start the business of the meeting, it is my sad duty to announce the deaths of the following members of the Institute since our last meeting: Dr O. A. E. Jackson, Honorary Life Fellow and Past President; C. Airth, T. L. Blunt, A. E. Frazer, C. L. Lamb, and K. Richardson, Life Fellows; and J. T. Beaumont, Fellow. As you know, there were a number of other deaths during the year, which were reported at previous General Meetings of the Institute. As a mark of respect to the memory of the deceased, and in sympathy with the bereaved, I ask you to rise and observe a few moments' silence. MINUTES The President: Ladies and gentlemen, the next item on your agenda is confirmation of the minutes of the General Meeting and Special General Meeting held on May 22nd, 1974. These will be published in the August issue of the Journal, and, since you have not yet received this, I must ask that they be held over to the next General Meeting. WELCOME The President: It is a very pleasant duty for me to welcome many members of our Institute and our guests, among whom we are particularly pleased to see the President of the Chamber of Mines, Mr Dolf Schumann, who is also Honorary President of this Institute. Mr Schumann, we are extremely pleased to have you with us today. And, we welcome an old friend of ours, Mr Dillon, Minister of Mines in Rhodesia, who has come down for our Annual General Meeting. Mr Dillon, we are very, very pleased to see you here this evening, and we look forward to seeing Mrs Dillon a little later. And we have with us, too, the presidents or representatives of many of our sister and brother associations, institutes, and societies. In particular, we welcome Mr Mike Gericke, President of the South African Council of Professional Engineers, and Professor Midgley, President of A. S. and T. S. We are also pleased to welcome the Presidents of the Mechanical Engineers, Electrical Engineers, Certificated Mechanical and Electrical Engineers, the Civil Engineers, the Joint Council of Scientific Societies, the Mine Ventilation Society, the South African Association of Consulting Engineers, the Association of Mine Managers, the Institute of Foundrymen, the Institute of Welding, the Federation of Societies of Professional Engineers, Mine Surveyors, Production Engineers (London), and the Institute of Production Engineering. We are very glad, too, to have with us a visitor from England, Professor Raynor and Mrs Raynor. Professor Raynor is Professor of Metallurgy at Birmingham University, and a very well-known metallurgist in Britain. We also have with us the Chairman of the Ferro-Alloys Association. We are expecting the Chairman of our Witbank/Middelburg Branch, the Chairman of the Engineers' Liaison Committee, Pretoria, the Director of the Witwatersrand College of Technical Education, and, of course, our old friend, Mr Eric Boden, the Manager of A.S. and T.S. It is a very great pleasure to have with us a number of persons who will receive honorary Life Fellowship at this meeting, and there are some Gold Medal winners and winners of our Student Prizes. We have apologies from a number of people who are away on business, and unfortunately some are ill. But we are extremely pleased to see those of you who are here, and we are also very pleased to see so many ladies. We expect to see many more of them later this evening, at our Cocktail Party. MEMBERSHIP The President: I have pleasure in announcing that, their names having been published in accordance with By-Law 5.2.2., the following have been elected by Council to membership in the following grades Fellows: B. Collins, D. W. Dixon, J. P. Dreyer, A. T. Hudson, and W. W. Pearce. Members: A. T. Fisher and I. F. Nagy. Associate Members : P. D. de Bruyn and H. C. Iverson. Graduates: D. P. O'Shaugnessy and M. F. Sadler. Associates: R. J. Bushell and A. MacDonald. Students : I. J. Barker, P. J. Charter, J. P. de Witt, G. S. Esterhuizen, N. Green, P. M. Jenner, M. J. R. Meyer, A. P. Nicol, W. J. C. Pothas, B. J. Robbetze, N. T. Sutherland, B. A. Statham, C. R. Thomas, N. C. Webb, M. Salamon, R. G. Jurd, and M. McChesney. Transfers to other grades of membership include the following: Member to Fellow: B. W. Holtzhousen. Graduate to Member: T. S. Schultz. Associate to Associate Member: C. L. Jordaan, H. J. L. Tomlinson, J. E. Forbes, G. H. S. Bamford, T. F. Carswell, J. W. Breidenhann, J. R. Garbutt, and L. S. Gibbs. Student to Graduate: C. J. Faueonnier and B. Lund. Student to Associate : G. P. Gooding. We welcome these new members

Jan 10, 1974

By A. J. S. Spearing, M. Sharifzadeh, K. V. Jessu

Empirical pillar design methods are commonly used in the mining industry. The parameters within which these methods are valid are frequently unknown to the user or ignored. In addition, empirical design may not consider essential parameters such as blasting effects, orebody dip and the presence of geological structures, which all adversely affect the stability of the pillars. This can result in potentially serious pillar design strength over-estimates. Although the commonly based tributary area method is generally conservative, as the spans are seldom that large relative to the depth, failing to consider other relevant parameters can result in errors. Problems associated with an under-designed pillar can range from a local pillar collapse to a catastrophic chain reaction collapse (or run). Over-designed pillars are generally safe but reduce the extraction of the orebody, thus adversely affecting the profitability of the mining operation. We used laboratory tests and numerical modelling to understand the effects of pillar orientation, blasting and the presence of discontinuities on pillar strength. Reduction factors were developed with these models to be implemented in conjunction with the existing empirical pillar design methods. For any pillar or mine design, once it is implemented, the actual performance of the system must be checked regularly by observation and monitoring and adjusted if needed. The pillar design approach outlined in this paper can better optimize the pillar mining method by considering other generally ignored but important parameters, thus improving safety, productivity, and economic aspects.

Oct 1, 2022

By D. Yu Pleev, V. G. Krivolapov

Mines of Southern Kuzbass working out, basically, coal formations of flat seams. Seams, as a rule, are inclined to self-ignition. Detection at early stages of the centers of endogenous underground fires has great value for safe conducting mountain works. One of methods of detection of an early stage of underground fires in the worked out space is the method of superficial radon survey. In the report the method is de-scribed and examples of superficial radon survey on concrete layers are given.

Jan 1, 2003

By Piotr M. Kapias

Keywords: extraction, lead refining, Pb-Tl solutions, PbCl2-TlCl solutions. The theoretical part of the paper presents an analysis of the conditions of Tl extraction from Pb using different extractants and determines the activity coefficients in liquid solutions of Pb-Tl and PbCl2-TlCl. The dependence of the solution activity coefficients upon the composition and temperature is presented in the form of Krupkowski and Krupkowski-Fitzner equations. An analysis and evaluation were made of the influence of the methods of PbCl2 introduction into a Pb-Tl solution upon the efficiency of the Tl extraction process under thermodynamic equilibrium conditions. The analysis made it possible to formulate relevant equations describing the dynamics of the process of Tl extraction from Pb under stirring conditions as well as under the extractant injection into the liquid Pb-Tl solution conditions. In the part concerning experimental work, results are given for tests on the Tl extraction process from Pb-Tl liquid solutions of initial Tl content of approximately 0.05% mass using PbCl2 or, alternatively, Cl2(g) conducted in laboratorial scale. The tests made it possible to establish the influence of time, temperature, mass and the method of introducing the extractants into the liquid upon the level of Tl extraction from a Pb-Tl solution. Labels used in the text. WT1m - TI content in metallic phase, % mass WT1s - TI content in chloride phase, % mass wpTlm - TI content in metallic phase in initial state, % mass W°Tlm - TI content in metallic phase in equilibrium conditions, % mass m°m - initial mass in metallic phase mm - mass in metallic phase mPbC12 - lead chloride mass fed to the system MPbC12-TIC1 - mass in chloride phase MPb - lead atomic mass, g/mole MT1 - thallium atomic mass, g/mole K - Nernst distribution coefficient Xi - mole friction of solution component X°PbC12 - mole friction of PbC12 in saturated solution X°T1C1 - mole friction of T1C1 in saturated solution T - temperature, K R - gas constant, J/(mole K) k - kinetic equation constant, 1/(%-min.) ?i - solution component activity coefficient e - extraction rate, %

Jan 1, 2008

The 89th Annual General Meeting of The South African Institute of Mining and Metallurgy was held at Kelvin House, Johannesburg, on 20th August, 1986. Mr. H. E. James (President) was in the chair and declared the meeting open at 16hoo. Obituaries President: It is my sad duty to announce the deaths of the following members of this Institute: Life Fellow D.L. Carson; Retired Fellows T.K. Adams, G.E. Carlyon, N.M. Holford, D.E. Maclver, C.J. Morgan; Fellows S.K. de Kock, R.R. Porter, Dr G.J. Rees; and Associate Sir Lindesay Clark. As a mark of respect to the memory of the deceased and in sympathy with the bereaved, please rise and observe a moment of silence. Minutes President: The 88th Annual General Meeting of the Institute was held on Wednesday, 14th August, 1985, and the minutes were published in the September 1985 issue of the Journal. The minutes were confirmed.

Jan 1, 1986

By C. Gatschlhofer, A. Krammer, H. Raupenstrauch, T. Hochsteiner, A. Holzer, L. Wiszniewski

The rising demand for lithium-ion batteries, coupled with international climate targets, emphasises the need for circular economy and zero-waste recycling approaches. However, so far, no industrial-scaled solutions are available that fulfil global recovery targets. Therefore, a novel pyrometallurgical reactor was developed at the Chair of Thermal Processing Technology at Montanuniversitaet Leoben to avoid lithium slagging and recover volatile elements via the gas phase. Nevertheless, previous results show that several impact factors, including interfering elements or pre-treatment steps, strongly limit the recycling efficiency of black mass. To simulate the black mass and provide feedback on possible influences of pre-treatment steps, cathode material from production with additives of interfering elements was analysed regarding melting behaviour. The results show that formation of a further processable alloy was increased by almost 50% when pretreatment steps were excluded, indicating pre-treatment steps as a major influence to be considered within this specific recycling route.

Jan 1, 2023

By J. van der Walt, W. Spiteri

Flyrock remains a significant threat to the health and safety of mine employees and integrity of infrastructure, as well as to the safety of the neighbouring communities and their property. This investigation was motivated by the general lack of fundamental research and mathematically quantifiable data in the literature regarding the relationship between blast design parameters and their impact on flyrock. The focus was to develop a concept that can be used to mathematically quantify the trajectory of flyrock resulting from a blast, which can be used for future research. The ultimate goal for this technique, once it has been fully developed, is to: ➤ Enable mining operations to generate a database with accurate historical flyrock measurements resulting from their blasting operations ➤ Allow research teams to conduct scientific investigations into flyrock and the impact of various blast design parameters ➤ Generate point-cloud data to visualize blasts and flyrock in a virtual reality environment for training and education purposes. This paper summarizes a conceptual technique and preliminary fieldwork that was carried out to determine the technique’s feasibility and motivate further development. The results show conclusively that a modified photogrammetric technique is capable of capturing flyrock data for further processing and analysis. The data acquisition procedure can, at this point, be used to meet the first aim of the project, namely to gather a field database of historical flyrock generation. Further development of the technique is ongoing and it is envisioned that the scientific-based technique will provide a method whereby future flyrock studies will be comparable and that assumptions will be limited.

Apr 5, 2023

By H. G. M. Rose

Contribution to the above paper by H. G. M. Rose* (Fellow) INTRODUCTION Dr Lawrence is to be congratulated on his most interesting and instructive paper, particularly on his suggestion for a model to increase mining productivity through improved management performance. In view of an experiment initiated in one Union Corporation mine (Mine A) and later extended to a second mine (Mine B), it might be of interest to review the many human factors involved and the initial productivity results achieved.

Jan 7, 1974

By B. Oladipo, E. Govender-Opitz, T. V. Ojumu

Bioleaching, one of the several important processes of biohydrometallurgy is an accepted technique for the extraction of desired metals from sulphide ores. Although the mechanism is well understood, the slow metal extraction rate due to passivating layer and ferric ion precipitation, especially in a typical chalcopyrite leaching, impact negatively on the overall efficiency of the process. Iron precipitates are common in many biohydrometallurgical operations and these precipitates represent the exit route for undesired iron, alkali ions or sulphate ion from the processing circuit. While there have been reports on approaches to slow the formation of these precipitates by manipulation of various operating conditions such as pH, redox potential and temperature, the precipitates become highly significant over the long term in the continuous operation of bioleaching and may render heap impermeable. Although there is evidence supporting the nature of the passivation to be precipitates of iron, their scavenging mode of reducing extraction efficiency is still not well understood. This paper thus discusses iron precipitation in biohydrometallurgical processes, including its formation and significance on bioleach processes. The paper also details the associated passivating species identified with heap bioleaching of sulphide minerals and provides some insight into sorption mechanism that limits metal recovery in a typical bioleach operation. Keywords: Iron precipitation, bioleaching, chalcopyrite, passivation, jarosite, metal sorption

Jan 1, 2020

By F. Wang, P. Rosario, A. Vazirizadeh

Advances in data science, machine learning, and artificial intelligence are transforming mining and mineral processing, and making them more algorithm intensive. The paradigm is shifting from one of detection and control to one of prediction and optimisation. To build up reliable prediction and optimisation models these steps should be passed: collect, aggregate, cleanse, and process large amounts of complex, structured, and unstructured data as a first stage. Next, the right tools must be used to extract meaningful features from the operational data for the build-up of a prediction model. A grinding circuit is one of the challenging areas in terms of determining its overall efficiency and the prediction of product quality. In a processing plant, some of the KPIs are typically unmeasurable or infrequently measured for real-time application, e.g. ore grindability and grind size. However, these variables are required to calculate the grinding circuit efficiency and to model the operation performance. In this paper, advanced analytic tools have been used to extract one selected KPI (cyclone overall P80 or final grind size) and its relationship with measured variables for an industrial dataset. The results illustrate that the performance of the grinding circuit can be predicted for real-time monitoring by means of measured data. Keywords: Grinding circuit, data-driven, machine learning, process modelling, hybrid modelling

Jan 1, 2020

"Chairman: Professor H. S. SICHEL Rapporteur: Miss M. I. WATSONPapers:Unrolling of Copperbelt orebodies by J. H. E. Perry and V. H. WiikAn exploration model for tabular orebodies by G. S. Koch and R. F. LinkHarmonic analysis of copper and gold occurrences in the Arbitibi area of the Canadian Shield by F. P. Agterberg and A. G. FabbriMathematical models of orebodies by M. J. Newton and A. G. Royle Estimation of lateritic-type orebodies by A. JournelIn his presentation Mr Wiik said that unrolling could be regarded as a reversal of the natural process of folding, so that the aim of an unrolling procedure would be the reconstruction of original pre-tectonic conditions. While simply formulated, this aim might not always be achieved. The geometrical relationship between points on the deformed surface and corresponding points on the original surface is process-dependent, and a true reconstruction could be achieved only if the deformation history were known in detail.In this computer unrolling procedure all these complexities were ignored. Referring to one particular marker horizon, Mr Wiik said that it was assumed in the procedure that this marker was deposited as a horizontal stratum and that it had subsequently been deformed by simple flexure-type folding.The procedure allowed the geologist to incorporate his knowledge and conception of the deposit through repeated re-contouring with dummy points. This 'manumatic' aspect of the procedure had proved invaluable, not only in resolving specific unrolling problems but also in making the system more acceptable to the geologists in general.Unrolling served towards removing what might be termed `tectonic noise' superimposed on the primary distribution patterns for regionalized variables such as metal content and orebody thickness. From this point of view, variograms derived on the basis of unrolled-plan co-ordinates should be more meaningful in terms of depositional environment than are variograms calculated from a normal map projection.Mr M. M. Oosterveld remarked that it appeared from the paper that there were problems in applying the unrolling technique to ore reserve calculation, and asked whether there were not other methods that might be used for that purpose.Mr Wiik replied that at present unrolling played only a minor role in practical ore reserve estimation within Roan Consolidated Mines, Limited. The techniques currently in use differed from one orebody to another, but in general they involved projection onto a vertical longitudinal section or a horizontal plan, with subsequent grid interpolation by means of a standard computer contouring package."

Jan 1, 2014

By F. K. Crundwell

The rate of dissolution of sulphide minerals is frequently interpreted in terms of the passivating behaviour of a layer of material on the surface. This interpretation has driven research to identify and possibly remove this layer from the surface, and thus yield higher rates of dissolution. The identification of such layers has proved difficult, with different researchers claiming different compositions for possible layers. An alternative framework has been pursued by the author and co-workers, who have argued that the rate of dissolution is governed by the electronic structure of the minerals which give rise to their semiconducting properties. Researchers sceptical of this approach have argued that semiconducting properties are only important in highly pure substances. In this paper, we review the electronic and semiconducting properties and discuss how they impact dissolution behaviour. These properties affect their colour and dissolution properties even though the minerals are not high purity substances. Keywords: Dissolution, leaching, passivation, semiconductor, chalcopyrite

Jan 1, 2020

By M. Seerane, R. Machaka, P. Ndlangamandla

"Metal injection moulding (MIM) is a near-net-shaping powder metallurgy technique suitable for the cost-effective mass production of small and complex components. In this paper, the effects of the metal powder particle size on the final properties of 17-4 PH stainless steel are reported. Three different particle sizes (d50 33.0, 7.91 and 4.04 µm) were used to prepare the injectable MIM feedstocks using a CSIR-developed wax-based binder system at a fixed solids loading of 60 vol.%. The distribution slope parameter and the rheological flow index behaviour were used to predict the flowability of the feedstocks. The effects of the particle size on MIM products were established. The results are discussed in terms of the subsequent microstructural and mechanical properties of MIM 17-4 PH stainless steel against the established MPIF Standard 35. IntroductionMetal injection moulding (MIM) is a near-netshape manufacturing process established as an alternative to produce complex small-tomedium shaped components that were previously fabricated by conventional methods at higher costs (Attia and Alcock, 2011; Todd and Sidambe, 2013).Although recent advances in micromanufacturing (mainly machining and electrodeposition-based) have enabled the fabrication of complex micro-size geometries directly into miniaturized parts, these processes are generally neither routine nor easily accessible at present (Attia and Alcock, 2011).Typically, the MIM process consists of four steps: mixing, injection moulding, debinding and sintering. Mixing involves blending of the desired metal powder composition with carefully selected multicomponent organic binders at the right proportion. This mixture, which is called feedstock, is then injected into a mould of a required shape to form a ‘green part’. Debinding is the removal of the binders by chemical, thermal, or catalytic means while maintaining the shape of the part. Finally, the debound part is sintered to a full or near-full density part (Sotomayor, Varez and Levenfeld, 2010). The MIM process is essentially a combination of plastic injection moulding with conventional powder metallurgy technologies."

Jan 1, 2016