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By J. A. Maritz, D. F. Malan

Pillar strength is affected by pillar shape, but this has largely been ignored in past research studies. Bord-and-pillar layouts are typically designed using empirical strength equations developed for square pillars. Owing to the poor quality of pillar cutting, many hard-rock pillars have an irregular shape and it is not clear how this affects pillar strength. Furthermore, the strength of rectangular pillars in comparison with square pillars is also difficult to quantify. The ‘perimeter rule’ is widely adopted for rectangular pillars, but its applicability for pillars with irregular shapes has never been tested. We used numerical modelling in this study to investigate the effect of pillar shape on strength. An analytical limit equilibrium model of a square and a strip pillar also provided useful insights. For slender pillars, the strength of a long rib pillar is essentially similar to that of a square pillar. In contrast, for rib pillars with a large width to height ratio, there is a substantial increase in strength. The study found that the perimeter rule should not be used for irregularly shaped pillars. Displacement discontinuity modelling, using a limit equilibrium approach, is proposed as an alternative to determine the strength of these pillars.

May 3, 2023

By M. E. Rossi, C. Badenhorst

Conditional bias occurs when the expected value of the true grade conditional on the estimated grade is not equal to the estimated grade. It is a quantification of how the average of estimates differs from the true value. Conditional bias is present in all resource estimates due to the unavoidable properties of kriging, and indeed all linear estimation (regression) methods. In a mining resource estimation context, the degree of conditional bias is dependent on the spacing of the conditioning data; more data leads to the expectation of less conditional bias This paper discusses conditional bias from two perspectives: 1. 2. Estimates seeking to eliminate, as much as possible, conditional bias; and Estimates that accept a larger amount of conditional bias in resource models, in order to achieve a specific outcome. The problem of conditional bias in estimation can only be fully appreciated if the objective or purpose of a resource model is understood. There are instances where conditional bias should be avoided because it is not reasonable to make decisions using estimates that are known to be wrong in expected value; for example, when making a final decision in grade control with respect to the destination of the material. In most instances in the mining resource estimation context, however, the estimated values will not be “final estimates”, but “interim estimates”, meaning that in the future more data will be obtained, and the ”interim estimate” will then be updated. In this context, the most useful resource model is an interim model that is able to predict the final model estimates, despite not having all the data available that will be collected in the future. This is the objective, for example, of a recoverable “long-term” model developed prior to operating a mine, for example at the feasibility stage. It attempts to predict the ore that a processing plant will receive, well into the future. In such cases, it can be unequivocally demonstrated that conditional bias is not only unavoidable, it is a necessity.

Sep 1, 2021

By J. C. Vreugdenburg, B. A. Dippenaar, J. Muller, T. L. de Vries

Iron ore fines are agglomerated in the sintering process to produce sinter: an important feed material for blast furnaces worldwide. A model of the iron ore sintering process has been developed with the objective of being representative of the sinter pot test, the standard laboratory process in which the behaviour of specific sinter feed mixtures is evaluated. The model aims to predict sinter quality, including chemical quality and physical strength, as well as key sinter process performance parameters such as production rate and fuel consumption rate. The model uses the finite difference method (FDM) to solve heat and mass distributions within the sinter pot over the sinter bed height and time dimensions. This method can further be used for establishing empirical relationships with measured sinter properties. Inputs into the model include the feed material physical properties, chemical compositions, and boundary conditions that vary over time. Sub-models describe relationships between applied pressure differential and gas flow rate through the bed of granulated fine ore particles, combustion of carbonaceous material, calcination of fluxes, evaporation and condensation of water, and melting and solidification. Four sinter pot tests were performed and the model predictions validated against temperatures measured at depths of 100, 230, and 420 mm. Differences between predicted and measured temperatures indicated the need for optimization of some model parameters that are uncertain. Optimization resulted in an improvement in the correlation between the predicted and measured temperatures for all tests, although an acceptable level of agreement was not achieved in all cases. Using these parameter values, reasonable agreement was found in terms of typical performance parameters for three out of the four tests.

Jan 1, 2014

By Ri McCrindle

"Analytical Chemistry is moving rapidly towards a concept where technicians have to do no more than press a button and print the result from an instrument that is a featureless ""black box"". In this environment we must ask how much traditional ''wet chemistry"" is still required for undergraduate students.Methods that can be fully automated will become increasingly important. An example of such a method is that of the slurry nebulisation and ICP-OES analysis of precious metal concentrate. Grinding the sample and adding Triton X100 as dispersant, complete analysis time is in the order of 90 min as apposed to the traditional Carius tube method which could take as long as 24 h. For most of the elements studied, the results using ""in-house"" reference material for calibration and as samples as well were within the 95% confidence level. Elements of low concentration in the sample (As, Bi and Se) were not within that level."

Jan 1, 2014

By A. J. H. Newell, K. Doherty

A copper-gold project has required a number of trade-off studies underpinned by test work to settle on pragmatic flowsheets and throughputs to support a pre-feasibility study that provides a compelling financial case. The primary trade-off studies were based on the mine schedule, ore type feed-grade recovery relationships, likely concentrate grades and typical marketing terms as well as the estimated capital and operating costs for a range of throughputs and mining strategies. Secondary trade-off studies were conducted for specific circuits and additional processing options. Although the details of these studies are not presented, the technical options and subsequent flowsheets are discussed. While the flowsheets will be optimised during the feasibility study stage, the basis is now fixed for the four ore types that would be mined from the copper-gold orebody. The ore types, resulting from a strong weathering profile, exhibit a wide range of copper mineralisation and gold associations, as well as gangue types. They display a range of characteristics that necessitated a nuanced approach to flowsheet development. The primary separation techniques that have been employed include gravity, classification, flotation and leaching while a range of comminution methods have been selected to suit the properties of the ore types. While technical issues are important factors in terms of maximising the quality of separations, recoveries and revenues, attention to material handling, equipment characteristics, the mine schedule, and capital and operating costs are equally important considerations for settling upon a suitable and robust flowsheet. Keywords: Flowsheet, testwork, studies, saprolite gold, native copper, chalcocite, chalcopyrite

Jan 1, 2020

By L. Xingwana

"The purpose of this study is to understand how ore loss and dilution affect the mine call factor, with the aim of subsequently improving the quality of ore mined and fed to the mill. It was necessary to know the relationship between ore mined and delivered for processing in order for the mine to operate efficiently. A review of the literature suggested the mine-to-mill integration approach as a standard intervention to address declining mine call factors. A case study was undertaken at a gold mine in the Free State on the influence of the fragment size distribution on ‘free gold’, the effect of ore loss and dilution on the mill efficiency, and time tracking of ore movement from source to the plant. The study revealed that fragmentation, underground accumulation of ore, and dilution have a significant influence on the mine call factor and mine output. It was difficult to quantify the total ore loss due to the time lag between mining and milling, which is extremely variable, when estimating the mine process inventory. However, it was possible to estimate the total dilution with some degree of precision by analysing the daily blast and head grades. It is therefore recommended that mines accept that some gold loss and dilution will always occur during blasting and transport of broken ore, and this loss must be minimized.IntroductionThe mining of high gold grades is obviously very beneficial for the economic viability of an operation, but optimum recovery of the product is required to maximize profits (Chapman and Bindoff, 2010, p. 13). Although integrating these two requirements is very difficult, due to the various activities occurring between mining and processing, it is indispensable. The main driver of this integration is the impact that different ore types and characteristics have on head grade. According to Isokangas et al. (2012, p. 871), mining and processing operations involve a series of well-defined sequential stages that are complementary in an efficiently operating mine, with the performance of one operation affecting that of another. An attempt to optimize each function separately without considering the whole extraction process will not result in the optimum efficiency of the entire mine. Several researchers have developed a proven methodology for revealing these inefficiencies (Dance et al., 2006, p. 1)."

Jan 1, 2016

The AMIRA Code of Practice and Guidelines for Metal Accounting was developed in response to demand from a number of sponsor companies, including one major platinum producer. Since its publication in 2007, the Code has become widely accepted in the mining industry world-wide as a guide for best practice in metal accounting. With the changes in the structure of the platinum mining industry in South Africa over the last 10 ? 15 years, in particular, the starting up of a number of small platinum producers who must have their concentrate smelted and the contained valuable metals refined by third parties, the need for metal accounting systems that are accurate and have an acceptable level of precision has become even more critical to the success of a platinum-producing operation. The current state of metal accounting in the industry is discussed and possible areas for improved accounting and associated metallurgical efficiencies are identified.

Jan 1, 2012

By G. Akdogan, Q. G. Reynolds, S. J. Baumgartner

A computational model of a submerged arc furnace (SAF) used in the production of ferrochrome is presented. The model‘s intended use is to investigate the extent to which intrinsic and extrinsic properties of the raw materials affect burden distribution and electrical resistance within the furnace. The model is built on the discrete element method and calculates the mechanical interactions of particle distributions resulting from the flow motion of typical raw materials used in the smelting of chromium ore. This model excludes the effects of thermodynamics, furnace chemistry, and heat transfer. It illustrates how the consumption of materials (chromite pellets, flux, and reductant) is affected by changes in electrode length, reductant fractions, and reductant sizing and density during the formation of a reductant bed. The resistance calculation algorithm developed by Mintek was applied to construct networks developed from particle contacts, which can quantitatively generate estimates of the electrode-to-electrode and electrode-to-bath electrical conduction conditions.

Apr 16, 2024

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

By F. Roelofse, D. Grobler, and M. Purchase, C. Gauert, E. Kotze

Scandium is an important industrial metal for which demand is projected to increase in the future. Although many Sc deposits are secondary, Sc is scavenged by clinopyroxene during fractional crystallization of primary, mafic-ultramafic magmas. Sc may thus occur in sub-economic concentrations in mafic-ultramafic intrusions. In this work, we present new data on the concentration of Sc in the Bushveld Complex (BC) of South Africa. The eastern and western limbs of the BC are considered to be largely pristine, primary magmatic deposits, whereas the northern limb shows evidence of largescale, localized crustal contamination. Samples from the primary magmatic cumulates of the eastern limb, from the mineralized Flatreef of the northern limb, and from the crustal-contaminated Footwall Assimilation Zone (FAZ) of the Flatreef were analysed for Sc. Despite the FAZ containing abundant clinopyroxene, interpreted to have recrystallized from the original cumulates in the presence of melted sedimentary rocks, no significant differences are seen in the concentration of Sc compared to other cumulate rocks of the BC containing less-abundant clinopyroxene. The concentration of Sc in the analysed samples is mainly controlled by mineralogy, with anorthosites, chromitites, and harzburgites containing under 20 ppm, and norites and pyroxenites containing 20–40 ppm. The parapyroxenites of the FAZ are less enriched in Sc than expected, suggesting that Sc may have been lost during alteration and recrystallization.

Sep 1, 2022

By V. Borissenkob, L. D. Ropera, M. J. Danielc

Eccentric High Pressure Centrifugal Comminution (eHPCC) is a novel comminution device that provides a single step to achieve a desired target grind size. The mechanisms within the unit mirror particle breakage that is akin to high-pressure-grinding rolls (HPGR) and high-intensity-attrition with air classification. eHPCC receives lump and can produce a product P80 such that the progeny are at or less than natural grain size of the feed. The unit operates in either closed or open-circuit. The grinding zone is dry and free of steel grinding media. This paper presents evidence of eHPCC-2 capable of selective and preferential mineral liberation. A recent test campaign on a blend of underground quartzgold- vein ore was completed. The feed to eHPCC-2 trial was SAG mill trommel oversize (low-grade pebble rejects). eHPCC-2 operated open-circuit with air-fluidisation in the rotating-grinding-chamber, classifying particles based on terminal velocity of the air-swept product particles, displaying size and mineral composition classification taking place at the same time. There is an opportunity for future industrial research targeting eHPCC as an advanced integrated comminution and classification technology. Keywords: High pressure, high intensity, compression, attrition, comminution, classification

Jan 1, 2020

The Annual General Meeting of the Institute was held in Kelvin House, Johannesburg, on Wednesday, 27th August, 1969, at 4.15 p.m. Mr. R. C. J. Goode (President) was in the Chair. There were also present seventy Members, ten As¬sociate Members, two Affiliates, one Student and twelve Visitors making a total of ninety-five. The President declared the meeting open at 4.20 p.m. OBITUARIES The President: "It is my very sad duty to announce the deaths of the following members of the Institute: Mr James Charles Napoleon Humphreys, a Life Member who joined the Institute on 1st April, 1935, and passed away on 6th February, 1969. Mr Michael John Worrall, Graduate Member, who joined the Institute in 1960 and passed away on 2nd June, 1969. Mr Eric Adam Conrad Dickson, Associate Member, who joined the Institute on 13th June, 1952 and who passed away on 8th June, 1969. Mr Robert Jack, Associate Member, who joined the Institute on 2nd August, 1956, and passed away on 14th June, 1969. Mr R. A. H. Flugge-de-Smidt, Honorary Life Member and Gold Medallist, who joined the Institute in 1922 and passed away on 17th June, 1969. Mr John Gordon Craig, a Member who joined the Institute on 23rd August, 1960, and passed away on 6th August, 1969. As a mark of respect to the memory of the deceased, and in sympathy with the bereaved, I would ask you to rise and observe a few moments silence." MINUTES The President: "May we confirm the Minutes of the General Meeting held on 18th June, 1969, as published in the July, 1969, issue of the Journal?"-Agreed. WELCOME TO VISITORS The President: "We are honoured this afternoon by the presence of the Institute's Honorary President, Mr R. S. Cooke, President of the Chamber of Mines of South Africa, and by one of our Honorary Vice-Presidents, Mr T. L. Gibbs, the Government Mining Engineer, as well as by the presence of many distinguished guests, to all of whom I extend a most cordial welcome. We are happy to have present, Mr S. C. M. Naude, Director of the Witwatersrand Technical College, Mr G. A. P. Louw, Vice-President of the Associated Scientific and Technical Societies, Mr R. P. Randall, Senior Vice-President of the South African Institute of Electrical Engineers, Mr W. T. L. Wayman, President of the South African Institution of Mechanical Engineers, Mr D. F. Odendaal, President of the Institution of Certificated Mechanical and Electrical Engineers of South Africa, Mr E. Haacke, President of the Institute of Land Surveyors of the Transvaal, Mr B. L. Loffell, Vice-President of the South African Institution of Civil Engineers, Mr J. F. Leatherbarrow, President of the South African Institute of Assayers and Analysts, Dr W. S. Rapson, President of the Joint Council of the South African Scientific Societies, Dr P. L. Carman, President of the South African Chemical Institute, Mr F. Jackson, President of the Federation of Societies of Professional Engineers, Mr W. E. Kirkwood, President, S.E.I.F.S.A., Mr J. Steele, President of the South African Institute of Foundrymen, Mr M. Waite, President of the South African Institution of Welding, Mr M. R. Gericke, President of the South African Council of Professional Engineers, Mr G. C. Sowry, Chairman, Witbank-Middelburg Branch, Mr T. Groenewald, Chairman of the South African Chemical Institute (Southern Transvaal Section), Professor O. B. Volckman, Chairman of the South African Institution of Chemical Engineers, Mr H. W. Le Roux, Chairman of the South African Federation of University Engineer¬ing Students, Dr R. E. Robinson, Director of the National Institute for Metallurgy, Mr P. H. Anderson, Deputy-Chairman of Rand Mines Limited, Mr E. Boden, Manager of the A.S. and T.S. and Count Folchi-Vici, from Italy, who has lime interests in this country. I also extend a very special welcome to the lady guests here this afternoon, and to all the visitors." MEMBERSHIP The President: "I have pleasure in announcing that the names of the following candidates, having been published in accordance with By-Law 5.2.2, Council has elected them to membership in the following grades: NEW APPLICATIONS Members: Stuart Denston Hill, Robert Roy Richardson, Gert Paulus van der Vyver. Affiliates: Henry Clifford Read, Allen Edward Hooper, Alan Edwin Edkins. Graduates: Lester Winston Sturgess, Erroll Vincent Bosman. Students: Terence Vernon van Heerden, David Curtis Lindley. MEMBERS TRANSFERRED TO A HIGHER GRADE From Associate Member to Member: Andries Willem van Zyl, Roy Lardner, Nugent Gerald Ward Comyn. From Student to Graduate: Michael John Worrell (now passed away), Peter John Hamilton Short. I wish to welcome the new members to the Institute, and to congratulate those members who have been transferred to a higher grade." ANNUAL REPORT OF THE COUNCIL AND ACCOUNTS FOR THE YEAR ENDED 30th JUNE, 1969 The President: "Ladies and gentlemen, It is with much pleasure that I present to you the Annual Report and Accounts for the year ended 30th June, 1969. These have been laid on the chairs and before calling for their adoption I would like to make a few comments. The Accounts show an excess of expenditure over income of R2,124 and our Honorary Treasurer, Mr D. G. Maxwell, will in due course comment on this. The main difficulty has again been the cost of the Journal and I think most of you are aware of the changes that we propose to make. I shall be sorry to see the last of our old format but then I have always had rather a con¬servative outlook.

By T. Szendrei, S. Tose

The Gurney approach to explosive/inert material interaction was adapted to analyse the face velocity in bench blasting. The model is based on the blasthole diameter, rock and explosive density, burden, spacing, linear charge density, and the Gurney energy constant. It is validated by comparing its predictions with a set of 20 field measurements of face velocities reported by Chiappetta et al. (1983) in an iron ore mine. The Gurney model links the observed large scatter of measured face velocities to the variation of the Gurney energy constant. This in turn is linked to the variability of the gas pressure acting on the burden. These variable pressures are generated when detonation product gases migrate into the extensive and complex fracture network around and between in-row blastholes. The energy efficiency of burden movement can be derived from the model. It is shown that ~7% of the explosive’s chemical energy is available for gas expansion work on the burden; of this quantity, 36% is actually converted to burden kinetic energy. That is, less than 3% of chemical energy is ultimately expended in burden displacement and throw. The model further indicatesnthat the projection of high-velocity (say, 100 m/s) flyrock is possible only when the path of leastnresistance through the burden has an effective density far less than the host rock. An equationnis derived that identifies the combinations of burden and path density that may yield flyrock. These values are specific to a particular baseline blast design.

Jan 30, 2026

By F. Nakhaei, M. Le Roux, Q. P. Campbell, S. Botlhoko

The results of coal sink and float tests are plotted as washability curves. Analysis of these curves indicates the most effective method by which the coal can be cleaned. Sink and float experiments are samplingdependent, destructive, and use toxic chemicals. The present research introduces an alternative method based on a 3D imaging system called RhoVol, in which the density of individual particles is determined from mass and volume measurements. A quantitative error analysis was conducted on coal sample density measurements obtained by RhoVol, and the main factors influencing the errors identified and investigated. The results show that the drawback of this technique is related to its not being able to detect hidden concavities in the particle, resulting in an overestimation of particle volume. Furthermore, it is difficult to capture the impact of porosity and cracks on the volume of coal particles obtained from 3D silhouette images. This mismatch between the RhoVol data and sink and float test results has led to attempts to apply neural network (NN) and linear regression techniques to produce a fully reliable model for correction and estimation of coal density. The NN approach offers superior predictive capability over linear regression, and the estimated density distribution is in line with the sink and float analysis. The root mean square error in estimation of density using the NN model was less than 0.05 g/cm³.

Aug 2, 2022

NOTICE The Institute has received requests for copies of Uranium in South Africa', Vols. 1 and 2, but is unable to supply, as all copies have been sold out. If any members have copies they wish to dispose of it would be appreciated if they would contact the Secretary, P.O. Box 1183, Johannesburg. Telephone 834-1271.

By A. Yañez, J. Yianatos, P. Vallejos, R. Grau

This paper presents an evaluation of the effect that the mineral feed characteristics have on the metallurgical performance in an industrial flotation circuit. Variables such as mineralogy, particle size, solid content and mineral grade were evaluated using a flotation simulator, which was previously developed and validated using industrial data from different concentrators. The metallurgical performance was evaluated not only from the point of view of recovery and concentrate grade, but also by analysing less common variables such as froth carrying rate, froth and collection recovery, water recovery and others. Then, new data from the industrial flotation circuit was used to complement this analysis and evaluate the simulator predictability by comparing simulated and measured data. The results allowed for the quantification of the significant effect that mineralogy and particle size have on recovery and/or concentrate grade. Therefore, the grinding stage and flotation cells design become important factors to avoid a significant loss in metallurgical performance when feed mineral characteristics change in an industrial operation. In this context, an evaluation of cells design and arrangement should be performed to compensate the loss in recovery and concentrate grade in order to find an optimal operating condition. Keywords: Flotation circuits, mineral feed, modelling, particle size, liberation, mineralogy

Jan 1, 2020

By I. Y. Motovilov, S. A. Telkov, M. B. Barmenshinova, Z. S. Abisheva

As a rule, removing waste rock at the beginning of the process improves the conditions for the flotation of minerals, and also reduces the operating costs of crushing, grinding and flotation. Lead-zinc ores in the Shalkiya deposit of the Republic of Kazakhstan are classified as difficult for enrichment, but taking into account their significant reserves, they are one of the main potential ores for the production of lead and zinc. Under industrial conditions, for processing ores of the Shalkiya deposit, a selective flotation concentration scheme with the production of lead and zinc concentrates is recommended. However, according to the recommended scheme, it is not possible to obtain high-quality concentrates of lead and zinc, with high metal recovery. The paper presents the results of studies of preliminary gravitational enrichment of lead-zinc ore in the Shalkiya deposit. Based on the fractional analysis for the particle size range of -40+8 mm, Henri- Reingard enrichment curves were constructed, separation density (2730 kg /m3) was established to isolate the light fraction with the lowest possible lead and zinc content, and gravity enrichment indices (0.7-0.71) were determined. It was found out that when using gravitational enrichment of the original large-sized ore in the Shalkiya deposit, tails are released at the beginning of the technological process with a yield of up to 20% with the extraction of silica up to 30%, calcite up to 11% and carbonaceous matter up to 12%. As a result of the studies, it was found that the beneficiation of crushed lump ore could be conducted in heavy suspensions. One of the positive aspects of the use of gravitational enrichment is the reduction of energy costs for grinding the heavy fraction, which was experimentally proved in this article. Keywords: Lead-zinc ores, Shalkiya deposit, fractional analysis, gravitational enrichment, floating fraction, sunken fraction, separation density

Jan 1, 2020

By L. Gutierrez, R. Yepsena

Enargite in porphyry copper deposits is an important mineral as it displays good floatability under the presence of the collectors usually used in the flotation of copper sulfides. As a result, copper concentrates grades are reduced. As scarcity of water resources is a problem relevant to Chilean mining, the use of seawater is a feasible solution. The behaviour of copper sulfides and molybdenite in the process of flotation in seawater was previously studied but not for enargite. The objective of this research is to study the behaviour of the enargite in different conditions of electrochemical potential during the process of flotation using seawater. The study was carried through micro-flotation tests using pure samples of enargite, at Eh values ranging from -300 to 500 mV(SHE), both in seawater and aqueous solutions containing calcium and magnesium. The results show that at pH 10.5 in seawater, the enargite and chalcopyrite recoveries are reduced throughout the whole range of Eh studied. At pH 9 in seawater, enargite and chalcopyrite are depressed under reducing and slightly oxidising conditions. The recovery of both minerals drastically decreases at Eh values lower than -100 mV and greater than 400 mV. The behaviour of enargite in seawater flotation differs from that observed in conventional water, since in the latter case the recovery of enargite decreases at higher potentials close to 500 mV. Keywords: Enargite, flotation, seawater, redox potential

Jan 1, 2020

By W. Wilmans

Electrokinetic dewatering of kimberlite slime under constant direct curents of 0,5 to 2 A and dewatering under constant applied potentia Is of 16,5 to 46,5 V are considered. The combined efects of electrophoresis and the addition of 8,3 x 10-3 M Mg2+ ions on the one hand, and 1 to 10 p.p.m. of the anionic polyacrylamide flocculant Praestol 2935 on the other, were investigated in a 3-litre Perspex electrophoretic cel. .The electro-osmotic dewatering experiments were conducted in a 3-litre Perspex electro-osmotic cel at various electrode spacings, as well as with a moving anode (top electrode). During electrophoretic dewatering, the zeta potential of the kimberlite particles did not change significantly, whereas the pH and temperature showed marked increases with time. The addition of Praestol 2935 enhanced the setling of the sludge bed owing to the additional effect of flocculation. The addition of electrolyte Mg (CIO4)2 retarded the separation process, partly as a result of gel formation in the slurry. During the electro-osmotic experiments, the rate of dewatering was found to be approximately proportional to the applied constant direct current, and to be independent of the electrode spacing. In general, electro-osmotic dewatering seemed to be more energy-efficient than electrophoretic dewatering.

Jan 1, 1987

By R. M. Mashishi, T. Malehase, O. J. Okonkwo

The concentrations of selected trace elements (As, Cd, Hg, and Pb in run-of-mine (ROM) coal, discard, and coal product were investigated to assess the efficiency of beneficiation in reducing trace element concentrations and ascertain any implications regarding environmental compliance to regulatory frameworks. Samples were collected from a colliery in Mpumalanga Province twice a month for a period of 24 months. The samples were ashed to approximately 0.21 mm, then digested in a mixture of 70% HNO3 and 40% HF and analysed using inductively coupled plasma-mass spectrometry (ICP-MS). Except for Pb, the mean concentration of all elements decreased from the ROM stage to the coal product stage. The order in which trace elements occurred from the highest to lowest throughout the production chain was Pb>As>Hg>Cd. With the exception of Cd, the mean trace element concentrations in the discard were above the total concentration threshold (TCT) set for landfill disposal. The As, Hg, and Cd concentrations in the product were well below the thresholds for all land uses. However, Pb concentrations in the product coal were above legal limits, which is of concern with regard to environmental compliance and the performance and marketability of the product.

Dec 13, 2023