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By P. G. Kovalchik

Overexposure to noise remains a widespread, serious health hazard in the US mining and other industries despite 25 years of regulation. Most categories of illnesses and injuries associated with mining have improved, with the exception of hearing loss. The drilling of rock in a confined work environment contributes to high levels of noise exposure in mining. The National Institute for Occupational Safety and Health (NIOSH) is conducting research to reduce the noise exposures of jackleg drill operators and to prevent additional cases of noise induced hearing loss (NIHL) by developing and evaluating low-cost retrofit noise controls for equipment. This report describes the procedure for the measurement and reporting of noise from portable pneumatic tools such as jackleg drills. The technique used in this research allows for the determination of the source A-weighted sound power levels and the radiation patterns in octave and 1/3 octave bands. Overall sound power level is also determined. This paper also reports the results obtained by using this procedure to evaluate a SECO S215 standard production drill and a CSIR Miningtek prototype rock drill incorporating engineering noise control measures. It was found that by using the manufacture?s recommended operating pressure of 496 kPa (72 psi) that the CSIR prototype?s sound power was 10 dB(A) less then that of the SECO S215.

Jan 1, 2009

By D. E. Sweeney

In May of 1980, a mine operated by Belmoral Mines Ltd experienced a failed crown pillar, resulting in the death of eight miners and putting sixteen others in harm?s way. The Ferderber mine was located in the Val d?Or region of the province of Quebec in Canada, and had been under development for 19 months and production for 9 months, since the opening of the portal. The crown pillar separating the 1?7 level from overlying overburden ultimately failed, permitting an estimated 1.5 million cubic feet of liquefied sediment to gain entry into the mine. This paper back-analyses the cave-in by applying decision error theory, in an examination of the organizational culture and the collective decisions contributing to the cave-in disaster. A case will be made for a greater understanding of mining methodology, geomechanics and risk assessment when operating in such challenging geologic conditions. Boundary condition and decision (BCD) analysis will be introduced as an innovative new method for the analysis of mine accidents and incidents. It will also be shown that BCD analysis can be applied to any event in an enterprise for which standards, norms or legislation exists. A cognitive profile will be presented that provides insight into the safety ethos existing within the Ferderber mine organization at the time of the tragedy.

Jan 1, 2007

By M. J. Little

Potgietersrust Platinums Ltd is Anglo Platinum?s only open pit operation and annually extracts 57 million tonnes of rock from 2 open pits. Over the past 3 years ~220 km of exploration drilling has been done, ~1000 km of rock face have been exposed for face mapping and over 7000 laboratory and field tests have been conducted. This has produced large amounts of geotechnical data to be utilised for feasibility studies, initial slope design and ongoing slope optimisation. It was necessary therefore to develop geotechnical databases to manage the vast amounts of data collected. SABLE and MineMapper 3D databases were created for logging and mapping respectively, with rock testing data incorporated into both. A pit inspections database was developed in MS Access and the existing groundwater and slope monitoring database was improved. The databases were linked to AutoCAD and Datamine to ensure that the latest geotechnical data is used for planning, draughting and modelling. The use of geotechnical databases ensures that no data is lost, standards are maintained and analysis can be easily performed. This increases the confidence of the analysis and allows the geotechnical engineers to optimise slope designs and blast designs on a regular basis. This reduces the risk of slope failure thus making the open pits more economical and safe.

Jan 1, 2006

By D. D. Aksenova, V. A. Ignatkina, L. A. Samatova, A. V. Lygach, E. D. Shepeta

Calcium minerals such as scheelite, phosphate, apatite are valuable minerals, which have similar flotation properties to the calcium gangue minerals. An additional problem is the fine dispersion and close mineral association of valuable and other minerals. Low polar compounds (non-ionic surfactant), such as fatty iso alcohols, neonol and phosphol, and their combinations with sodium oleate have been studied using flotation of monominerals and ore flotation; ATR IR spectroscopy and TEM for study surface of minerals; UV spectroscopy for control solubility, aggregation and de-aggregation processes. Increase in solubility of fatty acid collectors was confirmed by low soluble (heteropolar) compounds. Oxyethylated esters of phosphoric acid are adsorbed on phosphorite by -O2PO2R2 and on other rock minerals by donation of OH bond. Same effect shows difference of adsorption of fatty iso alcohols on calcite and scheelite. The different forms of adsorption of ionic and nonionic compound on a sparingly-soluble mineral surface creates distinction of the flotation kinetics and technological balance of ore flotation. The results of the separation of flotation of scheelite from calcite depend on the order of pouring into pulp of fatty iso alcohols and oleate, and their ratio in the mixture. Increasing scheelite recovery into rougher scheelite concentrate by 3.6% for both the flotation and sludge classes was obtained. Calcite recovery varied slightly upwards or downwards by 0.8-2.4%. The use of the non-ionic surfactant phosphol in combination with a fatty acid soap allows for obtaining a phosphate concentrate with more than 28% P2O5 content and almost 80% recovery in flotation operation. It is not obtainable with other reagent regimes. Keywords: Flotation, calcium minerals, oleate, fatty isoalcols, neonol, oxyethylated esters, adsorption

Jan 1, 2020

By L. R. Nelson

The efficiency and cost-effectiveness of the aluminothermic reduction process in the production of ferro-alloys and 'pure' metals depends strongly on appropriate balancing of the process energy required. Insufficient energy results in a poor metal yield, while over-supply can result in excessive fuming and possibly even ejection of the reactor contents in a potentially dangerous 'thermite bomb' reaction. This situation becomes even more critical when the suitability of limited quantities of oxide from new sources must be evaluated, dictating smaller-scale testwork. The resulting higher relative heat losses from the system complicates control of the energy balance, and usually requires the addition of thermal boosters or reactant preheating in order to sustain an autothermic process. This often detracts from the quality of the metal product, and adds to the hazards of batch aluminothermic- reduction testing. The development of a small-scale method (producing less than 2,5 kg of metal) for the plasma-assisted aluminothermic reduction of chromium oxide that overcomes such difficulties is described. The technique involves the use of a sealed 50 kVA plasma-arc furnace to provide controlled electrical ignition and supplementary energy to the reactants contained in a water-cooled copper crucible. The application of the method to the evaluation of the aluminothermic production of pure chromium metal from a unique chromic oxide source is reported.

Jan 1, 1996

Orange Free State Branch Minutes of a General Meeting held at the Welkom Mine Canteen on Wednesday, 21st November, 1973, at 4-.00 p.m. Present Mr E. T. Wilson (Chairman) in the Chair, 15 Fellows and Members, 12 Associates, Graduates, and Students, and 11 Visitors (Total 38). Book review Symposium on Environmental Engineering in Coal Mining The 20 papers presented at the symposium cover some 14 subjects related to environmental engineering in coal mines, such as dust, heat, gas emissions, ventilation, noise, and lighting. Competition for students Each year the Institute offers a prize (or prizes should the entries warrant it) of up to Rl00 for the best paper or dissertation on a topic appropriate to the interests of the Institute. A.8. & T.8. Trust The A.S. & T.S. Trust has been formed with the specific object of establishing a worthwhile source of funds which can be used to further the progress of science and technology in South Africa. Nim reports Report No. 1573 A pilot-plant investigation of a flotation model. Report No. 1597 The role of sulphur in the flotation of sulphide minerals. Report No. 1599 The analysis of silicate rocks and metallurgical slags by X -ray-fluorescence spectrometry. Report No. 1607 The analysis of ion-exchange resins by X-ray- fluorescence spectrometry. Report No. 1617 An electronic differential precision thermometer.

Jan 6, 1974

By T. R. Twiddle

The sequential flotation of copper, lead, and zinc in that order is practised at the Broken Hill Concentrator of the Black Mountain Mineral Development Company (Pty) Limited. The minerals of economic importance are chalcopyrite, galena, and sphalerite, with associated silver. The targets for recovery and grade in the lead and zinc circuits were reached quite readily after start-up, but the copper circuit failed to meet the performance requirements with respect to both recovery' and grade. The original circuit for copper is described, together with the subsequent investigations and modifications that were required to produce acceptable metallurgical results. Circuits for semi-bulk and bulk flotation were tried, and the effect of the oxidation state of the pulp was investigated extensively and found to be all important. Tests were conducted on the depression of lead in the cleaning circuit by the use of sodium dichromate, and on heating with the addition of sulphurous acid. The latter technique was ultimately the more successful. The proportion of fresh to recycle water entering the circuit was shown to be important. The original reagent regime was altered and augmented. A more recent problem has been the contamination of the ore with cemented backfill. The changes that this new condition necessitated are described. Success has been measured by a continuous improvement in the economics of the copper recovery.

Jan 1, 1984

By D. D. Hawat

The locations of potential reserves of chromite ores throughout the world are discussed. Reference is made to the marked changes in international trade in chromite ores during the past ten to fifteen years, and to the change in locality of the production of ferochromium aloys, which is curently largely carried out in the country of origin of the ores. The influence of these changes has been very profound in South Africa, which has the largest smelting capacity and the largest production of ferochromium aloys in the world. A proportion of South African ore is stil exported to meet the demands for the production of chromium chemicals and refractories, including a large tonnage of foundry sands. Ferochromium smelters in South Africa have a capacity of virtualy 1 Mt of aloy per annum. Nearly al this development has taken place since the introduction of the argon-oxygen decarburization (A.O.D.) process for the smelting of stainless steels. Formerly, expensive Iow-carbon ferochromium aloys were required as raw materials, but the AO.D. process, which is being used world wide, permits the use of high-carbon ferrochromium, the main product of the smelters in this country. The production in South Africa of chromium-containing corrosion- and heat-resistant steels is stil on a relatively smal scale, but serious atention is being paid to the exploitation of low-carbon weldable feritic chromium steel.

Jan 1, 1986

1. Reviews A concise world atlas of geology and mineral deposits, by D. R. Derry. London, Mining Journal Books, 1980. (Reviewer: B. C. Alberts) The geology of the Western Cordillera of northern Peru, by various authors. London, Institute of Geological Sciences, Overseas Memoir 5. (Reviewer: C. E. Feather) 2. New books Influence of diffusion coatings on the strenth of steel, by G. V. Karpenko, V. I. Pokhmurovskii, V. B. Dasilov, and V. S. Zamikhovskii, second revised and updated edition by A. Aladjem. Aedermannsdorf (Switzerland), Trans Tech Publications, 1979. 200 pp. Sw. Fr. 68.00. Mechanical and corrosion properties, by G. S. Ansell, P. Haasen, J. Weertman, D. J. Fisher, U. Gramberg, and F. W6hlbier (editors). Heat-resistant and refractory steels, by K. L. Lanskaya. Aedermannsdorf (Switzerland), Trans Tech Publications, 1979. 266 pp. Sw. Fr. 86.00. Hardening of metals, by P. Feltham (editor). Aedermannsdorf (Switzerland), Trans Tech Publications, 1980. 316 pp. Sw. Fr. 78.00. Precious metals The 6th International Precious Metals Conference will be held in Newport Beach, California, from 7th to 11th June, 1982. Strata mechanics A symposium on Strata Mechanics is to be held in Newcastle-upon-Tyne from 5th to 7th April, 1982. Over the past thirty years, mining of coal and stratified mineral deposits has become increasingly capital-intensive, and the level of investment demanded by modern methods has led to demands for improved assessment of their likely performance.

Jan 1, 1981

By A. J. Van Rensburg, N. B. Strydom, C. H. Van Graan

The design, construction, and use of a practical ice-jacket for miners by N. B. STRYDOM, Ph.D. (Illinois) (Fellow), D. MITCHELL, Ph.D. (Rand) (Member), A. J. VAN RENSBURG, M.Sc (Poteh) (Visitor), and C. H. VAN GRAAN, M.Sc (Pretoria) (Visitor) Microclimate suits have been shown to be very effective in decreasing physiological strain in hot, wet environments, thus enabling men to work without risk in areas that would normally carry a high risk of heat stroke. In this paper, some design considerations in the development of the frozen jacket are described. Water complied with most of the desirable properties required of a coolant material for use In a microclimate suit. The Human Sciences Laboratory has developed a jacket in which ice is used as the coolant and which is designed according to the most acceptable anthropometrical characteristics. The jacket consists of an inner poncho-type waistcoat containing 28 water compartments. Over this is worn an insulating jacket, which minimizes warming of the coolant by the environment. Suitable refrigeration units have been developed to freeze the jackets underground. Laboratory tests have shown that these jackets are effective for about 2,5 hours, Irrespective of the wet-bulb environment, when men are working at a moderate rate. Jackets should, however, be used only in environments in which the wet-bulb temperature is in the range of 32,S0 to 35,S °C.

Jan 9, 1974

By D. J. Bosman

Rapid fouling of condenser tubes in underground refrigeration plants is a frequent occurrence. It leads to low heat transfer efficiencies, with consequent serious reduction in capacity and increase in the horse-power requirement of the units. High pressures develop in the condensers, and frequent cleaning of the tube bundles is required. The cleaning operation takes up to 8 hours and in some cases results in significant loss of production. One of the possible causes of fouling is deposition of scale, but this can be readily overcome by controlling the concentration of the water. When water evaporates, the dissolved solids remain behind; thus evaporation increases the amount of dissolved solids per unit volume. If half the original volume evaporates, the concentration of the dissolved solids is doubled and the water is said to have a 'concentration' of two. Concentration may be controlled by regulating the amount of water allowed to bleed from the system. The actual concentration value required is a function of the chemical analysis of the circulating cooling water. In one instance, where the problem of scale formation had been eliminated, fouling still persisted, and the possibility of excessive quantities of dust in the re-circulating water was investigated. A dispersing reagent was added to the condenser cooling water as a means of preventing sludge deposition in the condenser tubes. As shown by curve A in Fig. 1 the reagent addition did not decrease the rate of fouling.

By D. B. Swanepoel

Hulamin Rolled Products (Ltd) developed a high Mn and Si containing alloy, EN 4017 as a scrap consuming alloy from the waste generated in producing their range of clad products for brazing of inter alia automotive heat exchangers. The multifaceted composition of this alloy (Al -1.2 wt% Si -1.1 wt% Mn -0.2 wt% Mg-0.26 wt% Cu) suggested that it might display some degree of strengthening via precipitate formation of the Mg2 Si-types. The aging isotherms constructed showed that EN 4017 with 0.19% Mg reached a lower peak strength (YS~210 MPa and UTS~260 MPa)compared to the EN 4017 material with 0.43% Mg (YS~270 MPa and UTS~325 MPa). The higher Mg variant of EN 4017 was comparable with the age-hardenable reference alloy EN 6061. Selected area electron diffraction (SAED) studies proved that the microstructure of age hardened EN 4017 contained a combination of ß', ß" and U2 phase after being aged at 175ºC for 65 h. The general microstructure contained precipitate free zones as well as grain boundary Si films, although these did not lead to significant embrittlement. The role of Mn dispersoids in the fracture mechanism of 4017 is also discussed. The article will compare the behaviour of EN 4017 with that EN6061. Keywords: Age-hardening, dispersoids, magnesium silicide, precipitate free zones

Jan 1, 2009

By L. W. Helle

In this investigation, which was conducted at the Metallurgical Research Plant, Lulea, Sweden, a series of experiments were carried out using a water-model to simulate the gas rinsing of a ladle containing liquid metal. The factors examined include the effect of gas flowrate, the position of a porous plug or lance, the immersion depth of the lance, and the geometry of the bath at the time of complete mixing. Mixing times were recorded by conductivity measurements. The results showed that there is a threshold level for mixing above which no advantage is to be gained from an increase in the gas flowrate. It is suggested that the results can be applied to rinsing ladles in working situations, the levels being approximately 270 dm3/min for 40 t ladles and 780 dm3/min for 150 t heats. The optimum siting of the lance or porous plug is a position that is three-quarters of the internal radius from the centre of the ladle with the lance penetrating as deeply as possible into the ladle. The best design of liquid bath is that having a diameter-to-height ratio of I. An equation was developed for the calculation, by dimensional analysis, of the time required for mixing during gas rinsing, and a comparison of the calculated mixing times with the results from production trials shows a satisfactory agreement (with a correlation factor of 0,91). Thus, an equation is available for the calculation of the stirring time needed to completely mix the bath in production situations.

Jan 1, 1981

By A. Koursaris, J. B. See

An investigation is described in which the resistivities of Mamatwan manganese ore, Delmas coal, and Iscor coke, at temperatures or up to 1400°C were determined, as well as the resistivities of mixtures of ore of a constant size range with Delmas coal or Iscor coke of three different size ranges. The resistivities of the ore and the coal were characteristic of those for semi-conducting materials, were strongly influenced by temperature, and decreased by several orders of magnitude between room temperature and IOOO°C. The resistivity of the coke changed only slightly between room temperature and 1400°C, and the resistivity of the coal approached that of the coke at I300°C. This provides support for the theory that the resistivity of carbonaceous reducing agents is primarily a function of heat treatment, and not of the rank and composition of the coal. Above 1200°C, the resistivity of mixtures of ore and coke fell steeply owing to an increase in the volume fraction of coke in the mixture and to the formation of slag. The results were similar for the three different size ranges of coke. The extremely high resistivities of ore-coke and ore-coal mixtures at Iow temperatures indicate that there is unlikely to be much conduction of current in the higher regions of a furnace. Thus, the resistance of a furnace is governed mainly by the conditions at the electrode tips and in the molten regions. To explain the very Iow resistances of furnaces, usually, about I m£?, it would be necessary for investigations to be conducted under conditions similar to those in the active zone of a furnace.

Jan 1, 1980

By L. W. Helle

This paper summarizes the investigations carried out into a defect involving the corners of billets rolled from continuously cast blooms, which broke open during the rolling process. As it was believed that the defect must be connected with the formation of subcutaneous blowholes in the bloom, the investigations were directed towards an understanding of the roles of the three gases involved in the process. In an extensive trial programme, samples were taken from the heat at all stages of processing, as well as from all the raw materials and alloys. The main sources of nitrogen were found to be re blows, pick-up from the alloys added to the ladle (especially graphite), and open-stream casting. The major source of hydrogen was moisture in the alloys, especially high-carbon ferromanganese and silicomanganese. Further, it was established that the moisture content of the alloys is closely related to the appearance of the defect in steels with a carbon content of less than 0,20 per cent; 72 per cent of all the defects were present in this type of steel. Most of the remaining defects were found in steels with a carbon content of more than 0,60 per cent, where the nitrogen content was substantially higher than in the lower-carbon steels. It is suggested that the defect arises from the combined effect of oxygen. nitrogen, and hydrogen. Its occurrence in low- and high-carbon steels is triggered by the formation of subcutaneous blowholes when the critical oxygen level for carbon monoxide blowholes is lowered by the presence of excessive amounts of hydrogen and nitrogen respectively.

Jan 1, 1984

By J. Manchisi

Laboratory investigations were conducted to establish the feasibility of bioleaching a mixed copper oxide/sulphide rougher concentrate from Nchanga Mine on the Zambian Copperbelt. The objective was to determine the kinetics and extent of copper extraction for this material. Batch experiments were conducted under different solution conditions in stirred tank bioreactors. The progress of (bio)leaching was monitored through measurements of soluble ferrous and ferric iron, copper, pH, and redox potentials, while bacterial activity was monitored online through 02 and C02 gas utilization rates. About 20 per cent copper was solubilized within 2 hours in all cases of non-oxidative (abiotic), oxidative (abiotic), and bioleaching experiments. This was attributed to the dissolution of mainly copper oxides. Subsequently, bioleaching experiments resulted in an overall copper extraction of 93 per cent, with up to 8 g.L-1 copper after six leaching days, compared to 58 per cent copper extraction in the abiotic oxidative acid leaching experiments. However, there was little effect of time (i.e. poor dissolution kinetics) on copper recovery for abiotic non-oxidative acid leaching of the material. Hence, the rate of sulphide leaching increased due to the activity of bacteria. Thus, the material is potentially bioleachable under mesophilic conditions. However, more exhaustive test work needs to be conducted to establish the effect of bioleaching variables and heat requirement.

Jan 1, 2012

By E. Hakami

The objective of the study was to estimate the largest shear displacement that could be expected on a pre-existing fracture located in the repository area, due to the heat release from deposited waste. Two-dimensional numerical analyses using UDEC have been performed. The maximum shear displacement, at the fracture centre, amounts to 0.2 – 13.8 cm depending on fracture parameters. The fracture extension, friction angle and shear stiffness are found to be the most important. Le but de cette étude est de déterminer le déplacement maximal en cisaillement qui puisse se développer le long d'une fracture préexistante en réaction à la chaleur dégagée par les déchets radioactifs enfouis dans la roche. Les analyses numériques ont été réalisées à l'aide du code 2D UDEC. Le déplacement maximal en cisaillement enregistré au centre de la fracture varie entre 0.2 et 13.8 cm en fonction des propriétés de la fracture. L'ouverture, l'angle de friction et la rigidité au cisaillement semblent avoir une influence dominante sur les résultats. Zielsetzung der Studie war die Abschätzung der maximalen Scherverschiebung, die auf einer innerhalb des Endlagergebietes existierenden Rissfläche infolge der Wärmeabstrahlung des eingelagerten Materials zu erwarten war. Es wurden zwei-dimensionale numerische Berechnungen mit UDEC durchgeführt. Die maximale Scherverschiebung im Zentrum der Rissfläche beträgt 0.2-13.8 cm, abhängig von den Risseigenschaften. Dabei hat sich herausgestellt, dass Rissgrösse,Reibungswinkel und Schersteifigkeit den grössten Einfluss haben.

Jan 1, 2003

By J. M. Paull, J. B. See

The rate of reaction between different carbonaceous reducing agents and silicon monoxide gas was studied by the use of a technique developed in Norway by Tuset and Raaness. Argon carrier gas was used to pass a known fixed concentration of silicon monoxide gas through an I1 cm3 sample of precalcined reducing agent at 1650°c. Silicon monoxide gas was generated by the heating of a mixture of silica and silicon carbide, and the progress of the reaction was followed by monitoring the carbon monoxide in the off-gas with an infrared spectrometer. The reactivity of silicon monoxide gas towards a number of carbonaceous reducing agents (charcoal, Iscor coke, Lurgi char, and petroleum coke) was shown to be similar to results obtained with the carbon dioxide reactivity test. The silicon monoxide reactivity test was able to indicate the extent to which fines were generated when the reducing agent was converted to silicon carbide. Of the reducing agents studied, Lurgi char appeared to be the most suitable for the production of ferrosilicon because it has a high reactivity towards silicon monoxide gas and high strength when converted to silicon carbide. So that industry could be given some indication of the suitability of certain reducing agents for the production of ferrosilicon and silicon metal, a reactivity scale similar to that of Tuset and Raaness was constructed that compares the volume of silicon monoxide gas required by a reducing agent to reach a carbon monoxide content of 10 per cent in the off-gas during the conversion of the reducing agent to silicon carbide. This scale assists in the selection of those reducing agents that require less silicon monoxide gas for conversion to silicon carbide, and that give savings in material and power costs because less silicon monoxide gas need be generated in the furnace.

Jan 1, 1979

By L. Cong, C. Liu, N. Zhang, W. Cao, C. Zhou, X. Fan

"The modes of occurrence of arsenic and the effects of low-intensity leaching-flotation on arsenic removal from coal slime from the Tanggongta Plant, Inner Mongolia, China were investigated. The coal slime was examined using hydride generation inductively coupled plasma optical emission spectrometry and X-ray diffraction to obtain the content of elements and the major minerals. The modes of occurrence of arsenic in minerals were determined using selective leaching, float-and-sink analysis, and polarized light microscopy. The results indicate that pyrite is the dominant carrier of arsenic in the coal slime, which predominantly exists in association with clay. Significant proportion of the arsenic is removed by a low-intensity leaching-flotation process, consistent with the data from selective leaching and flotation of gangue. The results show that low intensity leaching-alkali washing-flotation is more efficient than direct flotation and low-intensity leaching-flotation.IntroductionUnderstanding the occurrence of arsenic in coal and its removal is significant in optimizing coal utilization, because arsenic in the environment is viewed as a potentially toxic trace element (Finkelman, Belkin, and Zhang, 1999; Hall, 2002; Smith et al., 1992; Smedley et al., 2003; Zheng et al., 1999). Many studies on the modes of occurrence and concentration trends of arsenic in different coal and washing products have been performed (Diehl, Goldhaber, and Hatch, 2004; Kolker et al., 2000; Quick and Irons, 2002; Wang et al., 2006; Fan et al., 2016). Trace elements are usually preferentially associated with certain minerals and the form that these minerals take will influence the efficiency of removal during cleaning (Quick and Irons, 2002). Arsenic is mainly associated with minerals such as pyrite, carbonate, and silicate (Demir et al., 1998; Diehl, Goldhaber, and Hatch, 2004; Zhou et al., 2014). The existence of organically bound arsenic was also confirmed using X-ray absorption (Kolker et al., 2000). However, inorganic arsenic is the principal source of pollution because of its leachability and high concentration compared with organic arsenic (Fujino et al., 2004; Gao, Lu, and Wang, 2010; Jiang et al., 2008; Kolker et al., 2000)."

Jan 1, 2017

By N. A. Barcza

An investigation was conducted into the reactions between the slag system MnO-CaO-MgO-SiO2(AI2O3) and the alloy system Mn-Fe-Si-(C). Synthetic slags representative of plant melts and a plant alloy were reacted in alumina crucibles at temperatures of 1400°C, 1450°C, 1550°C, and 1600°C. In similar experiments, slags were used that comprised a South African manganese ore with various amounts of lime and several synthetic alloys with various silicon contents and manganese-to-iron ratios. These experiments were conducted in a vertical molybdenum-wound resistance furnace with full temperature control. Slag-to-alloy ratios were also varied during the tests. The rate of reduction of Mn.O3 and the MnO from the slag by the silicon in the alloy was extremely rapid, most of the reaction being completed within five minutes. The strongly exothermic nature of the reaction resulted in considerable generation of heat at the slag-alloy interface, causing convectional stirring of the contents of the crucible and promoting the rate of reaction. Equilibrium was usually attained after fifteen minutes. The major limitation governing the recovery of manganese is the need for the silicon content of the alloy to meet a maximum specification of 2 per cent. Higher concentrations of silicon in the final alloy of between 8 and 12 per cent favour good recoveries of manganese from the slag, but, since such an alloy is not salable, lower recoveries must apparently be tolerated. In alloys of 2 per cent silicon, low activities of the silicon are responsible for poor recoveries of manganese. The activity of MnO in the slag can be increased by moderate additions of CaO and small amounts of MgO, i.e., by an increase in the basicity of the slag.

Jan 1, 1979