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By J. P. Beukes

The production of ferrochrome alloy from chromium bearing chromite ores is conducted at high temperature under highly reducing conditions. However, albeit completely unintended, it is impossible to completely exclude oxygen from all high temperature process steps, with the corresponding possibility arising for the generation of small amounts of Cr(VI) species. Certain Cr(VI) species are regarded as a carcinogenic, with specifically airborne exposure to these Cr(VI) species being associated with cancer of the respiratory system. With approximately three-quarters of the world?s viable chromite ore reserves located in South Africa, and annual ferrochrome production approaching almost half of total annual global output, aspects of Cr(VI) generation and control are of particular relevance and importance to the local industry, and naturally to the global industry at large. This paper seeks to examine theoretical and practical aspects associated with Cr(VI)generation (based largely on experience within the local South African industry, but considered to be generally encountered in the broader global industry context), together with mitigating measures that can be applied within the context of the production processes. From the discussions it is clear that significant improvements in various Cr(VI)-related aspects have been made by the South African ferrochrome industry. However, it is also evident that several areas of uncertainty still exist, which require further research in order to better quantify risks and enhance the efficacy of mitigating steps. Keywords Hexavalent chromium, Cr(VI), ferrochrome production, South Africa.

Jan 1, 2010

By R. D. Agrawal, M. L. Kapoor

Cementation has been used extensively by chemists and metallurgists as an economical process for the purification and recovery of metals from dilute solutions. The paper deals. firstly. with the thermodynamic aspects of cementation. and. secondly, with the effects of various process variables, such as temperature. stirring speed. initial concentrationof copper ions. pH of the solution, atmosphere, and surface area of the precipitant metal. on the kinetics of the process in the light of the rate expressions.

Jan 1, 1982

Many industries base their decisions on the assaying of tiny analytical sub-samples. The problem is that most of the time several sampling and sub-sampling stages are required before the laboratory provides its ultimate assays using advanced chemical and physical methods of analysis. As long as each sampling and sub-sampling stage is the object of due diligence using the theory of sampling it is likely that the integrity of the sought after information has not been altered and the generated database is still capable to fulfil its informative mission. Unfortunately, more often than not, unawareness of the basic properties of heterogeneous materials combined with the unawareness of stringent requirements listed in the theory of sampling, lead to the conclusion that massive discrepancies may be observed between the expensive outcome of along chain of sampling and analytical custody, and reality. There are no areas that are more vulnerable to such misfortune than sampling and assaying for trace amounts of constituents of interest in the environment, in high purity materials, in precious metals exploration, food chain, chemicals, and pharmaceutical products. Without the preventive suggestions of the theory of sampling serious difficulties may arise when making Gaussian approximations or even lognormal manipulations in the subsequent interpretations. A complementary understanding of Poisson processes injected in the theory of sampling may greatly help the practitioner understand structural sampling problems and prevent unfortunate mistakes from being repeated over and over until a crisis is reached. This paper presents an overview of the theoretical, practical and economic difficulties often vastly underestimated in the search for quantifying trace amounts of valuable or unwelcome components.

Jan 1, 2010

By C. L. M. Gough, L. A. Vermeulen, D. D. Howat

Formulae expressing the dependence of the mass of a grinding ball on the amount of material milled by a ball mill are derived. It is shown that, with the aid of these formulae, it is relativel rsimple for the results of a marked-ball test to be analysed and for the relative performance and cost-effectiveness 0 the various types of ball under test to be evaluated. Predictions based on theory and the results obtained in a marked-ball test in a ball mill are compared detail and shown to be in close agreement. The difficulties associated with marked-ball tests are considered, and an explanation for the decrease in the calculated consumption of the balls, which follows naturally from the theory, is presented. The marked-ball anomaly explained, and it is demonstrated that the ball consumption in a ball mill can be predicted with fair accuracy from the results of a marked-ball test.

Jan 1, 1983

By Y. Jin

Magnesia ramming materials have been widely used in China instead of magnesia bricks as furnace lining materials of ferroalloy refining furnace. The paper introduces the development of the ramming material, recounts its chemical composition, physical property and application characteristics. Because of its high MgO contents and fine sintering property, the ramming furnace bottom has the properties of good refractory, monolithic construction and thermal shock resistance. The changes in mineral composition and furnace tearout characterization show the reasons for the bottom?s long service life. The obvious benefits are widely achieved, the annual saving cost in refractory is about 2 millions US dollars.

Jan 1, 2004

By Wm. Bleloch

SYNOPSIS The feasibility of rejection of nitrogen from stack gas by recycling of top-gas with cold-blast 95 to 98 per cent oxygen is assessed. It is concluded that nitrogen could be removed to a level below 3 per cent of the stack-gas using recycled cleaned cold top-gas and 95 to 98 per cent oxygen produced by a single-column air separation plant with liquid-air reflux instead of liquid nigroten reflux. The partial pressure of carbon monoxide in the stack-gas could be doubled without top pressure and the deposition of carbon and reduction of iron oxides by the stack gas could be markedly increased. It is concluded that rate of stock descent could be doubled compared with present-day practice and an iron make of 4400 kg/m 2 of hearth area/hour may be attainable with a working volume of 129 m2/m hearth diameter by this method. Oxygen consumption is estimated at possibly 280 m2 (0.4 t)/t iron made and carbon consumption at possibly 280 kg/t iron. Power consumption for oxygen including auxiliaries is estimated at 304 kWH/t 100 per cent oxygen as 95 to 98 per cent gas. The air separation cycle due to Schuftan is discussed in some detail, and the components of a 1 600 metric ton/day separation plant are briefly discussed. The paper is a theoretical essay.

By W. Bleloch

Published in the Journal, September 1970, and presented at a colloquium on 'Future of the Steel Industry', 17th March, 1971. Errata (a) The final sentence in the penultimate paragraph, left hand column p. 34 of the text should read: 'In the hot regions of the bosh and stack the C+CO2=2CO reaction proceeds to CO from coke carbon and carbon dioxide generated by reduction of iron oxides by CO (the so-called solution loss of carbon)'. The italicised words have been omitted in the text. (b) Temperature in Fig. 3 is K not C. (c) In Fig. 9, connection from top plate of column 10 to heat exchanger 9 has been omitted. DISCUSSION J. B. BEEDON AND C. J. JONKER* Dr Bleloch's paper has outlined the advantages of recycling stack-gas of low nitrogen content in the blast furnace. In the first instance it would appear to be extremely beneficial in controlling the hearth temperature and allowing a 100 per cent oxygen-blast to be used. On a second point however we have to disagree. It is claimed that heat is liberated in the combustion zones by the oxidation of CO to CO2 near the tuyeres and in the subsequent reduction of the CO2 by CO. The author has hypothesized as follows, and we quote: 'The C+CO2=2 CO reaction in the outer combustion zone at about 1 700°C is no longer endothermic due to loss of stability of CO2 and its consequent dissociation into CO and free oxygen.' This statement requires closer examination. If we consider the individual events occurring with the CO in the recycled topgas, with the oxygen in the blast and with the coke in the burden, as done by Dr Bleloch, the following heat considerations emerge. All heats of reaction are calculated from the enthalpy values of each reactant and product, as well as the temperature dependence of their molar heat capacities. (a) At the tuyeres: CO+1/2 O2-+CO2 . . . . . (1) CO, CO2 at 500°C; O2 at 25°C. ?H reaction = -65 000 cals/mole CO The reaction (1) is exothermic. (b) In the outer combustion zone: CO2+C?2 CO . . . . . . . . (2) C, CO at 1 700°C; CO2 at 500 0C. ?H reaction = -56 000 cals/mole CO Reaction (2) is endothermic. The overall heat gain of reactions (1) and (2) is ?H=+56 000 - 65 000= -9000 cals/mole CO i.e. the overall reaction is slightly exothermic, the amount of heat liberated is however smaller than suggested by Dr Bleloch. (c) The dissociation CO2+CO+1/2 O2 . . . . . (3) is a highly endothermic reaction at 1 700 0C, requiring 82 000 cals/mole CO2 to proceed to completion. Furthermore, this reaction (3) is energetically not favoured to proceed, as can be observed from the free energy-temperature relationship of figure (3), which favours the formation of CO2 at 1 700 0C. Hence direct dissociation of CO2 at 1 700 0C appears to be unlikely.* The concept of recycling topgas is however still intriguing from many other points of view. Apart from providing a very efficient method of hearth temperature control, it will create a much higher CO partial pressure in the stack. Whether the rate of indirect reduction in the stack will be proportional to this partial pressure or not is un-

Jan 9, 1970

By H. M. Friede

A study was made of the smelting process in two experimental furnaces patterned on Iron Age furnaces excavated at Melville Koppies Nature Reserve, Johannesburg. In a number of smelting experiments, the influences of air supply, temperature, time of operation, fuel consumption, and other operational factors were investigated. Metallurgical and metallographic aspects of the furnace operation and smelting products are discussed, and the experiments are compared with similar research work conducted in Europe and Africa.

Jan 1, 1984

By M. Steyn

This article captures the intrinsic differences of thermal coal products, their utilization and their substitution characteristics. South Africa produces approximately 245 million tonnes of coal annually. Eskom consumes 46% (approximately 112 million tonnes), 26% (approximately 65 million tonnes) is exported, and SASOL Synthetic Fuels consumes 18% (approximately 44 million tonnes) and a further 9% (approximately 22 million tonnes) is consumed by domestic users in various different industries. Marketing theory contributes significantly to understanding the importance of technical product and quality appreciation and comprehension, encompassing elements of price, distribution, and promotion. Coal product specification is determined by the inherent geology of a resource and the number of complex actions to market the product to a specific consuming market. Sampling, analyses, beneficiation application, and an array of parameters contribute to matching thermal coal products to the value-in-use it provides to the different markets and its consuming industries. Coal producer shave come under increased scrutiny since South Africa has been experiencing electricity shortages since early 2008. General misunderstandings were declared on public forums and in the media by both legislators and the South African public since a perception developed that South African coal producers are exporting coal that could be utilized by Eskom.

Jan 1, 2010

By J. D. Steenkamp

Keywords: Thermal, conductivity, diffusivity, expansion, history, density, specific heat capacity, industrial rich high-carbon manganese slag The thermal conductivity of slag is an important parameter in the design of furnace-containment systems based on freeze-lining technology. Literature indicates that the crystal content of a slag has a significant influence on its thermal conductivity. Industrial, rich, manganese-bearing slag was cooled at different rates to create samples with different microstructures. The coefficients of thermal conductivity of these samples were measured in a nitrogen atmosphere from room temperature to 990°C at 100°C intervals. The laser-flash measurement technique was used for this purpose. Follow-up investigations included XRF and XRD and modelling in FACTSage.

Jan 1, 2011

By J. A. Bakken, M. T. Jonsson, G. A. Saevarsdottir, H. Palsson

The electrodes of a Submerged Arc Furnaces carry a high current and are subject to enormous stresses caused by both the electric arc itself, and the current distribution within the electrode. The external effect of the arc on the electrode is treated in a different paper at this conference, The purpose of this paper is to analyze the thermal effects of ohmic heating within the electrode at the arc attachment on the carbon based electrode, using data for Søderberg electrodes. The thermal conditions are then used to examine stress conditions in the vicinity of an arc. Two types of models of an electrode are presented in the paper. The first type is an accurate finite element model, based on both two and three dimensional elements and the second type is an one dimensional model, providing better insight into the problem. For the second type, a spherical model of thermal conditions in a semi-infinite solid has been developed. Results show that the electrode surface is heated quickly up to a maximum temperature and for a specific test case, the surface can only withstand the load for about 10 seconds. Also, the thermal stresses on the surface are very high which will increase erosion on the surface in addition to normal evaporation.

Jan 1, 2007

By M. Q. W. Jones

This paper summarizes important features of a compilation of thermal properties of stratified rocks from Witwatersrand gold mining areas. The database consists of more than 1000 thermal conductivity measurements, more than 700 density measurements, and nearly 100 heat capacity measurements. Most important rock types and stratigraphic units are well represented. Heat capacity does not differ significantly from one rock type to another, and density is relatively uniform although particular rock types are characterized by distinct average values. Different rock types also have distinct thermal conductivities, but this parameter varies by a factor of four to five. Primary factors controlling the thermal properties are mineral composition, degree of metamorphism, and porosity. In addition, the temperature dependence of thermal conductivity and heat capacity of quartzite may significantly decrease the thermal diffusivity of this rock at deep mining levels.

Jan 1, 2003

By V. V. Getman, V. A. Chanturiya, T. N. Matveeva

Most of the Au and PGM ores in Russia are characterised by a thin mineral impregnation of noble metals in sulfide minerals, and a large variety of mineral forms that lead to high loss of precious metals with fine fractions during flotation. In modern flotation technology, the rational choice of reagents is one of the main trends for selective separation of minerals and effective metals recovery. New data on the selectivity of the thermo-sensitive polymer with specific functional groups (TMPPh) as a flocculant and collector of Au and Pt fine fractions are available. The selective modified collector (DEDTCm) for the recovery of Au and Pt from complex ores is discussed in this paper. Scanning electronic microscopy (SEAM), laser SIM and AFM microscopy, UV and IR spectroscopy were applied to study the adsorbed layer of new reagents on the mineral surface. Flotation tests of TMPPh on the gold-bearing ore of the Olimpiada deposit showed an increase in Au extraction and Au content in the concentrate of the rougher flotation. Using a combination of reagents TMPPh and ButX, the quality of the Au and Pt concentrates increased in 1.7 time with an increase in recovery up to 15 % compared with the traditional reagent mode. Testing of TMPPh polymers in flotation of Pt-Cu-Ni ore at Norilsk Nickel has shown the ability to obtain a concentrate with a higher Pt content. Recovery of platinum is 17% higher than recovery in an experiment without polymer. Application of DEDTCm helped to achieve higher technological parameters in flotation of lowgrade Rt-Cu-Ni ore. Compared to the basic mode Pt recovery was plus 13%, Pd recovery was plus 9% and the content of precious metals in the rougher flotation concentrate increased in 2,5 - 4 times. The studies have been supported by Grants of the President of RF “Scientific School of Academician V.A. Chanturiya” NSh-220.2012.5, NSh-748.2014.5. Keywords: Au and Pt complex ores, flotation, flocculation, thermo-sensitive polymer TMPPh, modified collector

Jan 1, 2020

By A. Kotze, D. Messina, E. Nagels, Y. Cryns, S. Arnout

The FlashPhos process aims to recover white phosphorus (P4) from sewage sludge by drying, flash combustion/gasification, and carbothermic refining steps. This study evaluates the material behaviour of sewage sludge ash melting and reduction in a refining furnace for the novel FlashPhos process. Thermodynamic modelling in FactSage 8.2 is combined with experiments from a tube furnace to determine the possible phosphorus recovery and minor element behaviour. For the two studied sludges, a yield of 40% and 75% white phosphorus is achieved after 1 hour at 1600°C, corresponding with a 60% and 25% loss to the metal phase. This is slightly above the calculated equilibrium yield of 28%–73%, which depends mainly on the Fe/P ratio of the sludge. Temperature is found to have a significant influence on the final phosphorus yield when leading to incomplete melting of the ash. A clean slag is produced in the process free of heavy metals making it suitable to be used as a cement-like binder material. The main heavy metals that co-evaporate with the phosphorus are Zn, Pb, As, Sb, and Sn. Additional processing steps will be required to remove these to produce a pure P4 product. The metal alloy consists of mostly Fe and P with smaller amounts of other components such as Mo, Cr, Cu, Mn, Sn, Sb, and V. The final slag consists of CaO, SiO2, MgO, and Al2O3 with virtually complete removal of P and heavy metals.

Oct 2, 2025

By N. X. Feng, S. G. Zhou, X. L. Wu, J. P. Peng, Y. Z. Di

"Szaibelyite–suanite type ore is rich in magnesium oxide and boron oxide. We propose a new method to extract both metallic magnesium and valuable residues rich in boron by reduction using metallic aluminium.Thermodynamic analysis of the reactions between aluminum and MgO, Mg2B2O5, and Mg3B2O6 was carried out. The effects of CaF2 addition, temperature, mass of Al, and pellet formation pressure on the extraction of magnesium were also investigated experimentally.The results indicate that the magnesium oxide phase can be displaced from 2MgO-B2O3 and 3MgO·B2O3 by CaO in the reduction system. The reduction ratio of magnesium oxide was 38% without calcium fluoride addition, increasing to 94% with 5.1% calcium fluoride. The reduction ratio increased with increasing temperature and mass of Al. To obtain a higher reduction ratio, the reduction pellet should be formed under a reasonable pressure.IntroductionBoron and its compounds are widely used in textiles, borosilicate glass, metallurgy, fertilizers, and nuclear shielding. Boron resources are mainly found in Turkey, the USA, Russia, and China. In Liaoning, China, there are abundant szaibelyite–suanite type ores that are rich in magnesium oxide and boron oxide. Szaibelyite and suanite ores are used to produce borax by a carbon dioxide– soda process. Annually, 2 Mt of waste materials containing 3–20% B2O3 and 2–25% MgO are produced during the process. It is necessary to make use of these waste materials containing high concentrations of boron oxide and magnesium oxide to avoid environmental problems as well as for economic reasons (Ozdemir and K1pcak, 2007)"

Jan 1, 2016

In this study, the effects of slag compositions, slag amount, temperature, and carbon content of steel on the manganese and phosphorus distribution ratios during converter steelmaking were analysed using the classical regular solution theory, and industrial tests were performed using two 80 t top-and-bottom combined blown converters (duplex melting process). The results indicate that the slag amount, temperature, and carbon content in steel are the main factors affecting the manganese yield when converter slag compositions remain constant. The FeO content of the slag has a strong impact on the manganese distribution ratio, while the slag basicity and MgO content have no obvious effect. The calculations and experimental results show that the phosphorus distribution ratio increases sharply with increasing slag basicity R, but then decreases with the increase of MgO and MnO contents in the slag. The final slag in converter steelmaking should have the following characteristics: 3.5 < R < 4.5, 15% < (FeO) < 20%, and 6% < (MgO) < 8%. The slag amount should be controlled appropriately at the same time. The results of this investigation would be useful in deciding on the application of manganese ore in alloying and identifying the slagging regime in converter steelmaking.

Jan 1, 2014

By M. Timucin

High-temperature phase relations and thermodynamics of the condensed phase region of the Pb-S-O system at 1473 K were analysed by use of the available information. The sub-regular solution models on Pb-PbS and PbO-PbSO4 continuous melts were used in conjunction to generate a consistent set of thermodynamic and phase equilibrium conditions for the Pb-S-O system. The directions and distributions of conjugation lines between melts of this system were derived with relevant activity and composition data. The calculations permitted the thermodynamic analysis of direct lead smelting and the construction of isothermal reaction diagrams for the system in terms of oxygen and sulphur partial pressures at 1473 K.

Jan 1, 1989

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

By T. Markus, K. Hilpert

Discharge vessels of advanced light sources are made of translucent polycrystalline Al2O3(PCA).These tubes contain salt mixtures, which essentially consist of metal halides. The salt mixture is present as a melt at the coldest spot of the vessel under operating conditions and vaporizes partly. The temperatures of the coldest spot range between 1200 K and 1300 K, depending on the lamp performance. The maximum wall temperatures range up to 1500 K and for special purposes up to1700 K. Important constituents of the melt are alkali halides AX (A = Na, Cs, X= Br, I) and rare earth metal halides LnX3(Ln = Dy, Ho, Tm). Severe corrosion attack on the wall material is observed in the PCA discharge vessels. The aim of this work is to elucidate the corrosion mechanism. Annealing experiments under well defined temperatures were carried out in order to understand the complex chemical corrosion processes. Two different annealing vessels were used, one for experiments under isothermal conditions with a temperature of 1473 K and one for experiments with a linear temperature gradient from 1450 K to 1600 K. The vessels were filled with salt mixtures of different compositions and annealed for 1000 h. The corrosion attack was characterised by XRD, analytical electron microscopy, high temperature mass spectrometry, and chemical analysis of the salt melts. The results of our investigations show that the corrosion attack is caused by vapour species and by the salt melt. The most severe corrosion is observed in vessels filled with mixtures of alkali halides and rare earth metal halides. No corrosion of the alumina is practically observed if pure alkali halides or pure rare earth metal halides are present in the annealing vessel. Keywords: thermodynamic, corrosion, lamps, metal halide salt

Jan 1, 2004

By A. D. Pelton, Y. -B. Kang, S. A. Decterov

Computerized thermodynamic databases for solid and liquid metal, slag and solid oxide phases in the Al2O3-CaO-CoO-CrO-Cr2O3-FeO-Fe2O3-MgO-MnO-NiO-SiO2-S system have been developed by critical evaluation/optimization of all available phase equilibrium and thermodynamic data. The databases contain parameters of models specifically developed for molten slags, liquid steel and solid oxide solutions such as spinels, pyroxenes, olivine, monoxide (wustite, periclase, lime), corundum, etc. By means of the optimization process, model parameters are found which reproduce all thermodynamic and phase equilibrium data within experimental error limits. Furthermore, the models permit extrapolation into regions of temperature and composition where data are not available. The databases are automatically accessed by user-friendly software that calculates complex equilibria involving simultaneously slag, metal, refractories and gases, for systems with many components, over wide ranges of temperature, oxygen potential and pressure. A short review of the available databases is presented. The critical evaluation/optimization procedure is outlined using the Al2O3-CaO-FeO-Fe2O3-SiO2and Al2O3-CaO-MnO-SiO2systemsas examples. Several applications of the databases to deoxidation of iron and to inclusion control in steel are discussed. Keywords: thermodynamics, phase equilibrium, phase diagrams, databases, ferrous metallurgy, steelmaking, inclusion control, slags, oxide systems.

Jan 1, 2004