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By H. Jalkanen, L. Holappa

The main role of slag in oxygen converter processes is to absorb the non-volatile oxidation products of hot metal impurities, Si, P, Mn, Ti, V, etc. The importance of converter slag as deP and de Smedia has ceased with implementation of special pre- and post-converter treatments. The transfer from top blowing (LD) to combined blowing converters has decreased the amount of slagged iron that, together with the tendency towards lower silicon and manganese contents, has decreased slag to steel ratio. Still the control of slag forming and behaviour during the blow is of great importance. In this paper the thermodynamics of the slag forming reactions, the role of slag in the modern oxygen converter process for impurity elimination, splashing, lining wear, dust formation and post combustion are discussed on the basis of common knowledge and experience of Finnish steel plants.

Jan 1, 2004

By R. T. Jones

Slags have been produced as by-products from pyrometallurgical processes for thousands of years, and have generally been regarded as waste. Many of these slags are no longer seen as residues merely to be discarded, but as potential economic sources of metals, or as useful by-products in their own right. Slag cleaning can enhance the recovery of valuable metals in existing pyrometallurgical processes, or can produce economic value from recycling old slag dumps. For example, a process has been developed and implemented industrially for recovering cobalt from copper smelting slag in a DC arc furnace. The relatively non-leachable behaviour of glassy slags allows them to be used as a very safe means of disposal of metallurgical waste streams, including many that are classified as hazardous. The high temperatures, reducing conditions, and good mixing that can be achieved in a DC arc furnace enable the effective functioning of this environmentally beneficial means of disposal. Lead blast furnace slag can be rendered safe for disposal by treating it using the Enviroplas process, which strips most of the hazardous lead from the slag (and traps the rest in an insoluble glassy slag) and recovers economic quantities of zinc by absorbing (in a lead splash condenser)the zinc vapour that is fumed off in the furnace. Another example can be seen in the recovery of a chromium- and nickel-containing alloy from stainless steel plant dust, while producing a disposable residual slag. The examples presented here illustrate that it is possible to develop processes that are both economic and environmentally beneficial. Keywords: DC arc furnace, plasma, slag cleaning, cobalt recovery, zinc fuming, Enviroplas, jigging, re-melting fines, environmental, economic

Jan 1, 2004

By L. Bam, R. Machaka, S. Chikosha, N. S. Muchavi

"Parts manufactured through power metallurgy (PM) typically contain pores that can be detrimental to the final mechanical properties. This paper explores the merits of 3D X-ray computed tomography over traditional microscopy for the characterization of the evolution of porosity in metal injection moulding (MIM) and direct powder rolling (DPR) products. 17-4 PH stainless steel (as-moulded, as-debound and sintered) dog-bone samples produced via MIM and Ti-HDH strips (as-rolled and sintered) produced via DPR and were analysed for porosity. 3D microfocus X-ray tomography (XCT) analysis on specimens from both processes revealed spatial variations in densities and the existence of characteristic moulding and roll compaction defects in agreement with traditional microscopic microstructural analysis. It was concluded that micro-focus XCT scanning can be used to study MIM and DPR parts for the characterization of the amount, position and distribution of porosity and other defects. However, the majority of the sub-micron sized pores could not be clearly resolved even at the highest possible instrument resolution. Higher-resolution scans such as nano-focus XCT could be utilized in order to fully study the porosity in MIM and DPR parts. IntroductionMetal injection moulding (MIM) is a novel process, which combines the advantages of powder metallurgy (PM) and plastic injection moulding. MIM has found widespread applications in the cost-effective production of high-sintered density small parts with complicated shapes and mechanical properties equivalent to those of wrought materials (German and Bose, 1977; Machaka and Chikwanda, 2015; German, 2013). There are four basic processing steps involved in MIM, namely; feedstock preparation, injection moulding, debinding and sintering. These steps are discussed in greater detail elsewhere (Machaka, Seerane and Chikwanda, 2014; German and Bose, 1977; Machaka and Chikwanda, 2015; German, 2013).Feedstock preparation involves mixing metal powder with a carefully selected composition of polymeric binder materials at a specific temperature. The feedstock is then granulated and injected into a predefined mould die with the desired shape. The part produced during the moulding step is referred to as a ‘green’ component. The green component typically contains no porosity since the spaces between adjacent powder particles are readily filled with the binder materials (German and Bose, 1977; Li, Li and Khalil, 2007). Debinding is the systemic removal of the binder components by chemical, catalytic, or/and thermal means while maintaining the shape of the component. The part produced after the debinding step is referred to as a ‘brown’ component. Debinding is known to be the source of porosity in brown components (Ji et al., 2001; Tsai and Cen, 1995). Finally, the brown debound part is sintered to full or nearfull density (Sotomayor, Varez and Levenfeld, 2010). The sintering step and associated densification closes up the majority of the pores. Sintered MIM parts are typically sintered to high density (95–99%) and retain an irreducible amount of residual porosity (Barriere, Liu and Gelin, 2003; German, 1990)."

Jan 1, 2016

By E. Milke, A. Arnold, B. Friedrich, A. Sydykov

CaF2is often used as a fluoride addition to the chloride salt flux in the melting of aluminium scrap. The solubility of CaF2in the chloride salt system is limited. Dissolved CaF2is considered to improve the properties of salt fluxes. Experimental investigations indicated that the solubility ofCaF2in 70 wt % NaCl/30 wt % KCl, German salt flux used in aluminium scrap melting, might be lower than expected according to literature data. The pseudo binary section CaF2-(70 wt % NaCl-30 wt % KCl) was investigated by differential thermal analysis (DTA). The determined solubility of CaF2appeared to be considerably lower than presented in the literature. The pseudo binary section calculated using thermodynamic data partially confirmed the results. DTA allowed us alsoto determine the crystallization temperature interval of the two phase eutectic consisting of the solid solution NaCl-KCl and CaF2. Keywords: aluminium recycling, phase system, salt flux, CaF2, NaCl, KCl, solubility

Jan 1, 2004

By Chandrakala Kari, S. Mohan Rao, Gajanan Kapure, K. S. Raju

High carbon ferrochrome production process is energy intensive, consumes approximately 3300-3400 kWh per ton of metal produced. This amounts to ~ 34% of the total ferrochrome production cost. The power costs in India are almost 4 times greater than the leading ferrochrome producing countries like South Africa. Hence there is a need to look for alternative sources of energy. In ferrochrome making process large volumes of high concentration CO gas (~ 85%V) is developed at ~400-5000C, which if combusted within furnace represents high potential for significant electrical energy savings. In a typical heat in the state-of-the-art submerged arc furnace, about 34 kmol of CO gas is generated per ton of ferrochrome metal, which, if post combusted to CO2, represents 7620 MJ of energy. Post combustion of the evolving CO (and H2) gas to CO2 can be achieved by providing additional oxygen before the generated CO gas leaves the furnace. In this paper, a concept of post combustion in submerged arc furnace as potential source of significant electrical energy saving in ferro-chrome making process has been explored. The prospects and limitations of the same are discussed. The value of this paper lies in its attempt to explore the post combustion application to submerged arc furnace with an objective of significant reduction in electrical energy consumption in ferrochrome production process.

Jan 1, 2007

By R. Boom, K. C. Mills, S. Riaz

This paper details the recent trends in slag-related research from 1999 to 2003. The trends in thefollowing are outlined: • Annual publication rate • Geographical origin of the work • Nature of the research (e.g. thermodynamics, kinetics) • Nature of the slag studied. This study has revealed that slag research in the USA and Europe has decreased to about a half over the last 20 years and that there has been a significant decrease in Japanese research in this area in recent years. However, these decreases have been offset by significant increases in Chinese and Korean research activity. There has been a significant increase in the amount of work carried out on the recycling and environmental aspects of slags in recent years.

Jan 1, 2004

Plant survey data has shown that gold recovery through a specific copper concentrator was significantly lower than copper recovery. Size-by-size analysis revealed that this was due to poor recovery of+75 µm and ?23 µm gold containing particles. In order to further investigate the nature of the gold losses, experiments were conducted at laboratory scale. Gold deportment studies on the laboratory flotation products revealed that coarse gold (+75 µm) reporting to the rougher tailing was predominantly associated with non-sulphide gangue. Further grinding of the plant rougher tailing improved recovery of gold and copper, while not affecting iron recovery, due to improved liberation of gold from non-sulphide gangue in coarse size fractions. EDTA extraction to remove surface contaminants showed a similar improvement for fine, liberated gold flotation.

Jan 1, 2003

By Pieter de Waal

The use of valuable minerals is a necessity to maintain a modern society. Not only the iron, aluminium, coal and oil that are used in large quantities, but also the uranium, copper, vanadium, tungsten, antimony and many others play an essential role in the bigger picture of our modern civilisation. Minerals occur in a form and in places determined by a long history starting at the dawn of creation. Over billions of years the elements have combined in wondrous combinations and structures. They have been broken up by massive explosions, movements in the earth's crust and erosion by wind and water. They have been restructured and recreated in even more configurations by the application of heat and pressure, leached by and exposed to new chemical compounds. The result is that most valuable minerals are found in impure form and mixed up with other, less useful waste material. 2. Mineral Beneficiation The processes used for the purification and enhancement of an ore, to satisfy the needs of downstream applications, are collectively referred to as mineral beneficiation. Mineral Beneficiation starts in the mine where only that portion of the ore, that can be economically processed, is selectively extracted. It may also include ore blending, to ensure a more consistent feed to the following stage of valuable mineral recovery. The next stage in mineral beneficiation is the liberation of the valuable minerals from the gangue. This is achieved by blasting, crushing, milling and grinding down to an adequately fine grain size to facilitate good separation. Separation can be achieved by a variety of different techniques. ?Screening coarse from fine particles is an easy method if the valuable mineral is dominant in a certain screen fraction. ?Magnetic separators can differentiate minerals on the basis of their difference in magnetic susceptibility. ? Electrostatic separators differentiate on the basis of electrical conductivity. ? The differences in density are exploited in spirals and jigs. ? Particular surface properties provide a separation technique in flotation. ?The selective sorption properties of a collector medium are another option.

Jan 1, 2007

The slags produced by the Imperial Smelting Process (ISP) are based on the system ZnO-?FeO?-Al2O3-CaO-SiO2. The slag chemistry is important to the process since it determines the fluxing practice and the operating temperature of the furnace required to produce fluid slag. The paper presents the results of the first systematic experimental investigation of these ZnO-containing slags in equilibrium with metallic iron, and provides information on the primary phase fields and liquidus temperatures in these slags over the range of compositions used in ISP practice. A feature of the slags is the presence of alumina, which has a major influence instabilizing the spinel phase. This information presented in the form of pseudo-ternary sections ZnO-?FeO?-(Al2O3+CaO+SiO2) enabling the data to be readily used by plant engineers. Keywords: liquidus temperature, ISP, EPMA, ZnO-?FeO?-Al2O3-CaO-SiO2, phase equilibria.

Jan 1, 2004

By Jo Katembo, Patty Bwando, Patient K. Ilunga, Yves Kalubi, Emman Mulaj

"From 2010, the dolomite concentration in the ore fed to the Usoke Plant increased, resulting in a significant increase in the gangue acid consumption and Mg build-up in the circuit, and thus an increase in the Mg:Co ratio in the plant solutions. This affected the Co salt grade, reagent consumption, filtration and drying capacity. Efforts were put in place to minimise the acid consumption and consequently the Mg dissolution (such as use of pre-diluted acid), but the benefits were negligible. Various efforts were then initiated by CHEMAF to improve the cobalt plant productivity (quantity and quality) by process changes, dual precipitation and seed recycle. The positive results obtained in the laboratory were successfully implemented on plant scale. A change in the process from a single-stage precipitation with Na2CO3 to dual precipitation using a combination of Na2CO3 and NaOH improved the capacity of the Co salt filtration by 30%, the Co salt grade and drying capacity by 50%, and reduced the reagent consumption by 22%. Implementation of precipitate seed recycle increased Mg rejection by 40%, improving the Co salt grade from 20% to 25%, and yielding a further drop in reagent consumption. INTRODUCTION CHEMAF (Chemicals of Africa), a mining company located in Katanga province of Democratic Republic of Congo (DRC), has been operating since 2003. The Usoke hydrometallurgical plant treats the Cu-Co ore from the Etoile pit to produce Cu cathodes via a leach–solvent-extraction (SX)–electrowinning (EW) circuit and Co salt via a selective precipitation process. The plant was designed to treat run-of-mine (ROM) ore grading 6% Cu and 1.5% Co; but, in 2008, due to a decline in grades, a heavy-media separation (HMS) plant was commissioned to enrich the low-grade ROM (3.5% Cu and 0.5% Co) up to 8% Cu and 1% Co before feeding it to the hydrometallurgical plant. Co is recovered by precipitation of Fe and Al with limestone, followed by Co precipitation as Co carbonate using sodium carbonate (Na2CO3), also known as soda ash. 85% of the final effluent from cobalt precipitation is recycled back to the plant as process water; the balance, 15%, is bled out and compensated for by fresh water top up to control and retard the rate of sodium sulfate build up."

Jan 1, 2015

By F. S. A. de Frey

The author would like to refer to his contribution to the paper `Design of pillar systems in South Africa' by Ozbay et al. 1. The authors agreed `wholeheartedly that further research, together with carefully planned field trials, in pursuit of this potentially highly rewarding concept' of the small span small pillar method is warranted. On 30 September 2010 the author went underground at the Kroondal Chrome Mine to observe how the concept of smaller spans was being applied. He was pleasantly surprised to find that the typical coal mine bord and pillar sytem was being used very successfully. Although the deepest mining was taking place at a depth of only 450 metres, Kroondal would be an ideal mine to do further research together with carefully planned field trials. At Crown Mines Gold Mine, where the author worked, he was informed that the first recorded rockburst took place at a depth of 635 metres below surface. The depth of the platinum and chrome mines is increasing, with the risk of an excalation in injuries and fatalities due to 'backbreaks' and siesmic activity. The rock engineer at Kroondal was not aware of backbreaks occuring on the mine. It is important that the rock engineers of the base mineral and gold mines get together and give more serious attention to the host rock environment in which the pillars are situated.

Jan 1, 2011

By B. Andresen, S. T. Johansen, H. Tveit, S. Grådahl, B. Ravary

The Norwegian ferroalloy industry has high ambitions regarding environmental standards. Basic research work has been performed to improve the fundamental understanding of ferroalloy processes and the environ-mental aspects. This paper will present work dealing with the understanding of formation and control of NOx, PAH and dioxins. During this work various techniques and methods have been applied, such as comprehensive industrial measurements, laboratory experiments, model development and application of Computational Fluid Dynamics (CFD). The main goal has been to reduce the environmental impact of ferroalloy plants, by means of improving the combustion processes done by introducing new charging routines and optimized furnace operations, instead of installing expensive gas treatment systems. The Norwegian obligations in accordance with the Gothenburg protocol are to reduce the NOx emissions by 30%, compared with the 1990 level within 2010. Measures developed in this work have resulted in 40-60%reduction in NOx emission, and major reductions in PAH and dioxins for ferrosilicon and silicon metal plants. This has been achieved by introducing semi continuous charging and improved furnace operations. Semi continuous charging and optimized furnace operations are shown to reduce the blowing activity (i.e. emission of large quantity of SiO over the charge by direct channelling from the crater zone). It also reduces variation in off-gas temperature and dust production. To understand the processes and to achieve our results we have used online equipment, with fast sample rates and response times, to measure the off-gas compositions and temperatures. Most of the measuring techniques used are based upon optical principles making use of the absorption- and emission spectrum of the gases. In addition a new prototype instrument is developed for continuous measurement of off-gas characteristics, total dust amount and off-gas temperature. The presented work is a result of a long term co-operation research and development teamwork, between the industry and the research community, and has improved both the process and reduced the emissions. The work has introduced new process design and operation standards, and has resulted in ferroalloy production with better environmental standards.

Jan 1, 2007

By X. Pan

Slag-metal equilibrium experiments were conducted at 1500ºC and 1580ºC under 0.03 atm, 0.05atm and 0.83 atm CO partial pressures using silica and Cr-oxide crucibles. The complex slags belonged to SiO2-CaO-Al2O3-MgO-FeOx-CrOxand the metal phase to the Cr-Fe-C-Si-(S)systems. The carbon saturation of the metal phase was avoided using oxide crucibles and thus the results are pertinent to ferrochromium refining slags and processes. From equilibrium data and thermodynamic calculations the CrO /(CrO+Cr2O3) ratio in the slag was determined as 0.75, 0.80and 0.86 under 0.83 atm and 0.05 atm of CO pressure at 1500ºC and 0.03 atm and CO pressure at1580ºC respectively. The results clearly demonstrated that a higher chromium content of the metal results in higher Cr in the slag, and chromium in slag decreases with increasing SiO2. The results were also sensitive to the crucibles used as these oxide crucibles saturated the slag either with respect to SiO2or Cr-oxides. It was also demonstrated that the relative amount of CrO in the slag was higher when SiO2crucibles were used in accord with thermodynamic calculations. Iso-concentration curves for carbon and chromium of the metal phase in equilibrium with the slag were drawn on pseudo ternary SiO2–(AI2O3+CaO+MgO)–(Cr2O3+Fe2O3) diagram. The activity coefficients and activities of carbon and chromium of the metal phase were also calculated from the experimental data and available thermodynamics information and were plotted as iso-activity curves in the same pseudo ternary diagram. Keywords: Chromium, slag, equilibrium

Jan 1, 2004

By M. Sanchez, I. Imris, G. Achurra

The Smelting and Converting El Teniente Process for copper concentrates as well as Slag Cleaning Furnace Technologies to treat slags coming out from the El Teniente Furnaces are widely applied today in Chile and around the world. Several industrial applications of this process have shown their capability to treat copper concentrates in a wide range of chemical and mineralogical compositions. Main operational parameters determining performance of the process are: oxygen enriched air flow rate, degree of oxygen enrichment, moisture content of the solid materials processed, molten material levels inside the vessel, frequency of molten materials tapping, bath temperature and copper losses in slags. In this work, the copper losses in the slags from El Teniente pyrometallurgical process are predicted by calculation from thermodynamic data and compared with those determined by microscopic examination and slag industrial data. Results obtained show that the main part of copper losses in the slag from El Teniente Furnace are mechanically entrapped or floated unsettled droplets of the coexisting matte phase. by the contrary the very low copper losses in the slag from slag cleaning furnace are limited by the physico-chemical form.

Jan 1, 2004

By H. Hu, T. S. Golosinski

The paper reports on use of neural network algorithms to model performance and condition of mining trucks. The model inputs are selected digital data streams collected by truck Vital Information Management System, VIMS, during its operation in a mine. The models built as the result of this work allow for projection of truck condition and performance into future. As such they facilitate more efficient management of mine truck fleets. Keywords: Modelling, modeling, neural networks, mining equipment, Vital Information Management System, Intelligent Miner, mining truck

Jan 1, 2003

Viscosity measurement was carried out over a narrow range of silica content around the fayalite composition. A wide range of temperature and oxygen potential was covered where the slag was completely liquid. In order to keep the slag composition and the Fe3+/Fe2+ratio constant, theCO2/CO ratio was kept constant as the temperature was varied. Increasing the Fe3+content has little effect on viscosity for slags with a silica mole fraction of 0.31. At higher silica contents, increasing the Fe3+content brings about a small decrease in the viscosity.

Jan 1, 2004

By T. Tamura

It is known that the CaO-FetO-P2O5slag system has a wide liquid miscibility gap at steelmaking temperatures and this two-liquid slag phase has many advantages such as high activities of both FetO and CaO and high amount of P2O5. The phosphorus distribution ratio between the two-liquid slag and molten steel was confirmed to be higher than that between CaOsat.-FetO-P2O5slag and molten steel. The two-liquid slag may be useful for dephosphorization of molten steel and reduction of slag volume. Furthermore, the phase equilibrium of two-liquid CaO-FetO-P2O5slagsaturated with MgO was measured to determine the applicability of the two-liquid slag to dephosphorization in steelmaking process. Keywords: slag, refractories, solid solution, two-liquid phase, dephosphorization, steelmaking, phase equilibrium.

Jan 1, 2004

By A. D. Pelton

The evolution of thermodynamic models of molten salts and slags, starting with Temkin in 1948, has culminated in today?s sublattice models. These modern models have permitted the development of large thermodynamic databases of model parameters, which can be used to calculate and predict accurately the properties of multicomponent solutions. The model parameters are mainly obtained by the critical evaluation and optimization of available thermodynamic and phase equilibrium data for binary and ternary subsystems. The models are then used to estimate the properties of multi component slags and salts from these assessed binary and ternary parameters. When used in conjunction with thermodynamic databases for solids and solid solutions (salts, oxides, sulphides, metals, etc.), other liquid solutions (such as liquid metals),and gases, these databases permit the calculation of complex multiphase equilibria in multicomponent systems, with applications in a wide variety of industries. These calculations can be performed with general commercial software for Gibbs energy minimization, which can also be incorporated into process simulation software packages. Keywords: slags, salts, solution models, thermodynamics, phase diagrams, oxide systems, molten salts

Jan 1, 2004

Council for 1999/2000 President M.H. Rogers President Elect Dr L.A. Cramer Vice Presidents Senior A.A.B. Douglas Junior S.J. Ramokgopa Immediate Past President J.R. Dixon Honorary Treasurer J.A. Cruise [ ] Annual report In accordance with the current management policy, this report on the activities of the Institute is presented under eight main headings: 1. Interests of Individual Members 2. Technical Meetings 3. Publications 4. Regional Development 5. Engineering Science and Technology in South Africa 6. International Liaison 7. State Liaison 8. Management and Administration.

Jan 1, 2001

Bacterial leaching represents an unusual problem in biochemical engineering, because the substrate for bacterial growth is not supplied directly, but is a product of another reaction, the leaching of mineral particles. Leaching arises from the bacterial oxidation of ferrous ions to ferric ions, which in turn oxidize the mineral. For the bacterial dissolution of pyrite, these reactions are: [ ] (Y represents a stoichiometric yield factor, and N represents the amount of bacteria.) Equations [1] and [2] represent a cyclic auto-catalytic system since more ferric ions are added to the system with an increase in the extent of leaching.

Jan 1, 2000