Low phosphorus content steels are essential for steel applications where high ductility is required, such as thin sheets, deep drawn, pipelines and automobile exteriors. In the past, phosphorus control was not considered a big challenge in steel production in the US because iron ores with low phosphorus contents were readily available and considered cheap. However, in the last decade, the iron ore price has risen by roughly 400% and lower cost iron sources generally have higher phosphorus content. In integrated steel plants, phosphorus removal usually takes place during the oxygen steelmaking process (OSM) but in Japan a intermediate step for hot metal dephosphorization is commonly used. There are various types of OSM furnaces but the most widely used remains the top-blown Basic Oxygen Furnace (BOF). The BOF slag can be recycled to a sinter plant or directly to the blast furnace, ultimately increasing the phosphorus input in the process. In order to meet new demands for phosphorus control, it is necessary to improve our understanding on the thermodynamics and kinetics of the phosphorus partitioning reaction between slag and metal melts during steelmaking. Therefore, the present work has been divided in three strongly correlated sections: phosphorus equilibrium between metal and slag; analysis of plant data; and observations of the reaction kinetics. Phosphorus equilibrium between liquid metal and slag has been extensively studied since the 1940's. It is well known that CaO and FeO are the main slag constituents that help promote dephosphorization. On the other hand, dephosphorization decreases with temperature due to the endothermic nature of the reaction. Many correlations have been developed to predict the phosphorus partition ratio as a function of metal and slag composition as well as temperature. Nevertheless, there are still disagreements in the laboratory data and the equilibrium phosphorus partition can be predicted with an uncertainty of a factor of up to 5. The first part of the present work focuses on generating more reliable equilibrium data for BOF-type slags by approaching equilibrium from both sides of the reaction. The experimental results were combined with two other sets of data from different authors to produce a new correlation that includes the effect of SiO2 on the phosphorus partition coefficient, LP . Although the quantification of phosphorus equilibrium is extremely important, most industrial furnaces do not operate at equilibrium, usually due to liquid slag formation, kinetics and time constraints. Thus, it is important to know how close to equilibrium different furnaces operate in order to suggest optimal slag compositions to promote dephosphorization. The present work analyzed four large sets of data containing the chemical compositions of both slag and metal phase as well as the tapping temperature of each heat. Each set of data corresponded to different furnaces: one AOD (Argon Oxygen Decarburization), two top-blown BOFs and one Q-BOP or OBM. It was found that the bulk slag composition can greatly \mask" the data due to solid phases coexisting with the liquid slag. The author used the software package FactSage to estimate the amount of solids in the slag and liquid slag composition. It was found that the AOD is the reactor closest to equilibrium, followed by the Q-BOP (OBM) and the two top-blown BOFs. It was noted that the stirring conditions and slag composition are two key variables to enable optimum phosphorus removal. Also, over saturating the slag with CaO and MgO does not seem to benefit the process to any extent. Lastly, interesting observations on the behavior of small metal droplets reacting with slag are presented and discussed. It was found that dynamic interfacial phenomena at the metal-slag interface is likely to play a significant role in the kinetic behavior of the system, due to the exchange of surface active elements, such as oxygen, which dramatically lowers the interfacial tension and cause spontaneous emulsification. Although this phenomenon has been studied, actual quantification of changes in interfacial area remain a challenge. The author developed an experimental method to enable better quantification of spontaneous emulsification and two sets of experiments were carried. One with an Fe containing 0.2 wt.% P and another in a P-free system where pure iron was oxidized. It was found that phosphorus did not play a role in spontaneous emulsification and it was rapidly removed before the onset of dynamic interfacial phenomena. Emulsificaion was maybe caused by de-oxidation of the metal after phosphorus removal took place and the metal became super saturated with oxygen by an unknown reason. The estimated surface area rapidly increases by over an order of magnitude during the beginning and intermediate periods of the reaction. The metal drop breaks into hundreds of small droplets, effectively emulsifying the metal into the slag. With time, the surface area decreases and the metal droplets coalesce. Similar results were observed for an Fe droplet being oxidized. Spontaneous emulsification takes place regardless of the direction of oxygen transfer and the changes in surface area are similar for both cases. The last chapter describes the industrial relevance of the present work, summarizes the findings, revisits the hypotheses and presents potential future work where further research is encouraged.

A indústria siderúrgica busca continuamente melhorias no desempenho dos refratários, como forma de melhorar sua competitividade, em um mercado caracterizado pela competição global. Um dos principais fatores de desgaste dos refratários é a corrosão, que no ambiente siderúrgico, está diretamente relacionada com a qualidade das escórias, na maioria dos equipamentos. Nesse contexto, o presente trabalho apresenta um estudo dos principais fatores que desgastam quimicamente o revestimento dolomítico, com o objetivo de entender os fenômenos que estavam impactando no desempenho dos refratários utilizados na panela de aço da Siderúrgica Riograndense. Para o estudo em questão, o comportamento químico dessas escórias foi monitorado de setembro de 2008 a outubro de 2009. Para análise didática os dados foram estratificados em três períodos, onde o período 01 corresponde aos meses de setembro, outubro e novembro de 2008, período 02 englobam os meses de fevereiro a junho de 2009 e o período 03 revela os resultados de julho a outubro de 2009. Os resultados de monitoração da qualidade da escória foram apresentados por equipamento forno elétrico a arco (FEA) e forno panela (FP). Os principais parâmetros de processo avaliados, foram a basicidade binária, teor de MgO e oxidação da escória. Os resultados foram relacionados com o desempenho do revestimento refratário aplicado na panela de aço. Para a análise dos dados foi utilizado o Minitab um software que oferece um conjunto de ferramentas estatísticas. Pode-se inferir, a partir da análise dos resultados apresentados nesse trabalho, que as ações de redução da oxidação da escória do forno elétrico através de ajustes no sistema de injeção de oxigênio das injetoras, propiciaram uma redução do óxido de ferro nas escórias do forno panela, permitindo correções da basicidade binária nesse mesmo equipamento. Estas ações em conjunto com a elevação na concentração do óxido de magnésio, através da introdução de cal dolomítica no processo, promoveram melhor formação do coating no revestimento refratário. As alterações no processo de produção do aço promoveram um significativo aumento na vida média das panelas de aço desta aciaria. / The steel industry is continually seeking improvements in the performance of refractories, as a way to improve their competitiveness in a global market. A major factor in refractories wear is chemical corrosion. In the steel industry this is directly related to the quality of the slag used in most of the equipment. In this context, this work presents a study of the main factors that causes chemical wear in dolomite refractory. The main objective was the understanding of the phenomena that were impacting on the performance of refractories used in steel ladle of Siderúrgica Riograndense. For this study, the chemical behavior of slags was monitored from September 2008 to October 2009. For better understanding the analysis, the data were stratified into three periods: period 01, from September to November 2008; period 02, from February to June 2009; and the period 03, from July to October 2009 . The results of slag quality monitoring were presented separated from the electric arc furnace (EAF) and the ladle furnace (LF). The main process parameters evaluated were the binary basicity, content of MgO and oxidation of the slag. The results were correlated with the performance of refractories used in steel ladle. For the analysis of data, it was used Minitab software which offers a set of statistical tools. It can be inferred, through out the analysis of the results presented here, that the actions to decrease oxidation of the EAF slag, by adjusting the feeding system of oxygen injectors, propitiated a reduction of iron oxide in the slag of ladle furnece, which allowed corrections in binary basicity in the same equipment. These actions together with the increase in the concentration of magnesium oxide in the FP slag, through the introduction of dolomitic lime in the process, promoted the creation of a better coating on the refractory lining. The changes in the process of steel production promoted a significant increase in average life of ladle refractory in this steel making plant.

A indústria siderúrgica busca continuamente melhorias no desempenho dos refratários, como forma de melhorar sua competitividade, em um mercado caracterizado pela competição global. Um dos principais fatores de desgaste dos refratários é a corrosão, que no ambiente siderúrgico, está diretamente relacionada com a qualidade das escórias, na maioria dos equipamentos. Nesse contexto, o presente trabalho apresenta um estudo dos principais fatores que desgastam quimicamente o revestimento dolomítico, com o objetivo de entender os fenômenos que estavam impactando no desempenho dos refratários utilizados na panela de aço da Siderúrgica Riograndense. Para o estudo em questão, o comportamento químico dessas escórias foi monitorado de setembro de 2008 a outubro de 2009. Para análise didática os dados foram estratificados em três períodos, onde o período 01 corresponde aos meses de setembro, outubro e novembro de 2008, período 02 englobam os meses de fevereiro a junho de 2009 e o período 03 revela os resultados de julho a outubro de 2009. Os resultados de monitoração da qualidade da escória foram apresentados por equipamento forno elétrico a arco (FEA) e forno panela (FP). Os principais parâmetros de processo avaliados, foram a basicidade binária, teor de MgO e oxidação da escória. Os resultados foram relacionados com o desempenho do revestimento refratário aplicado na panela de aço. Para a análise dos dados foi utilizado o Minitab um software que oferece um conjunto de ferramentas estatísticas. Pode-se inferir, a partir da análise dos resultados apresentados nesse trabalho, que as ações de redução da oxidação da escória do forno elétrico através de ajustes no sistema de injeção de oxigênio das injetoras, propiciaram uma redução do óxido de ferro nas escórias do forno panela, permitindo correções da basicidade binária nesse mesmo equipamento. Estas ações em conjunto com a elevação na concentração do óxido de magnésio, através da introdução de cal dolomítica no processo, promoveram melhor formação do coating no revestimento refratário. As alterações no processo de produção do aço promoveram um significativo aumento na vida média das panelas de aço desta aciaria. / The steel industry is continually seeking improvements in the performance of refractories, as a way to improve their competitiveness in a global market. A major factor in refractories wear is chemical corrosion. In the steel industry this is directly related to the quality of the slag used in most of the equipment. In this context, this work presents a study of the main factors that causes chemical wear in dolomite refractory. The main objective was the understanding of the phenomena that were impacting on the performance of refractories used in steel ladle of Siderúrgica Riograndense. For this study, the chemical behavior of slags was monitored from September 2008 to October 2009. For better understanding the analysis, the data were stratified into three periods: period 01, from September to November 2008; period 02, from February to June 2009; and the period 03, from July to October 2009 . The results of slag quality monitoring were presented separated from the electric arc furnace (EAF) and the ladle furnace (LF). The main process parameters evaluated were the binary basicity, content of MgO and oxidation of the slag. The results were correlated with the performance of refractories used in steel ladle. For the analysis of data, it was used Minitab software which offers a set of statistical tools. It can be inferred, through out the analysis of the results presented here, that the actions to decrease oxidation of the EAF slag, by adjusting the feeding system of oxygen injectors, propitiated a reduction of iron oxide in the slag of ladle furnece, which allowed corrections in binary basicity in the same equipment. These actions together with the increase in the concentration of magnesium oxide in the FP slag, through the introduction of dolomitic lime in the process, promoted the creation of a better coating on the refractory lining. The changes in the process of steel production promoted a significant increase in average life of ladle refractory in this steel making plant.

<p> An experimental evaluation of three desulphurisers for pig iron has been conducted. Sodium vapor, blast furnace slag enriched with cerium oxide and a rare earth alloy named misch metal have been used. </p> / Thesis / Master of Engineering (MEngr)

<p>The reduction of iron oxide from slag is involved in many processes, such as, bath smelting, EAF steelmaking and copper slag cleaning processes, and it is known to occur via gaseous intermediates. Four possible rate determining steps are involved during the reduction. Among them, these two interfacial chemical reactions, gas slag and gas carbon could ultimately limit the enhancement of these processes.</p><p>In this work, the gas slag reaction kinetics in slag cleaning of copper slags has been studied. The dissociation rate of CO2 on the surface of liquid copper slags is measured using an isotope exchange method, where the mass transfer in the gas phase was eliminated by using a sufficiently high gas flowrate.</p><p>It is found that, for slag of the FexO-SiO2-Al2O3-Cu2O system, the apparent rate constant remains fixed with Cu2O content from 1-10 wt pct at higher oxygen potentials. The rate constant becomes approximately 2 times higher after metallic copper is reduced from the slag, this is due to the suspension of small metal drops on the slag surface.</p><p>The effect of temperature in the range from 1200-1450°C on the rate constants was also studied. The activation energy was 190 kJ/mole for slag of composition 60FexO30SiO2-1 0Al2O3. In the presence of Cu metal~10%, the activation energy was reduced to 122 kJ/mole.</p> / Thesis / Master of Engineering (MEngr)

Slags are crystalline to vitreous by-product materials generated in many high temperature industrial processes. This study presents a general technique for the identification of the phases present in petroleum coke gasification slags. documents the phase assemblages and textures, and finally determines the dissolution of vanadium from these slags as part of the considerations of potential resource reclamation. The general identification procedure utilizes (1) recognition of separate phases using optical microscopy and scanning electron microscopy; (2) electron probe microanalysis (EPM) of chemical compositions of individual phases; (3) statistical analysis of the EPM data to eliminate spurious data; (4) estimation of valence states of transition metals using thermodynamic and computational methods; (5) derivation of chemical formulae for the phases using computational methods and chemistry of ionic substitutions; (6) verification of phase identity using X-ray diffraction analysis. More than twenty phases were determined in petroleum coke slags including oxides, silicates. vanadates, sulfate. sulfides and alloys. The reduced slags are rich in V₂>0₃ with silicates and minor amounts of sulfides and native metals whereas the oxidized slags are composed of V₂>0₄, nickel aluminum spinels. various vanadates and glass. Textural analysis provided information on the crystallization process, reaction with gasifier refractory lining materials, sulfide exsolution processes, glass devitrification. and the development of chemical zonation in some spinels. This information offers some perspectives on the potential of resource reclamation. Resource reclamation for petroleum coke slags is best assessed with a knowledge of phases, phase assemblages, textures and dissolution behavior of the material. The dissolution of vanadium. the most significant element. was examined using long term dissolution experiments. These demonstrate that vanadium concentrations are pH dependent ranging from 1500 ppm to 5000 ppm with a minimum concentration near pH 6. Vanadium dissolution rates range from L28xlO⁴ mol m² sec⁻¹ to 3.08xlO^-6 mol m² sec⁻¹. In view of the strategic nature of vanadium and the fact that the concentration of vanadium in slags is almost two orders of magnitude higher than the current mining grades, petroleum coke slags offer significant potential to serve as resources for vanadium. / Ph. D.

Le crassier du site MetalEurop (Noyelles-Godault) a accueilli des scories de première fusion entre les années 1936 à 2003. Il est actuellement constitué de 4 millions de tonnes de ces matériaux générés par les deux procédés pyrométallurgiques les plus usités dans le monde pour la production du plomb et du zinc : le procédé Lead Blast Furnace (LBF) et le procédé Impérial Smelting Furnace (ISF). L'utilisation de ces scories en tant que matériau de substitution dans les ciments et dans les routes a été envisagée et a fait l'objet de recherches, mais présente des risques environnementaux, c'est-à-dire, essentiellement la dissémination de polluants (Pb et Zn) / Primary smelting slags, known as Lead Blast Furnace (LBF) and Imperial Smelting Furnace (ISF), were generated by the former pyrometallurgical industries located in Noyelles-Godault, Northern France. Following its closure in 2003, 4 million tons of primary slags have been landfilled as a heap in the vicinity of the Deûle River, near the industrial basin of Nord-Pas-de-Calais. These slag materials are often enriched in particular metals (Pb, Zn) that can be released into the environment through alteration processes and leaching. Many biological and chemical processes might take place within these tailings and thus affect significantly the slag weathering. Predicting the environmental impact of these wastes requires an understanding of the mineral-water interactions as well as the influence of the biological activities (the involvement of microorganisms). Thus, this research is designed to simulate the natural weathering of slag by simulating different weathering conditions with or without the involvement of the microorganisms as well as by varying several chemical parameters. Chemical weathering of both LBF and ISF slags was studied by as a function of pHs (4, 5.5, 7, 8.5 and 10) as well as under two atmospheres (open air and nitrogen). Significant amounts of Ca, Fe and Zn were released under acidic conditions (pH 4) with a decrease towards the neutral to alkaline conditions (pH 7 and 10) for both slags. The concentrations of all elements increased gradually after 216 h compared to initial 24 h of leaching period. The presence of oxygen under open-air atmosphere not only enhanced oxidative weathering but also encouraged formation of secondary oxide and carbonate phases. In addition, Zn dissolution was related to extremes zinc isotopic signatures in the leachate; heavier δ66Zn values at low pH than at high pH for both slags under open-air atmosphere. On the other hand, bioweathering of both slags was studied in the presence of a pure heterotrophic bacterial strain (Pseudomonas aeruginosa) in a bioreactor operated in batch conditon as well as in a semi-flow through reactor with intermittent leachate renewal conditions. P. aeruginosa is shown to play a significant role in slags weathering by enhancing the leaching and solubility of Zn and Pb. In addition, the cumulative bulk release of dissolved Fe, Si, Ca and Mg doubled in the presence of bacteria, probably due to the release of soluble complexing organic molecules (e.g. siderophores). Bacterial biomass served as the bioadsorbent for Pb, Fe and Zn as 70-80% of Pb and Fe, 40-60% of Zn released are attached to and immobilized by the bacterial biomass. Oxides, hydroxides and carbonates were predicted as secondary phases during chemical weathering of slags whereas carbonates and phosphates were dominant phases during bioweathering. These predictions were in agreement with the observations by Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Analysis (EDS), Transmission Electron Microscopy (TEM) analysis, and X-ray Photoelectron Spectroscopy (XPS) analysis

Há uma demanda por competitividade entre as indústrias de aços, a fim de alcançar a excelência definida pelo termo clean steel. O processo de desgaseificação a vácuo (VD) ocorre durante o Refino Secundário de aços especiais. Sua principal função é remover gases indesejáveis, especialmente o hidrogênio. Entretanto, durante este processo, o fenômeno de flotação e a absorção de inclusões são reportados. O objetivo do presente trabalho foi estudar a viscosidade de escórias e a capacidade da estação de desgaseificação a vácuo do tipo tanque na limpeza de aços sob uma perspectiva industrial. Para realizar este objetivo, foram coletadas amostras de escória e aço antes e após a etapa de vácuo. Os resultados em limpeza de aço foram relacionados à energia de agitação durante o tratamento a vácuo (associada a um parâmetro cinético - βs) e ao efeito da viscosidade de escórias. É possível observar um decréscimo expressivo na população de inclusões entre as condições antes e após tratamento de desgaseificação a vácuo. A remoção de inclusões durante o vácuo atinge 64, 75 e 78% para as faixas de diâmetro de 2,5-5, 5-15 e ≥ 15 μm, respectivamente. Após o processo de desgaseificação, a composição das inclusões não-metálicas aproxima-se da composição química da escória. O processo de agitação na estação de desgaseificação a vácuo promove uma diminuição significativa na densidade de inclusões na faixa de diâmetro de 2,5-15 μm. Além disso, ao aumentar a intensidade do parâmetro cinético, a composição química de inclusões não-metálicas foi afetada e o teor de enxofre presente no aço líquido foi reduzido. Quanto às viscosidades efetiva das escórias, conclui-se que, para valores mais baixos (0,20 Pa.s) aumenta-se a capacidade da escória na remoção de inclusões, enquanto que valores mais altos (> 0,40 Pa.s) aparentaram ser prejudiciais à limpeza do aço. / There is a demand in competitiveness within the steel industry towards achieving excellence defined by clean steel term. The process of vacuum degassing (VD) occurs during the secondary refining of special steels. Its main function is to remove undesirable gases, primarily hydrogen. However, during this process, flotation phenomenon and inclusions absorption are reported. The aim of the present work was to study the slag viscosity and vacuum degassing (tank type) capacity in steel cleanliness from an industry perspective. To achieve this objective, slag and steel samples were taken before and after vacuum stage. The results in steel cleanliness were related to the stirring energy of the vacuum station (associated to a kinetic parameter – βs) and to the effect of slag viscosity. It is possible to observe an expressive decrease in the population of inclusions between the conditions before and after vacuum degassing treatment. The removal of inclusions during the vacuum stage reaches 64, 75 and 78% in the diameter ranges of 2,5-5, 5-15 and ≥ 15 μm, respectively. After the degassing process, the composition of non-metallic inclusions seemed to approach the slags’ chemical compositions. The stirring process in the vacuum degassing station promotes a significant decrease in the inclusion density with 2,5-15 μm diameter range. Also, by increasing the kinetic parameter intensity, the composition of non-metallic inclusions was affected. The sulfur content present in liquid steel was reduced. Regarding the effective viscosities of slags, it was concluded that lower values (0,20 Pa.s) increased slag capacity in inclusion removal, whereas higher values (> 0,40 Pa.s) was detrimental to steel cleanliness.

In the present work, the thermodynamic activites of ironoxide, denoted as "FeO" in the slag systems Al2O3-"FeO", CaO-"FeO", "FeO"-SiO2, Al2O3-"FeO"-SiO2, CaO-"FeO"-SiO2and "FeO"-MgO-SiO2were investigated by employing the gasequilibration technique at steelmaking temperatures. Thestrategy was to expose the molten slag mixtures kept inplatinum crucibles for an oxygen potential, determined by aCO/CO2-ratio. A part of the iron reduced from the "FeO"in the slag phase was dissolved into the Pt crucible. In order to obtain the activites of "FeO", chemical analysisof the quenched slag samples together with thermodynamicinformation of the binary metallic system Fe-Pt is required.Careful experimental work was carried out by employing asolid-state galvanic cell technique as well as calorimetricmeasurements in the temperature ranges of 1073-1273 K and300-1988 K respectively. The outcome of these experiments wasincorporated along with previous studies into a CALPHAD-type ofthermodynamic assessment performed with the Thermo-Calc™software. The proposed equilibrium diagram enabledextrapolation to higher temperatures. The experimentally obtained activites of "FeO" in thepresent work, along with earlier investigations were assessedwith the KTH slag model, THERMOSLAG©. New binaryparameters were evolved and incorporated in THERMOSLAG©.The present model calculations are compared with othercommercially available software such as F*A*C*T™andThermo-Calc™. The validity of the modified model wasinvestigated by measurements carried out in case of Al2O3-"FeO"-SiO2, CaO-"FeO"-SiO2and "FeO"-MgO-SiO2ternary slags. The potential of the model tocompute the activities in the case of multicomponent slags wasdemonstrated. A correlation between the activity of a metallic oxide in aternary slag system and the sulphide capacity of the slag wasinvestigated by using the solubility of sulphur in the binarysystems CaO-SiO2and Al2O3-CaO along with the sulphide capacity of the Al2O3-CaO-SiO2system. The estimated values of the activitieswere found to be in good agreement with the measured values.This correlation also gives the possibility to elucidate theapplicability of Henry's law to the activity of a metallicsulphide and to determine the order in the affinity of a cationto sulphur between two metallic oxides in a slag. Model calculations were performed with THERMOSLAG©, by using plant data from the ladle refiningprocess at OVAKO Steel, Hofors, Sweden. It was found thatoxygen estimations in the metal from the "FeO" analyses ofslags, obtained by conventional sampling and analysis methodwere less reliable. Reliable estimation of the oxygen levelsutilising the sulphur partition between the slag and the metalwere carried out using THERMOSLAG© software. <b>Keywords:</b>Thermodynamics, Activity, Galvanic cell,Calorimetry, Gas equilibration technique, Iron-platinum alloys,FeO, Slags, Modelling, Ladle

<p>In the present work, the thermodynamic activites of ironoxide, denoted as "FeO" in the slag systems Al₂O₃-"FeO", CaO-"FeO", "FeO"-SiO₂, Al₂O₃-"FeO"-SiO₂, CaO-"FeO"-SiO₂and "FeO"-MgO-SiO₂were investigated by employing the gasequilibration technique at steelmaking temperatures. Thestrategy was to expose the molten slag mixtures kept inplatinum crucibles for an oxygen potential, determined by aCO/CO₂-ratio. A part of the iron reduced from the "FeO"in the slag phase was dissolved into the Pt crucible.</p><p>In order to obtain the activites of "FeO", chemical analysisof the quenched slag samples together with thermodynamicinformation of the binary metallic system Fe-Pt is required.Careful experimental work was carried out by employing asolid-state galvanic cell technique as well as calorimetricmeasurements in the temperature ranges of 1073-1273 K and300-1988 K respectively. The outcome of these experiments wasincorporated along with previous studies into a CALPHAD-type ofthermodynamic assessment performed with the Thermo-Calc™software. The proposed equilibrium diagram enabledextrapolation to higher temperatures.</p><p>The experimentally obtained activites of "FeO" in thepresent work, along with earlier investigations were assessedwith the KTH slag model, THERMOSLAG©. New binaryparameters were evolved and incorporated in THERMOSLAG©.The present model calculations are compared with othercommercially available software such as F*A*C*T™andThermo-Calc™. The validity of the modified model wasinvestigated by measurements carried out in case of Al₂O₃-"FeO"-SiO₂, CaO-"FeO"-SiO₂and "FeO"-MgO-SiO₂ternary slags. The potential of the model tocompute the activities in the case of multicomponent slags wasdemonstrated.</p><p>A correlation between the activity of a metallic oxide in aternary slag system and the sulphide capacity of the slag wasinvestigated by using the solubility of sulphur in the binarysystems CaO-SiO₂and Al₂O₃-CaO along with the sulphide capacity of the Al₂O₃-CaO-SiO₂system. The estimated values of the activitieswere found to be in good agreement with the measured values.This correlation also gives the possibility to elucidate theapplicability of Henry's law to the activity of a metallicsulphide and to determine the order in the affinity of a cationto sulphur between two metallic oxides in a slag.</p><p>Model calculations were performed with THERMOSLAG^©, by using plant data from the ladle refiningprocess at OVAKO Steel, Hofors, Sweden. It was found thatoxygen estimations in the metal from the "FeO" analyses ofslags, obtained by conventional sampling and analysis methodwere less reliable. Reliable estimation of the oxygen levelsutilising the sulphur partition between the slag and the metalwere carried out using THERMOSLAG© software.</p><p><b>Keywords:</b>Thermodynamics, Activity, Galvanic cell,Calorimetry, Gas equilibration technique, Iron-platinum alloys,FeO, Slags, Modelling, Ladle</p>