Ladle slag is an internal by-product generated within the steelmaking industry during the refining of steel. The realisation of beneficial inherent properties of ladle slag as a binder supplement or substitute material is believed to be advantageous with respect to both economy and environment for steelmakers. For this reason, the current study has focused on highlighting the properties of ladle slag that are pertinent to the formation of calcium aluminate hydrates. Three fractions of ladle slag, two of which were based on different slag formers, have been characterised using XRF, XRD and calorimetric analysis. Commonly known hydraulic minerals such as mayenite, tricalcium aluminate and dicalcium silicate were detected during analysis. An important aspect in the utilisation of ladle slag is the slag handling methodology. Therefore, this study also highlights and discusses the need to reconsider slag handling procedures concerning unnecessary exposure to weathering and the possible need for further processing of the slag in order to better employ the inherent hydraulic properties of this material.

The present study is aimed at investigating the hydraulic characteristics of ladle furnace slag (LFS), under the pretence of using LFS as a cement substitute in certain applications. Furthermore, LFS has been considered as a possible activator in a blend containing 50% LFS, and 50% ground granulated blast furnace slag (GGBFS). Phases detected in LFS were quantified using Rietveld analysis. Calorimetric studies were performed at 20, 25 and 30 °C in order to calculate the apparent activation energy of hydration and thereby to suggest a kinetic model for the tested compositions within this temperature interval. In addition, compressive strength tests were performed on mortar prisms made with LFS, and LFS/GGBFS which had hydrated for 2, 7 and 28 days. Both compositions reached acceptable early strengths, (e.g. LFS, 33.1 MPa, and LFS/GGBFS, 17.9 MPa, after 2 days), but after 28 days hydration the blend was superior to neat LFS. Related apparent activation energies were determined using an Avrami–Erofeev model and gave Ea = 58 kJ/mol for neat LFS and Ea = 63 kJ/mol for the blend. The results imply that LFS or a LFS/GGBFS blend can be favourably used as supplement in binder applications such as binder in by-product metallurgical briquettes, which are used as recycle to the blast furnace or basic oxygen furnace depending on the specific briquette composition.

In the present work, the effects of the slag composition and heat-treatment conditions on the phase relationships in a number of Cr-containing industrial and synthetic slags were investigated with a view to control the precipitation of Cr-spinel in the slag phase. Gas/slag equilibrium technique was used for the chromium partition and the phase relationship study. The phase relationships in synthetic slags and industrial EAF slags supplied by Swedish steelmaking plants have been investigated experimentally in the temperature range of 1473–1873 K. The slags were re-melted, slow-cooled to, and soaked at targeted temperatures in controlled atmosphere. Two different heat-treatment sequences were used in the present experiments. The oxygen partial pressure () was maintained by a suitable mixture of CO and CO2 gases. Phases present and their compositions in the quenched slags were studied using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The chromium content in the phases present was analyzed using wavelength-dispersive spectrometer (WDS). Chromium partition was found to depend on the heat-treatment temperature

Mg-spinel phase is known to be important for control of Cr leaching from Cr-containing slags. The objective of the present study is to get an understanding of the phase relationships in the CaO-MgO-SiO2-Cr2O3 system with a view to control the precipitation of Cr-spinel in the slag phase. The equilibrium phases in CaO-MgO-SiO2-Cr2O3 slag system in the range of 1673 K to 1873 K (1400 °C to 1600 °C) have been investigated experimentally and compared with the results from thermodynamic calculations. The slag compositions close to the industrial slag systems were chosen. The Cr2O3 and MgO contents in the slag were fixed to be 6 and 8 wt pct, respectively. The basicity (CaO/SiO2) of the slag was varied in the range of 1.0 to 2.0. The slags were synthesized at a pre-determined oxygen partial pressure (10-4) or air (2.13 × 104 Pa) at a temperature above the liquidus temperature. The samples were then soaked at targeted temperatures for 24 hours in controlled atmosphere in order to achieve the equilibrium state before quenching in water. Four different heat-treatment regimes (defined as Ia, Ib, II.a and II.b) in Section II-D) were used in the present experiments. The lower oxygen partial pressure was maintained by a suitable mixture of CO and CO2 gases. Phases present and their compositions in the quenched slags were studied using scanning electron microscopy coupled with energy-dispersive spectroscopy and X-ray diffraction techniques. The chromium content in the phases present was analyzed using wavelength-dispersive spectrometer. The experimental results obtained are compared with the calculation results from Factsage software. The size of spinel crystals increased drastically after slow-cooling from 1873 K (1600 °C) followed by annealing at 1673 K (1400 °C) for 24 hours (heating regimes II) compared to samples being quenched directly after soaking at 1873 K (1600 °C) (heating regime I.a). It was found that the amount of foreign elements in the spinel phase, and other phases decreased after soaking at oxygen partial pressure of 10-4 Pa resulting in phases with less defects and foreign oxide contents compared to those treated in air. The size of spinel crystals was found to be larger in samples with lower basicity

The objective of the present work is to get an understanding of the impact of Al2O3 addition on the phase relationships in the CaO–MgO–Al2O3–SiO2–Cr2O3 slags at low oxygen partial pressures ( = 10−4 Pa), with a view to control the precipitation of Cr-spinel in the slag. The equilibrium phases in CaO–MgO–Al2O3–SiO2–Cr2O3 slag system in the range on 1673–1873 K have been investigated. The compositions close to the industrial slag systems were chosen. The Cr2O3 content was fixed at 6 wt% and MgO at 8 wt%. Al2O3 contents in the slag were varied in the range of 3–12 wt%. The basicity (CaO/SiO2) of slag was set to 1.6. Gas/slag equilibrium technique was adopted. The samples were heated to 1873 K and soaked at this temperature for 24 h. The samples were then slow cooled to 1673 K and equilibrated for an additional 24 h. The oxygen partial pressure was kept at 10−4 Pa. A gas mixture of CO/CO2 was used to control the oxygen partial pressure. After the equilibration, the samples were quenched in water. The chromium distribution and phase compositions in the quenched slags were studied using SEM–WDS and XRD techniques. The results were compared with the phase equilibrium calculations obtained from FACTSAGE software and the samples equilibrated in air. The size of spinel crystals increased drastically after slow cooling followed by annealing compared to samples being quenched after soaking at 1873 K. It was also found that low oxygen partial pressure had a strong impact on chromium partition. The amount of spinel phase increases with increased Al2O3 content.

Utilizing iron silicate copper slag as supplementary cementitious material (SCM) is a means to improve resource efficiency and lower the carbon dioxide emissions from cement production. Despite multiple studies on the performance of these slags in SCM applications, the variations in cooling procedure, grinding, and methods for evaluating reactivity limit the ability to assess the influence of chemical composition on reactivity from the literature data. In this study, a methodology was developed to synthesize iron silicate slags, which were then evaluated for their inherent reactivity using the R-3 calorimeter-based experiments. The results demonstrated that laboratory-scale granulation produced the same reactivity as industrially granulated slag. Furthermore, a synthesized triplicate sample showed high repeatability. Based on these two aspects, this method can be used to systematically study the influence of chemical composition on the inherent reactivity of iron silicate slags while producing results that are directly translatable to industrial slags.

The metallurgical and cement industries contribute significantly to anthropogenic carbon dioxide emissions. Utilizing oxidic by-products from the metallurgical industry as supplementary cementitious materials (SCMs) can improve resource efficiency and reduce emissions from cement production. Iron silicate copper slags have been studied as SCMs, but mainly in systems where Portland cement is used as an activator. There is limited research on the inherent reactivity of the slag under changing processing conditions. The present study offers insight into the effect of granulation temperature and grinding on the inherent reactivity of an industrially produced iron silicate copper slag. The results showed that granulation temperature had an insignificant effect on reactivity, while grinding generated substantial improvements. The latter effect was concluded to stem from the increased specific surface area, increased number of sites for nucleation and growth of hydrates, and changes in the inherent reactivity owing to structural changes induced by the grinding.

The transition to hydrogen-based reduction processes within the iron and steelmaking industry will generate new types of slag compositions that require valorization routes. Using slags as supplementary cementitious materials (SCMs) addresses the carbon dioxide emissions of the cement industry since the SCM requires neither calcination nor clinkering. Conventionally, ironmaking slags from the blast furnace (BF) are recycled as SCMs, i.e., ground granulated BF slag (GGBS). Ideally, future slags from electric arc furnaces (EAFs) operating on hydrogen-based direct reduced iron should be valorized analogously. Since the hydrogen-based process route is not yet realized in an industrial scale, the literature lacks data to support this valorization route, and additionally, literature on scrap-based EAF slags is scarce. Therefore, the present study aimed to offer insights into the utilization of ore-based EAF slags as SCMs based on an industrial slag sample from an EAF operating on hot briquetted iron. The slag was remelted, modified, and water-granulated in laboratory scale, and its performance as an SCM was compared to water-granulated ladle slag and two commercial GGBS. The results showed promising reactivities measured using the R3 isothermal calorimeter-based testing protocol. Based on the comparison to GGBS, the study indicated that generating reactive and appropriate SCMs from EAF slags will partly be a challenge in balancing the crystallization of the MeO-type solid solution rich in magnesia and addressing the iron oxide content in the amorphous phase.

The increased need for efficient material processing and efficient utilisation of more complex raw materials and the need for recycling or reusing byproduct and waste streams, are all increased challenges in material processing. To cope with these challenges, there is a need for new basic physical and thermodynamic data. The present paper gives four examples, as well as preliminary data, of areas where increased knowledge of fundamental parameters will increase the possibility for a sustainable extraction of metals. The examples include measurement of solubility of pure individual slag minerals, determination of distribution of leachable elements between different mineralogical phases in slag, influence of alumina on liquidus temperature of a copper slag and thermal diffusivity measurements in magnetite based iron ore pellets, all important in different ways to increase the sustainability of the respective materials involved

In the Basic Oxygen Steelmaking (BOS) process, a heterogeneous emulsion‐solid mix will form, consisting of an emulsion of liquid slag and metal droplets, in which 2nd phase particles of undissolved fluxes and solid in‐blow precipitates are suspended. When the carbon in the metal droplets reacts with iron oxide, small bubbles of CO gas are formed. If the upward movement of these bubbles is obstructed by the physical properties of the emulsion‐solid mix, foaming will occur. Certain process conditions may lead to an excessive foam growth, in the worst case forcing foam out of the vessel. This undesired process event is known as “slopping”. Extensive studies during recent decades have shown that emulsion characteristics strongly connected to foaming are: viscosity, surface tension, and density. The extent of foaming is also dependent on bubble size; foaming increasing with smaller bubble size. However, investigations into the influence of the mineralogy and morphology of the emulsion‐solid mix on foaming in basic oxygen steelmaking are scarce. In this work, samples from trials in a 6‐tonne pilot plant BOS vessel are examined by XRD and with SEM for the determination of emulsion‐solid mix mineralogy and morphology at different stages of the oxygen blow. The study confirms the importance of tight process control in order to minimize the emulsion‐solid mix apparent viscosity and, hence, the foam height, but this without over‐oxidizing the liquid slag phase, which would result in increased gas generation within the slag‐metal emulsion.

Slags are an indispensable tool for the pyrometallurgical industry to extract and purify metals at competitive prices. Large volumes are produced annually, leading to important economical and ecological issues regarding their afterlife. To maximise the recycling potential, slag processing has become an integral part of the valorisation chain. However, processing is often directed solely towards the cooled slag. In this article, the authors present an overview of the scientific studies dedicated to the hot stage of slag processing, i.e. from the moment of slag/metal separation to complete cooling at the slag yard. Using in-depth case studies on C2S driven slag disintegration and chromium leaching, it is shown that the functional properties of the cooled slag can be significantly enhanced by small or large scale additions to the high temperature slag and/or variations in the cooling path, even without interfering with the metallurgical process. The technology to implement such hot stage processing steps in an industrial environment is currently available. No innovative technological solutions are required. Rather, advances in hot stage slag processing seem to rely primarily on further unravelling the relationships between process, structure and properties. This knowledge is required to identify the critical process parameters for quality control. Moreover, it could even allow to consciously alter slag compositions and cooling paths to tailor the slag to a certain application.

The Swedish steelmaking industry produces large amounts of by-products. In 2006, the total amount of slag produced reached approximately 1 375 000 metric tons, of which 30% was deposited. Due to its strength, durability and chemistry, steel slag is of interest in the field of construction due to it's similarities with ordinary ballast stone. However, some steel slags face an array of quality concerns that might hinder their use. These concerns generally involve the following physical and chemical properties: Volume expansion, Disintegration, Leaching of metals By controlling and modifying process parameters during slag handling in liquid state, the physical properties of steel slags can be adequately modified to obtain a high-quality product for external application. The present work was undertaken as a research project within the Minerals and Metals Recycling Research Centre, MiMeR. The major objectives of this work have been to investigate how different cooling methods and cooling rates influence the properties of slag products. Four types of steel slags, Ladle slag, BOF (Basic Oxygen Furnace) slag and two different EAF (Electric Arc Furnace) slags, were characterized and modified by semi-rapid cooling in crucibles and rapid cooling by water granulation. Experiments were conducted in laboratory scale using an induction furnace. Analysis techniques used in this investigation include: thermodynamic calculations using FactSageTM, X-ray diffraction analyses (XRD), scanning electron microscope (SEM) and a standard leaching test (prEN 12457-2/3). The experimental results show that disintegrating ladle slag is volume stabilized by water granulation resulting in a product consisting of 98% glass. However EAF slag 1, EAF slag 2 and the BOF slag formed only 17%, 1% and 1% glass, respectively. The leaching tests showed that water granulation did not prevent leaching of minor elements from the modified slags. The solubility of chromium, molybdenum and vanadium varied in the different modifications, probably due to their presence in different minerals. Variations in crystal size as well as phase composition and distribution were observed in the different materials as a result of different cooling methods. The magnesium content of the wustite-type solid solution (Fe,Mg,Mn)O in BOF slag increased when rapid cooling was used. The reactivity factor, á, was calculated for the BOF and EAF slag 1. A majority of the elements of interests in the slags became more reactive when cooled rapidly. The reactivity for silica in BOF and EAF slag 1 was increased by ~4700% and ~1200%, respectively, and for chromium by ~5300% and ~1500%.

The Swedish steelmaking industry produces large amounts of by-products. In 2008, the total amount of slag produced reached approximately 1,300,000 metric tons, of which 20% was deposited. Due to its strength, durability and chemistry, steel slag is of interest in the field of construction, since it has similar or better qualities than ordinary ballast stone, which makes it a competitive construction material. However, some steel slags face an array of quality concerns that might hinder their use. These concerns generally involve the following physical and chemical properties:Volume expansion Disintegration Leaching of metalsBy controlling and modifying process parameters during slag handling in liquid state, the physical and chemical properties of steel slags can be adequately modified to obtain a high-quality product for external application. The present work was undertaken as a research project within the Minerals and Metals Recycling Research Centre, MiMeR. The major goal of this work has been to investigate how different treatment methods including hot stage processing, cooling rates, ageing time and chemical composition influence the final properties of the slag. Analysis techniques used in this investigation include: thermodynamic calculations using FactsageTM, X-ray diffraction analyses (XRD), scanning electron microscopy (SEM), leaching tests (EN12457-2/3) and thermo-gravimetric analyses (TG).The results from this study show that it is possible to control/change the properties of the final product by additions to the liquid slag, thereby changing the chemical composition, as well as by varying the rate and method of cooling. The mineralogical composition, the size of the crystals and the composition of some solid solutions are affected by the cooling rate. The solubility of elements such as chromium and molybdenum varies, probably due to their presence in different minerals. The reactivity of the investigated slag samples increases as the cooling rate increases.When steel slags are aged, the leaching properties of the materials are changed. The total leachability and the pH decrease for all the investigated samples. All elements except magnesium decrease in leachability. As the slags are aged CaCO3 is formed on the slag surfaces. The degree of carbonation differs between different slags, due to the presence of different calcium-rich minerals in the slag. In order to form CaCO3, the calcium-containing mineral must be dissolved. This means that the solubility of the calcium-containing mineral will affect the outcome of the carbonation. The rate of dissolution for six typical slag minerals was investigated in order to distinguish the difference in solubility between the different minerals. Acidic to alkaline pHs (4, 7 and 10) were selected to investigate the solubility of the minerals under conditions comparable to those prevailing in newly produced slags and the potential future pH values obtained under acid conditions. It can be concluded that all six minerals behave differently when dissolving and that the rate of dissolution is generally slower at higher pH. At pH 10, the solubility of merwinite, akermanite and gehlenite is considered slow. The dissolution of γ-Ca2SiO4 is not affected in the same way as the other minerals when the pH is changed.

Large amounts of oxidic by-product are annually produced by the steel industry worldwide. By far the largest in volume is slag, generated from different stages of steel production. In order to avoid landfilling, steelmakers usually try to process the slag into useful resources that can be used externally. However, leaching of different metals can sometimes be a problem. Since steel slags are a mixture of numerous types of minerals, the solubility of each mineral will affect the outcome of the leachability. The aim of this study was to investigate how six common slag minerals behave during dissolution. Mayenite (Ca12Al14O33), merwinite (Ca3MgSi2O8), akermanite (Ca2MgSi2O7), gehlenite (Ca2Al2SiO7), γ-dicalcium silicate (γ-Ca2SiO4) and tricalcium aluminate (Ca3Al2O6) were synthesized and their dissolution was evaluated through titration using HNO3 at constant pH. Acidic to alkaline pHs (4, 7 and 10) were selected to investigate the solubility of the minerals under conditions comparable to those prevailing in newly produced slags, and one pH value, representing acid conditions. It can be concluded that all six minerals behave differently when dissolving and that the rate of dissolution is generally slower at higher pH values, which are normal in the case of steelmaking slags. At pH 10, the solubility of merwinite, akermanite and gehlenite is considered low. The dissolution of γ-Ca2SiO4 is not affected in the same way as the other minerals when the pH is changed.

The present study was aimed at highlighting the final properties of two different steelmaking slags which undergo different cooling rates. The experiments were conducted in laboratory scale using an induction furnace. One of the slags originates from an electric arc furnace (EAF) (high-alloyed) and the second slag from a basic oxygen furnace (BOF). The treatment of the slag included re-melting along with different cooling rates. The material collected from the tests was characterized through X-ray diffraction, scanning electron microscopy as well as thermodynamic calculations which were compared with experimental results, for confirmation. The results indicate that both the EAF and BOF slags show increased reactivity with water, as well as a decrease in crystal size when rapid cooling is applied. The wüstite-type solid solution (Mg,Fe,Mn)O varies in composition depending on the cooling conditions. Metastable Ca3SiO5 was found in the rapidly- cooled BOF slag.

Large amounts of slag are generated by the Swedish Steel Industry each year. The Electric Arc Furnace process generates about 200 000 ton of slag per annum, from which approximately 40% is deposited. An alternative to deposit is to use slag as road construction material. However, leaching of metals from the slag can be a reason to limit slag use in road construction. The aim of this work was to investigate how stable these materials are when aged, in an environment open to seasonable weather conditions, with respect to leaching and mineralogy. Three different EAF-slags from domestic steel plants were used in this study. The materials were characterized after 0, 6, 12, 18, and 24 months to evaluate the ageing process. The analytical techniques that were used to evaluate the effect of ageing are scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and a standard test for leaching. The changes in ageing behavior differ between the three materials. The conductivity and the pH decreases with time for all samples. The leaching of calcium, chromium as well as aluminum decreases with time while the leaching of magnesium increases. CaCO3 was formed on slag surfaces as CaO reacts with moisture and CO2 from the air.

Large amounts of by-products are generated by the Swedish steel industry each year. The EAF-process generates about 400 000 ton of slag, from which 80% is deposit. An alternative to deposit is to use slag as road construction material. However, metal content in the slag can be a problem, due to the leaching. The aim of this work was to investigate how stable these materials are when ageing and kept outside. Five different EAF-slags from domestic steel plants were used in this study. The materials were characterised after 0, 6, 12, 18 and 24 month to evaluate the ageing process. Scanning electron microscope (SEM), x-ray diffraction pattern (XRD) and a standard test for leaching were used. The changes in behaviour differ between the five materials. The total leachability decreases with time for all samples. CaCO3 is formed on slag surfaces as CaO reacts with moister and CO2 in the air.

A number of studies are briefly reviewed dealing with hot stage processing of slags, i.e. additions during the molten state and variations of the cooling path, and the influence on the microstructure and properties of solidified slags. Emphasis is placed on research and developments in the last five years, although other works that created the thinking framework for several of the current practices are also mentioned. The additions include: a) quartz sand with concurrent oxygen injection for the minimisation of free CaO and MgO, b) various materials for the modification of the composition of liquid blast furnace slag after tapping, c) borates and boron wastes and their distribution in both synthetic and industrial stainless steel slags, d) phosphates in stainless steel slags and their distribution in BOF slags e) waste glass and fly ash for the stabilisation of stainless steel slags, f) K2CO3 for the production of potassium silicate fertiliser from steelmaking slag and g) bauxite, Al2O3 containing residues and aluminium metal that enhance the Cr recovery and minimise leaching in EAF slags. In terms of cooling, the effect of cooling rate on the final mineralogy, as a way to stabilise stainless steel slags and to control free lime formation in BOF slags, is presented. A more in-depth discussion regarding leaching performance, which has been identified as a key issue in slag valorisation, is also taking place. Although it is acknowledged that many research questions are still open and that both technical and economical barriers exist, it is strongly believed that a conscious hot stage processing step can both increase slag utilisation rates and make higher value applications achievable.

Mechanical activation of granulated copper slag (GCS) is carried out in the present study for the purposes of enhancing pozzolanic activity for the GCS. A vibration mill mills the GCS for 1, 2, and 3 h to produce samples with specific surface area of 0.67, 1.03 and 1.37 m²/g, respectively. The samples are used to replace 30% cement (PC) to get 3 PC-GCS binders. The hydration heat and compressive strength are measured for the binders and derivative thermogravimetric /thermogravimetric analysis (DTG/TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) are used to characterize the paste samples. It is shown that cumulative heat and compressive strength at different ages of hydration and curing, respectively, are higher for the binders blending the GCS milled for a longer time. The compressive strength after 90 d of curing for the binder with the longest milling time reaches 35.7 MPa, which is higher than the strength of other binders and close to the strength value of 39.3 MPa obtained by the PC pastes. The percentage of fixed lime by the binder pastes at 28 days is correlated with the degree of pozzolanic reaction and strength development. The percentage is higher for the binder blending the GCS with longer milling time and higher specific surface area. The pastes with binders blending the GCS of specific surface area of 0.67 and 1.37 m²/g fix lime of 15.20 and 21.15%, respectively. These results together with results from X-ray diffraction (XRD), FTIR, and SEM investigations demonstrate that the mechanical activation via vibratory milling is an effective method to enhance the pozzolanic activity and the extent for cement substitution by the GCS as a suitable supplementary cementitious material (SCM).

GCS, granulated copper slag, is currently utilized in cement and concrete with a low rate, due mainly to its low pozzolanic activity. The present study was thus performed by first mixing the GCS with CaO, and then melting and water-granulating the GCS-CaO mixtures, as to enhance the reactivity of GCS. Blended cements were formulated by replacing 30 wt. % of the cement, PC, with the modified GCS. The addition of CaO in GCS increased the release rates of heat from the early-age hydration of the blended cement pastes. The pastes with CSC20, the GCS of the highest CaO content (19.5%), acquired higher compressive strengths than those for the PC and other PC-GCS pastes at both 28 and 90 days of curing. The GCS richer in CaO consumed more calcium hydroxide for the formation of calcium silicate hydrates, with SEM micrographs showing a microstructure of more gel phases and less pores in PC-GCS paste. These results indicate that the modification by addition of CaO is an effective way to achieve a high reactivity for the GCS. It may then be possible to utilize the modified GCS as a high-quality supplementary cementitious material to enhance the sustainability for both copper and cement industries.

The neutralisation cost in bioleaching operations is one of the biggest operation costs and therefore the aim of the present study has been to replace the generally used lime/limestone with industrial oxidic by-products. A comparative study on the potential use of some selected industrial by-products as neutralising agents during biooxidation and their influence on subsequent gold recovery was carried out with reference to a commercial grade Ca(OH)2. The by-products used comprised of an electric arc furnace slag (EAF slag), and a slag from ladle refining (Ladle slag) both from scrap based steel production, an EAF dust and a lime sludge from paper and pulp industry (Mesa lime). Continuous biooxidation of a refractory gold concentrate was performed in single stage reactor at a retention time of 56 h with a mixed mesophilic culture. Biooxidation results as well as gold recoveries were good for all by-products investigated and similar to the results obtained with the slaked lime reference. However, cyanide consumption was elevated in the experiments with steel slags and the EAF dust partly because of a higher content of S° in the bioresidues in these experiments. It is however expected, that in a bioleaching operation with several reactors in series, that sulphur oxidation would be more complete, thereby possibly decreasing cyanide consumption.

The neutralization cost in bioleaching operations is one of the biggest operation costs and therefore the aim of the present study has been to replace the generally used lime/limestone with industrial oxidic by-products. A comparative study on the potential use of some selected industrial by-products as neutralizing agents during biooxidation and their influence on subsequent gold recovery was carried out with reference to a commercial grade Ca(OH)2. The by-products used comprised of an electric arc furnace slag (EAF slag), and a slag from ladle refining (Ladle slag) both from scrap based steel production, an EAF dust and a lime sludge from paper and pulp industry (Mesa lime). Continuous biooxidation of a refractory gold concentrate was performed in single stage reactor at a retention time of 56 h with a mixed mesophilic culture. Biooxidation results as well as gold recoveries were good for all by-products investigated and similar to the results obtained with the slaked lime reference. However, cyanide consumption was elevated in the experiments with steel slags and the EAF dust partly because of a higher content of S in the bioresidues in these experiments. It is however expected, that in a bioleaching operation with several reactors in series, that sulfur oxidation would be more complete, thereby possibly decreasing cyanide consumption.

A study on the possibilities to utilise steel slag as neutralising agent in biooxidation of a refractory gold concentrate has been done with reference to commercial grade slaked lime. The idea has been to reduce the operating costs for neutralisation in the biooxidation plant, which is known to be the second largest operating cost. Other benefits would be savings in cost for landfilling of slag, possibilities to recycle elements present in the slag and savings of virgin limestone deposits. The slags used were an EAF slag and a slag from ladle refining; both originating from Swedish scrap based steel-making. Continuous biooxidation of the refractory gold concentrate was conducted in a single-stage 5 L reactor at a retention time of 56 h. The neutralisation capacity was determined by comparing the amount needed, per ton of feed concentrate added, to maintain the desired pH of 1.5 during steady state operation. Slaked lime had the highest neutralisation capacity with 110 kg/ton feed followed by ladle slag and EAF slag with values of 152 and 267 kg/ton feed, respectively. Sulphide mineral oxidation was similar and high in all cases although the ladle slag results were slightly better. Gold recoveries after cyanide leaching on the residues obtained were also similar and were in the range of 86–89%. However, the cyanide consumption expressed as kilogram cyanide per ton of concentrate fed to biooxidation, was double in the case of ladle slag and three times as much for the EAF slag compared to the slaked lime experiment. The increased cyanide consumption could not be explained only by the increased amount of elemental sulphur obtained in the slag experiments. The elemental sulphur formed had different reactivities as seen from the thiocyanate formation and cyanide losses due to thiocyanate formation were 16%, 32% and 40% for EAF slag, slaked lime and ladle slag, respectively. It is concluded that the ladle slag could be a possible replacement for limestone if they are mixed in proper proportions so that the microbial carbon dioxide demand is met whereas the EAF slag is less suitable due to the very fine reaction products obtained which gave operational problems with filtration and washing. To come further, experiments with the normal multi-stage biooxidation set-up with total retention time of 120 h should be performed which would increase the sulphur oxidation and eventually also reduce the cyanide consumption.

Super-hot acid leach residue is generated during zinc production in the roasting–leaching–electrowinning route, where both primary and secondary resources are used as feed material. This residue may contain valuable metals, such as lead, zinc, and iron, as well as precious metals, such as gold and silver. Four materials, namely super-hot acid leach residue, a residue formed when super-hot acid leach residue is selectively leached for lead with triethylenetetramine, as well as flotation concentrate, and flotation tailings formed in a selective silver flotation process with super-hot acid leach residue as the feed material were characterized to obtain a deeper understanding of possible further metal extraction. These four materials were characterized for chemical composition, mineralogy, and mineral distribution via chemical analyses, X-ray diffraction, and energy-dispersive scanning electron microscopy, respectively. The scanning electron microscope images showed that the materials have large variations in particle size distribution and composition. The results showed that the main lead phase in super-hot acid leach residue is lead sulfate, whereas it is mostly converted to lead sulfide during the selective lead leaching of the super-hot acid leach residue. The remaining lead sulfate is found in a solid solution with barium sulfate. Extracting lead from super-hot acid leach residue via triethylenetetramine leaching resulted in increased concentrations of gold and silver by 41% and 42%, respectively. The identified silver phases in super-hot acid leach residue may correspond to silver sulfide, silver chloride, and elementary silver, where silver sulfide was the most commonly occurring silver phase. After leaching this selectively for lead with triethylenetetramine, similar silver phases were identified, but silver sulfide and silver chloride occurred to a similar extent. Additionally, silver copper sulfide was detected. The presence of different silver phases might pose a challenge to reaching high silver recovery during leaching as the optimum leaching conditions differ somewhat. Furthermore, elemental sulfur, with a tendency to coat gold and silver particle surfaces, which is indicated to be present in all materials except the silver flotation tailings, may hinder metal extraction.

To enhance utilization of wastes generated from steelmaking, a BOF slag sample from Ning Steel group in China is treated by oxidizing at 1500 °C for 30 min and then cooled by different methods. The treated samples are characterized, in combination with calculations using FactSage 6.4. XRD results show that iron oxides in BOF slag are converted largely by the oxidation to spinel phases, Fe₃O₄ and MgFe₂O₄, which also eliminates free CaO and MgO. EDS analyses show Fe element existing in di-calcium silicate and glass phase, which are Fe³⁺ ions formed by oxidation. An incorporation of Fe³⁺ ions into crystal structures has stabilized high temperature polymorph of C₂S, β-C₂S, and α’-C₂S, in the treated slag samples. Fe³⁺ ions may also act as a network former to facilitate glass formation. This may make it possible for the glass and α’-C₂S phase to complement each other, leading to a higher hydraulicity, while the BOF slag, after the spinel separation, is blended in cements. Some suggestions are proposed, based on the present and early studies, to enhance hydraulicity for the BOF slag, as well as grain sizes of spinel phases, which may result in economic and environmental benefits for steel and cement industries.

The zinc in the fayalite slag of copper smelters, in which Zn-containing raw materials are used, is mainly found to be in oxidic phases, such as glassy iron silicate. During the slag water granulation process, the molten slag is heated, whereby the granulated slag achieves varying granulation temperatures. Therefore, in this study, we aimed to characterize and assess the leaching behavior of a synthesized Fe-saturated (FeX,Zn(1−X))2SiO4 system to understand the dependance of the zinc leaching behavior on the parameters of the ZnO content (1–10 wt.%) and granulation temperature (1300 or 1400 °C). It was found that the Zn leaching increased with the increasing Zn content and granulation temperature, using both batch and static pH leaching methods. Zn leaching was further increased at pH 5 using diluted nitric acid under oxidation conditions. Among the oxides in the samples—fayalite, spinel, and glass—glass was found to contribute to Zn leaching, owing to its weathering during pH-titration.

Granulated iron silicate slag, a by-product of pyrometallurgical copper extraction, has excellent properties for construction applications. Slag modification with CaO enhances the application properties regarding pozzolanic reactivity, potentially extending slag use in the future. The slags’ short-term leaching behavior has already been investigated with promising results, while the long-term leaching effects are less studied. Therefore, this study aims to determine the long-term leaching effects on CaO-modified iron silicate slags. The CaO-modifications were conducted during full-scale slag treatment operation. The slags were characterized and leached, and the remaining slags were investigated regarding the formation of secondary phases. The long-term leaching of main and trace elements was determined over 30 days using a dynamic leaching method corresponding to an extended time period. The leaching tests showed increased leaching of the main slag elements (Si, Ca). Zn and Cu showed peak leaching after four days of leaching, and the leaching of As and Sb decreased with the increasing CaO content in the samples. After dynamic leaching, secondary phases formed on the Cu-containing inclusions on the sample surfaces. Independent of the CaO content, the leaching of Cu was increased when subjected to external acidic and oxidating conditions using static pH titration at pH 5 in dilute nitric acid.

Due to increased copper production and the associated environmental consequences, copper production processes need to be improved, considering the impact of their byproducts, among others slag. This study investigated the leaching of individual constituents of iron silicate slag from a copper smelter. This was done by characterising granulated samples of its constituents – glass, matte, speiss – to determine their leaching contribution. It was observed that leaching in distilled and deionised water without pH regulation achieved various natural pH for the constituents. At natural pH, glass (Cu, Zn) and speiss (Ni, Sb) contributed to leaching. Static pH titrations showed the increased leaching of Zn, Cu, Ni, As, and Sb with decreasing pH. The results showed that, an iron silicate slag consisting of glass, matte and speiss, contributes to leaching as follows: matte – Cu and Ni, speiss – Cu, Ni, As, and Sb. Zn leaching is similar among the constituents.En raison de l’augmentation de la production de cuivre et des conséquences environnementales associées, on a besoin d’améliorer les processus de production du cuivre, tenant compte de l’impact de leurs sous-produits, parmi lesquels les scories. Cette étude a examiné la lixiviation des constituants individuels des scories de silicate de fer provenant d’une fonderie de cuivre. Ceci a été accompli en caractérisant les échantillons granulés de ses constituants –verre, matte, smaltite–pour déterminer leur contribution à la lixiviation. On a observé que la lixiviation dans de l’eau distillée et désionisée sans régulation du pH atteignait divers pH naturels pour les constituants. Au pH naturel, le verre (Cu, Zn) et la smaltite (Ni, Sb) contribuaient à la lixiviation. Les titrages de pH statique ont montré une augmentation de la lixiviation du Zn, Cu, Ni, As et Sb avec une diminution du pH. Les résultats ont montré que les scories de silicate de fer composées de verre, de matte et de smaltite contribuent à la lixiviation comme suit: matte–Cu et Ni, smaltite–Cu, Ni, As et Sb. La lixiviation du Zn est similaire parmi les constituants.

Water-granulated CaO-modified iron-silicate slags have shown beneficial properties for cement applications. To further evaluate potential applications, the leaching properties must be understood. Therefore, this study aims to characterise and assess the metal leaching of iron-silicate slags (2.6% CaO) modified with lime (CaO, up to 20 wt.%) produced on both laboratory and industrial scales. The granulated samples showed amorphous contents for the studied CaO range. Generally, the metal content of the samples decreased with the increasing CaO content. Batch leaching tests were conducted on the slags, and the metal leaching and CaO content of the slag were strongly correlated. The leaching of Zn and Cu decreased with the increasing CaO content in the slag. Overall, the slags with 12–13% CaO exhibited minimal leaching of Zn, Cu, Ni, and Sb. These findings indicate that CaO influences the properties of the slag and can suppress metal leaching from water-granulated iron-silicate slags.

Chalcopyrite (CuFeS₂) is the most economically important and most refractory copper mineral when treated in conventional sulphate media leaching systems. In this study, the effect of solution redox potential on leaching of a pure and a pyritic chalcopyrite concentrate was investigated using concentrates with fresh and aged surfaces. In experiments using concentrates with fresh surfaces, the response to redox potential depended on the presence of pyrite: fresh pyritic concentrate leached more effectively at low redox potential (in agreement with reductive leaching mechanisms), while the leaching efficiencies from fresh pure concentrate were similar at high and low redox potentials. The data suggested that the reductive leaching mechanism does not necessarily result in higher and faster recoveries in the absence of the galvanic interaction induced by the presence of pyrite. It was also found that exposure of chalcopyrite to atmospheric oxidation prior to leaching (ageing) had an effect on leaching behaviour in response to redox potential: copper recoveries in leaching of aged concentrates were higher at high redox potentials. This behaviour was attributed to the presence of iron–oxyhydroxides on the surface of aged concentrates. Based on the data from this investigation and previous surface studies, it is proposed that iron–oxyhydroxides play an important role in triggering the hindered dissolution of chalcopyrite.

The results from a characterization of buildup in an electric smelting furnace for treating copper-rich feed material at the Boliden Rönnskär smelter in Sweden are presented. The aim of the work was to obtain better knowledge about the mechanisms behind the formation of the buildup. Samples from the buildup were taken during the rebuilding of the furnace. The samples were characterized using chemical and mineralogical techniques. The buildup consists mainly of different phases such as spinel, matte, olivine and metalloids and has a complex and varying mineralogy, which indicates that the buildup is not formed under equilibrium conditions.

Building on previous work reported in the literature, a dynamic model of the operation of the Peirce-Smith Converter has been developed to describe the distribution of the major elements present. The fundamental principle of the model was a thermodynamic calculation. The situation of non-equilibrium conditions was considered by dividing the converter into different zones linked by predefined flow parameters. The model was verified against actual converter plant data, with the simulated results for the major elements being in good agreement with the plant data. The agreement between plant and calculated data for Pb, and Zn was not as good and more work is required regarding this aspect.

Process simulation is an important tool for understanding the impact of process parameters on the product quality and for the purpose of process optimisation. In the present work a dynamic, non-equilibrium model based on thermodynamics over the Peirce-Smith converter has been developed. The non-equilibrium conditions have been simulated by introducing individual but linked segments. The purpose of using segments was to consider different reaction zones which yield different conditions within the converter. The model was validated using plant data and showed good agreement for the major elements

The effect of adding black copper, originating from treating waste electrical and electronic equipment (WEEE), to a Peirce-Smith converter has been investigated by using a thermodynamic process model. The model was formulated, by the authors, in an earlier publication and expanded, in the present work, to include the minor elements antimony and bismuth. The results show that the model describes the distribution of Bi well, whereas the distribution of Sb is not described as well and should only be used for trends. Addition of black copper lowers the removal of Bi and Sb compared to a converter cycle without addition. To maintain a good removal of Bi and Sb, black copper should be added as early as possible during a converter cycle.

Thermodynamic calculations were used to investigate the liquidus temperature of the slag and the possible influence on the buildup formation in an electric copper smelting furnace. The impact of parameters such as Fe/SiO₂ ratio, partial pressure of oxygen and the content of the oxides ZnO, Al₂O₃ and Cr₂O₃ in the slag were investigated with respect to the liquidus temperature of the slag. Results show that the chromium content in the slag has the greatest impact on the liquidus temperature and on the formation of solid particles. The characterization of the buildup done earlier showed that spinel phases were among the dominating phases. This is supported by the thermodynamic calculations in the present paper, where the chromite solid solution was found to be the primary precipitation phase.

Due to environmental regulations, steel producers in Europe, are obliged to reduce the amount of landfilled material, which is mainly slag. By fulfilling technical and environmental criteria, slag can be used in civil engineering applications. One of the most important environmental considerations is the leaching behaviour of the slag, especially with respect to chromium. A considerable research effort has been devoted to decrease the leaching of chromium from the slags by forming stable spinel phases. Most of the existing work focused on spinel forming agents. In this paper, influences of three different already formed spinels, in three different amounts, on an EAF slag from a low alloyed steel production are investigated. After re-melting and solidification, mineralogical properties of the samples were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Only one of the additives resulted in formation of distinguishable chromium rich spinels, which could immobilize chromium. The results are discussed by comparison with stable phases at equilibrium based on thermodynamic calculations.

It has been proven that pyrometallurgical slags can be given favorable physico-mechanical characteristics which make them suitable for use in civil engineering applications providing fulfillment of various technical and environmental criteria, of which slag leaching behavior is one of the main concerns. Numerous investigations have been carried out over the last several decades to clarify the influence of cooling rate on microstructure and properties of the slag systems; however, there is controversy in the literature as to the effect of rapid cooling, e.g. water granulation, on release of potentially toxic elements. In the current work, a ladle slag, a basic oxygen furnace (BOF) slag, two different electric arc furnace (EAF) slags, from low-alloyed and high-alloyed steel production, and three different “fayalite-type” slags, from zinc-copper smelting processes with different Fe/SiO2 ratios, are investigated. Semi-rapidly solidified (in crucible system) and water granulated samples for each composition were prepared. The solidified materials were characterized using commonly applied characterization techniques. The experimental work is compared with thermodynamic calculations using the FactSageTM thermodynamic package. Standard European leaching tests were carried out for all samples to investigate the slag leaching behaviors. Results show that rapid solidification and generated amorphous structure do not necessarily immobilize environmentally concerned elements in the glassy network. Instead, due to several factors, a higher reactivity is observed and trace elements dissolve more readily in the aqueous solution. The main reasons behind such a behavior including higher contents of metastable phases, different surface structures, oxidation and increased amount of grain boundaries are thoroughly discussed.

The presence of halogens has an adverse effect on the zinc extraction process through electrowinning, the last phase of the RLE (Roasting, Leaching and Electrowinning) zinc extraction route. Fluoride (F⁻) may be present as calcium fluoride (CaF₂) and this is, for example, the case in double leached Waelz oxide (DLWO). Efficient removal of F⁻ from primary and secondary raw materials for zinc extraction results in a simplified process and increases flexibility in the selection of raw materials. Understanding of the solubility behavior of pure CaF₂ can give valuable information on treatment for maximized halogen removal. Dissolution of CaF₂ was studied with the addition of sodium carbonate (Na₂CO₃) and sodium bicarbonate (NaHCO₃). Dissolution studies were combined with thermodynamic calculations to understand the solubility behavior of CaF₂ under different conditions. Results from the experiments and the thermodynamic calculations show that Na₂CO₃ and NaHCO₃ have similar behavior if the pH is controlled at the same value. The available carbonate (CO₃²⁻) ion in the system limits the concentration of calcium (Ca²⁺) ion by precipitation of CaCO₃, which enhances the dissolution of CaF₂. At higher temperatures and pH, calcite, vaterite, and aragonite were formed and co-precipitation of CaF₂ along with calcium carbonate (CaCO₃) was observed. At lower temperatures and lower pH levels, only calcite and vaterite were formed and a coating by CaCO₃ on CaF₂ was found to hinder complete dissolution reaction. The results of this study indicate that the temperature along with the reagents used for the dissolution tests have a significant impact on the CaCO₃ polymorph mixture (calcite, vaterite and aragonite) formation.

Double leached Waelz oxide (DLWO), with 76% zinc, is a secondary zinc containing raw materials obtained by the treatment of electric arc furnace dust. The content of fluoride in DLWO is still too high for direct leaching, as fluoride has a detrimental effect on electrowinning for zinc production. Knowledge of the characteristics of DLWO, and especially on how a fluoride mineral might exist, can contribute to further improvement of the selective leaching for the removal of fluoride. In this study, DLWO was characterized using analytical techniques, such as inductively coupled plasma-optical emission spectroscopy (ICP-OES), 19F liquid-state nuclear magnetic resonance (19F LS NMR), X-ray powder diffraction analysis (XRD), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) and 19F solid-state nuclear magnetic resonance (19F SS NMR). This study showed that DLWO mainly consisted of zincite (ZnO), cerussite (PbCO₃) and a spinel containing zinc, iron and manganese. The fluoride mineral identified was calcium fluoride (CaF₂). In SEM analysis, fluorine was found in larger grains together with calcium and oxygen, which was possibly calcium carbonate.

Slag produced as a by-product from steelmaking is not utilized to the extent that could be possible. In Sweden and Europe, too much steelmaking slag is still deposited in landfills. Of the slag that is re-used, most is used in road construction, whereas the amount used in other more high-value applications is very low. The main technical reasons for the limited re-use of steelmaking slags are usually: slag disintegration, slag expansion and leaching from the slag, of which the latter is the most difficult to control. This paper discusses the relationships between the mineralogy of steelmaking slag and factors such as leaching of chromium and ageing of the slag. Examples from laboratory experiments and full-scale trials to modify the slag are given.

Leaching of slag must be limited when slag is used in other areas than landfill. As slag is composed of different minerals, the properties of slag, inter alia the dissolution, depend on these minerals. If the leaching properties of each mineral are known, counter measurements can be taken to prevent the leaching of unwanted elements. In this study, the dissolution of three common slag minerals will be examined. The three minerals; boron-stabilised β-dicalcium silicate, pseudowollastonite and monticellite were synthesised. The dissolution was measured by setting pH to 4, 7 or 10 and adding 0.05 g mineral in the size range 20-38 μm, and the HNO3 consumption required 3 to maintain the pH level was recorded during 40 h. As expected, the dissolution increases for all minerals when pH decreases. The boron- stabilised β-dical cium silicate was the only mineral fully dissolved at all pH levels, while pseudowollastonite and monticellite only dissolved completely at pH 4.

Due to excellent properties as a construction material slag is rising in popularity as a resource. However, some properties prevent usage, one of those is leaching of chromium. The leaching of slag is governed by the solubility of theminerals. By eliminating soluble minerals that contain chromium the chromiumleaching should decrease. In some low alloy EAF slag, brownmillerite, has beensuspected to leach chromium. By increasing the basicity of slag the formation of brownmillerite should be avoided. Low alloy EAF slag with basicity of 2.7 was altered by remelting the slag with SiO₂ additions. The mineralogical composition was identified using SEM EDS and XRD. Slag samples were treated inan autoclave to simulate ageing. The autoclave treatment was successful as theremelted slag without modification leached with the same magnitude as the naturallyaged reference sample. At basicity 2.7, the investigated slag had the highest leaching of chromium, at average 2 mg/kg. The chromium leaching decreased to 0.2 mg/kg at basicity 2.4. The decrease of chromium leaching was connected to the decrease of brownmillerite. Lower basicity did not eliminate leaching ofchromium as merwinite, another mineral able to contain chromium, was formed instead of brownmillerite.

Ovako Hofors has adopted a zero-waste vision. The purpose of this vision is to identify application areas for all residues as alternatives to deposition. In terms of tonnage, the largest residue from the steel production at Ovako in Hofors is the slag from the electric arc furnace, EAF. The properties of EAF slag make it an excellent construction material, for instance, as an aggregate in asphalt. The leaching of chromium must be controlled if the slag is to be used as construction material in an environmentally friendly way. Ovako Hofors is actively working to keep the leaching of chromium at a low level. Progress has been made earlier by introducing dolomite in the slag forming agents. Phases capable of stabilising chromium are spinels and solid solution of MgO. The aim of this work is to investigate if it is possible to completely prevent leaching of chromium by stabilising the solid solution of MgO by increasing the FeO content.All the experiments were performed in the EAF at Ovako Hofors. Three different methods to raise the FeO content in the slag were tried and evaluated. Slag produced earlier was used as reference samples. From each test, three different slag samples were collected and analysed. To evaluate the results SEM, XRD, leaching and chemical analyses were conducted.A new oxygen burner increased the iron oxide content, while the other two methods did not show any additional increase. Leaching of chromium could only be detected in a few of the slag samples. Although this makes correlations harder to see, it indicates that a higher FeO content may affect the leaching in a positive way. It was discovered that the leaching of chromium does not depend on the chromium content in the slag, thereby proving the hypothesis that chromium can be bound in stable phases to prevent it from leaching.

Brownmillerite is connected to chromium leaching when present in steel slags. To prevent chromium leaching, brownmillerite in slag should be prevented. Two methods for decreasing brownmillerite content in low-alloy electric arc furnace (EAF) slag were investigated: decreasing the basicity and increasing the cooling rate. The methods were tried on both laboratory scale and in full-scale production. In the laboratory scale experiments, chromium leaching decreased as the basicity decreased until brownmillerite was no longer present, slower cooling resulted in increased chromium leaching, and faster cooling decreased chromium leaching. In full-scale production, basicity modified single batches, with a basicity below 2.2, generally leached less chromium than slag batches with higher basicity, thus verifying the correlation between basicity and chromium leaching seen in laboratory scale experiments. The cooling process in the full-scale experiments was achieved either by letting the slag cool by itself in the air or by water spraying. The water-sprayed slag, which cooled faster, had less chromium leaching than the air-cooled slag. The full-scale production experiments confirmed that both decreasing basicity below 2.2 and increasing the rate of cooling could be used to decrease chromium leaching.