Slag Phase Research Articles

Effect of CaO/MgO on rheological properties and structure of CaO–MgO–SiO2–Al2O3-50 % TiO2 slag with SiO2/Al2O3=1.0

The rheological properties, including viscosity, melting temperature, surface tension, density, and viscous activation energy (Eη) were systematically investigated in the CaO–MgO–SiO2–Al2O3-50 % TiO2 slag system with SiO2/Al2O3 = 1.0. The effect of CaO/MgO on the structure and phase composition of the slag was studied using Raman spectroscopy and X-ray diffraction (XRD). The results of viscosity properties indicate that as the CaO/MgO ratio in the slag increase, viscosity and the viscous activation tend to decrease. Melting temperature and surface tension decreases with increasing CaO/MgO, while density increases. As the CaO/MgO ratio in the slag increases, polymerization decreases, leading to the dissociated basic oxides into metal cations and oxygen anions. This addition of basic oxides provides more O2−, increasing the O/Si ratio, disintegrating complex silica-oxygen composite ions into simple silica-oxygen composite anion, and reducing viscosity. Anosovite (MgTi2O5), CaAl2Si2O8, Mg (Al, Ti)2O4, spinel (MgAl2O4), augite (Ca (Mg, Fe, Al) (Al, Si)2O6) and Ca12Al14O33 were identified as the primary phases in slag. The appropriate CaO/MgO should not exceed 0.76. These findings will serve as a valuable technical foundation to support the development of the direct reduction smelting process for the comprehensive utilization of vanadium titanomagnetite.

Wettability of non‐metallic inclusions and its impact on bubble‐induced flotation kinetics

AbstractCeramic refractory bubbling devices may be applied in the steel ladle to induce the flotation of non‐metallic inclusions to the slag phase. These inclusions have many origins along the steelmaking process and induce a detrimental effect on the mechanical properties of these metals. Therefore, the design of high‐performance ceramic plugs relies on understanding the fundamentals of non‐metallic inclusions captured by the gas bubbles. This study investigated the flotation dynamics of hydrophobic and hydrophilic hollow glass particles through experimentation using a water model and quantifying the particle concentration via light scattering. Both types of particles exhibited a comparable natural flotation removal rate, whereas a 40% increase for hydrophobic particles was observed when introducing 1.1 mm bubbles (at 25 NL/h) enhancing the efficiency from 43.1% to 65.2%. For hydrophilic particles, the efficiency increased from 59.1% to 86.2% when bubbles were injected into the system, whereas the removal rate decreased by 2.1‐fold. The consequence of the practice of inert gas purging to remove non‐metallic inclusions is also discussed.

Towards Integration of Ni-Slag Cleaning Process and Lithium-Ion Battery Recycling for an Efficient Recovery of Valuable Metals

Spent lithium-ion batteries (SBs) are important sources of valuable and critical raw materials. An integration of battery recycling with well-established primary processes for metals production has many advantages. In this work, the recycling of two battery scrap fractions obtained from mechanical pretreatment was integrated with a Ni-slag cleaning process at laboratory scale. Graphite from SBs acted as the main reductant, and the reduction behavior of major and trace elements was investigated as a function of time at 1350 °C. Major CO and CO2 concentrations, as well as minor amounts of SO2, NO2, CH4, and C2H4, were detected in the off-gas line. The evolution of gases took place within the first minutes of the experiments, which indicated that metal oxide reduction reactions as well as decomposition of the organic binders both happened very rapidly. This result is in line with the analytical results obtained for the slag phase, where the most significant metal oxide reduction was observed to take place within the first 5 to 10 minutes of the experiments. The distribution coefficient values for Co and Ni between metal alloy and slag as well as between matte and slag showed no significant differences when battery scrap fractions with different compositions were used. The addition of Ni-concentrate in the starting mixture resulted in increasing recoveries of Ni and Co, as well as improved settling of the matte phase.

Integrated experimental and thermodynamic modeling study of slag-matte-metal equilibrium in the Pb–Fe–O–S–Si-(Al, Ca, Zn) systems at 1100–1200 °C

Integrated experimental and thermodynamic modeling study was undertaken to characterize the effect of Al, Ca and Zn on the partitioning of elements between the slag, matte and metal phases in the Pb–Fe–O–S–Si-(Al), (-Ca), and (-Zn) systems in equilibrium with tridymite at 1100–1200 °C. The experimental methodology involved closed system equilibration in sealed ampoules, quenching and electron probe X-ray microanalysis (EPMA) of compositions of phases. FactSage thermodynamic database obtained by combining earlier assessments of sub-systems was used to plan the targeted experiments, and the results of new experiments were used to improve the thermodynamic database. Important effects were revealed for the conditions of the present study: CaO decreases the concentration of Pb and S in slag; Al2O3 has small effect on Pb in slag, but significantly decreases the concentration of S in slag; ZnO has small effect on Pb in slag, but increases the concentration of S in slag. These experimentally measured effects were reproduced by the model.

Thermodynamic modeling of interphase distribution of chromium and boron in slags of AOD reduction period

The paper presents the results of a thermodynamic modeling of the chromium and boron reduction from slags of reduction period of argon-oxygen decarburization (AOD) by a complex reducing agent containing silicon and aluminum. Using the simplex lattice method, an experiment planning matrix is constructed containing 16 compositions of the oxide system СаО – SiO2 – (3 – 6 %) В2О3 – 12 % Cr2O3 – 3 % Al2O3 – 8 % MgO of variable basicity 1.0 – 2.5. The results of thermodynamic modeling are graphically presented in form of dependence of equilibrium distribution of chromium and boron on the slag composition at temperatures of 1600 and 1700 °C. The constructed diagrams make it possible to quantify the influence of the temperature, basicity and B2O3 in the slag on equilibrium interphase distribution of chromium and boron. It is established that increasing the slag basicity from 1.0 to 2.5 improves the process of chromium reduction, but restores the boron stability. With an increase in B2O3 content in the slag, a slight deterioration of chromium reduction process occurs, while the boron content in the metal increases. With a simultaneous increase in basicity up to 2.5 and a decrease in boron oxide in the slag from 5 to 3 %, the interphase distribution coefficient of chromium is reduced to 1.5·10–3. Changing the process temperature from 1600 to 1700 °C does not have a negative effect on the process of chromium reduction, but worsens the boron reduction conditions. Based on analysis of the formed slag phases and thermodynamics of the reactions of their formation, it is established that chromium is mainly reduced by aliminum with only partial development of silicothermy. The residual silicon content reduces boron, thereby limiting its concentration in the metal. The results of high-temperature experiments showed high correspondence with the results of thermodynamic studies.

Thermodynamic re-optimization of the CaO–SiO2 system integrated with experimental phase equilibria studies

CaO–SiO2 is the key system in ferrous and non-ferrous metallurgy, ceramic manufacture, cement production, and other applications. A number of discrepancies and gaps in knowledge has been identified and resolved since the last thermodynamic optimization of this system. This study reports new experimental phase equilibria data measured using recent advances in equilibration, sample quenching, and Electron Probe X-ray Microanalysis (EPMA) technique. An updated self-consistent set of thermodynamic model parameters is provided. Most importantly, these updates are integrated with a complete re-assessment of the 20-component Cu–Pb–Zn–Fe–Ca–Si–O–S–Al–Mg–Cr–Na–As–Sn–Sb–Bi–Ag–Au–Ni–Co system directly relevant to applications in the ferrous and non-ferrous metallurgical industries. To obtain a large single set of model parameters, significant advances were made in the computational approach, with a focus on simultaneous parallel optimization of binary and ternary model parameters using an experimental dataset combining binary, ternary, and multicomponent information. The Modified Quasichemical Formalism is used for the liquid slag phase. Thermodynamic properties of solid phases and liquid endmembers are completely revised following the recommendations for the third generation of CALPHAD databases. Other notable changes include the revision of the melting temperature of CaO, justified by extrapolations from the multicomponent systems, as well as a physically realistic heat capacity function for metastable SiO2 below the glass transition temperature. These updated properties expand the areas of application of the database to amorphous and partially crystallized slags at ambient temperatures, such as thermodynamics and kinetics of leaching of toxic elements in an aqueous environment. The fundamental limitations of the existing Modified Quasichemical Formalism are also discussed, along with strategies for addressing them.

Mineralogy and environmental stability of metallurgical slags from the Euronickel smelter, Vozarci, North Macedonia

The laterite Ni-smelting operations at Vozarci, Republic North Macedonia have produced large amounts of smelting wastes dumped in the close vicinity of the smelter. We examined phase composition and chemistry of the various types of slags (electric furnace slags, converter slag, magnetic slag) with the special focus on the phases containing potentially toxic elements in terms of their mineralogy, chemical composition, and responses to weathering. Electric furnace slags contain between 35 and 47 wt.% SiO2, 21–40 wt.% Fe2O3, and 13–23 wt.% MgO; converter and magnetic slags are Fe-rich (76–77 wt.% of Fe2O3) with significant amounts of Ca (7.6–8.4 wt.% CaO) and S-portion (2–2.5 wt.% SO3). All slags contain substantial amounts of the potentially toxic elements: Co (20–87 ppm), Cr (9600–17400 ppm), Ni (170–730 ppm), and Zn (150–380 ppm). Further mineralogical analyses showed that the slags consist of silicate glass, synthetic equivalents of olivines, orthopyroxenes, clinopyroxenes, and subordinate spinel-group phases, sulfides, and intermetallic compounds. Some of the slags had been subject to weathering since their dumping in 1982. The weathering results in the release of metals from primary slag phases, particularly from glass, and the partial immobilization of these metals in secondary soluble and insoluble minerals in the slag heaps (hydroxy-iron oxides, gypsum, anhydrite, syngenite, aphthitalite). The majority of slag samples exhibited increased leaching under conditions of lower pH (2.9) compared to higher pH (4.9). The contrast between leaching treatments was particularly evident for nickel (Ni), with leaching at a low pH of 2.9 reaching up to 135 times higher (MS) than at pH 4.9. At lower pH conditions, other contaminants of interest were leached out at a rate 4 to 76 times faster compared to the leaching achieved at pH 4.9, because they are the major source of potentially toxic elements.

Optimization of ultrasonic enhanced chloride-hydrogen peroxide system for leaching platinum from propane dehydrogenation spent catalyst by response surface methodology

Based on the environmental pressure and the resource wastage caused by the spent catalyst of propane dehydrogenation, a novel approach for the comprehensive treatment of spent catalyst was proposed, which first pulverizing the waste catalyst, and then recovered platinum by chloride-hydrogen peroxide system. The results show that in the HCl-H2O2-NaClO3-AlCl3 system, the addition of AlCl3 can supplement the loss of chloride ions during the reaction. The addition of H2O2 and NaClO3 to HCl not only significantly increases the electrode potential of the reaction system, but also produces Cl2, which promotes the reaction between Pt and Cl2 and dissolves in the form of [PtCl6]2−. In addition, the addition of NaClO3 can also reduce the concentration of HCl and avoid waste. In the actual experimental process, a maximum platinum leaching rate of 96.91 % was achieved, representing a 15.00 % increase compared to conventional leaching methods. The results of Box–Behnken design (BBD) optimization showed that under the conditions of hydrochloric acid concentration of 5 mol/L, reaction temperature of 90 °C, reaction time of 150 min and ultrasonic power of 400 W, the actual leaching rate of Pt and the leaching rate predicted by the quadratic regression model were 97.17 % and 97.26 %, respectively, and the error between the two was less than 0.10 %. The characterization results of the residue showed that the process significantly reduced the toxicity of the residue while increasing the leaching rate of Pt, alleviated the environmental pressure caused by waste stacking, and enriched Al2O3 in the slag phase with high purity for further recycling.

Aluminothermic Reduction Kinetics of Calcium Silicate Slag for Silicon Alloy Production

We investigated the reaction kinetics and initial chemical conditions in the production of silicon alloys, employing aluminum as the reductant for calcium silicate slag, to enhance process economics and scalability to industrial levels. The apparent kinetics and transient chemical conditions were studied by immersing solid aluminum into molten slag, allowing the reaction to proceed for varying durations without external agitation, before quenching the reaction for chemical and microscopic analyses of the resulting silicon alloy and slag. The majority of the conversion was observed within the first 15 s at 1650 °C, driven by significant chemical interactions and interfacial turbulence introduced upon aluminum immersion. For Al-SiO2 stoichiometries ranging from 0.5 to 1.2, the slag phase reaction conformed to first-order kinetics during the initial two minutes, when it approached equilibrium. The mass transfer coefficients for Al2O3 were estimated at 1–2 × 10−4 m/s, comparable to those for SiO2 and CaO. A constant mass transfer coefficient could not be established for stoichiometries of 1.6 and 2, as these deviated from the standard slag mass transfer relationship and did not adhere to established relationships. Despite near-complete reactions, alloy–slag mixing was extensive, decreasing with lower stoichiometry values.

Analysis of the melting process of carbon-bearing pellets in iron bath, slag bath and graphite crucible

Background With the increase in the amount of scrap steel in society, the proportion of electric furnace steelmaking is increasing year by year, especially in China. Due to the high Zn content, the electric furnace arc dust (EAFD) needs to be recovered by non-blast furnace process. Due to EAFD containing a large amount of zinc ferrite, it needs to be recovered by fire process. It is a promising process to melt the EAFD pellets to get the discount and zinc-rich secondary ash. Methods To clarify the melting behavior of pellets in the metallurgical process, the slag phase diagram and the effect of temperature and FeO on slag viscosity were calculated using FactSage, and the melting process of electric furnace arc dust (EAFD) pellets in a graphite crucible, iron bath, and slag bath were experimentally investigated. Results The experimental results show that the viscosity of the slag system decreases with increasing temperature and FeO content, and the effect of FeO on viscosity is greater. The viscosity decreased from 0.305 to 0.276 Pa·s when the FeO content in the slag was increased from 0 wt. % to 2 wt.% at 1773 K. The melting process of the EAFD pellets in an iron bath and graphite crucible was consistent, and after the formation of liquid-phase slag in the pellets, the liquid-phase slag was diffused to melt the pellets. Conclusions The iron bath improved the heat transfer conditions of the pellets, reducing the smelting time from 600 to 360 s. The slag bath promoted the slagging reaction of the contact part to change the pellet melting process and increase the pellet melting speed, and the EAFD pellets melted within 240 s in a slag bath.

Phase Evolution Behavior during the Reduction Process of Medium‐Silica Fluxed Pellets

To enhance the proportion of domestically manufactured Chinese pellets in the furnace, it is crucial to investigate the impact of calcium flux on the metallurgical characteristics of pellets and analyze the phase evolution behavior during the reduction process of medium‐silica fluxed pellets. This study examines the metallurgical properties of medium‐silica acid pellets and low‐basicity medium‐silica fluxed pellets produced in China. The results indicate that incorporating a small amount of calcium flux significantly enhances reducibility index (RI), reduces reduction swelling index, and lowers reductive degradation index (RDI+3.15 mm) for fluxed pellets. At a basicity level of 0.6, RI for medium‐silica fluxed pellets reaches 66.86%, while RDI−0.5 mm increases to 1.62% with increasing basicity levels. As pellet basicity increases, charge pressure drop (APmax) decreases, CaO content in silicate liquid phase within slag phase increases, and softening–melting zone widens, consequently leading to reduced solid‐phase particle content within pellets and increased fluidity within slag phase.

Comprehensive recycling of slag from the smelting of spent automotive catalysts

Spent automotive catalyst is a valuable source of platinum group metals (PGMs), making them crucial secondary resources. Currently, the main process for recovering PGMs from these catalysts is metal capture method. The smelting process would produce a significant amount of residual slags containing various components like SiO2, Al2O3, CaO, Fe2O3, Na2O, as well as high levels of heavy metals including Cr, Pb, and Ni. These slags are considered either solid waste or hazardous waste and usually disposed of in landfills, which can have detrimental effects on the environment. Furthermore, the smelting slags also contain approximately 2–5 % rare earth elements and trace amounts of precious metal elements. In this study, vacuum carbothermal reduction is employed to pretreat the smelting slags. This method not only successfully removes the heavy metal element lead, but also efficiently achieves the recovery of rare earths, and the enrichment of platinum group metals by mineral phase transformation of cerium-zirconium solid solution and in-situ iron capture. The lead removal rate exceeded 99 %, and the grade of precious metals in the enrichment process was approximately 12 times higher than the original material, with a recovery rate more than 90 %. The leaching rate of rare earths also increased from less than 50 % to more than 95 % after vacuum carbothermal reduction. The effect of vacuum carbothermal reduction pretreatment on the smelting slag phase was systematically studied, and the mechanism behind the increasing rare earth leaching rate due to this pretreatment was further analyzed.

Microstructure and properties of high-strength lightweight ceramsites customised with ultra-fine copper tailings

The accumulation of copper tailings not only consumes a significant amount of land resources but also incurs substantial treatment expenses and causes environmental pollution. This article presents an investigation on the feasibility of utilizing ultra-fine copper tailings (CTs), polishing slag (PS), and fly ash (FA) to produce customised high-strength ceramsites for treating and reusing copper tailings.Additionally, the effects of raw material mass ratio and sintering temperature on the physical properties, thermal properties, chemical structure, and expansion mechanism of the high-strength ceramsites were investigated. The experimental results revealed that the well-formed ceramsites exhibited an apparent density of 486–2304 kg/m3, a bulk density of 288–1659 kg/m3, a 1-h water absorption rate of 0.13–3.9 %, and a particle compressive strength of 0.87–22.4 MPa with copper tailings content of 50∼100 % under preheating temperature 950 ℃ for 40 min and sintering temperature 1195–1225 ℃ for 40 min. The XRD analysis of crystal phases indicated that the mineral compositions of ceramsites contained quartz, anorthite, albite, and mullite. Moreover, the FTIR spectra displayed that [AlO4] and [SiO4] were interconnected into a complementary network which enhanced the strength of ceramsites. Additionally, the microstructure analysis revealed that more evenly distributed and smaller pore structures and rougher matrix were associated with higher compressive strength. The temperature difference between the interior and exterior led to the preferential formation of a slag phase which exerted a bonding effect on the composite feldspar phase. These findings suggest that ultra-finecopper tailings could be recycled in artificial aggregate technology in concrete engineering, and provide theoretical support for the large-scale utilization of tailings.

Slag Electrical Conductivity and Its Effect on Mass Transport and Interfacial Reaction Kinetics

Pyrometallurgical refining typically involves slag–metal reactions which are commonly controlled by transport of reactants in the slag or metal phase. For the simplicity of analysis, mass transport in slag is generally treated on a phenomenological basis as transport of molecules. Although this approach works well for many of the reaction systems over narrow ranges of conditions, it can fail when extrapolated over a wide range of conditions. In many refining processes, transport of oxygen in slag determines the kinetics of major reactions. Transport of oxygen in slag is strongly influenced by the electrical conductivity of slag. Whilst this has been well understood since the 1950s, there have been relatively few attempts to quantify the effects of slag electrical properties on the refining kinetics. Herein, an overview is presented focusing on the electrical properties of slags and their effects on the transport kinetics in steelmaking reactions. An analysis is conducted based on a modified version of the approach taken by Wagner to describe oxygen transport in solid oxides. Data from the literature including work from the authors’ laboratory is discussed in an evaluation of literature oxygen transport in CaO–SiO2–FetO, CaO–SiO2–Al2O3–FetO, and PbO–Fe2O3 slags.

Technology Selection for Slag Zinc Fuming Process

Circular economy and multi-metal extraction philosophies more and more encourage smelters to reprocess their by-products most significant of which is slag for recovery of valuable metals. Zinc, for instance, can be introduced to lead and copper smelting operations through different sources, including the recycling of waste electric and electronic equipment. During the conventional smelting processes from primary resources, or even those that are particularly developed for recycling purposes, e.g., Black Copper route, the zinc is typically deported to the slag phase as zinc oxide. Recovery of zinc from slag is typically carried out via a slag zinc fuming operation, where a reductant is used to reduce zinc oxide and volatilize zinc metal. In most cases, volatilized zinc is re-oxidized to produce zinc oxide, which can then be sent to hydrometallurgical unit processes for refining. Several technologies and reactors have been developed for efficient and cost-effective fuming processes, none of which can be considered the “best” and most suitable technology for all applications and smelter conditions/slag compositions. This paper reviews the advantages and disadvantages of each of the available technologies and recommends the most suitable process for common conditions.

The transformation behaviour of ZnFe2O4 spinel particles in the CaO-FexO-SiO2-ZnO slag system

Treating zinc hydrometallurgical residues and other Zn-bearing solid waste in direct lead smelting processes has been recognized as the preferred solution for the sustainable development of the lead and zinc industry. However, new technical problems occurred when changing the starting material of lead-making processes, the pyrometallurgical process for treating zinc hydrometallurgical residues and zinc bearing solid waste usually had the CaO-FexO-SiO2-ZnO slag. Along with the increasing of Zn content in the raw material, high ZnO slag formed, and the ZnFe2O4 spinel particles intended to precipitate from the molten slag. The understanding of the particle behaviour of ZnFe2O4 spinel was the core part of monitoring the slag properties. This study investigated the transformation behaviour of zinc ferrite spinel particles and the changes in glassy slag phase through the high-temperature phase equilibrium experimental technique, and the temperature was 1100 °C-1300 °C and the oxygen potential was 10−8 atm – 10−4 atm. It is found that the particle size of ZnFe2O4 spinel in the molten slag increased along with the increasing of the oxygen potential. The Zn/Fe mass ratio in spinel particles decreased when increasing of temperature and it increased when increasing of oxygen potential. The Fe/SiO2 mass ratio and the Zn content in glassy slag phase gradually increased along with increasing temperature and they decreased along with increasing oxygen potential. The growing and decomposition of ZnFe2O4 spinel was essentially a process of material exchange with the glassy slag phase.

Combined silicon refining for boron removal and Si-Kerf recycling using K2O-CaO-SiO2 slags

It is crucial for the photovoltaic (PV) industry to establish a circular materials flow for more sustainable solar silicon production. In the present work, a series of K2O-SiO2 and K2O-CaO-SiO2 slags were examined for the combination of silicon purification and Si-kerf waste recycling. The study revealed that the predominant mass transfer mechanism and the variation in slag composition during refining are due to the silicothermic reduction of K2O. The boron removal degree reached levels above 80% in most of tests, with boron gasification as potassium metaborate confirmed as an important mechanism for boron removal, especially in slags with high K2O content. In the case of ternary slags, the results indicated that an increase in CaO enhances boron partitioning in slag phase and a high K2O content also led to boron accumulation in the slag phase due to rapid reaction kinetics in the early stage of refining. The distinct behaviours of calcium and postassium ions in the slag phase were revealed by molecular dynamics simulations. It was found that potassium ions preferentially modify bridging oxygen, while calcium ions contribute more to depolymerizing the tectosilicate network and generating more non-bridging oxygens, which may further aid in the boron stabilization in slag phase. The oxidation layer of Si-kerf was removed successfully and enabled the coalescence of the silicon nanoparticles into the Si melt. Additionally, the presence of SiC clusters in the slag phase was also observed, indicating effective removal of SiC and the feasibility of Si-kerf waste recycling.

In-situ investigation on the carbonation behaviors of various mineral phases in steel slag: The role of RO phase

Exploring the mineral compositions of steel slag and the microstructure evolutions of its carbonation products is very important for deeply understanding the carbonation mechanism of steel slag, which can promote the application of steel slag in carbon capture and storage. In this paper, the carbonation behaviors of various mineral phases in steel slag were investigated by using an ingenious in-situ observation method through combing laser scanning confocal microscopy (LSCM), backscattered scanning electron microscopy (BSEM) and focused ion beam-transmission electron microscope (FIB-TEM). It is shown that dicalcium silicate (C2S) and free lime (f-CaO) had high carbonation reactivity, while the calcium aluminoferrite with different Al/Fe ratios and mayenite (C12A7) exhibited extremely poor carbonation reactivity. The carbonation reactivity of RO phase was positively correlated with its Mg/(Fe + Mn) ratio. RO phase with a Mg/(Fe + Mn) ratio below 0.5 owned almost no carbonation reactivity, while the Mg2+ would leach from RO phase with a Mg/(Fe + Mn) ratio higher than 2.0 during the carbonation process, inhibiting the precipitation of CaCO3, changing the micro morphology of CaCO3, and generating spheroidal aragonite. The ingenious in-situ observation method developed in this study provides a very visual information, which can be further extended to more fundamental research.

Volatilisation Behaviour and Mechanism of Lead-Containing Slag during Physical Property Tests.

According to physical property tests of lead-containing slag, the volatilisation behaviour of lead slag will have adverse impacts on test accuracy and further affect the control of chemical reactions, solidification and removal of inclusions during smelting. To analyse the volatilisation characteristics of lead slag, in this paper, four kinds of lead slags from lead direct reduction smelting with different PbO and ZnO content are taken. thermogravimetry, ISP-TOF were used. Additionally, the changes in volatiles and slag composition and phases were analysed with XRD and ICPS, and the volatilisation reaction mechanism was discussed. The results indicated that the volatilisation of lead slag can lead to a big weight loss of about to the slag with higher PbO content. The weight loss increases with the PbO content in slag increases. The volatile corresponding to the weight loss above 900 °C is mainly PbO and less ZnO. The higher the temperature is, the stronger the volatilisation is. With the increase in temperature and keeping time, most of the PbO can be evaporated and leaves little PbO in the residual slag. This will has great effect to physico-chemical property measurement of the slag with higher PbO content, especially to the property measurement that be kept at high temperature for a long time. Because the volatiles is trend to condense with the temperature decrease, mass spectrometer is limited by the condensation of volatiles, i.e., PbO, ZnO and so on, in the connection pipeline. The device should be modified for this use.

Investigation of Liquid-Liquid Reaction Phenomena of Aluminum in Calcium Silicate Slag.

To achieve better process control of silicon (Si) alloy production using aluminum as a reductant of calcium silicate (CaO-SiO2) slag, it is necessary to understand the reaction phenomena concerning the behavior of formed phases at the metal-slag interface during conversion. The interfacial interaction behavior of non-agitated melt was investigated using the sessile drop method for varying time and temperature, followed by EPMA phase analysis at the vicinity of the metal-slag interface. The most remarkable features of the reaction were the accumulation of solid calcium aluminate product layers at the Al alloy-slag interface and spontaneous emulsion of Si-alloy droplets in the slag phase. The reduction is strictly limited at 1550 °C due to the slow transfer of calcium aluminates away from the metal-slag interface into the partially liquid bulk slag. Reduction was significantly improved at 1600-1650 °C despite an interfacial layer being present, where the conversion rate is most intense in the first minutes of the liquid-liquid contact. A high mass transfer rate across the interface was shown related to the apparent interfacial tension depression of the wetting droplet along with a significant perturbed interface and emulsion due to Kelvin-Helmholtz instability driven by built-up interfacial charge at the interface. The increased reaction rate observed from 1550 °C to 1600-1650 °C for the non-agitated melt was attributed to the advantageous physical properties of the slag phase, which can be further regulated by the stoichiometry of metal-slag interactions and the composition of the slag.