Slag Viscosity Research Articles

Investigation on Ash Fusion and Slagging Properties of Coal under Reducing Atmosphere

ABSTRACT Liquid slag tapping at low operation temperature is a major challenge for the application of entrained-flow slagging gasifier. To obtain and elucidate a regulation on stable liquid slag tapping, the SiO2-Al2O3-(CaO+MgO+Na2O+K2O)-Fe2O3 phase diagrams of ash fusion temperatures as well as the ash viscosity and components were studied with ash fusibility apparatus, high-temperature viscometer, SEM-EDS and FactSage software. Meanwhile, the potential slagging properties were analyzed by the difference between soften temperature and deformation temperature (DSI), base/acid ratio (B/A) and slag viscosity index G. Results indicated that the contours of fluid temperature (FT) in the SiO2-Al2O3-(CaO+MgO+Na2O+K2O) pseudo-ternary diagrams presented inverted V-shaped distribution. Attributing to the positive effect of Al2O3 and the downward parabola effect of SiO2, the FT first decreased and then increased with the increased SiO2/Al2O3 at the minimum value of around 3.25. Also, with the increase of (SiO2+ Al2O3+ CaO+MgO+Na2O+K2O)/Fe2O3, the FT showed a V-type distribution with a minimum value at 94:6, yet the effect of Fe2O3 was slight. Besides, high content of CaO+MgO+Na2O+K2O effectively reduced the FT, which favored the formation of molten slag and operation economy; but it shortened the DSI, disadvantaging the formation of long slag and the operation stability. Moreover, decreased ratio of (CaO+MgO)/(Na2O+K2O) not only reduced the FT, but also enlarged the DSI. Finally, a regulation method concerning stable liquid slag tapping at low operation temperature based on ash fusion and slagging properties was proposed: adjusting SiO2/Al2O3 to 3.25 and the mass ratio of Fe2O3 nearby 6.0 wt.%, and doping CaO+MgO+Na2O+K2O with low (CaO+MgO)/(Na2O+K2O) ratio could effectively reduce the FT and viscosity and enlarge the DSI simultaneously, and vice versa.

Reduction for heavy metals in pickling sludge with aluminum nitride in secondary aluminum dross by pyrometallurgy, followed by glass ceramics manufacture

Secondary aluminum dross (SAD) from aluminum industry is classified as a hazardous solid waste due to containing aluminum nitride (AlN). In this work, AlN was first used to reduce heavy metals by pyrometallurgy. The reduction rates for iron, chromium and nickel were up to 90%, 80% and 100%, respectively. However, the reduction from AlN and oxygen oxidization of AlN occurred simultaneously. AlN which formed solid solution with alumina could reduce heavy metals, while the rest was oxidized by oxygen. In addition, the reduction rates for iron and chromium could be increased with increasing CaF2 from 6.7 to 9.0 wt%. CaF2 could decreased viscosity of molten slag, which favored the ion migration, and then increased the reduction rates. After the reduction, glass ceramics were manufactured from the molten slags. The bending strength, microhardness and alkali resistance of the glass ceramics were up to 77 MPa, 1011 HV and 98.7%, respectively. According to XRD and SEM results, glass ceramics with CaAl2SiO6 crystal phase, crosslinked network structure grains and smaller pores exhibited better bending resistance. In addition, glass ceramics with CaAl2SiO6 crystal phase possessed the highest microhardness and alkali resistance. After this process, hazardous pickling sludge and SAD were totally recycled.

Experimental Study of Blast Furnace Hearth Drainage Based on Image Analysis

A smooth hearth drainage is one of the key requirements for maintaining an efficient blast furnace operation. For achieving this, it is necessary to understand the hearth drainage behavior and the effect of related process parameters. To investigate the drainage, a set of experiments is conducted in a 2D Hele−Shaw model, where the influence of the initial accumulated amount of molten liquids (iron and slag), blast pressure, and slag viscosity on the drainage behavior is studied using water and oil as liquids. To quantify the findings, an image analysis‐based algorithm is applied to extract drainage information that is used to analyze the effect of the mentioned process factors on the evolution of the liquid levels and volumes, flow rates, share oil in the outflow, and angle of the interfaces at the outlet. Herein, the implications of the results for the operation of the blast furnace hearth are discussed.

Silicon recycling and iron, nickel removal from diamond wire saw silicon powder waste: Synergistic chlorination with CaO smelting treatment

During the processing of silicon wafers for photovoltaic power generation, nearly 30–40% of silicon ingot will be lost as diamond wire saw silicon powder (DWSSP) waste; this can result in reduced profits, potential danger, and environmental pollution. Driven by the rapid development of the photovoltaic industry, the demand for high-purity silicon and the production of silicon waste generated during silicon processing will continue to increase. Againstthistrend, the recycling of silicon from DWSSP waste is a desirable alternative to meet the growing demand for high-purity silicon. In this study, a novel process of chlorination with CaO smelting treatment is first proposed for the recycling of silicon and the removal of Fe and Ni from DWSSP waste. The results of this research indicate that the SiO2 shell can be absorbed by the added CaO, while eutectic NaCl-MgCl2 has a significant effect on the maximum recovery of silicon by reducing the viscosity of the molten slag and the removal of metals through the micro concentration cells. CaO and eutectic NaCl-MgCl2 play a synergistic role in the promotion of silicon separation and the removal of Fe and Ni. Silicon with a purity of 99.83% and a recovery rate of nearly 98.96% was obtained under the smelting conditions of DWSSP:CaO:NaCl:MgCl2 = 150.0:23.42:7.50:8.85 with a holding time of 2 h at 1823 K. This process overcomes the technical bottleneck of the removal of Fe and Ni via smelting treatment, which is favorable for the recycling of silicon from DWSSP waste at the industrial scale.

Effect of Unburned Pulverized Coal on the Melting Characteristics and Fluidity of Blast Furnace Slag

A substantial amount of attention has been paid to viscosity due to its substantial effect on the fluid dynamics of molten blast furnace slag and slag metal reaction kinetics during the pyrometallurgy process. To clarify the influence mechanism of unburned pulverized coal (UPC) on blast furnace (BF) slag viscosity, the effects of different contents of UPC on the BF slag viscosity, free-running temperature and viscous flow activation energy were investigated. The slag viscosity was measured by the rotating cylinder method, and the microstructure of the cooled slag was observed by SEM. As a result, the main reason for a change in the slag viscosity, free-running temperature and viscous flow activation energy was that the UPC entering the slag formed a large number of white particles that predominantly comprised deposited carbon and a high melting point solid solution. In addition, the disintegration or polymerization of the SixOyz- structure was also a contributing factor. When the content of the UPC was 0.6%, the free-running temperature and viscous flow activation energy of slag were 1623 K and 120.969 kJ/mol, respectively, which are lower than those of the slag without UPC. However, the free-running temperature and viscous flow activation energy increased to 1668 K and 286.625 kJ/mol, respectively, when the content of UPC increased to 4%, which are higher than those of slag without UPC.

Variation of viscosity and crystallization properties of synthetic ferronickel waste slag with Al2O3 content

Ferronickel slag is a by-product in the production of Ni–Fe alloy, which can be used to produce mineral wool. The crystallization and viscosity of ferronickel slag have great influence on the production process of mineral wool. The crystallization properties and viscosity of three kinds of ferronickel slags with different Al2O3 contents were investigated.It was studied by viscometer and high-temperature confocal scanning laser microscope (CSLM). The morphology and composition of crystals in the slag were characterized by field scanning electron microscope (FE-SEM) and energy dispersive spectrometer (EDS). The experimental results show that the crystallization process of molten slag conforms to the Johnson-Mehl-Avrami (JMA) crystallization kinetic model. With the increase of Al2O3 content, the crystal size of ferronickel slag becomes smaller, the crystallization time increases, and the crystallization capacity decreases. The main crystallization product of No.1 and 2 slag is orthopyroxene, and the main crystallization product in No.3 slag is alumina. With the increase of Al2O3 content, the transition temperature of ferronickel slag increases first and then decreases. The variation of viscosity is mainly related to the precipitation and growth of crystals, and is also affected by the type and the number of crystals.

Effect of the Initial P Content on Dephosphorization of Hot Metal with Low Basicity Slag at 1623 K

The effect of the initial P content ranging from 0.057% to 0.292% in hot metal on dephosphorization with low basicity (CaO/SiO2) slag at 1623 K is investigated using high‐temperature laboratorial experiments. With increasing initial P content in the hot metal, the dephosphorization ratio increases first and then decreases, with the highest dephosphorization ratio of 83.2% at the initial P content in the hot metal of 0.173%. The phases in dephosphorization slags are basically consistent, which are mainly composed of nCa2SiO4‐Ca3(PO4)2, Ca2SiO4, metal oxide, Ca3(PO4)2, Ca3Mg(SiO4)2, Ca2Fe2O5, and MgAl2O4. The compositions of all the P‐rich phases are close to the connection line between Ca2SiO4 and Ca3(PO4)2 in the phase diagram. In addition, with increasing the initial P content in hot metal, the viscosity and activation energy values of the dephosphorization slag increases at the present dephosphorization temperature of 1623 K and the values of the activation energy of the dephosphorization slags increase gradually. The area fractions of Q0 + Q1 (Qi, i is the number of bridging oxygen per silicon atom) units decrease, whereas those of the Q2 + Q3 units increase. The average number of nonbridging oxygen per silicon atom (NBO/Si) value decreases, indicating that the degree of the polymerization (DOP) of the corresponding dephosphorization slag increases resulting in the increased viscosity.

Effect of Al2O3 on the viscosity of CaO-SiO2-Al2O3-MgO-Cr2O3 slags

We investigated the effect of Al2O3 content on the viscosity of CaO-SiO2-Al2O3-8wt%MgO-1wt%Cr2O3 (mass ratio of CaO/SiO2 is 1.0, and Al2O3 content is 17wt%–29wt%) slags. The results show that the viscosity of the slag increases gradually with increases in the Al2O3 content in the range of 17wt% to 29wt% due to the role of Al2O3 as a network former in the polymerization of the aluminosilicate structure of the slag. With increases in the Al2O3 content from 17wt% to 29wt%, the apparent activation energy of the slags also increases from 180.85 to 210.23 kJ/mol, which is consistent with the variation in the critical temperature. The Fourier-transform infrared spectra indicate that the degree of polymerization of this slag is increased by the addition of Al2O3. The application of Iida’s model for predicting the slag viscosity in the presence of Cr2O3 indicates that the calculated viscosity values fit well with the measured values when both the temperature and Al2O3 content are at relatively low levels, i.e., the temperature range of 1673 to 1803 K and the Al2O3 content range of 17wt%–29wt% in CaO-SiO2-Al2O3-8wt%MgO-1wt%Cr2O3 slag.

Effect of MnO content on slag structure and properties under different basicity conditions: A molecular dynamics study

In this paper, molecular dynamics (MD) is used to simulate the local structural order, oxygen bond network and transportation characteristics of the slag system under different basicity, and the influence of MnO on the properties such as viscosity, liquidus temperature and enthalpy was studied. MnO or basicity will not affect the bond length and the coordination number of Si-O, but the coordination number of Al-O is slightly reduced. The conversion rate of BO and TOs to NBO or FO is accelerated when CaO/SiO2 ratio is 1.2 and MnO exceeds 4 wt%. It indicates that an increase in MnO content at high basicity will make the depolymerization of the slag structure more obvious. The total self-diffusion coefficient of each atoms increases with the increase of basicity and MnO, while the viscosity of slag showed an opposite trend. The enthalpy of the slag increases linearly and the conditions of low basicity and high MnO are beneficial for keeping a low liquidus temperature and realizing the stable and smooth of the blast furnace.

Thermochemical and analytical approach to describe secondary slag phase formation and local process conditions in a full-scale BGL gasifier

This study aims to directly analyze untreated process samples from a full-scale BGL gasifier. It assesses as well as categorizes the findings to identify the most important effects governing the behavior of slags under gasifier conditions. A process slag sample from the Schwarze Pumpe BGL-type waste gasifier is thoroughly analyzed via X-ray diffraction (XRD), X-ray fluorescence (XRF), and using a scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDX). The results are interpreted with the aid of thermodynamic equilibrium calculations using the FactSage™ software package to yield the main influence factors on slag viscosity and -structure. Since these are derived from full scale process samples, the severity of the impact to these processes can be assessed. Especially the effect of secondary phases apart from the main slag phase is evaluated. The differences between laboratory measurements and full-scale processes are identified. The composition of the gas atmosphere above the slag bath cannot easily be determined. This study uses a method to determine and include this gas atmosphere into the process slag analysis through thermodynamic equilibrium calculations. The temperature of the slag bath and the gas atmosphere around the slag is backtracked via analytically validated thermodynamic equilibrium calculations.

Vaporization of Vanadium Pentoxide from CaO-SiO2-VOx Slags During Alumina Dissolution

The vaporization of vanadium pentoxide from CaO-SiO2-VOx ternary slags using different gas treatment regimens and parallel vacuum gas extirpation to treat V-bearing slags at 1873 K has been developed in the present study. The novelty of the present study is to monitor the effect of parallel alumina dissolution on the vaporization phenomenon. Vanadium pentoxide has high vapor pressure at the temperatures over 1500 K. When CaO-SiO2-VOx ternary slags, kept in dense alumina crucibles, are injected with oxygen, V2O5 gas bubbles are formed which are forced out by using vacuum extirpation. The vanadium pentoxide could be then collected in the exhaust gases. The mechanism of the process phenomenon is described as the formation of V2O5 gas phase resulting from the oxidation of the lower-valent oxides present in the slag. This gas phase would form microbubbles in the molten slag bulk phase due to low surface tension between the gas phase and the slag, thereby increasing the contact surface. At the same time, the crucible material would dissolve in the slag causing an increase in the slag viscosity. Due to the high slag viscosity of the bulk slag, these microbubbles formed would have difficulty in coalescing and reaching the slag surface. The escaping of the bubbles into the gas phase is enabled by the vacuum extirpation.

Interface-Resolved Simulation of Bubbles–Metal–Slag Multiphase System in a Gas-Stirred Ladle

A grid-filtered scale interface-resolved volume of fluid (VoF) model coupling a sub-grid scale large eddy simulation (LES) was used to directly simulate bubble behavior and the evolution of multiphase interfaces and free surfaces in a bubble–metal–slag multiphase system. The model has been applied to an industrial 150-ton gas-stirred ladle. The results show transient behavior of the slag eye, with large variations over time of the eye size. Bubble detachment frequency and rise characteristics (including coalescence and breakup) directly affect the size, position and variation of the slag eye. The effects of the argon flow rate, slag thickness, slag viscosity, and slag–steel interfacial energy were investigated; the latter two have little effect. The calculated average slag eye size agrees with previously reported results for industrial ladles. A new correlation for the time-averaged slag eye area, based on the modified Froude number, is proposed for industrial ladles.

Influence of TiO2 on viscosity, phase composition and structure of chromium-containing high-titanium blast furnace slag

The viscous flow of CaO–SiO2–Al2O3–MgO–TiO2–Cr2O3 slag (CaO/SiO2 = 1.1, Cr2O3 = 0.5 mass%) were investigated to promote understanding of the effect of TiO2 addition on the viscous behavior of chromium-containing vanadium-titanium blast furnace slag. The viscosity of the slag was measured using a rotating crucible viscometer. Raman spectroscopy analysis was performed to correlate the viscosity to slag structure. The viscosity of slag was found to significantly decrease with increasing TiO2 content at a fixed basicity. It is because the Ti4+ continuously detached from the network structure, the content of [Ti2O6]4- decreased, and the content of [TiO4]4- tetrahedral monomer increased, which made the slag structure simplified. Consequently, the polymerization degree of the slag decreases with increasing TiO2 content. The variation in slag structure is consistent with the change in measured viscosity.

Influence of laterite nickel ore on extracting iron from Bayer red mud by carbothermal smelting reduction

In view of the difficulty of extracting iron from Bayer red mud, a new idea of adding laterite nickel ore into red mud was proposed to prepare a high value-added product. Toward this, the influences of laterite nickel ore on thermodynamic reaction, slagging and smelting reduction of extracting iron from red mud were studied. The results indicated that the product of extracting iron from red mud (R100) was changed with the addition of laterite nickel ore (R70L30). The slag of R100 was strongly basic, while the R70L30 was weakly acidic with composition closer to the ideal blast furnace slag. The metal recovery of R100 was 75.16% and that of R70L30 was 94.05%. At the same temperature, the slag viscosity of R70L30 was significantly lower than that of R100, which proved that laterite nickel ore can adjust the basicity, reduce melting point of slag and improve metal recovery. Because Fe, Ni and Cr in red mud and laterite nickel ore can be reduced sufficiently, a low Ni–Cr alloy cast iron can be directly prepared.

Effect of wet-grinding steel slag on the properties of Portland cement: An activated method and rheology analysis

Steel slag is a solid waste generated from the steelmaking process. With a very low utilization rate of 30% in China, a high discharging cost of steel slag is inevitable so that it is imperative to dispose of steel slag by new technology. In this study, steel slag was refined by wet-grinding technology to apply on cement. The results showed that the initial setting time and final setting time were prolonged by the increased dosage of 3 μm steel slag. Although the viscosity of wet-grinding steel slag – cement specimens increased significantly, the shear-thinning phenomenon happened by mechanical mixing. The wet-grinding specimens presented a higher hydration heat than that of raw steel slag specimens, and the microstructure of 3 μm-40% (3 μm steel slag mixed with cement as a dosage of 40%) is much denser and show more hydration products than that of raw-40% (raw steel slag mixed with cement as a dosage of 40%) which results in an enhanced compressive strength that could be guaranteed by the dosage of 20% (3 d), 30% (28 d) and 40% (60 d) under the condition of 3 μm steel slag incorporation with lower autogenous shrinkage. Hemicarboaluminate peak was found in wet-grinding specimens that show a higher calcium sulphoaluminate to calcium. The wet-grinding steel slag CO2 emission and cost showed a downward trend compared with cement.

Recovery of Copper and Cobalt from Converter Slags via Reduction–Sulfurization Smelting Using Spent Pot Lining as the Reductant

Large amounts of solid wastes are produced in copper and aluminum smelting processes, which not only cause losses of valuable resources but also threaten the ecology and environment. In this study, a reduction–sulfurization smelting method was used for recovering Cu and Co from converter slags by using spent pot lining (SPL) as the reductant. CaO was added to fix the fluorine from SPL into the cleaned slag. Thermodynamic analysis and experiments were performed to verify the feasibility and determine the optimal conditions of this smelting process. The optimum reductant addition of spent cathode carbon block (SCCB) and spent SiC side block (SSCB) was 8–12 wt %, and the copper and cobalt recovery reached more than 98 and 96%, respectively. The addition of 10 wt % CaO for SCCB improved slag viscosity and promoted the separation between slag and matte/alloy and fixed fluorine in the cleaned slag in the form of insoluble calcium fluoride. The metallized Cu–Co matte was obtained, in which Cu mainly existed in the form of sulfide and Co mainly existed in the form of an iron cobalt alloy.

Viscosity of CaO-MgO-Al2O3-SiO2-TiO2-FeO slag with varying TiO2 content: The Effect of Crystallization on Viscosity Abrupt Behavior

Reasonable slag fluidity is essential for stable HIsmelt process operation. During the slag-tapping process, crystallization will cause the slag viscosity to rise sharply, which is not conducive to stable slag-tapping operation, especially for smelting high-titanium slag. In this paper, the viscosity of the CaO-MgO-Al2O3-SiO2-TiO2-FeO slag with varying 10–50% TiO2 content was studied in the laboratory. The crystalline phases of water quenched slag samples at different temperatures were determined by XRD, and it was verified with the results of Factsage thermodynamic calculations. In addition, the effects of crystalline phase, crystalline morphology and crystal size on the critical viscosity of slag were discussed through SEM-EDS analysis. The results show that the proper TiO2 content in the slag is below 40%, the temperature of critical viscosity (Tcv) of the slag is between 1336 °C and 1360 °C, and the Tcv of the slag with a TiO2 content of 50% increases to 1500 °C. The sudden increase in viscosity is related to the crystallization behavior of the slag. With the increase of TiO2 content, the main precipitated titanium-rich phase in the slag changed from dendritic perovskite to plate-shaped pseudobrookite. Among them, when the TiO2 content is 10%, the sharp increase in viscosity of the slag is mainly determined by the precipitation amount of melilite. The amount of crystals in the slag between 20% and 43% causes the viscosity of the slag to rise rapidly, which is mainly due to the fact that the granular crystals have a greater influence on the viscosity than the plate crystals. Compared with the experimental results, it is found that Factsage software cannot accurately calculate the phase equilibrium of slag with a TiO2 content of 40–50%.

A FactsSage Simulation Study on the Interaction of Synthetic Petcoke Slags with Alumina Crucibles

In entrained flow gasifiers, inorganic species in solid fuels are converted to slag, which flows continuously along the gasifier’s refractory lining. Slag viscosity is critical for its continuous flow and, consequently, reliable operation of the gasifier. Viscosity of synthetic petcoke ash was measured in a high temperature viscometer (up to 1500 °C) using high alumina crucibles. Crucible material was found to dissolve in slag, causing thinning and leading to formation of holes on the walls. To explain this dissolution, thermodynamic equilibrium calculations were performed in FactSage™ (Thermfact/CRCT, Montreal, QC, Canada and GTT-Technologies, Aachen, Germany) using different synthetic petcoke ash compositions in 100% H2, 5% H2/ 95% N2, 69.5% CO/30.5% CO2, and 100% O2 atmospheres. An inverse correlation was found between crucible dissolution and alumina content in the slag. Rates of dissolution of alumina from crucible into slag varied significantly in the different atmospheres. The correlation was validated experimentally by heating six synthetic slags with varying compositions to 1500 °C in 5% H2/N2 (to simulate viscometer’s atmosphere) gas. SEM-EDS analysis of the samples confirmed that the sample with lower initial content of alumina in the slag showed higher amounts of aluminum at the slag–crucible interface. Additions of alumina in the synthetic petcoke ash (containing up to 49.74% V2O5) mitigated crucible dissolution.

Effect of FeO Content on Foaming and Viscosity Properties in FeO-CaO-SiO2-MgO-Al2O3 Slag System

The foaming process is an important part of the electric arc furnace (EAF) steelmaking process. It can promote thermal efficiency and reduce refractory consumption. FeO is a key material used during the foaming process. Unlike with other components used in forming foaming slag, the amount of FeO can be controlled by oxygen or carbon injection. Therefore, adjusting the content of FeO is the most economical foaming mode adopted for the EAFs steelmaking process. In this study, the influence of FeO content on the physical properties of slag was discussed. The melting temperature of the slag was evaluated using three methods: viscosity experiment, using Thermo-Calc simulation software, and high-temperature optical method. The experimental results revealed that the viscosity of slag increases as FeO content decreases. The results also revealed that foam height ratio exhibited a positive correlation with the viscosity of slag.

Comparison of Natural and Synthetic Petroleum Coke Slag Viscosities under Reducing Conditions: Applicability of Predictive Models Using Factsage and Modified Urbain Model

The viscosity of slag from an operating integrated gasification combined cycle (IGCC) plant utilising petroleum coke and a synthetic petcoke slag with the same composition made from chemical grade oxides in a reducing environment for gasification application were investigated in this study. A high temperature rotating bob-type viscometer was used to measure viscosity between temperatures of 1250–1375 °C. Natural and synthetic ash had similar viscosities above 1300 °C in this study. The viscosity was predicted by using FactSage, a thermodynamic modelling software, in conjunction with different viscosity models, available in the open literature. Percentage deviations of predicted viscosities from different models with experimentally measured values ranged from about 41 to 151%. Crystallisation of the slag was noted in SEM-EDS (scanning electron microscopy– energy dispersive spectroscopy) and FactSage results. Solid phases from FactSage predictions were used to modify the Kalmanovitch–Frank model with the Roscoe method. It predicted the viscosity of the slag accurately between 1250 and 1375 °C. Average percentage deviation from measured natural ash viscosity was about 11%.