Slag Metal Research Articles

Video registration of physicochemical processes in BOF cavity at bath top blowing at application oxygen lances of various designs. Report 3. The picture of bath blowing at application two-level oxygen lances

Further increase of resources- and energy-saving efficiency of BOF processes is unthinkable without development of new methods of blowing and designs of blowing devices. It requires information on the real physicochemical phenomena in the converter cavity accompanying the blowing of the converter bath using new designs of oxygen lances in order to assess the possible risks in the mastering of the proposed developments in industrial conditions. The paper presents the results of video filming of the top blowing of a 80-kg converter bath by groups of multi-pulse supersonic and sonic oxygen jets formed, respectively, by Laval and cylindrical two-level nozzles of two designs equipped with double-row tips with a circular arrangement of Laval nozzles and cylindrical ones and upper block with cylindrical nozzles. Previously unknown information was obtained on the picture of the bath blowing with the formation of a reaction zone of interaction of supersonic and sonic oxygen jets with a metal melt with a flow of carbon monoxide going out the bath and afterburning of CO to CO2 under conditions of a counter-directed double curtain of sonic oxygen jets at different levels of location of the foamed slag-metal emulsions. It was established that in the initial period of blowing during slag formation most of the thermal energy of CO to CO2 combustion flares is transferred to the surface of the bath with lumps of added lime, and the rest is transferred by forced convection to the converter walls and gases escaping from the bath to the neck. In the case of the location of the foamed slag level at the upper tier of the cylindrical nozzles of the lance, heat transfer from high-temperature flares of localized afterburning of CO to CO2 within a limited in size near-lance flow of exhaust gases from the reaction zone is carried out according to the laws of submerged combustion and is completed completely in foamed slag-metal emulsion with the prevention of aggressive action of afterburning flares and volumes of overheated slag on the converter lining. Revealed and recorded by video recording modes of blowing the converter bath, contributing to the development of such undesirable phenomena during smelting as the appearance of intense emissions of slag-metal suspension from the facility, coagulation of the slag with the cessation of dephosphorization of the metal melt, the development of intense dust formation and the removal of small metal particles and slag with the formation of crust on the lance barrel. A variant of the final stage of blowing with a transition to supplying nitrogen instead of oxygen through cylindrical nozzles of two-level lances was experimentally tested, which provides an effective reduction in the level of foamed slag-metal emulsion before the converter turning down. The data obtained were used in the development of an industrial design of a two-level lance with a double-row tip, blowing and slag modes of blowing a converter bath with its use.

High-Performance Method of Recovery of Metals from EAF Dust-Processing without Solid Waste.

A highly effective method of the processing of steelmaking dust in an arc-resistant furnace has been presented. The aim of the research was to investigate the possibility of processing steelmaking dust in terms of waste minimization and selective recovery of valuable components. For this purpose, an electric arc resistance furnace was used. Granulated steelmaking dust with reducer (coal dust) was the input material. The products of the process are zinc oxide, iron alloy and slag, with properties meeting high ecological requirements. The technology does not generate solid waste. Zinc recovery is over 99% and iron recovery over 98%. The content of heavy metals (Zn + Pb + Cu) in glassy slag is below 0.2%, which ensures very low leachability.

Variation in Multiphase Flow Characteristics by Nozzle‐Twisted Lance Blowing in Converter Steelmaking Process

A 3D gas–slag–metal model for a 120t converter with nozzle‐twisted lance is established, and the gas jet characteristics, slag–metal interface fluctuations, wall erosion, and changes in the molten pool flow field of the nozzle‐twisted lance of the blowing process are studied. The results reveal that, with the increase in the swirl angle, the length of the jet high‐velocity section, maximum velocity, and dynamic pressure decrease, radial distance increases, and wall shear stress first decreases and then increases. With an increase in the blowing time, the fluctuating intensity of the slag surface and the molten steel surface changes significantly, fluctuating slag surface stabilizes after 1.7 s (fluctuating intensity is 1.08–1.12), and fluctuating steel surface stabilizes after 1.3 s (fluctuating intensity is 1.23–1.33). The turbulent kinetic energy of the gas–slag–metal three‐phase interaction area increases and the wall shear stress gradually increases.

Study on Splashing Mechanism in Basic Oxygen Furnace Based on Slag Foaming Modeling

Inappropriate slag foaming is the main cause of splashing in basic oxygen furnace (BOF). Through the physical modeling, the effects of slag–metal reaction rate, viscosity of slag, slag–metal interface tension, and lance height on the slag foaming are investigated, and further analyzed the relation between the extent of BOF slag foaming and splashing. Consequently, two patterns of overflowing splashing and eruptive splashing and their critical conditions are summarized. The experimental results indicate that gas released by slag–metal reaction is primarily responsible for slag foaming in BOF, and the maximum height of foamed slag increases with increasing reaction rate of slag–metal. Moreover, an increase in dynamic viscosity of slag prevents the foam structure transforming from spherical foam to polyhedral foam, and thus improves the maximum foaming ability of slag and the stability of foam structure. With decreasing slag–metal interface tension, the slag–metal emulsification and the stability of foam structure are promoted. Finally, it is concluded that overflowing splashing occurs under the conditions of the higher dynamic viscosity of slag and the larger gas generation amount; whereas, eruptive splashing occurs under the conditions of the lower dynamic viscosity of slag and the higher gas generation rate.

Evaluation of the catalytic effect and migration behavior of potassium in the molten slag during the char/molten slag interfacial gasification

The reaction of coal char particles deposited on the molten slag surface in the entrained flow gasifier was of importance to the carbon conversion and slag discharge. In this study, the catalytic effect and migration behavior of the alkali metal (K) in molten slag during the gasification reaction of char particles on the molten slag surface were investigated and evaluated by using visualization and surface analytical techniques. The results showed the ionic K in the molten slag was not deactivated and accelerated the char gasification rate and carbon conversion of char particle on the molten slag surface as a catalytic effect. The complete conversion time of char particles on the molten slag with the addition of K was reduced by about 37%–67%, compared to the time of the char gasification without molten slag or the gasification on the slag with no addition of K. The carbon conversion of char particles was increased obviously with increasing the addition of K in the molten slag. From the analyses of scanning electron microscope (SEM) and energy dispersive spectrometry (EDS), the ionic K was found to gradually migrate and accumulate to the interface between the coal char particle and molten slag during the gasification process. The migrating and accumulating amount of K to the interface increased with the increases of both carbon conversion of the char particle and K addition of the slag. With a comparative experiment of the char combustion on the slag surface, a low temperature zone below the char particle during the gasification was key to cause a migration behavior of K with other elements (e.g. Si and Al) and further acted as a catalytic effect on the gasification reaction. Finally, a mechanism of the catalytic effect and migration behavior of ionic K in the slag during the char/molten slag interfacial gasification process was uncovered in this study.

A novel method for extraction of platinum from spent automotive catalyst: utilization of spent fluid catalytic cracking catalyst as flux

ABSTRACT A novel method of smelting of mixture of spent automotive catalyst (SAC) and spent fluid catalytic cracking catalyst (SFCC) to recover platinum and prepare glass slag was investigated. Compared to other metals collection processes for single hazardous waste solid, this method reduced the amount of fluxing materials addition and increased the processing types of hazardous solid waste simultaneously. The optimum SFCC addition, iron collector addition, Na2B2O4•10H2O addition, CaO/SiO2 mass ratio, temperature, and holding time for platinum recovery were 20, 11, 16 wt%, 0.6, 1550–1600°C, and 60 min, respectively. In this proposed combined process, more than 98% of platinum is efficiently recovered from SAC. Meanwhile, the concentration of platinum in glass slag was less than 7 g/t. The leaching characteristics of heavy metals in slag confirmed the obtained glass slag is a non-hazardous slag due to the low leaching rate of heavy metal ions. This article proposed an effective and environmentally friendly method for the recovery of platinum from SAC via a combined smelting process.

Effect of different direct revegetation strategies on the mobility of heavy metals in artificial zinc smelting waste slag: Implications for phytoremediation

The establishment of vegetation cover is an important strategy to reduce wind and water erosion at metal smelting waste slag sites. However, the mobility of heavy metals in waste slag-vegetation-leachate systems after the application of revegetation strategies is still unclear. Large microcosm experiments were conducted for revegetation of waste slag for 98 d using combined amendments, i.e., phosphate rock and an organic waste coming from the anaerobic digestion of pig manure (named as biogas residue), and by single- and co-planted perennial ryegrass (Lolium perenne L.) and Trifolium repens (T. repens). The results showed that the application of biogas residue slightly increased the concentrations of Zn and Cd in the leachates; however, the establishment of plants could avoid the excessive leaching of heavy metals coming from the biogas residue. The bioavailability of Cu, Zn, and Cd slightly increased, but Pb bioavailability significantly decreased regardless of single- or co-planting patterns. Additionally, the bioavailability of Cu, Zn, and Cd in the waste slag revegetated with perennial ryegrass was lower than that in T. repens under the single-planting pattern. The change in the heavy metals bioavailability under different revegetation strategies was mainly due to the root-induced change in the pH and speciation of heavy metals in the waste slag. The application of biogas residue and phosphate rock tends to the immobilization of Pb. Heavy metals mainly accumulated in the underground parts of the two herbs, and the heavy metal contents in the underground parts of perennial ryegrass were higher than those in T. repens regardless of single- or co-planting patterns. The heavy metals accumulated in T. repens were lower than those in perennial ryegrass in the single-planting pattern. The bioaccumulation and transportation factors of the two herbs were extremely low. Thus, the two herbs are potential candidates for phytostabilization of zinc smelting waste slag sites.

The potential environmental risk implications of heavy metals based on their geochemical and mineralogical characteristics in the size-segregated zinc smelting slags

Smelting slags must be classified as a typical hazardous solid, which represents the most important point sources of potentially harmful elements. In addition, it can be known that particle sizes have been considered as an important indicator of human exposure risks. In this context, the present work mainly concerned about the potential leachability, bioavailability, bioaccessibility and mobility of toxic heavy metals in four zinc smelting slag fractions under the strong influences of mineralogical and morphological factors. The results indicated that heavy metals were mostly enriched in the smallest particles, with the higher metal concentrations of 3558.19 g/t for As, 123.49 g/t for Cd, 6757.57 g/t for Cu, 1.76% for Pb and 1.78% for Zn. Geochemical evaluation revealed that Cd, Cu, Mn, Pb and Zn was the most worrying elements, due to their unstable geochemical properties. Moreover, XRD and SEM-EDS results confirmed the formation of gypsum (CaSO4.2H2O) phase in 0.075–0.15 mm (SS3) and <0.075 mm (SS4) of the zinc smelting slags. The combined results of various characterization clearly showed the particle size distribution, surface morphological structure and mineral weathered state had a profound impact on the geochemical stability of heavy metals in the zinc smelting slags. These combined results of geochemical analysis and technical characterization could update our fundamental knowledge to better understand the mineralogical and morphological controls influencing the geochemical behaviors of heavy metals. Meanwhile, these study results would be of great scientific and realistic significance to develop effective targeted strategies for the subsequent pollution control and risk reduction of smelting wastes.

Behavior of Gas–Slag–Metal Emulsion with Nozzle‐Twisted Lance in Converter Steelmaking Process

Oxygen lance is the key to realize the emulsification of gas–slag–metal in the converter steelmaking process, which determines successful completion of metallurgical tasks. Herein, a 3D full‐size gas–slag–metal coupling model of the nozzle‐twisted lance in a 120t converter is established. The behavioral characteristics of gas–slag–metal of nozzle‐twisted lances (swirl angle 0°/5°/10°/15°) are studied. With the increase in the swirl angle, the axial velocity is reduced; the radial and tangential velocities are increased, and the coverage area of the slag layer, the splashing amount, and its height are reduced. In the longitudinal section, when the swirl angle increases from 0° to 15°, the areas of high‐velocity and dead zones are reduced by 15% and 36%, respectively, and the area of low‐velocity zone is increased by 17%. At different depths of molten bath, with the increase in the swirl angle, the area of high‐velocity zone first increases and then decreases; the area of low‐velocity zone increases, and the area of dead zone decreases. Finally, the industrial experiment with the nozzle‐twisted lance is carried out in a 120t converter. The phosphorus content, the carbon–oxygen product, and the total iron content in slag are all reduced.

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.

Behavior of the Free Surface of Two-Phase Fluid Flow Near the Taphole in a Tank

The present study numerically investigated the deformation of the free-surface of two-phase fluid flow in a tank which is considered as a simplified blast furnace hearth. Actually, the fluids existing in a blast furnace hearth are gas, slag and hot metal from top to bottom. However, the present study considered only gas and cold molten iron in the tank. The porosity is considered as a substitute for void volume formed by the packed bed of the particles such as cokes. The single-phase flow and two-phase fluids flow without the porosity are analyzed for comparison. The porosity contributed the free surface to forming a viscous finger near the taphole. The axi-symmetry nature of the interface of two-phase fluids flow in the cylindrical tank is broken by viscous finger as the interface instability by the gas entrainment into taphole, which has been identified by the visualization of the free surface formation. The acceleration of the free surface falling velocity and the outflow near the taphole are associated by the viscous finger by the gas entrainment. The dimensionless gas break-through time is linear with respect to the porosity magnitude.

Investigation of the microstructure interaction mechanism of coke–slag–metal in deadman of blast furnace

ABSTRACT Coke–slag–metal samples located near the deadman edge and below the taphole of blast furnace were obtained by core drilling after cooling. The chemical composition, microstructure, phase composition and distribution of samples were studied in detail. In addition, the graphitisation degree of coke in hearth was also investigated. The results showed that coke larger than 60 mm still existed (more than 1%). Pores in coke are filled with molten slag and a small part of liquid iron. The pores in hearth coke are not completely filled, but there is still plenty of micropore, with a volume of less than 1 mm3. There are also a little alkali metals (K and Na) in ash, which causes the deterioration of coke. The iron–carbon interface is covered by a slag layer. The coke remained in deadman long enough to undergo the graphitisation process.

Determination of real-time oxygen transfer rate based on an electrochemical method

The interfacial oxygen transfer rate is one of the main factors to control the composition of alloys. The commonly employed method of studying the interfacial oxygen transfer rate is the chemical composition analysis; however, it is difficult to be studied in situ. Here, a new method of measuring the oxygen transfer rate at the gas–slag and slag–metal interfaces was reported based on electrochemical analyses. The interfacial oxygen transfer rate in the smelting process of Inconel 718 superalloy was investigated at 1723, 1773, 1823, and 1873 K. The experimental results show that the electrochemical method can measure the real-time oxygen content; hence, this method is promising in controlling the oxygen content in alloys. As the temperature increased, both the equilibrium oxygen content and the rate of oxygen absorption increased significantly, and the increase was the most obvious when the temperature was 1873 K. The possible reason is that the increase in temperature weakens the mass transfer resistance of the electric double layer at the interface, thus accelerating the oxygen transfer rate.

Harmless Treatment and Valuable Metals Recovery of Tungsten Leaching Residues: A Thermodynamic and Experimental Study

Tungsten leaching residues are industrial wastes that are largely generated during commercial tungsten production. The residues have been classified as hazardous solid wastes due to the presence of toxic elements. On the other hand, the residues contain valuable elements, such as W, Mn, and Fe which can be recovered for economic benefit. To utilize the residue, a carbothermic reduction process was studied to achieve the effective utilization of the residue and sustainable development of the tungsten industry. Fe-W-Mn alloys and nontoxic slags were obtained successfully at 1450°C, and can be used to produce wear-resisting iron materials and glass–ceramics, respectively. The more effective metal–slag separation was achieved by controlling the MnO concentration of the slag, which impacted the liquidus temperature and the viscosity of the slag. This study confirmed a method for utilizing the tungsten residues, which could be a step toward practical industrial-scale techniques.

A Numerical Study on Blowing Characteristics of a Dynamic Free Oxygen Lance Converter for Hot Metal Dephosphorization Technology Using a Coupled VOF-SMM Method

Numerical simulations are performed to explore the basic blowing characteristics of a dynamic free lance converter applied to hot metal dephosphorization technology, in which the sliding mesh model (SMM) is used to regulate the rotation motion of the top lance and the volume of fluid (VOF) model is inducted to simulate flows of gaseous oxygen, liquid slag and metal. The fundamental phenomena such as the motion of phase interfaces, slag–metal emulsion and mixing, and shape and magnitude of the velocity field inside the slag–metal bath are predicted reasonably well, and effects of lance designs including the lance twist angle and rotation speed on the blowing characteristics are evaluated. The results show that the rotation motion of the lance improves the flows inside the molten bath and induces remarkable circumferential and swirl flows around the hot spot. Such flows change the splashing mode and accelerate the dispersion of the splashed metal inside the slag layer, consequently producing a quite uniform distribution of metal phase in emulsion and promoting slag–metal emulsion and mixing. The slag–metal emulsion is strengthened when increasing the lance twist angle, but achieves its minimum at the lance rotation speed of 1.0472 rad/s. The effects of the lance twist angle and rotation speed on flow fields inside the molten bath vary with the bath depth.

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.

A Dynamic Mixed-Control Model for BOF Metal–Slag–Gas Reactions

A Dynamic Mixed-Control Model for BOF Metal–Slag–Gas Reactions

Precious Metal Distributions Between Copper Matte and Slag at High P_{{{text{SO}}_{ 2} }} in WEEE Reprocessing

The distributions of precious metals (gold, silver, platinum, and palladium) between copper matte and silica-saturated FeOx-SiO2/FeOx-SiO2-Al2O3/FeOx-SiO2-Al2O3-CaO slags were investigated at 1300 °C and P_{{{text{SO}}_{ 2} }} = 0.5 atm. The experiments were carried out in silica crucibles under flowing CO-CO2-SO2-Ar gas atmosphere. The concentrations of precious metals in matte and slag were analyzed by Electron Probe X-ray Microanalysis and Laser Ablation-High-Resolution Inductively Coupled Plasma-Mass Spectrometry, respectively. The precious metal concentrations in matte and slag, as well as the distribution coefficients of precious metals between matte and slag, were displayed as a function of matte grade. The present results obtained at P_{{{text{SO}}_{ 2} }} of 0.5 atm were compared with previous results at P_{{{text{SO}}_{ 2} }} of 0.1 atm for revealing the effects of P_{{{text{SO}}_{ 2} }} and selected slag modifiers (CaO and Al2O3) on precious metal distributions at copper matte smelting conditions. The present results also contribute experimental thermodynamic data of precious metal distributions in pyrometallurgical reprocessing of electronic waste via copper smelting processes.

Large Eddy Simulation of Multi-Phase Flow and Slag Entrapment in Molds with Different Widths

Slag entrapment is a critical problem that affects the quality of steel. In this work, a three-dimensional model is established to simulate the slag entrapment phenomenon, mainly focusing on the slag entrapment phenomenon at the interface between slag and steel in molds with different widths. The large eddy simulation (LES) model and discrete particle model (DPM) are used to simulate the movements of bubbles. The interactions between phases involve two-way coupling. The accuracy of our mathematical model is validated by comparing slag–metal interface fluctuations with practical measurements. The results reveal that the average interface velocity and transverse velocity decrease as the mold width increases, however, they cannot represent the severity of slag entrapment at the interface between slag and steel. Due to the influence of bubble motion behavior, the maximum interface velocity increases with mold width and causes slag entrapment readily, which can reflect the severity of slag entrapment. On this basis, by monitoring the change of impact depths in different molds, a new dimensionless number “C” is found to reveal the severity of slag entrapment at the interface between slag and steel. The results show that the criterion number C increases with mold width, which is consistent with the results of flaw detection. Therefore, criterion number C can be used to reflect the severity of slag entrapment in different molds.

Removal of arsenic from “Dirty acid” wastewater via Waelz slag and the recovery of valuable metals

The use of Waelz slag produced during zinc (Zn) hydrometallurgical processes to treat “dirty acid” wastewater was investigated in this study. As(III) in the wastewater was oxidized by performing a pre-oxidation process, after which oxidation leaching, Fe-As co-precipitation, Cu-As cementation, neutralization-hydrolysis, and hematite precipitation processes were performed. The initial As concentration was 8.56 g/L, and the treatment processes decreased the concentration to 0.5 mg/L, which meets the integrated wastewater discharge standard stipulated by the Ministry of Ecology and Environment, P.R China. Most of the As was removed during the Fe-As co-precipitation process as crystalline scorodite at atmospheric pressure, and most of the copper in the Waelz slag was removed during the Cu-As cementation process as Cu3As and Cu2O, which could be used to remove Co from the zinc sulfate (ZnSO4) leaching solution used during Zn hydrometallurgical processes. Fe was precipitated as hematite, which could be used as a raw material to make iron at high temperatures and pressures. The proposed treatment process can effectively remove As from “dirty acid: wastewater and allow the recycling of valuable metals in Waelz slag. The treatment process is therefore efficient and inexpensive, and offers promise for industrial use.