Reduction Of Slag Research Articles

Numerical Analysis of Blast Furnace Performance Under Charging Iron-Bearing Burdens With High Reducibility

The reducibility of iron-bearing burdens was emphasized for improving the operation efficiency of blast furnace. The blast furnace operation of charging the burdens with high reducibility has been numerically evaluated using a multi-fluid blast furnace model. The effects of reaction rate constants and diffusion coefficients were investigated separately or simultaneously for clarifying the variations of furnace state. According to the model simulation results, in the upper zone, the indirect reduction of the burdens proceeds at a faster rate and the shaft efficiency is enhanced with the improvement under the conditions of interface reaction and intra-particle diffusion. In the lower zone, direct reduction in molten slag is restrained. As a consequence, CO utilization of top gas is enhanced and the ratio of direct reduction is decreased. It is possible to achieve higher energy efficiency of the blast furnace, and this is represented by the improvement in productivity and the decrease in consumption of reducing agent. The use of high-reducibility burdens contributes to a better performance of blast furnace. More efforts are necessary to develop and apply high-reducibility sinter and carbon composite agglomerates for practical application at a blast furnace.

REDUCTION OF NICKEL-COPPER MATTE/OXYSULFIDE/SLAG

To improve the value of recovered metals, a new operating concept for the Inco flash furnace was investigated in which the flash furnace coke addition practice aimed to establish a reducing barrier on the surface of the molten bath. The descending partially oxidized sulfide mineral particles would reach the supernatant coke layer prior to the formation of slag. The key for success depends on the effectiveness of the coke layer to produce a sulfur deficient matte while maintaining the furnace production capacity.The mechanism and rate of carbon reduction of the phases formed in the flash flame (i.e., sulfide (matte) and oxysulfide) were investigated by means of crucible graphite reduction tests. The objective of these tests was to measure the rate of solid graphite reduction of matte, oxysulfide, slag and matte+slag mixture at different temperatures. These tests were expected to permit understanding and explain the reduction mechanism of each material by comparing the respective reaction rates, product reaction gas compositions, reduced material assays and other relevant parameters. Direct visual inspection of the test crucibles would provide additional information.Afin d’améliorer la valeur des métaux récupérés, on a étudié un nouveau concept d’opération du four éclair d’Inco, dans lequel la pratique d’addition de coke du four éclair visait à établir une barrière de réduction à la surface du bain fondu. Les particules minérales descendantes de sulfure, partiellement oxydées, attendraient la couche de coke surnageante avant la formation de scorie. La clé du succès dépend de l’efficacité de la couche de coke à produire une matte déficiente en souffre tout en maintenant la capacité de production du four.On a étudié le mécanisme et le taux de réduction du carbone des phases formées dans la flamme éclair (i.e. sulfure (matte) et oxysulfure) au moyen d’essais de réduction de creuset en graphite. L’objectif de ces essais était de mesurer le taux de réduction du graphite solide de la matte, de l’oxysulfure, de la scorie et du mélange matte+scorie, à différentes températures. On s’attendait à ce que ces essais permettent de comprendre et d’expliquer le mécanisme de réduction de chaque matériau en comparant les taux respectifs de réaction, la composition des gaz de réaction produits, les balances du matériau réduit et autres paramètres pertinents. L’inspection visuelle directe des creusets d’essai fournirait de l’information additionnelle.

Slag cleaning in crossed electric and magnetic fields

Slags from smelting of copper concentrate contains from 2% to 20% of copper and are directed to slag cleaning operation carry out in electric furnaces or other slag cleaning reactors with injection of carboneous reductant. Ionic structure of liquid slags points out the possibilities of utilization of slag electrolysis in reduction of magnetite and precipitation of dissolved copper as well as electrokinetic phenomena in acceleration of removal of metal or matte inclusions from the slag. Analysis of physico-chemical phenomena, mathematical and fluidodynamic modeling of slag reduction and cleaning allowed for development of a new concept of slag cleaning in crossed electric and magnetic fields. Results of slag cleaning in a large laboratory scale confirmed expectations, showing the possibilities of very intensive slag reduction and copper recovery.

Reduction Behaviour of BOF type Slags by Solid Carbon

Experiments were carried out on a system with artificially prepared slags in a graphite crucible, in order to examine the possibility of recycling BOF slags produced in the steelmaking process. More than 80% of FeO and P2O5 was reduced within 20 minutes and the FeO reduction rate was greater than that of P2O5. P2O5 reduction began after more than 60% of FeO was reduced. Increasing slag basicity enhanced the reduction of FeO and P2O5. Temperature also improved slag reduction. The overall reduction rate was controlled by the chemical reaction at the slag/carbon interface. The reduction rates of FeO and P2O5 were second and first order with respect to their respective contents. Most of the reduced phosphorus is believed to vaporize in the form of P2 gas.

Reduction Behaviour of BOF Slags by Carbon in Iron

Experiments were carried out in a system with BOF slags from industrial operations in order to optimize the conditions of recycling BOF slags produced in the steelmaking process. Reduction reactions of FeO and P2O5 proceeded steadily and the FeO reduction rate was almost identical to that of P2O5. The reduction reaction of FeO and P2O5 in BOF slag at the slag/gas interface is the rate‐controlling step. The reaction rates of FeO and P2O5 by dissolved carbon in molten iron are of first order with respect to their respective concentrations. The reduction reactions of FeO and P2O5 by dissolved carbon in iron are much closer to the equilibrium state compared with the reduction by solid carbon. It is necessary to control the portion of phosphorus vaporization during reduction treatment in order to obtain efficient operational conditions for BOF slag reduction.

Basic oxygen furnace based steelmaking processes and cleanliness control at Baosteel

Optical microscopy, total oxygen measurements and slime tests have been conducted to quantify the size distribution and amount of inclusions at various processing steps during basic oxygen furnace (BOF) based steel production at Baosteel. The effects on steel cleanliness of specific operational improvements during steel refining and continuous casting have been investigated. Such improvements to these processes and the resulting level of steel cleanliness at Baosteel are summarised in the present paper. Ladle slag reduction lowers FeO+MnO in the slag to below 5%, decreasing steel reoxidation by the slag. Calcium treatment by CaSi wire injection during ladle furnace (LF) refining is used to modify inclusions and improve submerged entry nozzle (SEN) clogging. Slag detection is employed at the ladle bottom during continuous casting. Flow control devices, CaO containing filters and high CaO based basic powder with CaO/SiO2>4 are used in the tundish to remove more inclusions. Several improvements to the castability and in the attainment of clean steel at mould operations have also been made. With this BOF based steelmaking process, impurity levels can be controlled to achieve total oxygen (TO)<16 ppm, [S]<5 ppm, [P]<35 ppm, [N]<29 ppm, [H]<1 ppm in line pipe steels, and [C]<16 ppm, TO<19 ppm, [N]<15 ppm in interstitial free (IF) steels.

Slag Reduction in the Coke Bed of a Blast Furnace

Slag Reduction in the Coke Bed of a Blast Furnace

Feasibility of manufacturing phosphoric acid by smelting reduction technology

In this paper, a new process for directly making phosphoric acid from phosphorus ore by smelting reduction with postcombustion is presented based on the experience in smelting reduction for iron-making. Theoretically, the new process can save energy when compared with the traditional pyro-process for the manufacture of phosphoric acid. Laboratory simulation shows that it is possible to make phosphoric acid by smelting reduction with postcombustion process. Fundamental research on phosphate reduction in molten slag is carried out. Experimental results show that the reduction rate increases with the increase of temperature, basicity of slag, and stirring intensity of the molten slag. Carbon dissolved in the liquid Fe–P–C alloy has a greater reduction potential than solid carbon. Under the condition of slag basicity (CaO/SiO2) equal to 1˙1, and the concentration of Al2O3 at 8˙3%, the reduction rate constant by solid carbon can be expressed as k = 1˙1 × 103 exp(–217 360/RT). The rate constant for reduction by carbon in liquid Fe–P–C alloy is about 10 times larger than that for solid carbon under similar conditions. The reduction by bubbling CO gas is close to the thermodynamic equilibrium assuming that bubbles escape from the slag bath.

Reduction of Chilean copper slags: a case of waste management project

The Chilean copper smelters are producing large amount of copper slags. These copper slags are deposited at landfills. In the present time, a huge amount of copper slags are accumulated in Chile. The main problem with landfilling is not only the land space, area which is used for copper slags deposition every year, but many environmental problems, high disposal and transport cost are associated with the landfilling of these slags. Therefore, the focus of environmental policy is now into waste minimization and recycling to minimize transport and disposal cost, saving resources as well as land space. Copper slag contains many useful metals and slag making oxides, which can be recovered and recycled by a high temperature direct reduction process. The laboratory scale tests show that by suggested high temperature direct reduction of copper slags two products can be obtained, a Fe–Cu–C alloy with precious metals content and an inert slag with low metal content. The Fe–Cu–C alloy can be used for metal production and inert slag for cement production similar to blast furnace slags. Suggested high temperature direct reduction process for copper slags treatment is commercially feasible and environmentally friendly without any solid or liquid waste.

Characterization of Si-Based Nanoparticulates Produced by Carbothermic Reduction of Silica-Containing Slag

Si-based nanoparticles, nanochains and nanowires were synthesized by smelting reduction method which includes a high temperature carbothermic reduction of silica-rich melt to SiO vapor and transfer of the vapor with Ar carrier-gas to cooler surfaces inside the experimental reactor where the nanoparticulates were deposited. Features of the process have been discussed in our previous paper. In this paper, the synthesized nanoparticulates were characterized by using XRD, XPS, EDX, TEM and HRTEM analysis. The deposition temperature was found to be the crucial parameter governing the nanoparticulate morphology and phase composition. The nanowires were obtained in the high temperature range of 1320–1570 K. It is found that the as-obtained nanowires were composed of a SiC core and an amorphous sheath of silicon suboxide. The nanowires had diameter ranging from 20 to 60 nm and length up to several microns. The rounded nanoparticles of 30–50 nm in diameter were deposited at locations under temperatures lower than 920 K. They were mainly composed of amorphous silicon suboxide which could be decomposed under certain conditions yielding Si nanocrystallites embedded into the oxygen enriched suboxide matrix. The nanocrystallite size was estimated to be of 3–8 nm although much larger, up to 50 nm, Si crystals were detected at high temperature locations.

Formation of SiO and Related Si-Based Materials Through Carbothermic Reduction of Silica-Containing Slag

Silicon based nanoparticulates of various composition and morphology have been produced by smelting reduction method which includes a carbothermic reduction of SiO2–Al2O3–CaO starting materials to SiO vapor at 2073 K and transfer of the vapor with a carrier-gas to cooler surfaces inside the experimental reactor where the nanoparticulates were deposited. The chemical composition of the starting materials was matched to the basic composition of silica-rich coal ash which is considered as a potential source of Si in this study. Special emphasis was placed upon examining the degree of SiO2 reduction from starting materials, purity and morphology of the as-obtained nanomaterials. It is shown that up to 20% of Si can be converted from the silica-based melt into rounded nanoparticles, nanoparticle chains and nanowires containing Si,O and C in variable proportions depending on deposition temperature and gas flow conditions. The diameter of nanoparticulates was estimated to be in the range of 20∼100 nm. The nanoparticles and chains were found to be deposited at lower temperature locations (293∼1320 K) while the nanowires were obtained at higher temperatures (1320∼1570 K). There was a tendency for an increase in Si concentration in order of nanowires, nanoparticles chains and nanoparticles. The carbon concentration, on the contrary, was much higher in nanowires as compared to that in nanoparticles. Although the degree of SiO2 reduction from silica-containing melt to SiO vapor is limited because a part of SiO2 reacts with C producing SiC, its good controllability, high productivity and possibility for processing cheap starting materials make the smelting reduction a very attractive technique for production of silicon based nanostructured materials.

Reduction of steel‐making slags for recovery of valuable metals and oxide materials

Extensive researches on slag reduction for recovery of valuable metals and oxide materials from metallurgical slags and other wastes using a DC furnace with a hollow electrode have been conducted in 2 major EU projects with close cooperation between MEFOS, FEhS and CRM. Steel slags and other residues were introduced into the reactor through the hollow electrode to the hot plasma. The materials were melted, reduced and mixed. The final products were a metal product, a slag product with targeted chemical composition and a dust fraction with a high content of ZnO. Different steel‐making slags and residues including BOF slag with low and high V‐content as well as EAF and AOD slags from stainless steel production, EAF dust, oily millscale, hydroxide sludge, BOF and BF dust have been treated. The slag products include a metallurgical powder for desulfurization of steel, hydraulic binder and slag stones for construction applications. The metals obtained are rich in Fe, Mn, V and Cr depending on the treated slag and residues. The environmental compatibility and mechanical properties of the slags have been improved after slag reduction.

電炉スラグの粒化処理

Recently, the improvement of working environment for treating electric arc furnace slag and the expansion of uses for treated slag as the product have become an important issue in Japan. To solve these problems, OJI Steel Co., Ltd. has introduced the new slag granulating equipment developed by Nippon Steel Corporation and Hamada Heavy Industries, Ltd. which has the following features. (1) The combination of mechanical crushing in a two-stage rotating drum and quick cooling by water spraying enables to direct production of granulated slag as the product from molten slag with low energy consumption. (2) The product is small spherical particles which promise wider applications due to their physical properties. (3) Compared to the conventional slag treatment which involves slow cooling in a pit and mechanical crushing of solid slag, the working environment is improved and plant space is economized. The manufacturing technology of slag particles with mixing the oxidation slag and the reduction slag has been established by Oji Steel though operation wise improvement for stable slag granulation after its start-up in May 2000.

Factors Governing Slag Cleaning in an Electric Furnace

Slags from the El Teniente Converter have high copper and magnetite contents. The reduction and copper impoverishment of these slags in an electric furnace were simulated in the laboratory as part of a conceptual study for the Las Ventanas Smelter of ENAMI. The effects of power input, electrode immersion, slag temperature and coke and solid revert additions on the rate of magnetite reduction and copper recovery were investigated. It was found that the rate of slag reduction is strongly dependent on electrode power density. The addition of solid reverts containing copper matte enhanced the recovery of copper. Magnetite stratification and a corresponding gradient in copper content occurred in the slag. The experimental results, combined with an analysis of the phenomena taking place in an electric furnace, led to an improved understanding of the slag cleaning mechanism and contributed to the successful start up of the slag cleaning electric furnace at the Las Ventanas Smelter.

Factors Governing Slag Cleaning in an Electric Furnace

Slags from the El Teniente Converter have high copper and magnetite contents. The reduction and copper impoverishment of these slags in an electric furnace were simulated in the laboratory as part of a conceptual study for the Las Ventanas Smelter of ENAMI. The effects of power input, electrode immersion, slag temperature and coke and solid revert additions on the rate of magnetite reduction and copper recovery were investigated. It was found that the rate of slag reduction is strongly dependent on electrode power density. The addition of solid reverts containing copper matte enhanced the recovery of copper. Magnetite stratification and a corresponding gradient in copper content occurred in the slag. The experimental results, combined with an analysis of the phenomena taking place in an electric furnace, led to an improved understanding of the slag cleaning mechanism and contributed to the successful start up of the slag cleaning electric furnace at the Las Ventanas Smelter.

The role of slag modifiers on the selective recovery of cobalt and copper from waste smelter slag

Slag cleaning is important from both an economical and environmental perspective. Dump slags from copper smelting prove to be a valuable source of base metals, but the abundance of iron in the slag leads to significant amounts of iron reporting to the alloy phase during carbothermic reduction, which poses a significant cost to remove in subsequent hydrometallurgical processes. A carbothermic reduction of nonferrous smelter slag was conducted under the influence of three different slag modifiers to investigate the recovery of cobalt (and copper) versus iron recovery. The test work was performed in two campaigns; one campaign was performed under a constant oxygen potential of 4.33×10 −9 atm, while the other set of test work was performed using graphite under a pure argon atmosphere. It is shown in both cases that, out of these slag modifiers used, TiO 2 had a more selective recovery of cobalt compared to CaO and CaF 2. It appears that TiO 2 reduces the activity coefficient of the FeO in slag due to its strong affinity for FeO in the slag phase.

Corrosion resistance of MgO–C refractory to smelting reduction slag containing titania

Interactions between smelting reduction slags containing titania (0·2-20 wt-%TiO2) and MgO-C refractories have been investigated by stationary immersion and rotary immersion at temperatures of 1773-1923 K. The relationship between the concentration of TiO2 in the slag and the corrosion rate of the refractories, the effects of slag basicity (CaO/SiO2), and the effect of the temperature of the molten bath on the corrosion rate were examined. Increasing the TiO2 concentration in the slag caused an increase in the corrosion rate of the MgO-C refractories. The corrosion rate also increased when the temperature was increased. Increasing the basicity of the acid slag decreased the corrosion rate, but this effect was not evident when the basicity of slag exceeded 1·0. The corrosion mechanism of MgO-C refractories in smelting reduction melts containing titania involves the oxidation of graphitic carbon by TiO2 and the formation of a deterioration layer containing Ti and TiC, together with the reaction of matrix MgO with slag to form MgAl2O4, MgCaSiO4, and MgSiO3.

Kinetic Modelling of MnO Reduction from Manganese Ore

This paper analyzes the results of MnO reduction from manganese ore and ferromanganese slag obtained at NTNU (Trondheim) and UNSW (Sydney). Manganese ore upon melting consists of two phases: solid MnO phase which may be a pure MnO oxide or a MnO-MgO solid solution and liquid slag. The process of manganese ore reduction includes MnO phase dissolution into the molten slag and MnO reduction from the slag. It is suggested that the reduction rate of MnO is controlled by the intrinsic kinetic step. The proposed kinetic model takes into account changes in the interfacial area and manganese oxide activity in the slag in the course of reduction. The kinetic model is used to examine effects of temperature, ore composition, CO partial pressure, coke size and reaction time on the extent of MnO reduction. Kinetic constraints in electric furnace and blast furnace ferromanganese making are also discussed.

Oxygen pressure in the Outokumpu flash smelting furnace—Part 2: the DON process

Oxygen-activity measurements and sampling for chemical assay were carried out in a nickel flash smelting furnace and slag-cleaning electric furnace during industrial operation. In the primary Direct Outokumpu Nickel (DON) smelting furnace, which produces high-grade nickel matte, the oxygen activity and chemical compositions of the slag and matte were quite uniform throughout the settler and no differences in oxygen potential were found across the slag-matte interface. In the course of batch slag reduction by surface coke a clear oxygen-activity gradient developed in the slag layer, but chemical gradients in the non-foamy bath were small. The distribution coefficients of selected impurity elements in DON smelting are reported.

Kinetics of iron oxide reduction in molten slag

Kinetics of iron oxide reduction in molten slag