Reduction Of Slag Research Articles

Fundamental Research on a Rational Steelmaking Slag Recycling System by Phosphorus Separation and Collection

Recently, reduction of the steelmaking slag stock in Japan has been required, but utilization of steelmaking slag is restricted due to its chemical properties. On the other hand, the price of phosphorus ore is increasing rapidly due to the very tight supply/demand balance worldwide. In this work, (FetO) and (P2O5) reduction in steelmaking slag and recovery as a phosphorus source were investigated in feasibility studies and laboratory-scale experiments in order to develop a rational recycling process for steelmaking slag. The results are summarized as follows: (a) Steelmaking slag was reduced by carbon under high temperature conditions (1373–1873 K), and high-P hot metal was recovered. The phosphorus content of the reduced slag was <0.3 mass%. (b) Higher temperatures were required for slag reduction with carbon, corresponding to increasing slag basicity. (c) The oxygen partial pressure calculated from the FeO content ranged from 10−13 to 10−17 atm. More than 50 mass% of phosphorus in the slag can be removed under the condition that FeO activity is less than 0.01. (d) From the mass balance of phosphorus, 0–30 mass% of undefined phosphorus was observed, which was estimated by thermodynamic calculations and SEM-EPMA analysis to be caused by gaseous dephosphorization. (e) The gaseous dephosphorization ratio becomes more than 10% at the condition of log LP ≤ 0. (f) Phosphorus was enriched in slag to higher than 30 mass% P2O5 by dephosphorization of high-P (1.05 mass%) hot metal.

Effect of Modification Treatment for Reduction of Dephosphorization Slag in Hot Metal Bath

To extract the valuable elements from the steel slag, a novel approach has been proposed by modification treatment to provide the stronger driving forces and accelerate the reduction. Three types of dephosphorization steel slags were reduced using carbon-saturated iron bath to extract iron and phosphorus simultaneously. During the process of reduction, slag composition, temperature, and original P2O5 content were investigated respectively. Slag modification treatment, adding either silica or alumina to vary the slag composition, was proven to accelerate the reduction of dephosphorization slag. The equilibrium time can be shortened from 60 to 30 min. Slag modification also allowed the reduction reaction to occur at lower temperature. After slag modification, the original P2O5 content in slag presents a slight difference on reduction process. Almost half of the reduced phosphorus was vaporized within 5 and 20 min. As more and more FeO was reduced, CO gas generation decreased, and evaporation amount of phosphorus therefore decreases.

Smelting Oxidation Desulfurization of Copper Slags

According to the mechanism of sulfur removal easily through oxidation, the process of smelting oxidation desulfurization of copper slags is studied, which supplies a new thinking for obtaining the molten iron of lower sulfur content by smelting reduction of copper slags. Special attention is given to the effects of the holding temperature, the holding time and CaF2, CaO addition amounts on the desulfurization rate of copper slags. The results mdicate that the rate of copper slags smelting oxidation desulfurization depends on the matte mass transfer rate through the slag phase After the oxidation treatment, sulfur of copper slags can be removed as SO2 efficiently. Amount of Ca2+ of copper slags affects the desulfurization rate greatly, and the slag desulfurization rate is reduced by adding amount of CaF2 and CaO. Compared with CaF2, CaO is negative to slags sulfur removal with equal Ca2+ addition. Under the air flow of 0.3 L/min, the sulfur content of copper slags can be reduced to 0.00467% in the condition of the holding time of 3 min and the holding temperature of 1500°C. The sulfur content of molten iron is reduced to 0.0008% in the smelting reduction of treated slags, and the problem of high sulfur content of molten iron obtained by smelting reduction with copper slag has been successively solved.

Valorisation of steelmaking slag by microwave treatment

In order to optimise the recovery process of Fe and P from industrial steelmaking slag by microwave irradiation, the recovery ratios of Fe and P from slag–graphite mixtures were investigated. In the reduction of industrial slag by graphite at a fixed microwave processing time of 900 s using a microwave oven, the recovery ratio of Fe increased with increasing carbon equivalent (Ceq.: the mole ratio of carbon/oxygen to reduce Fe2O3 and FeO, yielding CO gas) and reached 0·87 when Ceq. = 1·56. The recovery ratio of P also increased with Ceq. and showed 0·93 at the same condition. From the comparison between the present and previous studies by Kim and Lee employing a synthetic slag, it was found that almost similar results were obtained. From the chemical analysis of the slag and metal after experiments, it was found that the phosphorus distribution ratio (Lp) strongly depended on the total Fe content in the slag, namely, as the FeO content decreased, the Lp value decreased. Discrepancies observed between the present and previous studies are discussed in view of microwave power and thermodynamic analysis.

Induced polarization 3D tomography of an archaeological direct reduction slag heap

ABSTRACTBoth environmentalists and archaeologists are interested in the detection and quantification of the remains of mine slag heaps from ancient smelters: possible pollution of the slag heaps and information concerning the history of the smelter's mine. Although magnetic surveys can be used to detect subsurface slag accumulations, it is not possible to derive the total amount of material from such surveys or to accurately delineate the heaps through the use of this method. Conversely, ‘Induced Polarization’ (IP) surveying allows a relevant and robust assessment of the volume of slag concentrations to be determined. In the present study, we follow up on results obtained in a previous study, carried out at the 14th Castel‐Minier mine (Ariège, France) site, where we have shown that the chargeability is proportional to the slag concentration in the ground and have used this property to perform 3D tomography of the heap. Based on a previous investigation using spectral induced polarization along a simple profile showing that the phase peak related to the slags is situated at approximately 1 Hz, in the present paper we extend our prospection to 3D by using a Terrameter SAS1000 and measuring temporal chargeability. The set of three‐dimensional data is recorded by means of classical transect measurements along parallel close profiles and is then interpreted using the RES3DINV code. Finally, archaeological and auger soundings confirmed the assessments derived from this geophysical investigation. We also briefly discuss the source of the IP signal, which we suspect to be induced by magnetite particles embedded in the slags.

Electrolytic Reduction of Titania Slag in Molten Calcium Chloride Bath

Ferro-titanium is prepared by direct electrolytic reduction of titania-rich slag obtained from plasma smelting of ilmenite in molten CaCl2. The product after electro-reduction is characterized by x-ray diffraction, scanning electron microscopy, and electron probe microanalysis. The electrolysis is carried out at a cell voltage of 3.0 V, taking graphite as the electrolysis cell as well as the anode, and a titania-rich slag piece wrapped by a nichrome wire is used as the cathode.

Myocardial Ischemia in Women: Lessons From the NHLBI WISE Study

Cardiovascular disease (CVD) remains the leading cause of death for women. For almost 3 decades, more women than men have died from CVD, with the most recent annual statistics on mortality reporting that CVD accounted for 421 918 deaths among women in the United States. Although there have been significant declines in coronary heart disease (CHD) mortality for females, these reductions lag behind those seen in men. In addition, where there has been a decrease in mortality from CHD across all age groups over time in men, in the youngest women (age <55 years) there has been a notable increase in mortality from CHD. There are differences in the prevalence, symptoms, and pathophysiology of myocardial ischemia that occurs in women compared with men. In this paper, we review the pathophysiology and mechanisms of ischemic heart disease (IHD) in women, particularly focusing on what we have learned from the WISE study. We examine the sex-specific issues related to myocardial ischemia in women in terms of prevalence and prognosis, traditional and novel risk factors, diagnostic testing, as well as therapeutic management strategies for IHD.

Understanding stainless steelmaking through computational thermodynamics: Part 3 – AOD converting

The major issue in stainless steelmaking is the difficulty of oxidising carbon from molten steel without also oxidising large proportions of expensive chromium. This can, however, be achieved by reducing the partial pressure of the gaseous product of carbon oxidation, carbon monoxide, by dilution with argon. Modern stainless steelmaking is dominated by duplex processes which prepare a high carbon melt in an electric arc furnace, and then decarburise it in an argon–oxygen decarburisation (AOD) converter. In this work, the thermodynamic basis of preferential carbon oxidation by dilution of oxygen with argon is discussed, together with a review of AOD practice. The AOD process was simulated using computational thermodynamics software to illustrate the way in which it can achieve very low carbon levels in the molten steel bath without excessive co-oxidation of chromium. The slag reduction stage using ferrosilicon additions was also modelled and shown to be able to recover almost all oxidised chromium from the slag, limited only by the accompanying increase in the silicon content of the steel. The models, although simple and easy to develop, correctly predicted all trends in output variables as input parameters were changed and often matched plant data very well. The models provide a valuable learning tool for those interested in pyrometallurgical processing in general, and stainless steelmaking in particular.

ATDM炼镁工艺的物料的导热系数测定

采用稳态平板法研究了ATDM工艺过程物料的导热系数。实验结果表明：温度升高，原料中铝粉添加量增加，CaF2添加量增加都能提高物料的导热系数。原料中铝的熔化对物料的导热系数影响较大。随着还原反应进行，物料的导热系数降低。添加CaF2将降低还原渣的导热系数。导热系数随温度的变化满足线性关系。 The thermal conductivity of ATDM process’ materials was investigated by steady-state-flat method. The results show that thermal conductivity increased with the increase of temperature or the added amount of Al or the added amount of CaF2. There is an important effect of melt of Al on the thermal conductivity of raw materials. The thermal conductivity of reduction slag decreased with the proceeding reduction reaction and it will be decreased further when CaF2 was added. It indicated a good linear relation between thermal conductivity and temperature.

Recovery of iron from copper flash smelting slags

Copper slag is produced in large amounts in seven copper smelter plants in Chile, and it is estimated that around four million tons of slag are disposed every year, and another 40–45 million tons are historically cumulated. Copper slag contains iron in the range of 42–45%, which can be recovered and recycled along with the contained copper to obtain an iron–copper alloy and a final slag rich in oxides. Therefore, the present work shows the experimental results of the reduction of a flash smelting slag using coke as reductant up to 150% of the stoichiometric carbon required to reduce copper oxide and magnetite. The characterisation and thermodynamic stability of compounds contained in the slag are presented, and the obtained results show the feasibility for recovering an iron rich alloy with iron contents higher than 98% and copper in the range of 0·6–0·8% using a two‐step process.

Recovery of Fe and P from CaO-SiO&lt;SUB&gt;2&lt;/SUB&gt;-Fe&lt;SUB&gt;t&lt;/SUB&gt;O-P&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;5&lt;/SUB&gt; Slag by Microwave Treatment

In order to optimize the recovering process of Fe and P from steelmaking slag by the microwave irradiation, heating rates of various substances and recovery ratios of iron and phosphorus from slag-graphite mixtures were investigated. The heating rates of the examined substances are in the order of graphite >> Fe3O4 >> Fe2O3 > the synthesized CaO-SiO2-FetO-P2O5 slag > the industrial slag. From the maximum heating rates, it was considered that the microwave absorption ability of graphite was 40 times greater than that of the industrial slag. Consequently, it was considered that the heating rate of the graphite-slag mixture was dominantly determined by graphite. In the reduction of the synthetic slag (15 g) by graphite (0.816 g), the weight of the recovered metal was maximized at 900 s under the present experimental condition (1.7 kW, 2.45 GHz). At a fixed microwave processing time of 900 s, the recovery ratio of iron increased with increasing the carbon equivalent (Ceq.: the mole ratio of carbon to oxygen to reduce Fe2O3 and FeO, yielding CO gas), and reached 0.97 when Ceq.=1.69. The recovery ratio of phosphorus also increased with Ceq., and showed 0.89 at the same condition. From the chemical analysis of the slag and metal after experiments, it was found that the phosphorus distribution ratio (Lp) strongly depended on T. Fe content in slag, namely, as FeO content decreased, Lp value decreased.

Reduction of FeO in EAF Steelmaking Slag by Metallurgical Coke and Waste Plastics Blends

In Australia, the use of plastics has increased tremendously over the last few decades, but less than 20% of the waste plastics are recycled. The rest is usually landfilled, which poses major environmental problems. The solution to this problem involves the development of novel environmentally-benign technologies that would utilise these waste materials. This work investigates the reduction of EAF slags (47% FeO) by blends of metallurgical coke with High-Density Polyethylene (HDPE) plastics at 1550°C. The experiments were conducted in a laboratory-scale horizontal tube furnace, and were coupled with off-gas analysis using an infrared gas analyser and a multiple gas chromatographic analyser. The results indicate that the rate of FeO reduction in slags is significantly higher when the coke/plastics blends were used compared to pure coke, with the maximum rate of reduction (Blend 4) being over twice that of coke. Moreover, the CO2 content in the off-gas was observed to decrease (by ~75%) with increase in the polymer content of the blend. Additionally, the degree of carburisation and the removal of sulphur from the metal improved considerably when the coke was blended with plastics. The observed improvements in the rates of reduction, carburisation and desulphurisation are attributed to the reactions of hydrogen evolved from the waste plastics at these high temperatures.

Prevention of Fluorine Elution from Electric Arc Furnace Reducing Slag into Water

Elution of fluorine from landfill slag by rainwater or groundwater causes serious problems; hence, fixation of fluorine in electric arc furnace reducing slag (EAFRS) is crucial. The phase including fluorine was identified for some EAFRS specimens and confirmed is as (3CaO·2SiO2)·CaF2 in the current work. Experiments to determine the dissolution of fluorine from the EAFRS into water were conducted at pH 4, 7, and 10. It was found that fluorine tended to elute under acidic conditions. Therefore, the elution of fluorine from fluorine-containing substances into water at pH 4 was investigated in detail. It was found that 2(2CaO·SiO2)·CaF2, (3CaO·2SiO2)·CaF2, and CaF2 were unstable, while the 3(3CaO·P2O5)·CaF2 phase was stable; further, fluorine elution from 3(3CaO·P2O5)·CaF2 into water was found to be limited. On the basis of these results, it was concluded that the dissolution of fluorine into water can be suppressed by adding a sufficient amount of P2O5 to EAFRS, so that the formation of unstable fluorine-containing substances is prevented.

Interaction mechanism between refractory and melts in iron bath smelting reduction process

The corrosion behavior of three sorts of refractories based on alumina-graphite were studied by immersion tests. The melts included smelting reduction molten slag and corresponding carbon saturated molten iron. The influence of test temperature, FeO content in slag and specimen rotative velocity on the corrosion rate of refractories was examined. By means of SEM and EDS, the microstructure change of the refractories after immersion test in kinds of melts was studied. The morphology of the deteriorated layer showed the corrosion extent of refractories. With the addition of zirconia and titania into the refractories, the corrosion rate changed to some extent. The corrosion rate of three sorts of refractories increased dramatically with the increasing FeO content in smelting reduction slag. Compared with alumina-graphite refractory and alumina-graphite-zirconia refractory, alumina-graphite-titania refractory had stronger corrosion resistance in the smelting reduction conditions. By the results of SEM and EDS, the corrosion mechanism of refractories was developed.

Behavior of CO2 Absorption in Wet-grinding of Electronic Arc Furnace Reducing Slag by Vibration Ball Mill

A fundamental study was carried out in order to fix CO2 on slag. The electronic arc furnace reducing slag was wet-ground by a vibration ball mill under CO2 atmosphere. The effect of grinding conditions on the behavior of CO2 absorption was investigated.The rate of the absorption of CO2 under wet grinding was larger than that under dry grinding. The total amount of CO2 absorption increased with the increase in total amount of the slag and water in case that the weight ratio of the water to the slag was kept constant. The CO2 was fixed as CaCO3 and Ca4Si2O6(CO3)(OH, F)2. Any compounds of Mg were not detected by XRD after the experiment. In the early stage of grinding, the CO2 was absorbed even if the grinding was stopped. The concentration of Ca in the water was larger than the solubility of Ca(OH)2. Hence, the absorption of CO2 was determined by the surface reaction that consisted of chemical reaction and mass transfer in liquid. In the latter stage of grinding, the CO2 was not almost absorbed immediately after the grinding was stopped. The concentration of Ca in water was small. Accordingly, the absorption of CO2 was influenced by the dissolution of slag into water.The amount of the exhausted CO2 was calculated from the electronic power which was necessary for operating this experimental apparatus. The amount of CO2 absorption was larger than that of the exhausted CO2 from a solar, an atomic, a wind and a water power plant.

Absorption of CO2 in EAF Reducing Slag from Stainless Steel Making Process by Wet Grinding

Absorption of CO2 in EAF Reducing Slag from Stainless Steel Making Process by Wet Grinding

Experimental Investigations on V-containing Steelwork Slags with a Low V2O5 Content

Processing of ferrous slags with low vanadium content by pyrometallurgical processes represents one possibility for the simultaneous production of a ferrovanadium alloy and saleable slag for the building material industry. Besides the thermodynamic calculations, different experiments have to be carried out to investigate this process route that consists of an enrichment of V2O5 in the slag and a following aluminothermic reduction step to produce a ferrovanadium alloy that can be used in the steel industry. Different parameters like reduction time, stirring and slag ratio were investigated at the Institute of Nonferrous Metallurgy at the University of Leoben.

Cleaning of a copper matte smelting slag from a water-jacket furnace by direct reduction of heavy metals

Cleaning experiments of a copper matte smelting slag from the water-jacket furnace was undertaken by direct reduction in a laboratory-scale electric furnace. The effects of coal-to-slag ratio, w, and the reduction time, t, were considered for two different coal/slag mixing procedures. In the first procedure, metallurgical coal was added to the molten slag, whereas in the second procedure, coal was premixed with the solid slag before charging into the furnace. The recovery of heavy metals (Cu, Co), and the fuming of Pb and Zn were investigated. Contamination of the metal phase by iron and the acidity index of the final slag were analysed as these may impede the economical viability of the process. The lower w value of 2.56% yielded a recovery rate of less than 60% for copper and less than 50% for cobalt, and around 70% for zinc. However, increasing w to 5% allowed the recovery of 70–90% for Cu, Co and Zn simultaneously after 30–60 min reduction of the molten slag. After reduction, the cleaned slags contained only small amounts of copper and cobalt (<0.4 wt%). Fuming of lead and zinc was efficient as the %Pb of the residual slag dropped to levels lower than 0.04% after 30 min of reduction. Ninety percent of the lead was removed from the initial slag and collected in the dusts. The zinc content of the cleaned slags quickly dropped to between 1 and 3 wt% from the initial 8.2% after 30 min reduction for w value of 5 and after 60 min reduction for w value of 2.56. The dusts contained about 60% Zn and 10% Pb. Recovery of lead from fuming of the slag was higher than 90% in all the experimental conditions considered in this study.

Kinetic of Carbothermic Reduction of MnO from High-carbon Ferromanganese Slag by Graphite Materials

The kinetics of MnO reduction from a synthetic ferromanganese slag by different graphite materials was investigated using sessile drop wettability technique. It was found that the graphite substrates are not wetted by the slag drop at 1450°C, 1500°C and 1600°C. On the other hand, processing the photos taken during the reduction revealed that the contact angle between the graphite substrates and the slag drop is not changing appreciably during slag reduction, while the changes in the slag drop volume are more significant. A new method was developed and applied to convert the changes in the slag drop volume to the MnO concentration and therefore the MnO reduction curves for different graphite substrates were extracted. The relationship between the density of slag and its MnO content was also studied. A new kinetic interpretation method was developed and a main differential equation for carbothermic MnO reduction from a slag drop in sessile drop method was obtained. This method was used to calculate the MnO reduction rate constants for different graphite materials considering the changes in the slag/carbon contact area. Multivariate analysis was also used to determine the possible relationships between the graphite properties and the MnO reduction rate.

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.