Modeling of zinc solubility in stabilized/solidified electric arc furnace dust

Equilibrium models which attempt for the influence of pH on the solubility of metals can improve the dynamic leaching models developed to describe the long-term behavior of waste-derived forms. In addition, such models can be used to predict the concentration of metals in equilibrium leaching tests at a given pH. The aim of this work is to model the equilibrium concentration of Zn from untreated and stabilized/solidified (S/S) electric arc furnace dust (EAFD) using experimental data obtained from a pH-dependence leaching test (acid neutralization capacity, ANC). EAFD is a hazardous waste generated in electric arc furnace steel factories; it contains significant amounts of heavy metals such as Zn, Pb, Cr or Cd. EAFD from a local factory was characterized by X-ray fluorescence (XRF), acid digestion and X-ray diffraction (XRD). Zn and Fe were the main components while the XRD analysis revealed that zincite, zinc ferrite and hematite were the main crystalline phases. Different cement/EAFD formulations ranging from 7 to 20% dry weight of cement were prepared and subjected to the ANC leaching test. An amphoteric behavior of Zn was found from the pH dependence test. To model this behavior, the geochemical model Visual MINTEQ (VMINTEQ) was used. In addition to the geochemical model, an empirical model based on the dissolution of Zn in the acidic zone and the re-dissolution of zinc compounds in the alkaline zone was considered showing a similar prediction than that obtained with VMINTEQ. This empirical model seems to be more appropriate when the metal speciation is unknown, or when if known, the theoretical solid phases included in the database of VMINTEQ do not allow to describe the experimental data.     

Recycling of an electric arc furnace flue dust to obtain high grade ZnO

The production of steel in electric arc furnace (EAF) generates a by-product called EAF dusts. These steelmaking flue dusts are classified in most industrialized countries as hazardous residues because the heavy metals contained in them, tend to leach under slightly acidic rainfall conditions. However, and at the same time they contain zinc species which can be used as a source to obtain valuable by-products. The present investigation shows results on the processing of an EAF flue dust using ammonium carbonate solutions. Once zinc is dissolved: ZnO + 4NH3 + H2O --> Zn(NH3)4(2+) + 2OH- with other impurities (i.e. cadmium and copper), these are eliminated from the zinc solution via cementation with metallic zinc. The purified zinc solution was evaporated (distilled) until precipitation of a zinc carbonate species, which then was calcined to yield a zinc oxide of a high grade. For the unattacked dust residue from the leaching operation, mainly composed of zinc ferrite, several options can be considered: back-recycling to the furnace, further treatment by sodium hydroxide processing or a more safely dumping due to its relatively inertness.     

Stabilisation of dune sand using electric arc furnace dust

Dune sand is one of the predominant soils in the world, particularly in the Arabian Peninsula and North Africa. In order to use these soils in constructions, pre-treatment of sand is essential. Though the usage of cement for stabilising sand has long been the practice to achieve the required strength, it is not cost effective and its manufacturing consumes a lot of energy. Consequently, it would be noble to use industrial by-products, often considered as waste materials, such as electric arc furnace dust (EAFD), in the stabilisation of sand. This research reports the potentiality of using EAFD for improving the strength of dune sand. Specimens, mixed with 2% cement and mixed with 5, 10, 20 and 30% EAFD plus 2% cement, were evaluated using unconfined compressive strength, soaked CBR and durability tests. Results of this investigation indicated that dune sand stabilised with 20 and 30% EAFD plus 2% cement has been qualified as a construction material for sub-base in rigid and flexible pavements, respectively, as per ACI requirements. Scanning electron microscope, energy dispersive X-ray analysis and backscattered electron images, in addition to, XRD analysis were used to identify the various phases in the sand-2% cement-30% EAFD mixture.     

Integrated hydrometallurgical process for production of zinc from electric arc furnace dust in alkaline medium

In this study, a novel and integrated hydrometallurgical process for the production of zinc powder from electric arc furnace (EAF) dust in alkaline medium is reported. The dust is firstly hydrolysed in water, and then fused in caustic soda at 350°C for 1 h, followed by leaching in alkaline solution in which both zinc and lead are effectively extracted. Zinc powder is then produced by electrowinning from the leach solution after the lead is selectively removed by precipitation using sodium sulphide as precipitant. The EAF dust tested contained 25% Zn, 1.8% Pb and 33% Fe. It was found that 38% of zinc and 68% of lead could be extracted from the dust when leached directly in caustic soda solution. Leaching of zinc increased to 80% when dust was directly fused with caustic soda followed by alkaline leaching. However, the leaching further increased to 95% when the dust was hydrolysed first with water before fusion. Zinc powder with a purity of 99.95% was then produced by electrowinning from the lead depleted solution. Stainless electrodes were used as both anode and cathode.     

Long and short-term performance of a stabilized/solidified electric arc furnace dust

The application of class F fly ash, cement and lime to the Stabilization/Solidification (S/S) of electric arc furnace dust containing hazardous metals such as Zn, Pb, Cd, and Cr is described. The aim of the study was to determine the influence of the setting conditions during the S/S treatment and to know the behaviour of an aged solidified and stabilized waste. In order to determine the efficiency attained by the S/S process, USEPA TCLP, and other leaching tests have been accomplished. In addition, the compressive strength of the solidified waste at different times has been determined. In order to study the influence of the environmental conditions in which setting occurs, experiments were carried out with samples of the same composition, under different setting conditions: laboratory environment, stove at a temperature of 40-60 degrees C and setting in a hermetically sealed plastic bag at room temperature. All the samples were subjected to the TCLP test at 28 days, and the metal content of the resulting leachates was analysed. The results show that in some cases the setting conditions of the mixtures have a noticeable influence on the characteristics of the leachate. The evolution with time of some S/S solids, one month after their manufacture and more than 9 years after that has also been evaluated, by means of their leaching behaviour. The results obtained in this work have shown, in all the laboratory cured samples that the leachate pH decrease in the course of time, and consequently the leaching behaviour is in general worse. This could be due to the carbonation of the S/S solid and the subsequent loss of alkalinity.     

Electric arc furnace filter dust: Influence of organic material on the bulk density and flowability

In this study, the influence of condensed organic matter on the flowability and the bulk density of electric arc furnace (EAF) dust was investigated. The properties of the original dust samples containing some organic matter were compared with the properties of these samples after the removal of the condensed organic compounds by a deoiling procedure. The particle size distribution and the density of the three investigated dust samples were quite similar but the content of organic matter (TOC) was different. The values for the bulk density were lower for the original dust compared to the deoiled dust samples. The higher the TOC content, the higher the difference in the bulk density. Thus, the storage capacity of the dust silo was reduced by 9–17%. The flowability of all deoiled dust samples was very similar, whereas the flowability of the original dust was worse. The higher the TOC content, the worse the flowability. The average reduction of ff_c in comparison to the deoiled dust samples was 48, 38, and 17% for EAF dust samples with 0.65, 0.46, and 0.26% TOC, respectively. Evidently, the condensed organic matter on the dust particles reduces the flowability of the material. Therefore, the bulk density for dust with a higher TOC content is also lower.     

NO x emission from electric arc furnace in steel industry: contribution from electric arc and co-combustion reactions

Off-gas measurements were conducted at industrial electric arc furnaces (EAF) in Germany in order to investigate the interrelation of NO _x emission with installed plant equipment (e.g. gas burner) and process data (e.g. carbon input). Off-gas data monitor rapid changes in off-gas composition, temperature, and volume flow rates of air into the furnace indicating the transient state batch process of scrap melting. From the measurements two distinct sources of NO _x emission are clearly distinguished: (1) NO _x formation in the electric arc plasma during the start-up period of the melting process in an oxidizing furnace atmosphere after the charging of the furnace. (2) NO _x formation from post-combustion of CO/CO₂/H₂ gas with air inside and outside the furnace. Whereas the contribution from arc ignition is similar for different types of EAFs, other contributions depend on furnace equipment and operation, e.g. gas burners, use of air as carrier medium for carbon or dust injection, air-tightness of furnace, and parameters of off-gas extraction by EAF dedusting system. The positive effect of the minimum volume flow rate of air into the furnace by controlled off-gas extraction to total NO _x emission is shown.     

Synthesis,characterization and properties of calcium ferroaluminate belite cements produced with electric arc furnace steel slag as raw material

This study investigated the use of 10 (M1), 17 (M2) and 27 wt.% (M3) electric arc furnace steel slag (EAFS) as a raw material in the production of calcium ferroaluminate belite cement clinker, after firing at 1320 °C. The thermal behavior of the raw meals was studied by TG/DSC and XRD whereas for the analysis of the clinkers, XRD/QXRD, SEM/EDS and EPMA were employed. The resulting clinker was co-grinded with 5 and 20 wt.% Flue Gas Desulfurization (FGD) gypsum and the properties were determined by a series of tests in accordance to EN standards. The evolution of hydration was investigated by SEM and the development of compressive strength. The results revealed that the formed phases in the clinkers were C₂S, C₄AF and C₄A₃Ŝ. The main hydration products were ettringite, AFm and hydrogarnet. The leached Cr^VI was below 1 ppm in M3. Compressive strength in cements with 5 wt.% FGD gypsum was (in MPa): 18.3 for M1, 14.3 for M2 and 7.8 for M3 at 28 days, whereas for 20 wt.% FGD gypsum, the values were almost doubled.     

Characterization of chemical accelerators for sustainable recycling of fresh electric-arc furnace dust in cement pastes

A comprehensive investigation focusing on the effect of fresh EAFD on the setting of cement pastes was conducted. A new approach of using accelerators to counteract the extended retardation associated with using fresh EAFD was investigated. Two chloride-free chemical accelerators (CFCA), namely, calcium nitrite (CN) and calcium formate (CF) were used and their performance was benchmarked against calcium chloride (CC). Temperature profile was used for validating setting times by Vicat needle apparatus. Homogenization of fresh EAFD from different furnaces resulting in an average ZnO content of 15.1% was adopted to ensure consistent retardation in setting time. The use of an accelerator/homogenized EAFD ratio of 0.25 for CN and CF has shown significant reduction in setting time more than CC. Additional reduction was achieved with an increased ratio to 0.5. However, limited effect was noted for CN and CF with a further increase in the ratio compared to CC. Scanning electron microscope (SEM) was used to monitor the microstructure development of selected mixtures at early age. Finally, Prediction models were developed to predict the EAFD and CFCA effects on setting time. The results of this study are important in the quest to develop EAFD from waste byproducts into viable construction material.     

影响真空自耗电极电弧炉电弧稳定性的因素及对策

本文总结了影响真空自耗电极电弧炉电弧稳定的多种因素。通过理论分析，总结出在设计和控制方面采取的应对方案和方法。     

Mechanical properties of dusts collected from blast furnace dust catchers and cast house dedusting filters

ABSTRACT

Dust samples from blast furnace dust catchers and cast house dedusting systems were investigated with respect to flowability-relevant parameters. The mass median diameter of the dusts was in the range of 140 to 210 µm for the dust catcher dusts and approximately 6 µm for the cast house dusts. Generally, the flowability of the dust catcher dusts was better compared to the flowability of the cast house dusts. The flowability categories suggested by the three flowability indicators—the angle of repose, Hausner ratio, and Carr’s compressibility—were good for the coarser dusts, while for the finer dusts the flowability was overestimated. For the blast furnace dusts, from the dust catcher a considerable variation in the bulk density was found, which can presumably be attributed to the remarkable difference in the carbon content of the dusts investigated.     

ZHT100型1 t真空自耗电弧炉的研制

本文介绍了ZHT100型1t真空自耗电弧炉的结构、组成及工作过程。指出了调试过程中存在的问题，这种由我们自行设计、制造的1t真空自耗电弧炉已出口国外，一次试车成功并投入使用。     

Modeling of zinc solubility in stabilized/solidified electric arc furnace dust

The bacteria that could grow on media containing olive mill wastewater (OMW) were isolated and their lipase production capacities were investigated. The strain possessing the highest lipase activity among 17 strains grown on tributyrin agar medium was identified as Bacillus sp. The effect of initial pH on the lipase activity was investigated in tributyrin medium and pH 6 was found to be the optimal. The liquid medium composition was improved by replacing tributyrin with various carbon sources. Among the media containing different compositions of triolein, trimyristin, trilaurin, tricaprin, tricaprylin, tributyrin, triacetin, Tween 80, OMW, glucose, and whey; the medium contained 20% whey +1% triolein was found to give the highest lipase activity. Cultivation of Bacillus sp. in the optimal medium at pH 6 and 30 degrees C for 64h resulted in the extracellular and intracellular lipase activities of 15 and 168U/ml, respectively.     

Chemical, physical, structural and morphological characterization of the electric arc furnace dust

Electric arc furnace dust (EAFD) is a hazardous industrial waste generated in the collection of particulate material during steelmaking process via electric arc furnace. Important elements to the industry such as, Fe and Zn are the main ones in EAFD. Due to their presence, it becomes very important to know how these elements are combined before studying new technologies for its processing. The aim of this work was to carry out a chemical, physical, structural and morphological characterization of the EAFD. The investigation was carried out by using granulometry analysis, chemical analysis, scanning electron microscopy (SEM), energy dispersive spectroscopy via SEM (EDS), X-ray mapping analysis via SEM, X-ray diffraction (XRD) and Mössbauer spectroscopy. By XRD the following phases were detected: ZnFe₂O₄, Fe₃O₄, MgFe₂O₄, FeCr₂O ₄, Ca_0.15Fe_2.85O₄, MgO, Mn₃O₄, SiO₂ and ZnO. On the other hand, the phases detected by Mössbauer spectroscopy were: ZnFe₂O₄, Fe₃O₄, Ca_0.15Fe_2.85O₄ and FeCr₂O₄. Magnesium ferrite (MgFe₂O₄), observed in the XRD pattern as overlapped peaks, was not identified in the Mössbauer spectroscopy analysis.     

真空自耗电极电弧炉闭锁阀研制与使用功效

介绍了能安全可靠地在真空自耗电弧炉中炼钛时的高温、污染的环境下长期使用的闭锁阀的研制、阀的结构原理和实用中提高生产效率的例子。     

Study of electric-arc furnace dust (EAFD) in fly ash and rice husk ash-based geopolymers

Electric-arc furnace dust (EAFD) is an industrial waste produced by the volatilization of metals during scrap melting in electric arc furnaces. This waste is classified as Class I – hazardous, because lead and cadmium concentrations are above the limits set in the leaching test. Processes are carried out in many countries to recover the metals contained in EAFD. In Brazil, these processes are usually not conducted in the industry because the low percentage of commercially valuable metals makes it economically unfeasible to recover them. One of the study alternatives is the use of EAFD in civil construction. Studies have shown that EAFD increases the mechanical strength of mortars and Portland cement-based concretes. However, EAFD delayed cement setting time, which can jeopardize its use in construction. Thus, this study aims to evaluate the effect of EAFD when added to fly ash (FA) and rice husk ash (RHA) based geopolymers. Geopolymer mortars were prepared at a ratio of 1:3 (FA + RHA: sand, four different granulations) and added with 0, 10, 15, and 20% EAFD in relation to the mass of FA + RHA. Compressive mechanical strength and leaching tests were carried out at the ages of 7, 28, and 91 days. Microstructural analyses were performed using XRD, FTIR, and SEM/EDS. EAFD did not negatively influence the geopolymerization process. The highest compressive strength results for the mortars containing the waste were found for 20% of EAFD. All mortars, regardless of EAFD content, were classified as non- hazardous Class II at the age of 91 days.     

基于模糊控制和PID控制的电弧炉直流电源的研究

本文针对真空电弧炉直流电源在熔炼阶段数字PID控制存在电流超调与响应速度矛盾的问题,提出了模糊控制和PID控制相结合的控制策略,着重介绍了模糊控制方法的应用,并在Matlab中对单个电源模块进行仿真.实验结果证明了这种控制方式的可行性和优势,具有良好的应用前景,且符合直流电源智能化、模块化的发展趋势.     

影响VAR炉熔炼安全的因素及对策

总结了影响VAR炉熔炼安全的多种因素,通过理论分析,总结出在设计和控制方面采取的应对方案和方法.     

Acidic leaching both of zinc and iron from basic oxygen furnace sludge

During the steel production in the basic oxygen furnace (BOF), approximately 7-15 kg of dust per tonne of produced steel is generated. This dust contains approximately 1.4-3.2% Zn and 54-70% Fe. Regarding the zinc content, the BOF dust is considered to be highly problematic, and therefore new technological processes for recycling dusts and sludge from metallurgical production are still searched for. In this study the hydrometallurgical processing of BOF sludge in the sulphuric acid solutions under atmospheric pressure and temperatures up to 100 °C is investigated on laboratory scale. The influence of sulphuric acid concentration, temperature, time and liquid to solid ratio (L:S) on the leaching process was studied. The main aim of this study was to determine optimal conditions when the maximum amount of zinc passes into the solution whilst iron remains in a solid residue.     

Solidification/stabilization of electric arc furnace dust using coal fly ash. Analysis of the stabilization process

In this paper, the stabilization of electric arc furnace (EAF) dust containing hazardous metals such as Pb, Cd, Cr or Zn is described. The treatment involves a waste solidification/stabilization (S/S) process, using coal fly ash as the fundamental raw material and main binder. The article also contains a brief review of the most important recent publications related to the use of fly ash as S/S agents.The efficacy of the process has been evaluated mainly through leaching tests on the solidified products and compliance with some imposed leachate limits. The concentration of metals leaching from the S/S products was strongly leachate pH dependent; thus, the final pH of the leachate is the most important variable in reaching the limits and, therefore, in meeting the stabilization goals.In this study, the dependence relationship between the leachate pH and the concentrations of metals in the leachate are analyzed; in some cases, this allows us to estimate the speciation of contaminants in the S/S solids and to understand the mechanism responsible for reduced leachability of heavy metals from solidified wastes.