Thermodynamic modelling of the multiphase pyrometallurgical processing of electric arc furnace dust

Electric arc furnace (EAF) dust is produced when automobile scrap is remelted in an electric arc furnace and about 10–20 kilograms are generated per ton of steel. The major elements present in the dust are usually zinc, iron and calcium with smaller amounts of numerous other elements such as lead, copper and nickel. Typically, in the pyrometallurgical EAF dust treatment processes, the lead and zinc are separated as a crude zinc oxide while the iron is generally not worth recovering. Copper and nickel are usually not recovered as they report either to the oxide residue or to any metallic iron that is produced. In the present research, the recovery of the non-ferrous metals in a multiphase system consisting of gas, slag, matte, metal and solid carbon phases was investigated. The equilibrium compositions of the various phases, resulting from the smelting of the dust, were calculated using the SOLGASMIX module of Outokumpu HSC Chemistry. The effects of the following operating variables were investigated; carbon additions, sulphur additions, nitrogen and oxygen additions, temperature and dust composition. The thermodynamic modelling results show that the majority of the non-ferrous metals can be recovered, with the zinc and lead concentrating in the gas phase and the nickel and copper concentrating in the matte phase.     

Microwave caustic leaching of electric arc furnace dust

Electric arc furnace (EAF) dust is a waste product which is generated when steel scrap is melted in an electric arc furnace. It contains high concentrations of iron, zinc and lead. Numerous pyrometallurgical and hydrometallurgical processes have been developed to treat this material. Only a limited number of these have reached commercialization and the majority have been pyrometallurgical. However, the hydrometallurgical processes, such as caustic leaching, offer some potential advantages.In the present research, the application of microwave radiation at 2.45 GHz was employed, as the energy source, in the hydrometallurgical caustic leaching process for EAF dust treatment. The variables which were investigated were: leaching time, microwave power, caustic concentration and the solid to liquid ratio. The experimental results showed that the zinc recovery from the dust increased with a decrease in the solid to liquid ratio and an increase in the microwave power. The optimum caustic concentration for the maximum zinc recovery was 8M. The rates of zinc recovery were significantly higher under microwave conditions as compared to those observed with conventional leaching. Some possible mechanisms to explain this behaviour are discussed.     

含锌电炉粉尘配碳选择性还原的实验研究

为实现含锌电炉粉尘选择性还原、有效分离铁和锌资源,采用热力学计算和实验研究相结合,分析电炉粉尘中主要物相的还原分解行为,研究配碳量、反应温度和反应时间对还原产物的影响。结果表明,含锌电炉粉尘配碳选择性还原为铁氧化物和ZnO是可行的;在582~940 ℃之间,可实现铁酸锌的有效分解、ZnO过还原的抑制;随着反应温度增加和反应时间延长,铁氧化物遵循逐级还原规律,配碳量对产物并未产生明显影响;当温度为950 ℃时,ZnO被还原为锌蒸气而挥发,导致产物中锌含量明显降低。在配碳量1/10、反应温度850 ℃、反应时间1 h的优化条件下,ZnFe₂O₄分解率约为70%。     

电弧炉粉尘的治理

电弧炉粉尘含有某些重金属元素 ,堆放填埋对环境造成污染。至今已有约 2 0种方法处理这类粉尘回收有价金属 ,尤其是近几年来出现的 Ausmelt,Met Wool,Enviroplas,All Met,IBDR- ZIPP,Modified ZINCEX,Cashman,Rezada和 Rerra Gaia等技术正逐步趋于成熟。不锈钢和特种钢电弧炉粉尘中有价金属的综合回收虽未标准化 ,但越来越受到人们的关注。     

Use of mesalime and electric arc furnace (EAF) dust as neutralising agents in biooxidation and their effects on gold recovery in subsequent cyanidation

The cost of lime/limestone for neutralisation is the second largest operating cost in bioleaching. Therefore, these studies have been conducted with the aim to investigate the possibilities for use of by-products such as mesalime and electric arc furnace (EAF) dust for neutralisation during biooxidation of a refractory gold concentrate. Experiments were carried out using a retention time of 57 h in a one-stage reactor and the influence of two industrial by-products on the biooxidation performance was evaluated. The neutralising capacity of EAF dust was lower, while the mesalime was similar to the Ca(OH)₂ reference. The arsenopyrite oxidation in experiments ranged from 85% to 90%, whereas the pyrite oxidation was 63–74%. In subsequent cyanidation, final gold recoveries of 90% were achieved in bioresidues from mesalime and Ca(OH)₂, while the EAF dust bioresidue had a recovery of 85%. A comparatively high elemental sulphur content in EAF dust probably encapsulates part of the gold, which explains the lower recovery for the EAF dust bioresidue despite a longer residence time. Cyanide consumption was relatively high and ranged from 8.1 to 9.2 kg/ton feed after 24 h of cyanidation. Overall, the by-products tested here have proved to be feasible options as neutralising agents in bioleaching operations.     

Low CO2 emission technologies for iron and steelmaking as well as titania slag production

The world wide discussion on climate change caused by CO₂ and other greenhouse gases (GHGs) attributable to human activities has put the focus on the energy intensive production technologies for iron and steelmaking. Taking into account the enormous production increase for these versatile materials in the last years, modern technologies with lower CO₂ and GHGs emissions are imperative to keep at least today’s status, though a decrease is challenged.Outokumpu Technology has developed direct reduction technologies that allow in combination with smelting reduction processes or electric arc furnaces a substantial lowering of CO₂ emissions.In the presented contribution to MMME 06 three examples will be given:The Circofer^® process, already demonstrated in pilot plant scale, uses coal as reductant in a two stage CFB (circulating fluidized bed)/FB (fluidized bed) reactor configuration to obtain a highly metallized product suitable for charging into smelting processes.One possible application of Circofer is, in a single stage configuration, as prereduction unit in combination with HIsmelt^®, a smelting reduction technology to produce hot metal using iron ore and coal fines. Using Circofer as prereduction step, the capacity of a given HIsmelt installation can be increased by the factor three to four compared to cold feed and CO₂ emission can be lowered to values about 20% below the standard of a modern blast furnace, as this combination of technologies requires no agglomeration plant or coke ovens.A second application of Circofer is the combination with an electric arc furnace (EAF) to produce steel directly from direct reduced iron (DRI). The direct charging of metallic fines into an EAF was successfully tested, observing no increased dust emission from the furnace. Charging hot DRI into an EAF decreases drastically electric power consumption and thus further lowers CO₂ emission.Applying Circosmelt, the combination of a single stage Circofer system with an electric reduction furnace for ilmenite processing, only half of the electric power consumption required today for titania slag production using cold, unreduced feed material is required.A common additional advantage of all Circofer based routes is that a 99% pure CO₂ stream is removed for process reasons from the process gas and can be used for enhanced crude oil production or sequestration methods.The paper will report on the status of the different developments and its market introduction.Outokumpu Technology GmbH (formerly Lurgi Metallurgie) has been involved in the development, design and supply of plants for processing iron bearing ores in fluidized bed reactor systems for more than 30 years.     

冶炼炉腔内三相交流电弧热导机理研究

基于超高温冶金过程电弧炉产热导热计算，采用傅立叶热传导定律和牛顿冷却定律，对电弧产生热量沿固体轴向热导和流体横向热导机理进行研究。首先，描述电弧各部分的产热量；其次，计算电弧近极段经石墨电极和弧柱段的产热量及流向，提出电弧沿轴向和横向的热导计算方法；最后，以铍铜合金冶炼过程电弧炉温度分布和热量分析，验证电弧热导机理的有效性。研究结果表明，冶炼过程炉腔内热量的流动方式服从轴向热导和横向热导两个关键过程，完善了电弧炉热导机理理论研究。在此基础上对冶炼过程热量计算和利用进行相关分析，分析结果表明，1）炉腔内电弧近极段温度可由炉口火焰温度检测计算得到；2）降低轴向热导的热量耗散、提高横向热量占比是优化电弧炉有效能源利用率的关键方式之一。本文以期达到从热导机理角度优化冶金工艺的目标。     

高炉瓦斯泥球团制备参数优化研究

采用聚乙烯醇(PVA)作粘结剂,对攀枝花某钢铁厂高炉瓦斯泥进行造球,研究了瓦斯泥造球工艺参数并对其进行了优化。结果发现：制粒10min的瓦斯泥造球粉料较好;球团落下次数最高工艺条件：PVA浓度为0.4%,造球加水量为10g,成球压力8MPa;该工艺条件下得到生球和干球团落下次数分别为12.5次/个和22.5次/个,抗压强度分别为52.3N/个和136.4N/个,干球耐磨指数为1.59%,干球转鼓指数为97.87%,符合竖炉直接还原入炉球团的要求。     

国外电弧炉烟尘处理技术现状及发展

综合介绍了国外电弧炉烟尘处理的主要工艺——威尔兹、转底炉直接还原、ZINCEX、EZINEX及MRT(HST)工艺的发展现状。经综合评价后指出：采用先火法后湿法的联合工艺，可以一次回收电弧炉烟尘中全部的铁与锌等有价金属，并得到优质高纯的产品，是将来的发展方向。     

基于转底炉工艺的冶金含铁尘泥造球试验研究

基于转底炉工艺,分析了不同种类含铁尘泥的成球性能,并在此基础上开展了含铁尘泥造球试验,分别考察了膨润土、有机粘结剂C以及复合粘结剂对含铁尘泥球团性能的影响规律,结果表明,随着膨润土使用量逐渐增大,含铁尘泥生球的抗压强度、落下强度和爆裂温度逐渐提高;有机粘结剂C对生球的抗压强度影响不大,但能显著提高生球的水分和落下强度,当有机粘结剂C用量由0.50%提高至0.75%时,生球的水分由18.8%增至20.7%,落下强度由13次提高至40次,爆裂温度显著降低;单独使用膨润土或有机粘结剂C均不能达到较好的成球效果,而使用膨润土与有机粘结剂C组成的复合粘结剂可显著提高含铁尘泥球团的各项指标,且复合粘结剂的使用成本较低,生球全铁品位也有较大幅度提升。     

钒钛磁铁矿冷压含碳球团的粘结剂选择

为了提高钒钛磁铁矿冷压含碳球团的强度, 选用膨润土、糖浆及玉米面作粘结剂, 对比了3种粘结剂对球团性能的影响, 从而确定适合转底炉工艺的较优粘结剂及最佳配加量。结果表明: 膨润土加入量超过6%时, 制备球团性能能够达到转底炉工艺要求, 但导致球团内铁品位降低程度较大;添加糖浆作粘结剂时, 在实验研究范围内, 球团性能尚未达到工艺要求, 且存在压球过程中脱模困难问题;而选用玉米面作粘结剂制备球团时各方面都能达到工艺要求。玉米面(含量2.5%)加入到浓度为4%的NaOH溶液中发酵15 min左右, 所得球团的湿球落下强度为4.8次, 湿球抗压强度为55.1 N, 干球落下强度为24.8次, 干球抗压强度为648.1 N, 湿球爆裂温度为400 ℃, 满足转底炉生产的各项指标。     

Reduction of dioxin/furan emissions in the waste gas from electric arc furnaces

The iron and steel industry is under considerable pressure to continuously reduce the levels of generated dioxins and other harmful emissions from process offgas. In the early 1990s this industry commenced with the investigation of new offgas cleaning systems for sinter plants and electric arc furnaces (EAF) which resulted in a considerably improved offgas cleaning efficiency. The global tendency in the steel industry towards an increased application of the electric arc furnace for the production of steel and especially the introduction of scrap-pre-heating technologies in the late 1980s resulted in increased demands for VOC and dioxin reduction technologies. This paper presents an overview of the state-of-the-art of EAF offgas systems and its components with a special focus on the organic components of the offgas.     

Wärmerückgewinnung am Elektrolichtbogenofen und erste Erkenntnisse einer Versuchsanlage zur Materialuntersuchung

This paper deals with electric arc furnace off-gas heat recovery and first experiences with a testing plant. The testing plant based on molten salt as heat transfer fluid was installed inside the existing off-gas system of a German mini mill. The aim of the testing plant is to evaluate tube materials and to measure the influence of hot corrosion and dust deposit. First experimental results are presented. Apart from experimental measurements, numerical simulations were performed and are briefly presented.     

新型高效黏结剂铁精矿氧化球团试验

应用已研发的QTJ黏结剂取代膨润土制备磁铁精矿氧化球团,获得了优质的氧化球团,满足了高炉对冶炼炉料的苛刻要求。研究结果表明：当QTJ用量为0.5%时,可获得生球抗压强度大于18 N/个,爆裂温度大于650 ℃的优质生球;在预热温度为1 000 ℃、预热时间为10 min、焙烧温度为1 250 ℃、焙烧时间为12 min的条件下,获得优质的预热球抗压强度大于480 N/个,焙烧球抗压强度大于2 800 N/个;与添加2%膨润土球团矿相比较,成品球抗压强度低一些,但生球爆裂温度升高;两种黏结剂球团的还原性能基本接近,因而QTJ黏结剂完全能取代膨润土,且在氧化球团生产中具有良好的应用前景。     

含铁尾矿二次利用新途径探讨性试验研究

为了合理开发利用二次含铁资源,针对自行开发的一种新型球团添加剂--含铁添加剂进行了试验研究.结果表明,该添加剂不仅能满足工业生产对球团矿质量的要求,而且对球团矿的全铁品位降低幅度有所抑制,符合高炉精料入炉的要求,更重要的是利用了二次资源.     

Geopolymerization of coal fly ash in the presence of electric arc furnace dust

The results of synthesis of fly ash based geopolymers and the experimental investigations of the geopolymerization of fly ash in the presence of eclectic arc furnace dust were presented. The electric arc furnace dust (EAFD) is a hazardous solid waste formed during remelting processes of iron and steel scrap in an electric arc furnace. In this work, the possibility of immobilization of Zn (as a most abundant toxic metal in EAFD) from EAFD and the influence of EAFD addition and alkaline dosage on the mechanical and microstructural properties of fly ash based geopolymers was investigated. Our result show that the best mechanical properties of FA and FE geopolymers were obtained using 10 M NaOH and 10 wt.% EAFD. The X-ray phase analysis confirmed the presence of aluminosilicate and oxide phases in investigated samples of FA, EAFD, as well as FA and FE geopolymers. SEM–EDS results have revealed the presence of Zn in an amorphous aluminosilicate phase. This material is considered as mesoporous and the change of porosity is greatly dependent on the alkaline dosage. The efficiency of immobilization of Zn from EAFD was evaluated using TCLP, EN 12457-2 and EPA Method 1313 leaching tests. Results of TCLP and EN 12457-2 tests have shown that the increase of alkaline dosage leads to the more effective immobilization of Zn and other toxic metals present in EAFD. On the other hand, the results of EPA method 1313-pH dependent leaching test have indicated that FE geopolymers are relatively stable in neutral and alkali environment while in a pH range 2–5.5, solubility of Zn and Pb is a concern for this type of materials.     

Alkaline leaching of zinc from electric arc furnace steel dust

Electric arc furnaces (EAF) generate about 10–20 kg of dust per metric ton of steel, which constitute a hazardous waste, known as EAF dust. This dust contains a remarkable amount of non-ferrous metals, which include zinc, cadmium, lead, chromium and nickel that could be recovered, reducing the environmental impact of the leachable toxic metals, and generating revenue. In this paper, different alkaline leaching techniques were tested in order to dissolve the zinc present in an EAF dust: (i) conventional agitation leaching; (ii) pressure leaching; (iii) conventional leaching following a microwave pretreatment and (iv) leaching with agitation provided by an ultra-sonic probe. Temperature and sodium hydroxide concentration were the variables tested. The highest zinc recovery from the EAF dust, containing about 12% of zinc, was about 74%. This was achieved after 4 h of leaching in a temperature of 90 °C and with a sodium hydroxide concentration of 6 M of the leaching agent.     

润磨预处理对硫酸渣精矿球团性能的影响研究

为了研究润磨对硫酸渣精矿球团性能的影响, 将配加1.7%膨润土, 15%H₂O和润磨6 min的硫酸渣精矿进行造球, 并对球团进行预热和焙烧实验研究。结果表明, 与未经润磨的硫酸渣精矿制备的球团相比较, 经润磨的精矿球团的预热温度降低150 ℃, 预热时间从12 min降低至6 min; 焙烧温度可降低75 ℃, 焙烧时间从15 min降低到8 min。在预热温度1 075 ℃, 预热时间12 min, 焙烧温度1 225 ℃, 焙烧时间13 min的优化条件下, 成品球团的抗压强度为4 726 N, 还原度指数达到87.56%, 还原膨胀指数为8.48%, 润磨精矿球团的冶金性能指标能满足高炉冶炼的要求。     

电炉含锌粉尘在微波场下脱锌的试验研究

微波能是一种清洁型能源，可以对物料进行选择性体加热。利用电炉含锌粉中和煤粉吸收微波能力强的特点，试验研究了微波加热还原电炉含锌粉尘的脱锌效果。结果表明，在大气条件下，脱锌率可达到80％左右；脱锌率随着配煤最、煤粉粒度和微波功率的增加而提高。     

钒钛海砂矿转底炉直接还原研究

针对印尼钒钛海砂选矿后的精矿,采用转底炉直接还原—电炉熔分工艺,先后完成了小型基础试验研究和中试试验。得到最佳的条件是,m（海砂精矿）:m（兰炭）:m（膨润土）:m（有机粘结剂）=100:25:3:1,含碳球团3层（54 mm）,还原温度1 260℃,还原时间30 min,中试得到球团平均金属化率88.63%,球团中剩碳4.81%。将金属化球团热装入300 kVA的直流电炉进行冶炼,得到含钒铁水,铁水中铁品位96.25%,钒品位0.443%,铁与钒回收率分别为99.64%和88.96%,炉渣中TiO₂品位38.86%,钛回收率为98.95%。结果表明,转底炉直接还原—电炉熔分处理海砂精矿技术上可行。