Study on Phosphorus Removal of High-Phosphorus Oolitic Hematite by Coal-Based Direct Reduction and Magnetic Separation

In this article, mineralogical phase changes and structural changes of iron oxides and phosphorus-bearing minerals during the direct reduction roasting process were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). It has been found that the reduction of hematite follows the following general pathway: Fe₂O₃ → Fe₃O₄ → FeO → Fe. The last step of the reduction process contains two side reactions: either FeO → Fe₂SiO₄ → Fe or FeO → FeAl₂O₄ → Fe depending on the micro mineralogical makeup of the ore. In the reduction process of FeO → Fe, oolitic structure was destroyed completely and fluorapatite was diffused into gangue while metallic phase is coarsening at temperatures below 1200°C. Therefore, the separation of phosphorus-bearing gangue and metallic iron can be achieved by wet grinding and magnetic separation, and low phosphorus content metallic iron powder can be obtained. However, when the temperature reached 1250°C and beyond, some of the fluorapatite was reduced to elemental P and diffused into the metallic iron phase, making the P content higher in the metallic iron powder.     

江西某铅锌银复杂多金属矿综合回收试验研究

江西某铅锌银多金属矿的特点是含硫高,并含有铅、锌、银、铁、锰等多种有用金属矿物可以回收利用.试验针对该多金属矿物中伴生复杂的情况,对比了铜铅锌优先浮选和铜铅锌优先浮选-锌粗精矿再磨-锌中矿磁选的工艺流程,后者获得了较好指标:铅精矿含Pb 49.57%,Pb回收率87.53%;锌精矿含Zn 45.82%,Zn回收率75.12%;硫精矿含S 44.69%,S回收率71.35%.针对铁锰以碳酸盐的形式存在,且与脉石伴生严重呈细粒嵌布的情况,采用了磁选-焙烧-磁选的试验方案回收浮选尾矿中的铁锰.      

Behaviour of manganese oxides during magnetising reduction of Baharia iron ore by CO–CO2 gas mixture

Abstract

High manganese containing iron ore samples were isothermally reduced with a CO–CO₂ gas mixture at 600–1000°C. The course of reduction was followed by a weight loss technique. The influence of reducing gas composition and temperature on the reduction kinetics was investigated. The different phases formed during reduction were identified by X-ray phase analysis, while their structures were microscopically examined. The reduced samples were magnetically tested by means of a Davis tube tester. The effect of grain size, drum speed, and cleaning conditions on the efficiency of magnetic separation was studied using a Box-Mag wet low intensity magnetic separator. The separation efficiency was determined by analysing total iron, manganese, and acid insoluble contents in both magnetic and non-magnetic fractions. Best testing results were obtained on separation of the sample reduced with 80CO–20CO₂ (vol.-%) at 800°C. The optimum grain size for magnetic separation is below 0·15 mm while that of the drum speed is 100 rev min^-1 . The cleaning of the magnetic fraction increases the iron content and decreases the manganese and acid insoluble contents.     

PERMANENT MAGNETS FROM ELONGATED SINGLE-DOMAIN PARTICLES

Abstract

A process is described for producing elongated single-domain (ESD) fine-particle magnets. The 150-Å. ESD iron or iron–cobalt alloy particles are prepared by controlled electrodeposition into mercury, followed by thermal growth and treatment with a third metal to attain optimum particle shape and magnetic properties. The particles are then aligned by a magnetic field, compacted under pressure, freed of mercury by vacuum distillation, and embedded in a suitable matrix. This is ground to a coarse powder and fed into automatic presses for realigning and compacting to the final magnet shape. The factors controlling each step of the process are discussed, and the advantages of magnets with artificial microstructures synthesized by this approach are pointed out. The process described produces commercial ESD iron and iron–cobalt magnets with energy products of 2·2 and 3·5 million gauss-oersteds, and laboratory ESD iron and iron–cobalt magnets of 4·2 and 5·0 million gauss-oersteds.     

Strength and high temperature behaviour of carbon composite pellets containing BOF fine dust

Abstract

Steel plants produce significant amounts of dust and sludge during iron and steel production. These wastes contain valuable elements, such as Fe, Cr, Ni, C, K and Na and should be handled properly to prevent them from polluting the environment. In order to utilise the BOF fine dust, the effects of the dust on cold bonded pelletising, solid state reduction and reduction melting behaviours of composite pellets made from iron ore and anthracite with added BOF fine dust were investigated at laboratory scale. The BOF dust was found to improve the cold compressive strength of the wet green carbon composite pellet, and increased with increasing dust content. Almost four times the amount of dust was needed to get the same effect on the strength of the pellet when it was used to replace bentonite. The carbothermic reduction of the composite pellet proceeded effectively at temperatures above 1200°C. The BOF dust had a positive effect on the reduction rate of the pellet, and the rate increased with increased dust content. The reduction of iron oxide was topochemical and conformed to a shrinking core kinetic model. The dust was found to improve the iron and slag melting separation rate of reduced pellets at 1400°C when its content was less than 23·11 wt-%. The liquidus temperature of the slag would decrease with the content of BOF dust increasing from zero to ～30 wt-% and then increase if the content continued to become more in the experiment. Utilising the BOF dust as the binder and flux to adjust the composition of the slag system can potentially reduce the slag ratio and production cost compared with using bentonite and limestone. This work can help to find a new process for the effective utilisation of BOF dust in a more appropriate and environmentally friendly way.     

Preparation of metallic iron powder from copper slag by carbothermic reduction and magnetic separation

Copper slag is a solid waste that has to be treated for metals recovery. In order to recover iron from copper slag, the technology of carbothermic reduction and magnetic separation was developed. During the reduction roasting, additive CaO reacted with Fe₂SiO₄ of copper slag, forming CaO·SiO₂ and 2CaO·SiO₂, which ameliorates the separation between iron and other minerals during magnetic separation. Meanwhile, additive CaF₂ improved the growth of iron grains, increasing the iron grade and iron recovery. The metallic iron powder obtained contained 90.95?wt-% TFe at 91.87?wt-% iron recovery under the optimum conditions, which can be briquetted as a burden material for steel making by electric arc furnace to replace part of scrap.     

Reduction roasting of high iron bearing zinc calcine for recovery of zinc and iron

High iron bearing zinc sulphide ore is an important resource for zinc, and the reserve is very great in the world. It is very difficult to effectively obtain zinc and iron from the source by traditional technology. In this study, a novel method was proposed for recovery of zinc and iron from high iron bearing zinc calcine, and the key procedure, reduction roasting, was investigated. The effects of CO concentration, CO₂ concentration, temperature and time on reduction roasting were studied respectively. The experimental results show that the content of soluble zinc and magnetic susceptibility reached 91·15% and 4·1×10^?4 m³ kg^?1 under the optimum conditions respectively. About 90%Zn and 9·5%Fe were dissolved from the reduction roasted zinc calcine by low acid leaching, and simultaneously, 84·3%Fe was recycled to the iron concentrate containing iron of 53·2% from zinc leaching residue by low intensity magnetic separation.

Le minerai de sulfure de zinc à haute teneur en fer est une ressource importante du zinc et il en existe une grande quantité dans le monde. Il est très difficile d’obtenir efficacement le zinc et le fer de cette source par la technologie traditionnelle. Dans cette étude, on propose une nouvelle méthode pour la récupération du zinc et du fer à partir de produit calciné de zinc à haute teneur en fer, et on examine la procédure clef, le grillage réducteur. On a étudié respectivement les effets de la concentration de CO, de la concentration de CO₂, de la température et de la durée sur le grillage réducteur. Les résultats expérimentaux montrent que la teneur en zinc soluble et la susceptibilité magnétique atteignaient respectivement 91·15% et 4·1×10^?4 m³ kg^?1 en conditions optimales. Environ 90% du Zn et 9·5% du Fe étaient dissous à partir du produit calciné de zinc de grillage réducteur par lessivage à acide faible, et simultanément, 84·3% du Fe était recyclé en concentré de fer contenant 53·2% de fer à partir du résidu de lessivage du zinc par séparation magnétique à faible intensité.     

含锌除尘灰锌铁分离研究

摘要：含锌除尘灰是钢铁厂重要的固体废弃物,属于危废,为了探索妥善解决该种危废的方法,模拟回转窑工艺对国内某钢厂含锌除尘灰进行焙烧 磁选锌铁分离研究,研究不同焙烧温度、时间以及不同内配C含量对焙烧矿金属化率、脱锌率以及对磁选后精矿铁品位、Fe回收率的影响。结果表明,在C质量分数为12%、焙烧温度1100℃、焙烧时间60min的条件下,得到铁品位53.45%、金属化率91.95%、脱锌率99.05%的焙烧物料,挥发物中ZnO质量分数高达95.04%。焙烧物料经过磨矿磁选后可得到铁品位91.30%,Fe回收率82.37%的金属铁粉。     

EAF and secondary dust characterisation

Abstract

The basic knowledge of the physical and chemical properties of the electric arc furnace (EAF) and secondary dust (SD) obtained by the characterisation provides important information on the potential problems that could be encountered during the processing of such materials. EAF dust consists mainly of very fine spherical particles. The most common phases in the EAF dust are solid solution of iron spinels generally enclosed into a matrix of calcium–iron silicate glass. Leaching tests show that as the Zn/Fe ratio increases, there is an increase in the zinc extraction, whereas the iron extraction decreases as the Zn/Fe ratio increases. It was possible to produce a SD containing 55.8% zinc by means of charging EAF primary dust–coal composite pellets into an induction furnace. SD consists of very fine particles presenting a mean particle size of 0.26μm. In addition, SD contains significant levels of iron, chloride and fluoride. The iron content in the SD was identified as being iron droplets ejected from the bath caused by high intensity gas generation during the smelting of the EAF primary dust–coal composite pellets.     

Separation behaviour of zinc dross from hot dip galvanising melts of different aluminium concentrations by alternating magnetic field

Abstract

Dross in zinc pots is the most important factor that impairs the surface quality of hot dip galvanising automobile steel sheet. Separation behaviour of zinc dross from galvanising melts of different Al concentrations (0·12, 4·5 and 55·0 wt-% by an alternating magnetic field has been investigated in order to reduce the dross defects on steel sheets. The properties of different zinc drosses were investigated by means of EDAX and the quantitative metallographic method and the conductivities were measured by physics property measurements system. The experimental results show that the zinc dross in different hot dip galvanising melts has different morphologies, compositions and structures, and the average particle size of the dross increases with the Al concentration. In the case of extra iron (above the solubility limit) in the zinc melt, zinc dross quantity also increases with the Al concentration. All of the three types of zinc dross particles >5 μm can be successfully separated when the magnetic frequency is 17·5 kHz, effective magnetic flux intensity is 0·05 T, imposed time is 15 s and the cross-section of the ceramic square pipe is 5 × 5 mm.     

Integrated Technology for Processing Rhenium-containing Molybdenite Concentrates to Recover Molybdenum and Rhenium into Commercial Products

Abstract

The paper reports on processing of molybdenite concentrate to recover molybdenum and rhenium products. The process involves roasting of molybdenite in a fluid bed. The fluid bed exhaust is passed through a cyclone, a electrostatic separator and finally subjected to wet gas scrubbing. The scrub is sent to solid ion exchange resin to produce ammonium perrhenate. The cinder from fluid bed roaster is processed to calcium molybdate and the dust from dust recovery is processed to ammonium paramolybdate.     

Characteristics of steelmaking flue dust

Abstract

The physicochemical and surface properties of steelmaking flue dust have been investigated by scanning electron (SEM) and X-ray diffraction (XRD) measurements, chemical analysis, FT-IR studies, zeta potential measurement, Brunauer–Emmett–Teller (BET) surface area determination, and potentiometric titration techniques. The results show that the dust consists of very fine spherical particles, which contain mainly iron oxide, iron ferrite, calcium (magnesium) oxide, calcium (magnesium) carbonate, and other metal oxides. The dust possesses a high BET surface area (14·65 m² g^-1 ) and a reversible surface charge. The point of zero charge pH_pzc of the surface is around pH 6. Solubility tests show that the dust releases very little heavy metals in solution in the pH range 4·5–11·8 and has a high capacity to neutralise strong acid in solution.     

Correlation of BOS process variables with dust mass formation and zinc content

Abstract

The basic oxygen steelmaking (BOS) process typically produces a dust rich in valuable iron units and often contaminated with zinc. This paper takes a look at statistical correlation and multiple regressions of process variables with the quantity of dust and the zinc mass contained in the dust. A robust inline sampling system was designed and installed to isokinetically sample the primary BOS dust slurry from a 248 m³ capacity BOS converter at Tata Steelworks Port Talbot (UK). This system was used to measure the dust mass and composition changes against time for 12 large scale trial heats and to compare with the process information data for a statistical evaluation of the variables. Statistically significant Pearson linear correlations were measured for the total dust mass produced with the iron ore and for the zinc mass contained in the dust with the addition of waste oxide briquettes (WOBs). A multiple regression analysis model showed strong associated correlations between the zinc mass contained in the dust with the galvanised scrap and WOB additions and explained 73% of the zinc mass variance.     

Recovery Improvement of Fine Magnetic Particles by Floc Magnetic Separation

The performance of floc magnetic separation (FMS) has been compared with wet high-intensity magnetic separator (WHIMS). This study was performed on low-grade iron ore slime contained 59.58% Fe with 4.57% silica and 3.78% alumina. Detailed characterization data indicated that a substantial amount of the slime was below 20 µm in size. Beneficiation studies indicated that the FMS process is effective to recover fine hematite and goethite particles, compared with the conventional magnetic separation. In conventional magnetic separation, the extent of the fluid drag force exceeds the magnetic force exerted on ultrafine particles. Thus, ultrafine magnetic particles were usually not recovered effectively by magnetic separators, resulting in the loss of valuable ultrafine slime particles. The FMS process significantly increases the magnetic force on the ultrafine iron ore in the form of hydrophobic flocs in a magnetic field, thus the ultrafine particles can be picked up effectively as magnetic concentrates. The FMS process improved the Fe recovery from 37.35% to 79.60%.     

高炉瓦斯灰基础性能与磁化焙烧试验

对高炉瓦斯灰的基础性能（粒度分布、化学组成、物相组成）进行研究,在此基础上,对瓦斯灰进行磁化焙烧-弱磁选工艺试验研究。研究表明,瓦斯灰按粒度分组的化学组成不均匀,碳主要集中于较大的颗粒中,铁和锌主要集中于较小的颗粒中; 3号、6号高炉瓦斯灰主要由Fe2O3、Fe3O4、SiO2和FeZn13组成,5号高炉瓦斯灰主要由Fe2O3、Fe3O4、SiO2和CaZn(Si2O6)组成;瓦斯灰磁化焙烧-弱磁选工艺的最佳试验条件为：焙烧温度为750℃,焙烧保温时间为60min,磁选激磁电流为0.4A。利用该工艺,磁选后的瓦斯灰铁品位达57.9%,锌质量分数为0.25%,回收率达67%。     

Separation of aluminium and preparation of powdered DRI from lateritic iron ore based on direct reduction process

Lateritic iron ore has not been used effectively due to excess content of multiple metals. In this work, separation of aluminium from a high-aluminium lateritic iron ore was achieved by the process of ‘direct reduction with sodium sulfate-magnetic separation’, with a powdered direct reduced iron (DRI) produced. It is found that the presence of 12% sodium sulphate during reductive roasting significantly improves separation of iron and aluminium in magnetic separation: the total iron grade (TFe) of powdered DRI increases from 80.6 to 92.0% and the Al₂O₃ content decreases from 9.8 to 1.3% correspondingly. The presence of sodium sulphate results in formation of sodium aluminosilicates instead of FeAlO₂. Moreover, sodium sulphate significantly promotes growth of metallic iron grains which is beneficial to sufficient liberation and separation of metallic iron grains from gangue minerals in grinding and magnetic separation.     

钠盐对低品位菱铁矿制备碳化铁的影响

在用低品位菱铁矿制备电炉原料(碳化铁)的过程中,考察了钠盐对菱铁矿渗碳的影响以及对碳化铁和脉石分离的作用机理。结果表明,钠盐能显著提高渗碳效率,强化碳化铁颗粒长大,改善碳化铁和脉石的嵌布关系,从而促进了碳化铁和脉石的分离。当菱铁矿球团中分别添加15%的Na2SO4和Na2CO3后,磁选精矿的铁品位、铁回收率和化合碳质量分数分别从57.59%、26.18%、2.68%提高到73.23%、88.03%、4.56%和70.00%、83.81%、3.89%。     

炼铁厂含锌尘泥中铁、锌、碳分离技术探讨

为充分利用炼铁厂的二次资源,在归纳分析采用湿法、火法和物理方法处理含锌尘泥的基础上,针对炼铁厂含锌尘泥矿物组成的差异,探讨了不同的选矿方法回收铁、碳和锌的可行性,提出了多段磁选—浮碳—浮锌、磁选—重选—浮碳—浮锌以及水力/风力分级-浮锌、直接浮锌的联合工艺流程,以实现含锌尘泥中铁、锌、碳有用资源的高效分离及回收利用,满足高炉冶炼的需求。     

Effect of alumina on slag–metal separation during iron nugget formation from high alumina Indian iron ore fines

Abstract

Iron nuggets can be obtained from ore–coal composite pellets by high temperature reduction. Alumina in the ore plays a vital role in slag–metal separation during nugget formation, as it increases the liquidus temperature of the slag. In this study, the effect of carbon content, reduction temperature and lime addition on slag–metal separation and nugget formation of varying alumina iron ore fines were studied by means of thermodynamic modelling. The results were validated by conducting experiments using iron ore fines with alumina levels ranging from 1·85 to 6·15%. Results showed that increase in reduction temperature enhances slag metal separation, whereas increasing alumina and carbon content beyond the optimum level adversely affects separation. Carbon below the required amount decreases the metal recovery, and carbon above the required amount reduces the silica and alters the slag chemistry. Optimum conditions were established to produce iron nuggets with complete slag–metal separation using iron ore–coal composite pellets made from high alumina iron ore fines. These were reduction temperature of 1400°C, reduction time minimum of 15 min, carbon input of 80% of theoretical requirement and CaO input of 2·3, 3·0 and 4·2 wt-% for 1·85, 4·0 and 6·15 wt-% alumina ores respectively.     

冶炼钢铁过程中多种固体废物的鉴别

在钢铁的冶炼过程中,主要产生炉渣、除尘灰和氧化皮等固体废物,其中氧化皮是国家规定可以进口的固体废物,炉渣和除尘灰属于不能进口的固体废物。实验针对冶炼钢铁过程中产生的固体粉末进行鉴别,首先利用肉眼和扫描电镜(SEM)对样品进行初步判断,例如炉渣的外观不是正常天然矿物的块状或粉状,而除尘灰颗粒较细、较轻,氧化皮呈鳞片状、有金属光泽。再利用X射线荧光光谱(XRF)对制得粉末中的元素进行分析,炉渣的主要元素为钙、硅、镁和铝,铁的含量极低;而除尘灰中铁的含量很高,同时含有锌和钙;氧化皮的主要元素也是铁。最后利用X射线衍射(XRD)技术对粉末中存在的物相进行分析,从而推断出固体粉末的属性,炉渣中的主要物质是CaO-MgO-Al₂O₃-SiO₂形式存在的配合物;除尘灰中的主要物质是铁的氧化物以及一些氧化锌;氧化皮的主要物质也是铁的氧化物,其中氧化亚铁的含量高。通过实验建立了这3种固体废物的鉴别方法,对进口固体废物的监管提供指导。