Characterisation of electric arc furnace dust generated during plain carbon steel production

Abstract

Electric arc furnace (EAF) dust is a waste generated in the EAF during the steel production process. Among different wastes, EAF dust represents one of the most hazardous, since it contains heavy metals such as Zn, Fe, Cr, Cd and Pb. The goal of the present work is to characterise the waste through chemical analysis, particle size distribution, X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive spectroscopy detection and thermal analysis. The waste sample is composed essentially of spherical particles and has a very small particle size and the majority of the identified elements were Fe, Zn, Ca, Cr, Mn, K and Si. The XRD has presented compounds such as ZnO, ZnFe₂O₄, Fe₂O₃, MnO, SiO₂, FeFe₂O₄ and MnAl₂O₄. According to the thermal analysis results, up to 1000°C the total weight loss was ～5%. The results of waste characterisation are very important to these further investigations.     

Caustic roasting and leaching of electric arc furnace dust

Electric arc furnace (EAF) dust is produced when iron and steel scrap is remelted in an electric arc furnace. There are still significant problems associated with the pyrometallurgical and/or hydrometallurgical processes for the treatment of this dust. In the present research, the dust was roasted with caustic soda at low temperatures. It was found that the zinc ferrite (ZnFe₂O₄) in the dust was converted into sodium zincate (Na₂ZnO₂) and iron oxide (Fe₂O₃). In the subsequent dilute caustic leaching process both the zincite (ZnO) and the sodium zincate were soluble and the hematite was relatively insoluble. After roasting and leaching, the zinc recovery was found to be about 95%, while the majority of the iron oxide remained in the leach residue. The lead, cadmium and chromium recoveries were approximately 85, 89 and 37%, respectively, for roasting tests in which moisture was added. Without a moisture addition in roasting, the lead recovery decreased to 63% while the chromium recovery increased to 81%. Based on the experimental results, a hybrid low temperature roasting and dilute caustic leaching process followed by zinc cementation and electrowinning is proposed and discussed. This proposed hybrid EAF dust treatment process provides some potential advantages in comparison to the other hybrid processes which have been described in the literature.     

Combined processing of metallurgical slurry and gas-purification dust

Information is provided on the combined hydrometallurgical processing of slurry from blast-furnace gas treatment and metallurgical dust. The proposed method includes hydrochloric-acid leaching, reduction (Fe³⁺ → Fe²⁺), crystallization of FeCl₂ · 4H₂O, decomposition of chlorides to obtain oxides Fe _x O _y , and reduction of iron oxides to obtain thread crystals of PZh-1 powder iron. Approximate calculations show that the cost of such PZh-1 powder may be 15000–18000 rub/t.     

Removal of iron from quartz sands: A study by column leaching using a complete factorial design

The aim of the work was to decrease the iron content of ferrous quartz sands by fixed-bed column leaching with recycling of the leaching solutions in order to attain a product suitable for industrial use. Dissolution of iron was achieved by treating the sands in an acid medium with a reducing agent (oxalic acid) to convert Fe^III into Fe^II.The factors assumed to affect dissolution of iron, such as temperature, oxalic acid concentration, pH and flow-rate, were studied with a 2⁴ full factorial design in order to assess the main effects and the interactions among the factors.Removal of 46.1% iron gives a product containing 0.0163% Fe₂O₃ which is fit for industrial applications.     

Enhancement of Electric Arc Furnace Dust by Recycling to Electric Arc Furnace

Electric arc furnace (EAF) dust is a hazardous waste product of the steelmaking industry with a high concentration of heavy metals, especially Zn and Pb. Existing treatment processes are industrially viable only when the zinc content is sufficiently high. In this research we present an industrial-scale process to enhance EAF dust by recycling it to the same furnace in which it was generated. This process, called RECUMET?, involves two parts: (1) the manufacturing of self-reducing briquettes composed of dust from the steelmaking process, reducing agents and agglutinant agents; and (2) the loading of the briquettes into the EAF. Several tests have been performed to improve the chemical, mechanical and thermal properties of the briquettes. These include determinations of compressive, breaking and abrasion strength, softening and melting points, and thermal behavior. The theoretical energy balance calculated from the process of loading briquettes into the EAF has yielded a positive value of ～ 5×105?kcal/t of briquettes, showing that extra energy is clearly supplied to the furnace. Results corresponding to trials in the EAF are also shown. These include data on taps, slags, energy consumption and the quality of new dust.     

Removal of Iron From Quartz Ore Using Different Acids: A Laboratory-Scale Reactor Study

The purification of quartz using chemical processes is extremely important for many industries, including the glass, electronic, detergent, ceramics, paint, refractory, and metallurgy industries, as well as for advanced technology products. The purpose of this work was to investigate the removal of iron as an impurity from quartz ores using a chemical leaching method with different reagents.

The iron content of the quartz ore sample was 310 ppm, and the iron was in the form of Fe₂O_3. In the first step, pre-enrichment studies were conducted based on the particle size, and the Fe₂O₃ content of the quartz ore was decreased to 88 ppm. A statistical design of the experiments and an ANOVA (analysis of variance) were performed in the second step to determine the main effects and interactions of the researched factors, which were the concentration of the leaching reagent (H₂SO₄, HCl, H₃PO₄, HClO₄, and NTA [Nitrilotriacetic acid]), solid/liquid ratio, leaching temperature, and leaching time. The highest Fe₂O₃ removal was 86.6%, and a 11.8 ppm Fe₂O₃ content quartz product with a whiteness index (WI) value of 90.6 was obtained after 120 min of treatment at 90°C with a 10% S/L ratio and 1 M H₂SO₄.     

Selective separation of iron and scandium from Bayer Sc-bearing red mud

In this study, we investigated the separation of iron and scandium from Sc-bearing red mud. The red mud object of our study contained 31.11 wt% total iron (TFe), 0.0045 wt% Sc, hematite (Fe₂O₃) and ferrosilite (FeO·SiO₂) as the main Fe-bearing minerals. The Sc-bearing red mud was treated by a novel deep reduction roasting and magnetic separation process that includes the addition of coke and CaO to extract Fe and enriching Sc from the Sc-bearing red mud. The addition of coke and CaO enhances the transformation of hematite (Fe₂O₃) to metallic iron (Fe⁰) and magnetite (Fe₃O₄) as well as the transformation of ferrosilite into metallic iron (Fe⁰). The test results show that utilizing the new process a Fe concentrate with a TFe content of 81.22 wt% and Fe recovery of 92.96% was obtained. Furthermore, magnetic separation tailings with Sc content of 0.0062 wt% and Sc recovery of 98.65% were also obtained. The test results were achieved under the following process conditions: roasting temperature of 1373 K, roasting time of 45 min, calcium oxide dosage of 20 wt%, coke dosage of 25 wt%, grinding fineness of 90% < 0.04 mm, and magnetic field intensity of 0.24 T. The major minerals in the Fe concentrate are metallic iron (Fe⁰) and magnetite (Fe₃O₄). The main minerals in the magnetic separation tailings with a low TFe content of 2.62% are CaO·SiO₂, Na₂O·SiO₂, FeO·SiO₂, Ca₃Fe₂Si₃O₁₂, CaAl₂SiO₆ and CaFe(SiO₃)₂.     

电弧炉烟尘球团焙烧-洗涤脱卤制备低卤含量氧化锌的试验研究

针对电炉弧烟尘处理利用,进行了电弧炉烟尘球团焙烧-洗涤脱制备低卤含量氧化锌的试验研究,取得了满意的结果,在最佳球团焙烧工艺条件下,锌的挥发率>94%、铅的挥发率>90%,氟主要以难挥发的MnF2形式留在窑渣中,挥发氧化锌烟尘中难溶氟化物含量少,洗涤脱卤效果明显,洗涤后含锌62.14%,氟0.011%、氯0.20%,基本满足株冶氧化锌系统浸出原料的要求。     

Recycling Waste Plastics in EAF Steelmaking: Carbon/Slag Interactions of HDPE‐Coke Blends

Due to the inherent limitations of current methods of plastic waste disposal, there have been concerted efforts worldwide towards developing alternative, environment friendly and economic recycling processes. With an aim to recycle waste plastics in EAF steelmaking, carbon/slag interactions for a number of blends made of metallurgical coke and HDPE (high density polyethylene) and an EAF slag (34.8 mass‐% Fe₂O₃) have been investigated at 1550°C using a sessile drop arrangement. The rate of gas generation showed an increase with increasing HDPE concentration, reaching a maximum for blend #3 (with appr. 30 % HDPE) and decreasing thereafter. Among all the blends investigated, blend #3 showed significantly higher levels of slag foaming as compared to metallurgical coke. HDPE‐coke blends also showed better wetting compared to metallurgical coke with contact angles in some cases improving from 140° to 70° after 10 minutes of contact. These results have been discussed in terms of ash and sulphur contents of carbonaceous residues and dynamic changes in slag composition. Industrial trials on blend #3 showed a good agreement with laboratory results. This work opens novel avenues for the utilisation of plastics wastes as a valuable carbon resource in EAF steelmaking.     

Understanding Environmental Leachability of Electric Arc Furnace Dust

Dust from production of steel in an electric arc furnace (EAF) contains a mixture of elements that pose a challenge for both recovery and disposal. This paper relates the leachability of six Canadian EAF dusts in four leaching tests [distilled water, Ontario Regulation 347 Leachate Extraction Procedure, Amount Available for Leaching (AALT), and pH 5 Stat] to their mineralogy. Chromium and nickel contaminants in EAF dust are largely unleachable (<5% available in AALT and pH 5 Stat), as they are found with the predominant spinel ferrite phase in EAF dust. However, even a small proportion of oxidized chromium can result in significant leachate concentrations of highly toxic chromate. The leachability of zinc (7–50% available), lead (2–17% available), and cadmium (9–55% available) can be significant, as large fractions of these contaminants are found as chlorides and oxides. The leaching of these metals is largely controlled by pH. The acid neutralization capacity of the EAF dusts appeared to be controlled by dissolution of lime and zincite, and results from regulatory leaching tests can be misleading because the variable acid neutralization capacity of EAF dusts can lead to very different final leachate pHs (5–12.4). A more informative approach would be to evaluate the total amounts of contaminants available in the long term, and the acid neutralization capacity.     

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.     

A Clean and Efficient Method for Recovery of Vanadium from Vanadium Slag: Nonsalt Roasting and Ammonium Carbonate Leaching Processes

A cleaner method has been developed for the extraction of vanadium from vanadium slag. Compared to the traditional alkaline salts roasting followed by the water leaching process, in the nonsalt roasting process because no additives are added, the chromium spinel in the raw vanadium slag will not be converted to carcinogenic chromate salts and exhaust gas will not be produced. The ammonium metavanadate is precipitated from the water leach solution. The wastewater from the vanadate precipitation process can be recycled into the leaching process. The leaching residue can be comprehensively utilized in conjunction with an iron-making process using blast furnace. The nonsalt roasting mechanism was systematically investigated in a laboratory study. The XRD and morphology analysis of roasted vanadium slag showed that the oxidation of vanadium spinel occurred in the following steps: (1) the destruction of vanadium spinel and the formation of solid solution of Fe₂O₃·V₂O₃; (2) the oxidation of solid solution of Fe₂O₃·V₂O₃ to Fe₂O₃·V₂O₄ and a portion of the V(IV) in the Fe₂O₃·V₂O₄ was reacted with basic oxide such as MgO to generate the low-valence vanadate Mg₂VO₄; (3) the formation by further oxidation of highest-valence vanadates Mn₂V₂O₇ and Mg₂V₂O₇. The effects of particle size, oxygen concentration, gas flow rate, and temperature on vanadium recovery were investigated. Simultaneously, the effects of leaching variables, including ammonium carbonate concentration and temperature, were examined. The thermodynamics of the system are also reported.     

The oxidation behaviour of amorphous and crystalline Fe78Si9B13

A combination of thermogravimetry, scanning and transmission electron microscopy, electron probe microanalysis and differential scanning calorimetry has been used to investigate the oxidation kinetics, and oxide morphology, structure and composition in amorphous and crystalline Fe₇₈Si₉B₁₃ alloys. Kinetic data indicate that the oxidation reactions of both amorphous and crystalline Fe₇₈Si₉B₁₃ obey a parabolic rate law over the temperature range 300 to 450°C with activation energies of 120 and 86 kJ/mol respectively, indicating that grain boundary diffusion is probably the rate controlling process. The parabolic rate constant for oxidation of crystalline Fe₇₈Si₉B₁₃ is consistently higher than for amorphous Fe₇₈Si₉B₁₃ over the temperature range 300–450°C, so that the amorphous alloy always shows a better oxidation resistance. Electron microscopy and electron probe microanalysis show that the oxide scales formed on both amorphous and crystalline Fe₇₈Si₉B₁₃ consist of SiO₂, Fe₃O₄ and Fe₂O₃, but the detailed microstructure and compositions are different. The oxide scale formed on amorphous Fe₇₈Si₉B₁₃ contains more SiO₂ and has a small particle size, while the oxide scale formed on crystalline Fe₇₈Si₉B₁₃ contains more Fe₃O₄ and consists of larger particles. The difference in oxide growth between amorphous and crystalline Fe₇₈Si₉B₁₃ is caused by the difference in alloy microstructure.     

不锈钢粉尘的物理化学特性分析

不锈钢粉尘是一种产生量大、粒度细小、杂质含量高、极具回收利用价值的二次资源。为了开发不锈钢粉尘高效利用工艺,采用化学分析、XRD、扫描电镜等方法,对EAF和AOD不锈钢除粉尘的化学成分、粒度、物相组成、Cr~(6+)浸出及微观形貌进行了研究。结果表明,不锈钢粉尘中Ni、Cr、Fe含量较高,且均以氧化物形式存在;粉尘中的主要物相有铬铁尖晶石、磁铁矿、钙镁橄榄石、石英及石灰等;粉尘中的Cr~(6+)含量极少,低于国家危险废弃物的限制要求,但高于饮用水国家标准。     

Efficient removal of K2O and Fe2O3 impurities from bauxite tailings through active calcination combined with acid leaching

In the present study, direct acid and active calcination–acid leaching processes were employed to remove K₂O and Fe₂O₃ impurities from bauxite tailings. For direct acid leaching, the results indicated that Fe₂O₃ can be removed with the addition of 3?mol?L^?1 HCL, whereas K₂O cannot be removed even when the concentration of HCl is higher than 7?mol?L^?1. As the bauxite tailings were calcined at 400–700°C, both K₂O and Fe₂O₃ were removed at low HCl concentration (3?mol?L^?1), which was ascribed to the removal of hydroxyls and increased K activity, derived from X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.     

Effect of Iron Oxides on Activity of Calcium Aluminate Clinker in CaO-Al_2O_3-SiO_2 System

The sintering characteristics at 1350℃ and leaching property at 80℃ of calcium aluminate clinkers in the CaO-Al2O3-SiO2 （C-A-S） system with different additions of FeO and Fe2O3 were investigated. FeO inhibits the conversion of β-Ca2SiO4 to γ-Ca2SiO4 and makes the clinker not pulverizable. FeO and Fe2O3 inhibit the formation of CaAl2O4, but promote the formation of Ca12Al14O33. The interplanar spacing at （2 1 1） crystal face of Ca12 Al14O33 in the clinker increases with the increase of FeO addition, which indicates that FeO forms solid solutions in Ca12Al14O33. The clinkers with Fe2O3 addition form a new phase Ca2Fe2O5, and the amount of Ca2Fe2o5 increases with the in crease of Fe2O3 addition. Both FeO and Fe2O3 do not affect the Al2O3 leaching rate of calcium aluminate clinker in sodium carbonate solution, but they increase the molar ratio of caustic Na2O to Al2O3 in the leached liquor.     

The oxidation behaviour of amorphous alloy Fe40Ni40P14B6

A combination of thermogravimetry, optical microscopy, scanning and transmission electron microscopy, electron probe microanalysis and differential scanning calorimetry has been used to investigate the oxidation behaviour of amorphous Fe₄₀Ni₄₀P₁₄B₆. The oxide layer formed on amorphous Fe₄₀Ni₄₀uB₆ has a whisker-like α-Fe₂O3 structure, which grows very rapidly to build up a thick layer of oxide. Kinetic data indicate that the oxidation of amorphous Fe₄₀Ni₄₀P₁₄B₆ obeys a parabolic rate law as long as the alloy remains amorphous and the rate controlling process is diffusion of iron in the amorphous alloy matrix. However, the oxidation rate drops sharply if crystallization of amorphous Fe₄₀Ni₄₀P₁₄B₆ takes place during oxidation annealing. Crystalline Fe₄₀Ni₄₀P₁₄B₆ also obeys a parabolic rate law but with as much smaller rate constant than the amorphous alloy. The rate controlling process for oxidation of crystalline Fe₄₀Ni₄₀P₁₄B₆ is diffusion of iron and nickel in the multiphase oxide layer, which consists of a fine scale mixture of NiO, Fe₃O₄, Fe₂O₃ and NiFe₂O₄, crystals. The difference in oxidation behaviour between amorphous and crystallized Fe₄₀Ni₄₀P₁₄B₆ is caused by the different alloy microstructures.     

First-Principles Investigation on the Electronic Structure and Stability of In-Substituted ZnFe2O4

The geometric structure, electronic structure, and stability of In-substituted ZnFe₂O₄ (Zn₇InFe₁₆O₃₂ and Zn₈Fe₁₅InO₃₂) are investigated by the density functional theory at generalized gradient approximation level. Compared with the perfect ZnFe₂O₄ (Zn₈Fe₁₆O₃₂), the unit cell volume of In-substituted ZnFe₂O₄ increases and the structure deforms slightly. The formation energy of In substitution for Zn is smaller than that of In substitution for Fe, indicating that Zn₇InFe₁₆O₃₂ is easier to be formed than Zn₈Fe₁₅InO₃₂. In substitution changes the properties of ZnFe₂O₄ from semiconducting character to metallic character. For ZnFe₂O₄ and In-substituted ZnFe₂O₄, the strength of O–Zn bond is stronger than O–Fe bond and both of them have a covalent bond character. The strength of O-In bond is similar to that of O–Zn bond in Zn₇InFe₁₆O₃₂, but weaker than O–Fe in Zn₈Fe₁₅InO₃₂. In substitution for Zn causes the strength of O–Fe bonds around In atom to weaken. In substitution for Fe causes the strength of O–Zn bonds around In atom to weaken obviously, while the strength of O–Fe bonds strengthen slightly.     

Preparation and photocatalytic activity of Fe3O4@SiO2@ZnO:La

In this study, Fe₃O₄@SiO₂@ZnO:La microspheres were successfully prepared. The microspheres have the advantages of both ZnO doped with La and the Fe₃O₄@SiO₂ structure such that the former improves the photocatalytic activity of ZnO and the latter can be reused. The X-ray diffraction (XRD), a field emission scanning electron microscope (SEM), a field emission transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and a vibrating sample magnetometer (VSM) were used to characterize Fe₃O₄@SiO₂@ZnO:La microspheres. Methyl orange was used as the model molecule to study the effect of the Zn²⁺ concentration and the doping amount of La on the photocatalytic activity of Fe₃O₄@SiO₂@ZnO:La microspheres. Results show that in the synthesis of Fe₃O₄@SiO₂@ZnO:La microspheres, photocatalytic activity of the microspheres is enhanced first and weakened later with the increase of Zn²⁺ concentration. In the La doping process, the photocatalytic activity of Fe₃O₄@SiO₂@ZnO:La microspheres is enhanced with the increase in the La doping amount. The magnetic photocatalysts not only have high photocatalytic activity, but also can be reused. After being reused five times, the photocatalyst's degradation rate of methyl orange is still as high as 81%, which shows that magnetic photocatalysts have prospective wider applications in photocatalytic degradation of dye wastewater.