Treatment Of Electric Arc Furnace Dust Research Articles

Selective removal of zinc and lead from electric arc furnace dust by chlorination–evaporation reactions

Re-melting of scrap in an electric arc furnace (EAF) results in the accumulation of filter dust from off-gas treatment that predominantly consists of iron and zinc oxides. Filter dust is classified as hazardous waste due to its high contents of potentially toxic or ecotoxic elements such as Pb, Cr, Cd, and As. A promising processing route for this waste is selective chlorination, in which the non-ferrous metal oxides are chlorinated and selectively evaporated in form of their respective chlorides from the remaining solids via the process gas flow. Here, we investigate stepwise thermochemical treatment of EAF dust with either waste iron(II) chloride solution or hydrochloric acid at 650, 800, and 1100 °C. The Zn and Pb contents of the thermochemically processed EAF dust could be lowered from 29.9% and 1.63% to 0.09% and 0.004%, respectively. Stepwise heating allowed high separation between zinc chloride at the 650 °C step and sodium-, potassium-, and lead-containing chlorides at higher temperatures. Furthermore, the lab-scale results were transferred to the use of an experimental rotary kiln highlighting the possibilities of upscaling the presented process. Selective chlorination of EAF dust with liquid chlorine donors is, therefore, suggested as a potential recycling method for Zn-enriched steelworks dusts.

Material Cost and Benefit Analysis for Dust Injection Technology in EAF Steelmaking Process and EAF Dust Treatment with CaO Addition

In the electric arc furnace (EAF) steelmaking process, electric arc furnace dust (EAFD) is inevitably generated. The dust injection method is known as one of the effective technologies to reduce the total amount of EAFD generation. In this technology, Zn in the injected dust is enriched in the secondary dust, and Fe is transferred to the slag. In this work, the effect of dust injection technology on the recovered/lost amounts of Zn and Fe is quantitatively evaluated based on the mass balance calculation. Furthermore, in terms of dust and slag treatment costs, the potential of new EAFD treatment technology (the lime addition method) which enables simultaneous Zn and Fe recovery is discussed. By introducing the lime addition method, Zn and Fe can be recovered as resources, and the total income from these sales outweighs the cost of the chemicals used for recovery. This indicates that the treatment costs paid by EAF companies can be significantly low. The dust injection technology reduces the total quantity of dust shipped, but increases the total amount of slag and Fe loss. Therefore, it is necessary to determine the appropriate value of the amount of dust injection by balancing the waste treatment cost and the amount of metal resource recovery.

Effect of Electric Arc Furnace Dust Treatment on the Properties of Fresh and Hardened Mortar

Electric arc-furnace dust (EAFD) is generated in considerable amounts by the electric arc steelmaking process. Use of EAFD in concrete improved many properties of concrete. Yet, the prolonged setting time even at low dosages of EAFD was a serious limitation. This phenomenon was attributed to the presence of transition metal in the material of EAFD. Therefore, it was necessary to stabilize the transition metal in an insoluble crystalline matrix. The calcination with high-temperature was done to fix the transition metal in a complex matrix with the cementitious properties. This material was called Engineered Dust (ED). The use of ED with different replacement levels of 0, 5, 10, 15 and 20% at w/b ratio of 0.5 was carried out. The results showed that the use of ED solved the prolonged setting time which the replacement up to 20% had a normal setting time of 5 to 6 hours. Furthermore, the material of ED was used up to 15% replacement level with the replacement of 20% ED that gave the lowest electric charge values in the RCPT.

Hydrometallurgical Treatment of EAF Dust by Direct Sulphuric Acid Leaching at Atmospheric Pressure

The present paper presents a part of the research efforts of the laboratory of Metallurgy, National Technical University of Athens, Greece, aiming at developing a purely hydrometallurgical method, able to treat the zincferous dust, generated during the production of steel from scraps in Electric Arc Furnace (EAF), efficiently and economically and especially so for annual capacities lower than 50,000 tonnes of dust, for which the currently applied industrial methods are not economical. The proposed method is based on direct sulphuric acid leaching of the EAF dust and it succeeds to recover the valuable metals contained in it, such as zinc, lead and cadmium, converting the initially hazardous waste into a residue suitable to be fed to cement industry. The EAF dust sample, provided by a Greek steel plant, was initially leached with water, at certain conditions, to remove as much of the contained calcium as possible without co-dissolution of other metals. The washed dust was further subjected to three–stage leaching at atmospheric pressure, using sulphuric acid concentrations of 2N and 3N and temperatures 25 °C, at the first stage, and 95 °C, at the second and third stages. Total percent extraction values achieved were 97 % for zinc and 97 % for cadmium. Almost all lead, 99.7 %, remained undissolved as lead sulphate in the leach residues. It was shown experimentally that lead can be recovered as saleable lead sulphide while zinc can be recovered from the pregnant solution by solvent extraction with D2EHPA. Finally, based on the results, a conceptual flowsheet of the proposed integrated hydrometallurgical method for the treatment of EAF dust was established and is given.

Stabilization and solidification of electric arc furnace dust originating from steel industry by using low grade MgO

Abstract In this study, solidification/stabilization (S/S) of electric arc furnace dust (EAFD) which is generated during the production of steel from scrap metals and classified as hazardous waste were investigated by using different ratios of cement and low grade MgO (LG MgO) as binding agents. Type I PC 42.5 R portland cement and LG MgO which contains 70–80% MgO were used. S/S blocks that contain different ratios of binding agents which have 1/0.5 – 1/1 – 1/2 – 1/3 – 1/4 – 1/5 cement/LG MgO ratio and S/S blocks which contain only cement and no LG MgO agents were prepared. These blocks, which contain 3 different waste ratios according to weight, 20%, 30% and 40% respectively, were produced and exposed to 28-day water purification. At the end of the purification process, S/S blocks were extracted using TCLP (Toxicity Characteristic Leaching Procedure) tests in order to determine the leaching behavior of Zn, Pb, and Cd in S/S blocks. By the end of this study, it was concluded that the recovery of EAFD is possible and applicable by immobilization. The findings of the study concluded that environmental performances or structural properties of blocks contain 30% waste by weight are suitable. This method is a proper one for recovering and treatment of EAFD with mixture of cement and LG MgO.

Electric Arc Furnace Dust Treatment by the Combination of Pyro/Hydrometallurgical Processes

This project researched a mechanism of the decomposition of zinc ferrite (ZnFe2O4) to be zinc oxide (ZnO) and calcium ferrite (Ca2Fe2O5) by using calcium oxide (CaO) from lime as a reducing agent. Zinc ferrite was mostly found in electric arc furnace dust (EAFD), which is a by product from a steel making industry. The experiment was simple as following. The EAFD was mixed with lime in mole ratio of zinc ferrite and calcium oxide at 1:2, 1:3 and 1:4 and then compressed into pellets. Effects of mole ratio, temperatures and times on the decomposition were studied. The conditions used in these experiments were 800, 900, 1,000 and 1,100 oC for 2, 4 and 6 hours. The results showed that the suitable conditions for the decomposition of zinc ferrite by calcium oxide could be as low as 800 oC for only 2 hours with mole ratio of zinc ferrite from EAFD and calcium oxide from lime as 1:2. A solubility test was provided to processed samples at the conditions as 0.1 M hydrochloric acid (HCl) at 50 oC for 20 minutes. It was found that EAFD from pyrometallurgical treatment could be decomposed to be zinc oxide and the following by hydrometallurgical treatment could recovery high zinc yield from the remaining residue. However, EAFD treated by only hydrometallurgical process obtained lower zinc recovery due to the high stability of zinc ferrite in HCl and most of the solutions.

New pyrometallurgical process of EAF dust treatment with CaO addition

The non-carbothermic zinc pyrometallurgical processing of electric arc furnace (EAF) dust was investigated on a laboratory scale. The main objective of this process was to convert highly stable zinc ferrite (ZnFe2O4), which accounts for more than half of total zinc in the EAF dust, into ZnO and Ca2Fe2O5 by CaO addition. The EAF dust was mixed with CaO powder in various ratios, pressed into pellets, and heated in a muffle furnace in air at temperatures ranging from 700 to 1100°C for a predetermined holding time. All ZnFe2O4 was transformed into ZnO and Ca2Fe2O5 at a minimum temperature of 900°C within 1 h when sufficient CaO to achieve a Ca/Fe molar ratio of 1.1 was added. However, at higher temperatures, excess CaO beyond the stoichiometric ratio was required because it was consumed by reactions leading to the formation of compounds other than ZnFe2O4. The evaporation of halides and heavy metals in the EAF dust was also studied. These components could be preferentially volatilized into the gas phase at 1100°C when CaO was added.

Electric Arc Furnace Dust Treatment Process by Iron Powder

Electric arc furnace dust is a byproduct from steelmaking, contained up to 50%wt of zinc ferrite. It also contains about 10-20%wt of zinc oxide and the other metal oxides. Approximately 100,000 tons of EAF dust are generated per annum within Thailand. All of the dust has been sent to landfill. The objective of this research is to investigate the kinetics mechanism of the decomposition of zinc ferrite in EAF dust to obtain zinc oxide and iron oxide by using iron powder as a reducing agent. The process was carried out by mixing zinc ferrite or EAF dust with iron powder then compressed them in a mold. The samples from compression were treated by pyrometallurgical process. The factors required to be concerned were temperatures, particle sizes of iron powder, and mole ratios of zinc ferrite per iron powder, respectively. The treated samples were analyzed by X-ray diffraction (XRD) in order to characterize zinc ferrite phase transformation. It was found that the quantity of zinc ferrite, both either pure zinc ferrite and zinc ferrite in EAF dust, were decreased after treating by the pyrometallurgical process when increasing treating time from 30 to 180 minutes at 600°C, the particle size of iron powder at 10 micron, and the mole ratio of zinc ferrite per iron powder at 1:3. Moreover about 70%wt of zinc ferrite was decomposed and the products obtained were zinc oxides (ZnO) and iron oxides (Fe3O4, FeO, Fe2O3). The reduction of zinc ferrite with iron powder was well-defined taking place by diffusion thru product layer control. The activation energy of the reduction process was found to be 47.21±2.83 kJ/mol. Therefore, the decomposition of zinc ferrite by iron powder could be carried out at 1 atm with low pyrometallurgical temperature (600°C) and equipped with hydrometallurgical process to obtain high zinc yield.

Behavior of Zn and Fe Content in Electric Arc Furnace Dust as Submitted to Chlorination Methods

This work covers initially a general thermodynamics assessment regarding the zinc ferrite (ZnFe2O4) behavior toward direct and reducing chlorination. Then, the use of alternative chlorination agents were also theoretically appreciated, before a set of experiments has been carried out with industrial residue (electric arc furnace dust). Besides identifying zinc ferrite (95.4 pct), the XRD analysis indicated the presence of ZnO (4.6 pct). Therefore, the main objective of the present work is related to a theoretical (thermodynamics) and experimental (kinetics) evaluation of the mentioned residue chemical behavior as submitted to chlorination methods. Several characterization methods were used, such as X-ray diffraction, scanning electron microscopy, X-ray fluorescence, mass spectroscopy (ICP-MS), and energy-dispersive X-ray spectroscopy (EDS). It was observed that zinc was present, mostly, in the form of zinc ferrite (franklinite). The thermodynamics study revealed that Zn has a more susceptible behavior regarding the oxides conversion into chlorides. However, this tendency is not necessarily associated with a selective reaction, as showed for the chlorination in the presence of carbon, as both iron and zinc chlorides formation is feasible. The experimental results have indicated that some reaction systems can be further studied in order to identify operational conditions that enable selective formations. So, it was observed that for the calcium chloride reaction conducted at 1273 K (1000 °C) for 30 minutes, the iron content in the residue slightly increases (with 15 pct removal), whereas the zinc content decreases from 20 to 12 pct (53 pct removal), suggesting complementary studies where this possible selectivity could be even more determinant. Such results have also indicated that the direct action of chlorine at 1073 K (800 °C) allowed complete removal of zinc, followed by conversion in the order of 40 pct in iron. Therefore, a complementary investigation over these alternatives is identified as a promising option in the field of electric arc furnace dust treatment, particularly when the Zn content is very low.

Formation of the ZnFe2O4 phase in an electric arc furnace off-gas treatment system

To better understand the phenomena of ZnFe2O4 spinel formation in electric arc furnace dust, the dust was characterized with particle size analysis, X-ray fluorescence (XRF), electron backscatter diffraction (EBSD), and electron probe micro-analysis (EPMA). Different ZnFe2O4 formation reaction extents were observed for iron oxide particles with different particle sizes. ZnO particles were present as both individual particles and aggregated on the surface of larger particles. Also, the slag particles found in the off-gas were shown not to react with the zinc vapor.After confirming the presence of a ZnFe2O4 formation reaction, the thermodynamic feasibility of in-process separation – a new electric arc furnace dust treatment technology – was reevaluated. The large air intake and the presence of iron oxide particles in the off-gas were included into the thermodynamic calculations. The formation of the stable ZnFe2O4 spinel phase was shown to be thermodynamically favorable in current electric arc furnace off-gas ducts conditions even before reaching the post combustion chamber.

Comparison of electric arc furnace dust treatment technologies using exergy efficiency

Abstract Multiple methods exist to treat electric arc furnace dust (EAFD), aiming at high metal recovery and low landfilling needs. However, a technology that is energy efficient and recovers both Zn and Fe has only recently been developed to a commercial scale with the Rotary Hearth Furnace. Various other technologies have been proposed as alternatives to the historically preferred Waelz Kiln process. This gate-to-gate study presents an objective method to compare the overall thermodynamic performance and efficiency of treatment technologies through the use of an exergy analysis incorporating the dominant factors without the need of examining every process detail. In addition, the influence of the EAFD zinc content on the exergy efficiency of both the Waelz Kiln and Rotary Hearth Furnace process was studied. The efficiencies of these high temperature metal recovery processes were also compared to the efficiency of the newly proposed In-Process Separation technology.

Measurement of polychlorinated dibenzo-p-dioxin and dibenzofuran emission from EAF steel making proces

Electric arc furnace (EAF) steel manufacturing is an important recycling activity which contributes to the recovery of steel resources and steel scrap/waste minimization. Because of the content of plastics, coatings and paintings as well as other nonferrous materials in the charge during melting, a strong emission of pollutants, including polluting substance group consists of persistent organic pollutions (POPs) represented by polycyclic aromatic hydrocarbon (PAH), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) occurs. This study was set out to investigate emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs) from the stack of a new electric-arc furnace-dust treatment plant installed during modernisation of the Melt Shop in CMC SISAK d.o.o., Croatia. Obtained results have been compared with previously obtained results of PCDDs/Fs emission measurements from the old electric-arc furnace dust treatment without dust drop-out box, as well as quenching tower. The total PCDDs/Fs concentration in the stack off gases of both electric arc furnaces EAF A and EAF B were 0.2098 and 0.022603 ng I-TEQ/Nm3 respectively, and these results are close to previous obtained results by other authors. The calculated values of the emission factors for PCDDs/Fs calculated on the basis of measured PCDDs/Fs concentration in the stack off gases in 2008 and 2011 were 1.09 and 0.22 ng I-TEQ/ ton steel, respectively.

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.

Assessment of polychlorinated dibenzo-p-dioxins and dibenzofurans contribution from different media to surrounding duck farms

Since the "Toxic Egg Event" broke out in central Taiwan, the possible sources of the high content of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in eggs have been a serious concern. In this study, the PCDD/F contents in different media (feed, soil and ambient air) were measured. Evaluation of the impact from electric arc furnace dust treatment plant (abbreviated as EAFDT plant), which is site-specific to the "Toxic Egg Event", on the duck total-PCDD/F daily intake was conducted by both Industrial Source Complex Short Term model (ISCST) and dry and wet deposition models. After different scenario simulations, the worst case was at farm A and at 200 g feed and 5 g soil for duck intake, and the highest PCDD/F contributions from the feed, original soil and stack flue gas were 44.92, 47.81, and 6.58%, respectively. Considering different uncertainty factors, such as the flow rate variation of stack flue gas and errors from modelling and measurement, the PCDD/F contribution fraction from the stack flue gas of EAFDT plant may increase up to twice as that for the worst case (6.58%) and become 13.2%, which was still much lower than that from the total contribution fraction (86.8%) of both feed and original soil. Fly ashes contained purposely in duck feed by the farmers was a potential major source for the duck daily intake. While the impact from EAFDT plant has been proven very minor, the PCDD/F content in the feed and soil, which was contaminated by illegal fly ash landfills, requires more attention.

Basic Consideration on EAF Dust Treatment Using Hydrometallurgical Processes

Electric Arc Furnace (EAF) dust, defined as special industrial waste in Japan, is treated through pyrometallurgical processes in which crude ZnO powder is recovered. An on-site type process, however, is desired to reduce treatment cost and cost of transportation of the dust. A hydrometallurgical process is considered to be suitable for such an on-site treatment. Although many EAF dust treatment processes by hydrometallurgical method have been proposed, most of them have not been commercialized in Japan. A short review of hydrometallurgical processes for EAF dust was done and a new hydrometallurgical process for EAF dust was proposed in this study. Nitric acid solution is used for the extraction of ZnO from the dust. Some characteristics of the process are as follows: (1) Recovery of Zn from zinc ferrite in EAF dust is the target, while the dissolution of Fe is limited by controlling the pH of the solution. (2) Zn is recovered as metallic Zn by electrowinning from the solution and nitric acid is regenerated in the anode.

Mathematical Model of Over-micron and Nano-scale Powders Accumulation in a Coke Fixed-Bed Filter

The advances in Electric Arc Furnace (EAF) dust treatment have been slowed down by high treatment costs and the large amount of residue to be processed and disposed. A process of direct separation and recovery of iron and zinc is now under development, which adds environmental and economical perspectives to the EAF dust treatment process. In this process, a coke bed filter can be directly connected to an EAF, collecting metallic iron and slag components, whereas the gas containing zinc and lead vapors flows to a zinc condenser. It results in zero amount of dust liberated to the environment. A two dimensional, axisymmetric and steady state mathematical model describing a coke fixed-bed filter is developed. The model solves coupled equations for gas-powder flow and is specifically applied in the investigation of over-micron and nano-scale powders (similar to EAF dust particle size) collection behavior. The theoretical model results are compared with the cold model experimental results, in which both injection of glass (over-micron) and silica (nano-scale) powders are considered. Microscopic observations and analysis are performed in order to describe better the injected powder behavior through the filter. EAF dust samples morphology is characterized as agglomerates of small particles. Its particle size distribution is obtained by the combination of leaching treatment and image analysis. Calculated results show that the powders particle size distribution has a direct effect in the static hold up. The model has been validated by its enough agreement for static hold up and pressure drop with experimental data from cold model experiments.

Stabilization of Electrical Arc Furnace Dust with Low-Grade MgO Prior to Landfill

In Spain, the stabilization of electric arc furnace (EAF) dust prior to landfill is mainly carried out using a mixture of lime and Portland cement. This paper describes the treatment of EAF dust with low-grade MgO (LG MgO) and the results are compared to those obtained with a lime and Portland cement mixture used as a stabilizer agent. The effectiveness of the treatment was assessed with leaching tests results. The use of LG MgO allows us to manage this waste as a nontoxic residue according to tests decreed by Spanish regulations. Low-grade MgO acts as a buffering agent giving the final pH mixture a value within the range of minimum heavy metal solubility.

Electric arc furnace dust treatment: investigation on mechanical and magnetic separation methods.

Electric arc furnace dust (EAFD) is a major issue for processing technologies: Several million tons per year are generated, it contains both valuable and hazardous metals and yet no available treatment process has proven to be superior to all others. Processes currently applied or being developed are either of hydro- or pyrometallurgical type, which are very costly. In the paper testing of some physical separation methods of electric arc furnace dust from Polish steel industry were investigated. SEM, EDX analyses as well as grain size observations of dust particles were additionally performed. All investigations confirmed a possibility of effective magnetic and mechanical separation of EAFD particles.

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.

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 (ZnFe 2O 4) in the dust was converted into sodium zincate (Na 2ZnO 2) and iron oxide (Fe 2O 3). 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.