Method for dechlorinating zinc-comprising dust from electric arc furnaces by oxidative roasting with minimal zinc losses
Oxidative roasting of EAF dust at 1000°C for 9 hours addresses the inefficiencies and high costs of existing methods by achieving nearly complete chlorine removal with minimal zinc loss, preparing dust for high-quality zinc oxide production.
Patent Information
- Authority / Receiving Office
- RU · RU
- Patent Type
- Patents
- Current Assignee / Owner
- FEDERALNOE GOSUDARSTVENNOE AVTONOMNOE OBRAZOVATELNOE UCHREZHDENIE VYSSHEGO OBRAZOVANIYA YUZHNO URALSKIJ GOSUDARSTVENNYJ UNIV (NATSIONALNYJ ISSLEDOVATELSKIJ UNIV) (FGAOU VO YUURGU (NIU))
- Filing Date
- 2025-12-10
- Publication Date
- 2026-06-30
AI Technical Summary
Existing methods for removing chlorides and fluorides from electric arc furnace (EAF) dust are inefficient, costly, and result in significant zinc losses due to high temperatures required for complete halide removal, limiting the processing of EAF dust with elevated chlorine and fluorine content.
Oxidative roasting of EAF dust at optimized conditions of 1000°C and a holding time of 9 hours to achieve nearly complete chlorine removal (99.4%) with minimal zinc losses (20%) by directly treating the initial dust, reducing the process temperature and complexity.
The method effectively removes nearly all chlorine from EAF dust while minimizing zinc losses, making it suitable for further processing into high-quality zinc oxide, thus enhancing the efficiency and reducing costs.
Abstract
Description
[0001] The proposed invention relates to the production of zinc oxide and can be used to improve the quality of the zinc obtained during the disposal of electric arc furnace (EAF) dust.
[0002] This method is used to remove chlorine from the dust produced by electric arc remelting and can be used for recycling EAF dust.
[0003] The method applies to the metallurgy of non-ferrous and ferrous metals, in particular to the removal of chlorine by roasting under oxidizing conditions, and can be used in the pyrometallurgical processing of zinc-containing materials with a high halide content.
[0004] It is known that EAF dust contains chlorides in certain amounts, up to 10%; these chlorides are introduced along with the amortization scrap, which in turn is contaminated with polyvinyl chloride compounds. The chlorine contained in the dust reduces the quality of the resulting Waelz zinc oxide. Because chlorides are present in EAF dust, they must be removed for further processing and the extraction of valuable metals. According to the analyzed data, various methods for thermal chlorine removal exist.
[0005] A method for removing chlorides and fluorides from dusty zinc-containing materials is known. (RU2653394C1 under class C22B7 / 02, C22B19 / 00, C22B19 / 38, declared on 23.03.2017, published on 08.05.2018). The essence of the method is as follows: a charge consisting of dusty zinc-containing materials is mixed with calcium oxide (from 70% to 110% of the iron oxide content in the dust), as well as coke in an amount of 1-2% of the dust weight. Next, the charge is fed to a granulator, into which water is fed, the resulting granules are loaded into a Waelz kiln, in which the sublimation of chlorides and fluorides occurs. The disadvantages of this method are the use of expensive charge, the complexity of the technological operation, and the addition of calcium oxide of less than 70%, which does not allow for the complete decomposition of zinc ferrite.
[0006] A known method for removing chlorine and fluorine from dusty zinc-containing materials includes a calcination stage (oxidative roasting) at an operating temperature of 650–700°C and further processing of secondary sublimates Abdeev M.A., Kolesnikov A.V., Ushakov N.N. Waelz treatment of zinc-lead-containing materials. Moscow: Metallurgy. - 1985. - P.94. The main disadvantage of the method is the use of pyrometallurgical methods that are effective for removing chlorine; however, as a result of sublimation, partial sublimation of zinc and its losses occur.
[0007] The closest in technological essence to the claimed method is the method for removing chlorine from Waelz oxide (RU2813068C1 under class C22B19 / 02, C22B19 / 38, C22B1 / 14, C22B7 / 02, C01G9 / 03, declared 29.11.2022, published 06.02.2024), obtained during the processing of electric arc furnace (EAF) dust. According to this method, Waelz oxide is granulated with moistening with water to a moisture content of 8%, after which the granulated material is directly loaded into a calcining furnace. Calcination (Welz II) is carried out at a temperature of 1200°C in the reaction zone, while the exhaust gas temperature is maintained at 530–550°C. The furnace gas flow rate is 4.0 m / s. The Waelz oxide contains 4.8% chlorine and 0.09% fluorine. The distillation efficiency is 96% for chlorine and 90% for fluorine. The resulting calcined Waelz oxide contains 0.04% chlorine and less than 0.01% fluorine, which meets the quality requirements for solutions used in hydrometallurgical zinc production.
[0008] The disadvantages of this method include: the low degree of halide distillation limits the processing of Waelz oxide with elevated chlorine content (over 6%) and fluorine content (over 0.25%). To achieve the required impurity content in the final product, the calcination temperature is increased to 1200°C. Increasing the temperature leads to melting of the Waelz oxide granules. This reduces the intensity of halide sublimation, since the rate of their diffusion through the molten material layer into the gas phase is significantly reduced. Also, with increasing temperature, a partial transition of zinc into the gas phase occurs.
[0009] The technical objective and result of the invention is the dechlorination and preservation of zinc oxide in EAF dust by oxidative roasting with the selection of optimal parameters, which makes it possible to obtain dust with virtually no chlorine in its composition and preserve zinc oxide with minimal losses.
[0010] The technical task is achieved due to the fact that EAF dust is subjected to oxidative roasting under various conditions, the main conditions can be considered: temperature and holding time, it has been established that under optimal conditions, namely a temperature of 1000 ° C and a holding time of 9 hours, the degree of chlorine removal reaches 99%, with insignificant zinc losses of 20%.
[0011] The method of dechlorinating zinc-containing dust from electric arc furnaces by oxidative roasting is characterized by the fact that the electric arc furnace waste in the form of dust, chemical composition, wt.%: iron 39.5 - 40.9; zinc 12.6 - 13.1; manganese 4.4 - 4.6; calcium 3.7 - 4.1; sodium 1.9 - 2.8; silicon 2.1 - 2.3; chlorine 1.7 - 2.0; potassium 1.6 - 1.7; lead 0.8 - 1.1; sulfur 0.8 - 0.9; copper 0.4 - 0.5, subjected to oxidative roasting in a muffle furnace at a temperature of 1000 °C and a holding time of 9 hours, while the removal of chlorine reaches 99.4%, and zinc losses do not exceed 20%.
[0012] The proposed method for dechlorination of EAF dust by oxidative roasting is as follows. Roasting of EAF dust is carried out in a muffle furnace in the temperature range from 900 to 1100 °C with a holding time of 3.6 and 9 hours, the following EAF dust chemical composition is used as the starting materials (dust composition is presented in wt.%): iron 39.5 - 40.9; zinc 12.6 - 13.1; manganese 4.4 - 4.6; calcium 3.7 - 4.1; sodium 1.9 - 2.8; silicon 2.1 - 2.3; chlorine 1.7 - 2.0; potassium 1.6 - 1.7; lead 0.8 - 1.1; sulfur 0.8 - 0.9; copper 0.4 – 0.5.
[0013] The technical result achieved by the oxidative roasting method is as follows. At a temperature of 900°C and an increase in the holding time from 3 to 9 hours, the degree of chlorine removal increases significantly - from 19% to 77.6%. However, zinc losses increase insignificantly: from 20.8% to 23.0%. Increasing the temperature to 1000°C dramatically intensifies the process. In just 3 hours of holding, 73.5% of chlorine is removed with a zinc loss of 20.8%. With an increase in the holding time to 9 hours, dechlorination is almost complete (99.4%), zinc losses amount to 19.8%. A further increase in temperature to 1100°C ensures almost complete chlorine removal in just 3 hours (91.2%), but this leads to sharp zinc losses, which reach 37.8%. Extending the holding time to 6 hours allows for the removal of 99.4% of the chlorine, but zinc losses also increase, reaching approximately 40.1%. After roasting, the resulting EAF dust is purified of chlorine and suitable for the subsequent Waelz process, producing "pure" zinc oxide.
[0014] The difference between the proposed method and the prototype is the method of removing chlorine directly from the initial EAF dust, since the removal of chlorine from the final Waelz oxide is accompanied by high economic costs and complicates the technological process.
[0015] In the closest method, chlorine removal is carried out from Waelz oxide, which results in additional zinc losses as a result of the dechlorination process being carried out at higher temperatures.
[0016] In the claimed method, dechlorination of zinc-containing dust is carried out directly from the original EAF dust, which significantly reduces the process temperature and significantly reduces zinc losses during dechlorination, making the process more cost-effective and suitable for use on dusts with poorer zinc content.
[0017] Example. To conduct experiments on the dechlorination of EAF dust by oxidative roasting (the chemical composition is presented in Table 1), standard samples weighing 10.0 ± 0.1 g were prepared, placed in corundum crucibles, and then loaded into a preheated muffle furnace. The studies were conducted under strictly controlled conditions at temperatures ranging from 900 to 1100 °C. At each temperature, a series of experiments were carried out with varying holding times of 3, 6, and 9 hours, which made it possible to obtain comprehensive data on the dynamics of the dechlorination process, which is presented in Table 2. The chemical composition of the dust before and after roasting was determined by X-ray microanalysis on a Jeol JSM-7001F scanning electron microscope with an EDS Oxford INCA X-max 80 energy-dispersive system.The study of the samples after firing showed that increasing the temperature and increasing the holding time lead to a significant removal of chlorides, but significantly increase the loss of zinc from dust, which is an undesirable factor that should be taken into account. At a temperature of 900 °C and a holding time of 3 hours, the degree of Cl removal is 19%. With a holding time of 6 hours, the degree of Cl removal reaches 40% with Zn losses of 20.8%. With a holding time of 9 hours, the degree of chlorine removal increases to 77.6% with comparable Zn losses of 23.0%. At a firing temperature of 1000 °C and a holding time of 3 hours, the degree of Cl removal is 73.5%, and Zn losses remain within 20.8%. With a holding time of 9 hours, Cl removal is almost complete, reaching 99.4%, while Zn losses are within 19.8%. At a firing temperature of 1100°C and a holding time of 3 hours, the Cl removal rate is 91.2%, and the Zn loss increases significantly, reaching 37.8%.After a 6-hour holding period, the Cl removal process is virtually complete, reaching 99.4% with Zn losses remaining at approximately the same high level of 40.1%. Thus, the optimal conditions for oxidative roasting with maximum chlorine removal and minimal zinc losses are a temperature of 1000°C and a holding time of 9 hours. Under these conditions, chlorine removal reaches 99.4%, and zinc losses do not exceed 20%.
[0018] Table 1. Average composition of the studied EDP dust, mass %
[0019] Elements O Na Mg Si S Cl K Ca Cr Mn Fe Cu Zn Pb Summ Average value 27,00 2,30 0,80 2,20 0,80 1,80 1,70 3,90 0,50 4,50 40,20 0,50 12,90 1,00 100,00
[0020] Table 2. Dust composition after oxidative roasting, mass%.
[0021] Temperature Time O Na Mg S Si Cl K Ca Mn Fe Cu Zn Pb Cr Total 900℃ 3 hours 28,08 2,04 0,67 0,56 1,61 1,38 1,03 5,58 4,52 41,99 0,49 10,70 0,85 0,49 99,99 6 hours 25,08 2,77 0,79 0,59 1,67 1,02 0,93 5,77 5,00 43,94 0,30 11,25 0,33 0,56 100,00 9 hours 28,53 2,04 0,68 0,49 1,82 0,38 0,53 5,69 5,09 43,1 0,29 10,91 0,05 0,38 99,98 1000℃ 3 hours 25,48 2,38 0,85 0,35 1,79 0,45 0,37 5,37 5,31 45,03 0,36 11,24 0,55 0,48 100,01 6 hours 24,32 1,39 0,82 0,65 1,67 0,37 0,51 5,93 5,03 47,27 0,23 10,85 0,13 0,83 100,00 9 hours 25,18 0,94 0,70 0,28 1,91 0,01 0,33 5,78 5,38 47,31 0,25 11,39 0,03 0,50 99,99 1100℃ 3 hours 29,44 2,67 0,43 0,56 2,57 0,15 0,38 6,12 4,40 43,09 0,35 8,83 0,48 0,56 100,03 6 hours 32,05 0,93 0,57 0,67 2,56 0,01 0,46 6,18 4,60 42,55 0,05 8,50 0,23 0,66 100,02 9 hours 31,19 0,11 - 0,62 2,42 0,04 0,44 6,15 4,60 44,76 0,31 8,89 - 0,69 100,22
[0022] The proposed method of high-temperature oxidative roasting with optimally selected parameters (temperature of 1000°C and holding time of 9 hours, minimizing zinc loss) can be successfully applied for dechlorination of steelmaking dust.