A method for dezincing of electric furnace dust

Abstract

The application discloses a zinc removal treatment method of electric furnace dust, which comprises the following steps: mixing electric furnace dust and calcium-based semi-dry desulfurization ash, uniformly mixing, and then pressing into raw material pellets; carrying out medium-temperature roasting on the raw material pellets, and obtaining a zinc-containing product and sulfur-containing flue gas after the roasting is completed; and removing zinc by acid leaching treatment or magnetic separation treatment after the zinc-containing product is crushed. The zinc removal treatment method of electric furnace dust fully utilizes effective components in the electric furnace dust and the desulfurization ash, changes the phase state of zinc in the electric furnace dust and sulfur in the desulfurization ash through medium-temperature roasting, and then removes the zinc in the electric furnace dust by acid leaching or magnetic separation, and simultaneously, the sulfur in the calcium-based semi-dry desulfurization ash is directly decomposed by the medium-temperature roasting and removed by conversion and decomposition of iron oxides which are rich in the electric furnace dust.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment and resource utilization technology, and in particular relates to a method for dezincification treatment of electric furnace ash. Background Technology

[0002] Electric arc furnace (EAF) dust includes dust from carbon steel, alloy steel, and stainless steel. With the development of my country's steel and power industries, the increasing amount of scrap steel, and the growing demand for special steels, EAF steelmaking output will continue to rise, and the amount of dust generated will also increase annually. EAF smelting produces approximately 15-30 kg of dust per ton of steel. my country's EAF steelmaking output is approximately 70 million tons, generating over 2 million tons of dust annually. EAF ash is rich in zinc, with an average content of about 10%, equivalent to over 200,000 tons of metallic zinc. Given the relative scarcity of zinc resources globally, its recycling value is significant. EAF dust is rich in elements such as Fe, Zn, and Pb. Improper handling can lead to serious environmental pollution from toxic elements like Pb and Zn. Directly returning it to the blast furnace for ironmaking would cause Zn and Pb to accumulate within the blast furnace, shortening furnace lining life, causing nodules and clogging gas pipelines, and negatively impacting blast furnace production. Therefore, EAF ash is now generally dezincified and reused in production.

[0003] Electric furnace ash contains a high amount of zinc, which mainly exists as zinc ferrite mineral phase. Its spinel structure is stable, making it difficult to dissolve and leach with acid and also difficult to dissolve in alkaline solutions. Therefore, high-temperature metallurgical reduction processes are generally used for zinc removal, such as carbon-based reduction technology and high-temperature molten reduction technology. In the carbon-based reduction technology, carbon-based reducing agent is added to the electric furnace ash and then fed into a rotary hearth furnace or rotary kiln. After heating, it enters the reduction zone. Most of the iron oxides are reduced to reduced iron, and the Zn compounds in the dust are reduced to Zn vapor, which volatilizes in the solid layer and is rapidly oxidized in the upper part and cooled to ZnO before being discharged with the flue gas. High-temperature smelting reduction technology reduces valuable metal oxides in waste materials to metals using carbon-based reducing agents. Low-boiling-point metals such as Zn and Pb volatilize and are then re-oxidized in the gas phase to form zinc oxide and lead oxide, which are recovered as oxides for zinc smelting. High-boiling-point metals, primarily Fe, form pig iron that can be used as raw material in electric furnaces for steelmaking. If Ni and Cr are present, it can be used as raw material for stainless steel smelting. Other oxides such as CaO and SiO2 are converted into slag, which can be used as building materials after cooling. The high-temperature metallurgical smelting reduction furnace operates at approximately 1400℃, uses electricity as its energy source, and can recover zinc oxide with a purity exceeding 60%, with complete Fe recovery and stable slag properties. However, both of these high-temperature metallurgical reduction processes suffer from high reaction temperatures and require the addition of carbon-based reducing agents, resulting in high carbon and energy consumption, and thus are not well-suited to low-carbon requirements.

[0004] Semi-dry desulfurization ash is a byproduct of calcium-based semi-dry desulfurization of industrial flue gas in industries such as steel, power plants, and cement. It is grayish-white in appearance, has low moisture content, and fine particle size. Its main components are CaSO3·1 / 2H2O, CaSO4·2H2O, CaCO3, and Ca(OH)2, and it also contains a small amount of CaCl2, heavy metals, and fly ash. Because it contains calcium sulfite and a small amount of chlorine, it is unstable or corrosive, making it difficult to utilize.

[0005] In view of the above, there is an urgent need to develop a new dezincification technology for electric furnace ash to solve the defects of high energy consumption and high carbon in the existing technology, and to synergistically utilize the effective components in semi-dry desulfurization ash and electric furnace ash. Summary of the Invention

[0006] To address the high energy consumption and high carbon footprint of existing mainstream technologies, the present invention aims to provide a relatively low-carbon method for zinc removal from electric furnace ash. This method utilizes the effective components in electric furnace ash and calcium-based semi-dry desulfurization ash, and through medium-temperature roasting, transforms the phases of zinc and sulfur in the ash and desulfurization ash. Specifically, zinc ferrite in the electric furnace ash reacts with calcium oxide generated or present in the desulfurization ash to form zinc oxide and calcium ferrite. Zinc is then removed from the electric furnace ash through acid leaching or magnetic separation. Simultaneously, the sulfur in the calcium-based semi-dry desulfurization ash is converted to SO2 and removed through direct decomposition via medium-temperature roasting and the conversion and decomposition of iron oxides abundant in the electric furnace ash.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for dezincification treatment of electric furnace ash.

[0009] Electric furnace ash and calcium-based semi-dry desulfurization ash are mixed evenly and then pressed into pellets to obtain raw material pellets. The raw material pellets are then roasted at a medium temperature to obtain zinc-containing products and sulfur-containing flue gas. The zinc-containing products are crushed and then the zinc is removed by acid leaching or magnetic separation.

[0010] Preferably, the electric furnace ash and the calcium-based semi-dry desulfurization ash are mixed in a calcium-iron molar ratio of 1.1 to 1.3.

[0011] Preferably, the electric furnace ash comprises the following components by weight percentage of oxides: TFe 35-45%, CaO 5-15%, SiO2 2-8%, MgO 2-3%, Al2O3 0.5-2%, ZnO 5-20%, with the balance being other components;

[0012] The calcium-based semi-dry desulfurization ash comprises the following components by weight percentage of oxides: TFe 0.1-2%, CaO 45-65%, SiO2 0.5-5%, MgO 0.5-2%, Al2O3 0.5-2%, S 3-10%, with the balance being other components.

[0013] Preferably, during the medium-temperature roasting process, the roasting temperature is 950–1100℃ and the roasting time is 2–4 hours.

[0014] Preferably, the sulfur-containing flue gas, after dust removal, is absorbed by water and converted into sulfuric acid.

[0015] Preferably, during the crushing process, the roasted product is crushed to a particle size ≤ 400 mesh.

[0016] Preferably, in the acid leaching process, the crushed zinc-containing product is immersed in dilute sulfuric acid with a concentration of 1.5 to 2.5 mol / L for extraction, the solid-liquid ratio is controlled at 1:3 to 6, the acid leaching temperature is 70 to 100°C, and the acid leaching time is 2 to 4 hours, finally obtaining a zinc-rich leaching solution and leaching residue.

[0017] Preferably, the zinc-rich leaching solution is purified and then electrolyzed to obtain metallic zinc; the leaching residue is returned to the sintering process or the steelmaking process for reuse.

[0018] Preferably, the zinc recovery rate reaches over 80%.

[0019] The beneficial effects of the dezincification treatment method for electric furnace ash provided by this invention are as follows:

[0020] 1. The zinc removal treatment method of electric furnace ash of the present invention transforms the zinc in the electric furnace ash by medium-temperature roasting, and then removes the zinc in the electric furnace ash by acid leaching or magnetic separation. This method can not only make comprehensive use of the effective components in calcium-based semi-dry desulfurization ash, but also solve the defects of high energy consumption and high carbon in conventional electric furnace ash zinc removal technology.

[0021] 2. The zinc removal method for electric furnace ash of the present invention utilizes medium-temperature roasting decomposition and the conversion and decomposition of iron oxides rich in electric furnace ash to achieve the conversion and removal of sulfur from calcium-based semi-dry desulfurization ash.

[0022] 3. The zinc removal treatment method for electric furnace ash of the present invention does not require carbon addition. It uses a combination of pyrometallurgical and wet processes to separate zinc from the electric furnace ash. The entire process comprehensively considers the full utilization of by-products and the prevention and control of secondary pollution from the perspective of waste co-treatment and utilization, and is low-carbon and environmentally friendly.

[0023] 4. The dezincification treatment method for electric furnace ash of the present invention makes full use of the effective calcium component of calcium-based semi-dry desulfurization ash, while removing and converting sulfur in calcium-based semi-dry desulfurization ash, thereby realizing the effective utilization of calcium-based semi-dry desulfurization ash. The entire treatment process is simple and the cost is low. Attached Figure Description

[0024] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0025] Figure 1 This is a flowchart of the dezincification treatment method for electric furnace ash according to the present invention. Detailed Implementation

[0026] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with embodiments.

[0027] Combination Figure 1 As shown, the dezincification treatment method for electric furnace ash provided by the present invention specifically includes the following steps:

[0028] (1) Batching and molding: Electric furnace ash and calcium-based semi-dry desulfurization ash are mixed evenly and then pressed into pellets to obtain raw material pellets;

[0029] The specific process is as follows: Electric furnace ash and calcium-based semi-dry desulfurization ash are mixed at a calcium-to-iron molar ratio of 1.1 to 1.3, meaning the molar ratio of calcium in the calcium-based semi-dry desulfurization ash to iron in the electric furnace ash is 1.1 to 1.3. A binder and water are added, mixed thoroughly, and pressed into pellets to obtain raw material pellets. The electric furnace ash comprises the following components by weight percentage of oxides: TFe 35-45%, CaO 5-15%, SiO2 2-8%, MgO 2-3%, Al2O3 0.5-2%, ZnO 5-20%, with the remainder being other trace components. The calcium-based semi-dry desulfurization ash comprises the following components by weight percentage of oxides: TFe 0.1-2%, CaO 45-65%, SiO2 0.5-5%, MgO 0.5-2%, Al2O3 0.5-2%, S 3-10%, with the remainder being other trace components. The binder accounts for 3-7 wt% of the total mass of the raw material pellets, and the water accounts for 10-15 wt% of the total mass of the raw material pellets.

[0030] (2) Medium-temperature roasting: The raw material pellets are roasted at a medium temperature. Sulfur-containing flue gas is generated during the roasting process. After roasting is completed, zinc-containing products are obtained.

[0031] The specific process is as follows: the raw material pellets are roasted at a medium temperature, and the roasting temperature is controlled at 950-1100℃ in an air atmosphere for 2-4 hours. During this process, the zinc ferrite in the electric furnace ash and the calcium phase in the calcium-based semi-dry desulfurization ash react to generate zinc oxide and calcium ferrite. At the same time, the calcium sulfite and calcium sulfate in the calcium-based semi-dry desulfurization ash are converted into SO2 through direct decomposition or chemical reaction and enter the flue gas. After roasting, sulfur-containing flue gas and zinc-containing products are obtained respectively.

[0032] (3) By-product treatment: after the zinc-containing product is crushed, zinc is removed by acid leaching or magnetic separation.

[0033] The specific process is as follows: During the medium-temperature roasting process, the zinc-containing product obtained is mainly in the form of calcium ferrite and zinc oxide. To fully separate the zinc from the zinc-containing product, it is first crushed to a particle size ≤400 mesh. Then, the crushed zinc-containing product can be separated from the zinc by acid leaching or magnetic separation, ultimately achieving zinc removal. When using acid leaching, the crushed zinc-containing product is placed in dilute sulfuric acid with a concentration of 1.5–2.5 mol / L for extraction, controlling the solid-liquid ratio at 1:3–6, the acid leaching temperature at 70–100℃, and the acid leaching time at 2–4 hours, ultimately obtaining a zinc-rich leachate and leaching residue. The zinc-rich leachate, after impurity removal, is electrolyzed to obtain metallic zinc; the leaching residue can be returned to the sintering or steelmaking process. After the above treatment, the zinc recovery rate of the electric furnace ash reaches over 85%.

[0034] The dezincification treatment method for electric furnace ash of the present invention will be further described below with specific examples.

[0035] Example 1

[0036] The dezincification treatment method for electric furnace ash in this embodiment is as follows:

[0037] The composition of electric furnace ash is: TFe 44.1%, CaO 9.9%, SiO2 3.2%, MgO 3.3%, Al2O3 1.4%, ZnO 7.9%; the composition of calcium-based semi-dry desulfurization ash is: TFe 1.9%, CaO 62.8%, SiO2 3.6%, MgO 1.0%, Al2O3 2.0%, S 3.5%; High-zinc electric furnace ash and calcium-based semi-dry desulfurization ash were mixed at a calcium-iron molar ratio of 1.1, and after adding binder and water and mixing evenly, they were pressed into pellets to obtain raw material pellets. The binder and water accounted for 4wt% and 11wt% of the total mass of the batch, respectively. Then, the raw material pellets were put into a roasting furnace and heated to 1100℃ for medium-temperature roasting for 3 hours. During this process, the sulfur-containing flue gas was removed by dust removal and then absorbed with water to produce sulfuric acid. The zinc-containing product after roasting was crushed to a particle size of less than 400 mesh. Then, the crushed zinc-containing product was leached in dilute sulfuric acid with a concentration of 1.5mol / L, with the solid-liquid ratio controlled at 1:3, the acid leaching temperature at 80℃, and the acid leaching time at 2.5 hours. Finally, zinc-rich leaching solution and leaching residue were obtained. The zinc-rich leaching solution was purified and then electrolyzed to obtain metallic zinc. The leaching residue was returned to the sintering process for batching.

[0038] In the above-mentioned dezincification treatment method for electric furnace ash, the zinc recovery rate reaches 83%.

[0039] Example 2

[0040] The dezincification treatment method for electric furnace ash in this embodiment is as follows:

[0041] The composition of electric furnace ash is: TFe 41.0%, CaO 7.3%, SiO2 3.6%, MgO 2.9%, Al2O3 0.5%, ZnO 15.6%; the composition of calcium-based semi-dry desulfurization ash is: TFe 0.2%, CaO 57.5%, SiO2 0.9%, MgO 1.7%, Al2O3 0.5%, S 6.9%; High-zinc electric furnace ash and calcium-based semi-dry desulfurization ash were mixed at a calcium-iron molar ratio of 1.3, and after adding binder and water and mixing evenly, they were pressed into pellets to obtain raw material pellets. The binder and water accounted for 5 wt% and 12 wt% of the total mass of the batch, respectively. Then the raw material pellets were put into a roasting furnace and heated to 1000℃ for medium-temperature roasting for 4 hours. During this process, the sulfur-containing flue gas was dusted and then absorbed with water to produce sulfuric acid. The zinc-containing product after roasting was crushed to a particle size of less than 400 mesh. Then the crushed zinc-containing product was leached in dilute sulfuric acid with a concentration of 1.8 mol / L, with the solid-liquid ratio controlled at 1:4, the acid leaching temperature at 90℃, and the acid leaching time at 3 hours. Finally, zinc-rich leaching solution and leaching residue were obtained. The zinc-rich leaching solution was purified and then electrolyzed to obtain metallic zinc. The leaching residue was returned to the sintering process for batching.

[0042] In the above-mentioned dezincification treatment method for electric furnace ash, the zinc recovery rate reaches 93%.

[0043] Example 3

[0044] The dezincification treatment method for electric furnace ash in this embodiment is as follows:

[0045] The composition of electric furnace ash is: TFe 41.1%, CaO 11.6%, SiO2 3.1%, MgO 3.3%, Al2O3 1.8%, ZnO 9.9%; the composition of calcium-based semi-dry desulfurization ash is: TFe 1.2%, CaO 64.3%, SiO2 3.4%, MgO 0.8%, Al2O3 1.6.0%, S 3.8%; High-zinc electric furnace ash and calcium-based semi-dry desulfurization ash were mixed at a calcium-iron molar ratio of 1.2, and after adding binder and water, they were pressed into pellets to obtain raw material pellets. The binder and water accounted for 3.5 wt% and 12 wt% of the total mass of the mixture, respectively. The raw material pellets were then placed in a roasting furnace and heated to 1050℃ for medium-temperature roasting for 2 hours. During this process, the sulfur-containing flue gas was removed by dust removal and then absorbed with water to produce sulfuric acid. The zinc-containing product after roasting was crushed to a particle size of less than 400 mesh. The crushed zinc-containing product was then extracted with 2 mol / L dilute sulfuric acid, with the solid-liquid ratio controlled at 1:6, the acid leaching temperature at 100℃, and the acid leaching time at 4 hours. Finally, a zinc-rich leaching solution and leaching residue were obtained. The zinc-rich leaching solution was purified and then electrolyzed to obtain metallic zinc. The leaching residue was returned to the sintering process for batching.

[0046] In the above-mentioned dezincification treatment method for electric furnace ash, the zinc recovery rate reaches 90%.

[0047] Example 4

[0048] The dezincification treatment method for electric furnace ash in this embodiment is as follows:

[0049] The composition of electric furnace ash is: TFe 42.7%, CaO 4.0%, SiO2 2.9%, MgO 1.7%, Al2O3 0.6%, ZnO 17.1%; the composition of calcium-based semi-dry desulfurization ash is: TFe 0.3%, CaO 50.5%, SiO2 1.2%, MgO 1.5%, Al2O3 0.6%, S 5.7%; High-zinc electric furnace ash and calcium-based semi-dry desulfurization ash were mixed at a calcium-iron molar ratio of 1.3, and a binder and water were added and pressed into pellets to obtain raw material pellets. The binder and water accounted for 6 wt% and 14 wt% of the total mass after mixing, respectively. Then, the raw material pellets were put into a roasting furnace and heated to 950℃ for medium-temperature roasting for 4 hours. During this process, the sulfur-containing flue gas was removed by dust removal and then absorbed with water to produce sulfuric acid. The zinc-containing product after roasting was crushed to a particle size of less than 400 mesh and leached in dilute sulfuric acid with a concentration of 2.3 mol / L. The solid-liquid ratio was controlled at 1:5, the acid leaching temperature was 80℃, and the acid leaching time was 3 hours. Finally, zinc-rich leaching solution and leaching residue were obtained. The zinc-rich leaching solution was purified and then electrolyzed to obtain metallic zinc. The leaching residue was returned to the steelmaking process for batching.

[0050] In the above-mentioned dezincification treatment method for electric furnace ash, the zinc recovery rate reaches 92%.

[0051] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for dezincification treatment of electric furnace ash, characterized in that, After the electric furnace ash and calcium-based semi-dry desulfurization ash are mixed evenly, they are pressed into pellets to obtain raw material pellets. The electric furnace ash comprises the following components by weight percentage of oxides: TFe 35-45%, CaO 5-15%, SiO2 2-8%, MgO 2-3%, Al2O3 0.5-2%, ZnO 5-20%, with the balance being other components; The calcium-based semi-dry desulfurization ash comprises the following components by weight percentage of oxides: TFe 0.1-2%, CaO 45-65%, SiO2 0.5-5%, MgO 0.5-2%, Al2O3 0.5-2%, S 3-10%, with the balance being other components; The raw material pellets were roasted at a medium temperature, and after roasting, zinc-containing products and sulfur-containing flue gas were obtained respectively. During the medium-temperature roasting process, the roasting temperature is 950–1100℃; the roasting time is 2–4 hours. The zinc-containing product is crushed and then subjected to acid leaching or magnetic separation to remove zinc. During the crushing process, the zinc-containing product is crushed to a particle size ≤ 400 mesh; In the acid leaching process, the crushed zinc-containing product is immersed in dilute sulfuric acid with a concentration of 1.5–2.5 mol / L for extraction, controlling the solid-liquid ratio at 1:3–6, the acid leaching temperature at 70–100℃, and the acid leaching time at 2–4 hours. This yields a zinc-rich leachate and leaching residue. After impurity removal, the zinc-rich leachate is electrolyzed to obtain metallic zinc. The zinc recovery rate reaches over 80%.

2. The method for dezincification treatment of electric furnace ash according to claim 1, characterized in that, The calcium-based semi-dry desulfurization ash and the electric furnace ash are mixed in a calcium-iron molar ratio of 1.1 to 1.

3.

3. The method for dezincification treatment of electric furnace ash according to claim 1, characterized in that, The sulfur-containing flue gas, after dust removal, is absorbed by water and converted into sulfuric acid.

4. The method for dezincification treatment of electric furnace ash according to claim 1, characterized in that, The leaching residue is returned to the sintering process or the steelmaking process.

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