Method for preparing water purifying agent polyaluminum sulfate from aluminum smelting furnace dust

Abstract

This invention discloses a method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust, belonging to the technical field of hazardous waste resource utilization. The method includes the following steps: S1. After aluminum smelting furnace flue dust is mixed evenly with water, alkali solution and calcium hydroxide are added for stirring and reaction. After the reaction, the floating insoluble carbon black is collected and used as a heating material during aging, resulting in a solid-liquid mixture with carbon black removed; S2. The solid-liquid mixture with carbon black removed is subjected to plate and frame filter press for solid-liquid separation, yielding solid filter residue and filtrate A; the solid filter residue is treated to achieve inertization, yielding inertized high-alumina material; S3. Ferrous sulfate is added to filtrate A under stirring conditions. After the reaction is complete, solid-liquid separation is performed to obtain solid filter residue (iron sulfide) and filtrate B; S4. Sulfuric acid is added to filtrate B, and after aging, polyaluminum sulfate, the water purification agent, is prepared. This invention has a high utilization rate of molten aluminum flue dust and good economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of hazardous waste resource utilization technology, specifically relating to a method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust. Background Technology

[0002] Aluminum is the second most abundant metallic material after steel and is one of the essential metals required for national economic infrastructure construction. Its main products include aluminum and aluminum alloy sheets, coils, strips, foils, and pipelines, which are widely used in various sectors of the national economy. my country's aluminum industry suffers from insufficient reserve resources and declining supply capacity, necessitating a resource-saving development path for its aluminum industry. Among various industrial metals, aluminum has the highest resource utilization rate and the greatest recycling benefits. The resource utilization of the aluminum industry offers significant advantages in resource conservation, energy saving, and environmental protection. The current energy, resource, and environmental challenges in my country's economic development all demand a strong emphasis on developing the resource utilization of the aluminum industry.

[0003] Current market research on aluminum resource utilization mainly focuses on primary and secondary aluminum ash. Primary aluminum ash primarily consists of metallic aluminum and aluminum oxides, with metallic aluminum content ranging from 10% to 70%. Secondary aluminum ash is the residue after primary aluminum ash or other waste aluminum has undergone physical or chemical methods to extract metallic aluminum. It has a low metallic aluminum content and a relatively complex composition, mainly containing small amounts of aluminum, salt flux, oxides, and aluminum nitride. However, the aluminum smelting furnace dust generated during the aluminum smelting process is largely ignored. According to testing, the aluminum content in aluminum smelting furnace dust can reach 20%-40%. Furthermore, current research on aluminum ash resource utilization primarily focuses on the resource utilization of secondary aluminum ash, which does not contain heavy metals. Patent document CN112850765B discloses a method for quality control of polyaluminum ferric chloride produced from aluminum ash. In this implementation example, the main chemical composition of the raw materials is Al2O3: 34.87%, AlN: 1.74%, Al: 0.66%, F: 1.21%, Fe2O3: 2.17%, SiO2: 9.10%, Cl: 2.19%, and heavy metals (as Pb) 50 ppm. However, in actual aluminum smelting processes, due to variations in raw materials, large amounts of metal oxides such as zinc oxide and copper oxide are produced. Therefore, the product obtained using the method described in this patent for preparing polyaluminum ferric chloride may contain metallic impurities, limiting its market application.

[0004] In existing technologies, natural gas is mainly used for aluminum smelting in furnaces, and nitrogen is used to prevent excessive hydrogen accumulation and deflagration. This results in a large amount of flue dust and furnace ash being generated during the aluminum smelting process. In addition, incomplete combustion of natural gas produces carbon black, and sulfides in natural gas react with aluminum at high temperatures to form aluminum sulfide. Carbon black and aluminum sulfide are also mixed in with the aluminum smelting dust, resulting in aluminum smelting furnace dust with the following main chemical components: Al2O3: 10%-20%, AlN: 10%-30%, Al: 1%-5%, F: 0.01%-0.1%, Fe2O3: 0.1%-1%, SiO2: 3%-10%, Cl: 3%-15%, and heavy metals: Zn: 0.01%-0.05%, Cu: 0.01%-0.07%, Ni: 0.01%-0.03%. Therefore, there is an urgent need for a method for the resource utilization of flue dust generated in the process of smelting aluminum in a furnace using natural gas, as well as primary and secondary aluminum ash. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust, thereby solving the problem of low resource utilization rate of aluminum-containing waste.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust includes the following steps:

[0008] S1. After the aluminum smelting furnace flue dust is mixed evenly with water, alkaline solution and calcium hydroxide are added and stirred to react. After the reaction is completed, the floating insoluble carbon black is collected and used as raw material for heating during aging to obtain a solid-liquid mixture to remove carbon black.

[0009] S2. The solid-liquid mixture after removing carbon black is separated by plate and frame filter press to obtain solid filter residue and filtrate A; the solid filter residue is treated to achieve inert conversion, and the inert high-alumina material does not have leaching toxicity and reactivity, and the high-alumina material is used as a substitute raw material for bauxite;

[0010] S3. Ferrous sulfate is added to filtrate A under stirring conditions. After the reaction is complete, solid-liquid separation is performed to obtain solid filter residue iron sulfide and filtrate B.

[0011] S4. Add sulfuric acid to filtrate B and react and mature it at 60-80℃ to prepare polyaluminum sulfate, a water purification agent.

[0012] Furthermore, in S1, the ratio of aluminum smelting furnace dust, water, alkaline solution and calcium hydroxide is 1:2:2:0.01-0.03.

[0013] Furthermore, the concentration of the alkaline solution in S1 is 10%-20%.

[0014] Furthermore, the alkaline solution in S1 includes a sodium hydroxide solution or a potassium hydroxide solution.

[0015] Furthermore, the exhaust gas generated during the S1 stirring reaction process, including ammonia, hydrogen sulfide, and methane, is absorbed and treated with sulfuric acid, sodium hydroxide, or activated carbon.

[0016] Furthermore, the amount of ferrous sulfate used in S3 is 1.1-1.3 times the sulfur content in filtrate A.

[0017] Furthermore, the concentration of sulfuric acid in S4 is 50%.

[0018] Furthermore, the amount of sulfuric acid used in S4 is four times the mass of the solute in the alkaline solution of S1.

[0019] Furthermore, the stirring speed is 100-300 rpm.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. This invention provides a method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust. It utilizes the characteristic of the mutual reaction between impurities in the aluminum smelting flue dust to achieve the purpose of pretreatment and impurity removal of the flue dust. During the reaction process, the generated gas is effectively collected, achieving true harmless treatment of aluminum smelting flue dust, effectively improving the resource utilization rate of aluminum waste, and having good economic benefits.

[0022] 2. This invention first performs alkali pretreatment to remove impurities from aluminum smelting furnace flue dust. Sulfides in the molten aluminum flue dust are used to remove heavy metal compounds. Since carbon black has a low density and is insoluble in water, alkali, calcium hydroxide, and flue dust are reacted to collect the insoluble carbon black floating on the alkaline solution. The carbon black can be used as a heating material during the curing of polyaluminum sulfate. The resulting ammonia, hydrogen sulfide, methane, and other tail gases are absorbed by sulfuric acid, sodium hydroxide, or activated carbon, and can be utilized as resources after absorption. In this process, the chemical reaction formulas include formulas 1-5:

[0023] AlN+NaOH+H2O=NaAlO2+NH3↑(Formula 1)

[0024] Al4C3 + 4NaOH + 4H2O = 4NaAlO2 + 3CH4↑ (Equation 2)

[0025] 2F - +Ca 2+ =CaF2 (Equation 3)

[0026] Cu 2+ +2OH-=Cu(OH)2 (Equation 4)

[0027] Zn 2+ +2OH-=Zn(OH)2 (Equation 5)

[0028] Aluminum sulfide hydrolyzes under alkaline conditions to produce aluminum hydroxide and hydrogen sulfide. Aluminum hydroxide and hydrogen sulfide react with sodium hydroxide to produce sodium aluminate and sodium sulfide, respectively. Zinc hydroxide further dissolves under alkaline conditions, and sodium sulfide reacts with zinc ions to form zinc sulfide precipitate. A small amount of copper ions react with sodium sulfide to form copper sulfide. In this process, the chemical reaction formulas include Formulas 6-7:

[0029] S 2- +Zn 2+ =ZnS (Equation 6)

[0030] S 2- +Cu 2+ =CuS (Equation 7)

[0031] The tail gas generated during the reaction of alkali and aluminum smelting furnace dust can be absorbed by sulfuric acid and sodium hydroxide to obtain ammonium sulfate and sodium sulfide solutions, which can be further used to produce the corresponding byproducts ammonium sulfate and sodium sulfide. After the reaction is complete, ferrous sulfate can be added to the filtrate to remove excess sulfides and prepare iron sulfide, as shown in Formula 8:

[0032] S 2- +Fe 2+ =FeS (Equation 8)

[0033] After the pretreatment and impurity removal process, sulfuric acid is added, and polyaluminum sulfate is prepared by aging and polymerization at 60-80℃. This realizes the resource utilization of aluminum smelting furnace dust and produces a water purification agent with economic value: polyaluminum sulfate. In this process, the chemical reaction formulas include Formulas 9-10:

[0034] 2NaAlO2 + H2SO4 (small amount) + H2O = 2Al(OH)3↓ + Na2SO4 (Equation 9)

[0035] 2NaAlO2 + 4H2SO4 (excess) = Al2(SO4)3 + Na2SO4 + 2H2O (Equation 10)

[0036] 3. This invention has a wide range of applications. It is not only applicable to the smoke and dust generated during aluminum smelting in aluminum furnaces, but also to primary aluminum ash and secondary aluminum ash, which can be used to prepare water purification agents.

[0037] 4. This invention not only eliminates the reactivity of aluminum ash by alkalizing it, making it inert, but also renders the inert high-alumina material non-toxic and non-reactive. The high-alumina material can be used as a substitute for bauxite, and a large amount of carbon black can be collected for use as raw material in the curing of polyaluminum sulfate.

[0038] 5. Compared with other methods of preparing polyaluminum chloride from aluminum ash resources, this invention removes heavy metal impurities from aluminum ash through the sulfides in the aluminum ash itself and alkalization reactions, thereby obtaining pure polyaluminum sulfate.

[0039] 6. This invention achieves carbon black collection by scraping off carbon black that is insoluble in alkaline solution, and carbon black can be used as an energy source.

[0040] 7. The present invention firstly removes ammonia nitrogen from aluminum nitride by adding alkali to dissolve aluminum, which can also avoid the violent reaction that occurs during acidification, and increases the aluminum dissolution rate by utilizing the heat released by the reaction.

[0041] 8. All the secondary waste generated by this invention can be recycled, thus achieving the goal of turning waste into treasure. Attached Figure Description

[0042] The present invention will now be further described with reference to the accompanying drawings.

[0043] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0045] Please see Figure 1 A method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust includes the following steps:

[0046] S1. Add water to the reactor, then slowly add aluminum smelting furnace dust, mix evenly, then add 10%-20% alkaline solution and calcium hydroxide, and stir the reaction at a stirring rate of 100-300 rpm. After the reaction is completed, let it stand and collect the floating insoluble carbon black, which will be used as the heating raw material during aging to obtain a solid-liquid mixture with carbon black removed; the tail gas generated during the reaction is absorbed by a tail gas absorption device.

[0047] S2. The solid-liquid mixture after removing carbon black is separated by plate and frame filter press to obtain solid filter residue and filtrate A; the solid filter residue is treated to achieve inert conversion, and the inert high-alumina material does not have leaching toxicity and reactivity, and the high-alumina material is used as a substitute raw material for bauxite;

[0048] Under stirring conditions of 100-300 rpm, ferrous sulfate with a mass of 1.1-1.3 times the sulfur content in filtrate A is added to filtrate A. After the reaction is complete, solid-liquid separation is performed to obtain solid filter residue iron sulfide and filtrate B.

[0049] S4. Add 50% sulfuric acid to filtrate B. The amount of sulfuric acid is 4 times the mass of the solute in the alkaline solution in S1. React and mature at 60-80℃ to prepare polyaluminum sulfate, a water purification agent.

[0050] In one specific implementation, the ratio of aluminum smelting furnace dust, water, alkaline solution and calcium hydroxide in S1 is 1:2:2:0.01-0.03.

[0051] In one specific implementation, the exhaust gas generated during the S1 stirring reaction process, including ammonia, hydrogen sulfide, and methane, is absorbed and treated with sulfuric acid, sodium hydroxide, or activated carbon.

[0052] In one specific implementation, the alkaline solution in S1 includes sodium hydroxide solution and potassium hydroxide solution.

[0053] Example 1

[0054] Please see Figure 1 A method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust includes the following steps:

[0055] S1. Turn on the tail gas adsorption device, add 2 tons of water to the reactor, then slowly add 1 ton of aluminum smelting furnace dust, stir for 1 hour and mix evenly, then add 2 tons of 10% sodium hydroxide solution and 0.02 tons of calcium hydroxide, stir at a stirring rate of 200 rpm, after the reaction is completed, let stand and collect the floating insoluble carbon black, which will be used as the heating raw material during aging, to obtain a solid-liquid mixture with carbon black removed;

[0056] S2. The solid-liquid mixture after removing carbon black is separated by plate and frame filter press to obtain solid filter residue and filtrate A; the solid filter residue is treated to achieve inert conversion, and the inert high-alumina material does not have leaching toxicity and reactivity, and the high-alumina material is used as a substitute raw material for bauxite;

[0057] Under stirring conditions of 3.200 rpm, 40 kg of ferrous sulfate was added to filtrate A. After the reaction was complete, iron sulfide precipitate was formed. After solid-liquid separation, filtrate B and filter residue were obtained. The filter residue can be used to prepare iron sulfide.

[0058] S4. Add 400L of 50% sulfuric acid to filtrate B and react and mature at 60℃ to prepare polyaluminum sulfate, a water purification agent.

[0059] Example 2

[0060] Please see Figure 1 A method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust includes the following steps:

[0061] S1. Turn on the tail gas adsorption device, add 2 tons of water to the reactor, then slowly add 1 ton of aluminum smelting furnace dust, stir for 1 hour and mix evenly, then add 2 tons of 15% sodium hydroxide solution and 0.02 tons of calcium hydroxide, stir at a stirring rate of 200 rpm, after the reaction is completed, let stand and collect the floating insoluble carbon black, which will be used as the heating raw material during aging, to obtain a solid-liquid mixture with carbon black removed;

[0062] S2. The solid-liquid mixture after removing carbon black is separated by plate and frame filter press to obtain solid filter residue and filtrate A; the solid filter residue is treated to achieve inert conversion, and the inert high-alumina material does not have leaching toxicity and reactivity, and the high-alumina material is used as a substitute raw material for bauxite;

[0063] Under stirring conditions of 3.200 rpm, 40 kg of ferrous sulfate was added to filtrate A. After the reaction was complete, iron sulfide precipitate was formed. After solid-liquid separation, filtrate B and filter residue were obtained. The filter residue can be used to prepare iron sulfide.

[0064] S4. Add 450L of 50% sulfuric acid to filtrate B and react and mature at 70℃ to prepare polyaluminum sulfate, a water purification agent.

[0065] Example 3

[0066] Please see Figure 1 A method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust includes the following steps:

[0067] S1. Turn on the tail gas adsorption device, add 2 tons of water to the reactor, then slowly add 1 ton of aluminum smelting furnace dust, stir for 1 hour and mix evenly, then add 2 tons of 20% sodium hydroxide solution and 0.02 tons of calcium hydroxide, stir at a stirring rate of 200 rpm, after the reaction is completed, let stand and collect the floating insoluble carbon black, which will be used as the heating raw material during aging, to obtain a solid-liquid mixture with carbon black removed;

[0068] S2. The solid-liquid mixture after removing carbon black is separated by plate and frame filter press to obtain solid filter residue and filtrate A; the solid filter residue is treated to achieve inert conversion, and the inert high-alumina material does not have leaching toxicity and reactivity, and the high-alumina material is used as a substitute raw material for bauxite;

[0069] Under stirring conditions of 3.200 rpm, 40 kg of ferrous sulfate was added to filtrate A. After the reaction was complete, iron sulfide precipitate was formed. After solid-liquid separation, filtrate B and filter residue were obtained. The filter residue can be used to prepare iron sulfide.

[0070] S4. Add 500L of 50% sulfuric acid to filtrate B and react and mature at 70℃ to prepare polyaluminum sulfate, a water purification agent.

[0071] The water purification effect of the polyaluminum sulfate prepared in Examples 1-3 was tested: The water purification effect of the water purification agents obtained in the above examples was tested. The water purification agent was added to 1L of experimental sewage sample at a dosage of 10wt%. After adding, the mixture was mixed evenly and the test was carried out after 1 hour. The heavy metal content, COD, turbidity and SS were tested respectively.

[0072] The test results are shown in Table 1. The water quality data of the experimental wastewater samples before purification and the water quality data of each embodiment after purification are shown in Table 2.

[0073] Table 1

[0074]

[0075] Table 2

[0076] COD (mg / L) Total phosphorus (mg / L) Turbidity Experimental wastewater 532 18 89 Example 1 102 5 14 Example 2 89 3 8 Example 3 78 2 5

[0077] As shown in Tables 1 and 2, the present invention removes heavy metal impurities from aluminum ash through the sulfides and alkalization reaction in the aluminum ash itself, resulting in a water purification agent with pure polyaluminum sulfate and good water purification effect.

[0078] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0079] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust, characterized in that, Includes the following steps: S1. Add water to the reactor, then slowly add aluminum smelting furnace dust, mix evenly, then add 10%-20% alkaline solution and calcium hydroxide and stir to react. After the reaction is completed, let it stand and collect the floating insoluble carbon black, which is used as the heating raw material during aging to obtain a solid-liquid mixture to remove carbon black. The ratio of aluminum smelting furnace dust, water, alkaline solution and calcium hydroxide in S1 is 1:2:2:0.01-0.03; S2. The solid-liquid mixture after removing carbon black is separated by plate and frame filter press to obtain solid filter residue and filtrate A; the solid filter residue is then treated to achieve inertization conversion to obtain inert high-alumina material; S3. Ferrous sulfate is added to filtrate A under stirring conditions. After the reaction is complete, solid-liquid separation is performed to obtain solid filter residue iron sulfide and filtrate B. The amount of ferrous sulfate used in S3 is 1.1-1.3 times the sulfur content in filtrate A; S4. Add 50% sulfuric acid to filtrate B. The amount of sulfuric acid is 4 times the mass of the solute in the alkaline solution in S1. React and mature at 60-80℃ to prepare polyaluminum sulfate, a water purification agent.

2. The method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust according to claim 1, is characterized in that, The alkaline solution in S1 includes sodium hydroxide solution or potassium hydroxide solution.

3. The method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust according to claim 1, is characterized in that... The exhaust gas generated during the S1 stirring reaction includes ammonia, hydrogen sulfide and methane, and the exhaust gas is absorbed and treated with sulfuric acid, sodium hydroxide or activated carbon.

4. The method for preparing polyaluminum sulfate, a water purification agent, from aluminum smelting furnace flue dust according to claim 1, is characterized in that, The stirring speed is 100-300 rpm.

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