A method for preparing regenerated fluorite by using desulfurization gypsum residue and waste electrolyte

Abstract

This application relates to a method for preparing recycled fluorite using desulfurized gypsum slag and waste electrolyte, belonging to the field of metallurgical engineering technology. This invention targets the hazardous solid waste of waste electrolyte generated during aluminum electrolysis, employing a desulfurized gypsum slag calcination-leaching-flotation process to convert soluble fluorides in the waste electrolyte into insoluble calcium fluoride. The waste electrolyte is mixed with desulfurized gypsum slag and calcined, converting the fluorine-containing phase into water-insoluble calcium fluoride, sodium into water-soluble Na₂SO₄, and aluminum into Al₂O₃. Na₂SO₄ is then separated into the liquid phase by water washing, leaving CaF₂ and Al₂O₃ in the washed residue. The washed residue is then subjected to flotation to separate CaF₂ and Al₂O₃. This method can produce a product with a CaF₂ purity greater than 80%, and lithium, sodium, and aluminum can also be recovered through comprehensive treatment.

Description

Technical Field

[0001] This application relates to the field of metallurgical engineering technology, and in particular to a method for preparing recycled fluorite using desulfurized gypsum slag and waste electrolyte. Background Technology

[0002] Waste electrolyte is a typical hazardous solid waste (hazardous waste code HW48) generated in the aluminum electrolysis industry. Its environmental hazards are multi-dimensional, persistent, and severe, primarily stemming from its high fluoride content, high cyanide toxicity, high salinity and alkalinity, and the risk of heavy metal leaching. When waste electrolyte is left in the open or improperly landfilled, rainwater leaching causes large amounts of soluble fluorides (such as sodium fluoride and cryolite) to leach out, leading to severely excessive fluoride concentrations in groundwater. This, in turn, causes soil degradation and harms human health through the food chain, resulting in diseases such as dental fluorosis and skeletal fluorosis. Even more dangerous is the presence of cyanides (such as sodium cyanide) generated during electrolysis, which, upon contact with water or acid, may release highly toxic hydrogen cyanide gas or cyanide ions, posing an acute toxic risk to the surrounding ecosystem and human safety.

[0003] Desulfurization gypsum slag is a solid byproduct generated during flue gas desulfurization processes in coal-fired power plants and other enterprises. Its main component is calcium sulfate dihydrate, and it may also contain trace amounts of heavy metals, fluorides, chlorides, and unreacted lime. Although it is not generally listed as hazardous waste in my country's current management catalog, its actual storage or disposal process is prone to producing acidic leachate due to rainwater leaching, leading to the migration of heavy metals and other pollutants, posing potential environmental risks to soil and groundwater. If not properly treated, long-term accumulation of desulfurization gypsum slag may also cause dust pollution and salinization.

[0004] To overcome the challenge of solely treating and utilizing overhaul slag and desulfurization gypsum, a novel process was proposed: using desulfurization gypsum to solidify harmful fluorides in waste electrolytes and extract high-value CaF2. Against this backdrop, recovering fluorine from fluorine-rich secondary resources such as aluminum electrolysis waste electrolytes and converting it into high-value recycled fluorite products has dual strategic significance: firstly, it achieves the harmless treatment and reduction of hazardous waste, solving environmental problems; secondly, it opens up an important alternative supply channel for fluorine resources, helping to alleviate dependence on primary fluorite mines and ensuring the security and stability of the national fluorochemical industry chain.

[0005] Against this backdrop, recovering fluorine from fluorine-rich secondary resources such as waste electrolytes from aluminum electrolysis and converting them into high-value fluorite products has dual strategic significance: on the one hand, it achieves the harmlessness and reduction of hazardous waste, solving environmental problems; on the other hand, it opens up an important alternative supply channel for fluorine resources, helping to alleviate dependence on primary fluorite mines and ensuring the safety and stability of the national fluorochemical industry chain. Summary of the Invention

[0006] In view of the current insufficient recycling of waste electrolytes and the increasing scarcity of calcium fluoride resources, the purpose of this invention is to provide a method for high-value recycling of waste electrolytes produced in the aluminum smelting process, in particular, by calcination roasting to convert soluble fluorides in waste electrolytes into calcium fluoride, and then purifying the calcium fluoride by leaching, flotation and other methods.

[0007] A method for preparing fluorite using waste electrolyte-desulfurized gypsum residue roasting-leaching-flotation in this application includes the following steps: (1) The waste electrolyte is crushed and refined, and then mixed with desulfurized gypsum residue to obtain a mixture; (2) The mixture described in step (1) is roasted to obtain a cooked product; (3) The clinker described in step (2) is crushed and refined, then washed with water to obtain a slurry. The slurry is then subjected to liquid-solid separation to obtain a washing residue and a washing liquid. (4) The water-washed residue from step (3) is dried and pretreated before being floated to obtain fluorite concentrate and flotation tailings.

[0008] Furthermore, in step (1), the mass ratio of waste electrolyte to desulfurized gypsum residue is 1g:2g-1g:3g.

[0009] Furthermore, in step (2), the calcination temperature is 400℃-800℃, the heating rate is 10℃ / min, and the calcination time is 0.5h-2h.

[0010] Furthermore, in step (3), the washing solution is subjected to comprehensive treatment to recover lithium salt and sodium sulfate.

[0011] Furthermore, in step (4), the flotation tailings are comprehensively treated to recover alumina.

[0012] Furthermore, in step (4), sodium oleate is used as the collector and water glass is used as the depressant in the flotation operation.

[0013] The reaction equations involved in this application are shown below: CaSO4·2H2O = CaSO4 + 2H2O↑ 2Na3AlF6+ 6CaSO4= 6CaF2+ 3Na2SO4+Al2(SO4)3 2LiF + CaSO4 = CaF2 + Li2SO4 2AlF3+ 3CaSO4= 3CaF2+Al2(SO4)3 2KF + CaSO4 = K2SO4 + CaF2 2NaF + CaSO4 = CaF2 + Na2SO4 Al2(SO4)3 = Al2O3 + 3SO3↑ 2LiNa2AlF6 +5CaSO4 = 2LiF + 5CaF2+2Na2SO4 + Al2(SO4)3 2K2NaAlF6+4CaSO4= 4KF + 4CaF2+Na2SO4 + Al2(SO4)3 The mechanism of this application is as follows: This application proposes a method for recovering fluorine and lithium and preparing recycled fluorite from the waste electrolyte solid waste generated during the electrolytic aluminum production process using a roasting, washing, and flotation process. The core mechanism is as follows: (1) Calcination and conversion: The waste electrolyte is mixed with desulfurized gypsum residue and calcined to convert the fluorine-containing phase (mainly cryolite) into calcium fluoride that is difficult to dissolve in water, convert sodium into Na2SO4 that is soluble in water, and convert aluminum into Al2O3.

[0014] (2) Water washing separation: The calcined clinker is treated with water washing. During the water washing process, Na2SO4 and Li2SO4 are separated into the liquid phase, and the substances in the water washing residue are CaF2 and Al2O3.

[0015] (3) Flotation purification: After drying, the water-washed residue is subjected to flotation treatment to separate CaF2 and Al2O3. This method can prepare CaF2 products with a grade greater than 80%, which have high crystallinity and good crystal form, and alumina can also be recovered.

[0016] (4) Recycling and resource utilization: The aqueous solution can be recycled back to the washing step, and the lithium concentration in the washing solution is continuously enriched, from which lithium salts can be recovered (such as precipitation method, extraction method, etc.).

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Simple process and easy to control: It only requires three main steps: roasting, washing and flotation. It does not involve complex equipment or harsh reaction conditions and is easy to implement industrially.

[0018] 2. Low cost and recyclable reagents: The cost of flotation is far lower than the acid reagent cost in current wet recovery methods. The washing solution can be recycled, reducing wastewater discharge and reagent consumption, and lowering treatment costs.

[0019] 3. Highly efficient separation of fluorine and lithium: Lithium is preferentially extracted through water washing, avoiding the problems of large lithium loss and low recovery rate caused by the adsorption of lithium by neutralization precipitate residue in traditional processes. The lithium-rich solution contains fewer fluorine and aluminum impurities, which is beneficial for the subsequent efficient recovery of lithium.

[0020] 4. High purity of fluorite products: The fluorine phase in the final solid product is mainly CaF2, with a grade of over 80%. It can be used as recycled fluorite in the fluorochemical or metallurgical industries, realizing the high-value utilization of waste electrolytes.

[0021] 5. Comprehensive resource recovery: In addition to fluorite, lithium salts can be recovered from the washing solution, and aluminum (in the form of alumina) can be recovered from the flotation tailings, realizing the full utilization of fluorine, lithium and aluminum in the waste electrolyte.

[0022] 6. Environmentally friendly: It transforms hazardous waste (HW48) into valuable industrial raw materials, achieving harmlessness and volume reduction, and eliminating the risk of fluorine and cyanide pollution to soil and water bodies. Attached Figure Description

[0023] The above and other objects, features and advantages of this application will become more apparent from the more detailed description of exemplary embodiments thereof in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments thereof.

[0024] Figure 1 This is a schematic diagram of the process flow in this application; Figure 2 The image shows the XRD pattern of the waste electrolyte raw material from Example 1. Figure 3 The image shows the XRD pattern of the desulfurized gypsum residue from Example 1. Figure 4 The image shows the XRD pattern of the clinker from Example 1. Figure 5 Here is a SEM image of the clinker from Example 1; Figure 6 Here is a SEM image of the water-washed residue from Example 1; Figure 7 EDS diagram of the water washing residue from Example 1; Figure 8 The image shows the XRD pattern of the CaF2 product in Example 1. Figure 9 Here is a SEM image of the CaF2 product from Example 1; Figure 10 Here is a SEM image of the CaF2 product from Example 2; Figure 11 This is the EDS diagram of the CaF2 product in Example 2. Detailed Implementation

[0025] The embodiments of this application will now be described in more detail with reference to the examples. While embodiments of this application are shown in the examples, it should be understood that this application can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0026] Example 1 This embodiment provides a method for preparing recycled fluorite using desulfurized gypsum slag and waste electrolyte, the process flow of which is as follows: Figure 1 As shown, the specific steps are as follows: (1) The waste electrolyte (containing 53.11% fluorine and 1.55% lithium) was ball-milled to 100 mesh, and then thoroughly mixed with desulfurized gypsum slag at mass ratios of 100g:160g, 100g:200g, and 10g:240g respectively to obtain a mixture. The main components of the waste electrolyte are shown in Table 1, and the XRD phase analysis of the waste electrolyte is as follows. Figure 2 As shown, the main phases are Na3AlF6, Na2LiAlF6 and KNa2AlF6, CaF2, Al2O3, etc. XRD phase analysis of desulfurized gypsum slag is as follows... Figure 3 As shown, the main phases are CaSO4·2H2O and Ca(OH)2.

[0027] Table 1 Main components of waste electrolyte Table 2 Main components of desulfurized gypsum slag (2) The mixture obtained in step (1) is placed in a calcining furnace and heated to 900°C at a heating rate of 10°C / min under air atmosphere (gas partial pressure of 1 standard atmosphere) for calcination for 2 hours to obtain clinker. The XRD analysis of the clinker is as follows: Figure 4 As shown, the SEM image is as follows: Figure 5 As shown. The main phases in the clinker are CaF2, NaF, and Ca. 12 Al 14 O 33 After calcination, the microstructure undergoes a significant transformation, exhibiting a clear trend towards densification and sintering: the blurred boundaries of fine particles in the original sample gradually fuse at high temperatures, forming blocky or plate-like crystals with a size of 20–40 μm and clear outlines.

[0028] (3) Add deionized water to the clinker obtained in step (2), and wash it at 70℃ for 2 hours at a liquid-to-solid ratio of 10 mL: 1 g. Then, separate the liquid and solid to obtain the washed residue and the washing liquid. The SEM image of the washed residue is shown below. Figure 6 As shown, the EDS diagram of the water-washed residue is as follows: Figure 7As shown, calcium fluoride and alumina in the water-leached residue dissociate well from each other and do not adhere to each other, creating ideal material conditions for subsequent flotation separation.

[0029] (4) The water-washed residue obtained in step (3) is subjected to flotation. The concentration of sodium oleate collector is 90 mg / L, the concentration of water glass inhibitor is 300 mg / L, and the pH value is 7. Fluorite concentrate and flotation tailings are obtained after flotation.

[0030] (5) The washing solution described in step (3) is subjected to MVR method to recover sodium sulfate. The concentration factor of the washing solution is determined according to the lithium ion concentration in the washing solution. The lithium-containing solution is treated to recover lithium in the form of lithium phosphate, lithium titanate, etc.

[0031] (6) The fluorite concentrate was dried at 105℃ to obtain a recycled fluorite product. The purity of calcium fluoride in the recycled fluorite product was 81.29%, and the calcium fluoride recovery rate was 84.98%. XRD analysis of the recycled fluorite product showed the following phase composition: Figure 8 As shown, the SEM image of the recycled fluorite product is as follows: Figure 9 As shown, calcium fluoride exhibits very significant diffraction characteristics, with the flotation concentrate particles in a state of monomeric dissociation and having clean surfaces, which is beneficial for its direct application as a raw material in fluorochemicals or a metallurgical flux.

[0032] (7) Al2O3 can be recovered by comprehensively treating flotation tailings.

[0033] Example 2 This embodiment provides a method for preparing recycled fluorite using desulfurized gypsum slag and waste electrolyte. The specific steps are as follows: (1) The waste electrolyte (containing 53.11% fluorine and 1.55% lithium) was ball-milled to 100 mesh, and then fully mixed with desulfurized gypsum slag at a mass ratio of 100g:200g to obtain a mixture.

[0034] (2) The mixture obtained in step (1) is placed in a roasting furnace. Under air atmosphere, the gas partial pressure in the furnace is 1 standard atmosphere. Then the temperature is raised to 800℃ at a rate of 5℃ / min. The mixture is roasted for 2 hours to obtain clinker.

[0035] (3) Add deionized water to the clinker obtained in step (2), and wash it at 70°C for 1.5 hours at a liquid-solid ratio of 10 mL: 1 g. Then, after liquid-solid separation, obtain the washing residue and washing liquid.

[0036] (4) The water-washed residue obtained in step (3) is subjected to flotation. The concentration of sodium oleate collector is 70 mg / L, the concentration of water glass inhibitor is 200 mg / L, and the pH value is 8. Fluorite concentrate and flotation tailings are obtained after flotation.

[0037] (5) The washing solution described in step (3) is subjected to MVR method to recover sodium sulfate. The concentration factor of the washing solution is determined according to the lithium ion concentration in the washing solution. The lithium-containing solution is treated to recover lithium in the form of lithium phosphate, lithium titanate, etc.

[0038] (6) The fluorite concentrate was dried at 105℃ to obtain a recycled fluorite product. The purity of calcium fluoride in the recycled fluorite product was 80.82%, and the calcium fluoride recovery rate was 82.98%. The SEM image of the recycled fluorite product is shown below. Figure 10 As shown, the EDS diagram of the recycled fluorite product is as follows: Figure 11 As shown, calcium fluoride is the dominant element in the flotation concentrate, while impurity elements (Na, Al, Si) are present in very low amounts and exist in an independent dispersed form, without forming a close symbiotic relationship with calcium fluoride.

[0039] (7) Al2O3 can be recovered by comprehensively treating flotation tailings.

[0040] It should be understood that the application of this invention is not limited to the examples described above; this method can also be applied to other solid wastes containing cryolite (such as overhaul slag, carbon slag, aluminum ash, etc.). Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

[0041] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing recycled fluorite using desulfurized gypsum slag and waste electrolyte, characterized in that, Including the following steps: (1) The waste electrolyte is crushed and refined, and then mixed with desulfurized gypsum residue to obtain a mixture; (2) The mixture is roasted to obtain cooked material; (3) The clinker is crushed and refined and then washed with water to obtain a slurry. The slurry is then subjected to liquid-solid separation to obtain a washing residue and a washing liquid. (4) The water-washed residue is dried and pretreated before being floated to obtain fluorite concentrate and flotation tailings; (5) The washing solution from step (3) is subjected to comprehensive treatment to recover lithium salt and sodium sulfate; (6) The fluorite concentrate described in step (4) is dried to obtain a recycled fluorite product; (7) The flotation tailings described in step (4) are processed in a comprehensive manner to recover aluminum.

2. The method for preparing recycled fluorite using desulfurized gypsum slag and waste electrolyte according to claim 1, characterized in that, In step (1), the particle size of the mixture is ground to -100 mesh.

3. The method for preparing recycled fluorite using desulfurized gypsum slag and waste electrolyte according to claim 1, characterized in that, In step (1), the mass ratio of waste electrolyte to desulfurized gypsum slag is 1:1.2-1:2.

4.

4. The method for preparing recycled fluorite using desulfurized gypsum slag and waste electrolyte according to claim 1, characterized in that, In step (2), the calcination temperature is 400℃-1000℃, the heating rate is 10℃ / min, and the calcination time is 0.5h-3h.

5. The method for preparing recycled fluorite using desulfurized gypsum slag and waste electrolyte according to claim 1, characterized in that, In step (3), the washing solution is recycled for washing.

6. The method for preparing recycled fluorite using desulfurized gypsum slag and waste electrolyte according to claim 1, characterized in that, In step (4), sodium oleate is used as the collector and water glass is used as the inhibitor.

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