Method for preparing high-purity iron phosphate from red mud

Abstract

The invention discloses a method for preparing high-purity iron phosphate from red mud, which comprises the following steps: (1) grinding the red mud to obtain red mud powder with predetermined fineness; (2) adding the red mud powder into mixed acid, carrying out acid leaching treatment at 30-50 DEG C, carrying out ultrasonic treatment assisted in the acid leaching process to obtain a leaching mixed solution, and carrying out solid-liquid separation on the leaching mixed solution to obtain leaching residues and a leaching solution containing iron ions; the mixed acid is a mixed solution of hydrochloric acid, oxalic acid and phosphoric acid, the molar ratio of hydrochloric acid to oxalic acid is (2-5): (2-5), and the ratio of the amount of phosphoric acid substance to the amount of iron substance in the red mud is (0.9-1.2): 1; the molar concentration of H < + > in the mixed acid solution is 4-10 mol / L; (3) adjusting the pH value of the leachate, carrying out auxiliary stirring reaction under a set temperature condition, and then aging and filtering to obtain crude iron phosphate and filtrate; and (4) calcining the crude iron phosphate, and cooling to obtain the battery-grade iron phosphate. Through innovative acid dissolution and precipitation process design, iron resources in the red mud are fully extracted and recycled and are converted into high-purity iron phosphate products.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy and resource recovery, and in particular to a method for preparing high-purity ferric phosphate by utilizing red mud. Background Art

[0002] Red mud is a large amount of solid waste generated during the Bayer process of extracting alumina from bauxite. Its main components include iron oxide (Fe2O3) and aluminum oxide (Al2O3). In addition, red mud also contains a small amount of titanium, silicon and rare earth elements, which makes it have potential recycling value. The amount of red mud produced by the global aluminum industry is huge every year. Long-term accumulation not only occupies a large amount of land resources, but also pollutes the environment and poses a threat to soil and water. Due to its high alkalinity and complex composition, red mud's resource utilization and harmless treatment have become a hot topic and difficulty in current research.

[0003] In recent years, with the rapid development of new energy technologies, lithium iron phosphate (LiFePO4), as the preferred cathode material for lithium-ion batteries, has attracted much attention due to its high thermal stability, safety and excellent cycle life. High-purity iron phosphate (FePO4) is a key precursor of lithium iron phosphate materials and is widely used in electric vehicles, energy storage power stations and other fields. Using iron resources in red mud to prepare high-purity iron phosphate can not only meet the market demand for lithium-ion battery materials, but also provide a new way for the efficient use of red mud, thereby achieving the dual benefits of resource recovery and environmental protection.

[0004] Traditional red mud treatment methods mainly include stockpiling, building materials application and metal extraction. However, direct stockpiling of red mud will cause alkaline substances and heavy metal ions to infiltrate the soil and groundwater under the immersion of rainwater, polluting the ecological environment. Although the use of red mud in building materials production can partially alleviate the pressure of red mud storage, due to the complex composition of red mud, the quality of building materials products is difficult to control and the added value is low. For metal extraction, acid leaching or alkaline leaching is usually used to recover iron resources in red mud, but these methods often face high temperature and high pressure process conditions. Not only does the acid and alkali consumption increase, but the waste liquid generated during the leaching process is difficult to treat and the environmental burden is heavy.

[0005] In order to achieve efficient utilization of iron resources in red mud, researchers have begun to try to develop new resource recovery methods, especially to prepare high-purity iron phosphate to meet market demand. Among the existing process methods, how to dissolve and separate iron under milder conditions while reducing impurity co-precipitation to improve the purity of iron phosphate is one of the technical difficulties. Through a reasonably designed acid dissolution and precipitation process, high-purity iron phosphate can be extracted from red mud to ensure that it meets the standard requirements of battery-grade materials and has a high added value, providing a feasible path for the large-scale industrial application of red mud. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing high-purity iron phosphate using red mud. Through innovative acid dissolution and precipitation process design, the iron resources in the red mud are fully extracted and recovered, and converted into a high-purity iron phosphate product. The iron phosphate product meets the strict standards for lithium-ion battery positive electrode materials, has the characteristics of high purity, few impurities and stable performance, and can meet the demand of the lithium iron phosphate battery market for high-quality precursor materials.

[0007] In order to achieve the above object, the present invention provides a method for preparing high-purity ferric phosphate using red mud, comprising the following steps:

[0008] (1) grinding the red mud to obtain red mud powder of a predetermined fineness;

[0009] (2) adding the red mud powder obtained in step (1) to a mixed acid, performing an acid leaching treatment at 30 to 50° C., performing ultrasonic treatment to assist the acid leaching process, obtaining a leached mixed solution, and performing solid-liquid separation on the leached mixed solution to obtain a leached residue and a leached solution containing iron ions;

[0010] The mixed acid is a mixed solution of hydrochloric acid, oxalic acid and phosphoric acid, the molar ratio of hydrochloric acid to oxalic acid is (2-5):(2-5), the ratio of the amount of phosphoric acid to the amount of iron in red mud is 0.9-1.2:1; H + The molar concentration is 4 to 10 mol / L;

[0011] (3) adjusting the pH of the leaching solution obtained in step (2), assisting the reaction with stirring under set temperature conditions, and then aging and filtering to obtain crude iron phosphate and a filtrate;

[0012] (4) calcining the crude iron phosphate obtained in step (3) and cooling it to obtain battery-grade iron phosphate.

[0013] Preferably, in step (1), the red mud is ground to obtain D 90 Red mud powder <74μm.

[0014] Preferably, in step (2), the acid leaching treatment time is 0.5 to 5 hours, and the power of the ultrasonic treatment is 200 to 1000W.

[0015] Preferably, in step (2), the liquid-to-solid ratio of the mixed acid solution to the red mud powder is 4 to 8:1, and the ratio of the amount of phosphoric acid to the amount of iron in the red mud is 0.9 to 1.2:1.

[0016] Preferably, in step (3), after the pH of the leaching solution is adjusted to 1.6-2.6, the reaction is stirred at room temperature-90°C for 5-15 minutes to allow the iron phosphate precipitate to be fully precipitated, and then crude iron phosphate is formed at an aging time of 15-60 minutes.

[0017] Preferably, in step (4), the calcination temperature of the crude ferric phosphate is 550-750° C., and the calcination time is 0.5-4 hours to obtain anhydrous ferric phosphate.

[0018] The present invention proposes a new method for preparing high-purity iron phosphate using red mud. Through the step-by-step treatment of ternary mixed acid dissolution and pH control, the iron resources in the red mud are effectively recovered, and the aluminum resources are retained in the filtrate obtained in step (3), so as to realize the preparation of iron phosphate. Iron phosphate is a precursor of lithium iron phosphate, a positive electrode material of lithium batteries, and has excellent electrochemical properties and stability, and has a large market demand. The present invention reduces the usage and treatment cost of acid and alkali while realizing resource recovery by reasonably controlling the acid leaching conditions, pH value and temperature parameters, and effectively solves the environmental protection problem of waste liquid treatment.

[0019] During the acid leaching process of red mud, the synergistic effect between the ternary mixed acid (hydrochloric acid, oxalic acid and phosphoric acid) significantly improves the leaching efficiency of metals. Hydrochloric acid provides a strong acidic environment to quickly dissolve the metal oxides in the red mud; oxalic acid forms soluble complexes with metal ions through complexation reactions to increase their solubility; phosphoric acid helps to form iron phosphate precipitation and promotes the recovery of iron phosphate. Acid leaching treatment under low temperature conditions (30-50°C) effectively controls the reaction rate, avoids side reactions at high temperatures, and ensures the efficient recovery of major metals. Ultrasonic-assisted acid leaching further improves the dissolution rate and reaction efficiency. The cavitation effect of ultrasound enhances the contact between the acid solution and the solid surface, accelerates the dissolution of metal oxides, and reduces the reaction time. The synergistic effect of the three not only improves the recovery rate of iron and aluminum, but also optimizes the processing conditions, reduces energy consumption, and improves the economy and efficiency of the overall process.

[0020] Compared with the existing technology, the present invention has the following beneficial effects:

[0021] 1) The present invention realizes efficient recovery of iron resources in red mud through optimized acid dissolution and precipitation processes. Compared with traditional treatment methods, the recovery rate of iron is significantly improved, so that the precious iron resources in red mud can be fully utilized, the discharge of waste is reduced, and the efficiency of resource utilization is improved. At the same time, the method converts iron into high-purity iron phosphate products with higher added value and good economic benefits.

[0022] 2) The present invention can generate high-purity iron phosphate with purity that meets battery-grade standards through precise pH adjustment and calcination control. Compared with the existing methods, the present invention effectively inhibits the co-precipitation of impurities during the precipitation process, and the obtained iron phosphate has pure content and stable performance, which meets the strict requirements of lithium-ion battery materials for high purity and broadens the high-end application of red mud resources.

[0023] 3) The acid dissolution and precipitation process of the present invention is carried out under relatively mild conditions, avoiding the high temperature and high pressure environment often required in traditional processes, with high operational safety, low requirements on equipment, and reduced energy consumption and equipment costs. At the same time, the acid dissolution is completed under low acid consumption conditions, which significantly reduces production costs, making the process more economically advantageous in industrial applications.

[0024] 4) The process has low acid consumption and generates less waste liquid. Compared with the traditional high-concentration acid-base leaching process, it reduces the amount of wastewater and waste residue generated, facilitates subsequent treatment, and reduces the burden on the environment. The process design avoids the large-scale generation of hazardous waste, meets green environmental protection requirements, and improves the sustainability and ecological benefits of red mud treatment.

[0025] 5) The process of the present invention is simple and easy to operate, the overall process is easy to control, and it is suitable for large-scale production. The steps of acid dissolution, pH adjustment and calcination are all conventional operations, and no complex equipment support is required, which is convenient for industrial promotion. Compared with the traditional treatment method, the present invention can be widely promoted and applied, which is helpful to realize the comprehensive recycling of red mud resources and promote the sustainable development of red mud resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings and appendices required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0028] The following are specific implementation cases given by the inventor. It should be noted that these embodiments are only for better interpretation of the present invention and are not intended to limit the scope of implementation of the present invention. All parameter selections within the scope of the technical solution of the present invention belong to the scope of protection of the present invention.

[0029] The following is further described through specific embodiments and drawings.

[0030] Example 1

[0031] A method for preparing high-purity ferric phosphate using red mud, comprising:

[0032] Grind the red mud to D 90 The red mud powder was then added to a mixed acid solution of hydrochloric acid, oxalic acid, and phosphoric acid (the molar ratio of hydrochloric acid to oxalic acid was 5:2). +The molar concentration is 7 mol / L, the liquid-solid ratio of the mixed acid solution to the red mud powder is 7:1, the ratio of the amount of phosphoric acid to the amount of iron in the red mud is 1:1, acid leaching is carried out at 40°C, the acid leaching process is assisted by ultrasonic 500W treatment, and a leached mixed solution is obtained after acid leaching for 2 hours, and the leached mixed solution is subjected to solid-liquid separation to obtain leached residue and iron ion-containing leaching solution;

[0033] Ammonia water was added to the leachate to adjust the pH value of the leachate to 2.0, and the mixture was stirred and reacted at 60° C. for 10 minutes. The mixture was aged for 15 minutes and filtered to obtain crude iron phosphate. The crude iron phosphate was calcined at 700° C. for 2 hours and cooled to obtain battery-grade iron phosphate.

[0034] In Example 1, the iron leaching rate was 99.51%, the purity of iron phosphate was 99.03%, and the iron-phosphorus ratio was 0.986.

[0035] Table 1 shows the quality of the iron phosphate product prepared in Example 1. The obtained iron phosphate meets the requirements of the standard "HG / T 4701-2021 Iron Phosphate for Batteries" and has a purity of 99.03%.

[0036] Table 1 "HG / T4701-2021 Iron phosphate for batteries" standard requirements and element content of iron phosphate products

[0037]

[0038] Example 2

[0039] A method for preparing high-purity ferric phosphate using red mud, comprising:

[0040] Grind the red mud to D 90 The red mud powder was then added to a mixed acid solution of hydrochloric acid, oxalic acid, and phosphoric acid (the molar ratio of hydrochloric acid to oxalic acid was 2:5). + The molar concentration is 7 mol / L, the liquid-solid ratio of the mixed acid solution to the red mud powder is 6:1, the ratio of the amount of phosphoric acid to the amount of iron in the red mud is 1:1, acid leaching is carried out at 50°C, the acid leaching process is assisted by ultrasonic 200W treatment, and a leached mixed solution is obtained after acid leaching for 2 hours, and the leached mixed solution is subjected to solid-liquid separation to obtain leached residue and a leached solution containing iron and aluminum ions;

[0041] Ammonia water was added to the leachate to adjust the pH value of the leachate to 2.0, stirred at 60°C for 10 minutes, aged for 15 minutes, filtered to obtain crude iron phosphate, calcined the crude iron phosphate at 700°C for 2 hours, and cooled to obtain battery-grade iron phosphate.

[0042] In Example 2, the iron leaching rate was 90.85%, the purity of iron phosphate was 95.63%, and Fe / P=1.07.

[0043] Comparative Example 1

[0044] In order to further demonstrate the advantages of the process of the present invention, especially the effect of improving the iron leaching rate and the purity of the final product, the comparative example did not use all the optimized conditions of the present invention, but adjusted some parameters.

[0045] (1) pre-treating red mud into red mud powder with D90 less than 74 μm, adding the red mud powder into a mixed acid solution of hydrochloric acid and phosphoric acid, wherein the concentration of hydrochloric acid is 5 M, the ratio of the amount of phosphoric acid to the molar mass of iron in the red mud is 0.8, and the liquid-solid ratio is 5:1, acid dissolving is performed at 70° C., stirring for 1.5 hours to obtain a leaching mixture, and solid-liquid separation is performed on the leaching mixture to obtain a leaching residue and a leaching solution containing iron and aluminum ions;

[0046] (2) adding ammonia water to the leachate to adjust the pH value of the leachate to 2.0, stirring the reaction at 60° C. for 10 minutes, aging for 15 minutes, filtering to obtain crude iron phosphate, calcining the crude iron phosphate at 700° C. for 2 hours, and cooling to obtain iron phosphate.

[0047] Table 2 Leaching rate and product purity of the embodiments and comparative examples

[0048] project Example 1 Example 2 Comparative Example 1 Iron leaching rate 99.51％ 90.85％ 75.30％ Purity of iron phosphate 99.03％ 95.63％ 89.47％ Fe / P ratio 0.986 1.07 0.85

[0049] Comparative Example 1 is significantly lower than Examples 1 and 2 of the present invention in terms of iron leaching rate and product purity.

[0050] In summary, the present invention significantly improves the iron leaching rate and the purity of the product iron phosphate by optimizing the red mud leaching process, which is better than the effect of the comparative example, verifying the advantages of the process method in resource recovery and product purity.

[0051] The preferred embodiments of the present invention are described in detail above, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing high-purity ferric phosphate using red mud, characterized in that: The following steps are involved: (1) grinding the red mud to obtain red mud powder of a predetermined fineness; (2) adding the red mud powder obtained in step (1) to a mixed acid, performing an acid leaching treatment at 30 to 50° C., performing ultrasonic treatment to assist the acid leaching process, obtaining a leached mixed solution, and performing solid-liquid separation on the leached mixed solution to obtain a leached residue and a leached solution containing iron ions; The mixed acid is a mixed solution of hydrochloric acid, oxalic acid and phosphoric acid, the molar ratio of hydrochloric acid to oxalic acid is (2-5):(2-5), the ratio of the amount of phosphoric acid to the amount of iron in red mud is 0.9-1.2:1; H + The molar concentration is 4 to 10 mol / L; (3) adjusting the pH of the leaching solution obtained in step (2), assisting the reaction with stirring under set temperature conditions, and then aging and filtering to obtain crude iron phosphate and a filtrate; (4) calcining the crude iron phosphate obtained in step (3) and cooling it to obtain battery-grade iron phosphate.

2. The method for preparing high-purity ferric phosphate using red mud according to claim 1, characterized in that: In step (1), the red mud is ground to obtain D 90 Red mud powder <74μm.

3. The method for preparing high-purity ferric phosphate using red mud according to claim 1, characterized in that: In step (2), the acid leaching treatment time is 0.5 to 5 hours, and the power of the ultrasonic treatment is 200 to 1000W.

4. A method for preparing high-purity ferric phosphate using red mud according to claim 1 or 3, characterized in that: In step (2), the liquid-to-solid ratio of the mixed acid solution to the red mud powder is 4 to 8:1, and the ratio of the amount of phosphoric acid to the amount of iron in the red mud is 0.9 to 1.2:

1.

5. The method for preparing high-purity ferric phosphate using red mud according to claim 1, characterized in that: In step (3), after the pH of the leaching solution is adjusted to 1.6-2.6, the solution is stirred and reacted at room temperature-90°C for 5-15 minutes to allow the iron phosphate to be fully precipitated, and then the crude iron phosphate is formed at an aging time of 15-60 minutes.

6. The method for preparing high-purity ferric phosphate using red mud according to claim 1, characterized in that: In step (4), the calcination temperature of the crude ferric phosphate is 550-750° C., and the calcination time is 0.5-4 hours.

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