Method for preparing iron phosphate and aluminum oxide through step-by-step leaching of red mud

Abstract

The invention discloses a method for preparing iron phosphate and aluminum oxide by utilizing step-by-step leaching of red mud, which comprises the following steps: (a) carrying out ore grinding treatment on the red mud to obtain red mud powder with preset fineness; (b) 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 and aluminum 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; (c) 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; (d) calcining the crude iron phosphate, and cooling to obtain battery-grade iron phosphate; (e) adjusting the pH value of the filtrate, carrying out auxiliary stirring reaction under a preset temperature condition, and then aging and filtering to obtain aluminum hydroxide precipitate; and (f) calcining the aluminum hydroxide precipitate, and cooling to obtain the aluminum oxide.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy and resource recovery, and in particular to a method for preparing iron phosphate and aluminum oxide by step-by-step leaching of red mud. Background Art

[0002] Red mud is a solid waste produced during the Bayer process of extracting alumina from bauxite. A large amount of alkali is added during its formation, resulting in a high alkalinity of red mud. At the same time, a variety of valuable metals and impurities remain, and the composition is complex. About 1 to 2 tons of red mud are produced for every ton of alumina produced. The amount of red mud produced worldwide each year is huge. Its long-term accumulation not only occupies land resources, but also may pollute soil and water bodies, posing a serious threat to the ecological environment. The presence of iron, aluminum, titanium and a small amount of rare earth elements in red mud makes it worth recycling. However, since iron mainly exists in the form of Fe2O3, and aluminum mostly exists in the form of aluminum hydroxide or aluminum oxide, both of which have fine particle sizes and complex embedding, it is difficult for iron and aluminum resources to be directly leached. Therefore, the resource recovery and harmless treatment of red mud have become important research topics in the fields of materials and environmental protection.

[0003] Traditional red mud treatment methods mostly rely on stockpiling, backfilling, building materials utilization and metal extraction. However, direct stockpiling can easily lead to heavy metal ions infiltrating into the soil and groundwater under the action of rainwater, and backfilling requires neutralization of the red mud to reduce its alkalinity, but the effect is limited. Although the use of red mud in the building materials industry can achieve partial resource utilization, the red mud composition is unstable and contains harmful substances, making it difficult to control the quality of building materials products, and it is impossible to achieve efficient recovery of valuable elements such as iron and aluminum. In addition, the added value of using the iron and aluminum resources in red mud to produce building materials is low, making it difficult to achieve efficient utilization of red mud.

[0004] In recent years, researchers have tried to extract valuable metal resources such as iron, aluminum, titanium, and rare earths from red mud through processes such as acid-base leaching, roasting and reduction. However, the extraction of metal resources from red mud by acid leaching or alkaline leaching faces high temperature and high pressure process conditions. Not only is the acid and alkali consumption large, but the leaching effect is limited, and the production cost remains high. At the same time, the waste liquid produced by acid-base leaching is difficult to handle and can easily cause secondary pollution to the environment. In addition, in order to increase the recovery rate of iron and aluminum in red mud, roasting or reduction treatment is usually required to destroy its crystal structure and improve the leaching effect. However, the roasting or reduction process has high energy consumption, large greenhouse gas emissions, and high equipment requirements, which greatly restricts these methods in industrial promotion. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing iron phosphate and aluminum oxide by step-by-step leaching of red mud, so as to solve the problems existing in the prior art such as "low resource recovery rate, large acid and alkali consumption, high temperature and high pressure, complex waste liquid treatment, high energy consumption in roasting or reduction process, and large greenhouse gas emissions". The method achieves efficient separation and recovery of iron and aluminum resources in red mud by optimizing acid leaching conditions and step-by-step precipitation process, thereby preparing high-purity iron phosphate and aluminum oxide. Iron phosphate has important applications in the new energy field as a precursor of lithium-ion battery positive electrode material, and aluminum hydroxide can be further calcined to prepare high-purity aluminum oxide for various industrial uses such as aluminum smelting, electrolytic production and catalyst carrier.

[0006] The core of the present invention is to use a ternary mixed acid leaching method (hydrochloric acid + oxalic acid + phosphoric acid) to dissolve iron and aluminum from red mud, and then adjust the pH value in steps to make iron precipitate preferentially in the form of iron phosphate, and then adjust the solution pH to precipitate aluminum hydroxide, thereby ensuring the purity and recovery rate of the two products. The method can achieve step-by-step recovery of iron and aluminum in red mud at a relatively low acid concentration and temperature by reasonably controlling the acid dissolution conditions, acid leaching temperature, pH value, and solid-liquid separation steps, thereby reducing acid and alkali consumption, and reducing production costs and environmental burdens.

[0007] In order to achieve the above object, the present invention provides a method for preparing iron phosphate and aluminum oxide by step-by-step leaching of red mud, comprising the following steps:

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

[0009] (b) adding the red mud powder obtained in step (a) 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 and aluminum 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] (c) adjusting the pH of the leaching solution obtained in step (b), assisting the reaction with stirring under set temperature conditions, and then aging and filtering to obtain crude iron phosphate and a filtrate;

[0012] (d) calcining the crude iron phosphate obtained in step (c) and cooling it to obtain battery-grade iron phosphate;

[0013] (e) adjusting the pH of the filtrate obtained in step (c), assisting the reaction with stirring at a predetermined temperature, and then aging and filtering to obtain aluminum hydroxide precipitate;

[0014] (f) calcining the aluminum hydroxide precipitate obtained in step (e), and cooling it to obtain aluminum oxide.

[0015] In a preferred embodiment, in step (a), the red mud is ground to obtain D 90 Red mud powder <74μm.

[0016] In a preferred embodiment, in step (b), the acid leaching treatment time is 0.5 to 5 hours, and the power of the ultrasonic treatment is 200 to 1000W.

[0017] In a preferred embodiment, in step (b), 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.

[0018] In a preferred embodiment, in step (c), the pH of the leaching solution is adjusted to 1.6 to 2.6, and then the reaction is stirred at room temperature to 90°C for 5 to 15 minutes to allow the iron phosphate to be fully precipitated, and then crude iron phosphate is formed at an aging time of 15 to 60 minutes.

[0019] In a preferred embodiment, in step (d), 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.

[0020] In a preferred embodiment, in step (e), sodium hydroxide or ammonia solution is gradually added to adjust the pH of the filtrate to 4.5-5.0, and the reaction is stirred at room temperature to 90° C. for 5-15 minutes to control the particle size and purity of the aluminum hydroxide precipitate, and then the aluminum hydroxide precipitate is obtained by aging for 15-60 minutes and filtering.

[0021] In a preferred embodiment, in step (f), the temperature for calcining the aluminum hydroxide precipitate is controlled between 1000 and 1200° C., and the calcination time is 1 to 2 hours.

[0022] The present invention proposes a new step-by-step leaching process for red mud. Through the step-by-step treatment of ternary mixed acid dissolution and pH control, the iron and aluminum resources in the red mud are effectively recovered, and the preparation of iron phosphate and aluminum oxide is realized. Iron phosphate is a precursor of lithium iron phosphate, a positive electrode material for lithium batteries, and has excellent electrochemical properties and stability, and has a large market demand; while aluminum hydroxide can be further calcined to prepare high-purity aluminum oxide for aluminum smelting, electrolytic production or as a catalyst carrier. The present invention reduces the usage and treatment costs 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.

[0023] During the acid leaching process of red mud, the synergistic effect between the ternary mixed acids (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.

[0024] The present invention not only improves the recovery efficiency of iron and aluminum in red mud, but also has the advantages of being green, environmentally friendly and low-cost, and meets the environmental protection requirements of modern industry. The innovation of this process is that the dissolution and precipitation of iron and aluminum are controlled separately through step-by-step leaching technology, avoiding the interference of multi-metal co-precipitation, and ensuring the purity and added value of the product. This process provides a practical solution for the resource utilization and harmlessness of red mud, and has broad industrial application prospects, is in line with the direction of sustainable development, and provides a new way for large-scale industrial treatment of red mud.

[0025] Compared with the existing technology, the present invention has the following beneficial effects:

[0026] 1) Efficient recovery of iron and aluminum resources: The present invention effectively avoids the mutual interference of iron and aluminum in red mud during the leaching and precipitation process through the design of step-by-step leaching and step-by-step precipitation, ensuring that the product recovered in each step has a high purity. Through reasonable acid dissolution conditions and pH control, iron is precipitated in the form of ferric phosphate, and aluminum is separated in the form of aluminum hydroxide, effectively realizing the efficient separation and recovery of iron and aluminum resources in red mud.

[0027] 2) Improve recovery rate: Through the synergistic effect of ternary mixed acid (hydrochloric acid, oxalic acid, phosphoric acid), the leaching efficiency of iron and aluminum in red mud can be effectively improved, and the recovery rate of iron phosphate and aluminum oxide can be significantly improved. The complexation of oxalic acid and the precipitation of phosphoric acid make the dissolution and separation of metals more efficient.

[0028] 3) Low-temperature and high-efficiency treatment: The present invention adopts low-temperature (30-50°C) acid leaching treatment, which not only reduces energy consumption, but also effectively avoids side reactions that may occur under high-temperature conditions, helps to selectively recover iron and aluminum, and reduces the dissolution of other harmful metals.

[0029] 4) Ultrasonic assisted effect: Ultrasonic assisted acid leaching increases the contact area between the acid and the red mud surface, promotes the dissolution of solid minerals, significantly shortens the reaction time, and improves the reaction efficiency. The cavitation effect of ultrasound can also destroy the passivation layer on the surface of the mineral and enhance the dissolution rate of metal ions.

[0030] 5) Optimizing operating conditions: The present invention optimizes the separation process of iron phosphate and aluminum oxide by accurately adjusting the pH value, temperature and time of each reaction step, thereby ensuring the purity and yield of the product. In addition, operations such as aging and filtration in the steps help improve the quality of the precipitate and further reduce the content of pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] 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.

[0032] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0033] 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.

[0034] The following is further described through specific embodiments and drawings.

[0035] Example 1

[0036] A method for preparing iron phosphate and aluminum oxide by step-by-step leaching of red mud, comprising:

[0037] 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 a leached solution containing iron and aluminum ions;

[0038] 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;

[0039] The pH of the filtrate was adjusted to 4.5, stirred at 60°C for 10 minutes, aged for 15 minutes to precipitate aluminum hydroxide, filtered to obtain aluminum hydroxide precipitate, calcined the aluminum hydroxide precipitate at 1100°C for 1.5 hours, and cooled to obtain aluminum oxide.

[0040] The iron leaching rate using this method is 99.51%, the aluminum leaching rate is 95.63%, the iron phosphate purity is 99.03%, the iron-phosphorus ratio is 0.986, and the alumina purity is 99.5%, reaching the industrial-grade alumina standard.

[0041] 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%.

[0042] Table 1 "HG / T4701-2021 Iron phosphate for batteries" standard requirements and element content of iron phosphate products

[0043]

[0044] Example 2

[0045] A method for preparing iron phosphate and aluminum oxide by step-by-step leaching of red mud, comprising:

[0046] 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;

[0047] 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;

[0048] The pH of the filtrate was adjusted to 5, stirred at 60°C for 10 minutes, aged for 15 minutes to precipitate aluminum hydroxide, filtered to obtain aluminum hydroxide precipitate, calcined the aluminum hydroxide precipitate at 1100°C for 1.5 hours, and cooled to obtain aluminum oxide.

[0049] The iron leaching rate using this method is 90.85%, the aluminum leaching rate is 85.23%, the iron phosphate purity is 95.63%, Fe / P=1.07, and the aluminum oxide purity is 98.3%.

[0050] Comparative Example 1

[0051] In order to further demonstrate the advantages of the process method of the present invention, especially the effect of improving the leaching rate of iron and aluminum 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.

[0052] (1) pre-treating red mud into red mud powder with D90 < 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 0.8:1, 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;

[0053] (2) adding ammonia water to the leachate to adjust the pH value of the leachate to 2.0, stirring 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 battery-grade iron phosphate;

[0054] (3) The pH of the filtrate is adjusted to 4.5, stirred at 60°C for 10 minutes, aged for 15 minutes to precipitate aluminum hydroxide, filtered to obtain the aluminum hydroxide precipitate, calcined the aluminum hydroxide precipitate at 1100°C for 1.5 hours, and cooled to obtain aluminum oxide.

[0055] Table 2 Leaching rate and product purity of the embodiments and comparative examples

[0056] project Example 1 Example 2 Comparative Example 1 Iron leaching rate 99.51％ 90.85％ 75.30％ Aluminum leaching rate 95.63％ 85.23％ 70.12％ Purity of iron phosphate 99.03％ 95.63％ 89.47％ Fe / P ratio 0.986 1.07 0.85 Alumina purity 99.5％ 98.3％ 93.4％

[0057] The leaching rate of iron and aluminum and the purity of the product in Comparative Example 1 are obviously lower than those in Examples 1 and 2 of the present invention.

[0058] In summary, the present invention significantly improves the leaching rates of iron and aluminum and the purity of the product iron phosphate and aluminum oxide 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.

[0059] 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 iron phosphate and aluminum oxide by step-by-step leaching of red mud, characterized in that: The following steps are involved: (a) grinding the red mud to obtain red mud powder of a predetermined fineness; (b) adding the red mud powder obtained in step (a) 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 and aluminum 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; (c) adjusting the pH of the leaching solution obtained in step (b), assisting the reaction with stirring under set temperature conditions, and then aging and filtering to obtain crude iron phosphate and a filtrate; (d) calcining the crude iron phosphate obtained in step (c) and cooling it to obtain battery-grade iron phosphate; (e) adjusting the pH of the filtrate obtained in step (c), assisting the reaction with stirring at a predetermined temperature, and then aging and filtering to obtain aluminum hydroxide precipitate; (f) calcining the aluminum hydroxide precipitate obtained in step (e), and cooling it to obtain aluminum oxide.

2. The method for preparing iron phosphate and aluminum oxide by step-by-step leaching of red mud according to claim 1, characterized in that: In step (a), red mud is ground to obtain D 90 Red mud powder <74μm.

3. The method for preparing iron phosphate and aluminum oxide by step-by-step leaching of red mud according to claim 1, characterized in that: In step (b), the acid leaching treatment time is 0.5 to 5 hours, and the power of the ultrasonic treatment is 200 to 1000W.

4. The method for preparing iron phosphate and aluminum oxide by step-by-step leaching of red mud according to claim 1 or 3, characterized in that: In step (b), the liquid-to-solid ratio of the mixed acid solution to the red mud powder is 4 to 8:

1.

5. The method for preparing iron phosphate and aluminum oxide by step-by-step leaching of red mud according to claim 1, characterized in that: In step (c), 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 iron phosphate and aluminum oxide by step-by-step leaching of red mud according to claim 1, characterized in that: In step (d), the calcination temperature of the crude ferric phosphate is 550-750° C., and the calcination time is 0.5-4 hours.

7. The method for preparing iron phosphate and aluminum oxide by step-by-step leaching of red mud according to claim 1, characterized in that: In step (e), sodium hydroxide or ammonia solution is gradually added to adjust the pH of the filtrate to 4.5-5.0, and the reaction is stirred at room temperature to 90° C. for 5-15 minutes, and then aged for 15-60 minutes and filtered to obtain aluminum hydroxide precipitate.

8. The method for preparing iron phosphate and aluminum oxide by step-by-step leaching of red mud according to claim 1, characterized in that: In step (f), the temperature for calcining the aluminum hydroxide precipitate is controlled between 1000 and 1200° C., and the calcination time is 1 to 2 hours.

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