A method of converting red mud into mineral resource usage

Abstract

The application discloses a method for converting red mud into mineral resources, and realizes efficient extraction of Fe2O3, Al2O3 and TiO2 in the red mud and recycling of NaOH through an acid leaching-alkali precipitation-membrane separation process.The method comprises the following steps: first, red mud is leached by using dilute sulfuric acid; metal hydroxides are precipitated in steps; NaOH is regenerated through electrodialysis; TiO2 is extracted by using concentrated sulfuric acid acidolysis; and finally, the residual slag is harmlessly treated.The method has the advantages of high resource recovery rate, low cost, environmental friendliness and the like, and is suitable for scale resource utilization of red mud.

Description

Technical Field

[0001] This invention belongs to the field of red mud treatment technology, and specifically relates to a method for converting red mud into mineral resources. Background Technology

[0002] Red mud is an industrial waste residue from the extraction of alumina from bauxite, with an annual production exceeding 150 million tons and a global cumulative stockpile exceeding 4 billion tons. Red mud has the following characteristics: 1. High alkalinity: Contains 8-12% Na2O, direct storage will lead to soil alkalization and groundwater pollution; 2. Heavy metal risk: Contains valuable metals such as Fe, Al, and Ti, as well as heavy metal elements such as Cr and Ni; 3. Defects of traditional processing methods: When used in building materials (bricks, tiles, cement), the high alkalinity leads to poor product stability; landfill disposal occupies land and poses environmental risks; existing wet extraction technology is costly and complex, making it difficult to apply industrially. Summary of the Invention

[0003] To address the current challenge of large-scale resource utilization of red mud, this invention utilizes an acid leaching-alkali precipitation-membrane separation process to achieve efficient extraction of valuable metals from red mud and harmless treatment of residues, providing a novel solution for red mud resource utilization.

[0004] This invention is achieved through the following technical solution: A method for converting red mud into mineral resources includes the following steps: S1: Mix red mud with 10%-20% dilute sulfuric acid at a solid-liquid ratio of 1:5-1:10, stir at 25-85℃ for 30-90 minutes, and then separate the solid and liquid by filtration or centrifugation to obtain leachate and neutral residue I. The leachate mainly contains Fe³⁺, Al³⁺, and Na⁺, while the neutral residue mainly contains TiO2, SiO2, and CaSO4. The reaction equations for the leaching process are as follows: Na2O + H2SO4 → Na2SO4 + H2O; Fe2O3 + 3H2SO4 → Fe2(SO4)3 + 3H2O; Al2O3 + 3H2SO4 → Al2(SO4)3 + 3H2O.

[0005] S2: While stirring, add NaOH to the leachate until pH=4 to generate Fe(OH)3 precipitate. Then separate the Fe(OH)3 precipitate and calcine it to obtain high-purity Fe2O3. The remaining filtrate is I.

[0006] S3: Continue to add NaOH to filtrate I while stirring until pH=8.5, forming Al(OH)3 precipitate. Then separate the Al(OH)3 precipitate and calcine it to obtain high-purity Al2O3. The remaining filtrate is II.

[0007] S4: Continue stirring in filtrate II while adding MgSO4 to adjust the pH to >9, generating MgSiO3 precipitate. Separate the MgSiO3 precipitate, leaving filtrate III.

[0008] S5: Filtrate III is reacted with ammonia water through an electrodialysis membrane stack to generate NaOH solution and ammonium sulfate. The generated NaOH is then recycled in step S2. Filtrate III mainly contains Na2SO4. Na2SO4 reacts with ammonia water through the electrodialysis membrane stack to achieve ion recombination, as shown in the following reaction formula: Na2SO4 + 2NH3·H2O → 2NaOH + (NH4)2SO4.

[0009] In an electrodialysis membrane stack, when sodium sulfate solution enters the sodium sulfate water chamber and ammonia water enters the ammonia water chamber, under the influence of an electric field, sodium ions permeate through the cation exchange membrane into the sodium hydroxide water chamber, while hydroxide ions in the ammonia water chamber also migrate to the sodium hydroxide water chamber, where they combine to form sodium hydroxide. Simultaneously, sulfate ions in the sodium sulfate water chamber permeate through the anion exchange membrane into the ammonium sulfate water chamber, and ammonium ions in the ammonia water chamber permeate through the cation exchange membrane into the ammonium sulfate water chamber. This continuous reaction achieves the following transformation: Na2SO4 + 2NH3·H2O = 2NaOH + (NH4)2SO4.

[0010] S6: Neutral residue I is reacted with concentrated sulfuric acid at 100°C to generate TiOSO4. The H2TiO3 precipitate generated by hydrolysis of the generated TiOSO4 solution is calcined to obtain TiO2.

[0011] S7: Use the final residue produced in step S6 to prepare building materials or for soil improvement.

[0012] As a further improvement of the present invention, a metal positive electrode is provided on the left side of the electrodialysis membrane stack and a metal negative electrode is provided on the right side. A sodium sulfate water chamber, a sodium hydroxide water chamber, an ammonia water chamber and an ammonium sulfate water chamber are arranged sequentially between the metal positive electrode and the water chamber. A protective liquid is also provided between the metal positive electrode, the metal negative electrode and the water chamber. As a further improvement of the present invention, a cation exchange membrane is provided between the sodium sulfate water chamber and the sodium hydroxide water chamber, an anion exchange membrane is provided between the sodium hydroxide water chamber and the ammonia water chamber, a cation exchange membrane is provided between the ammonia water chamber and the ammonium sulfate water chamber, and an anion exchange membrane is provided between the ammonium sulfate water chamber and the sodium sulfate water chamber.

[0013] Preferably, in step S6, the concentration of concentrated sulfuric acid is ≥50% by mass, the reaction temperature is 100℃, and the reaction time is ≥2h.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The method of the present invention achieves a high recovery rate of red mud resources. The red mud treated by the method of the present invention has an extraction rate of Fe2O3 and Al2O3 >95%, sodium oxide extraction rate >98%, and TiO2 extraction rate >90%.

[0015] 2. The method of the present invention realizes the self-recycling of materials, regenerates NaOH through electrodialysis, and uses the regenerated NaOH in the leaching process, thereby reducing the consumption of chemical reagents.

[0016] 3. The method of the present invention has no secondary pollution throughout the entire process, and the residue is utilized in a harmless manner. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention.

[0018] Figure 2 This is a schematic diagram of the structure of an electrodialysis membrane stack.

[0019] Figure labels: 1-metal positive electrode, 2-metal negative electrode, 3-sodium sulfate aqueous chamber, 4-sodium hydroxide aqueous chamber, 5-ammonia water aqueous chamber, 6-ammonium sulfate aqueous chamber, 7-protective solution. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings. In the embodiments, unless otherwise specified, the technical means used are all conventional technical means in the art. Example 1

[0021] A method for converting red mud into mineral resources includes the following steps: S1: Red mud and 10% dilute sulfuric acid were mixed at a solid-liquid ratio of 1:10 and stirred at 25°C for 90 min. The mixture was then filtered to separate the solid and liquid components, yielding leachate and neutral residue I. The leachate mainly contained Fe³⁺, Al³⁺, and Na⁺, while the neutral residue mainly contained TiO2, SiO2, and CaSO4. The reaction equations for the leaching process are as follows: Na2O + H2SO4 → Na2SO4 + H2O; Fe2O3 + 3H2SO4 → Fe2(SO4)3 + 3H2O; Al2O3 + 3H2SO4 → Al2(SO4)3 + 3H2O.

[0022] S2: While stirring, add NaOH to the leachate until pH=4 to generate Fe(OH)3 precipitate. Then separate the Fe(OH)3 precipitate and calcine it to obtain high-purity Fe2O3. The remaining filtrate is I.

[0023] S3: Continue to add NaOH to filtrate I while stirring until pH=8.5, forming Al(OH)3 precipitate. Then separate the Al(OH)3 precipitate and calcine it to obtain high-purity Al2O3. The remaining filtrate is II.

[0024] S4: Continue stirring in filtrate II while adding MgSO4 to adjust the pH to >9, generating MgSiO3 precipitate. Separate the MgSiO3 precipitate, leaving filtrate III.

[0025] S5: Filtrate III is reacted with ammonia water through an electrodialysis membrane stack to generate NaOH solution and ammonium sulfate. The generated NaOH is then recycled in step S2. Filtrate III mainly contains Na2SO4. Na2SO4 reacts with ammonia water through the electrodialysis membrane stack to achieve ion recombination, as shown in the following reaction formula: Na2SO4 + 2NH3·H2O → 2NaOH + (NH4)2SO4.

[0026] In an electrodialysis membrane stack, when sodium sulfate solution enters the sodium sulfate water chamber and ammonia water enters the ammonia water chamber, under the influence of an electric field, sodium ions permeate through the cation exchange membrane into the sodium hydroxide water chamber, while hydroxide ions in the ammonia water chamber also migrate to the sodium hydroxide water chamber, where they combine to form sodium hydroxide. Simultaneously, sulfate ions in the sodium sulfate water chamber permeate through the anion exchange membrane into the ammonium sulfate water chamber, and ammonium ions in the ammonia water chamber permeate through the cation exchange membrane into the ammonium sulfate water chamber. This continuous reaction achieves the following transformation: Na2SO4 + 2NH3·H2O = 2NaOH + (NH4)2SO4.

[0027] like Figure 2 As shown, the electrodialysis membrane stack has a metal positive electrode 1 on the left and a metal negative electrode 2 on the right. Between the metal positive electrode 1 and the metal positive electrode 2, there are sodium sulfate water chamber 3, sodium hydroxide water chamber 4, ammonia water chamber 5 and ammonium sulfate water chamber 6 in sequence. A protective liquid 7 is also provided between the metal positive electrode 1, the metal negative electrode 2 and the water chambers. A cation exchange membrane is provided between the sodium sulfate water chamber 3 and the sodium hydroxide water chamber 4; an anion exchange membrane is provided between the sodium hydroxide water chamber 4 and the ammonia water chamber 5; a cation exchange membrane is provided between the ammonia water chamber 5 and the ammonium sulfate water chamber 6; and an anion exchange membrane is provided between the ammonium sulfate water chamber 6 and the sodium sulfate water chamber 3.

[0028] S6: Neutral residue I is reacted with concentrated sulfuric acid (≥50% by mass) at 100℃ for ≥2 hours to generate TiOSO4. The H2TiO3 precipitate generated by hydrolysis of the generated TiOSO4 solution is then calcined to obtain TiO2.

[0029] S7: Use the final residue produced in step S6 to prepare building materials or for soil improvement. Example 2

[0030] A method for converting red mud into mineral resources includes the following steps: S1: Red mud and 20% dilute sulfuric acid were mixed at a solid-liquid ratio of 1:5 and stirred at 85°C for 30 minutes. Then, solid-liquid separation was carried out by centrifugation to obtain leachate and neutral residue I. The leachate mainly contained Fe³⁺, Al³⁺ and Na⁺, and the neutral residue mainly contained TiO2, SiO2 and CaSO4. The reaction equations for the leaching process are as follows: Na2O + H2SO4 → Na2SO4 + H2O; Fe2O3 + 3H2SO4 → Fe2(SO4)3 + 3H2O; Al2O3 + 3H2SO4 → Al2(SO4)3 + 3H2O.

[0031] S2: While stirring, add NaOH to the leachate until pH=4 to generate Fe(OH)3 precipitate. Then separate the Fe(OH)3 precipitate and calcine it to obtain high-purity Fe2O3. The remaining filtrate is I.

[0032] S3: Continue to add NaOH to filtrate I while stirring until pH=8.5, forming Al(OH)3 precipitate. Then separate the Al(OH)3 precipitate and calcine it to obtain high-purity Al2O3. The remaining filtrate is II.

[0033] S4: Continue stirring in filtrate II while adding MgSO4 to adjust the pH to >9, generating MgSiO3 precipitate. Separate the MgSiO3 precipitate, leaving filtrate III.

[0034] S5: Filtrate III is reacted with ammonia water through an electrodialysis membrane stack to generate NaOH solution and ammonium sulfate. The generated NaOH is then recycled in step S2. Filtrate III mainly contains Na2SO4. Na2SO4 reacts with ammonia water through the electrodialysis membrane stack to achieve ion recombination, as shown in the following reaction formula: Na2SO4 + 2NH3·H2O → 2NaOH + (NH4)2SO4.

[0035] In an electrodialysis membrane stack, when sodium sulfate solution enters the sodium sulfate water chamber and ammonia water enters the ammonia water chamber, under the influence of an electric field, sodium ions permeate through the cation exchange membrane into the sodium hydroxide water chamber, while hydroxide ions in the ammonia water chamber also migrate to the sodium hydroxide water chamber, where they combine to form sodium hydroxide. Simultaneously, sulfate ions in the sodium sulfate water chamber permeate through the anion exchange membrane into the ammonium sulfate water chamber, and ammonium ions in the ammonia water chamber permeate through the cation exchange membrane into the ammonium sulfate water chamber. This continuous reaction achieves the following transformation: Na2SO4 + 2NH3·H2O = 2NaOH + (NH4)2SO4.

[0036] like Figure 2 As shown, the electrodialysis membrane stack has a metal positive electrode 1 on the left and a metal negative electrode 2 on the right. Between the metal positive electrode 1 and the metal positive electrode 2, there are sodium sulfate water chamber 3, sodium hydroxide water chamber 4, ammonia water chamber 5 and ammonium sulfate water chamber 6 in sequence. A protective liquid 7 is also provided between the metal positive electrode 1, the metal negative electrode 2 and the water chambers. A cation exchange membrane is provided between the sodium sulfate water chamber 3 and the sodium hydroxide water chamber 4; an anion exchange membrane is provided between the sodium hydroxide water chamber 4 and the ammonia water chamber 5; a cation exchange membrane is provided between the ammonia water chamber 5 and the ammonium sulfate water chamber 6; and an anion exchange membrane is provided between the ammonium sulfate water chamber 6 and the sodium sulfate water chamber 3.

[0037] S6: Neutral residue I is reacted with concentrated sulfuric acid (≥50% by mass) at 100℃ for ≥2 hours to generate TiOSO4. The H2TiO3 precipitate generated by hydrolysis of the generated TiOSO4 solution is then calcined to obtain TiO2.

[0038] S7: Use the final residue produced in step S6 to prepare building materials or for soil improvement. Example 3

[0039] A method for converting red mud into mineral resources includes the following steps: S1: Red mud and 15% dilute sulfuric acid were mixed at a solid-liquid ratio of 1:8 and stirred at 55°C for 60 min. Then, solid-liquid separation was carried out by centrifugation to obtain leachate and neutral residue I. The leachate mainly contained Fe³⁺, Al³⁺ and Na⁺, and the neutral residue mainly contained TiO2, SiO2 and CaSO4. The reaction equations for the leaching process are as follows: Na2O + H2SO4 → Na2SO4 + H2O; Fe2O3 + 3H2SO4 → Fe2(SO4)3 + 3H2O; Al2O3 + 3H2SO4 → Al2(SO4)3 + 3H2O.

[0040] S2: While stirring, add NaOH to the leachate until pH=4 to generate Fe(OH)3 precipitate. Then separate the Fe(OH)3 precipitate and calcine it to obtain high-purity Fe2O3. The remaining filtrate is I.

[0041] S3: Continue to add NaOH to filtrate I while stirring until pH=8.5, forming Al(OH)3 precipitate. Then separate the Al(OH)3 precipitate and calcine it to obtain high-purity Al2O3. The remaining filtrate is II.

[0042] S4: Continue stirring in filtrate II while adding MgSO4 to adjust the pH to >9, generating MgSiO3 precipitate. Separate the MgSiO3 precipitate, leaving filtrate III.

[0043] S5: Filtrate III is reacted with ammonia water through an electrodialysis membrane stack to generate NaOH solution and ammonium sulfate. The generated NaOH is then recycled in step S2. Filtrate III mainly contains Na2SO4. Na2SO4 reacts with ammonia water through the electrodialysis membrane stack to achieve ion recombination, as shown in the following reaction formula: Na2SO4 + 2NH3·H2O → 2NaOH + (NH4)2SO4.

[0044] In an electrodialysis membrane stack, when sodium sulfate solution enters the sodium sulfate water chamber and ammonia water enters the ammonia water chamber, under the influence of an electric field, sodium ions permeate through the cation exchange membrane into the sodium hydroxide water chamber, while hydroxide ions in the ammonia water chamber also migrate to the sodium hydroxide water chamber, where they combine to form sodium hydroxide. Simultaneously, sulfate ions in the sodium sulfate water chamber permeate through the anion exchange membrane into the ammonium sulfate water chamber, and ammonium ions in the ammonia water chamber permeate through the cation exchange membrane into the ammonium sulfate water chamber. This continuous reaction achieves the following transformation: Na2SO4 + 2NH3·H2O = 2NaOH + (NH4)2SO4.

[0045] like Figure 2 As shown, the electrodialysis membrane stack has a metal positive electrode 1 on the left and a metal negative electrode 2 on the right. Between the metal positive electrode 1 and the metal positive electrode 2, there are sodium sulfate water chamber 3, sodium hydroxide water chamber 4, ammonia water chamber 5 and ammonium sulfate water chamber 6 in sequence. A protective liquid 7 is also provided between the metal positive electrode 1, the metal negative electrode 2 and the water chambers. A cation exchange membrane is provided between the sodium sulfate water chamber 3 and the sodium hydroxide water chamber 4; an anion exchange membrane is provided between the sodium hydroxide water chamber 4 and the ammonia water chamber 5; a cation exchange membrane is provided between the ammonia water chamber 5 and the ammonium sulfate water chamber 6; and an anion exchange membrane is provided between the ammonium sulfate water chamber 6 and the sodium sulfate water chamber 3.

[0046] S6: Neutral residue I is reacted with concentrated sulfuric acid (≥50% by mass) at 100℃ for ≥2 hours to generate TiOSO4. The H2TiO3 precipitate generated by hydrolysis of the generated TiOSO4 solution is then calcined to obtain TiO2.

[0047] S7: Use the final residue produced in step S6 to prepare building materials or for soil improvement.

[0048] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A method for converting red mud into mineral resources, characterized in that, Includes the following steps: S1: Mix red mud with 10%-20% dilute sulfuric acid at a solid-liquid ratio of 1:5-1:10, stir at 25-85℃ for 30-90 minutes, and then separate the solid and liquid by filtration or centrifugation to obtain leachate and neutral residue I. S2: While stirring, add NaOH to the leachate until pH=4 to generate Fe(OH)3 precipitate. Then separate the Fe(OH)3 precipitate and calcine it to obtain high-purity Fe2O3. The remaining filtrate is I. S3: Continue to add NaOH to filtrate I while stirring until pH=8.5, forming Al(OH)3 precipitate. Then separate the Al(OH)3 precipitate and calcine it to obtain high-purity Al2O3. The remaining filtrate is II. S4: Continue stirring in filtrate II while adding MgSO4 to adjust the pH to >9, generating MgSiO3 precipitate. Separate the MgSiO3 precipitate, leaving filtrate III; S5: Filtrate III is reacted with ammonia water through an electrodialysis membrane stack to generate NaOH solution and ammonium sulfate. The generated NaOH is then recycled in step S2. The electrodialysis membrane stack has a metal positive electrode (1) on the left and a metal negative electrode (2) on the right. Between the metal positive electrode (1) and the metal negative electrode (2), there are sodium sulfate water chamber (3), sodium hydroxide water chamber (4), ammonia water chamber (5) and ammonium sulfate water chamber (6) in sequence. A protective liquid (7) is also provided between the metal positive electrode (1), the metal negative electrode (2) and the water chamber. A cation exchange membrane is provided between the sodium sulfate water chamber (3) and the sodium hydroxide water chamber (4), an anion exchange membrane is provided between the sodium hydroxide water chamber (4) and the ammonia water chamber (5), a cation exchange membrane is provided between the ammonia water chamber (5) and the ammonium sulfate water chamber (6), and an anion exchange membrane is provided between the ammonium sulfate water chamber (6) and the sodium sulfate water chamber (3). S6: Neutral residue I is reacted with concentrated sulfuric acid to generate TiOSO4. The H2TiO3 precipitate generated by hydrolysis of the generated TiOSO4 solution is calcined to obtain TiO2. S7: Use the final residue produced in step S6 to prepare building materials or for soil improvement.

2. The method for converting red mud into mineral resources according to claim 1, characterized in that: In step S6, the concentration of concentrated sulfuric acid is ≥50% by mass, the reaction temperature is 100℃, and the reaction time is ≥2h.

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