Method for converting red mud into mineral resources

Abstract

The invention discloses a method for converting red mud into mineral resources for use, which realizes efficient extraction of FeO, AlO and TiO in the red mud and recycling of NaOH through an acid leaching-alkali precipitation-membrane separation process. The method specifically comprises the following steps: leaching red mud by using dilute sulfuric acid, precipitating metal hydroxides step by step, regenerating NaOH through electrodialysis, extracting TiO by using concentrated sulfuric acid through acidolysis, and finally performing innocent treatment on residues. The method has the advantages of high resource recovery rate, low cost, environmental friendliness and the like, and is suitable for large-scale resource utilization of the red mud.

Description

Technical Field

[0001] The present invention belongs to the technical field of red mud treatment, and particularly relates to a method for converting red mud into mineral resources for use. Background Art

[0002] Red mud is an industrial waste residue after extracting alumina from bauxite, with an annual output exceeding 150 million tons, and the global cumulative stockpile has reached more than 4 billion tons. Red mud has the following characteristics: 1. High alkalinity: containing 8 - 12% of Na2O, direct stacking will cause soil alkalization and groundwater pollution; 2. Heavy metal risk: containing valuable metals such as Fe, Al, Ti and heavy metal elements such as Cr, Ni; 3. Defects of traditional treatment methods: used in building materials (bricks, tiles, cement), the product stability is poor due to excessive alkalinity; landfill treatment occupies land and there are environmental risks; the existing wet extraction technology has high costs and complex processes, making it difficult to be industrially applied. Summary of the Invention

[0003] Aiming at the problem of difficult large-scale resource utilization of red mud at present, the present invention realizes the efficient extraction of valuable metals in red mud and the harmless treatment of residues through an acid leaching - alkali precipitation - membrane separation process, providing a new solution for red mud resource utilization.

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

[0005] S2: Add NaOH to the leaching solution while stirring until pH = 4 to form Fe(OH)3 precipitate, then separate and calcine the Fe(OH)3 precipitate to obtain high-purity Fe2O3, and the remaining filtrate I.

[0006] S3: Continuously add NaOH to the filtrate I while stirring until the pH reaches 8.5 to form Al(OH)3 precipitate. Then separate and calcine the Al(OH)3 precipitate to obtain high-purity Al2O3, leaving the remaining filtrate II.

[0007] S4: Continuously add MgSO4 to the filtrate II while stirring to adjust the pH > 9 to form MgSiO3 precipitate. Separate the MgSiO3 precipitate, leaving the remaining filtrate III.

[0008] S5: React the filtrate III with ammonia water through an electrodialysis membrane stack to generate NaOH solution and ammonium sulfate. Then use the generated NaOH for recycling in step S2; the main component in the filtrate III is Na2SO4. After the reaction of Na2SO4 and ammonia water through the electrodialysis membrane stack, ion recombination is achieved, and the reaction formula is as follows: Na2SO4 + 2NH3·H2O → 2NaOH + (NH4)2SO4.

[0009] In the electrodialysis membrane stack, when the sodium sulfate solution enters the sodium sulfate water chamber and the ammonia water enters the ammonia water chamber, under the action of the electric field, sodium ions pass through the cation exchange membrane into the sodium hydroxide water chamber, and the hydroxide ions in the ammonia water chamber also migrate to the sodium hydroxide water chamber, and the two combine to form sodium hydroxide; at the same time, the sulfate ions in the sodium sulfate water chamber pass through the anion exchange membrane into the ammonium sulfate water chamber, and the ammonium ions in the ammonia water chamber pass through the cation exchange membrane into the ammonium sulfate water chamber. Through continuous reaction, the conversion of the following reaction formula is achieved: Na2SO4 + 2NH3・H2O = 2NaOH + (NH4)2SO4.

[0010] S6: Stir and react the neutral residue I with concentrated sulfuric acid at 100 °C to generate TiOSO4. Calcinate the H2TiO3 precipitate produced by hydrolyzing the TiOSO4 solution 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. Between the metal positive electrodes, there are successively provided a sodium sulfate water chamber, a sodium hydroxide water chamber, an ammonia water chamber, and an ammonium sulfate water chamber. There is also a protective liquid provided between the metal positive electrode, the metal negative electrode, and the water chambers; 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 fraction, the reaction temperature is 100 °C, and the reaction time is ≥ 2 h.

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

[0015] 2. The method of the present invention realizes the self - recycling of materials. Through electrodialysis treatment, NaOH regeneration is achieved, and the regenerated NaOH is used in the leaching process, reducing the consumption of chemical reagents.

[0016] 3. The method of the present invention has no secondary pollution in the whole process, and the residue realizes harmless utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the process flow chart of the present invention.

[0018] Figure 2 It is the structural schematic diagram of the electrodialysis stack.

[0019] Reference numerals: 1 - metal positive electrode, 2 - metal negative electrode, 3 - sodium sulfate water chamber, 4 - sodium hydroxide water chamber, 5 - ammonia water chamber, 6 - ammonium sulfate water chamber, 7 - protective liquid. DETAILED DESCRIPTION OF THE EMBODIMENTS

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

[0021] A method for converting red mud into mineral resources includes the following steps: S1: Mix red mud with dilute sulfuric acid with a mass fraction of 10% according to a solid - liquid ratio of 1:10, stir at 25 °C for 90 min, and then perform solid - liquid separation by filtration to obtain a leaching solution and neutral residue I. The leaching solution mainly contains Fe³⁺, Al³⁺, Na⁺, and the neutral residue mainly contains TiO2, SiO2, CaSO4; The reaction equations during the leaching process are as follows: Na2O + H2SO4 → Na2SO4 + H2O; Fe2O3 + 3H2SO4 → Fe2(SO4)3 + 3H2O; Al2O3 + 3H2SO4 → Al2(SO4)3 + 3H2O.

[0022] S2: Add NaOH to the leaching solution with stirring until the pH reaches 4 to form Fe(OH)3 precipitate. Then separate and calcine the Fe(OH)3 precipitate to obtain high-purity Fe2O3, and the remaining filtrate I.

[0023] S3: Continuously add NaOH to filtrate I with stirring until the pH reaches 8.5 to form Al(OH)3 precipitate. Then separate and calcine the Al(OH)3 precipitate to obtain high-purity Al2O3, and the remaining filtrate II.

[0024] S4: Continuously add MgSO4 to filtrate II with stirring to adjust the pH > 9 to form MgSiO3 precipitate. Separate the MgSiO3 precipitate, and the remaining filtrate III.

[0025] S5: React filtrate III with ammonia water through an electrodialysis membrane stack to generate NaOH solution and ammonium sulfate. Then use the generated NaOH for recycling in step S2; mainly Na2SO4 remains in filtrate III. After the reaction of Na2SO4 and ammonia water through the electrodialysis membrane stack, ion recombination is achieved, and the reaction formula is as follows: Na2SO4 + 2NH3·H2O → 2NaOH + (NH4)2SO4.

[0026] In the electrodialysis membrane stack, when the sodium sulfate solution enters the sodium sulfate water chamber and the ammonia water enters the ammonia water chamber, under the action of the electric field, sodium ions pass through the cation exchange membrane and enter the sodium hydroxide water chamber, and the hydroxide ions in the ammonia water chamber also migrate to the sodium hydroxide water chamber, and the two combine to form sodium hydroxide; at the same time, the sulfate ions in the sodium sulfate water chamber pass through the anion exchange membrane and enter the ammonium sulfate water chamber, and the ammonium ions in the ammonia water chamber pass through the cation exchange membrane and enter the ammonium sulfate water chamber. Through continuous reaction, the transformation of the following reaction formula is achieved: Na2SO4 + 2NH3・H2O = 2NaOH + (NH4)2SO4.

[0027] As Figure 2 shown, a metal positive electrode 1 is provided on the left side of the electrodialysis membrane stack, and a metal negative electrode 2 is provided on the right side. Between the metal positive electrode 1 and the metal positive electrode 2, a sodium sulfate water chamber 3, a sodium hydroxide water chamber 4, an ammonia water chamber 5, and an ammonium sulfate water chamber 6 are successively arranged. 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: React the neutral residue I with concentrated sulfuric acid with a mass fraction of ≥50% by stirring at 100 °C for ≥2 h to produce TiOSO4. Calcinate the H2TiO3 precipitate produced by the hydrolysis of the TiOSO4 solution 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 for use, comprising the following steps: S1: Mix red mud with dilute sulfuric acid with a mass fraction of 20% at a solid-liquid ratio of 1:5, stir at 85 °C for 30 min, and then perform solid-liquid separation by centrifugation to obtain a leaching solution and a neutral residue I. The leaching solution mainly contains Fe³⁺, Al³⁺, and Na⁺, and the neutral residue mainly contains TiO2, SiO2, and CaSO4; The reaction equations during the leaching process are as follows: Na2O + H2SO4 → Na2SO4 + H2O; Fe2O3 + 3H2SO4 → Fe2(SO4)3 + 3H2O; Al2O3 + 3H2SO4 → Al2(SO4)3 + 3H2O.

[0031] S2: Add NaOH to the leaching solution while stirring until pH = 4 to form a Fe(OH)3 precipitate, then separate and calcinate the Fe(OH)3 precipitate to obtain high-purity Fe2O3, and the remaining filtrate I.

[0032] S3: Continue to add NaOH to filtrate I while stirring until pH = 8.5 to form an Al(OH)3 precipitate, then separate and calcinate the Al(OH)3 precipitate to obtain high-purity Al2O3, and the remaining filtrate II.

[0033] S4: Continue to add MgSO4 to filtrate II while stirring to adjust pH > 9 to form a MgSiO3 precipitate, separate the MgSiO3 precipitate, and the remaining filtrate III.

[0034] S5: React filtrate III with ammonia water through an electrodialysis membrane stack to generate a NaOH solution and ammonium sulfate, and then use the generated NaOH for recycling in step S2; filtrate III mainly contains Na2SO4, and after the reaction of Na2SO4 with ammonia water through the electrodialysis membrane stack, ion recombination is achieved, and the reaction formula is as follows: Na2SO4 + 2NH3·H2O → 2NaOH + (NH4)2SO4.

[0035] In an electrodialysis membrane stack, when a sodium sulfate solution enters the sodium sulfate water chamber and ammonia water enters the ammonia water chamber, under the action of an electric field, sodium ions pass through the cation exchange membrane into the sodium hydroxide water chamber, and the hydroxide ions in the ammonia water chamber also migrate to the sodium hydroxide water chamber, where the two combine to form sodium hydroxide. At the same time, the sulfate ions in the sodium sulfate water chamber pass through the anion exchange membrane into the ammonium sulfate water chamber, and the ammonium ions in the ammonia water chamber pass through the cation exchange membrane into the ammonium sulfate water chamber. Through continuous reaction, the conversion of the following reaction formula is achieved: Na2SO4 + 2NH3・H2O = 2NaOH + (NH4)2SO4.

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

[0037] S6: React the neutral residue I with concentrated sulfuric acid with a mass fraction ≥ 50% at 100 °C for ≥ 2 h to generate TiOSO4, and calcine the H2TiO3 precipitate produced by hydrolyzing the generated TiOSO4 solution 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 for use, comprising the following steps: S1: Mix red mud with dilute sulfuric acid with a mass fraction of 15% at a solid-liquid ratio of 1:8, stir at 55 °C for 60 min, and then perform solid-liquid separation by centrifugation to obtain a leaching solution and a neutral residue I. The leaching solution mainly contains Fe³⁺, Al³⁺, Na⁺, and the neutral residue mainly contains TiO2, SiO2, CaSO4; The reaction equations during 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 leaching solution until the pH reaches 4 to form Fe(OH)3 precipitate. Then separate and calcine the Fe(OH)3 precipitate to obtain high-purity Fe2O3, leaving filtrate I.

[0041] S3: While stirring, continue to add NaOH to filtrate I until the pH reaches 8.5 to form Al(OH)3 precipitate. Then separate and calcine the Al(OH)3 precipitate to obtain high-purity Al2O3, leaving filtrate II.

[0042] S4: While stirring, continue to add MgSO4 to filtrate II to adjust the pH > 9 to form MgSiO3 precipitate. Separate the MgSiO3 precipitate, leaving filtrate III.

[0043] S5: React filtrate III with ammonia water through an electrodialysis membrane stack to generate NaOH solution and ammonium sulfate. Then use the generated NaOH for recycling in step S2; mainly Na2SO4 remains in filtrate III. After the reaction of Na2SO4 and ammonia water through the electrodialysis membrane stack, ion recombination occurs, and the reaction formula is as follows: Na2SO4 + 2NH3·H2O → 2NaOH + (NH4)2SO4.

[0044] In the electrodialysis membrane stack, when the sodium sulfate solution enters the sodium sulfate water chamber and the ammonia water enters the ammonia water chamber, under the action of an electric field, sodium ions pass through the cation exchange membrane into the sodium hydroxide water chamber, and the hydroxide ions in the ammonia water chamber also migrate to the sodium hydroxide water chamber, and the two combine to form sodium hydroxide; at the same time, the sulfate ions in the sodium sulfate water chamber pass through the anion exchange membrane into the ammonium sulfate water chamber, and the ammonium ions in the ammonia water chamber pass through the cation exchange membrane into the ammonium sulfate water chamber. Continuous reaction realizes the conversion of the following reaction formula: Na2SO4 + 2NH3・H2O = 2NaOH + (NH4)2SO4.

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

[0046] S6: React the neutral residue I with concentrated sulfuric acid with a mass fraction of ≥50% under stirring at 100 °C for ≥2 h to produce TiOSO4. Calcinate the H2TiO3 precipitate generated by the hydrolysis of the TiOSO4 solution 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 only exemplary embodiments of the present invention and are not used to limit the present invention. The protection scope of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements within the essence and protection scope of the present invention, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of the present invention.

Claims

1. A method for converting red mud into mineral resources for use, characterized in that, It includes the following steps: S1: Mix red mud with dilute sulfuric acid with a mass fraction of 10%-20% according to a solid-liquid ratio of 1:5-1:10, stir at 25-85 °C for 30-90 min, and then perform solid-liquid separation by filtration or centrifugation to obtain a leaching solution and neutral residue I; S2: While stirring, add NaOH to the leaching solution until pH = 4 to form Fe(OH)3 precipitate, then separate and calcine the Fe(OH)3 precipitate to obtain high-purity Fe2O3, and the remaining filtrate I; S3: While stirring, continue to add NaOH to filtrate I until pH = 8.5 to form Al(OH)3 precipitate, then separate and calcine the Al(OH)3 precipitate to obtain high-purity Al2O3, and the remaining filtrate II; S4: While stirring, continue to add MgSO4 to filtrate II to adjust pH > 9 to form MgSiO3 precipitate, separate the MgSiO3 precipitate, and the remaining filtrate III; S5: React filtrate III with ammonia water through an electrodialysis membrane stack to generate NaOH solution and ammonium sulfate, and then use the generated NaOH for recycling in step S2; S6: Stir and react neutral residue I with concentrated sulfuric acid to generate TiOSO4, calcine the H2TiO3 precipitate produced by hydrolysis of the generated TiOSO4 solution to obtain TiO2; S7: Use the final residue generated in step S6 to prepare building materials or for soil improvement.

2. The method for converting red mud into mineral resources as claimed in claim 1, wherein: A metal positive electrode (1) is arranged on the left side of the electrodialysis membrane stack, and a metal negative electrode (2) is arranged on the right side. Between the metal positive electrode (1) and the metal positive electrode (2), there are successively arranged a sodium sulfate water chamber (3), a sodium hydroxide water chamber (4), an ammonia water chamber (5), and an ammonium sulfate water chamber (6). A protective liquid (7) is also arranged between the metal positive electrode (1), the metal negative electrode (2), and the water chambers.

3. The method for converting red mud into mineral resources according to claim 1, characterized in that: A cation exchange membrane is arranged between the sodium sulfate water chamber (3) and the sodium hydroxide water chamber (4), an anion exchange membrane is arranged between the sodium hydroxide water chamber (4) and the ammonia water chamber (5), a cation exchange membrane is arranged between the ammonia water chamber (5) and the ammonium sulfate water chamber (6), and an anion exchange membrane is arranged between the ammonium sulfate water chamber (6) and the sodium sulfate water chamber (3).

4. The method for converting red mud into mineral resources as claimed in claim 1, characterized in that: In step S6, the concentration of the concentrated sulfuric acid is a mass fraction ≥ 50%, the reaction temperature is 100 °C, and the reaction time ≥ 2 h.

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