A method for red mud biological activation, de-alkalization and sodium recovery
Patent Information
- Application Number
- CN202411077607.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-07
- Publication Date
- 2025-04-01
- Estimated Expiration
- 2044-08-07
AI Technical Summary
In the prior art, the red mud treatment method has problems with high acid consumption and secondary pollution of waste liquid, making it difficult to achieve harmless and resource utilization of red mud, and biological dealtitude method will cause the red mud to adhere to microorganisms to affect subsequent utilization.
Pretreatment of Aspergillus niger biofermentation broth and red mud, combining multiple leaching steps of dilute acid and alkaline water. Through the simultaneous action of biological activation and chemistry, the leaching rate of sodium is increased, the acid consumption is reduced, and the redness is removed. The acid root in the mud is obtained for subsequent resource utilization.
It improves the leaching rate of sodium, reduces the consumption of acid, avoids secondary pollution, realizes the harmless and resource utilization of red mud, and provides a simple and efficient decaling treatment method.
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Figure CN118929697A8_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of solid resource utilization and relates to a method for bioactivating and dealkalizing red mud and recovering sodium. Background Art
[0002] Red mud is a solid waste generated in the alumina production process. Currently, most red mud treatment methods are dry storage, which can easily cause serious environmental pollution and ecological damage. Therefore, the resource utilization of red mud is a bottleneck restricting the sustainable development of the alumina industry and deserves high attention.
[0003] At present, the most widely used method for the resource utilization of red mud is to use it as cement and roadbed materials, but due to its high alkalinity and complex composition, it is difficult to apply it on a large scale. The alkaline substances in red mud are mainly divided into soluble alkalis such as NaOH, Na2CO3 and NaAlO2 and chemically bound alkalis present in the solid phase. Because the bound alkalis are mostly present in the insoluble solid phase of red mud, a higher concentration of acid is required to completely remove them. Chinese patent CN112095009A discloses a process for leaching red mud with hydrochloric acid to recover calcium, sodium, aluminum, iron, and rare earth chlorides, Chinese patent CN116516156A discloses a method for recovering iron and aluminum from red mud, and Chinese patent CN116144919A discloses a red mud treatment system and method thereof. The process methods disclosed in the above Chinese patents all use a relatively high concentration of acid leaching treatment, which not only has high requirements on equipment, but also has the problem of secondary pollution of waste liquid.
[0004] Biological activation is a green and environmentally friendly red mud treatment method that is currently on the rise. It has the characteristics of low cost, short cycle, simple process and low equipment corrosion rate. Aspergillus niger, as a microorganism with strong acid production, can produce a large amount of acid. It has the advantages of spontaneity and environmental friendliness as a microbial treatment method. Chinese patent CN107915386A discloses a biological de-alkali method for red mud, which uses Aspergillus niger to de-alkali red mud, but mainly Aspergillus niger and red mud are de-alkali treated in the same system, which will cause part of the red mud to adhere to the Aspergillus niger hyphae, affecting the subsequent use of red mud. The biochemical treatment mainly relies on microbial acid production and extracellular polymers to leach red mud. Aspergillus niger can be used to produce fermentation broth, and the organic acids and enzymes in the fermentation broth can be used to destroy the special crystal structure of red mud to achieve the activation effect.
[0005] It is of great significance to develop a simple and efficient new technology for dealkalization treatment of red mud, make extensive resource utilization of red mud, and solve the problem of large-scale accumulation of red mud. Summary of the invention
[0006] In order to solve the problems existing in the prior art, the present invention provides a method for recovering sodium by bioactivating red mud, thereby reducing acid consumption and achieving harmlessness and resource utilization of red mud. The specific technical scheme is as follows:
[0007] A method for bioactivating red mud to dealkalize and recover sodium comprises the following steps:
[0008] The following steps are involved:
[0009] (1) mixing crushed red mud, desalted water, and Aspergillus niger biological fermentation liquid with a pH value less than 2.5, stirring, and then performing solid-liquid separation to obtain biochemical circulating liquid and biologically activated red mud;
[0010] (2) mixing the bioactivated red mud obtained in step (1) with a dilute acid solution, stirring and leaching under heating conditions, and obtaining a sodium solution and red mud residue after solid-liquid separation;
[0011] (3) fully mixing the red mud residue obtained in step (2) with desalted water, stirring and separating the solid and liquid to obtain a sodium washing solution and a sodium-free red mud residue;
[0012] (4) fully mixing the sodium-free red mud residue obtained in step (3) with alkaline water, stirring and separating the solid and liquid to obtain a sodium salt solution and acid-free red mud residue;
[0013] (5) Concentrating the sodium solution of step (2) and the sodium washing solution obtained in step (3) to obtain a sodium salt solid.
[0014] Furthermore, the preparation method of the Aspergillus niger biological fermentation liquid in the step (1) is to inoculate a bacterial community mainly composed of Aspergillus niger in a Chabon medium or a mold culture medium, wherein the number of Aspergillus niger in the bacterial community accounts for 60-90%, and after culturing at 20-35° C. for 7-14 days, the bacterial community is filtered by solid-liquid separation to obtain an Aspergillus niger biological fermentation liquid with a pH value less than 2.5.
[0015] Furthermore, in step (1), the red mud includes Bayer process red mud, sintering process red mud or combined process red mud.
[0016] Furthermore, in the step (1), the red mud crushing means include but are not limited to ball milling and roller milling, and the red mud is crushed to a particle size of 60 to 200 meshes.
[0017] Furthermore, in step (1), the mass ratio of the red mud to the desalted water and the biological fermentation liquid is 10:(70-75):(15-20), and the stirring time is 15 min to 12 h.
[0018] Furthermore, in step (2), the mass concentration of the dilute acid is 1% to 2.5%, the mass ratio of the bioactivated red mud to the dilute acid solution is 1:5, the stirring time is 15 min to 12 h, the stirring temperature is 55-60° C., and the separated red mud residue is subjected to at least one more dilute acid treatment.
[0019] Furthermore, in the step (3), the mass ratio of red mud residue to desalted water is (3-4):20, the stirring time is 15min to 12h, and the separated sodium red mud residue is subjected to desalted water treatment at least once more.
[0020] Furthermore, in the step (4), the acid-free red mud residue is separated and subjected to alkaline water treatment at least once, the pH of the alkaline water is 8-11, the mass volume ratio of the total amount of sodium-free red mud residue and alkaline water is 1kg: (1L-5L), and the stirring time for each treatment is 15min-12h.
[0021] Furthermore, the step (1) is specifically as follows: drying, crushing, grinding and then passing the red mud through a 60-mesh sieve, mixing the red mud with a biological fermentation liquid with a pH value less than 2.5 that has been cultured and fermented for 9 days, wherein the mass ratio of the red mud to the fermentation liquid is 10 g:15 g, stirring evenly and then standing for half an hour, and then adding water to 100 g, placing in a water bath constant temperature oscillator, and reacting at 25° C. for 1 hour; after the reaction is completed, filtering is performed to obtain biologically activated red mud and biochemical circulating liquid.
[0022] Furthermore, the biochemical circulating fluid in step (1) is used as a solvent for preparing Chamarel's medium or mold culture medium after impurities are removed; the low sodium solution in step (2) is used as water for preparing dilute acid, and in step (2), the heating method includes but is not limited to water bath heating and steam heating; and the concentration in step (5) is carried out by membrane concentration or evaporation concentration or a combination of the two.
[0023] The beneficial effects of the present invention are:
[0024] The method for red mud biological activation, de-alkalization and sodium recovery of the present invention comprises the following steps: firstly, the red mud is pretreated by biological activation, and the biological activation improves the leaching rate of Na under the simultaneous biological and chemical effects, reduces the consumption of acid, and has no secondary pollution in the biological fermentation liquid; on the basis of sodium recovery, the newly added acid radicals in the red mud residue can be removed at the same time, and the obtained sodium-free red mud residue can be subsequently utilized as a resource. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 The present invention is a process flow chart of the method for bioactivation and dealkalization of red mud and recovery of sodium;
[0026] Figure 2 This is the EDS test diagram of red mud and leaching residue without added acid radicals in Example 1. DETAILED DESCRIPTION
[0027] The instruments, reagents, materials, etc. involved in the following embodiments, unless otherwise specified, are all conventional instruments, reagents, materials, etc. in the prior art and can be obtained through regular commercial channels. The experimental methods, detection methods, etc. involved in the following embodiments, unless otherwise specified, are all conventional experimental methods, detection methods, etc. in the prior art.
[0028] In the following embodiments and comparative examples of the present invention:
[0029] The water used is desalted water.
[0030] The red mud used comes from the Bayer process red mud of Shandong Xinfa Group, in which the contents of the three main metal elements Na, Fe and Al are 5.78%, 20.29% and 9.67% respectively.
[0031] The biological fermentation liquid used is Aspergillus niger biological fermentation liquid. The preparation method is as follows: a bacterial community dominated by Aspergillus niger is inoculated into a Cha's medium or a mold medium, wherein the Aspergillus niger accounts for 60-90% of the bacterial community. After culturing at 20-35°C for 7-14 days, the bacterial community is filtered through solid-liquid separation to obtain an Aspergillus niger biological fermentation liquid with a pH value less than 2.5.
[0032] The diluted salt used is diluted hydrochloric acid, and the mass concentration of concentrated hydrochloric acid used to prepare the diluted hydrochloric acid is 37%. Dilute sulfuric acid or dilute nitric acid can also be used.
[0033] Example 1
[0034] like Figure 1 As shown, a method for bioactivating red mud to dealkalize and recover sodium comprises the following steps:
[0035] (1) drying, crushing, grinding and then passing red mud through a 60-mesh sieve, mixing the red mud with a biological fermentation liquid with a pH value less than 2.5 after 9 days of culture and fermentation, the mass ratio of red mud to fermentation liquid being 10 g:15 g, then adding water to 100 g, placing in a water bath constant temperature oscillator, reacting at 25° C. for 2 h; filtering after the reaction to obtain bioactivated red mud and biochemical circulating liquid;
[0036] (2) mixing the bio-activated red mud with a dilute acid having a mass concentration of 1.5%. In this embodiment, dilute hydrochloric acid is used, and the mixture is placed in a water bath constant temperature oscillator at 60° C. for reaction for 1.5 h. The mass ratio of red mud to dilute acid is 20%. After the reaction is completed, sodium solution and red mud residue are obtained by filtration. This step adopts a small amount of multiple reactions. In this step, the dilute acid is initially prepared by water and concentrated acid. When a sodium solution is produced, the sodium solution is used to prepare the dilute acid to achieve the effect of enriching sodium salts.
[0037] (3) mixing the red mud residue obtained in step (2) with desalted water in a mass ratio of 15%, reacting the mixture in a water bath constant temperature oscillator at 25° C. for 30 min, and after solid-liquid separation, treating the obtained solid once in the above manner to obtain a sodium washing solution and a sodium-free red mud residue;
[0038] (4) mixing the sodium-free red mud residue obtained in step (3) with a solution adjusted to pH 10 using NaOH, reacting the mixture in a water bath constant temperature oscillator at 25° C. for 30 min, and after solid-liquid separation, treating the obtained solid once in the above manner, wherein the total amount of the sodium-free red mud residue and the NaOH solution used has a mass volume ratio of 1 kg:3 L, thereby obtaining a sodium salt solution and acid-free red mud residue;
[0039] (5) The sodium solution of step (2) and the sodium washing solution obtained in step (3) are concentrated by membrane, and the concentrated solution is evaporated to obtain a sodium salt solid.
[0040] Example 2
[0041] like Figure 1 As shown, a method for bioactivating red mud to dealkalize and recover sodium comprises the following steps:
[0042] (1) drying, crushing, grinding and then passing red mud through a 60-mesh sieve, mixing the red mud with a biological fermentation liquid with a pH value less than 2.5 after 7 days of culture and fermentation, the mass ratio of red mud to fermentation liquid being 10 g:20 g, then adding water to 100 g, placing in a water bath constant temperature oscillator, reacting at 25° C. for 1.5 h; filtering after the reaction to obtain bioactivated red mud and biochemical circulating liquid;
[0043] (2) mixing the bio-activated red mud with a dilute acid having a mass concentration of 1.2%. In this embodiment, dilute hydrochloric acid is used, and the mixture is placed in a water bath constant temperature oscillator at 60° C. for reaction for 1.5 h. The mass ratio of red mud to dilute acid is 20%. After the reaction is completed, sodium solution and red mud residue are obtained by filtration. This step adopts a small amount of multiple reactions. In this step, the dilute acid is initially prepared by water and concentrated acid. When a sodium solution is produced, the sodium solution is used to prepare the dilute acid to achieve the effect of enriching sodium salts.
[0044] (3) mixing the red mud residue obtained in step (2) with desalted water in a mass ratio of 20%, reacting the mixture in a water bath constant temperature oscillator at 25° C. for 1 h, and after solid-liquid separation, treating the obtained solid once in the above manner to obtain a sodium washing solution and a sodium-free red mud residue;
[0045] (4) mixing the sodium-free red mud residue obtained in step (3) with a solution adjusted to pH 10 using NaOH, reacting the mixture in a water bath constant temperature oscillator at 25° C. for 30 min, and after solid-liquid separation, treating the obtained solid once in the above manner, wherein the total amount of the sodium-free red mud residue and the NaOH solution used has a mass volume ratio of 1 kg:3 L, thereby obtaining a sodium salt solution and acid-free red mud residue;
[0046] (5) The sodium solution of step (2) and the sodium washing solution obtained in step (3) are concentrated by membrane, and the concentrated solution is evaporated to obtain a sodium salt solid.
[0047] Example 3
[0048] like Figure 1 As shown, a method for bioactivating red mud to dealkalize and recover sodium comprises the following steps:
[0049] (1) drying, crushing, grinding and then passing red mud through a 60-mesh sieve, mixing the red mud with a biological fermentation liquid with a pH value less than 2.5 after 9 days of culture and fermentation, the mass ratio of red mud to fermentation liquid being 10 g:15 g, then adding water to 100 g, placing in a water bath constant temperature oscillator, reacting at 25° C. for 2 h; filtering after the reaction to obtain bioactivated red mud and biochemical circulating liquid;
[0050] (2) mixing the bio-activated red mud with a dilute acid having a mass concentration of 1.5%. In this embodiment, dilute hydrochloric acid is used, and the mixture is placed in a water bath constant temperature oscillator at 60° C. for reaction for 2 h. The mass ratio of red mud to dilute acid is 20%. After the reaction is completed, sodium solution and red mud residue are obtained by filtration. This step adopts a small amount of multiple reactions. In this step, the dilute acid is initially prepared by water and concentrated acid. When a sodium solution is produced, the sodium solution is used to prepare the dilute acid to achieve the effect of enriching sodium salts.
[0051] (3) mixing the red mud residue obtained in step (2) with desalted water in a mass ratio of 20%, reacting the mixture in a water bath constant temperature oscillator at 25° C. for 30 min, and after solid-liquid separation, treating the obtained solid twice in the above manner to obtain a sodium washing solution and a sodium-free red mud residue;
[0052] (4) mixing the sodium-free red mud residue obtained in step (3) with a solution adjusted to pH 10 using NaOH, reacting in a water bath constant temperature oscillator at 25° C. for 1 h, and after solid-liquid separation, treating the obtained solid twice in the above manner, wherein the total amount of sodium-free red mud residue and NaOH solution used has a mass volume ratio of 1 kg:3 L, to obtain a sodium salt solution and acid-free red mud residue;
[0053] (5) The sodium solution of step (2) and the sodium washing solution obtained in step (3) are concentrated by membrane, and the concentrated solution is evaporated to obtain a sodium salt solid.
[0054] Example 4
[0055] like Figure 1 As shown, a method for bioactivating red mud to dealkalize and recover sodium comprises the following steps:
[0056] (1) The red mud is dried, crushed, ground, and then passed through a 60-mesh sieve. The red mud is mixed with a biological fermentation liquid with a pH value of less than 2.5 that has been cultured and fermented for 9 days. The mass ratio of red mud to fermentation liquid is 10 g:15 g. After stirring evenly, the mixture is allowed to stand for half an hour, and then water is added to 100 g. The mixture is placed in a water bath constant temperature oscillator and reacted at 25°C for 1 hour. After the reaction is completed, the mixture is filtered to obtain bioactivated red mud and biochemical circulating liquid. The red mud and fermentation liquid are first fully mixed and allowed to stand so that the fermentation liquid can first penetrate the red mud. Then, a large amount of water is added to dilute the red mud so that it can be better oscillated, stirred, and dispersed in the oscillator, so that the biological fermentation liquid can better react with the red mud, thereby shortening the overall reaction time.
[0057] (2) mixing the bio-activated red mud with a dilute acid having a mass concentration of 1.5%. In this embodiment, dilute hydrochloric acid is used, and the mixture is placed in a water bath constant temperature oscillator at 60° C. for reaction for 1.5 h. The mass ratio of red mud to dilute acid is 20%. After the reaction is completed, sodium solution and red mud residue are obtained by filtration. This step adopts a small amount of multiple reactions. In this step, the dilute acid is initially prepared by water and concentrated acid. When a sodium solution is produced, the sodium solution is used to prepare the dilute acid to achieve the effect of enriching sodium salts.
[0058] (3) mixing the red mud residue obtained in step (2) with desalted water in a mass ratio of 15%, reacting the mixture in a water bath constant temperature oscillator at 25° C. for 30 min, and after solid-liquid separation, treating the obtained solid once in the above manner to obtain a sodium washing solution and a sodium-free red mud residue;
[0059] (4) mixing the sodium-free red mud residue obtained in step (3) with a solution adjusted to pH 10 using NaOH, reacting the mixture in a water bath constant temperature oscillator at 25° C. for 30 min, and after solid-liquid separation, treating the obtained solid once in the above manner, wherein the total amount of the sodium-free red mud residue and the NaOH solution used has a mass volume ratio of 1 kg:3 L, thereby obtaining a sodium salt solution and acid-free red mud residue;
[0060] (5) The sodium solution of step (2) and the sodium washing solution obtained in step (3) are concentrated by membrane, and the concentrated solution is evaporated to obtain a sodium salt solid.
[0061] Comparative Example 1
[0062] A method for bioactivating red mud to dealkalize and recover sodium comprises the following steps:
[0063] (1) Red mud is dried, crushed, ground, and then passed through a 60-mesh sieve, and mixed with dilute acid with a mass concentration of 2.3%. In this comparative example, dilute hydrochloric acid is used, and the mixture is placed in a water bath constant temperature oscillator at 60° C. for reaction for 2 h. The mass ratio of red mud to dilute acid is 20%. After the reaction is completed, a sodium solution containing sodium salt and leached residue are obtained by filtration; the sodium solution is used to prepare dilute acid (treated in the same manner as in Example 1) to achieve the effect of enriching sodium salt;
[0064] (2) mixing the leached residue obtained in step (1) with desalted water in a mass ratio of 20%, reacting in a water bath constant temperature oscillator at 25° C. for 1 h, and after solid-liquid separation, treating the solid in the above manner for 3 times to obtain a sodium salt washing solution and a sodium-free red mud leached residue;
[0065] (3) The sodium-free red mud residue obtained in step (2) is mixed with a solution adjusted to pH 10 using NaOH, and reacted in a water bath constant temperature oscillator at 25° C. for 1 h. After solid-liquid separation, the solid is treated three times in the above manner, and the total amount of sodium-free red mud residue and NaOH solution is in a mass volume ratio of 1 kg:3 L, thereby obtaining a sodium salt solution and acid-free red mud residue.
[0066] Comparative Example 2
[0067] A method for bioactivating red mud to dealkalize and recover sodium comprises the following steps:
[0068] (1) drying, crushing, grinding and then passing red mud through a 60-mesh sieve, mixing the red mud with a biological fermentation liquid with a pH value less than 2.5 after 9 days of culture and fermentation, the mass ratio of red mud to fermentation liquid being 10 g:15 g, then adding water to 100 g, placing in a water bath constant temperature oscillator, reacting at 25° C. for 2 h; filtering after the reaction to obtain bioactivated red mud and biochemical circulating liquid;
[0069] (2) mixing the bioactivated red mud obtained in step (1) with desalted water in a mass ratio of 20%, reacting in a water bath constant temperature oscillator at 25° C. for 1 hour, and after solid-liquid separation, treating the solid in the above manner for 3 times to obtain a sodium washing solution and a sodium-free red mud residue;
[0070] The Na ion content in the solution after each step of the reaction in each embodiment and the comparative example was measured, and the Na content of the finally obtained leaching residue was digested and tested, and the pH of the leaching residue was tested to obtain the Na leaching rate, the Na content of the leaching residue and the pH of the leaching residue. The results are shown in the table below.
[0071] The red mud and the acid-free leaching residue in Example 1 were subjected to EDS testing. The results are shown in Figure (2). The Na content was significantly reduced, while the Fe and Si elements, which are of concern in resource utilization, did not change significantly. The percentages in the following table refer to mass percentages.
[0072]
[0073] It can be seen from the data in the above table that after the red mud is activated by adding biochemical fermentation liquid, the present invention has a higher Na leaching rate and a lower Na content in the leached residue, and effectively reduces the acid dosage to achieve a higher Na leaching rate and de-alkali effect. In comparative example 1, inorganic acid was not used for leaching, and the Na element leaching rate was only 54.72%. The pH of the red mud after washing reached 8.28, which shows that the chemically bound alkali present in the solid phase was not effectively leached. In comparative example 2, alkaline solution washing with a pH of 10 was not adopted, and the acid radical content in the leached residue was as high as 0.24%, indicating that the alkaline solution effectively removed the acid radicals in the leached residue.
[0074] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.
Claims
1. A method for bioactivating red mud to dealkalize and recover sodium, characterized in that: The following steps are involved: (1) mixing crushed red mud, desalted water, and Aspergillus niger biological fermentation liquid with a pH value less than 2.5, stirring, and then performing solid-liquid separation to obtain biochemical circulating liquid and biologically activated red mud; (2) mixing the bioactivated red mud obtained in step (1) with a dilute acid solution, stirring and leaching under heating conditions, and obtaining a sodium solution and red mud residue after solid-liquid separation; (3) fully mixing the red mud residue obtained in step (2) with desalted water, stirring and separating the solid and liquid to obtain a sodium washing solution and a sodium-free red mud residue; (4) fully mixing the sodium-free red mud residue obtained in step (3) with alkaline water, stirring and separating the solid and liquid to obtain a sodium salt solution and acid-free red mud residue; (5) The sodium solution of step (2) and the sodium washing solution obtained in step (3) are concentrated to obtain a sodium salt solid.
2. The method for red mud biological activation and dealkalization and sodium recovery according to claim 1, characterized in that: The method for preparing the Aspergillus niger biological fermentation liquid in the step (1) is as follows: inoculating a bacterial community mainly composed of Aspergillus niger into a Chabon medium or a mold culture medium, wherein the number of Aspergillus niger in the bacterial community accounts for 60-90%, culturing at 20-35° C. for 7-14 days, filtering the bacterial community through solid-liquid separation, and obtaining the Aspergillus niger biological fermentation liquid with a pH value less than 2.
5.
3. The method for red mud biological activation and dealkalization and sodium recovery according to claim 1, characterized in that: In the step (1), the red mud includes Bayer process red mud, sintering process red mud or combined process red mud.
4. The method for red mud biological activation and dealkalization and sodium recovery according to claim 1, characterized in that: In the step (1), the red mud crushing means include but are not limited to ball milling and roller milling, and the red mud is crushed to a particle size of 60 to 200 meshes.
5. The method for red mud biological activation and dealkalization and sodium recovery according to claim 1, characterized in that: In the step (1), the mass ratio of the red mud to the desalted water and the biological fermentation liquid is 10:(70-75):(15-20), and the stirring time is 15 min to 12 h.
6. The method for red mud biological activation and dealkalization and sodium recovery according to claim 1, characterized in that: In the step (2), the mass concentration of the dilute acid is 1% to 2.5%, the mass ratio of the bioactivated red mud to the dilute acid solution is 1:5, the stirring time is 15 min to 12 h, the stirring temperature is 55-60° C., and the separated red mud leaching residue is subjected to at least one more dilute acid treatment.
7. The method for red mud biological activation and dealkalization and sodium recovery according to claim 1, characterized in that: In the step (3), the mass ratio of the red mud residue to the desalted water is (3-4):20, the stirring time is 15 min to 12 h, and the separated sodium red mud residue is subjected to desalted water treatment at least once.
8. The method for red mud biological activation and dealkalization and sodium recovery according to claim 1, characterized in that: In the step (4), the acid-free red mud residue is separated and subjected to alkaline water treatment at least once, the pH of the alkaline water is 8-11, the mass volume ratio of the total amount of sodium-free red mud residue and alkaline water is 1kg: (1L-5L), and the stirring time for each treatment is 15min-12h.
9. The method for red mud biological activation and dealkalization and sodium recovery according to claim 1, characterized in that: The step (1) specifically comprises: drying, crushing and grinding the red mud and then passing it through a 60-mesh sieve; mixing the red mud with a biological fermentation liquid with a pH value less than 2.5 that has been cultured and fermented for 9 days, wherein the mass ratio of the red mud to the fermentation liquid is 10 g:15 g; stirring evenly and then standing for half an hour; then adding water to 100 g; placing the mixture in a water bath constant temperature oscillator and reacting at 25° C. for 1 hour; and filtering after the reaction to obtain biologically activated red mud and biochemical circulating liquid.
10. The method for red mud biological activation and dealkalization and sodium recovery according to claim 2, characterized in that: The biochemical circulating fluid in step (1) is used as a solvent for preparing Chabon culture medium or mold culture medium after impurities are removed; the low sodium solution in step (2) is used as water for preparing dilute acid; in step (2), the heating method includes but is not limited to water bath heating and steam heating; in step (5), the concentration is carried out by membrane concentration or evaporation concentration or a combination of the two.