A method for biological activation of red mud to remove alkali and recover sodium

Abstract

The present invention belongs to the field of solid resource utilization and relates to a method for biological activation of red mud to remove alkali and recover sodium, comprising the following steps: (1) obtaining a biochemical circulating solution and biologically activated red mud; (2) obtaining a sodium solution and red mud leaching residue; (3) obtaining a sodium washing solution and sodium-free red mud residue; (4) obtaining a sodium salt solution and red mud residue without newly added acid radicals; (5) obtaining solid sodium salt. The present invention first pre-treats red mud by biological activation. The biological activation improves the leaching rate of Na under the simultaneous action of biology and chemistry, reduces the consumption of acid, and the biological fermentation liquid has no secondary pollution. On the basis of recovering sodium, the newly added acid radicals in the red mud residue can be removed simultaneously, and the obtained sodium-free red mud residue can be subjected to subsequent resource utilization.

Description

Technical Field

[0001] The present invention belongs to the field of solid resource utilization, and relates to a method for bio-activating red mud to remove alkali and recover sodium. Background Art

[0002] Red mud is a solid waste generated in the alumina production process. At present, most of the treatment methods for red mud are dry stacking, which is extremely easy to cause serious environmental pollution and ecological damage. Therefore, the resource utilization of red mud restricts the sustainable development bottleneck of the alumina industry and deserves high attention.

[0003] At present, the most extensive method for red mud resource utilization is to use it as cement and subgrade materials. However, due to its high alkalinity and complex composition, it is difficult to be actually applied 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 existing in the solid phase. Since the bound alkalis mostly exist in the insoluble solid phase of red mud, higher concentration of acid is required to completely remove them. Chinese Patent CN112095009A discloses a process for recovering calcium, sodium, aluminum, iron, and rare earth chlorides by hydrochloric acid leaching of red mud. 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 its method. The process methods disclosed in the above Chinese patents all adopt high-concentration acid leaching treatment, which not only has high requirements for equipment but also has the problem of secondary pollution of waste liquid.

[0004] Bio-activation is a currently emerging green and environmentally friendly red mud treatment method, which 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 and has the advantages of spontaneity and environmental friendliness as a microbial treatment method. Chinese Patent CN107915386A discloses a bio-alkali removal method for red mud, which uses Aspergillus niger to remove alkali from red mud. However, mainly the Aspergillus niger and red mud are in the same system for alkali removal treatment, which will cause some red mud to adhere to the mycelium of Aspergillus niger and affect the subsequent utilization of red mud. And biochemical treatment mainly relies on acid production by microorganisms and extracellular polymers to leach red mud. Fermentation broth can be produced by Aspergillus niger, 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] How to develop a simple and efficient new technology for alkali removal treatment of red mud, widely utilize red mud resources, and solve the problem of large accumulation of red mud is of great significance. Summary of the Invention

[0006] In order to solve the problems existing in the prior art, the present invention provides a method for bio-activating red mud to recover sodium, thereby reducing acid consumption and realizing the harmlessness and resource utilization of red mud. The specific technical solutions are as follows:

[0007] A method for biologically activating red mud to remove alkali and recover sodium, comprising the following steps:

[0008] Comprising the following steps:

[0009] (1) Mix crushed red mud, desalted water, and a biological fermentation broth of Aspergillus niger with a pH less than 2.5. After stirring, perform solid-liquid separation to obtain a biochemical circulating liquid and biologically activated red mud;

[0010] (2) Mix the biologically activated red mud obtained in step (1) with a dilute acid solution, continuously stir and leach under heating conditions, and perform solid-liquid separation to obtain a sodium solution and red mud leaching residue;

[0011] (3) Thoroughly mix the red mud leaching residue obtained in step (2) with desalted water, stir and perform solid-liquid separation to obtain a sodium washing liquid and sodium-free red mud leaching residue;

[0012] (4) Thoroughly mix the sodium-free red mud residue obtained in step (3) with alkaline water, stir and perform solid-liquid separation to obtain a sodium salt solution and acid-free red mud leaching residue;

[0013] (5) Concentrate the sodium solution in step (2) and the sodium washing liquid obtained in step (3) to obtain solid sodium salts.

[0014] Furthermore, the preparation method of the Aspergillus niger biological fermentation broth in step (1) is to inoculate a flora mainly composed of Aspergillus niger in Czapek's medium or mold medium. The proportion of Aspergillus niger in the flora is 60-90%, and after culturing at 20-35°C for 7-14 days, filter the flora through solid-liquid separation to obtain an Aspergillus niger biological fermentation broth with a pH less than 2.5.

[0015] Furthermore, in step (1), the red mud includes Bayer red mud, sintering red mud, or combined process red mud.

[0016] Furthermore, in step (1), the red mud crushing means includes but is not limited to ball milling and roll crushing, and the crushing particle size of the red mud is 60-200 mesh.

[0017] Furthermore, in step (1), the mass ratio of the red mud, desalted water, and biological fermentation broth 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%-2.5%, the mass ratio of the biologically activated 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 obtained red mud leaching residue is subjected to at least one more dilute acid treatment.

[0019] Further, in the step (3), the mass ratio of the red mud leaching residue to the demineralized water is (3 - 4):20, the stirring time is 15 min to 12 h, and the obtained sodium red mud leaching residue is subjected to at least one more demineralized water treatment.

[0020] Further, in the step (4), the obtained acid - free red mud leaching residue is subjected to at least one more alkaline water treatment. The pH of the alkaline water is 8 - 11, the mass - to - volume ratio of the sodium - free red mud residue and the total amount of the alkaline water used is 1 kg:(1 L - 5 L), and the stirring time for each treatment is 15 min to 12 h.

[0021] Further, the step (1) is specifically as follows: The red mud is dried, crushed, ground, and then sieved through a 60 - mesh sieve. The red mud is mixed with a biological fermentation broth with a pH < 2.5 that has been cultured and fermented for 9 d. The mass ratio of the red mud to the fermentation broth is 10 g:15 g. After stirring evenly, it is left standing for half an hour, and then water is added to 100 g. It is placed in a water - bath constant - temperature oscillator and reacted at 25°C for 1 h. After the reaction, filtration is carried out to obtain biologically activated red mud and a biochemical circulating solution.

[0022] Further, the biochemical circulating solution in the step (1) is used as a solvent for preparing Czapek medium or mold medium after removing impurities; the low - sodium solution in the step (2) is used as water for preparing dilute acid. In the step (2), the heating methods include but are not limited to water - bath heating and steam heating; in the step (5), the concentration is carried out by membrane concentration or evaporation concentration or a combination of both.

[0023] The beneficial effects of the present invention are as follows:

[0024] In the method for biologically activating red mud to remove alkali and recover sodium of the present invention, biological activation is first used to pretreat the red mud. Biological activation improves the leaching rate of Na under the simultaneous action of biology and chemistry, reduces the consumption of acid, and the biological fermentation broth has no secondary pollution. On the basis of recovering sodium, the newly added acid radicals in the red mud residue can be removed simultaneously, and the obtained sodium - free red mud residue can be used for subsequent resource utilization. Description of the Drawings

[0025] Figure 1 is the process flow chart of the method for biologically activating red mud to remove alkali and recover sodium of the present invention;

[0026] Figure 2 is the EDS test chart of the red mud and the leaching residue without newly added acid radicals in Example 1. Detailed Embodiments

[0027] For the instruments, reagents, materials, etc. involved in the following embodiments, unless otherwise specified, they are all conventional instruments, reagents, materials, etc. existing in the prior art and can be obtained through regular commercial channels. For the experimental methods, detection methods, etc. involved in the following embodiments, unless otherwise specified, they are all conventional experimental methods, detection methods, etc. existing in the prior art.

[0028] In the following examples and comparative examples of the present invention:

[0029] Desalted water is used.

[0030] The red mud used is from the Bayer red mud of Shandong Xinfa Group, and the contents of the three main metal elements of Na, Fe, and Al are 5.78%, 20.29%, and 9.67% respectively.

[0031] The biological fermentation broth used is Aspergillus niger biological fermentation broth. The preparation method is to inoculate the flora mainly composed of Aspergillus niger in Czapek medium or mold medium. The proportion of Aspergillus niger in the flora is 60 - 90%. After culturing at 20 - 35°C for 7 - 14 days, the flora is filtered by solid-liquid separation to obtain Aspergillus niger biological fermentation broth with a pH less than 2.5.

[0032] The dilute salt used is dilute hydrochloric acid, and the mass concentration of the concentrated hydrochloric acid used to prepare the dilute hydrochloric acid is 37%. Dilute sulfuric acid or dilute nitric acid can also be used.

[0033] Example 1

[0034] As Figure 1 shown, a method for biological activation of red mud to remove alkali and recover sodium includes the following steps:

[0035] (1) Dry, crush, grind the red mud and then pass it through a 60-mesh sieve. Mix the red mud with the biological fermentation broth with a pH < 2.5 that has been cultured and fermented for 9 days. The mass ratio of red mud to fermentation broth is 10 g:15 g, and then add water to 100 g. Place it in a water bath constant temperature oscillator and react at 25°C for 2 h; after the reaction, filter to obtain biologically activated red mud and biochemical circulating liquid;

[0036] (2) Mix the biologically activated red mud with dilute acid with a mass concentration of 1.5%. In this example, dilute hydrochloric acid is used. Place it in a water bath constant temperature oscillator and react at 60°C for 1.5 h. The mass ratio of red mud to dilute acid is 20%. After the reaction, filter to obtain a sodium solution and red mud leaching residue; in this step, a small amount of multiple reactions are used. 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) Mix the red mud leaching residue obtained in step (2) with demineralized water. The mass ratio of the red mud leaching residue to demineralized water is 15%. React at 25 °C in a water bath constant temperature oscillator for 30 min. After solid-liquid separation, treat the obtained solid in the aforementioned manner once to obtain a sodium washing solution and a sodium-free red mud leaching residue;

[0038] (4) Mix the sodium-free red mud leaching residue obtained in step (3) with a solution adjusted to pH 10 using NaOH. React at 25 °C in a water bath constant temperature oscillator for 30 min. After solid-liquid separation, treat the obtained solid in the aforementioned manner once. The mass-volume ratio of the total amount of the sodium-free red mud residue and the NaOH solution is 1 kg: 3 L to obtain a sodium salt solution and an acid radical-free red mud leaching residue;

[0039] (5) After membrane concentration of the sodium solution in step (2) and the sodium washing solution obtained in step (3), evaporate the concentrated solution to obtain a sodium salt solid.

[0040] Example 2

[0041] As Figure 1 shown, a method for biological activation of red mud to remove alkali and recover sodium includes the following steps:

[0042] (1) Dry, crush, grind the red mud and then pass it through a 60-mesh sieve. Mix the red mud with a biological fermentation broth with a pH < 2.5 that has been cultured and fermented for 7 d. The mass ratio of the red mud to the fermentation broth is 10 g: 20 g, and then add water to 100 g. Place it in a water bath constant temperature oscillator and react at 25 °C for 1.5 h; after the reaction, filter to obtain biologically activated red mud and a biochemical circulating solution;

[0043] (2) Mix the biologically activated red mud with a dilute acid with a mass concentration of 1.2%. In this example, dilute hydrochloric acid is used. Place it in a water bath constant temperature oscillator and react at 60 °C for 1.5 h. The mass ratio of the red mud to the dilute acid is 20%. After the reaction, filter to obtain a sodium solution and a red mud leaching residue; in this step, a small amount of reaction is carried out multiple times. In this step, the dilute acid is initially prepared by mixing water and concentrated acid. When a sodium solution is produced, the dilute acid is prepared with the sodium solution to achieve the effect of enriching sodium salts;

[0044] (3) Mix the red mud leaching residue obtained in step (2) with demineralized water. The mass ratio of the red mud leaching residue to demineralized water is 20%. React at 25 °C in a water bath constant temperature oscillator for 1 h. After solid-liquid separation, treat the obtained solid in the aforementioned manner once to obtain a sodium washing solution and a sodium-free red mud leaching residue;

[0045] (4) Mix the residue of sodium-free red mud obtained in step (3) with a solution adjusted to pH 10 using NaOH, react at 25 °C for 30 min in a water bath thermostatic oscillator, after solid-liquid separation, treat the obtained solid in the aforementioned manner once, and the mass-volume ratio of the total usage of sodium-free red mud residue and NaOH solution is 1 kg: 3 L to obtain a sodium salt solution and an acid-free red mud leaching residue;

[0046] (5) After membrane concentration of the sodium solution in step (2) and the sodium washing solution obtained in step (3), evaporate the concentrated solution to obtain a sodium salt solid.

[0047] Example 3

[0048] As Figure 1 shown, a method for biological activation of red mud to remove alkali and recover sodium includes the following steps:

[0049] (1) Dry, crush, grind the red mud and then pass it through a 60-mesh sieve, mix the red mud with a biological fermentation broth with a pH < 2.5 that has been cultured and fermented for 9 days, the mass ratio of red mud to fermentation broth is 10 g: 15 g, then add water to 100 g, place it in a water bath thermostatic oscillator, and react at 25 °C for 2 h; after the reaction, filter to obtain biologically activated red mud and a biochemical circulating solution;

[0050] (2) Mix the biologically activated red mud with a dilute acid with a mass concentration of 1.5%. In this example, dilute hydrochloric acid is used. Place it in a water bath thermostatic oscillator and react at 60 °C for 2 h. The mass ratio of red mud to dilute acid is 20%. After the reaction, filter to obtain a sodium solution and a red mud leaching residue; in this step, a small amount of reaction is carried out multiple times. In this step, the dilute acid is initially prepared by mixing 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) Mix the red mud leaching residue obtained in step (2) with demineralized water, the mass ratio of the red mud leaching residue to demineralized water is 20%, react at 25 °C for 30 min in a water bath thermostatic oscillator, after solid-liquid separation, treat the obtained solid in the aforementioned manner twice to obtain a sodium washing solution and a sodium-free red mud leaching residue;

[0052] (4) Mix the sodium-free red mud leaching residue obtained in step (3) with a solution adjusted to pH 10 using NaOH, react at 25 °C for 1 h in a water bath thermostatic oscillator, after solid-liquid separation, treat the obtained solid in the aforementioned manner twice, and the mass-volume ratio of the total usage of sodium-free red mud residue and NaOH solution is 1 kg: 3 L to obtain a sodium salt solution and an acid-free red mud leaching residue;

[0053] (5) After membrane concentration of the sodium solution in step (2) and the sodium washing solution obtained in step (3), evaporate the concentrated solution to obtain a sodium salt solid.

[0054] Example 4

[0055] As Figure 1 shown, a method for bio-activating red mud to remove alkali and recover sodium includes the following steps:

[0056] (1) Dry, crush, grind the red mud and then pass it through a 60-mesh sieve. Mix the red mud with a bio-fermentation liquid that has been cultured and fermented for 9 days and has a pH < 2.5. The mass ratio of red mud to fermentation liquid is 10 g:15 g. After stirring evenly, let it stand for half an hour, then add water to 100 g, place it in a water bath constant temperature oscillator, and react at 25 °C for 1 h. After the reaction, filter to obtain bio-activated red mud and biochemical circulating liquid. First, fully mix the red mud and the fermentation liquid and let it stand, so that the fermentation liquid can penetrate the red mud first, and then add a large amount of water to dilute the red mud, so that it can be better oscillated and stirred in the oscillator, making the bio-fermentation liquid react better with the red mud and shortening the overall reaction time.

[0057] (2) Mix the bio-activated red mud with a dilute acid with a mass concentration of 1.5%. In this example, dilute hydrochloric acid is used. Place it in a water bath constant temperature oscillator and react at 60 °C for 1.5 h. The mass ratio of red mud to dilute acid is 20%. After the reaction, filter to obtain a sodium solution and red mud leaching residue. In this step, a small amount of acid is added multiple times. In this step, the dilute acid is initially prepared by mixing water and concentrated acid. When the sodium solution is produced, the dilute acid is prepared with the sodium solution to achieve the effect of enriching sodium salts.

[0058] (3) Mix the red mud leaching residue obtained in step (2) with demineralized water. The mass ratio of the red mud leaching residue to demineralized water is 15%. React in a water bath constant temperature oscillator at 25 °C for 30 min. After solid-liquid separation, treat the obtained solid in the aforementioned manner once to obtain a sodium washing liquid and a sodium-free red mud leaching residue.

[0059] (4) Mix the sodium-free red mud leaching residue obtained in step (3) with a solution adjusted to pH 10 with NaOH. React in a water bath constant temperature oscillator at 25 °C for 30 min. After solid-liquid separation, treat the obtained solid in the aforementioned manner once. The mass-volume ratio of the total amount of sodium-free red mud residue and NaOH solution is 1 kg:3 L to obtain a sodium salt solution and an acid-free red mud leaching residue.

[0060] (5) After membrane concentration of the sodium solution in step (2) and the sodium washing liquid obtained in step (3), evaporate the concentrated liquid to obtain sodium salt solids.

[0061] Comparative Example 1

[0062] A method for bio-activating red mud to remove alkali and recover sodium includes the following steps:

[0063] (1) The red mud is dried, crushed, ground, and then sieved through a 60-mesh sieve. It is mixed with dilute acid with a mass concentration of 2.3%. In this comparative example, dilute hydrochloric acid is used. It is placed in a water bath thermostatic oscillator and reacted at 60 °C for 2 h. The mass ratio of red mud to dilute acid is 20%. After the reaction, filtration is carried out to obtain a sodium solution containing sodium salts and a leaching residue; the sodium solution is used to prepare dilute acid (treated in the same way as in Example 1) to achieve the effect of enriching sodium salts;

[0064] (2) The leaching residue obtained in step (1) is mixed with demineralized water. The mass ratio of the leaching residue to demineralized water is 20%. It is reacted in a water bath thermostatic oscillator at 25 °C for 1 h. After solid-liquid separation, the solid is treated in the aforementioned manner 3 times repeatedly to obtain a sodium salt washing solution and a sodium-free red mud leaching residue;

[0065] (3) The sodium-free red mud leaching residue obtained in step (2) is mixed with a solution adjusted to pH 10 with NaOH. It is reacted in a water bath thermostatic oscillator at 25 °C for 1 h. After solid-liquid separation, the solid is treated in the aforementioned manner 3 times repeatedly. The mass-volume ratio of the total amount of the sodium-free red mud residue and the NaOH solution is 1 kg: 3 L to obtain a sodium salt solution and an acid radical-free red mud residue.

[0066] Comparative Example 2

[0067] A method for biologically activating and de-alkalizing red mud and recovering sodium includes the following steps:

[0068] (1) The red mud is dried, crushed, ground, and then sieved through a 60-mesh sieve. The red mud is mixed with a biological fermentation broth with a pH < 2.5 that has been cultured and fermented for 9 d. The mass ratio of red mud to fermentation broth is 10 g: 15 g, and then water is added to 100 g. It is placed in a water bath thermostatic oscillator and reacted at 25 °C for 2 h; after the reaction, filtration is carried out to obtain biologically activated red mud and a biochemical circulating solution;

[0069] (2) The biologically activated red mud obtained in step (1) is mixed with demineralized water. The mass ratio of the biologically activated red mud to demineralized water is 20%. It is reacted in a water bath thermostatic oscillator at 25 °C for 1 h. After solid-liquid separation, the solid is treated in the aforementioned manner 3 times repeatedly to obtain a sodium washing solution and a sodium-free red mud leaching residue;

[0070] The Na ion content in the solution after the reaction in each step in the examples and comparative examples is measured, and the final obtained leaching residue is digested to test the Na content, and the pH of the leaching residue is 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 following table.

[0071] EDS testing is carried out on the red mud and the acid radical-free leaching residue in Example 1. The results are shown in Figure (2). The Na element content shows a significant decrease, and the Fe and Si elements that are concerned in resource utilization do not show obvious changes. The percentages in the following table all 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 the biochemical fermentation broth in the present invention, the Na leaching rate is higher, the Na content in the leaching residue is lower, and the acid consumption is effectively reduced to achieve a higher Na leaching rate and the de-alkalization effect. In Comparative Example 1, inorganic acid was not used for leaching, and the Na element leaching rate was only 54.72%. After washing, the pH of the red mud reached 8.28, indicating that the chemically bound alkali in the solid phase was not effectively leached. In Comparative Example 2, the alkali solution with a pH of 10 was not used for washing, and the acid radical content in the leaching residue was as high as 0.24%, indicating that the alkali solution effectively removed the acid radicals in the leaching residue.

[0074] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for biological activation of red mud to remove alkali and recover sodium, characterized in that, It includes the following steps: (1) Mix the red mud after crushing, desalted water, and Aspergillus niger biological fermentation broth with a pH less than 2.

5. After stirring, perform solid-liquid separation to obtain a biochemical circulating liquid and biologically activated red mud; (2) Mix the biologically activated red mud obtained in step (1) with a dilute acid solution, continuously stir and leach under heating conditions, and perform solid-liquid separation to obtain a sodium solution and red mud leaching residue; (3) Thoroughly mix the red mud leaching residue obtained in step (2) with desalted water, perform solid-liquid separation after stirring to obtain a sodium washing liquid and sodium-free red mud leaching residue; (4) Thoroughly mix the sodium-free red mud residue obtained in step (3) with alkaline water, perform solid-liquid separation after stirring to obtain a sodium salt solution and acid-free red mud leaching residue; (5) Concentrate the sodium solution in step (2) and the sodium washing liquid obtained in step (3) to obtain solid sodium salts; The preparation method of the Aspergillus niger biological fermentation broth in step (1) is to inoculate a flora mainly composed of Aspergillus niger in Czapek medium or mold medium. The proportion of Aspergillus niger in the flora is 60-90%. After culturing at 20-35 °C for 7-14 d, filter the flora through solid-liquid separation to obtain an Aspergillus niger biological fermentation broth with a pH less than 2.5; In step (2), the mass concentration of the dilute acid is 1% - 2.5%, the mass ratio of the biologically activated red mud to the dilute acid solution is 1:5, the stirring time is 15 min - 12 h, the stirring temperature is 55-60 °C, and the obtained red mud leaching residue is subjected to at least one more dilute acid treatment.

2. The method for biological activation of red mud to remove alkali and recover sodium according to claim 1, characterized in that, In step (1), the red mud includes Bayer process red mud, sintering process red mud, or combined process red mud.

3. The method for biological activation of red mud to remove alkali and recover sodium according to claim 1, characterized in that, In step (1), the red mud crushing means includes ball milling or roll crushing, and the crushing particle size of the red mud is 60-200 mesh.

4. The method for bio-activating red mud to remove alkali and recover sodium according to claim 1, wherein, In step (1), the mass ratio of the red mud, desalted water, and biological fermentation broth is 10:(70-75):(15-20), and the stirring time is 15 min - 12 h.

5. The method for biological activation of red mud to remove alkali and recover sodium according to claim 1, characterized in that, In step (3), the mass ratio of the red mud leaching residue to desalted water is (3-4):20, the stirring time is 15 min - 12 h, and the obtained sodium-free red mud leaching residue is subjected to at least one more desalted water treatment.

6. The method for bio-activating red mud to remove alkali and recover sodium according to claim 1, wherein In step (4), the obtained acid-free red mud leaching residue is subjected to at least one more alkaline water treatment. The pH of the alkaline water is 8-11, the mass-volume ratio of the total amount of the sodium-free red mud residue and the alkaline water is 1 kg:(1L - 5L), and the stirring time for each treatment is 15 min - 12 h.

7. The method for biological activation of red mud for de-alkalization and sodium recovery according to claim 1, wherein Step (1) is specifically: Dry, crush, and grind the red mud, then pass it through a 60-mesh sieve. Mix the red mud with a biological fermentation broth with a pH < 2.5 that has been cultured and fermented for 9 d. The mass ratio of the red mud to the fermentation broth is 10 g:15 g. Stir evenly and let it stand for half an hour, then add water to 100 g, place it in a water bath constant temperature oscillator, and react at 25 °C for 1 h; After the reaction, filter to obtain biologically activated red mud and a biochemical circulating liquid.

8. The method for bio-activating red mud to remove alkali and recover sodium according to claim 2, characterized in that, The biochemical circulating liquid in the step (1), after removing impurities, is used as a solvent for preparing Czapek medium or mold medium; in the step (2), the heating method includes water bath heating or steam heating; in the step (5), membrane concentration or evaporation concentration or a combination of both is used for concentration.

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