A method for soilizing biphase reaction red mud and application thereof

Abstract

The application discloses a kind of double-phase reaction red mud soilization method and application, it is related to industrial solid waste resource and soil engineering technical field, including the following steps: step one: red mud is input into spiral reactor and carries out high solid-liquid ratio reaction with dilute sulfuric acid;Step two: the red mud after reaction is sent into reaction tank gelation and obtains dealkalization gel red mud;Step three: the dealkalization gel red mud obtained is filtered by filter press and is stirred into biomass waste residue and organic fertilizer;Step four: the dealkalization gel red mud stirred into biomass waste residue and organic fertilizer is prepared into crop planting matrix.The double-phase reaction red mud soilization method provided in the application solves the triple problems of incomplete dealkalization of red mud, poor soil physical and chemical properties and poor multi-crop adaptability.

Description

Technical Field

[0001] This invention relates to the fields of industrial solid waste resource utilization and soil engineering technology, and in particular to a two-phase reaction red mud soilification method and its application. Background Technology

[0002] Red mud, a major waste product of the alumina industry, has accumulated to billions of tons globally. Its strong alkalinity (pH often reaching 10-13) is the core constraint on its resource utilization. Existing technologies have significant limitations: water washing requires massive amounts of water resources and can only remove surface free alkali, leaving deep-seated bound alkali (such as sodalite and nepheline) residues that cause pH rebound; biological methods rely on microbial metabolic dealkalization, with reaction cycles lasting weeks or even months, making it difficult to meet the needs of continuous industrial production; traditional acid leaching methods often use low-solids systems (solid-liquid ratio ≤ 3:1, where the solid-liquid ratio is the ratio of solid mass (g) to liquid volume (mL), resulting in low equipment utilization and the formation of rigid agglomerates between red mud particles after acid leaching, leading to soil compaction, poor aeration, and inability to be directly used for crop cultivation.

[0003] The dealkali removal method disclosed in Chinese patent CN119138299A can simultaneously remove alkali and soil, but it relies on calcium nitrate-citric acid composite dealkali removal liquid, which has high raw material costs and a solid-liquid ratio as low as 1:3-6, resulting in high energy consumption for subsequent dehydration.

[0004] High-biomass crops such as sugarcane and forage grass have stringent requirements for soil water retention capacity, aeration, and pH stability. Currently, no technology can simultaneously solve the triple challenges of incomplete red mud dealkalization, poor soil physicochemical properties, and poor compatibility with multiple crops. Therefore, developing red mud utilization technologies that combine efficient dealkalization, soil improvement, and good crop compatibility has significant innovative value. Summary of the Invention

[0005] The purpose of this invention is to provide a two-phase reaction red mud soilification method and its application, which solves the triple problem mentioned in the background art that there is currently no technology that can simultaneously solve the problems of incomplete red mud dealkalization, poor soil physicochemical properties, and poor adaptability to multiple crops.

[0006] The present invention adopts the following technical solution:

[0007] This invention discloses a method for converting red mud into soil through a two-phase reaction, comprising the following steps:

[0008] Step 1: Red mud is added to a spiral reactor and reacted with dilute sulfuric acid in a high solid-liquid ratio reaction;

[0009] Step 2: The reacted red mud is sent into a reaction tank for gelation to obtain dealkalized gel red mud;

[0010] Step 3: After the obtained dealkali-reduced gel red mud is filtered through a filter press, it is mixed with biomass waste and organic fertilizer;

[0011] Step 4: Prepare crop planting substrate by mixing dealkalized gel red mud with biomass waste residue and organic fertilizer.

[0012] Preferably, the concentration of dilute sulfuric acid in step one is 4%-6%.

[0013] Preferably, in step one, the solid-liquid ratio of the red mud to dilute sulfuric acid in the spiral reactor is 1:1 to 1:1.5, and the temperature is 30-35℃.

[0014] The reaction time of the red mud and dilute sulfuric acid in the spiral reactor in step one is 5-15 minutes.

[0015] In step one, the pH at the end point of the spiral reactor reaction is controlled between 3.0 and 5.5.

[0016] Preferably, calcium carbonate is added to the reaction tank in step two, and the mass of calcium carbonate added accounts for 0.5%-1% of the mass of red mud.

[0017] Preferably, in step three, the filtrate produced by the filter press is diverted to a dilution tank for holding dilute sulfuric acid, and participates in the reaction in step one again together with the dilute sulfuric acid;

[0018] The biomass waste in step three can be any one or more of sugarcane bagasse, fallen leaves, and rice husks, wherein the amount of biomass waste added is 0.5%-1% of the mass of red mud;

[0019] The amount of organic fertilizer added in step three is 2%-4% of the mass of the red mud.

[0020] Preferably, the spiral reactor in step one includes a shell, a feed spiral shaft rotatably connected inside the shell, a red mud inlet on the upper side of one end of the shell, a red mud outlet on the lower side of the other end of the shell, and a feeding section, a reaction section, and a homogenization section arranged sequentially inside the shell from the red mud inlet to the red mud outlet.

[0021] The feed section is provided with a sulfuric acid spray pipe inside the housing, and the feed screw shaft corresponding to the feed section is provided with double-pitch composite blades.

[0022] The reaction section is provided with a sulfuric acid spray pipe inside the shell corresponding to the reaction section, and staggered pitch blades are provided on the feed screw shaft corresponding to the reaction section.

[0023] The homogenization section is provided with a sulfuric acid spray nozzle inside the housing, and the feed screw shaft corresponding to the homogenization section is provided with pitch decreasing blades.

[0024] Preferably, the proportions of the length of the spiral reactor occupied by the feeding section, the reaction section, and the homogenization section are 1 / 4, 2 / 4, and 1 / 4, respectively.

[0025] The amount of acid sprayed from the sulfuric acid nozzle in the feeding section is 20% of the total acid amount, the amount of acid sprayed from the sulfuric acid nozzle in the reaction section is 60% of the total acid amount, and the amount of acid sprayed from the sulfuric acid nozzle in the homogenization section is 20% of the total acid amount.

[0026] Preferably, the shell is inclined downwards from the red mud inlet to the red mud outlet, with an inclination angle of 3°-5°.

[0027] Preferably, the dual-pitch composite blade, the staggered pitch blade, and the pitch decreasing blade are all provided with circular holes;

[0028] The pitch of the staggered pitch blades alternately increases or decreases by 8%-12%;

[0029] The pitch of the pitch-decreasing blades gradually decreases by 8%-10%.

[0030] Preferably, a circulating water pipe is rotatably connected inside the feed screw shaft.

[0031] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0032] The biphasic reaction red mud soilification method provided in this invention has the following beneficial effects:

[0033] (1) Thorough dealkali removal from red mud: Through the innovative spiral reactor, free alkali is removed in a short reaction time with high solid content, while the bound alkali is removed in the subsequent reaction tank, which has the advantage of thorough dealkali removal;

[0034] (2) Improve soil physical and chemical properties: by dissolving aluminum, silicon and other compounds in red mud, and using the combined alkali in the subsequent reaction tank to adjust the pH, and at the same time generating aluminum-silicon composite gel under the action of calcium carbonate, the aluminum-silicon composite gel spontaneously constructs a porous network structure, thereby optimizing its water retention and air permeability, and reducing compaction, etc.

[0035] (3) Multi-crop adaptability: Under the premise of thorough dealkalization and improvement of soil physical and chemical properties, the nutrients in red mud soil are enriched by mixing in biomass waste such as sugarcane bagasse, dead leaves, and rice husks, thereby adapting it to the planting of multiple crops;

[0036] (4) Beneficial effects of the spiral reactor: The spiral reactor in this invention is structurally upgraded, with a focus on optimizing the blade system and the acid dispersion system. This not only ensures the uniformity of red mud crushing and reaction stability, but also efficiently removes free alkali and simultaneously promotes aluminum and silicon dissolution. The key is the high solid-liquid reaction, which increases the concentration of aluminum and calcium ions and makes it easier to form a gel. The generated aluminum-silicon composite gel spontaneously constructs a porous network structure, thereby significantly optimizing its water retention and air permeability. This provides an efficient and environmentally friendly solution for the agricultural resource utilization of red mud and provides a high-quality pretreatment guarantee for the preparation of crop planting substrate. Attached Figure Description

[0037] The present invention will be further described below with reference to the accompanying drawings.

[0038] Figure 1 This is a process route diagram of the two-phase reaction red mud soilification method of the present invention in Example 1;

[0039] Figure 2 This is a schematic diagram of the spiral reactor structure in the two-phase reaction red mud soilification method of the present invention in Example 1;

[0040] Figure 3 This is a comparison diagram of the water retention performance of the biphase reaction red mud soilification method of the present invention in Example 1;

[0041] Figure 4 This is a comparison diagram of the structure of dried dealkalized gel red mud and ordinary dealkalized red mud in Example 1;

[0042] Figure 5 This is an illustration of the effect of planting sugarcane in dealkali-removed gel red mud in Example 1;

[0043] Figure 6 This is a process route diagram of the two-phase reaction red mud soilification method of the present invention in Example 2.

[0044] Explanation of reference numerals in the attached diagram: 1. Red mud inlet; 2. Shell; 3. Feed screw shaft; 4. Red mud outlet; 5. Circulating water pipe; 6. Feed section; 6-1. Sulfuric acid spray nozzle in the feed section; 6-2. Double-pitch composite blade; 7. Reaction section; 7-1. Sulfuric acid spray nozzle in the reaction section; 7-2. Staggered pitch blade; 8. Homogenization section; 8-1. Sulfuric acid spray nozzle in the homogenization section; 8-2. Pitch decreasing blade; 9. Circular hole. Detailed Implementation

[0045] To make the technical problems, technical solutions, and beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0046] like Figure 1 As shown, this embodiment discloses a two-phase reaction red mud soilification method and its application, including the following steps:

[0047] Step 1: Red mud is added to a spiral reactor and reacted with dilute sulfuric acid at a high solid-liquid ratio; the concentration of dilute sulfuric acid is 4%-6%.

[0048] The solid-liquid ratio of the reaction between red mud and dilute sulfuric acid in the spiral reactor is 1:1-1:1.5, and the temperature is 30-35℃.

[0049] The reaction time of red mud and dilute sulfuric acid in the spiral reactor is 5-15 minutes.

[0050] The pH value at the end point of the spiral reactor reaction is controlled between 3.0 and 5.5.

[0051] Step 2: Add calcium carbonate to the reaction tank, and continuously feed the reacted red mud into the reaction tank for gelation to obtain dealkalized gel red mud;

[0052] The mass of calcium carbonate added to the reaction tank is 0.5%-1% of the mass of the red mud;

[0053] Step 3: After the obtained dealkali-reduced gel red mud is filtered through a filter press, it is mixed with biomass waste and organic fertilizer;

[0054] The biomass waste residue can be any one or more of sugarcane bagasse, fallen leaves, and rice husks, and the amount of biomass waste residue added is 0.5%-1% of the mass of red mud;

[0055] The amount of organic fertilizer added is 2%-4% of the mass of red mud.

[0056] Step 4: Prepare crop planting substrate by mixing dealkalized gel red mud with biomass waste residue and organic fertilizer.

[0057] like Figure 2 As shown, this embodiment also discloses the aforementioned spiral reactor. Addressing the problems of feed accumulation, axial backmixing, and localized over-acidity inherent in traditional spiral reactors, this invention improves upon the traditional spiral reactor. The spiral reactor in this invention adopts a horizontal cylindrical structure, with the entire structure inclined at an angle of 3°-5° from the feed inlet to the discharge outlet, achieving material self-flow.

[0058] The spiral reactor includes a shell 2, inside which a feed spiral shaft 3 is rotatably connected. A red mud inlet 1 is provided on the upper side of one end of the shell 2, and a red mud outlet 4 is provided on the lower side of the other end of the shell 2. Inside the shell 2, from the red mud inlet 1 to the red mud outlet 4, there are a feeding section 6, a reaction section 7, and a homogenization section 8 arranged sequentially. The proportions of the length of the spiral reactor occupied by the feeding section 6, the reaction section 7, and the homogenization section 8 are 1 / 4, 2 / 4, and 1 / 4, respectively.

[0059] The housing 2 corresponding to the feeding section 6 is equipped with a feeding section sulfuric acid spray pipe 6-1, and the amount of acid sprayed by the feeding section sulfuric acid spray pipe 6-1 is 20% of the total acid amount; the feeding screw shaft 3 corresponding to the feeding section 6 is equipped with a double-pitch composite blade 6-2, which is a blade with adjacent blade pitches of a, b, a, b arranged alternately, where a is not equal to b, the large pitch blade plays the role of conveying, and the small pitch blade plays the role of crushing.

[0060] The housing 2 corresponding to reaction section 7 is equipped with a sulfuric acid spray nozzle 7-1. The amount of acid sprayed by the sulfuric acid spray nozzle 7-1 is 60% of the total acid. The feed screw shaft 3 corresponding to reaction section 7 is equipped with staggered pitch blades 7-2, wherein the pitch of the staggered pitch blades 7-2 alternately increases or decreases by 8%-12%. Specifically, taking an 8% increase or decrease as an example, the pitch of adjacent blades is a, a 92%, a, a 92% of the arrangement. The staggered pitch blades 7-2 design creates a periodic compression-release cycle, which promotes solid-liquid exchange.

[0061] The homogenization section 8 is housed within the casing 2, which contains a homogenization section sulfuric acid spray nozzle 8-1. The amount of acid sprayed from the homogenization section sulfuric acid spray nozzle 8-1 is 20% of the total acid volume. The feed screw shaft 3 corresponding to the homogenization section 8 is equipped with pitch-decreasing blades 8-2, wherein the pitch of the pitch-decreasing blades 8-2 gradually decreases by 8%-10%. Taking an 8% decrease as an example, the pitches of adjacent blades are a, a... 92%, a 84%, a The arrangement of 76% and so on, in this way, promotes the homogenization of solid and liquid.

[0062] In this embodiment, the double-pitch composite blade 6-2, the staggered pitch blade 7-2, and the pitch decreasing blade 8-2 are all provided with round holes 9 to facilitate the entry of liquid sulfuric acid into the red mud, while also enhancing the uniformity of solid-liquid mixing.

[0063] The feed section sulfuric acid spray pipe 6-1, the reaction section sulfuric acid spray pipe 7-1, and the homogenization section sulfuric acid spray pipe 8-1 are connected to an external dilution tank. The dilution tank contains sulfuric acid solution, and dilute sulfuric acid is pumped into these three pipes using an external pump for spraying. The feed section sulfuric acid spray pipe 6-1, the reaction section sulfuric acid spray pipe 7-1, and the homogenization section sulfuric acid spray pipe 8-1 all use spray heads of the same specification (with the same spray flow rate). The ratio of the number of spray heads in each of these pipes is 1:3:1, ensuring that the amount of acid sprayed within the same time period is 20%, 60%, and 20%, respectively.

[0064] In this embodiment, a circulating water pipe 5 is rotatably connected to the feed screw shaft 3 via bearings. The inlet of the circulating water pipe 5 is on the side of the red mud outlet 4, and the outlet is on the side of the red mud inlet 1. The circulating water temperature is 30-35℃. The circulating water injected into the circulating water pipe 5 serves a cooling function. The end of the feed screw shaft 3 located outside the housing 2 is driven to rotate by an external drive system (such as by connecting it to a motor via a synchronous pulley).

[0065] In this embodiment, a pH online monitoring probe is installed inside the shell 2 at one end near the red mud outlet 4 to monitor the pH value at the reaction endpoint in real time.

[0066] In this embodiment, in step one, the blocky red mud after pressure filtration enters the shell 2 of the spiral reactor through the red mud inlet 1. It is rapidly broken down by the action of the double-pitch composite blades 6-2, the staggered pitch blades 7-2, and the decreasing pitch blades 8-2. Simultaneously, a 5% (w / w) dilute sulfuric acid solution is added at a solid-liquid ratio of 1:1. The acid is sprayed according to the design: 20% from the feed section sulfuric acid spray nozzle 6-1, 60% from the reaction section sulfuric acid spray nozzle 7-1, and 20% from the homogenization section sulfuric acid spray nozzle 8-1. The reaction is carried out at 35℃ and 180 r / min for 10 minutes, with the final pH stabilizing at 5.0. At this stage, the free alkali removal rate reaches 96%, the aluminum dissolution rate is 62%, and the silicon dissolution rate is 48%.

[0067] Red mud mainly consists of 1%-3% free alkali (such as NaOH), 5%-10% structurally bound alkali (such as sodalite, nepheline and other aluminosilicate minerals), and a large amount of amphoteric metal oxides (such as... 10-20%, (7-20%). The reaction principle in this invention is as follows: dilute sulfuric acid first rapidly neutralizes the free alkali, then destroys the mineral lattice of the bound alkali, causing the alkali metal ions to dissolve and be neutralized. Simultaneously, and crucially, it converts the inert aluminum and silicon components into active ones. And silicate ions dissolve. This process not only generates soluble salts (such as...) This process achieves dealkalization and produces the aluminum-silicon composite gel precursor necessary for subsequent gelation.

[0068] Unlike traditional low solid-liquid ratio acid leaching methods, this invention uses a high solid-liquid ratio (1:1-1:1.5) to create a localized high ion concentration environment. Combined with the segmented acid addition design of the spiral reactor, it ensures efficient and uniform reaction, not only achieving thorough dealkali removal (free alkali removal rate of 96%), but more importantly, laying a solid foundation for the in-situ generation of aluminosilicate gel with a porous network structure in step two. This is the key chemical basis for solving soil compaction and improving water retention and air permeability in this invention, and it is also a significant feature that distinguishes it from simple dealkali removal technologies.

[0069] In step two, the red mud discharged from the spiral reactor is continuously fed into the reaction tank, and 0.8% calcium carbonate is added. The mixture is stirred and reacted at 35°C for 75 minutes. Utilizing the combined alkali slow-release effect, the pH rises to 7.3, and an aluminum-silicon composite gel is generated in situ, forming a stable porous network.

[0070] It should be noted that bound alkali refers to deeply bonded alkaline minerals (such as sodalite and nepheline) within the red mud. These differ from surface free alkali (such as NaOH) and are firmly bound within the red mud particles in a crystalline structure. These minerals slowly dissolve under natural conditions, releasing alkaline ions (such as...) This causes the pH value to gradually rise, a process known as the slow-release effect. This invention transforms this "negative effect" into an advantage by actively utilizing the slow-release properties of bound alkali during the gelation stage to achieve a self-recovery of pH, avoiding the use of external acid, while simultaneously promoting the formation of aluminosilicate gel and solving the problem of soil compaction.

[0071] It should be noted that in-situ generation refers to the technology of synthesizing the target product on-site using existing components within the reaction system, without the need for external pre-preparation or addition of finished substances. In this invention, it specifically refers to the direct formation of the aluminum-silicon composite gel within the red mud reaction tank, rather than pre-preparation followed by incorporation. Its core lies in utilizing the aluminum and silicon ions dissolved from the dealkali phase (products within the system) and the bound alkali's slow-release effect to autonomously polymerize into a gel network during pH recovery.

[0072] It should be noted that the added calcium carbonate ( The key reaction occurs between calcium carbonate and the red mud system after acid treatment in step one. The core of this process lies in using a neutralization reaction to achieve precise pH control and promote the formation of characteristic gel products. Specifically, calcium carbonate mainly reacts with the residual dilute sulfuric acid in the system (…). Neutralization reaction occurs:

[0073]

[0074] This reaction consumes the residual free acid, causing the system pH to controllably rise from an acidic environment (3.0-5.5) to near neutral (approximately 7.3). This pH shift is the key switch triggering subsequent gelation; under near-neutral conditions, the active components dissolved in step one (especially aluminum ions) can be released. ( ) and silicate ions no longer exist stably in solution, but instead cross-link in situ through co-precipitation and polymerization to form a hydrated aluminum silicate as the main component, with a small amount of calcium sulfate added. This is due to the unique "aluminum-silicon-calcium" composite gel network of gypsum crystal nuclei. The gel product exhibits a three-dimensional porous structure significantly different from simple dealkalized red mud or ordinary mixtures, such as... Figure 4As shown on the left, its spontaneously constructed loose framework is the fundamental reason for the excellent air permeability and anti-caking properties of the final matrix. Therefore, the addition of calcium carbonate in this invention is not a simple pH adjustment, but rather a creative transformation of harmful acid and alkali residues into components of a beneficial gel skeleton through a precise chemical reaction pathway. This process of product structure reconstruction through a specific chemical reaction sequence constitutes a significant distinguishing feature from existing technologies that only involve physical mixing or simple acid-base neutralization.

[0075] In step three, after the reaction in step two is complete, the mixture is fed into a filter press for solid-liquid separation. The filter cake is the dealkalized gel red mud. The filtrate is diverted to a dilution tank and mixed with sulfuric acid solution, which can then be returned to the system as a diluent. The dealkalized gel red mud is mixed with 1% sugarcane bagasse and 2% organic fertilizer to prepare a crop planting substrate.

[0076] In step four, after the crop planting substrate is completed, it is laid with a thickness of 35cm, and sugarcane, pasture, etc. are planted with a row spacing of 1.1m and a plant spacing of 0.22m, while maintaining the field water holding capacity at 50%.

[0077] like Figure 3 As shown, the water retention performance of dealkali-gelled red mud and ordinary dealkali-gelled red mud is compared at 40℃. The water retention capacity of dealkali-gelled red mud is better than that of ordinary dealkali-gelled red mud, which can improve the water retention capacity of sugarcane planting areas.

[0078] like Figure 4 As shown, the dried dealkalized gel red mud ( Figure 4 Left) and ordinary dealkalized red mud ( Figure 4 (Right) Comparison of effects: dried dealkalized gel red mud ( Figure 4 (Left) The interior is filled with a porous structure and has a softer texture, which can improve the ventilation and prevent compaction of sugarcane fields.

[0079] Example 2

[0080] like Figure 6 As shown, this embodiment, based on Embodiment 1, also adds dilute sulfuric acid to the reaction tank, and an online pH monitoring probe is installed on the reaction tank for pH monitoring. Simultaneously, an appropriate amount of calcium carbonate is added to adjust the pH value to 7.3, optimizing the formation of aluminosilicate gel, and extending the reaction time to 2.5 hours. The amount of dilute sulfuric acid added is determined by the pH monitoring probe value; that is, the added dilute sulfuric acid must be combined with the newly added calcium carbonate to adjust the pH value to 7.3. Other technical features in this embodiment are the same as in Embodiment 1.

[0081] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for converting red mud into soil using a two-phase reaction, characterized in that: Includes the following steps: Step 1: The red mud is added into the spiral reactor and reacted with dilute sulfuric acid; Step 2: The reacted red mud is sent into a reaction tank, where calcium carbonate is added to gel the mud to obtain dealkalized gel red mud. Step 3: After the obtained dealkalized gel red mud is filtered by a filter press, it is mixed with biomass waste and organic fertilizer; Step 4: Prepare crop planting substrate by mixing the dealkalized gel red mud with biomass waste residue and organic fertilizer; The spiral reactor includes a shell (2), a feed spiral shaft (3) rotatably connected inside the shell (2), a red mud inlet (1) on the upper side of one end of the shell (2), a red mud outlet (4) on the lower side of the other end of the shell (2), and a feed section (6), a reaction section (7), and a homogenization section (8) arranged sequentially inside the shell (2) from the red mud inlet (1) to the red mud outlet (4). The feed section (6) is provided with a sulfuric acid spray pipe (6-1) inside the housing (2) corresponding to the feed section (6), and a double-pitch composite blade (6-2) is provided on the feed screw shaft (3) corresponding to the feed section (6). The reaction section (7) is provided with a sulfuric acid spray pipe (7-1) inside the shell (2) corresponding to the reaction section (7), and the feed screw shaft (3) corresponding to the reaction section (7) is provided with staggered pitch blades (7-2). The pitch of the staggered pitch blades (7-2) alternately increases or decreases by A, and the value of A ranges from 8% to 12%. The homogenization section (8) is provided with a homogenization section sulfuric acid spray pipe (8-1) inside the shell (2), and the feed screw shaft (3) corresponding to the homogenization section (8) is provided with a pitch decreasing blade (8-2). The pitch of the pitch decreasing blade (8-2) gradually decreases according to B, and the value of B is 8%-10%. The double-pitch composite blade (6-2), the staggered pitch blade (7-2), and the pitch decreasing blade (8-2) are all provided with round holes (9).

2. The method for converting biphasic reactive red mud into soil according to claim 1, characterized in that: The concentration of dilute sulfuric acid in step one is 4%-6%.

3. The method for converting biphasic reactive red mud into soil according to claim 1, characterized in that: In step one, the solid-liquid ratio of the red mud to dilute sulfuric acid in the spiral reactor is 1:1 to 1:1.5, and the temperature is 30-35℃. The reaction time of the red mud and dilute sulfuric acid in the spiral reactor in step one is 5-15 minutes. In step one, the pH at the end point of the spiral reactor reaction is controlled between 3.0 and 5.

5.

4. The method for converting biphasic reactive red mud into soil according to claim 1, characterized in that: In step two, the amount of calcium carbonate added to the reaction tank is 0.5%-1% of the mass of the red mud.

5. The method for converting biphasic reactive red mud into soil according to claim 1, characterized in that: In step three, the filtrate produced by the filter press is diverted to a dilution tank for holding dilute sulfuric acid, and participates in the reaction in step one again together with the dilute sulfuric acid. The biomass waste in step three is any one or more of sugarcane bagasse, fallen leaves, and rice husks, wherein the amount of biomass waste added is 0.5%-1% of the mass of red mud; The amount of organic fertilizer added in step three is 2%-4% of the mass of the red mud.

6. The method for converting biphasic reactive red mud into soil according to claim 1, characterized in that: The proportions of the length of the spiral reactor occupied by the feeding section (6), the reaction section (7), and the homogenization section (8) are 1 / 4, 2 / 4, and 1 / 4, respectively. The amount of acid sprayed by the sulfuric acid nozzle (6-1) in the feeding section is 20% of the total acid amount, the amount of acid sprayed by the sulfuric acid nozzle (7-1) in the reaction section is 60% of the total acid amount, and the amount of acid sprayed by the sulfuric acid nozzle (8-1) in the homogenization section is 20% of the total acid amount.

7. The method for converting biphasic reactive red mud into soil according to claim 1, characterized in that: The shell (2) is inclined downward from the red mud inlet (1) to the red mud outlet (4) at an angle of 3°-5°.

8. The method for converting biphasic reactive red mud into soil according to claim 1, characterized in that: The feed screw shaft (3) is provided with a rotatingly connected circulating water pipe (5).

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