In-situ dealkalization and ecological matrix layer construction method for red mud storage yard

Abstract

The invention discloses an in-situ dealkalization and ecological matrix layer construction method for a red mud storage yard, and belongs to the field of solid waste recycling. A percolation and reflux reaction system integrating biological acid production, forced circulation neutralization and in-situ humic soil formation is constructed on the surface layer of the red mud storage yard; acidic leachate generated by oxidizing pyrite solid waste by using sulfur-oxidizing bacteria uniformly permeates and neutralizes the alkalinity of lower-layer red mud under forced reflux power; in combination with in-situ degradation of biomass waste, reagglomeration and physicochemical property curing of red mud particles are realized through subsequent stirring and mixing; according to the invention, the problems of non-uniform reaction, low efficiency and lack of organic matters in the traditional remediation are solved, and the ecological matrix improvement of the red mud under the condition of treating wastes with wastes is realized.

Description

Technical Field

[0001] This invention belongs to the field of ecological restoration engineering and solid waste resource utilization. Specifically, it relates to a method for in-situ dealkalization and construction of ecological matrix layer in red mud dumps. In particular, it relates to a method for using waste-to-waste treatment and biochemical enhancement processes to achieve in-situ and integrated deep dealkalization and soil structure reconstruction in highly alkaline red mud dumps, thereby constructing an ecological matrix layer for vegetation growth. Background Technology

[0002] Red mud is a highly alkaline industrial solid waste discharged during the extraction of alumina from bauxite. It accumulates in large quantities and occupies significant land resources. Red mud typically has a pH value above 10 and contains both free strong alkalis and structurally bound alkalis that are difficult to release. Its particles are extremely fine, with low porosity, making it prone to compaction. Furthermore, it is severely lacking in organic matter and available trace elements, making it unsuitable for supporting vegetation growth under natural conditions. Traditional methods for closing red mud tailings ponds often involve covering them with imported soil, which is costly and prone to causing secondary ecological damage due to the need for excavation. This method only provides physical isolation and does not eliminate the high alkalinity of the underlying red mud. Under capillary action, soluble salts and alkalis easily migrate upwards, leading to salinization of the cover layer. Therefore, directly utilizing red mud to construct a soil matrix layer is an effective way to reduce the ecological and environmental risks of mining areas and achieve comprehensive utilization of solid waste resources.

[0003] The method of neutralizing the alkalinity of red mud using acid-producing solid waste has been proposed and applied. The acid production from the weathering and oxidation of pyrite mining waste is prolonged, and co-treatment with red mud offers advantages in acid-base neutralization. However, existing co-treatment methods largely rely on simple physical stratification and natural heap leaching, which have significant engineering limitations. On the one hand, the acid production process of sulfur-oxidizing bacteria requires sufficient oxygen and suitable water circulation, but localized anaerobic conditions easily form within the heap under natural stacking, limiting the efficiency of biological oxidation. On the other hand, the extremely low permeability coefficient of red mud causes acid to easily find the path of least resistance, forming channels, resulting in highly uneven neutralization reactions. Conventional natural leaching lacks continuous fluid dynamics and cyclic mass transfer mechanisms, making it difficult for acid to break down the stable aluminosilicate structure within the red mud, leading to incomplete dealkalization and a high likelihood of alkalinity rebound later.

[0004] In the process of constructing the soil matrix of red mud, simple acid-base neutralization cannot fundamentally improve its physical structure. After dealkalization, the red mud remains powdery, extremely lacking in organic matter, and unable to form a water-stable aggregate structure that maintains water retention and aeration. Simply adding biomass waste, without a suitable degradation and composting environment and in-situ mechanical compounding mechanism, makes it difficult to efficiently transform it into a soil cementing agent. Existing technologies often separate the dealkalization process from the soil physicochemical structure reconstruction process, making it impossible to achieve thorough improvement of red mud within the same engineering cycle.

[0005] In summary, there is an urgent need in this field to develop an in-situ ecological restoration technology for red mud dumps, in order to overcome the internal mass transfer resistance and oxygen supply limitations of red mud, achieve long-lasting and uniform deep dealkalization, and reconstruct the soil aggregate structure through in-situ biochemical coupling, so as to completely transform the highly alkaline red mud into an ecological matrix layer that can support vegetation growth. Summary of the Invention

[0006] This invention provides a method for in-situ dealkalization and construction of an ecological matrix layer in red mud dumps. The surface of the red mud dump is transformed into a controllable infiltration and reflux bioreactor. Through the synergy of biological acid production, forced circulation mass transfer, and in-situ humification granulation, the problem of high alkalinity and poor structure of red mud is efficiently solved.

[0007] This invention is achieved through the following technical solution: A method for in-situ dealkalization and construction of an ecological matrix layer in red mud dumps, the specific steps of which are as follows: (1) Site preparation and active layer construction: Mechanically loosen the surface layer of the red mud dump area to be repaired to form a loosened red mud layer, and pre-bury a collection system at the bottom of the loosened red mud layer; Coarse waste material is laid on top of the red mud loosening layer to form a drainage and aeration layer, and an aeration system is evenly distributed inside the drainage and aeration layer. Above the drainage and aeration layer, an acid-producing and fertilizer-enriching active layer is laid, which is a mixture of solid waste from pyrite mining and beneficiation and crushed biomass waste. A water distribution system is installed at the top of the acid-producing and fertilizing active layer. A collection system pre-buried at the bottom of the red mud loosening layer is connected to the water distribution system through a pump to form a closed loop. The water distribution system includes multiple nozzles installed on the pipe. The aeration system inside the drainage aeration layer is connected to an air supply blower for uniform aeration; (2) Bio-chemical enhanced neutralization: The sulfur-oxidizing bacteria solution is injected into the acid-producing-fertilizing active layer through the top water distribution system to start the biological acid production process; oxygen-containing gas is introduced into the aeration system of the drainage aeration layer to make the gas evenly diffused throughout the entire pile layer and maintain a micro-oxygen environment. (3) Percolation-reflux circulation dealkalization: The sulfur-oxidizing bacteria in the bacterial solution oxidize the pyrite mining solid waste in the acid-fertilizing active layer under micro-oxygen environment. The resulting acidic leachate permeates into the drainage and aeration layer under gravity, and then continues to permeate downward into the red mud loosening layer. It undergoes a deep acid-base neutralization reaction with the alkaline substances inside the red mud. The leachate after the reaction is collected by the collection system pre-buried at the bottom of the red mud loosening layer, and the leachate is forced back to the water distribution system at the top for circulation leaching through the pumping circuit. (4) In-situ soil formation and matrix reconstruction: Once the pH value at the bottom of the red mud loosening layer has been monitored to remain stable at 7.0–9.0 for 72 consecutive hours, the circulating leaching and gas introduction are stopped. After the system is allowed to air dry naturally until the moisture content drops to 5%–45%, a mechanical device is used to deeply mix the acid-fertilizing active layer, the drainage aeration layer, and the dealkalized red mud loosening layer in situ. The humus produced by the degradation of biomass waste is used as a binder to form an ecological matrix layer with an aggregate structure by combining with the red mud mineral particles.

[0008] In step (1), the thickness of the red mud loosening layer is 10-100cm; the thickness of the drainage aeration layer is 10-50cm; and the thickness of the acid-fertilizing active layer is not less than 20cm.

[0009] In step (1), the coarse waste material includes coarse crushed stone waste, coarse coal gangue waste, etc.

[0010] In step (1), the solid waste from pyrite mining and beneficiation is one or more mixtures of tailings, gangue, smelting slag and other materials generated during mining and beneficiation; the main mineral of the solid waste from pyrite mining and beneficiation is solid waste of pyrite, in which the content of FeS2 exceeds 20%.

[0011] In step (1), the biomass waste includes one or more of sugarcane bagasse, peanut shells, walnut shells, and crop straw in any proportion. The particle size of the crushed biomass waste after sieving should be 5-10 mm.

[0012] In step (1), the volume ratio of pyrite mining solid waste to biomass waste in the acid-fertilizing active layer is 1 / 20 to 1 / 10.

[0013] In step (1), pH meters are installed at the bottom of the red mud loosening layer and inside the collection system.

[0014] In step (2), the sulfur-oxidizing bacterial solution is one of the following: *Thiobacillus acidophilus*, *Leptospira*, *Acidophilus*, *Sulphophyllum*, *Metrolactone*, *Acidophilus*, *Tylomycinus*, *Metrolactone*, *Acidophilus thermophilus*, *Isomycinus*, and *Sulphobicia*, or a mixture thereof in any proportion. Furthermore, the effective viable count in the mixed bacterial solution is ≥10. 6 cfu / mL, initial injection pH 1.0–5.0.

[0015] In step (2), the oxygen-containing gas is a mixed gas with an oxygen volume fraction of not less than 2%, and the mixed gas also contains other component gases such as nitrogen.

[0016] In step (3), after circulating the leachate until the pH value of the leachate is greater than 6.0, replace it with a new bacterial solution containing sulfur-oxidizing bacteria.

[0017] This invention achieves deep dealkalization and physical structure reconstruction of red mud through multiple couplings of bio-acid production, forced circulation mass transfer, and in-situ granulation of humic substances. Its principle is embodied in: (1) In the micro-oxygen environment provided by the aeration system through the uniform diffusion of aeration in the drainage aeration layer, sulfur-oxidizing bacteria efficiently oxidize the pyrite in the active layer and continuously produce acidic leachate; the acidic liquid penetrates the entire structure under the action of gravity and enters the bottom red mud loosening layer. Combined with the closed-loop circulation constructed by the pumping return system, it breaks the low physical mass transfer resistance of the red mud, eliminates local short-circuit flow, and makes the acidic substances undergo a uniform and continuous neutralization reaction with the free alkali and stable bound alkali inside the red mud.

[0018] (2) Red mud is extremely alkaline. When acidic leachate flows down through the red mud layer, its hydrogen ions are continuously consumed and buffered by the alkaline substances in the red mud. As the reaction cycle proceeds, the bound alkali of the red mud is continuously decomposed and released, and a large number of aluminum, iron, silicon and other ions dissolve from the mineral lattice. The original dense porous structure of the red mud is changed. The bound alkali of the red mud is stably transformed into free alkali, and its in-situ solid phase pH value is stable in the neutral or weakly alkaline range of 7.0 to 9.0. The soluble salts and alkalis in the system are continuously decomposed and transformed through the percolation and reflux process, and the salt and alkali pool capacity of the red mud is reduced.

[0019] (3) After the bottom layer of red mud reaches a stable neutral pH and is properly dried, the original stratification is broken by mechanical deep mixing; the large amount of humus formed by the degradation and transformation of biomass waste in the acidic microenvironment in the early stage acts as a natural polymer cementing agent; the humus complexes with the free aluminum and iron ions in the system, and produces strong physicochemical complexes with the fine particles of red mud and the coarse skeleton of the drainage layer, in-situ inducing the formation of soil aggregate structure with excellent water stability, and finally transforming red mud into ecological soil that meets the needs of plant growth.

[0020] The beneficial effects of this invention are: (1) The innovative introduction of drainage aeration layer and infiltration return closed-loop circulation, using the forced hydraulic drive of water pump to break the mass transfer resistance of red mud, completely solves the channel flow and dead zone problems of traditional heap leaching.

[0021] (2) Sulfur-oxidizing bacteria act as a biological slow-release acid source, and with the help of forced reflux, hydrogen ions can fully destroy the aluminosilicate-bound alkali inside the red mud, thus achieving deep dealkali removal.

[0022] (3) By utilizing the degradation of biomass waste in an acidic microenvironment, the humic substances act as natural polymer binders during the final deep mixing process. They combine with the fine particles of red mud and the coarse skeleton of the drainage layer to synthesize large-diameter water-stable aggregates in situ, which can fundamentally change the physical defects of red mud hardening and impermeability. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the method for in-situ dealkalization and construction of ecological matrix layer in red mud dumps according to the present invention; Figure 2This is a schematic diagram of the in-situ dealkalization and ecological matrix layer construction system for red mud dumps according to the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments.

[0025] Example 1 To address the need for rapid shallow remediation of red mud dumps, a method for in-situ dealkalization and construction of an ecological matrix layer in red mud dumps is proposed, such as... Figure 1 As shown, the specific steps are as follows: (1) Site preparation and active layer construction, such as Figure 2 As shown: The surface of the red mud stockpile is loosened by machinery to form a 10cm thick red mud loosening layer, and perforated PVC infiltration pipes wrapped with anti-clogging geotextile are pre-embedded at the bottom as a collection system. A 10cm thick layer of coarse gravel is laid on the loosened red mud layer to form a drainage and aeration layer, and microporous aeration discs are arranged in the coarse gravel; the microporous aeration discs are connected to an air supply fan for uniform aeration. Pyrite tailings with pyrite as the main mineral and containing 22% FeS2 by mass are mixed with crushed sugarcane bagasse with a sieve particle size of 5mm at a volume ratio of 1:20 and laid on top of the drainage aeration layer to form an acid-producing and fertilizer-enhancing active layer with a thickness of 20cm. A water distribution system is installed at the top of the acid-producing and fertilizing active layer. A collection system pre-buried at the bottom of the red mud loosening layer is connected to the water distribution system through a pump to form a closed loop. The water distribution system includes a water pipe with multiple nozzles, which are directly facing the acid-producing and fertilizing active layer. pH meters were installed at the bottom of the red mud loosening layer and inside the collection system; (2) Biochemical enhancement neutralization: Prepare a bacterial suspension containing sulfur-oxidizing bacteria, specifically a suspension containing *Thiobacillus acidophilus*, with an effective viable count of 10-1. 6 cfu / mL, the initial pH value is adjusted to 5.0 (the pH value of the bacterial solution is adjusted with 1 mol / L dilute sulfuric acid), the bacterial solution containing sulfur-oxidizing bacteria is injected into the acid-producing-fertilizing active layer through the top water distribution system, the air supply fan is started, and a mixed gas with an oxygen volume concentration of 2% (the rest is nitrogen) is introduced into the microporous aeration disc of the drainage aeration layer to maintain a micro-oxygen environment. (3) Percolation reflux circulation dealkalization: The sulfur-oxidizing bacteria in the bacterial solution oxidize the pyrite mining solid waste in the acid-fertilizing active layer under micro-oxygen environment. The resulting acidic leachate permeates into the drainage and aeration layer under gravity, and then continues to permeate downward into the red mud loosening layer. It undergoes a deep acid-base neutralization reaction with the alkaline substances inside the red mud. The leachate after the reaction is collected by the collection system pre-buried at the bottom of the red mud loosening layer. The pumping circuit is started to force the leachate back to the water distribution system at the top for circulation leaching. The pH meter inside the collection system monitors the pH value of the circulating acidic leaching solution in real time. When the pH value is higher than 6.0, it is necessary to replace it with a new bacterial solution containing sulfur-oxidizing bacteria. The pumping rate was adjusted throughout the process to ensure that the acid-producing fertilizer active layer was completely wetted on the first day of reaction, the top 50cm of the pile was completely wetted on the third day of reaction, and all materials in the pile were completely wetted after the 14th day of reaction, and the collection system continuously and stably discharged leachate. (4) In-situ soil formation and matrix reconstruction: A pH meter inside the bottom of the red mud loosening layer monitors the pH value of the solid phase at the bottom of the red mud loosening layer in real time. When it remains stable at 9.0 for 72 consecutive hours, the circulating leaching and gas introduction are stopped, and the system is allowed to air dry naturally until the moisture content drops to 45%. The collection system, microporous aeration discs, and pH meter are then removed. A rotary tiller is used to deeply mix the three layers (acid-producing and fertilizing active layer, drainage and aeration layer, and dealkalized red mud loosening layer) in situ. The red mud and gravel are cemented together by the humus degraded from sugarcane bagasse, and a soil aggregate structure with excellent water stability is induced in situ, completing the construction of the ecological matrix layer and transforming the red mud into ecological soil that meets the needs of plant growth.

[0026] After sampling and testing, the physical and chemical properties of the ecological matrix layer soil after final mixing and reconstruction were improved: the solid phase pH value dropped to about 8.2, the organic matter content increased to 25g / kg, the proportion of water-stable aggregates >0.25mm reached 45%, the total porosity increased to 40%, the compaction phenomenon of the original red mud was improved, and it initially possessed good air permeability and moisture retention performance.

[0027] Example 2 For the closure and sealing of red mud tailings ponds of conventional size, a method for in-situ dealkalization and construction of an ecological matrix layer in red mud tailings dumps is proposed. The specific steps are as follows: (1) Site preparation and active layer construction: Mechanical methods were used to loosen the surface of the red mud stockpile, forming a 50cm thick red mud loosening layer, and a permeable corrugated pipe wrapped with a filter membrane was pre-buried at the bottom as a collection system. A 30cm thick layer of coarse coal gangue is laid on the loosened red mud layer to form a drainage and aeration layer, and a high-density microporous aeration pipe network is laid inside it; the high-density microporous aeration pipe network is connected to an air supply blower for uniform aeration. Pyrite tailings with pyrite as the main mineral and 30% FeS2 by mass are mixed with crushed peanut shells with a sieve particle size of 8mm at a volume ratio of 1:15 and laid on top of the drainage and aeration layer to form an acid-producing and fertilizer-enhancing active layer with a thickness of 30cm. A water distribution system is installed at the top of the acid-producing and fertilizing active layer. A collection system pre-buried at the bottom of the red mud loosening layer is connected to the water distribution system through a pump to form a closed loop. The water distribution system includes a water pipe with multiple nozzles, which are directly facing the acid-producing and fertilizing active layer. pH meters were installed at the bottom of the red mud loosening layer and inside the collection system; (2) Biochemical enhancement neutralization: Prepare a bacterial suspension containing sulfur-oxidizing bacteria, specifically a suspension containing *Thiobacillus acidophilus*, with an effective viable count of 10-1. 7 The initial pH value was adjusted to 3.0 (the pH value of the bacterial solution was adjusted with 1 mol / L dilute sulfuric acid). The bacterial solution containing sulfur-oxidizing bacteria was injected into the acid-producing and fertilizing active layer through the top water distribution system. The air supply fan was started to introduce a mixed gas with an oxygen volume concentration of 6% (the rest was nitrogen) into the high-density microporous aeration pipe network of the drainage aeration layer to maintain a micro-oxygen environment. (3) Percolation reflux circulation dealkalization: The sulfur-oxidizing bacteria in the bacterial solution oxidize the pyrite mining solid waste in the acid-fertilizing active layer under micro-oxygen environment. The resulting acidic leachate permeates into the drainage and aeration layer under gravity, and then continues to permeate downward into the red mud loosening layer. It undergoes a deep acid-base neutralization reaction with the alkaline substances inside the red mud. The leachate after the reaction is collected by the collection system pre-buried at the bottom of the red mud loosening layer. The pumping circuit is started to force the leachate back to the water distribution system at the top for circulation leaching. The system uses an internal pH meter to monitor the pH of the circulating acidic leaching solution in real time. When the pH is higher than 6.0, a new high-concentration, highly active, strongly acidic bacterial solution in the logarithmic growth phase is pumped in. Throughout the process, the pumping rate was adjusted, and the hydraulic load control was strictly implemented for active layer wetting on day 1, shallow layer wetting on day 3, and full layer wetting on day 14 to ensure that the leachate remained in each layer of the reactor, and that leachate was continuously discharged from the collection system at a relatively stable rate. (4) In-situ soil formation and matrix reconstruction: A pH meter inside the bottom of the red mud loosening layer monitors the pH value of the solid phase at the bottom of the red mud loosening layer in real time. When it is stable at 8.0 for 72 consecutive hours, the circulating leaching and gas introduction are stopped, and the system is naturally dried until the moisture content drops to 25%. The collection system, high-density microporous aeration pipe network, and pH meter are removed, and a large agricultural plow is started to deeply mix the above three layers (acid-producing-fertilizing active layer, drainage aeration layer and red mud loosening layer after dealkalization) in situ.

[0028] Sampling and testing showed that the physicochemical properties of the reconstructed ecological matrix layer met the standards for revegetation matrix: the solid phase pH value was stable at around 7.8, the organic matter content was significantly increased to 40g / kg, the proportion of water-stable aggregates >0.25mm reached 52%, the total porosity increased to 50%, and the soluble salt content was significantly reduced after dealkalization treatment, forming an ecological soil with rich aggregate structure and loose texture, which can then be directly sown with alkali-tolerant grass seeds for revegetation.

[0029] Example 3 For old red mud dumps with deep pollution and extremely high alkalinity, a method for in-situ dealkalization and construction of an ecological matrix layer is proposed. The specific steps are as follows: (1) Site preparation and active layer construction: The surface of the red mud stockpile is loosened by machinery to form a 100cm thick red mud loosening layer, and a permeable pipe network covered with geotextile is pre-buried at the bottom as a collection system. A 50cm thick layer of coarse coal gangue is laid on the loosened red mud layer to form a drainage and aeration layer, and a pressure-resistant microporous aeration hose is installed inside it. Pyrite tailings with pyrite as the main mineral and 45% FeS2 by mass are mixed with crushed straw with a sieve particle size of 10mm at a volume ratio of 1:10 and laid on top of the drainage aeration layer to form an acid-producing and fertilizer-enriching active layer with a thickness of 50cm. A water distribution system is installed at the top of the acid-producing and fertilizing active layer. A collection system pre-buried at the bottom of the red mud loosening layer is connected to the water distribution system through a pump to form a closed loop. The water distribution system includes a water pipe with multiple nozzles, which are directly facing the acid-producing and fertilizing active layer. The microporous aeration pipe network inside the drainage aeration layer is connected to an air supply blower for uniform aeration; pH meters were installed at the bottom of the red mud loosening layer and inside the collection system; (2) Biochemical enhancement neutralization: The bacterial suspension containing sulfur-oxidizing bacteria is a highly efficient mixed bacterial suspension (in any proportion) containing Leptospira and Thiobacillus, with an effective viable count of 10-1. 8 cfu / mL, the initial pH value is adjusted to 1.0, and the bacterial solution containing sulfur-oxidizing bacteria is injected into the acid-producing-fertilizing active layer through the top water distribution system. The air supply fan is started to introduce a mixed gas with an oxygen concentration of 10% (the rest is nitrogen) into the microporous aeration disc of the drainage aeration layer to maintain a micro-oxygen environment. (3) Percolation reflux circulation dealkalization: The sulfur-oxidizing bacteria in the bacterial solution oxidize the pyrite mining solid waste in the acid-fertilizing active layer under micro-oxygen environment. The resulting acidic leachate permeates into the drainage and aeration layer under gravity, and then continues to permeate downward into the red mud loosening layer. It undergoes a deep acid-base neutralization reaction with the alkaline substances inside the red mud. The leachate after the reaction is collected by the collection system pre-buried at the bottom of the red mud loosening layer. The pumping circuit is started, and the leachate is forced back to the water distribution system at the top for circulation leaching through the powerful pumping circuit. The pH meter inside the collection system monitors the pH value of the circulating acidic leachate in real time. When the pH value is higher than 6.0, it is necessary to replace it with a new bacterial solution containing sulfur-oxidizing bacteria. Throughout the process, the pumping rate was adjusted to penetrate and neutralize the 1-meter-thick red mud layer as quickly as possible, and the full-layer immersion flow was maintained strictly according to the specified time nodes to ensure that the leachate was stably discharged through the geotextile. (4) In-situ soil formation and matrix reconstruction: A pH meter inside the bottom of the red mud loosening layer monitors the pH value of the solid phase at the bottom of the red mud loosening layer in real time. Due to the high acid production intensity, the machine is stopped when the pH value of the solid phase at the bottom of the red mud loosening layer stabilizes at 7.0 (completely neutral) for 72 consecutive hours. The collection system, microporous aeration pipe network, and pH meter are then removed. A large agricultural plow is started to deeply mix the above three layers (acid-producing-fertilizing active layer, drainage and aeration layer, and dealkalized red mud loosening layer) in situ. After a long period of drying, the moisture content is reduced to the lower limit of 5%. Heavy rotary tillage equipment is used again for deep plowing to completely crush the compacted clumps. The large amount of humus produced by the high proportion of straw decomposition strongly binds the fine red mud powder into soil aggregates, realizing the complete reconstruction of the deep ecological matrix.

[0030] Sampling and testing revealed that the soil properties of the deep ecological matrix after final mixing and reconstruction were improved: the solid phase pH value dropped to a neutral level of 7.3, the organic matter content reached 65g / kg, the proportion of water-stable aggregates >0.25mm jumped to over 58%, and the total porosity increased to 54%.

[0031] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for in-situ dealkalization and construction of an ecological matrix layer in a red mud dump, characterized in that, The specific steps are as follows: (1) Site preparation and active layer construction: Mechanically loosen the surface layer of the red mud dump area to be repaired to form a loosened red mud layer, and pre-bury a collection system at the bottom of the loosened red mud layer; Coarse waste material is laid on top of the red mud loosening layer to form a drainage and aeration layer, and an aeration system is evenly distributed inside the drainage and aeration layer. Above the drainage and aeration layer, an acid-producing and fertilizer-enriching active layer is laid, which is a mixture of solid waste from pyrite mining and beneficiation and crushed biomass waste. A water distribution system is installed at the top of the acid-producing and fertilizing active layer, and a collection system pre-buried at the bottom of the red mud loosening layer is connected to the water distribution system through a pump to form a closed loop. The aeration system inside the drainage aeration layer is connected to an air supply fan; (2) Bio-chemical enhanced neutralization: The biological acid production process is initiated by injecting sulfur-oxidizing bacteria solution into the acid-producing-fertilizing active layer through the top water distribution system; oxygen-containing gas is introduced into the aeration system of the drainage aeration layer. (3) Percolation-reflux circulation dealkalization: The sulfur-oxidizing bacteria in the bacterial solution oxidize the pyrite mining solid waste in the acid-fertilizing active layer under micro-oxygen environment. The resulting acidic leachate permeates into the drainage and aeration layer under gravity, and then continues to permeate downward into the red mud loosening layer. It undergoes a deep acid-base neutralization reaction with the alkaline substances inside the red mud. The leachate after the reaction is collected by the collection system and pumped back to the top water distribution system for circulating leaching. (4) In-situ soil formation and matrix reconstruction: When the pH value of the lower part of the red mud loosening layer is monitored to be stable at 7.0-9.0 for 72 consecutive hours, the circulating leaching and gas introduction are stopped. After natural drying until the moisture content drops to 5%-45%, the acid-producing-fertilizing active layer, drainage aeration layer and dealkalized red mud loosening layer are deeply mixed in situ. The humus produced by the degradation of biomass waste is used as a binder to form an ecological matrix layer with an aggregate structure by combining with red mud mineral particles.

2. The method for in-situ dealkalization and ecological matrix layer construction of red mud dumps according to claim 1, characterized in that, In step (1), the thickness of the red mud loosening layer is 10-100cm; the thickness of the drainage aeration layer is 10-50cm; and the thickness of the acid-fertilizing active layer is not less than 20cm.

3. The method for in-situ dealkalization and ecological matrix layer construction of red mud dumps according to claim 1, characterized in that, In step (1), the coarse waste material is coarse crushed stone and coarse coal gangue.

4. The method for in-situ dealkalization and ecological matrix layer construction of red mud dumps according to claim 1, characterized in that, In step (1), the solid waste from pyrite mining and beneficiation is one or more mixtures of tailings, gangue, and smelting slag generated during mining and beneficiation; the solid waste from pyrite mining and beneficiation is solid waste from pyrite, in which the FeS2 content exceeds 20%.

5. The method for in-situ dealkalization and ecological matrix layer construction of red mud dumps according to claim 1, characterized in that, In step (1), the biomass waste includes one or more of sugarcane bagasse, peanut shells, walnut shells, and crop straw in any proportion. The crushed biomass waste has a particle size of 5-10 mm after sieving.

6. The method for in-situ dealkalization and ecological matrix layer construction of red mud dumps according to claim 1, characterized in that, In step (1), the volume ratio of pyrite mining solid waste to biomass waste in the acid-fertilizing active layer is 1:10 to 20.

7. The method for in-situ dealkalization and ecological matrix layer construction of red mud dumps according to claim 1, characterized in that, In step (1), pH meters are installed at the bottom of the red mud loosening layer and inside the collection system.

8. The method for in-situ dealkalization and ecological matrix layer construction of red mud dumps according to claim 1, characterized in that, In step (2), the bacterial suspension containing sulfur-oxidizing bacteria is one of the following: *Thiobacillus acidophilus*, *Leptospira*, *Acidophilus*, *Sulphophyllum*, *Metrolactone*, *Acidophilus*, *Typhae*, *Metrolactone*, *Metrolactone*, *Acidophilus thermophilus*, *Metrolactone*, and *Sulphophyllum*, or a mixture thereof in any proportion, with an effective viable count ≥ 102 6 cfu / mL, initial injection pH = 1.0–5.

0.

9. The method for in-situ dealkalization and ecological matrix layer construction of red mud dumps according to claim 1, characterized in that, In step (2), the oxygen-containing gas is a mixture of gases with an oxygen volume fraction of not less than 2%.

10. The method for in-situ dealkalization and ecological matrix layer construction of red mud dumps according to claim 1, characterized in that, In step (3), after circulating the leachate until the pH value of the leachate is greater than 6.0, replace it with a new bacterial solution containing sulfur-oxidizing bacteria.

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