A mine wastewater treatment system and method for coupling organic matter reduction and alkali production from red mud

Abstract

The present invention provides a mine wastewater treatment system and method for coupling and reducing alkali production from red mud organic matter, belonging to the technical field of ecological restoration. This treatment system includes: a pre-sedimentation tank, a reaction tank, and a post-sedimentation tank connected in sequence; the interior of the reaction tank is filled with fillers, and the fillers include inorganic fillers and composite fillers filled in layers from bottom to top; the composite filler is formed by mixing biomass and red mud in a certain proportion and fermenting and maturing, specifically: the biomass and red mud are uniformly mixed according to a preset weight ratio; natural fermentation is carried out for a preset first time; during the maturing period, turning the pile is carried out once every preset second time, and the overall water content and temperature are controlled within a preset range. After a preset total number of pile-turning times, the maturing is completed. This treatment method includes the preparation of the composite filler, the construction of the treatment system, the hydraulic retention of the wastewater to be treated in the treatment system, and the regeneration preparation of the waste composite filler to repair soil. The present invention improves the treatment effect of acidic mine wastewater and the repair effect of mine soil.

Description

Technical Field

[0001] The present invention belongs to the technical field of ecological restoration, and particularly relates to a mine wastewater treatment system and method for coupling red mud with organic matter to reduce alkalinity production. Background Art

[0002] After the coal mine is closed, acidic mine wastewater with strong acidity and high iron and manganese contents is easily generated, causing serious harm to the ecological environment, and it is urgent to carry out pollution treatment.

[0003] Red mud (RM: Red Mud) is a highly saline and alkaline solid waste generated during the process of extracting aluminum from bauxite. Since it contains a large amount of Fe2O3 and appears red, it is commonly called red mud. The main components of red mud are generally SiO2, Al2O3, CaO, Fe2O3, and Na2O, etc. Red mud has alkalinity and adsorption properties. However, red mud has a poor physical structure and lacks nutrients, and it is difficult to be soilized even after dealkalization, and it usually cannot be directly used for growing plants.

[0004] The reduction and alkalinity production system is a passive treatment technology for treating acidic mine wastewater. It has good stability in treating mine wastewater with low acidity load, and the daily operation and maintenance management cost is relatively low. The reduction and alkalinity production system mainly includes three layers: the water layer, the composite filler layer, and the alkalinity production medium layer. The water layer mainly plays the role of isolating oxygen and precipitating some metal ions; the composite filler layer mainly provides a living environment for microorganisms, reduces sulfate and ferric ions, and it can also remove some metal ions through adsorption and neutralization precipitation. The limestone layer mainly plays the role of increasing the pH of the water body, and the unreduced ferric ions and aluminum ions will precipitate and be removed in the limestone layer; ferrous ions and the remaining metal ions will precipitate and be removed in the post-sedimentation tank.

[0005] However, the reduction and alkalinity production system has a weak ability to treat mine wastewater with high acidity load, and it is urgent to be improved to enhance the treatment effect on mine wastewater with low pH, high iron, and high sulfate. Summary of the Invention

[0006] To solve the above problems of the prior art, the present invention provides a mine wastewater treatment system and method for coupling red mud with organic matter to reduce alkalinity production. Through the coupling of red mud and organic matter to reduce alkalinity production, on the one hand, the anti-acidity load capacity is improved, and the treatment effect on acidic mine wastewater, especially mine wastewater with low pH, high iron, and high sulfate, is enhanced; on the other hand, the number of water-stable large particle aggregates is increased, the conversion and fixation rate of nutrients such as C and N and the anti-rain erosion ability of organic matter are enhanced, which can be used for soil restoration and realize the resource utilization of red mud.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A mine wastewater treatment system for coupling organic matter and reduction to produce alkali from red mud, comprising:

[0009] A pre-sedimentation tank, a reaction tank and a post-sedimentation tank connected in sequence;

[0010] The interior of the reaction tank is filled with fillers, which include inorganic fillers and composite fillers. The inorganic fillers and composite fillers are filled in layers from bottom to top to form an inorganic filler layer and a composite filler layer;

[0011] The composite filler is formed by mixing biomass and red mud in a certain proportion and fermenting and composting. Specifically: the biomass and red mud are uniformly mixed according to a preset weight ratio; natural fermentation is carried out for a preset first time; during the composting period, turning is carried out once every preset second time, and the overall water content is kept at a preset water content value. During the composting period, the temperature is controlled within a preset temperature range. After a preset total number of turning times, the composting is completed.

[0012] Further, the length of the pre-sedimentation tank is not less than 0.8 times the length of the reaction tank, the width of the pre-sedimentation tank is not less than 0.7 times the width of the reaction tank, and the depth of the pre-sedimentation tank is not less than 1 times the depth of the reaction tank;

[0013] The length of the post-sedimentation tank is not less than 1.5 times the length of the reaction tank, the width of the post-sedimentation tank is not less than 1.5 times the width of the reaction tank, and the depth is not less than 1.5 times the width of the reaction tank.

[0014] Further, the mine wastewater to be treated enters the reaction tank to form a water layer, the water layer is above the composite filler layer, and the thickness of the water layer is not less than 60 cm; the thickness of the composite filler layer is 20 - 60 cm; the thickness of the inorganic filler layer is not less than 100 cm.

[0015] Further, the inorganic filler is limestone, and the particle size of the limestone is 1 - 3 cm.

[0016] Further, the reaction tank is provided with a flushing system, and the flushing system includes an upper layer pipeline and a lower layer pipeline. The upper layer pipeline is located in the middle of the inorganic filler layer. During operation, water flows out from the upper layer pipeline in an overflow manner; the lower layer pipeline is located at the lower part of the inorganic filler layer. When the inorganic filler layer is blocked and needs to be flushed, the sediment is flushed out from the lower layer pipeline.

[0017] A mine wastewater treatment method for coupling organic matter and reduction to produce alkali from red mud, comprising the following steps:

[0018] Step S1: Construct the mine wastewater treatment system for coupling organic matter and reduction to produce alkali from red mud;

[0019] Step S2: Lead the mine wastewater to be treated to the pre-sedimentation tank, and the hydraulic retention time of the pre-sedimentation tank is 24 - 72 h to remove part of the ferric ions in the form of iron hydrate;

[0020] Step S3: Introduce the effluent from the pre-sedimentation tank into the reaction tank. The hydraulic retention time of the reaction tank is 48 - 120 h to remove metal ions and sulfate ions.

[0021] Step S4: Drain the effluent from the reaction tank into the post-sedimentation tank, and regularly flush the sediment in the reaction tank. The hydraulic retention time of the post-sedimentation tank is 24 - 72 h to remove ferric ions by precipitation.

[0022] Further, in the said step S1, it includes:

[0023] Step S101: Excavate the pre-sedimentation tank, reaction tank, and post-sedimentation tank according to the design dimensions. Lay the lower-layer pipeline at the bottom of the reaction tank, and set a horizontal flushing port. The flushing port is equipped with a ball valve, and the length of the lower-layer pipeline is the same as the length of the reaction tank.

[0024] Step S102: Fill half of the designed thickness of the inorganic filler layer with limestone particles without calcium, then lay the upper-layer pipeline on the limestone particles, and then fill the other half of the thickness of limestone particles; after the upper-layer pipeline leads out of the reaction tank, use a tee joint to lift it to the position at the same height as the designed water layer as the overflow port.

[0025] Step S103: Lay a geotextile on the inorganic filler layer, and then fill a composite filler on the geotextile.

[0026] Further, in the said step S103, the preparation process of the composite filler is:

[0027] Uniformly mix biomass and red mud in a weight ratio of 1:1 - 5:1. The biomass includes animal excrement, wood chips, and straw.

[0028] Take out the biomass and red mud mixture after 3 months of natural fermentation for ripening.

[0029] During the ripening of the fermented biomass and red mud mixture, turn the pile every 6 days, keep the overall water content at 45% - 55%, control the temperature during ripening in the range of 40°C to 70°C, and complete the ripening after a total of 5 times of turning the pile.

[0030] A method for preparing a compost substrate by coupling and reducing red mud with organic matter includes the following steps:

[0031] Air-dry the composite filler for treating mine wastewater, and supplement and add red mud to obtain a new organic matter and red mud mixture. The proportion of red mud in the new organic matter mixture reaches 10% - 30%.

[0032] Mix evenly and continuously spray water, and carry out a ripening reaction for 5 - 10 days again.

[0033] Turn the pile of the ripened organic matter and red mud mixture to drain water, and add 0.2% - 0.4% of composite microbial agents to obtain the compost substrate.

[0034] A method for mine restoration of compost substrate based on the coupling reduction of red mud organic matter:

[0035] Spray water on the compost substrate to make the moisture content of the heap reach 50%-60%. Add the aluminum-iron minerals precipitated in the post-sedimentation tank to the compost substrate at a ratio of 1:100-5:100 to form short-range ordered minerals to promote the formation of soil aggregates. After natural development for 1-3 months, it is used for the restoration of open-pit mined bauxite and other mining areas.

[0036] The main principle of the present invention is:

[0037] Biomass and red mud are mixed and fermented and decomposed in a certain proportion to form a composite filler. The composite filler is filled to form a composite filler layer, which can create a reducing environment, reduce sulfate ions, and reduce ferric iron to ferrous iron;

[0038] During use, mine water with low pH, high iron, and high sulfate is led to the pre-sedimentation tank, and part of the ferric iron ions will be removed in the form of iron hydrates in the pre-sedimentation tank;

[0039] After that, the water outlet of the pre-sedimentation tank is led to the top of the reaction tank through a pipeline, and the influent flow rate is determined according to the size of the reaction tank (the influent of the reaction tank is the water outlet of the pre-sedimentation tank).

[0040] The influent of the reaction tank first passes through the water layer, and part of the ferric iron ions will be removed in the form of iron hydrates in the water layer; then it passes through the composite filler layer. The microorganisms in the composite filler layer will consume dissolved oxygen to form a reducing environment, and sulfate ions are reduced and removed. The coupling of red mud and biomass can also improve the stability of the alkalinity increase in the composite filler layer, so that part of the ferric iron will be removed in the form of precipitation in the composite filler layer;

[0041] After that, it flows through the inorganic material layer composed of limestone. The dissolution of limestone increases the pH value of the water body, causing the precipitation of metal ions such as iron and aluminum and thus removing them;

[0042] Finally, the effluent of the reaction tank is discharged into the sedimentation tank, and ferric iron ions are further removed in the sedimentation tank.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention utilizes the principle of coupling reduction and alkali production of red mud and organic matter to treat acidic mine wastewater, and prepares the red mud organic matter after treating acidic mine wastewater into a compost substrate to repair and improve the mine soil. The treatment benefits are good, mainly reflected in:

[0045] 1. It can improve the alkali production rate of red mud, achieve the slow-release alkali production effect, and combine clay minerals and organic matter in red mud to form an organic clay complex, effectively realizing the resource utilization of red mud.

[0046] 2. It can enhance the treatment effect of the reduction alkali production system, as well as the anti-acidity load capacity and alkali degree improvement ability. Red mud has a high alkali degree and strong adsorption ability, which can enhance the alkali degree improvement ability of the reduction alkali production system and the treatment effect on acidic mine wastewater; the co-composting of red mud and compost can form a humic acid-humate buffer system, increasing the anti-acidity load capacity of the composite filler layer.

[0047] 3. The addition of red mud can increase the number of large particle aggregates in organic matter, improve the conversion and fixation rate of nutrients such as C and N, and the anti-rain erosion ability of organic matter. The composite filler treated with mine wastewater can be prepared into a compost substrate and directly used for planting plants, overcoming the defect that red mud cannot be directly used for plant planting, achieving the effect of "treating waste with waste", fully reducing the comprehensive treatment cost, and being very beneficial to mine restoration. Description of the Drawings

[0048] Figure 1 It is a schematic diagram of the overall structure of the mine wastewater treatment system for the coupling of red mud and organic matter with reduction alkali production according to an embodiment of the present invention;

[0049] Figure 2 It is a flowchart of the mine wastewater treatment method for the coupling of red mud and organic matter with reduction alkali production according to an embodiment of the present invention;

[0050] Figure 3 It is a schematic diagram of the comparison of the changes in the available nitrogen content in the soil during the cultivation period of different plants according to an embodiment of the present invention;

[0051] Figure 4 It is a schematic diagram of the comparison of the changes in the available phosphorus content in the soil during the cultivation period of different plants according to an embodiment of the present invention;

[0052] Figure 5 It is a schematic diagram of the comparison of the changes in the organic matter content in the soil during the cultivation period of different plants according to an embodiment of the present invention.

[0053] In the figure:

[0054] 1 - Pre-sedimentation tank, 2 - Water layer, 3 - Water level line, 4 - Red mud, 5 - Composite filler layer, 6 - Inorganic filler layer, 7 - Upper layer pipeline, 8 - Lower layer pipeline, 9 - Ball valve, 10 - Outlet of the reaction tank, 11 - Post-sedimentation tank. Detailed Embodiments

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0056] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0057] In the present invention, unless otherwise clearly defined and limited, terms such as "installation", "connection", "coupling", "fixation", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0058] In addition, if "and / or" or "and / or" appears throughout the text, its meaning includes three parallel scenarios. Taking "A and / or B" as an example, it includes scenario A, scenario B, or the scenario where both A and B are satisfied simultaneously. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0059] To better understand the objectives, structure, and functions of the present invention, the following will be described in detail with reference to the accompanying drawings.

[0060] Embodiment 1

[0061] As Figure 1 shown, this embodiment provides a mine wastewater treatment system for the coupled reduction and alkali production of red mud and organic matter, including:

[0062] A pre-sedimentation tank, a reaction tank, and a post-sedimentation tank connected in sequence;

[0063] The interior of the reaction tank is filled with fillers, which include inorganic fillers and composite fillers. The inorganic fillers and composite fillers are filled in layers from bottom to top to form an inorganic filler layer and a composite filler layer;

[0064] The composite filler is formed by mixing biomass and red mud in a certain proportion and fermenting until maturity. Specifically: the biomass and red mud are uniformly mixed according to a preset weight ratio; naturally fermented for a preset first time; during the ripening process, turning the pile is carried out every preset second time, and the overall water content is maintained at a preset water content value, and the temperature during the ripening process is controlled within a preset temperature range. After a preset total number of pile-turning times, the ripening is completed.

[0065] Further, the length of the pre-sedimentation tank is not less than 0.8 times the length of the reaction tank, the width of the pre-sedimentation tank is not less than 0.7 times the width of the reaction tank, and the depth of the pre-sedimentation tank is not less than 1 time the depth of the reaction tank;

[0066] The length of the post-sedimentation tank is not less than 1.5 times the length of the reaction tank, the width of the post-sedimentation tank is not less than 1.5 times the width of the reaction tank, and the depth is not less than 1.5 times the width of the reaction tank.

[0067] Further, the mine wastewater to be treated enters the reaction tank to form a water layer above the composite filler layer, and the thickness of the water layer is not less than 60 cm; the thickness of the composite filler layer is 20 - 60 cm; the thickness of the inorganic filler layer is not less than 100 cm.

[0068] Further, the inorganic filler is limestone, and the particle size of the limestone is 1 - 3 cm.

[0069] Further, the reaction tank is provided with a flushing system, which includes an upper layer pipeline and a lower layer pipeline. The upper layer pipeline is located in the middle of the inorganic filler layer. During operation, water flows out from the upper layer pipeline in an overflow manner; the lower layer pipeline is located at the lower part of the inorganic filler layer. When the inorganic filler layer is blocked and needs to be flushed, the sediment is flushed out from the lower layer pipeline.

[0070] Example 2

[0071] As Figure 2 shown, this example provides a method for treating mine wastewater by coupling reduction and alkali production of red mud organic matter, including the following steps:

[0072] Step S1: Construct the mine wastewater treatment system for coupling reduction and alkali production of red mud organic matter;

[0073] Step S2: Lead the mine wastewater to be treated to the pre-sedimentation tank, and the hydraulic retention time of the pre-sedimentation tank is 24 - 72 h to remove part of the ferric ions in the form of iron hydrate;

[0074] Step S3: Lead the effluent of the pre-sedimentation tank to the reaction tank, and the hydraulic retention time of the reaction tank is 48 - 120 h to remove metal ions and sulfate ions;

[0075] Step S4: Drain the effluent from the reaction tank into the post-sedimentation tank, and regularly flush the sediment in the reaction tank. The hydraulic retention time of the post-sedimentation tank is 24 - 72 h, and ferric ions are removed by sedimentation.

[0076] Further, in the said step S1, it includes:

[0077] Step S101: Excavate the pre-sedimentation tank, reaction tank, and post-sedimentation tank according to the design dimensions. Lay the lower-layer pipeline at the bottom of the reaction tank, and set a horizontal flushing port. The flushing port is equipped with a ball valve, and the length of the lower-layer pipeline is the same as the length of the reaction tank;

[0078] Step S102: Fill half of the designed thickness of the inorganic filler layer with limestone particles without calcium. Then lay the upper-layer pipeline on the limestone particles, and then fill the other half of the thickness of limestone particles. After the upper-layer pipeline leads out of the reaction tank, it is lifted to the position with the same height as the designed water layer by a tee joint as the overflow port;

[0079] Step S103: Lay a geotextile on the inorganic filler layer, and then fill the composite filler on the geotextile.

[0080] Further, in the said step S103, the preparation process of the composite filler is as follows:

[0081] Uniformly mix biomass and red mud in a weight ratio of 1:1 - 5:1. The biomass includes animal excrement, wood chips, and straw;

[0082] The mixture of biomass and red mud is taken out and decomposed after 3 months of natural fermentation;

[0083] For the fermented mixture of biomass and red mud, turning the pile is carried out every 6 days during the decomposition period. The overall water content is kept at 45% - 55%, and the temperature during the decomposition period is controlled in the range of 40°C to 70°C. After a total of 5 times of turning the pile, the decomposition is completed.

[0084] Example 3

[0085] This example provides a method for preparing a compost substrate by coupling and reducing red mud organic matter, including the following steps:

[0086] Air-dry the composite filler that has treated mine wastewater, and supplement and add red mud to obtain a new organic matter - red mud mixture. The proportion of red mud in the new organic matter mixture reaches 10% - 30%;

[0087] Mix evenly and continuously spray water, and carry out a decomposition reaction for 5 - 10 days again;

[0088] Turn the pile and drain the water from the decomposed organic matter - red mud mixture, and add 0.2% - 0.4% of composite microbial agents to obtain the compost substrate.

[0089] Example 4

[0090] This embodiment provides a method for mine restoration using a compost substrate based on the coupling reduction of red mud organic matter:

[0091] The compost substrate is treated by water spraying to make the moisture content of the heap reach 50%-60%. The aluminum-iron minerals precipitated in the post-sedimentation tank are added to the compost substrate at a ratio of 1:100 to 5:100 to form short-range ordered minerals to promote the formation of soil aggregates. After natural development for 1-3 months, it is used for the restoration of open-pit mined bauxite and other mining areas.

[0092] In this embodiment, the mine wastewater treatment system for the coupling reduction of red mud organic matter to produce alkali also includes a mine restoration soil preparation area, and the treatment of the compost substrate is completed in the preparation area.

[0093] Example 5

[0094] In this embodiment, the present invention is applied to a pilot test site. After inspection, it is confirmed that the present invention can improve the treatment effect of mine wastewater, and the compost substrate obtained by the coupling reduction of red mud organic matter can be directly used for plant cultivation, as follows:

[0095] (1) Verification of the treatment effect of mine wastewater

[0096] A certain pilot test site covers an area of about 400 m 2 , and is composed of 1 pre-sedimentation tank, 1 reduction and alkali production reaction tank, and 1 oxidation and sedimentation tank. The influent water is introduced by raising the water level of the acidic mine wastewater outlet channel by a water retaining dam. The hydraulic retention time of the pre-sedimentation tank is 24 h, the hydraulic retention time of the reaction tank is 72 h, the hydraulic retention time of the post-sedimentation tank is 72 h, and the operation time is 110 days.

[0097] The co-composting reduction and alkali production reaction tank is designed to add organic matter with a mass ratio of 10% red mud as the organic matter layer during the composting and ripening stage. The designed dimensions are: 3.37 m × 2.70 m × 1.83 m. Among them, the designed water layer thickness is 40 cm, the organic matter layer thickness is 25 cm, and the alkali production medium layer thickness is 100 cm. The organic matter layer and the limestone layer are separated by a geotextile. The outlet pipe divides the limestone layer into two layers, and the hydraulic retention time is 72 h.

[0098] The designed dimensions of the post-sedimentation tank of the co-composting reduction and alkali production system are: 1.77 m × 3.58 m × 2.67 m, and the hydraulic retention time is 72 h.

[0099] The red mud-organic matter coupling reduction and alkali production system has a strong ability to increase the pH. During the operation, the pH decline of the effluent is small, and the ability to increase the alkalinity is stable; it has a strong ability to consume dissolved oxygen, and the treatment effect on conventional indexes is shown in Table 1.

[0100] Table 1 Detection of conventional indexes of influent and effluent of the red mud-organic matter coupling reduction and alkali production system

[0101]

[0102] The red mud-organic matter coupled reduction and alkali production system has a strong ability to remove iron and aluminum. The pre-sedimentation tank, wetland, and post-sedimentation tank can remove 21.36%, 61.23%, and 28.02% of the total iron, 24.50%, 73.31%, and 24.36% of aluminum, and 2.95%, 14.38%, and 4.01% of sulfate radicals respectively compared to their own influents. The specific treatment effects are shown in Table 2.

[0103] Table 2 Removal of metal ions and sulfate radicals by the red mud-organic matter coupled reduction and alkali production system

[0104]

[0105] During the operation, the heavy metal leaching risk is relatively low. The heavy metal indexes of the influent and the effluent of the reaction tank are detected. The heavy metal concentration limits in the total influent refer to the Environmental Quality Standards for Surface Water (GB 3838—2002), and the heavy metal concentration limits in the effluent of the reaction tank refer to the Integrated Wastewater Discharge Standard (GB 8978-1996). The specific corresponding limits are shown in Table 3, and the heavy metal concentrations in the effluent of the reaction tank are shown in Table 4. During the experiment, the heavy metal concentrations in the influent varied greatly. The average concentration of Cu during the detection period was 0.51 mg / L, and there was one day when the detection index exceeded the concentration limit of Class V surface water; the average detected concentration of Cd was 0.02 mg / L, and there were 5 days when the detection indexes exceeded the concentration limit of Class V surface water; the average detected concentration of Pb was 0.33 mg / L, all exceeding the concentration limit standard of Class V surface water; the average detected concentration of As was 0.03 mg / L, and there was one day exceeding the concentration limit of Class V surface water; Zn was all within the concentration limit of Class V surface water; the average leaching concentration of Cr was 0.570 mg / L, all exceeding the concentration limit of Class V surface water. After being treated by the reaction tank, all indexes were within the concentration limits of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0106] Table 3 Heavy metal leaching concentration limits

[0107]

[0108] Note: "-" indicates that there is no such item in the standard

[0109] Table 4 Heavy metal concentrations in the influent and the effluent of the reaction tank

[0110]

[0111] (2) Verification of the mine soil remediation effect

[0112] A pot experiment was conducted on the organic matter after treating acid mine wastewater. PVC pots (inner diameter at the bottom 10 cm, upper diameter 15 cm, height 10 cm) were uniformly used for the pot experiment. The total mass of the mixed samples in each pot was 500 g. Each treatment in the experiment had 3 replicates, and a total of 63 pots were potted. The soil cultivation time of the pots in the greenhouse was set to 8 weeks, and 30 mL of water was sprayed every 2 days during the cultivation period. The physical and chemical properties of the improved substrate were measured every other week. When sampling each time, samples were mixed from different positions as the representative samples of the day.

[0113] The selected plants for planting were Viola philippica, Dianthus chinensis, and Lolium perenne. Seeds with plump grains and uniform sizes were selected and soaked and disinfected with 10% H2O2 for 10 min, and then washed with distilled water and set aside. The tested substrate was the organic matter after treating acid mine wastewater. After taking out the organic matter, it was dried in the sun, crushed, and evenly mixed. The basic physical and chemical properties of the organic matter layer substrate are shown in Table 5.

[0114] Table 5 Basic physical and chemical properties of the tested substrate

[0115]

[0116] Lolium perenne is different from Coronilla varia and Dianthus chinensis. Before 30 days, the growth of Lolium perenne is not yet mature and its roots are not well-developed. After 30 days, Lolium perenne is basically grown and rapidly expands its root structure. After the 7th week, a rich network tissue was observed to form in the soil substrate. In the soil of the Lolium perenne group, the vast majority of N and P elements were absorbed and fixed by the plants, and only a small amount of N and P was lost through watering and leaching. And the roots filled the pots, and through the interpenetration and extrusion effects, it was easier to make the substrate particles agglomerate.

[0117] The effects of organic matter on different herbaceous plants are different ( Figure 3 Table 6). During the entire cultivation period, except for the Lolium perenne treatment, the soil available nitrogen of the other plant treatments generally showed a trend of first decreasing and then increasing. From 21 to 49 days of cultivation, the content of soil available nitrogen increased significantly with time, especially in the 3 - 5 weeks, the rising rates were relatively fast, with the increase amplitudes being 283.6, 316.7, and 304.2 mg / kg respectively, and the increase amplitude slowed down in the 5 - 7 weeks. In the Lolium perenne treatment, the available nitrogen always showed an increasing trend, rising from 851.8 mg / kg in the 1st week to 987.7 mg / kg in the 7th week. In the non-composted Coronilla varia and Lolium perenne groups, the content of soil available nitrogen first increased and then decreased, and the content of available nitrogen in the 7th week was 797.3 and 833.9 mg / kg respectively. The Dianthus chinensis and Viola philippica groups always showed an increasing trend, and the content of available nitrogen increased to 886.8 and 852.1 mg / kg in the 7th week, as shown in Table 6.

[0118] Table 6 Changes in soil available nitrogen content during the cultivation period

[0119]

[0120] Applying herbaceous plant materials significantly reduced the available phosphorus level in the soil ( Figure 4 , Table 7). During the cultivation period, the available phosphorus content in the soil of the plant treatments showed a trend of first decreasing and then increasing. The decrease in ryegrass was relatively small and gradually stabilized in the later stage of the experiment. The content at the 7th week was 38.2 mg / kg. The available phosphorus contents of the other Coronilla varia, Viola philippica, and Dianthus chinensis treatments were 35.9, 32.1, and 36.5 mg / kg at the 7th week, as shown in Table 7.

[0121] Table 7 Changes in available phosphorus content in the soil during the cultivation period

[0122]

[0123] Applying herbaceous plant materials significantly increased the soil organic matter level (Table 8, Figure 5 ). The Coronilla varia group increased from 31.4% to 34.4%; the Viola philippica group increased from 29.7% to 38.7%; the Dianthus chinensis group increased from 29.2% to 33.7%; the ryegrass group increased from 31.3% to 33.7%.

[0124] Table 8 Changes in soil organic matter content during the cultivation period

[0125]

[0126]

[0127] Ryegrass was the crop with the best growth during the experiment. The cultivation substrate mainly affects plant growth through the nutritional status of the plants and the harmful components in the substrate. Available phosphorus exists in the soil and can be directly absorbed and utilized by plants, including all water-soluble phosphorus, part of the adsorbed phosphorus, and organic phosphorus. Soil alkaline hydrolyzable nitrogen includes water-soluble nitrogen, exchangeable nitrogen, and easily hydrolyzable organic nitrogen in the soil. At the initial stage of the experiment, the soil water content was relatively high and the watering frequency was too dense in the two weeks before germination. The denitrification effect in the soil environment was strong, reducing the soil nitrogen mineralization rate. As the pot experiment progressed, the mineralization gradually became greater than the biological fixation, and the alkaline hydrolyzable nitrogen content began to gradually increase.

[0128] Different from Coronilla varia and Dianthus chinensis, before 30 days, the growth of ryegrass was not yet mature and its roots were not well-developed. After 30 days, ryegrass was basically grown and rapidly expanded its root structure. After the 7th week, a rich network structure was observed in its soil matrix. In the soil of the ryegrass group, the vast majority of N and P elements were absorbed and fixed by the plants, and only a small part of N and P was lost through watering and leaching. And the roots filled the pots, and through the interpenetration and extrusion effects, it was easier to make the substrate particles agglomerate.

[0129] The compost substrate prepared by the method of the present invention using the composite filler after treating acidic mine wastewater can be directly used for planting plants and can be widely applied to mine soil remediation.

[0130] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A mine wastewater treatment system for coupling organic matter and reduction to produce alkali from red mud, characterized in that Including: A pre-sedimentation tank, a reaction tank, and a post-sedimentation tank connected in sequence; The interior of the reaction tank is filled with fillers, including inorganic fillers and composite fillers. The inorganic fillers and composite fillers are filled in layers from bottom to top to form an inorganic filler layer and a composite filler layer; The preparation process of the composite filler is as follows: Mix biomass and red mud evenly at a weight ratio of 1:1 - 5:

1. The biomass includes animal excrement, wood chips, and straw; The mixture of biomass and red mud is taken out and decomposed after 3 months of natural fermentation; For the fermented mixture of biomass and red mud, turning the pile is carried out every 6 days during the decomposition period, the overall water content is kept at 45% - 55%, and the temperature during the decomposition period is controlled in the range of 40°C to 70°C. After a total of 5 times of turning the pile, the decomposition is completed.

2. The mine wastewater treatment system for producing alkali by coupling reduction of red mud with organic matter as claimed in claim 1, wherein: The length of the pre-sedimentation tank is not less than 0.8 times the length of the reaction tank, the width of the pre-sedimentation tank is not less than 0.7 times the width of the reaction tank, and the depth of the pre-sedimentation tank is not less than 1 times the depth of the reaction tank; The length of the post-sedimentation tank is not less than 1.5 times the length of the reaction tank, the width of the post-sedimentation tank is not less than 1.5 times the width of the reaction tank, and the depth is not less than 1.5 times the width of the reaction tank.

3. The mine wastewater treatment system for coupling and reducing alkali production with red mud and organic matter as claimed in claim 1, wherein, The mine wastewater to be treated enters the reaction tank to form a water layer above the composite filler layer, and the thickness of the water layer is not less than 60 cm; the thickness of the composite filler layer is 20 - 60 cm; the thickness of the inorganic filler layer is not less than 100 cm.

4. The mine wastewater treatment system for coupling reduction and alkali production of red mud and organic matter as described in claim 1, wherein, The inorganic filler is limestone, and the particle size of the limestone is 1 - 3 cm.

5. The mine wastewater treatment system for coupling and reducing alkali production from red mud and organic matter as described in claim 1, wherein, The reaction tank is equipped with a flushing system, which includes an upper layer pipeline and a lower layer pipeline. The upper layer pipeline is located in the middle of the inorganic filler layer. During operation, water flows out from the upper layer pipeline in an overflow manner; the lower layer pipeline is located at the lower part of the inorganic filler layer. When the inorganic filler layer is blocked and needs to be flushed, the sediment is flushed out from the lower layer pipeline.

6. A method for treating mine wastewater by coupling organic matter reduction and alkali production from red mud, characterized in that, Including the following steps: Step S1: Construct a mine wastewater treatment system for coupled reduction and alkali production of red mud organic matter as described in any one of claims 1 - 5; Step S2: Introduce the mine wastewater to be treated into the pre-sedimentation tank. The hydraulic retention time of the pre-sedimentation tank is 24 - 72 h, and part of the ferric ions are removed in the form of iron hydrate; Step S3: Introduce the effluent from the pre-sedimentation tank into the reaction tank. The hydraulic retention time of the reaction tank is 48 - 120 h, and metal ions and sulfate ions are removed; Step S4: Discharge the effluent from the reaction tank into the post-sedimentation tank, and regularly flush the sediment in the reaction tank. The hydraulic retention time of the post-sedimentation tank is 24 - 72 h, and ferric ions are removed by precipitation.

7. The method for treating mine wastewater by coupling reduction of red mud and organic matter to produce alkali according to claim 6, characterized in that, In step S1, it includes: Step S101: Excavate the pre-sedimentation tank, reaction tank, and post-sedimentation tank according to the design dimensions. Lay the lower layer pipeline at the bottom of the reaction tank, and set a horizontal flushing port. The flushing port is equipped with a ball valve, and the length of the lower layer pipeline is the same as the length of the reaction tank; Step S102: Fill limestone grains with half of the designed thickness of the inorganic filler layer, then lay the upper layer pipeline on the limestone grains, and then fill the other half of the thickness of limestone grains; after the upper layer pipeline is led out of the reaction tank, it is lifted to the position with the same height as the designed water layer by a three-way joint as the overflow port; Step S103: Lay a geotextile on the inorganic filler layer, and then fill the composite filler on the geotextile.

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