Combined treatment process for treatment of difficult-to-treat acid mine wastewater

Abstract

The invention discloses a combined treatment process for treatment of difficult-to-treat acid mine wastewater. The combined treatment process comprises the following steps: conveying the acid mine wastewater into a pre-precipitation tank, and introducing hydrogen sulfide gas for pre-precipitation; supernate in the pre-sedimentation tank is conveyed into a biological mineralization tank to be subjected to biological mineralization treatment; the effluent of the biomineralization pool is subjected to gradient pH regulation and control for treatment, wherein the gradient pH regulation and control comprises first-stage pH regulation and control, first-stage flocculent precipitation, second-stage pH regulation and control, second-stage flocculent precipitation and third-stage pH regulation and control; and feeding the gradient pH three-stage regulation and control effluent into a deep desulfurization tank for deep desulfurization, and returning hydrogen sulfide gas generated by the deep desulfurization tank to the pre-sedimentation tank for cyclic utilization. According to the invention, wastewater treatment is carried out through a physical-chemical-biological-micro-electric coupling process, the defects that heavy metals in the effluent of acid mine wastewater are difficult to reach the standard, the use amount of chemicals is large, the generation amount of sludge is large and the desulfurization cost is high are overcome, meanwhile, by-products such as Schwertmannite and sulfurized heavy metals can be recovered, and the final effluent is ensured to stably reach the standard.

Description

[0001] The present application belongs to the technical field of wastewater treatment, and particularly relates to a combined treatment process for treating refractory acid mine wastewater. 2- The present application belongs to the technical field of wastewater treatment, and particularly relates to a combined treatment process for treating refractory acid mine wastewater. 2- The present application belongs to the technical field of wastewater treatment, and particularly relates to a combined treatment process for treating refractory acid mine wastewater. BACKGROUND

[0002] With the continuous development of mineral resources, acid mine wastewater containing various heavy metals is generated in the process of mining, ore dressing and tailings stacking. Most of the acid mine wastewater (AMD) is directly discharged without treatment. AMD has high concentration of heavy metals and low pH value, which has caused serious negative impact on mining production and ecological environment, and has attracted extensive attention of domestic and foreign scholars. How to effectively treat AMD, protect the ecological environment and ensure the sustainable development of resources is an important problem currently faced. Physical and chemical method, microbial method and artificial wetland method are commonly used methods for treating AMD. The most commonly used method in chemical method is neutralization and precipitation method. The neutralization method is to add a neutralizing agent to adjust the pH value of AMD, so that the metal ions in the wastewater form hydroxide and separate from water. Common neutralizing agents include lime, limestone, soda and caustic soda. The neutralization and precipitation method using lime and limestone is most widely used in AMD treatment.

[0003] Because these acid waters are generally rich in copper, iron, sulfate and other substances, the commonly used treatment method is step-by-step precipitation method, that is, first iron removal pretreatment is carried out, then valuable copper is recovered by sulfidation method, and then other heavy metals in the acid water are removed by lime neutralization method (HDS method). However, this method will produce a large amount of neutralization slag, and because iron ions form a precipitate with calcium sulfate in the neutralization section, the neutralization slag not only contains calcium sulfate, but also contains a large amount of iron hydroxide and other precipitates, and thus the grade of calcium sulfate cannot meet the standard of industrial by-product gypsum for cement, and cannot be comprehensively utilized, but can only be stored and disposed as general industrial solid waste, which not only wastes resources, but also occupies a large amount of land.

[0004] In addition, the technology for removing manganese from acid mine wastewater is extremely difficult. In industry, acid mine wastewater is usually first treated by sulfidation precipitation method to recover or remove copper ions, then lime milk is added and aeration is carried out to adjust the pH value of the wastewater to 7-8 for neutralization treatment. After neutralization treatment, the Cu 2+ , Pb 2+ , Zn2+ The concentration of metal ions can generally reach the discharge standard, while the concentration of Mn 2+ is usually higher than 15 mg / L, failing to reach the discharge standard (the discharge standard of Mn 2+ is <2 mg / L).

[0005] In order to solve the technical problem of removing manganese from acid mine wastewater and reduce the treatment cost, the patent application 202510677508.3 provides a method for removing manganese and recovering manganese from acid mine wastewater. The method comprises: removing iron from acid mine wastewater to obtain an iron-removed supernatant, adding a manganese removal agent to the iron-removed supernatant to obtain manganese precipitation slag and a manganese-removed supernatant, mixing the manganese precipitation slag with sulfuric acid to obtain leaching liquid and leaching residue, and electrolyzing the leaching liquid to obtain metallic manganese; the manganese removal agent is sodium silicate and / or sodium metasilicate. However, experimental research shows that this method is difficult to be used for treating acid mine wastewater with pH of 2.1-3.5, Mn concentration of ≥200 mg / L, Cu, Fe, Zn, Al, SO4 2- content exceeding the standard.

[0006] Therefore, it is urgent to develop a method for efficiently treating acid mine wastewater with seriously excessive Mn, Cu, Fe, Zn, Al, SO4 2- content, which has low cost, high efficiency and stable effluent. SUMMARY

[0007] The purpose of the present application is to provide a combined treatment process for treating acid mine wastewater, which can not only efficiently and energy-savingly ensure that the effluent of the mine acid wastewater treatment facility is stable and meets the standard, but also recover by-product minerals, sulfidized heavy metals and the like.

[0008] To achieve the above-mentioned purpose of the present application, a combined treatment process for treating acid mine wastewater is implemented by the following steps:

[0009] S1, pre-deposition

[0010] The acid mine wastewater with pH of 2.1-3.5, Mn concentration of ≥200 mg / L, Fe concentration of ≥300 mg / L and SO4 2- concentration of ≥5000 mg / L is transported into a pre-deposition tank and hydrogen sulfide gas is introduced for pre-deposition; the residence time of the wastewater in the pre-deposition tank is 20-40 min, and the amount of hydrogen sulfide gas introduced is determined according to the pH of the acid mine wastewater and the concentrations of Mn, Cu, Fe, Zn, Al and SO4 2-The content is calculated and determined. By pre-deposition, part of the heavy metal ions in the wastewater, such as copper and mercury, can be removed. The heavy metal sulfide generated at the bottom of the pre-deposition tank can be sent to the flotation process to recover heavy metals.

[0011] S2, biomineralization

[0012] The supernatant in the pre-deposition tank is transported to the biomineralization tank for biomineralization treatment, and carbon fiber filament fillers with good conductivity are uniformly hung in the biomineralization tank. An aeration disc is arranged at the bottom of the biomineralization tank. The residence time of the supernatant in the biomineralization tank is 30-50 min, and the dissolved oxygen in the biomineralization tank is controlled at 1.5-4 mg / L. The carbon fiber filament fillers are pre-coated with microorganisms by Acidophilic Ferrous Oxidizing Thiobacillus (At.f). Under the action of oxygen and At.f bacteria, divalent iron in the wastewater is oxidized to trivalent iron or schulte mineral (a kind of iron hydroxyl sulfate mineral) or other iron oxides precipitate. Among them, the schulte mineral or other iron oxide precipitate can be recycled as adsorbent or pigment.

[0013] S3, gradient pH regulation

[0014] (1) pH primary regulation: the effluent of the biomineralization tank is fed into the pH primary regulation tank, and the pH of the effluent is increased to 5-6 by adding an alkaline agent. The residence time of the effluent of the biomineralization tank in the pH primary regulation tank is 40-60 min.

[0015] (2) Primary flocculation and precipitation: the mixed wastewater treated by the pH primary regulation tank is fed into the primary flocculation and precipitation tank. A pipe mixer is arranged at the inlet of the primary flocculation and precipitation tank, and a flocculant polyacrylamide is added in the pipe mixer. After the mixed wastewater is precipitated in the precipitation zone of the flocculation and precipitation tank, it is divided into an upper clear water layer, a middle sludge layer and a bottom sludge layer. An outlet for sludge is arranged at the bottom of the precipitation zone of the flocculation and precipitation tank. 28%-36% of the sludge in the bottom sludge layer is returned to the primary pH regulation tank, and the remaining sludge is discharged to a sludge tank for subsequent pressure filtration disposal.

[0016] (3) pH secondary regulation: the supernatant after the primary flocculation and precipitation is fed into the pH secondary regulation tank, and the pH of the effluent is increased to more than 10 by adding an alkaline agent. The residence time of the supernatant in the pH secondary regulation tank is 20-40 min.

[0017] (4) Secondary flocculation and sedimentation: the mixed wastewater treated by the pH secondary regulating tank is fed into a secondary flocculation and sedimentation tank, a pipe mixer is arranged at the water inlet end of the secondary flocculation and sedimentation tank, and a flocculant polyacrylamide is added in the pipe mixer; the mixed wastewater is settled in the settling zone of the secondary flocculation and sedimentation tank, and is divided into an upper clear water layer, a middle sludge layer and a bottom sediment layer; a sludge outlet is arranged at the bottom of the settling zone of the secondary flocculation and sedimentation tank, and 28% to 36% of the sediment in the bottom sediment layer is returned to the pH secondary regulating tank, and the remaining sediment is discharged to a sludge tank for subsequent pressure filtration disposal;

[0018] (5) pH tertiary regulation: the supernatant of the secondary flocculation and sedimentation tank is fed into a pH tertiary regulating tank, and oxalic acid is added to adjust the pH value to 7 to 8; most of the heavy metals and part of the sulfate radicals in the wastewater can be removed in this process; and the gradient pH regulation process can effectively reduce the addition of alkaline agents and the amount of sludge.

[0019] S4, deep desulfurization

[0020] The water treated by the gradient pH tertiary regulation is fed into a deep desulfurization tank for deep desulfurization, the residence time of the water in the deep desulfurization tank is not less than 20 h, and the water with a pH of 7 to 9, a concentration of Mn of 0.05 to 1.8 mg / L, a concentration of Cu of less than 0.006 mg / L, a concentration of Fe of 0.03 to 0.5 mg / L, a concentration of Zn of less than 0.006 mg / L, a concentration of Al of 0.3 to 1.5 mg / L and a concentration of SO4 2- ≤1300 mg / L is obtained; carbon fiber filaments with good conductivity are uniformly hung in the deep desulfurization tank, an exhaust pipe is arranged at the top of the deep desulfurization tank, and hydrogen sulfide gas generated in the deep desulfurization tank is discharged to the pre-sedimentation tank in S1 for recycling; the carbon fiber filaments are pre-coated with a microbial film by sulfate-reducing bacteria. Under anaerobic conditions, the sulfate-reducing bacteria reduce sulfate to negative divalent sulfur ions through dissimilation, and then generate sulfide or hydrogen sulfide. This step can deeply remove sulfate ions and residual heavy metals in the wastewater.

[0021] Further, the top end of the filler in the reaction chamber of the biological mineralization tank in S2 is connected to the anode of a micro power supply through an electric lead, and a connecting hole is arranged in the side wall of the reaction chamber of the biological mineralization tank; the side wall of the reaction chamber of the deep desulfurization tank in S4 is also provided with a connecting hole, the connecting holes of the biological mineralization tank and the deep desulfurization tank are connected to each other, and a proton exchange membrane is installed between the two connecting holes; the micro power supply provides a micro direct current of 5 to 30 mA.

[0022] Further, in S4, the top end of the filler in the reaction chamber of the deep desulfurization tank is connected to the cathode of a micro power supply through an electric lead, and the micro power supply provides a micro direct current of 5 to 30 mA.

[0023] Furthermore, in step S3, the alkaline agent is any one or any combination of two or more of quicklime, hydrated lime, and sodium hydroxide.

[0024] Preferably, the acidic mine wastewater fed in step S1 has a pH of 2.1–3.5, a Mn content of 250–350 mg / L, a Cu content of 12–30 mg / L, a Fe content of 300–400 mg / L, a Zn content of 90–110 mg / L, an Al content of 200–400 mg / L, and an SO4 content of [missing information]. 2- The concentration was between 5000 and 8000 mg / L; by adjusting the technical parameters of each step, step S4 achieved a pH of 7 to 9, with the following concentrations of pollutants: Mn 0.08–1.8 mg / L, Cu < 0.006 mg / L, Fe 0.03–0.5 mg / L, Zn < 0.006 mg / L, Al 0.3–1.5 mg / L, and SO42-. 2- 800~1300 mg / L of effluent.

[0025] Compared with existing technologies, this invention provides a combined treatment process for treating difficult-to-treat acidic mine wastewater. Through a physicochemical-biological-micro-electrostatic coupling process, it addresses the shortcomings of acidic mine wastewater effluent failing to meet heavy metal standards and incurring high desulfurization costs. Simultaneously, it can recover byproducts such as styrene minerals and heavy metal sulfides, ensuring efficient and energy-saving maintenance of stable effluent compliance from mine acidic wastewater treatment facilities. Specifically, it offers the following beneficial effects:

[0026] (1) The present invention adopts a physical-chemical-biological micro-electric coupling process, which can effectively increase the pH value of wastewater and remove heavy metals and sulfate from the water. On the other hand, the styrene minerals and heavy metal sulfides generated in the process of treating wastewater can be used as recyclable resources, thereby improving resource utilization and reducing desulfurization costs.

[0027] (2) The present invention adopts a micro-electrochemical catalytic process, which can provide oxygen in the biomineralization stage, reduce the aeration volume, and reduce the energy consumption of the blower. On the other hand, it can catalyze the reduction process of sulfate-reducing bacteria in the deep desulfurization stage, reduce the total amount of organic matter required for the sulfate reduction process, and the power consumption required by the micro-current power supply is quite small and can be ignored. Therefore, the water treatment facility using the process of the present invention can reduce the treatment cost and the amount of reagent used is small, which is especially suitable for the treatment of acidic mine wastewater with high sulfate concentration.

[0028] (3) The present invention adopts a combination of gradient pH control and sludge return process, which can effectively increase pH and improve the utilization rate of alkaline agents. Compared with the traditional neutralization method, it can reduce the consumption of alkaline agents, sludge volume and sludge moisture content.

[0029] (4) Experimental studies have shown that when the pH of the fed acidic mine wastewater is 2.1~3.5, the Mn content is 250~350 mg / L, the Cu content is 12~30 mg / L, the Fe content is 300~400 mg / L, the Zn content is 90~110 mg / L, the Al content is 200~400 mg / L, and the SO4 content is high, the water quality is suitable for the following conditions: 2- With a concentration of 5000-8000 mg / L, the final results showed a pH of 7-9 and concentrations of each pollutant as follows: Mn 0.08-1.8 mg / L, Cu < 0.006 mg / L, Fe 0.03-0.5 mg / L, Zn < 0.006 mg / L, Al 0.3-1.5 mg / L, and SO42-0.5 mg / L. 2- 800~1300 mg / L of effluent. Attached Figure Description

[0030] Figure 1 This is a principle flow diagram of a combined treatment process for treating difficult-to-treat acidic mine wastewater according to the present invention.

[0031] Figure 2 for Figure 1 The principle process flow diagram of the gradient pH control process unit. Detailed Implementation

[0032] To further understand the content of this invention, a detailed description of the invention is provided in conjunction with the embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0033] Example

[0034] The acidic mine wastewater from a certain mine was treated using the method of this invention. The specific treatment process is as follows, and the influent and effluent water quality are shown in Table 1.

[0035] S1, Pre-precipitation

[0036] Acidic mine wastewater is transported to a pre-sedimentation tank for pre-sedimentation, and hydrogen sulfide gas is introduced into the pre-sedimentation tank. The wastewater retention time in the pre-sedimentation tank is 30 minutes.

[0037] S2, biomineralization

[0038] The supernatant from the pre-sedimentation tank is transferred to a biomineralization tank for biomineralization treatment. The biomineralization tank contains uniformly suspended carbon fiber packing material with good electrical conductivity, and an aeration disc is installed at the bottom. The wastewater retention time in the biomineralization tank is approximately 30 minutes, and the dissolved oxygen is controlled at 1.5~4 mg / L. The carbon fiber packing material is pre-treated with *Thiobacillus ferrooxidans* (At.f.) to form a microbial biofilm. The top of the packing material is connected to the anode of a micro-power source via an electrical conductor.

[0039] S3, gradient pH control

[0040] (1) pH primary control: The effluent from the biomineralization tank is fed into the pH primary control tank. A certain amount of 10% quicklime slurry is added to raise the pH of the effluent to between 5 and 6. The retention time in the pH primary control tank is 60 min.

[0041] (2) Primary flocculation and sedimentation: The mixed wastewater, after pH adjustment in the primary pH control tank, enters the primary flocculation and sedimentation tank. A pipeline mixer is installed at the inlet of the primary flocculation and sedimentation tank, and polyacrylamide flocculant is added to the pipeline mixer at a dosage of 1 mg / L. After sedimentation in the sedimentation zone of the flocculation and sedimentation tank, the fed mixed wastewater is divided into an upper clear water layer, a middle sludge layer, and a bottom sediment layer; 1 / 3 of the sludge from the primary flocculation and sedimentation tank is returned to the pH control tank. The sedimentation time is 2 hours.

[0042] (3) pH secondary control: The supernatant after primary flocculation and sedimentation enters the pH secondary control tank. A certain amount of 10% quicklime milk is added to raise the pH of the effluent to above 10. The residence time in the pH secondary control tank is 20 min.

[0043] (4) Secondary flocculation and sedimentation: The mixed wastewater, after being adjusted by the pH secondary control tank, enters the secondary flocculation and sedimentation tank. A pipeline mixer is installed at the inlet of the secondary flocculation and sedimentation tank, and polyacrylamide flocculant is added to the pipeline mixer at a dosage of 1 mg / L. After sedimentation in the sedimentation zone of the secondary flocculation and sedimentation tank, the fed mixed wastewater is divided into an upper clear water layer, a middle sludge layer, and a bottom sediment layer; 1 / 3 of the sludge from the secondary flocculation and sedimentation tank is returned to the pH control tank. The sedimentation time is 2 hours.

[0044] (5) pH three-stage adjustment: feed the supernatant of the secondary flocculation sedimentation tank into the pH three-stage adjustment tank and add 5% oxalic acid solution to adjust the pH value back to between 7 and 8.

[0045] S4, Deep Desulfurization

[0046] The effluent from the gradient pH control process enters a deep desulfurization tank for further desulfurization. The wastewater retention time is no less than 20 hours. The deep desulfurization tank contains uniformly suspended carbon fiber packing material with good conductivity. An exhaust pipe is installed at the top of the deep desulfurization tank, through which hydrogen sulfide gas generated in the deep desulfurization tank is directed to a pre-precipitation tank. The carbon fiber packing material is pre-treated with sulfate-reducing bacteria to form a microbial biofilm. The top of the packing material is connected to the cathode of a micro-power source via an electrical conductor. A connection hole is located between the sidewall of the reaction chamber of the biomineralization tank and the deep desulfurization tank, and a proton exchange membrane is installed within the connection hole. The micro-power source provides a 20mA micro-DC current.

[0047] Comparative Example

[0048] To better compare treatment effects, the traditional lime neutralization method was used as a control to treat the acidic wastewater from the mine. The treatment steps for the control were as follows:

[0049] Wastewater is pumped by a peristaltic pump to a neutralization reaction bottle for neutralization. The stirring rate is set to 400 r / min, and the dosing rate of the alkaline neutralizing agent is adjusted to stabilize the pH of the effluent between 9.8 and 10.2. The alkaline agent is 10% quicklime slurry, and the neutralization residence time is 0.5 h. The effluent then enters a flocculation bottle for flocculation. The flocculant dosage is 2 mg / L, and the stirring rate is set to 100 r / min. The effluent then enters an inclined plate sedimentation tank for sedimentation, with a residence time of 2 h. The effluent then enters the neutralization bottle for neutralization. A 5% oxalic acid solution is used for acid correction. The dosing rate of the dilute acid peristaltic pump is set to maintain the pH of the effluent from the acid correction bottle between 6 and 9. The effluent then enters an effluent tank.

[0050] Table 1. Influent and Effluent Water Quality of Examples and Comparative Examples

[0051]

[0052] As shown in Table 1, the acidic mine wastewater treated in the examples had a pH of only 2.1-3.3, while the Mn content was as high as 250-350 mg / L, and SO4 content was also high. 2- The concentration of pollutants is as high as 5000-8000 mg / L, with high levels of other elements such as Cu, Fe, Zn, and Al, making it an extremely difficult-to-treat acidic mine wastewater. In the examples, the method of this invention was used to treat a certain acidic mine wastewater, ultimately yielding a solution with a pH of 7-9 and the following concentrations of pollutants: Mn 0.08-1.8 mg / L, Cu < 0.006 mg / L, Fe 0.03-0.5 mg / L, Zn < 0.006 mg / L, Al 0.3-1.5 mg / L, and SO42-120 mg / L. 2-The effluent concentration of 800-1300 mg / L exceeded the requirements of the emission standard for pollutants from iron ore mining and beneficiation industry, GB 28661-2012, achieving unexpected technical results. In contrast, the traditional lime neutralization method resulted in effluent with Mn content frequently exceeding the standard, and the sulfur reduction effect was not significant.

Claims

1. A combined treatment process for treating difficult-to-treat acidic mine wastewater, characterized in that... The following steps are adopted: S1, Pre-precipitation pH range of 2.1-3.5, Mn concentration ≥200 mg / L, Fe concentration ≥300 mg / L, SO4 2- Acidic mining wastewater with a concentration ≥5000 mg / L is transported to a pre-sedimentation tank where hydrogen sulfide gas is introduced for pre-sedimentation. The wastewater retention time in the pre-sedimentation tank is 20-40 minutes, and the amount of hydrogen sulfide gas introduced is determined based on the pH of the acidic mining wastewater and the concentrations of Mn, Cu, Fe, Zn, Al, and SO42-. 2- The content level is determined by calculation. S2, biomineralization The supernatant in the pre-sedimentation tank is transferred to a biomineralization tank for biomineralization treatment. The biomineralization tank contains uniformly suspended carbon fiber packing material with good electrical conductivity, and an aeration disc is installed at the bottom. The residence time of the supernatant in the biomineralization tank is 30-50 minutes, and the dissolved oxygen level is controlled at 1.5-4 mg / L. The carbon fiber packing material is pre-treated with *Thiobacillus ferrooxidans* for microbial biofilm formation. S3, gradient pH control (1) pH primary control: The effluent from the biomineralization tank is fed into the pH primary control tank, and the pH of the effluent is raised to between 5 and 6 by adding alkaline agents. The residence time of the effluent from the biomineralization tank in the pH primary control tank is 40 to 60 minutes. (2) Primary flocculation sedimentation: The mixed wastewater that has been adjusted by the pH primary control tank enters the primary flocculation sedimentation tank. A pipeline mixer is installed at the inlet end of the primary flocculation sedimentation tank. Flocculant polyacrylamide is added to the pipeline mixer. After the mixed wastewater is settled in the sedimentation zone of the flocculation sedimentation tank, it is divided into an upper clear water layer, a middle sludge layer and a bottom sludge layer. A sludge outlet is provided at the bottom of the sedimentation zone of the flocculation sedimentation tank. 28% to 36% of the sludge in the bottom sludge layer is returned to the primary pH control tank. The remaining sludge is discharged to the sludge tank for subsequent pressure filtration treatment. (3) pH secondary control: The supernatant after primary flocculation and sedimentation enters the pH secondary control tank. Alkaline agents are added to raise the pH of the effluent to above 10. The supernatant stays in the pH secondary control tank for 20-40 minutes. (4) Secondary flocculation sedimentation: The mixed wastewater, after being regulated by the pH secondary control tank, enters the secondary flocculation sedimentation tank. A pipeline mixer is installed at the inlet end of the secondary flocculation sedimentation tank. Flocculant polyacrylamide is added to the pipeline mixer. After sedimentation in the sedimentation zone of the secondary flocculation sedimentation tank, the mixed wastewater is divided into an upper clear water layer, a middle sludge layer and a bottom sludge layer. A sludge outlet is provided at the bottom of the sedimentation zone of the secondary flocculation sedimentation tank. 28% to 36% of the sludge in the bottom sludge layer is returned to the pH secondary control tank, and the remaining sludge is discharged into the sludge tank for subsequent pressure filtration treatment. (5) Three-stage pH adjustment: The supernatant from the secondary flocculation sedimentation tank is fed into the three-stage pH adjustment tank and oxalic acid is added to adjust the pH value back to between 7 and 8; S4, Deep Desulfurization The effluent with a three-stage pH gradient control is fed into a deep desulfurization tank for advanced desulfurization. The retention time of the effluent in the deep desulfurization tank is no less than 20 hours, resulting in a pH of 7-9 and the following concentrations of pollutants: Mn 0.05-1.8 mg / L, Cu < 0.006 mg / L, Fe 0.03-0.5 mg / L, Zn < 0.006 mg / L, Al 0.3-1.5 mg / L, and SO42-. 2- The effluent concentration is ≤1300mg / L; the deep desulfurization tank is uniformly filled with carbon fiber packing material with good electrical conductivity. An exhaust pipe is installed at the top of the deep desulfurization tank. The hydrogen sulfide gas generated in the deep desulfurization tank is circulated to the pre-precipitation tank in step S1 through the exhaust pipe. The carbon fiber filler is pre-treated with sulfate-reducing bacteria to form a microbial film.

2. The combined treatment process for treating difficult-to-treat acidic mine wastewater as described in claim 1, characterized in that: In step S2, the top of the packing material in the reaction chamber of the biomineralization tank is connected to the anode of the micro-power source by an electrical wire, and there is a connection hole on the side wall of the biomineralization tank reaction chamber; in step S4, the side wall of the deep desulfurization tank reaction chamber is also provided with a connection hole, and the connection hole of the biomineralization tank reaction chamber is connected to the connection hole of the deep desulfurization tank reaction chamber, and a proton exchange membrane is installed between the two connection holes; the micro-power source provides a micro DC current of 5~30mA.

3. The combined treatment process for treating difficult-to-treat acidic mine wastewater as described in claim 2, characterized in that: In step S4, the top of the packing material in the reaction chamber of the deep desulfurization tank is connected to the cathode of a micro power source by an electrical wire, and the micro power source provides a small DC current of 5~30mA.

4. A combined treatment process for treating difficult-to-treat acidic mine wastewater as described in claim 1, 2, or 3, characterized in that: In step S3, the alkaline agent is any one or any two or more of quicklime, hydrated lime, and sodium hydroxide.

5. The combined treatment process for treating difficult-to-treat acidic mine wastewater as described in claim 4, characterized in that: The acidic mine wastewater fed into step S1 has a pH of 2.1–3.3, a Mn content of 250–350 mg / L, a Cu content of 12–30 mg / L, a Fe content of 300–400 mg / L, a Zn content of 90–110 mg / L, an Al content of 200–400 mg / L, and an SO4 content of [missing information]. 2- The concentration was between 5000 and 8000 mg / L; by adjusting the technical parameters of each step, step S4 achieved a pH of 7 to 9, with the following concentrations of pollutants: Mn 0.08–1.8 mg / L, Cu < 0.006 mg / L, Fe 0.03–0.5 mg / L, Zn < 0.006 mg / L, Al 0.3–1.5 mg / L, and SO42-. 2- 800~1300 mg / L of effluent.

6. The combined treatment process for treating difficult-to-treat acidic mine wastewater as described in claim 4, characterized in that: In step S1, the heavy metal sulfides generated at the bottom of the pre-sedimentation tank are comprehensively recovered using flotation.

7. The combined treatment process for treating difficult-to-treat acidic mine wastewater as described in claim 4, characterized in that: The precipitates of Schist minerals or other iron oxides generated in step S2 can be used as adsorbents or pigments.

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