An acid mine wastewater treatment process and wastewater treatment system

Abstract

This application relates to the field of wastewater treatment technology, specifically disclosing a process and system for treating acidic mine wastewater. The acidic mine wastewater treatment process provided by this application includes the following steps: wastewater pretreatment, three-stage alkali precipitation, sludge recycling, multi-effect deep filter treatment, and fiber filter plate deep filtration. The three-stage alkali precipitation involves adjusting the pH value of the water using a composite alkali, followed by three stages of reaction precipitation. The pH value of the water in the first-stage reaction precipitation is 3.5-4.5, the pH value of the water in the second-stage reaction precipitation is 5.5-7.0, and the pH value of the water in the third-stage reaction precipitation is 8.5-9.5. The acidic mine wastewater treatment process provided by this application can completely remove various metals such as iron, manganese, copper, zinc, cadmium, nickel, and aluminum from acidic wastewater. Furthermore, it has low operating costs, low sludge production, and long filter lifespan, showing promising application prospects.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology, specifically to an acidic mine wastewater treatment process and wastewater treatment system. Background Technology

[0002] Mining and non-ferrous metal smelting processes continuously generate large quantities of acidic mine wastewater. This wastewater is highly acidic, contains high levels of sulfates, and is rich in various toxic and harmful heavy metals such as iron, manganese, copper, zinc, cadmium, nickel, and aluminum. Long-term, uncontrolled discharge of this wastewater can cause severe damage to surrounding soil, waterways, and the ecological environment. With increasing environmental awareness and stricter standards, the effective treatment of acidic mine wastewater can not only reduce environmental pollution but also achieve water resource recycling, demonstrating significant environmental and economic value.

[0003] Currently, the commonly used methods for treating acidic wastewater in the industry mainly involve a single-stage neutralization with lime, single-stage flocculation sedimentation, and pre-filter filtration. However, these methods have several drawbacks: First, the precision of adjusting pH with a single alkali is poor, making it unsuitable for the differentiated precipitation requirements of various heavy metals, resulting in the easy residue and excessive levels of difficult-to-remove heavy metals such as manganese and nickel. Furthermore, a single-stage alkali addition can cause drastic fluctuations in the water's pH, leading to a rebound in heavy metal dissolution and making the effluent quality extremely unstable. Second, most filters are located at the upstream stage of the process, directly contacting wastewater with high sediment and high concentrations of metal flocs, making them prone to scaling, caking, and clogging of the filter media, resulting in high maintenance frequency and short service life. Third, single-stage sedimentation cannot achieve stratified separation of pollutants, leading to a large amount of sludge production and high solid waste disposal costs. Fourth, conventional filtration equipment has limited purification precision, making it difficult to remove ultrafine colloidal pollutants from the water. The effluent only meets the wastewater discharge limits and cannot meet the high-standard water use requirements for ecological replenishment and landscape reuse.

[0004] Therefore, developing a novel acidic mine wastewater treatment process that features precise graded neutralization, low operating costs, low sludge production, long filter life, and effluent that meets surface water standards is a pressing technical challenge in this field. Summary of the Invention

[0005] In order to overcome the problems of high operating costs, unstable or substandard effluent quality, and short service life of existing acidic wastewater treatment methods, this application provides an acidic mining wastewater treatment process and wastewater treatment system.

[0006] In a first aspect, this application provides an acidic mine wastewater treatment process, employing the following technical solution: An acidic mine wastewater treatment process includes the following steps: wastewater pretreatment, three-stage alkali precipitation, sludge recycling, multi-effect deep filter treatment, and fiber filter plate deep filtration; The three-stage alkali precipitation process involves adjusting the pH of the water using a compound alkali, followed by three stages of reaction precipitation. The pH of the water in the first-stage reaction precipitation is 3.5-4.5, the pH of the water in the second-stage reaction precipitation is 5.5-7.0, and the pH of the water in the third-stage reaction precipitation is 8.5-9.5.

[0007] This application provides a treatment process for acidic mining wastewater. The process first removes large pieces of slag and suspended silt from the acidic mining wastewater through pretreatment, balancing the water quality, quantity, and influent acidity to reduce the load on subsequent treatment. Then, a three-stage alkali precipitation process is used: the first stage removes iron and aluminum ions; the second stage separates copper and zinc heavy metal ions; and the third stage deeply removes cadmium, manganese, and nickel heavy metal ions. This three-stage alkali precipitation process precisely matches the precipitation conditions for various heavy metals, ensuring complete removal of iron, manganese, copper, zinc, cadmium, nickel, and aluminum without residue or rebound. The sludge recycling process utilizes the returned settled sludge as seed crystals, accelerating floc formation and reducing reagent dosage and sludge discharge. Multi-effect deep filter treatment and fiber filter plate deep filtration further treat the settled water, improving the effluent quality.

[0008] Optionally, the composite alkali is composed of quicklime, limestone powder and sodium carbonate in a weight ratio of 8:(6-7):(4-6).

[0009] This application uses a compound alkali composed of quicklime, limestone powder, and sodium carbonate in a specific weight ratio. This compound alkali can replace traditional single lime, resulting in a smoother and more controllable neutralization reaction, more precise pH adjustment, and better suitability for the differentiated precipitation needs of various heavy metals. It avoids the problem of poor pH adjustment accuracy with single alkali agents leading to excessive residues of some difficult-to-remove heavy metals, and also prevents drastic pH fluctuations caused by single alkali additions, thus avoiding heavy metal dissolution rebound and ensuring stable effluent quality. Furthermore, the above ratio reduces the amount of reagents required, thereby significantly lowering overall operating costs.

[0010] The wastewater pretreatment involves passing the wastewater through a screen, a grit chamber, and a water quality equalization tank in sequence.

[0011] In this application, the wastewater pretreatment process enables acidic mine wastewater to first pass through a screen to intercept large particles such as stones and slag, then pass through a grit chamber to remove suspended silt, and finally pass through a water quality equalization tank to balance the water quality, quantity and acidity of the influent, thereby stabilizing the influent water quality and reducing the load on subsequent treatment.

[0012] Optionally, the multi-effect deep filter treatment step involves filtration using an alkaline filter media layer.

[0013] Optionally, the alkaline filter media layer includes a limestone filter media layer and a dolomite filter media layer.

[0014] The alkaline filter media layer of this application can further stabilize the pH of the water body by using limestone and dolomite slow-release alkaline filter media, construct a stable water environment that is conducive to inhibiting the re-dissolution of heavy metals, comprehensively improve the quality of the effluent, and ensure that all indicators of the effluent stably meet the requirements of the "Surface Water Environmental Quality Standard".

[0015] Optionally, in the fiber filter plate deep filtration step, the pore size of the fiber filter plate is 5-20 μm.

[0016] Secondly, this application provides a wastewater treatment system, including: a pretreatment unit, a multi-stage sedimentation unit, a sludge return unit, a deep filtration unit, and a compound alkali dosing system.

[0017] Optionally, the pretreatment unit includes a screen, a sedimentation tank, and a water quality conditioning tank connected in sequence.

[0018] Optionally, the outlet of the water quality conditioning tank is connected to the inlet of the primary reaction sedimentation tank, the outlet of the primary reaction sedimentation tank is connected to the inlet of the secondary reaction sedimentation tank, and the outlet of the secondary reaction sedimentation tank is connected to the inlet of the tertiary reaction sedimentation tank.

[0019] Optionally, the water quality regulating tank is also equipped with a submersible agitator and a level gauge, an inlet gate is provided at the inlet of the water quality regulating tank, and an outlet weir is provided at the outlet of the water quality regulating tank.

[0020] Optionally, the multi-stage sedimentation unit includes a primary reaction sedimentation tank, a secondary reaction sedimentation tank, and a tertiary reaction sedimentation tank; the compound alkali dosing system is connected to the three reaction sedimentation tanks respectively and is used to add compound alkali to each stage of the reaction sedimentation tank.

[0021] Optionally, the bottom of the three-stage reaction sedimentation tank is arranged in an inverted cone shape, and the aeration assembly includes a blower and an aeration disc. The blower is located outside the three-stage reaction sedimentation tank, and the aeration disc is located inside the bottom of the three-stage reaction sedimentation tank. The air outlet pipe of the blower is connected to the aeration disc.

[0022] Optionally, the sludge return unit includes a sludge return pipe, a sludge thickening filter press, and a return pump.

[0023] In this application, after the wastewater is treated by the pretreatment unit and the multi-stage sedimentation unit, the sludge return pipe of the sludge return unit can return the sludge deposited at the bottom of each sedimentation tank to the front-end reaction tank in proportion. The remaining sludge is then concentrated and filtered by the sludge thickening filter press. The return pump provides power for the sludge return, accelerates the floc coagulation and formation, and can greatly reduce the amount of reagents and sludge discharge, thereby reducing the cost of solid waste treatment.

[0024] Optionally, the sludge return pipe is also equipped with a sludge diversion valve and a sludge metering pump. The sludge diversion valve is located in front of the feed inlet of the sludge thickening filter press, and the sludge metering pump is located between the return pump and the sludge thickening filter press. The filtrate outlet of the sludge thickening filter press is connected to the water quality equalization tank through the filtrate return pipe.

[0025] Optionally, one end of the sludge return pipe is connected to the bottom sludge discharge port of the primary reaction sedimentation tank, the secondary reaction sedimentation tank, and the tertiary reaction sedimentation tank, respectively, and the other end of the sludge return pipe is connected to the inlet of the primary reaction sedimentation tank and the secondary reaction sedimentation tank; the sludge return pipe includes a first branch pipe, a second branch pipe, and a third branch pipe, one end of the first branch pipe, the second branch pipe, and the third branch pipe are respectively connected to the bottom sludge discharge port of the primary reaction sedimentation tank, the secondary reaction sedimentation tank, and the tertiary reaction sedimentation tank, and the other end of the first branch pipe, the second branch pipe, and the third branch pipe are all connected to the feed inlet of the sludge thickening filter press, and the liquid outlet of the sludge thickening filter press is connected to the inlet of the primary reaction sedimentation tank through the return pump.

[0026] Optionally, the deep filtration unit includes a multi-effect deep filter tank and a fiber filter plate filtration device; the multi-effect deep filter tank is provided with an alkaline filter media layer, and the fiber filter plate filtration device is provided with a fiber filter plate.

[0027] In this application, the multi-effect deep filter tank in the deep filtration unit is equipped with an alkaline filter media layer, which can accurately stabilize the pH of the effluent, adsorb trace amounts of residual heavy metals in the water, and trap escaped fine flocs; the fiber filter plate filtration device is equipped with a fiber filter plate, which can trap ultrafine suspended particles and nanoscale metal colloids, thereby improving the quality of the effluent.

[0028] Optionally, the outlet of the three-stage reaction sedimentation tank is connected to the inlet of the multi-effect depth filter, and the outlet of the multi-effect depth filter is connected to the inlet of the fiber filter plate filtration device.

[0029] Optionally, the multi-effect deep filter tank is provided with a support layer, the alkaline filter media layer and the effluent collection tank in sequence from bottom to top. The alkaline filter media layer includes a limestone filter media layer and a dolomite filter media layer.

[0030] Optionally, the support layer is located at the bottom of the pool body, and the effluent collection tank is located above the alkaline filter media layer and communicates with the inlet of the fiber filter plate filtration device.

[0031] Optionally, the fiber filter plate filtration device includes a filter box and a backwashing assembly; the fiber filter plate is inclinedly disposed in the filter box, and a drain outlet is provided at the bottom of the filter box; the backwashing assembly includes a backwashing water pipe and a backwashing pump; one end of the backwashing water pipe is connected to the backwashing pump, and the other end of the backwashing water pipe extends into the filter box and is located below the fiber filter plate.

[0032] Optionally, the composite alkali dosing system includes a quicklime storage tank, a limestone powder storage tank, a sodium carbonate storage tank, and a mixing tank.

[0033] Optionally, the outlets of the quicklime storage tank, limestone powder storage tank, and sodium carbonate storage tank are all connected to the inlet of the mixing tank.

[0034] Optionally, the wastewater treatment system further includes a water quality monitoring component; the water quality monitoring component includes a pH sensor and a heavy metal ion concentration sensor.

[0035] Optionally, the pH sensor and the heavy metal ion concentration sensor are respectively installed at the outlets of the primary reaction sedimentation tank, the secondary reaction sedimentation tank and the tertiary reaction sedimentation tank, and an electric regulating valve is installed on the dosing pipe, which is electrically connected to the water quality monitoring component.

[0036] In summary, this application has the following beneficial effects: 1. This application uses compound alkali instead of single lime, which can accurately adjust the pH value of the water in each stage of the reaction sedimentation tank, adapt to the different precipitation needs of various heavy metals, and make iron, manganese, copper, zinc, cadmium, nickel and aluminum completely removed without residue or rebound.

[0037] 2. The multi-stage sedimentation unit of this application adopts an independent tank structure, and the sedimentation of each stage does not interfere with each other, which can realize the separation of different materials and sludge. In conjunction with the sludge return unit, the settled sludge is returned to the front-end reaction tank as flocculant seeds, which can reduce the amount of sludge produced and reduce the cost of solid waste treatment.

[0038] 3. The multi-effect deep filter in the deep filtration unit of this application is placed after the filter, away from sewage with high sediment and high flocs, so there will be no scaling, caking, or clogging problems. The internal alkaline filter media can stabilize the pH of the water and adsorb trace amounts of residual heavy metals. Then, the fiber filter plate filtration device intercepts ultrafine suspended particles and nano-sized metal colloids, making the effluent clear and clean, and all indicators stably meet the surface water standards. Detailed Implementation

[0039] This application provides a process for treating acidic mine wastewater, comprising the following steps: (1) Wastewater pretreatment: Acidic mine wastewater from a polymetallic mining area is sequentially passed through a screen, a sedimentation tank, and a water quality regulating tank to remove large pieces of slag and suspended silt; (2) Three-stage alkali precipitation: After pretreatment, the wastewater is sent to the first-stage reaction sedimentation tank, and compound alkali is added to adjust the pH of the water to 3.5-4.5, which quickly precipitates and removes most of the iron and aluminum ions in the water; then the effluent from the first-stage sedimentation is sent to the second-stage reaction sedimentation tank, and compound alkali is added to adjust the pH to 5.5-7.0; then the effluent from the second stage is sent to the third-stage reaction sedimentation tank, the aeration device is turned on to fully oxidize, and compound alkali is added to adjust the pH to 8.5-9.5, which thoroughly precipitates and separates cadmium, manganese, and nickel, which are difficult to degrade heavy metals; the compound alkali is composed of quicklime, limestone powder and sodium carbonate in a weight ratio of 8:(6-7):(4-6); (3) Sludge recycling: 20-40% of the sludge settled at the bottom of the three-stage sedimentation tank is extracted and recycled to each stage of the reaction tank as flocculant seed, and the remaining sludge is sent to the filter press for dewatering. (4) Multi-effect deep filter treatment: The supernatant from the three-stage sedimentation flows into the multi-effect deep filter (containing limestone and dolomite filter media layers), using the slow-release alkaline filter media in the tank to stabilize the pH of the water and adsorb trace amounts of residual heavy metals in the water. (5) Fiber filter plate deep filtration: The effluent from the multi-effect deep filter flows through a fiber filter plate filtration device with a pore size of 5-20μm and is then treated.

[0040] All raw materials, reagents, solvents, etc. used in this application are commercially available.

[0041] The present application will be further described in detail below with reference to embodiments and performance testing. Example 1

[0042] Example 1 provides a process for treating acidic mine wastewater, comprising the following steps: (1) Wastewater pretreatment: Acidic mine wastewater from a polymetallic mining area is passed through a screen, a sedimentation tank and a water quality regulating tank in sequence to remove large pieces of slag and suspended silt. (2) Three-stage alkali precipitation: After pretreatment, the wastewater is sent to the first-stage reaction sedimentation tank, and compound alkali is added to adjust the pH of the water to 4.1±0.2, which quickly precipitates and removes most of the iron and aluminum in the water; then the effluent from the first-stage sedimentation is sent to the second-stage reaction sedimentation tank, and compound alkali is added to adjust the pH to 6.4±0.2; then the effluent from the second stage is sent to the third-stage reaction sedimentation tank, the aeration device is turned on to fully oxidize, and compound alkali is added to adjust the pH to 8.8±0.2, which thoroughly precipitates and separates cadmium, manganese, and nickel, which are difficult to degrade heavy metals; the compound alkali is composed of quicklime, limestone powder and sodium carbonate in a weight ratio of 8:6.5:5; (3) Sludge recycling: 30% of the sludge settled at the bottom of the three-stage sedimentation tank is extracted and recycled to each stage of the reaction tank as flocculant seed, and the remaining sludge is sent to the filter press for dewatering. (4) Multi-effect deep filter treatment: The supernatant from the three-stage sedimentation flows into the multi-effect deep filter (containing limestone and dolomite filter media layers), using the slow-release alkaline filter media in the tank to stabilize the pH of the water and adsorb trace amounts of residual heavy metals in the water. (5) Fiber filter plate deep filtration: The effluent from the multi-effect deep filter flows through a fiber filter plate filtration device with a pore size of 10μm and is then treated. Example 2

[0043] Example 2 provides a process for treating acidic mine wastewater. The difference between the above embodiment and Embodiment 1 is that the compound alkali is quicklime, limestone powder and sodium carbonate in a weight ratio of 8:6:4. Example 3

[0044] Example 3 provides a process for treating acidic mine wastewater. The difference between the above embodiment and Embodiment 1 is that the compound alkali is quicklime, limestone powder and sodium carbonate in a weight ratio of 8:7:5. Example 4

[0045] Example 4 provides a process for treating acidic mine wastewater. The difference between the above embodiments and Embodiment 1 is that the compound alkali is quicklime, limestone powder and sodium carbonate in a weight ratio of 1:1:1. Comparative Example 1

[0046] Comparative Example 1 provides an acidic mine wastewater treatment process. The difference between the above comparative example and Example 1 is that the compound alkali is replaced with single lime added in one step to neutralize to pH 8.8±0.2, and the three-stage alkali precipitation is not used. Comparative Example 2

[0047] Comparative Example 2 provides an acidic mine wastewater treatment process. The difference between the above comparative example and Example 1 is that the (4) multi-effect deep filter treatment is set after the wastewater pretreatment process and before the three-stage alkali precipitation, as a pre-filtration unit. Performance testing

[0048] Acidic mine wastewater (pH 2.3-3.9, metal concentrations: Fe 3534-6217 mg / L, Al 271-324 mg / L, Zn 186-228 mg / L, Cu 186-193 mg / L, Mn 290-574 mg / L, Cr 58-63 mg / L, Ni 3.5-6.2) from a polymetallic mining area was treated according to the treatment processes provided in Examples 1-4 and Comparative Examples 1-2, respectively. The test results of the treated wastewater and the operating cycle of the filter in the system are shown in Table 1 below.

[0049] Table 1. Test results of treated wastewater indicators obtained from Examples 1-4 and Comparative Examples 1-2

[0050] Table 1 shows that the heavy metal indicators in the effluent treated by Examples 1-4 consistently met the Class III standard requirements of the "Surface Water Environmental Quality Standard" (GB 3838-2002), with a comprehensive removal rate exceeding 99.8%, and the removal rates of Fe, Al, Cu, and Zn approaching 100%. Further comparison revealed that the treatment effect of Example 4 (compound alkali ratio of 1:1:1) was slightly worse than that of Examples 1-3, with relatively higher concentrations of difficult-to-remove heavy metals such as Mn and Ni in the effluent. This indicates that a low proportion of quicklime in the compound alkali affects the efficiency of the neutralization reaction and the precipitation effect of heavy metals. This demonstrates that the application's further use of quicklime, limestone powder, and sodium carbonate in a weight ratio of 8:(6-7):(4-6) as the compound alkali, along with a three-stage gradient alkali precipitation method, can accurately match the optimal precipitation pH range for various heavy metals, achieving graded and orderly removal of pollutants such as iron, aluminum, copper, zinc, manganese, chromium, and nickel.

[0051] Comparative Example 1, which used only a single lime addition for neutralization, resulted in effluent with Mn concentrations as high as 1.7 mg / L and Ni concentrations as high as 0.09 mg / L, significantly higher than Examples 1-4, and unable to consistently meet surface water standards. This is because single lime has poor precision in adjusting pH, cannot adapt to the differentiated precipitation requirements of various heavy metals, and the single addition of alkali caused drastic pH fluctuations in the water, leading to the rebound of some heavy metal dissolution.

[0052] Comparative Example 2 placed a multi-effect depth filter pre-filter. Although the concentrations of various heavy metals in the effluent basically met the standards, the filter's operating cycle was significantly shortened to less than 30 days. This is because the pre-filter directly contacts the wastewater with high sediment and high concentration of metal flocs, causing rapid scaling, compaction, and clogging of the filter media surface. In contrast, Examples 1-3 placed the multi-effect depth filter post-filter after all sedimentation processes, away from the wastewater with high sediment and high flocs. The filter's operating cycle could reach more than 180 days, significantly reducing the frequency and cost of operation and maintenance.

[0053] In summary, this application, through the synergistic effect of multiple processes including compound alkali three-stage gradient alkali precipitation, sludge recirculation seeding, post-processed multi-effect deep filter, and fiber filter plate fine filtration, not only achieves long-term stable compliance of effluent standards, but also effectively solves the operation and maintenance problem of filter clogging, while reducing sludge production and reagent dosage, resulting in significant economic and environmental benefits.

[0054] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A process for treating acidic mine wastewater, characterized in that, Includes the following steps: Wastewater pretreatment, three-stage alkali precipitation, sludge recycling, multi-effect deep filter treatment, and fiber filter plate deep filtration; The three-stage alkali precipitation process involves adjusting the pH of the water using a compound alkali, followed by three stages of reaction precipitation. The pH of the water in the first-stage reaction precipitation is 3.5-4.5, the pH of the water in the second-stage reaction precipitation is 5.5-7.0, and the pH of the water in the third-stage reaction precipitation is 8.5-9.

5.

2. The acidic mine wastewater treatment process according to claim 1, characterized in that, The composite alkali is composed of quicklime, limestone powder and sodium carbonate in a weight ratio of 8:(6-7):(4-6).

3. The acidic mine wastewater treatment process according to claim 1, characterized in that, The wastewater pretreatment involves passing the wastewater through a screen, a grit chamber, and a water quality equalization tank in sequence.

4. The acidic mine wastewater treatment process according to claim 1, characterized in that, The multi-effect deep filter treatment step involves filtration using an alkaline filter media layer.

5. The acidic mine wastewater treatment process according to claim 4, characterized in that, The alkaline filter media layer includes a limestone filter media layer and a dolomite filter media layer.

6. The acidic mine wastewater treatment process according to claim 1, characterized in that, In the deep filtration step using the fiber filter plate, the pore size of the fiber filter plate is 5-20 μm.

7. A wastewater treatment system, characterized in that, include: The system includes a pretreatment unit, a multi-stage sedimentation unit, a sludge return unit, a deep filtration unit, and a compound alkali dosing system.

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