A method for treating mine wastewater

Abstract

The application provides a mine wastewater treatment method, and belongs to the technical field of environmental engineering. The mine wastewater treatment method comprises the following steps: S1: performing pre-oxidation treatment on wastewater, then adding a composite flocculant to perform magnetic flocculation and precipitation, and performing magnetic powder recovery on obtained precipitation sludge to obtain non-magnetic sludge and magnetic flocculation effluent; S2: passing the magnetic flocculation effluent into a chelating resin column to perform adsorption; S3: adding a neutralizing agent to the resin effluent to perform precipitation and obtain neutralized effluent; S4: passing the neutralized effluent into an anaerobic biological filter tank to obtain purified water and biological sludge; and S5: mixing the non-magnetic sludge, neutralized precipitation sludge and biological sludge, adding a composite conditioning agent to perform conditioning, and then performing dewatering treatment. The method considers stable removal of pollutants, recovery of valuable metals and sludge reduction, solves problems such as unstable removal of heavy metals and inability to recover valuable metals in traditional methods, and is suitable for popularization and application.

Description

Technical Field

[0001] This application relates to the field of environmental engineering technology, and in particular to a method for treating mine wastewater. Background Technology

[0002] Acidic mine wastewater typically has a low pH (2-4), contains high concentrations of sulfate (2000-5000 mg / L) and various heavy metal ions such as iron, arsenic, lead, cadmium, nickel, copper, zinc, and manganese, and is accompanied by high levels of suspended solids.

[0003] Currently, the most common method for treating acidic mine wastewater is lime neutralization precipitation. This method adjusts the pH by adding lime, causing most heavy metals to precipitate as hydroxides, and simultaneously generating gypsum to remove some sulfates. However, neutralization precipitation has the following significant drawbacks: First, for amphoteric metal pollutants such as arsenic, the removal rate of neutralization precipitation alone is unstable, especially when pH is not properly controlled, which can easily lead to redissolution; second, the neutralization process generates a large amount of hydrophilic metal hydroxide sludge, which has high water content and poor dewatering performance, making subsequent treatment and disposal difficult; third, valuable metals in the wastewater, such as nickel, cobalt, and cadmium, are diluted by a large amount of neutralized sludge, almost losing their recovery value.

[0004] To overcome some of the problems, sulfide precipitation and biological methods have also been researched and applied. Sulfide precipitation involves adding sodium sulfide to form sulfides with extremely low solubility in metals, but its removal effect on anions such as arsenate is limited, and the reagents are expensive and prone to generating hydrogen sulfide gas, causing secondary pollution. Biological methods mainly utilize sulfate-reducing bacteria (SRB) to reduce sulfate to sulfides while simultaneously precipitating metal ions. However, SRB are sensitive to influent pH and heavy metal toxicity. Conventional acidic mine wastewater requires large amounts of alkali for pre-neutralization before entering the biological system, and the system has slow start-up, its operational stability is significantly affected by water quality fluctuations, and problems such as deterioration of sulfate removal efficiency or even reactor acidification often occur. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a method for treating mine wastewater.

[0006] Specifically, the first aspect of this application provides a method for treating mine wastewater, including the following steps: S1: The wastewater is pre-oxidized, then a composite flocculant is added for magnetic flocculation and sedimentation, and the resulting precipitated sludge is recovered by magnetic powder to obtain non-magnetic sludge and magnetically flocculated effluent. S2: Pass the magnetically flocculated effluent into a chelating resin column for adsorption, and collect the resin effluent; S3: Add lime slurry to the resin effluent as the first neutralizing agent for primary precipitation, control the pH at 5.0-5.5, and after solid-liquid separation, add a mixed slurry containing lime and lightly calcined magnesium oxide to the obtained clear liquid as the second neutralizing agent for secondary precipitation, control the pH at 9.0-9.5, and obtain neutralized effluent; S4: Adjust the pH of the neutralized effluent to 6.8-7.2, and then pass it into an anaerobic biological filter to obtain purified water and biological sludge; the anaerobic biological filter is filled with iron-carbon micro-electrolysis packing material and biological carrier. S5: Mix the non-magnetic sludge produced in step S1, the secondary sedimentation sludge produced in step S3, and the biological sludge produced in step S4, add a composite conditioner for conditioning, and then perform dewatering treatment.

[0007] Furthermore, the pre-oxidation treatment in step S1 uses hydrogen peroxide as the oxidant.

[0008] Furthermore, the composite flocculant is composed of polyferric sulfate, magnetic powder and anionic polyacrylamide, with a mass ratio of 100:15-25:0.5-1.0.

[0009] Furthermore, step S2 also includes reducing and filtering the magnetic flocculation effluent; Sodium bisulfite is added during the reduction process to remove residual oxidant; The filtration accuracy is 5-10 μm.

[0010] Furthermore, the chelating resin column mentioned in step S2 is an aminophosphonic acid-based chelating resin.

[0011] Furthermore, in the mixed slurry containing lime and lightly calcined magnesium oxide described in step S3, the dry weight ratio of lime to lightly calcined magnesium oxide is 2.5~3.5:1.

[0012] Furthermore, in step S4, carbon dioxide-containing gas is introduced into the neutralized effluent to adjust the pH; the carbon dioxide-containing gas comes from industrial flue gas or biogas purification tail gas.

[0013] Further, in step S4, the volume ratio of the iron-carbon micro-electrolysis filler to the biological carrier is 1:2-4; The operating temperature of the anaerobic biological filter is controlled at 25-35℃, and the hydraulic retention time is 18-24 hours.

[0014] Furthermore, the composite conditioner described in step S5 comprises acidic waste liquid, plant fiber powder, and polyacrylamide; The acidic waste liquid is steel pickling waste liquid, the plant fiber powder is rice husk powder, and the polyacrylamide is cationic polyacrylamide.

[0015] Furthermore, based on the absolute dry weight of the sludge to be treated, the dosage of the steel pickling waste liquid is 8-12%, the dosage of the rice husk powder is 3-5%, and the dosage of the cationic polyacrylamide is 0.1-0.2%.

[0016] The present invention has the following beneficial effects: This invention achieves preliminary removal of suspended solids and some heavy metals through pre-oxidation-magnetic flocculation sedimentation, recovers magnetic powder to reduce treatment costs, and then recovers valuable metals through chelation resin adsorption, realizing the resource utilization of waste. A two-stage neutralization sedimentation process, through precise pH control, gradually removes different types of heavy metals, effectively avoiding the re-dissolution of amphoteric metals and improving the stability of heavy metal removal. An anaerobic biological filter is simultaneously equipped with iron-carbon micro-electrolysis packing and biological carriers. The microenvironment generated by iron-carbon micro-electrolysis can alleviate the toxic inhibition of heavy metals on sulfate-reducing bacteria, improve system operational stability, and efficiently remove sulfates and residual organic matter. For mixed sludge from multiple sources, a composite conditioner composed of steel pickling waste liquid, rice husk powder, and cationic polyacrylamide is used for conditioning. While utilizing acidic waste liquid to improve sludge dewatering, plant fibers are used to improve the sludge pore structure, further enhancing the dewatering effect and reducing the difficulty of subsequent sludge treatment and disposal.

[0017] This method combines stable removal of pollutants, recovery of valuable metals, and reduction of sludge volume, solving the problems of unstable heavy metal removal, inability to recover valuable metals, and poor sludge dewatering performance in traditional mine wastewater treatment methods. It is suitable for widespread application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0019] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0020] An embodiment of the first aspect of this application provides a method for treating mine wastewater, comprising the following steps: S1: The wastewater is pre-oxidized, then a composite flocculant is added for magnetic flocculation and sedimentation, and the resulting precipitated sludge is recovered by magnetic powder to obtain non-magnetic sludge and magnetically flocculated effluent. S2: Pass the magnetically flocculated effluent into a chelating resin column for adsorption, and collect the resin effluent; S3: Add lime slurry to the resin effluent as the first neutralizing agent for primary precipitation, control the pH at 5.0-5.5, and after solid-liquid separation, add a mixed slurry containing lime and lightly calcined magnesium oxide to the obtained clear liquid as the second neutralizing agent for secondary precipitation, control the pH at 9.0-9.5, and obtain neutralized effluent; S4: Adjust the pH of the neutralized effluent to 6.8-7.2, and then pass it into an anaerobic biological filter to obtain purified water and biological sludge; the anaerobic biological filter is filled with iron-carbon micro-electrolysis packing material and biological carrier. S5: Mix the non-magnetic sludge produced in step S1, the secondary sedimentation sludge produced in step S3, and the biological sludge produced in step S4, add a composite conditioner for conditioning, and then perform dewatering treatment.

[0021] In this embodiment, the pre-oxidation treatment in step S1 uses hydrogen peroxide as the oxidant. The oxidant is industrial-grade hydrogen peroxide with a mass concentration of 27.5%, and the dosage is calculated based on 1.2 times the chemical oxygen demand (COD) of As(III) and Fe(II) in the influent. The acidic mine wastewater contains Fe... 2+ When the concentration is 200-800 mg / L, the dosage of hydrogen peroxide (27.5%) is 0.5-1.5 L / m³. 3 Wastewater. No external ferrous catalyst is needed; the wastewater itself has a high concentration of Fe. 2+ A Fenton-like system was formed. The reaction was carried out with stirring for 18 minutes, and the system pH was naturally maintained between 2.5 and 4.0. ORP monitoring values ​​were controlled at +450 to +550 mV to ensure complete oxidation of As(III) to As(V) and Fe. 2+ Partially oxidized to Fe 3+ .

[0022] In this embodiment, the pre-oxidized wastewater enters a two-stage mechanically stirred reaction tank (rapid mixing tank + slow mixing tank) + inclined tube sedimentation tank. The stirring speed in the rapid mixing tank is 150 rpm, and the stirring speed in the slow mixing tank is 30 rpm. Lime slurry (Ca(OH)2 concentration 10%) is added at the front end of the rapid mixing tank to precisely adjust the pH to 7.2±0.2. The composite flocculant is composed of polyferric sulfate, magnetic powder, and anionic polyacrylamide in a mass ratio of 100:15-25:0.5-1.0. The dosage of polyferric sulfate is 200 mg / L; the dosage of magnetic powder (Fe3O4, particle size 150-200 mesh) is 40 mg / L. Magnetic powder is surface-modified with a silane coupling agent (KH-550) to achieve hydrophobicity. Specifically, the magnetic powder is immersed in a 1% (w / w) KH-550 ethanol aqueous solution, stirred for 30 minutes, then removed, rinsed three times with ethanol, and dried in a 105℃ oven. It is then sealed and stored for later use. Anionic polyacrylamide (APAM, molecular weight 10-12 million): dosage 1-2 mg / L (0.8% of PFS mass), added at the front end of the slow mixing tank.

[0023] The sludge portion (mixed liquor with a sludge content of 0.5-1%) from the inclined tube sedimentation tank is pumped into a magnetic separator (magnetic field strength 3000-5000 GS) for magnetic powder recovery. The magnetic powder recovery rate is >99%. The recovered magnetic powder is directly returned to the rapid mixing tank for recycling, and the replenishment amount is only 2-5% of the initial amount to compensate for losses. The non-magnetic sludge discharged from the magnetic separator (mainly containing ferric hydroxide, ferric arsenate, and unrecovered fine flocs) is discharged into a non-magnetic sludge storage tank.

[0024] In this embodiment, the reduction treatment in step S2 involves adding 10% dilute sulfuric acid to the magnetic flocculation effluent to adjust the pH from 7.2 to 5.0±0.3. This range represents the optimal conditions for aminophosphonic acid resin adsorption of Cd, Ni, and Co. Sodium bisulfite (NaHSO3, purity ≥99%) is then added at a dosage of 5-10 mg / L to reduce the residual oxidant, lowering the ORP to below +200 mV and ensuring the absence of oxidizing properties.

[0025] The filtration system employs tubular or bag-type security filters with a filtration accuracy of 5-10 μm. The filter element is made of polypropylene. It is used to trap broken magnetic powder and fine particles that may penetrate the inclined tube sedimentation tank, protecting the chelating resin.

[0026] In this embodiment, the chelating resin column mentioned in step S2 is an aminophosphonic acid-based chelating resin. A two-stage tandem ion exchange column is used, with each column filled with an equal amount of the same type of chelating resin. Wastewater first enters the first-stage column, and its effluent is not directly discharged but used as the feed water for the second-stage column. The chelating resin used is a macroporous aminophosphonic acid chelating resin, brand Lanxess. During operation, the wastewater flows from top to bottom at a flow rate of 5-8 BV / h (bed volume / hour) and a contact time of 7-12 minutes. When the effluent from the first-stage exchange column has a Cd... 2+ or Ni 2+ When the concentration exceeds 0.01 mg / L, switch to regeneration and operate the second-stage column independently, connecting to a newly regenerated column. Regenerate countercurrently with 2 times the resin bed volume of 5% dilute sulfuric acid (approximately 50 g / L) at a flow rate of 2 BV / h, collecting a high-concentration solution rich in Cd, Ni, and Co (concentration can be enriched by 50-100 times), which can be directly recovered by subsequent electrowinning or precipitation.

[0027] In this embodiment, in step S3, the first neutralizing agent added to the resin effluent during the primary precipitation is lime milk, and the pH is precisely controlled between 5.0 and 5.5 to neutralize the residual Fe. 3+ Al 3+ and most of AsO4 3- Stable iron-aluminum arsenate precipitates are formed, and the settled sludge is discharged into an iron-arsenic sludge storage tank for separate treatment as hazardous waste or for stabilization, resulting in solid-liquid separation.

[0028] Preparation of the second neutralizing agent: Lime (CaO) and magnesium oxide (MgO, active content ≥85%, particle size 100-200 mesh) are mixed in a slurry tank with water at a dry weight ratio of 3:1 to prepare a 10% concentration slurry. The mixture is stirred and hydrated for more than 30 minutes to ensure that the MgO is fully pre-hydrated. This ensures that the lightly calcined magnesium oxide (MgO) has fully reacted with water to generate magnesium hydroxide Mg(OH)2 colloid with high chemical activity and large specific surface area before being added to the wastewater.

[0029] Add the second neutralizing agent to the neutralization tank, stir thoroughly, adjust the pH to 9.0-9.5, and react for 18-20 minutes to carry out secondary precipitation. The newly formed Mg(OH)₂ colloid carries a positive surface charge at pH 9.0-9.5, efficiently adsorbing negatively charged gypsum microcrystals and residual anions such as arsenate and leadate in the water.

[0030] The final effluent concentrations of heavy metals such as Cu, Zn, Mn, and Pb meet the Class I standard of the "Integrated Wastewater Discharge Standard". SO4 2- The concentration decreased from 3000 mg / L to approximately 800-1000 mg / L. The settled sludge was discharged into a neutralized sludge storage tank.

[0031] In this embodiment, in step S4, carbon dioxide-containing gas is introduced into the neutralized effluent to adjust the pH; the carbon dioxide-containing gas comes from industrial flue gas or biogas purification tail gas. Under stirring, the CO2 gas is blown into the water through a distributor, and an online pH meter controls the gas valve to precisely adjust the pH of the effluent from 9.5 to 7.0 ± 0.2.

[0032] In this embodiment, the anaerobic biological filter in step S4 is filled with iron-carbon micro-electrolysis packing material and biological carrier, and the volume ratio of the iron-carbon micro-electrolysis packing material to the biological carrier is 1:2-4. The iron-carbon micro-electrolysis filler (25%) is spherical or ellipsoidal in shape, with a particle size of 15-25 mm. The raw materials, by mass parts, include: 50 parts reduced iron powder, 50 parts carbon powder, 6 parts bentonite, and 1 part manganese dioxide. The porosity is ≥65%, and the bulk density is approximately 1.0 g / cm³. 3 It is filled into the lower 2-meter area of ​​the anaerobic biological filter.

[0033] The biological carrier is a modified volcanic rock biological carrier (75%): with a particle size of 20-40 mm and a specific surface area ≥15 m². 2 / g, bulk density approximately 0.8 g / cm³, surface positively charged. Filled in the upper middle part.

[0034] The modified volcanic rock biocarrier was prepared as follows: Volcanic rock was soaked in 1% dilute hydrochloric acid for 12 hours to remove surface impurities and micro-enlarge pores, then washed with water until neutral and dried. A mixed salt solution containing 1.0 mol / L magnesium chloride and 0.5 mol / L aluminum chloride was prepared. The pretreated volcanic rock was immersed in the above mixed salt solution and soaked in a 60℃ water bath for 6 hours. After draining, it was dried at 110℃ for 2 hours. The dried carrier was calcined at 400-500℃ for 3 hours.

[0035] A sulfate-reducing bacteria (SRB) biofilm is loaded onto a modified volcanic rock biocarrier. The biofilm is formed as follows: sulfate-reducing bacteria (manufactured by Shanghai Ruichu Biotechnology Co., Ltd.) are added to an anaerobic biological filter. Under conditions of pH 6.5-7.5 and temperature 25-35℃, sulfate-containing wastewater pretreated with carbon (pH 7.0±0.2) is used as the influent. The filter is continuously acclimatized and cultured until a visible blackish-gray biofilm forms on the surface of the modified volcanic rock biocarrier, and the sulfate removal rate in the effluent consistently reaches over 80% for 3 consecutive days. The entire start-up period typically lasts 7-15 days. The selected modified volcanic rock carrier is modified to be positively charged at pH 6.5-7.5. The surface of the SRB bacteria is typically negatively charged; the electrostatic adsorption between the two accelerates the initial attachment of the bacteria to the carrier surface, promoting rapid biofilm formation.

[0036] The anaerobic biological filter operates at a temperature of 25-35℃ with a hydraulic retention time of 18-24 hours. Glycerol or industrial ethanol is added as an external carbon source during operation to control COD / SO4. 2- The mass ratio is 0.6:1.

[0037] After every 25-30 days of continuous operation, shut off the inlet and outlet water, and perform low-intensity air-water combined backwashing with the treated effluent (stored in the clear water tank), at an air intensity of 5 L / (m²). 2 ·s), water strength 3 L / (m 2 The backwashing process takes 8-10 minutes. The recovery period after backwashing is approximately 4-6 hours.

[0038] In this embodiment, step S5 receives sludge from the non-magnetic sludge storage tank, the neutralized sludge storage tank, and the biological sludge storage tank in the actual production ratio (volume ratio, approximately 5:3:2), and the water content after mixing is approximately 96-98%.

[0039] The composite conditioning agent comprises acidic waste liquid, plant fiber powder, and polyacrylamide; the acidic waste liquid is steel pickling waste liquid, the plant fiber powder is rice husk powder, and the polyacrylamide is cationic polyacrylamide. Further, based on the oven-dry weight of the sludge to be treated, the dosage of the steel pickling waste liquid is 8-12%, used to partially dissolve inorganic sludge and break down cells; the dosage of the rice husk powder is 3-5%, serving as a framework building block; and the dosage of the cationic polyacrylamide (CPAM, molecular weight 8-10 million, ionicity 30%) is 0.1-0.2%, added in the later stages of conditioning to enhance floc size.

[0040] First, add the pickling waste liquid and stir for 15 minutes, then add the rice husk powder and stir for 10 minutes, and finally add the dissolved CPAM solution and stir for 5 minutes.

[0041] Dewatering is performed using a filter press at a pressure of 1.0-1.6 MPa and a diaphragm pressing pressure of 1.8-2.0 MPa. The resulting mud cake has a stable moisture content of ≤55% and a volume reduction of over 90%. The mud cake can be directly used as a mineralizer in cement production or as a raw material for soil amendment substrates.

[0042] Example The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0043] The raw water samples used in the following examples and comparative examples were taken from an acidic discharge outlet of a polymetallic sulfide mining area. The main water quality indicators were: pH=3.2, SS=480 mg / L, SO42-200 mg / L. 2- =3120 mg / L, total Fe=560 mg / L (of which Fe 2+ =380 mg / L), As=2.8 mg / L, Pb=1.5 mg / L, Cd=0.32 mg / L, Ni=0.85 mg / L, Cu=4.2 mg / L, Zn=6.8 mg / L, Mn=12.5 mg / L.

[0044] Polyferric sulfate: Manufacturer is Gongyi Yiqing Water Purification Materials Co., Ltd.; Polyacrylamide: The manufacturer is Guangdong Jinyigu Environmental Protection Technology Co., Ltd.

[0045] Example 1 A method for treating mine wastewater includes the following steps: S1: Add 27.5% H2O2 to the wastewater, with the dosage controlled by an online ORP instrument. Set the ORP endpoint value to +480 mV. Retain the wastewater in the oxidation tank for 18 min for pre-oxidation treatment. Then, add lime slurry to adjust the pH to 7.2, followed by 200 mg / L of polyferric sulfate and 40 mg / L of silane coupling agent-modified magnetic powder (200 mesh). Mix at 150 rpm for 4 min, then add 1.6 mg / L of anionic polyacrylamide and mix at 30 rpm for 12 min. Perform magnetic flocculation sedimentation. The precipitated sludge is treated with a magnetic separator to recover the magnetic powder, while the non-magnetic sludge is discharged into a storage tank. The SS of the magnetic flocculated effluent is 12 mg / L. S2: Add 10% dilute sulfuric acid to the magnetic flocculation effluent to adjust the pH from 7.2 to 5.0, and add sodium bisulfite at a dosage of 80 mg / L; filter using a 5μm security filter. After filtration, enter a two-stage aminophosphonic acid resin column (Lanxess brand), with a water flow rate of 6 BV / h, contact for 10 minutes, and collect the resin effluent; regenerate the resin with 5% dilute sulfuric acid to recover the metal liquid; S3: First, adjust the pH of the resin effluent to 5.3 with lime slurry, allow it to settle for 30 minutes, then add a mixture of lime and lightly calcined magnesium oxide (85% activity, 150 mesh) slurry (dry weight ratio 3:1, 10% concentration) to the clear liquid to adjust the pH to 9.3. Stir and react for 30 minutes, allowing the effluent to settle and yield neutralized effluent containing SO4. 2- =820 mg / L, settled sludge is discharged into neutralized sludge storage tank; S4: The neutralized effluent is fed with industrial flue gas containing 15% CO2 (N2 73.1%, CO2 15%, H2O 11.8%, SO2 0.1%), and the pH is adjusted to 7.0. Then it is fed into an anaerobic biological filter. The anaerobic biological filter is filled with iron-carbon packing material and modified volcanic rock biological carrier in a volume ratio of 1:3. The average particle size of the iron-carbon packing material is 20 mm, and the Fe:C ratio is 1:1. The average particle size of the modified volcanic rock biological carrier is 30 mm. A sulfate-reducing bacterial biofilm is loaded onto a modified volcanic rock biocarrier. The biofilm is formed as follows: sulfate-reducing bacteria (manufactured by Shanghai Ruichu Biotechnology Co., Ltd.) are added to an anaerobic biological filter. Under conditions of pH 6.5-7.5 and temperature 25-35℃, sulfate-containing wastewater (pH 7.0) is used as the influent. The filter is continuously acclimatized and cultured until a visible blackish-gray biofilm forms on the surface of the modified volcanic rock biocarrier, and the sulfate removal rate in the effluent consistently reaches over 80% for 3 consecutive days. At this point, the filter is started up. The entire start-up period typically lasts 7-15 days. Ethanol is added to increase the external COD / SO4 concentration. 2- With a mass ratio of 0.6:1, HRT=20 h, and temperature of 32℃, purified water and biological sludge were obtained. S5: Mix the non-magnetic sludge produced in step S1, the secondary sedimentation sludge produced in step S3, and the biological sludge produced in step S4 at a volume ratio of 5:3:2. Add 10% (by weight of oven-dried sludge) of steel pickling waste liquid and stir for 15 minutes, 4% of rice husk powder (100 mesh) and stir for 10 minutes, and 0.15% of CPAM and stir for 5 minutes. After conditioning, filter under 1.5 MPa to obtain sludge cake and filter effluent.

[0046] Results: The pH of the filtered water was 7.5, SS was 9 mg / L, and SO42- was 10 mg / L. 2- =168 mg / L, As 0.01 mg / L, Pb 0.02 mg / L, Cd 0.003 mg / L, Ni 0.02 mg / L, Cu 0.03 mg / L, Zn 0.04 mg / L, Mn 0.08 mg / L. Valuable metal recovery rates: Cd 97.2%, Ni 96.3%. Sludge cake moisture content 53.2%.

[0047] Example 2 This embodiment is basically the same as Embodiment 1, except that, based on the stable operation of Embodiment 1, on the 15th day of continuous operation, sodium arsenite solution was manually added to the influent tank, causing the total As concentration in the influent to gradually increase to 16.5 mg / L over 4 hours. This concentration was maintained for 48 hours, after which the As concentration was restored to the normal level of 2.8 mg / L. The As concentration in the effluent of each process and the final effluent quality were monitored throughout the entire process.

[0048] Results: Before the shock (stabilized data on day 14): final effluent As 0.01 mg / L, all indicators were the same as in Example 1; Shock period (days 15-16): The As concentration in the magnetic flocculation effluent from step S1 increased from the normal 0.35 mg / L to 2.8 mg / L (the removal rate decreased from 87.5% to about 83%, due to the significant increase in the influent concentration base, the absolute removal amount increased but the residual amount also increased). In step S2, the As concentration in the resin effluent is approximately 1.5 mg / L (the resin has low selectivity for As, and removal mainly relies on the front end). In step S3, the concentration of As in the effluent after secondary neutralization is controlled at 0.18-0.25 mg / L under the adsorption and co-precipitation effect of magnesium oxide. It only slightly exceeds the standard (As in Class III surface water ≤ 0.05 mg / L), but is far lower than the influent shock concentration. In step S4, the anaerobic biological filter showed no significant inhibition of microbial activity (sulfate-reducing bacteria have a certain tolerance to As, and most of it has already been intercepted upstream), with an effluent As concentration of 0.06-0.09 mg / L and a slight decrease in sulfate removal rate from 93% to 88%. Recovery period (days 17-19): After the influent As recovered to 2.8 mg / L, the effluent As dropped to 0.03 mg / L on day 18 and recovered to <0.01 mg / L on day 19. The sulfate removal rate recovered to over 92% on day 19. No system failure or restart was required throughout the process.

[0049] Results Analysis: Under an arsenic shock load nearly six times the normal concentration, relying solely on the system's segmented interception, the highest effluent As concentration only rose to 0.09 mg / L, far lower than the influent concentration of 16.5 mg / L, and autonomously recovered to the acceptable level within 48 hours. This fully demonstrates the buffering tolerance of the method of this invention to high arsenic shock loads. Even in the actual scenario of large fluctuations in the quality and quantity of acidic mine wastewater, it can still stably ensure that the effluent meets the standards, demonstrating excellent process resilience.

[0050] Example 3 This embodiment is basically the same as Embodiment 1, except that in step S3, the dry weight ratio of lime to lightly calcined magnesium oxide is adjusted to 4:1, the concentration of the mixed slurry is still 10%, and the secondary pH is 9.2.

[0051] Result: SO4 in effluent 2- =920 mg / L, slightly higher than 820 mg / L in Example 1 (due to reduced magnesium oxide, the inducing effect on gypsum co-precipitation is weakened), and the final effluent SO4² - =195 mg / L, still meeting the standard. The remaining indicators are the same as in Example 1.

[0052] Example 4 This embodiment is basically the same as embodiment 1, except that in step S4, the volume ratio of iron-carbon filler to volcanic rock carrier is adjusted from 1:3 to 1:4.

[0053] Result: Effluent SO4² - =210 mg / L, slightly exceeding 200 mg / L, but still far superior to conventional biological methods. This indicates that 1:3 is the preferred ratio.

[0054] Comparative Example 1 This comparative example is basically the same as Example 1, except that in step S2, sodium bisulfite is not added to the magnetic flocculation effluent for reduction, and a security filter is not used for filtration; the effluent is directly introduced into the resin column (pH adjusted to 5.0).

[0055] Results: After only 12 days of operation, the resin column pressure drop increased by 1.8 times, the resin color darkened, and the adsorption capacity decreased by approximately 35%. The iron content in the regenerated solution increased significantly, and the purity of the recovered Cd / Ni decreased. This demonstrates that the reduction safety step is crucial for extending resin life and maintaining high recovery purity.

[0056] Comparative Example 2 This comparative example is basically the same as Example 1, except that in step S3, the pH is adjusted to 9.3 using only lime milk, without adding lightly calcined magnesium oxide.

[0057] Result: Neutralized SO4 in effluent 2- The concentration of As was 1350 mg / L, approximately 65% ​​higher than the 820 mg / L in Example 1; the As concentration was 0.12 mg / L, which no longer met the requirements for subsequent biological influent (As is toxic to SRB). The final biological stage was affected by residual As and a higher SO4 load. 2- Impact, effluent SO4 2- =420 mg / L, the sulfate removal rate decreased significantly. This indicates that the adsorption and co-precipitation effects of magnesium oxide are indispensable for ensuring the overall performance of the system.

[0058] Comparative Example 3 This comparative example is basically the same as Example 1, except that in step S4, the neutralized effluent is not introduced into industrial flue gas containing 15% CO2, but the neutralized effluent with pH≈9.3 is directly pumped into the anaerobic filter.

[0059] Results: After 3 days of operation, the pH of the filter effluent rose to 8.9, and obvious white calcium scale and iron precipitates appeared on the surface of the micro-electrolysis packing material. + The leaching amount decreased to 1 / 5 of that in Example 1, SRB activity was suppressed, and the sulfate removal rate plummeted from >90% to about 40%, bringing the system close to collapse. This indicates that the neutral buffer environment formed by carbon conditioning is a necessary condition for the stable operation of the anaerobic biological filter. Utilizing carbon dioxide from industrial flue gas to adjust the pH not only saves on acid addition costs but also realizes the resource utilization of carbon dioxide in the flue gas, making the process green and environmentally friendly.

[0060] Comparative Example 4 This comparative example is basically the same as Example 1, except that the anaerobic biological filter in step S4 is not filled with iron-carbon packing material, but is entirely carried by volcanic rock carrier, while the other conditions are the same.

[0061] Results: To achieve a considerable sulfate removal rate (SO4) 2- <200 mg / L), so it is necessary to add ethanol to reduce COD / SO4. 2- Increasing the mass ratio to 1.2:1 doubles the carbon source consumption; furthermore, the system is extremely sensitive to fluctuations in influent pH. When the influent pH drops below 6.5, the effluent SO4 content increases significantly. 2- The concentration fluctuated to 300-400 mg / L. This comparative example demonstrates that the iron-carbon packing provides additional electron donors and pH buffering capacity, significantly reducing dependence on external carbon sources and improving system stability.

[0062] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for treating mine wastewater, characterized in that, Includes the following steps: S1: The wastewater is pre-oxidized, then a composite flocculant is added for magnetic flocculation and sedimentation, and the resulting precipitated sludge is recovered by magnetic powder to obtain non-magnetic sludge and magnetically flocculated effluent. S2: Pass the magnetically flocculated effluent into a chelating resin column for adsorption, and collect the resin effluent; S3: Add lime slurry to the resin effluent as the first neutralizing agent for primary precipitation, control the pH at 5.0-5.5, and after solid-liquid separation, add a mixed slurry containing lime and lightly calcined magnesium oxide to the obtained clear liquid as the second neutralizing agent for secondary precipitation, control the pH at 9.0-9.5, and obtain neutralized effluent; S4: Adjust the pH of the neutralized effluent to 6.8-7.2, and then pass it into an anaerobic biological filter to obtain purified water and biological sludge; the anaerobic biological filter is filled with iron-carbon micro-electrolysis packing material and biological carrier. S5: Mix the non-magnetic sludge produced in step S1, the secondary sedimentation sludge produced in step S3, and the biological sludge produced in step S4, add a composite conditioner for conditioning, and then perform dewatering treatment.

2. The method for treating mine wastewater according to claim 1, characterized in that, The pre-oxidation treatment in step S1 uses hydrogen peroxide as the oxidant; And / or, the composite flocculant is composed of polyferric sulfate, magnetic powder and anionic polyacrylamide in a mass ratio of 100: 15-25: 0.5-1.

0.

3. The method for treating mine wastewater according to claim 1, characterized in that, Step S2 also includes reduction treatment and filtration of the magnetic flocculation effluent; Sodium bisulfite is added during the reduction process; The filtration accuracy is 5-10 μm.

4. The method for treating mine wastewater according to claim 1, characterized in that, The chelating resin column mentioned in step S2 is an aminophosphonic acid-based chelating resin.

5. The method for treating mine wastewater according to claim 1, characterized in that, The dry weight ratio of lime to lightly calcined magnesium oxide in step S3 is 2.5~3.5:

1.

6. The method for treating mine wastewater according to claim 1, characterized in that, In step S4, carbon dioxide gas is introduced into the neutralized effluent to adjust the pH.

7. The method for treating mine wastewater according to claim 1, characterized in that, In step S4, the volume ratio of the iron-carbon micro-electrolysis filler to the biological carrier is 1:2-4. The operating temperature of the anaerobic biological filter is controlled at 25-35℃, and the hydraulic retention time is 18-24 hours.

8. The method for treating mine wastewater according to claim 1, characterized in that, The composite conditioner described in step S5 comprises acidic waste liquid, plant fiber powder, and polyacrylamide; The acidic waste liquid is steel pickling waste liquid, the plant fiber powder is rice husk powder, and the polyacrylamide is cationic polyacrylamide.

9. The method for treating mine wastewater according to claim 8, characterized in that, Based on the absolute dry weight of the sludge to be treated, the dosage of the steel pickling waste liquid is 8-12%, the dosage of the rice husk powder is 3-5%, and the dosage of the cationic polyacrylamide is 0.1-0.2%.