In-situ remediation method for acidic wastewater in coal mine goaf

Abstract

The invention relates to the technical field of wastewater treatment, and particularly discloses an in-situ remediation method for acid wastewater in a coal mine goaf. The remediation method provided by the invention comprises the following steps: injecting a calcium hydroxide suspension into the acidic wastewater from an injection well until the pH value of a water sample in a monitoring well is not lower than 3.5 continuously for 12 hours, and then stopping injection; after 1-3 days, a composite bacteriostatic agent is injected into the acid wastewater from the upstream injection well; 3-7 days later, calcium hydroxide turbid liquid is injected into the acid wastewater from the upstream injection well, and injection is stopped until the pH of the water sample of the monitoring well is not lower than 5.0 continuously for 12 hours; continuously monitoring the pH of the water sample of the monitoring well; and when the pH value is continuously lower than 4.0 for 12 hours, repeatedly injecting the composite bacteriostatic agent and the calcium hydroxide suspension until the pH value of the water sample of the monitoring well is not lower than 4.5 for 6 months, and completing the restoration. The restoration method provided by the invention can efficiently restore the acidic wastewater in the coal mine goaf, and is low in restoration cost and good in restoration effect.

Description

Technical Field

[0001] The present application relates to the technical field of wastewater treatment, and in particular to an in-situ remediation method for acidic wastewater in coal mine goafs. Background Art

[0002] Since the pyrite contained in the coal seam is exposed to the air after mining and oxidized to generate acidic substances, the acidic substances will dissolve in water to make the mine water acidic, and will also continuously dissolve various soluble substances in the coal seam, resulting in the concentration of harmful components in the mine water increasing or even exceeding the standard, and the water quality will deteriorate greatly. In addition, in the closed goaf environment, microorganisms such as acidophilic oxidizing bacteria also play an important role in the process of mine water becoming acidic. Therefore, how to effectively treat acidic wastewater in goafs has become an urgent problem that needs to be solved.

[0003] At present, the methods for treating acidic wastewater in coal mine goafs mainly include chemical precipitation, physical separation and biological treatment technology. Among them, the chemical precipitation method is to adjust the pH value by adding alkaline substances to the wastewater, so that the metal ions therein form insoluble compounds and can be removed; the physical separation method uses filtration or other separation equipment to remove suspended particles in the wastewater; and biological treatment uses the metabolism of microorganisms to degrade harmful substances in the wastewater and improve water quality conditions. However, the above existing methods are all terminal treatment after the acidic wastewater is discharged, which does not fundamentally solve the pollution problem at the source of the acidic wastewater, and these methods require continuous maintenance and operation during implementation, which increases the treatment cost and makes it difficult to achieve economical, efficient and long-lasting treatment. Summary of the invention

[0004] In order to overcome the problem that traditional methods cannot fundamentally solve the pollution source of acidic wastewater in coal mine goaf areas, the present application provides an in-situ remediation method for acidic wastewater in coal mine goaf areas.

[0005] The in-situ remediation method for acidic wastewater in coal mine goaf provided in this application adopts the following technical scheme: An in-situ remediation method for acidic wastewater in coal mine goafs comprises the following steps: (1) Inject calcium hydroxide suspension into the acidic wastewater from the injection well upstream of the coal mine goaf until the pH of the water sample in the monitoring well downstream of the coal mine goaf is not less than 3.5 for 12 consecutive hours, then stop the injection; (2) After an interval of 1-3 days, the composite antibacterial agent is continuously injected into the acidic wastewater from the upstream injection well for 36-48 hours; the injection flow rate of the composite antibacterial agent is 1-2‰ of the flow rate of the acidic wastewater; (3) After an interval of 3-7 days, inject calcium hydroxide suspension into the acidic wastewater from the upstream injection well until the pH of the water sample in the monitoring well is not less than 5.0 for 12 consecutive hours, and then stop the injection; (4) Continuously monitor the pH of the water sample in the monitoring well; when the pH is lower than 4.0 for 12 consecutive hours, repeatedly inject the composite antibacterial agent and calcium hydroxide suspension, that is, repeat steps (2-3); until the pH of the water sample in the monitoring well is not lower than 4.5 for 6 consecutive months, stop the operation and the repair is completed.

[0006] The present application provides an in-situ remediation method for acidic wastewater in coal mine goafs. The method first adds an appropriate amount of calcium hydroxide suspension to the acidic wastewater in the initial stage, which can quickly adjust the pH value of the water body to not less than 3.5, so as to prepare for the subsequent antibacterial agent to better exert the bactericidal effect; then, a certain amount of composite antibacterial agent is added to effectively inhibit the growth of acidophilic oxidizing bacteria, thereby inhibiting further acidification of the water body; then, calcium hydroxide suspension is added to increase the pH value of the acidic wastewater in the goaf to above 5.0, so that metal ions such as Al in the acidic wastewater are reduced. 3+ , Fe 3+ The flocs are formed to cover the surface of the mineral layer, which can remove metal ions on the one hand, and on the other hand, the flocs covering the surface of the mineral layer can achieve the effect of coating, which can isolate the contact between oxygen and minerals, inhibit the oxidation of minerals, and further reduce the generation of acidic wastewater; finally, by long-term monitoring of water quality changes and repeating the antibacterial and pH adjustment steps when necessary, it is ensured that the final effluent pH remains within the safe range (not less than 4.5) for 6 consecutive months, and shows a gradually improving trend, thereby achieving a stable repair effect. The in-situ remediation method for acidic wastewater in coal mine goafs provided in this application adopts a method that combines dynamic management and scientific regulation to achieve in-situ remediation of acidic wastewater in coal mine goafs, and has low remediation costs, good remediation effects, and good environmental protection.

[0007] Optionally, the composite antibacterial agent includes water, sodium lauryl sulfate, isothiazolinone and montmorillonite.

[0008] Optionally, the weight ratio of water, sodium dodecyl sulfate, isothiazolinone and montmorillonite is 100:(2.0-4.0):(1.6-2.3):(3-6).

[0009] The present application adopts sodium dodecyl sulfate, isothiazolinone and montmorillonite to prepare a composite antibacterial agent with a sustained-release effect. The composite antibacterial agent can inhibit the growth of acidophilic oxidizing bacteria in the acidic wastewater in the coal mine goaf for a long time, inhibit its oxidation and acid production, and thus inhibit the dissolution of heavy metals in the ore layer; in addition, under the joint action of sodium dodecyl sulfate, isothiazolinone and montmorillonite, not only the antibacterial effect can be improved, but also the stability of the system can be enhanced, ensuring that the pH value and heavy metal content of the acidic wastewater in the coal mine goaf are controlled within an ideal range, and finally realizing efficient and stable treatment of wastewater, completing the in-situ remediation goal, and significantly improving the environmental protection effect.

[0010] Optionally, the weight ratio of water, sodium dodecyl sulfate, isothiazolinone and montmorillonite is 100:(2.5-3.0):(1.8-2):(4-5).

[0011] In the present application, the ratio of the three components of sodium dodecyl sulfate, isothiazolinone and montmorillonite is further controlled within the above range, which can make the composite antibacterial agent have a more significant and longer-lasting bactericidal function, thereby making the remediation of acidic wastewater more thorough, and can make the heavy metal content of acidic wastewater lower after the remediation is completed. The pH and heavy metal content of water quality can be maintained in a stable and ideal state within 6-12 months, thereby achieving thorough treatment of acidic wastewater in coal mine goafs.

[0012] In some embodiments, the weight ratio of water, sodium dodecyl sulfate, isothiazolinone and montmorillonite can be 100:3:(2.0-2.5):5, 100:3:(2.0-3.0):5, 100:3:(2.0-4.0):5, 100:3:(2.5-3.0):5, 100:3:(2.5-4.0):5, 100:3:(3-4.0):5, 100:3:2:(3-4), 100:3:2:(3-5), 100:3:2:(3-6), 100:3:2:(4-5), 100:3:2:(4-6) or 100:3:2:(5-6).

[0013] In a specific embodiment, the weight ratio of water, sodium dodecyl sulfate, isothiazolinone and montmorillonite can also be 100:3:1.6:5, 100:3:1.8:5, 100:3:2:5, 100:3:2.3:5, 100:3:2:3, 100:3:2:4 or 100:3:2:6.

[0014] Optionally, the weight ratio of water, sodium dodecyl sulfate, isothiazolinone and montmorillonite is 100:3:2:5.

[0015] Optionally, the preparation method of the calcium hydroxide suspension is: mixing calcium hydroxide and water in a weight ratio of 1: (2.5-8), stirring evenly, and obtaining the calcium hydroxide suspension.

[0016] Optionally, the acidic wastewater from the coal mine goaf contains acidophilic oxidizing bacteria, aluminum ions and heavy metal ions.

[0017] Optionally, the heavy metal ions are one or more of iron, manganese, arsenic, lead, zinc, cadmium, chromium and copper.

[0018] Optionally, the pH of the acidic wastewater in the coal mine goaf is less than 4.5.

[0019] The method provided in this application is suitable for treating acidic wastewater in coal mine goafs with a pH value of less than 4.5. The water quality of the goafs treated by the in-situ remediation method provided in this application can gradually improve and stabilize, thereby achieving complete remediation of acidic wastewater in coal mine goafs. It should be noted that when the initial pH value of acidic wastewater in coal mine goafs is higher than 3.5, step (1) can be omitted and step (2) can be performed directly.

[0020] In summary, this application has the following beneficial effects: 1. The present application provides an in-situ remediation method for acidic wastewater in coal mine goafs. The method adjusts the pH of the wastewater by alternately using a calcium hydroxide suspension and a composite antibacterial agent, and inhibits the growth and reproduction of harmful microorganisms such as acidophilic oxidizing bacteria in the acidic wastewater, thereby preventing microorganisms from aggravating the acidification problem.

[0021] 2. The in-situ remediation method for acidic wastewater in coal mine goafs provided in the present application can cause the metal ions in the acidic wastewater to form flocs that cover the surface of the mineral layer. On the one hand, it can achieve the removal of heavy metal ions. On the other hand, the flocs covering the surface of the mineral layer can isolate the contact between oxygen and minerals, inhibit the oxidation of minerals, and further reduce the generation of acidic wastewater.

[0022] 3. The in-situ remediation method for acidic wastewater in coal mine goafs provided in this application adopts a method that combines dynamic management and scientific regulation to achieve in-situ remediation of acidic wastewater in coal mine goafs, and has low remediation costs, good remediation effects, and good environmental performance. DETAILED DESCRIPTION

[0023] An in-situ remediation method for acidic wastewater in coal mine goafs comprises the following steps: (1) An injection well is set up upstream of the coal mine goaf, and a monitoring well is set up downstream; calcium hydroxide suspension is added to the acidic wastewater in the coal mine goaf from the upstream injection well until the pH of the water sample in the monitoring well is not less than 3.5 for 12 consecutive hours, and then the addition is stopped; (2) After an interval of 1-3 days, a composite antibacterial agent is added from an upstream injection well to the acidic wastewater in the coal mine goaf for 36-48 hours; the injection flow rate of the composite antibacterial agent is 1-2‰ of the flow rate of the acidic wastewater; the composite antibacterial agent includes water, sodium dodecyl sulfate, isothiazolinone and montmorillonite; further, the weight ratio of the water, sodium dodecyl sulfate, isothiazolinone and montmorillonite is 100:(2.0-4.0):(1.6-2.3):(3-6); further, the weight ratio of the water, sodium dodecyl sulfate, isothiazolinone and montmorillonite is 100:(2.5-3.0):(1.8-2):(4-5).

[0024] (3) After an interval of 3-7 days, calcium hydroxide suspension is then added from the upstream injection well to the acidic wastewater in the coal mine goaf until the pH of the water sample in the monitoring well is not less than 5.0 for 12 consecutive hours, and then the addition is stopped; (4) Continuously monitor the pH of the water sample in the monitoring well; when the pH is lower than 4.0 for 12 consecutive hours, repeatedly inject the composite antibacterial agent and calcium hydroxide suspension, that is, repeat steps (2-3); until the pH of the water sample in the monitoring well is not lower than 4.5 for 6 consecutive months, stop the operation and the repair is completed.

[0025] In the present application, the CAS number of sodium dodecyl sulfate is 151-21-3, the CAS number of isothiazolinone is 55965-84-9, and the CAS number of montmorillonite is 1318-93-0. The raw materials, reagents, solvents, etc. used in the present application can all be obtained commercially.

[0026] The present application is further described in detail below in combination with preparation examples, embodiments, and performance testing experiments.

[0027] Preparation Example 1-7 Preparation Examples 1-7 each provide a composite antibacterial agent.

[0028] The difference between the above preparation examples is that the weight ratios of water, sodium dodecyl sulfate, isothiazolinone and montmorillonite in the composite antibacterial agent are specifically shown in Table 1 below.

[0029] The preparation method of the composite antibacterial agent provided in Preparation Example 1-7 is as follows: sodium dodecyl sulfate, isothiazolinone and montmorillonite are uniformly mixed according to the weight ratio shown in Table 1, and then dissolved in water to obtain the composite antibacterial agent.

[0030] Table 1 Weight ratio of sodium dodecyl sulfate, isothiazolinone and montmorillonite in the composite antibacterial agent of Preparation Example 1-7 Examples 1-7 Examples 1-7 respectively provide an in-situ remediation method for acidic wastewater in coal mine goaf areas.

[0031] The difference between the above embodiments is that the composite antibacterial agent is derived from Preparation Examples 1-7 respectively.

[0032] The in-situ remediation method for acidic wastewater in coal mine goaf provided in Examples 1-7 comprises the following steps: (1) A coal mine goaf was selected as the test area. The pH of the acidic wastewater in the coal mine goaf was 3.44, the iron content was 2778 mg / L, the manganese content was 54 mg / L, and the aluminum content was 1679 mg / L. The coal mine goaf was divided into 7 separate areas (test areas 1-7) from upstream to downstream, and injection wells were set up upstream and monitoring wells were set up downstream.

[0033] (2) Add calcium hydroxide suspension to the acidic wastewater in the coal mine goaf from the injection well upstream of the coal mine goaf until the pH of the water sample in the monitoring well is not less than 3.5 for 12 consecutive hours, then stop adding; (3) Two days later, a composite antibacterial agent was added from the upstream injection well to the acidic wastewater in the coal mine goaf for 42 hours (Test Areas 1-7 were added with Preparation Examples 1-7, respectively); the injection rate of the composite antibacterial agent was 1.5‰ of the acidic wastewater flow rate.

[0034] (4) After 5 days, calcium hydroxide suspension is added from the upstream injection well to the acidic wastewater in the coal mine goaf until the pH of the water sample in the monitoring well is not less than 5.0 for 12 consecutive hours, and then the addition is stopped; (5) Continuously monitor the pH of the water sample in the monitoring well; when the pH is lower than 4.0 for 12 consecutive hours, repeatedly inject the composite antibacterial agent and calcium hydroxide suspension, that is, repeat steps (3-4); until the pH of the water sample in the monitoring well is not lower than 4.5 for 6 consecutive months, stop the operation and the repair is completed.

[0035] The preparation method of the calcium hydroxide suspension is as follows: calcium hydroxide and water are mixed in a weight ratio of 1:5, and stirred evenly to obtain the calcium hydroxide suspension.

[0036] Example 8 Example 8 provides an in-situ remediation method for acidic wastewater in coal mine goaf areas.

[0037] The difference between the above embodiment and embodiment 3 is that: there is acidic wastewater in the coal mine goaf.

[0038] The acidic wastewater in the coal mine goaf treated in Example 8 had a pH of 2.71, an iron content of 609 mg / L, a manganese content of 70 mg / L, and an aluminum content of 572 mg / L.

[0039] Performance testing The acidic wastewater in the coal mine goaf was repaired in situ using the methods of Examples 1-8. The pH and heavy metal content of the water samples in the monitoring wells were tested 6 months and 12 months after the repair was completed. The results are shown in Table 2 below.

[0040] (1) pH test: Conducted in accordance with the "Electrode Method for Determination of pH Value of Water Quality" (HJ 1147-2020).

[0041] (2) Iron, manganese and aluminum ion content: in accordance with the "Determination of 65 elements in water quality by inductively coupled plasma mass spectrometry" (HJ 700-2014).

[0042] Table 2 Water sample test results after in-situ repair by the methods provided in Examples 1-8 According to the test results in Table 2, the pH of the water quality can be increased from 3.44 to above 5.5 in the 6th month after the acidic wastewater from the mine goaf is treated by the repair method provided in Examples 1-7, and the iron content in the water quality can be reduced from 2778 mg / L to 513-739 mg / L, the manganese content is reduced from 54 mg / L to 35-46 mg / L, and the aluminum content is reduced from 1679 mg / L to 0.15-0.51 mg / L; and within 6-12 months after treatment, the pH of the water quality shows a gradually increasing trend, and the metal content also continues to show a downward trend. In the sixth month after the acidic wastewater from the mine goaf was treated by the repair method provided in Example 8, the pH of the water quality was able to be increased from 2.71 to above 5.0, and the iron content in the water quality was able to be reduced from 609 mg / L to 46 mg / L, the manganese content was reduced from 70 mg / L to 48 mg / L, and the aluminum content was reduced from 572 mg / L to 1.04 mg / L; and within 6-12 months after treatment, the pH of the water quality showed a trend of gradual increase, and the content of each metal also continued to show a downward trend. Therefore, it is explained that the in-situ repair method for acidic wastewater from coal mine goafs provided in this application can efficiently treat acidic wastewater containing a large amount of acidophilic oxidizing bacteria and metal ions, and realize the in-situ repair of acidic wastewater from coal mine goafs.

[0043] Further comparison of the test results of Examples 1-7 shows that, in the sixth month after the acidic wastewater from the mine goaf was treated by the methods of Examples 2-3 and Example 6, the pH of the water quality was increased from 3.44 to 5.58-5.62 (>5.55), the iron content in the water quality was reduced from 2778 mg / L to 513-576 mg / L (<600 mg / L), and the manganese content was reduced from 54 mg / L to 35-38 mg / L (<4 0mg / L), while in the 6th month after the acidic wastewater from the mine goaf was treated by the methods of Example 1, Example 4-5, and Example 7, the pH of the water quality could be increased from 3.44 to 5.51-5.54 (<5.55), the iron content in the water quality could be reduced from 2778mg / L to 675-739mg / L (>600mg / L), and the manganese content could be reduced from 54mg / L to 41-46mg / L (>40mg / L). It is explained that the present application further adopts water, sodium dodecyl sulfate, isothiazolinone and montmorillonite in a weight ratio of 100: (2.5-3.0): (1.8-2): (4-5) as the raw materials of the composite antibacterial agent, which can make the repair effect of the acidic wastewater in the coal mine goaf better, the water quality has a higher pH, a lower metal content, and the treatment effect of the acidic wastewater in the coal mine goaf is more thorough.

[0044] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. An in-situ remediation method for acidic wastewater in coal mine goaf, characterized in that: The following steps are involved: (1) Inject calcium hydroxide suspension into the acidic wastewater from the injection well upstream of the coal mine goaf until the pH of the water sample in the monitoring well downstream of the coal mine goaf is not less than 3.5 for 12 consecutive hours, then stop the injection; (2) After an interval of 1-3 days, the composite antibacterial agent is continuously injected into the acidic wastewater from the upstream injection well for 36-48 hours; the injection flow rate of the composite antibacterial agent is 1-2‰ of the flow rate of the acidic wastewater; (3) After an interval of 3-7 days, inject calcium hydroxide suspension into the acidic wastewater from the upstream injection well until the pH of the water sample in the monitoring well is not less than 5.0 for 12 consecutive hours, then stop the injection; (4) Continuously monitor the pH of the water sample in the monitoring well; when the pH is lower than 4.0 for 12 consecutive hours, repeatedly inject the composite antibacterial agent and calcium hydroxide suspension, that is, repeat steps (2-3); until the pH of the water sample in the monitoring well is not lower than 4.5 for 6 consecutive months, stop the operation and the repair is completed.

2. The in-situ remediation method for acidic wastewater in coal mine goaf according to claim 1, characterized in that: The composite antibacterial agent comprises water, sodium lauryl sulfate, isothiazolinone and montmorillonite.

3. The in-situ remediation method for acidic wastewater in coal mine goaf according to claim 1, characterized in that: The weight ratio of water, sodium lauryl sulfate, isothiazolinone and montmorillonite is 100:(2.0-4.0):(1.6-2.3):(3-6).

4. The in-situ remediation method for acidic wastewater in coal mine goaf according to claim 3, characterized in that: The weight ratio of water, sodium lauryl sulfate, isothiazolinone and montmorillonite is 100:(2.5-3.0):(1.8-2):(4-5).

5. The in-situ remediation method for acidic wastewater in coal mine goaf according to claim 4, characterized in that: The weight ratio of the water, sodium lauryl sulfate, isothiazolinone and montmorillonite is 100:3:2:

5.

6. The in-situ remediation method for acidic wastewater in coal mine goaf according to claim 1, characterized in that: The preparation method of the calcium hydroxide suspension is as follows: calcium hydroxide and water are mixed in a weight ratio of 1: (2.5-8), and stirred evenly to obtain the calcium hydroxide suspension.

7. The in-situ remediation method for acidic wastewater in coal mine goaf according to claim 1, characterized in that: The acidic wastewater in the coal mine goaf contains acidophilic oxidizing bacteria, aluminum ions and heavy metal ions.

8. The in-situ remediation method for acidic wastewater in coal mine goaf according to claim 7, characterized in that: The heavy metal ions are one or more of iron, manganese, arsenic, lead, zinc, cadmium, chromium and copper.

9. The in-situ remediation method for acidic wastewater in coal mine goaf according to any one of claims 1 to 8, characterized in that: The pH of the acidic wastewater in the coal mine goaf is less than 4.5.

Images