In-situ remediation method of coal mine goaf acidic wastewater

Abstract

The application 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 comprises the following steps: injecting calcium hydroxide suspension liquid into the acid wastewater from an injection well until the pH of a water sample in a monitoring well is not lower than 3.5 for 12 hours in succession, and then stopping the injection; after 1-3 days, injecting a composite bacteriostatic agent into the acid wastewater from an upstream injection well; after 3-7 days, injecting calcium hydroxide suspension liquid into the acid wastewater from the upstream injection well until the pH of the water sample in the monitoring well is not lower than 5.0 for 12 hours in succession, and then stopping the injection; continuously monitoring the pH of the water sample in the monitoring well; when the pH is lower than 4.0 for 12 hours in succession, the composite bacteriostatic agent and the calcium hydroxide suspension liquid are repeatedly injected until the pH of the water sample in the monitoring well is not lower than 4.5 for 6 months in succession, and the remediation is completed. The remediation method can efficiently remediate the acid wastewater in the coal mine goaf, and has low remediation cost and good remediation 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] After mining, pyrite in coal seams is exposed to air and oxidized to produce acidic substances. These acidic substances, while dissolving in water, make the mine water acidic. Furthermore, they continuously dissolve various soluble substances in the coal seams, causing the concentration of harmful components in the mine water to continuously increase, even exceeding standards, and significantly deteriorating water quality. Furthermore, in the closed environment of goafs, microorganisms such as acidophilic oxidizing bacteria also play a significant role in the acidification of mine water. Therefore, the effective treatment of acidic wastewater in goafs has become a pressing issue.

[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 particulate matter 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-mentioned existing methods all carry out end-of-pipe treatment after the acidic wastewater is discharged, and do not fundamentally solve the pollution problem at the source of the acidic wastewater. In addition, these methods require continuous maintenance and operation during implementation, which increases the treatment cost and makes it difficult to achieve economical, efficient, and long-term effective treatment. Summary of the Invention

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

[0005] The in-situ remediation method for acidic wastewater in coal mine goafs provided in this application adopts the following technical solutions:

[0006] An in-situ remediation method for acidic wastewater in coal mine goafs comprises the following steps:

[0007] (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;

[0008] (2) After an interval of 1-3 days, inject a composite antibacterial agent into the acidic wastewater from an upstream injection well for 36-48 hours; the injection flow rate of the composite antibacterial agent is 1-2‰ of the acidic wastewater flow rate;

[0009] (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;

[0010] (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.

[0011] 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 its 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; and then, calcium hydroxide suspension is added to raise 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 formation of flocs covering the surface of the mineral layer can, on the one hand, achieve the removal of metal ions, and on the other hand, the flocs covering the surface of the mineral layer achieve the effect of a membrane, 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 a 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 the remediation cost is low, the remediation effect is good, and the environmental performance is good.

[0012] Optionally, the composite antibacterial agent includes water, sodium lauryl sulfate, isothiazolinone and montmorillonite.

[0013] Optionally, the weight ratio of the water, sodium lauryl sulfate, isothiazolinone and montmorillonite is 100:(2.0-4.0):(1.6-2.3):(3-6).

[0014] The present application uses 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 of 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 can the antibacterial effect 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 the ideal range, and ultimately achieving efficient and stable treatment of wastewater, completing the in-situ remediation goal, and significantly improving the environmental protection effect.

[0015] Optionally, the weight ratio of the water, sodium lauryl sulfate, isothiazolinone and montmorillonite is 100:(2.5-3.0):(1.8-2):(4-5).

[0016] In the present application, the ratio of the three ingredients, sodium lauryl sulfate, isothiazolinone and montmorillonite, is further controlled within the above range, which can enable the composite antibacterial agent to 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 the water quality can be maintained in a stable and ideal state within 6-12 months, thereby achieving complete treatment of acidic wastewater in coal mine goafs.

[0017] In some embodiments, the weight ratio of water, sodium lauryl 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).

[0018] In a specific embodiment, the weight ratio of water, sodium lauryl 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.

[0019] Optionally, the weight ratio of water, sodium lauryl sulfate, isothiazolinone and montmorillonite is 100:3:2:5.

[0020] 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, to obtain the calcium hydroxide suspension.

[0021] Optionally, the acidic wastewater from the coal mine goaf contains acidophilic oxidizing bacteria, aluminum ions and heavy metal ions.

[0022] Optionally, the heavy metal ions are one or more of iron, manganese, arsenic, lead, zinc, cadmium, chromium and copper.

[0023] Optionally, the pH of the acidic wastewater in the coal mine goaf is less than 4.5.

[0024] The method provided in this application is suitable for treating acidic wastewater from coal mine goafs with a pH value less than 4.5. The water quality of the goafs treated using the in-situ remediation method provided in this application can gradually improve and stabilize, achieving complete remediation of the acidic wastewater from coal mine goafs. It should be noted that when the initial pH value of the acidic wastewater from coal mine goafs is higher than 3.5, step (1) can be omitted and step (2) can be performed directly.

[0025] In summary, this application has the following beneficial effects:

[0026] 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.

[0027] 2. The in-situ remediation method for acidic wastewater in coal mine goafs provided in this 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, this 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.

[0028] 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 protection. DETAILED DESCRIPTION

[0029] An in-situ remediation method for acidic wastewater in coal mine goafs comprises the following steps:

[0030] (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;

[0031] (2) After an interval of 1-3 days, a composite antibacterial agent is added to the acidic wastewater in the coal mine goaf from an upstream injection well for 36-48 hours; the injection flow rate of the composite antibacterial agent is 1-2‰ of the acidic wastewater flow rate; the composite antibacterial agent includes water, sodium lauryl sulfate, isothiazolinone and montmorillonite; further, the weight ratio of the water, sodium lauryl sulfate, isothiazolinone and montmorillonite is 100:(2.0-4.0):(1.6-2.3):(3-6); further, the weight ratio of the water, sodium lauryl sulfate, isothiazolinone and montmorillonite is 100:(2.5-3.0):(1.8-2):(4-5).

[0032] (3) After an interval of 3-7 days, 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 5.0 for 12 consecutive hours, and then the addition is stopped;

[0033] (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.

[0034] In the present application, the CAS number of sodium lauryl 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.

[0035] The present application is further described in detail below with reference to preparation examples, embodiments, and performance testing.

[0036] Preparation Examples 1-7

[0037] Preparation Examples 1-7 each provide a composite antibacterial agent.

[0038] The difference between the above preparation examples is that the weight ratios of water, sodium lauryl sulfate, isothiazolinone and montmorillonite in the composite antibacterial agent are shown in Table 1 below.

[0039] The preparation method of the composite antibacterial agent provided in Preparation Example 1-7 is as follows: sodium lauryl 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.

[0040] Table 1 Weight ratio of sodium lauryl sulfate, isothiazolinone and montmorillonite in the composite antibacterial agent of Preparation Example 1-7

[0041]

[0042] Examples 1-7

[0043] Examples 1-7 respectively provide an in-situ remediation method for acidic wastewater in coal mine goafs.

[0044] The difference between the above examples is that the composite antibacterial agents are derived from Preparation Examples 1-7 respectively.

[0045] The in-situ remediation method for acidic wastewater in coal mine goaf provided in Examples 1-7 comprises the following steps:

[0046] (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.

[0047] (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;

[0048] (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 flow rate of the composite antibacterial agent was 1.5‰ of the acidic wastewater flow rate.

[0049] (4) After 5 days, calcium hydroxide suspension was 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 was not less than 5.0 for 12 consecutive hours, and then the addition was stopped;

[0050] (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.

[0051] 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.

[0052] Example 8

[0053] Example 8 provides an in-situ remediation method for acidic wastewater in coal mine goafs.

[0054] The difference between the above embodiment and embodiment 3 is that: acidic wastewater in the coal mine goaf.

[0055] 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.

[0056] Performance testing

[0057] The methods of Examples 1-8 were used to perform in-situ remediation of acidic wastewater in coal mine goafs. The pH and heavy metal content of water samples in the monitoring wells were tested 6 months and 12 months after the remediation was completed. The results are shown in Table 2 below.

[0058] (1) pH test: Conducted in accordance with the "Electrode Method for Determination of pH Value of Water Quality" (HJ 1147-2020).

[0059] (2) Iron, manganese and aluminum ion content: carried out in accordance with the "Determination of 65 elements in water by inductively coupled plasma mass spectrometry" (HJ 700-2014).

[0060] Table 2 Water sample test results after in-situ repair using the methods provided in Examples 1-8

[0061]

[0062]

[0063] 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 sixth month after the treatment of the acidic wastewater in the mine goaf using the remediation 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 using the repair method provided in Example 8, the pH of the water was able to be increased from 2.71 to above 5.0, and the iron content in the water 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 showed a gradual upward trend, and the content of each metal also continued to show a downward trend. Therefore, it is illustrated 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 in-situ repair of acidic wastewater from coal mine goafs.

[0064] Further comparison of the test results of Examples 1-7 shows that, after the acidic wastewater from the mine goaf is treated by the methods of Examples 2-3 and Example 6, the pH of the water can be increased from 3.44 to 5.58-5.62 (>5.55), the iron content in the water can be reduced from 2778 mg / L to 513-576 mg / L (<600 mg / L), and the manganese content can be reduced from 54 mg / L to 35-38 mg / L (<4 0mg / L), while in the sixth 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). This shows that the present application further adopts water, sodium lauryl sulfate, isothiazolinone and montmorillonite in a weight ratio of 100: (2.5-3.0): (1.8-2): (4-5) as raw materials for the composite antibacterial agent, which can make the remediation effect of the acidic wastewater from the coal mine goaf better, the water quality has a higher pH, a lower metal content, and the treatment effect of the acidic wastewater from the coal mine goaf is more thorough.

[0065] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

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, a composite antibacterial agent is continuously injected into the acidic wastewater from an 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; the composite antibacterial agent includes water, sodium lauryl sulfate, isothiazolinone and montmorillonite; (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 compound 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 weight ratio of the water, sodium lauryl sulfate, isothiazolinone and montmorillonite is 100: (2.0-4.0): (1.6-2.3): (3-6).

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

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

5.

5. 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 comprises: mixing calcium hydroxide and water in a weight ratio of 1: (2.5-8), stirring evenly, and obtaining the calcium hydroxide suspension.

6. 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.

7. The in-situ remediation method for acidic wastewater in coal mine goaf according to claim 6, characterized in that: The heavy metal ions are one or more of iron, manganese, lead, zinc, cadmium, chromium and copper.

8. The in-situ remediation method for acidic wastewater in coal mine goaf according to any one of claims 1 to 7, characterized in that: The pH value of the acidic wastewater in the coal mine goaf is less than 4.5.

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