Preparation method and application of a tunnel construction wastewater treatment agent

Abstract

The present invention provides a method for preparing a tunnel construction wastewater treatment agent, comprising the following steps: S1, sieving quartz sand; S2, preparing iron salt into a saturated solution, adding magnesium salt and calcium salt under water bath heating conditions to obtain a mixed solution A; S3, mixing sulfuric acid and water to prepare an acid leaching solution B; S4, immersing quartz sand in the acid leaching solution B to obtain a mixed slurry C; S5, mixing the mixed solution A and the mixed slurry C under stirring conditions, stirring the reaction, and then stirring and dropping a silicate solution until the pH of the solution rises to 1.5-3.5 to obtain a mixed slurry D; S6, evaporating and drying the mixed slurry D to obtain a quartz sand-supported polysilicate composite flocculant. The present invention also provides an application of a tunnel construction wastewater treatment agent. The quartz sand-supported polysilicate composite flocculant prepared by the present invention only needs to add one agent to achieve the effects of pH adjustment, flocculation and turbidity removal, and accelerated precipitation.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel construction wastewater treatment, and specifically relates to a preparation method and application of a tunnel construction wastewater treatment agent. Background Art

[0002] Tunnel construction wastewater is highly alkaline and highly turbid. pH adjustment and coagulation / flocculation are key steps in treating this type of wastewater. The common processes are: pH adjustment-coagulation / flocculation-sedimentation-filtration, etc. pH adjusters and coagulation / flocculation agents are added in the pH adjustment process section and coagulation / flocculation process section respectively.

[0003] Regarding the pH adjustment process, since strong acids such as sulfuric acid, hydrochloric acid, and nitric acid are chemicals that are easy to make drugs and explosives, they are not suitable for tunnel construction projects such as railways, highways, and water conservancy projects, but are inconvenient to manage. Therefore, the pH value is usually adjusted by adding oxalic acid and citric acid. Organic acids are not only expensive, but also bring in high concentrations of organic matter, which greatly increases the COD of the effluent. Adding oxalic acid will also cause the formation of white precipitates due to the formation of calcium oxalate, affecting the treatment effect.

[0004] For the coagulation / flocculation process, currently used is a simple combination of inorganic coagulants and organic flocculants with single functions, such as single inorganic coagulants such as polyaluminium chloride, aluminium sulfate, ferric chloride, etc., and single organic flocculants such as anionic polyacrylamide, cationic polyacrylamide, etc. In view of the fact that the pH of tunnel construction wastewater is generally 9-12 and has the characteristics of high alkalinity, it is difficult for single conventional coagulants such as aluminium series and iron series to play a good flocculation role in alkaline wastewater of different pH values, and the pH of the effluent after treatment is greater than 9, which does not meet the pH requirement of 6-9 in the discharge standard.

[0005] Therefore, there is an urgent need to develop a tunnel construction wastewater treatment agent that integrates pH adjustment and coagulation / flocculation functions, which is suitable for the treatment of high-alkalinity and high-turbidity tunnel construction wastewater with different pH values ​​to meet the water quality purification requirements for tunnel construction wastewater discharge and reuse. Summary of the invention

[0006] The purpose of the present invention is to provide a preparation method and application of a tunnel construction wastewater treatment agent, so as to solve the problem proposed in the background technology that the pH of tunnel construction wastewater is still alkaline after using conventional coagulants to remove turbidity, and the subsequent addition of oxalic acid and citric acid to adjust the pH will cause the turbidity and COD to increase, and the cost of the agent is high.

[0007] To achieve the above object, the present invention provides a method for preparing a tunnel construction wastewater treatment agent, comprising the following steps:

[0008] S1, sieving quartz sand with a particle size of 0.1-0.2 mm and washing it, drying the washed quartz sand with a particle size of 0.1-0.2 mm and cooling it to room temperature;

[0009] S2. The iron salt is configured into a saturated solution, and magnesium salt and calcium salt are added under water bath heating conditions to obtain a mixed solution A, wherein the iron salt is ferric chloride or ferric sulfate, the magnesium salt is magnesium sulfate or / and magnesium chloride, and the calcium salt is calcium sulfate or / and calcium chloride; when the pH of the wastewater is ≤10, the molar mass ratio of the iron salt: magnesium salt: calcium salt in the mixed solution A is 5-10:1-2:1; when the pH of the wastewater is >10, the molar mass ratio of the iron salt: magnesium salt: calcium salt in the mixed solution A is 1-3:1-2.5:1;

[0010] S3, mixing sulfuric acid and water to prepare acid leaching solution B;

[0011] S4, placing the quartz sand that has been dried and cooled to room temperature in the acid leaching solution B to obtain a mixed slurry C;

[0012] S5. Under stirring conditions, the mixed solution A and the mixed slurry C are mixed in a mixing ratio of 1 to 5:2 by mass ratio of iron salt to quartz sand, and stirred for reaction, and then the silicate solution is added dropwise while stirring until the pH of the solution obtained by mixing the mixed solution A and the mixed slurry C rises to 1.5 to 3.5, and stirring is continued to obtain a mixed slurry D;

[0013] S6. Evaporating and drying the mixed slurry D to obtain a quartz sand-loaded polysilicate composite flocculant for tunnel construction wastewater treatment.

[0014] In a specific embodiment, in S1, the cleaning process is to mix quartz sand and water in a mass ratio of 1:5 for ultrasonic cleaning, and the drying temperature of the quartz sand is 105°C.

[0015] In a specific embodiment, in S2, magnesium salt and calcium salt are added under heating conditions of 50-70°C in a water bath.

[0016] In a specific embodiment, in S3, the volume ratio of sulfuric acid to water in the acid leaching solution B is 0.1~1:1.

[0017] In a specific embodiment, in S4, the immersion time is 24 to 48 hours.

[0018] In a specific embodiment, in S5, the silicate solution is a sodium silicate solution or a potassium silicate solution.

[0019] In a specific embodiment, in S5, the stirring reaction time after the mixed solution A and the mixed slurry C are mixed is 2 to 6 hours, and the stirring time after the pH rises to 1.5 to 3.5 is 1 to 4 hours.

[0020] In a specific embodiment, in S6, the evaporation temperature of the mixed slurry D is 110-140°C, and the drying temperature is 200-250°C.

[0021] The present invention also provides an application of a tunnel construction wastewater treatment agent, the specific steps of which include:

[0022] Step 1: determining the molar mass ratio of iron salt, magnesium salt and calcium salt in the mixed solution A according to the pH value of the tunnel construction wastewater to be treated, and then preparing the quartz sand-supported polysilicate composite flocculant by the preparation method of the tunnel construction wastewater treatment agent as described above;

[0023] Step 2, preparing the quartz sand-loaded polysilicic acid composite flocculant obtained in step 1 into a slurry with a mass concentration of 3-30%, and continuously stirring to prevent it from sinking to the bottom;

[0024] Step 3, adding the slurry prepared in step 2 to the tunnel construction wastewater at a dosage of 100-500 mg of quartz sand-loaded polysilicic acid composite flocculant per liter of wastewater, and stirring for reaction;

[0025] Step 4: The wastewater after the stirring reaction is allowed to settle to meet the discharge standards.

[0026] In a specific embodiment, the stirring reaction time in step 3 is 1 to 3 minutes; the standing sedimentation time in step 4 is 3 to 10 minutes.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) Quartz sand with roughened surface and activated by acid leaching is introduced into the flocculant system as a heavy medium carrier, and the particle size of the carrier is controlled. The overall stability of the flocculant is improved. During the flocculation process, the flocs formed use the carrier as the floc nucleus, and through collision, larger and more stable flocs are generated, which is more conducive to rapid precipitation.

[0029] 2) The composite ingredients are used. After being dissolved in water, their own ionic components and ionic components generated by hydrolysis can be used to remove alkaline substances in wastewater through neutralization, precipitation, etc., and adjust the pH of wastewater. Different flocculation components in the composite flocculant have different optimal flocculation pH values, and can play a good flocculation effect at different pH values. The proportion of each component in the formula can be adjusted according to the composition and pH value of the alkaline substances in the wastewater to ensure low cost and optimal treatment effect.

[0030] Compared with the prior art which requires the addition of three agents, the quartz sand-loaded polysilicate composite flocculant prepared by the present invention only requires the addition of one agent, which can simultaneously achieve the effects of pH adjustment, flocculation and turbidity removal, and accelerated sedimentation. The prior art's four-stage process of pH adjustment-coagulation-flocculation-sedimentation can be simplified to a two-stage process of flocculation-sedimentation, and the size of the sedimentation tank can also be greatly reduced.

[0031] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention is further described in detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0033] Figure 1 The present invention is a process flow chart of a method for preparing a tunnel construction wastewater treatment agent. DETAILED DESCRIPTION

[0034] The embodiments of the present invention are described in detail below. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] Example 1

[0036] The tunnel construction wastewater with pH of 11.98 and SS of 126.27 mg / L was treated. When the wastewater pH was greater than 10, CO3 2- OH - The quartz sand-loaded polysilicate composite flocculant used for tunnel construction wastewater treatment is prepared by the following preparation method:

[0037] First, quartz sand with a particle size of 0.1-0.12 mm was sieved, mixed with water in a mass ratio of 1:5, and ultrasonically cleaned, then dried at 105°C and cooled to room temperature.

[0038] Then, ferric chloride was prepared into a saturated solution, and magnesium sulfate and calcium sulfate were added in a molar mass ratio of ferric chloride: magnesium sulfate: calcium sulfate of 2.5:2.5:1 under the condition of heating in a water bath at 60° C., to obtain a mixed solution A.

[0039] Then, sulfuric acid and water were mixed to prepare an acid leaching solution B with a volume ratio of 0.4:1.

[0040] Then, the quartz sand dried and cooled to room temperature is immersed in the acid leaching solution B for 24 to 48 hours to obtain a mixed slurry C.

[0041] Then, under stirring conditions, the mixed solution A and the mixed slurry C are mixed in a mixing ratio of ferric chloride to quartz sand of 3:2, and stirred for reaction for 2 hours, and then the silicate solution is added dropwise while stirring until the pH of the solution rises to 1.8, and stirring is continued for 2 hours to obtain a mixed slurry D. The silicate is sodium silicate or potassium silicate.

[0042] Finally, the mixed slurry D was evaporated at 120° C. and then dried at 200° C. to obtain the quartz sand-supported polysilicate composite flocculant for tunnel construction wastewater treatment.

[0043] The quartz sand-loaded polysilicate composite flocculant prepared above is prepared into a slurry with a mass concentration of 10%, and is continuously stirred to prevent sinking to the bottom; under stirring conditions, 100-500 mg of the quartz sand-loaded polysilicate composite flocculant is added to the tunnel construction wastewater at a dosage of 8 < pH < 9 per liter of wastewater, and the reaction is stirred for 1-3 minutes; then the solution is allowed to settle for 10 minutes.

[0044] Example 2

[0045] In Example 2, the difference from Example 1 is that the molar mass ratio of ferric chloride:magnesium sulfate:calcium sulfate is 1:1:1.

[0046] Example 3

[0047] In Example 3, the difference from Example 1 is that the molar mass ratio of ferric chloride:magnesium sulfate:calcium sulfate is 2.5:2:1.

[0048] Example 4

[0049] In Example 4, the difference from Example 1 is that the molar mass ratio of ferric chloride:magnesium sulfate:calcium sulfate is 2.5:1.25:1.

[0050] Conventional acid, coagulant and combination thereof were used to treat the tunnel construction wastewater in Example 1, and the treatment methods were Comparative Examples 1 to 7, as follows:

[0051] Comparative Example 1

[0052] Prepare oxalic acid into a 10% solution, add it into the tunnel construction wastewater under stirring until the pH value reaches 8<pH<9, and then let it stand and settle for 10 minutes.

[0053] Comparative Example 2

[0054] Prepare a 10% solution of citric acid by mass concentration, add it into the tunnel construction wastewater under stirring conditions until the pH value reaches 8<pH<9, and then let it stand and settle for 10 minutes.

[0055] Comparative Example 3

[0056] Prepare a solution with a mass concentration of 10% polyaluminium chloride and a solution with a mass concentration of 0.1% anionic polyacrylamide. Add the polyaluminium chloride solution to the tunnel construction wastewater under stirring until the pH value reaches 8 < pH < 9, and then add the anionic polyacrylamide solution until obvious flocs are produced. Continue stirring for 40 seconds and then let it settle for 10 minutes.

[0057] Comparative Example 4

[0058] Prepare oxalic acid into a solution with a mass concentration of 10%, polyaluminium chloride into a solution with a mass concentration of 10%, and anionic polyacrylamide into a solution with a mass concentration of 0.1%. First, add oxalic acid solution to the tunnel construction wastewater under stirring conditions until the pH value reaches 9.8 < pH < 10.2, then add polyaluminium chloride solution to 8 < pH < 9, and then add anionic polyacrylamide solution until obvious flocs are produced. Continue stirring for 40 seconds, and then let it settle for 10 minutes.

[0059] Comparative Example 5

[0060] Prepare a solution with a mass concentration of 10% magnesium sulfate, a solution with a mass concentration of 10% polyaluminium chloride, and a solution with a mass concentration of 0.1% anionic polyacrylamide. First add the magnesium sulfate solution to the tunnel construction wastewater under stirring conditions, then add the polyaluminium chloride solution to 8<pH<9, and then add the anionic polyacrylamide solution to produce obvious flocs. Continue stirring for 40 seconds, and then let it stand and settle for 10 minutes.

[0061] Comparative Example 6

[0062] Prepare a solution with a mass concentration of 10% ferric chloride and a solution with a mass concentration of 0.1% anionic polyacrylamide. First, add the ferric chloride solution to the tunnel construction wastewater under stirring until the pH value is 8 < pH < 9, and then add the anionic polyacrylamide solution until obvious flocs are produced. Continue stirring for 40 seconds, and then let it stand and settle for 10 minutes.

[0063] Comparative Example 7

[0064] Ferric chloride, magnesium sulfate and calcium sulfate were prepared into a 10% solution with a molar mass ratio of 2.5:2.5:1, and anionic polyacrylamide was prepared into a 0.1% solution. Under stirring conditions, the mixed solution of ferric chloride, calcium sulfate and magnesium sulfate was first added to the tunnel construction wastewater until the pH value was 8 < pH < 9, and then the anionic polyacrylamide solution was added until obvious flocs were produced. Stirring was continued for 40 seconds, and then allowed to settle for 10 minutes.

[0065] The reagent addition costs and treatment effects of Comparative Examples 1 to 7 are compared with those of Examples 1 to 4, and the comparison is shown in the table below.

[0066]

[0067] It can be seen from Comparative Examples 1 and 2 that the use of acidic substances such as oxalic acid and citric acid can only play a role in adjusting pH, but cannot play a role in removing suspended solids SS by flocculation and precipitation. After treatment with oxalic acid, the SS pollution concentration in the wastewater even increases.

[0068] It can be seen from Comparative Example 3 that the common combination of polyaluminium chloride coagulant and anionic polyacrylamide flocculant has a cost of 2.6 times that of Example 1, a slag production amount of 2.9 times that of Example 1, and a higher SS of the effluent after treatment than Example 1. The slag production amount is the amount of precipitated sludge, and in the treatment of tunnel construction wastewater, the less the better, because the more slag production there is, the more precipitated sludge needs to be further treated.

[0069] It can be seen from Comparative Example 4 that by using oxalic acid as the pH regulator and combining the common polyaluminum chloride coagulant and anionic polyacrylamide flocculant, the cost of adding the agent and the amount of slag produced are reduced compared with Comparative Example 3, but the cost of adding the agent is still 1.9 times that of Example 1, and the amount of slag produced is 2.2 times that of Example 1. The SS of the effluent after treatment is much higher than that of Example 1.

[0070] It can be seen from Comparative Example 5 that the reagent combination of magnesium sulfate, polyaluminium chloride graded coagulation and anionic polyacrylamide flocculation has a reagent addition cost of up to 4.32 yuan / ton of water, which is 4.9 times that of Example 1, and the slag production is 6.6 times that of Example 1. The SS of the effluent after treatment is also slightly higher than that of Example 1.

[0071] It can be seen from Comparative Example 6 that the reagent combination of ferric chloride coagulation and anionic polyacrylamide flocculation has a reagent addition cost of 1.51 yuan / ton of water, which is 1.7 times that of Example 1, and the slag production is 1.1 times that of Example 1. The SS of the effluent after treatment is relatively high, which is 29.92 mg / L. It can be seen that the treatment effect of the method of Comparative Example 6 is biased.

[0072] It can be seen from Comparative Example 7 that the reagent combination of ferric chloride, calcium sulfate, and magnesium sulfate as a coagulant and anionic polyacrylamide as a flocculant has a reagent addition cost of 1.81 yuan / ton of water, which is twice that of Example 1, and the slag production is 1.9 times that of Example 1. The SS of the effluent after treatment is 9.33 mg / L.

[0073] It is not difficult to find that the tunnel construction wastewater treatment agent prepared by the present invention, compared with the existing agents, can not only adjust the pH at the same time, but also has a higher SS removal capacity than the existing agents, and the agent addition cost is low.

[0074] It has been verified that when the pH of the wastewater is greater than 10, the molar mass ratio of iron salt: magnesium salt: calcium salt in the mixed solution A is 1~3:1~2.5:1, which can achieve better results; more preferably, the molar mass ratio of iron salt: magnesium salt: calcium salt in the mixed solution A is 2~3:1.5~2.5:1.

[0075] Example 5

[0076] The tunnel construction wastewater with pH of 9.96 and SS of 1554.29 mg / L was treated. When the wastewater pH was ≤10, the wastewater pH did not exceed the standard. 2- 、HCO3 - The quartz sand-loaded polysilicate composite flocculant used for tunnel construction wastewater treatment is prepared by the following preparation method:

[0077] First, quartz sand with a particle size of 0.1-0.12 mm was sieved, mixed with water in a mass ratio of 1:5, and ultrasonically cleaned, then dried at 105°C and cooled to room temperature.

[0078] Then, ferric chloride was prepared into a saturated solution, and magnesium sulfate and calcium sulfate were added in a Fe:Mg:Ca molar mass ratio of 10:1:1 under the condition of heating in a water bath at 50° C., to obtain a mixed solution A.

[0079] Then, sulfuric acid and water are mixed to prepare an acid leaching solution B with a volume ratio of 0.2:1.

[0080] Then, the quartz sand dried and cooled to room temperature was immersed in the acid leaching solution B for 48 hours to obtain a mixed slurry C.

[0081] Then, under stirring conditions, the mixed solution A and the mixed slurry C are mixed in a mixing ratio of 4:2 of ferric chloride to quartz sand, and stirred for reaction for 2 hours, and then the silicate solution is added dropwise while stirring until the pH of the solution rises to 3.5, and stirring is continued for 2 hours to obtain a mixed slurry D. The silicate is sodium silicate or potassium silicate.

[0082] Finally, the mixed slurry D was evaporated at 120° C. and then dried at 200° C. to obtain the quartz sand-supported polysilicate composite flocculant for tunnel construction wastewater treatment.

[0083] The quartz sand-loaded polysilicate composite flocculant prepared above is prepared into a slurry with a mass concentration of 10%, and is continuously stirred to prevent sinking to the bottom; under stirring conditions, 100-500 mg of the quartz sand-loaded polysilicate composite flocculant is added to the tunnel construction wastewater at a dosage of 8 < pH < 9 per liter of wastewater, and the reaction is stirred for 1-3 minutes, and then allowed to settle for 10 minutes.

[0084] Example 6

[0085] In Example 6, the difference from Example 5 is that the molar mass ratio of ferric chloride:magnesium sulfate:calcium sulfate is 10:2:1.

[0086] Example 7

[0087] In Example 7, the difference from Example 5 is that the molar mass ratio of ferric chloride:magnesium sulfate:calcium sulfate is 5:1:1.

[0088] Example 8

[0089] In Example 8, the difference from Example 5 is that the molar mass ratio of ferric chloride:magnesium sulfate:calcium sulfate is 8:1:1.

[0090] Conventional acid, coagulant and combination thereof were used to treat the tunnel construction wastewater in Example 5, and the treatment methods were respectively Comparative Examples 8 to 13, as follows:

[0091] Comparative Example 8

[0092] Prepare oxalic acid into a 10% solution, add it into the tunnel construction wastewater under stirring until the pH value reaches 8<pH<9, and then let it stand and settle for 10 minutes.

[0093] Comparative Example 9

[0094] Prepare a 10% solution of citric acid by mass concentration, add it into the tunnel construction wastewater under stirring conditions until the pH value reaches 8<pH<9, and then let it stand and settle for 10 minutes.

[0095] Comparative Example 10

[0096] Prepare a solution with a mass concentration of 10% polyaluminium chloride and a solution with a mass concentration of 0.1% anionic polyacrylamide. Add the polyaluminium chloride solution to the tunnel construction wastewater under stirring until the pH value reaches 8 < pH < 9, and then add the anionic polyacrylamide solution until obvious flocs are produced. Continue stirring for 40 seconds and then let it settle for 10 minutes.

[0097] Comparative Example 11

[0098] Prepare a solution with a mass concentration of 10% magnesium sulfate, a solution with a mass concentration of 10% polyaluminium chloride, and a solution with a mass concentration of 0.1% anionic polyacrylamide. First add the magnesium sulfate solution to the tunnel construction wastewater under stirring conditions, then add the polyaluminium chloride solution to 8<pH<9, and then add the anionic polyacrylamide solution to produce obvious flocs. Continue stirring for 40 seconds, and then let it stand and settle for 10 minutes.

[0099] Comparative Example 12

[0100] Prepare a solution with a mass concentration of 10% ferric chloride and a solution with a mass concentration of 0.1% anionic polyacrylamide. First, add the ferric chloride solution to the tunnel construction wastewater under stirring until the pH value is 8 < pH < 9, and then add the anionic polyacrylamide solution until obvious flocs are produced. Continue stirring for 40 seconds, and then let it stand and settle for 10 minutes.

[0101] Comparative Example 13

[0102] Ferric chloride, magnesium sulfate and calcium sulfate were prepared into a 10% solution with a molar mass ratio of 10:1:1, and anionic polyacrylamide was prepared into a 0.1% solution. Under stirring conditions, the mixed solution of ferric chloride, magnesium sulfate and calcium sulfate was first added to the tunnel construction wastewater until the pH value was 8 < pH < 9, and then the anionic polyacrylamide solution was added until obvious flocs were produced. The stirring was continued for 40 seconds, and then the solution was allowed to settle for 10 minutes.

[0103] The reagent addition costs and treatment effects of Comparative Examples 8 to 13 are compared with those of Examples 5 to 8, and the comparison is shown in the table below.

[0104]

[0105] It can be seen from Comparative Examples 8 and 9 that a small amount of oxalic acid and citric acid can make the wastewater pH meet the discharge standard requirements, but it cannot play the role of flocculation and precipitation to remove suspended solids SS.

[0106] It can be seen from Comparative Example 10 that the common combination of polyaluminium chloride coagulant and anionic polyacrylamide flocculant has a cost of 2.7 times that of Example 5, and the effluent SS and slag production after treatment are also higher than those of Example 5.

[0107] It can be seen from Comparative Example 11 that the combination of magnesium sulfate, polyaluminium chloride graded coagulation and anionic polyacrylamide flocculation has lower effluent SS than Comparative Example 10, but the cost of adding the reagents is as high as 3.93 yuan / ton of water, and the amount of slag produced is also large.

[0108] It can be seen from Comparative Example 12 that the reagent combination of ferric chloride coagulation and anionic polyacrylamide flocculation has a reagent addition cost of 0.57 yuan / ton of water, and the SS of the effluent after treatment is relatively high.

[0109] It can be seen from Comparative Example 13 that the reagent combination of ferric chloride, calcium sulfate, and magnesium sulfate as a coagulant and anionic polyacrylamide as a flocculant has a reagent addition cost of 0.62 yuan / ton of water, which is 2.5 times that of Example 5. The SS content of the effluent after treatment is relatively low in the comparative example.

[0110] It is not difficult to find that for tunnel construction wastewater with a pH value of ≤ 10, the tunnel construction wastewater treatment agent prepared by the present invention, compared with the existing agents, can make the wastewater pH meet the discharge standards while having a significantly higher SS removal capacity and being more economical.

[0111] It has been verified that when the pH of the wastewater is ≤10, the molar mass ratio of iron salt: magnesium salt: calcium salt in the mixed solution A is 5~10:1~2:1 and can achieve better results.

[0112] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for preparing a tunnel construction wastewater treatment agent, characterized in that: The following steps are involved: S1, sieving quartz sand with a particle size of 0.1-0.2 mm and washing it, drying the washed quartz sand with a particle size of 0.1-0.2 mm and cooling it to room temperature; S2. The iron salt is configured into a saturated solution, and a magnesium salt and a calcium salt are added under a water bath heating condition of 50 to 70° C. to obtain a mixed solution A, wherein the iron salt is ferric chloride, the magnesium salt is magnesium sulfate, and the calcium salt is calcium sulfate; when the pH of the wastewater is ≤10, the molar mass ratio of the iron salt: the magnesium salt: the calcium salt in the mixed solution A is 10:1:1; when the pH of the wastewater is greater than 10, the molar mass ratio of the iron salt: the magnesium salt: the calcium salt in the mixed solution A is 2.5:2 to 2.5:1; S3, mixing sulfuric acid and water to prepare acid leaching solution B; In S3, the volume ratio of sulfuric acid to water in the acid leaching solution B is 0.1 to 1:1; S4, placing the quartz sand that has been dried and cooled to room temperature in the acid leaching solution B to obtain a mixed slurry C; In S4, the immersion time is 24 to 48 hours; S5. Under stirring conditions, the mixed solution A and the mixed slurry C are mixed in a mixing ratio of 1 to 5:2 by mass ratio of iron salt to quartz sand, and stirred for reaction, and then the silicate solution is added dropwise while stirring until the pH of the solution obtained by mixing the mixed solution A and the mixed slurry C rises to 1.5 to 3.5, and stirring is continued to obtain a mixed slurry D; In S5, the stirring reaction time after the mixed solution A and the mixed slurry C are mixed is 2 to 6 hours, and the stirring time after the pH rises to 1.5 to 3.5 is 1 to 4 hours; S6. Evaporating and drying the mixed slurry D to obtain a quartz sand-loaded polysilicate composite flocculant for tunnel construction wastewater treatment.

2. The method for preparing a tunnel construction wastewater treatment agent according to claim 1, characterized in that: In S1, the cleaning process is to mix quartz sand and water in a mass ratio of 1:5 and perform ultrasonic cleaning, and the temperature of drying the quartz sand is 105°C.

3. The method for preparing a tunnel construction wastewater treatment agent according to claim 1, characterized in that: In S5, the silicate solution is a sodium silicate solution or a potassium silicate solution.

4. The method for preparing a tunnel construction wastewater treatment agent according to claim 1, characterized in that: In the step S6, the evaporation temperature of the mixed slurry D is 110-140°C, and the drying temperature is 200-250°C.

5. An application of a tunnel construction wastewater treatment agent, characterized in that: The specific steps include: Step 1: Determine the molar mass ratio of iron salt, magnesium salt and calcium salt in the mixed solution A according to the pH value of the tunnel construction wastewater to be treated, and then prepare the quartz sand-supported polysilicate composite flocculant by the preparation method of the tunnel construction wastewater treatment agent according to any one of claims 1 to 4; Step 2, preparing the quartz sand-loaded polysilicic acid composite flocculant obtained in step 1 into a slurry with a mass concentration of 3 to 30%, and continuously stirring to prevent it from sinking to the bottom; Step 3, adding the slurry prepared in step 2 to the tunnel construction wastewater at a dosage of 100 to 500 mg of quartz sand-loaded polysilicic acid composite flocculant per liter of wastewater, and stirring for reaction; Step 4: The wastewater after the stirring reaction is allowed to settle to meet the discharge standards.

6. The use of the tunnel construction wastewater treatment agent according to claim 5, characterized in that: The stirring reaction time in step 3 is 1 to 3 minutes; the static sedimentation time in step 4 is 3 to 10 minutes.

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