A fracturing flowback fluid treatment process

Abstract

The application relates to the technical field of wastewater treatment, and particularly discloses a fracturing flowback fluid treatment process. Sodium hypochlorite is used as an oxidant, and a synergistic catalyst containing nickel oxide and iron oxide is selected to synergize the oxidant, compared with potassium permanganate gel breaker, the sodium hypochlorite not only has better gel breaking effect, but also avoids the introduction of manganese ions, and can fully exert the advantage that the sodium hypochlorite has little influence on chroma. After gel breaking treatment, the viscosity of the fracturing flowback fluid is obviously reduced, which is beneficial to the uniform dispersion of various additives, and therefore the treatment effect on the fracturing flowback fluid is improved.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology, and more specifically, to a fracturing flowback fluid treatment process. Background Technology

[0002] Fracturing flowback fluid refers to the liquid that returns from the formation to the surface after fracturing operations during oil and gas extraction. This fluid typically contains various pollutants, such as oil, solid particles, and chemical additives. Direct discharge without treatment can have serious environmental impacts. Therefore, effectively treating fracturing flowback fluid and reducing its environmental impact is essential for protecting the ecological environment and achieving sustainable development.

[0003] In practical applications, fracturing flowback fluids are often characterized by complex composition, high viscosity, high organic matter content, and high salt content, requiring comprehensive treatment using multiple methods, including flotation, coagulation and sedimentation, and filtration purification. Regardless of the method used, reducing the viscosity of the fracturing flowback fluid is paramount; otherwise, the dispersion effect of various additives will be significantly compromised. Generally, the viscosity of fracturing flowback fluids primarily originates from colloids formed by high-molecular-weight polymers. To address this, studies have indicated that adding colloid breaker agents such as potassium permanganate, sodium hypochlorite, hydrogen peroxide, and polyaluminum chloride can reduce the viscosity of fracturing flowback fluids to some extent.

[0004] Regarding the aforementioned technologies, the inventors believe that, in current processes, hydrogen peroxide, polyaluminum chloride, and sodium hypochlorite all have relatively poor gel-breaking effects. While potassium permanganate has a better gel-breaking effect, it darkens the color of the wastewater after treatment, and the introduced manganese ions are difficult to remove, which will bring new problems to subsequent treatment. Summary of the Invention

[0005] In related technologies, breaker agents such as potassium permanganate, sodium hypochlorite, hydrogen peroxide, and polyaluminum chloride all have certain drawbacks, making it difficult to achieve a balance between breaker effectiveness and the difficulty of subsequent processing. To improve this, this application provides a fracturing flowback fluid treatment process.

[0006] This application provides a fracturing flowback fluid treatment process, which adopts the following technical solution: A fracturing flowback fluid treatment process includes the following steps: (1) Add the fracturing flowback fluid to the primary sedimentation tank and let it stand. After the mud and sand settle to the bottom of the sedimentation tank, scrape off the surface oil and then discharge the remaining raw water into the debonding tank. (2) Add oxidant and synergistic catalyst to the oxidative depolymerization tank for destabilization treatment, and discharge the destabilized wastewater into the coagulation sedimentation tank; the oxidant includes sodium hypochlorite, the synergistic catalyst consists of nickel oxide and iron oxide, and the weight ratio of the synergistic catalyst to sodium hypochlorite is 1:(2.8-3.5). (3) Add coagulant and coagulant aid to the coagulation sedimentation tank. After coagulation sedimentation treatment, the sludge is removed to obtain sludge dewatering wastewater. Discharge the sludge dewatering wastewater into the flotation tank. (4) The desludge wastewater is treated by flotation in the flotation tank, and then the desludge wastewater after flotation is filtered and membrane separated to complete the treatment of fracturing flowback fluid.

[0007] By adopting the above technical solution, this application uses sodium hypochlorite as an oxidant and selects a synergistic catalyst containing nickel oxide and iron oxide to enhance the oxidant's effect. Nickel oxide accelerates the decomposition of sodium hypochlorite and promotes the redox cycle. Iron oxide and nickel oxide have a synergistic effect; under the combined action of iron oxide and nickel oxide, sodium hypochlorite decomposes to produce more highly active atomic oxygen, thereby significantly improving the oxidation performance and utilization rate of sodium hypochlorite. Compared with potassium permanganate breaker in related technologies, the oxidant and synergistic catalyst in this application not only have a better breaker effect but also avoid the introduction of manganese ions, fully leveraging the advantage of sodium hypochlorite's minimal impact on color. After the breaker treatment, the viscosity of the fracturing flowback fluid decreases significantly, which is beneficial for the uniform dispersion of various additives, thus improving the treatment effect of the fracturing flowback fluid.

[0008] Preferably, the enhancing catalyst is prepared according to the following method: (1) Nickel oxide, iron oxide and base material are mixed and ground together, and then sodium silicate solution is added to the ground product to obtain a plastic mixture; in this step, the base material includes diatomaceous earth. (2) The plastic mixture is molded to obtain a green body, and the green body is calcined to obtain an synergistic catalyst.

[0009] By adopting the above technical solution, this application uses a base material containing diatomaceous earth as a foundation, adds nickel oxide and iron oxide, and then uses sodium silicate solution for bonding. After molding, plasticizing, and calcining, nickel oxide and iron oxide are loaded into the base material, resulting in an synergistic catalyst containing nickel oxide and iron oxide. The porous structure of diatomaceous earth allows the nickel oxide and iron oxide loaded in the base material to fully contact with sodium hypochlorite, effectively activating the sodium hypochlorite.

[0010] Preferably, the nickel oxide content in the enhancing catalyst is 10-16 wt%.

[0011] By adopting the above technical solution, this application limits the nickel oxide content in the synergistic catalyst. Within this content range, the synergistic catalyst can promote the decomposition of sodium hypochlorite.

[0012] Preferably, the nickel oxide content in the enhancing catalyst is 13-15 wt%.

[0013] By adopting the above technical solution, this application optimizes the nickel oxide content, which helps to promote the decomposition of sodium hypochlorite and improves the debriding effect of oxidant and synergistic catalyst.

[0014] Preferably, the content of iron oxide in the synergistic catalyst is 2-4 wt%.

[0015] By adopting the above technical solution, this application optimizes the iron oxide content, which helps to promote the decomposition of sodium hypochlorite and improves the debriding effect of oxidant and synergistic catalyst.

[0016] Preferably, the base material is prepared according to the following method: (1) Wash the diatomaceous earth with distilled water, filter it, mix the diatomaceous earth with hydrochloric acid, stir it, let it stand and filter it, and then wash and dry it to obtain pretreated diatomaceous earth. (2) Mix pretreated diatomaceous earth, magnesium acetate and water, stir and dry, grind the dried product and calcine to obtain the base material.

[0017] By adopting the above technical solution, this application first pretreated diatomaceous earth with hydrochloric acid, and then loaded magnesium acetate onto the pretreated diatomaceous earth. After calcination, the magnesium acetate in the diatomaceous earth forms porous magnesium oxide. The combination of porous magnesium oxide and diatomaceous earth yields a base material with excellent adsorption properties. The synergistic catalyst prepared using this base material can fully contact sodium hypochlorite, which helps to improve the promoting effect on the decomposition of sodium hypochlorite.

[0018] Preferably, in the method for preparing the base material, the weight ratio of magnesium acetate to diatomaceous earth is (0.45-0.75):1.

[0019] By adopting the above technical solution, this application defines the weight ratio range of magnesium acetate to diatomaceous earth, within which the combination of porous magnesium oxide and diatomaceous earth can be achieved.

[0020] Preferably, in the method for preparing the base material, the weight ratio of magnesium acetate to diatomaceous earth is (0.55-0.65):1.

[0021] By adopting the above technical solution, this application has optimized the weight ratio range of magnesium acetate to diatomaceous earth, which helps to fully improve the promoting effect on the decomposition of sodium hypochlorite.

[0022] Preferably, in step (3) of the process, a dechlorinating agent is added to the coagulation sedimentation tank. The dechlorinating agent includes modified fly ash, which is prepared according to the following method: Fly ash and nitric acid solution are mixed and reacted to obtain acidified fly ash. Calcium carbonate and calcium oxide are added to the acidified fly ash, and after grinding, hydrogen peroxide is added and stirred to obtain a premix. The premix is ​​calcined, and then the cooled calcined product is ground and pulverized to obtain modified fly ash.

[0023] By adopting the above technical solution, this application defines a method for preparing modified fly ash. In this method, fly ash is pretreated with nitric acid through acidification and oxidation. Then, calcium carbonate is used as a foaming agent and calcium oxide is used as a flux to calcine the fly ash and the premixed mixture obtained by the two, resulting in modified fly ash with a certain porosity. Because the modified fly ash has undergone nitric acid pretreatment, it contains a large number of cations, which can undergo ion exchange and charge neutralization reactions with chloride ions. In addition, the presence of the porosity increases the specific surface area of ​​the modified fly ash. Under the combined effect of the two, the modified fly ash has a good adsorption effect on chloride ions. In step (3), the dechlorinating agent can be separated with the sludge after adsorbing chloride ions, thereby reducing the difficulty of subsequent wastewater treatment.

[0024] Preferably, the dechlorination agent further includes a hardened slag slurry, which is prepared by the following method: slag and calcium oxide are mixed together as a cementing material, and water is added and stirred to obtain a slag mixture; the slag mixture is molded and water-cured to obtain the hardened slag slurry.

[0025] By adopting the above technical solution, this application also uses hardened slag slurry as a dechlorinating agent and specifies the preparation method of hardened slag slurry. In the above method, calcium oxide reacts with alumina in the slag, and after hydration, forms calcium aluminate hydrate, which is retained in the hardened slag slurry. Calcium aluminate hydrate can combine with chloride ions to form calcium chloroaluminate hydrate, which has the function of solidifying chloride ions. Moreover, other components in the hardened slag slurry also have the effect of physically adsorbing chloride ions, thus effectively achieving the removal of chloride ions.

[0026] In summary, this application has the following beneficial effects: 1. This application uses sodium hypochlorite as an oxidant and selects a synergistic catalyst containing nickel oxide and iron oxide to enhance the oxidant's effect. Compared with potassium permanganate breaker, it not only has a better breaker effect but also avoids the introduction of manganese ions, fully leveraging the advantage of sodium hypochlorite's minimal impact on color. After the breaker treatment, the viscosity of the fracturing flowback fluid decreases significantly, which is beneficial for the uniform dispersion of various additives, thus improving the treatment effect on the fracturing flowback fluid.

[0027] 2. This application uses a base material containing diatomaceous earth as a foundation, adds nickel oxide and iron oxide, and then uses sodium silicate solution for bonding. After molding, plasticizing, and calcination, a synergistic catalyst containing nickel oxide and iron oxide is obtained. Based on this, this application also obtains a base material containing porous magnesium oxide through modification of diatomaceous earth. The porous structure provided by the porous magnesium oxide and diatomaceous earth allows the nickel oxide and iron oxide loaded in the base material to fully contact with sodium hypochlorite, effectively activating the sodium hypochlorite. Detailed Implementation

[0028] The present application will be further described in detail below with reference to the embodiments, preparation examples and comparative examples. The raw materials involved in the present application can all be obtained commercially.

[0029] Example of preparation of synergistic catalyst The following explanation uses Preparation Example 1 as an example.

[0030] Preparation Example 1 In this preparation example, the enhancing catalyst was prepared according to the following method: (1) Nickel oxide, iron oxide, and the base material are mixed and ground together. Then, a sodium silicate solution (concentration of 40 wt%), equivalent to 5% of the total weight of the ground product, is added to the ground product to obtain a plastic mixture. In this step, the base material with a specific surface area of ​​45 m² is selected. 2 / g of diatomaceous earth; (2) The plastic mixture is molded to obtain a green body. The green body is calcined at 200℃ for 2 hours and at 400℃ for 6 hours to obtain the synergistic catalyst.

[0031] In this preparation example, nickel oxide and iron oxide were added at a ratio of 10 wt% and 1 wt% of the total weight of the synergistic catalyst, respectively.

[0032] As shown in Table 1, the difference between Preparation Examples 1-5 is that the percentage of nickel oxide in the total weight of the synergistic catalyst (referred to as nickel oxide percentage in Table 1) is different.

[0033] Table 1 Nickel content Preparation Example 1 10 Preparation Example 2 13 Preparation Example 3 14 Preparation Example 4 15 Preparation Example 5 16 As shown in Table 2, the difference between Preparation Example 3 and Preparation Examples 6-8 is that the percentage of iron oxide in the total weight of the synergistic catalyst (referred to as iron oxide percentage in Table 2) is different.

[0034] Table 2 Iron content Preparation Example 3 1 Preparation Example 6 2 Preparation Example 7 3 Preparation Example 8 4 Preparation Example 9 The difference between this preparation example and preparation example 8 is that the base material is prepared according to the following method: (1) Compare the surface area of ​​45m² with distilled water.2 / g of diatomaceous earth was washed, filtered, and then immersed in 1mol / L hydrochloric acid. After stirring magnetically at a rate of 500r / min for 2h, it was allowed to stand and filtered. After washing and drying, pretreated diatomaceous earth was obtained. (2) Pretreated diatomaceous earth, magnesium acetate and water were mixed in a weight ratio of 1:0.45:10, stirred at a rate of 350r / min for 24h, and then dried at 50℃. The dried product was ground and then calcined at 400℃ for 2h to obtain the base material.

[0035] As shown in Table 3, the difference between preparation examples 9-13 is that the weight ratio of magnesium acetate to diatomaceous earth is different.

[0036] Table 3. Weight ratio of magnesium acetate to diatomaceous earth Preparation example of modified fly ash The following explanation uses Preparation Example 14 as an example.

[0037] Preparation Example 14 In this preparation example, the fly ash used is Class I fly ash of type F.

[0038] In this preparation example, the modified fly ash was prepared according to the following method: Fly ash and nitric acid solution were mixed and reacted at a ratio of 9 mL of 1.8 mol / L nitric acid solution per gram of fly ash to obtain acidified fly ash. Calcium carbonate was added at 30% of the mass of acidified fly ash, followed by calcium oxide at 8% of the mass of acidified fly ash. After grinding, hydrogen peroxide (containing 2% of the hydrogen peroxide content of acidified fly ash) was added and stirred to obtain a premix. The premix was calcined at 920℃ for 1 hour, and the cooled calcined product was then ground and pulverized to obtain modified fly ash.

[0039] Preparation example of hardened slag slurry The following explanation uses Preparation Example 15 as an example.

[0040] Preparation Example 15 In this preparation example, S95 slag was selected.

[0041] In this preparation example, the hardened slag slurry was prepared according to the following method: Slag and calcium oxide (equivalent to 5% of the slag weight) were mixed together as a cementing material. Water was added and stirred at a water-cement ratio of 0.5 to obtain a slag mixture. The slag mixture was molded and demolded after 1 day. It was then transferred to a standard curing environment for water curing. After 28 days, a hardened slag slurry was obtained. Example

[0042] Examples 1-5 The following description uses Example 1 as an example.

[0043] Example 1 In the processing of this embodiment, the fracturing flowback fluid used has an initial viscosity of 2.8 mPa·s and an initial chloride ion content of 8580 mg / L.

[0044] This embodiment provides a fracturing flowback fluid treatment process, including the following steps: (1) Add the fracturing flowback fluid to the primary sedimentation tank and let it stand. After the mud and sand settle to the bottom of the sedimentation tank, scrape off the surface oil and then discharge the remaining raw water into the debonding tank. (2) Add oxidant and synergistic catalyst to the oxidative de-gelling tank for destabilization treatment, and discharge the destabilized wastewater into the coagulation sedimentation tank; In this step, sodium hypochlorite is selected as the oxidant, the dosage of sodium hypochlorite is 2g / L, the reaction time is 90min, and the synergistic catalyst is prepared according to the method of Preparation Example 1, with a weight ratio of synergistic catalyst to sodium hypochlorite of 1:2.8; (3) Add dechlorinating agent, coagulant and coagulant aid to the coagulation sedimentation tank. After coagulation sedimentation treatment, the sludge is removed to obtain desludge wastewater, which is discharged into the flotation tank. In this step, the dosage of dechlorinating agent is 20 g / L, and the dechlorinating agent is the modified fly ash of Preparation Example 14. Copper sulfate is selected as the coagulant, and the dosage of the coagulant is 120 mg / L. Cationic polyacrylamide is selected as the coagulant aid, and the dosage of the coagulant is 2 mg / L. (4) The desludge wastewater is treated by flotation in the flotation tank, and then the desludge wastewater after flotation is filtered and membrane separated to complete the treatment of fracturing flowback fluid.

[0045] As shown in Table 4, the main difference between Examples 1-3 lies in the different weight ratios of the synergistic catalyst and sodium hypochlorite.

[0046] Table 4. Weight ratio of synergistic catalyst to sodium hypochlorite Synergistic catalyst: Sodium hypochlorite 1:2.8 1:3.1 1:3.5 As shown in Table 5, the difference between Examples 3-15 is that the preparation examples of the synergistic catalysts are different.

[0047] Example 16 The difference between this embodiment and Example 1 is that the dechlorinating agent is the hardened slag slurry of Preparation Example 15. The hardened slag slurry is crushed and ground to a fineness comparable to that of Class I fly ash of Type F before use, and the same applies below.

[0048] Example 17 The difference between this embodiment and Example 1 is that the dechlorination agent is prepared by mixing the modified fly ash of Preparation Example 14 and the hardened slag slurry of Preparation Example 15 in a weight ratio of 1:1.

[0049] Example 18 The difference between this embodiment and Embodiment 1 is that the dechlorination agent selected has a specific surface area of ​​45m². 2 / g of diatomaceous earth.

[0050] Example 19 The difference between this embodiment and Embodiment 1 is that the dechlorination agent used is Class F Grade I fly ash.

[0051] Example 20 The difference between this embodiment and Embodiment 1 is that the dechlorination agent used is S95 slag, which is crushed and ground to a fineness comparable to Class I fly ash of the F category before use.

[0052] Comparative Example Comparative Example 1 The difference between this comparative example and Example 1 is that no synergistic catalyst is added in step (2).

[0053] Comparative Example 2 The difference between this comparative example and Example 1 is that potassium permanganate is used as the oxidant in step (2).

[0054] Comparative Example 3 The difference between this comparative example and Example 1 is that the components of the synergistic catalyst do not include iron oxide.

[0055] Performance testing methods I. Debonding effect After adding oxidant for 90 minutes in step (2), water samples were collected from the oxidation debonding tank and the viscosity of the water samples was measured. The ratio of this viscosity to the initial viscosity of the fracturing flowback fluid was calculated. The absolute value of the difference between this ratio and 100% was recorded as the debonding rate, which represents the residual viscosity after treatment. The results are shown in Table 6.

[0056] II. Dechlorination effect After adding the dechlorinating agent and completing the coagulation and sedimentation in step (3), a water sample is collected from the coagulation and sedimentation tank, the chloride ion concentration in the water sample is detected, and the ratio of this concentration to the initial chloride ion concentration of the fracturing flowback fluid is calculated. The absolute value of the difference between this ratio and 100% is recorded as the dechlorination rate. The results are shown in Table 6.

[0057] Table 6 Test Results As can be seen from Examples 1-15 and Table 6, the dechlorination rate shows an upward trend as the breakage rate decreases. This is because the decrease in the viscosity of the fracturing flowback fluid helps to disperse the dechlorinating agent, thereby improving the dechlorination effect of the dechlorinating agent.

[0058] As can be seen from Examples 1-3 and Comparative Example 1, and Table 6, the debonding rate measured in Examples 1-3 was lower than that in Comparative Example 1, while the dechlorination rate was higher than that in Comparative Example 1. This is because, under the combined action of iron oxide and nickel oxide in the synergistic catalyst, sodium hypochlorite can generate more atomic oxygen with good activity after decomposition, thereby significantly improving the oxidation performance and utilization rate of sodium hypochlorite, thus improving the debonding effect.

[0059] As can be seen from Example 1 and Comparative Example 2, and in conjunction with Table 6, this application achieves a better degelatinizing effect than potassium permanganate through the synergistic combination of sodium hypochlorite and the synergistic catalyst.

[0060] Based on Example 1 and Comparative Example 3, and in conjunction with Table 6, it can be seen that when iron oxide is lacking in the synergist, nickel oxide and diatomaceous earth alone are insufficient to fully improve the oxidation performance of sodium hypochlorite. Therefore, the debinding effect of Comparative Example 3 is poor.

[0061] As can be seen from Examples 3-7 and Table 6, when the nickel oxide content in the synergistic catalyst is 13-15 wt%, the synergistic catalyst can more fully improve the oxidation performance of sodium hypochlorite. Therefore, the debinding effect of Examples 4-6 is relatively good.

[0062] Based on Examples 5, 8-10, and Table 6, it can be seen that when the iron oxide content in the synergistic catalyst is 2-4 wt%, the synergistic catalyst can more fully improve the oxidation performance of sodium hypochlorite. Therefore, the debinding effect of Examples 8-10 is relatively good.

[0063] Combining Examples 10, 11-15, and Table 6, it can be seen that the debonding rates measured in Examples 11-15 are all relatively low, indicating that Examples 11-15 achieved debonding more fully. Based on the data from Examples 11-15, it can be seen that in the method for preparing the base material, when the weight ratio of magnesium acetate to diatomaceous earth is (0.55-0.65):1, the synergistic catalyst is more helpful in improving the debonding effect of sodium hypochlorite.

[0064] Based on Examples 1, 16, and 17 and Table 6, it can be seen that the breaking rate of Example 1 and Examples 16-17 is similar, while the dechlorination rate of Example 17 is higher. This indicates that when hardened slag slurry is used in combination with modified fly ash, it can achieve a better dechlorination effect than when the two are used alone.

[0065] As can be seen from Examples 1, 18-20 and Table 6, diatomaceous earth, fly ash and slag have limited effects on chloride ion removal when used alone.

[0066] The above embodiments are merely explanations of this application and are not intended to limit it. After reading this specification, those skilled in the art can make modifications to the embodiments of this application without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of this application.

Claims

1. A process for treating fracturing flowback fluid, characterized in that, The process includes the following steps: (1) Add the fracturing flowback fluid to the primary sedimentation tank and let it stand. After the sludge settles to the bottom of the sedimentation tank, scrape off the surface oil and then discharge the remaining raw water into the debonding tank; (2) Add an oxidant and a synergistic catalyst to the debonding tank for destabilization treatment and discharge the destabilized wastewater into the coagulation sedimentation tank; the oxidant includes sodium hypochlorite, the synergistic catalyst consists of nickel oxide and iron oxide, and the weight ratio of the synergistic catalyst to sodium hypochlorite is 1:(2.8-3.5); (3) Add a coagulant and a coagulant aid to the coagulation sedimentation tank, and remove the sludge after coagulation sedimentation treatment to obtain desludge wastewater, which is then discharged into the flotation tank; (4) Perform flotation treatment on the desludge wastewater in the flotation tank, and then filter and membrane separate the flotation-treated desludge wastewater to complete the treatment of the fracturing flowback fluid. The synergistic catalyst is prepared by the following method: (1) Nickel oxide, iron oxide and base material are mixed and ground together, and then sodium silicate solution is added to the ground product to obtain a plastic mixture; in this step, the base material includes diatomaceous earth; (2) The plastic mixture is molded to obtain a green body, and the green body is calcined to obtain the synergistic catalyst. The nickel oxide content in the aforementioned enhancing catalyst is 10-16 wt%. The synergistic catalyst contains 2-4 wt% iron oxide. The base material is prepared by the following method: (1) Wash the diatomaceous earth with distilled water, filter it, mix the diatomaceous earth with hydrochloric acid, stir it and let it stand for filtration, and then wash and dry it to obtain pretreated diatomaceous earth; (2) Mix the pretreated diatomaceous earth, magnesium acetate and water, stir it and dry it, grind the dried product and calcine it to obtain the base material.

2. The fracturing flowback fluid treatment process of claim 1, wherein, The nickel oxide content in the synergistic catalyst is 13-15 wt%.

3. The fracturing flowback fluid treatment process according to claim 1, characterized in that, In the method for preparing the base material, the weight ratio of magnesium acetate to diatomaceous earth used is (0.45-0.75):

1.

4. The fracturing flowback fluid treatment process according to claim 3, characterized in that, In the method for preparing the base material, the weight ratio of magnesium acetate to diatomaceous earth used is (0.55-0.65):

1.

5. The fracturing flowback fluid treatment process according to claim 1, characterized in that, In step (3) of the process, a dechlorinating agent is added to the coagulation sedimentation tank. The dechlorinating agent includes modified fly ash. The modified fly ash is prepared by the following method: fly ash and nitric acid solution are mixed and reacted to obtain acidified fly ash. Calcium carbonate and calcium oxide are added to the acidified fly ash. After grinding, hydrogen peroxide is added and stirred to obtain a premix. The premix is ​​calcined, and then the cooled calcined product is ground and pulverized to obtain modified fly ash.

6. The fracturing flowback fluid treatment process according to claim 5, characterized in that, The dechlorination agent also includes hardened slag slurry, which is prepared by the following method: slag and calcium oxide are mixed together as a cementing material, and water is added and stirred to obtain a slag mixture; the slag mixture is molded and water-cured to obtain the hardened slag slurry.

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