Shale gas flowback fluid treatment and lithium extraction method

Abstract

The invention relates to the field of shale gas flow-back fluid treatment and resource utilization, and particularly discloses a shale gas flow-back fluid treatment and lithium extraction method which comprises the following units: (1) wastewater treatment; (2) extracting lithium; and (3) evaporation treatment. The adsorption device is added in front of the evaporation unit, and the modified lithium adsorbent with high adsorption strength is specifically added, so that standard treatment discharge and lithium resource recovery of the shale gas flow-back fluid are synchronously realized, the whole process method is safe and environment-friendly, efficient reuse of treatment substances in each unit is realized, and the method is suitable for industrial production. And the treatment and resource recovery cost of the shale gas flowback fluid is also reduced.

Description

Technical Field

[0001] The invention relates to the field of shale gas flowback fluid treatment and resource utilization, and specifically discloses a shale gas flowback fluid treatment and lithium extraction method. Background Art

[0002] At present, the main means of development of most shale gas mining areas is hydraulic fracturing. The most important step of hydraulic fracturing technology is to prepare hydraulic fracturing fluid. The specific process is to prepare fracturing fluid with water, chemical additives, proppants, etc. Among them, chemical additives are a very important part of the entire fracturing process and also the most complicated part. The hydraulic fracturing fluid passes through a series of high-pressure equipment and is injected into a deep well, so that the shale gas reservoir is subjected to strong force and cracked, the pressure of the gas reservoir is reduced, and the shale gas reaches the wellhead through the rock cracks and pipelines. The shale gas fracturing flowback fluid obtained in the shale gas development process is the wastewater after the completion of the shale gas well.

[0003] The invention patent with the publication number CN 114835281 A discloses a method for treating shale gas flowback liquid and a device for treating shale gas flowback liquid. The method comprises: performing sedimentation and filtration treatment on the shale gas flowback liquid through a sedimentation unit; filtering the primary filtered liquid for impurities to obtain a secondary filtered liquid; and performing reverse osmosis treatment on the secondary filtered liquid to obtain an external discharge liquid. The invention sequentially performs sedimentation, impurity filtration and reverse osmosis filtration on the shale gas flowback liquid. During the sedimentation treatment process, the scale-forming ions and part of the organic matter in the flowback liquid are removed; during the impurity filtration process, the pollution characteristics of the liquid are reduced; during the reverse osmosis treatment process, the liquid reaches the final discharge standard. Through the step-by-step treatment of the liquid, the metal ions, pollutants and microparticles in the liquid are gradually discharged, and finally the shale gas flowback liquid meets the discharge standard, thereby improving the safety of the discharge of the shale gas flowback liquid. However, the invention does not consider the recycling of important resource lithium, and the comprehensive utilization rate of the treated materials of each unit in the entire treatment method is not high. Summary of the invention

[0004] In view of the defects of the prior art, the present invention discloses a method for treating shale gas flowback liquid and extracting lithium. The present invention adds an adsorption device before the evaporation unit and specifically adds a modified lithium adsorbent with high adsorption strength, which simultaneously achieves the standard treatment and discharge of shale gas flowback liquid and lithium resource recovery. The entire process method is safe and environmentally friendly, realizes the efficient reuse of the processed materials of each unit, and also reduces the treatment and resource recovery costs of shale gas flowback liquid.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: The present invention provides a method for treating shale gas flowback fluid and extracting lithium, the method comprising the following units: (1) Wastewater treatment: The shale gas return liquid is passed through a regulating tank and a coagulation sedimentation tank in sequence. Flocculants and coagulants are added to the coagulation sedimentation tank for stirring and mixing to remove suspended solids and some organic matter, thereby obtaining a supernatant and wastewater containing high-concentration suspended solids. The supernatant is passed through a sand filtration device to separate large-volume suspended solids to obtain sand filtration produced water. The sand filtration produced water is passed through an ultrafiltration device to separate small-volume suspended solids and ultrafiltration produced water. (2) Lithium extraction treatment: a portion of the ultrafiltration product water of step (1) is passed through a nanofiltration device to separate concentrated water containing high-valent ions and large molecular weight organic matter and nanofiltration product water, the nanofiltration product water is passed through a reverse osmosis No. 1 device to separate reverse osmosis No. 1 product water and concentrated water, the concentrated water is passed through an adsorption device to separate the adsorption device tail liquid and a decomposition liquid, the decomposition liquid is passed through a reverse osmosis No. 2 device to separate reverse osmosis No. 2 product water and a lithium-containing concentrated liquid; (3) Evaporation treatment: The tail liquid of the adsorption device in step (2) is passed into an evaporation device to evaporate and obtain sodium chloride.

[0006] In some embodiments of the present invention, the flocculant in step (1) is polyiron or polyaluminum, and the added amount is 2-3 g / L; the coagulant aid is anionic polyacrylamide, and the added amount is 3-4 mg / L.

[0007] In some embodiments of the present invention, in step (1), wastewater containing high-concentration suspended matter, large-volume suspended matter and small-volume suspended matter are respectively passed to a plate and frame dewatering device, filtered to obtain a filtrate and dewatered sludge, the dewatered sludge is dried and transported out, and the filtrate is returned to the equalization tank.

[0008] In some embodiments of the present invention, in step (2), a portion of the reverse osmosis 1# produced water is discharged in compliance with the standards, and another portion of the reverse osmosis 1# produced water is passed into the adsorption device; and the reverse osmosis 2# produced water is refluxed to the reverse osmosis 1# device.

[0009] In some embodiments of the present invention, in step (1), a pH adjuster is added to the regulating tank to adjust the pH to 8-11.

[0010] Preferably, in step (1), the operating pressure of the ultrafiltration device is 2-3 bar.

[0011] Preferably, in step (2), the operating pressure of the nanofiltration device is 10-13 bar.

[0012] Preferably, in step (2), the operating pressure of the reverse osmosis device #1 is 70-80 bar.

[0013] In some embodiments of the present invention, in step (2), the operating pressure of the reverse osmosis unit 2# is 65-70 bar.

[0014] The present invention concentrates lithium ions to 4400 mg / L through a complete set of processes including wastewater treatment, lithium extraction treatment and evaporation treatment, thereby achieving efficient resource recovery. The present invention first performs separation, pre-concentration, adsorption and concentration treatments on shale gas return liquid in sequence. After the shale gas return liquid is regulated in a regulating tank to achieve uniform water quantity and quality, it enters a coagulation sedimentation tank. In the reaction tank of the coagulation sedimentation tank, flocculants and coagulants are added to the reaction tank and stirred to quickly mix uniformly. After the reaction, it enters the sedimentation tank of the coagulation sedimentation tank; the supernatant of the sedimentation tank is passed into a sand filtration device, and the wastewater containing high-concentration suspended matter at the bottom of the sedimentation tank is pumped into a plate-and-frame dewatering device for pressure filtration to obtain a filtrate and dehydrated sludge. The dehydrated sludge is then dried and transported out, and the filtrate is returned to the regulating tank; large-volume suspended matter is separated by the sand filtration device, and the sand filtration product water obtained is passed into an ultrafiltration device, and its backwash water flows to the plate-and-frame; the remaining small-volume suspended matter is separated by the ultrafiltration device to obtain ultrafiltration product water; in step (2) lithium extraction treatment, a part of the ultrafiltration product water is passed into a nanofiltration device, and its backwash water flows to the plate-and-frame, and the Ca-containing 2+ Mg 2+ The concentrated water containing high-valent ions and large molecular weight organic matter is separated out, which effectively reduces the occurrence of fouling in the rear reverse osmosis device. The nanofiltration produced water is passed into the reverse osmosis 1# device to separate the reverse osmosis 1# produced water and concentrated water. A part of the reverse osmosis 1# produced water is discharged in compliance with the standards, and a part is used as washing water to enter the adsorption device in the rear stage. The concentrated water is directly passed into the adsorption device to separate the tail liquid and the analytical liquid. The analytical liquid of the adsorption device is passed into the reverse osmosis 2# device to separate the reverse osmosis 2# produced water and the lithium-containing concentrated liquid. The reverse osmosis 2# produced water is returned to the water inlet tank of the reverse osmosis 1# device. In the evaporation treatment of step (3), the tail liquid of step (2) is passed into the evaporation device to obtain sodium chloride through evaporation, thereby realizing efficient standard treatment of shale gas return fluid and efficient lithium extraction.

[0015] In some embodiments of the present invention, in step (2), the adsorbent of the adsorption device is a modified lithium adsorbent, and the preparation steps are as follows: Inorganic lithium adsorbent powder, dispersant, dichloromethane and N,N-dimethylacetamide are added to a reactor, stirred and mixed, and then added to a mixture containing acrylamide monomers, initiators and crosslinking agents, reacted at 25-30° C. for 10-30 minutes, and granulated, pore-formed and filtered to obtain the modified lithium adsorbent.

[0016] In some embodiments of the present invention, the mass ratio of the inorganic lithium adsorbent powder to the acrylamide monomer is 1:(0.3-0.6).

[0017] Preferably, the mass ratio of the inorganic lithium adsorbent powder to the acrylamide monomer is 1:0.45.

[0018] In some embodiments of the present invention, the acrylamide monomer is a mixture of acrylamide and hydroxyethyl acrylamide.

[0019] Preferably, the mass ratio of acrylamide to hydroxyethyl acrylamide is 1:(0.5-0.7).

[0020] In some embodiments of the present invention, the particle size of the inorganic lithium adsorbent powder is 5-30 μm, and the free water content is less than 5 wt %.

[0021] Preferably, the dispersant is polyethylene glycol or Tween 80.

[0022] In the prior art, aluminum-based lithium adsorbents, as an inorganic adsorbent, can selectively adsorb lithium ions and block other metal ions by utilizing their own structural characteristics, thereby achieving efficient separation of lithium, and can be used for low-concentration lithium extraction, with readily available raw materials, simple preparation process, and environmentally friendly. However, the adsorption strength and pressure resistance of commonly used aluminum-based lithium adsorbents are not high, and they are prone to dissolution during use, shortening their service life. In view of this, the adsorption capacity and pressure resistance of the modified lithium adsorbent prepared by the present invention are further improved. At the same time, the adsorbent can not only adsorb lithium, but also adsorb organic matter, helping to reduce the evaporator fouling and blockage, and reducing the maintenance cost of the entire process. This may be due to the increase in the copolymer structure and active adsorption sites of acrylamide and hydroxyethyl acrylamide during modification, especially the balanced introduction of hydrophilic and lipophilic monomers, which enables the modified lithium adsorbent to have a strong ability to synergistically adsorb and accommodate organic matter in wastewater, achieving efficient adsorption and further improving the adsorption effect of the adsorption device.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention adds an adsorption device before the evaporation unit and specifically adds a modified lithium adsorbent with high adsorption strength, thereby simultaneously achieving the standard treatment and discharge of shale gas return fluid and lithium resource recovery. The entire process method is safe and environmentally friendly, and also reduces the treatment and resource recovery costs of shale gas return fluid.

[0025] (2) The backflow liquid treatment method of the present invention achieves the standard discharge of wastewater, and the water produced by the reverse osmosis 1# device and the reverse osmosis 2# device can be reused in the adsorption device for washing and analysis. No additional water is required during the adsorption process, thereby achieving efficient reuse of the treated materials of each treatment unit. The process is energy-saving and efficient, and has excellent application potential.

[0026] (3) The method of the present invention adds an adsorption device before the evaporation device and adds a specially prepared modified lithium adsorbent, which can not only adsorb lithium but also adsorb organic matter. The modified lithium adsorbent has a strong ability of synergistic adsorption and inclusive absorption for organic matter in wastewater, achieves efficient adsorption, further improves the adsorption effect of the adsorption device, helps reduce the evaporator fouling, and reduces the maintenance cost of the entire process. DETAILED DESCRIPTION

[0027] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0028] Unless otherwise specified, the reagents used below can be easily obtained from commercial companies. Among them, the anionic polyacrylamide used has a viscosity-average molecular weight of 16 million and is purchased from Shandong Huanjing Chemical Co., Ltd.; the inorganic lithium adsorbent powder used is LiCl·2Al(OH)3·H2O with a particle size of 20 μm and a free water content of 4 wt%, which can be prepared according to the method disclosed in the reference "Aluminium hydroxide as selective sorbent of lithium salts from brines and technical solutions"; the model of the polyethylene glycol used is PEG-400.

[0029] Unless otherwise specified, this application does not limit the processing work in the "sand filtration device", "ultrafiltration device", "plate and frame dehydration device", "nanofiltration device", "reverse osmosis 1# device", "reverse osmosis 2# device" and "evaporation device" involved in the shale gas return liquid treatment and lithium extraction method, and the selection and processing work can be carried out according to the device components and conventional operations familiar to technical personnel in this field.

[0030] Unless otherwise specified, the post-processing steps such as "granulation" and "filtration" used below are routine operations of those skilled in the art and can be selected according to actual operations.

[0031] Preparation Example 1 The preparation steps of the modified lithium adsorbent are as follows: Add 20 g of inorganic lithium adsorbent powder, 1.5 g of polyethylene glycol, 30 mL of dichloromethane and 30 mL of N,N-dimethylacetamide into the reactor, stir and mix, then add into a mixture containing 5.6 g of acrylamide, 3.4 g of hydroxyethyl acrylamide, 0.2 g of ammonium persulfate and 0.8 g of piperazine at a rate of 0.5 drops / s, react at 26 °C for 25 min, granulate, transfer to 600 mL of deionized water, heat to 40 °C for 3 h to form pores, and filter to obtain the modified lithium adsorbent.

[0032] Preparation Example 2 The preparation steps of the modified lithium adsorbent are the same as those of Preparation Example 1, except that 14 g of inorganic lithium adsorbent powder is added.

[0033] Preparation Example 3 The preparation steps of the modified lithium adsorbent are the same as those of Preparation Example 1, except that 5 g of acrylamide and 4 g of hydroxyethyl acrylamide are added.

[0034] Example 1 A method for treating shale gas flowback fluid and extracting lithium, the method comprising the following units: (1) Wastewater treatment: The shale gas return liquid is passed through a regulating tank (sodium hydroxide is added to adjust the pH to 10) and a coagulation sedimentation tank in sequence. Polyferric sulfate (the ratio of polyferric sulfate added to the shale gas return liquid is 2 g / L) is added to the coagulation sedimentation tank and stirred at a speed gradient of 600 r / s for 5 min. Anionic polyacrylamide (the ratio of anionic polyacrylamide added to the shale gas return liquid is 3 mg / L) is then added and stirred at a speed gradient of 80 r / s for 10 min to obtain a supernatant and wastewater containing high-concentration suspended matter. The supernatant is passed through a sand filter device to separate large-volume suspended matter to obtain sand filtration water. The sand filtration water is passed through an ultrafiltration device (operating pressure is 2.5 bar) to separate small-volume suspended matter and ultrafiltration water. At the same time, the wastewater containing high-concentration suspended matter, large-volume suspended matter and small-volume suspended matter are passed to a plate and frame dehydration device for pressure filtration to obtain filtrate and dehydrated sludge. The dehydrated sludge is dried and transported out, and the filtrate is returned to the regulating tank. (2) Lithium extraction treatment: a portion of the ultrafiltration product water of step (1) is passed into a nanofiltration device (operating pressure of 12 bar) to separate concentrated water containing high-valent ions and large molecular weight organic matter and nanofiltration product water, the nanofiltration product water is passed into a reverse osmosis 1# device (using InnoECSW-8040XLE reverse osmosis membrane, operating pressure of 75 bar), to separate reverse osmosis 1# product water and concentrated water, the concentrated water is passed into an adsorption device to separate tail liquid and analytical solution, the analytical solution is passed into a reverse osmosis 2# device (using InnoECSW-8040XHD reverse osmosis membrane, operating pressure of 67 bar), to separate reverse osmosis 2# product water and lithium-containing concentrated solution; (3) Evaporation treatment: The ultrafiltration water produced in another part of step (1) is passed into an evaporation device to be condensed water, and the tail liquid in step (2) is passed into an evaporation device to evaporate and obtain sodium chloride.

[0035] Wherein, the adsorbent used in the adsorption device is obtained from Preparation Example 1.

[0036] The shale gas flowback fluid in this embodiment comes from a well site in Sichuan. Its original CODcr (GB 11914-89) is 412.52 mg / L, BOD5 (GB 7488-87) is 104.16 mg / L, and TDS (TDS water quality detector) is 16040 mg / L. During the operation, the produced water of the reverse osmosis 1# device was sampled for water quality analysis, and the CODcr was measured to be 8 mg / L, BOD5 was 3.8 mg / L, and TDS was 186.1 mg / L. The effluent water quality meets the standards for reinjection and multiple reuse; at the same time, the lithium ion concentration of the reverse osmosis 1# produced water (inductively coupled plasma emission spectrometer) was measured to be 220 mg / L, and the lithium ion concentration of the lithium-containing concentrate was 4440 mg / L.

[0037] Example 2 A method for treating shale gas flowback fluid and extracting lithium, the method comprising the following units: (1) Wastewater treatment: The shale gas return liquid is passed through a regulating tank (sodium hydroxide is added to adjust the pH to 8) and a coagulation sedimentation tank in sequence. Polyaluminium chloride is added to the coagulation sedimentation tank (the ratio of polyaluminium chloride added to the shale gas return liquid is 3 g / L) and stirred at a speed gradient of 400 r / s for 2 min. Anionic polyacrylamide is then added (the ratio of anionic polyacrylamide added to the shale gas return liquid is 4 mg / L) and stirred at a speed gradient of 40 r / s for 12 min to obtain a supernatant and wastewater containing high-concentration suspended matter. The supernatant is passed through a sand filter device to separate large-volume suspended matter to obtain sand filtration water. The sand filtration water is passed through an ultrafiltration device (operating pressure is 2 bar) to separate small-volume suspended matter and ultrafiltration water. At the same time, the wastewater containing high-concentration suspended matter, large-volume suspended matter and small-volume suspended matter are passed to a plate and frame dehydration device for pressure filtration to obtain filtrate and dehydrated sludge. The dehydrated sludge is dried and transported out, and the filtrate is returned to the regulating tank. (2) Lithium extraction treatment: a portion of the ultrafiltration product water of step (1) is passed into a nanofiltration device (operating pressure of 10 bar) to separate concentrated water containing high-valent ions and large molecular weight organic matter and nanofiltration product water, the nanofiltration product water is passed into a reverse osmosis 1# device (using InnoECSW-8040XLE reverse osmosis membrane, operating pressure of 70 bar), to separate reverse osmosis 1# product water and concentrated water, the concentrated water is passed into an adsorption device to separate tail liquid and analytical solution, the analytical solution is passed into a reverse osmosis 2# device (using InnoECSW-8040XHD reverse osmosis membrane, operating pressure of 65 bar), to separate reverse osmosis 2# product water and lithium-containing concentrated solution; (3) Evaporation treatment: The ultrafiltration water produced in another part of step (1) is passed into an evaporation device to be condensed water, and the tail liquid in step (2) is passed into an evaporation device to evaporate and obtain sodium chloride.

[0038] Wherein, the adsorbent used in the adsorption device is obtained from Preparation Example 1.

[0039] The source of shale gas flowback liquid in this embodiment is the same as that in Example 1. During the operation, the produced water of the reverse osmosis 1# device was sampled for water quality analysis, and the CODcr was measured to be 8.7 mg / L, BOD5 was 4.5 mg / L, and TDS was 191 mg / L. The effluent water quality met the standards for reinjection and multiple reuse. At the same time, the lithium ion concentration of the reverse osmosis 1# produced water was measured to be 217.5 mg / L, and the lithium ion concentration of the lithium-containing concentrate was 4405 mg / L.

[0040] Example 3 A method for treating shale gas flowback fluid and extracting lithium, the method comprising the following units: (1) Wastewater treatment: The shale gas return liquid is passed through a regulating tank (sodium hydroxide is added to adjust the pH to 8) and a coagulation sedimentation tank in sequence. Polyaluminium chloride is added to the coagulation sedimentation tank (the ratio of polyaluminium chloride added to the shale gas return liquid is 2.5 g / L) and stirred at a speed gradient of 800 r / s for 0.5 min. Anionic polyacrylamide is then added (the ratio of anionic polyacrylamide added to the shale gas return liquid is 3 mg / L) and stirred at a speed gradient of 100 r / s for 8 min to obtain a supernatant and wastewater containing high-concentration suspended matter. The supernatant is passed through a sand filter device to separate large-volume suspended matter to obtain sand filtration water. The sand filtration water is passed through an ultrafiltration device (operating pressure is 3 bar) to separate small-volume suspended matter and ultrafiltration water. At the same time, the wastewater containing high-concentration suspended matter, large-volume suspended matter and small-volume suspended matter are passed to a plate and frame dehydration device for pressure filtration to obtain filtrate and dehydrated sludge. The dehydrated sludge is dried and transported out, and the filtrate is returned to the regulating tank. (2) Lithium extraction treatment: a portion of the ultrafiltration product water of step (1) is passed into a nanofiltration device (operating pressure of 13 bar) to separate concentrated water containing high-valent ions and large molecular weight organic matter and nanofiltration product water, the nanofiltration product water is passed into a reverse osmosis 1# device (using InnoECSW-8040XLE reverse osmosis membrane, operating pressure of 80 bar), to separate reverse osmosis 1# product water and concentrated water, the concentrated water is passed into an adsorption device to separate tail liquid and analytical solution, the analytical solution is passed into a reverse osmosis 2# device (using InnoECSW-8040XHD reverse osmosis membrane, operating pressure of 70 bar), to separate reverse osmosis 2# product water and lithium-containing concentrated solution; (3) Evaporation treatment: The ultrafiltration water produced in another part of step (1) is passed into an evaporation device to be condensed water, and the tail liquid in step (2) is passed into an evaporation device to evaporate and obtain sodium chloride.

[0041] Wherein, the adsorbent used in the adsorption device is obtained from Preparation Example 1.

[0042] The source of shale gas flowback liquid in this embodiment is the same as that in Example 1. During the operation, the produced water of the reverse osmosis 1# device was sampled for water quality analysis, and the CODcr was measured to be 8.4 mg / L, BOD5 was 4.0 mg / L, and TDS was 188 mg / L. The effluent water quality met the standards for reinjection and multiple reuse. At the same time, the lithium ion concentration of the reverse osmosis 1# produced water was measured to be 218.2 mg / L, and the lithium ion concentration of the lithium-containing concentrate was 4388 mg / L.

[0043] Example 4 A method for treating shale gas flowback liquid and extracting lithium, the specific implementation method is the same as Example 1, except that the adsorbent used in the adsorption device is obtained from Preparation Example 2. During the operation, the water produced by the reverse osmosis 1# device was sampled for water quality analysis, and the CODcr was measured to be 8.9 mg / L, BOD5 was 4.7 mg / L, TDS was 193 mg / L, and the effluent water quality met the standards for reinjection and multiple reuse; the lithium ion concentration of the lithium-containing concentrate was measured to be 4293.1 mg / L.

[0044] Example 5 A method for treating shale gas flowback liquid and extracting lithium, the specific implementation method is the same as Example 1, except that the adsorbent used in the adsorption device is obtained from Preparation Example 3. During the operation, the water produced by the reverse osmosis 1# device was sampled for water quality analysis, and the CODcr was measured to be 9.2 mg / L, BOD5 was 4.9 mg / L, TDS was 197.6 mg / L, and the effluent water quality met the standards for reinjection and multiple reuse; the lithium ion concentration of the lithium-containing concentrate was measured to be 4275.8 mg / L.

[0045] Comparative Example 1 A method for treating shale gas flowback liquid and extracting lithium, the specific implementation method is the same as that of Example 1, except that the adsorbent used in the adsorption device is a commercially available aluminum adsorbent (model HPL800, purchased from Jiangsu Haipu Functional Materials Co., Ltd.). During the operation, the water produced by the reverse osmosis 1# device was sampled for water quality analysis, and the CODcr was measured to be 9.7 mg / L, the BOD5 was 5.3 mg / L, and the TDS was 199.8 mg / L. The effluent water quality met the standards for reinjection and multiple reuse; the lithium ion concentration of the lithium-containing concentrate was measured to be 4185.2 mg / L.

[0046] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for treating shale gas flowback fluid and extracting lithium, characterized in that: The method comprises the following units: (1) Wastewater treatment: The shale gas return liquid is passed through a regulating tank and a coagulation sedimentation tank in sequence. Flocculants and coagulants are added to the coagulation sedimentation tank for stirring and mixing to remove suspended solids and some organic matter, thereby obtaining a supernatant and wastewater containing high-concentration suspended solids. The supernatant is passed through a sand filtration device to separate large-volume suspended solids to obtain sand filtration produced water. The sand filtration produced water is passed through an ultrafiltration device to separate small-volume suspended solids and ultrafiltration produced water. (2) Lithium extraction treatment: a portion of the ultrafiltration product water of step (1) is passed through a nanofiltration device to separate concentrated water containing high-valent ions and large molecular weight organic matter and nanofiltration product water, the nanofiltration product water is passed through a reverse osmosis No. 1 device to separate reverse osmosis No. 1 product water and concentrated water, the concentrated water is passed through an adsorption device to separate the adsorption device tail liquid and a decomposition liquid, the decomposition liquid is passed through a reverse osmosis No. 2 device to separate reverse osmosis No. 2 product water and a lithium-containing concentrated liquid; (3) Evaporation treatment: The tail liquid of the adsorption device in step (2) is passed into an evaporation device to evaporate and obtain sodium chloride.

2. The method for treating shale gas flowback fluid and extracting lithium according to claim 1, characterized in that: The flocculant in step (1) is polyferric or polyaluminum, and the addition amount is 2-3 g / L; the coagulant aid is anionic polyacrylamide, and the addition amount is 3-4 mg / L.

3. The method for treating shale gas flowback fluid and extracting lithium according to claim 1, characterized in that: In step (1), wastewater containing high-concentration suspended solids, large-volume suspended solids and small-volume suspended solids are respectively passed to a plate-and-frame dewatering device, filtered to obtain a filtrate and dewatered sludge, the dewatered sludge is dried and transported out, and the filtrate is returned to the regulating tank.

4. The method for treating shale gas flowback fluid and extracting lithium according to claim 1, characterized in that: A part of the water produced by reverse osmosis 1# is discharged in compliance with the standards, and another part of the water produced by reverse osmosis 1# is passed into the adsorption device; the water produced by reverse osmosis 2# is returned to the reverse osmosis 1# device.

5. The method for treating shale gas flowback fluid and extracting lithium according to claim 1, characterized in that: In step (1), a pH adjusting agent is added to the regulating tank to adjust the pH to 8-11.

6. The method for treating shale gas flowback fluid and extracting lithium according to claim 1, characterized in that: In step (2), the operating pressure of the reverse osmosis 2# device is 65-70 bar.

7. The method for treating shale gas flowback fluid and extracting lithium according to claim 1, characterized in that: In step (2), the adsorbent of the adsorption device is a modified lithium adsorbent, and the preparation steps are as follows: Inorganic lithium adsorbent powder, dispersant, dichloromethane and N,N-dimethylacetamide are added to a reactor, stirred and mixed, and then added to a mixture containing acrylamide monomers, initiators and crosslinking agents, reacted at 25-30° C. for 10-30 minutes, and granulated, pore-formed and filtered to obtain the modified lithium adsorbent.

8. The method for treating shale gas flowback fluid and extracting lithium according to claim 7, characterized in that: The mass ratio of the inorganic lithium adsorbent powder to the acrylamide monomer is 1:(0.3-0.6).

9. The method for treating shale gas flowback fluid and extracting lithium according to claim 7, characterized in that: The acrylamide monomer is a mixture of acrylamide and hydroxyethyl acrylamide.

10. The method for treating shale gas flowback fluid and extracting lithium according to claim 7, characterized in that: The inorganic lithium adsorbent powder has a particle size of 5-30 μm and a free water content of less than 5 wt %.