Removal agent for simultaneously removing COD (Chemical Oxygen Demand) and heavy metals in shale gas wastewater and preparation method

Abstract

The invention belongs to the field of shale gas wastewater treatment, and discloses a remover for removing COD (chemical oxygen demand) and heavy metals in shale gas wastewater and a preparation method thereof, and the remover comprises active carbon and carboxylated tara tannin in a mass ratio of (1.5-2.6): 1. Micropores and mesopores of the activated carbon capture organic pollutants through physical adsorption, the competition between the organic pollutants and carboxylated tara tannin is reduced, the contact between the carboxylated tara tannin and heavy metals is increased, and the chelating efficiency is improved. The remover can also comprise modified montmorillonite generated by intercalating and modifying montmorillonite through tetramethylammonium chloride, and the modified montmorillonite can share the load of the activated carbon, adsorb polar organic matters, promote chelate precipitation of carboxylated tara tannin and improve the removal efficiency. The carboxylated tara tannin reduces the hydrophilicity of the organic matter and promotes the organic matter to be adsorbed by the activated carbon and the modified montmorillonite. The synergistic effect improves the wastewater treatment efficiency, and provides a new way for water environment protection.

Description

Technical Field

[0001] The invention relates to the field of shale gas wastewater treatment, and in particular to a remover for removing COD and heavy metals in shale gas wastewater and a preparation method thereof. Background Art

[0002] Shale gas wastewater, as a by-product produced during shale gas extraction, contains a variety of chemical substances, including additives in fracturing fluid, minerals in the formation, heavy metals, etc. It has the characteristics of complex composition, high salt content, high organic content, and high suspended matter. These characteristics make the treatment of shale gas wastewater much more difficult than conventional industrial wastewater. Its treatment and disposal have always been a major challenge in the field of environmental engineering. Therefore, the development of effective shale gas wastewater treatment technology is the key to achieving sustainable development of the shale gas industry.

[0003] At present, the treatment technologies for shale gas wastewater mainly include physical, chemical, biological and membrane separation methods. Physical methods such as sedimentation, filtration and centrifugation are mainly used to remove suspended solids; chemical methods include chemical precipitation, oxidation and flocculation, which are used to remove dissolved organic matter and heavy metals; biological methods use microorganisms to degrade organic matter; membrane separation technologies such as reverse osmosis and nanofiltration can remove dissolved salts and organic matter.

[0004] However, each of these methods has its limitations, and it is difficult for each of them to meet the comprehensive needs of shale gas wastewater treatment. Although the physical method is simple to operate, it is difficult to remove soluble pollutants, and the treatment effect on shale gas wastewater with high salinity and high organic content is limited. Although the chemical method can effectively remove certain specific pollutants, it may introduce secondary pollution, increasing the difficulty and cost of subsequent treatment. The biological method is effective in treating organic pollutants, but it has poor adaptability to high-salt environments and a long treatment cycle, making it difficult to meet the needs of large-scale wastewater treatment. Although the membrane separation method can effectively remove soluble salts and organic matter, it is prone to membrane fouling, requires frequent cleaning and replacement, has high operating costs, and the treatment of the resulting concentrate is also a major problem.

[0005] Especially in terms of removing COD and heavy metals at the same time, existing technologies often have difficulty in taking both into account and require a combination of multiple treatment units, which increases the complexity of the process and the cost of treatment. For example, although conventional chemical precipitation can remove heavy metals, it has limited effect on the removal of organic matter; and although biological treatment can degrade organic matter, it is not able to remove heavy metals. This requires the use of multiple treatment technologies in series, which not only increases the complexity of the process, but also greatly increases the cost of treatment.

[0006] In addition, the high concentration of salt in shale gas wastewater will interfere with the effectiveness of conventional treatment methods, further increasing the difficulty of treatment. High-salinity environments will inhibit the activity of microorganisms and reduce the efficiency of biological treatment; they will also affect chemical precipitation and flocculation processes, reducing the removal of pollutants. High salt content will also accelerate the corrosion of equipment and increase maintenance costs. Summary of the invention

[0007] The purpose of the present invention is to provide a remover that can remove both COD and heavy metals in shale gas wastewater, so as to solve the problems of low efficiency, high cost, complex operation and the like faced by existing wastewater treatment technologies in treating shale gas wastewater, and achieve efficient and economical simultaneous removal of COD and heavy metals.

[0008] To achieve the above objectives, on the one hand, the present invention provides a remover that can remove both COD and heavy metals in shale gas wastewater.

[0009] A remover for removing both COD and heavy metals from shale gas wastewater, comprising activated carbon and carboxylated tara tannin in a mass ratio of (1.5-2.6):1.

[0010] Preferably, the mass ratio of activated carbon to carboxylated tara tannin is (1.9-2.2):1.

[0011] Preferably, modified montmorillonite is also included, and the ratio of the mass of the modified montmorillonite to the total mass of the activated carbon and the carboxylated tara tannin is (0.11-0.18):1.

[0012] Preferably, it also includes iron oxide nanoparticles and polyaluminium chloride, wherein the ratio of the mass of the iron oxide nanoparticles to the total mass of the activated carbon and the carboxylated tara tannin is (0.02-0.05):1, and the ratio of the mass of the polyaluminium chloride to the total mass of the activated carbon and the carboxylated tara tannin is (0.02-0.05):1.

[0013] Preferably, the modified montmorillonite is generated by intercalating montmorillonite with tetramethylammonium chloride, and the modified montmorillonite forms an organic-inorganic composite structure.

[0014] In a second aspect, the present invention provides a method for preparing a remover that can remove both COD and heavy metals in shale gas wastewater.

[0015] The preparation method of a remover for removing COD and heavy metals from shale gas wastewater comprises the following steps: After mixing the activated carbon and carboxylated tara tannin and ball milling for 2-3 hours, a binder is added and mixed evenly, and heated and stirred until a viscous slurry is formed; The slurry is pressed into a shape, dried, heat treated at 200-300°C for 2-3 hours, and ground into granules.

[0016] Preferably, the preparation method of carboxylated tara tannin is: After adjusting the pH value of the tara tannin solution to 8.5-9.0, adding chloroacetic acid solution, reacting in a constant temperature water bath at 70-80° C. for 4-5 hours to obtain a first reaction solution; The first reaction solution is cooled to room temperature, the pH value is adjusted to 6.5-7.0, a precipitant is added for precipitation, the precipitate is filtered, and the precipitate is washed, dried, and ground.

[0017] Preferably, the mass ratio of chloroacetic acid to tara tannin is (2-3):1.

[0018] Preferably, modified montmorillonite is also added for mixed ball milling, and the preparation method of the modified montmorillonite is: The tetramethylammonium chloride solution and the montmorillonite suspension are mixed, the pH is adjusted to 8.0-9.0, and the mixture is reacted in an oil bath at 80-85° C. for 6-7 hours to obtain a second reaction solution; The second reaction solution was cooled to room temperature, centrifuged and the supernatant was discarded, the precipitate was redispersed with deionized water, and the centrifugation and washing were repeated until no chloride ions were detected in the supernatant, and the solution was washed with ethanol for the last time, dried, and ground.

[0019] Preferably, the mass ratio of tetramethylammonium chloride to montmorillonite is (0.8-1.2):1.

[0020] Preferably, iron oxide nanoparticles and polyaluminium chloride are added and mixed and ball-milled.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The remover of the present invention can simultaneously and efficiently remove COD and heavy metals in shale gas wastewater, solving the problem that the prior art can only treat a single or a few pollutants.

[0022] 2. The remover of the present invention has enhanced treatment capacity and can treat various types of organic pollutants and heavy metals, adapting to the complexity and diversity of shale gas wastewater components.

[0023] 3. The treatment stability of the remover of the present invention is improved, and the multiple action mechanisms provide multiple safeguards. Even if the effect of one component is affected, the other components can still play a role.

[0024] 4. The remover of the present invention is easy to operate during use, and can remove multiple pollutants once added, thereby simplifying the treatment process and improving economic benefits. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The first embodiment of the present invention provides a remover for removing both COD and heavy metals in shale gas wastewater, comprising activated carbon and carboxylated tara tannin in a mass ratio of (1.5-2.6):1.

[0027] Activated carbon is a specially treated carbon material with a highly developed pore structure and a huge specific surface area. It can effectively remove organic matter and some heavy metals in shale gas wastewater through physical adsorption and chemical adsorption. The surface functional groups of activated carbon interact with pollutants in wastewater, adsorbing COD and heavy metal ions on its surface through van der Waals forces, π-π stacking and hydrogen bonds, thereby purifying water quality.

[0028] Carboxylated taratannin is a modified product obtained by introducing carboxyl (-COOH) groups into the taratannin molecule. This modification significantly enhances its ability to chelate heavy metal ions. Carboxylated taratannin forms stable chelates with heavy metal ions through its multiple carboxyl groups, effectively reducing the concentration of heavy metals in wastewater. In addition, carboxylated taratannin can also remove some organic matter through adsorption, thereby improving wastewater treatment efficiency.

[0029] The removal mechanism of the remover of the present invention is as follows: a large number of micropores and mesopores on the surface of activated carbon can effectively capture organic pollutant molecules in wastewater through physical adsorption such as van der Waals force and hydrophobic interaction, reducing the competition between these organic matter and carboxylated tara tannin for adsorption sites, increasing the contact opportunities between carboxylated tara tannin and heavy metal ions, so that the chelating sites of carboxylated tara tannin are more used for reaction with heavy metal ions, thereby improving the overall chelating efficiency and the effect of removing heavy metals. Carboxylated tara tannin enhances the interaction with amino compounds by forming amide bonds or ion pair interactions, which reduces the hydrophilicity of amino compounds and enhances the hydrophobic interaction between organic matter and the functional groups on the surface of activated carbon, which makes the organic matter more easily adsorbed by activated carbon, thereby improving the removal efficiency of organic matter.

[0030] The present invention achieves a synergistic effect by controlling the mass ratio of activated carbon to carboxylated tara tannin to (1.5-2.6):1, thereby improving the removal rate of COD and heavy metals in shale gas wastewater. In some preferred embodiments, the mass ratio of activated carbon to carboxylated tara tannin is (1.9-2.2):1.

[0031] In some preferred embodiments, in order to further improve the removal effect, the remover also includes modified montmorillonite, and the ratio of the mass of the modified montmorillonite to the total mass of the activated carbon and the carboxylated tara tannin is (0.11~0.18):1.

[0032] The modified montmorillonite is generated by intercalating and modifying montmorillonite with tetramethylammonium chloride, and the modified montmorillonite forms an organic-inorganic composite structure.

[0033] In the embodiment of the present invention, the modified montmorillonite is intercalated and modified by tetramethylammonium chloride, which can increase the interlayer distance of the montmorillonite and improve its adsorption capacity for organic pollutants and heavy metal ions. The organic-inorganic composite structure formed between the layers of the modified montmorillonite makes it have stronger selectivity and adsorption capacity. This structure not only enhances the physical adsorption of organic matter, but also effectively removes heavy metal ions in wastewater through ion exchange, thereby realizing the comprehensive treatment of shale gas wastewater.

[0034] The interlayer structure and surface functional groups of modified montmorillonite can adsorb some organic pollutants, especially organic molecules with strong polarity. This effect effectively shares the adsorption load of activated carbon. The adsorption sites on activated carbon can be used more effectively to adsorb other organic matter that is difficult to be adsorbed by modified montmorillonite, significantly improving the overall removal efficiency of organic matter in wastewater, and indirectly improving the effect of carboxylated tara tannin in removing heavy metals.

[0035] The interlayer and surface functional groups of the modified montmorillonite can also adsorb the chelate formed by carboxylated taratannin and heavy metals, increasing the particle size of the chelate, thereby promoting precipitation and facilitating subsequent solid-liquid separation.

[0036] In some preferred embodiments, in order to further improve the removal effect, the remover also includes iron oxide nanoparticles and polyaluminum chloride, wherein the ratio of the mass of iron oxide nanoparticles to the total mass of activated carbon and carboxylated tara tannin is (0.02~0.05):1, and the ratio of the mass of polyaluminum chloride to the total mass of activated carbon and carboxylated tara tannin is (0.02~0.05):1.

[0037] Iron oxide nanoparticles have high reactivity and large specific surface area, which makes them show excellent adsorption and catalytic properties in wastewater treatment. These nanoparticles interact with organic matter and heavy metal ions through their surface active sites, promoting the adsorption and precipitation of pollutants. Iron oxide nanoparticles can also catalytically oxidize organic pollutants and convert them into low-toxic or non-toxic substances, thereby effectively removing COD and heavy metals from shale gas wastewater.

[0038] Polyaluminium chloride is a commonly used inorganic polymer flocculant. It forms a large number of positively charged polymers in water, which neutralize and adsorb suspended solids and some soluble organic matter in wastewater. This effect makes tiny suspended particles aggregate into larger flocs, speeding up their sedimentation rate, thereby effectively removing suspended solids and some organic matter in wastewater and reducing COD.

[0039] It is understandable that the modified montmorillonite, iron oxide nanoparticles and polyaluminium chloride may be contained at the same time, and the removal effect is better at this time.

[0040] The second embodiment of the present invention provides a method for preparing a remover that can remove COD and heavy metals in shale gas wastewater, comprising the following steps: mixing activated activated carbon and carboxylated tara tannin and ball-milling for 2 to 3 hours, adding a binder evenly, heating and stirring until a viscous slurry is formed; pressing the slurry into a shape, drying, heat-treating at 200 to 300°C for 2 to 3 hours, and grinding it into granules.

[0041] It should be noted that heat treatment at 200-300℃ for 2-3h can promote the formation of a stable structure between activated carbon and carboxylated tara tannin, while avoiding decomposition of carboxylated tara tannin due to excessively high temperature. When the temperature is lower than 200℃, the bond is not tight enough; when the temperature is higher than 300℃, the structure of carboxylated tara tannin will be destroyed, reducing the adsorption performance.

[0042] In some preferred embodiments, the remover is ground into particles with a particle size of 1 to 2 mm.

[0043] Wherein, the preparation method of carboxylated tara tannin is: After adjusting the pH value of the tara tannin solution to 8.5-9.0, adding chloroacetic acid solution, reacting in a constant temperature water bath at 70-80° C. for 4-5 hours to obtain a first reaction solution; The first reaction solution is cooled to room temperature, the pH value is adjusted to 6.5-7.0, a precipitant is added for precipitation, the precipitate is filtered, and the precipitate is washed, dried, and ground.

[0044] In some preferred embodiments, the mass ratio of chloroacetic acid to taratannin is (2-3): 1. If the amount of chloroacetic acid is too low (<2:1), the degree of carboxylation is insufficient, affecting the subsequent adsorption performance; if the amount is too high (>3:1), it will cause a waste of raw materials and will not further improve the degree of carboxylation.

[0045] In some preferred embodiments, the precipitant is anhydrous ethanol.

[0046] In some preferred embodiments, the preparation method of modified montmorillonite is: The tetramethylammonium chloride solution and the montmorillonite suspension are mixed, the pH is adjusted to 8.0-9.0, and the mixture is reacted in an oil bath at 80-85° C. for 6-7 hours to obtain a second reaction solution; The second reaction solution was cooled to room temperature, centrifuged and the supernatant was discarded, the precipitate was redispersed with deionized water, and the centrifugation and washing were repeated until no chloride ions were detected in the supernatant, and the solution was washed with ethanol for the last time, dried, and ground.

[0047] In some preferred embodiments, the mass ratio of tetramethylammonium chloride to montmorillonite is (0.8-1.2): 1. If the mass ratio is lower than 0.8: 1, the degree of modification is insufficient and the ideal modification effect cannot be achieved; if the mass ratio is higher than 1.2: 1, the excess modifier will not further improve the modification effect, but will increase the cost.

[0048] In order to make the technical solution of the present invention clearer, the remover, preparation method and effect of the present invention are described in detail through multiple specific embodiments below.

[0049] Some of the test equipment and preparations used in the following examples are as follows: Electronic balance (Sartorius, Germany), electric blast constant temperature dryer (Shanghai Fomar Experimental Equipment), stainless steel reactor (Shanghai Laibei), electric constant temperature water bath (Jiangsu Kedao), rotary evaporator (Shanghai Darlo Scientific Instruments), pulverizer (Shandong Tianfang Machinery), magnetic stirrer (Shanghai Meiyingpu), Soxhelt extractor (Qingdao Juchuang); Tara tannin was purchased from Wufeng Chicheng Biotechnology Co., Ltd., activated carbon was purchased from Ningxia Zhongchuan Carbon Intelligent Manufacturing Co., Ltd., montmorillonite was purchased from Inner Mongolia Mengchuang Jiamu Biotechnology Co., Ltd., and chemicals and reagents were purchased from Sigma-Aldrich.

[0050] Example 1 A remover that takes into account the removal of COD and heavy metals in shale gas wastewater, wherein the raw materials are activated carbon and carboxylated tara tannin in a mass ratio of 1.94:1.

[0051] Wherein, the preparation method of carboxylated tara tannin is: Weigh chloroacetic acid and tara tannin in a mass ratio of 2:1, and dissolve them in deionized water to obtain a chloroacetic acid solution and a tara tannin solution; After adjusting the pH value of the tara tannin solution to 8.5-9.0, slowly dropwise add the prepared chloroacetic acid solution in a constant temperature water bath at 70-80°C. After the dropwise addition is completed, continue the reaction for 4-5 hours, maintain the temperature and stirring, and obtain a first reaction solution; The first reaction liquid is cooled to room temperature, the pH value of the reaction liquid is adjusted to 6.5-7.0, anhydrous ethanol is added for precipitation, the precipitate is filtered, the precipitate is washed with anhydrous ethanol, the washed precipitate is dried at 60-70° C. for 12-24 hours, and the dried product is ground into fine powder.

[0052] The preparation method of the remover for removing COD and heavy metals in shale gas wastewater is as follows: The activated carbon was activated in a muffle furnace at 400-500°C for 2-3 hours, cooled, washed with deionized water, and dried at 70-80°C for 12-24 hours to obtain activated activated carbon; Put the activated carbon and carboxylated tara tannin into a ball mill, add anhydrous ethanol, and ball mill for 2-3 hours to obtain a mixture. Transfer the mixture to a beaker, add 5% polyvinyl alcohol solution, stir evenly, and evaporate part of the solvent at 60-70°C until a viscous slurry is formed; The viscous slurry is pressed into a shape, dried in an oven at 70-80°C for 12-24 hours, the dried remover is heat-treated at 260°C for 2 hours to obtain a prepared remover, and the prepared remover is ground into particles with a particle size of 1-2 mm.

[0053] Example 2 A remover that takes into account the removal of COD and heavy metals in shale gas wastewater, the raw materials of which are activated carbon and carboxylated tara tannin in a mass ratio of 2:1.

[0054] The preparation method of carboxylated Tara tannin and the preparation method of the remover are referred to Example 1. The mass ratio of chloroacetic acid to Tara tannin in the carboxylated Tara tannin is 3:1, and the remover is heat treated at 300°C for 2h during the preparation process.

[0055] Example 3 A remover that takes into account the removal of COD and heavy metals in shale gas wastewater, the raw materials of which are activated carbon and carboxylated tara tannin in a mass ratio of 2:1.

[0056] The preparation method of carboxylated tara tannin and the preparation method of the remover are referred to Example 1, the mass ratio of chloroacetic acid to tara tannin is 3:1, and the remover is heat treated at 200°C for 3h during preparation.

[0057] Example 4 A remover that takes into account the removal of COD and heavy metals in shale gas wastewater, wherein the raw materials are activated carbon and carboxylated tara tannin in a mass ratio of 2.25:1.

[0058] The preparation method of carboxylated tara tannin and the preparation method of the remover are referred to Example 1.

[0059] Example 5 The remover for removing COD and heavy metals from shale gas wastewater is made of activated carbon, carboxylated tara tannin and modified montmorillonite. The mass ratio of activated carbon to carboxylated tara tannin is 1.94:1, and the ratio of modified montmorillonite mass to the total mass of activated carbon and carboxylated tara tannin is 0.15:1.

[0060] The modified montmorillonite is generated by intercalating montmorillonite with tetramethylammonium chloride. The modified montmorillonite forms an organic-inorganic composite structure. The specific preparation method is as follows: Weigh tetramethylammonium chloride and montmorillonite in a mass ratio of 1:1, and dissolve them in deionized water to obtain a tetramethylammonium chloride TMAC solution and a montmorillonite suspension; Slowly add the TMAC solution to the montmorillonite suspension, adjust the pH to 8.0-9.0, and react in an oil bath at 80-85°C for 6-7 hours; The reaction mixture was cooled to room temperature, centrifuged and the supernatant was discarded, the precipitate was redispersed with deionized water, and the centrifugation and washing were repeated until no chloride ions were detected in the supernatant, and the last wash was with ethanol to remove the residual water; The washed sample was dried at 60-70°C for 12-24 h, and the dried sample was ground into the desired particle size.

[0061] The preparation method of carboxylated tara tannin and the preparation method of the remover are referred to Example 1.

[0062] Example 6 The remover for removing COD and heavy metals from shale gas wastewater is made of activated carbon, carboxylated tara tannin, modified montmorillonite, iron oxide nanoparticles and polyaluminium chloride. The mass ratio of activated carbon to carboxylated tara tannin is 1.94:1, the mass ratio of modified montmorillonite to the total mass of activated carbon and carboxylated tara tannin is 0.15:1, the mass ratio of iron oxide nanoparticles to the total mass of activated carbon and carboxylated tara tannin is 0.05:1, and the mass ratio of polyaluminium chloride to the total mass of activated carbon and carboxylated tara tannin is 0.05:1.

[0063] The preparation method of modified montmorillonite refers to Example 5, where the mass ratio of tetramethylammonium chloride to montmorillonite is 1.2:1. The preparation method of carboxylated tara tannin and the preparation method of the remover refer to Example 1.

[0064] Comparative Example 1 Compared with Example 1, the only difference is that the carboxylated Tara tannin is replaced by an equal amount of unmodified Tara tannin, that is, the mass ratio of activated carbon to Tara tannin is 1.94:1.

[0065] Comparative Example 2 Compared with Example 1, the only difference is that the composition of the remover is that the mass ratio of activated carbon to carboxylated tara tannin is 2.84:1.

[0066] Comparative Example 3 Compared with Example 1, the only difference is that the composition of the remover is that the mass ratio of activated carbon to carboxylated tara tannin is 1.3:1.

[0067] Comparative Example 4 Compared with Example 5, the only difference is that the carboxylated Tara tannin is replaced by an equal amount of unmodified Tara tannin.

[0068] Comparative Example 5 Compared with Example 5, the only difference is that the modified montmorillonite is replaced by an equal amount of modified montmorillonite prepared by the modification method in the prior art.

[0069] The preparation method of modified montmorillonite is: Purify montmorillonite, and prepare montmorillonite dispersion according to the solid-liquid mass ratio of 1:2~5 after purification; Adding the hydroxyaluminum ion solution to the prepared montmorillonite dispersion, ultrasonically dispersing for 10 to 30 minutes, and then drying the solution to obtain intercalated modified montmorillonite, wherein the mass ratio of the montmorillonite dispersion to the hydroxyaluminum ion solution is 1:3 to 7; The obtained intercalation modified montmorillonite is calcined at 300-450°C for 1-1.5 hours; The calcined intercalated modified montmorillonite was added into 6 mol / L sodium chloride solution, ultrasonically treated for 15 to 20 minutes, and dried to obtain the modified montmorillonite heavy metal adsorbent.

[0070] Test example The removal effects of the removers in Examples 1 to 6 and Comparative Examples 1 to 5 in shale gas wastewater were tested and verified. The specific method is as follows: 1. Determine the COD concentration and heavy metal concentration (nickel, chromium, cadmium) of shale gas wastewater samples.

[0071] 2. Carry out batch tests for each formulation, prepare 500 mL of shale gas wastewater, add 5 g of remover, stir at room temperature for 2 h, and collect the treated water samples after filtration.

[0072] 3. Determine the COD concentration and heavy metal concentration (nickel, chromium, cadmium) of the treated water samples.

[0073] Determination of COD concentration: Use the potassium dichromate method, take a certain volume of water sample, and dilute it as needed. Add a certain amount of potassium dichromate standard solution, as well as an appropriate amount of mercuric sulfate and silver sulfate-sulfuric acid solution. Heat the mixed water sample to reflux for a certain period of time, usually 2 hours. After cooling, add the ferrous acid indicator and titrate with ammonium ferrous sulfate standard solution until the solution color changes to reddish brown. Calculate the COD value based on the volume of ammonium ferrous sulfate standard solution consumed in the titration.

[0074] Determination of heavy metal concentration (nickel, chromium, cadmium): Prepare a series of multi-element standard solutions (national standard samples) with known concentrations to establish a standard curve, inject the pretreated sample solution into the ICP-OES instrument, and determine the heavy metal concentration in the sample through instrumental analysis.

[0075] The removal of COD and heavy metals in shale gas wastewater by the removers of various embodiments and comparative examples are shown in Table 1.

[0076] Table 1 Removal of COD and heavy metals from shale gas wastewater in Examples and Comparative Examples

[0077] The following analysis was conducted on the effects of the embodiments and comparative examples in removing COD and heavy metals (nickel, chromium, cadmium) from shale gas wastewater: 1. COD removal effect: The removal efficiency of the removers of Examples 1 to 6 is significantly better than that of Comparative Examples 1 to 5. The COD removal efficiency of the embodiments ranges from 85.51% to 94.43%, while that of the comparative examples ranges from 50.40% to 83.89%. Example 6 performs best, with a removal efficiency of 94.43%, while Comparative Example 1 performs worst, with a removal efficiency of only 50.40%. This shows that the remover of the present invention has significant advantages in removing organic pollutants.

[0078] 2. Heavy metal removal effect: Nickel: The removal efficiency of the embodiment is 90.00%~98.89%, and the comparative example is 30.56%~66.11%. The best effect of Example 6 is 98.89%, and the worst effect of Comparative Example 1 is 30.56%. Chromium: The removal efficiency of the embodiment is 89.52%~98.19%, and the comparative example is 25.3%~61.45%. The best effect of Example 6 is 98.19%, and the worst effect of Comparative Example 1 is 25.3%. Cadmium: The removal efficiency of the embodiment is 88.93%~97.86%, and the comparative example is 14.29%~60.71%. The best effect of Example 6 is 97.86%, and the worst effect of Comparative Example 1 is 14.29%. In general, the embodiments show obvious advantages in removing heavy metals, especially Examples 5 and 6, which have high removal efficiency for the three heavy metals.

[0079] 3. Comparative analysis of the composition of the removers in the examples: Examples 1 to 4 are mainly composed of activated carbon and carboxylated tara tannin, wherein the mass ratio of activated carbon to carboxylated tara tannin is between 1.94:1 and 2.25:1. These formulations show good results in COD and heavy metal removal, but are not as good as Examples 5 and 6. Example 5 adds modified montmorillonite on the basis of Examples 1 to 4, which significantly improves the removal efficiency, especially the removal of heavy metals. Example 6 further adds iron oxide nanoparticles and polyaluminium chloride on the basis of Example 5, achieving the best removal effect, whether it is COD or heavy metals.

[0080] 4. Comparative analysis: Comparative Example 1 (activated carbon + tara tannin) has the worst effect, indicating that the uncarboxylated tara tannin has a poor effect. Although there are some improvements in Comparative Examples 2 to 5, the overall effect is not as good as that of the embodiment, especially in the removal of heavy metals. The COD removal rate of Example 5 is about 8.54 percentage points higher than that of Comparative Example 5. This may be because the montmorillonite modified with tetramethylammonium chloride has a larger interlayer spacing and a higher organic carbon content, which is conducive to the adsorption of organic pollutants. The removal rates of nickel, chromium and cadmium in Example 5 are about 32.11, 35.54 and 35.54 percentage points higher than those of Comparative Example 5, respectively, which shows that the montmorillonite modified with tetramethylammonium chloride has a stronger adsorption capacity for heavy metal ions. Example 5 is superior to Comparative Example 5 in all indicators, showing the superiority of the tetramethylammonium chloride modification method.

[0081] Conclusion: The formulations of the present invention, especially Examples 5 and 6, show excellent effects in removing COD and heavy metals from shale gas wastewater. This may be due to the synergistic effect of carboxylated tara tannin, modified montmorillonite, iron oxide nanoparticles and polyaluminium chloride, which can effectively remove organic pollutants and efficiently adsorb heavy metal ions. This multifunctional composite remover provides an efficient and economical solution for shale gas wastewater treatment.

[0082] Finally, it should be noted that: Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A remover for removing both COD and heavy metals from shale gas wastewater, characterized in that: It contains activated carbon and carboxylated tara tannin in a mass ratio of (1.5~2.6):

1.

2. The remover according to claim 1, characterized in that The mass ratio of activated carbon to carboxylated tara tannin is (1.9~2.2):

1.

3. The remover according to claim 1, characterized in that It also includes modified montmorillonite, and the ratio of the mass of the modified montmorillonite to the total mass of the activated carbon and the carboxylated tara tannin is (0.11~0.18):

1.

4. The remover according to any one of claims 1 to 3, characterized in that: It also includes iron oxide nanoparticles and polyaluminium chloride, wherein the ratio of the mass of the iron oxide nanoparticles to the total mass of activated carbon and carboxylated tara tannin is (0.02~0.05):1, and the ratio of the mass of polyaluminium chloride to the total mass of activated carbon and carboxylated tara tannin is (0.02~0.05):

1.

5. The remover according to claim 3, characterized in that The modified montmorillonite is generated by intercalating and modifying montmorillonite with tetramethylammonium chloride, and the modified montmorillonite forms an organic-inorganic composite structure.

6. The method for preparing a remover for removing COD and heavy metals from shale gas wastewater according to any one of claims 1 to 5, characterized in that: The following steps are involved: After mixing the activated carbon and carboxylated tara tannin and ball milling, a binder is added and mixed evenly, and heated and stirred until a viscous slurry is formed; The slurry is pressed into a shape, dried, heat treated at 200-300°C for 2-3 hours, and ground into granules.

7. The preparation method according to claim 6, characterized in that: The preparation method of carboxylated tara tannin is: After adjusting the pH value of the tara tannin solution to 8.5-9.0, adding chloroacetic acid solution, reacting in a constant temperature water bath at 70-80° C. for 4-5 hours to obtain a first reaction solution; The first reaction solution is cooled to room temperature, the pH value is adjusted to 6.5-7.0, a precipitant is added for precipitation, the precipitate is filtered, and the precipitate is washed, dried, and ground.

8. The preparation method according to claim 7, characterized in that: The mass ratio of chloroacetic acid to taratannin is (2~3):

1.

9. The preparation method according to claim 6, characterized in that: Modified montmorillonite is also added and mixed and ball-milled. The preparation method of the modified montmorillonite is as follows: The tetramethylammonium chloride solution and the montmorillonite suspension are mixed, the pH is adjusted to 8.0-9.0, and the mixture is reacted in an oil bath at 80-85° C. for 6-7 hours to obtain a second reaction solution; The second reaction solution was cooled to room temperature, centrifuged and the supernatant was discarded, the precipitate was redispersed with deionized water, and the centrifugation and washing were repeated until no chloride ions were detected in the supernatant, and the solution was washed with ethanol for the last time, dried, and ground.

10. The preparation method according to claim 9, characterized in that: The mass ratio of tetramethylammonium chloride to montmorillonite is (0.8~1.2):1.

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