Remover for removing COD and heavy metals in shale gas wastewater and preparation method thereof

Abstract

The present application belongs to the field of shale gas wastewater treatment, and discloses a removing agent for removing COD and heavy metals in shale gas wastewater and a preparation method thereof. The removing agent comprises activated carbon and carboxylated tara tannin in a mass ratio of (1.5-2.6):1. The micropores and mesopores of the activated carbon capture organic pollutants through physical adsorption, reduce the competition of the organic pollutants with the carboxylated tara tannin, increase the contact of the carboxylated tara tannin with heavy metals, and improve the chelation efficiency. The removing agent can also comprise modified montmorillonite generated by intercalation modification of montmorillonite with tetramethylammonium chloride. The modified montmorillonite can share the load of the activated carbon, adsorb polar organic matter, promote the precipitation of chelates of the carboxylated tara tannin, and improve the removal efficiency. The carboxylated tara tannin reduces the hydrophilicity of organic matter, and promotes the adsorption of the organic matter 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 present application relates to the field of shale gas wastewater treatment, and particularly relates to a removal agent for removing COD and heavy metals in shale gas wastewater and a preparation method. BACKGROUND

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

[0003] Currently, 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 including chemical precipitation, oxidation, and flocculation are used to remove dissolved organic matter and heavy metals. Biological methods utilize 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 cannot fully meet the comprehensive needs of shale gas wastewater treatment. Physical methods, although simple to operate, are difficult to remove dissolved pollutants and have limited effectiveness for high-salinity and high-organic-content shale gas wastewater. Chemical methods can effectively remove certain specific pollutants, but may introduce secondary pollution, increasing the difficulty and cost of subsequent treatment. Biological methods are effective in treating organic pollutants, but have poor adaptability to high-salinity environments and long treatment periods, making them difficult to meet the needs of large-scale wastewater treatment. Membrane separation methods can effectively remove dissolved salts and organic matter, but are prone to membrane fouling, requiring frequent cleaning and replacement, resulting in high operating costs and the challenge of disposing of the concentrated liquid.

[0005] In particular, in terms of simultaneously removing COD and heavy metals, existing technologies often cannot be considered together, requiring multiple treatment units to be combined, increasing the complexity of the process and the cost of treatment. For example, conventional chemical precipitation can remove heavy metals, but has limited effectiveness for organic matter. Biological treatment can degrade organic matter, but has insufficient heavy metal removal capacity. This requires the use of multiple treatment technologies in series, which not only increases the complexity of the process, but also significantly increases the cost of treatment.

[0006] Furthermore, the high salt concentration in shale gas wastewater interferes with the effectiveness of conventional treatment methods, further increasing the difficulty of treatment. A high-salt environment inhibits microbial activity, reducing the efficiency of biological treatment; it also affects chemical precipitation and flocculation processes, decreasing pollutant removal efficiency. High salt content also accelerates equipment corrosion, increasing maintenance costs. Summary of the Invention

[0007] The purpose of this invention is to provide a removal agent that can remove both COD and heavy metals from shale gas wastewater, thereby solving the problems of low efficiency, high cost, and complex operation faced by existing wastewater treatment technologies when treating shale gas wastewater, and achieving efficient and economical removal of both COD and heavy metals simultaneously.

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

[0009] This agent effectively removes COD and heavy metals from shale gas wastewater, containing activated carbon and carboxylated taratanine in a mass ratio of (1.5~2.6):1.

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

[0011] Preferably, it also includes modified montmorillonite, wherein the mass ratio of modified montmorillonite to the total mass of activated carbon and carboxylated taratanine is (0.11~0.18):1.

[0012] Preferably, the mixture also includes iron oxide nanoparticles and polyaluminum chloride, wherein the mass ratio of the iron oxide nanoparticles to the total mass of activated carbon and carboxylated tararatanin is (0.02~0.05):1, and the mass ratio of the polyaluminum chloride to the total mass of activated carbon and carboxylated tararatanin is (0.02~0.05):1.

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

[0014] Secondly, the present invention provides a method for preparing a removal agent that can remove both COD and heavy metals from shale gas wastewater.

[0015] A method for preparing a removal agent that simultaneously removes COD and heavy metals from shale gas wastewater includes the following steps:

[0016] After mixing activated carbon and carboxylated taratin, the mixture is ball-milled for 2-3 hours, then a binder is added and mixed evenly. The mixture is then heated and stirred until a viscous slurry is formed.

[0017] The slurry is pressed into shape, dried, heat-treated at 200~300℃ for 2~3 hours, and then ground into granules.

[0018] The preferred method for preparing carboxylated taratanine is as follows:

[0019] After adjusting the pH of the taratin solution to 8.5-9.0, chloroacetic acid solution was added, and the mixture was reacted in a constant temperature water bath at 70-80℃ for 4-5 hours to obtain the first reaction solution.

[0020] Cool the first reaction solution to room temperature, adjust the pH to 6.5-7.0, add a precipitant to precipitate, filter the precipitate, wash the precipitate, dry it, and grind it.

[0021] Preferably, the mass ratio of chloroacetic acid to taratanine is (2~3):1.

[0022] Preferably, modified montmorillonite is also added and ball-milled, wherein the modified montmorillonite is prepared by:

[0023] Tetramethylammonium chloride solution was mixed with montmorillonite suspension, the pH was adjusted to 8.0-9.0, and the mixture was reacted in an oil bath at 80-85℃ for 6-7 hours to obtain the second reaction solution.

[0024] Cool the second reaction solution to room temperature, centrifuge and discard the supernatant, redisperse the precipitate with deionized water, repeat centrifugation and washing until no chloride ions are detected in the supernatant, wash with ethanol for the last time, and dry and grind.

[0025] Preferably, the mass ratio of tetramethylammonium chloride to montmorillonite is (0.8~1.2):1.

[0026] Preferably, iron oxide nanoparticles and polyaluminum chloride are also added and ball-milled.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1. The removal agent of the present invention can simultaneously and efficiently remove COD and heavy metals from shale gas wastewater, solving the problem that existing technologies can often only treat single or a few pollutants.

[0029] 2. The removal agent of the present invention has enhanced treatment capacity and can treat a variety of types of organic pollutants and heavy metals, adapting to the complexity and diversity of shale gas wastewater composition.

[0030] 3. The removal agent of the present invention has improved treatment stability, and the multiple action mechanisms provide multiple safeguards. Even if the effect of one component is affected, the other components can still play their role.

[0031] 4. The removal agent of the present invention is easy to operate during use, and can remove multiple pollutants with a single addition, simplifying the treatment process and improving economic efficiency. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The first embodiment of the present invention provides a removal agent that can remove COD and heavy metals from shale gas wastewater, comprising activated carbon and carboxylated taratanine in a mass ratio of (1.5~2.6):1.

[0034] Activated carbon is a specially treated carbon material with a highly developed pore structure and a large specific surface area. Through physical and chemical adsorption, it can effectively remove organic matter and some heavy metals from shale gas wastewater. The surface functional groups of activated carbon interact with pollutants in the wastewater, adsorbing COD and heavy metal ions onto its surface through van der Waals forces, π-π stacking, and hydrogen bonding, thereby purifying the water.

[0035] Carboxylated tararatanine is a modified product obtained by introducing carboxyl (-COOH) groups onto the tararatanine molecule. This modification significantly enhances its chelating ability for heavy metal ions. Carboxylated tararatanine effectively reduces the concentration of heavy metals in wastewater by forming stable chelates with heavy metal ions through its multiple carboxyl groups. Furthermore, carboxylated tararatanine can also remove some organic matter through adsorption, improving wastewater treatment efficiency.

[0036] The removal mechanism of the removal agent of this invention is as follows: The numerous micropores and mesopores on the surface of activated carbon can effectively capture organic pollutant molecules in wastewater through physical adsorption processes such as van der Waals forces and hydrophobic interactions. This reduces the competition between these organic compounds and carboxylated tararatanine for adsorption sites, increasing the contact opportunities between carboxylated tararatanine and heavy metal ions. Consequently, more of the chelating sites of carboxylated tararatanine are used for reactions with heavy metal ions, thereby improving the overall chelation efficiency and the effect of heavy metal removal. Carboxylated tararatanine enhances its interaction with amino compounds by forming amide bonds or ion pair interactions. This interaction reduces the hydrophilicity of amino compounds and enhances the hydrophobic interaction between organic matter and the functional groups on the surface of activated carbon. This makes it easier for organic matter to be adsorbed by activated carbon, thereby improving the removal efficiency of organic matter.

[0037] This invention achieves a synergistic effect by controlling the mass ratio of activated carbon to carboxylated tararatanine at (1.5~2.6):1, thereby improving the removal rate of COD and heavy metals from shale gas wastewater. In some preferred embodiments, the mass ratio of activated carbon to carboxylated tararatanine is (1.9~2.2):1.

[0038] In some preferred embodiments, to further improve the removal effect, the removal agent also includes modified montmorillonite, wherein the mass ratio of modified montmorillonite to the total mass of activated carbon and carboxylated taratanine is (0.11~0.18):1.

[0039] The modified montmorillonite was generated by intercalation modification of montmorillonite with tetramethylammonium chloride, and the modified montmorillonite formed an organic-inorganic composite structure.

[0040] In this embodiment of the invention, modified montmorillonite is intercalated with tetramethylammonium chloride, which increases the interlayer spacing of montmorillonite and enhances its adsorption capacity for organic pollutants and heavy metal ions. The organic-inorganic composite structure formed between the layers of the modified montmorillonite gives it stronger selectivity and adsorption capacity. This structure not only enhances the physical adsorption of organic matter but also effectively removes heavy metal ions from wastewater through ion exchange, achieving comprehensive treatment of shale gas wastewater.

[0041] The interlayer structure and surface functional groups of modified montmorillonite can adsorb some organic pollutants, especially highly polar organic molecules. This effectively reduces the adsorption load of activated carbon, allowing the adsorption sites on the activated carbon to be utilized more effectively to adsorb other organic substances that are difficult for modified montmorillonite to adsorb, significantly improving the overall removal efficiency of organic matter in wastewater, and indirectly enhancing the effect of carboxylated tararatanine in removing heavy metals.

[0042] The interlayer and surface functional groups of modified montmorillonite can also adsorb chelates formed by carboxylated taratin and heavy metals, increasing the particle size of the chelates and thus promoting precipitation, which is beneficial for subsequent solid-liquid separation.

[0043] In some preferred embodiments, to further improve the removal effect, the remover further includes iron oxide nanoparticles and polyaluminum chloride, wherein the mass ratio of iron oxide nanoparticles to the total mass of activated carbon and carboxylated tararatanine is (0.02~0.05):1, and the mass ratio of polyaluminum chloride to the total mass of activated carbon and carboxylated tararatanine is (0.02~0.05):1.

[0044] Iron oxide nanoparticles possess high reactivity and a large specific surface area, enabling them to exhibit excellent adsorption and catalytic performance 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, converting them into low-toxicity or non-toxic substances, thereby effectively removing COD and heavy metals from shale gas wastewater.

[0045] Polyaluminum chloride (PAC) is a commonly used inorganic polymeric flocculant. It works by forming numerous positively charged polymers in water, which neutralize and adsorb suspended solids and some dissolved organic matter in wastewater. This process causes tiny suspended particles to aggregate into larger flocs, accelerating their settling speed and effectively removing suspended solids and some organic matter from wastewater, thus reducing COD.

[0046] Understandably, it can also contain modified montmorillonite, iron oxide nanoparticles, and polyaluminum chloride simultaneously, in which case the removal effect is even better.

[0047] The second embodiment of the present invention provides a method for preparing a removal agent that can remove COD and heavy metals from shale gas wastewater, comprising the following steps: mixing activated carbon with carboxylated tararatannin and ball milling for 2-3 hours, adding a binder evenly, heating and stirring until a viscous slurry is formed; pressing the slurry into shape, drying, heat-treating at 200-300℃ for 2-3 hours, and grinding into granules.

[0048] It should be noted that heat treatment at 200~300℃ for 2~3 hours promotes the formation of a stable structure between activated carbon and carboxylated tararatanine, while avoiding the decomposition of carboxylated tararatanine due to excessively high temperatures. When the temperature is below 200℃, the binding is not tight enough; when the temperature is above 300℃, the structure of carboxylated tararatanine will be destroyed, reducing adsorption performance.

[0049] In some preferred embodiments, the remover is ground into particles with a particle size of 1-2 mm.

[0050] The preparation method of carboxylated taratanine is as follows:

[0051] After adjusting the pH of the taratin solution to 8.5-9.0, chloroacetic acid solution was added, and the mixture was reacted in a constant temperature water bath at 70-80℃ for 4-5 hours to obtain the first reaction solution.

[0052] Cool the first reaction solution to room temperature, adjust the pH to 6.5-7.0, add a precipitant to precipitate, filter the precipitate, wash the precipitate, dry it, and grind it.

[0053] In some preferred embodiments, the mass ratio of chloroacetic acid to taratanine is (2~3):1. If the amount of chloroacetic acid used is too low (<2:1), the degree of carboxylation is insufficient, affecting the subsequent adsorption performance; if the amount used is too high (>3:1), it will cause waste of raw materials and will not further improve the degree of carboxylation.

[0054] In some preferred embodiments, the precipitant is anhydrous ethanol.

[0055] In some preferred embodiments, the modified montmorillonite is prepared by:

[0056] Tetramethylammonium chloride solution was mixed with montmorillonite suspension, the pH was adjusted to 8.0-9.0, and the mixture was reacted in an oil bath at 80-85℃ for 6-7 hours to obtain the second reaction solution.

[0057] Cool the second reaction solution to room temperature, centrifuge and discard the supernatant, redisperse the precipitate with deionized water, repeat centrifugation and washing until no chloride ions are detected in the supernatant, wash with ethanol for the last time, and dry and grind.

[0058] In some preferred embodiments, the mass ratio of tetramethylammonium chloride to montmorillonite is (0.8~1.2):1. If this mass ratio is lower than 0.8:1, the degree of modification is insufficient and the desired modification effect cannot be achieved; if this mass ratio is higher than 1.2:1, the excess modifier will not further improve the modification effect, but will instead increase the cost.

[0059] To make the technical solution of the present invention clearer, the removal agent, preparation method and effect of the present invention will be described in detail below through several specific embodiments.

[0060] The following examples use some of the experimental equipment and formulations:

[0061] Electronic balance (Sartorius, Germany), electric heating blower constant temperature dryer (Shanghai Fuma Experimental Equipment), stainless steel reaction vessel (Shanghai Laibei), electric heating constant temperature water bath (Jiangsu Kedao), rotary evaporator (Shanghai Daluo Scientific Instruments), pulverizer (Shandong Tianfang Machinery), magnetic stirrer (Shanghai Meiyingpu), Soxhelt extractor (Qingdao Juchuang); taratanin 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.

[0062] Example 1

[0063] The removal agent is effective in removing COD and heavy metals from shale gas wastewater. The raw materials are activated carbon and carboxylated tararatanine in a mass ratio of 1.94:1.

[0064] The preparation method of carboxylated taratanine is as follows:

[0065] Weigh out chloroacetic acid and taratin in a mass ratio of 2:1, and dissolve them separately in deionized water to obtain chloroacetic acid solution and taratin solution.

[0066] After adjusting the pH of the taratin solution to 8.5-9.0, the prepared chloroacetic acid solution was slowly added dropwise in a constant temperature water bath at 70-80℃. After the addition was complete, the reaction was continued for 4-5 hours while maintaining the temperature and stirring to obtain the first reaction solution.

[0067] Cool the first reaction solution to room temperature, adjust the pH of the reaction solution to 6.5~7.0, add anhydrous ethanol to precipitate, filter the precipitate, wash the precipitate with anhydrous ethanol, dry the washed precipitate at 60~70℃ for 12~24h, and grind the dried product into fine powder.

[0068] The preparation method of the removal agent that can remove both COD and heavy metals from shale gas wastewater is as follows:

[0069] Activated carbon is activated in a muffle furnace at 400-500℃ for 2-3 hours, cooled, washed with deionized water, and dried at 70-80℃ for 12-24 hours to obtain activated carbon.

[0070] Activated carbon and carboxylated taratanine are placed in a ball mill, anhydrous ethanol is added, and the mixture is milled for 2-3 hours to obtain a mixture. The mixture is then transferred to a beaker, 5% polyvinyl alcohol solution is added, and the mixture is stirred evenly. Part of the solvent is evaporated by stirring at 60-70°C until a viscous slurry is formed.

[0071] The viscous slurry is pressed into shape and dried in an oven at 70~80℃ for 12~24h. The dried removal agent is then heat-treated at 260℃ for 2h to obtain the prepared removal agent. The prepared removal agent is then ground into particles with a particle size of 1~2mm.

[0072] Example 2

[0073] This agent effectively removes both COD and heavy metals from shale gas wastewater. The raw materials are activated carbon and carboxylated tararatanine in a mass ratio of 2:1.

[0074] The preparation methods for carboxylated taratanine and the removal agent are as described in Example 1. The mass ratio of chloroacetic acid to taratanine in carboxylated taratanine is 3:1. The removal agent is heat-treated at 300°C for 2 hours during preparation.

[0075] Example 3

[0076] This agent effectively removes both COD and heavy metals from shale gas wastewater. The raw materials are activated carbon and carboxylated tararatanine in a mass ratio of 2:1.

[0077] The preparation methods for carboxylated taratanine and the removal agent are as described in Example 1. The mass ratio of chloroacetic acid to taratanine is 3:1. The removal agent is heat-treated at 200°C for 3 hours during preparation.

[0078] Example 4

[0079] The removal agent is effective in removing COD and heavy metals from shale gas wastewater. The raw materials are activated carbon and carboxylated tararatanine in a mass ratio of 2.25:1.

[0080] The preparation methods for carboxylated taratanine and the removal agent are described in Example 1.

[0081] Example 5

[0082] This agent effectively removes both COD and heavy metals from shale gas wastewater. The raw materials are activated carbon, carboxylated tararatanine, and modified montmorillonite. The mass ratio of activated carbon to carboxylated tararatanine is 1.94:1, and the mass ratio of modified montmorillonite to the total mass of activated carbon and carboxylated tararatanine is 0.15:1.

[0083] Modified montmorillonite is produced by intercalation modification of montmorillonite with tetramethylammonium chloride, resulting in an organic-inorganic composite structure. The specific preparation method is as follows:

[0084] Tetramethylammonium chloride and montmorillonite were weighed at a mass ratio of 1:1 and dissolved in deionized water to obtain a tetramethylammonium chloride TMAC solution and a montmorillonite suspension.

[0085] The TMAC solution was slowly added dropwise to the montmorillonite suspension, the pH was adjusted to 8.0-9.0, and the reaction was carried out in an oil bath at 80-85℃ for 6-7 hours.

[0086] Cool the reaction mixture to room temperature, centrifuge and discard the supernatant, redisperse the precipitate with deionized water, repeat centrifugation and washing until no chloride ions are detected in the supernatant, and finally wash with ethanol to remove residual water.

[0087] Dry the washed sample at 60-70℃ for 12-24 hours, and then grind the dried sample to the required particle size.

[0088] The preparation methods for carboxylated taratanine and the removal agent are described in Example 1.

[0089] Example 6

[0090] This agent effectively removes COD and heavy metals from shale gas wastewater. The raw materials are activated carbon, carboxylated tararatanine, modified montmorillonite, iron oxide nanoparticles, and polyaluminum chloride. The mass ratio of activated carbon to carboxylated tararatanine is 1.94:1; the mass ratio of modified montmorillonite to the total mass of activated carbon and carboxylated tararatanine is 0.15:1; the mass ratio of iron oxide nanoparticles to the total mass of activated carbon and carboxylated tararatanine is 0.05:1; and the mass ratio of polyaluminum chloride to the total mass of activated carbon and carboxylated tararatanine is 0.05:1.

[0091] The preparation method of modified montmorillonite is described in Example 5, with a mass ratio of tetramethylammonium chloride to montmorillonite of 1.2:1. The preparation methods of carboxylated taratanine and the removal agent are described in Example 1.

[0092] Comparative Example 1

[0093] Compared with Example 1, the only difference is that the carboxylated taratanine is replaced with an equal amount of unmodified taratanine, i.e., the mass ratio of activated carbon to taratanine is 1.94:1.

[0094] Comparative Example 2

[0095] Compared with Example 1, the only difference is that the composition of the remover is that the mass ratio of activated carbon to carboxylated taratanine is 2.84:1.

[0096] Comparative Example 3

[0097] Compared with Example 1, the only difference is that the composition of the remover is that the mass ratio of activated carbon to carboxylated taratanine is 1.3:1.

[0098] Comparative Example 4

[0099] Compared to Example 5, the only difference is that the carboxylated taratanine is replaced with an equal amount of unmodified taratanine.

[0100] Comparative Example 5

[0101] Compared with Example 5, the only difference is that the modified montmorillonite is replaced with an equal amount of modified montmorillonite prepared by the modification method in the prior art.

[0102] The preparation method of modified montmorillonite is as follows:

[0103] Montmorillonite was purified, and a montmorillonite dispersion was prepared at a solid-liquid mass ratio of 1:2~5.

[0104] Add hydroxyl aluminum ion solution to the prepared montmorillonite dispersion, ultrasonically disperse for 10-30 minutes, and then dry the solution to obtain intercalated modified montmorillonite, wherein the mass ratio of montmorillonite dispersion to hydroxyl aluminum ion solution is 1:3-7.

[0105] The prepared intercalated modified montmorillonite was calcined at 300~450℃ for 1~1.5 hours;

[0106] The calcined intercalated modified montmorillonite was added to a 6 mol / L sodium chloride solution, sonicated for 15-20 minutes, and dried to obtain the modified montmorillonite heavy metal adsorbent.

[0107] Test case

[0108] The removal effects of the removal agents in Examples 1-6 and Comparative Examples 1-5 on COD and heavy metal removal from shale gas wastewater were experimentally verified. The specific methods are as follows:

[0109] 1. Determine the COD concentration and heavy metal concentration (nickel, chromium, cadmium) of shale gas wastewater samples.

[0110] 2. Batch tests were conducted for each formulation. 500 mL of shale gas wastewater was prepared, 5 g of removal agent was added, and the mixture was stirred at room temperature for 2 hours. After filtration, the treated water sample was collected.

[0111] 3. The COD concentration and heavy metal concentration (nickel, chromium, cadmium) of the treated water sample were determined.

[0112] COD concentration determination: The potassium dichromate method is used. A certain volume of water sample is taken and diluted as needed. A certain amount of potassium dichromate standard solution, as well as appropriate amounts of mercuric sulfate and silver sulfate-sulfuric acid solution are added. The mixed water sample is heated under reflux for a certain time, usually 2 hours. After cooling, ferroin indicator is added, and titration is performed with ferrous ammonium sulfate standard solution until the solution color changes to reddish-brown. The COD value is calculated based on the volume of ferrous ammonium sulfate standard solution consumed in the titration.

[0113] 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 instrument analysis.

[0114] Table 1 shows the removal performance of COD and heavy metals from shale gas wastewater by the various removal agents in the embodiments and comparative examples.

[0115] Table 1. Removal of COD and heavy metals from shale gas wastewater in examples and comparative studies.

[0116]

[0117] The following analysis was conducted on the effectiveness of the examples and comparative examples in removing COD and heavy metals (nickel, chromium, cadmium) from shale gas wastewater:

[0118] 1. COD Removal Efficiency: The COD removal agents in Examples 1-6 showed significantly better COD removal efficiency than those in Comparative Examples 1-5. The COD removal efficiencies of the examples ranged from 85.51% to 94.43%, while those of the comparative examples ranged from 50.40% to 83.89%. Example 6 performed best, achieving a removal efficiency of 94.43%, while Comparative Example 1 performed worst, at only 50.40%. This demonstrates that the removal agent of the present invention has significant advantages in removing organic pollutants.

[0119] 2. Heavy Metal Removal Efficiency: Nickel: The removal efficiency of the examples was 90.00%~98.89%, and that of the comparative examples was 30.56%~66.11%. Example 6 showed the best effect at 98.89%, while the comparative example 1 showed the worst at 30.56%. Chromium: The removal efficiency of the examples was 89.52%~98.19%, and that of the comparative examples was 25.3%~61.45%. Example 6 showed the best effect at 98.19%, while the comparative example 1 showed the worst at 25.3%. Cadmium: The removal efficiency of the examples was 88.93%~97.86%, and that of the comparative examples was 14.29%~60.71%. Example 6 showed the best effect at 97.86%, while the comparative example 1 showed the worst at 14.29%. Overall, the examples showed a significant advantage in removing heavy metals, especially Examples 5 and 6, which had high removal efficiencies for all three heavy metals.

[0120] 3. Comparative Analysis of the Removal Agent Composition in Examples: Examples 1-4 mainly consisted of activated carbon and carboxylated tararatanine, with the mass ratio of activated carbon to carboxylated tararatanine ranging from 1.94:1 to 2.25:1. These formulations showed good effects in both COD and heavy metal removal, but not as good as Examples 5 and 6. Example 5 added modified montmorillonite to Examples 1-4, significantly improving removal efficiency, especially for heavy metals. Example 6 further added iron oxide nanoparticles and polyaluminum chloride to Example 5, achieving the best removal effect for both COD and heavy metals.

[0121] 4. Comparative Example Analysis: Comparative Example 1 (activated carbon + tararatanine) showed the worst performance, indicating that uncarboxylated tararatanine is ineffective. While Comparative Examples 2-5 showed some improvement, their overall performance was still inferior to the Example 1, especially in heavy metal removal. Example 5 achieved a COD removal rate approximately 8.54 percentage points higher than Comparative Example 5. This may be because the tetramethylammonium chloride-modified montmorillonite has a larger interlayer spacing and higher organic carbon content, which is beneficial for adsorbing organic pollutants. Example 5 achieved removal rates for nickel, chromium, and cadmium that were approximately 32.11, 35.54, and 35.54 percentage points higher than Comparative Example 5, respectively, indicating that the tetramethylammonium chloride-modified montmorillonite has a stronger adsorption capacity for heavy metal ions. Example 5 outperformed Comparative Example 5 in all indicators, demonstrating the superiority of the tetramethylammonium chloride modification method.

[0122] Conclusion: The formulations of this invention, particularly Examples 5 and 6, demonstrate excellent performance in removing COD and heavy metals from shale gas wastewater. This is likely due to the synergistic effect of carboxylated tararatanine, modified montmorillonite, iron oxide nanoparticles, and polyaluminum chloride, which 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.

[0123] Finally, it should be noted that although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An application of a removal agent in simultaneously removing COD and heavy metals from shale gas wastewater, characterized in that, The preparation of the removal agent includes the following steps: The activated carbon and carboxylated taratin were mixed and ball-milled at a mass ratio of (1.5~2.6):

1. The binder was added and mixed evenly. The mixture was heated and stirred until a viscous slurry was formed. The slurry is pressed into shape, dried, heat-treated at 200~300℃ for 2~3 hours, and then ground into granules; The preparation method of carboxylated taratanine is as follows: after adjusting the pH value of the taratanine solution to 8.5~9.0, chloroacetic acid solution is added, and the mixture is reacted in a constant temperature water bath at 70~80℃ for 4~5 hours to obtain the first reaction solution; The first reaction solution was cooled to room temperature, the pH was adjusted to 6.5-7.0, a precipitant was added to precipitate, the precipitate was filtered, and the precipitate was washed, dried and ground.

2. The application as described in claim 1, characterized in that, The mass ratio of activated carbon to carboxylated taratanine is (1.9~2.2):

1.

3. The application as described in claim 1, characterized in that, The removal agent also includes modified montmorillonite, with the mass ratio of modified montmorillonite to the total mass of activated carbon and carboxylated taratin being (0.11~0.18):

1.

4. The application as described in claim 3, characterized in that, The modified montmorillonite was generated by intercalation modification of montmorillonite with tetramethylammonium chloride, and the modified montmorillonite formed an organic-inorganic composite structure.

5. The application as described in claim 3, characterized in that, The modified montmorillonite is added and mixed in a ball mill. The method for preparing the modified montmorillonite is as follows: Tetramethylammonium chloride solution was mixed with montmorillonite suspension, the pH was adjusted to 8.0-9.0, and the mixture was reacted in an oil bath at 80-85℃ for 6-7 hours to obtain the second reaction solution. Cool the second reaction solution to room temperature, centrifuge and discard the supernatant, redisperse the precipitate with deionized water, repeat centrifugation and washing until no chloride ions are detected in the supernatant, wash with ethanol for the last time, and dry and grind.

6. The application as described in claim 5, characterized in that, The mass ratio of tetramethylammonium chloride to montmorillonite is (0.8~1.2):

1.

7. The application as described in any one of claims 1-6, characterized in that, The removal agent also includes iron oxide nanoparticles and polyaluminum chloride, wherein the mass ratio of iron oxide nanoparticles to the total mass of activated carbon and carboxylated tararatanine is (0.02~0.05):1, and the mass ratio of polyaluminum chloride to the total mass of activated carbon and carboxylated tararatanine is (0.02~0.05):

1.

8. The application as described in claim 1, characterized in that, The mass ratio of chloroacetic acid to taratanine is (2~3):1.

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