A method for treating high-calcium coalbed methane produced water and recovering lithium and strontium resources

Abstract

This invention relates to the field of wastewater treatment and resource utilization technology, specifically to a method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources. The method involves adding sodium sulfate, hydrogen peroxide, a demulsifier, and a flocculant to the produced water, allowing each to react. After the reaction, solid impurities are removed through solid-liquid separation. The effluent undergoes nanofiltration A treatment, with the nanofiltration A permeate and nanofiltration A concentrate treated separately. The treatment method for the nanofiltration A permeate is: electrolytic oxidation A, high-pressure reverse osmosis, and adsorption desorption. The treatment method for the nanofiltration A concentrate is: thermogravimetric precipitation, electrolytic oxidation B, resin adsorption, and nanofiltration B. The nanofiltration B permeate and nanofiltration B concentrate are then evaporated and crystallized to obtain NaCl and strontium chloride, respectively. The condensate is discharged or reused. This invention's treatment process achieves compliant discharge or reuse of produced water and separates byproducts such as calcium, strontium, and lithium from the water.

Description

Technical Field

[0001] This invention relates to a method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources, belonging to the field of wastewater treatment and resource utilization technology. Background Technology

[0002] Coalbed methane produced water mainly refers to groundwater discharged through drainage equipment. The produced water generated during the production stage has a complex composition, primarily containing high concentrations of calcium, sodium, chlorine, organic matter, ammonia nitrogen, suspended solids, and petroleum hydrocarbons. It also contains barium, strontium, and lithium, classifying it as high-calcium, high-salt produced water. Total dissolved solids (TDS) can typically exceed 40,000 mg / L, making treatment difficult and operating costs high. Typical water quality data for high-calcium, high-salt coalbed methane produced water are shown in the table below:

[0003] index content Suspended solids (mg / L) 80-500 Turbidity (NTU) 200-1000 Color 50-150 Petroleum products (mg / L) 50-500 COD (mg / L) 1000-3000 Ammonia nitrogen (mg / L) 100-500 Barium (mg / L) 100-1000 Calcium (mg / L) 10,000 to 50,000 Magnesium (mg / L) 50-150 Strontium (mg / L) 0.5-30,000 Lithium (mg / L) 30-150 TDS (mg / L) 40,000 to 120,000

[0004] Currently, coalbed methane produced water is mainly treated using a process of "air flotation oil removal + coagulation sedimentation + oxidation + evaporation." The treated water is then discharged in compliance with standards or reused. However, the treatment effect of the air flotation process is not ideal, especially when the emulsified oil content is high; the petroleum content in the effluent is generally difficult to reach below 5 mg / L, affecting the operation of downstream systems. In the coagulation sedimentation process, even after adding flocculants, suspended solids are still difficult to settle completely, resulting in high suspended solids and turbidity in the effluent, causing frequent clogging of downstream systems. Oxidation treatment generally employs Fenton oxidation, ozone catalytic oxidation, and electrochemical oxidation, but due to the high salinity of coalbed methane produced water, regardless of the catalytic oxidation method used, the hydroxyl radicals generated during the treatment process are easily annihilated by chloride ions, resulting in extremely low oxidation efficiency. The COD removal rate is generally only around 30%, and the oxidation treatment cost is high. Evaporation treatment generally yields mixed salts as the final solid, which become hazardous waste. The cost of hazardous waste treatment is generally as high as 3000-5000 yuan / ton, resulting in an overall operating cost of 200 yuan / m³ for the produced water. 3 Therefore, developing efficient and low-cost technologies for the treatment and resource utilization of coalbed methane produced water has broad application prospects. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources. This method enables the water to meet discharge standards or be reused, and also separates byproducts such as calcium, strontium, and lithium from the water. All byproducts can be utilized as resources, reducing or avoiding the generation of hazardous waste. The economic benefits from the byproducts can offset part of the wastewater treatment costs, ultimately reducing treatment costs.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources, wherein the method is as follows:

[0007] S1. Three-phase baffle reaction: Sodium sulfate, hydrogen peroxide, demulsifier and flocculant are added to the coalbed methane produced water and reacted separately. After the reaction is completed, solid impurities are removed by solid-liquid separation.

[0008] S2, Nanofiltration A treatment: The effluent from step S1 is treated with nanofiltration A, and the nanofiltration A permeate and nanofiltration A concentrate are treated separately;

[0009] The treatment methods for S2' and nanofiltration A permeate are as follows:

[0010] S2'-1, Electrolytic Oxidation A: Electrolytic oxidation A is used to treat nanofiltration A permeate to remove ammonia nitrogen and residual COD from the nanofiltration A permeate;

[0011] S2'-2, High-pressure reverse osmosis: The water after electrolytic oxidation A treatment is treated by high-pressure reverse osmosis. The high-pressure reverse osmosis permeate is discharged or reused, and the high-pressure reverse osmosis concentrate is treated for subsequent processes.

[0012] S2'-3, Adsorption and Desorption: Lithium in water is adsorbed by a lithium adsorbent, and then the lithium adsorbent after lithium adsorption is desorbed by hydrochloric acid to obtain a lithium-rich solution. The lithium-rich solution is concentrated and refined to obtain lithium carbonate. The effluent from the adsorption and desorption is evaporated and crystallized to obtain NaCl, and the condensate is discharged or reused.

[0013] The treatment methods for S2” and nanofiltration A concentrate are as follows:

[0014] S2”-1, Thermogravimetric precipitation: Sodium hydroxide is added to the concentrated water of nanofiltration A to carry out a precipitation reaction, and calcium hydroxide product is obtained by solid-liquid separation;

[0015] S2”-2, Electrolytic Oxidation B: The effluent after thermogravimetric precipitation is treated with electrolytic oxidation B to remove TOC and ammonia nitrogen from the water;

[0016] S2”-3, Resin Adsorption: Water treated by electrolytic oxidation B is subjected to resin adsorption treatment to reduce the total organic carbon (TOC) in the water;

[0017] S2”-4, Nanofiltration B: After the resin adsorption, the effluent is separated from sodium by nanofiltration B. The permeate and concentrate are then evaporated and crystallized to obtain NaCl and strontium chloride, respectively. The condensate is discharged or reused.

[0018] Furthermore, in step S1, the amount of sodium sulfate added is 80-800 mg / L, and the reaction time is 5-10 min; the mass concentration of hydrogen peroxide is 27.5%, the amount added is 1-3 g / L, and the reaction time after adding hydrogen peroxide is 1-10 min.

[0019] The amount of demulsifier added is 5-50 mg / L, and the reaction time after the demulsifier is added is 10-30 min;

[0020] The amount of flocculant added is 1-10 mg / L, and the reaction time after the flocculant is added is 1-10 min.

[0021] Furthermore, in step S2, the operating pressure of nanofiltration A is 10-90 bar, and it can be a single stage or multiple stages to ensure that the calcium ion content of the water produced by nanofiltration A is within 100 mg / L.

[0022] Furthermore, the current density in both the electrolytic oxidation of A in step S2'-1 and the electrolytic oxidation of B in step S2”-2 is 200-600 A / m. 2 The voltages are all 3-6V, and the oxygen evolution potential of the anode materials is all 2-3V.

[0023] Furthermore, after the electrolytic oxidation A treatment, the effluent is first treated with a reducing agent to reduce the ORP to below 150mV before undergoing the high-pressure reverse osmosis treatment. The operating pressure of the high-pressure reverse osmosis is 40-90 bar, and the concentrate from the high-pressure reverse osmosis is Li... + The content is 150-500 mg / L or higher.

[0024] Furthermore, in step S2”-1, the concentration of sodium hydroxide added is related to the Ca concentration in the nanofiltration A concentrate. 2+ The mass concentration ratio is (1-2):1; the reaction temperature is 60℃-100℃; and the stirring reaction time is 0.5-2h.

[0025] Furthermore, after thermogravimetric precipitation, hydrochloric acid is added to adjust the pH to 6-8, and then the water is subjected to electrolytic oxidation to remove TOC and ammonia nitrogen.

[0026] Furthermore, a reducing agent is first added to the effluent from the electrolytic oxidation of B to reduce the ORP from 800-1200mV to below 150mV before resin adsorption; the resin adsorption is a series operation of 1-3 stages of adsorption.

[0027] During the resin adsorption process in steps S2”-3, the resin filtration rate is 0.5-2 BV / h, and the residence time is 0.5-2h.

[0028] Furthermore, during the operation of nanofiltration B in steps S2”-4, the operating pressure is 20-60 bar, and the pH of the influent to nanofiltration B is 6-8.

[0029] Furthermore, NaCl product is obtained by MVR evaporation and crystallization, and SrCl2 product is obtained by multi-effect evaporation and crystallization.

[0030] The beneficial effects of this invention are:

[0031] (1) Through the cooperation of various process steps, this invention not only achieves the standard discharge or reuse of water, but also separates by-products such as calcium, strontium, and lithium from the water. All by-products can be utilized as resources, reducing or avoiding the generation of hazardous waste. The economic benefits brought by the by-products can offset part of the wastewater treatment cost, which is equivalent to reducing the treatment cost.

[0032] (2) Conventional high-calcium and high-salt produced water generally involves separate processes of air flotation for oil removal and coagulation and sedimentation. The process is complex, requires a large area, and has poor oil and suspended solids removal effects, resulting in high levels of suspended solids and turbidity in the effluent. This invention designs a three-phase baffled reactor that integrates coagulation, sedimentation, and air flotation functions. It adds sodium sulfate, hydrogen peroxide, demulsifier, and flocculant to the high-calcium and high-salt produced water for baffled reaction, extending the reaction path and residence time in each reaction zone, avoiding short-circuiting, and allowing the chemical agents to react fully. This causes the structure and polarity of stable macromolecules in the water to change and rapidly settle. The reactor effectively separates water, air, and solids (oil, suspended solids, macromolecules, colloidal substances, etc.) into three phases without the need for additional air flotation tanks or sedimentation tanks, thus improving the treatment effect. It has a high degree of integration and a small footprint.

[0033] (3) This invention uses nanofiltration A to separate high concentrations of calcium in the effluent, replacing the conventional dual-alkali hardening technology, avoiding the problems of high operating costs and large sludge volume caused by adding a large amount of chemical agents; at the same time, nanofiltration A can be set to multiple stages according to the water quality. When the calcium content of the effluent from the first-stage nanofiltration A does not meet the effluent requirements, two stages, three stages, etc. can be set until the effluent quality meets the design requirements. It can be seen that the system can not only guarantee the effluent effect, but also has strong adaptability and flexibility.

[0034] (4) Generally speaking, during the oxidation process of high-chlorine wastewater, the Cl in the water... - The oxidation process generates hydroxyl radicals, leading to low oxidation efficiency. This invention employs nanofiltration A to first separate and remove calcium chloride from the water, significantly reducing the salinity of the nanofiltration A product. Then, electrolytic oxidation A is used, greatly improving oxidation efficiency and effectively avoiding the negative impact of high salt on oxidation efficiency. This allows for more thorough oxidation of residual organic matter in the water, reducing COD to below 30 mg / L and ammonia nitrogen to below 1 mg / L, ensuring the quality of the downstream NaCl salt. The NaCl meets the requirements for premium-grade industrial dry salt in "Industrial Salt" (GBT5462-2015). Furthermore, due to thermal resorption precipitation, the salt and Cl in the water are removed... - The content is also very high. Electrolytic oxidation of B can efficiently remove ammonia nitrogen, but it is difficult to completely remove organic matter. Therefore, after electrolytic oxidation of B, resin adsorption is used to deeply remove residual organic matter in the water, which can ensure the quality of the downstream SrCl2 salt. Strontium chloride meets the first-class requirements in "Industrial Strontium Chloride" (HGT4501-2013).

[0035] (5) The concentration of calcium and strontium in nanofiltration A water is very high. The salt produced by direct evaporation is hazardous waste. This invention utilizes the basic principle that the solubility of calcium hydroxide gradually decreases with increasing temperature and the solubility of strontium hydroxide gradually increases with increasing temperature to separate them by thermal precipitation, and finally obtain calcium hydroxide by-product. The calcium hydroxide meets the requirements of first-class product in "Industrial Calcium Hydroxide" (HG4120-2009), can be utilized as a resource, avoids the formation of a large amount of calcium chloride and strontium chloride mixture that would generate hazardous waste, and reduces the cost of hazardous waste treatment. Attached Figure Description

[0036] Figure 1 This is a flow chart of the process for resource utilization treatment of produced water from high-calcium and high-salt coalbed methane according to the present invention.

[0037] Figure 2 This is a process diagram of the equipment for the resource utilization treatment of produced water from high-calcium and high-salt coalbed methane as described in this invention.

[0038] Figure 3 This is a front view of a three-phase baffled reactor;

[0039] Figure 4 This is a right view of a three-phase baffled reactor;

[0040] Figure 5 This is a top view of the interior of a three-phase baffled reactor;

[0041] In the diagram, 1 is the sodium sulfate reaction zone; 2 is the hydrogen peroxide reaction zone; 3 is the demulsification zone; 4 is the slag collection zone; 5 is the flocculation zone; 6 is the water collection zone; and 7 is the jet injector. Detailed Implementation

[0042] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0044] like Figure 1-2 As shown, a method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources is described, wherein the method comprises:

[0045] S1. Three-phase baffled reaction: Adding sodium sulfate allows it to react with barium ions in the water to form barium sulfate precipitate, removing barium from the water. Simultaneously, controlling the sodium sulfate dosage (80-800 mg / L) ensures sufficient sulfate reaction with minimal residue, preventing the formation of calcium sulfate precipitate. Then, adding hydrogen peroxide (27.5% concentration) at 1-3 g / L and reacting for 10-30 minutes, followed by the sequential addition of a demulsifier (polyoxyethylene polyoxypropylene polyether) at 5-50 mg / L and reacting for 10-30 minutes, and then PAM at 1-10 mg / L and reacting for 1-10 minutes. The process mainly utilizes hydrogen peroxide and demulsifiers to reduce the surface tension of oil droplets in water and decrease the strength of the interfacial film. The absolute value of the Zeta potential decreases from 30-50mV to below 5-10mV. The attraction between particles gradually becomes greater than the repulsion, and the oil and colloidal particles in the water lose stability and aggregate. They then form a large number of flocs through bridging. Some of the flocs settle to the bottom sludge hopper to form sludge, while the other part floats to the scum trough and is discharged by a scraper. This completes the separation and removal of impurities such as oil, suspended solids, turbidity, color, and colloids in the wastewater.

[0046] S2, Nanofiltration A: The effluent from step S1 undergoes nanofiltration A treatment. The number of nanofiltration A stages is determined to be 1-3 stages based on the calcium ion content and effluent requirements. Each nanofiltration A stage can use one or more brands such as DuPont, Veolia, Hydranautics, and TimeWalton. The nanofiltration A membrane model can be one or more combinations, ensuring that the calcium ion content in the final nanofiltration A effluent is below 100 mg / L. The operating pressure during nanofiltration A operation is 10-90 bar. The final concentrate TDS is between 130,000-160,000 mg / L, and the final product TDS is between 3,000-50,000 mg / L, with a total recovery rate of 60-90%. The nanofiltration A product and nanofiltration A concentrate are treated separately.

[0047] The treatment methods for S2' and nanofiltration A permeate are as follows:

[0048] S2'-1, Electrolytic Oxidation A: Electrolytic oxidation A primarily removes ammonia nitrogen and residual COD from the water, ensuring the purity of downstream lithium and NaCl products. The effluent from electrolytic oxidation A has a COD ≤ 30 mg / L and an ammonia nitrogen ≤ 1 mg / L. The current density during the electrolytic oxidation process is 200-600 A / m³. 2 Voltage 3-6V, pH = 5-8.5, oxygen evolution potential of anode material 2-3V.

[0049] S2'-2, High-Pressure Reverse Osmosis: Before high-pressure reverse osmosis concentration, a reducing agent, such as hydrogen peroxide, needs to be added to reduce the ORP from 800-1200mV to below 150mV. The operating pressure should be controlled at 40-90 bar. The concentrate, Li... + The content reaches 150-500 mg / L or more, and the TDS reaches 70,000 mg / L or more.

[0050] S2'-3, Adsorption and Desorption: Lithium in the water is adsorbed using a lithium adsorbent, which is either titanium-based or manganese-based, with an adsorption capacity of over 10 mg / g and a lithium recovery rate of over 90%. The lithium adsorbent after adsorption is desorbed by hydrochloric acid to obtain a lithium-rich solution with a lithium content of over 500 mg / L. This lithium-rich solution can be sold directly as a lithium feedstock or further concentrated and refined to obtain lithium carbonate, thus achieving resource utilization. The effluent from the adsorption and desorption process is evaporated and crystallized to obtain NaCl industrial salt. The condensate is either discharged or reused.

[0051] The treatment methods for S2” and nanofiltration A concentrate are as follows:

[0052] S2”-1, Thermogravimetric precipitation: By adding sodium hydroxide, the dosage of sodium hydroxide is related to the Ca in the nanofiltration A concentrate. 2+ The mass concentration ratio is (1-2):1. The temperature is raised to 60℃-100℃, and the reaction is stirred for 0.5-2 hours. Solid calcium hydroxide precipitates from the bottom of the reactor, and calcium hydroxide (quicklime) is recovered. Strontium hydroxide will not precipitate at this time because the solubility of strontium hydroxide increases with increasing temperature, while that of calcium hydroxide decreases. At 60-100℃, the solubility of calcium hydroxide is only 0.076-0.121 g / 100g, while the solubility of strontium hydroxide is 8.42-91.2 g / 100g, showing a significant difference. Furthermore, under alkaline conditions, ammonia in the water exists as weakly alkaline ammonia water, which can inhibit the precipitation of strontium hydroxide, ensuring maximum precipitation of calcium hydroxide (quicklime) and obtaining high-purity solid calcium hydroxide. The separated clear liquid is cooled to below 40℃, at which point Ca... 2+ The content is below 50 mg / L, and the other main substances are strontium, sodium, and chlorine.

[0053] S2”-2, Electrolytic Oxidation of B: The effluent after thermogravimetric precipitation is adjusted to pH 6-8 by adding hydrochloric acid, and then subjected to electrolytic oxidation of B to remove TOC and ammonia nitrogen from the water. The current density during the electrolytic oxidation of B is 200-600 A / m³. 2 With a voltage of 3-6V and an oxygen evolution potential of 2-3V for the anode material, ammonia nitrogen is reduced to below 1mg / L after electrolytic oxidation B treatment. However, due to the high chloride wastewater system, the degradation efficiency of electrolytic oxidation B for organic matter is not high, and the organic matter removal rate is only about 20-30%.

[0054] S2”-3, Resin Adsorption: Before resin adsorption, a reducing agent (hydrogen peroxide) needs to be added to reduce the ORP from 800-1200mV to below 150mV before entering the resin adsorption system. The resin adsorption system operates in 1-3 stages in series based on the total organic carbon (TOC) concentration of the effluent. Each stage can use the same or different types of resin. The resin filtration rate is 0.5-2 BV / h, the residence time is 0.5-2h, the influent TOC is 50-150mg / L, and the effluent TOC is ≤20mg / L. The regenerated solution after resin adsorption can be regenerated using any one of methanol, ethanol, or sodium hydroxide. The regenerated resin can be reused repeatedly. In this embodiment of the invention, the resin types used are one or more of LS-109D, LSV-16, and SD300.

[0055] S2”-4, Nanofiltration B: After resin adsorption, the effluent passes through nanofiltration B to separate strontium and sodium in the water. The product water and concentrate are then evaporated and crystallized separately to obtain NaCl and strontium chloride, respectively, thus achieving resource recovery of strontium chloride. The condensate is discharged or reused, achieving resource utilization and avoiding the hazardous waste generated by the direct evaporation and crystallization of the calcium-strontium mixture in conventional treatment processes, which would result in huge hazardous waste disposal costs. The operating pressure of nanofiltration B is 20-60 bar, the pH of the nanofiltration B influent is 6-8, the SrCl2 content in the concentrate reaches over 140,000 mg / L, and the NaCl content in the product water is over 70,000 mg / L.

[0056] Since NaCl has a lower boiling point and SrCl2 has a higher boiling point, in order to save energy and obtain salt products, NaCl products are obtained by treating the permeate after lithium adsorption and desorption by MVR evaporation and crystallization, and SrCl products are obtained by treating the concentrated water of nanofiltration B by multi-effect evaporation and crystallization.

[0057] Specifically, the equipment and process flow of the high-calcium, high-salt coalbed methane produced water resource utilization treatment method is as follows: Figure 2 As shown in the figure. The structure of the three-phase baffled reactor is as follows: Figures 3-5 As shown, the three-phase baffled reactor includes a sodium sulfate reaction zone 1, a hydrogen peroxide reaction zone 2, a demulsification zone 3, a slag collection zone 4, a flocculation zone 5, and a water collection zone 6. Both the sodium sulfate reaction zone 1 and the hydrogen peroxide reaction zone 2 are equipped with jet injectors 7. High-calcium, high-salt coalbed methane produced water reacts with sodium sulfate in the sodium sulfate reaction zone 1, then enters the hydrogen peroxide reaction zone 2, where it reacts with hydrogen peroxide; in the demulsification zone 3, it reacts with a demulsifier; in the flocculation zone 5, it reacts with PAM; and finally, it enters the subsequent nanofiltration A process through the water collection zone 6.

[0058] Example 1

[0059] A method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources, the method comprising:

[0060] S1. Three-phase baffled reaction: 800 mg / L of sodium sulfate (10% mass concentration) solution is added and reacted for 10 min. Then, 2 g / L of hydrogen peroxide (27.5%) is added and reacted for 20 min. Next, 25 mg / L of demulsifier (polyoxyethylene polyoxypropylene polyether) is added and reacted for 20 min, and PAM is added at 5 mg / L and reacted for 5 min. A large amount of floc is generated in the system. Part of the floc settles to the bottom sludge hopper to form sludge, and the other part floats to the scum tank and is discharged by the scum scraper. This completes the separation and removal of impurities such as oil, suspended solids, turbidity, color, and colloids in the wastewater.

[0061] S2, Nanofiltration A: The effluent from step S1 undergoes three-stage nanofiltration A treatment. The operating pressure of the nanofiltration A process is 60 bar. The final calcium ion content in the nanofiltration A effluent is below 100 mg / L, the TDS of the concentrate is between 130,000 and 160,000 mg / L, and the TDS of the permeate is between 3,000 and 50,000 mg / L. The nanofiltration A permeate and nanofiltration A concentrate are treated separately.

[0062] The treatment methods for S2' and nanofiltration A permeate are as follows:

[0063] S2'-1, Electrolytic oxidation primarily removes ammonia nitrogen and residual COD from the water, ensuring the purity of downstream lithium and NaCl products. The effluent from electrolytic oxidation has a COD ≤ 30 mg / L and an ammonia nitrogen ≤ 1 mg / L. The current density during the electrolytic oxidation process is 600 A / m³. 2 Voltage 4V, pH = 5-8.5, oxygen evolution potential of anode material 3V.

[0064] S2'-2, High-Pressure Reverse Osmosis: Before high-pressure reverse osmosis concentration, a reducing agent (hydrogen peroxide) needs to be added to reduce the ORP from 800-1200mV to below 150mV, controlling the operating pressure at 60bar. The concentrate, Li... + The content reaches 150-500 mg / L or more, and the TDS reaches 70,000 mg / L or more.

[0065] S2'-3, Adsorption and Desorption: Lithium in the water is adsorbed using a titanium-based adsorbent (adsorbent model G-100). The adsorbent after lithium adsorption is desorbed by hydrochloric acid to obtain a lithium-rich solution, which can be further concentrated and purified to obtain lithium carbonate. The effluent from the adsorption and desorption process is evaporated and crystallized to obtain NaCl, and the condensate is either discharged or reused.

[0066] The treatment methods for S2” and nanofiltration A concentrate are as follows:

[0067] S2”-1, Thermogravimetric precipitation: By adding sodium hydroxide, the dosage of sodium hydroxide is related to the Ca in the nanofiltration A concentrate. 2+The mass concentration ratio is 2:1. The heating temperature is 80℃, and the reaction is stirred for 1 hour. Calcium hydroxide solid is precipitated from the bottom of the reactor, and calcium hydroxide (quicklime) is recovered. The supernatant mainly contains Sr, sodium, chlorine, and a small amount of residual calcium. The supernatant is cooled to below 40℃.

[0068] S2”-2, Electrolytic Oxidation B: After thermogravimetric precipitation, the effluent is adjusted to pH 6-8 by adding hydrochloric acid. Electrolytic oxidation B then removes TOC and ammonia nitrogen from the water, reducing ammonia nitrogen to below 1 mg / L and TOC to below 300 mg / L. The current density during the electrolytic oxidation process is 500 A / m³. 2 The voltage is 4V, and the oxygen evolution potential of the anode material is 3V.

[0069] S2”-3, Resin Adsorption: Before resin adsorption, a reducing agent (hydrogen peroxide) needs to be added to reduce the ORP from 800-1200mV to below 150mV before entering the resin adsorption system. The resin adsorption system operates in a three-stage series. The primary, secondary, and tertiary resins used are LS-109D, LSV-16, and SD300, respectively. The resin filtration rate is 1 BV / h, the residence time is 1h, the influent TOC is 50-150mg / L, and the effluent TOC is ≤20mg / L. The regenerated solution after resin adsorption is regenerated by one of methanol, ethanol, or sodium hydroxide. The regenerated resin can be reused repeatedly.

[0070] S2”-4, Nanofiltration B: After resin adsorption, the effluent passes through nanofiltration B to separate strontium and sodium in the water. The product water and concentrate are then evaporated and crystallized separately to obtain NaCl and strontium chloride, respectively. This achieves resource recovery of the crude strontium chloride product. The condensate is discharged or reused, realizing resource utilization throughout the process. This avoids the direct evaporation and crystallization of the calcium-strontium mixture, which results in hazardous waste due to the high cost of hazardous waste disposal, as is common in conventional treatment processes. The operating pressure of nanofiltration B is 40 bar, the influent pH is 6-8, the concentrate SrCl2 content reaches over 140,000 mg / L, and the product NaCl content is over 70,000 mg / L.

[0071] NaCl product is obtained by MVR evaporation and crystallization, and SrCl2 product is obtained by multi-effect evaporation and crystallization.

[0072] Example 2

[0073] A method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources, the method comprising:

[0074] S1, Three-phase baffled reaction:

[0075] By adding 100 mg / L of sodium sulfate (10% by mass) solution and reacting for 10 min, followed by adding 1 g / L of hydrogen peroxide (27.5%) and reacting for 30 min, and then sequentially adding 50 mg / L of demulsifier (polyoxyethylene polyoxypropylene polyether) and reacting for 10 min, and then adding PAM at 10 mg / L and reacting for 1 min, a large amount of floc is generated in the system. Part of the floc settles to the bottom sludge hopper to form sludge, while the other part floats to the scum trough and is discharged by a scum scraper, thereby completing the separation and removal of impurities such as oil, suspended solids, turbidity, color, and colloids in the wastewater.

[0076] S2, Nanofiltration A: The effluent from step S1 undergoes three-stage nanofiltration A treatment. The operating pressure of the nanofiltration A process is 90 bar. The final calcium ion content in the nanofiltration A effluent is below 100 mg / L, the TDS of the concentrate is between 130,000 and 160,000 mg / L, and the TDS of the permeate is between 3,000 and 50,000 mg / L. The nanofiltration A permeate and nanofiltration A concentrate are treated separately.

[0077] The treatment methods for S2' and nanofiltration A permeate are as follows:

[0078] S2'-1, Electrolytic oxidation primarily removes ammonia nitrogen and residual COD from the water, ensuring the purity of downstream lithium and NaCl products. The effluent COD from electrolytic oxidation is ≤30 mg / L, and ammonia nitrogen is ≤1 mg / L. The current density during the electrolytic oxidation process is 200 A / m³. 2 Voltage 3V, pH = 5-8.5, oxygen evolution potential of anode material 2V.

[0079] S2'-2, High-Pressure Reverse Osmosis: Before high-pressure reverse osmosis concentration, a reducing agent (hydrogen peroxide) needs to be added to reduce the ORP from 800-1200mV to below 150mV, controlling the operating pressure at 40bar. The concentrate, Li... + The content reaches 150-500 mg / L or more, and the TDS reaches 70,000 mg / L or more.

[0080] S2'-3, Adsorption and Desorption: Lithium in the water is adsorbed using a titanium-based adsorbent (adsorbent model G-100). The adsorbent after lithium adsorption is desorbed by hydrochloric acid to obtain a lithium-rich solution, which can be further concentrated and purified to obtain lithium carbonate. The effluent from the adsorption and desorption process is evaporated and crystallized to obtain NaCl, and the condensate is either discharged or reused.

[0081] The treatment methods for S2” and nanofiltration A concentrate are as follows:

[0082] S2”-1, Thermogravimetric precipitation: By adding sodium hydroxide, the dosage of sodium hydroxide is related to the Ca in the nanofiltration A concentrate. 2+The mass concentration ratio is 1.5:1. The heating temperature is 60℃, and the reaction is stirred for 2 hours. Calcium hydroxide solid is precipitated from the bottom of the reactor, and calcium hydroxide (quicklime) is recovered. The supernatant mainly contains Sr, sodium, chlorine, and a small amount of residual calcium. The supernatant is cooled to below 40℃.

[0083] S2”-2, Electrolytic Oxidation B: The effluent after thermogravimetric precipitation is adjusted to pH 6-8 by adding hydrochloric acid. Electrolytic oxidation B then removes TOC and ammonia nitrogen from the water, reducing ammonia nitrogen to below 1 mg / L and TOC to 300 mg / L. The current density during the electrolytic oxidation process is 200 A / m³. 2 The voltage is 3V, and the oxygen evolution potential of the anode material is 2V.

[0084] S2”-3, Resin Adsorption: Before resin adsorption, a reducing agent (hydrogen peroxide) needs to be added to reduce the ORP from 800-1200mV to below 150mV before entering the resin adsorption system. The resin adsorption system operates in three stages in series. The primary, secondary, and tertiary resins used are LS-109D, LSV-16, and SD300, respectively. The resin filtration rate is 2 BV / h, the residence time is 0.5h, the influent TOC is 50-150mg / L, and the effluent TOC is ≤20mg / L. The regenerated solution after resin adsorption is regenerated using one of methanol, ethanol, or sodium hydroxide. The regenerated resin can be reused repeatedly.

[0085] S2”-4, Nanofiltration B: After resin adsorption, the effluent passes through nanofiltration B to separate strontium and sodium in the water. The product water and concentrate are then evaporated and crystallized separately to obtain NaCl and strontium chloride, respectively. This achieves resource recovery of the crude strontium chloride product. The condensate is discharged or reused, realizing resource utilization throughout the process. This avoids the direct evaporation and crystallization of the calcium-strontium mixture, which results in hazardous waste due to the high cost of hazardous waste disposal, as is common in conventional treatment processes. The operating pressure of nanofiltration B is 20 bar, the influent pH is 6-8, the concentrate SrCl2 content reaches over 140,000 mg / L, and the product water NaCl content is over 70,000 mg / L.

[0086] NaCl product is obtained by MVR evaporation and crystallization, and SrCl2 product is obtained by multi-effect evaporation and crystallization.

[0087] Experiments revealed that after treatment using the process described in this invention, the effluent quality of both Examples 1 and 2 met the requirements for "makeup water for open-loop circulating cooling water systems" in the "Water Quality Standard for Industrial Water Use in Urban Wastewater Reuse" (GBT 19923-2005), and both could achieve compliant discharge or reuse. The resulting lithium-rich liquid can be sold as a lithium raw material or further refined to obtain lithium products. The obtained byproduct NaCl meets the requirements of "Industrial Salt".

[0088] The requirements for superior quality industrial dry salt in GB / T 5462-2015 are met; the obtained strontium chloride meets the requirements of "Industrial Strontium Chloride".

[0089] The first-class product requirements in (HGT4501-2013) are met by centrifugation and drying of the obtained calcium hydroxide, which also meets the first-class product requirements in "Industrial Calcium Hydroxide" (HG4120-2009). This fully realizes the resource utilization of by-products and reduces the cost of hazardous waste treatment.

[0090] Comparative Example 1

[0091] The same method as in Example 1 was used for the treatment of produced water from high-calcium coalbed methane and the recovery of lithium and strontium resources. The difference was that step S1 of Comparative Example 1 did not involve a three-phase baffled reactor. Instead, conventional air flotation for oil removal and coagulation sedimentation were used for pretreatment. The subsequent treatment process was the same as in Example 1. The pretreatment operation in this comparative example was as follows: a demulsifier (polyoxyethylene polyoxypropylene polyether) was added to the air flotation reactor to demulsify the water, removing emulsified oil and suspended solids through air flotation. The effluent then entered the coagulation sedimentation reactor, where PAC and PAM were added and stirred for reaction. The resulting sludge and water were then mixed and sent to a sedimentation tank for sludge-water separation. The water quality data before and after pretreatment are shown in the table below:

[0092] Table 1 Water quality data before and after pretreatment

[0093]

[0094] A comparison of the data from Example 1 and Comparative Example 1 shows that if the three-phase baffle reactor of the present invention is not used for treatment, the water quality indicators such as suspended solids, turbidity, and oil in the effluent are all high, which can easily cause serious clogging problems in the downstream nanofiltration A system. Furthermore, barium is not removed, which will lead to excessive barium content in the extracted calcium hydroxide and strontium chloride products, thereby affecting the quality of the two products.

[0095] Comparative Example 2

[0096] The same method as in Example 1 was used for the treatment of produced water from high-calcium coalbed methane and the recovery of lithium and strontium resources. The difference was that in step S2”-1 of Comparative Example 2, sodium hydroxide was replaced with sodium carbonate during thermogravimetric precipitation. The main components of the solid obtained after centrifugation and drying after thermogravimetric precipitation are shown in the table below:

[0097] Table 2. Composition of the solid obtained after thermogravimetric precipitation and centrifugation drying

[0098] Sample Main components of solids solid properties Example 1 Calcium hydroxide, and trace amounts of other impurities. Industrial-grade product, recyclable Comparative Example 2 Calcium carbonate, strontium carbonate, and other impurities It is mostly hazardous waste.

[0099] A comparison of the data from Example 1 and Comparative Example 2 shows that if sodium hydroxide is replaced with sodium carbonate during thermogravimetric precipitation, the solid obtained from thermogravimetric precipitation is mainly a mixture of calcium carbonate, strontium carbonate, etc., which is basically hazardous waste and has high treatment costs.

[0100] Comparative Example 3

[0101] The same method as in Example 1 was used for the treatment of produced water from high-calcium coalbed methane and the recovery of lithium and strontium resources. The difference was that in step S2”-1 of Comparative Example 3, heating was not performed during thermogravimetric precipitation. Sodium hydroxide was added at room temperature to carry out the reaction. The relevant data of the solid product obtained by centrifugation and drying of the calcium hydroxide are shown in the table below:

[0102] Table 3. Relevant data on the solid products obtained after thermogravimetric precipitation and centrifugal drying.

[0103]

[0104] A comparison of the data from Example 1 and Comparative Example 3 shows that if no heating is performed during thermogravimetric precipitation and sodium hydroxide is added at room temperature for the reaction, the solubility of calcium hydroxide is high, making it difficult to precipitate solid from the solution. As a result, the amount of solid precipitated is small, and the recovery rate of calcium hydroxide is greatly reduced. Furthermore, even if a small amount of solid is obtained, its impurity content is high, especially the strontium content, which may lead to the solid becoming hazardous waste and increasing treatment costs.

[0105] Comparative Example 4

[0106] The same method as in Example 1 was used for the treatment of produced water from high-calcium coalbed methane and the recovery of lithium and strontium resources. The difference was that Comparative Example 4 did not perform the resin adsorption operation in steps S2”-3, but instead directly performed nanofiltration operation B after electrolytic oxidation B treatment. The specific results are shown in Table 4 below.

[0107] Table 4. Experimental results data for Example 1 and Comparative Example 4

[0108]

[0109]

[0110] The data comparison between Example 1 and Comparative Example 4 shows that if there is no resin adsorption operation and nanofiltration B is performed directly after electrolytic oxidation B treatment, the organic matter COD, TOC, and ammonia nitrogen content in the final nanofiltration B permeate and concentrate will be high, which will directly affect the quality of sodium chloride and strontium chloride extracted in the downstream process, resulting in both salts failing to meet the requirements for qualified products, as well as the water quality of the evaporation condensate.

[0111] Comparative Example 5

[0112] The same method as in Example 1 was used for the treatment of produced water from high-calcium coalbed methane and the recovery of lithium and strontium resources. The difference was that in Comparative Example 5, the electrolytic oxidation A operation was replaced with a conventional ozone catalytic oxidation operation. The specific operation method of ozone catalytic oxidation in Comparative Example 5 was to add solid catalyst packing (carbon-based catalyst, catalyst type OC-4) into the oxidation tower, introduce wastewater, and simultaneously introduce ozone gas for reaction. Other process operations were the same as in Example 1. The specific treatment results are shown in Table 5 below.

[0113] Table 5. Experimental results data for Example 1 and Comparative Example 5.

[0114]

[0115]

[0116] A comparison of the data from Example 1 and Comparative Example 5 shows that if the electrolytic oxidation B operation is replaced with a conventional ozone oxidation operation, the COD and ammonia nitrogen in the oxidized effluent are both higher, affecting the quality of lithium-rich liquid and sodium chloride products, as well as the water quality of the evaporation condensate.

[0117] Comparative Example 6

[0118] The same method as in Example 1 was used for the treatment of produced water from high-calcium coalbed methane and the recovery of lithium and strontium resources. The difference was that in Comparative Example 6, the electrolytic oxidation B operation was replaced with a conventional Fenton oxidation operation. In Comparative Example 6, the Fenton oxidation process conditions were as follows: hydrochloric acid was added to the wastewater to adjust the pH to 3-5, followed by the sequential addition of ferrous chloride and hydrogen peroxide, and the reaction was carried out with stirring. Other process operations were the same as in Example 1. The specific results are shown in Table 6 below.

[0119] Table 6 shows the experimental results data for Example 1 and Comparative Example 6.

[0120]

[0121] The data comparison between Example 1 and Comparative Example 6 shows that if the electrolytic oxidation B operation is replaced with the conventional Fenton oxidation operation, the TOC removal efficiency is low and ammonia nitrogen is not removed. This not only affects the water quality of the condensate from the multi-effect evaporation, but also easily affects the quality of the strontium chloride product obtained by multi-effect evaporation crystallization.

[0122] Comparative Example 7

[0123] The same method as in Example 1 was used for the treatment of produced water from high-calcium coalbed methane and the recovery of lithium and strontium resources. The difference was that in step S1 of Comparative Example 7, sodium sulfate was not added to the three-phase baffle reactor; instead, hydrogen peroxide, demulsifier, and PAM were added directly for treatment. Other process operations were the same as in Example 1. The pretreated water quality and the content of solids obtained by thermogravimetric precipitation and centrifugation drying are shown in Table 7 below.

[0124] Table 7. Pretreated water quality and content of solids obtained after thermogravimetric precipitation and centrifugal drying.

[0125]

[0126] A comparison of the data from Example 1 and Comparative Example 7 shows that if sodium sulfate is not added to the three-phase baffle reactor, both the final calcium hydroxide and strontium chloride will contain barium, which will affect the quality of the two products and may even turn them into hazardous waste, increasing the treatment cost.

[0127] The above examples and comparative examples all used the same batch of coal seam produced water, meaning that the quality of the coal seam produced water used was the same.

[0128] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0129] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources, characterized in that, The method is as follows: S1. Three-phase baffle reaction: Sodium sulfate, hydrogen peroxide, demulsifier and flocculant are added sequentially to the coalbed methane produced water, and baffle reactions are carried out respectively. After the reaction is completed, solid impurities are removed by solid-liquid separation. S2, Nanofiltration A treatment: The effluent from step S1 is treated with nanofiltration A, and the nanofiltration A permeate and nanofiltration A concentrate are treated separately; The treatment methods for S2' and nanofiltration A permeate are as follows: S2'-1, Electrolytic Oxidation A: Electrolytic oxidation A is used to treat nanofiltration A permeate to remove ammonia nitrogen and residual COD from the nanofiltration A permeate; S2'-2, High-pressure reverse osmosis treatment: The effluent after electrolytic oxidation A treatment is subjected to high-pressure reverse osmosis treatment. The high-pressure reverse osmosis permeate is discharged or reused, and the high-pressure reverse osmosis concentrate is subjected to subsequent treatment. S2'-3, Adsorption and Desorption: Lithium in water is adsorbed by a lithium adsorbent, and then the lithium adsorbent after lithium adsorption is desorbed by hydrochloric acid to obtain a lithium-rich solution, which can be sold as a lithium raw material. The effluent from the adsorption and desorption process is evaporated and crystallized to obtain NaCl, and the condensate is either discharged or reused. The treatment methods for S2” and nanofiltration A concentrate are as follows: S2”-1, Thermogravimetric precipitation: Sodium hydroxide is added to the concentrated water of nanofiltration A to carry out a precipitation reaction, and calcium hydroxide product is obtained by solid-liquid separation; S2”-2, Electrolytic Oxidation B: The effluent after thermogravimetric precipitation is treated with electrolytic oxidation B to remove total organic carbon (TOC) and ammonia nitrogen from the water; S2”-3, Resin Adsorption: Water treated by electrolytic oxidation B is subjected to resin adsorption treatment to reduce the total organic carbon (TOC) in the water; S2”-4, Nanofiltration B treatment: The effluent after resin adsorption is separated from sodium by nanofiltration B. The permeate and concentrate are then evaporated and crystallized to obtain NaCl and strontium chloride, respectively. The condensate is discharged or reused.

2. The method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources according to claim 1, characterized in that, In step S1, the amount of sodium sulfate added is 80-800 mg / L, and the reaction time is 5-10 min; the mass concentration of hydrogen peroxide is 27.5%, the amount added is 1-3 g / L, and the reaction time after adding hydrogen peroxide is 1-10 min. The amount of demulsifier added is 5-50 mg / L, and the reaction time after the demulsifier is added is 10-30 min; The amount of flocculant added is 1-10 mg / L, and the reaction time after the flocculant is added is 1-10 min.

3. The method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources according to claim 1, characterized in that, In step S2, the operating pressure of nanofiltration A is 10-90 bar, and the recovery rate is 60-90%. Nanofiltration A can be a single stage or multiple stages to ensure that the calcium ion content of the produced water is within 100 mg / L.

4. The method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources according to claim 1, characterized in that, The current density in both the electrolytic oxidation of A in step S2'-1 and the electrolytic oxidation of B in step S2”-2 is 200-600 A / m. 2 The voltages are all 3-6V, and the oxygen evolution potential of the anode material is 2-3V.

5. The method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources according to claim 1, characterized in that, After the electrolytic oxidation A treatment, a reducing agent is first added to the effluent to reduce the ORP to below 150mV before the high-pressure reverse osmosis treatment is carried out. The operating pressure of the high-pressure reverse osmosis is 40-90 bar.

6. The method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources according to claim 1, characterized in that, In step S2”-1, the concentration of sodium hydroxide added is different from that of Ca in the nanofiltration A concentrate. 2+ The mass concentration ratio is (1-2):1; the reaction temperature is 60℃-100℃, and the stirring reaction time is 0.5-2h.

7. The method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources according to claim 1, characterized in that, After thermogravimetric precipitation, hydrochloric acid is added to adjust the pH to 6-8, and then electrolytic oxidation is performed to remove TOC and ammonia nitrogen from the water.

8. The method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources according to claim 1, characterized in that, A reducing agent is first added to the effluent from the electrolytic oxidation of B to reduce the ORP to below 150mV before resin adsorption; the resin adsorption is a series operation of 1-3 stages. During the resin adsorption process in steps S2”-3, the resin filtration rate is 0.5-2 BV / h, and the residence time is 0.5-2h.

9. The method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources according to claim 1, characterized in that, During the operation of nanofiltration B in steps S2”-4, the operating pressure is 20-60 bar, and the pH of the influent to nanofiltration B is 6-8.

10. The method for treating produced water from high-calcium coalbed methane and recovering lithium and strontium resources according to claim 1, characterized in that, NaCl was obtained by MVR evaporation and crystallization, and SrCl2 was obtained by multi-effect evaporation and crystallization.

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