A nucleation granulation method for recovering valuable metal ions from water using co2

Abstract

The application provides a nucleation granulation method for recycling valuable metal ions in water by CO2, and relates to the field of wastewater treatment. The method provided by the application introduces CO2-containing gas into wastewater containing valuable metal ions, adjusts the pH value to be alkaline, and in the presence of nucleation granulation seeds, CO2 hydrolysis generates carbonate ions, which induce the ordered crystallization and precipitation of valuable metal ions in the wastewater on the surface of the nucleation granulation seeds. The method has high treatment efficiency, simple process, can recycle the wastewater, and fully utilizes the CO2 discharged by enterprises. The method can simultaneously achieve the double goals of recycling valuable metal ions in wastewater and fixing and reducing CO2, and has important practical significance and popularization value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, and particularly relates to a nucleation granulation method for recovering valuable metal ions in water by using CO2. BACKGROUND

[0002] There are a large number of wastewater containing high-valence metal ions discharged in the energy chemical industry, waste incineration, thermal power, petroleum processing, metal smelting and other industries. If the metal ions such as copper, zinc, nickel and lead in these wastewaters are not properly treated and directly discharged into the environment, they will cause serious pollution to water bodies, soil and ecosystems. In addition, the accumulation of metal ions in water bodies may enter the human body through the food chain, posing a potential threat to human health. Therefore, effective recovery of valuable metal ions in wastewater not only concerns the efficient use of resources, but also is an urgent need to protect the ecological environment and human health.

[0003] For the recovery of valuable metal ions in wastewater, there are many traditional treatment methods, such as chemical precipitation method, ion exchange method, electrolysis method, etc. However, these methods have many limitations in practical application. The chemical precipitation method is simple to operate, but has low recovery rate and produces sludge that is difficult to handle; the ion exchange method has high recovery rate, but requires large equipment investment and high operating cost; the electrolysis method consumes a large amount of electric energy and has high requirements for the water quality of wastewater. In addition, these methods often only focus on the recovery of metal ions, ignoring the secondary pollution problems that may occur in the wastewater treatment process.

[0004] At the same time, a large amount of carbon dioxide is contained in the flue gas generated in the production process of energy chemical industry and other industries. The emission of these carbon dioxide not only exacerbates global climate change, but also wastes valuable carbon resources. At present, although there are some technologies that can capture and store carbon dioxide, these technologies often have high cost and require additional energy support. How to convert carbon dioxide into valuable resources and realize its resource utilization has become one of the current research hotspots.

[0005] With the increasing emphasis on environmental protection and sustainable development around the world, wastewater treatment and carbon dioxide emission reduction are no longer isolated problems, but important issues that need to be considered and solved comprehensively. Therefore, developing a technology that can not only efficiently recover valuable metal ions in wastewater, but also simultaneously fix carbon dioxide, not only helps to solve the problems in the fields of wastewater treatment and carbon dioxide emission reduction, but also makes an important contribution to achieving the goal of green and low-carbon sustainable development. SUMMARY

[0006] In order to solve the above technical problems, the present application provides a nucleation granulation method for recovering valuable metal ions in water by using CO2. The method provided by the present application combines CO2 sequestration with wastewater treatment, uses the nucleation granulation technology, promotes the hydrolysis of gaseous CO2 into carbonate under alkaline conditions, and reacts with the valuable metal ions to crystallize and precipitate on the surface of the nucleation granulation seed. The method can not only efficiently recover the valuable metal ions in wastewater, but also simultaneously fix CO2 to reduce its emission, thereby achieving the dual goals of wastewater treatment and CO2 fixation.

[0007] In a first aspect, the present application provides a nucleation granulation method for recovering valuable metal ions in water by using CO2, characterized in that the method comprises the following steps:

[0008] CO2-containing gas is introduced into the wastewater containing valuable metal ions, and the pH value is adjusted to be alkaline. In the presence of nucleation granulation seeds, CO2 is hydrolyzed to generate carbonate ions, which induce the valuable metal ions in the wastewater to crystallize and precipitate in the form of carbonate on the surface of the nucleation granulation seeds, thereby forming carbonate granules.

[0009] It should be noted that the timing of adjusting the pH value is not earlier than the timing of introducing the CO2-containing gas. When the method is continuously operated, the introduction of the alkaline agent to adjust the pH value is preferably started after the introduction of the CO2-containing gas is started. During the operation, the CO2-containing gas and the alkaline agent are introduced synchronously.

[0010] In the present application, CO2 is used as a carbon source and is hydrolyzed to generate carbonate under alkaline conditions, which in turn induces the valuable metal ions in the wastewater to crystallize and precipitate, thereby simultaneously achieving the removal and recovery of valuable metal ions in wastewater and the mineralization and fixation of CO2.

[0011] In the present application, the volume content of CO2 in the CO2-containing gas is preferably above 80%; for example, it can be 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98% or 100%, etc.

[0012] In the present application, the source of CO2 is not particularly limited, which can be obtained by enriching atmospheric air, or high-purity CO2 generated in the production process of large enterprises and in urgent need of sequestration, such as CO2 generated in the industrial processes of oil and gas exploration, chemical production or power generation, etc.

[0013] In some embodiments of the present application, the valuable metal ions include one or more of manganese ions, lead ions, cadmium ions, nickel ions and cobalt ions.

[0014] The valuable metal ions in the present application include metal ions that can react with carbonate ions to form carbonate precipitates, including but not limited to one or more of manganese ions, lead ions, cadmium ions, nickel ions and cobalt ions.

[0015] In the present application, the pH value range can be selected according to the type of valuable metal ions to be removed (solubility product). For example, carbonate precipitation of manganese ions usually starts to form at pH > 8; carbonate precipitation of Pb 2+ starts to form at a pH value of about 8 to 9, and the precipitation is relatively complete at a pH value of 9; cadmium ions form cadmium carbonate precipitate in a pH range of about 9-10; nickel ions form nickel carbonate precipitate in a pH range of 6.4-8.4; carbonate precipitation of cobalt ions forms at a pH value of about 7.65-9.15. As a non-limiting example, the pH value range is 8-10, which can substantially cover the pH range of the above-mentioned valuable metal ions to form precipitates.

[0016] The present application adjusts the pH to an alkaline environment, which helps to promote the hydrolysis of CO2 into carbonate, and improves the hydrolysis efficiency and absorption capacity of CO2.

[0017] In some embodiments of the present application, the pH value is adjusted using an alkaline agent.

[0018] In some embodiments of the present application, the alkaline agent comprises one or more of sodium hydroxide, potassium hydroxide, and preferably sodium hydroxide.

[0019] In some embodiments of the present application, the molar ratio of valuable metal ions to CO2 in the wastewater is 1:(0.8-1.3); for example, it can be 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, or 1:1.3, etc. However, the present application is not limited to the listed values, and other unlisted values within this range are also applicable.

[0020] In some embodiments of the present application, the core seed for granulation comprises a carrier material and alkaline active sites loaded on the carrier material; the material of the alkaline active sites comprises one or more of alkali metal oxides and alkaline earth metal oxides.

[0021] In some embodiments of the present application, the alkali metal oxides comprise one or more of Na2O, K2O, and Rb2O, and the alkaline earth metal oxides comprise CaO.

[0022] In some embodiments of the present application, the carrier material comprises one or more of alumina, molecular sieve, zeolite, activated carbon, and mesoporous silica.

[0023] The nucleation and prilling seed crystal has abundant basic active sites on the surface, the basic active sites have high selectivity and activity, can promote the dissolution and hydrolysis process of gaseous CO2 micro-bubbles, improve the conversion efficiency of carbonate ions, and then induce the valuable metal ions in the wastewater to orderly crystallize with the carbonate ions on the surface of the nucleation and prilling seed crystal to form carbonate precipitates.

[0024] In the present application, the preparation method of the nucleation and prilling seed crystal comprises the following steps:

[0025] (1) mixing a carrier material with a solution of a basic active site precursor, loading the basic active site precursor on the carrier material, and drying to obtain a carrier material loaded with the basic active site precursor;

[0026] (2) calcining the carrier material loaded with the basic active site precursor in a protective atmosphere, decomposing the basic active site precursor to form basic active sites, and obtaining the seed crystal.

[0027] In some embodiments of the present application, the basic active site precursor is one or more of a hydroxide of a metal element in the basic active site, a strong acid-strong base salt, preferably a nitrate of a metal element in the basic active site.

[0028] As a non-limiting example, the basic active site precursor in the present application can include one or more of potassium nitrate, potassium fluoride, potassium hydroxide, sodium nitrate, calcium nitrate and rubidium nitrate.

[0029] In some embodiments of the present application, the ratio of the molar amount of the metal element in the solution of the basic active site precursor to the mass of the carrier material is 0.25-1.7 mmol / g.

[0030] In some embodiments of the present application, the concentration of the metal element in the solution of the basic active site precursor is 0.1-0.5 mol / L.

[0031] In some embodiments of the present application, the mass-to-volume ratio of the carrier material to the solution of the basic active site precursor is 300-400 g / L.

[0032] In some embodiments of the present application, the mixing in step (1) is carried out under stirring.

[0033] In some embodiments of the present application, the temperature of the mixing in step (1) is 40-50℃.

[0034] In some embodiments of the present application, the mixing time in step (1) is 3-5 h.

[0035] In some embodiments of the present invention, the drying temperature in step (1) is 60-80°C.

[0036] In some embodiments of the present invention, the drying time in step (1) is 24-36 hours.

[0037] As a non-limiting example of the present invention, the calcination temperature in step (2) is 600-800°C.

[0038] As a non-limiting example of the present invention, the calcination time in step (2) is 2-4 hours.

[0039] In some embodiments of the present invention, the heating rate of calcination in step (2) is 5-8°C / min.

[0040] In some embodiments of the present invention, the method for preparing the nucleus crystal granulation seed crystal further includes the following steps: before mixing in step (1), the carrier material is ground, sieved through a 60-80 mesh sieve, cleaned and dried.

[0041] In some embodiments of the present invention, the method for preparing the nucleus granulation seed crystal further includes the following steps: after calcination in step (2), the seed crystal is cooled and sieved to remove possible impurities and non-compliant particles, ensuring that the size and performance of the seed crystal meet the requirements.

[0042] In some embodiments of the present invention, the reaction is carried out in a nucleation granulation reactor, which includes a reactor body and an aeration device disposed inside the reactor body. The reactor body is provided with a water inlet, an air inlet, a reagent dosing port and a water outlet, and the air inlet is connected to the aeration device.

[0043] In the main body of the nucleogranulation reactor of the present invention, the air inlet is used for the entry of CO2 gas, the water inlet is used for the entry of wastewater, the water outlet is used for the discharge of treated wastewater, and the reagent dosing port is used for the addition of the alkaline reagent. The aeration device includes an aeration disc or an aeration pipe. The aeration device can ensure that the bubbles are as small as possible to increase the distribution density of CO2 bubbles in the nucleogranulation reactor, increase the amount of CO2 dissolved in the system, accelerate CO2 hydrolysis, increase the concentration of carbonate ions, and at the same time avoid turbulence caused by bubbling from interfering with the fluidization state.

[0044] In some embodiments of the present invention, the method includes the following steps:

[0045] The nucleus crystal granulation seed is filled into the nucleus crystal granulation reactor, and the CO2 gas and the wastewater containing valence metal ions are introduced into the nucleus crystal granulation reactor. The nucleus crystal granulation seed forms a fluidized state under the combined action of water flow and air flow.

[0046] The alkaline agent is simultaneously introduced into the nuclear crystal granulation reactor to adjust the pH of the wastewater to 8-10;

[0047] Under the combined action of the nucleus crystal seed and the alkaline agent, CO2 hydrolyzes to produce carbonate ions, which induce valuable metal ions in the wastewater to crystallize orderly on the surface of the nucleus crystal seed in the form of carbonate precipitates. Further, under the action of volumetric compression, the crystals shrink and dehydrate to form carbonate granules.

[0048] The continuous operation of the nucleogranulation reactor described in this invention allows carbonate precipitates to continuously adhere to the surface of the seed crystals. Under high-intensity volumetric compression, the water in the liquid film between the particles is rapidly removed, forming a local negative pressure that generates a shrinkage and dehydration effect, ultimately forming a dense carbonate granule that can be directly separated and recovered from the reactor.

[0049] In this invention, no special restrictions are placed on the specific reaction conditions during the nucleation process, such as aeration flow rate, water inflow rate, and hydraulic residence time (reaction time). Those skilled in the art can adjust these conditions according to the actual wastewater quality and treatment efficiency to ensure that metal ions and CO2 react fully to form carbonate precipitates.

[0050] As a non-limiting example, the filling amount of the nucleation granulation seed crystal is 25-30% of the effective height of the nucleation granulation reactor, such as 26%, 27%, 28%, 29%, etc.

[0051] As a non-limiting example, the hydraulic residence time of the wastewater in the nucleogranulation reactor is ≥5 min, for example, it can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 50 min, 60 min, etc.

[0052] As a non-limiting example, the flow rate of CO2-containing gas (calculated as CO2) in this invention can be 200-400 mL / min (e.g., 200 mL / min, 220 mL / min, 250 mL / min, 280 mL / min, 300 mL / min, 320 mL / min, 350 mL / min, 380 mL / min, 400 mL / min, etc.). To avoid the interference of dilution on the metal ion removal efficiency, the influent flow rate of the alkaline agent can be 5-10% of the influent flow rate (e.g., 5%, 6%, 7%, 8%, 9%, 10%, etc.), and the influent concentration can be 1.1-1.25 times the metal ion concentration. The influent flow rate of the nucleogranulation reactor can be 20-40 L / h, and the hydraulic retention time ≥5 min, to ensure that carbon dioxide is fully hydrolyzed into carbonate ions, inducing metal ion precipitation and forming carbonate granules, thereby enabling the recovery of as many valuable metal ions as possible.

[0053] In some embodiments of the present invention, the method further includes: when the concentration of valuable metal ions in the effluent of the nucleo-granulation reactor does not meet the treatment requirements or emission standards, returning the effluent to the nucleo-granulation reactor for further treatment until the concentration of valuable metal ions in the effluent meets the treatment requirements or emission standards.

[0054] If the concentration of valuable metal ions in the wastewater is too high, it can be circulated into the nucleation granulation reactor until the effluent meets the requirements for reuse or discharge.

[0055] The method described in this invention is not only applicable to simultaneous carbon sequestration in wastewater treatment alone, but can also be applied to the simultaneous treatment of waste gas and wastewater discharged from waste incineration plants, thermal power plants, oil processing enterprises, metal smelting industries, etc., to achieve carbon dioxide fixation and storage, efficient recovery of valuable ions, wastewater recycling and reuse, and full utilization of limited resources.

[0056] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art:

[0057] 1. High processing efficiency: The method provided by this invention utilizes nucleus crystal granulation technology. Through the combined action of water flow and air flow, the seed crystals inside the reactor are fluidized. The gas and liquid collide and react with each other to generate carbonates, which crystallize and precipitate on the surface of the seed crystals. This improves the efficiency of the reaction and the quality of the precipitation, making the carbonate precipitate easier to separate and process.

[0058] 2. Resource utilization: The method provided by this invention converts gaseous CO2 into carbonate ions, which are used as a precipitant, thereby enabling the resource utilization of carbon dioxide and reducing its emissions. At the same time, it simultaneously achieves the efficient recovery of valuable metal ions in wastewater and the fixation and storage of gaseous CO2.

[0059] 3. Simple operation: The device used in the method provided by this invention has a simple structure and is easy to operate. It is suitable for wastewater treatment of various scales in various energy and chemical industries such as waste incineration plants, thermal power plants, oil processing, and metal smelting.

[0060] 4. Good economic benefits: The method provided by this invention can further reduce the cost of wastewater treatment and improve economic benefits by recovering and utilizing carbonate precipitates, and has broad application prospects. Detailed Implementation

[0061] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0062] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0063] The seed crystals used in this embodiment of the invention include a carrier coconut shell activated carbon and alkaline active sites K2O loaded on the carrier coconut shell activated carbon. The preparation method is as follows:

[0064] Select coconut shell activated carbon with a high specific surface area (strength 95%, specific surface area approximately 950 m²). 2 / g) as the carrier material. First, the coconut shell activated carbon was ground and sieved to obtain 60-80 mesh. It was repeatedly washed three times with deionized water and dried in an oven at 80℃ for 6 hours to constant weight. 5.06g of KNO3 was dissolved in 200mL of deionized water to prepare a 0.25mol / L potassium nitrate solution. 60g of the pretreated coconut shell activated carbon carrier was added to the potassium nitrate solution and stirred continuously at 45℃ for 4 hours to fully load the potassium nitrate. Then, it was dried in an oven at 70℃ for 32 hours to obtain potassium nitrate-loaded coconut shell activated carbon. Subsequently, it was placed in a covered crucible and heated to 700℃ at a heating rate of 6℃ / min under a nitrogen atmosphere and held at that temperature for 3 hours. After calcination, it was naturally cooled and sieved again to obtain 60-80 mesh nucleated seed crystals (named FC-ac).

[0065] Example 1

[0066] This embodiment provides a method for recovering calcium ions from water using CO2, including the following steps:

[0067] The nuclear crystal granulation reactor is filled with nuclear crystal seed FC-ac, with a filling amount of 25% of the effective height of the reactor. 50L of wastewater to be treated (initial calcium ion concentration of 1200mg / L) is introduced into the nuclear crystal granulation reactor at a flow rate of 40L / h. At the same time, gaseous CO2 is introduced into the nuclear crystal granulation reactor through the aeration disc at a flow rate of 200mL / min. The nuclear crystal seed forms a fluidized state under the combined action of water flow and air flow.

[0068] Sodium hydroxide solution was simultaneously introduced into the nucleation granulation reactor at an influent flow rate of 7% to make the sodium hydroxide concentration in the reactor reach 1.2 times the initial calcium ion concentration (1440 mg / L), maintain the pH value of the wastewater in the reaction zone at about 9, and the hydraulic retention time in the reactor is about 14 min.

[0069] Under the combined action of nucleation crystal seed crystals and sodium hydroxide solution, gaseous CO2 undergoes efficient hydrolysis to produce carbonate ions. These carbonate ions react with calcium ions in the wastewater to form a white calcium carbonate precipitate. Due to the presence of proprietary nucleation crystal seed crystals inside the nucleation granulation reactor, the precipitate gradually adheres to the seed crystal surface. Subsequently, under high-intensity volumetric compression, water in the liquid film between particles is rapidly expelled, creating a localized negative pressure. This causes the calcium carbonate precipitate to grow stepwise on the seed crystal surface and shrink and dehydrate, ultimately forming a dense, almost anhydrous calcium carbonate granule.

[0070] After treatment, the calcium ion concentration was reduced to 78 mg / L, and the calcium ion recovery rate was 93.5%. The separated calcium carbonate granules can be used to produce building materials, fertilizers, etc. after drying.

[0071] Example 2

[0072] This embodiment provides a method for recovering manganese ions from water using CO2, including the following steps:

[0073] The nuclear crystal granulation reactor is filled with nuclear crystal seed crystals FC-ac, with a filling volume of 30% of the effective height of the reactor. 50L of wastewater to be treated (initial manganese ion concentration of 1000mg / L) is introduced into the nuclear crystal granulation reactor at a flow rate of 35L / h. At the same time, gaseous CO2 is introduced into the nuclear crystal granulation reactor through an aeration disc at a flow rate of 300mL / min. The nuclear crystal seed crystals are fluidized under the combined action of water flow and air flow.

[0074] Sodium hydroxide solution was simultaneously introduced into the nucleation granulation reactor at an influent flow rate of 8% to make the sodium hydroxide concentration in the reactor reach 1.1 times the initial manganese ion concentration (1100 mg / L), maintain the pH value of the wastewater in the reaction zone at about 8, and the hydraulic retention time in the reactor was about 15.87 min.

[0075] Under the combined action of nucleation crystal seed crystals and sodium hydroxide solution, gaseous CO2 undergoes efficient hydrolysis to produce carbonate ions. These carbonate ions react with calcium ions in the wastewater to form a white manganese carbonate precipitate. Due to the presence of proprietary nucleation crystal seed crystals inside the nucleation crystal granulation reactor, the precipitate gradually adheres to the seed crystal surface. Subsequently, under high-intensity volumetric compression, water in the liquid film between particles is rapidly expelled, creating a localized negative pressure. This causes the manganese carbonate precipitate to grow stepwise on the seed crystal surface and then shrink and dehydrate, ultimately forming a dense, almost anhydrous manganese carbonate granule.

[0076] After treatment, the manganese ion concentration was reduced to 57 mg / L, and the manganese ion recovery rate was 94.3%. The separated manganese carbonate granules can be directly fed into an electrolytic cell for electrolytic production of metallic manganese products, such as manganese oxide and manganese sulfate. These manganese salts have wide industrial applications, such as in the production of steel, electronic products, and chemical products.

[0077] Example 3

[0078] This embodiment provides a method for recovering cobalt ions from water using CO2. The initial cobalt ion concentration is 2500 mg / L. Due to the excessively high initial cobalt ion concentration, single-stage nucleation granulation cannot achieve efficient recovery of cobalt ions. This embodiment utilizes a nucleation granulation reactor with three cycles to achieve granulation recovery of cobalt ions from wastewater. The steps include:

[0079] The nuclear crystal granulation reactor is filled with nuclear crystal seed FC-ac, with a filling amount of 30% of the effective height of the reactor. 50L of wastewater to be treated is introduced into the nuclear crystal granulation reactor at a flow rate of 35L / h. At the same time, gaseous CO2 is introduced into the nuclear crystal granulation reactor through the aeration disc at a flow rate of 300mL / min. The nuclear crystal seed forms a fluidized state under the combined action of water flow and air flow.

[0080] Sodium hydroxide solution was introduced into the nucleation granulation reactor at a flow rate of 5% per liter of cobalt ion in each cycle. The total amount of sodium hydroxide added in the three cycles was 1.15 times the initial cobalt ion concentration (i.e., the total amount of sodium hydroxide added per liter of cobalt-containing wastewater was 2875 mg). The concentration of sodium hydroxide in the reactor was 1550 mg / L in the first cycle, 730 mg / L in the second cycle, and 595 mg / L in the third cycle. The pH value of the wastewater in the reaction zone was maintained at around 8.5 in each cycle, and the hydraulic retention time in the reactor was about 16.33 min.

[0081] Under the combined action of nucleation crystal seed crystals and sodium hydroxide solution, gaseous CO2 undergoes efficient hydrolysis to produce carbonate ions. These carbonate ions react with calcium ions in the wastewater to form a white cobalt carbonate precipitate. Due to the presence of proprietary nucleation crystal seed crystals inside the nucleation crystal granulation reactor, the precipitate gradually adheres to the seed crystal surface. Subsequently, under high-intensity volumetric compression, the water in the liquid film between the particles is rapidly expelled, creating a localized negative pressure. This causes the cobalt carbonate precipitate to grow stepwise on the seed crystal surface and shrink and dehydrate, ultimately forming a dense cobalt carbonate granule that is almost anhydrous.

[0082] Analysis of the effluent from the nucleation granulation reactor revealed that the cobalt ion concentration decreased to 1153 mg / L after the first treatment, 524 mg / L after the second treatment, and 48 mg / L after the third treatment. After three cycles of treatment, the final cobalt ion recovery rate was 98.08%. The separated cobalt carbonate granules can be used in battery manufacturing for the new energy industry, or to produce other cobalt salts and cobalt oxide for use in chemical, metallurgical, and other fields, or as a mineral processing agent to achieve efficient separation and purification of ores.

[0083] Comparative Example 1

[0084] This comparative example provides a method for recovering cobalt ions from water using CO2. The difference from Example 1 is that the nucleated crystal granulation seed FC-ac is replaced with ordinary seed quartz sand.

[0085] In this comparative study, the calcium ion concentration in the effluent of the nucleogranulation reactor was reduced to 521 mg / L, and the calcium ion recovery rate was 56.58%.

[0086] The results of Example 1 and Comparative Example 1 show that the removal efficiency of metal ions by the nucleus crystal granulation seed used in this invention is significantly higher than that of ordinary seed garnet. Furthermore, since the metal ions are converted into carbonates, the mineralization and fixation efficiency of carbon dioxide is also significantly higher than that of ordinary seed garnet.

[0087] In summary, the method for recovering valuable metal ions from water using CO2 provided by this invention can not only efficiently recover valuable metal ions from wastewater, but also simultaneously fix carbon dioxide, reducing its emissions. This achieves the dual goals of wastewater treatment and carbon dioxide fixation, making an important contribution to achieving green and low-carbon sustainable development goals, and has broad application prospects.

[0088] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0089] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for nucleogranulation to recover valuable metal ions from water using CO2, characterized in that, The method includes the following steps: CO2 gas is introduced into wastewater containing valence metal ions, and the pH value is adjusted to alkaline. In the presence of nucleus crystal seed crystals, CO2 hydrolyzes to produce carbonate ions, which induce the valence metal ions in the wastewater to crystallize in an orderly manner on the surface of the nucleus crystal seed crystals in the form of carbonate precipitates, forming carbonate granules. The nucleus crystal granulation seed crystal includes a carrier material and basic active sites loaded on the carrier material; The materials for the basic active sites include one or more of alkali metal oxides and alkaline earth metal oxides; The alkali metal oxide includes one or more of Na2O, K2O and Rb2O, and the alkaline earth metal oxide includes CaO.

2. The method according to claim 1, characterized in that, The valuable metal ions include one or more of manganese ions, lead ions, cadmium ions, nickel ions, and cobalt ions.

3. The method according to claim 1, characterized in that, The pH value ranges from 8 to 10.

4. The method according to claim 3, characterized in that, The pH value is adjusted using an alkaline agent.

5. The method according to claim 4, characterized in that, The alkaline agent includes one or more of sodium hydroxide and potassium hydroxide.

6. The method according to claim 4, characterized in that, The alkaline agent is sodium hydroxide.

7. The method according to claim 1, characterized in that, The molar ratio of valuable metal ions to CO2 in the wastewater is 1:(0.8-1.3).

8. The method according to claim 1, characterized in that, The volume content of CO2 in the CO2-containing gas is above 80%.

9. The method according to claim 1, characterized in that, The carrier material includes one or more of alumina, molecular sieve, zeolite, activated carbon, and mesoporous silica.

10. The method according to any one of claims 1-9, characterized in that, The reaction is carried out in a nucleation granulation reactor, which includes a reactor body and an aeration device disposed inside the reactor body. The reactor body is provided with a water inlet, an air inlet, a reagent dosing port and a water outlet, and the air inlet is connected to the aeration device.

11. The method according to claim 10, characterized in that, The method includes the following steps: The nucleus crystal granulation seed is filled into the nucleus crystal granulation reactor, and the CO2 gas and the wastewater containing valence metal ions are introduced into the nucleus crystal granulation reactor. The nucleus crystal granulation seed forms a fluidized state under the combined action of water flow and air flow. The alkaline agent is simultaneously introduced into the nuclear crystal granulation reactor to adjust the pH of the wastewater to 8-10; Under the combined action of the nucleus crystal seed and the alkaline agent, CO2 hydrolyzes to produce carbonate ions, which induce valuable metal ions in the wastewater to crystallize orderly on the surface of the nucleus crystal seed in the form of carbonate precipitates. Further, under the action of volumetric compression, the crystals shrink and dehydrate to form carbonate granules.

12. The method according to claim 11, characterized in that, The amount of seed crystals used in the nucleo-granulation process is 25-30% of the effective height of the nucleo-granulation reactor.

13. The method according to claim 11, characterized in that, The hydraulic residence time of the wastewater in the nucleogranulation reactor is ≥5 min.

14. The method according to claim 11, characterized in that, The method further includes: when the concentration of valuable metal ions in the effluent of the nucleo-granulation reactor does not meet the treatment requirements or emission standards, returning the effluent to the nucleo-granulation reactor for further treatment until the concentration of valuable metal ions in the effluent meets the treatment requirements or emission standards.