Nucleus granulation method for recycling valuable metal ions in water by using CO2

Abstract

The invention provides a nucleation granulation method for recycling valuable metal ions in water by using CO2, and relates to the field of wastewater treatment. According to the method provided by the invention, CO2-containing gas is introduced into wastewater containing valuable metal ions, the pH value is adjusted to be alkaline, CO2 is hydrolyzed to generate carbonate ions in the presence of nucleation granulation seed crystals, and the valuable metal ions in the wastewater are induced to be crystallized and precipitated orderly on the surfaces of the nucleation granulation seed crystals. The method is high in treatment efficiency and simple and convenient in process, wastewater can be recycled, CO2 discharged by enterprises can be fully utilized, the dual purposes of recovery of valuable metal ions in wastewater and fixed emission reduction of CO2 can be synchronously achieved, and the method has important practical significance and popularization value.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a nucleus crystal granulation method for recovering valuable metal ions in water by utilizing CO2. Background Art

[0002] There is a large amount of wastewater discharge containing high-valent metal ions in the energy and chemical industry, waste incineration, thermal power, oil processing, metal smelting and other industries. If the metal ions in these wastewaters, such as copper, zinc, nickel, lead, etc., are directly discharged into the environment without proper treatment, they will cause serious pollution to water bodies, soil and ecosystems. In addition, metal ions accumulate in water bodies and may enter the human body through the food chain, posing a potential threat to human health. Therefore, the effective recovery of valuable metal ions in wastewater is not only related to the efficient use of resources, but also an urgent need to protect the ecological environment and human health.

[0003] There are many traditional treatment methods for the recovery of valuable metal ions in wastewater, such as chemical precipitation, ion exchange, electrolysis, etc. However, these methods have many limitations in practical applications. Although the chemical precipitation method is simple to operate, the recovery rate is low, and the sludge produced is difficult to handle; although the ion exchange method has a high recovery rate, the equipment investment is large and the operating cost is high; the electrolysis method consumes a lot of electricity and has high requirements for the water quality of the wastewater. In addition, these methods often only focus on the recovery of metal ions, while ignoring the secondary pollution problems that may occur during the wastewater treatment process.

[0004] At the same time, the flue gas generated by the energy and chemical industries during the production process contains a large amount of carbon dioxide. The emission of these carbon dioxide not only exacerbates global climate change, but also wastes precious carbon resources. At present, although there are some technologies that can capture and store carbon dioxide, these technologies are often costly 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 global attention paid to environmental protection and sustainable development, wastewater treatment and carbon dioxide emission reduction are no longer isolated issues, but important topics that require comprehensive consideration and coordinated solutions. Therefore, developing a technology that can both efficiently recover valuable metal ions in wastewater and simultaneously fix carbon dioxide will not only help solve the difficult problems in the fields of wastewater treatment and carbon dioxide emission reduction, but also make important contributions to achieving green, low-carbon and sustainable development goals. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a nuclear crystal granulation method for recovering valuable metal ions in water using CO2. The method provided by the present invention combines CO2 storage with wastewater treatment, and utilizes nuclear crystal granulation technology to promote the hydrolysis of gaseous CO2 into carbonate under alkaline conditions and react with valuable metal ions, and crystallizes and precipitates on the surface of nuclear crystal granulation seeds, which can not only efficiently recover valuable metal ions in wastewater, but also simultaneously fix carbon dioxide and reduce its emission, thereby achieving the dual goals of wastewater treatment and carbon dioxide fixation.

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

[0008] CO2 gas is introduced into wastewater containing valuable metal ions, and the pH value is adjusted to alkaline. In the presence of nucleus crystal granulation seeds, CO2 is hydrolyzed to produce carbonate ions, which induce the valuable metal ions in the wastewater to crystallize in an orderly manner on the surface of the nucleus crystal granulation seeds in the form of carbonate precipitates to form carbonate granules.

[0009] It should be noted that the timing of adjusting the pH value in the present invention is not earlier than the timing of introducing the CO2-containing gas. When the method is continuously operated, it is preferred that the alkaline agent is introduced to adjust the pH value after the CO2-containing gas is introduced, and the CO2-containing gas and the alkaline agent are introduced simultaneously during the operation.

[0010] In the present invention, CO2 is used as a carbon source and is hydrolyzed under alkaline conditions to generate carbonate ions, which then induce the crystallization and precipitation of valuable metal ions in the wastewater, thereby simultaneously achieving the removal and recovery of valuable metal ions in the wastewater and the mineralization and fixation of carbon dioxide.

[0011] In the present invention, 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] The present invention does not impose any special restrictions on the source of CO2, which can be obtained by enriching the atmosphere, or it can be high-purity carbon dioxide generated in the production process of large enterprises and urgently needs to be sealed, such as CO2 generated in industrial processes such as oil and gas extraction, chemical production or power generation.

[0013] In some embodiments of the present invention, 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 described in the present invention include metal ions that can react with carbonate ions to generate 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 invention, the pH range can be selected according to the type (solubility product) of the valuable metal ions to be removed. For example, carbonate precipitation of manganese ions usually begins to form at pH>8; 2+ The carbonate precipitation of ions begins to form at a pH value of about 8 to 9, and the precipitation is relatively complete at a pH value of 9; the pH range for cadmium ions to form cadmium carbonate precipitation is about 9-10; the pH range for nickel ions to form nickel carbonate precipitation is 6.4-8.4; and the carbonate precipitation of cobalt ions is formed between pH values ​​of about 7.65-9.15. As a non-limiting example, the pH range is 8-10, which can basically cover the pH range for the above-mentioned valuable metal ions to form precipitation.

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

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

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

[0019] In some embodiments of the present invention, the molar ratio of the 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 invention is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0020] In some embodiments of the present invention, the nucleation granulation seed comprises a carrier material and alkaline active sites supported 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 invention, the alkali metal oxide includes one or more of Na2O, K2O and Rb2O, and the alkaline earth metal oxide includes CaO.

[0022] In some embodiments of the present invention, the support material includes one or more of alumina, molecular sieves, zeolites, activated carbon and mesoporous silica.

[0023] The surface of the core crystal granulation seed described in the present invention is rich in alkaline active sites, which are highly selective and active, can promote the dissolution and hydrolysis process of gaseous CO2 microbubbles, improve the conversion efficiency of carbonate ions, and further induce the orderly crystallization of valuable metal ions and carbonate ions in the wastewater on the surface of the core crystal granulation seed to form carbonate precipitates.

[0024] In the present invention, the method for preparing the nucleus crystal granulation seed comprises the following steps:

[0025] (1) mixing a support material with a solution of an alkaline active site precursor so that the alkaline active site precursor is loaded on the support material, and drying to obtain a support material loaded with the alkaline active site precursor;

[0026] (2) calcining the carrier material carrying the alkaline active site precursor in a protective atmosphere to decompose the alkaline active site precursor to form alkaline active sites, thereby obtaining the seed crystal.

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

[0028] As a non-limiting example, the alkaline active site precursor in the present invention may 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 invention, the ratio of the molar amount of the metal element in the solution of the alkaline active site precursor to the mass of the support material is 0.25-1.7 mmol / g.

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

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

[0032] In some embodiments of the present invention, the mixing in step (1) is performed under stirring conditions.

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

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

[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 in the present invention, the calcination temperature in step (2) is 600-800°C.

[0038] As a non-limiting example in 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 the calcination in step (2) is 5-8°C / min.

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

[0041] In some embodiments of the present invention, the method for preparing the core crystal granulation seed further comprises the following steps: after the calcination in step (2), cooling and screening the seed to remove possible impurities and particles that do not meet the requirements, so as to ensure that the size and performance of the seed meet the requirements.

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

[0043] In the nuclear crystal granulation reactor body of the present invention, the air inlet is used for the entry of CO2-containing 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 injection port is used for the injection of the alkaline reagent. The aeration device includes an aeration disk or an aeration tube, and the aeration device can ensure that the bubbles are as small as possible to increase the distribution density of CO2 bubbles in the nuclear crystal granulation reactor, increase the amount of CO2 dissolved in the system, accelerate CO2 hydrolysis, and increase the concentration of carbonate ions, while avoiding turbulence caused by bubbling to interfere with the fluidization state.

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

[0045] The nuclear crystal granulation reactor is filled with the nuclear crystal granulation seeds, the CO2-containing gas and the wastewater containing the valuable metal ions are introduced into the nuclear crystal granulation reactor, and the nuclear crystal granulation seeds form a fluidized state under the combined action of the water flow and the air flow;

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

[0047] Under the joint action of the core crystal granulation seed and the alkaline agent, CO2 is hydrolyzed to produce carbonate ions, which induce the valuable metal ions in the wastewater to crystallize in an orderly manner on the surface of the core crystal granulation seed in the form of carbonate precipitation, and further shrink and dehydrate under the action of volume extrusion to form carbonate granulation bodies.

[0048] The continuous operation of the nuclear crystal granulation reactor described in the present invention can make the carbonate precipitate continuously adhere to the surface of the seed crystal. Under the high-intensity volume extrusion effect, the moisture in the liquid film between the particles is quickly removed, forming a local negative pressure to produce a shrinkage and dehydration effect, and finally forming a dense carbonate granulation body, which can be directly separated and recovered from the reactor.

[0049] In the present invention, there is no special restriction on the specific reaction conditions in the nuclear crystal granulation process, such as ventilation flow rate, water inlet flow rate, hydraulic retention time (reaction time), etc., and those skilled in the art can adjust them according to the water quality and treatment efficiency of the actual wastewater to ensure that the metal ions and CO2 fully react to form carbonate precipitates.

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

[0051] As a non-limiting example, the hydraulic retention time of the wastewater in the core crystal granulation 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 gas flow rate of the CO2-containing gas of the present invention (in terms of CO2) can be 200-400mL / min (for example, 200mL / min, 220mL / min, 250mL / min, 280mL / min, 300mL / min, 320mL / min, 350mL / min, 380mL / min, 400mL / min, etc.). In order to avoid the interference of dilution on the metal ion removal efficiency, the feed flow rate of the alkaline agent can be 5-10% of the water flow rate (for example, 5%, 6%, 7%, 8%, 9%, 10%, etc.), the feed concentration can be 1.1-1.25 times the metal ion concentration, the water flow rate of the nuclear crystal granulation reactor can be 20-40L / h, and the hydraulic retention time is ≥5min, so as to ensure that the carbon dioxide is fully hydrolyzed into carbonate ions, induce metal ion precipitation, and form carbonate granulation bodies, so that as many valuable metal ions as possible are recovered.

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

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

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

[0057] 1. High processing efficiency: The method provided by the present invention utilizes the nuclear crystal granulation technology to form a fluidized state of the seed crystals inside the reactor through the combined action of water flow and air flow. The gas and liquid collide with each other to react and generate carbonate crystals that precipitate on the surface of the seed crystals, thereby improving the reaction efficiency and precipitation quality, and making the carbonate precipitate easier to separate and process.

[0058] 2. Resource utilization: The method provided by the present invention converts gaseous CO2 into carbonate ions and uses them as precipitants, thereby making resource utilization of carbon dioxide and reducing its emissions. At the same time, it simultaneously achieves efficient recovery of valuable metal ions in wastewater and fixed storage of gaseous CO2.

[0059] 3. Easy operation: The device used in the method provided by the present 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 the present 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 DESCRIPTION

[0061] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0062] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0063] The core crystal granulation seed used in the embodiment of the present invention includes a carrier coconut shell activated carbon and alkaline active sites K2O supported on the carrier coconut shell activated carbon, and the preparation method thereof is as follows:

[0064] Choose coconut shell activated carbon with high specific surface area (strength 95%, specific surface area about 950m 2 / g) as a carrier material. First, grind and screen to obtain 60-80 mesh coconut shell activated carbon, wash it repeatedly three times with deionized water, and dry it in an oven at 80°C for 6h to constant weight; dissolve 5.06g KNO3 in 200mL deionized water to prepare a potassium nitrate solution with a concentration of 0.25mol / L; add 60g of pretreated coconut shell activated carbon carrier to the above potassium nitrate solution, stir continuously at 45°C for 4 hours to fully load potassium nitrate, and then dry it in an oven at 70°C for 32 hours to obtain coconut shell activated carbon loaded with potassium nitrate; then place it in a covered crucible, heat it to 700°C at a heating rate of 6°C / min under a nitrogen atmosphere, and keep it warm for 3 hours; after calcination, cool it naturally and screen it again to obtain 60-80 mesh nuclear crystal granulation seeds (named FC-ac).

[0065] Example 1

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

[0067] Fill the nuclear crystal granulation reactor with nuclear crystal granulation seeds FC-ac, the filling amount of which is 25% of the effective height of the reactor, and introduce 50L of wastewater to be treated (with an initial calcium ion concentration of 1200mg / L) into the nuclear crystal granulation reactor at a flow rate of 40L / h, and at the same time introduce gaseous CO2 into the nuclear crystal granulation reactor through an aeration plate at a gas flow rate of 200mL / min, so that the nuclear crystal granulation seeds form a fluidized state under the combined action of water flow and air flow;

[0068] Sodium hydroxide solution was introduced into the nuclear crystal granulation reactor at a water 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), and the pH value of the wastewater in the reaction zone was maintained at about 9. The hydraulic retention time in the reactor was about 14 minutes;

[0069] Under the combined action of the nuclear crystal granulation seeds and the sodium hydroxide solution, the gaseous CO2 is efficiently hydrolyzed to produce carbonate ions, which react with the calcium ions in the wastewater to form white calcium carbonate precipitates. Due to the presence of the proprietary nuclear crystal granulation seeds inside the nuclear crystal granulation reactor, the precipitate will gradually adhere to the surface of the seeds, and then under the high-intensity volume extrusion, the water in the liquid film between the particles is quickly removed to form a local negative pressure, so that the calcium carbonate precipitate grows step by step on the surface of the seeds and shrinks and dehydrates, and finally forms a dense calcium carbonate granulation body that is almost free of water.

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

[0071] Example 2

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

[0073] The nuclear crystal granulation reactor is filled with nuclear crystal granulation seeds FC-ac, the filling amount of which is 30% of the effective height of the reactor, 50L of wastewater to be treated (with an initial manganese ion concentration of 1000mg / L) is introduced into the nuclear crystal granulation reactor at a flow rate of 35L / h, and gaseous CO2 is introduced into the nuclear crystal granulation reactor at a flow rate of 300mL / min through an aeration plate, and the nuclear crystal granulation seeds form a fluidized state under the combined action of water flow and air flow;

[0074] Sodium hydroxide solution was introduced into the nuclear crystal granulation reactor at a water 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), and the pH value of the wastewater in the reaction zone was maintained at about 8. The hydraulic retention time in the reactor was about 15.87 min.

[0075] Under the combined action of the nuclear crystal granulation seeds and the sodium hydroxide solution, the gaseous CO2 is efficiently hydrolyzed to produce carbonate ions, which react with the calcium ions in the wastewater to form white manganese carbonate precipitates. Due to the presence of the proprietary nuclear crystal granulation seeds inside the nuclear crystal granulation reactor, the precipitate will gradually adhere to the surface of the seeds, and then under the high-intensity volume extrusion, the water in the liquid film between the particles is quickly removed to form a local negative pressure, so that the manganese carbonate precipitates on the surface of the seeds grow step by step and shrink and dehydrate, and finally form a dense manganese carbonate granulation body that is almost free of water.

[0076] After treatment, the manganese ion concentration is reduced to 57 mg / L, and the manganese ion recovery rate is 94.3%. The separated manganese carbonate granules can be directly put into the electrolytic cell for electrolysis to produce metallic manganese products, such as manganese oxide and manganese sulfate. These manganese salts are widely used in industry, such as in the production of steel, electronic products, chemical products, etc.

[0077] Example 3

[0078] This embodiment provides a method for recovering cobalt ions in water using CO2. The initial concentration of cobalt ions is 2500 mg / L. Since the initial concentration of cobalt ions is too high, single-stage nuclear crystal granulation cannot achieve efficient recovery of cobalt ions. This embodiment realizes granulation recovery of cobalt ions in wastewater by three cycles of nuclear crystal granulation reactor. The steps are as follows:

[0079] Fill the nuclear crystal granulation reactor with nuclear crystal granulation seeds FC-ac, the filling amount of which is 30% of the effective height of the reactor, and introduce 50L of wastewater to be treated into the nuclear crystal granulation reactor at a flow rate of 35L / h. Meanwhile, gaseous CO2 is introduced into the nuclear crystal granulation reactor through an aeration plate at a gas flow rate of 300mL / min. The nuclear crystal granulation seeds form a fluidized state under the combined action of water flow and air flow;

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

[0081] Under the combined action of the nuclear crystal granulation seeds and the sodium hydroxide solution, the gaseous CO2 is efficiently hydrolyzed to produce carbonate ions, which react with the calcium ions in the wastewater to form white cobalt carbonate precipitates. Due to the presence of the proprietary nuclear crystal granulation seeds inside the nuclear crystal granulation reactor, the precipitate will gradually adhere to the surface of the seeds, and then under the high-intensity volume extrusion, the water in the liquid film between the particles is quickly removed to form a local negative pressure, causing the cobalt carbonate precipitate to grow step by step on the surface of the seeds and shrink and dehydrate, eventually forming a dense cobalt carbonate granulation body that is almost free of water.

[0082] Testing of the effluent from the nuclear crystal granulation reactor revealed that the concentration of cobalt ions in the effluent was reduced 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 recovery rate of cobalt ions in the effluent was 98.08%. The separated cobalt carbonate granules can be used for battery manufacturing in the new energy industry, and can also be used to produce other cobalt salts and cobalt oxides for use in chemical, metallurgical and other fields, or used as a mineral separation agent to achieve efficient separation and purification of ores.

[0083] Comparative Example 1

[0084] This comparative example provides a method for recovering cobalt ions in water by utilizing CO2, which differs from Example 1 in that the nucleus crystal granulation seed FC-ac is replaced by ordinary seed quartz sand.

[0085] In this comparative example, the calcium ion concentration of the effluent from the nuclear crystal granulation reactor was reduced to 521 mg / L, and the calcium ion recovery rate was 56.58%.

[0086] It can be seen from the results of Example 1 and Comparative Example 1 that the core crystal granulation seeds used in the present invention have a significantly higher removal efficiency for metal ions than ordinary seed garnets, and because the metal ions are converted into carbonates, the corresponding mineralization and fixation efficiency of carbon dioxide is also significantly higher than ordinary seed garnets.

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

[0088] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0089] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be 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 present invention. Therefore, the present invention will not be limited to the embodiments described herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for recovering valuable metal ions from water using CO2, characterized in that: The method comprises the following steps: CO2 gas is introduced into wastewater containing valuable metal ions, and the pH value is adjusted to alkaline. In the presence of nucleus crystal granulation seeds, CO2 is hydrolyzed to produce carbonate ions, which induce the valuable metal ions in the wastewater to crystallize in an orderly manner on the surface of the nucleus crystal granulation seeds in the form of carbonate precipitates to form carbonate granules.

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 or 2, characterized in that: The pH value ranges from 8 to 10; Preferably, the pH value is adjusted using an alkaline agent; Preferably, the alkaline agent includes one or more of sodium hydroxide and potassium hydroxide, preferably sodium hydroxide.

4. The method according to any one of claims 1 to 3, characterized in that: The molar ratio of the valuable metal ions to CO2 in the wastewater is 1:(0.8-1.3); Preferably, the volume content of CO2 in the CO2-containing gas is above 80%.

5. The method according to any one of claims 1 to 4, characterized in that: The nucleation granulation seed 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; Preferably, the alkali metal oxide includes one or more of Na2O, K2O and Rb2O, and the alkaline earth metal oxide includes CaO; Preferably, the support material comprises one or more of alumina, molecular sieve, zeolite, activated carbon and mesoporous silica.

6. The method according to any one of claims 1 to 5, characterized in that: The reaction is carried out in a nuclear crystal granulation reactor, which includes a reactor body and an aeration device arranged inside the reactor body. The reactor body is provided with a water inlet, an air inlet, a reagent addition port and a water outlet, and the air inlet is connected to the aeration device.

7. The method according to claim 6, characterized in that The method comprises the following steps: The nuclear crystal granulation reactor is filled with the nuclear crystal granulation seeds, the CO2-containing gas and the wastewater containing the valuable metal ions are introduced into the nuclear crystal granulation reactor, and the nuclear crystal granulation seeds form a fluidized state under the combined action of the water flow and the air flow; The alkaline agent is simultaneously introduced into the nuclear crystal granulation reactor to adjust the pH value of the wastewater to 8-10; Under the joint action of the core crystal granulation seed and the alkaline agent, CO2 is hydrolyzed to produce carbonate ions, which induce the valuable metal ions in the wastewater to crystallize in an orderly manner on the surface of the core crystal granulation seed in the form of carbonate precipitation, and further shrink and dehydrate under the action of volume extrusion to form carbonate granulation bodies.

8. The method according to any one of claims 1 to 7, characterized in that: The filling amount of the core crystal granulation seeds is 25-30% of the effective height of the core crystal granulation reactor.

9. The method according to any one of claims 1 to 8, characterized in that: The hydraulic retention time of the wastewater in the core crystal granulation reactor is ≥5 min.

10. The method according to any one of claims 1 to 9, characterized in that: The method also includes: when the concentration of valuable metal ions in the effluent of the core crystal granulation reactor does not meet the treatment requirements or emission standards, returning the effluent to the core crystal granulation reactor for further treatment until the concentration of valuable metal ions in the effluent meets the treatment requirements or emission standards.