A method for carbonation of co2 sequestration based on vanadium-containing shale tailings

Abstract

The present application relates to the field of industrial solid waste resourceization and carbon sequestration, in particular to a carbon sequestration method based on carbonate mineralization of CO2 from vanadium-containing shale tailings, comprising: S1 crushing, ball milling and grading the tailings, mixing with a composite activator, and ultrasonic activation under inert atmosphere; S2 mixing the three-stage tailings, adding circulating filtrate for slurry preparation, adding a modified catalyst, and removing oxygen by nitrogen; S3 passing CO2 through double aeration discs, gradient temperature control, pressure reaction, and adding sodium carbonate to control pH; S4 screen filtration and ceramic membrane filtration of the reaction liquid, and mixing and curing after drying; S5 desalination of the filtrate by electrodialysis, reuse of concentrated water by adding activator, and reuse of fresh water for slurry preparation. The present application reduces the energy consumption of CO2 sequestration, controls the dissolution of heavy metals, improves the safety and resource potential of the product, realizes the recycling of activators and water resources, reduces waste, and balances environmental protection and economy.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of industrial solid waste resourceization and carbon sequestration, in particular to a method for carbon sequestration of CO2 by carbonate mineralization based on vanadium-containing shale tailings. BACKGROUND

[0002] CO2 sequestration technology is a key means to address global climate change and achieve the "double carbon" goal. Carbonate mineralization sequestration has become a research hotspot in recent years due to its high product stability and no leakage risk. This technology reacts CO2 with minerals rich in alkaline metal elements such as calcium and magnesium to generate stable carbonate solids, achieving long-term fixation of CO2. Vanadium-containing shale tailings, as solid waste generated during the mining and smelting of vanadium ore, produce about 100-150 tons of tailings per ton of vanadium product, with a cumulative stockpile exceeding 100 million tons. Not only does it occupy a large amount of land resources, but it also easily pollutes soil and groundwater with heavy metal ions such as vanadium and iron leached by rainwater, causing serious ecological risks. At the same time, vanadium-containing shale tailings contain 20-35% of alkaline components such as CaO and MgO, which have natural conditions for mineralization reaction with CO2. If they can be used for CO2 sequestration, they can achieve dual benefits of "waste disposal-carbon sequestration" and meet the needs of circular economy development.

[0003] Current carbonate mineralization CO2 sequestration technology based on industrial solid waste still has many technical bottlenecks. In the tailings pretreatment stage, traditional processes mostly use single crushing or simple acid-base soaking, without considering the influence of tailings particle size distribution on reaction activity, resulting in low dissolution efficiency of alkaline components in tailings and slow subsequent mineralization reaction rate. Although some processes introduce activators, they are mostly single sodium hydroxide or sodium carbonate, which cannot effectively destroy the dense structure of silicate and aluminate minerals in the tailings, and the activation process lacks auxiliary strengthening means, with an activation efficiency generally lower than 60%. In addition, the problem of vanadium ion dissolution in raw vanadium-containing shale tailings has not been paid attention to, and direct use for mineralization may lead to excessive heavy metals in the product, limiting subsequent resource utilization.

[0004] In terms of mineralization reaction system construction and reaction control, existing technologies mostly use single solid-liquid ratio and constant temperature and pressure reaction conditions, without dynamically adjusting parameters according to CO2 dissolution kinetics and mineral reaction characteristics, resulting in low CO2 mass transfer efficiency and incomplete mineralization. For example, the solubility of CO2 is low under low temperature and pressure conditions, and the reaction rate is slow. Although high temperature and pressure can improve reaction efficiency, the energy consumption is too high, with unit CO2 sequestration energy consumption often exceeding 300 kWh / ton, which is economically inefficient. At the same time, the selection of catalysts is mostly traditional metal oxides, which have problems such as poor dispersibility and low catalytic activity, making it difficult to significantly improve the reaction rate, and lacking precise control of the pH value of the reaction system, which may lead to carbonate dissolution due to too low pH value, reducing the sequestration efficiency.

[0005] The product processing and resource recycling link also has short boards. Traditional processes mostly use single filtration method to separate mineralized products, which cannot realize coarse and fine particle classification, and the product purity and uniformity are poor, which is difficult to be resource utilization as building aggregate and the like. The filtrate treatment is mostly discharged after simple neutralization, which not only wastes water resources, but also leads to loss of useful components such as activators, thereby increasing the process cost. In addition, the existing technology pays insufficient attention to the later maintenance of the mineralized product, and the product has low compressive strength and is easy to be broken in the storage or utilization process, thereby having the risk of secondary pollution.

[0006] From the industry application, the existing carbonate mineralization technology mostly focuses on steel slag, fly ash and other solid wastes, and there are few special technologies for vanadium-containing shale tailings, and a whole-process closed-loop system of "tailings pretreatment-reaction control-product utilization-filtrate circulation" has not been formed, which limits the industrial application of the technology. In summary, it is urgent to develop a CO2 sequestration method capable of realizing efficient activation of vanadium-containing shale tailings, rapid mineralization of CO2, high-value utilization of products and whole-process resource recycling, so as to break through the current technical bottleneck and promote the collaborative development of solid waste resource utilization and carbon sequestration industry. SUMMARY

[0007] (1) Technical problems solved

[0008] In view of the deficiencies of the prior art, the present application provides a carbonate mineralization CO2 sequestration method based on vanadium-containing shale tailings.

[0009] (2) Technical solutions

[0010] A carbonate mineralization CO2 sequestration method based on vanadium-containing shale tailings, comprising the following steps:

[0011] S1. Tailings classification pretreatment

[0012] The vanadium-containing shale tailings are crushed to a particle size of not more than 5 mm, and then ball milled to 80-120 μm, and after sieving, the three levels of particles with particle sizes of 20-50 μm, 50-80 μm and 80-120 μm are obtained; the three levels of particles are mixed with a composite activator at a mass ratio of 0.15-0.22:1, and the composite activator is composed of sodium hydroxide, sodium peroxide and calcium fluoride at a mass ratio of 4:1:0.8; the mixture is stirred at 90-110°C in an inert atmosphere for 40-60 min, and ultrasonic wave is applied simultaneously for auxiliary activation;

[0013] S2. Construction of double-circulation reaction system

[0014] The three levels of tailings are mixed at a mass ratio of 2:3:5, and a suspension is prepared by adjusting the solid-liquid ratio of the tailings to 1:4-1:6; 3-5% of a modified catalyst is added to the suspension, the modified catalyst is nano magnesium oxide loaded on graphene quantum dots; nitrogen is introduced into the suspension for 15 min to remove oxygen;

[0015] S3. Gradient pressurized mineralization reaction

[0016] First, the suspension is bubbled with CO2 at a concentration of 95-99% at a rate of 0.8-1.0 L / min, and reacted at 65-75°C and 0.6-0.9 MPa for 1 h; then the temperature is raised to 80-90°C, the pressure is increased to 1.2-1.6 MPa, the CO2 flow rate is adjusted to 1.2-1.5 L / min, and the reaction is continued for 2-3 h; the stirring rate is maintained at 400-600 r / min throughout the reaction, and the pH value of the reaction system is measured every 30 min to maintain the pH value in the range of 8.5-10.5;

[0017] S4. Product gradient separation

[0018] After the reaction is completed, the coarse particle product is first separated by a 200-mesh sieve, and the filtrate is then filtered through a ceramic membrane with a pore size of 0.1 μm to separate the fine particle product; the coarse particles and fine particles are dried separately at 70-90°C for 18-24 h, and after drying, the fine particle product is mixed with the coarse particle product at a mass ratio of 1:0.3 to obtain a composite carbonate product;

[0019] S5. Filtrate closed-loop treatment

[0020] The filtrate produced by ceramic membrane filtration is desalted in an electrodialysis device, and the operating voltage is 15-20 V; the concentrated water after desalination is supplemented with a composite activator and then reused in step S1, and the fresh water is reused in step S2 to prepare the suspension, achieving a closed-loop water circulation in the whole process.

[0021] Preferably, it also includes a tailings conditioning step before step S1: the original vanadium-containing shale tailings are mixed with an oxalic acid solution with a mass fraction of 5-8% at a solid-liquid ratio of 1:2, and stirred at 25-35°C for 20 min; after stirring, the filter residue is washed with deionized water until it is neutral, and then dried at 60°C.

[0022] Preferably, it also includes a preparation process of the modified catalyst in step S2: graphene quantum dots are dispersed in a mixture of ethanol and water, and the volume ratio of ethanol to water is 1:3; magnesium nitrate solution is added to the dispersion, the pH value of the mixture is adjusted to -9-10, and the mixture is refluxed at 80°C for 3 h; after the reaction, centrifugation, washing, and calcination at 500°C for 2 h, a modified catalyst with a particle size distribution in the range of 30-60 nm is obtained.

[0023] Preferably, in step S3, a double-aeration-disk collaborative aeration method is used, the bottom aeration disk has a hole diameter of 0.2 mm, the side annular aeration disk has a hole diameter of 0.1 mm, the two are staggered at an angle of 45°, and the bottom and side aeration amounts are in a ratio of 3:2.

[0024] Preferably, the composite carbonate product in step S4 needs to be cured: the composite carbonate product is placed in an environment with a temperature of 25±2℃ and a relative humidity of 90±5% for 7 days; and a 2% sodium silicate solution is sprayed every day during the standing period, and the amount of solution used is 1% of the mass of the composite carbonate product.

[0025] Preferably, the electrodialysis desalination in step S5 uses a homogeneous cation exchange membrane, and the current density of the membrane stack is controlled at 30-50 mA / cm 2 .

[0026] Preferably, the inert atmosphere in step S1 is a mixture of nitrogen and argon, the volume ratio of nitrogen to argon is 4:1, and the flow rate of the mixed gas is maintained at 0.3-0.5 L / min.

[0027] Preferably, in step S3, an automatic pH supplementing system is provided, and when the pH value of the reaction system is detected to be lower than 8.5, the system pumps in a 10% sodium carbonate solution in real time, and the supplementing rate is linked to the amount of CO2 introduced, with 0.8-1.2 mL of sodium carbonate solution being supplemented per liter of CO2.

[0028] Preferably, in step S4, ceramic membrane filtration is performed in a cross-flow filtration mode, the operating pressure is 0.2-0.3 MPa, the membrane surface flow rate is 1.5-2.0 m / s, and the cleaning cycle is not less than 8 h.

[0029] Preferably, in step S2, the nitrogen introduction rate is 0.5-0.8 L / min, and the stirring rate of the suspension is 200-300 r / min, to ensure uniform dispersion of the nitrogen.

[0030] (III) Beneficial technical effects

[0031] Compared with the existing technology, the beneficial effects of the present application are:

[0032] 1. By using the hierarchical crushing ball milling and composite activator synergistic ultrasonic activation technology, combined with the optimization of the mixing ratio according to the particle size distribution difference of the tailings, the dense structure of the tailings can be fully destroyed, the dissolution of the alkaline components is promoted, and the risk of vanadium ion dissolution is reduced through the oxalic acid conditioning before pretreatment, which lays a foundation for the subsequent mineralization reaction and safe use of the product. Compared with the traditional single pretreatment method, the tailings are more fully activated, and the problem of heavy metal pollution is avoided, which widens the resource utilization scene of the product.

[0033] 2. The introduction of the modified catalyst significantly improves the CO2 conversion efficiency. Its unique loading structure enhances the catalytic activity and dispersion. Combined with the double circulation reaction system and nitrogen deoxidation operation, it provides a stable environment for mineralization reaction. The gradient pressure reaction mode dynamically adjusts the temperature, pressure and CO2 input rate according to the reaction stage, taking into account the reaction efficiency and energy consumption control, avoiding the problem of high energy consumption or incomplete reaction caused by traditional constant parameters. At the same time, the pH value automatic supplement system ensures that the reaction system is always in the appropriate alkaline range, preventing the dissolution of carbonates and ensuring the CO2 storage effect.

[0034] 3. The gradient separation technology realizes the classification of coarse and fine particles, and improves the product purity and mechanical properties through post-curing treatment, so that the composite carbonate can be used as building aggregate and other high-value utilization, instead of simple landfill disposal, improving the resource value of solid waste. The closed-loop treatment of filtrate realizes water resource and activator recovery through electrodialysis desalination. The concentrated water is used for pretreatment after supplementing the activator, and the fresh water is used for slurry preparation, forming a whole process water and reagent circulation, greatly reducing water consumption and reagent waste, reducing process cost, and meeting the green production concept.

[0035] 4. The double aeration disc is used to optimize the CO2 mass transfer path and improve the gas utilization rate. Inert atmosphere protection prevents the oxidation of reducing components in tailings, ensuring the stability of the reaction. Cross-flow filtration extends the service life of ceramic membranes and reduces equipment maintenance costs. Overall, this method realizes the multiple goals of efficient disposal of vanadium-containing shale tailings, stable CO2 storage, high-value utilization of products, and resource recycling, taking into account ecological, economic and social benefits. It provides a feasible technical path for the coordinated development of solid waste resource utilization and carbon sequestration, and has broad industrial application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0036] Fig. 1 is a carbonate mineralization CO2 sequestration method flow chart based on vanadium-containing shale tailings proposed by the present invention;

[0037] Fig. 2 is a unit CO2 sequestration energy consumption line comparison chart of examples and comparative examples;

[0038] Fig. 3 is a tailings activation rate and CO2 mineralization rate columnar comparison chart of examples and comparative examples;

[0039] Fig. 4 is a radar comparison chart of process performance and product quality comparison data of examples and comparative examples after uniform dimensioning. DETAILED DESCRIPTION

[0040] According to Figs. 1 to 4 , the specific embodiments of the present invention are as follows:

[0041] Raw materials and equipment preparation

[0042] Raw material specification

[0043] Vanadium-containing shale tailings: taken from a vanadium smelting plant, the main components are SiO248%, CaO 22%, Al2O312%, Fe2O38%, V2O51.2%, and the rest are impurities.

[0044] Composite activator: sodium hydroxide purity 99%, sodium peroxide purity 98%, calcium fluoride purity 97%, mixed in a mass ratio of 4:1:0.8.

[0045] Modified catalyst: nano-magnesium oxide particle size 30-60 nm, loaded on graphene quantum dots (particle size 5-10 nm), loading capacity 15%.

[0046] Auxiliary reagent: oxalic acid (analytical pure, mass fraction 5-8%), sodium silicate (analytical pure, mass fraction 2%), sodium carbonate (analytical pure, mass fraction 10%), nitrogen (purity 99.99%), argon (purity 99.99%), CO2(purity 99%).

[0047] Circulating filtrate: ceramic membrane filtration filtrate from the previous batch process, desalted by electrodialysis.

[0048] Equipment list

[0049] Jaw crusher: crushing particle size 0-5 mm; ball mill: grinding particle size 50-150 μm; standard sieve: 20 mesh, 50 mesh, 80 mesh, 120 mesh, 200 mesh.

[0050] Constant temperature stirring reaction kettle: temperature control range 20-150℃, pressure control range 0-3 MPa, stirring rate 0-1000 r / min, with ultrasonic generator.

[0051] Double aeration disc system: bottom aeration disc hole diameter 0.2 mm, side ring aeration disc hole diameter 0.1 mm, with flow regulating valve.

[0052] Ceramic membrane filtration equipment: membrane pore size 0.1 μm, cross-flow filtration mode, operating pressure 0-0.5 MPa.

[0053] Electrodialysis device: homogeneous cation exchange membrane, membrane stack current density 0-100 mA / cm 2 , operating voltage 0-30 V.

[0054] Constant temperature and humidity curing box: temperature control range 0-50℃, humidity control range 40-95% RH.

[0055] Detection equipment: pH meter (accuracy ±0.01), electronic balance (accuracy 0.001 g), laser particle size analyzer (detection range 0.1-1000 μm).

[0056] Example 1

[0057] S0: Tailings conditioning

[0058] Take 100 kg of original vanadium-containing shale tailings and mix with 6% oxalic acid solution by solid-liquid ratio 1:2 into a stainless steel stirring tank. Set the temperature to 30℃ and the stirring rate to 200 r / min. After stirring for 20 min, filter the mixture with a plate and frame filter to collect the filter residue. Wash the filter residue repeatedly with deionized water, and test the pH value of the washing water every 3 times until the pH value reaches 7.0. Then, place the filter residue in a 60℃ air-drying oven and dry for 12 h to obtain 98.5 kg of conditioned tailings.

[0059] S1: Tailings classification pretreatment

[0060] Break the conditioned tailings into particles with a particle size not greater than 5 mm with a jaw crusher, and then send them into a ball mill. Adjust the grinding time to 30 min and grind them to 80-120 μm. Classify them with 20 mesh, 50 mesh, 80 mesh and 120 mesh standard sieves to collect 18 kg of 20-50 μm particles, 27 kg of 50-80 μm particles and 45 kg of 80-120 μm particles. Take a composite activator (14.4 kg of sodium hydroxide, 3.6 kg of sodium peroxide and 2.88 kg of calcium fluoride) by mass ratio 0.18:1, mix it uniformly with the three-stage particles, and pour it into a constant-temperature stirring reaction kettle. Pass nitrogen and argon mixed gas (volume ratio 4:1) into the kettle at a flow rate of 0.4 L / min, set the temperature to 100℃ and the stirring rate to 300 r / min, turn on a 180 W ultrasonic generator at the same time, and activate for 50 min to obtain 97.38 kg of pretreated tailings.

[0061] S2: Construction of double-circulation reaction system

[0062] Mix the three-stage tailings by mass ratio 2:3:5 (i.e. 18 kg of 20-50 μm particles, 27 kg of 50-80 μm particles and 45 kg of 80-120 μm particles), add the circulating filtrate, and adjust it into a suspension by solid-liquid ratio 1:5. Take 4.8 kg of modified catalyst accounting for 4% of the total mass of the tailings, and add it into the suspension.

[0063] Process for preparing the modified catalyst: disperse 5 g of graphene quantum dots in a mixture of ethanol and water (100 mL of ethanol and 300 mL of water), add 50 mL of 0.5 mol / L magnesium nitrate solution, adjust the pH to 9.5 with 1 mol / L sodium hydroxide solution, reflux at 80℃ for 3 h, centrifugally separate, wash with deionized water for 3 times, and calcine in a 500℃ muffle furnace for 2 h to obtain the catalyst.

[0064] Pass nitrogen gas (rate 0.6 L / min) into the suspension, and stir at a stirring rate of 250 r / min for 15 min to remove oxygen to obtain a reaction suspension.

[0065] S3: Gradient pressurized mineralization reaction

[0066] Install double aeration discs (bottom and side aeration ratio 3:2), open CO2 cylinder, first pass in CO2 at a rate of 0.9 L / min, set the temperature of the reactor to 70°C, the pressure to 0.7 MPa, the stirring rate to 500 r / min, and react for 1 h. Adjust the temperature to 85°C, the pressure to 1.4 MPa, and the CO2 passing rate to 1.3 L / min, and continue to react for 2.5 h. Open the pH automatic supplement system, when the pH value drops to 8.5, pump in 10% sodium carbonate solution, 1.0 mL of sodium carbonate solution is added for each liter of CO2, and the pH value is maintained at 8.5 to 10.5 throughout the process, and the mineralization reaction solution is obtained.

[0067] S4: Gradient separation and curing of product

[0068] The reaction solution is first filtered through a 200-mesh screen to collect coarse granular product 15 kg; the undersize filtrate is sent to a ceramic membrane filtration device, the operating pressure is set to 0.25 MPa, and the membrane surface flow rate is 1.8 m / s, and the cross-flow filtration separates the fine granular product 28 kg. The coarse and fine granular products are respectively placed in a 80°C air drying oven and dried for 20 h.

[0069] After drying, mix according to the mass ratio 1:0.3 (fine granular 28 kg, coarse granular 8.4 kg), place in a constant temperature and humidity curing box, set the temperature to 25°C, the relative humidity to 90%, and stand for 7 days; during the standing period, spray 2% sodium silicate solution every day, the amount is 1% of the mass of the composite carbonate product (i.e. 0.364 kg), and the composite carbonate product 36.4 kg is obtained.

[0070] S5: Closed loop treatment of filtrate

[0071] The ceramic membrane filtrate is sent to an electrodialysis device, a homogeneous cation exchange membrane is used, the membrane stack current density is set to 40 mA / cm 2 , the operating voltage is 18 V, and the desalination treatment is 2 h. Collect 30 L of desalination concentrated water, supplement the composite activator (sodium hydroxide 0.5 kg, sodium peroxide 0.125 kg, calcium fluoride 0.1 kg), and return to the next batch S1 step; collect 80 L of desalination fresh water, and return to the next batch S2 step for slurry preparation.

[0072] Example 2

[0073] S0: Tailings conditioning

[0074] Take 100 kg of original vanadium-containing shale tailings, mix with 5% oxalic acid solution by solid-liquid ratio 1:2, pour into a stainless steel stirring tank. Set the temperature to 25℃, stirring rate 200r / min, stir for 20 min, then filter with a plate and frame filter, collect the filter residue. Wash the filter residue with deionized water repeatedly, test the pH value of the washing water every 3 times, until the pH value reaches 7.0, put the filter residue into a 60℃ air drying oven, dry for 12h, get 98.2kg of conditioned tailings.

[0075] S1: Tailings classification pretreatment

[0076] The conditioned tailings are crushed by a jaw crusher to a particle size of not more than 5mm, then sent to a ball mill, adjust the grinding time to 30min, grind to 80 to 120μm. Graded with 20 mesh, 50 mesh, 80 mesh, 120 mesh standard sieve, collect 17kg of 20 to 50μm particles, 25.5kg of 50 to 80μm particles, 42.5kg of 80 to 120μm particles. Take the composite activator (sodium hydroxide 12kg, sodium peroxide 3kg, calcium fluoride 2.4kg) by mass ratio 0.15:1, mix evenly with the three-stage particles, pour into a constant temperature stirring reaction kettle. Pass in nitrogen and argon mixed gas (volume ratio 4:1), flow rate 0.3L / min, set the temperature to 90℃, stirring rate 300r / min, start the 150W ultrasonic generator at the same time, activate for 40min, get 95.4kg of pretreated tailings.

[0077] S2: Double circulation reaction system construction

[0078] Mix the three-stage tailings by mass ratio 2:3:5 (i.e. 17kg of 20 to 50μm particles, 25.5kg of 50 to 80μm particles, 42.5kg of 80 to 120μm particles), add the circulating filtrate, adjust to a suspension by solid-liquid ratio 1:4. Take 3.6kg of modified catalyst accounting for 3% of the total mass of the tailings, add to the suspension.

[0079] The preparation process of the modified catalyst is the same as in Example 1: disperse 5g of graphene quantum dots in a mixture of ethanol and water (100mL of ethanol, 300mL of water), add 50mL of 0.5mol / L magnesium nitrate solution, adjust the pH to 9.5 with 1mol / L sodium hydroxide solution, reflux at 80℃ for 3h, centrifuge and wash 3 times with deionized water, calcine at 500℃ in a muffle furnace for 2h, get the catalyst.

[0080] Pass nitrogen into the suspension (rate 0.5L / min), stirring rate 200r / min, deoxygenate for 15min, get the reaction suspension.

[0081] S3: Gradient pressurized mineralization reaction

[0082] Install double aeration disc (the ratio of bottom and side aeration is 3:2), open CO2 cylinder, first input CO2 at the rate of 0.8 L / min, set the temperature of the reactor to 65℃, the pressure to 0.6 MPa, and the stirring rate to 500 r / min, and react for 1 h. Adjust the temperature to 80℃, the pressure to 1.2 MPa, and the input rate of CO2 to 1.2 L / min, and continue to react for 2 h. Open the automatic pH supplement system, when the pH value is reduced to 8.5, pump in 10% sodium carbonate solution, and each liter of CO2 corresponds to 0.8 mL of supplement, and maintain the pH value to be 8.5 to 10.5 throughout the process, and obtain the mineralization reaction solution.

[0083] S4: Gradient separation and maintenance of the product

[0084] First filter the reaction solution through a 200-mesh sieve, and collect the coarse granular product 14 kg; send the filtrate under the sieve into a ceramic membrane filtration device, set the operating pressure to 0.2 MPa, and the membrane surface flow rate to 1.5 m / s, and separate the fine granular product 26 kg by cross-flow filtration. Put the coarse granular and fine granular into a 70℃ air-drying oven respectively, and dry for 18 h.

[0085] After drying, mix according to the mass ratio 1:0.3 (fine granular 26 kg, coarse granular 7.8 kg), and put into a constant temperature and humidity maintenance box, set the temperature to 23℃, and the relative humidity to 85%, and stand for 7 days; spray 2% sodium silicate solution every day during the standing period, and the amount is 1% of the mass of the composite carbonate product (0.338 kg), and obtain the composite carbonate product 33.8 kg.

[0086] S5: Closed loop treatment of the filtrate

[0087] Send the ceramic membrane filtration filtrate into an electrodialysis device, use homogeneous cation exchange membrane, set the membrane stack current density to 30 mA / cm 2 , the operating voltage to 15 V, and desalination treatment for 2 h. Collect the desalination concentrated water 28 L, supplement the composite activator (sodium hydroxide 0.45 kg, sodium peroxide 0.11 kg, calcium fluoride 0.09 kg), and use it for the next batch S1 step; collect the desalination fresh water 75 L, and use it for the next batch S2 step for slurry preparation.

[0088] Example 3

[0089] S0: Conditioning of tailings

[0090] Take 100 kg of original vanadium-containing shale tailings, mix with 8% oxalic acid solution according to the solid-liquid ratio 1:2, and pour into a stainless steel stirring tank. Set the temperature to 35℃, and the stirring rate to 200 r / min, stir for 20 min, then filter with a plate and frame filter, and collect the filter residue. Wash the filter residue repeatedly with deionized water, and detect the pH value of the washing water every 3 times, until the pH value reaches 7.0, then put the filter residue into a 60℃ air-drying oven, and dry for 12 h, and obtain the conditioned tailings 98.8 kg.

[0091] S1: Tailings classification pretreatment

[0092] The conditioning tailings were crushed to a particle size of no more than 5 mm by a jaw crusher, and then sent to a ball mill. The grinding time was adjusted to 30 min, and the tailings were ground to 80-120 μm. The tailings were classified by 20 mesh, 50 mesh, 80 mesh, and 120 mesh standard sieves, and 19 kg of 20-50 μm particles, 28.5 kg of 50-80 μm particles, and 47.5 kg of 80-120 μm particles were collected. A composite activator (17.6 kg of sodium hydroxide, 4.4 kg of sodium peroxide, and 3.52 kg of calcium fluoride) was weighed according to a mass ratio of 0.22:1, and mixed uniformly with the three-stage particles. The mixture was poured into a constant-temperature stirring reaction kettle. Nitrogen and argon mixed gas (volume ratio of 4:1) was introduced at a flow rate of 0.5 L / min, the temperature was set to 110°C, the stirring rate was 300 r / min, a 200 W ultrasonic generator was turned on, and the tailings were activated for 60 min. A pretreated tailings of 100.32 kg was obtained.

[0093] S2: Construction of a double-circulation reaction system

[0094] The three-stage tailings were mixed according to a mass ratio of 2:3:5 (i.e., 19 kg of 20-50 μm particles, 28.5 kg of 50-80 μm particles, and 47.5 kg of 80-120 μm particles), and the circulating filtrate was added to prepare a suspension according to a solid-liquid ratio of 1:6. A modified catalyst of 6 kg, which was 5% of the total mass of the tailings, was added to the suspension.

[0095] The modified catalyst was prepared according to the process of Example 1. Graphene quantum dots 5 g were dispersed in a mixture of ethanol and water (100 mL of ethanol and 300 mL of water), 50 mL of 0.5 mol / L magnesium nitrate solution was added, the pH was adjusted to 9.5 with 1 mol / L sodium hydroxide solution, and the mixture was refluxed at 80°C for 3 h. After centrifugal separation, the catalyst was washed with deionized water three times, and calcined in a muffle furnace at 500°C for 2 h.

[0096] Nitrogen was introduced into the suspension (rate of 0.8 L / min) at a stirring rate of 300 r / min, and the oxygen was removed for 15 min to obtain a reaction suspension.

[0097] S3: Gradient pressurization mineralization reaction

[0098] Install double aeration disc (the ratio of bottom and side aeration is 3:2), open CO2 cylinder, first input CO2 at the rate of 1.0 L / min, set the temperature of the reactor to 75℃, the pressure to 0.9 MPa, and the stirring rate to 500 r / min, and react for 1 h. Adjust the temperature to 90℃, the pressure to 1.6 MPa, and the CO2 input rate to 1.5 L / min, and continue to react for 3 h. Open the pH automatic supplement system, when the pH value is reduced to 8.5, pump in 10% sodium carbonate solution, 1.2 mL of sodium carbonate solution is added for each liter of CO2, and the pH value is maintained at 8.5 to 10.5 throughout the process, and the mineralization reaction solution is obtained.

[0099] S4: Product gradient separation and maintenance

[0100] The reaction solution is first filtered through a 200-mesh screen to collect coarse granular product 16 kg; the undersize filtrate is sent to a ceramic membrane filtration device, and the operating pressure is set to 0.3 MPa and the membrane surface flow rate is set to 2.0 m / s, and the cross-flow filtration is used to separate fine granular product 30 kg. The coarse granules and fine granules are respectively placed in a 90℃ air drying oven and dried for 24 h.

[0101] After drying, mix according to the mass ratio of 1:0.3 (fine granules 30 kg, coarse granules 9 kg), place in a constant temperature and humidity maintenance box, set the temperature to 27℃ and the relative humidity to 95%, and stand for 7 days; during the standing period, spray 2% sodium silicate solution every day, the amount of which is 1% of the mass of the composite carbonate product (i.e. 0.39 kg), and obtain the composite carbonate product 39 kg.

[0102] S5: Filtrate closed loop treatment

[0103] The ceramic membrane filtrate is sent to an electrodialysis device, a homogeneous cation exchange membrane is used, the membrane stack current density is set to 50 mA / cm 2 , the operating voltage is set to 20 V, and the desalination treatment is performed for 2 h. Collect 32 L of desalination concentrated water, supplement the composite activator (sodium hydroxide 0.55 kg, sodium peroxide 0.14 kg, calcium fluoride 0.11 kg), and return it to the next batch S1 step; collect 85 L of desalination fresh water, and return it to the next batch S2 step for slurry preparation.

[0104] Comparative example

[0105] S1: Simple treatment of tailings

[0106] Take 100 kg of original vanadium-containing shale tailings, without conditioning step, directly crush to a particle size of not more than 5 mm by a jaw crusher, without classification treatment, without adding composite activator, and without ultrasonic activation, to obtain 99 kg of treated tailings.

[0107] S2: Construction of reaction system

[0108] The tailings were mixed with deionized water at a solid-liquid ratio of 1:5 to prepare a suspension, without adding a modified catalyst, without passing nitrogen to remove oxygen, to obtain a reaction suspension.

[0109] S3: Constant condition mineralization

[0110] A single aeration plate (bottom aeration plate hole diameter 0.2 mm) was installed, a CO2 cylinder was opened, CO2 was passed at a rate of 1.0 L / min, the temperature of the reaction kettle was set to 75°C, the pressure was 1.0 MPa, the stirring rate was 400 r / min, the reaction was continued for 3.5 h, no pH value adjustment was performed, and a mineralization reaction liquid was obtained.

[0111] S4: Product treatment

[0112] The reaction liquid was filtered through a 100-mesh sieve, and the product 30 kg was collected, no ceramic membrane fractionation filtration was performed, it was placed in a 80°C air drying oven for drying for 20 h, and no curing treatment was performed.

[0113] S5: Filtrate treatment

[0114] The filtrate produced by filtration was added to a sodium hydroxide solution and neutralized to a pH value of 7.0, and was directly discharged, without recycling.

[0115] The process performance and product quality of the examples and comparative examples are compared as follows:

[0116] Table 1

[0117]

[0118] The safety and resource potential of the mineralized products of the examples and comparative examples are compared as follows:

[0119] Table 2

[0120]

[0121]

[0122] As can be seen from the above specific embodiments, each embodiment describes in detail the operation details of tailings conditioning, classification pretreatment, double circulation system construction, gradient pressurization mineralization, product separation and curing, and filtrate closed loop treatment. By comparison with the comparative examples, the examples have better performance in tailings utilization rate, CO2 sequestration effect, product stability and resource recycling due to the use of classification activation, gradient reaction, double circulation and other innovative designs, which verifies the advancement and feasibility of the method.

[0123] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A method for carbonation of CO2 sequestration based on vanadium-containing shale tailings, characterized in that, Comprising the following steps: S1. Tailings grading pretreatment The vanadium-containing shale tailings are crushed to a particle size of not more than 5 mm, and then ball milled to 80-120 μm. After sieving, the tailings are divided into three levels of particles with particle sizes of 20-50 μm, 50-80 μm, and 80-120 μm, respectively. The total mass of the three levels of particles is mixed with a composite activator at a mass ratio of 1:0.15-0.

22. The composite activator is composed of sodium hydroxide, sodium peroxide, and calcium fluoride at a mass ratio of 4:1:0.

8. The mixture is stirred at 90-110 ℃ in an inert atmosphere for 40-60 min, and ultrasonic wave is applied simultaneously for auxiliary activation. S2. Construction of double-circulation reaction system The three levels of tailings are mixed at a mass ratio of 2:3:5, and are adjusted into a suspension with the circulating filtrate at a solid-liquid ratio of 1:4-1:

6. A modified catalyst accounting for 3-5% of the total mass of the tailings is added to the suspension, and the modified catalyst is nano-magnesium oxide loaded on graphene quantum dots. Nitrogen is introduced into the suspension for 15 min to remove oxygen. S3. Gradient pressurization mineralization reaction First, 95-99% CO2 is introduced into the suspension at a rate of 0.8-1.0 L / min, and the reaction is carried out at 65-75 ℃ and 0.6-0.9 MPa for 1 h. Then, the temperature is increased to 80-90 ℃, the pressure is increased to 1.2-1.6 MPa, the CO2 introduction rate is adjusted to 1.2-1.5 L / min, and the reaction is continued for 2-3 h. The stirring rate is maintained at 400-600 r / min throughout the reaction, and the pH value of the reaction system is measured every 30 min to maintain the pH value in the range of 8.5-10.

5. S4. Product gradient separation After the reaction is completed, the coarse particle product is separated first by passing through a 200-mesh sieve, and then the undersize filtrate is filtered through a ceramic membrane with a pore size of 0.1 μm to separate the fine particle product. The coarse particles and fine particles are dried at 70-90 ℃ for 18-24 h, respectively. After drying, the fine particle product is mixed with the coarse particle product at a mass ratio of 1:0.3 to obtain a composite carbonate product. S5. Filtrate closed-loop treatment The filtrate produced by the ceramic membrane filtration is subjected to desalination in an electrodialysis device at an operating voltage of 15-20 V. The concentrated water after desalination is supplemented with a composite activator and is reused in step S1, and the fresh water is reused in step S2 to prepare the suspension, thereby realizing the closed-loop circulation of water in the whole process.

2. The vanadium-containing shale tailings-based carbonation CO2sequestration process according to claim 1, characterized in that, Further comprising a tailings conditioning step before step S1: the original vanadium-containing shale tailings are mixed with an oxalic acid solution with a mass fraction of 5-8% at a solid-liquid ratio of 1:2, and are stirred at 25-35 ℃ for 20 min. After stirring, the filtrate is washed with deionized water until neutral, and is then dried at 60 ℃.

3. The vanadium-containing shale tailings-based carbonation CO2sequestration process according to claim 1, characterized in that, Further comprising a preparation process of the modified catalyst in step S2: graphene quantum dots are dispersed in a mixed solution of ethanol and water at a volume ratio of 1:

3. A magnesium nitrate solution is added to the dispersion to adjust the pH value of the mixed solution to 9-10, and the mixture is refluxed at 80 ℃ for 3 h. After the reaction, the modified catalyst is obtained by centrifugation, washing, and calcination at 500 ℃ for 2 h, and the particle size distribution of the modified catalyst is in the range of 30-60 nm.

4. The vanadium-containing shale tailings-based carbonation CO2sequestration process according to claim 1, characterized in that, In step S3, the double aeration disc is used in the way of collaborative aeration, the bottom aeration disc has a hole diameter of 0.2 mm, the side aeration disc has a hole diameter of 0.1 mm, and the two discs are staggered at an angle of 45°, the ratio of the bottom and side aeration is 3:

2.

5. The vanadium-containing shale tailings-based carbonate mineralization C02sequestration method according to claim 1, characterized in that, In step S4, the composite carbonate product needs to be cured: the composite carbonate product is placed in an environment with a temperature of 25±2℃ and a relative humidity of 90±5% for 7 days; during the standing period, a 2% sodium silicate solution is sprayed every day, and the solution amount is 1% of the mass of the composite carbonate product.

6. The vanadium-containing shale tailings-based carbonate mineralization C02sequestration method according to claim 1, characterized in that, In step S5, the electrodialysis desalination uses a homogeneous cation exchange membrane, and the membrane stack current density is controlled at 30-50 mA / cm².

7. The vanadium-containing shale tailings-based carbonate mineralization C02sequestration method according to claim 1, characterized in that, In step S1, the inert atmosphere is a mixture of nitrogen and argon, the volume ratio of nitrogen to argon is 4:1, and the flow rate of the mixed gas is maintained at 0.3-0.5 L / min.

8. The vanadium-containing shale tailings-based carbonate mineralization C02sequestration method according to claim 1, characterized in that, In step S3, an automatic pH supplement system is set up, when the pH value of the reaction system is detected to be lower than 8.5, the system pumps in a 10% sodium carbonate solution in real time, the supplement rate is linked with the CO2 input amount, and 0.8-1.2 mL of sodium carbonate solution is supplemented per liter of CO2.

9. The vanadium-containing shale tailings-based carbonate mineralization C02sequestration method according to claim 1, characterized in that, In step S4, the ceramic membrane filtration uses a cross-flow filtration method, the operating pressure is 0.2-0.3 MPa, the membrane surface flow rate is 1.5-2.0 m / s, and the cleaning period is not less than 8 h.

10. The vanadium-containing shale tailings-based carbonate mineralization C02sequestration method according to claim 1, characterized in that, In step S2, the nitrogen gas is introduced at a rate of 0.5-0.8 L / min, and the stirring rate of the suspension is 200-300 r / min, to ensure uniform dispersion of nitrogen gas.

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