Method for storing carbon dioxide by wet mineralization of vanadium titano-magnetite tailing sand

Abstract

The invention relates to the field of carbon dioxide sequestration, in particular to a method for sequestration of carbon dioxide by wet mineralization of vanadium titano-magnetite tailing sand, which comprises the following steps: collecting emissions containing CO2; the method comprises the following steps: collecting vanadium titano-magnetite tailing sand, naturally air-drying and sieving to obtain a reactant; the reactants are dissolved in water according to a preset solid-to-liquid ratio and stirred on a magnetic stirrer at a preset stirring speed for 5-10 minutes, the preset solid-to-liquid ratio is obtained through experimental optimization, and the stirring speed is obtained through experimental optimization; carbon dioxide emissions are introduced into the reaction mixture according to a preset passing rate for carbon dioxide curing, and the preset passing rate is obtained through experimental optimization; the carbon sequestration effect is detected by detecting the pH drop rate of the reaction mixture. The vanadium titano-magnetite tailing sand can be used for curing carbon dioxide, so that the utilization efficiency of resources is improved.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide sequestration, and more particularly to a method for wet mineralization and sequestration of carbon dioxide from vanadium-titanium magnetite tailings sand. Background Technology

[0002] Our current dependence on fossil fuels has led to massive CO2 emissions, causing the greenhouse effect and a series of international challenges, including climate change and frequent extreme weather events. There are currently three main methods for controlling CO2 emissions: improving energy efficiency, developing clean energy, and deploying carbon capture, utilization, and storage (CCUS) projects—that is, capturing, fixing, separating, and utilizing CO2.

[0003] Carbon sequestration is mainly divided into four types based on different technologies: geological sequestration, marine sequestration, ore carbonization and industrial utilization, and eco-sequestration. While geological sequestration helps reduce CO2 emissions, it is costly, prone to leakage, and technologically immature. Marine sequestration can easily lead to ocean acidification, ecosystem damage, and high maintenance costs for equipment. Eco-sequestration relies on the photosynthesis of various plants, offering a low-cost and easy-to-operate method, but it is time-consuming. Mineral carbonization, however, shows great promise, utilizing various minerals or solid waste containing metal salts to combine with CO2 to form carbonate solids. For example, Qin Zhixing et al. used carbide slag mineralization to capture CO2 from aluminum electrolysis flue gas to produce calcium carbonate. Utilizing natural ores for carbon sequestration is difficult, costly, and causes significant environmental pollution. Vanadium-titanium magnetite, a type of alkaline solid waste, is a strategic mineral resource primarily composed of iron, but also containing titanium, vanadium, cobalt, chromium, nickel, gallium, scandium, and other elements, making it highly valuable for economic utilization. China is the world's largest steel producer, producing approximately 1.5 billion tons annually. Of this, vanadium-titanium magnetite tailings account for 5%-10%, or 70-150 million tons. The Panxi region alone produces about 50 million tons of tailings annually. The massive waste of tailings not only causes soil, water, and air pollution, threatening human health and biological survival, but also results in a low comprehensive utilization rate of tailings. Summary of the Invention

[0004] The purpose of this invention is to provide a method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings, which aims to improve resource utilization efficiency by using vanadium-titanium magnetite tailings for carbon dioxide solidification.

[0005] To achieve the above objectives, the present invention provides a method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings sand, including collecting emissions containing CO2. The tailings sand of vanadium-titanium magnetite is collected, air-dried, and then sieved to obtain the reactants; The reactants were dissolved in water according to a preset solid-liquid ratio and stirred on a magnetic stirrer at a preset stirring speed for 5-10 minutes. The preset solid-liquid ratio and the stirring speed were obtained through experimental optimization. Carbon dioxide emissions are introduced into the reaction mixture at a preset rate for carbon dioxide solidification, the preset rate being determined through experimental optimization. The carbon fixation effect is detected by measuring the rate of pH decrease in the reaction mixture.

[0006] The specific steps for collecting vanadium-titanium magnetite tailings sand, air-drying it naturally, and then sieving it to obtain the reactants include: Raw tailings sand samples were collected from vanadium-titanium magnetite tailings. The original tailings sand sample was placed in a well-ventilated environment without direct sunlight and spread out to air dry until all the moisture evaporated, thus obtaining dry tailings sand. The dried tailings sand is sieved using a standard sieve, and the undersize material passing through the target sieve is collected.

[0007] The tailings of the vanadium-titanium magnetite include SiO2, Al2O3, CaO, and Fe2O3; the content of CaO is 12.8-15.5%, and the content of CaCO3 is less than one-thousandth.

[0008] The specific steps for optimizing the preset solid-liquid ratio through experiments include: The stirring speed was set to 200 r / min and the gas flow rate was 100 mL / min. Multiple liquid-solid ratios were selected for the experiment. After the reaction time is preset, the pH value of each sample is measured, and curve fitting is performed based on the pH to obtain the first curve; Based on the first fitted curve, the liquid-solid ratio corresponding to the lowest pH value is selected as the preset liquid-solid ratio.

[0009] The specific steps for optimizing the stirring speed through experiments include: The liquid-to-solid ratio was set to 15:1, the gas flow rate was 100 mL / min, and multiple stirring speeds were selected for the experiment. After the reaction time is preset, the pH value of each sample is measured, and a curve is fitted based on the pH to obtain a second curve; Based on the fitted second curve, the liquid-solid ratio corresponding to the lowest pH value is selected as the preset liquid-solid ratio.

[0010] The specific steps involved in optimizing the preset throughput rate through experiments include: At a liquid-to-solid ratio of 15:1 and a stirring speed of 200 r / min, experiments were conducted using multiple gas introduction rates. After the reaction time is preset, the pH value of each sample is measured, and a curve is fitted based on the pH to obtain the third curve; Based on the fitted third curve, the liquid-solid ratio corresponding to the lowest pH value is selected as the preset liquid-solid ratio.

[0011] The step of introducing carbon dioxide emissions into the reaction mixture under preset conditions for carbon dioxide solidification, including the introduction rate, further includes: Based on the single-factor experimental results of liquid-solid ratio, stirring speed and gas introduction rate, a three-factor four-level orthogonal experimental design was used for optimization.

[0012] The specific steps for detecting the carbon fixation effect by detecting the pH decrease rate of the reaction mixture include: Before introducing carbon dioxide-containing gas into the reaction mixture, the initial pH value is measured in real time using a pH meter; from the start of gas introduction, the instantaneous pH value of the reaction mixture is measured and recorded in real time using the pH meter at fixed time intervals, and this is continuously monitored for a period of time. Based on the recorded time series and corresponding instantaneous pH data, calculate the pH decrease rate of the reaction mixture within a specific time period.

[0013] This invention discloses a method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings, comprising: collecting CO2-containing emissions; collecting vanadium-titanium magnetite tailings, air-drying them, and then sieving them to obtain reactants; dissolving the reactants in water at a preset solid-liquid ratio and stirring them on a magnetic stirrer at a preset stirring speed for 5-10 minutes, wherein the preset solid-liquid ratio and stirring speed are determined experimentally; introducing carbon dioxide emissions into the reaction mixture at a preset flow rate for carbon dioxide solidification, wherein the preset flow rate is determined experimentally; and detecting the carbon sequestration effect by measuring the pH decrease rate of the reaction mixture. This method utilizes vanadium-titanium magnetite tailings for carbon dioxide solidification, improving resource utilization efficiency. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 These are the XRD patterns of experimental samples T1 and T2 of this invention.

[0016] Figure 2This is the thermogravimetric (TG) curve of the present invention.

[0017] Figure 3 These are SEM-EDS analysis images of samples RM, T1, and T2 from this invention.

[0018] Figure 4 This is a flowchart of a wet mineralization and carbon dioxide sequestration process for vanadium-titanium magnetite tailings sand according to the present invention.

[0019] Figure 5 This is a flowchart of the process of collecting vanadium-titanium magnetite tailings sand, air-drying it, and then sieving it to obtain the reactants.

[0020] Figure 6 This is a flowchart showing how the preset solid-liquid ratio of the present invention was optimized through experiments.

[0021] Figure 7 This is a flowchart showing how the preset stirring speed of the present invention was optimized through experiments.

[0022] Figure 8 This is a flowchart derived from experimental optimization of the preset throughput rate of the present invention.

[0023] Figure 9 This invention uses the pH decrease rate of the reaction mixture to detect the carbon fixation effect. Detailed Implementation

[0024] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0025] First Embodiment Please see Figures 1-9 This invention provides a method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings sand, comprising: S101 collects emissions containing CO2; Industrial emissions containing CO2 are collected. The emissions originate from flue gas generated during steel smelting, cement production, or thermal power generation. The CO2 volume concentration is 12% to 25%. The emissions are pretreated by dust removal and desulfurization to remove impurities such as particulate matter and sulfur oxides, resulting in purified CO2-containing gas for later use.

[0026] S102 collects vanadium-titanium magnetite tailings sand, air-dries it naturally, and then sieves it to obtain the reactants; The specific steps include: S201 collected raw tailings sand samples from vanadium-titanium magnetite tailings; The tailings of the vanadium-titanium magnetite include SiO2, Al2O3, CaO, and Fe2O3; wherein the content of CaO is 12.8-15.5%, and the content of CaCO3 is less than one-thousandth.

[0027] Raw tailings sand samples were collected from the tailings pond or discharge pipeline of the vanadium-titanium magnetite beneficiation plant. The raw tailings sand was a wet, fine-grained material with a moisture content between 20% and 40%. The main chemical components of the vanadium-titanium magnetite tailings, by mass percentage, were: SiO2 45%–55%, Al2O3 8%–13%, CaO 12.8%–15.5%, Fe2O3 10%–18%, and small amounts of MgO, TiO2, and MnO. Among them, free CaO was the main active component, while the CaCO3 content was less than 0.1% (i.e., one-thousandth), indicating that the carbonate mineral content in the tailings was extremely low, which was conducive to the subsequent direct carbonization reaction. S202 The original tailings sand sample is placed in a well-ventilated environment without direct sunlight and spread out to air dry naturally until its moisture is completely evaporated, thus obtaining dry tailings sand. The original tailings sand sample was evenly spread in a clean, well-ventilated, and dry room or under a shade shed without direct sunlight. The spreading thickness was controlled at 3 cm to 5 cm. It was turned over every 6 to 8 hours and air-dried for 48 to 72 hours until the moisture content of the tailings sand dropped to below 2% and reached a constant weight state, thus obtaining dry and loose tailings sand material. This natural air-drying method avoids the mineral structure changes or microcrack closure caused by high-temperature drying, thereby maintaining its surface activity and reaction potential. S203 uses a standard sieve to screen the dried tailings sand and collects the undersize material that passes through the target sieve.

[0028] The air-dried tailings sand was mechanically sieved using a standard test sieve, preferably a standard sieve with an aperture of 75 μm (i.e., 200 mesh). The tailings sand was fed into a vibrating sieve in batches and sieved for 5 to 10 minutes. The fine particles that passed through the 75 μm sieve were collected as the undersize, which is the target reactant. The coarse particles that did not pass through the sieve were discarded as the oversize or returned for crushing. The resulting undersize has a large specific surface area and good flowability, which is suitable for subsequent wet or dry carbonization reactions, ensuring effective contact and mineralization transformation between CO2 and CaO in the tailings.

[0029] S103 Dissolve the reactants in water according to a preset solid-liquid ratio, and stir on a magnetic stirrer at a preset stirring speed for 5-10 minutes. The preset solid-liquid ratio and the stirring speed are obtained through experimental optimization. The specific steps involved in optimizing the preset solid-liquid ratio through experiments include: S301 was set with a stirring speed of 200 r / min and a gas flow rate of 100 mL / min, and multiple liquid-solid ratios were selected for the experiment. After the S302 reaction has been performed for a preset time, the pH value of each sample is measured, and a curve is fitted based on the pH to obtain the first curve. Based on the fitted first curve, S303 selects the liquid-solid ratio corresponding to the lowest pH value as the preset liquid-solid ratio.

[0030] To investigate the carbon fixation effect of vanadium-titanium magnetite tailings on CO2, experiments were conducted at five liquid-to-solid ratios: 5:1, 10:1, 15:1, 20:1, and 30:1, with a stirring speed of 200 r / min and a gas flow rate of 100 mL / min. The changes in pH over time and the rate of pH decrease in the experiments are shown below. Figure 4 As shown, the pH value of the solution decreased with the progress of the reaction time. After the experiment, the pH decrease rate was as follows: 15:1 (46.57%) > 30:1 (46.56%) > 20:1 (45.45%) > 10:1 (45.10%) > 5:1 (37.74%).

[0031] The specific steps involved in optimizing the stirring speed through experiments include: S401 was set with a liquid-to-solid ratio of 15:1 and a gas flow rate of 100 mL / min. Multiple stirring speeds were selected for the experiment. After the S402 reaction has been performed for a preset time, the pH value of each sample is measured, and a curve is fitted based on the pH to obtain a second curve. S403 selects the liquid-solid ratio corresponding to the lowest pH value as the preset liquid-solid ratio based on the fitted second curve.

[0032] To investigate the carbon fixation effect of vanadium-titanium magnetite tailings on CO2, experiments were conducted at a liquid-to-solid ratio of 15:1 and a gas flow rate of 100 mL / min, using four stirring speeds: 0 r / min, 200 r / min, 400 r / min, and 600 r / min. As the reaction time progressed, the pH value of the solution consistently decreased. At the end of the experiment, the pH decrease rate was in the following order: 200 r / min (46.70%) > 0 r / min (46.68%) > 400 r / min (46.28%) > 600 r / min (45.73%).

[0033] S104 introduces carbon dioxide emissions into the reaction mixture at a preset rate for carbon dioxide solidification, the preset rate being optimized through experiments; The specific steps involved in optimizing the preset throughput rate through experiments include: S501 was tested at a liquid-to-solid ratio of 15:1 and a stirring speed of 200 r / min, with multiple gas introduction rates selected. After the S502 reaction time is preset, the pH value of each sample is measured, and a curve is fitted based on the pH to obtain the third curve. Based on the fitted third curve, S503 selects the liquid-solid ratio corresponding to the lowest pH value as the preset liquid-solid ratio.

[0034] To investigate the carbon fixation effect of vanadium-titanium magnetite tailings on CO2, experiments were conducted at a liquid-to-solid ratio of 15:1 and a stirring speed of 200 r / min, using four gas introduction rates of 50 mL / min, 100 mL / min, 200 mL / min, and 300 mL / min. As the reaction time progressed, the pH value of the solution consistently decreased. At the end of the experiment, the pH decrease rate was in the following order: 200 mL / min (47.35%) > 50 mL / min (46.06%) > 100 mL / min (46.06%) > 300 mL / min (45.20%). S105 was optimized using a three-factor, four-level orthogonal experimental method based on single-factor experimental results of liquid-solid ratio, stirring speed, and gas introduction rate.

[0035] Single-factor experiments were conducted to investigate the carbon fixation effect of vanadium-titanium magnetite tailings on CO2. Optimal conditions were determined by optimizing the liquid-to-solid ratio, stirring speed, and gas flow rate. The results showed that a liquid-to-solid ratio of 15:1, a stirring speed of 200 r / min, and a gas flow rate of 200 mL / min resulted in the largest decrease in pH during carbon fixation. No significant differences were found among the factors (P < 0.05). Considering both resource utilization and the rate of pH decrease before and after the reaction, a liquid-to-solid ratio of 15:1, stirring speed of 200 r / min, and gas flow rate of 200 mL / min were selected as the optimal conditions (denoted as T1).

[0036] Based on the results of single-factor experiments, and referring to the orthogonal experimental design method of An Jiakang et al., three key factors—liquid-to-solid ratio, stirring speed, and gas introduction rate—were selected. A three-factor, four-level orthogonal experimental design was adopted, and the orthogonal scheme was generated using SPSS 23 software to explore the influence of each factor on the carbon fixation effect of vanadium-titanium magnetite tailings. The orthogonal experimental results (n=4) are shown in Table 1. Range analysis showed that the influence of factors was in the order of liquid-to-solid ratio (A) > gas introduction rate (C) > stirring speed (B). The optimal combination was A4B1C3 (denoted as T2), i.e., a liquid-to-solid ratio of 30:1, a stirring speed of 0 r / min, and a gas introduction rate of 200 mL / min. The variance analysis results further verified the significance of this combination, showing that its carbon fixation effect was significantly better than the optimal single-factor combination, indicating that orthogonal design can effectively overcome the interaction between factors and optimize experimental conditions.

[0037] Table 1. Results of Analysis of Variance Source of variance Sum of squared deviations Degrees of freedom Mean Square F Statistical differences A 15.87 3 5.29 18.379 p=0.002＜0.01 B 4.114 3 1.371 4.765 p=0.05 C 7.364 3 2.455 8.528 p=0.014＜0.05 error 1.727 6 0.288 Table 1 shows that the liquid-to-solid ratio (A) has a highly significant effect on the pH decrease rate, while the gas introduction rate (C) and stirring speed (B) have significant effects on the pH decrease rate. Based on the orthogonal experimental analysis results, three parallel experiments were conducted according to combination T2, with pH decrease rates of 49.68%, 48.83%, and 49.42%, respectively, and an average pH decrease rate of 49.31%. The pH decrease rate of T1 is higher than the mean of the orthogonal experiments, which is consistent with the expectations of range and variance analysis, and can be used as the optimal condition for CO2 sequestration in the wet mineralization of vanadium-titanium magnetite tailings.

[0038] S106 detects the carbon fixation effect by measuring the rate of pH decrease in the reaction mixture.

[0039] The specific steps include: S601 Before introducing carbon dioxide-containing gas into the reaction mixture, the initial pH value is measured in real time using a pH meter; Before introducing carbon dioxide-containing gas into the reaction mixture, the prepared tailings sand and deionized water are mixed at a solid-liquid ratio of 1:5 to 1:20 (g / mL), stirred until a suspension is formed, and allowed to stand for 10 to 30 minutes to stabilize the system. Subsequently, the electrode of a pH meter calibrated with a standard buffer solution (such as pH 4.01, 7.00, and 9.18) is immersed in the reaction mixture while stirring, and its initial pH value is measured in real time and recorded as the reference value at t=0. This initial pH value is usually between 10.5 and 12.5, depending on the content of alkaline oxides such as CaO in the tailings and the slurry concentration. S602 From the start of aeration, the instantaneous pH value of the reaction mixture is measured and recorded in real time at fixed time intervals, and the monitoring is continued for a period of time. Starting from the moment CO2-containing gas is introduced into the reaction mixture, the instantaneous pH value of the reaction system is continuously measured and recorded using the same pH meter at fixed time intervals (preferably every 5 minutes, 10 minutes, or 15 minutes). The entire monitoring process lasts from 60 minutes to 240 minutes, or until the pH value tends to stabilize and no longer decreases significantly. Each time a measurement is taken, the pH reading should be allowed to stabilize (fluctuation less than ±0.05 units / minute) before the data is recorded to ensure measurement accuracy. S603 calculates the pH decrease rate of the reaction mixture within a specific time period based on the recorded time series and corresponding instantaneous pH value data.

[0040] Based on the time series data (time t, unit: min) recorded in S602 and the corresponding instantaneous pH value, a "time-pH value" change curve is plotted. Further, data from the linear decrease segment in the initial reaction phase (e.g., the first 60 minutes) are selected, and a linear regression method is used to fit the slope of pH change over time, which is the pH decrease rate (unit: Δph / min) under this condition. For example, if pH decreases from 11.8 to 10.2 within the first 60 minutes, the pH decrease rate is (11.8−10.2) / 60 ≈ 0.027 Δph / min. The larger this value, the faster the CO2 is absorbed and reacts, and the better the carbon fixation reaction kinetics. In addition, a correlation analysis can be performed between the endpoint pH value and the theoretical carbonate production to comprehensively evaluate the carbonization efficiency under different tailings samples or process parameters.

[0041] Optionally, to further verify the correlation between pH decrease rate and carbon fixation amount, the reaction products can be separated into solid and liquid phases after the reaction is completed. The content of calcium carbonate (CaCO3) generated can be determined by thermogravimetric analysis (TGA), X-ray diffraction (XRD) or acid titration, and a quantitative relationship model between pH decrease rate and actual carbon fixation amount can be established, thereby achieving rapid and online evaluation of carbon fixation effect.

[0042] To demonstrate its effectiveness, this experiment used deionized water as the soaking solution. The deionized water needed to be boiled for 2-5 minutes to remove CO2 before cooling. Furthermore, preliminary experiments showed that the pH of the liquid in the conical flask only gradually decreased to below 7 and remained constant after 10 minutes of CO2 introduction; therefore, the gas introduction time for subsequent experiments was set to 10 minutes.

[0043] Take 10 g of tailings sand sample and place it in a 250 mL or 500 mL conical flask. Add a certain amount of deionized water, mix, and stir at 200 r / min for five minutes on a magnetic stirrer until it is fully mixed and the pH remains constant. Measure the initial pH of the resulting solid-liquid mixture, which is generally maintained at around 9.0-9.3. After resetting the stirring speed, open the carbon dioxide cylinder and use the dedicated pressure reducing valve to adjust the gas pressure to below 0.2 MPa. Set the gas flow rate using a glass rotor gas flow meter. Place the conical flask on the magnetic stirrer and simultaneously introduce CO2 for 10 minutes. Record the pH value every 30 seconds during the reaction. The reacted solid-liquid mixture was filtered using 0.45 μm filter paper and a vacuum filtration device, namely a vacuum filtration flask and a circulating water vacuum pump. After the solid sample was filtered out, it was placed in a 50 mL beaker and the stir bar was removed. The solid sample and beaker were placed in an oven and dried at 70 °C until constant weight. After cooling, the solid sample was weighed, recorded, and bagged for storage. Finally, it was sent for thermogravimetric analysis and characterization.

[0044] When CO2 is introduced into water, it causes the pH to drop and generates CO3. 2- CO3 2- With Ca 2+ Combining will promote this process, and the pH decrease rate is positively correlated with the carbon fixation effect. Therefore, the pH decrease rate is used to preliminarily examine the carbon fixation effect.

[0045] pH decrease rate = (Pre-reaction pH - Post-reaction pH) / Pre-reaction pH * 100% XRD analysis was performed on tailings sand samples from temperature cycling treatments T1 and T2, and the mineral composition was analyzed, such as... Figure 1 and 2 As shown in the figure, in terms of the proportion of major minerals, the vanadium-titanium magnetite tailings sand is mainly composed of Fe2O3, SiO2, CaO, Al2O3, TiO2, and MgO, with T1 accounting for 94.4% and T2 accounting for 95.2%.

[0046] As shown in Table 2, the content of each oxide in experimental samples T1 and T2 is not significantly different from that in Table 1.

[0047] Table 2. Content of various oxides in experimental samples T1 and T2 substance <![CDATA[Na2O]]> MgO <![CDATA[Al2O3]]> <![CDATA[SiO2]]> <![CDATA[P2O5]]> <![CDATA[SO3]]> CaO <![CDATA[TiO2]]> T1 content (%) 0.78 7.3 8.7 23 1.4 0.90 12.8 8.6 T2 content (%) 0.77 7.2 8.1 22 1.3 0.88 13.1 8.8 substance MnO <![CDATA[Fe2O3]]> SrO <![CDATA[K2O]]> <![CDATA[Cr2O3]]> NiO CuO ZnO T1 content (%) 0.54 34 0.59 0.27 0.16 0.13 0.076 0.071 T2 content (%) 0.58 36 0.66 0.26 0.14 0.12 0.085 0.074 The main minerals in samples T1 and T2 are calcium and magnesium compounds, with a certain amount of iron and aluminum silicates. Calcium compounds CaSiO3, Ca[Al,Si]2O4, and Ca[Mg,Al][Si,Al]2O6 should show significant peaks in the XRD patterns, with CaO content ranging from approximately 12.8% to 13.1%. The CaO content in T1 and T2 is slightly higher than that of the original tailings sand, while the P2O5 content is significantly higher than that in RM, corresponding to the new minerals such as CaCO3 and Ca2P2O7 detected by XRD. The Fe2O3 and Al2O3 contents in T1 and T2 show little change, but the slight enrichment of SiO2 suggests that silicate minerals may have decomposed and participated in carbonation reactions, further supporting the formation of new minerals, mainly calcium carbonate, during the treatment process.

[0048] The XRD results of the two experimental samples, T1 and T2, are as follows: Figure 1 Comparative analysis of the two sets of X-ray diffraction patterns clearly revealed significant differences in mineral composition between treatment groups T1 and RM. RM was dominated by silicate minerals, including Mg2Al4Si5O. 18Complex solid solutions such as Ca[Mg,Fe]Si2O6 (C peak) and Ca[Mg,Fe]Si2O6 (C peak) reflect the diversity of the original phases. After treatment, sample T1 showed a significant strong characteristic diffraction peak of CaCO3 (2θ≈29.4°), and phosphate and aluminosilicate phases such as Ca2P2O7 and CaAl2Si2O8 were newly formed. In addition to CaCO3, sample T2 also formed new aluminosilicate phases such as Ca[Al,Si]2O4, while retaining some of the original phases, such as Mg2Al4Si5O. 18 It is noteworthy that both treated samples showed significant calcium carbonate formation. Combined with the presence of Ca2P2O7 in T1, this likely indicates carbonation and phosphate formation during the treatment process. The formation of these new mineral phases, particularly CaCO3, suggests significant mineral reorganization of the tailings sand after chemical treatment, with its crystalline phase transforming from the original silicate system to a carbonate-phosphate-aluminosilicate multi-component system, providing a mineralogical basis for subsequent resource utilization.

[0049] The reaction products from vanadium-titanium magnetite tailings sand (RM), single-factor (T1), and orthogonal (T2) experiments were analyzed by TG-DTG, and the results are as follows: Figure 2 As shown.

[0050] The RM sample experienced weight loss in the temperature range of 422–846 °C, with a weight loss of 3.32%. The T1 sample's weight loss was primarily in the temperature range of 412–1100 °C, with a weight loss of 3.98%; while the T2 sample's weight loss was primarily in the temperature range of 418–1100 °C, with a weight loss of 3.62%. The RM sample showed a slight weight gain at the beginning of the test, possibly due to gas buoyancy, mechanical strain, or moisture adsorption, but this is within the error range and does not affect the experimental results. Furthermore, the temperature range of weight loss in the RM ore sample suggests that the sample contains little or no CaCO3, as the decomposition temperature of CaCO3 is generally 800–900 °C, but it begins to decompose around 530 °C and decomposes rapidly after 910 °C, with the main decomposition temperature range being 500–950 °C. The temperature range in which the weight loss of the two experimental samples, T1 and T2, occurred precisely covers this range, and there was a significant weight loss, which proves that CaCO3 was generated in the experiment. The weight loss of both experimental combinations was between 3% and 4%, but the weight loss of T1 was slightly greater. From this perspective, the optimal carbon fixation effect of the T1 combination is slightly better than that of the optimal T2 combination.

[0051] The reaction products from vanadium-titanium magnetite tailings (RM), single-factor (T1), and orthogonal (T2) experiments were analyzed using SEM-EDS. The results are as follows: Figure 3The microstructure of tailings sand is generally observed and analyzed from four aspects: (1) particle size, shape, and surface undulation; (2) particle arrangement; (3) pore distribution or pore size; and (4) particle contact relationship. The particle morphology of samples RM, T1, and T2 is mainly irregular blocky, with rough surfaces and obvious undulations, and some particles have angular edges. The original morphology of tailings sand has obvious stratification, uneven particle size distribution, and a wide range of particle sizes. Among them, some fine particles in samples T1 and T2 are attached to the surface of large particles, which is because the CaCO3 produced during the reaction process is attached to and wrapped on the tailings sand. In terms of arrangement, the particles are mostly loosely packed, with local areas showing directional arrangement, but the overall disorder is strong, the pore distribution is uneven, and the pore size difference is significant, with both micron-sized large pores and nano-sized gaps. The contact relationship between particles is complex, with both direct point contact and surface contact connected by calcium and magnesium compounds generated by the reaction. The porosity of samples T1 and T2 was slightly lower than that of RM, possibly due to the filling effect of the reaction product CaCO3 in the pores. However, some areas still retained larger pores, indicating that the carbonation reaction did not completely change the original structure. In addition, more fine deposits were visible on the surface of the particles in sample T2, presumably amorphous substances formed during the carbonation process, further confirming its poor crystallization effect.

[0052] As shown in Table 4, the heavy metal content in RM, T1, and T2 samples fluctuated within a certain range. Heavy metals such as As, Pb, and Zn were present in the tailings sand, but in relatively small amounts. No samples of Cu, V, Ni, Cr, or Cd in the T1, T2, and RM test products exceeded the screening and control values ​​of the "Soil Environmental Quality Standard for Construction Land Soil Pollution Risk Control" (GB 36600-2018). Comparing these values ​​with the screening and control values ​​for construction land soil pollution risk, the current contents of Ni, Cu, Cr, Cd, and V are all far below the risk control values. However, the contents of some heavy metals exceed the screening values, indicating that the raw tailings sand ore poses a certain risk of soil pollution. Continuous monitoring and assessment are necessary to prevent adverse impacts on the surrounding environment and ensure the safety of construction land soil.

[0053] Table 4. Statistical results of heavy metal content in T1, T2 and RM project Fe (mg / kg) Ni (mg / kg) Cu (ug / kg) Cr (ng / kg) Cd (ug / kg) V (ug / kg) Minimum value 10.67 34.97 7.42 1.09 0.14 3.64 Maximum value 10.83 55.31 42.23 14.16 1.23 5.05 Median 10.82 50.89 18.69 1.26 0.19 6.47 Screening values ​​for soil pollution risk in construction land —— 150 <![CDATA[2.0×10 6 ]]> <![CDATA[3.0×10 6 ]]> <![CDATA[2.0×10 4 ]]> <![CDATA[1.65×10 5 ]]> Construction land soil pollution risk control value —— 600 <![CDATA[8.0×10 6 ]]> <![CDATA[3.0×10 7 ]]> <![CDATA[4.7×10 5 ]]> <![CDATA[3.30×10 5 ]]> The elements Na, Mg, K, and Ca exhibit a pattern of initial increase followed by a decrease in the mineralization reaction solutions at times T1 and T2. Vanadium-titanium magnetite tailings react with CO2 to form carbonate minerals, which release Na, Mg, K, and Ca under acidification. Simultaneously, in aqueous solution, vanadium-titanium magnetite tailings also release some Na, Mg, K, and Ca. The majority of these elements are present as Na+, K+, and Ca. 2+ Mg 2+Ionic forms exist in large quantities in the solution, with the concentrations of Na, Mg, and Ca all showing a higher concentration at T2 than T1. The leaching amounts of Na, Mg, and K are highest at 10 minutes, while Ca is highest at 4 minutes. The concentrations in the solution are Ca > Na > K > Mg. 2+ The leaching amount was approximately 16 times that of Mg. The highest orthogonal leaching amount of Ca²⁺ was 0.614 mg / kg, and the lowest was 0.193 mg / kg, a difference of 0.421 mg / kg. The difference in single-factor Ca leaching amount was 0.181 mg / kg, but the relative error of the single-factor leaching was smaller. In comparison, the single-factor Ca leaching amount... 2+ The leaching yield is relatively good. Similarly, it can be concluded that Na... + Leaching amount T2>T1, Mg 2+ Leaching amount T1>T2, K + The leaching amount is T1>T2.

[0054] CO2 dissolves in water to form CO3. 2- Mg 2+ With CO3 2- Combine to form MgCO3, Al 3+ With CO3 2- Combined to form Al2(CO3)3, but mainly Ca 2+ With CO3 2- The reaction involves the ionization of CaO from the tailings sand into Ca(OH)2 formed by the combination of CaO and water. 2+ When CaCO3 is formed, it adheres to and encapsulates CaO, which also affects its dissolution.

[0055] Carbon dioxide mineral sequestration achieves long-term stable carbon sequestration through carbonation reactions. To improve mineralization efficiency, reduce CO2 emissions, and increase carbon sink capacity, several methods are employed: First, optimize particle size. Smaller particles have a larger total surface area. When the particle size is between 400 and 500 μm, the carbonation efficiency is 12.69%, and when the particle size is reduced to below 45 μm, the efficiency increases to 22.73%. Second, appropriately heat the reaction. The mineralization reaction involves many carbonation reactions, which are strongly exothermic processes. The reaction can rapidly increase the temperature of the slurry in a short time, and heating allows reactant molecules to gain more energy, accelerating their movement. According to molecular collision theory, the frequency of intermolecular collisions is proportional to the speed of molecular motion; the higher the temperature, the faster the reaction. However, above 60°C, the carbonation rate decreases significantly with increasing temperature, and excessively high temperatures will reduce efficiency. For the three pairs of reactions, appropriate pressure can be applied to promote the gas-to-solid phase conversion using Le Chatelier's principle. Increasing the pressure shifts the reaction towards the direction with fewer gas molecules, and vice versa. According to collision theory, pressure can change the energy state of reactant molecules under certain conditions, lowering the activation energy and further increasing the reaction rate. The maximum storage capacity is reached when the pressure exceeds 3.03 × 10⁵ Pa. For the four-way reaction, appropriate amounts of acid-base auxiliaries are added, typically Na₂CO₃ / NaHCO₃ / NaCl, to adjust the pH and enhance reaction activity. However, excessive amounts must be avoided to prevent pollution or inhibition. The addition of acid-base auxiliaries needs to be strictly controlled. While considering the effects of different types of acid auxiliaries, the amount and concentration of auxiliaries added must also be considered. Excessive acid or base may pollute the environment or inhibit the reaction.

[0056] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings sand. Its features are, This includes: collecting emissions containing CO2; The tailings sand of vanadium-titanium magnetite is collected, air-dried, and then sieved to obtain the reactants; The reactants were dissolved in water according to a preset solid-liquid ratio and stirred on a magnetic stirrer at a preset stirring speed for 5-10 minutes. The preset solid-liquid ratio and the stirring speed were obtained through experimental optimization. Carbon dioxide emissions are introduced into the reaction mixture at a preset rate for carbon dioxide solidification, the preset rate being determined through experimental optimization. The carbon fixation effect is detected by measuring the rate of pH decrease in the reaction mixture.

2. The method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings as described in claim 1, characterized in that, The specific steps for collecting vanadium-titanium magnetite tailings sand, air-drying it naturally, and then sieving it to obtain the reactants include: Raw tailings sand samples were collected from vanadium-titanium magnetite tailings. The original tailings sand sample was placed in a well-ventilated environment without direct sunlight and spread out to air dry until all the moisture evaporated, thus obtaining dry tailings sand. The dried tailings sand is sieved using a standard sieve, and the undersize material passing through the target sieve is collected.

3. The method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings as described in claim 2, characterized in that, The tailings of the vanadium-titanium magnetite include SiO2, Al2O3, CaO, and Fe2O3; wherein the content of CaO is 12.8-15.5%, and the content of CaCO3 is less than one-thousandth.

4. The method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings as described in claim 3, characterized in that, The specific steps involved in optimizing the preset solid-liquid ratio through experiments include: The stirring speed was set to 200 r / min and the gas flow rate was 100 mL / min. Multiple liquid-solid ratios were selected for the experiment. After the reaction time is preset, the pH value of each sample is measured, and curve fitting is performed based on the pH to obtain the first curve; Based on the first fitted curve, the liquid-solid ratio corresponding to the lowest pH value is selected as the preset liquid-solid ratio.

5. The method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings as described in claim 4, characterized in that, The specific steps involved in optimizing the stirring speed through experiments include: The liquid-to-solid ratio was set to 15:1, the gas flow rate was 100 mL / min, and multiple stirring speeds were selected for the experiment. After the reaction time is preset, the pH value of each sample is measured, and a curve is fitted based on the pH to obtain a second curve; Based on the fitted second curve, the liquid-solid ratio corresponding to the lowest pH value is selected as the preset liquid-solid ratio.

6. The method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings as described in claim 5, characterized in that, The specific steps involved in optimizing the preset throughput rate through experiments include: At a liquid-to-solid ratio of 15:1 and a stirring speed of 200 r / min, experiments were conducted using multiple gas introduction rates. After the reaction time is preset, the pH value of each sample is measured, and a curve is fitted based on the pH to obtain the third curve; Based on the fitted third curve, the liquid-solid ratio corresponding to the lowest pH value is selected as the preset liquid-solid ratio.

7. The method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings as described in claim 6, characterized in that, The step of introducing carbon dioxide emissions into the reaction mixture under preset conditions for carbon dioxide solidification, including the introduction rate, further includes: Based on the single-factor experimental results of liquid-solid ratio, stirring speed and gas introduction rate, a three-factor four-level orthogonal experimental design was used for optimization.

8. The method for wet mineralization and carbon dioxide sequestration of vanadium-titanium magnetite tailings as described in claim 7, characterized in that, The specific steps for detecting the carbon fixation effect by detecting the rate of pH decrease in the reaction mixture include: Before introducing carbon dioxide-containing gas into the reaction mixture, the initial pH value is measured in real time using a pH meter; from the start of gas introduction, the instantaneous pH value of the reaction mixture is measured and recorded in real time using the pH meter at fixed time intervals, and this is continuously monitored for a period of time. Based on the recorded time series and corresponding instantaneous pH data, calculate the pH decrease rate of the reaction mixture within a specific time period.

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