A high-silicon calcium tailing-based heavy metal solidifying agent of calcium-based hydrotalcite / porous silicon oxide and a preparation method and application thereof

Abstract

This invention relates to the field of comprehensive resource utilization and environmental remediation technology, and particularly to a method for preparing a calcium-based hydrotalcite / porous silica heavy metal solidifying agent from high-silica calcium tailings, its preparation method, and its application. The method includes the following steps: (1) obtaining high-silica calcium tailings and pretreating them; (2) calcination activation; (3) silicon and calcium element leaching; (4) introduction of exogenous trivalent aluminum and iron ions; (5) co-precipitation; (6) crystallization treatment, followed by washing, drying, and grinding to obtain the calcium-based hydrotalcite / porous silica heavy metal solidifying agent. The calcium-based hydrotalcite / porous silica heavy metal solidifying agent prepared by the above method has characteristics such as small grain size, low crystallinity, loose and porous structure, and large specific surface area, which can significantly improve the solidification efficiency of heavy metal ions.

Description

Technical Field

[0001] This invention relates to the field of comprehensive resource utilization and environmental remediation technology, and in particular to a method for preparing calcium-based hydrotalcite / porous silica heavy metal curing agent from high-silica calcium tailings, its preparation method, and its application. Background Technology

[0002] In recent years, with technological advancements and increased energy demand, soil heavy metal pollution has become increasingly severe. Heavy metals in soil are difficult to degrade and easily accumulate, leading to decreased soil fertility and reduced microbial activity, thus affecting crop yield and quality. Through the food chain, they also pose a serious threat to human health. Among numerous remediation technologies, in-situ solidification technology has attracted much attention due to its relatively simple operation, low cost, and minimal soil disturbance, making it suitable for the remediation of large-scale contaminated soils. This technology involves adding a solidifying agent to the contaminated soil, causing a change in the in-situ state of heavy metals, thereby reducing their bioavailability and mobility. However, the solidifying agents used in traditional in-situ passivation technologies have some problems. For example, some solidifying agents have poor stability, easily decomposing and leaching in the soil environment, making it difficult to maintain a stable remediation effect in the long term; others may introduce new pollutants, leading to secondary soil pollution.

[0003] Against this backdrop, hydrotalcite materials, due to their unique structure and properties, are gradually emerging in the field of soil heavy metal pollution remediation. For heavy metal cations such as lead, zinc, cadmium, and copper, hydrotalcite can rapidly anchor them into the mineralizer lattice structure through isomorphous substitution and dissolution-reconstruction mechanisms. For anionic heavy metals such as arsenate and chromate, hydrotalcite achieves solidification through intercalation and surface precipitation. Through these multiple mechanisms, it reacts with heavy metal ions to form ultra-low solubility product compounds, thereby achieving long-term stable solidification of heavy metals. However, hydrotalcite also faces many challenges in practical applications. First, the specific surface area of ​​a single hydrotalcite is limited, which to some extent restricts its solidification capacity for heavy metal ions. Second, the preparation of hydrotalcite usually requires the use of high-purity metal salts as raw materials, resulting in high production costs. At the same time, large-scale mining and utilization of mineral resources generate a large amount of tailings waste. High-silica calcium tailings (i.e., tailings containing large amounts of quartz and calcite (or dolomite)) are a common type of tailings, with wide sources and large discharge volumes. Currently, the comprehensive utilization rate of high-silicon calcium tailings is generally low, with most being directly stockpiled or simply landfilled. However, it is worth noting that high-silicon calcium tailings contain high levels of silicon and calcium, which provides favorable conditions for the preparation of calcium-based hydrotalcite / porous silica heavy metal solidifying agents.

[0004] In conclusion, developing a method that can efficiently utilize high-silica and calcium tailings as a waste resource while simultaneously producing stable, effective, and environmentally friendly remediation materials for heavy metal-contaminated soil is of paramount practical significance and urgency. This not only responds to relevant national policies but also provides new ideas and methods for addressing current environmental and resource challenges. Summary of the Invention

[0005] This invention provides a method for preparing calcium-based hydrotalcite / porous silica heavy metal curing agent from high-silica calcium tailings, and its application. The purpose is to increase the specific surface area of ​​hydrotalcite and reduce the production cost of hydrotalcite curing agent.

[0006] To achieve the above objectives, the present invention provides a method for preparing a calcium-based hydrotalcite / porous silica heavy metal curing agent from high-silica calcium tailings, comprising the following steps:

[0007] (1) Obtain high-silicon calcium tailings and pre-treat them;

[0008] (2) Calcination activation: The high-silicon calcium tailings pretreated in step (1) are calcined and then taken out at high temperature and directly water-cooled for activation;

[0009] (3) Leaching of silicon and calcium elements: The activated tailings are acid-leached to obtain a mixed system containing free calcium ions and porous silica solids;

[0010] (4) Introduction of exogenous trivalent aluminum and iron ions: Add aluminum source and / or iron source to obtain a mixed system of free calcium ions, aluminum ions and / or iron ions and porous silica solid.

[0011] (5) Coprecipitation process: Add a mixed solution of sodium carbonate and sodium hydroxide to the above mixed system and stir continuously to adjust the pH of the system;

[0012] (6) Crystallization treatment: The above-mentioned pH-adjusted mixture is heated and stirred, and subjected to hydrothermal treatment at normal pressure; after a period of reaction, the solid and liquid are separated to obtain a solid, which is then washed, dried and ground to obtain calcium-based hydrotalcite / porous silica heavy metal curing agent.

[0013] High-silicon calcium tailings contain high levels of silicon and calcium elements, along with other components, providing favorable conditions for preparing calcium-based hydrotalcite / porous silica heavy metal curing agents with high reactivity and good heavy metal curing performance; and significantly reducing production costs. Firstly, the tailings contain a large number of impurity elements (such as Mn, Zn, Ti, etc.), and the leaching process generates a large amount of nanoscale sols (such as silica sol). These ions and colloids, as impurities, can effectively inhibit the crystal growth process of calcium-based hydrotalcite during hydrothermal processes, thereby promoting the formation of hydrotalcite structures with small size, low crystallinity, many defects, and high internal energy, rather than the conventional hydrotalcite with a complete structure, few defects, and high crystallinity. The former has better chemical reactivity than the latter, exhibiting stronger adsorption, reaction, and curing capabilities for heavy metals. Secondly, compared to magnesium ions, calcium ions have a larger ionic radius, making them more prone to "vacancies" or "twisting" when connecting with smaller iron / aluminum ions. This results in calcium-based hydrotalcite layers being more easily deformed, having lower structural order, and more readily accommodating larger and more complex anionic groups (such as arsenate and chromate) between layers, thus leading to better solidification of heavy metals. Furthermore, the size difference between calcium and iron / aluminum ions is significantly greater than that between magnesium and iron / aluminum ions. This size mismatch easily leads to the destruction and fracture of the hydrotalcite structure. Therefore, calcium-based hydrotalcite has smaller crystallites and better dispersion on porous silica surfaces, forming a more porous mesoporous structure, which is more conducive to the adsorption and solidification of heavy metal ions. In addition, calcium ions have lower polarization than magnesium ions, resulting in weaker polarity when used as the anode layer of hydrotalcite. This makes it easier to form "polydentate coordination" or "bridging adsorption" with heavy metal ions, significantly increasing the solidification effect. Finally, since calcium hydroxide is a slightly soluble substance and has the property of maintaining soil pH, it promotes the precipitation of heavy metals in the form of hydroxides and further complexes with the calcium anode layer to form a more stable complex, which can effectively reduce the risk of heavy metal re-leaching. Therefore, in summary, the calcium-based hydrotalcite / porous silica heavy metal solidifying agent prepared by this invention using high-silica calcium tailings as raw material not only has significant economic advantages, but also has better heavy metal adsorption and fixation performance than conventional calcium-based hydrotalcite, especially magnesium-based hydrotalcite, and will have better results in soil heavy metal solidification applications.

[0014] In the specific steps, calcination activation is achieved through high-temperature calcination and direct water cooling. During this process, the minerals in the tailings undergo complex physicochemical reactions. Some minerals transform from an insoluble state to a water-soluble or citric acid-soluble state through mineral phase reconstruction; some minerals experience a decrease in particle size, an increase in specific surface area, and enhanced surface reactivity; and some minerals undergo crystal structure distortion and destruction, resulting in a significant increase in defects, a significant decrease in crystal order, and an increase in internal energy. These transformations greatly enhance the activity of key elements such as silicon and calcium. The energy consumption and acid usage required in subsequent leaching operations can be effectively reduced for tailings that have undergone calcination pretreatment.

[0015] Acid leaching can convert calcium in tailings into free calcium ions and simultaneously generate silica with a nanoporous structure. The resulting material state is a key prerequisite for the subsequent preparation of high specific surface area calcium-based hydrotalcite / porous silica heavy metal curing agents.

[0016] The layered structure of hydrotalcite originates from the combination of trivalent and divalent metal ions through hydroxyl coordination. Given the potential deficiency of trivalent metal ions in tailings, the exogenous introduction of trivalent ions can effectively compensate for this deficiency. Simultaneously, by selectively controlling the ratio and composition of divalent and trivalent metal ions, the heavy metal solidification performance of the material can be precisely adjusted.

[0017] Under alkaline conditions, divalent and trivalent metal ions precipitate simultaneously, forming a positively charged lamellar structure through coordination with hydroxyl groups. Simultaneously, the hydroxyl groups of the hydrotalcite and the porous silica surface combine via interfacial chemical interactions to form a stable synergistic structure, constituting the composite material. This process offers significant advantages: mild reaction conditions, high industrial feasibility, and simple, convenient, and low-cost equipment.

[0018] To further enhance the adhesion of calcium-based hydrotalcite to the porous silica surface and improve the composite effect of the material, a hydrothermal step is needed to further promote the hydroxyl condensation and dehydration reaction between the two, thereby strengthening their bonding strength.

[0019] Preferably, in step (1), the high-silicon calcium tailings include one or more of iron tailings, phosphorus tailings, copper tailings, titanium tailings or lead-zinc tailings, the high-silicon calcium tailings contain quartz, calcite or dolomite, the sum of the mass content of silicon and calcium in the tailings is greater than 35% of the total mass of the tailings, and the silicon / calcium molar ratio is 0.75-2.0.

[0020] The pretreatment is mechanical grinding, and the particle size needs to be ground to 80 mesh or below.

[0021] Preferably, in step (2), the calcination temperature is 1000-1500 ℃ and the calcination time is 1-4 h.

[0022] Preferably, in step (3), the acid used in the acid leaching is hydrochloric acid and / or nitric acid, the acid concentration is 2-6 mol / L, the leaching temperature is 40-80 ℃, the leaching time is 0.5-6 h, and the solid-liquid ratio in the mixed system containing free calcium ions and porous silica solid is 1:5-1:40, with the solid-liquid ratio unit being g / mL.

[0023] Preferably, in step (4), the aluminum source and / or iron source includes one or more of aluminum nitrate, aluminum chloride, aluminum hydroxide, ferric nitrate or ferric chloride; the molar ratio of the total molar amount of calcium to trivalent aluminum and / or iron ions in the mixed system is 6:1-1:1.

[0024] Preferably, the concentration of sodium hydroxide in step (5) is 0.5-6 mol / L, and the concentration of sodium carbonate solution is 0.2-1.0 mol / L.

[0025] Preferably, the pH of the system described in step (5) is adjusted to 10-12.

[0026] Preferably, the temperature of the atmospheric pressure hydrothermal treatment in step (6) is 60-80 ℃ and the time is 12-48 h.

[0027] Under the same technical concept, the present invention also provides a calcium-based hydrotalcite / porous silica heavy metal curing agent prepared by the preparation method described above, wherein the calcium-based hydrotalcite is uniformly dispersed and grown on the porous silica substrate.

[0028] Under the same technical concept, the present invention also provides an application of the calcium-based hydrotalcite / porous silica heavy metal solidifying agent for remediating heavy metal contaminated soil.

[0029] The above-described solution of the present invention has the following beneficial effects:

[0030] (1) The preparation method of the present invention first activates the silicon and calcium components in the tailings by calcination, and then uses acid leaching, aluminum or (and) iron, and atmospheric pressure hydrothermal method to successfully convert the activated silicon and calcium into calcium-based hydrotalcite / porous silica heavy metal solidifying agent. Using high silicon and calcium tailings as the main raw material, the silicon and calcium elements in the tailings are activated and materialized to prepare a heavy metal solidifying agent for the treatment of heavy metal contaminated soil. The raw materials are widely available and low cost, and can realize the safe disposal and resource utilization of tailings. At the same time, it solves the problems of high cost and low specific surface area of ​​hydrotalcite solidifying agent.

[0031] (2) The present invention is based on calcium-based hydrotalcite / porous silica material prepared from tailings. Its loose and porous mesoporous characteristics enable heavy metals to quickly combine with the material, significantly improving the heavy metal solidification efficiency of the material. The small amount of calcium and silicon mineral components that are not fully utilized due to insufficient activation and leaching during the preparation process are harmless to the soil environment and also have a certain adsorption and solidification effect on heavy metal ions in the soil.

[0032] (3) The low crystallinity and small size of the calcium-based hydrotalcite / porous silica material prepared from the above tailings are conducive to the dissolution-recrystallization of the calcium-based hydrotalcite / porous silica material structure, promoting the formation of compounds with ultra-low solubility products with heavy metals, and reducing the risk of secondary leaching of heavy metals.

[0033] (4) The calcium-based hydrotalcite / porous silica heavy metal curing agent prepared from tailings in this invention exhibits higher efficiency and stability in the adsorption-curing process of heavy metals due to the impurity ions and nanoscale silica sol formed by the leaching of tailings themselves, which result in low crystallinity of the hydrotalcite structure, uneven layer structure, easy generation of defects, and uneven distribution of interlayer charge. In addition, compared with traditional magnesium-based hydrotalcite, calcium-based hydrotalcite is more conducive to forming a better-performing heavy metal ion curing material by combining with porous silica.

[0034] (5) The calcium-based hydrotalcite / porous silica heavy metal curing agent material prepared by this invention has the unique advantages of both hydrotalcite and porous silica, and can promote the mineralization reaction of heavy metal ions, showing excellent application effect in the field of in-situ remediation of heavy metal pollution in soil. The calcium-based hydrotalcite / porous silica heavy metal curing agent is structurally based on porous silica, with calcium aluminum hydrotalcite or (and) calcium iron hydrotalcite uniformly dispersed on the silica. This heavy metal curing agent combines the characteristics of hydrotalcite and porous silica, has an ultra-high specific surface area and abundant surface hydroxyl groups, and can adsorb heavy metals on the material surface through surface complexation and electrostatic interaction. Then, through isomorphous substitution, heavy metal ions replace calcium ions in hydrotalcite to form ultra-low solubility product compounds. The curing has long-term stability and avoids the re-release of heavy metal ions. At the same time, a large number of calcium ions and silicon that have not participated in the heavy metal curing can be released and used as nutrients to promote crop growth.

[0035] (6) This invention uses high-silicon calcium tailings as raw materials for preparing heavy metal solidifying agents, truly realizing the green concept of "treating hazardous waste with waste". Based on the mineral composition and chemical composition characteristics of high-silicon calcium tailings, a new process of "calcination activation-acid leaching-aluminum or (and) iron supplementation-atmospheric pressure hydrothermal" for preparing heavy metal solidifying agents from tailings is proposed. The preparation process is short, the required equipment is conventional and simple, the process is highly applicable, and the process cost is low. In addition, the low cost of using tailings as raw materials makes the heavy metal solidifying agent have a significant cost advantage. It not only effectively solves the environmental problems caused by the long-term accumulation of tailings and promotes the resource utilization of tailings, but also greatly reduces the preparation cost of materials, providing an economical, efficient and environmentally friendly innovative solution for soil pollution remediation.

[0036] In summary, this invention develops a method and application for preparing calcium-based hydrotalcite / porous silica heavy metal solidifier from high-silica calcium tailings. The tailings can be transformed into a novel heavy metal solidifier through a simple process of "calcination activation - acid leaching - aluminum and / or iron supplementation - atmospheric pressure hydrothermal treatment." This method offers advantages such as strong applicability, low preparation cost, simple process, convenient application, and multifunctionality. This invention not only provides a new approach for the high-value utilization of high-silica calcium tailings, but also enables this solidifier to perform multiple functions in contaminated soil remediation, including heavy metal solidification, soil property improvement, and supply of secondary elements, thereby effectively reducing soil remediation costs. Attached Figure Description

[0037] Figure 1 The images show the XRD patterns of the calcium-based hydrotalcite / porous silica heavy metal curing agent prepared in Examples 1-5 of this invention and the calcium aluminum hydrotalcite, calcium iron hydrotalcite and calcium iron aluminum hydrotalcite prepared in Comparative Examples 1, 3 and 5.

[0038] Figure 2 SEM images of the calcium-based hydrotalcite / porous silica heavy metal curing agent prepared in Examples 1-5 of this invention and the calcium-aluminum hydrotalcite, calcium-iron hydrotalcite, calcium-aluminum hydrotalcite, and calcium-iron-aluminum hydrotalcite prepared in Comparative Examples 1, 2, 3, and 5 are shown below: a) is the heavy metal curing agent prepared from iron tailings in Example 1; b) is the heavy metal curing agent prepared from phosphorus tailings in Example 2; c) is the heavy metal curing agent prepared from copper tailings in Example 3; d) is the heavy metal curing agent prepared from titanium tailings in Example 4; e) is the heavy metal curing agent prepared from lead-zinc tailings in Example 5; f) is the calcium-aluminum hydrotalcite prepared in Comparative Example 1; g) is the calcium-iron hydrotalcite prepared in Comparative Example 2; h) is the calcium-aluminum hydrotalcite prepared in Comparative Example 3; and i) is the calcium-iron-aluminum hydrotalcite prepared in Comparative Example 5. Detailed Implementation

[0039] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0041] Example 1

[0042] A method for preparing a calcium-based hydrotalcite / porous silica heavy metal curing agent from high-silica calcium tailings specifically includes the following steps:

[0043] (1) Using iron tailings as raw material, the mass content of silicon in the total tailings is 19.76%, the mass content of calcium in the total tailings is 21.10%, and the silicon / calcium molar ratio is 1.34; after mechanical grinding, the tailings particle size is less than 100 mesh.

[0044] (2) The tailings were calcined in a muffle furnace at 1200 °C for 4 h and then directly removed and water-cooled;

[0045] (3) Take 10.0 g of calcined iron tailings and add it to 200 mL of 2.0 mol / L hydrochloric acid, and leach it at 80 °C for 2 h;

[0046] (4) Add 6.60 g of aluminum nitrate nonahydrate and stir until homogeneous. The molar ratio of calcium to aluminum in the mixture is approximately 3.0.

[0047] (5) Slowly add a mixed solution of 2.0 mol / L sodium hydroxide and 0.5 mol / L sodium carbonate to the above solution and adjust the pH value to 10.5;

[0048] (6) Subsequently, the mixture was transferred to an oven at 60 °C and heated under normal pressure for 18 h. After filtration, it was dried and ground to obtain calcium aluminum hydrotalcite / porous silica heavy metal curing agent.

[0049] Figure 1 The images show the XRD patterns of the calcium-based hydrotalcite / porous silica heavy metal curing agent prepared in Examples 1-5 of this invention and the calcium-aluminum hydrotalcite, calcium-iron hydrotalcite, and calcium-iron-aluminum hydrotalcite prepared in Comparative Examples 1, 3, and 5; wherein the curve corresponding to the iron tailings is the calcium-based hydrotalcite / porous silica heavy metal curing agent in Example 1.

[0050] XRF analysis of the calcium-aluminum hydrotalcite / porous silica heavy metal curing agent showed that the mass contents of calcium, aluminum, and silicon were 16.78%, 3.52%, and 14.56%, respectively. XRD confirmed the presence of amorphous silica and calcium-aluminum hydrotalcite phases; SEM showed that nanosheet-like calcium-aluminum hydrotalcite was interwoven and stacked on porous silica particles. Figure 2 a) Specific surface area is 302.12 g / m² 2 .

[0051] Comparative Example 1:

[0052] 5.85 g of calcium chloride and 6.60 g of aluminum nitrate nonahydrate were weighed and added to 200 mL of deionized water. Then, a mixed solution of 2.0 mol / L sodium hydroxide and 0.5 mol / L sodium carbonate was slowly added dropwise to the solution to adjust the pH to 10.5. The mixture was then transferred to an oven at 40 °C and subjected to hydrothermal treatment at atmospheric pressure for 18 h. After filtration, the mixture was dried and ground to obtain calcium aluminum hydrotalcite. The specific surface area of ​​this calcium aluminum hydrotalcite was 66.78 g / m². 2 .

[0053] Figure 1 The images show the XRD patterns of the calcium-based hydrotalcite / porous silica heavy metal curing agent prepared in Examples 1-5 of this invention and the calcium-aluminum hydrotalcite, calcium-iron hydrotalcite, and calcium-iron-aluminum hydrotalcite prepared in Comparative Examples 1, 3, and 5; wherein the curve corresponding to the calcium-aluminum hydrotalcite is the calcium-aluminum hydrotalcite in Comparative Example 1.

[0054] Figure 2 f is a SEM image of the calcium aluminum hydrotalcite prepared in Comparative Example 1, whose structure consists of stacked blocks of varying sizes.

[0055] Remediation of contaminated soil by calcium aluminum hydrotalcite / porous silica heavy metal solidification agent: Soil samples contaminated with Cd (Cd content 112.34 mg / kg, far exceeding the soil risk screening value) were tested. Three groups of 1000 g soil samples were mixed thoroughly in 1 L beakers with a blank (no additives), 20 g of calcium aluminum hydrotalcite prepared in Comparative Example 1, and 20 g of calcium aluminum hydrotalcite / porous silica heavy metal solidification agent prepared in Example 1. 500 ml of deionized water was added, and the mixture was left to stand naturally. Samples were taken at regular intervals to determine the effective concentration of Cd. The results showed that compared to the blank control, the effective concentration of Cd in Example 1 decreased by 94.63% after 28 days; compared to the calcium aluminum hydrotalcite in Comparative Example 1, the effective concentration of Cd in Example 1 decreased by 51.11% after 28 days. See Table 1 for details.

[0056] Table 1. Changes in the effective concentration of Cd at different remediation time periods (mg / kg)

[0057]

[0058] Example 2

[0059] A method for preparing a calcium-based hydrotalcite / porous silica heavy metal curing agent from high-silica calcium tailings specifically includes the following steps:

[0060] (1) Using phosphorus tailings as raw material, the silicon content is 23.25%, the calcium content is 35%, the silicon-calcium molar ratio is 0.95, and the tailings are ground into powder by mechanical grinding with a particle size of less than 150 mesh.

[0061] (2) The tailings were calcined in a muffle furnace at 1250 °C for 4 h and then directly removed and water-cooled;

[0062] (3) Take 10.0 g of calcined tailings and add it to 200 mL of 3.0 mol / L hydrochloric acid, and leach it at 60 °C for 4 h;

[0063] (4) Add 5.84g of aluminum chloride and stir until homogeneous. The molar ratio of calcium to aluminum in the mixture is approximately 2.0.

[0064] (5) Then slowly add a mixed solution of 2.0 mol / L sodium hydroxide and 0.5 mol / L sodium carbonate to the above solution to adjust the pH value to 11.0;

[0065] (6) Subsequently, the mixture was transferred to an oven at 60 °C and heated under normal pressure for 12 h. After filtration, it was dried and ground to obtain calcium aluminum hydrotalcite / porous silica heavy metal curing agent.

[0066] Figure 1 The XRD patterns are of the calcium-based hydrotalcite / porous silica heavy metal curing agent prepared in Examples 1-5 of this invention and the calcium-aluminum hydrotalcite, calcium-iron hydrotalcite and calcium-iron-aluminum hydrotalcite prepared in Comparative Examples 1, 3 and 5; wherein the curve corresponding to the phosphorus tailings is the calcium-based hydrotalcite / porous silica heavy metal curing agent in Example 2.

[0067] XRF analysis showed that the mass contents of calcium, aluminum, and silicon in the calcium-aluminum hydrotalcite / porous silica heavy metal curing agent were 28.76%, 9.11%, and 19.46%, respectively. XRD confirmed the presence of amorphous silica and calcium-aluminum hydrotalcite phases; SEM showed that nanosheet-like calcium-aluminum hydrotalcite was interwoven and stacked on porous silica particles. Figure 2 b), Specific surface area is 246.58 g / m² 2 .

[0068] Comparative Example 2

[0069] 14.57 g of calcium chloride and 8.75 g of aluminum chloride were weighed and added to 200 mL of deionized water. Then, a mixed solution of 2.0 mol / L sodium hydroxide and 0.5 mol / L sodium carbonate was slowly added dropwise to the solution to adjust the pH to 11.0. The mixture was then transferred to a 60 °C oven and hydrothermally dried at atmospheric pressure for 12 h. After filtration, the mixture was dried and ground to obtain calcium-aluminum hydrotalcite. The specific surface area of ​​this calcium-aluminum hydrotalcite was 74.35 g / m². 2 .

[0070] Figure 2 g is a SEM image of the calcium-iron hydrotalcite prepared in Comparative Example 2, which has a dense bulk structure composed of stacked platy bodies.

[0071] Remediation of contaminated soil by calcium aluminum hydrotalcite / porous silica heavy metal solidification agent: Soil samples contaminated with Pb, Zn, and Cu (Pb, Zn, and Cu contents were 2506 mg / kg, 1200.98 mg / kg, and 432 mg / kg, respectively, far exceeding the soil risk screening value) were taken. Three groups of 1000 g soil samples were mixed with a blank (without any added substances), 20 g of calcium iron hydrotalcite prepared in Comparative Example 2, and 20 g of calcium aluminum hydrotalcite / porous silica heavy metal solidification agent prepared in Example 2 in 1 L beakers. After thorough mixing, 500 ml of deionized water was added and the mixture was left to stand naturally. The effective concentrations of Pb, Zn, and Cu were measured at regular intervals. The results showed that, compared with the blank control, the effective concentrations of Pb, Zn, and Cu in Example 2 decreased by 83.22%, 87.38%, and 90.15% respectively after 28 days; compared with the calcium aluminum hydrotalcite in Comparative Example 2, the effective concentrations of Pb, Zn, and Cu in Example 2 decreased by 27.27%, 65.55%, and 39.09% respectively after 28 days. See Table 2 for details.

[0072] Table 2. Changes in the available concentrations of Pb, Zn, and Cu at different remediation time periods (mg / kg)

[0073]

[0074] Example 3

[0075] A method for preparing a calcium-based hydrotalcite / porous silica heavy metal curing agent from high-silica calcium tailings specifically includes the following steps:

[0076] (1) Using copper tailings as raw material, the silicon content is 21.82%, the calcium content is 23.04%, the silicon-calcium molar ratio is 1.35, and it is mechanically ground to a particle size of less than 200 mesh;

[0077] (2) The tailings were calcined in a muffle furnace at 1180 °C for 2 h and then directly removed and water-cooled;

[0078] (3) Take 10.0 g of calcined tailings and add it to 100 mL of 3.0 mol / L hydrochloric acid, and leach it at 40 °C for 3 h;

[0079] (4) Add 2.34g of ferric chloride solution and stir until homogeneous. The molar ratio of calcium to iron in the mixed system is approximately 4.0.

[0080] (5) Then slowly add a mixed solution of 2.0 mol / L sodium hydroxide and 0.5 mol / L sodium carbonate to the above solution to adjust the pH value to 11.0;

[0081] (6) Subsequently, the mixture was transferred to an oven at 60 °C and heated under normal pressure for 36 h. After filtration, it was dried and ground to obtain calcium iron hydrotalcite / porous silica heavy metal curing agent.

[0082] Figure 1 The XRD patterns are of the calcium-based hydrotalcite / porous silica heavy metal curing agent prepared in Examples 1-5 of this invention and the calcium-aluminum hydrotalcite, calcium-iron hydrotalcite and calcium-iron-aluminum hydrotalcite prepared in Comparative Examples 1, 3 and 5; wherein the curve corresponding to the copper tailings is the calcium-based hydrotalcite / porous silica heavy metal curing agent in Example 3.

[0083] XRF analysis showed that the mass contents of calcium, iron, and silicon in the calcium-iron hydrotalcite / porous silica heavy metal curing agent were 19.76%, 4.68%, and 17.46%, respectively. XRD confirmed the presence of amorphous silica and calcium-iron hydrotalcite phases; SEM showed that nanosheet-like calcium-iron hydrotalcite particles were interwoven and stacked on porous silica particles. Figure 2 c), with a specific surface area of ​​316.17 g / m². 2 .

[0084] Comparative Example 3

[0085] 4.80 g of calcium chloride and 1.74 g of ferric chloride were weighed and added to 200 mL of deionized water. Then, a mixed solution of 2.0 mol / L sodium hydroxide and 0.5 mol / L sodium carbonate was slowly added dropwise to the solution to adjust the pH to 11.0. The mixture was then transferred to a 60 °C oven and hydrothermally dried at atmospheric pressure for 36 h. After filtration, the mixture was dried and ground to obtain calcium-iron hydrotalcite. The specific surface area of ​​this calcium-iron hydrotalcite was 58.34 g / m². 2 .

[0086] Figure 1 The images show the XRD patterns of the calcium-based hydrotalcite / porous silica heavy metal curing agent prepared in Examples 1-5 of this invention and the calcium-aluminum hydrotalcite, calcium-iron hydrotalcite, and calcium-iron-aluminum hydrotalcite prepared in Comparative Examples 1, 3, and 5; wherein the curve corresponding to the calcium-aluminum hydrotalcite is the calcium-based hydrotalcite / porous silica heavy metal curing agent in Comparative Example 3.

[0087] Figure 2 h is a SEM image of the calcium aluminum hydrotalcite prepared in Comparative Example 3, which is composed of stacked sheet-like structures of uneven size.

[0088] Remediation of contaminated soil by calcium-iron hydrotalcite / porous silica heavy metal solidification agent: Soil samples contaminated with As and Hg (As and Hg contents of 2380 mg / kg and 1300 mg / kg, respectively, far exceeding the soil risk screening value) were tested. Three groups of 1000 g soil samples were mixed thoroughly in 1 L beakers with a blank (without any added substances), 20 g of calcium-aluminum hydrotalcite prepared in Comparative Example 3, and 20 g of calcium-iron hydrotalcite / porous silica heavy metal solidification agent prepared in Example 3. After mixing, 500 ml of deionized water was added, and the mixture was left to stand naturally. Samples were taken at regular intervals, and the effective concentrations of As and Hg were measured. The results showed that compared to the blank control, the effective concentrations of As and Hg in Example 3 decreased by 87.46% and 91.92%, respectively, after 28 days; compared to the calcium-iron hydrotalcite in Comparative Example 3, the effective concentrations of As and Hg in Example 3 decreased by 39.46% and 57.83%, respectively, after 28 days. See Table 3 for details.

[0089] Table 3. Changes in the effective concentrations of As and Hg at different remediation time periods (mg / kg)

[0090]

[0091] Example 4

[0092] A method for preparing a calcium-based hydrotalcite / porous silica heavy metal curing agent from high-silica calcium tailings specifically includes the following steps:

[0093] (1) Using titanium tailings as raw material, the silicon content is 21.48%, the calcium content is 18.29%, the silicon-calcium molar ratio is 1.68, and it is mechanically ground to a particle size of less than 150 mesh.

[0094] (2) The tailings were calcined in a muffle furnace at 1230 °C for 1 h and then directly removed and water-cooled;

[0095] (3) Take 10.0 g of calcined tailings and add it to 100 mL of 3.0 mol / L hydrochloric acid, and leach it at 40 °C for 4 h;

[0096] (4) Add 6.72g of ferric nitrate hexahydrate solution and stir until homogeneous. The molar ratio of calcium to iron in the mixed system is approximately 1.98.

[0097] (5) Then slowly add a mixed solution of 2.0 mol / L sodium hydroxide and 0.5 mol / L sodium carbonate to the above solution to adjust the pH value to 11.0;

[0098] (6) Subsequently, the mixture was transferred to an oven at 60 °C and heated under normal pressure for 36 h. After filtration, it was dried and ground to obtain calcium aluminum hydrotalcite / porous silica heavy metal curing agent.

[0099] Figure 1 The images show the XRD patterns of the calcium-based hydrotalcite / porous silica heavy metal curing agent prepared in Examples 1-5 of this invention and the calcium-aluminum hydrotalcite, calcium-iron hydrotalcite, and calcium-iron-aluminum hydrotalcite prepared in Comparative Examples 1, 3, and 5; wherein the curve corresponding to titanium tailings is the calcium-based hydrotalcite / porous silica heavy metal curing agent in Example 4.

[0100] XRF analysis showed that the calcium, iron, and silicon content of the calcium-iron hydrotalcite / porous silica heavy metal curing agent was 16.12%, 5.78%, and 18.33% by mass, respectively. XRD confirmed the presence of amorphous silica and calcium-iron hydrotalcite phases; SEM showed that nanosheet-like calcium-iron hydrotalcite particles were interwoven and stacked on porous silica particles. Figure 2 d), specific surface area is 377.26 g / m² 2 .

[0101] Comparative Example 4

[0102] 5.10 g of calcium chloride and 6.72 g of ferric nitrate hexahydrate were weighed and added to 200 mL of deionized water. Then, a mixed solution of 2.0 mol / L sodium hydroxide and 0.5 mol / L sodium carbonate was slowly added dropwise to the solution to adjust the pH to 11.0. The mixture was then transferred to an oven at 40 °C and subjected to hydrothermal treatment at atmospheric pressure for 36 h. After filtration, the mixture was dried and ground to obtain calcium-iron hydrotalcite. The specific surface area of ​​this calcium-iron hydrotalcite was 46.49 g / m². 2 .

[0103] Remediation of contaminated soil using calcium iron hydrotalcite / porous silica heavy metal solidification agent: Soil samples contaminated with Cr and As (Cr and As content 1335 mg / kg) -1 and 63.9 mg kg -1(The concentrations were far higher than the soil risk screening values). Three groups of 1000 g soil samples were taken and thoroughly mixed with a blank (without any added substances), 20 g of calcium aluminum hydrotalcite prepared in Comparative Example 4, and 20 g of calcium iron hydrotalcite / porous silica heavy metal solidifying agent prepared in Example 4 in 1 L beakers. 500 ml of deionized water was added, and the mixtures were left to stand naturally. Samples were taken at regular intervals, and the effective concentrations of Cr and As were measured. The results showed that compared with the blank control, the effective concentrations of As and Cr in Example 4 decreased by 97.75% and 92.14% respectively after 28 days; compared with the calcium iron hydrotalcite in Comparative Example 4, the effective concentrations of As and Cr in Example 4 decreased by 50% and 60.84% ​​respectively after 28 days. See Table 4 for details.

[0104] Table 4. Changes in the effective concentrations of As and Cr at different remediation time periods (mg / kg)

[0105]

[0106] Example 5

[0107] A method for preparing a calcium-based hydrotalcite / porous silica heavy metal curing agent from high-silica calcium tailings specifically includes the following steps:

[0108] (1) Using lead-zinc tailings as raw material, the silicon content is 25.36%, the calcium content is 24.45%, the silicon-calcium molar ratio is 1.48, and it is mechanically ground to a particle size of less than 200 mesh;

[0109] (2) The tailings were calcined in a muffle furnace at 1300 °C for 2 h and then directly removed and water-cooled;

[0110] (3) Take 10.0 g of calcined tailings and add it to 100 mL of 2.0 mol / L hydrochloric acid, and leach it at 40 °C for 4 h;

[0111] (4) Add 2.00 g of aluminum chloride and 2.50 g of ferric chloride and stir until homogeneous. The molar ratio of calcium to trivalent aluminum and iron in the mixed system is approximately 2.0.

[0112] (5) Then slowly add a mixed solution of 2.0 mol / L sodium hydroxide and 0.5 mol / L sodium carbonate to the above solution to adjust the pH value to 11.0;

[0113] (6) Subsequently, the mixture was transferred to an oven at 60 °C and heated under normal pressure for 36 h. After filtration, it was dried and ground to obtain calcium aluminum iron hydrotalcite / porous silica heavy metal curing agent.

[0114] Figure 1The images show the XRD patterns of the calcium-based hydrotalcite / porous silica heavy metal curing agent prepared in Examples 1-5 of this invention and the calcium-aluminum hydrotalcite, calcium-iron hydrotalcite, and calcium-iron-aluminum hydrotalcite prepared in Comparative Examples 1, 3, and 5; wherein the curve corresponding to the lead-zinc tailings is the calcium-based hydrotalcite / porous silica heavy metal curing agent in Example 5.

[0115] XRF analysis showed that the mass contents of calcium, aluminum, iron, and silicon in the calcium-aluminum-iron hydrotalcite / porous silica heavy metal curing agent were 18.79%, 2.31%, 2.81%, and 21.34%, respectively. XRD confirmed the presence of amorphous silica and calcium-aluminum-iron hydrotalcite phases; SEM showed that nanosheet-like calcium-aluminum-iron hydrotalcite was interwoven and stacked on porous silica particles. Figure 2 e), with a specific surface area of ​​313.58 g / m². 2 .

[0116] Comparative Example 5

[0117] 14.05 g of calcium chloride, 4.16 g of aluminum chloride, and 5.06 g of ferric chloride were weighed and added to 200 mL of deionized water. Then, a mixed solution of 2.0 mol / L sodium hydroxide and 0.5 mol / L sodium carbonate was slowly added dropwise to the above solution to adjust the pH to 11.0. Subsequently, the mixture was transferred to an oven at 40 °C and subjected to hydrothermal treatment at atmospheric pressure for 36 h. After filtration, the mixture was dried and ground to obtain calcium-aluminum-iron hydrotalcite. The specific surface area of ​​this calcium-aluminum-iron hydrotalcite was 55.38 g / m². 2 .

[0118] Figure 1 The images show the XRD patterns of the calcium-based hydrotalcite / porous silica heavy metal curing agent prepared in Examples 1-5 of this invention and the calcium-aluminum hydrotalcite, calcium-iron hydrotalcite, and calcium-iron-aluminum hydrotalcite prepared in Comparative Examples 1, 3, and 5; wherein the curve corresponding to the calcium-iron-aluminum hydrotalcite is the calcium-aluminum-iron hydrotalcite in Comparative Example 5.

[0119] Figure 2 i is a SEM image of calcium-iron-aluminum hydrotalcite prepared in Comparative Example 5, which has a loose structure composed of interspersed granular and a small amount of platy structures.

[0120] Remediation of contaminated soil using calcium aluminum iron hydrotalcite / porous silica heavy metal solidification agent: Soil samples contaminated with Cr and As (Cr and As content 1335 mg kg) -1 and 63.9 mg kg -1(The concentration of Cr and As was far higher than the soil risk screening value). Three groups of 1000g soil samples were taken and thoroughly mixed with the blank (without any added substances), 10g of calcium aluminum hydrotalcite prepared in Comparative Example 5, and 10g of calcium aluminum iron hydrotalcite / porous silica heavy metal solidifying agent prepared in Example 5 in 1 L beakers. After mixing, 500 ml of deionized water was added and the mixture was left to stand naturally. Samples were taken at regular intervals and the effective concentrations of Cr and As were measured. The results showed that compared with the blank control, the effective concentrations of As and Cr in Example 5 decreased by 87.93% and 87.79% respectively after 28 days; compared with the calcium aluminum iron hydrotalcite in Comparative Example 5, the effective concentrations of As and Cr in Example 5 decreased by 23.31% and 50.39% respectively after 28 days. See Table 5 for details.

[0121] Table 5. Changes in the effective concentrations of Cr and As at different remediation time periods (mg / kg)

[0122]

Claims

1. A high-silica calcium tailings to produce calcium-based hydrotalcite / porous silica heavy metal solidifier, characterized in that, The calcium-based hydrotalcite / porous silica heavy metal curing agent uses porous silica as a substrate, with calcium-based hydrotalcite uniformly dispersed and grown on the porous silica. The preparation method of the calcium-based hydrotalcite / porous silica heavy metal curing agent from high-silica calcium tailings includes the following steps in sequence: (1) Obtaining high-silicon calcium tailings and pre-treating them; wherein, the high-silicon calcium tailings include one or more of iron tailings, phosphorus tailings, copper tailings, titanium tailings or lead-zinc tailings, the high-silicon calcium tailings contain quartz, calcite or dolomite, the sum of the mass contents of silicon and calcium in the tailings is greater than 35% of the total mass of the tailings, and the silicon / calcium molar ratio is 0.75-2.0; (2) Calcination activation: The high-silicon calcium tailings pretreated in step (1) are calcined and then taken out at high temperature and directly water-cooled for activation; wherein the calcination temperature is 1180-1500 ℃ and the calcination time is 1-4 h; (3) Leaching of silicon and calcium elements: The activated tailings are acid-leached to obtain a mixed system containing free calcium ions and porous silica solids; (4) Introduction of exogenous trivalent aluminum and iron ions: Add aluminum source and / or iron source to obtain a mixed system of free calcium ions, aluminum ions and / or iron ions and porous silica solid. (5) Coprecipitation process: Add a mixed solution of sodium carbonate and sodium hydroxide to the above mixed system and stir continuously to adjust the pH of the system; (6) Crystallization treatment: The above-mentioned pH-adjusted mixture is heated and stirred, and subjected to hydrothermal treatment at normal pressure; after a period of reaction, the solid and liquid are separated to obtain a solid, which is then washed, dried and ground to obtain calcium-based hydrotalcite / porous silica heavy metal curing agent.

2. The method for preparing a calcium-based hydrotalcite / porous silica heavy metal solidification agent from high-silica calcium tailings according to claim 1, characterized by, The steps are as follows: (1) Obtaining high-silicon calcium tailings and pre-treating them; wherein, the high-silicon calcium tailings include one or more of iron tailings, phosphorus tailings, copper tailings, titanium tailings or lead-zinc tailings, the high-silicon calcium tailings contain quartz, calcite or dolomite, the sum of the mass contents of silicon and calcium in the tailings is greater than 35% of the total mass of the tailings, and the silicon / calcium molar ratio is 0.75-2.0; (2) Calcination activation: The high-silicon calcium tailings pretreated in step (1) are calcined and then taken out at high temperature and directly water-cooled for activation; wherein the calcination temperature is 1180-1500 ℃ and the calcination time is 1-4 h; (3) Leaching of silicon and calcium elements: The activated tailings are acid-leached to obtain a mixed system containing free calcium ions and porous silica solids; (4) Introduction of exogenous trivalent aluminum and iron ions: Add aluminum source and / or iron source to obtain a mixed system of free calcium ions, aluminum ions and / or iron ions and porous silica solid. (5) Coprecipitation process: Add a mixed solution of sodium carbonate and sodium hydroxide to the above mixed system and stir continuously to adjust the pH of the system; (6) Crystallization treatment: The above-mentioned pH-adjusted mixture is heated and stirred, and subjected to hydrothermal treatment at normal pressure; after a period of reaction, the solid and liquid are separated to obtain a solid, which is then washed, dried and ground to obtain calcium-based hydrotalcite / porous silica heavy metal curing agent.

3. The production method according to claim 2, characterized by, In step (1), the pretreatment is mechanical grinding, and the particle size needs to be ground to 80 mesh or below.

4. The production method according to claim 2, characterized by, In step (3), the acid used in the acid leaching is hydrochloric acid and / or nitric acid, the acid concentration is 2-6 mol / L, the leaching temperature is 40-80 ℃, the leaching time is 0.5-6 h, and the solid-liquid ratio in the mixed system containing free calcium ions and porous silica solid is 1:5-1:40, with the solid-liquid ratio unit being g / mL.

5. The preparation method according to claim 2, characterized in that, In step (4), the aluminum source and / or iron source includes one or more of aluminum nitrate, aluminum chloride, aluminum hydroxide, ferric nitrate or ferric chloride; the molar ratio of the total molar amount of calcium to trivalent aluminum and / or iron ions in the mixed system is 6:1-1:

1.

6. The preparation method according to claim 2, characterized in that, In step (5), the concentration of sodium hydroxide is 0.5-6 mol / L, and the concentration of sodium carbonate solution is 0.2-1.0 mol / L.

7. The preparation method according to claim 2, characterized in that, In step (5), the pH of the system is adjusted to 10-12.

8. The preparation method according to claim 2, characterized in that, In step (6), the temperature of the atmospheric pressure hydrothermal treatment is 60-80 ℃ and the time is 12-48 h.

9. The application of a calcium-based hydrotalcite / porous silica heavy metal solidifying agent prepared from high-silica calcium tailings as described in claim 1, or a calcium-based hydrotalcite / porous silica heavy metal solidifying agent prepared by any one of claims 2-8, in the remediation of heavy metal contaminated soil.

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