A method for preparing aluminum-based hydrotalcite using aluminum-containing solid waste, the obtained aluminum-based hydrotalcite and its applications

Abstract

The present invention discloses a method for preparing aluminum-based hydrotalcite using aluminum-containing solid waste, the obtained aluminum-based hydrotalcite, and its application. The method for preparing aluminum-based hydrotalcite using aluminum-containing solid waste includes: (1) taking the aluminum-containing solid waste generated during the synthesis of benzotriazole ultraviolet absorbers for calcination to obtain low-grade Al2O3; (2) measuring the aluminum content in the low-grade Al2O3; (3) taking the low-grade Al2O3 as the aluminum source, adding an appropriate amount of divalent metal hydroxide, anion source, and deionized water, stirring evenly, and then carrying out a hydrothermal reaction to obtain aluminum-based hydrotalcite. The present invention provides the application of the described aluminum-based hydrotalcite as a heavy metal ion treatment agent in water bodies or soil. The present invention not only reduces the difficulty and cost of recycling aluminum resources in aluminum-containing solid waste, realizes the resource utilization of aluminum-containing solid waste, but also reduces the production cost of aluminum-based hydrotalcite, and the obtained aluminum-based hydrotalcite has good adsorption performance for heavy metal ions.

Description

Technical Field

[0001] The present invention relates to the field of comprehensive utilization of aluminum resources, and specifically relates to a method for preparing aluminum-based hydrotalcite using aluminum-containing solid waste (i.e., aluminum-containing solid waste), the obtained aluminum-based hydrotalcite, and its application in adsorbing heavy metal ions. Background Art

[0002]

[0003] In the process of reducing azo intermediates to benzotriazole ultraviolet absorbers, alkaline aluminum-containing waste liquid is generated due to the use of aluminum powder as a reducing agent, and its main component is NaAlO 2 . Then, the waste acid generated during the pickling of the product is used to neutralize the alkaline aluminum-containing waste liquid, generating aluminum-containing waste residue mainly composed of Al(OH) 3 , which also contains impurities such as Cl - , SO 4 2- , nitrogen-containing organic matter, and tar. Most of the existing treatment methods are to calcine the waste residue at high temperature to burn off organic impurities and form low-grade Al 2 O 3 for recycling. According to the existing production scale of benzotriazole ultraviolet absorber products, tens of thousands of tons of aluminum-containing waste residue are generated every year, causing great environmental protection pressure and treatment costs to industry enterprises. Moreover, the low-grade Al 2 O 3 has low added value and low utilization rate. Therefore, there is an urgent need to develop new treatment technologies for aluminum-containing waste to effectively recycle aluminum-containing waste and improve the market competitiveness of enterprises.

[0004] Currently, most of the research on waste aluminum resources focuses on waste aluminum recycling and reuse. Inevitably, the quality of recycled aluminum will decrease during waste aluminum recycling. Generally, aluminum resource recycling can be divided into three categories, namely downgraded recycling, grade-preserved recycling, and cross-grade recycling (extracting primary aluminum from waste aluminum alloys). At present, waste aluminum recycling in China is still mainly based on remelting and downgraded recycling. This recycling method involves two aspects: sorting technology and selective purification to remove impurities. It has high energy consumption, generates a large amount of waste residue, and the recycling rate of aluminum is also very low, and it is difficult to meet the material requirements for forged aluminum. Unless innovative aluminum recycling technologies are developed, approximately 3.6 million tons of secondary aluminum will become "dead metal" by 2040. Grade-preserved recycling of waste aluminum can maintain most of the value of waste aluminum. Currently, grade-preserved recycling is the main method of waste aluminum recycling. However, a large amount of aluminum generated by grade-preserved recycling cannot be digested, which will also lead to the accumulation of a large amount of aluminum resources. Cross-grade recycling is the main direction of the future recycled aluminum industry, but cross-grade recycling requires a high level of technology and is difficult for small and medium-sized aluminum industries to afford and cannot be widely promoted on a large scale.

[0005] It can be seen that for the current comprehensive utilization of waste aluminum resources, most efforts are focused on recycling metallic aluminum from waste aluminum resources through various recycling technologies to achieve the reuse of aluminum resources. There is little research on using waste aluminum resources to prepare aluminum-containing materials with high added value.

[0006] Aluminum-based hydrotalcite, as a type of layered double hydroxide (LDHs), has a two-dimensional layered structure, and its chemical composition can be expressed as:

[0007]

[0008] Among them, M 2+ is a divalent metal cation such as Mg 2+ , Ni 2+ , Co 2+ , Zn 2+ , Cu 2+ ; M 3+ is Al 3+ ; A n- is an anion, such as CO 3 2- , NO 3 - , Cl - , OH - , SO 4 2- , PO 4 3- , C 6 H 4 (COO) 2 2- and other inorganic and organic ions as well as complex ions. Different interlayer anions result in different layer spacings of LDHs.

[0009] Due to its special layered structure and physicochemical properties, aluminum-based hydrotalcite exhibits significant application potential in adsorbing heavy metal ions. Aluminum-based hydrotalcite can be used to treat wastewater containing heavy metal ions, removing heavy metal ions from the wastewater through adsorption to achieve the purpose of purifying the water body. For soil contaminated by heavy metals, aluminum-based hydrotalcite can be used as a soil remediation agent, adsorbing and fixing heavy metal ions in the soil to reduce their bioavailability, thereby reducing the harm to the environment and human body. In industrial fields such as electroplating, metallurgy, and chemical engineering, the wastewater generated often contains high concentrations of heavy metal ions. Aluminum-based hydrotalcite can be used as a treatment agent for these industrial wastewaters to effectively remove heavy metal ions from the wastewater and achieve the standard discharge of the wastewater.

[0010] The present invention uses the aluminum-containing solid waste generated in the synthesis process of benzotriazole ultraviolet absorbers as raw materials. After calcination and washing, aluminum-based hydrotalcite is prepared and applied in the field of heavy metal pollution treatment, realizing the effective utilization of aluminum resources. And unexpectedly, it is found that the aluminum-based hydrotalcite has an even better treatment effect on heavy metal cadmium ions than the aluminum-based hydrotalcite prepared from pure alumina. Summary of the Invention

[0011] Aiming at the deficiencies in the utilization of existing waste aluminum resources, the purpose of the present invention is to provide a method for preparing aluminum-based hydrotalcite using aluminum-containing solid waste generated in the synthesis process of benzotriazole ultraviolet absorbers as the aluminum source raw material, the aluminum-based hydrotalcite prepared according to this method, and the application of this aluminum-based hydrotalcite in the treatment of heavy metal ions. The present invention not only reduces the difficulty and cost of recycling aluminum resources in aluminum-containing solid waste, realizes the resource utilization of aluminum-containing solid waste, but also the prepared aluminum-based hydrotalcite has a good adsorption effect on heavy metal ions.

[0012] To achieve the above-mentioned invention purpose, the technical solution of the present invention is as follows:

[0013] In the first aspect, the present invention provides a method for preparing aluminum-based hydrotalcite using aluminum-containing solid waste, including the following steps:

[0014] (1) Take the aluminum-containing solid waste generated in the synthesis process of benzotriazole ultraviolet absorbers for calcination to burn off organic impurities and obtain low-grade Al 2 O 3 ;

[0015] (2) Measure the aluminum content in the low-grade Al 2 O 3 obtained in step (1);

[0016] (3) Weigh a certain amount of the low-grade Al 2 O 3 obtained in step (1) as the aluminum source and place it in a hydrothermal reaction kettle. According to the aluminum content measured in step (2), add an appropriate amount of divalent metal hydroxide and anion source to the hydrothermal reaction kettle. The divalent metal hydroxide is calcium hydroxide, and the anion source is a chlorine source, so that the molar ratio of calcium to aluminum in the feed is 1:1 to 5:1. Add deionized water, stir evenly, and then carry out hydrothermal reaction in an oven. The hydrothermal reaction temperature is 60-150°C, and the hydrothermal reaction time is 8-36h. After sufficient reaction, take out the reaction mixture from the hydrothermal reaction kettle, cool it, filter and wash the precipitate until the filtrate is neutral, and then obtain aluminum-based hydrotalcite after drying and grinding.

[0017] Preferably, in step (1), the calcination temperature is 550 - 750 °C, more preferably 600 - 700 °C, and even more preferably 600 °C; the calcination time is 2 - 6 h, more preferably 3 - 4 h, and even more preferably 3 h.

[0018] Preferably, step (1) is specifically implemented as follows: Put the aluminum-containing waste into a crucible, then transfer it into a muffle furnace, heat it up to the calcination temperature, keep it at the calcination temperature for a certain time, then cool it down and take it out, wash it with water, dry it, and grind it to obtain low-grade Al 2 O 3 。

[0019] Preferably, in step (2), the obtained low-grade Al 2 O 3 is acid-dissolved at high temperature, and after it is dissolved, the aluminum content therein is determined by the EDTA titration method. More preferably, the acid is sulfuric acid with a concentration of 0.1 - 1 mol / L, preferably 0.2 - 0.5 mol / L. For the high-temperature acid dissolution, the reaction temperature is 60 - 100 °C, preferably 80 - 100 °C.

[0020] Preferably, in step (3), the chlorine source is sodium chloride or calcium chloride, and most preferably calcium chloride. The addition amount of the anion source is determined according to the element stoichiometry of the aluminum-based hydrotalcite and the amounts of aluminum and divalent metal in the system.

[0021] As a further preference, in step (3), the molar ratio of calcium to aluminum in the feed is 2:1 to 4:1, and even more preferably 2:1.

[0022] Preferably, in step (3), the feed ratio of the low-grade alumina to deionized water is 1 - 2 g : 40 - 60 mL.

[0023] Preferably, in step (3), the hydrothermal reaction temperature is 120 - 150 °C, more preferably 150 °C; the hydrothermal reaction time is 16 - 24 h, more preferably 24 h.

[0024] Preferably, in step (3), the drying temperature is 60 - 100 °C, preferably 80 - 90 °C; the drying time is 4 - 8 h.

[0025] The present invention particularly preferably adopts the following technical solution: In step (3), the divalent metal hydroxide is calcium hydroxide, the anion source is calcium chloride, the molar ratio of calcium to aluminum in the feed is controlled to be 2:1, the hydrothermal reaction temperature is 150 °C, and the hydrothermal reaction time is 24 h.

[0026] In the second aspect, the present invention provides an aluminum-based hydrotalcite prepared by the method according to the first aspect.

[0027] Thirdly, the present invention provides the use of the aluminum-based hydrotalcite described in the second aspect as a heavy metal ion treatment agent in water bodies or soil.

[0028] Preferably, the heavy metal ion is a cadmium ion.

[0029] Compared with the existing technologies for the utilization of aluminum-containing solid wastes, the present invention has the following advantages:

[0030] (1) Starting from aluminum-containing solid wastes, low-grade alumina is obtained by calcination at a suitable temperature, and then aluminum-based hydrotalcite is prepared through a simple hydrothermal reaction, which can be used for the effective treatment of heavy metals in water bodies and soil, and has good application prospects. The treatment technology involved in the present invention reduces the difficulty and cost of the recycling and utilization of aluminum resources in aluminum-containing solid wastes, realizes the resource utilization of aluminum-containing solid wastes, and has good application and promotion value.

[0031] (2) When the aluminum-based hydrotalcite prepared from aluminum-containing solid wastes in the present invention is used for the treatment of heavy metals in water bodies and soil, its best treatment effect exceeds that of the aluminum-based hydrotalcite prepared from pure alumina. Therefore, the present invention can not only turn waste into treasure for aluminum-containing solid wastes, significantly reduce the production cost of aluminum-based hydrotalcite, but also improve its treatment effect on heavy metal ions. Description of the Drawings

[0032] Figure 1 XRD pattern of solid aluminum waste;

[0033] Figure 2 XRD pattern of the aluminum source after calcination in Examples 1-4;

[0034] Figure 3 XRD pattern of the aluminum-based hydrotalcite prepared in Example 5;

[0035] Figure 4 XRD pattern of the aluminum-based hydrotalcite prepared in Example 6;

[0036] Figure 5 XRD pattern of the aluminum-based hydrotalcite prepared in Example 7;

[0037] Figure 6 XRD pattern of the aluminum-based hydrotalcite prepared in Example 8;

[0038] Figure 7 XRD pattern of the aluminum-based hydrotalcite prepared in Example 9;

[0039] Figure 8 Infrared spectrum of the aluminum-based hydrotalcite prepared in Example 6;

[0040] Figure 9 Showing the influence of the initial pH of cadmium nitrate aqueous solution on the adsorption of Cd by aluminum-based hydrotalcite 2+ by;

[0041] Figure 10 Show the influence of the dosage of aluminum-based hydrotalcite on the removal of Cd 2+ ;

[0042] Figure 11 Show the influence of the oscillation time on the removal of Cd by aluminum-based hydrotalcite 2+ ; Specific embodiments

[0043] The present invention will be further described below in conjunction with embodiments and the accompanying drawings. However, the embodiments of the present invention are not limited thereto, and there can be many variations. If there are no particularly detailed descriptions below, those skilled in the art can understand them according to the usual expressions or implement them according to the existing technology.

[0044] Examples 1-4

[0045] Take a certain amount of aluminum-containing solid waste (the measured COD value is 591 mg / L, and the XRD pattern is shown in Figure 1 ) and put it into a crucible, then transfer it to a muffle furnace and heat it to 550 °C (Example 1), 600 °C (Example 2), 650 °C (Example 3), 700 °C (Example 4) at a rate of 5 °C / min, and calcine it at this temperature for 3 h. After cooling, take it out, wash it with water, dry it, and grind it to obtain low-grade alumina. The XRD pattern of this low-grade alumina is shown in Figure 2 .

[0046] Take a certain amount of low-grade alumina and dissolve it in 0.5 mol / L dilute sulfuric acid at 100 °C for 2 h. After it is dissolved, determine its aluminum content by the EDTA titration method, and convert the aluminum content into Al 2 O 3 content. The results are shown in Table 1.

[0047] Table 1 Al in the low-grade alumina obtained from Examples 1-4 2 O 3 content

[0048]

[0049] Example 5

[0050] Weigh 2.368 g of Ca(OH) 2 , 0.932 g of NaCl and 1.432 g of low-grade alumina obtained by calcining at 650 °C for 3 h in Example 3 and place them in a 100 mL hydrothermal reaction kettle. Add 50 mL of deionized water and stir for 15 min, then heat and react at 150 °C for 24 h. After the reaction is completed, wait for the reaction kettle to cool, filter and wash the precipitate until the pH of the filtrate is neutral, then dry it at 80 °C, grind it, and sieve it to obtain aluminum-based hydrotalcite CaAl-LDHs with a calcium-aluminum molar ratio of 2:1. The XRD pattern is shown in Figure 3。

[0051] Example 6

[0052] Weigh 1.776 g of Ca(OH) 2 , 0.888 g of CaCl 2 , and 1.432 g of low-grade alumina obtained by calcining at 600 °C for 3 h in Example 2 and place them in a 100 mL hydrothermal reactor. Add 50 mL of deionized water and stir for 15 min, then heat and react at 150 °C for 24 h. After the reaction is completed, wait for the reactor to cool, filter and wash the precipitate until the pH of the filtrate is neutral, then dry at 80 °C, grind, and sieve to obtain aluminum-based hydrotalcite CaAl-LDHs with a calcium-aluminum molar ratio of 2:1. Its XRD pattern is shown in Figure 4 , and its infrared spectrum is shown in Figure 8 。

[0053] Example 7

[0054] Weigh 1.776 g of Ca(OH) 2 , 0.888 g of CaCl 2 , and 1.432 g of low-grade alumina obtained by calcining at 700 °C for 3 h in Example 4 and place them in a 100 mL hydrothermal reactor. Add 50 mL of deionized water and stir for 15 min, then heat and react at 120 °C for 16 h. After the reaction is completed, wait for the reactor to cool, filter and wash the precipitate until the pH of the filtrate is neutral, then dry at 80 °C, grind, and sieve to obtain aluminum-based hydrotalcite CaAl-LDHs with a calcium-aluminum molar ratio of 2:1. Its XRD pattern is shown in Figure 5 。

[0055] Example 8

[0056] Weigh 2.96 g of Ca(OH) 2 , 0.888 g of CaCl 2 , and 1.432 g of low-grade alumina obtained by calcining at 600 °C for 3 h in Example 2 and place them in a 100 mL hydrothermal reactor. Add 50 mL of deionized water and stir for 15 min, then heat and react at 90 °C for 16 h. After the reaction is completed, wait for the reactor to cool, filter and wash the precipitate until the pH of the filtrate is neutral, then dry at 80 °C, grind, and sieve to obtain aluminum-based hydrotalcite CaAl-LDHs with a calcium-aluminum molar ratio of 3:1. Its XRD pattern is shown in Figure 6 。

[0057] Example 9

[0058] Weigh 4.144 g of Ca(OH) 2 , 0.888 g of CaCl 2And 1.432 g of low-grade alumina obtained by calcining at 600 °C for 3 h in Example 2 were placed in a 100 mL hydrothermal reactor, 50 mL of deionized water was added and stirred for 15 min, and then heated and reacted at 60 °C for 8 h. After the reaction was completed, the reactor was cooled, the precipitate was filtered and washed until the pH of the filtrate was neutral, and then dried at 80 °C, ground and sieved to obtain aluminum-based hydrotalcite CaAl-LDHs with a calcium-aluminum molar ratio of 4:1. The XRD pattern is shown in Figure 7 .

[0059] Comparative Example 1

[0060] Weigh 3.552 g of Ca(OH) 2 , 0.888 g of CaCl 2 and 0.816 g of pure γ-Al 2 O 3 (200-300 mesh, Shanghai Macklin Biochemical Co., Ltd.) were placed in a 100 ml hydrothermal reactor, 50 ml of deionized water was added and stirred for 15 min, and then heated and reacted at 150 °C for 24 h. After the reaction was completed, the reactor was cooled, the precipitate was filtered and washed until the pH of the filtrate was neutral, and then dried at 80 °C, ground and sieved to obtain aluminum-based hydrotalcite CaAl-LDHs with a calcium-aluminum molar ratio of 2:1.

[0061] Example 10

[0062] Prepare 50 ml of cadmium nitrate aqueous solutions with cadmium nitrate concentrations of 100 ppm and pH adjusted to 2, 3, 4, 5, 6, and 7 with 0.1 mol / L nitric acid, and pour them into 100 ml stoppered Erlenmeyer flasks. Add 0.05 g of the aluminum-based hydrotalcite prepared in Example 6, then place the Erlenmeyer flasks in a constant temperature shaker and shake and react at 25 °C and 200 rpm for 2 h. After that, take out and filter, and the Cd 2+ concentration in the filtrate was measured by an atomic absorption spectrophotometer, and the Cd 2+ removal rate was calculated. The results are shown in Figure 9 . The figure shows that the aluminum-based hydrotalcite has good removal effects on 100 ppm cadmium solutions in a wide pH range (between pH 3 and 7).

[0063] Example 11

[0064] Prepare 50 ml of 100 ppm cadmium nitrate aqueous solution and pour it into a 100 ml stoppered Erlenmeyer flask. Add 0.01 g, 0.02 g, 0.035 g, 0.05 g, 0.075 g, 0.1 g, 0.15 g, and 0.2 g of the aluminum-based hydrotalcite prepared in Example 6 respectively, then place the Erlenmeyer flasks in a constant temperature shaker and shake and react at 25 °C and 200 rpm for 2 h. After that, take out and filter, and the Cd in the filtrate was measured by an atomic absorption spectrophotometer2+ Concentration, calculate Cd 2+ Removal rate, the results are as Figure 10 shown. The illustration shows that when the dosage of the aluminum-based hydrotalcite is 0.01 g, the removal rate of cadmium ions can reach 90%; when the dosage is 0.05 g, the removal rate of cadmium ions basically remains unchanged and can reach 98 - 99%, showing good removal efficiency for cadmium ions.

[0065] Example 12

[0066] Prepare 50 ml of 100 ppm cadmium nitrate aqueous solution and pour it into a 100 ml stoppered conical flask. Add 0.05 g of the aluminum-based hydrotalcite prepared in Example 6. Then place the conical flask in a constant temperature oscillator and oscillate and react at 25 °C and 200 rpm. After reacting for 2 min, 5 min, 10 min, 20 min, 30 min, 60 min, 90 min, and 2 h, sample and filter respectively. The filtrate is measured for Cd 2+ Concentration, calculate Cd 2+ Removal rate, the results are as Figure 11 shown. The illustration shows that when the oscillation time is 5 min, the removal rate of cadmium ions by the aluminum-based hydrotalcite can reach over 97%, showing excellent removal rate in a short time.

[0067] Example 13

[0068] The aluminum-based hydrotalcites prepared in Examples 5 - 9 are respectively used for the treatment of simulated cadmium-containing wastewater. Measure 50 mL of 100 ppm and pour it into a 100 mL stoppered conical flask. Add 0.05 g of the aluminum-based hydrotalcites prepared in Examples 5 - 9 respectively. Then place the conical flask in a constant temperature oscillator and oscillate and react at 25 °C and 200 rpm for 2 h. After that, take it out and filter. The filtrate is measured for Cd 2+ Concentration, calculate Cd 2+ Removal rate, the results are shown in Table 2; in addition, use 0.05 g of the aluminum-based hydrotalcites prepared in Example 6 and Comparative Example 1 to treat 50 mL of cadmium-containing solutions with different concentrations, and oscillate and react at 25 °C and 200 rpm for 2 h. The results are shown in Tables 3 and 4.

[0069] Table 2. Treatment results of the aluminum-based hydrotalcites prepared in Examples 5 - 9 for simulated cadmium-containing wastewater

[0070]

[0071] Table 3. Treatment results of the aluminum-based hydrotalcite prepared in Example 6 for simulated cadmium-containing wastewater with different concentrations

[0072]

[0073] Table 4 Treatment results of the aluminum-based hydrotalcite prepared in Comparative Example 1 for simulated cadmium-containing wastewater with different concentrations

[0074]

[0075] As can be seen from Table 2, the aluminum-based hydrotalcite prepared in Examples 5-9 has good adsorption effects on cadmium ions. The example data shows that the calcium-aluminum molar ratio and hydrothermal reaction conditions in the aluminum-based hydrotalcite have great influences on the adsorption effect; and it is preferably to introduce intercalated Cl in the form of calcium chloride - . The comparison of the experimental data in Table 3 and Table 4 shows that the aluminum-based hydrotalcite prepared by the present invention using low-grade alumina has better adsorption performance for cadmium ions than the aluminum-based hydrotalcite prepared using pure γ-Al 2 O 3 . This may be related to the impurities contained in the low-grade alumina. The present invention not only reduces the difficulty and cost of recycling aluminum resources in aluminum-containing solid wastes, realizes the resource utilization of aluminum-containing solid wastes, significantly reduces the production cost of aluminum-based hydrotalcite, but also the obtained aluminum-based hydrotalcite has good adsorption performance for heavy metal ions, even better than the aluminum-based hydrotalcite prepared using pure γ-Al 2 O 3 .

Claims

1. A method for preparing aluminum-based hydrotalcite using aluminum-containing solid waste, characterized in that: The method comprises the following steps: (1) Calcining aluminum-containing solid waste generated during the synthesis of benzotriazole ultraviolet absorbers to burn out organic impurities and obtain low-grade Al2O3; (2) determining the aluminum content in the low-grade Al2O3 obtained in step (1); (3) Weigh a certain amount of low-grade Al2O3 obtained in step (1) as an aluminum source and place it in a hydrothermal reactor. According to the aluminum content measured in step (2), add an appropriate amount of divalent metal hydroxide and an anion source into the hydrothermal reactor, wherein the divalent metal hydroxide is calcium hydroxide and the anion source is a chlorine source, so that the molar ratio of calcium to aluminum is 1:1 to 5:1, and add deionized water. After stirring evenly, carry out a hydrothermal reaction in an oven. The hydrothermal reaction temperature is 60 to 150°C and the hydrothermal reaction time is 8 to 36 hours. After sufficient reaction, take out the reaction mixture from the hydrothermal reactor, cool it, filter it, wash the precipitate until the filtrate is neutral, and then dry and grind it to obtain aluminum-based hydrotalcite.

2. The method according to claim 1, characterized in that: In step (1), the calcination temperature is 550-750°C and the calcination time is 2-6h.

3. The method according to claim 1, characterized in that: In step (3), the chlorine source is sodium chloride or calcium chloride.

4. The method according to any one of claims 1 to 3, characterized in that: In step (3), the molar ratio of calcium to aluminum is set at 2:1 to 4:

1.

5. The method according to claim 4, characterized in that: In step (3), the molar ratio of calcium to aluminum is 2:

1.

6. The method according to any one of claims 1 to 3, characterized in that: In step (3), the hydrothermal reaction temperature is 120 to 150° C. and the hydrothermal reaction time is 16 to 24 hours.

7. The method according to claim 1, characterized in that: In step (3), the divalent metal hydroxide is calcium hydroxide, the anion source is calcium chloride, the molar ratio of calcium to aluminum is controlled to be 2:1, the hydrothermal reaction temperature is 150° C., and the hydrothermal reaction time is 24 h.

8. Aluminum-based hydrotalcite prepared according to the method of any one of claims 1 to 7.

9. Use of the aluminum-based hydrotalcite as claimed in claim 8 as a heavy metal ion treatment agent in water or soil.

10. The use according to claim 9, characterized in that: The heavy metal ions are cadmium ions.

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