A soil heavy metal activated adsorption composite material, its preparation method and application

Abstract

This invention belongs to the field of soil heavy metal pollution remediation, and discloses a soil heavy metal activated adsorption composite material, its preparation method, and its application. The preparation method of the soil heavy metal activated adsorption composite material includes the following steps: adding sodium alginate or sodium carboxymethyl cellulose and calcium carbonate to water to obtain a mixed solution; acidifying and rinsing the solution in an acidic solution to obtain blank high-molecular-weight sodium gel spheres SA; immersing and rinsing the SA gel spheres in a calcium salt solution for the first time to obtain high-molecular-weight calcium gel spheres SA-Ca; further immersing and washing the SA-Ca gel spheres in a sulfide solution for a second time to obtain sulfide-containing high-molecular-weight sodium gel spheres SA-S; allowing the SA-S gel spheres to float in water under stirring conditions; adding iron salt solution until the surface of the SA-S gel spheres turns white; then rinsing, freeze-drying, and obtaining the soil heavy metal activated adsorption composite material. This invention integrates activation and adsorption, is simple, green, and economical, and has broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of soil heavy metal pollution remediation, specifically relating to a soil heavy metal activation and adsorption composite material, its preparation method and application. Background Technology

[0002] With economic development, wastewater and chemicals discharged from various mining activities, paint factories, smelting industries, textile mills, steelmaking, and agricultural fertilizers have caused serious pollution to the surrounding soil, and the pollution situation is getting worse. Common heavy metal pollution in soil mainly includes Pb, Cd, Zn, As, and Cu. Once their content exceeds the critical value that the soil can purify, it will damage the soil properties. When substances in the soil adsorb heavy metals, a series of chemical reactions occur to form mixtures. Most of these mixtures cannot be decomposed by soil organisms and will accumulate in the soil, making it difficult to migrate out. Moreover, heavy metals in the soil can directly or indirectly enter the human body through crops, endangering human health. Therefore, the remediation of heavy metal pollution in soil has become an important task in current agricultural development. In recent years, various methods for remediating heavy metal pollution in soil have been developed, including chemical fixation, soil washing, microbial or phytoremediation, physicochemical adsorption, or electrochemical remediation. Currently, the most popular technology is soil heavy metal adsorption and fixation technology, such as using biochar, humus, and porous materials to adsorb and fix acid-soluble and reducible heavy metals in the soil, thereby reducing the heavy metal residue in the soil. Soil leaching agents use organic acids to activate and remove heavy metals fixed in the soil. However, this technology inevitably produces a large amount of leaching waste liquid, which is costly to treat. Furthermore, the soil's properties and structure are damaged to varying degrees after leaching.

[0003] Chen Wenzhao (Research on the Activation and Removal of Cd from Soil by Alginate-Based Composite Materials [D], 2019) first prepared uniform calcium carbonate / alginate gel spheres (Ca-gel) in a specific mold. The Ca-gel was freeze-dried to obtain calcium alginate aerogel material (CAA), which was then treated with ferric chloride solution and subjected to in-situ carbothermic reaction to obtain magnetic hollow carbon composite material (MHCC). This research required the preparation of two materials for activation and adsorption, specifically MHCC activation and desorption, and CAA adsorption and removal of Cd from the soil. This involved multiple steps, and the resulting material was not an integrated activation-adsorption material. Both materials needed to be applied, making cost a significant concern in practical applications. CN 107398251 A discloses a material for removing metals from water and soil. However, this material requires high-temperature carbonization during preparation, and the pH needs to be adjusted to a certain range before effective adsorption of heavy metals in soil or water, making the operation complex. Therefore, developing a simple, economical material that integrates activation and adsorption of heavy metals in soil and does not require pH adjustment during application has broad application prospects. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing a soil heavy metal activation and adsorption composite material. This method utilizes sodium carboxymethyl cellulose or sodium alginate, calcium carbonate, iron salts, and sulfides as main raw materials, employing a heterogeneous process to prepare an aerogel sphere composite material with an integrated activation-adsorption structure and a floating nature, consisting of an inner adsorption layer, a buffer layer, and an outer activation layer—a "sandwich" structure. This method requires only multiple soakings, eliminates the need for complex preparation processes, and is simple to use. The prepared aerogel spheres exhibit excellent mechanical properties, high water absorption, easy recyclability, and high adsorption capacity.

[0005] Another objective of this invention is to provide a soil heavy metal activation and adsorption composite material prepared by the above preparation method.

[0006] Another objective of this invention is to provide the application of the aforementioned soil heavy metal activation and adsorption composite material in the field of heavy metal removal from soil. In the application process, the aerogel microsphere composite material implements a "first activation, then adsorption" strategy. The acidic substances generated in the outer layer are entirely used to locally acidify the heavy metals fixed in the soil. The buffer layer separates the inner adsorption layer and the outer activation layer to prevent the acidic substances in the outer layer from neutralizing each other with the core. The inner adsorption layer adsorbs the activated free heavy metals. During the activation and adsorption process, the composite material absorbs water and expands to float, and is finally retrieved and recovered through a screen, maximizing the removal of heavy metals from the soil at their source.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a soil heavy metal activated adsorption composite material includes the following steps:

[0009] (1) Add sodium alginate or sodium carboxymethyl cellulose and calcium carbonate to water, stir to dissolve and obtain a mixed solution. Add the mixed solution to an acid solution, acidify, soak and rinse to obtain blank high molecular weight sodium gel ball SA.

[0010] (2) After soaking and rinsing the SA gel balls in the calcium salt solution for the first time, the high molecular weight calcium gel balls SA-Ca are obtained. After soaking and washing in the sulfide solution for the second time, the loose and porous sulfide-containing high molecular weight sodium gel balls SA-S are obtained.

[0011] (3) Under stirring conditions, SA-S gel balls float in water. Iron salt solution is added until the surface of SA-S gel balls turns white. The balls are then retrieved, rinsed, and freeze-dried to obtain soil heavy metal activated adsorption composite material SA-S@Fe.

[0012] Preferably, the mass ratio of sodium carboxymethyl cellulose or sodium alginate, calcium carbonate and water in step (1) is (1-8):(0.2-2):(80-160).

[0013] Preferably, the stirring speed in step (1) is 800 to 1200 rpm.

[0014] Preferably, the acid in the acid solution in step (1) is at least one of hydrochloric acid, acetic acid, sulfuric acid, phosphoric acid, and nitric acid, and the concentration of the acid solution is 0.1 to 0.5 wt%.

[0015] Preferably, the addition of the mixed solution to the acid solution in step (1) is done by slow dripping.

[0016] The acidification soaking time is 12 to 24 hours.

[0017] Preferably, the rinsing in step (1) is washing with water until the surface of the ball is neutral.

[0018] Preferably, the first soaking time in step (2) is 3 to 8 hours, and the second soaking time is 10 to 60 minutes.

[0019] Preferably, the washing in step (2) is a rapid rinse with water.

[0020] Preferably, the calcium salt in step (2) is at least one of calcium chloride, calcium nitrate, calcium bromide, and calcium iodide, and the concentration of the calcium salt solution is 0.5-3 wt%.

[0021] The sulfide mentioned in step (2) is at least one of ammonium sulfide, sodium sulfide, and potassium sulfide, and the concentration of the sulfide solution is 0.2 to 3 wt%.

[0022] Preferably, the stirring speed in step (3) is 200 to 500 rpm.

[0023] Preferably, the iron salt in step (3) is at least one of ferric chloride, ferric sulfate, ferric nitrate, and ferric acetate, and the concentration of the iron salt solution is 0.2 to 2.5 wt%.

[0024] Preferably, the rinsing in step (3) is a rapid rinse with purified water;

[0025] Preferably, the freeze-drying conditions in step (3) are: freeze-drying at -90℃ to -180℃ for 24 to 48 hours.

[0026] A soil heavy metal activation and adsorption composite material is prepared by the above method.

[0027] Application of the above-mentioned soil heavy metal activation and adsorption composite material in the removal of heavy metals in soil.

[0028] Preferably, the application includes the following steps: adding the soil heavy metal activation and adsorption composite material to flooded soil and letting it stand for a period of time;

[0029] Preferably, the added mass of the soil heavy metal activation and adsorption composite material is 0.1-0.5% of the soil mass, and the settling time is more than 48 hours.

[0030] Preferably, the water holding capacity of the flooded soil is more than 200% of the maximum water holding capacity of the soil.

[0031] Preferably, the heavy metal is Cd.

[0032] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0033] (1) The main materials of this invention are natural polymer materials such as sodium alginate and sodium carboxymethyl cellulose, which have the advantages of being simple, green, economical and biodegradable.

[0034] (2) The present invention adopts an integrated activation and adsorption technology, which first activates and then adsorbs. The outer layer of the aerogel microsphere composite material with a "sandwich" structure releases acidic substances to acidify the insoluble heavy metals in the soil, while the inner adsorption layer adsorbs the activated free heavy metals to achieve the removal of insoluble heavy metals.

[0035] (3) The aerogel microsphere composite material prepared by the present invention is easy to operate. It does not require adjusting the soil pH value before application. It can be directly added to flooded soil. After adsorption, it can be retrieved by sieve to achieve complete removal of heavy metals in the soil without secondary pollution. Attached Figure Description

[0036] Figure 1 The diagram shows the "sandwich" structure of the SA-S@Fe gel spheres and aerogel spheres obtained in Example 1. A is a half-section of the SA-S@Fe gel sphere, showing different pH values ​​in the inner, middle and outer layers. B is a half-section of the SA-S@Fe gel sphere, and C is a half-section of the SA-S@Fe aerogel sphere.

[0037] Figure 2 The experimental process for preparing the SA-S@Fe aerogel spheres obtained in Example 1 and the SEM image of the SA-S@Fe aerogel spheres are shown.

[0038] Figure 3 The graph shows the floating time and floating rate of different aerogel balls obtained in Example 1 in water.

[0039] Figure 4 The graph shows the changes in the content of different forms of heavy metal Cd before and after treatment with different aerogel balls obtained in Example 1.

[0040] Figure 5The graph shows the changes in total Cd in the soil on day 2 and day 5 after different aerogel ball treatments obtained in Example 1. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0042] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0043] Example 1

[0044] (1) At room temperature, 1g of sodium alginate and 0.2g of calcium carbonate solid powder were added to 80ml of water and mechanically stirred at 800rpm until completely dispersed and dissolved to obtain a mixed solution. Then, the solution was slowly added dropwise to 0.1wt% hydrochloric acid solution using a dropping funnel, acidified and soaked for 12h, and rinsed with pure water until the surface of the small ball was neutral to obtain blank high molecular weight sodium gel ball (SA).

[0045] (2) The SA gel balls were first soaked in 0.5wt% calcium chloride solution for 3h, and then rinsed with pure water to obtain high molecular weight calcium gel balls (SA-Ca); they were then soaked in 0.2wt% sodium sulfide solution for 10min for a second time, and then quickly washed with pure water to obtain sulfide-containing high molecular weight sodium gel balls (SA-S).

[0046] (3) Under magnetic stirring at 200 rpm, SA-S gel balls were floated in water. 0.2 wt% ferric chloride solution was slowly added dropwise using a dropping funnel until the surface of the gel balls turned white. The balls were then scooped out and rinsed quickly with pure water. They were then dried in a freeze dryer at -90 ℃ for 24 h to obtain a loose and porous sulfide-containing polymer aerogel ball composite material (SA-S@Fe).

[0047] Figure 1 In sample A, three different colors can be clearly observed on the pH test paper measured by the half-section of the SA-S@Fe gel spheres, corresponding to the three-layer structure. Figure 1 In sample B, we can also see that the outermost layer of the SA-S@Fe gel spheres is transparent white, the middle layer is dark black, and the innermost layer is light black. Figure 1 In the half-section image of SA-S@Fe aerogel spheres shown in C, a "sandwich" structure can be clearly seen from the outside in. The outermost activation layer is yellowish, the middle buffer layer is black, and the innermost adsorption layer is white. Figure 2 The SEM image of D shows that the SA-S@Fe composite material has a loose and porous structure.

[0048] Example 2

[0049] (1) At room temperature, 8g of sodium alginate and 2g of calcium carbonate solid powder were added to 160ml of water and mechanically stirred at 1200rpm until completely dispersed and dissolved to obtain a mixed solution. Then, the solution was slowly added dropwise to 0.5wt% sulfuric acid solution using a dropping funnel, and the solution was acidified and soaked for 24h. The solution was then rinsed with pure water until the surface of the small ball was neutral to obtain blank high molecular weight sodium gel ball (SA).

[0050] (2) The SA gel balls were first soaked in a 3wt% calcium chloride solution for 8 hours and then rinsed with pure water to obtain calcium alginate gel balls (SA-Ca); they were then soaked in a 0.2wt% ammonium sulfide solution for 60 minutes and then quickly washed with pure water to obtain sodium sulfide-containing polymer gel balls (SA-S).

[0051] (3) Under magnetic stirring at 500 rpm, SA-S gel balls were floated in water. 2.5 wt% ferric nitrate solution was slowly added dropwise using a dropping funnel until the surface of the gel balls turned white. The balls were then scooped out and rinsed quickly with pure water. They were then dried in a freeze dryer at -90℃ for 48 h to obtain a loose and porous sulfide-containing polymer aerogel ball composite material (SA-S@Fe).

[0052] Example 3

[0053] (1) At room temperature, 1g of sodium alginate and 2g of calcium carbonate solid powder were added to 80ml of water and mechanically stirred at 1200rpm until completely dispersed and dissolved to obtain a mixed solution. Then, the solution was slowly added dropwise to 0.1wt% phosphoric acid solution using a dropping funnel, and the solution was acidified and soaked for 24h. The solution was then rinsed with pure water until the surface of the small ball was neutral to obtain blank high molecular weight sodium gel ball (SA).

[0054] (2) The SA gel balls were first soaked in 0.5wt% calcium nitrate solution for 8 hours, and then rinsed with pure water to obtain high molecular weight calcium gel balls (SA-Ca); they were then soaked in 0.2wt% sodium sulfide solution for 60 minutes, and then quickly washed with pure water to obtain high molecular weight sodium gel balls containing sulfide (SA-S).

[0055] (3) Under magnetic stirring at 200 rpm, SA-S gel balls were floated in water. 2.5 wt% ferric sulfate solution was slowly added dropwise using a dropping funnel until the surface of the gel balls turned white. The balls were then scooped out and rinsed quickly with pure water. They were then dried in a freeze dryer at -90 ℃ for 24 h to obtain a loose and porous sulfide-containing polymer aerogel ball composite material (SA-S@Fe).

[0056] Example 4

[0057] (1) At room temperature, 8g of sodium alginate and 0.2g of calcium carbonate solid powder were added to 160ml of water and mechanically stirred at 800rpm until completely dispersed and dissolved to obtain a mixed solution. Then, the solution was slowly added dropwise to 0.5wt% acetic acid solution using a dropping funnel, acidified and soaked for 12h, and rinsed with pure water until the surface of the small ball was neutral to obtain blank high molecular weight sodium gel ball (SA).

[0058] (2) The SA gel balls were first soaked in a 3wt% calcium bromide solution for 3 hours and then rinsed with pure water to obtain high molecular weight calcium gel balls (SA-Ca); they were then soaked in a 3wt% potassium sulfide solution for 10 minutes and then quickly washed with pure water to obtain high molecular weight sodium gel balls containing sulfides (SA-S).

[0059] (3) Under magnetic stirring at 500 rpm, SA-S gel balls were floated in water. 0.2 wt% ferric nitrate solution was slowly added dropwise using a dropping funnel until the surface of the gel balls turned white. The balls were then scooped out and rinsed quickly with pure water. They were then dried in a freeze dryer at -90℃ for 45 h to obtain a loose and porous sulfide-containing polymer aerogel ball composite material (SA-S@Fe).

[0060] Example 5

[0061] (1) At room temperature, 4.5g sodium carboxymethyl cellulose and 1.1g calcium carbonate solid powder were added to 120ml of water and mechanically stirred at 1000rpm until completely dispersed and dissolved to obtain a mixed solution. Then, the solution was slowly added dropwise to 0.3wt% nitric acid solution using a dropping funnel, and the solution was acidified and soaked for 18h. The solution was then rinsed with pure water until the surface of the small ball was neutral to obtain blank sodium polymer gel ball (SA).

[0062] (2) The SA gel balls were first soaked in 1.8wt% calcium iodide solution for 5.5h, and then rinsed with pure water to obtain high molecular weight calcium gel balls (SA-Ca); they were then soaked in 1.6wt% sodium sulfide solution for 35min for a second time, and then quickly washed with pure water to obtain high molecular weight sodium gel balls containing sulfides (SA-S).

[0063] (3) Under magnetic stirring at 350 rpm, SA-S gel balls were floated in water. 1.3 wt% ferric acetate solution was slowly added dropwise using a dropping funnel until the surface of the gel balls turned white. The gel balls were then scooped out and rinsed quickly with pure water. They were then dried in a freeze dryer at -90 ℃ for 36 h to obtain a loose and porous sulfide-containing polymer aerogel ball composite material (SA-S@Fe).

[0064] Example 6: Flotation ability test of aerogel ball composite material

[0065] Different types of aerogel spheres were prepared according to the method in Example 1, and their buoyancy was tested for 21 days. 2.0 g of each type of freeze-dried aerogel sphere was placed in an Erlenmeyer flask containing 50 mL of deionized water and shaken. The number of buoyant spheres was recorded daily to investigate the buoyancy performance of the aerogel spheres. The buoyancy rate (FR) was calculated according to Formula 1:

[0066] FR(%) = N1 / N * 100% (1)

[0067] Where N is the total number of aerogel spheres, and N1 is the number of aerogel spheres still floating. Three measurements were taken for each type of aerogel sphere, and the average value was used.

[0068] like Figure 3 As shown, after 21 days, 90% of the SA-S@Fe aerogel spheres remained floating, achieving a floatability of up to 90%, ensuring the integrity of the spheres under water disturbance conditions. Furthermore, due to the low density and porous structure of the aerogel spheres, the SA-S@Fe aerogel sphere composite material exhibits ideal floatability, facilitating the practical application and recovery of adsorbents in farmland. The poor floatability of SA microspheres, SA-Ca microspheres, and SA-S microspheres is because SA spheres only use acid to locally precipitate alginic acid on the outer layer, resulting in very weak mechanical strength and an uneven structure in pure sodium alginate gel spheres. SA-Ca microspheres, on the other hand, are further cross-linked with calcium salts based on SA microspheres, resulting in a more uniform structure and considerable stability. The SA-S microspheres, under high Na+ conditions, experienced a significant decrease in gel mechanical strength because some of the tightly cross-linked calcium alginate was converted to sodium alginate and gradually dissolved in the strong alkaline environment.

[0069] Example 7: Activation and Adsorption Experiment of Integrated Activation-Adsorption Composite Material

[0070] To simulate flooded paddy fields, 20g of cadmium (Cd) contaminated soil was weighed and mixed with 18.6g of water (200% of the soil's field capacity (31%)). Then, 0.05g of the activated-adsorption integrated aerogel sphere composite material prepared in Example 1 was added. The mixture was incubated at 25℃ for 48h and 5d, and then allowed to stand for a period to separate the water and soil layers. The soil sample was air-dried, ground, and passed through a 100-mesh sieve for later use. The contents of acid-soluble, reducible, and oxidizable cadmium in the soil were determined sequentially using the BCR three-step method, and the residual cadmium content was determined using a microwave-assisted total digestion method. Simultaneously, the change in total Cd in the soil was measured. The experimental results are as follows: Figure 4 and Figure 5 As shown.

[0071] Figure 4In the study, compared with the control group (CK group) without any adsorbent, the content of all four Cd forms decreased to some extent after adsorption by the integrated activation-adsorption composite material. The decrease was most significant for acid-soluble Cd, followed by that of reducible Cd. Simultaneously, Cd was released into the water after activation and adsorbed by the composite material, thus reducing the total Cd content. Furthermore, among various aerogel spheres, the SA-S@Fe aerogel sphere composite material exhibited superior activation and adsorption effects. Figure 4 Among them, the intermediate products SA, SA-Ca, SA-S, and SA-Fe aerogel balls of SA-S@Fe aerogel balls all had lower removal rates of Cd in soil than SA-S@Fe aerogel balls. The removal rates of SA-S@Fe aerogel balls after 2 days and 5 days of treatment were 20.3% and 23.7%, respectively, showing a significant effect on removing Cd content in soil. Moreover, the removal efficiency can be achieved with 2 days as the standard.

[0072] Example 8

[0073] Simulating a paddy field flooding state, 20g of cadmium (Cd) contaminated soil was weighed and 12.4g of water (200% of the soil's field capacity (31%)) was added. Then, 0.05g of the activated-adsorption integrated aerogel ball composite material prepared in Examples 1-5 was added. The activated and desorbed soil was incubated at 25℃ for 48h and 5d, respectively, and then left to stand for a period of time. The Cd content was determined using an atomic absorption spectrophotometer. The removal rates of the SA-S@Fe aerogel balls prepared in Examples 1-5 after 2d and 5d of treatment were calculated as follows: Example 1: 20.3% and 23.7%; Example 2: 22.4% and 26.3%; Example 3: 21.8% and 25.2%; Example 4: 20.8% and 23.1%; Example 5: 21.6% and 24.8%.

[0074] Comparative Example 1

[0075] Unlike Example 1, in step (2), the SA gel balls from step (1) were directly immersed in a 0.2 wt% sodium sulfide solution for 10 minutes without an initial immersion in calcium chloride solution. This caused the already formed SA gel balls to easily disintegrate and collapse, making further FeCl3 immersion impossible and resulting in experimental failure. The reasons are as follows:

[0076] In step (1), after sodium alginate and calcium carbonate are mixed with acid, the sodium alginate on the outer layer of the droplet will locally precipitate alginic acid upon contact with the strong acid environment, forming a relatively hard outer shell and initially forming a spherical shape. Simultaneously, the calcium carbonate in the droplet will rapidly decompose to produce Ca. 2+ and CO2, Ca 2+It will undergo local cross-linking with free sodium alginate, forming a partial calcium alginate network structure inside the gel. The released CO2 gas increases the internal pressure, causing the formation of a network structure and numerous air bubbles, making the gel porous and loose. This helps reduce the gel density and improve the buoyancy of gel spheres and aerogel spheres. The homogeneous method also helps to evenly distribute this porous structure inside the gel, forming... Figure 2 A loose, porous, blank SA floating sphere. However, this releases Ca through calcium carbonate. 2+ The network structure formed by localized cross-linking is not robust, and a significant amount of free sodium alginate remains, resulting in poor mechanical properties within the gel. Immersing the gel spheres in Na₂S under these conditions, due to the strong alkalinity and high Na₂S content, further deteriorates the gel. + In the environment, Na + and Ca 2+ Competition occurs for two reasons: the nascent gel spheres are prone to disintegration and collapse, preventing further FeCl3 soaking and leading to experimental failure. Therefore, before soaking in Na2S, the nascent gel spheres need to be further solidified with CaCl2 to obtain... Figure 2 The SA-Ca gel spheres in B are uniform, porous, and possess good mechanical strength. These gel spheres can be immersed in Na₂S for extended periods while maintaining their original basic structure. The loose, porous structure also facilitates the complete penetration of Na₂S into the innermost part of the gel sphere. Figure 2 C consists of floatable SA-S gel spheres that are completely loaded with a large amount of Na2S and have a uniform structure.

[0077] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a soil heavy metal activated adsorption composite material, characterized in that, Includes the following steps: (1) Add sodium alginate or sodium carboxymethyl cellulose and calcium carbonate to water, stir to dissolve and obtain a mixed solution. Add the mixed solution to an acid solution, acidify, soak and rinse to obtain blank high molecular weight sodium gel balls SA. (2) After soaking and rinsing the SA gel balls in the calcium salt solution for the first time, the high molecular weight calcium gel balls SA-Ca are obtained. After soaking and washing in the sulfide solution, the high molecular weight sodium gel balls containing sulfide SA-S are obtained. (3) Under stirring conditions, SA-S gel balls float in water. Iron salt solution is added until the surface of SA-S gel balls turns white. The balls are then retrieved, rinsed, and freeze-dried to obtain soil heavy metal activated adsorption composite material SA-S@Fe. The acid in step (1) is at least one of hydrochloric acid, acetic acid, sulfuric acid, phosphoric acid, and nitric acid, and the concentration of the acid solution is 0.1~0.5wt%; the acidification soaking time is 12~24h. The calcium salt mentioned in step (2) is at least one of calcium chloride, calcium nitrate, calcium bromide, and calcium iodide, and the concentration of the calcium salt solution is 0.5~3 wt%. The sulfide mentioned in step (2) is at least one of ammonium sulfide, sodium sulfide, and potassium sulfide, and the concentration of the sulfide solution is 0.2~3 wt%. The iron salt mentioned in step (3) is at least one of ferric chloride, ferric sulfate, ferric nitrate, and ferric acetate, and the concentration of the iron salt solution is 0.2~2.5 wt%.

2. The preparation method of the soil heavy metal activation and adsorption composite material according to claim 1, characterized in that, In step (1), the mass ratio of sodium carboxymethyl cellulose or sodium alginate, calcium carbonate and water is (1~8):(0.2~2):(80~160).

3. The method for preparing the soil heavy metal activated adsorption composite material according to claim 1 or 2, characterized in that, The first soaking time in step (2) is 3~8h, and the second soaking time is 10~60min.

4. The preparation method of the soil heavy metal activated adsorption composite material according to claim 1, characterized in that, The freeze-drying conditions in step (3) are: freeze-drying at -90℃ to -180℃ for 24 to 48 hours.

5. A soil heavy metal activation and adsorption composite material, characterized in that, It is prepared by the method described in any one of claims 1 to 4.

6. The application of the soil heavy metal activation and adsorption composite material according to claim 5 in the removal of heavy metals in soil.

7. The application according to claim 6, characterized in that, The heavy metal is Cd.

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