A soil heavy metal visualizing and coloring adsorption composite material, a preparation method and application thereof

Abstract

The application belongs to the field of soil heavy metal pollution treatment, and discloses a soil heavy metal visual coloration adsorption composite material and a preparation method and application thereof. Sodium alginate and calcium salt are mixed with water to obtain a mixed solution, a color developing agent is added, stirring is performed, gluconolactone is added, coagulation molding is performed, freeze drying is performed, and a color developing inner core pellet is obtained. Polylactic acid, polyethylene glycol, an activator and water are high-temperature blended and stirred to obtain a molten mixed solution. The color developing inner core pellet of the step is placed in a mold, and the molten mixed solution is injected to obtain a composite material with a core-shell structure. The obtained composite material with the functions of activation and visual adsorption is cracked to release the activator to activate heavy metals, the inner core is expanded in the process of water absorption, free heavy metals are efficiently adsorbed, a complex reaction occurs between the color developing agent and the free heavy metals, and the color of the pellet changes. The visual coloration adsorption material can realize real-time monitoring of the adsorption process, and the synthetic raw materials are low in price and extremely valuable in application.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of soil heavy metal pollution treatment, and particularly relates to a soil heavy metal visual coloration adsorption composite material and a preparation method and application thereof. BACKGROUND

[0002] Due to the high toxicity, persistence, non-biodegradability and bioaccumulation of heavy metals, heavy metal pollution has attracted widespread attention worldwide. Compared with treating cadmium contaminated wastewater, treating soil cadmium pollution is much more difficult. The fundamental difficulty lies in that the heavy metals in the soil are usually fixed by soil particles or compounds in the soil, and the concentration of free heavy metals is extremely low, which cannot be effectively removed by traditional and simple adsorption method.

[0003] For soil heavy metals, the commonly used treatment methods at present are in-situ fixation and ex-situ removal. In-situ fixation generally adds chemical reagents to the soil, and through adsorption, precipitation and complexation reactions between them and metals, the free heavy metals are re-fixed from the soil water phase to the solid phase, thereby temporarily reducing the effective concentration of heavy metals in the soil and reducing the diffusion and migration of heavy metals in the soil. In-situ fixation has the advantages of low cost, good engineering applicability, etc., and is a simple, fast and relatively economical treatment method. However, it has a serious drawback that heavy metals cannot be removed from the soil, and the total content of heavy metals in the soil before and after fixation does not change. Ex-situ removal represented by soil washing can better make up for this serious shortcoming. The principle is to use various leaching agents to activate and desorb heavy metals in the soil into the water phase, and then wash the leaching agent clean with a large amount of clean water. However, this technology also has many shortcomings. For example, most of the leaching agents cannot be recycled and are difficult to degrade, which can easily cause adverse effects on the soil ecosystem; after leaching, the soil properties will deteriorate, and inorganic nutrients and organic matter will also be lost, which cannot meet the needs of crop planting; leaching will generate a large amount of wastewater, and the treatment cost is high.

[0004] At the same time, the dosage of the treatment materials used in various treatment methods needs to be adjusted according to the pollution degree, which cannot be effectively monitored in real time and on site, and is easy to cause material waste or incomplete treatment. Even if other detection means are used for monitoring, such as the detection equipment described in the invention "Soil heavy metal remediation dynamic detection device and method" (CN116593415A), which is complex and requires professional operation, and another invention "Portable soil heavy metal detector" (CN219574100U), which also needs time-consuming and laborious pretreatment of the detection sample. Therefore, it is of great significance to develop a new coloration material for adsorbing and removing soil heavy metals and simultaneously visualizing monitoring. SUMMARY

[0005] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing a composite material for visually stimulating the adsorption of heavy metals in soil. First, sodium alginate and calcium carbonate or calcium chloride are mixed with water, a colorimetric agent is added, and the mixture is cast into a film to obtain core-shell microspheres. Then, polylactic acid, polyethylene glycol, and different activators are blended and stirred at high temperature, and the mixture is injected into a mold containing freeze-dried core-shell microspheres to obtain a composite material with a core-shell structure. This method prepares a composite material integrating activation, visually stimulating adsorption, and removal.

[0006] Another object of the present invention is to provide a composite material for visual removal of heavy metals in soil prepared by the above method.

[0007] Another objective of this invention is to provide the application of the aforementioned composite material for visually removing heavy metals from soil. During application, the outer shell of the integrated activation-visualization colorimetric adsorption composite material breaks down to release an activator that activates the heavy metals. The core absorbs water and swells, efficiently adsorbing free heavy metals, which then undergo a complexation reaction with the colorimetric agent, causing a color change in the microspheres. The adsorption process is monitored in real time by observing the color change of the core microspheres, allowing for adjustment of the amount of adsorbent material used.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing a soil heavy metal visualization and colorimetric adsorption composite material includes the following steps:

[0010] (1) Sodium alginate and calcium salt are mixed with water to obtain a mixed solution. A colorimetric reagent is added and stirred. Gluconolactone is added and poured into a mold. The mixture is solidified and then freeze-dried to obtain a colorimetric core microsphere.

[0011] (2) Polylactic acid, polyethylene glycol, activator and water are mixed and stirred at high temperature to obtain a molten mixture;

[0012] (3) Place the colorimetric core microspheres from step (1) into a mold and inject the molten mixture to obtain a soil heavy metal visualization colorimetric adsorption composite material with a core-shell structure.

[0013] Preferably, the mass ratio of sodium alginate, calcium salt and water in step (1) is (1-15):(1-10):(5-300), more preferably (3-15):(1-10):(100-300).

[0014] Preferably, the colorimetric agent in step (1) is at least one of tetraaldehyde phenylporphyrin, 5,10,15,20-tetra(4-methoxyphenyl)porphyrin, 5,10,15,20-tetra(4-aminophenyl)porphyrin, 5,10,15,20-tetra(4-N-methylpyridyl)porphyrin p-toluenesulfonate, tetra-p-tolylporphyrin, and brasilienin;

[0015] The calcium salt is one of calcium carbonate, calcium chloride, calcium gluconate, calcium sulfate, or calcium phosphate.

[0016] Preferably, the mass ratio of the color developer to water in step (1) is (1-20):(1-500), more preferably (1-2):(100-500).

[0017] Preferably, the mass ratio of gluconolactone and the mixed solution in step (1) is (1-5):(1-500), more preferably (2-5):(100-300).

[0018] Preferably, the mass ratio of polylactic acid, polyethylene glycol, activator and water in step (2) is (1-100):(1-500):(1-500):(1-500), more preferably (60-100):(100-400):(200-400):(300-500).

[0019] Preferably, the activator in step (2) is at least one of citric acid, lactide and chelating agent EDTA, and the high temperature is 80-200°C.

[0020] Preferably, the diameter of the core microspheres in step (1) is 3.5 to 10 mm, and the diameter of the adsorption composite material is 10 to 50 mm, more preferably 13 to 50 mm;

[0021] The mixing speed in step (1) is 300-1200 rpm and the time is 1-4 h; the stirring speed is 500-1000 rpm and the time is 0.5-2 h; the solidification time is 0.5-4 h; and the freeze-drying time is 24-72 h.

[0022] The above method yields a soil heavy metal visualization and colorimetric adsorption composite material.

[0023] The above-mentioned composite materials are used in the adsorption and removal of heavy metals in soil.

[0024] Preferably, the heavy metal is cadmium;

[0025] The application includes the following steps:

[0026] The above-mentioned composite material is added to the soil, water is added, and the amount of composite material added is controlled by the color change of the core microspheres. The composite material is added at once or in several batches.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] (1) The main materials of this invention have the advantages of being non-toxic, non-polluting, and easily degradable.

[0029] (2) The present invention adopts an integrated activation-colorization adsorption technology. The super absorbent composite material rapidly releases the activator during the process of water absorption and expansion, and adsorbs and activates the insoluble heavy metals, thereby realizing the dissolution of the insoluble heavy metals in the soil and their removal after adsorption.

[0030] (3) The composite material described in this invention can be simply added to flooded soil, and the adsorption process can be monitored in real time by observing the color change of the core microspheres, allowing for precise control of the amount of composite material added. This is the first time that refined and visual detection of the removal process has been achieved. At the same time, in practical applications, it can be added in multiple stages, greatly saving costs.

[0031] (4) The composite material of the present invention can adsorb cadmium in soil at a rate of 61.67%. Attached Figure Description

[0032] Figure 1 The bar chart shows the water absorption ratio of the core microspheres in Examples 1-4 and Comparative Examples 2 and 3.

[0033] Figure 2 The images show the comparison of the core-shell composite material used in Example 6 before and after the soil heavy metal removal experiment.

[0034] Figure 3 The images show the accumulation bar charts of different forms of Cd heavy metal content in the soil before and after the adsorption experiments in Examples 4 and 5 and Comparative Examples 4 and 5, as well as before and after the three heavy metal removal experiments in Example 7.

[0035] Figure 4 The color change of the core microspheres before and after three heavy metal removal experiments in soil, as shown in Example 7. Detailed Implementation

[0036] 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.

[0037] The soil used in all examples and comparative examples was from the same batch, and the cadmium content in the soil was 6.00 ppm.

[0038] Example 1

[0039] (1) Add 3g sodium alginate and 1g calcium chloride to 100mL of water and stir mechanically at 800rpm until completely dissolved.

[0040] (2) Add 1g of brassinolide to the mixed solution and stir continuously at 1000rpm for 2h. While stirring, add 2g of gluconolactone to the mixed solution; quickly pour the mixed solution into a 10mm mold, solidify into a gel, and freeze-dry for 48h to obtain the core microspheres.

[0041] (3) In a 500mL beaker, first add 400mL of distilled water, then add 0.5g of the aforementioned core microspheres. Next, let the beaker stand at room temperature until adsorption equilibrium is reached. Then, remove the core microspheres from the beaker and weigh them to obtain the mass of the saturated water-absorbing core microspheres. The calculated water absorption ratio is 1122%. Figure 1 .

[0042] (4) Add 60g polylactic acid, 100g polyethylene glycol and 200g citric acid to 500mL pure water, keep at 140℃ and stir at 150rpm to melt; place the core spheres in a 13mm mold, inject the molten mixture into the mold, and obtain a composite material with a core-shell structure after cooling.

[0043] Example 2

[0044] (1) Add 3g sodium alginate and 1g calcium carbonate to 100mL of water and stir mechanically at 800rpm until completely dissolved.

[0045] (2) Add 1g of brassinolide to the mixed solution and stir continuously at 1000rpm for 2h. While stirring, add 2g of gluconolactone to the mixed solution; quickly pour the mixed solution into a 10mm mold, solidify into a gel, and freeze-dry for 48h to obtain the core microspheres.

[0046] (3) In a 500mL beaker, first add 400mL of distilled water, then add 0.5g of the aforementioned core-shell microspheres. Next, let the beaker stand at room temperature until adsorption equilibrium is reached. Then, remove the core-shell microspheres from the beaker and weigh them to obtain the mass of the saturated water-absorbing core-shell microspheres. The calculated water absorption ratio is 1299%. Figure 1 .

[0047] (4) Add 60g polylactic acid, 100g polyethylene glycol and 200g citric acid to 500mL pure water, keep at 140℃ and stir at 150rpm to melt; place the core spheres in a 13mm mold, inject the molten mixture into the mold, and obtain a composite material with a core-shell structure after cooling.

[0048] Example 3

[0049] (1) Add 3g sodium alginate and 1g calcium carbonate to 100mL of water and stir mechanically at 800rpm until completely dissolved.

[0050] (2) 1 g of 5,10,15,20-tetra(4-N-methylpyridinyl)porphyrin p-toluenesulfonate was added to the mixed solution and stirred continuously at 1000 rpm for 2 h. While stirring, 2 g of gluconolactone was added to the mixed solution; the mixed solution was quickly poured into a 10 mm mold, solidified into a gel, and freeze-dried for 48 h to obtain the core microspheres.

[0051] (3) In a 500mL beaker, first add 400mL of distilled water, then add 0.5g of the aforementioned core microspheres. Next, let the beaker stand at room temperature until adsorption equilibrium is reached. Then, remove the core microspheres from the beaker and weigh them to obtain the mass of the saturated water-absorbing core microspheres. The calculated water absorption ratio is 1566%. Figure 1 .

[0052] (4) Add 60g polylactic acid, 100g polyethylene glycol and 200g citric acid to 500mL pure water, keep at 140℃ and stir at 150rpm to melt; place the core spheres in a 13mm mold, inject the molten mixture into the mold, and obtain a composite material with a core-shell structure after cooling.

[0053] Example 4

[0054] (1) Add 3g sodium alginate and 1g calcium carbonate to 100mL of water and stir mechanically at 800rpm until completely dissolved.

[0055] (2) Add 1g of 5,10,15,20-tetra(4-methoxyphenyl)porphyrin to the mixed solution and stir continuously at 1000rpm for 2h. While stirring, add 2g of gluconolactone to the mixed solution; quickly pour the mixed solution into a 10mm mold, solidify into a gel, and freeze-dry for 48h to obtain core microspheres.

[0056] (3) In a 500mL beaker, first add 400mL of distilled water, then add 0.5g of the aforementioned core-shell microspheres. Next, let the beaker stand at room temperature until adsorption equilibrium is reached. Then, remove the core-shell microspheres from the beaker and weigh them to obtain the mass of the saturated water-absorbing core-shell microspheres. The calculated water absorption ratio is 1365%. Figure 1 .

[0057] (4) Add 60g polylactic acid, 100g polyethylene glycol and 200g citric acid to 500mL pure water, keep at 140℃ and stir at 150rpm to melt; place the core spheres in a 13mm mold, inject the molten mixture into the mold, and obtain a composite material with a core-shell structure after cooling.

[0058] (5) Weigh 100g of cadmium-contaminated soil and add 62g of water (62% of the soil's maximum field water holding capacity) to simulate the flooding state of a paddy field. Add 20g of the core-shell composite material prepared in step (4) to a beaker and incubate at 25℃ for 48h. Take out 1 / 5 of the water layer and soil layer respectively, air dry the soil sample, grind it, and pass it through a 100-mesh sieve for later use.

[0059] (6) The content of cadmium in various forms in the air-dried soil samples from step (5) was determined. The contents of acid-soluble, reducible, and oxidizable cadmium forms were determined sequentially using the BCR three-step method. Finally, the content of residual cadmium in the soil was determined using a microwave-assisted acid digestion method. The experimental results are as follows: Figure 3 As shown, the adsorption rate is 25.00%.

[0060]

[0061] C0 represents the total cadmium content in the soil before adsorption, and C1 represents the total cadmium content in the soil after adsorption.

[0062] Example 5

[0063] (1) Add 3g sodium alginate and 1g calcium carbonate to 100mL of water and stir mechanically at 800rpm until completely dissolved.

[0064] (2) Add 1g of 5,10,15,20-tetra(4-methoxyphenyl)porphyrin to the mixed solution and stir continuously at 1000rpm for 2h. While stirring, add 2g of gluconolactone to the mixed solution; quickly pour the mixed solution into a 10mm mold, solidify into a gel, and freeze-dry for 48h to obtain core microspheres.

[0065] (3) Add 60g polylactic acid, 100g polyethylene glycol and 200g lactide to 500mL pure water, keep at 140℃ and stir at 150rpm to melt; place the core spheres in a 13mm mold, inject the molten mixture into the mold, and obtain a composite material with a core-shell structure after cooling.

[0066] (4) Weigh 100g of cadmium-contaminated soil and add 62g of water (62% of the soil's maximum field water holding capacity) to simulate the flooding state of a paddy field. Add 20g of the core-shell composite material prepared in step (3) to a beaker and incubate at 25℃ for 48h. Take out 1 / 5 of the water layer and soil layer respectively, air dry the soil sample, grind it, and pass it through a 100-mesh sieve for later use.

[0067] (5) The content of cadmium in various forms in the air-dried soil samples from step (4) was determined. The contents of acid-soluble, reducible, and oxidizable cadmium forms were determined sequentially using the BCR three-step method. Finally, the content of residual cadmium in the soil was determined using a microwave-assisted acid digestion method. The experimental results are as follows: Figure 3As shown, the adsorption rate was 18.33%. Examples 4 and 5 compared the adsorption effects of composite materials with different activators, and the activator citric acid was more conducive to the adsorption of cadmium.

[0068] Example 6

[0069] (1) Weigh 20g of cadmium-contaminated soil into two 100mL beakers and add 12.4g of water (62% of the maximum field water holding capacity of the soil) to simulate the flooding state of paddy fields.

[0070] (2) Add one core microsphere prepared in step (2) of Example 3 to one beaker, and add one core-shell composite material prepared in step (4) of Example 3 to the other beaker. After incubation at 25°C for 48 hours, photographs are taken to compare the changes before and after adsorption and the changes in the core microsphere without the outer shell. The results are as follows: Figure 2 As shown, Figure 2 From left to right, the images show the core-shell composite material after 48 hours in flooded soil, the core-shell composite material immediately placed in the beaker, and the core-shell composite material after 48 hours in the beaker. The results indicate that without prior activation, the core-shell composite material shows no color change after 48 hours of placement, resulting in unsatisfactory adsorption. In the right image, the outer shell cracks, and the core-shell composite material turns green after adsorbing heavy metals, demonstrating the effectiveness of the pre-activation adsorption strategy.

[0071] Example 7

[0072] (1) Weigh 20g of cadmium-contaminated soil. The contents of acid-soluble, reducible, and oxidizable cadmium states were determined sequentially using the BCR three-step method. Finally, the residual cadmium content in the soil was determined using microwave-assisted acid digestion. The experimental results are as follows: Figure 3 As shown in the blank group. Weigh 100g of cadmium-contaminated soil and add 62g of water (62% of the soil's field capacity) to simulate the flooding state of a paddy field.

[0073] (2) First adsorption: Add 20g of the core-shell composite material prepared in Example 3 to a beaker and incubate at 25℃ for 48h. Take out 1 / 5 of the water layer and soil layer respectively. Air dry, grind, and pass the soil sample through a 100-mesh sieve for later use. Take out the pellets and continue to use the remaining water-soil mixture.

[0074] (3) Secondary adsorption: Add 20g of the core-shell composite material prepared in Example 3 to the beaker in (2), and incubate at 25℃ for 48h. Take out 1 / 4 of the water layer and soil layer respectively. Air dry, grind, and pass the soil sample through a 100-mesh sieve for later use. Take out the small ball, and continue to use the remaining water-soil mixture.

[0075] (4) Three adsorptions: Add 10g of the core-shell composite material prepared in Example 3 to the beaker in (3), and incubate at 25℃ for 48h. After removing the small balls, take out 1 / 3 of the water layer and soil layer respectively. Air dry, grind, and pass the soil sample through a 100-mesh sieve for later use.

[0076] (5) The contents of various forms of cadmium in the air-dried soil samples from steps (2), (3), and (4) were determined. The contents of acid-soluble, reducible, and oxidizable cadmium forms were determined sequentially using the BCR three-step method. Finally, the contents of residual cadmium in the soil were determined using a microwave-assisted acid digestion method. The experimental results are as follows: Figure 3 As shown, the adsorption rates for the three adsorption processes were 31.66%, 48.33%, and 61.67%, respectively. Photos were taken to record the removal of the small balls in steps (2), (3), and (4). The results are as follows. Figure 4 As shown.

[0077] Figure 3 and Figure 4 The results showed that with increasing adsorption cycles, the content of various forms of cadmium in the soil decreased significantly. Acid-soluble cadmium was more easily activated into water, while residual cadmium, fixed in the soil, was more difficult to activate and remove. The color of the core microspheres changed from dark green to light green to light yellow. These two results demonstrate that observing the color change of the core microspheres can help control the adsorption progress, precisely control the amount of composite material applied, and achieve refined and controllable removal.

[0078] Comparative Example 1

[0079] (1) Mix 3g sodium alginate, 2g calcium carbonate and 1g brassinolide, add to 100mL water and stir mechanically at 800rpm until completely dissolved.

[0080] (2) Increase the rotation speed to 1000 rpm and stir continuously for 2 hours. While stirring, add 2g of gluconolactone to the mixture; quickly pour the mixture into a 10mm mold, solidify into a gel, and freeze-dry for 48 hours to obtain the core microspheres.

[0081] Results: The obtained core microspheres were not spherical. The order of adding the color developer affected the preparation of the microspheres. Adding the color developer in advance resulted in uneven color distribution of the mixture.

[0082] Comparative Example 2

[0083] (1) Add 3g sodium alginate and 1g calcium carbonate to 100mL of water and stir mechanically at 800rpm until completely dissolved.

[0084] (2) 20 g of 5,10,15,20-tetra(4-N-methylpyridinyl)porphyrin p-toluenesulfonate was added to the mixed solution and stirred continuously at 1000 rpm for 2 h. While stirring, 2 g of gluconolactone was added to the mixed solution; the mixed solution was quickly poured into a 10 mm mold, solidified into a gel, and freeze-dried for 48 h to obtain the core microspheres.

[0085] (3) In a 500mL beaker, first add 400mL of distilled water, then add 0.5g of the aforementioned core-shell microspheres. Next, let the beaker stand at room temperature until adsorption equilibrium is reached. Then, remove the core-shell microspheres from the beaker and weigh them to obtain the mass of the saturated water-absorbing core-shell microspheres. The calculated water absorption ratio is 799%. Figure 1 .

[0086] (4) Add 60g polylactic acid, 100g polyethylene glycol and 200g citric acid to 500mL pure water, keep at 140℃ and stir at 150rpm to melt; place the core spheres in a 13mm mold, inject the molten mixture into the mold, and obtain a composite material with a core-shell structure after cooling.

[0087] Comparative Example 3

[0088] (1) Add 3g sodium alginate and 1g calcium carbonate to 100mL of water and stir mechanically at 800rpm until completely dissolved.

[0089] (2) Add 2g of gluconolactone to the mixed solution while stirring; quickly pour the mixed solution into a 10mm mold, solidify into a gel, and freeze-dry for 48h to obtain the core microspheres.

[0090] (3) In a 500mL beaker, first add 400mL of distilled water, then add 0.5g of the aforementioned core microspheres. Next, let the beaker stand at room temperature until adsorption equilibrium is reached. Then, remove the core microspheres from the beaker and weigh them to obtain the mass of the saturated water-absorbing core microspheres. The calculated water absorption ratio is 566%. Figure 1 .

[0091] (4) Add 60g polylactic acid, 100g polyethylene glycol and 200g citric acid to 500mL pure water, keep at 140℃ and stir at 150rpm to melt; place the core spheres in a 13mm mold, inject the molten mixture into the mold, and obtain a composite material with a core-shell structure after cooling.

[0092] Comparative Example 4

[0093] (1) Add 3g sodium alginate and 1g calcium carbonate to 100mL of water and stir mechanically at 800rpm until completely dissolved.

[0094] (2) Add 1g of 5,10,15,20-tetra(4-methoxyphenyl)porphyrin to the mixed solution and stir continuously at 1000rpm for 2h. While stirring, add 2g of gluconolactone to the mixed solution; quickly pour the mixed solution into a 10mm mold, solidify into a gel, and freeze-dry for 48h to obtain core microspheres.

[0095] (3) Add 60g polylactic acid and 100g polyethylene glycol to 500mL pure water, keep at 140℃ and stir at 150rpm to melt; place the core spheres in a 13mm mold, inject the molten mixture into the mold, and obtain a composite material with a core-shell structure after cooling.

[0096] (4) Weigh 100g of cadmium-contaminated soil and add 62g of water (62% of the soil's maximum field water holding capacity) to simulate the flooding state of a paddy field. Add 20g of the core-shell composite material prepared in step (3) to a beaker and incubate at 25℃ for 48h. Take out 1 / 5 of the water layer and soil layer respectively, air dry the soil sample, grind it, and pass it through a 100-mesh sieve for later use.

[0097] (5) The content of cadmium in various forms in the air-dried soil samples from step (4) was determined. The contents of acid-soluble, reducible, and oxidizable cadmium forms were determined sequentially using the BCR three-step method. Finally, the content of residual cadmium in the soil was determined using a microwave-assisted acid digestion method. The experimental results are as follows: Figure 3 As shown, without the addition of an activator, the adsorption rate of the adsorbent material for cadmium is only 1.67%.

[0098] Comparative Example 5

[0099] (1) Add 3g sodium alginate and 1g calcium carbonate to 100mL of water and stir mechanically at 800rpm until completely dissolved.

[0100] (2) Add 1g of 5,10,15,20-tetra(4-methoxyphenyl)porphyrin and 200g of citric acid to the mixed solution and stir continuously at 1000rpm for 2h. While stirring, add 2g of gluconolactone to the mixed solution; quickly pour the mixed solution into a 10mm mold, solidify into a gel, and freeze-dry for 48h to obtain the core microspheres.

[0101] (3) Weigh 100g of cadmium-contaminated soil and add 62g of water (62% of the soil's maximum field water holding capacity) to simulate the flooding state of a paddy field. Add 20g of the composite material prepared in step (2) to a beaker and incubate at 25℃ for 48h. Take out 1 / 5 of the water layer and 1 / 5 of the soil layer respectively. Air dry the soil sample, grind it, and pass it through a 100-mesh sieve for later use.

[0102] (4) The content of cadmium in various forms in the air-dried soil samples from step (3) was determined. The contents of acid-soluble, reducible, and oxidizable cadmium forms were determined sequentially using the BCR three-step method. Finally, the content of residual cadmium in the soil was determined using a microwave-assisted acid digestion method. The experimental results are as follows: Figure 3 As shown, the adsorption rate was 6.67%. When the activator was directly added to the core microspheres and adsorption occurred simultaneously, the adsorption effect was not ideal.

[0103] Comparative Examples 4, 5, and Example 4 correspond to three heavy metal removal sequences: no pre-activation, simultaneous activation and adsorption, and activation followed by adsorption. Comparing the adsorption effects of the three experiments, it can be seen that the removal sequence of activation followed by adsorption has the best adsorption effect.

[0104] 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 visualization and colorimetric adsorption composite material, characterized in that, Includes the following steps: (1) Sodium alginate and calcium salt are mixed with water to obtain a mixed solution. A colorimetric reagent is added, the mixture is stirred, gluconolactone is added, the mixture is solidified, and the mixture is freeze-dried to obtain a colorimetric core microsphere. (2) Polylactic acid, polyethylene glycol, activator and water are mixed and stirred at high temperature to obtain a molten mixture; (3) Place the colorimetric core microspheres from step (1) into a mold and inject the molten mixture to obtain a soil heavy metal visualization colorimetric adsorption composite material with a core-shell structure; The colorimetric agent in step (1) is at least one of the following: tetraaldehyde phenylporphyrin, 5,10,15,20-tetra(4-methoxyphenyl)porphyrin, 5,10,15,20-tetra(4-aminophenyl)porphyrin, 5,10,15,20-tetra(4-N-methylpyridyl)porphyrin p-toluenesulfonate, tetra-p-tolylporphyrin, and brasilienin; The activator in step (2) is at least one of citric acid, lactide and chelating agent EDTA, and the high temperature is 140-200°C.

2. The preparation method of the soil heavy metal visualization colorimetric adsorption composite material according to claim 1, characterized in that, The mass ratio of sodium alginate, calcium salt and water in step (1) is 1-15:1-10:5-300.

3. The preparation method of the soil heavy metal visualization colorimetric adsorption composite material according to claim 1, characterized in that, The calcium salt is one of calcium carbonate, calcium chloride, calcium gluconate, calcium sulfate, or calcium phosphate.

4. The preparation method of the soil heavy metal visualization colorimetric adsorption composite material according to claim 1, characterized in that, The mass ratio of the color developer to water in step (1) is 1-20:1-500.

5. The preparation method of the soil heavy metal visualization colorimetric adsorption composite material according to claim 1, characterized in that, The mass ratio of gluconolactone and the mixed solution in step (1) is 1-5:1-500.

6. The preparation method of the soil heavy metal visualization colorimetric adsorption composite material according to claim 1, characterized in that, The mass ratio of polylactic acid, polyethylene glycol, activator and water in step (2) is 1-100:1-500:1-500:1-500.

7. The preparation method of the soil heavy metal visualization colorimetric adsorption composite material according to claim 1, characterized in that, The diameter of the core microspheres in step (1) is 3.5-10 mm, and the diameter of the adsorption composite material is 10-50 mm; The mixing speed in step (1) is 300-1200 rpm, and the time is 1-4 hours; The stirring speed is 500-1000 rpm, and the time is 0.5-2 hours; The solidification time is 0.5 to 4 hours, and the freeze-drying time is 24 to 72 hours.

8. A soil heavy metal visualization and colorimetric adsorption composite material, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

9. The application of the composite material according to claim 8 in the removal of heavy metals from soil.

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