CN116328734A - Composite material for synchronously removing heavy metal cadmium and arsenic in soil and preparation method and application thereof - Google Patents
Composite material for synchronously removing heavy metal cadmium and arsenic in soil and preparation method and application thereof Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Abstract
The invention discloses a composite material for synchronously removing heavy metal cadmium and arsenic in soil, and a preparation method and application thereof. According to the invention, sodium carboxymethyl cellulose is firstly dissolved in water, a proper amount of acid is added for protonation to prepare a protonated sodium carboxymethyl cellulose solution, then sucrose-coated calcium peroxide powder and chitosan powder are added, and freeze-drying is carried out to prepare a ball, thus preparing the floatable high-adsorption hydrogel composite material integrating oxidation and adsorption. The high-adsorptivity composite material prepared by the method has excellent mechanical property, high water-swelling property and high elasticity, high adsorptivity to heavy metal, easy recovery, suitability for repairing and treating and safely utilizing cadmium-arsenic composite pollution paddy field soil, simple operation, small dosage and remarkable and stable effect.
Description
Technical Field
The invention belongs to the field of soil heavy metal pollution treatment technology and farmland environment restoration thereof, and particularly relates to a composite material for synchronously removing soil heavy metal cadmium and arsenic, and a preparation method and application thereof.
Background
The Cd and As composite pollution of paddy soil is often caused by the combustion of fossil fuel, the discharge of industrial waste, the exploitation of metal mines, the mass application of chemical fertilizers containing cadmium and arsenic, pesticides and organic fertilizers, and the like. Compared with other elements, cd and As are easier to be absorbed by rice to poison crops, so that the yield is reduced, meanwhile, heavy metals are transported and enriched in rice grains, and the heavy metals have high toxicity, durability, non-biodegradability and bioaccumulation, so that the long-term low-dose ingestion of the heavy metals can seriously harm the health of human beings. For example, cadmium ingestion is strongly carcinogenic and can cause impaired renal function and reproductive defects; lead intake affects mental development in children, respiratory tract and cardiovascular diseases in adults, and arsenic can cause skin cancer, bladder cancer, etc.
As cadmium and arsenic are elements with opposite chemical behaviors, the remediation of the rice field cadmium and arsenic combined pollution becomes a great difficulty in the environmental field. The chemical properties of cadmium and arsenic are quite opposite, the pH is raised to be beneficial to stabilizing Cd but increasing the solubility of As, the lower oxidation-reduction potential is beneficial to reducing the absorption of cadmium by plants, but the reduction of arsenic is promoted to further increase the toxicity of arsenic, so that the cadmium-arsenic polluted soil is difficult to synchronously restore by adjusting the pH value or Eh and the like of the soil, and the problems and the great challenges are clearly brought to the restoration of the cadmium-arsenic combined polluted soil of the paddy field and the safe production of the paddy. The soil and water body polluted by cadmium and arsenic can be finally enriched in human bodies through the food chains, and the human bodies are greatly threatened.
The current technical means for treating the cadmium-arsenic composite pollution of the soil are relatively lacking, the common repair means are in-situ passivation repair methods, and the technology for reducing the effective state content of the heavy metal in the soil is achieved by changing the physical and chemical properties of the soil, adsorption, oxidation reduction, complexation, precipitation, antagonism and other mechanisms. Common soil heavy metal passivator materials comprise inorganic minerals, organic passivators, phosphates, biomass charcoal, lime, novel nano materials and the like, and the content of calcium, magnesium and the like in the soil can be improved by applying the inorganic minerals in practical application, so that the cost is low, but the supplement of organic fertility is lacked, and the passivation effect is limited; the application of the organic passivating agent can provide soil nutrients, improve soil properties, adsorb and complex soil heavy metals, but possibly introduce new pollutants, and easily cause recontamination when environmental conditions change. The application of phosphate can effectively reduce the effectiveness of cadmium and can provide nutrients for plants, but arsenic in soil is easily replaced due to the similar chemical properties of arsenate and phosphate, so that the mobility of the arsenic is increased; the biomass charcoal has strong anti-decomposition capability, rich surface oxygen-containing functional group structure, larger specific surface area, good environment and high repair efficiency, but the application of the biomass charcoal is likely to improve the mobility of soil heavy metals, and has higher cost and the risk of secondary release of cadmium and arsenic. Lime can be applied to reduce the effectiveness of heavy metals, improve acid soil and increase crop yield, but soil hardening is often caused, which is unfavorable for the growth and development of plants. The nano material has good passivation effect, but has high cost and easy agglomeration. The method can also be used for extracting cadmium and arsenic in soil by using super-accumulated plants and reducing the cadmium and arsenic content in the soil by harvesting the plants, but has the problems of long restoration time, wide occupied cultivated land area, high cost and the like.
In conclusion, cadmium and arsenic are two heavy metal elements with extremely strong toxic action, and have opposite chemical behaviors, so that antagonism exists in the treatment of the heavy metal elements, and the cadmium and arsenic pollution is simultaneously repaired in the rice field polluted by the cadmium and arsenic, so that the common repair method has a certain defect.
Therefore, development of a new material which is easy to apply, stable and efficient and can synchronously remove cadmium and arsenic combined pollution of rice fields is needed.
Disclosure of Invention
In order to solve the defects and shortcomings of the prior art, the primary purpose of the invention is to provide a preparation method for synchronously removing heavy metal cadmium and arsenic in soil.
According to the invention, sodium carboxymethyl cellulose is firstly dissolved in water, a proper amount of acid is added for protonation to prepare a protonated sodium carboxymethyl cellulose solution, then sucrose and/or polyethylene glycol coated calcium peroxide powder and chitosan powder are added, and freeze-drying is carried out to prepare a ball, thus preparing the floatable high-adsorption hydrogel composite material integrating oxidation and adsorption. The high-adsorptivity composite material prepared by the method has excellent mechanical property, high water-swelling property and high elasticity, high adsorptivity to heavy metal, easy recovery, suitability for repairing and treating and safely utilizing cadmium-arsenic composite pollution paddy field soil, simple operation, small dosage and remarkable and stable effect.
The invention further aims to provide the composite material for synchronously removing the heavy metal cadmium and arsenic in the soil.
The invention also aims to provide the application of the composite material for synchronously removing the heavy metal cadmium and arsenic in the soil in the field of removing the heavy metal in the soil. In the application process, the floatable high-adsorption hydrogel composite material slowly releases oxygen to oxidize trivalent arsenic into pentavalent arsenic, so that toxicity of arsenic is greatly reduced, meanwhile, the composite material efficiently adsorbs effective heavy metals in the water absorption expansion process, and finally, the heavy metals in soil are thoroughly removed from the root to the maximum extent through simple salvage and recovery.
The invention aims at realizing the following technical scheme:
a preparation method of a composite material for synchronously removing heavy metal cadmium and arsenic in soil comprises the following steps:
(1) Adding acid into the sodium carboxymethyl cellulose water solution to protonate carboxylic acid groups in the sodium carboxymethyl cellulose;
(2) Adding peroxide into sucrose and/or polyethylene glycol (PEG) solution, mixing, and drying to obtain coated peroxide powder;
(3) Uniformly mixing the coated peroxide powder and chitosan powder, adding the mixture into the protonated sodium carboxymethyl cellulose aqueous solution in the step (1), uniformly mixing, standing for molding, and freeze-drying to obtain an oxidation-adsorption integrated high-adsorption composite material; wherein, free H in the mixed solution + Mainly with amino (-NH) in chitosan 2 ) Binding to make-NH 2 Protonation to positively charged NH 3 + In the form, the effect of the chitosan with positive charges and the carboxymethyl cellulose with negative charges is gradually enhanced, and finally the hydrogel electrostatic network is obtained.
Preferably, the acid of step (1) is at least one of analytically pure (AR) hydrochloric acid, superior pure (GR) hydrochloric acid, dilute sulfuric acid, and dilute acetic acid; the dilute sulfuric acid and the dilute acetic acid are dilute acid solutions with volume concentration of 1-3%.
Preferably, the sodium carboxymethyl cellulose aqueous solution in the step (1) is obtained by adding sodium carboxymethyl cellulose (CMC) into water and stirring until the sodium carboxymethyl cellulose aqueous solution is completely dissolved; the stirring speed is 300-1000 rpm, and the stirring time is 0.5-2 h.
Preferably, in the sodium carboxymethyl cellulose aqueous solution in the step (1), the mass ratio of sodium carboxymethyl cellulose to water is (0.5-2): (25-100).
Preferably, the mass ratio of the acid to the sodium carboxymethyl cellulose in the step (1) is (1-2): (1-2).
Preferably, the stirring speed of the protonation in the step (1) is 200-400 rpm, and the time is 0.5-1 h.
Preferably, the peroxide in step (2) is at least one of calcium peroxide, magnesium peroxide, zinc peroxide and sodium peroxide.
Preferably, the mass ratio of the total mass of sucrose and/or polyethylene glycol to the peroxide in step (2) is 10:0.1 to 1.
Preferably, in the sucrose and/or polyethylene glycol (PEG) solution in the step (2), the mass ratio of the total mass of sucrose and/or polyethylene glycol to the solvent is (2-10): (10-50); the solvent is at least one of water and ethanol.
Preferably, the sucrose solution in the step (2) is obtained by adding sucrose into water, heating and stirring at 60-200 ℃ for 0.5-6 h; the rotating speed of the heating and stirring is 800-1500 rpm.
Preferably, the stirring speed of the uniform mixing in the step (2) is 800-1500 rpm.
Preferably, when the peroxide is coated by the sucrose in the step (2), the peroxide is added into the sucrose solution and uniformly mixed, then pre-frozen, the pre-freezing temperature is between-4 and-100 ℃, the time is between 3 and 9 hours, and then the drying is carried out.
Preferably, the drying in the step (2) means freeze-drying at-80 ℃ and below for 24-48 hours.
Preferably, the coated peroxide powder of step (2) is further crushed and screened through a 200-400 mesh screen; more preferably a 300 mesh screen.
Preferably, the mass ratio of the coated peroxide powder and the chitosan powder in the step (3) is 1.3-1.4: 1.0.
preferably, the mass ratio of the chitosan powder to the sodium carboxymethyl cellulose in the step (3) is (2-10): (1-10).
Preferably, the chitosan powder in step (3) has a number average molecular weight of 5 to 10 ten thousand.
Preferably, the uniformly mixed stirring rotating speed in the step (3) is 1500-2500 rpm; the time is 30-120 s.
Preferably, the freeze drying in the step (3) refers to freeze drying at the temperature of-80 to-100 ℃ for 24 to 48 hours.
Preferably, in the step (3), after being uniformly mixed, the mixture is subjected to reverse die and static molding, wherein the die is a spherical silica gel die with the diameter of 1-2 cm.
The composite material for synchronously removing the heavy metal cadmium and arsenic in the soil is prepared by the method.
The application of the composite material for synchronously removing the heavy metal cadmium and arsenic in the soil in the field of removing the heavy metal in the soil is provided.
Preferably, in said application, the composite material is applied in an amount of 0.05 to 2% of the soil mass.
The invention uses natural polymer sodium carboxymethyl cellulose (CMC) with abundant sources and chitosan as raw materials, and the sodium carboxymethyl cellulose is protonated by adding acid and belongs to anionic cellulose ethers, contains abundant carboxyl and hydroxyl groups and has negative charge. The chitosan contains a large amount of free amino groups and active hydroxyl groups, is the only basic polysaccharide in the natural polysaccharide, and is free H in the solution + With amino (-NH) groups in chitosan 2 ) Binding to make-NH 2 Protonation to positively charged NH 3 + In the form, the action of polyelectrolyte with positive and negative charges (chitosan with positive charges and sodium carboxymethyl cellulose with negative charges) is gradually enhanced, and finally the hydrogel electrostatic network is obtained. Trivalent arsenic is very toxic and mainly exists inIn the reducing environment, toxicity is reduced by 60 times after the arsenic is easily oxidized into pentavalent arsenic in the oxidizing environment. CaO used in the present invention 2 Is an oxidant which slowly releases O in water environment 2 However, the generated alkaline substances raise the pH value in the surrounding environment, and the high pH value is harmful to animals, plants and microorganisms in water body, soil and damages the ecological environment. Thus, caO is suppressed 2 Direct contact with the body of water is achieved by the application of CaO 2 The key problem to be solved. CaO is treated in the invention 2 Coating in polyelectrolyte gel, not only can prevent CaO 2 The method is in direct contact with a water body, alkaline substances are generated in a local microenvironment of gel, the pH is improved, the stability of adsorbed cadmium is enhanced, oxygen can be slowly released, an oxidizing atmosphere is provided for the surrounding environment, and As (III) with high toxicity is oxidized into As (V) with weak toxicity and the most stable state, so that the arsenic detoxification effect is realized; caO (CaO) 2 Ca produced by the reaction 2+ The mechanical strength of the gel can be enhanced, meanwhile, the slow-release oxygen can further enrich the pore structure in the gel network, and the active adsorption sites in the polyelectrolyte gel are exposed, so that the purposes of reducing the effectiveness of cadmium and arsenic and improving the restoration effect of cadmium and arsenic composite pollution are achieved. The process of slowly releasing oxygen is also beneficial to the floatation of the composite material; increasing the oxygen content of paddy field and being beneficial to improving the water quality of paddy field. Because the heavy metal cadmium and arsenic have opposite chemical properties and are oppositely charged, the electrostatic network of the high-water-absorption hydrogel formed by CMC and CS through electrostatic action can simultaneously adsorb two heavy metal ions with different charges, reduce the toxicity of the cadmium and arsenic in the paddy field and thoroughly remove the cadmium and arsenic from the environment.
Compared with the prior art, the invention has the following advantages:
(1) The sodium carboxymethyl cellulose and chitosan adopted by the raw materials are natural high molecular compounds, have the advantages of environmental protection, safety, no toxicity, degradability and the like, are healthier and more environment-friendly than the existing adsorption materials, and show unique superiority.
(2) The invention adopts an oxidation-adsorption integrated technology, the super absorbent composite material slowly releases oxygen to oxidize trivalent arsenic and adsorb effective heavy metals in the water absorption expansion process, and provides a new idea for removing cadmium and arsenic combined pollution of paddy fields, and the super absorbent composite material has the advantages of simple components, wide sources, less consumption, obvious and stable effect and is convenient for farmers to apply and use by themselves.
(3) The invention adopts the slow-release oxygen technology to enable the material to slowly release oxygen to oxidize trivalent arsenic, and simultaneously has low material density, floatability, and is beneficial to subsequent collection and treatment, saves material resources and cost, and is simple and quick.
(4) The composite material can be simply added into water or flooded soil, and after adsorption is finished, the composite material is recovered through salvage, so that the soil heavy metal is thoroughly removed, and the risk of secondary release is avoided.
Drawings
Fig. 1 (a) and (b) are Scanning Electron Microscope (SEM) images of the high-adsorption composite material integrated with oxidation-adsorption obtained by directly adding calcium peroxide in comparative example 1, and (c) and (d) are Scanning Electron Microscope (SEM) images of the floatable high-adsorption composite material integrated with oxidation-adsorption obtained by coating calcium peroxide with sucrose in example 1.
Fig. 2 is a water absorption bar graph of the oxidation-adsorption integrated floatable high adsorption composite obtained in example 1, comparative example 1, example 2 and comparative example 2.
Fig. 3 shows the dissolved oxygen content of the oxidation-adsorption integrated floatable high adsorption composite obtained in example 1, comparative example 1, example 2 and comparative example 2.
FIG. 4 is a graph showing arsenic (III) accumulation in soil from a blank (without any adsorbent), and from soil heavy metal removal experiments performed in example 3, comparative example 3, and example 4, wherein the conditions of arsenic (As) contamination are the same.
FIG. 5 is a graph showing arsenic (V) accumulation in soil after performing soil heavy metal removal experiments in a blank group (without any adsorbent), example 3, comparative example 3 and example 4, wherein the conditions of arsenic (As) contamination and the like are the same.
FIG. 6 is a bar graph showing the removal rates of soil cadmium (Cd) and arsenic (As) single adsorption tests performed in example 3, comparative example 3 and example 4.
FIG. 7 is a bar graph showing the removal rates of the soil cadmium (Cd) arsenic (As) composite adsorption tests performed in example 3, comparative example 3 and example 4.
Fig. 8 is a view showing adsorption and material recovery before and after the paddy soil heavy metal removal experiment in example 1.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but embodiments of the present invention are not limited thereto.
The specific conditions are not noted in the examples of the present invention, and are carried out according to conventional conditions or conditions suggested by the manufacturer. The raw materials, reagents, etc. used, which are not noted to the manufacturer, are conventional products commercially available.
Example 1
(1) At room temperature, 0.6g of sodium carboxymethylcellulose (CMC) was added to 30ml of deionized water and stirred mechanically at 500rpm for 1h until complete dissolution, to give a homogeneous solution of sodium carboxymethylcellulose.
(2) To the solution obtained in the step (1) was added 0.4ml of high-grade pure hydrochloric acid at a stirring speed of 200rpm, and stirred for 0.5h to protonate carboxylic acid groups in sodium carboxymethylcellulose.
(3) Weighing 10.0g of sucrose into 30mL of water by taking a 50mL beaker, and stirring for 1h at 80 ℃ and 800 rpm; adding 0.3g of calcium peroxide powder, rapidly stirring at 1200rpm for 0.05h, immediately pre-freezing at-20deg.C for 6h after the calcium peroxide powder is uniformly dispersed, freeze-drying at-80deg.C for 24h, pulverizing by a pulverizer, and sieving with 300 mesh sieve.
(4) Uniformly mixing the sucrose-coated calcium peroxide powder prepared in the step (3) with 1.0g of Chitosan (CS) powder with the molecular weight of 5-10 ten thousand, adding the mixture into the solution in the step (2), vigorously stirring the mixture at 1500rpm for 30 seconds, pouring the mixture into a spherical silica gel mold with the diameter of 1.0cm, and standing the mixture for molding to obtain a floatable high-adsorption hydrogel composite material; pre-freezing at-20deg.C for 6 hr, and lyophilizing at-80deg.C for 24 hr; obtaining an oxidation-adsorption integrated high-adsorption composite material; the electron microscope image is shown in figure 1.
(5) And (3) measuring the water absorption rate of the oxidation-adsorption integrated super-absorbent composite material by a natural filtration method. In a 500mL beaker, 400mL of distilled water was added, and then 1.0g of the above-mentioned oxidation-adsorption integrated super absorbent composite was put into the beaker. And then standing the beaker at normal temperature, pouring the composite material in the beaker onto gauze after the water absorption balance of the sample is observed, and weighing the composite material after the composite material is not dripped any more, so as to obtain the quality of the water absorption saturated composite material. The calculated water absorption capacity is shown in fig. 2.
(6) Adopting nitrogen aeration to make DO value of deionized water after high-temperature sterilization be zero, accurately measuring 200mL, and placing the deionized water into a self-made closed oxygen release reactor with volume of 200 mL; 1.0g of the oxidation-adsorption integrated high adsorption composite material of example 1 was added, and then the reactor was placed in a total temperature oscillator (constant temperature 20 ℃ C., constant rotation speed 170 r/min) to measure the change of DO value in the aqueous phase on line (YSK 607A type oxygen dissolving meter). The measured DO values are shown in FIG. 3.
Comparative example 1
(1) At room temperature, 0.6g of sodium carboxymethylcellulose (CMC) was added to 30ml of deionized water and stirred mechanically at 500rpm for 1h until complete dissolution, to give a homogeneous solution of sodium carboxymethylcellulose.
(2) To the solution obtained in the step (1) was added 0.4ml of high-grade pure hydrochloric acid at a stirring speed of 200rpm, and stirred for 0.5h to protonate carboxylic acid groups in sodium carboxymethylcellulose.
(3) Weighing 0.3g of calcium peroxide powder and 1.0g of Chitosan (CS) powder with molecular weight of 5-10 ten thousand, uniformly mixing, adding into the solution in the step (2), vigorously stirring for 30s at 1500rpm, pouring into a spherical silica gel mold with diameter of 1.0cm, and standing for molding to obtain a floatable high-adsorption hydrogel composite material; pre-freezing at-20deg.C for 6 hr, and lyophilizing at-80deg.C for 24 hr; obtaining an oxidation-adsorption integrated high-adsorption composite material; the electron microscope image is shown in figure 1.
(4) And (3) measuring the water absorption rate of the oxidation-adsorption integrated super-absorbent composite material by a natural filtration method. In a 500ml beaker, 400ml of distilled water was added, and then 1.0g of the above-mentioned oxidation-adsorption integrated high adsorption composite material was put into the beaker. And then standing the beaker at normal temperature, pouring the composite material in the beaker onto gauze after the water absorption balance of the sample is observed, and weighing the composite material after the composite material is not dripped any more, so as to obtain the quality of the water absorption saturated composite material. The calculated water absorption capacity is shown in fig. 2.
(5) Adopting nitrogen aeration to make DO value of deionized water after high-temperature sterilization be zero, accurately measuring 200mL, and placing the deionized water into a self-made closed oxygen release reactor with volume of 200 mL; 1.0g of the high adsorption composite material integrated with oxidation-adsorption in comparative example 1 was added, and then the reactor was placed in a total temperature oscillator (constant temperature 20 ℃ C., constant rotation speed 170 r/min), and the change in DO value in the aqueous phase was measured on line (YSK 607A type oxygen dissolving meter). The measured DO values are shown in FIG. 3.
Example 2
(1) At room temperature, 0.6g of sodium carboxymethylcellulose (CMC) was added to 30ml of deionized water and stirred mechanically at 500rpm for 1h until complete dissolution, to give a homogeneous solution of sodium carboxymethylcellulose.
(2) To the solution obtained in the step (1) was added 0.4ml of high-grade pure hydrochloric acid at a stirring speed of 200rpm, and stirred for 0.5h to protonate carboxylic acid groups in sodium carboxymethylcellulose.
(3) Weighing 50mL beaker, dissolving 10.0g PEG in 30mL absolute ethanol, adding 0.3g calcium peroxide, rapidly stirring at 1200rpm for 0.25h, drying in a blast drying oven at 80deg.C for 4h, pulverizing, and sieving with 300 mesh sieve.
(4) Uniformly mixing the PEG-coated calcium peroxide powder prepared in the step (3) with 1.0g of Chitosan (CS) powder with the molecular weight of 5-10 ten thousand, adding the mixture into the solution in the step (2), vigorously stirring the mixture at 1500rpm for 30 seconds, pouring the mixture into a spherical silica gel mold with the diameter of 1.0cm, and standing the mixture for molding to obtain a floatable high-adsorption hydrogel composite material; pre-freezing at-20deg.C for 6 hr, and lyophilizing at-80deg.C for 24 hr; and obtaining the high-adsorption composite material integrating oxidation and adsorption.
(5) And (3) measuring the water absorption rate of the oxidation-adsorption integrated super-absorbent composite material by a natural filtration method. In a 500ml beaker, 400ml of distilled water was added, and then 1.0g of the above-mentioned oxidation-adsorption integrated super absorbent composite was put into the beaker. And then standing the beaker at normal temperature, pouring the composite material in the beaker onto gauze after the water absorption balance of the sample is observed, and weighing the composite material after the composite material is not dripped any more, so as to obtain the quality of the water absorption saturated composite material. The calculated water absorption capacity is shown in fig. 2.
(6) Adopting nitrogen aeration to make DO value of deionized water after high-temperature sterilization be zero, accurately measuring 200mL, and placing the deionized water into a self-made closed oxygen release reactor with volume of 200 mL; 1.0g of the oxidation-adsorption integrated high adsorption composite material of example 2 was added, and then the reactor was placed in a total temperature oscillator (constant temperature 20 ℃ C., constant rotation speed 170 r/min) to measure the change of DO value in the aqueous phase on line (YSK 607A type oxygen dissolving meter). The measured DO values are shown in FIG. 3.
Comparative example 2
(1) At room temperature, 0.6g of sodium carboxymethylcellulose (CMC) was added to 30ml of deionized water and stirred mechanically at 500rpm for 1h until complete dissolution, to give a homogeneous solution of sodium carboxymethylcellulose.
(2) To the solution obtained in the step (1) was added 0.4ml of high-grade pure hydrochloric acid at a stirring speed of 200rpm, and stirred for 0.5h to protonate carboxylic acid groups in sodium carboxymethylcellulose.
(3) Adding 1.0g of Chitosan (CS) powder with the molecular weight of 5-10 ten thousand into the solution in the step (2), vigorously stirring for 30s at a rotating speed of 1500rpm, pouring the mixture into a spherical silica gel mold with the diameter of 1.0cm after the chitosan is uniformly distributed, and standing and forming to obtain a floatable high-adsorption hydrogel composite material; immediately pre-freezing at-20deg.C for 6 hr, and lyophilizing at-80deg.C below in a lyophilization machine for 24 hr.
(4) A50 ml centrifuge tube was weighed to dissolve 0.3g of the calcium peroxide powder in 30ml of absolute ethanol. Soaking the composite material subjected to freeze drying in the step (3) in an absolute ethanol solution of calcium peroxide, putting the composite material into a shaking table, setting the temperature to 25 ℃, the rotating speed to 150rpm, and the soaking time to 1h, so that the calcium peroxide is loaded into the composite material from outside to inside; finally, drying for 0.5h in a blast drier at 60 ℃ to obtain the high-adsorption composite material integrating oxidation and adsorption.
(5) And (3) measuring the water absorption rate of the oxidation-adsorption integrated super-absorbent composite material by a natural filtration method. In a 500ml beaker, 400ml of distilled water was added, and then 1.0g of the above-mentioned oxidation-adsorption integrated high adsorption composite material was put into the beaker. And then standing the beaker at normal temperature, pouring the composite material in the beaker onto gauze after the water absorption balance of the sample is observed, and weighing the composite material after the composite material is not dripped any more, so as to obtain the quality of the water absorption saturated composite material. The calculated water absorption capacity is shown in fig. 2.
(6) Adopting nitrogen aeration to make DO value of deionized water after high-temperature sterilization be zero, accurately measuring 200mL, and placing the deionized water into a self-made closed oxygen release reactor with volume of 200 mL; 1.0g of the high adsorption composite material integrated with oxidation-adsorption in comparative example 2 was added, and then the reactor was placed in a total temperature oscillator (constant temperature 20 ℃ C., constant rotation speed 170 r/min), and the change in DO value in the aqueous phase was measured on line (YSK 607A type oxygen dissolving meter). The measured DO values are shown in FIG. 3.
Example 3
Application example of oxidation-adsorption integrated high water absorption composite material
Experiment one: cadmium single heavy metal adsorption experiment
Weighing 20g of rice field soil polluted by cadmium (Cd), wherein the concentration of Cd (II) in the soil is 100mg/L, adding 12.4g of water (200% of the maximum field water holding capacity (31%) of the rice field soil), simulating a rice field flooding state, adding 3 (0.1 g in total) of the super absorbent composite material prepared in the example 1, culturing at the constant temperature of 25 ℃ for 48 hours, fishing the composite material, separating a water layer from a soil layer, and then air-drying, grinding and sieving with a 100-mesh sieve for later use.
Experiment II: arsenic single heavy metal adsorption experiment
And (3) introducing nitrogen to drive away oxygen in the beaker, weighing 20g of rice field soil polluted by arsenic (As) in a nitrogen atmosphere, wherein the concentration of arsenic (III) in the soil is 50mg/L, adding 12.4g of water (200% of the maximum water holding capacity (31%) of the rice field soil in the field), simulating the flooding state of the rice field, adding 3 (0.1 g in total) of the super absorbent composite material prepared in the embodiment 1, sealing the cup mouth, culturing at the constant temperature of 25 ℃ for 48 hours, fishing the composite material, separating a water layer from a soil layer, airing, grinding a soil sample, and sieving with a 100-mesh sieve for later use.
Experiment III: cadmium-arsenic compound heavy metal adsorption experiment
And (3) introducing nitrogen to drive away oxygen in the beaker, weighing 20g of rice field soil subjected to cadmium and arsenic (Cd, as) combined pollution in a nitrogen atmosphere, wherein the concentration of Cd (II) in the soil is 100mg/L, the concentration of arsenic (III) in the soil is 50mg/L, adding 12.4g of water (200% of the maximum field water holding capacity (31%) of the rice field soil), simulating a rice field flooding state, adding 3 (0.1 g in total) of the super absorbent composite material prepared in the embodiment 1, sealing a cup opening, culturing at the constant temperature of 25 ℃ for 48 hours, fishing the composite material, separating a water layer from a soil layer, and then air-drying, grinding and sieving the soil sample with a 100-mesh sieve for later use.
After the soil sample is digested according to the microwave digestion method, the concentrations of As (III) and As (V) in the soil are measured by adopting a liquid chromatography coupled atomic fluorescence spectrometry, the experimental results are shown in figures 4 and 5, and no adsorbent is added in a blank group. The concentration of cadmium and arsenic in the soil is measured by using an inductively coupled plasma mass spectrometry and an atomic fluorescence method, and the removal efficiency is calculated, and the experimental results are shown in fig. 6 and 7. The solid materials before and after adsorption and the material recovery of the oxidation-adsorption integrated high water absorption composite material soil heavy metal removal experiment obtained in the example 1 are shown in fig. 8.
Comparative example 3
(1) At room temperature, 0.6g of sodium carboxymethylcellulose (CMC) was added to 30ml of deionized water and stirred mechanically at 500rpm for 1h until complete dissolution, to give a homogeneous solution of sodium carboxymethylcellulose.
(2) To the solution obtained in the step (1) was added 0.4ml of high-grade pure hydrochloric acid at a stirring speed of 200rpm, and stirred for 0.5h to protonate carboxylic acid groups in sodium carboxymethylcellulose.
(3) Adding 1.0g of Chitosan (CS) powder with the molecular weight of 5-10 ten thousand into the solution in the step (2), vigorously stirring for 30s at a rotating speed of 1500rpm, pouring the mixture into a spherical silica gel mold with the diameter of 1.0cm after the chitosan is uniformly distributed, and standing and forming to obtain a floatable high-adsorption hydrogel composite material; -immediately pre-freezing for 6h at-20 ℃, freeze-drying for 24h in a freeze-dryer below-80 ℃; a floatable high adsorption composite material is obtained.
Experiment one: cadmium single heavy metal adsorption test
Weighing 20g of rice field soil polluted by cadmium (Cd), wherein the concentration of Cd (II) in the soil is 100mg/L, adding 12.4g of water (200% of the maximum field water holding capacity (31%) of the rice field soil), simulating a rice field flooding state, adding 3 (0.1 g in total) of the high-adsorption composite material prepared in the step (3), culturing at the constant temperature of 25 ℃ for 48 hours, fishing the composite material, separating a water layer from a soil layer, and then air-drying, grinding and sieving a soil sample with a 100-mesh sieve for later use.
Experiment II: arsenic single heavy metal adsorption test
And (3) introducing nitrogen to drive away oxygen in the beaker, weighing 20g of rice field soil polluted by arsenic (As) in a nitrogen atmosphere, wherein the concentration of arsenic (III) in the soil is 50mg/L, adding 12.4g of water (200% of the maximum water holding capacity (31%) of the rice field soil field), simulating the rice field flooding state, adding 3 (0.1 g in total) of the high-adsorption composite material prepared in the step (3), sealing the cup mouth, culturing at the constant temperature of 25 ℃ for 48 hours, fishing the composite material, separating a water layer from a soil layer, airing a soil sample, grinding, and sieving with a 100-mesh sieve for later use.
Experiment III: cadmium-arsenic compound heavy metal adsorption test
And (3) introducing nitrogen to drive away oxygen in the beaker, weighing 20g of rice field soil subjected to cadmium and arsenic (Cd, as) combined pollution in a nitrogen atmosphere, wherein the concentration of Cd (II) in the soil is 100mg/L, the concentration of arsenic (III) in the soil is 50mg/L, adding 12.4g of water (200% of the maximum field water holding capacity (31%) of the rice field soil), simulating the rice field flooding state, adding 3 pieces (0.1 g in total) of the super absorbent composite material prepared in the step (3), sealing the cup opening, culturing at the constant temperature of 25 ℃ for 48 hours, fishing the composite material, separating a water layer from a soil layer, and then air-drying, grinding and sieving the soil sample with a 100-mesh sieve for later use.
After the soil sample is digested according to the microwave digestion method, the concentrations of As (III) and As (V) in the soil are measured by adopting a liquid chromatography coupled atomic fluorescence spectrometry, the experimental results are shown in figures 4 and 5, and no adsorbent is added in a blank group. The concentration of cadmium and arsenic in the soil is measured by using an inductively coupled plasma mass spectrometry and an atomic fluorescence method, and the removal efficiency is calculated, and the experimental results are shown in fig. 6 and 7.
Example 4
(1) At room temperature, 0.6g of sodium carboxymethylcellulose (CMC) was added to 30ml of deionized water and stirred mechanically at 500rpm for 1h until complete dissolution, to give a homogeneous solution of sodium carboxymethylcellulose.
(2) To the solution obtained in the step (1) was added 0.4ml of high-grade pure hydrochloric acid at a stirring speed of 200rpm, and stirred for 0.5h to protonate carboxylic acid groups in sodium carboxymethylcellulose.
(3) Weighing 10.0g of sucrose into 20mL of water by taking a 50mL beaker, and stirring for 1h at 80 ℃ and 800 rpm; adding 0.4g of calcium peroxide powder, rapidly stirring at 1200rpm for 0.05h, immediately pre-freezing at-20deg.C for 6h after the calcium peroxide powder is uniformly dispersed, freeze-drying at-80deg.C for 24h, pulverizing by a pulverizer, and sieving with 300 mesh sieve.
(4) Uniformly mixing the sucrose-coated calcium peroxide powder prepared in the step (3) with 1.0g of Chitosan (CS) powder with the molecular weight of 5-10 ten thousand, adding the mixture into the solution in the step (2), vigorously stirring the mixture at 1500rpm for 30 seconds, pouring the mixture into a spherical silica gel mold with the diameter of 1.0cm, and standing the mixture for molding to obtain a floatable high-adsorption hydrogel composite material; pre-freezing at-20deg.C for 6 hr, and lyophilizing at-80deg.C for 24 hr; and obtaining the high-adsorption composite material integrating oxidation and adsorption.
Experiment one: cadmium single heavy metal adsorption test
Weighing 20g of rice field soil polluted by cadmium (Cd), wherein the concentration of Cd (II) in the soil is 100mg/L, adding 12.4g of water (200% of the maximum field water holding capacity (31%) of the rice field soil), simulating a rice field flooding state, adding 3 (0.1 g in total) of the high-adsorption composite material prepared in the step (4), culturing at the constant temperature of 25 ℃ for 48 hours, fishing the composite material, separating a water layer from a soil layer, and then air-drying, grinding and sieving a soil sample with a 100-mesh sieve for later use.
Experiment II: arsenic single heavy metal adsorption test
And (3) introducing nitrogen to drive away oxygen in the beaker, weighing 20g of rice field soil polluted by arsenic (As) in a nitrogen atmosphere, wherein the concentration of arsenic (III) in the soil is 50mg/L, adding 12.4g of water (200% of the maximum water holding capacity (31%) of the rice field soil field), simulating the rice field flooding state, adding 3 (0.1 g in total) of the high-adsorption composite material prepared in the step (4), sealing the cup mouth, culturing at the constant temperature of 25 ℃ for 48 hours, fishing the composite material, separating a water layer from a soil layer, airing a soil sample, grinding, and sieving with a 100-mesh sieve for later use.
Experiment III: cadmium-arsenic compound heavy metal adsorption test
And (3) introducing nitrogen to drive away oxygen in the beaker, weighing 20g of rice field soil subjected to cadmium and arsenic (Cd, as) combined pollution in a nitrogen atmosphere, wherein the concentration of Cd (II) in the soil is 100mg/L, the concentration of arsenic (III) in the soil is 50mg/L, adding 12.4g of water (200% of the maximum field water holding capacity (31%) of the rice field soil), simulating the rice field flooding state, adding 3 pieces (0.1 g in total) of the super absorbent composite material prepared in the step (4), sealing the cup opening, culturing at the constant temperature of 25 ℃ for 48 hours, fishing the composite material, separating a water layer from a soil layer, and then air-drying, grinding and sieving the soil sample with a 100-mesh sieve for later use.
After the soil sample is digested according to the microwave digestion method, the concentrations of As (III) and As (V) in the soil are measured by adopting a liquid chromatography coupled atomic fluorescence spectrometry, the experimental results are shown in figures 4 and 5, and no adsorbent is added in a blank group. The concentration of cadmium and arsenic in the soil is measured by using an inductively coupled plasma mass spectrometry and an atomic fluorescence method, and the removal efficiency is calculated, and the experimental results are shown in fig. 6 and 7.
As can be seen from (a-b) in FIG. 1, the floatable high-adsorption composite material has a plurality of pores, is honeycomb-shaped and regular in pore wall, forms a plurality of crosslinking sites, provides favorable conditions for adsorption and removal of heavy metals, but greatly reduces the content of calcium peroxide due to the introduction of hydrochloric acid into a gel system, and is unfavorable for arsenic (III) oxide to achieve the purpose of reducing toxicity. As can be seen in FIG. 1 (c), ca is obtained after adding sucrose-coated calcium peroxide 2+ The cross-linking is sufficient, caking and hardening phenomena are avoided, and meanwhile, compared with the floatable high-adsorption composite material, the floatable high-adsorption hydrogel composite material integrating oxidation and adsorption is shorter and smaller in pore diameter, denser in pore diameter and greatly increases the specific surface area of the composite material, so that more adsorption sites are provided for heavy metal ions. As can be seen in FIG. 1 (d), caO is successfully introduced into the pores of the oxide-adsorbent integrated floatable high-adsorption hydrogel composite material 2 This will effectively embed CaO 2 The direct contact and the rapid reaction of the water and the water are reduced, so that the uniform and long-term slow release effect is achieved; it also provides advantages for enhancing the mechanical properties of the composite material and reducing the toxicity of the arsenic (III) oxide.
As can be seen from fig. 2, the water absorption capacities of example 1, comparative example 1, example 2 and comparative example 2 are 5475%, 2970%, 5290% and 3867%, respectively.
As can be seen from fig. 3, the rate of oxygen release is the fastest when unencapsulated calcium peroxide is added to the reaction system. CaO (CaO) 2 The powder reacts with water rapidly, the dissolved oxygen value is in a linear trend along with the reaction time, the content of the generated dissolved oxygen is higher in a short time, after the reaction is carried out for 10 hours, the measured DO value (8.34 mg/L) already exceeds the saturated dissolved oxygen value of the natural water body at normal temperature and normal pressure, therefore, if CaO is directly added into the material 2 The powder has shorter oxygen release duration, and the effect of oxidized As (III) is not obvious; while sucrose or PEG is used as embedding agent to embed CaO 2 Then, the oxygen release curve of the composite material prepared by adding the composite material into a reaction system is relatively slow, the oxygen release rate is obviously reduced, the oxygen release period is obviously prolonged, and the oxygen release period does not reach the saturated dissolved oxygen content after 160 hours of operation in a water body. The reason is due to CaO 2 After being embedded by the embedding agent, the contact area with water is reduced, so that CaO 2 Is contacted with water slowly to slow down the oxygen release rate, thereby realizing CaO 2 The oxygen is slowly released for a long time, so that the dissolved oxygen can be stabilized at a higher level for a long time in the heavy metal soil remediation process. As can be seen from FIG. 4, the contents of As (III) in the soil treated in example 3, comparative example 3 and example 4 were reduced by 96.15%, 81.83% and 97.47% respectively, compared with the soil treated in the blank group.
As can be seen from FIG. 5, the As (V) content of the soil treated in example 3, comparative example 3 and example 46 was increased by 1762%, 36% and 2572% respectively, as compared with the soil treated in the blank group.
Table 1 adsorption amount of floatable high-adsorption hydrogel composite material integrated with oxidation-adsorption after single adsorption experiment and composite adsorption experiment of cadmium arsenic in soil in example 3, comparative example 3 and example 4
As can be seen from fig. 6, 7 and table 1, the adsorption and removal effect of the arsenic (iii) oxide and cadmium-arsenic composite pollution soil of example 4 is optimal, and the comparative example has poor oxidation effect and low adsorption amount because of no oxidizing agent. In the heavy metal removal experiment, the effect of reducing the concentration of heavy metal by single adsorption is better than that by composite adsorption.
The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.
Claims (10)
1. The preparation method of the composite material for synchronously removing the heavy metal cadmium and arsenic in the soil is characterized by comprising the following steps of:
(1) Adding acid into the sodium carboxymethyl cellulose water solution to protonate carboxylic acid groups in the sodium carboxymethyl cellulose;
(2) Adding peroxide into sucrose and/or polyethylene glycol solution, mixing uniformly, and drying to obtain coated peroxide powder;
(3) Uniformly mixing the coated peroxide powder and chitosan powder, adding the mixture into the sodium carboxymethyl cellulose aqueous solution protonated in the step (1), uniformly mixing, standing for molding, and freeze-drying to obtain the high-adsorption composite material integrating oxidation and adsorption.
2. The method for preparing the composite material for synchronously removing the heavy metal cadmium and arsenic in the soil, which is characterized in that the peroxide in the step (2) is at least one of calcium peroxide, magnesium peroxide, zinc peroxide and sodium peroxide;
the mass ratio of the total mass of sucrose and/or polyethylene glycol to the peroxide in the step (2) is 10:0.1 to 1.
3. The preparation method of the composite material for synchronously removing the heavy metal cadmium and arsenic in the soil, which is characterized by comprising the following steps of (3) coating peroxide powder and chitosan powder, wherein the mass ratio of the peroxide powder to the chitosan powder is 1.3-1.4: 1.0;
the mass ratio of the chitosan powder to the sodium carboxymethyl cellulose in the step (3) is (2-10): (1-10).
4. The method for preparing the composite material for synchronously removing the heavy metal cadmium and arsenic in the soil, which is characterized in that the acid in the step (1) is at least one of analytically pure hydrochloric acid, superior pure hydrochloric acid, dilute sulfuric acid and dilute acetic acid; the volume concentration of the dilute sulfuric acid and the dilute acetic acid is 1-3%; the mass ratio of the acid to the sodium carboxymethyl cellulose in the step (1) is (1-2): (1-2);
the stirring speed of the protonation in the step (1) is 200-400 rpm, and the time is 0.5-1 h.
5. The method for preparing the composite material for synchronously removing the heavy metal cadmium and arsenic in the soil, which is characterized in that the chitosan powder in the step (3) has a number average molecular weight of 5-10 ten thousand;
when the peroxide is coated by the sucrose in the step (2), the peroxide is added into the sucrose solution and uniformly mixed, then pre-freezing is carried out, the pre-freezing temperature is between-4 and-100 ℃, the time is between 3 and 9 hours, and then drying is carried out.
6. The preparation method of the composite material for synchronously removing the heavy metal cadmium and arsenic in the soil, which is characterized in that in the step (1), the mass ratio of the sodium carboxymethyl cellulose to the water in the sodium carboxymethyl cellulose solution is (0.5-2): (25-100);
the sodium carboxymethyl cellulose aqueous solution in the step (1) is obtained by adding sodium carboxymethyl cellulose into water and stirring until the sodium carboxymethyl cellulose aqueous solution is completely dissolved; the stirring speed is 300-1000 rpm, and the stirring time is 0.5-2 h;
in the sucrose and/or polyethylene glycol solution in the step (2), the mass ratio of the total mass of the sucrose and/or the polyethylene glycol to the solvent is (2-10): (10-50); the solvent is at least one of water and ethanol;
the sucrose solution in the step (2) is obtained by adding sucrose into water, heating and stirring at 60-200 ℃ for 0.5-6 h; the rotating speed of the heating and stirring is 800-1500 rpm.
7. The method for preparing the composite material for synchronously removing the heavy metal cadmium and arsenic in the soil, which is characterized in that the peroxide powder coated in the step (2) is further crushed and screened by a screen mesh of 200-400 meshes;
the stirring rotation speed of the uniformly mixed materials in the step (2) is 800-1500 rpm;
the stirring speed of the uniformly mixed materials in the step (3) is 1500-2500 rpm; the time is 30-120 s;
the drying in the step (2) means freeze-drying for 24-48 hours at the temperature of minus 80 ℃;
and (3) freeze-drying at-80 to-100 ℃ for 24-48 hours.
8. The method according to any one of claims 1 to 7, wherein the soil heavy metal cadmium and arsenic composite material is synchronously removed.
9. The application of the composite material for synchronously removing the heavy metals in the soil in the field of removing the heavy metals in the soil in the invention of claim 8.
10. Use according to claim 9, characterized in that the composite material is applied in an amount of 0.05-2% of the soil mass.
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