CN111250529A

CN111250529A - Passivating agent, preparation method thereof and method for adjusting cadmium form in acid soil

Info

Publication number: CN111250529A
Application number: CN202010078926.8A
Authority: CN
Inventors: 李亚东; 倪红; 汤行春; 杨升; 姚伦广; 段鹏飞; 王友平; 汪华; 陈勋
Original assignee: Hubei University; Nanyang Normal University; Institute of Plant Protection and Soil Fertilizer of Hubei Academy of Agricultural Science
Current assignee: Hubei University; Nanyang Normal University; Institute of Plant Protection and Soil Fertilizer of Hubei Academy of Agricultural Science
Priority date: 2020-02-03
Filing date: 2020-02-03
Publication date: 2020-06-09

Abstract

The invention provides a passivator, a preparation method thereof and a method for adjusting cadmium form in acid soil. The method for adjusting the cadmium form in the acid soil comprises the following steps: mixing one or a mixture of at least two of quick lime, calcium oxide and hydrated lime with a solvent to obtain a calcium-containing emulsion; mixing the protein raw material with the calcium-containing emulsion, and uniformly stirring to obtain a mixed solution; reacting the mixed solution under a heating condition, filtering to obtain a filtrate after the reaction is finished, and concentrating the filtrate to a concentrated solution with the concentration of 20-30%; the concentrated solution is applied to acid soil to increase the conversion of the weak acid bound Cd. When the method is used for cadmium-polluted acidic soil, the conversion of the weak acid binding state Cd can be promoted, the Cd can be released from the soil easily, the cadmium pollution of the soil can be relieved, and the weak acid binding state Cd is not easy to be absorbed by crops compared with the effective state Cd, so that the safety of planting the crops in the cadmium-polluted acidic soil is improved.

Description

Passivating agent, preparation method thereof and method for adjusting cadmium form in acid soil

Technical Field

The invention relates to the technical field of polluted soil treatment, in particular to a passivating agent, a preparation method thereof and a method for adjusting cadmium form in acid soil.

Background

With the rapid development of modern industry and agriculture, the situation of heavy metal pollution of soil is more and more severe, the heavy metal pollution event in China is entering a high-rise period, and the heavy metal pollution is a prominent problem in a plurality of polluted sites. In 2014, "national soil pollution condition survey bulletin" issued by the ministry of environmental protection and the ministry of land resources shows that the point standard exceeding rate of 8 inorganic pollutants of cadmium, mercury, arsenic, copper, lead, chromium, zinc and nickel is respectively 7.0%, 1.6%, 2.7%, 2.1%, 1.5%, 1.1%, 0.9% and 4.8%, wherein cadmium pollution is the most prominent.

Heavy metal pollution of soil is mainly caused by three reasons:

1) the sewage irrigation refers to the irrigation with the sewage which is treated and meets the requirement of irrigation water quality standard as a water source. The sewage irrigation is a double-edged sword, although urban sewage is not only an important fertilizer source but also an important water source of suburban crops, the sewage contains a large amount of heavy metal elements which are not beneficial to the growth of the crops, and particularly in industrial sewage, a plurality of environmental problems can be caused. China is a big agricultural country, and large-area cultivated land and suburb land in cities are polluted by heavy metals to a greater or lesser extent. Moreover, with the rapid development of the industry in China, a large amount of industrial sewage is discharged into a sewer and mixed with domestic sewage without diversion and purification treatment, so that a large amount of heavy metals enter soil in a farmland irrigation area, and serious heavy metal pollution of the soil is caused. According to statistics, the heavy metal pollution area of cultivated land in China accounts for more than 16% of the total cultivated land area, the heavy metal polluted grain reaches astonishing 1200 ten thousand tons every year, the yield of grain is reduced to 1000 ten thousand tons, and the problem is urgently solved.

2) Secondly, China is a big agricultural country and uses a large amount of pesticides and fertilizers every year to promote the rapid development of agriculture. However, fertilizers generally contain a certain amount of heavy metals, and excessive use of fertilizers and pesticides results in an increase in the heavy metal content of soil.

3) Industrial activities such as energy exploitation, metal smelting, fuel burning and the like discharge a large amount of waste gas, the waste gas contains a large amount of heavy metals, most of the heavy metals enter the atmosphere in the state of aerosol, and enter the soil through a series of natural sedimentation and precipitation, and statistics show that when fossil fuels are burned, 10% -30% of the heavy metals naturally settle within 10km of the emission source, and enter the atmosphere along with smoke dust and finally enter the soil.

The heavy metal cadmium mainly comes from lead zinc ore, non-ferrous metal smelting, electroplating and the like. Research shows that the function of renal tubules is destroyed by eating cadmium-polluted food for a long time, because cadmium enters human body and is mainly accumulated in the kidney and liver of human body to form cadmium sulfur protein, and cadmium can be combined with protein molecules containing hydroxyl, amino and the like to influence the normal function of endocrine organs, so that the body suffers diseases.

The existing research shows that the cadmium resolution rate of acid soil types such as red soil, yellow soil and the like at different temperatures is over 15 percent and is obviously higher than that of alkaline soil types such as grey desert soil, chestnut calcium soil and the like (less than 10 percent). In addition, according to the test data statistical analysis of 902 ten thousand soil samples of the soil testing formula fertilization in 2005-2011, compared with the second soil general investigation before 30 years, the soil pH of cultivated land in China is reduced by 0.13-1.3, the average reduction is 0.8, and 40% of cultivated land soil in China is below pH 6.5.

The detection of the total amount of heavy metals has been a main basis for preliminary judgment of soil quality. However, the binding degree of different heavy metals and the soil solid phase is different, and the ratio of the heavy metals absorbed and utilized by crops is not in positive correlation with the total amount of the heavy metals in the soil. The influence of fertilizers on heavy metals in soil is not only related to the growth of crops, but also related to the monitoring of soil environment, so that it is necessary to carry out more intensive research on various states of heavy metals in soil in different periods of crop growth.

Disclosure of Invention

The invention mainly aims to make up the defects of the prior art and provides a passivator, a preparation method and a method for adjusting the cadmium form in acid soil.

The invention provides a method for adjusting cadmium form in acid soil, which comprises the following steps: mixing a calcium source material and a solvent to obtain a calcium-containing emulsion; mixing the protein raw material with the calcium-containing emulsion, and uniformly stirring to obtain a mixed solution; reacting the mixed solution under a heating condition, filtering to obtain a filtrate after the reaction is finished, and concentrating the filtrate to a concentrated solution with the concentration of 20-30%; the concentrate is applied to acidic soil to increase the conversion of weak acid bound Cd.

In the above method, the calcium source material is selected from one or a mixture of at least two of quicklime, calcium oxide and slaked lime, preferably quicklime.

In the above method, the solvent may be one selected from the group consisting of purified water, ultrapure water, distilled water, tap water and deionized water, preferably tap water.

In the above method, the protein material may be selected from protein waste, and the protein waste may be selected from one or a mixture of at least two of plant protein waste, microbial cells, sludge, animal hair, animal hoof and horn, and blood.

In the method, the mass ratio of the calcium source raw material, the solvent and the protein raw material is (10-70): (80-1400): 100.

In the method, the heating temperature is 100-200 ℃, preferably 110-180 ℃, and more preferably 120-160 ℃; the reaction time is 1-8 h, preferably 1.5-6 h, and more preferably 2-5 h.

In the above method, the concentration method is evaporation using a multi-effect evaporator; the pH value of the final product is 10-14, preferably 11-13.

In the above method, quicklime and water are mixed to obtain a calcium-containing emulsion; mixing rapeseed cakes with the calcium-containing emulsion, wherein the mass ratio of the quick lime to the water to the rapeseed cakes is 11:100:50, and uniformly stirring to obtain a mixed solution; reacting the mixed solution at 137 ℃ for 3 hours, filtering to obtain filtrate after the reaction is finished, and evaporating the filtrate by using a multi-effect evaporator to obtain a concentrated solution with the pH value of 12-13 and the concentration of 25-30%; the concentrate is applied to soil to increase the conversion of weak acid bound Cd.

The invention also provides an application of the passivator in adjusting the cadmium form in acid soil, wherein a preparation method of an optional passivator comprises the following steps: mixing a calcium source raw material and a solvent to obtain calcium-containing emulsion; mixing the protein raw material with the calcium-containing emulsion, and uniformly stirring to obtain a mixed solution; and (3) reacting the mixed solution under a heating condition, filtering to obtain a filtrate after the reaction is finished, and concentrating the filtrate to a concentrated solution with the concentration of 20-30%.

In the above applications, the regulation of cadmium form in acid soil includes promoting the conversion of cadmium in weak acid binding state, and/or inhibiting the conversion of cadmium in active state.

The invention distinguishes the existing forms of heavy metal cadmium in soil into effective cadmium, weak acid combined cadmium, reducible cadmium and oxidizable cadmium, however, researches are carried out on heavy metals in various forms of crop seedling stage and jointing stage, and the passivant provided by the invention can well promote the conversion of the weak acid combined cadmium and has a certain effect on the improvement of soil environment.

The passivator provided by the invention is simple in preparation method, can be completely dissolved in water, can promote the conversion of weak acid binding state cadmium in soil, is beneficial to the release of Cd from the soil and the relief of cadmium pollution of the soil, and the weak acid binding state Cd is more difficult to be absorbed by crops compared with the effective state Cd, so that the safety of the crops planted in the soil is improved.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below, and it should be apparent that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.

The invention provides a preparation method of a passivator, which comprises the following steps:

step 1: mixing the calcium source material and the solvent to obtain the calcium-containing emulsion.

In step 1, the calcium source material may be one or a mixture of not less than two selected from quicklime, calcium oxide and slaked lime, and is preferably quicklime.

In step 1, the solvent may be one or a mixture of not less than two selected from the group consisting of purified water, ultrapure water, distilled water, tap water and deionized water, preferably tap water.

Step 2: mixing the protein material and the calcium-containing emulsion, and stirring uniformly to obtain a mixed solution.

In step 2, the protein material may include protein waste, and the protein waste may be selected from one or a mixture of at least two of plant protein waste, microbial cells, sludge, animal hair, animal hoof and horn, and blood.

In the step 1 and the step 2, the mass ratio of the calcium source raw material, the solvent and the protein raw material is (10-70): (80-1400): 100.

And step 3: and (3) reacting the mixed solution under a heating condition, filtering after the reaction is finished, and concentrating the filtrate to a concentrated solution with the concentration of 20-30%.

In step 3, the reaction temperature is 100-200 ℃, preferably 110-180 ℃, and more preferably 120-160 ℃.

In the step 3, the reaction time is 1-8 h, preferably 1.5-6 h, and more preferably 2-5 h.

In step 3, the method of concentration is evaporation using a multiple effect evaporator.

In step 3, the pH value of the final product is in the range of 10-14, preferably 11-13.

Examples

Adding 1000kg of pulverized rapeseed cake into a mixing barrel, and using 2m³Dissolving 220kg of quicklime in tap water to prepare lime emulsion, inputting the lime emulsion into a mixing barrel added with rapeseed cakes, uniformly stirring, inputting the uniformly stirred mixture into a reaction kettle by using a pump, introducing 0.2Mpa of water vapor into the reaction kettle, and heatingAnd keeping the temperature at 137 ℃ for 3h, taking a sample from a measuring cylinder, and if the solution is in a turbid state, indicating that the slightly water-soluble lime is not converted into the final product. If precipitation is rapid and the supernatant is a clear liquid, it indicates that the clear liquid has been converted to the final product, i.e., the peptide calcium salt. At this time, use is made of 40m²Filtering with plate-and-frame machine, and concentrating the filtrate with multi-effect evaporator until the filtrate is 20Be⁰The concentration of the peptide calcium salt was determined to be 28% (w/v) by spectrophotometry, and the pH value was determined to be 12.2 by pH paper, and the concentrated solution was the passivating agent provided in this example, i.e., the peptide calcium salt.

Experimental materials: the plant variety is Zheng wheat 103.

Normal soil: the soil to be tested was collected from the soil around the sand lake of the Wuchang district in Wuhan City, which was acid red soil. Removing pebbles and animal and plant residues in the soil by using tweezers, naturally drying, crushing the soil by using a mortar, sieving by using a 2mm sieve, and uniformly mixing for later use.

And (3) polluted soil: as the cadmium concentration in most cadmium-polluted soil in China is about 2mg/kg, the polluted soil with the total cadmium concentration of 2mg/kg and 5mg/kg is prepared. Uniformly spraying the standard cadmium stock solution on the standby normal soil to ensure that the total cadmium concentration reaches 2mg/kg and 5mg/kg respectively, fully and uniformly stirring, and filling into a plastic basket. Adding tap water according to 80% of the field water holding capacity, covering and sealing, opening the cover every 3 days for ventilation, aging after 30 days, taking out 3 soil samples for air drying, and sieving by using a 2mm nylon sieve for later use.

0mg/kg, 2mg/kg and 5mg/kg of soil are briefly described below as Cd0, Cd2 and Cd 5.

Compound fertilizer: nitrogen 14-phosphorus 5-potassium 6 type compound fertilizer produced by complete fertilizer industry limited of yellow stone city.

1. The fertilizing method comprises the following steps: respectively applying peptide calcium salt in normal soil and polluted soil, and adding compound fertilizer as a control group. The normal soil is filled with 4 kg/basin of soil, the polluted soil is filled with 2 kg/basin of soil, and in order to ensure that the nitrogen content of each basin is 1g, namely the nitrogen application amount of the normal soil is 0.25g/kg, and the nitrogen application amount of the polluted soil is 0.5 g/kg. It was calculated that 6.25g of compound fertilizer was applied, 10g of peptide calcium salt +4.5g of potassium dihydrogen phosphate. Each treatment was repeated twice.

2. The sample processing method comprises the following steps: respectively planting wheat seeds in wet normal soil and contaminated soil, applying compound fertilizer or peptide calcium salt + potassium dihydrogen phosphate for treatment, and sampling for four times when the wheat seeds are cultured for 50 days, 80 days, 110 days and 140 days, namely a seedling stage 1, a seedling stage 2, an elongation stage 1 and an elongation stage 2. Gently digging out wheat plants, keeping the root hairs complete, collecting rhizosphere soil and non-rhizosphere soil, air-drying, grinding, and sieving with a 2mm nylon sieve for later use.

3. Determination of the experiment

The heavy metal form refers to the actual form of metal elements existing in certain ions or molecules in the environment, and in the experiment, the effective state, the weak acid binding state, the reducible state and the oxidizable state of cadmium are respectively measured.

The main reagents used in the experiments are shown in table 1.

Table 1: main reagent for experiment

Primary reagent	Molecular formula	Purity of	Manufacturer(s)
				Nitric acid	HNO₃	Super grade pure	Group of traditional Chinese medicines
Hydrochloric acid	HCl	Super grade pure	Group of traditional Chinese medicines
				Glacial acetic acid	CH₃COOH	Super grade pure	Group of traditional Chinese medicines
DTPA	C₁₄H₂₃N₃O₁₀	Super grade pure	Group of traditional Chinese medicines
				TEA	C₆H₁₅N	Super grade pure	Group of traditional Chinese medicines
Hydroxylamine hydrochloride	NH₃O·HCl	Super grade pure	Group of traditional Chinese medicines
				Anhydrous calcium chloride	CaCl₂	Super grade pure	Group of traditional Chinese medicines
30% hydrogen peroxide solution	H₂O₂	Super grade pure	Group of traditional Chinese medicines
				Ammonium acetate	CH₃COONH₄	Super grade pure	Group of traditional Chinese medicines
Potassium dihydrogen phosphate	KH₂PO₄	Super grade pure	Group of traditional Chinese medicines
				Cadmium standard stock solution	Cd(NO₃)₂		Quality control of Chinese medicine

(1) Determination of available cadmium

① preparation of DTPA extractant comprises weighing 3.934g DTPA in a beaker, adding 26.6mL TEA, weighing 2.22g anhydrous calcium chloride, dissolving with purified water, transferring into a 2L volumetric flask, adding deionized water, adjusting pH to 7.3 with hydrochloric acid, and diluting to desired volume.

② weighing 5g of spare soil sample, placing in a 100mL conical flask, adding 25mL of DTPA extractant into each flask, shaking for a while, placing on a shaker, shaking for 2h at 180r/min, taking out the sample, filtering, and using a liquid-transferring gun to transfer clear and impurity-free intermediate liquid into a 25mL colorimetric tube for later measurement.

③ Standard Curve (hereinafter called nominal curve) is prepared by preparing standard solution with concentration gradient of 0, 0.1, 0.5, 1.0, 1.5 and 2.0 from cadmium standard stock solution, and diluting to 50mL colorimetric cylinder with DTPA extractant for use.

④ blank test (CK) processing, an empty centrifuge tube is marked as CK, no soil sample is added, the method in ② is used for processing, and blank Control is performed.

(2) Determination of weak acid bound cadmium

① preparation of acetic acid solution, the pipette sucks 6.27mL of glacial acetic acid into a 1L volumetric flask, uses deionized water to fix the volume to 1L, and the mixture is left for standby after being mixed uniformly.

② weighing 1g of soil sample, placing the soil sample in a 100mL centrifuge tube, adding 40mL of 0.11mol/L acetic acid solution into each bottle, shaking for a while, placing the soil sample on a shaker, shaking for 16h at 180r/min, taking out the sample, centrifuging for 20 min at 4000r/min, sucking the intermediate solution in a 25mL colorimetric tube by a liquid transfer gun, and measuring.

③ adding 16mL deionized water into the centrifuge tube, placing on a shaker for 15 minutes, taking out the sample, centrifuging for 5 minutes at 4000r/min, pouring out the supernatant, and reserving the soil sample for later use.

④ Standard Curve is prepared by preparing standard solution with concentration gradient of 0, 0.2, 0.4, 0.6, 0.8 and 1.0 from cadmium standard stock solution, and diluting to 50mL colorimetric tube with acetic acid solution.

⑤ blank experiment (CK), marking the empty centrifuge tube as CK, adding no soil sample, adopting the operation steps in ② to process, and making blank Control.

(3) Determination of reducible cadmium

① preparation of hydroxylamine hydrochloride solution, dissolving 34.75g hydroxylamine hydrochloride in a beaker, fully dissolving with deionized water, adding into a 1L volumetric flask, adding to about 900mL with deionized water, adjusting pH to 2 with 2mol/L nitric acid, and fixing volume.

② taking the standby precipitate, adding 40mL of 0.5mol/L hydroxylamine hydrochloride solution, shaking for a while, placing on a shaking bed, shaking for 16h at 180r/min, taking out the sample, centrifuging for 20 min at 4000r/min, sucking the intermediate solution into a 25mL colorimetric tube by a pipette, and measuring.

③ adding 16mL deionized water into the centrifuge tube, placing on a shaker for 15 minutes, taking out the sample, centrifuging at 4000r/min for 5 minutes, and pouring out the supernatant to leave the precipitate for later use.

④ Standard Curve is prepared by preparing standard solution with concentration gradient of 0, 0.1, 0.2, 0.4, 0.6 and 0.8 from standard stock solution of cadmium, and metering the volume into a 50mL colorimetric tube by using hydroxylamine hydrochloride solution for later use.

⑤ blank test (CK) processing, an empty centrifuge tube is marked CK, no soil sample is added, and the CK is processed by the same procedure in ② as blank Control.

(4) Determination of cadmium in oxidizable state

① preparation of ammonium acetate solution 77.08g of ammonium acetate is weighed into a beaker, dissolved with deionized water, placed in a 1L volumetric flask, adjusted to pH 2 with concentrated nitric acid and made to volume.

② taking the precipitate, adding 10mL of 30% hydrogen peroxide solution, sealing, shaking for a while, standing at room temperature for 1h, and heating in 85 deg.C water bath.

③ when the solution was evaporated to dryness, 10mL of 30% hydrogen peroxide solution was added, and the above operation was repeated and the mixture was heated in a water bath.

④ taking out the precipitate, standing for a while, adding 50mL ammonium acetate solution with pH 2, shaking for a while, placing on a shaking bed, shaking for 16h at 180r/min, taking out the sample, centrifuging for 20 min at 4000r/min, and transferring the intermediate solution into a colorimetric tube by using a liquid transfer gun for testing.

⑤ adding 16mL deionized water into the centrifuge tube, placing on a shaker for 15 minutes, taking out the sample, centrifuging at 4000r/min for 5 minutes, and pouring out the supernatant to leave the precipitate for later use.

⑥ Standard Curve is prepared by preparing standard solution with concentration gradient of 0, 0.01, 0.02, 0.04, 0.06 and 0.08 from standard stock solution of cadmium, and metering to 50mL colorimetric tube with ammonium acetate solution for use.

⑦ blank test (CK) processing, an empty centrifuge tube is marked CK, no soil sample is added, and the CK is processed by the same procedure in ① as blank Control.

4. Analysis of Experimental data

Treating the planted wheat by different fertilizing modes, extracting acid soil when the wheat grows for 50 days, 80 days, 110 days and 140 days, treating according to a sample treatment method, and determining the cadmium ion form. Measuring rhizosphere soil and non-rhizosphere soil of wheat applied with compound fertilizer, and measuring rhizosphere soil and non-rhizosphere soil of wheat applied with peptide calcium salt. The rhizosphere is a micro-area soil area which is influenced by the activity of a plant root system and is different from a soil body in physical, chemical and biological properties, the range of the rhizosphere is very small, the distance is generally within several millimeters from the surface of the root system, and the rhizosphere soil is the soil in the rhizosphere area.

(1) Influence of peptide calcium salt on available cadmium in acid soil

Table 2 shows the content of available cadmium ions in acid soils (note: g is rhizosphere soil and f is non-rhizosphere soil).

TABLE 2 content of available cadmium ions in acid soil (note: -g is rhizosphere soil, -f is non-rhizosphere soil)

As shown in Table 2, it can be seen that, in the acidic soil of Cd0 group, regardless of the addition of peptide calcium salt or compound fertilizer, the content of Cd in the effective state in the soil is mostly 0, the average content of Cd in the effective state in the peptide calcium salt group soil is 0.02mg/kg, and the average content of Cd in the effective state in the compound fertilizer group soil is 0.06 mg/kg.

In the acid soil of Cd2 group, the content of effective Cd in the peptide calcium salt group soil is entirely lower than that of the compound fertilizer group, the mean value is 3.16mg/kg, the compound fertilizer group is 4.95mg/kg, and the content of effective Cd in the original soil of the acid soil of Cd2 group is 5.02 mg/kg. It can be seen that in the soil polluted by 2mg/kg of cadmium, the compound fertilizer almost has no inhibiting effect on the effective Cd, and the peptide calcium salt has obvious inhibiting effect.

In the acid soil of Cd5 group, it can be seen that the content of effective Cd in peptide calcium salt group is obviously lower than that in compound fertilizer group, the average value is 10.36mg/kg and 12.94mg/kg respectively, while the content of effective Cd in original soil of acid soil of Cd5 group is 14.05mg/kg, and the change of effective Cd content in Cd5 soil is similar to that in Cd2 soil.

Therefore, it can be concluded that in cadmium-contaminated soil, the peptide calcium salt is beneficial for inhibiting the conversion of cadmium ions in the soil to available Cd.

(2) Influence of peptide calcium salt on weak acid binding state cadmium in acid soil

Table 3 shows the content of weakly acid-bound cadmium ions in acid soils (note: g is rhizosphere soil and f is non-rhizosphere soil).

TABLE 3 content of weakly acid bound cadmium ions in acid soils (note: -g is rhizosphere soil, -f is non-rhizosphere soil)

As shown in Table 3, it can be seen that in the acidic soil of Cd0 group, the content of Cd in weak acid binding state in the soil was 0 regardless of the addition of peptide calcium salt or the addition of compound fertilizer. Probably because the content of Cd ions in normal soil is very low, most Cd ions exist in the soil in an effective state, are absorbed and utilized by plants, and the content of Cd which can be converted into a weak acid binding state is very low and is lower than the detection range.

In the acid soil of Cd2 group, the overall content of Cd in weak acid binding state in peptide calcium salt group is higher than that in compound fertilizer group, the average value is 1.38mg/kg, the compound fertilizer group is 0.44mg/kg, and the content of Cd in weak acid binding state in the original soil of Cd2 group acid soil is 3.05mg/kg, which is hypothesized that the added peptide calcium salt increases the pH of the soil, promotes the formation of carbonate, and further the content of Cd in weak acid binding state increases. It can be seen that the change of the content of Cd in the weak acid binding state is very regular, the content of Cd in the weak acid binding state is reduced to the lowest value from the seedling stage 1 to the seedling stage 2, the Cd in the weak acid binding state is increased and reaches the peak value after entering the jointing stage 1, and finally the Cd in the jointing stage 2 is in the reduction trend.

In the acid soil of Cd5 group, it can be seen that the content of weak-acid binding state Cd in the peptide calcium salt group is obviously higher than that in the compound fertilizer group, the average values are 3.73mg/kg and 2.08mg/kg respectively, and the change of the content of weak-acid binding state Cd in Cd5 soil is similar to that in Cd2 soil.

Therefore, it can be concluded that in cadmium contaminated soil, the peptide calcium salt is beneficial for promoting the conversion of cadmium ions in the soil to the weak acid binding state Cd.

(3) Content analysis of cadmium form in each period of Cd5 contaminated soil

Table 4 shows the percentage content of cadmium ions in the form of cadmium in the cadmium-contaminated acidic soil of the Cd5 group.

Table 4 percentage content of cadmium ion in cadmium form in cadmium-contaminated acidic soil of Cd5 group

As shown in table 4, it can be seen that, in 5mg/kg cadmium-contaminated soil, most of Cd is in an effective state, wherein the percentage content of the effective state Cd in the peptide calcium salt group soil is 57.25% to 67.23%, and the percentage content of the effective state Cd in the compound fertilizer group soil is 64.49% to 79.70%, and in each period of observation, the percentage content of the effective state Cd in the peptide calcium salt group soil is less than that of the compound fertilizer group, so that the peptide calcium salt can inhibit Cd ions in other forms from being converted into the effective state Cd better than that of the compound fertilizer.

In addition, the percentage content of the weak acid binding state Cd in the two groups of soils is observed, so that the percentage content of the weak acid binding state Cd in the peptide calcium salt group soil is 16.70-27.47%, the percentage content of the weak acid binding state Cd in the compound fertilizer group soil is 9.50-15.35%, and the percentage content of the weak acid binding state Cd in the peptide calcium salt group soil is more than that of the compound fertilizer group in each period of observation, so that the peptide calcium salt can promote the conversion of Cd ions in other forms to the weak acid binding state Cd compared with the compound fertilizer.

Therefore, it can be concluded that in 5mg/kg cadmium-contaminated soil, the peptide calcium salt is beneficial to promoting the conversion of cadmium ions in the soil to weak acid binding state Cd and inhibiting the conversion of cadmium ions in the soil to effective state Cd.

(4) Content analysis of cadmium form in each period of Cd2 contaminated soil

Table 5 shows the percentage content of cadmium ions in the form of cadmium in the cadmium-contaminated acidic soil of the Cd2 group.

Table 5 percentage content of cadmium ion in cadmium form in cadmium-contaminated acidic soil of Cd2 group

As shown in table 5, it can be seen that most of Cd in the soil polluted by 2mg/kg of cadmium is also in an effective state, wherein the percentage content of the effective state Cd in the peptide calcium salt group soil is 49.59% -54.43%, the percentage content of the effective state Cd in the compound fertilizer group soil is 70.21% -89.77%, and the percentage content of the effective state Cd in the peptide calcium salt group soil is less than that of the compound fertilizer group in each observation period, so that the peptide calcium salt can inhibit Cd ions in other forms from being converted into the effective state Cd more than the compound fertilizer.

In addition, the percentage content of the weak acid binding state Cd in the two groups of soils is observed, so that the percentage content of the weak acid binding state Cd in the peptide calcium salt group soil is 9.34-28.24%, the percentage content of the weak acid binding state Cd in the compound fertilizer group soil is 1.08-12.49%, and the percentage content of the weak acid binding state Cd in the peptide calcium salt group soil is more than that of the compound fertilizer group in each period of observation, so that the peptide calcium salt can promote the conversion of Cd ions in other forms to the weak acid binding state Cd compared with the compound fertilizer.

Therefore, it can be concluded that in 2mg/kg cadmium-contaminated soil, the peptide calcium salt is beneficial to promoting the conversion of cadmium ions in the soil to weak acid binding state Cd and inhibiting the conversion of cadmium ions in the soil to effective state Cd.

In the embodiment, morphological analysis and biological effectiveness of cadmium element are taken as research backgrounds, red soil beside a sand lake in the Wuchang district, Wuhan is taken as a research object, peptide calcium salt is used for treatment, compound fertilizer is used for comparison, and morphological change of Cd in the soil is determined by using a single extraction method through collection, air drying, grinding and other treatments. To study the regulation effect of the peptide calcium salt on the form of Cd in acid soil, the summary is as follows:

(1) the peptide calcium salt has an inhibiting effect on the transformation of the available Cd.

(2) The peptide calcium salt can promote the conversion of the weak acid binding state Cd.

The existing research shows that weak acid binding heavy metal is weakly bound with soil, is easy to release and has larger mobility. Therefore, other forms of Cd are converted into the weak acid binding state Cd, so that the Cd can be released from the soil conveniently, the cadmium pollution of the soil is relieved, and the weak acid binding state Cd is less prone to being absorbed by crops compared with the effective state Cd, so that the method has an important effect on improving the heavy metal pollution degree of the soil and improving the production quality of the crops.

In conclusion, the peptide calcium salt prepared by the embodiment can be applied to cadmium-polluted acidic soil to adjust the form of cadmium in the soil. The peptide calcium salt can inhibit the conversion of effective cadmium and promote the conversion of weak acid binding cadmium. The method is beneficial to the release of Cd from the acid soil, relieves the cadmium pollution of the acid soil and also helps to inhibit the absorption of cadmium by plants.

It should be noted that the above embodiments are only examples, and those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be construed as the protection scope of the present invention.

Claims

1. A method for regulating cadmium morphology in acid soil, comprising the steps of:

mixing a calcium source raw material and a solvent to obtain calcium-containing emulsion;

mixing a protein raw material with the calcium-containing emulsion, and uniformly stirring to obtain a mixed solution;

reacting the mixed solution under a heating condition, filtering to obtain a filtrate after the reaction is finished, and concentrating the filtrate to a concentrated solution with the concentration of 20-30%;

wherein the calcium source raw material is selected from one or a mixture of at least two of quick lime, calcium oxide and hydrated lime;

the concentrate is applied to acidic soil to increase the conversion of weak acid bound Cd.

2. The application of the passivator in adjusting the cadmium form in acid soil is characterized in that the passivator is prepared by the following steps:

and (3) reacting the mixed solution under a heating condition, filtering to obtain a filtrate after the reaction is finished, and concentrating the filtrate to a concentrated solution with the concentration of 20-30%.

3. The use of claim 2, wherein the modulating cadmium morphology in acid soils comprises promoting the conversion of cadmium in weak acid bound state and/or inhibiting the conversion of cadmium in available state.