Cadmium passivation-selenium enrichment double-effect conditioner based on pyrolytic eggshell biochar

Abstract

The invention discloses a cadmium passivation-selenium enrichment double-effect conditioner based on pyrolytic eggshell biochar. The conditioner is prepared from the following raw materials in parts by mass: 60-80 parts of green eggshells and 1-5 parts of nano-selenium. Wherein the conditioner is obtained by pyrolyzing green eggshells to prepare biochar and modifying the biochar with nano-selenium, and the nano-selenium is nano-selenium particles (SeNPs) with the particle size of 10-100 nm. The invention relates to the technical field of soil remediation and agricultural waste resource utilization, in particular to a cadmium passivation-selenium enrichment double-effect conditioner based on pyrolytic eggshell biochar, and by adopting the technical scheme, the cadmium passivation-selenium enrichment double-effect conditioner has the following advantages that the double effects are remarkable, the raw materials are environmentally friendly, the process is optimized, and the crop safety is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation and agricultural waste resource utilization, and in particular to a cadmium passivation-selenium enrichment dual-effect conditioner based on pyrolysis eggshell biochar. Background Art

[0002] Cadmium (Cd) is a highly hazardous heavy metal in soil, easily accumulating through the food chain and posing a threat to human health. In the karst regions of southwestern my country, soil cadmium concentrations are generally higher than in non-karst areas (1.2–3.8 mg / kg vs. 0.3–1.5 mg / kg) due to geological anomalies and human activities. This significantly increases the risk of excessive cadmium in crops. Traditional remediation methods are plagued by high costs and secondary pollution, necessitating an urgent need for environmentally friendly remediation materials.

[0003] Green eggshells are rich in calcium carbonate (95–97%) and trace elements, making them an ideal raw material for preparing biochar. Biochar can passivate cadmium by increasing soil pH and providing adsorption sites, but the cadmium control effect of single biochar is limited. Selenium (Se) modification can enhance the antagonistic effect through mechanisms such as Se-Cd complexation and inhibition of cadmium transporters. In particular, nanoselenium (SeNPs) have become a research hotspot for modifiers due to their good biocompatibility and strong controlled release ability. However, existing modification methods (such as traditional stirring) have problems such as uneven dispersion of nanoselenium and low adsorption efficiency. There is an urgent need to optimize the preparation process to improve the modification effect. Summary of the Invention

[0004] In view of this, the embodiments of the present invention hope to provide a cadmium passivation-selenium enrichment dual-effect conditioner based on pyrolyzed eggshell biochar to solve or alleviate the technical problems existing in the prior art and at least provide a beneficial option.

[0005] The purpose of the present invention can be achieved by the following technical measures: a cadmium passivation-selenium enrichment dual-effect conditioning agent based on pyrolysis eggshell biochar, the conditioning agent is composed of the following raw materials in parts by mass:

[0006] 60-80 parts of green eggshell, 1-5 parts of nano-selenium;

[0007] The conditioning agent is obtained by preparing biochar by pyrolyzing green eggshells and modifying the biochar with nano-selenium, wherein the nano-selenium is nano-selenium particles (SeNPs) with a particle size of 10-100 nm.

[0008] The purpose of the present invention can also be achieved by the following technical measures:

[0009] The green eggshell pretreatment step is to wash and dry at 80°C to constant weight, and crush to pass through a 100-mesh sieve; the pyrolysis condition is to burn at 600°C in a muffle furnace for 2-4 hours, preferably 3 hours, and the heating rate is 5°C / min.

[0010] The purpose of the present invention can also be achieved by the following technical measures:

[0011] During the nano-selenium modification process, the mass ratio of nano-selenium to distilled water is 1:30-1:50, preferably 1:40, the ultrasonic oscillation frequency is 30-50kHz, preferably 40kHz, the oscillation time is 1-3 hours, preferably 2 hours, the standing time is 20-28 hours, preferably 24 hours, and the drying temperature is 70-90°C, preferably 80°C.

[0012] The purpose of the present invention can also be achieved by the following technical measures:

[0013] The carrier material is pyrolyzed eggshell biochar, the surface of which has a rough wrinkled structure and irregular pores, and the nano-selenium loading is 15-45% (weight percentage), preferably 24.17%.

[0014] The purpose of the present invention can also be achieved by the following technical measures:

[0015] A method for preparing a cadmium passivation-selenium enrichment dual-effect conditioner based on pyrolyzed eggshell biochar comprises the following steps:

[0016] Step 1: Wash, dry, and grind the green eggshells through a 100-mesh sieve to obtain eggshell powder;

[0017] Step 2: heating the eggshell powder to 600°C in a muffle furnace at 5°C / min, firing for 2-4 hours, preferably 3 hours, and then grinding and sieving to obtain eggshell biochar;

[0018] Step 3: Mix nano-selenium and distilled water in a mass ratio of 1:30-1:50, add eggshell biochar, ultrasonically vibrate for 1-3 hours, preferably 2 hours, and let stand for 20-28 hours, preferably 24 hours;

[0019] Step 4: After filtering, wash the solid, and dry it at 70-90°C, preferably 80°C, to constant weight to obtain the finished product.

[0020] The purpose of the present invention can also be achieved by the following technical measures:

[0021] The particle size of the eggshell biochar in step 2 is ≤0.15 mm, and the ultrasonic oscillation power in step 3 is 200-300 W.

[0022] The purpose of the present invention can also be achieved by the following technical measures:

[0023] The mass ratio of the conditioner to the contaminated soil is 1:40-1:60, preferably 1:50, and the conditioner is evenly mixed and then used for planting crops.

[0024] The purpose of the present invention can also be achieved by the following technical measures:

[0025] A cadmium passivation-selenium enrichment dual-effect conditioner based on pyrolyzed eggshell biochar is used in the remediation of cadmium-contaminated soil. The crops include allium serrata, which are planted using a bulb seedling method, with a root length of 4-6 cm, preferably 5 cm, and a stem length of 12-14 cm, preferably 13 cm. The planting cycle is 25-35 days, preferably 30 days.

[0026] The purpose of the present invention can also be achieved by the following technical measures:

[0027] After the conditioner is applied to the soil, the effective cadmium content in the soil can be reduced by 35-40%, preferably 38.65%, and the selenium concentration in the aboveground part of crops can be increased by 20-30%, preferably 3.48 mg / kg.

[0028] The purpose of the present invention can also be achieved by the following technical measures:

[0029] The nano selenium is complexed with SeO3 2- +Cd 2+ →CdSeO3), competitive adsorption (Ca 2+ with cd 2 + competition for soil colloid sites) and redox reactions to achieve cadmium passivation, while selenium enrichment is achieved through root absorption and transport to the aboveground parts of plants.

[0030] The embodiment of the present invention adopts the above technical solution, which has the following advantages:

[0031] 1. Significant dual effects: It simultaneously achieves soil cadmium passivation (effective cadmium reduced by 38.65%) and crop selenium enrichment (selenium concentration increased by 21.3-29.8%), balancing environmental safety and agricultural productivity.

[0032] 2. Raw material environmental protection and process optimization: Using agricultural waste (eggshells) as raw materials, the nano-selenium adsorption efficiency is improved through ultrasonic vibration modification (adsorption capacity reaches 24.17%), which has better dispersion and more complete pore utilization than the traditional stirring method.

[0033] 3. Improved crop safety: significantly improves the microstructure of plant cells, reduces cadmium-induced oxidative damage, reduces stomatal and chloroplast damage, and improves crop quality (for example, the cadmium content compliance rate of alliums is increased by more than 80%).

[0034] The above summary is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments and features described above, further aspects, embodiments and features of the present invention will be readily apparent by reference to the accompanying drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or technical descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 This is a flow chart of an embodiment of a dual-effect conditioner for cadmium passivation and selenium enrichment based on pyrolyzed eggshell biochar of the present invention;

[0037] Figure 2 A diagram of the steps for preparing and modifying biochar in the present invention;

[0038] Figure 3 This is the SEM-EDS characterization image of the modified biochar in the present invention;

[0039] Figure 4 This is a graph showing changes in the available cadmium and selenium content in soil under different treatments in the present invention;

[0040] Figure 5 This is a schematic diagram of the NBT staining results in the present invention;

[0041] Figure 6 Schematic diagram of Cd content in allium under different treatments in the present invention;

[0042] Figure 7 Schematic diagram of the color content of allium roots, white parts and green parts under different treatments in the present invention. DETAILED DESCRIPTION

[0043] Hereinafter, only certain exemplary embodiments are briefly described. As will be appreciated by those skilled in the art, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and description are to be considered as illustrative in nature and not restrictive.

[0044] It should be noted that the terms "first," "second," "symmetrical," "array," etc. are used only to distinguish descriptions from positional descriptions and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, limitations on features such as "first" and "symmetrical" may explicitly or implicitly include one or more of these features; similarly, when the number of certain features is not limited in the form of words such as "two" or "three," it should be noted that these features also explicitly or implicitly include one or more of the number of features.

[0045] In the present invention, unless otherwise expressly specified or limited, terms such as "installation," "connection," and "fixation" should be understood broadly; for example, they may refer to fixed connection, detachable connection, or integral molding; they may refer to mechanical connection, direct connection, welding, or indirect connection through an intermediate medium; they may refer to internal communication between two components or interaction between two components. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on the specification and drawings in conjunction with specific circumstances.

[0046] The embodiments of the present invention are described in detail below.

[0047] The present invention discloses a dual-effect conditioner for cadmium passivation and selenium enrichment based on pyrolysis eggshell biochar. The conditioner is composed of the following raw materials in parts by mass: 60-80 parts of green eggshell and 1-5 parts of nano-selenium; wherein the conditioner is prepared by pyrolyzing green eggshell to prepare biochar, and modified with nano-selenium, wherein the nano-selenium is nano-selenium particles (SeNPs) with a particle size of 10-100 nm; the green eggshell is pretreated by washing, drying at 80° C. to constant weight, and crushing through a 100-mesh sieve; the pyrolysis conditions are calcining at 600° C. in a muffle furnace for 2-4 hours, preferably 3 hours, and heating at a rate of 100-250° C. The rate is 5°C / min. During the nano-selenium modification process, the mass ratio of nano-selenium to distilled water is 1:30-1:50, preferably 1:40, the ultrasonic oscillation frequency is 30-50kHz, preferably 40kHz, the oscillation time is 1-3 hours, preferably 2 hours, the standing time is 20-28 hours, preferably 24 hours, the drying temperature is 70-90°C, preferably 80°C, the carrier material is pyrolyzed eggshell biochar, whose surface has a rough wrinkled structure and irregular pores, and the nano-selenium loading amount is 15-45% (weight percentage), preferably 24.17%.

[0048] like Figure 1-7 As shown, a preparation method of a dual-effect conditioner for cadmium passivation and selenium enrichment based on pyrolysis eggshell biochar of the present invention is provided, and the preparation method comprises:

[0049] (1) Clean, dry, and grind green eggshells through a 100-mesh sieve to obtain eggshell powder;

[0050] (2) heating the eggshell powder in a muffle furnace at 5°C / min to 600°C, firing for 2-4 hours, preferably 3 hours, and then grinding and sieving to obtain eggshell biochar;

[0051] (3) Mix nano-selenium and distilled water in a mass ratio of 1:30-1:50, add eggshell biochar, ultrasonically vibrate for 1-3 hours, preferably 2 hours, and let stand for 20-28 hours, preferably 24 hours;

[0052] (4) After filtering and washing the solid, drying at 70-90°C, preferably 80°C, to constant weight to obtain the finished product.

[0053] (2) The particle size of the eggshell biochar is ≤0.15 mm, (3) The ultrasonic oscillation power is 200-300 W

[0054] A cadmium passivation-selenium enrichment dual-effect conditioner based on pyrolyzed eggshell biochar, the application method of the dual-effect conditioner comprising: uniformly mixing the conditioner and contaminated soil at a mass ratio of 1:40-1:60, preferably 1:50, and then using the mixture to plant crops, wherein the crops include alliums, which are planted using a bulb seedling method, with a root length of 4-6 cm, preferably 5 cm, and a stem length of 12-14 cm, preferably 13 cm. The planting cycle is 25-35 days, preferably 30 days. After the conditioner is applied to the soil, the effective cadmium content in the soil can be reduced by 35-40%, preferably 38.65%, and the selenium concentration in the aboveground part of the crop can be increased by 20-30%, preferably 3.48 mg / kg. Nano-selenium is complexed with the surface (SeO3 2- +Cd 2+ →CdSeO3), competitive adsorption (Ca 2+ with cd 2+ Compete for soil colloid sites) and redox reactions to achieve cadmium passivation, while selenium is absorbed and transported to the aboveground parts of plants through the roots to achieve selenium enrichment.

[0055] The following are several specific embodiments of the present invention:

[0056] Example 1

[0057] (1) Selection of raw material composition

[0058] Green eggshell biochar raw material: 100 parts (pretreated eggshell powder, passed through a 100-mesh sieve);

[0059] Selenium nanoparticles (SeNPs): 2.5 parts (particle size 50 nm, mass ratio to distilled water 1:40).

[0060] (2) Preparation method

[0061] Step 1: Eggshell biochar pyrolysis

[0062] The green eggshells were washed and dried at 80°C to constant weight, crushed and passed through a 100-mesh sieve, and 1000 g of eggshell powder was placed in a muffle furnace. The temperature was increased to 600°C at a rate of 5°C / min and pyrolyzed at a constant temperature for 3 hours. After cooling, the powder was ground and passed through a 100-mesh sieve to obtain 700 g of eggshell biochar.

[0063] Step 2: Nano-selenium modification

[0064] 25 g of nano-selenium was dissolved in 1000 mL of distilled water, 200 g of eggshell biochar was added, and the mixture was shaken in an ultrasonic oscillator (40 kHz, 200 W) for 2 hours. After standing for 24 hours, it was filtered. The solid was washed three times with distilled water and dried at 80°C to constant weight to obtain 215 g of modified biochar (6-3S) with a nano-selenium loading of 24.17% (EDS detection).

[0065] (3) Application method

[0066] Soil remediation: Select cadmium-contaminated soil (initial effective cadmium 2.56 mg / kg, pH 6.2), mix it evenly at a mass ratio of conditioner to soil of 1:50 (i.e. 20 g conditioner / kg soil), and put it into a flower pot (20 cm in diameter).

[0067] Crop planting: Use the bulb seedling method to plant alliums, keep the root length 5cm and the stem length 13cm, plant 5 plants in each pot with a spacing of 10cm, and harvest after 30 days of regular watering management.

[0068] (4) Application effect

[0069] Soil indicators: The effective cadmium content dropped from 2.56 mg / kg to 1.92 mg / kg, a decrease of 38.65%; the total selenium content in the soil increased from 0.69 mg / kg to 1.79 mg / kg, an increase of 159.4%.

[0070] Crop indicators: The cadmium content in the white part of all-season onions was 0.62 mg / kg (1.43 mg / kg in the control group, a decrease of 56.64%), and the cadmium content in the green part of all-season onions was 0.18 mg / kg (1.05 mg / kg in the control group, a decrease of 82.69%); the selenium concentration in the aboveground part was 3.48 mg / kg (2.69 mg / kg in the control group, an increase of 29.8%).

[0071] Microstructure: The stomatal opening and closing functions of the leaves were restored, and the dissolution of guard cell plasma decreased by 44.2%; the chloroplast thylakoids were arranged neatly, the number of starch grains decreased by 60%, and the NBT-stained oxidative damage area decreased from 39.03% to 24.00%.

[0072] Example 2 (Pyrolysis Temperature Optimization Verification)

[0073] (1) Selection of raw material composition

[0074] The same as Example 1, except that the pyrolysis temperature was adjusted to 500° C., and the other raw material ratios remained unchanged.

[0075] (2) Preparation method

[0076] The pyrolysis step was adjusted to: constant temperature pyrolysis at 500° C. for 3 hours, and the remaining modification steps were the same as in Example 1, to obtain modified biochar (5-3S) with a nano-selenium loading of 12.7%.

[0077] (3) Application method

[0078] Same as Example 1, the initial available cadmium in the soil was 2.61 mg / kg.

[0079] (4) Application effect

[0080] Soil indicators: the effective cadmium content dropped to 2.12 mg / kg, a decrease of 18.8% (lower than 38.65% in Example 1);

[0081] Crop indicators: The cadmium content in green onions was 0.52 mg / kg, a decrease of 50.5%; the selenium concentration in the aboveground part was 2.91 mg / kg, an increase of 8.2%.

[0082] Example 3 (Comparison of Nano-Selenium Loading Process)

[0083] (1) Selection of raw material composition

[0084] Same as Example 1, except that the ultrasonic oscillation time in the modification step was adjusted to 1 hour (other conditions remained unchanged).

[0085] (2) Preparation method

[0086] The ultrasonic oscillation time was shortened to 1 hour, and the nano-selenium loading amount was 18.5% (lower than 24.17% in Example 1).

[0087] (3) Application method

[0088] Same as Example 1, the initial available cadmium in the soil was 2.58 mg / kg.

[0089] (4) Application effect

[0090] Soil indicators: Available cadmium content dropped to 2.05 mg / kg, a decrease of 20.5%;

[0091] Crop indicators: The cadmium content in the white part of onion was 0.98 mg / kg, a decrease of 31.5%; the selenium concentration in the aboveground part was 3.02 mg / kg, an increase of 12.3%.

[0092] Example 4 (field application verification)

[0093] (1) Selection of raw material composition

[0094] The same method as in Example 1 was used, but the preparation scale was expanded to 10 kg of eggshell powder to obtain 7.15 kg of modified biochar.

[0095] (2) Application method

[0096] Cadmium-contaminated farmland (Huishui County, Guizhou Province, with an initial effective cadmium concentration of 2.73 mg / kg) was applied with a conditioner at a rate of 200 kg / hectare, plowed to a depth of 20 cm, and planted with leek (seed seedlings) for a growing period of 45 days.

[0097] (3) Application effect

[0098] Soil indicators: Available cadmium content dropped to 1.67 mg / kg, a decrease of 38.8%;

[0099] Crop indicators: leek leaves had a cadmium content of 0.25 mg / kg (control: 1.12 mg / kg, a decrease of 77.7%), and a selenium concentration of 2.95 mg / kg (an increase of 26.1%);

[0100] Yield indicators: The fresh weight of leeks increased by 18%, and the glossiness and fiber content of leaves improved.

[0101] Comparative example (unmodified biochar)

[0102] (1) Selection of raw material composition

[0103] Nano-selenium modification was omitted, and eggshell biochar pyrolyzed at 600 °C for 3 h was directly used (6-3).

[0104] (2) Application method

[0105] Same as Example 1, the initial available cadmium in the soil was 2.56 mg / kg.

[0106] (3) Application effect

[0107] Soil indicators: effective cadmium content 2.42 mg / kg, a decrease of 5.5%;

[0108] Crop indicators: The cadmium content in the white part of the onion was 1.36 mg / kg, a decrease of 5.6%; the selenium concentration in the aboveground part was 2.80 mg / kg (only from the selenium in the eggshell itself).

[0109] The above example data show that the conditioner of the present invention has the best effect on soil cadmium passivation and crop selenium enrichment under the process conditions of pyrolysis at 600°C for 3 hours + nano-selenium ultrasonic modification for 2 hours, and is suitable for laboratory simulation and actual field remediation sites.

[0110] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various modifications and substitutions within the technical scope disclosed in the present invention, and such modifications and substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A dual-effect conditioner for cadmium passivation and selenium enrichment based on pyrolyzed eggshell biochar, characterized in that: The conditioning agent is composed of the following raw materials in parts by mass: 60-80 parts of green eggshell, 1-5 parts of nano-selenium; The conditioning agent is obtained by preparing biochar by pyrolyzing green eggshells and modifying the biochar with nano-selenium, wherein the nano-selenium is nano-selenium particles (SeNPs) with a particle size of 10-100 nm.

2. The dual-effect conditioner for cadmium passivation and selenium enrichment based on pyrolyzed eggshell biochar according to claim 1, characterized in that: The green eggshell pretreatment step is to wash and dry at 80°C to constant weight, and crush to pass through a 100-mesh sieve; the pyrolysis condition is to burn at 600°C in a muffle furnace for 2-4 hours, preferably 3 hours, and the heating rate is 5°C / min.

3. The dual-effect conditioner for cadmium passivation and selenium enrichment based on pyrolyzed eggshell biochar according to claim 1, characterized in that: During the nano-selenium modification process, the mass ratio of nano-selenium to distilled water is 1:30-1:50, preferably 1:40, the ultrasonic oscillation frequency is 30-50kHz, preferably 40kHz, the oscillation time is 1-3 hours, preferably 2 hours, the standing time is 20-28 hours, preferably 24 hours, and the drying temperature is 70-90°C, preferably 80°C.

4. The dual-effect conditioner for cadmium passivation and selenium enrichment based on pyrolyzed eggshell biochar according to claim 1, characterized in that: The carrier material is pyrolyzed eggshell biochar, the surface of which has a rough wrinkled structure and irregular pores, and the nano-selenium loading is 15-45% (weight percentage), preferably 24.17%.

5. A method for preparing a dual-effect conditioner for cadmium passivation and selenium enrichment based on pyrolysis eggshell biochar according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Wash, dry, and grind the green eggshells through a 100-mesh sieve to obtain eggshell powder; Step 2: heating the eggshell powder to 600°C in a muffle furnace at 5°C / min, firing for 2-4 hours, preferably 3 hours, and then grinding and sieving to obtain eggshell biochar; Step 3: Mix nano-selenium and distilled water in a mass ratio of 1:30-1:50, add eggshell biochar, ultrasonically vibrate for 1-3 hours, preferably 2 hours, and let stand for 20-28 hours, preferably 24 hours; Step 4: After filtering, wash the solid, and dry it at 70-90°C, preferably 80°C, to constant weight to obtain the finished product.

6. The method for preparing a dual-effect cadmium passivation and selenium enrichment conditioner based on pyrolyzed eggshell biochar according to claim 5, characterized in that: The particle size of the eggshell biochar in step 2 is ≤0.15 mm, and the ultrasonic oscillation power in step 3 is 200-300 W.

7. Use of a dual-effect conditioner for cadmium passivation and selenium enrichment based on pyrolyzed eggshell biochar according to any one of claims 1 to 4 in the remediation of cadmium-contaminated soil, characterized in that: The mass ratio of the conditioner to the contaminated soil is 1:40-1:60, preferably 1:50, and the conditioner is evenly mixed and then used for planting crops.

8. The use of a dual-effect cadmium passivation and selenium enrichment conditioner based on pyrolyzed eggshell biochar in the remediation of cadmium-contaminated soil according to claim 7, characterized in that: The crops include alliums, which are planted using a bulb seedling method, with a root length of 4-6 cm, preferably 5 cm, a stem length of 12-14 cm, preferably 13 cm, and a planting period of 25-35 days, preferably 30 days.

9. The dual-effect conditioner for cadmium passivation and selenium enrichment based on pyrolyzed eggshell biochar according to claim 1, characterized in that: After the conditioner is applied to the soil, the effective cadmium content in the soil can be reduced by 35-40%, preferably 38.65%, and the selenium concentration in the aboveground part of crops can be increased by 20-30%, preferably 3.48 mg / kg.

10. The dual-effect conditioner for cadmium passivation and selenium enrichment based on pyrolyzed eggshell biochar according to claim 1, characterized in that: The nano selenium is complexed with SeO3 2- +Cd 2+ →CdSeO3), competitive adsorption (Ca 2+ with cd 2+ Compete for soil colloid sites) and redox reactions to achieve cadmium passivation, while selenium is absorbed and transported to the aboveground parts of plants through the roots to achieve selenium enrichment.

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