Acidified soil conditioner and preparation method thereof

Abstract

The invention discloses an acidified soil conditioner and a preparation method thereof. The preparation method of the conditioner comprises the following steps: preparing a nano composite material: drying and crushing oyster shells, sieving and calcining to obtain oyster shell powder, namely the nano composite material; the preparation method comprises the following steps: preparing composite biochar powder: drying and grinding cleaned agricultural waste rice straws into powder, and carrying out sieving and calcining treatment to obtain straw biochar; mixing alkaline phosphate, sulfide, hemi-ferrite, manganese salt, clay, a microbial agent and straw charcoal in proportion to obtain composite charcoal powder; and preparing the acidified soil conditioner: compounding the nano composite material and the composite charcoal powder in proportion, and carrying out molding treatment on the complexing agent powder to obtain the acidified soil conditioner. The method has the beneficial effects that the available heavy metals in the soil can be reduced, the cation exchange capacity of the soil is enhanced, the acidification is neutralized, the soil fertility is improved, and the heavy metal pollution of the acidified farmland is repaired.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural soil improvement, in particular to an acidified soil conditioner and a preparation method thereof. Background Art

[0002] With atmospheric acid deposition and excessive fertilizer application, farmland soil acidification is a serious problem. Soil acidification not only causes a significant loss of basic ions such as calcium, magnesium, and potassium, reducing soil fertility, but also significantly increases the activity of heavy metals in the soil. Mineral-rich southern my country, coupled with mining and smelting, irrational use of pesticides and fertilizers, and wastewater irrigation, has led to increasing contamination of farmland soil with heavy metals such as copper (Cu), cadmium (Cd), and lead (Pb), seriously impacting the quality and safety of agricultural products. These heavy metals are transported into plants and enter the food chain, posing a potential risk to human health.

[0003] Currently, the effective remediation of heavy metal-contaminated soils has become a research hotspot of widespread international concern. Soil conditioners are an important means of remediating heavy metals in farmland soils. They have been widely used in the improvement of degraded soils, with specific benefits reflected in the following aspects: First, they improve the physical properties of the soil, enhance its water and soil retention capacity, and increase the availability of nutrients, thereby enhancing soil fertility; second, they promote the activity of beneficial microorganisms and enzymes, inhibit pathogenic microorganisms, and enhance plant resistance; finally, they reduce the migration capacity of heavy metals (such as Cd, Pb, and As) in contaminated soils, thereby inhibiting their absorption by crops.

[0004] Although natural soil conditioners have contributed to remediation efforts, they suffer from issues such as short duration and limited reserves. Synthetic polymers, on the other hand, are limited in their application due to high costs and potential environmental pollution risks. Furthermore, single soil conditioners (such as zeolite, fly ash, sewage sludge, green manure, and polyacrylamide) often have incomplete improvement effects and may bring varying degrees of negative impacts. Biochar has great potential for improving soil acidification and remediating heavy metal pollution, but its direct application in soil acidification and heavy metal pollution control still has limitations. Biochar is not alkaline enough, and to achieve a similar acidity neutralization effect, a large amount of biochar is required, resulting in high costs and unfavorable for actual production. Summary of the Invention

[0005] Based on this, the present invention proposes an acidifying soil conditioner and a preparation method thereof, which can solve the problems of soil heavy metal pollution and acidification at a low cost, while increasing soil pH and improving soil physical and chemical properties.

[0006] The present invention provides an acidified soil conditioner and a preparation method thereof. The preparation of the acidified soil conditioner comprises the following steps:

[0007] Preparation of nanocomposite materials: washing oyster shells, drying them, and then crushing them; sieving the crushed oyster shell powder; and finally calcining the oyster shell powder to obtain a solid powdered oyster shell powder, which is the nanocomposite material;

[0008] Preparation of composite biochar powder: washing agricultural waste rice straw is dried and then ground into powder, the rice straw powder is sieved, and finally the rice straw powder is calcined to obtain straw biochar; adding 5% to 10% alkaline phosphate, 1.5% to 4.5% sulfide, 1.5% to 4.5% semi-ferrous salt, 1% to 3.5% manganese salt, clay, microbial agent, and straw biochar in a proportionate ratio of biochar weight to obtain composite biochar powder;

[0009] Preparation of the acidified soil conditioner: compounding the nanocomposite material and the composite biochar powder in proportion to obtain composite agent powder, and molding the composite agent powder to obtain the acidified soil conditioner.

[0010] In addition, the acidified soil conditioner and preparation method thereof provided by the present invention may also have the following additional technical features:

[0011] Furthermore, the step of screening the oyster shell powder includes:

[0012] The oyster shell powder was passed through a 100-mesh sieve.

[0013] Furthermore, the step of sieving the rice straw powder includes:

[0014] The rice straw powder was sieved through a 100-mesh sieve.

[0015] Furthermore, the step of calcining the oyster shell powder includes:

[0016] Adding 15-30% of silicate mineral zeolite powder to the oyster shell powder for compounding;

[0017] The composite powder is placed in a furnace at a high temperature of 600-800°C for calcination and activation for 1.5-3.5 hours.

[0018] Furthermore, the step of calcining the rice straw powder includes:

[0019] The rice straw powder is placed in a furnace at a high temperature of 600-800°C and calcined to activate carbonization.

[0020] Furthermore, the step of molding the composite powder includes:

[0021] The composite powder is prepared into a formed granular product by disk granulation, extrusion molding and hot pressing molding.

[0022] The acidified soil conditioner prepared by the preparation method of the present invention uses biomass waste such as oyster shells and zeolite and silicate-rich ores as raw materials, fully recycling the waste. Oyster shells are a natural nanocomposite material composed of a brick-like calcium carbonate layer (approximately 96% by weight) and a thin layer of protein as an organic glue. Its main components are CaO, CaCO3, etc., and it can efficiently and quickly increase soil pH and passivate soil heavy metals. Zeolite is a natural porous aluminosilicate mineral. It has a unique pore structure and is rich in silicon. In the agricultural field, zeolite can be used to improve soil water retention and air permeability. In environmental management, zeolite can be used to treat industrial wastewater and exhaust gas and remove harmful substances by utilizing its abundant pores. Composite biochar powder is composed of rice straw biochar, alkaline phosphate, sulfide, iron manganese compound, clay and microbial agents. It is rich in cations and can adsorb heavy metals in the soil, exchange ions, improve the acid buffering capacity of the soil, improve soil fertility, break up soil compaction, loosen the soil, improve soil permeability, and reduce soil bulk density, so that acidified farmland contaminated by heavy metals can be turned into usable resources again.

[0023] The beneficial effects of the present invention are as follows: the composite new material for treating mixed heavy metal pollution in acidified rice fields integrates functions such as adsorption, precipitation, complexation, and fertilization. It can not only reduce the effective heavy metals therein, but also enhance its cation exchange capacity, neutralize acidification, and improve soil fertility, so as to achieve the purpose of repairing heavy metal pollution in acidified farmland and improving the physical and chemical properties of the soil.

[0024] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0026] Figure 1 is a flow chart of a method for preparing an acidified soil conditioner according to a first embodiment of the present invention;

[0027] Figure 2 XRD patterns of oyster shells before and after calcination. DETAILED DESCRIPTION

[0028] To make the objects, features, and advantages of the present invention more readily apparent, the following detailed description of specific embodiments of the present invention is provided in conjunction with the accompanying drawings. The accompanying drawings illustrate several embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0029] Example 1:

[0030] An acidified soil conditioner and its preparation method, the preparation method process is as follows Figure 1 As shown, the specific steps are:

[0031] Step S1, preparing nanocomposite material (Product A):

[0032] Step S11: Wash the oyster shell powder with ultrapure water to remove surface impurities.

[0033] Step S12: then place the raw material in an oven and dry it at 80°C to ensure the purity and dryness of the raw material.

[0034] For purposes of illustration and not limitation, the present invention adopts the drying of oyster shell powder at 80°C as a preferred embodiment. For other embodiments, the drying equipment and the drying setting temperature used are not specifically limited.

[0035] Step S13: mechanically grinding the dried oyster shells to refine them into powder.

[0036] Step S14: Sieve through a 100-mesh sieve to ensure the uniformity of the powder.

[0037] Step S15: uniformly mix the sieved oyster shell powder and the silicate mineral zeolite powder in a mass ratio of 4:1, then place the mixture in a muffle furnace and calcine and activate it for 3 hours to enhance the activity and stability of the material.

[0038] Please refer to the following for details: Figure 2 , Figure 2 The XRD patterns of oyster shells before and after calcination are shown. The left side shows the XRD pattern before calcination, and the right side shows the XRD pattern after calcination. The calcination process changes the properties of the oyster shells and increases their activity.

[0039] The operating temperature range of the muffle furnace is 600-800° C., and the calcination time range in the muffle furnace is 1.5-3.5 hours. The specific calcination time is adjusted based on the powder forming condition after the final calcination.

[0040] In addition, the mass ratio of 4:1 in the embodiment of the present invention is only used as a more preferred method. As long as the oyster shell powder and the silicate mineral zeolite powder are uniformly mixed in a mass ratio of 15% to 30%, the soil improvement effect of the final prepared nanocomposite material is similar.

[0041] Step S16: In order to better stimulate the material properties, the calcined composite is cooled and then mechanically ground again, and sieved to obtain oyster shell powder (Product A) with a particle size of less than 500 nanometers.

[0042] Step S2: preparing composite biochar powder (product B):

[0043] Step S21: Wash the agricultural waste rice straw.

[0044] Step S22: drying in an oven at 80°C to ensure the dryness and purity of the raw materials.

[0045] Step S23: mechanically grinding the dried rice straw and sieving it through a 100-mesh sieve to obtain uniform straw powder.

[0046] Step S24: calcining in a muffle furnace to obtain straw biochar.

[0047] Among them, the operating temperature range of the muffle furnace is 600~800℃.

[0048] Step S25: Add 8% alkaline phosphate, 7% sulfide, 3% semi-ferrous salt, 2% manganese salt, and appropriate amounts of clay and microbial agent based on the mass of the biochar, and mix them thoroughly in proportion to obtain composite biochar powder (product B).

[0049] It should be noted that the contents of the above-mentioned alkaline phosphate, sulfide, semi-ferrous salt, and manganese salt in the embodiment of the present invention are only used as a more preferred solution. In the embodiment of the present invention, when the alkaline phosphate content is in the range of 5% to 10%, the sulfide content is in the range of 1.5% to 4.5%, the semi-ferrous salt content is in the range of 1.5% to 4.5%, and the manganese salt content is in the range of 1% to 3.5%, the soil conditioning effect of the finally prepared acidified soil conditioner is similar.

[0050] Step S3: preparing an acidified soil conditioner:

[0051] The composite conditioner powder obtained by compounding product A and product B obtained in step S1 and step S2 in different mass proportions is further mixed and crushed to obtain a soil conditioner for treating heavy metal pollution in acidified farmland.

[0052] It should be noted that the material can be subsequently prepared into granular products through disc granulation, extrusion molding, hot pressing molding, etc., which is convenient for subsequent storage, transportation and field application.

[0053] Experiment 1

[0054] The test soil was collected from a heavy metal polluted area in Jiangxi Province. The copper and cadmium heavy metal contents in the surface soil of this area were higher than the agricultural land soil pollution risk screening value of the "Soil Environmental Quality Standard" (GB15618-2018).

[0055] Samples were taken from the soil, air-dried, and crushed. Deionized water and soil were mixed in a ratio of 10:1, shaken thoroughly, and the supernatant was collected after standing to simulate irrigation water in the irrigation canal.

[0056] A soil conditioner obtained by compounding Product A and Product B in different mass ratios based on Example 1 was added to 20 ml of simulated copper and cadmium heavy metal contaminated water, shaken for 24 hours, and filtered to complete adsorption. A sample was taken from the filtered solution, and the adsorbed heavy metal concentration was measured by ICP-MS. The final results are shown in Table 1 below:

[0057] Table 1

[0058]

[0059] Experiment 2

[0060] The test soil was collected from a heavy metal polluted area in Jiangxi Province. The copper and cadmium heavy metal contents in the surface soil of this area were higher than the agricultural land soil pollution risk screening value of the "Soil Environmental Quality Standard" (GB15618-2018).

[0061] Samples were taken from the soil, which was air-dried, crushed, and sieved to reduce the soil particle size to less than 1 cm.

[0062] Add 2.5% of product B to 800g of soil and mix evenly for 7 days. During this period, add 2.5% of product A and culture for 7 days. Then culture products A and B together for another 15 days to keep the soil at 60% of field water capacity.

[0063] After the cultivation, the effective state of heavy metals was extracted with DTPA, the heavy metal content in the extract was detected by ICP-MS, and the concentration of different heavy metals was determined by BCR continuous extraction method.

[0064] Table 2 New composite materials for the treatment of heavy metal pollution in acidified rice fields and restoration of heavy metal pollution in acidified rice fields

[0065]

[0066] Table 3 New composite materials for the treatment of heavy metal pollution in acidified rice fields and restoration of heavy metal pollution in acidified rice fields

[0067]

[0068] Table 4 New composite materials for treating heavy metal pollution in acidified rice fields improve soil physical and chemical properties

[0069]

[0070] Table 5 New composite materials for treating heavy metal pollution in acidified rice fields improve soil physical and chemical properties

[0071]

[0072] From the results in Tables 2-5, it can be seen that the combined use of Products A and B can effectively reduce the concentration of heavy metal acid-extractable forms (F1), increase the concentrations of iron-manganese-bound forms (F2), organically bound forms (F3), and residual forms (F4), reduce available copper and available cadmium in the soil, increase soil pH, reduce soil bulk density, and improve soil fertility.

[0073] In summary, the acidified soil conditioner prepared by the preparation method of the present invention uses biomass waste such as oyster shells and zeolites and silicate-rich ores as raw materials, fully recycling the waste. Oyster shells are a natural nanocomposite material composed of a brick-like calcium carbonate layer (about 96% by weight) and a thin layer of protein as an organic glue. The main components are CaO, CaCO3, etc., which can efficiently and quickly increase the pH value of the soil and passivate soil heavy metals. Zeolite is a natural porous aluminosilicate mineral. They have a unique pore structure and are rich in silicon. In the agricultural field, zeolite can be used to improve soil and improve soil water retention and air permeability. In terms of environmental governance, zeolite can be used to treat industrial wastewater and exhaust gas with its abundant pores to remove harmful substances. Composite biochar powder is composed of rice straw biochar, alkaline phosphate, sulfide, iron manganese compound, clay and microbial agents. It is rich in cations and can adsorb heavy metals in the soil, exchange ions, improve the acid buffering capacity of the soil, improve soil fertility, break up soil compaction, loosen the soil, improve soil permeability, and reduce soil bulk density, so that acidified farmland contaminated by heavy metals can be turned into usable resources again.

[0074] The acidified soil conditioner prepared by the preparation method of the present invention has the beneficial effects of integrating functions such as adsorption, precipitation, complexation, and fertilization. The new composite material for treating mixed heavy metal pollution in acidified rice fields can not only reduce the effective heavy metals therein, but also enhance its cation exchange capacity, neutralize acidification, and improve soil fertility, thereby achieving the purpose of repairing heavy metal pollution in acidified farmland and improving the physical and chemical properties of the soil.

[0075] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0076] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. An acidified soil conditioner and a preparation method thereof, characterized in that: The preparation of the acidified soil conditioner comprises the following steps: Preparation of nanocomposite materials: washing oyster shells, drying them, and then crushing them; sieving the crushed oyster shell powder; and finally calcining the oyster shell powder to obtain a solid powdered oyster shell powder, which is the nanocomposite material; Preparation of composite biochar powder: washing agricultural waste rice straw is dried and then ground into powder, the rice straw powder is sieved, and finally the rice straw powder is calcined to obtain straw biochar; adding 5% to 10% alkaline phosphate, 1.5% to 4.5% sulfide, 1.5% to 4.5% semi-ferrous salt, 1% to 3.5% manganese salt, clay, microbial agent, and straw biochar in a proportionate ratio of biochar weight to obtain composite biochar powder; Preparation of the acidified soil conditioner: compounding the nanocomposite material and the composite biochar powder in proportion to obtain composite agent powder, and molding the composite agent powder to obtain the acidified soil conditioner.

2. The acidified soil conditioner and preparation method thereof according to claim 1, characterized in that: The step of sieving the oyster shell powder comprises: The oyster shell powder was passed through a 100-mesh sieve.

3. The acidified soil conditioner and preparation method thereof according to claim 1, characterized in that: The step of sieving the rice straw powder comprises: The rice straw powder was sieved through a 100-mesh sieve.

4. The acidified soil conditioner and preparation method thereof according to claim 1, characterized in that: Before the step of calcining the oyster shell powder, the method further comprises: Adding 15-30% of silicate mineral zeolite powder to the oyster shell powder for compounding; The composite powder is placed in a furnace at a high temperature of 600-800°C for calcination and activation for 1.5-3.5 hours.

5. The acidified soil conditioner and preparation method thereof according to claim 1, characterized in that: The step of calcining the rice straw powder comprises: The rice straw powder is placed in a furnace at a high temperature of 600-800°C and calcined to activate carbonization.

6. The acidified soil conditioner and preparation method thereof according to claim 1, characterized in that: The step of molding the composite powder comprises: The composite powder is prepared into a formed granular product by disk granulation, extrusion molding and hot pressing molding.

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