Rare earth slow-release fertilizer as well as preparation method and application thereof

Abstract

The invention provides a rare-earth slow-release fertilizer as well as a preparation method and application thereof. The rare-earth slow-release fertilizer comprises rare-earth slow-release particles and a basic fertilizer, the rare earth sustained-release particle comprises an inner core formed by rare earth ions and a chelating agent, and a coating layer coating the inner core, the chelating agent comprises unsubstituted and / or alkyl substituted dithiocarbamate; the basic fertilizer comprises any one or a combination of at least two of nitrogenous fertilizer, phosphatic fertilizer or potash fertilizer. The rare earth slow-release fertilizer provided by the invention realizes gradient release of rare earth ions, has slow-release stability in a wide pH range, reduces soil rare earth loss, improves the bioavailability of the rare earth ions, and reduces the risk of environmental pollution.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically relating to a rare earth slow-release fertilizer, its preparation method, and its application. Background Technology

[0002] Rare earth elements promote seed germination, enhance photosynthesis, and improve crop resistance. However, traditional rare earth fertilizers are primarily in the form of inorganic salts (such as lanthanum nitrate). Firstly, in soils with a pH greater than 6.5, rare earth ions readily combine with phosphate and carbonate ions to form insoluble substances, reducing plant utilization efficiency. Secondly, rare earth ions are rapidly leached during rainfall or irrigation, failing to provide long-term slow release, while short-term release results in an excessively short absorption window for crops. Furthermore, excessive free rare earth ions can inhibit plant root development and even accumulate through the food chain, posing a potential toxicity risk.

[0003] In fertilizer production processes, the main methods for slow-release of rare earth ions include physical slow-release and chemical slow-release. Physical slow-release involves extruding fertilizer particles to achieve a certain hardness, thus achieving a slow-release effect. However, the slow-release effect varies greatly depending on the extrusion intensity, and the release rate reaches its peak shortly after the particles come into contact with water, resulting in a less than ideal slow-release effect. Chemical slow-release mainly uses two common coating-type slow-release materials: sulfur coating (SCU) and urea-formaldehyde (UF). The release of fertilizer is synchronized with microbial activity, and there is no risk of physical coating detachment. However, its fertilizer efficiency is poor in the initial application stage, the production process is complex, and the yield is low. Furthermore, the use of urea-formaldehyde materials can lead to environmental safety issues due to the introduction of formaldehyde.

[0004] CN111592386A discloses a method for preparing chelated rare earth elements, using EDTA (ethylenediaminetetraacetic acid) and polyphosphate to chelate rare earth ions. However, this method has drawbacks: the long settling time is unfavorable for large-scale production; the product is an aqueous solution, making long-distance transportation inconvenient and resulting in high packaging costs; under high summer temperatures, the polyphosphate hydrolyzes to form phosphates, which easily cause turbidity when mixed with rare earth elements, hindering long-term storage; and the rare earth raw material is rare earth nitrate, which produces sodium nitrate as a byproduct that is difficult to separate.

[0005] CN115417721A discloses a method for preparing highly stable and high-purity chelated rare earth fertilizer, which uses DTPA (diethylenetriaminepentaacetic acid) to chelate rare earth ions. Although this method improves the stability of rare earth ions by chelating them with DTPA, the dissociation rate is still as high as 35-40% in acidic soils with a pH less than 5.

[0006] Therefore, there is an urgent need to develop a rare earth slow-release fertilizer to solve the problems of poor stability, uncontrollable release, and environmental risks associated with traditional rare earth fertilizers. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a rare earth slow-release fertilizer, its preparation method and application. The rare earth slow-release fertilizer of this invention has slow-release stability over a wide pH range and realizes the gradient release of rare earth ions.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a rare earth slow-release fertilizer, wherein the components of the rare earth slow-release fertilizer include rare earth slow-release granules and basic fertilizer.

[0010] The rare earth slow-release particles comprise a core formed by rare earth ions and a chelating agent, and a coating layer covering the core; the chelating agent comprises unsubstituted and / or alkyl-substituted dithiocarbamates.

[0011] The basic fertilizer includes any one or a combination of at least two of nitrogen fertilizer, phosphorus fertilizer, or potassium fertilizer.

[0012] This invention utilizes dithiocarbamate to chelate rare earth ions, constructing core-membrane structured rare earth slow-release particles. This achieves gradient release of rare earth ions and exhibits slow-release stability over a wide pH range. It reduces soil rare earth leaching, improves the bioavailability of rare earth ions, and lowers the risk of environmental pollution. It extends fertilizer effectiveness to over 60 days, and when combined with basic fertilizers, significantly increases crop yield.

[0013] Preferably, the rare earth slow-release fertilizer comprises, by weight, 10-20 parts of rare earth slow-release granules and 80-90 parts of basic fertilizer.

[0014] The weight percentages of the rare earth slow-release particles can be 10, 11.2, 12.5, 13.7, 14.3, 15.5, 16.8, 17, 18, 19, or 20 parts, etc.

[0015] The weight percentage of the base fertilizer can be 80 parts, 81.2 parts, 82.5 parts, 83.7 parts, 84.3 parts, 85.5 parts, 86.8 parts, 87 parts, 88 parts, 89 parts, or 90 parts, etc.

[0016] Other specific point values ​​within the range of the above values ​​can be selected, and will not be elaborated on here.

[0017] The mass ratio of the core to the envelope is (2-8):(8-12).

[0018] The specific point values ​​in (2-8) can be 2, 2.2, 2.5, 2.7, 3, 3.3, 3.5, 3.8, 4, 5, 6, 7 or 8, etc.

[0019] The specific point values ​​in (8-12) can be 8, 8.2, 8.5, 8.7, 9, 9.3, 9.5, 9.8, 10, 11 or 12, etc.

[0020] Other specific point values ​​within the range of the above values ​​can be selected, and will not be elaborated on here.

[0021] The molar ratio of the rare earth ions to the chelating agent is 1:(1.2-1.5).

[0022] The specific point values ​​in (1.2-1.5) can be 1.2, 1.21, 1.22, 1.25, 1.27, 1.3, 1.33, 1.35, 1.38, 1.4, 1.45 or 1.5, etc.

[0023] Other specific point values ​​within the range of the above values ​​can be selected, and will not be elaborated on here.

[0024] Preferably, the chelating agent comprises any one or a combination of at least two of dimethyl dithiocarbamate, diethyl dithiocarbamate, dipropyl dithiocarbamate, dibutyl dithiocarbamate, or dipentyl dithiocarbamate.

[0025] Dithiocarbamate (DTC) chelating agents primarily chelate rare earth ions through two sulfur atoms, while the substituent groups on the nitrogen atom further influence the binding energy. These DTC chelating agents possess suitable coordination binding capabilities with rare earth ions, controlling the release of rare earth ions within a reasonable range and avoiding problems such as excessively strong binding capacity leading to slow release or excessively weak binding capacity leading to rapid release. They maintain stable and slow release of rare earth ions even in acidic or alkaline soils (pH 3-9), simultaneously passivating soil heavy metals and reducing heavy metal absorption by crops.

[0026] Preferably, the chelating agent comprises dimethyl dithiocarbamate and diethyl dithiocarbamate.

[0027] Dimethyl dithiocarbamate and diethyl dithiocarbamate have a synergistic effect. The dimethyl and diethyl substitution of nitrogen atoms regulates the binding energy between the DTC chelating agent and rare earth ions to the optimal value, thereby achieving the best sustained-release effect.

[0028] Preferably, the molar ratio of dimethyl dithiocarbamate to diethyl dithiocarbamate is (1-10):(1-10).

[0029] The specific point values ​​in the first (1-10) can be 1, 2.2, 3.5, 4.7, 5, 6.3, 7.5, 8.8, 9 or 10, etc.

[0030] The specific point values ​​in the second (1-10) can be 1, 2.2, 3.5, 4.7, 5, 6.3, 7.5, 8.8, 9 or 10, etc.

[0031] Other specific point values ​​within the range of the above values ​​can be selected, and will not be elaborated on here.

[0032] Preferably, the dithiocarbamate includes any one or a combination of at least two of the sodium, potassium, zinc, magnesium, manganese or ammonium salts of dithiocarbamate.

[0033] The cations of the dithiocarbamates involved in this invention include, but are not limited to, sodium ions, potassium ions, zinc ions, magnesium ions, manganese ions, or ammonium ions. Soluble dithiocarbamates can be used in this invention.

[0034] Preferably, the rare earth ions include any one or a combination of at least two of the following: lanthanum ions, cerium ions, neodymium ions, praseodymium ions, samarium ions, europium ions, gadolinium ions, terbium ions, dysprosium ions, holmium ions, erbium ions, thulium ions, ytterbium ions, lutetium ions, yttrium ions, or scandium ions.

[0035] The rare earth ions involved in this invention include, but are not limited to, those shown above. The type of rare earth ions does not affect the rare earth sustained-release performance of the sustained-release particles.

[0036] Preferably, the components of the coating layer include any one or a combination of at least two of polylactic acid, polycaprolactone, polyhydroxyoctanoate, polyvinyl alcohol, polyvinyl acetate, polyglycolic acid, or polybutylene succinate.

[0037] This invention uses the above-mentioned biodegradable polymer material for particle coating. The coating layer begins to degrade naturally after 30 days, achieving slow release of rare earth elements without adverse environmental impact.

[0038] Preferably, the components of the coating layer include polylactic acid, polycaprolactone, and polyhydroxyoctanoate.

[0039] Polylactic acid, polycaprolactone, and polyhydroxyoctanoate, when used as coating layers, have a synergistic effect, and when adapted to the core, they have a better effect on the sustained release of rare earth ions.

[0040] Preferably, the mass ratio of polylactic acid, polycaprolactone, and polyhydroxyoctanoate is (1-10):(1-10):(1-8).

[0041] The specific point values ​​in the first (1-10) can be 1, 2.2, 3.5, 4.7, 5, 6.3, 7.5, 8.8, 9 or 10, etc.

[0042] The specific point values ​​in the second (1-10) can be 1, 2.2, 3.5, 4.7, 5, 6.3, 7.5, 8.8, 9 or 10, etc.

[0043] The specific point values ​​in (1-8) can be 1, 1.2, 1.5, 1.7, 2, 2.3, 2.5, 2.8, 3, 3.5, 4, 5, 6, 7 or 8, etc.

[0044] Other specific point values ​​within the range of the above values ​​can be selected, and will not be elaborated on here.

[0045] Preferably, the core components also include an adhesive.

[0046] Preferably, the adhesive has a mass percentage content of 3-6% in the core, for example, it can be 3%, 3.2%, 3.5%, 3.7%, 4%, 4.3%, 4.5%, 4.8%, 5%, 5.5% or 6%, etc.

[0047] Other specific point values ​​within the range of the above values ​​can be selected, and will not be elaborated on here.

[0048] Preferably, the adhesive comprises any one or a combination of at least two of carboxymethyl starch, sodium alginate, xanthan gum, chitosan, carboxymethyl chitosan, methylcellulose, hydroxypropyl methylcellulose, sodium carboxymethyl cellulose, or carboxymethyl guar gum.

[0049] Preferably, the particle size of the core is 0.5-3 mm, for example, it can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.2 mm, 1.5 mm, 1.7 mm, 2 mm, 2.3 mm, 2.5 mm, 2.8 mm or 3 mm; the thickness of the coating layer is 5-40 μm, for example, it can be 5 μm, 6.2 μm, 7.3 μm, 8.5 μm, 9.7 μm, 10.8 μm, 15 μm, 20 μm, 25 μm, 30 μm or 40 μm.

[0050] Other specific point values ​​within the range of the above values ​​can be selected, and will not be elaborated on here.

[0051] In a second aspect, the present invention provides a method for preparing rare earth slow-release fertilizer as described in the first aspect, the method comprising:

[0052] An acid solution containing rare earth ions is mixed with a chelating agent and reacted to generate a precipitate, which is then granulated to obtain core particles. The core particles are coated with a coating layer to obtain rare earth slow-release particles. The rare earth slow-release particles are mixed with basic fertilizer to obtain the rare earth slow-release fertilizer.

[0053] Preferably, the acid includes any one or a combination of at least two of nitric acid, hydrochloric acid, citric acid, oxalic acid, or sulfuric acid.

[0054] Preferably, the pH value of the acid solution is 2-3, for example, it can be 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3, etc.

[0055] Preferably, the reaction temperature is 50-60℃, for example, 50℃, 51.2℃, 52.5℃, 53.7℃, 54℃, 55.3℃, 56.5℃, 57.8℃, 58℃, 59℃, or 60℃; and the reaction time is 3-4 hours, for example, 3 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, 3.5 hours, 3.6 hours, 3.7 hours, 3.8 hours, 3.9 hours, or 4 hours.

[0056] Other specific point values ​​within the range of the above values ​​can be selected, and will not be elaborated on here.

[0057] Preferably, the precipitation process further includes washing and drying steps.

[0058] Preferably, the granulation process also includes the addition of an adhesive.

[0059] Preferably, the temperature of the coating process is 40-60℃, for example, it can be 40℃, 41.2℃, 42.5℃, 43.7℃, 44℃, 45.3℃, 46.5℃, 47.8℃, 48℃, 49℃, 50℃, 55℃ or 60℃, etc.

[0060] Other specific point values ​​within the range of the above values ​​can be selected, and will not be elaborated on here.

[0061] Thirdly, the present invention provides the application of rare earth slow-release fertilizers as described in the first aspect in increasing crop yield.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] This invention utilizes dithiocarbamate to chelate rare earth ions, constructing core-membrane structured rare earth slow-release particles. This achieves gradient release of rare earth ions and exhibits slow-release stability over a wide pH range. It reduces soil rare earth leaching, improves the bioavailability of rare earth ions, and lowers the risk of environmental pollution. It extends fertilizer effectiveness to over 60 days, and when combined with basic fertilizers, significantly increases crop yield. Detailed Implementation

[0064] To further illustrate the technical means and effects of the present invention, the following describes the technical solution of the present invention in conjunction with preferred embodiments of the present invention. However, the present invention is not limited to the scope of the embodiments.

[0065] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0066] The sources of materials used in the following specific embodiments are as follows:

[0067] Carboxymethyl starch is derived from Maclean's reagent grade; sodium alginate is derived from Maclean's reagent grade (90%); xanthan gum is derived from Aladdin and PharmPure. TM USP; Polylactic acid is from Maclean, particle size: 3mm, Mw~110000; Polycaprolactone is from Maclean, Mn 2000; Polyhydroxyoctanoate is from Shanghai Yuanye Biotechnology, purity ≥99%; Nitrogen, phosphorus and potassium compound fertilizer is from Stanley, total nutrients ≥57%.

[0068] Example 1

[0069] This embodiment provides a rare earth slow-release fertilizer, the preparation method of which is as follows:

[0070] (1) Dissolve lanthanum oxide in 4M nitric acid, adjust the pH to 2.5, filter to obtain lanthanum ion solution; add 0.6mol sodium dimethyl dithiocarbamate and 0.8mol zinc diethyl dithiocarbamate to the above solution containing 1mol lanthanum ions, react at 55℃ for 3.5h to generate precipitate, wash and dry to obtain lanthanum chelate powder; then add 4% carboxymethyl starch of the total system mass and mix, granulate to obtain core particles (particle size 1.5mm);

[0071] (2) Polylactic acid, polycaprolactone and polyhydroxyoctanoate were mixed in a mass ratio of 5:5:3 to obtain a coating material; a fluidized bed coating technology was used at 50°C to coat the core particles with a coating material (thickness 15μm) to obtain rare earth slow-release particles, wherein the mass ratio of the core to the coating layer was 3:10.

[0072] (3) By weight, 15 parts of rare earth slow-release granules and 85 parts of nitrogen, phosphorus and potassium compound fertilizer are mixed to obtain the rare earth slow-release fertilizer.

[0073] Example 2

[0074] This embodiment provides a rare earth slow-release fertilizer, the preparation method of which is as follows:

[0075] (1) Dissolve cerium oxide in 6M hydrochloric acid, adjust the pH to 2, filter to obtain a cerium ion solution; add 0.7mol potassium dimethyl dithiocarbamate and 0.5mol magnesium diethyl dithiocarbamate to the above solution containing 1mol cerium ions, react at 60℃ for 3h to generate a precipitate, wash and dry to obtain cerium chelate powder; then add sodium alginate with a total mass percentage of 3% and mix, granulate to obtain core particles (particle size 1mm);

[0076] (2) Polylactic acid, polycaprolactone and polyhydroxyoctanoate were mixed in a mass ratio of 10:10:1 to obtain a coating material; a fluidized bed coating technology was used at 40°C to coat the core particles with the coating material (thickness 10μm) to obtain rare earth slow-release particles, wherein the mass ratio of the core to the coating layer was 1:6.

[0077] (3) By weight, 20 parts of rare earth slow-release granules and 80 parts of nitrogen, phosphorus and potassium compound fertilizer are mixed to obtain the rare earth slow-release fertilizer.

[0078] Example 3

[0079] This embodiment provides a rare earth slow-release fertilizer, the preparation method of which is as follows:

[0080] (1) Dissolve neodymium oxide in 3M citric acid, adjust the pH to 3, filter to obtain a neodymium ion solution; add 0.9mol sodium dimethyl dithiocarbamate and 0.6mol magnesium diethyl dithiocarbamate to the above solution containing 1mol of neodymium ions, react at 50℃ for 4h to generate a precipitate, wash and dry to obtain neodymium chelate powder; then add xanthan gum with a total mass percentage of 6% and mix, granulate to obtain core particles (particle size 2mm);

[0081] (2) Polylactic acid, polycaprolactone and polyhydroxyoctanoate were mixed in a mass ratio of 1:1:8 to obtain a coating material; a fluidized bed coating technology was used at 60°C to coat the core particles with the coating material (thickness 30μm) to obtain rare earth slow-release particles, wherein the mass ratio of the core to the coating layer was 1:1.

[0082] (3) By weight, 10 parts of rare earth slow-release granules are mixed with 90 parts of nitrogen, phosphorus and potassium compound fertilizer to obtain the rare earth slow-release fertilizer.

[0083] Example 4

[0084] This embodiment provides a rare earth slow-release fertilizer, which differs from Example 1 only in that "0.6 mol of sodium dimethyl dithiocarbamate and 0.8 mol of zinc diethyl dithiocarbamate" is replaced with "1.4 mol of sodium dimethyl dithiocarbamate", while the other raw materials and steps remain unchanged.

[0085] Example 5

[0086] This embodiment provides a rare earth slow-release fertilizer, which differs from Example 1 only in that "0.6 mol of sodium dimethyl dithiocarbamate and 0.8 mol of zinc diethyl dithiocarbamate" is replaced with "1.4 mol of zinc diethyl dithiocarbamate", while the other raw materials and steps remain unchanged.

[0087] Example 6

[0088] This embodiment provides a rare earth slow-release fertilizer, which differs from Example 1 only in that "0.6 mol of sodium dimethyl dithiocarbamate and 0.8 mol of zinc diethyl dithiocarbamate" is replaced with "1.4 mol of sodium dipropyl dithiocarbamate", while the other raw materials and steps remain unchanged.

[0089] Example 7

[0090] This embodiment provides a rare earth slow-release fertilizer, which differs from Example 1 only in that "0.6 mol of sodium dimethyl dithiocarbamate and 0.8 mol of zinc diethyl dithiocarbamate" is replaced with "1.4 mol of sodium dibutyl dithiocarbamate", while the other raw materials and steps remain unchanged.

[0091] Example 8

[0092] This embodiment provides a rare earth slow-release fertilizer, which differs from Example 1 only in that "0.6 mol of sodium dimethyl dithiocarbamate and 0.8 mol of zinc diethyl dithiocarbamate" is replaced with "1.4 mol of sodium dipentyl dithiocarbamate", while the other raw materials and steps remain unchanged.

[0093] Example 9

[0094] This embodiment provides a rare earth slow-release fertilizer, which differs from Example 1 only in that "0.6 mol sodium dimethyl dithiocarbamate and 0.8 mol zinc diethyl dithiocarbamate" are replaced with "1.4 mol sodium dithiocarbamate", while the other raw materials and steps remain unchanged.

[0095] Example 10

[0096] This embodiment provides a rare earth slow-release fertilizer, which differs from Embodiment 1 only in that: polylactic acid is not added to the coating material, and its reduction is proportionally allocated to polycaprolactone and polyhydroxyoctanoate, while the other raw materials and steps remain unchanged.

[0097] Example 11

[0098] This embodiment provides a rare earth slow-release fertilizer, which differs from Embodiment 1 only in that: polycaprolactone is not added to the coating layer material, and its reduction is proportionally allocated to polylactic acid and polyhydroxyoctanoate, while the other raw materials and steps remain unchanged.

[0099] Example 12

[0100] This embodiment provides a rare earth slow-release fertilizer, which differs from Embodiment 1 only in that: polyhydroxyoctanoate is not added to the coating layer material, and its reduction is proportionally allocated to polylactic acid and polycaprolactone, while the remaining raw materials and steps remain unchanged.

[0101] Comparative Example 1

[0102] This comparative example provides a rare earth slow-release fertilizer, which differs from Example 1 only in that "0.6 mol of sodium dimethyl dithiocarbamate and 0.8 mol of zinc diethyl dithiocarbamate" is replaced with "1.4 mol of disodium ethylenediaminetetraacetate", while the other raw materials and steps remain unchanged.

[0103] Comparative Example 2

[0104] This comparative example provides a rare earth slow-release fertilizer, which differs from Example 1 only in that "0.6 mol of sodium dimethyl dithiocarbamate and 0.8 mol of zinc diethyl dithiocarbamate" is replaced with "1.4 mol of sodium diethylenetriaminepentaacetate", while the other raw materials and steps remain unchanged.

[0105] Test Example 1

[0106] The tested potted plants were ryegrass, and the soil pH was 5. The fertilizers provided in Examples 1-12 and Comparative Examples 1-2 were applied in groups. The initial available cadmium content in the soil was 2.5 mg / kg. Each group consisted of 5 pots of ryegrass, with an application rate of 0.5 g / kg. The cultivation period was 60 days. The aboveground biomass of the ryegrass and the available cadmium content in the soil were recorded. A control group was used, with an equal amount of NPK compound fertilizer applied. The increase rate of aboveground biomass and the decrease rate of available cadmium content in the soil were calculated compared to the control group. The increase rate of aboveground biomass (%) = ((experimental group - control group) / control group) × 100%, and the decrease rate of available cadmium content in the soil (%) = ((control group - experimental group) / control group) × 100%.

[0107] The test results are shown in Table 1. This invention is based on dithiocarbamate chelating rare earth ions, which has a high rare earth ion bioavailability, significantly improves crop yield, and can passivate soil heavy metals, reducing the absorption of heavy metals by crops.

[0108] In the control group, the aboveground biomass was 1.25 g / pot and the available cadmium content in the soil was 2.5 mg / kg, while in Example 1, the aboveground biomass was 2.26 g / pot and the available cadmium content in the soil was 1.82 mg / kg. The DTC metal chelation system of Example 1 has significant advantages in promoting plant growth and reducing the available cadmium content in the soil.

[0109] The increase in available cadmium content in the soil after treatments in Comparative Examples 1-2 demonstrates that traditional EDTA and DTPA chelating agents form water-soluble complexes with cadmium in the soil. These agents also compete with cadmium, which is originally present in the form of clay minerals, forming soluble EDTA-Cd or DTPA-Cd complexes and other heavy metal activators. This leads to an increase in the concentration of available cadmium in the soil, making it more easily absorbed by plants and more readily leached downwards by rainwater, highlighting environmental risks – an unavoidable technical defect. In contrast, all embodiments of this invention exhibit excellent cadmium passivation effects. DTC chelating agents, while chelating rare earth elements, effectively fix heavy metal cadmium in the soil, forming extremely insoluble chelate precipitates, achieving the dual effects of "fertilization" and "pollution reduction."

[0110] As shown in Examples 4-9, the alkyl substitution of the nitrogen atom in dithiocarbamate affects the coordination binding of the chelating agent with rare earth ions, resulting in a better chelating effect compared to unsubstituted dithiocarbamate. With increasing alkyl chain length, both the biomass promotion effect and the heavy metal passivation effect show a decreasing trend, while the combination of dimethyl dithiocarbamate and diethyl dithiocarbamate is the optimal choice.

[0111] Polylactic acid, polycaprolactone, and polyhydroxyoctanoate, as coating layers, have a synergistic effect on film-forming properties, degradation rate, and controlled release performance. When adapted to the core, they have a better sustained release effect of rare earth ions.

[0112] In summary, the rare earth slow-release fertilizer provided by this invention can not only efficiently promote plant growth, but also effectively passivate heavy metals in the soil, solving the industry problem of low utilization rate and environmental pollution caused by traditional rare earth fertilizers.

[0113] Table 1

[0114] Test sample Aboveground biomass increase rate (%) Reduction rate of available cadmium content in soil (%) Example 1 80.8 27.2 Example 2 74.4 24.2 Example 3 68.8 23.0 Example 4 56.0 17.3 Example 5 51.2 15.3 Example 6 45.6 12.1 Example 7 42.4 9.3 Example 8 40.0 6.5 Example 9 39.0 1.2 Example 10 64.0 23.4 Example 11 68.0 24.6 Example 12 72.0 25.4 Comparative Example 1 34.4 -14.9 Comparative Example 2 37.6 -12.1

[0115] This invention illustrates a rare earth slow-release fertilizer, its preparation method, and its application through the above embodiments. However, this invention is not limited to the above embodiments, meaning that this invention does not necessarily rely on the above embodiments for implementation. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection and disclosure scope of this invention.

[0116] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0117] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. A rare earth slow-release fertilizer, characterized in that, The components of the rare earth slow-release fertilizer include rare earth slow-release granules and base fertilizer. The rare earth slow-release particles comprise a core formed by rare earth ions and a chelating agent, and a coating layer covering the core; the chelating agent comprises unsubstituted and / or alkyl-substituted dithiocarbamates. The basic fertilizer includes any one or a combination of at least two of nitrogen fertilizer, phosphorus fertilizer, or potassium fertilizer.

2. The rare earth slow-release fertilizer according to claim 1, characterized in that, The components of the rare earth slow-release fertilizer, by weight, include 10-20 parts of rare earth slow-release granules and 80-90 parts of basic fertilizer. The mass ratio of the core to the envelope layer is (2-8):(8-12); The molar ratio of the rare earth ions to the chelating agent is 1:(1.2-1.5).

3. The rare earth slow-release fertilizer according to claim 1 or 2, characterized in that, The chelating agent includes any one or a combination of at least two of dimethyl dithiocarbamate, diethyl dithiocarbamate, dipropyl dithiocarbamate, dibutyl dithiocarbamate or dipentyl dithiocarbamate. Preferably, the chelating agent comprises dimethyl dithiocarbamate and diethyl dithiocarbamate; Preferably, the molar ratio of dimethyl dithiocarbamate to diethyl dithiocarbamate is (1-10):(1-10).

4. The rare earth slow-release fertilizer according to any one of claims 1-3, characterized in that, The dithiocarbamate includes any one or a combination of at least two of the sodium, potassium, zinc, magnesium, manganese or ammonium salts of dithiocarbamate. Preferably, the rare earth ions include any one or a combination of at least two of the following: lanthanum ions, cerium ions, neodymium ions, praseodymium ions, samarium ions, europium ions, gadolinium ions, terbium ions, dysprosium ions, holmium ions, erbium ions, thulium ions, ytterbium ions, lutetium ions, yttrium ions, or scandium ions.

5. The rare earth slow-release fertilizer according to any one of claims 1-4, characterized in that, The components of the coating layer include any one or a combination of at least two of polylactic acid, polycaprolactone, polyhydroxyoctanoate, polyvinyl alcohol, polyvinyl acetate, polyglycolic acid, or polybutylene succinate. Preferably, the components of the coating layer include polylactic acid, polycaprolactone, and polyhydroxyoctanoate; Preferably, the mass ratio of polylactic acid, polycaprolactone, and polyhydroxyoctanoate is (1-10):(1-10):(1-8).

6. The rare earth slow-release fertilizer according to any one of claims 1-5, characterized in that, The core also includes adhesives; Preferably, the adhesive comprises 3-6% by mass in the core; Preferably, the adhesive comprises any one or a combination of at least two of carboxymethyl starch, sodium alginate, xanthan gum, chitosan, carboxymethyl chitosan, methylcellulose, hydroxypropyl methylcellulose, sodium carboxymethyl cellulose, or carboxymethyl guar gum.

7. The rare earth slow-release fertilizer according to any one of claims 1-6, characterized in that, The core has a particle size of 0.5-3 mm, and the coating layer has a thickness of 5-40 μm.

8. The method for preparing rare earth slow-release fertilizer according to any one of claims 1-7, characterized in that, The method includes: An acid solution containing rare earth ions is mixed with a chelating agent and reacted to generate a precipitate, which is then granulated to obtain core particles. The core particles are coated with a coating layer to obtain rare earth slow-release particles. The rare earth slow-release particles are mixed with basic fertilizer to obtain the rare earth slow-release fertilizer.

9. The method according to claim 8, characterized in that, The acid includes any one or a combination of at least two of nitric acid, hydrochloric acid, citric acid, oxalic acid, or sulfuric acid; Preferably, the reaction temperature is 50-60℃ and the time is 3-4 hours; Preferably, the precipitation process further includes washing and drying steps; Preferably, the granulation process further includes the addition of a binder; Preferably, the temperature of the coating process is 40-60°C.

10. The application of rare earth slow-release fertilizer according to any one of claims 1-7 in increasing crop yield.