1. The method for preparing the slow-release fertilizer by using the nanofiltration seawater to capture the carbon dioxide product is characterized by comprising the following steps of: adding a certain amount of calcium carbonate and magnesium carbonate powder obtained by trapping carbon dioxide with nanofiltration seawater into a liquid-phase coating material, then adding a dispersing agent and a surfactant to prepare a slow-release coating material with better slow-release performance, coating the slow-release coating material on the surface of the granular fertilizer, and drying to obtain the slow-release fertilizer.

2. The method for preparing a slow release fertilizer by capturing a carbon dioxide product with nanofiltration seawater according to claim 1, wherein the method comprises the following steps: the calcium carbonate and the magnesium carbonate obtained by trapping the carbon dioxide by the nanofiltration seawater are powdery calcium carbonate and magnesium carbonate with the diameter of 10nm-1000nm, and the purity of the calcium carbonate and the magnesium carbonate is 60-99%.

3. The method for preparing a slow release fertilizer by capturing a carbon dioxide product with nanofiltration seawater according to claim 1, wherein the method comprises the following steps: the liquid-phase coating material is one or a mixture of more than two of 1-20% modified starch aqueous solution, amide aqueous solution, polyvinyl alcohol aqueous solution, polylactic acid aqueous solution and sodium silicate aqueous solution.

4. The method for preparing a slow release fertilizer by capturing a carbon dioxide product with nanofiltration seawater according to claim 1, wherein the method comprises the following steps: the addition amount of the calcium carbonate and the magnesium carbonate is 1 to 30 percent of the mass of the slow-release coating material.

5. The method for preparing a slow release fertilizer by capturing a carbon dioxide product with nanofiltration seawater according to claim 1, wherein the method comprises the following steps: the dispersing agent is one or a mixture of more than two of sodium silicate, sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate, the surfactant is one or a mixture of more than two of fatty glyceride, polysorbate, stearic acid and sodium dodecyl benzene sulfonate, and the dosage of the dispersing agent and the surfactant is 0.1-2% of that of the slow-release coating material respectively.

6. The method for preparing a slow release fertilizer by capturing a carbon dioxide product with nanofiltration seawater according to claim 1, wherein the method comprises the following steps: the dosage of the slow-release coating material is 1-10% of the total amount of the fertilizer.

Background

The slow and controlled release fertilizer is a novel fertilizer and has great significance for improving the utilization rate of the fertilizer and reducing the application of the fertilizer. The slow and controlled release fertilizer has the action principle that the nutrient release curve of the fertilizer is fitted with the fertilizer requirement curve of crops by physical or chemical means, and nutrients are released when the crops require fertilizer, so that the distribution according to needs is realized, the waste of the fertilizer is reduced, and the utilization rate of the fertilizer is improved. For the coated slow-release fertilizer, the problems that the nutrient release period is too short and the coated material cannot realize biodegradation exist.

The coating of synthetic polymer (including polyurethane, polyethylene, polyvinyl chloride, polypropylene, polyvinyl alcohol, polyacrylamide, thermosetting resin, etc.) features controllable thickness, not very sensitive to soil conditions, and controlled diffusion rate of nutrients by the chemical nature of polymer, so realizing controlled release of nutrients. The coating has the defects of high price, water insolubility, organic solvent dissolution, complex coating process and environmental pollution caused by slow decomposition in soil.

CN101759497A discloses a polyurethane resin coated controlled release fertilizer, the particle size range of which is 2.0-5.0mm, the coating rate is 2-9%, the nutrient release period is 1-12 months, and the preparation method is as follows: weighing solute and adding the solute into dimethylbenzene to be uniformly stirred, preparing coating solution, then spraying the coating solution on the surface of the granulated fertilizer in a fluidized bed, quickly volatilizing the dimethylbenzene, and solidifying the solute on the surface of the fertilizer granules to form a film until the coating process is finished to obtain the polyurethane resin coated controlled release fertilizer. The method uses organic solvent, has high cost and difficult recovery, and the coating material can not be biodegraded. CN101973808B discloses a starch coating material and application thereof in coating of slow-release fertilizers. The coating material consists of starch, cellulose, humic acid and a cross-linking agent, has good film-forming and water-resistant performances, is degradable, and is environment-friendly in production and application. By adjusting the component composition of the coating material and the proportion of the coating material and the granulated fertilizer, the slow and controlled release fertilizer with different release periods can be prepared. The coated slow-release fertilizer prepared by the method has the defect of short nutrient release period. The invention discloses a degradable composite coating material, a preparation method and application thereof in slow-release fertilizers, and CN 102167647B. The composite coating material consists of starch, cellulose, polyvinyl alcohol, a cross-linking agent, a compound modifier and a powder filler, and the preparation method comprises the following steps: firstly, adding water into starch, cellulose and polyvinyl alcohol, uniformly stirring, adding a cross-linking agent, gradually heating and pasting, and then adding a compound modifier and a powder filler into the mixture, and uniformly stirring. The water-based emulsion-shaped composite coating material is uniformly sprayed on the surfaces of fertilizer particles, and is heated and dried to obtain the coated slow-release fertilizer. This method also has a problem of short nutrient release period. CN112159269A discloses a vegetable oil-based polyurethane coated fertilizer and a preparation method thereof, and the invention is characterized in that a micro-nano super-hydrophobic coating is constructed by doping nano carbon black with low surface energy, low price and easy availability in a vegetable oil-based polyurethane coating, so that the vegetable oil-based polyurethane controlled release fertilizer with an ultralow coating rate is prepared, the nutrient content of the controlled release fertilizer per unit mass is improved, and the purposes of prolonging the controlled release effect of the coated fertilizer and reducing the using amount of a coating material can be achieved. However, degradation of the coating material remains a problem.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for preparing a slow-release fertilizer by using a product of trapping carbon dioxide by using nanofiltration seawater. According to the invention, the nano-scale calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide by nanofiltration seawater are dispersed into the degradable coating material, so that a compact hydrophobic layer can be formed, and a good slow release effect can be achieved after the surface of the granular fertilizer is coated. The degradable coating materials such as starch and the like have the problem of too short nutrient release period, and the invention adds the nano calcium carbonate and magnesium carbonate into the coating materials as reinforcing materials, thus improving the water resistance and strength of the coating materials, greatly prolonging the nutrient release period of the coated fertilizer and having no influence on the biodegradability of the coating materials.

The invention adopts the following technical scheme:

the method for preparing the slow-release fertilizer by using the nanofiltration seawater to capture the carbon dioxide product is characterized by comprising the following steps of: adding a certain amount of calcium carbonate and magnesium carbonate powder obtained by trapping carbon dioxide with nanofiltration seawater into a liquid-phase coating material, then adding a dispersing agent and a surfactant to prepare a slow-release coating material with better slow-release performance, coating the slow-release coating material on the surface of the granular fertilizer, and drying to obtain the slow-release fertilizer.

The calcium carbonate and the magnesium carbonate obtained by trapping the carbon dioxide by the nanofiltration seawater are powdery calcium carbonate and magnesium carbonate with the diameter of 10nm-1000nm, and the purity of the calcium carbonate and the magnesium carbonate is 60-99%.

The liquid-phase coating material is one or a mixture of more than two of 1-20% modified starch aqueous solution, amide aqueous solution, polyvinyl alcohol aqueous solution, polylactic acid aqueous solution and sodium silicate aqueous solution.

The addition amount of the calcium carbonate and the magnesium carbonate is 1 to 30 percent of the mass of the slow-release coating material.

The dispersing agent is one or a mixture of more than two of sodium silicate, sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate, the surfactant is one or a mixture of more than two of fatty glyceride, polysorbate, stearic acid and sodium dodecyl benzene sulfonate, and the dosage of the dispersing agent and the surfactant is 0.1-2% of that of the slow-release coating material respectively.

The dosage of the slow-release coating material is 1-10% of the total amount of the fertilizer.

Compared with the conventional coating method for preparing the slow release fertilizer, the method has the following outstanding advantages:

1. the process is simple to operate, the traditional compound fertilizer manufacturing process is adopted, and additional equipment is not needed; 2. the preparation cost is low, calcium carbonate and magnesium carbonate are used as components of the coating material, and calcium and magnesium elements required for improving the growth of plants are added, so that the comprehensive cost of the fertilizer is reduced; 3. the slow release performance is good, and the nutrient release period of the prepared coated slow release fertilizer reaches the international standard; 4. the preparation method is environment-friendly, the used calcium carbonate and magnesium carbonate are low-carbon and environment-friendly, the carbon emission is reduced, the preparation and the use of the slow-release material can not generate any environmental problem, and compared with the difficult degradation of resin coating, the method is environment-friendly.

Detailed Description

The present invention will be further described with reference to examples. The examples are given in mass percent.

Example one

Powdery calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide with nanofiltration seawater accounting for 10% of the slow-release coating material are added into a modified starch solution with the mass concentration of 15% (the modified starch solution accounts for 89% of the slow-release coating material) and are uniformly stirred, the powdery calcium carbonate and the powdery magnesium carbonate with the diameter of 10nm are obtained by trapping the carbon dioxide with the nanofiltration seawater, the purity of the powdery calcium carbonate and the powdery magnesium carbonate with the diameter of 60% are obtained, and then sodium silicate accounting for 0.5% of the slow-release coating material and 0.5% of fatty acid glyceride are sequentially added to obtain uniform suspension emulsion, namely the slow-release coating material. Feeding granulated fertilizer (compound fertilizer 15-15-15) into a coating machine, spraying a slow-release coating material accounting for 2% of the weight of the fertilizer in the rolling process of the fertilizer, drying and screening to obtain the coated slow-release compound fertilizer. The strength of the obtained slow release fertilizer particles is 40N, the nutrient release period is 60 days, and the degradation period of the membrane material is 90 days.

Example two

Powdery calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide with nanofiltration seawater accounting for 15% of the slow-release coating material are added into a polyvinyl alcohol aqueous solution with the mass concentration of 20% (the polyvinyl alcohol aqueous solution accounts for 83.8% of the slow-release coating material) and are uniformly stirred, the powdery calcium carbonate and the powdery magnesium carbonate with the diameter of 1000nm are obtained by trapping the carbon dioxide with the nanofiltration seawater, the purity of the powdery calcium carbonate and the powdery magnesium carbonate with the diameter of 80% are obtained, and then sodium tripolyphosphate accounting for 0.2% of the slow-release coating material and sodium dodecyl benzene sulfonate accounting for 1% of the slow-release coating material are sequentially added to obtain uniform suspension emulsion, namely the slow-release coating material. Feeding the granular fertilizer diammonium phosphate into a coating machine, spraying a slow-release coating material accounting for 5% of the weight of the fertilizer in the rolling process of the fertilizer, drying and screening to obtain the coating slow-release DAP. The particle strength of the obtained slow release fertilizer is 45N, the nutrient release period is 90 days, and the membrane material degradation period is 120 days.

EXAMPLE III

Adding powdery calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide with nanofiltration seawater accounting for 20% of the slow-release coating material into a polylactic acid aqueous solution with the mass concentration of 10% (the polylactic acid aqueous solution accounts for 78.8% of the slow-release coating material), uniformly stirring, wherein the powdery calcium carbonate and the powdery magnesium carbonate with the diameter of 100nm are obtained by trapping the carbon dioxide with the nanofiltration seawater, the purity of the powdery calcium carbonate and the powdery magnesium carbonate with the purity of 99% are obtained, and then sequentially adding sodium pyrophosphate accounting for 1% of the slow-release coating material and 0.2% of polysorbate to obtain uniform suspension emulsion, namely the slow-release coating material. Feeding the round granular potassium sulfate into a coating machine, spraying a slow-release coating material accounting for 10% of the weight of the fertilizer in the rolling process of the fertilizer, drying and screening to obtain the coated slow-release potassium fertilizer. The particle strength of the obtained slow release fertilizer is 60N, the nutrient release period is 120 days, and the membrane material degradation period is 150 days.

Example four

Powdery calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide with nanofiltration seawater accounting for 1% of the slow-release coating material are added into a modified starch solution with the mass concentration of 1% (the modified starch solution accounts for 96.9% of the slow-release coating material) and are uniformly stirred, the powdery calcium carbonate and the powdery magnesium carbonate with the diameter of 100nm are obtained by trapping the carbon dioxide with the nanofiltration seawater, the purity of the powdery calcium carbonate and the powdery magnesium carbonate with the purity of 70% are obtained, and then sodium silicate accounting for 1% of the slow-release coating material, 1% of sodium hexametaphosphate and 0.1% of stearic acid are sequentially added to obtain uniform suspension emulsion, namely the slow-release coating material. Feeding granulated fertilizer (compound fertilizer 15-15-15) into a coating machine, spraying a slow-release coating material accounting for 1% of the weight of the fertilizer in the rolling process of the fertilizer, drying and screening to obtain the coated slow-release compound fertilizer. The particle strength of the obtained slow release fertilizer is 45N, the nutrient release period is 70 days, and the membrane material degradation period is 100 days.

EXAMPLE five

Adding powdery calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide with nanofiltration seawater accounting for 30% of the slow-release coating material into an amide aqueous solution with the mass concentration of 5% (the amide aqueous solution accounts for 67.9% of the slow-release coating material), uniformly stirring, wherein the powdery calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide with the nanofiltration seawater are powdery calcium carbonate and magnesium carbonate with the diameters of 200nm, the purity of the calcium carbonate and the magnesium carbonate is 70%, and then sequentially adding 0.1% of sodium tripolyphosphate, 1% of sodium dodecyl benzene sulfonate and 1% of polysorbate accounting for the slow-release coating material to obtain uniform suspension emulsion, namely the slow-release coating material. Feeding the granular fertilizer diammonium phosphate into a coating machine, spraying a slow-release coating material accounting for 5% of the weight of the fertilizer in the rolling process of the fertilizer, drying and screening to obtain the coating slow-release DAP. The particle strength of the obtained slow release fertilizer is 50N, the nutrient release period is 95 days, and the membrane material degradation period is 120 days.

EXAMPLE six

Powdery calcium carbonate and magnesium carbonate obtained by trapping carbon dioxide with nanofiltration seawater accounting for 20% of the slow-release coating material are added into a sodium silicate aqueous solution with the mass concentration of 10% (the sodium silicate aqueous solution accounts for 78.8% of the slow-release coating material) and are uniformly stirred, the powdery calcium carbonate and the powdery magnesium carbonate with the diameter of 100nm are obtained by trapping the carbon dioxide with the nanofiltration seawater, the purity of the powdery calcium carbonate and the powdery magnesium carbonate with the diameter of 99%, and then sodium pyrophosphate accounting for 1% of the slow-release coating material and polysorbate accounting for 0.2% of the slow-release coating material are sequentially added to obtain uniform suspension emulsion, namely the slow-release coating material. Feeding the round granular potassium sulfate into a coating machine, spraying a slow-release coating material accounting for 10% of the weight of the fertilizer in the rolling process of the fertilizer, drying and screening to obtain the coated slow-release potassium fertilizer. The particle strength of the obtained slow release fertilizer is 50N, the nutrient release period is 110 days, and the membrane material degradation period is 150 days.