Macroelement solid fertilizer and preparation method using temperature difference phase separation method

Abstract

The invention discloses a major element solid fertilizer. The major raw material is a crystal obtained by chelating iminodisuccinic acid potassium salt and divalent metal salt and then crystallizing, the divalent metal salt is at least one of nitrate containing divalent metal and sulfate containing divalent metal. The macroelement solid fertilizer provided by the invention has the function of supplying macroelement nutrients, and also has the functions of biological stimulation, buffering and water retention, soil conditioning, medium trace element supply and the like; meanwhile, original columnar or rhombic inorganic salt crystals with smooth surfaces are converted into crystals with loose structures and unsmooth surfaces on the basis of chelating crystallization, so that the obtained solid fertilizer is easily adsorbed by soil colloids, and the solid fertilizer can be better stored in soil to play a role. Meanwhile, liquid obtained after crystal separation can also be used for preparing an IDS chelate fertilizer, and comprehensive utilization of raw materials and products is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of solid fertilizers, and specifically to a macronutrient solid fertilizer and a method for preparing a macronutrient solid fertilizer by using a temperature difference phase separation method. Background Art

[0002] Solid fertilizers are a main form of base fertilizers. They have received much praise because of their wide raw material sources, low production costs, and convenient use. Therefore, they are widely valued by fertilizer manufacturers and users. Moreover, special fertilizer spreading equipment has emerged to facilitate the use of solid fertilizers. However, these characteristics also bring problems such as low entry threshold and easy occurrence of a series of negative effects for solid fertilizers. Specifically, first, in the production process, manufacturers increasingly use by-products based on cost, such as common ammonium chloride, ammonium sulfate, or amino acid industrial nitrogen concentrated waste liquid. As the raw material sources become more extensive, the residual toxic and harmful substances, such as caprolactam in industrial by-product ammonium chloride and hexamine in glycine industrial concentrated waste liquid, will also be transmitted along the ecological chain, thus causing food safety problems. Second, the influx of a large number of manufacturers has led to single product functions, and the abnormal development of the industry has caused more serious price wars. Some manufacturers, in order to maintain their benefits, do not hesitate to use toxic and harmful materials prohibited by the state, such as using industrial sewage containing heavy metals as raw materials for the production of solid fertilizers, bringing serious safety risks to solid fertilizer products. Due to the above reasons, the fertilizer efficiency of current solid fertilizers is generally poor. Although it has no impact on the field experiment results, it limits the improvement space in aspects such as increasing efficiency and improving fertilizer utilization rate.

[0003] Research findings indicate that iminodisuccinate (IDS) can play a positive role in enhancing the efficiency of solid fertilizers and improving fertilizer utilization. Firstly, the anion of tetrasodium iminodisuccinate can form chelates with metal cations within a wide pH range from weak acid to strong base. In particular, its chelating ability for medium and trace elements such as calcium, zinc, copper, iron, and manganese exceeds that of conventional chelating agents like EDTA. After being applied to the soil, it can effectively release the fixed phosphorus element, thereby simultaneously improving the utilization rates of both macronutrient phosphorus and medium and trace elements. Secondly, as a new generation of amino carboxylic acid chelating agent, tetrasodium iminodisuccinate has the advantages of being non-toxic, pollution-free, and easily biodegradable, meeting the direction of green development, etc. Finally, iminodisuccinic acid also has a certain biological stimulation function. However, there are also some problems when using tetrasodium iminodisuccinate solely as a synergist for solid fertilizers. For example, in production, to balance solubility and price, IDS is mainly in the form of sodium salt. But the demand for sodium, a beneficial element, by crops is not very high, and the excess sodium will instead cause secondary salinization of the soil. Secondly, the cost of IDS is relatively high. Adding a large amount alone will result in too high a cost for solid fertilizers. Therefore, IDS chelated fertilizers are popular in liquid fertilizers or granular fertilizers for high-end cash crops, but are restricted in ordinary solid fertilizers. If the application of IDS in solid fertilizers can be realized under the premise of controlling costs, it will have significant market value. Summary of the Invention

[0004] To address the deficiencies of the above-mentioned existing technologies, the present invention provides a macronutrient solid fertilizer. Potassium iminodisuccinate is chelated and crystallized to obtain potassium nitrate or potassium sulfate crystals containing partial potassium iminodisuccinate chelate salts and a small amount of fumarate salts. Based on the characteristics of the elements and substances contained in the crystals, it is used as the main raw material for producing macronutrient solid fertilizers, which can not only significantly improve the efficacy of macronutrient solid fertilizers, but also effectively control the product cost. Moreover, the liquid after crystallization can be used to produce potassium iminodisuccinate chelated fertilizers, realizing the comprehensive utilization of potassium iminodisuccinate and its chelate salts.

[0005] To achieve the above object, the macronutrient solid fertilizer provided by the present invention has crystals obtained by chelating potassium iminodisuccinate with a divalent metal salt and then crystallizing; the divalent metal salt is at least one of a nitrate containing a divalent metal and a sulfate containing a divalent metal.

[0006] As a limitation to the above technical solution, the crystals contain potassium nitrate or potassium sulfate, as well as potassium iminodisuccinate chelate salts remaining from co-crystallization, and fumarate salts and aspartate salts obtained by crystallizing the impurities contained in the liquid potassium iminodisuccinate product.

[0007] The solid fertilizer of the present invention uses potassium nitrate or potassium sulfate crystals obtained by chelating salts of potassium iminodisuccinate as the main raw materials; in addition to the main components potassium nitrate / salt or potassium sulfate / salt in the potassium nitrate or potassium sulfate crystals (in these materials, due to the simultaneous presence of nitrate ions, potassium ions, iminodisuccinate ions, and other metal ions, taking metal ion zinc as an example, two nitrates, potassium nitrate and zinc nitrate, will be formed in the materials and it is very difficult to completely distinguish them, so it is expressed as potassium nitrate / salt), it also contains part of the chelating salts of potassium iminodisuccinate, as well as potassium fumarate / salt and potassium aspartate / salt (with the same meaning as above) obtained by crystallization of the impurities contained in the liquid potassium iminodisuccinate product. Potassium fumarate / salt in the solid fertilizer can play the following roles: ① It can form a buffer system with the co-crystallized potassium iminodisuccinate chelate / salt and potassium aspartate / salt, making the supply of metal ions (i.e., the metal ions introduced by nitrates and sulfates) more hierarchical and having a longer sustained effect, that is, the metal ions will be continuously supplied due to the combined influence of the chelating degree and release rate of different acid radicals on them; ② The unsaturated bonds it contains can resist the oxidation of nutrient ions caused by oxygen change formed at high temperature during the processing; ③ Part of the potassium fumarate / salt will be transformed into potassium succinate / salt, a substance with certain biostimulatory effects, which has a better promoting effect on the transport of plant photosynthesis products, the regulation of soil enzyme activity, root growth, and nutrient absorption, thus making the growth of crops more sustainable. Therefore, the present invention obtains a solid fertilizer containing chelated medium and trace elements (derived from the metal ions remaining in the crystals during the separation process), organic matter (potassium iminodisuccinate / salt, fumarate, etc.), biostimulants, and macronutrients, so that the obtained fertilizer not only has the function of supplying macronutrient nutrients but also has functions such as biostimulation, buffer water retention, soil conditioning, and supply of medium and trace elements.

[0008] Most of the salts, unreacted raw materials, and a small amount of chelating salts of potassium iminodisuccinate in potassium iminodisuccinate are precipitated in the form of co-crystals through crystallization. Specifically, most of the precipitated crystals are potassium nitrate and potassium sulfate (obtained by the reaction of potassium iminodisuccinate with nitrates or sulfates), and a small part are organic salts such as potassium maleate and potassium fumarate co-crystallized with inorganic salts (obtained by the reaction of fumaric acid or maleic acid impurities contained in iminodisuccinate with nitrates or sulfates) and chelating salts of potassium iminodisuccinate. Due to the mutual interference of the co-crystallized crystals, an intersected crystal structure is formed, making the originally columnar / rhombic inorganic salt crystals become crystals with a loose structure and an uneven surface, which are more easily adsorbed by soil colloids when used as fertilizers, so that they can be better preserved in the soil and play an effect for a longer time. In addition, the mixing of multiple substances will cause uneven dissolution of the crystals, making it easier to achieve hierarchical absorption of nutrients by the roots and better improving the fertilizer efficiency utilization rate.

[0009] As a limitation to the above technical solution, the solid fertilizer further contains a wetting and dispersing agent. Preferably, the wetting and dispersing agent is a lignosulfonate dispersing agent.

[0010] The functions of the wetting and dispersing agent are not only related to the product particles and quality; more importantly: First, to avoid secondary polymerization of sulfates or nitrates and maintain a dispersed state; Second, to enhance the effect of solid fertilizers.

[0011] As a limitation to the above technical solution, the nitrate containing divalent metal is a nitric acid compound containing at least one divalent metal among calcium, magnesium, copper, iron, zinc, and manganese; the sulfate containing divalent metal is a sulfuric acid compound containing at least one divalent metal among magnesium, copper, iron, zinc, and manganese.

[0012] As a limitation to the above technical solution, the crystallization conditions are: for crystalline nitrate, control the crystallization temperature difference > 50°C; for crystalline sulfate, control the crystallization temperature difference > 45°C;

[0013] Preferably, it is required to cool the crystallization to below 5°C.

[0014] As a limitation to the above technical solution, for crystalline nitrate, control the crystallization temperature to drop from 55 - 75°C to 5 ± 1°C; for crystalline sulfate, control the crystallization temperature to drop from 50 - 70°C to 5 ± 1°C; the crystallization time is 8 - 10 h.

[0015] Meanwhile, the present invention also provides a method for preparing macronutrient solid fertilizer using the temperature difference phase separation method as described above, including the following preparation steps:

[0016] a. Prepare a chelating solution: Under stirring, add water, potassium iminodisuccinate, and divalent metal salt, mix evenly until the solid is completely dissolved to obtain an iminodisuccinic acid chelated metal salt solution; Preferably, adjust the pH of the iminodisuccinic acid chelated metal salt solution by adjusting the dosages of potassium iminodisuccinate and divalent metal salt.

[0017] b. Crystallize: Heat the iminodisuccinic acid chelated metal salt solution to the crystallization high temperature, keep it warm for 1 - 3 h, then quickly transfer it to the crystallization low temperature environment, control the crystallization time to be 8 - 10 h, and separate and collect the crystals;

[0018] c. Prepare the solid fertilizer: Weigh the precipitated crystals quantitatively, add a wetting and dispersing agent and mix evenly, then use wet grinding to make the crystal particle size reach 3 - 5 μm, and then control the moisture content to be below 5% wt through a fluidized bed to obtain loose soluble granules; continue to perform secondary processing on the soluble granules through a roll crusher to obtain the powder of macronutrient solid fertilizer.

[0019] Since the crystals formed by crystallization contain a large amount of water, no additional water needs to be added during the preparation of solid fertilizer. At the same time, wet grinding can reduce dust and easily form loose soluble particles and their aggregates. Therefore, a colloid mill can be used for wet grinding of the crystals. In the colloid mill stage, the material is generally continuously ground through 3 - 4 sets of series-connected colloid mills. The crystals can pass through the colloid mill equipment at a rate of 800 - 1200 kg / h to obtain a crystal slurry with the required particle size. In the fluidized bed stage, to meet the production needs, the length of the fluidized bed is generally not less than 16 meters, the width is generally not less than 0.5 meters, the water evaporation rate is controlled > 200 kg / h, and the crushing amount in the roll crusher stage is > 600 kg / h.

[0020] As a limitation to the above technical solution, in step a, the molar ratio of potassium iminodisuccinate to divalent metal salt is 1:1.0 - 1.1, and a potassium iminodisuccinate chelated metal salt solution with a solid content of 40 - 42% is prepared.

[0021] As a limitation to the above technical solution, during the process of separating and collecting crystals in step b, the separation temperature should not be higher than the crystallization low temperature by 10 - 15°C; and / or, the dosage of the wetting and dispersing agent used in step c is 0.1 - 0.5% of the crystal mass.

[0022] As a limitation to the above technical solution, the mass content of nitrogen, phosphorus, and potassium in the solid fertilizer is > 50%, the mass content of potassium sulfate is > 92.60% or the mass content of potassium nitrate is > 83.0%, and the sum of the mass contents of potassium iminodisuccinate chelated salt and maleate is > 5.0%.

[0023] The separation temperature directly affects the yield of the chelated fertilizer product. Keeping the temperature during the separation operation process not higher than the crystallization low temperature by 10 - 15°C, that is, the separation temperature should not be higher than 20°C, can ensure the crystal yield.

[0024] In summary, after iminodisuccinic acid potassium chelates with nitrate / sulfate containing divalent metal, nitrate / sulfate, unreacted raw materials, by-products and other impurities contained in the iminodisuccinic acid potassium product, as well as a small amount of iminodisuccinic acid potassium chelate salt, etc. are precipitated in the form of co-crystallization through crystallization. Using the co-crystallized crystals as raw materials to produce macronutrient solid fertilizers not only supplies macronutrient nutrients, but also has functions such as biological stimulation, buffering and water retention, soil conditioning, and supplying medium and micronutrients. At the same time, due to the change in the crystal structure from smooth-surface, columnar / rhombic inorganic salt crystals to loose-structured and non-smooth-surface crystals, the macronutrient fertilizers are more easily adsorbed by soil colloids, so that they can be better preserved in the soil and play a long-term role. At the same time, the liquid obtained after crystal separation can also be used to produce IDS chelate fertilizers, which not only effectively separates the salts and impurities of the raw material IDS, significantly improves the quality, stability and application performance of the chelate fertilizers, but also solves the technical problems existing in the existing liquid fertilizers, realizing the comprehensive utilization of raw materials and products. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 SEM photos of the crystalline crystal sample of Example 1 (left figure) and the commercially available potassium nitrate crystal sample (right figure) magnified 1000 times;

[0026] Figure 2 SEM photos of the crystalline crystal sample of Example 1 (left figure) and the commercially available potassium nitrate crystal sample (right figure) magnified 1500 times;

[0027] Figure 3 SEM photos of the crystalline crystal sample of Example 1 (left figure) and the commercially available potassium nitrate crystal sample (right figure) magnified 2000 times;

[0028] Figure 4 Photos of the emergence situation of the potting seedlings experiment using the solid fertilizer of Example 1, the solid fertilizer of Example 7 and the blank control on the third day after breeding and planting;

[0029] Figure 5 Photos of the emergence situation of the potting seedlings experiment using the solid fertilizer of Example 1 and the solid fertilizer of Example 7 and the blank control on the fifth day after breeding and planting. DETAILED DESCRIPTION OF THE INVENTION

[0030] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] In the experimental methods of the following examples, unless otherwise specified, they are all conventional methods. The raw materials or test materials used in the following examples, unless otherwise specified, are all typical products purchased from the market. In the quantitative tests of the following examples, three repeated experiments are set, and the results are averaged.

[0032] The solid content or moisture content of the following samples was determined by the method of HG / T 3822-2020 Water Treatment Agent Polyaspartic Acid (Salt), the pH was determined by the method of NY / T 1973 Determination of Water Insoluble Matter Content and pH in Water Soluble Fertilizer, the metal ion content was determined by the method of NY / T 1974 Determination of Copper, Iron, Manganese, Zinc, Boron, and Molybdenum Contents in Water Soluble Fertilizer, the content of nitrogen, phosphorus, and potassium was determined by the method of NY / T 1977-2010 Determination of Total Nitrogen, Phosphorus, and Potassium Contents in Water Soluble Fertilizer, and the detection of iminodisuccinic acid chelate salt, aspartate, and fumarate contents was carried out in accordance with the relevant regulations of HG / T 5749-2020 Sodium Iminodisuccinate.

[0033] Example 1

[0034] A macronutrient solid fertilizer was prepared by the temperature difference phase separation method, and the specific operations were as follows:

[0035] a. Chelating solution preparation section: Under stirring, 44.54 g of water, 416.34 g of potassium iminodisuccinate (i.e., potassium iminodisuccinate tetrapotassium, in the liquid product of potassium iminodisuccinate tetrapotassium used in each example of the present invention, its solid content is 42.20%, the conversion rate is 82.50%, and the effective content of potassium iminodisuccinate tetrapotassium is calculated to be 34.82%, used as a chelating agent), and 114.36 g of zinc nitrate hexahydrate solid with a purity of 98% were added. After continuing to stir until the zinc nitrate hexahydrate was completely dissolved, it was heated to boiling and maintained for 15 min; at this time, the pH of the system was 5.82, the solid content was 41.70%, and the molar ratio of the chelating agent to zinc was 1:1.05.

[0036] b. Crystallization section: The above-mentioned zinc iminodisuccinate chelate salt solution was naturally cooled from boiling to 65 °C, kept warm for 2 h, and then quickly transferred to a low-temperature environment of 5 °C for crystallization. The crystallization time was controlled for 9 h, separated (the temperature during the separation process was maintained at 5-15 °C), and the crystals were collected for standby;

[0037] c. Preparation of solid fertilizer section: Weigh out 400 g of the precipitated crystals (with a moisture content of 45.36% wt) quantitatively, add 1.0 g of the wetting and dispersing agent sodium lignosulfonate and mix evenly. Then, use wet grinding to reduce the crystal particle size to 3 - 5 μm (grind for 0.5 h each with three series-connected colloid mills, for a total of 1.5 h, with a grinding rate of 7500 r / min, using zirconium beads as the grinding medium, and cooling with water to keep the material temperature below 45°C). Then, control the moisture content below 5% wt through a fluidized bed to obtain loose soluble granules. Continue to process the soluble granules through a roll crusher and crush them to 100 mesh (meaning 95% of the material can pass through 100 mesh) to obtain the powder of the macronutrient solid fertilizer.

[0038] In the macronutrient solid fertilizer powder obtained according to the above process, the content of potassium oxide + nitrogen is 52.94% (calculated as potassium nitrate is 87.66%), the content of iminodisuccinic acid chelated zinc is 4.56%, the content of zinc aspartate is 1.02%, the content of zinc maleate is 2.73%, the content of sodium lignosulfonate is 0.5%, and the rest is water.

[0039] Example 2

[0040] Prepare the macronutrient solid fertilizer using the temperature difference phase separation method, and the specific operations are as follows:

[0041] a. Chelating solution preparation section: Under stirring, add 41.92 g of water, 416.34 g of potassium iminodisuccinate, and 119.81 g of solid zinc nitrate hexahydrate with a purity of 98%. Continue to stir until the zinc nitrate hexahydrate is completely dissolved, then heat to boiling and maintain for 15 min. At this time, the pH of the system is 5.62, the solid content is 41.94%, and the molar ratio of the chelating agent to zinc is 1:1.10.

[0042] b. Crystallization section: Naturally cool the above-mentioned iminodisuccinic acid chelated zinc salt solution to 55°C, keep it warm for 3 h, then quickly transfer it to a low-temperature environment of 5°C for crystallization, control the crystallization time to 8 h, separate (the temperature during the separation process is maintained at 5 - 15°C), and collect the crystals for standby;

[0043] c. Preparation of solid fertilizer section: The material dosage and operation process are the same as those in Example 1.

[0044] In the macronutrient solid fertilizer powder obtained according to the above process, the content of potassium oxide + nitrogen is 53.62% (calculated as potassium nitrate is 88.78%), the content of iminodisuccinic acid chelated zinc is 4.02%, the content of zinc aspartate is 0.95%, the content of zinc maleate is 2.43%, the content of sodium lignosulfonate is 0.5%, and the rest is water.

[0045] Example 3

[0046] Prepare the macronutrient solid fertilizer using the temperature difference phase separation method, and the specific operations are as follows:

[0047] a. Chelating solution preparation section: Under stirring, add 52.30 g of water, 416.34 g of potassium iminodisuccinate, and 108.91 g of solid zinc nitrate hexahydrate with a purity of 98%. Continue stirring until the zinc nitrate hexahydrate is completely dissolved, then heat to boiling and maintain for 15 min. At this time, the pH of the system is 6.02, the solid content is 40.93%, and the molar ratio of the chelating agent to zinc is 1:1.

[0048] b. Crystallization section: Naturally cool the above-mentioned zinc iminodisuccinate chelate solution to 75 °C, keep it warm for 1 h, then quickly transfer it to a low-temperature environment of 5 °C for crystallization. Control the crystallization time to be 10 h, separate (the temperature during the separation process is maintained at 5 - 15 °C), and collect the crystals for standby.

[0049] c. Solid fertilizer preparation section: The material dosage and operation process are the same as those in Example 1.

[0050] In the macronutrient solid fertilizer powder obtained according to the above process, the content of potassium oxide + nitrogen is 51.54% (calculated as potassium nitrate is 85.34%), zinc iminodisuccinate chelate is 5.23%, zinc aspartate is 1.22%, zinc maleate content is 2.78%, sodium lignosulfonate is 0.5%, and the rest is water.

[0051] Example 4

[0052] Prepare macronutrient solid fertilizer by using the temperature difference phase separation method, and the specific operations are as follows:

[0053] a. Chelating solution preparation section: Under stirring, add 57.33 g of water, 250 g of potassium iminodisuccinate, and 38.90 g of solid manganese sulfate monohydrate with a purity of 99%. Continue stirring until the manganese sulfate monohydrate is completely dissolved, then heat to boiling and maintain for 15 min. At this time, the pH of the system is 6.50, the solid content is 40.51%, and the molar ratio of the chelating agent to manganese is 1:1.05.

[0054] b. Crystallization section: The material dosage and operation process are the same as those in Example 1.

[0055] c. Solid fertilizer preparation section: The wetting and dispersing agent is selected as calcium lignosulfonate, and the dosage is 0.70 g. The dosage of other materials and the operation process are the same as those in Example 1.

[0056] In the macronutrient solid fertilizer powder obtained according to the above process, the potassium oxide content is 50.13% (calculated as potassium sulfate is 94.26%), manganese iminodisuccinate chelate is 1.43%, manganese aspartate is 1.13%, manganese maleate content is 1.58%, calcium lignosulfonate is 0.35%, and the rest is water.

[0057] Example 5

[0058] Prepare macronutrient solid fertilizer by using the temperature difference phase separation method, and the specific operations are as follows:

[0059] a. Chelating solution preparation section: Under stirring, add 65.32 g of water, 350 g of potassium iminodisuccinate, and 79.26 g of solid calcium nitrate tetrahydrate with a purity of 95%. Continue stirring until the calcium nitrate tetrahydrate is completely dissolved, then heat to boiling and maintain for 20 min. At this time, the pH of the system is 5.16, the solid content is 41.00%, and the molar ratio of the chelating agent to calcium is 1:1.05.

[0060] b. Crystallization section: The material dosage and operation process are the same as those in Example 1.

[0061] c. Solid fertilizer preparation section: Select calcium lignosulfonate as the wetting and dispersing agent, with a dosage of 0.50 g, and the dosages of other materials and the operation process are the same as those in Example 1.

[0062] In the macronutrient solid fertilizer powder obtained according to the above process, the content of potassium oxide + nitrogen is 50.94% (calculated as potassium nitrate is 84.34%), calcium chelated by iminodisuccinic acid is 4.30%, calcium aspartate is 2.02%, the content of calcium maleate is 4.08%, calcium lignosulfonate is 0.25%, and the rest is water.

[0063] Example 6

[0064] Prepare macronutrient solid fertilizer by using the temperature difference phase separation method, and the specific operations are as follows:

[0065] a. Chelating solution preparation section: Under stirring, add 108.69 g of water, 608.38 g of potassium iminodisuccinate, 78.26 g of solid calcium nitrate tetrahydrate with a purity of 95%, and 62.38 g of ferrous sulfate heptahydrate with a purity of 95%. Continue stirring until completely dissolved, then heat to boiling and maintain for 15 min. At this time, the pH of the system is 5.84, the solid content is 40.25%, and the molar ratio of the chelating agent to calcium and iron is 2:1:1.

[0066] b + c. Crystallization section and solid fertilizer preparation section: The material dosage and operation process are the same as those in Example 1.

[0067] In the macronutrient solid fertilizer powder obtained according to the above process, the content of potassium oxide + nitrogen is 50.54%, the iminodisuccinic acid chelate salt is 4.23%, the aspartate salt is 1.22%, the content of maleate salt is 1.78%, sodium lignosulfonate is 0.5%, and the rest is water.

[0068] Example 7

[0069] Prepare macronutrient solid fertilizer by using the temperature difference phase separation method, and the specific operations are as follows:

[0070] a. Chelating solution preparation section: While stirring, add 30.30 g of water, 350 g of potassium iminodisuccinate, and 70.70 g of solid magnesium nitrate hexahydrate with a purity of 98%. Continue stirring until the magnesium nitrate hexahydrate is completely dissolved, then heat to boiling and maintain for 20 min. At this time, the pH of the system is 5.04, the solid content is 41.00%, and the molar ratio of the chelating agent to magnesium is 1:1.0.

[0071] b. Crystallization section: The material dosage and operation process are the same as those in Example 1.

[0072] c. Solid fertilizer preparation section: The wetting and dispersing agent is selected as calcium lignosulfonate with a dosage of 0.50 g. The dosages of other materials and the operation process are the same as those in Example 1.

[0073] In the macronutrient solid fertilizer powder obtained according to the above process, the content of potassium oxide + nitrogen is 51.23% (calculated as potassium nitrate is 84.82%), the content of iminodisuccinic acid chelated magnesium is 4.65%, the content of magnesium aspartate is 1.78%, the content of magnesium maleate is 3.62%, the content of calcium lignosulfonate is 0.25%, and the rest is water.

[0074] Example 8

[0075] To prepare macronutrient solid fertilizer by the temperature difference phase separation method, the specific operations are as follows:

[0076] a + b. The material dosage and operation process of the chelating solution preparation section and the crystallization section are the same as those in Example 1.

[0077] c. Solid fertilizer preparation section: Weigh 400 g of the precipitated crystals (with a moisture content of 45.36% wt). Without adding a wetting and dispersing agent, wet-grind the crystals to reduce the particle size (grind for 0.75 h each with three series-connected colloid mills, a total of 2.25 h, the grinding rate is 7500 r / min, using zirconium beads as the grinding medium, and cooling with water to keep the material below 45 °C). The rest of the operation process is the same as that in Example 1 to obtain the powder of macronutrient solid fertilizer.

[0078] In the macronutrient solid fertilizer powder obtained according to the above process, the content of potassium oxide + nitrogen is 52.94% (calculated as potassium nitrate is 87.66%), the content of iminodisuccinic acid chelated zinc is 4.66%, the content of zinc aspartate is 1.12%, the content of zinc maleate is 2.53%, and the rest is water.

[0079] Comparative Example 1

[0080] To prepare macronutrient solid fertilizer by the temperature difference phase separation method, the difference from Example 1 is only that the molar ratio of the chelating agent to the divalent metal ion is not in the range of 1:1.0 - 1.1. The specific operations are as follows:

[0081] a. Chelating solution preparation section: Under stirring, add 416.34 g of potassium iminodisuccinate and 136.14 g of zinc nitrate hexahydrate solid with a purity of 98%. Continue stirring until the zinc nitrate hexahydrate is completely dissolved, then heat to boiling and maintain for 15 min. At this time, the pH of the system is 4.96, the solid content is 47.48%, and the ratio of chelating agent to zinc is 1:1.29.

[0082] b + c. Crystallization section and solid fertilizer preparation section: The material dosage and operation process are the same as those in Example 1.

[0083] In the macronutrient solid fertilizer powder obtained according to the above process, the content of potassium oxide + nitrogen is 56.00% (calculated as potassium nitrate is 92.72%), zinc chelated by iminodisuccinic acid is 1.56%, zinc aspartate is 0.23%, zinc maleate content is 0.53%, sodium lignosulfonate is 0.5%, and the rest is water.

[0084] In this Comparative Example 1, the solid fertilizer contains less crystals accompanied by potassium iminodisuccinate impurities, resulting in the inhibition of the long-term efficacy performance of the solid fertilizer, and the promotion effect on soil enzymes also fails to meet the expectations. At the same time, it will also make the liquid fertilizer unstable.

[0085] Comparative Example 2

[0086] The macronutrient solid fertilizer is prepared by the temperature difference phase separation method. The difference from Example 1 is only that the crystallization time is insufficient. The specific operations are as follows:

[0087] a. Chelating solution preparation section: The material dosage and operation process are the same as those in Example 1.

[0088] b. Crystallization section: The above-mentioned zinc chelated iminodisuccinate solution is naturally cooled from boiling to 65 °C, kept warm for 5 h, then quickly transferred to a low-temperature environment of 5 °C for crystallization, control the crystallization time to 6 h, and separate (the temperature during the separation process is kept at 5 - 15 °C) to collect the crystals for standby.

[0089] c. Solid fertilizer preparation section: The material dosage and operation process are the same as those in Example 1.

[0090] In the macronutrient solid fertilizer powder obtained according to the above process, the content of potassium oxide + nitrogen is 50.94% (calculated as potassium nitrate is 84.34%), zinc chelated by iminodisuccinic acid is 8.52%, zinc aspartate is 1.74%, zinc maleate content is 2.69%, sodium lignosulfonate is 0.5%, and the rest is water.

[0091] In this Comparative Example 2, insufficient crystallization time will lead to difficult separation of the liquid and crystals, resulting in excessive retention of zinc chelated by iminodisuccinic acid in the crystals, ultimately leading to a decrease in the nutrients of the solid fertilizer and a decrease in the yield of the liquid fertilizer, thus increasing the cost.

[0092] Comparative Example 3

[0093] The preparation of the macronutrient solid fertilizer by the temperature difference phase separation method is different from that of Example 1 only in the high temperature of the crystallization section (i.e., the crystallization temperature difference is small). The specific operations are as follows:

[0094] a. Chelating solution preparation section: The material dosage and operation process are the same as those in Example 1;

[0095] b. Crystallization section: The above-mentioned iminodisuccinic acid chelated zinc salt solution is naturally cooled from boiling to 40 °C. After holding for 2 h, it is quickly transferred to a low-temperature environment at 5 °C for crystallization. The crystallization time is controlled for 9 h, and then separated (the temperature is maintained at 5-15 °C during the separation process), and the crystals are collected for standby;

[0096] c. Solid fertilizer preparation section: The material dosage and operation process are the same as those in Example 1.

[0097] In the macronutrient solid fertilizer powder obtained according to the above process, the content of potassium oxide + nitrogen is 50.25% (calculated as potassium nitrate is 83.20%), iminodisuccinic acid chelated zinc is 8.96%, zinc aspartate is 2.02%, the content of zinc maleate is 2.73%, sodium lignosulfonate is 0.5%, and the rest is water.

[0098] The low high temperature of crystallization in this Comparative Example 3 directly affects the crystallization efficiency and the content of chelated salts therein. Similarly, if the high temperature of crystallization is too high, it will also lead to a decrease in crystallization efficiency and an increase in the content of chelated salts, and the crystallization effect is worse than that of Comparative Example 2.

[0099] Comparative Example 4

[0100] The preparation of the macronutrient solid fertilizer by the temperature difference phase separation method is different from that of Example 1 only in that the low crystallization temperature in the crystallization section is at room temperature. The specific operations are as follows:

[0101] a. Chelating solution preparation section: The material dosage and operation process are the same as those in Example 1;

[0102] ② Crystallization section: The above-mentioned iminodisuccinic acid chelated zinc salt solution is naturally cooled to 65 °C. After holding for 2 h, it is crystallized at room temperature (the indoor temperature of the laboratory is 25-35 °C), and the crystallization time is controlled for 9 h to collect the crystals for standby;

[0103] c. Solid fertilizer preparation section: The material dosage and operation process are the same as those in Example 1.

[0104] In the macronutrient solid fertilizer powder obtained according to the above process, the content of potassium oxide + nitrogen is 57.94% (calculated as potassium nitrate is 95.93%), the content of zinc chelated by iminodisuccinic acid is 0.22%, the content of zinc aspartate is 0.13%, the content of zinc maleate is 0.52%, the content of sodium lignosulfonate is 0.5%, and the rest is water.

[0105] Application Example 1

[0106] For the electron microscopy observation experiment, the crystalline crystals obtained in Example 1 and commercially available potassium nitrate crystals were observed for their appearance and internal structure at different magnifications under a transmission electron microscope (TEM), as shown in the appendix Figures 1 to 3 .

[0107] The results showed that: ① The crystals obtained in Example 1 had a loose and multi-void structure. Among them, zinc chelated by iminodisuccinic acid, zinc maleate, and zinc aspartate penetrated into the structure, preventing the formation of characteristic crystals during the crystallization process, increasing the efficiency of co-crystallization, and thus resulting in more of the above substances in the solid fertilizer obtained in the subsequent processing. The occurrence of this phenomenon would improve the nutrient utilization rate; ② The activation degree of the crystal surface layer in Example 1 was increased, making it easier to exert the fertilizer effect, making it easier to combine with soil colloids, and thus facilitating nutrient storage; ③ The multi-void structure on the crystal surface layer of Example 1 was more likely to combine with synergistic substances in the environment, thus better realizing the hierarchy and sustainability of nutrient supply.

[0108] Compared with commercially available conventional potassium nitrate crystals, the crystals in Example 1 had changes in the crystallization morphology, and there were obvious traces of activation of the crystal surface layer structure.

[0109] Application Example 2

[0110] For the comparison of wetting angle data, the solid fertilizers produced in Example 1 and Example 8 were respectively diluted 500 times, and the wetting angle was measured by the static sessile drop method and the surface tension was measured by the pendant drop method. At the same time, the data of pure water was measured. The specific measurement data are shown in Table 1.

[0111] Judgment basis: The lower the liquid surface tension and the smaller the wetting angle, the easier the liquid is to wet the solid surface and the easier it is to absorb.

[0112] Table 1 Comparison data of wetting angles

[0113] Processing Test Conditions / °C Wetting Angle / ° Surface Tension / mN / cm Example 1 20 21 17.5 Example 8 20 48 45.6 Pure Water 20 87 72.8

[0114] From the data in Table 1, it can be seen that the solid fertilizer in Example 1 can effectively reduce the surface tension and wetting angle of water, thus greatly improving the fertilizer effect and increasing its utilization rate.

[0115] Application Example 3

[0116] Corn germination period experiment comparison: The solid fertilizers produced in Example 1 and Example 7 were used for seed soaking during the seedling stage of corn, and their effects on corn germination and seedling growth were compared with those of soaking seeds in clear water.

[0117] This experiment was carried out in the agricultural bioassay laboratory of Hebei Xietong Chemical Co., Ltd. Seed soaking treatments of Example 1 (containing IDS-Zn), Example 7 (containing IDS-Mg), and soaking seeds in clear water were set up, and were respectively denoted as: IDS-Zn, IDS-Mg, and CK. One concentration was set for the experiment, which was an aqueous solution of 100 mg / kg (calculated based on the chelate); the experiment was set with 4 replicates, and the number of treatments in each replicate experiment was 6 pots × 10 seeds; treatment plan: Select 100 grams of corn seeds (pre-experiment germination rate 94.50%), place them in 250 mL of the above solution, soak the seeds statically for 2 h, then drain the water for standby; plant the treated seeds at a density of 10 seeds per small pot, and investigate the emergence rate and plant height after planting, and the method was carried out with reference to the relevant requirements of general agronomy; the data was statistically sorted using the method of comprehensive statistical analysis, and the one-way analysis of variance was continued using the SPSS 20.0 data analysis system, and the Dunckan method was used for significance test of differences; the comprehensive data results are shown in Table 2.

[0118] Table 2 Comparison of corn germination experiments

[0119]

[0120] It can be seen from the data in Table 2 that in terms of germination rate, after soaking seeds with the solid fertilizers obtained in Example 1 and Example 7, the germination rate of corn increased significantly. The peak germination rate appeared around 1 day, while the peak of the CK treatment appeared on the 3rd day. This made the germination of corn very concentrated, which was conducive to obtaining strong seedlings. The reason is that both solid fertilizers in the two treatments contain a certain amount (4.56%, 4.65%) of iminodisuccinic acid chelate salts. After soaking the seeds with these substances, it can promote the accelerated synthesis of hydrolases in the aleurone layer of corn seeds; the synthesized protease, amylase, etc. are transported to the endosperm of corn, promoting the decomposition of nutrients into small molecular substances and assisting their transportation to the radicle, stimulating the growth of the radicle, and then accelerating the germination of the seeds. A similar phenomenon also occurred in terms of the average plant height, as shown in the appendix Figure 4 、 5 , which corroborated the above principle. It can be seen that using the solid fertilizers obtained in Example 1 and Example 7 can effectively promote the germination of corn seeds and the growth of seedlings.

[0121] Application Example 4

[0122] Solid fertilizer application test: Field tests were carried out on the solid fertilizers prepared in Example 1 and Comparative Examples 1-4.

[0123] Apply 20 kg / 667 m of solid fertilizer during sowing2 And diammonium phosphate 25kg / 667m 2 As base fertilizer, the solid fertilizers of Example 1 and Comparative Examples 1 to 4 and the base fertilizer of diammonium phosphate were applied to the production of summer corn in different test areas, which were recorded as T1 to T5. At the same time, 20 kg / 667 m3 of ordinary potassium nitrate was added. 2 and diammonium phosphate 25kg / 667m 2 The above treatments were recorded as separate test plots, each with an area of ​​300m 2 Each treatment was repeated three times, and all experimental areas were randomized (randomized blocks refer to random arrangement to eliminate experimental errors).

[0124] This experiment was conducted in Gaocheng District, Shijiazhuang City, Hebei Province (114°52′49E, 38°01′27N). The experimental area was a typical brown soil with a soil organic matter content of 1.93%, total nitrogen of 1.23g / kg, available phosphorus of 31.57mg / kg, and available potassium of 117.23mg / kg. It was a low organic matter and medium nitrogen, phosphorus and potassium level plot. The experimental period was from the sowing period of summer corn to the harvest of corn. The yield of each plot was measured separately. Among the measured items, N, P 2 O 5 and K 2 The determination of O was carried out in accordance with the relevant provisions of the "Tutorial on Physical and Chemical Analysis of Soil, Water and Plants", and the nutrient recovery rate was calculated in accordance with the nutrient usage to characterize the fertilizer utilization rate. The other indicators were designed and analyzed in accordance with the relevant requirements of the General Introduction to Agronomy, and then the comprehensive statistical analysis method was used to verify the effect of solid fertilizer. SPSS20.0 data analysis system was continued to be used for one-way analysis of variance and the Dunckan method was used for significant difference test; the comprehensive data results are shown in Table 3.

[0125] Table 3 Comparison of summer corn yield and nutrients with solid fertilizer

[0126]

[0127]

[0128] From the data in Table 3, we can see that in terms of nutrient recovery rate of each treatment, T1 treatment was significantly higher than the other treatments, indicating that the comprehensive efficiency of T1 treatment was significant; although some comparative treatments, such as T3 and T4, 2 O 5 and K 2The O nutrient recovery rate is comparable to that of the T1 treatment. However, since the content of iminodisuccinic acid chelate salts in it (8.52%, 8.96%) is significantly higher than that of the T1 treatment (4.56%), it has no advantage in terms of cost (the selling price of zinc iminodisuccinate is 32 - 36 yuan / kg) (the price difference per ton of solid fertilizer > 1250 yuan). Considering comprehensively, in terms of nutrient recovery rate, the T1 treatment is the optimal solution among all treatments.

[0129] In addition to the nutrient recovery rate, in terms of the yield in Table 3, the T1 treatment is significantly higher than other treatments. Although in terms of 1000-grain weight and the number of grains per ear, some treatments (T3, T4) have comparable effects, but overall they still have no advantage. Considering the fertilizer recovery rate data comprehensively, it can be judged that in the experiment involved in Application Example 4, T1 has significant advantages both in terms of yield and nutrient recovery rate.

[0130] To sum up, the solid fertilizer of the present invention not only has the function of supplying macronutrient nutrients, but also has functions such as biological stimulation, buffering and water retention, soil conditioning, and supplying medium and trace elements. At the same time, based on chelation crystallization, the original columnar or rhombic inorganic salt crystals with a smooth surface are transformed into crystals with a loose structure and a non-smooth surface, making the obtained solid fertilizer easily adsorbed by soil colloids, so that it can be better preserved in the soil and play its effect.

Claims

1. A macronutrient solid fertilizer, characterized in that: The main raw material of the solid fertilizer is crystals obtained by chelating potassium iminodisuccinate with a divalent metal salt; the divalent metal salt is at least one of a nitrate containing a divalent metal and a sulfate containing a divalent metal.

2. The macronutrient solid fertilizer according to claim 1, characterized in that: The crystals contain potassium nitrate or potassium sulfate, and also contain potassium iminodisuccinate chelate salt remaining from co-crystallization, as well as butenedioate and aspartate salts obtained from crystallization of impurities contained in the liquid potassium iminodisuccinate product.

3. The macronutrient solid fertilizer according to claim 1, characterized in that: The solid fertilizer also contains a wetting and dispersing agent. Preferably, the wetting and dispersing agent is a lignin sulfonate dispersant.

4. The macronutrient solid fertilizer according to claim 1, characterized in that: The nitrate containing a divalent metal is a nitrate compound containing at least one divalent metal of calcium, magnesium, copper, iron, zinc, and manganese; the sulfate containing a divalent metal is a sulfate compound containing at least one divalent metal of magnesium, copper, iron, zinc, and manganese.

5. The macronutrient solid fertilizer according to claim 1, characterized in that: The crystallization conditions are: Crystallize nitrate, control the crystallization temperature difference> 50℃; Crystallize sulfate, control the crystallization temperature difference>45℃; Preferably, the crystallization temperature is lowered to below 5°C.

6. The macronutrient solid fertilizer according to claim 4, characterized in that: For crystallizing nitrate, control the crystallization temperature from 55-75℃ to 5±1℃; for crystallizing sulfate, control the crystallization temperature from 50-70℃ to 5±1℃; the crystallization time is 8-10h.

7. A method for preparing a macronutrient solid fertilizer according to any one of claims 1 to 6 by using a temperature difference phase separation method, characterized in that: The method comprises the following preparation steps: a. preparing a chelating solution: adding water, potassium iminodisuccinate and a divalent metal salt under stirring, mixing evenly and until the solid is completely dissolved, to obtain an iminodisuccinic acid chelated metal salt solution; preferably, the pH of the iminodisuccinic acid chelated metal salt solution is regulated by adjusting the dosage of potassium iminodisuccinate and the divalent metal salt; b. Crystallization: Heat the iminodisuccinic acid chelate metal salt solution to a crystallization high temperature, keep it warm for 1 to 3 hours, then quickly transfer it to a crystallization low temperature environment, control the crystallization time to 8 to 10 hours, and separate and collect the crystals; c. Preparation of solid fertilizer: quantitatively weigh the precipitated crystals, add a wetting dispersant and mix well, wet-grind the crystals to reduce the particle size to 3-5 μm, and then control the moisture content below 5% wt through a fluidized bed to obtain loose soluble granules; continue to perform secondary processing on the soluble granules through a double-roll mill to obtain a powder of a large amount of element solid fertilizer.

8. The method for preparing a large amount of element solid fertilizer by temperature difference phase separation method according to claim 7, characterized in that: In step a, the molar ratio of potassium iminodisuccinate to divalent metal salt is 1:1.0-1.1, and an iminodisuccinic acid chelated metal salt solution with a solid content of 40-42% is prepared.

9. The method for preparing a large amount of element solid fertilizer by utilizing temperature difference phase separation method according to claim 7, characterized in that: In the process of separating and collecting the crystals in step b, the separation temperature is maintained at not higher than the crystallization low temperature by 10-15° C.; and / or, the amount of the wetting and dispersing agent used in step c is 0.1-0.5% of the mass of the crystals.

10. The method for preparing a large amount of element solid fertilizer by using a temperature difference phase separation method according to claim 7, characterized in that: The mass content of nitrogen, phosphorus and potassium in solid fertilizer is greater than 50%, the mass content of potassium sulfate is greater than 92.60% or the mass content of potassium nitrate is greater than 83.0%, and the sum of the mass contents of potassium iminodisuccinate chelate and butenedioate is greater than 5.0%.

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