Method for preparing polymerized calcium-magnesium fertilizer from yellow phosphorus slag

Abstract

The invention belongs to the technical field of fertilizers. The invention discloses a method for preparing a polymerized calcium-magnesium fertilizer by using yellow phosphorus slag, and aims to solve the technical problems that the pH value of the yellow phosphorus slag as a fertilizer raw material is too high, and effective calcium, magnesium and silicon elements of the yellow phosphorus slag are difficult to utilize. A product obtained by reaction of the yellow phosphorus slag and the raffinate acid is used as a raw material, and phosphorus, calcium and magnesium elements in the phosphoric acid slag and the yellow phosphorus slag are fully utilized to form phosphorus, calcium and magnesium elements in a polymerization state. In terms of P2O5, the polymerization rate of the polymerized calcium-magnesium fertilizer is greater than or equal to 80%. Phosphorus in the prepared product has a slow release property, when the product is applied to soil, the phosphorus in the product cannot be rapidly fixed but slowly releases orthophosphate to meet the requirements of crops, magnesium and calcium are not prone to being greatly leached by water due to the action of polyphosphoric acid, and the product is especially suitable for crops with high requirements for calcium and magnesium.

Description

Technical Field

[0001] The invention relates to the technical field of fertilizers, and in particular to a method for preparing polymerized calcium-magnesium fertilizer by using yellow phosphorus slag. Background Art

[0002] Yellow phosphorus slag is a solid waste produced when yellow phosphorus is produced by the electric furnace method. For every ton of yellow phosphorus produced by the electric furnace method, about 8 to 10 tons of phosphorus slag will be produced as a by-product. Ca0 and SiO2 are the main components of yellow phosphorus slag. At the same time, during the reaction process, because the minerals contain impurities and the reaction cannot be completely carried out, the impurities and unreacted minerals will be discharged with the molten slag, so it also contains a small amount of Mg0, P205, and other substances. Yellow phosphorus slag contains rich silicon and calcium resources, and these elements each have their own unique role in the life metabolism of crops. With the continuous development of my country's phosphorus chemical industry and the continuous increase in social demand, the accumulation problem of yellow phosphorus slag is becoming more and more serious.

[0003] At present, the utilization of yellow phosphorus slag in my country is mainly reflected in the following aspects:

[0004] First, yellow phosphorus slag is used as a raw material for preparing building materials, ceramic materials and thermal insulation materials. Although the above method can consume a part of the yellow phosphorus slag and alleviate the situation of large-scale accumulation of yellow phosphorus slag to a certain extent, it does not make full use of the yellow phosphorus slag, resulting in a waste of some useful elements in the yellow phosphorus slag.

[0005] Second, using the alkalinity of yellow phosphorus slag to neutralize industrial waste acid, Chinese patent publication number CN102259969B discloses "a method for neutralizing titanium dioxide waste acid and wastewater using yellow phosphorus slag". This method is to directly add yellow phosphorus slag to the titanium dioxide waste acid and / or wastewater according to the reaction amount and stir, and then add high calcium slag or calcium oxide to adjust the pH to 6-9. Due to the addition of high calcium slag, the final liquid is weakly alkaline, so that the impurity ions in the titanium dioxide waste acid and / or wastewater are precipitated together. After the precipitation is complete, the supernatant is recycled or directly discharged; the precipitate is directly transported to the slag yard for disposal, which will not cause pollution to the environment. The raw materials of this method are all industrial wastes that pollute the environment. The alkalinity of yellow phosphorus slag is used to neutralize industrial waste acid, but the effective phosphorus, calcium, magnesium, silicon and other beneficial elements in the yellow phosphorus slag and waste acid are not fully utilized.

[0006] Third, yellow phosphorus slag is used to prepare fertilizers through certain technical means, among which the existing technologies include: Chinese patent publication number CN113582780A discloses "a phosphorus-rich and silicon-rich compost product prepared by adding yellow phosphorus slag and its production method", a phosphorus-rich and silicon-rich organic fertilizer and its preparation method, the invention prepares phosphorus-rich and silicon-rich compost products by adding yellow phosphorus slag, including the following steps: after adding 5-20% (w:w) yellow phosphorus slag to livestock and poultry manure, evenly mixing with compost conditioner, performing high-temperature aerobic composting, and obtaining compost products after heating period, high temperature period, cooling period and decomposition period. The compost products produced by this method have a total phosphorus content higher than 2%, a total silicon content higher than 10%, a citric acid-soluble phosphorus content not less than 0.5%, and a citric acid-soluble silicon content not less than 0.9%. The implementation of this patent can consume a certain amount of yellow phosphorus slag and prepare fertilizer, but the prepared product only utilizes the silicon element of the yellow phosphorus slag, and contains less effective calcium, magnesium and phosphorus, and has a low nutrient content. The product takes effect slowly and has a poor agronomic application effect.

[0007] Although the comprehensive utilization of yellow phosphorus slag involves many fields, the overall utilization rate is not high, and there is still a large amount of yellow phosphorus slag accumulation. Since yellow phosphorus slag is rich in silicon, calcium and other nutrients that can be absorbed and utilized by crops, it has great development potential as a fertilizer. However, the high pH of yellow phosphorus slag prevents it from being directly mixed with water-soluble fertilizers. In order to make full use of the calcium, magnesium and silicon nutrients rich in yellow phosphorus slag, it is necessary to solve the problems of low utilization rate of yellow phosphorus slag and excessively high pH.

[0008] In summary, it is necessary to develop a method that can fully utilize the useful elements in yellow phosphorus slag to prepare a product with slow-release phosphorus, phosphorus that is not easily fixed, calcium and magnesium that are not easily leached and easily absorbed by crops, which has important economic and environmental significance. Summary of the invention

[0009] The purpose of the present invention is to provide a method for preparing polymerized calcium-magnesium fertilizer from yellow phosphorus slag, so as to solve the environmental pollution caused by the large amount of accumulation of yellow phosphorus slag and the technical problem that in the prior art, when yellow phosphorus slag is used as a raw material to prepare fertilizer, ammonia volatilization and phosphorus degradation are generated due to its excessively high alkalinity, so as to obtain polymerized phosphorus, calcium and magnesium nutrient elements with better effectiveness.

[0010] Terminology Note:

[0011] The effective phosphorus, effective magnesium and effective calcium in the present invention refer to the phosphorus (measured in P2O5), magnesium (measured in MgO) and calcium content (measured in CaO) that can be extracted by EDTA under alkaline conditions of pH 12 to 13.

[0012] The polymerization rate of the present invention refers to the percentage of the effective phosphorus (in terms of P2O5) in the product minus the phosphorus in the form of orthophosphate (in terms of P2O5) to the effective phosphorus (in terms of P2O5).

[0013] The scheme of the present invention is

[0014] A method for preparing polymerized calcium-magnesium fertilizer from yellow phosphorus slag, characterized in that it comprises the following steps:

[0015] 1) Initial reaction

[0016] Yellow phosphorus slag and raffinate acid are used as raw materials and mixed evenly at room temperature to obtain a reaction mixture;

[0017] 2) Calcination

[0018] calcining the reaction mixture in a mixing reactor;

[0019] 3) Reaction

[0020] In the mixed reactor reaction, when the phosphoric acid polymerization rate is ≥80%, the reaction is stopped and the product is ground to obtain polymerized calcium magnesium fertilizer; the phosphoric acid polymerization rate is calculated as P2O5.

[0021] In the step 3), the reaction temperature is 100-800°C. As the reaction temperature increases, the polyphosphorus content in the product gradually increases from 1% to 26%, and the polymerization rate in the product gradually increases from 5% to 84%. This process can be regarded as the transformation of positive P2O5 to dimer and trimer forms. When the temperature continues to increase, the polymerization rate increases less and the orthophosphate is exhausted. Among them, the calcination temperature has a greater influence on the polymerization rate of the polymerized neutralized product. When the temperature is lower than 200°C, the product polymerization rate is less than 20%, and when the temperature is higher than 500°C, the product polymerization rate is greater than 80%.

[0022] As the reaction temperature increases, the effective phosphorus and total phosphorus contents remain basically unchanged, while the effective calcium content gradually increases from 14% to 22%, reaching a maximum at 600°C, and then begins to decrease from 22% to 16%. The effective magnesium content gradually increases from 2.2 to 3.16% as the temperature increases.

[0023] As a preferred technical solution, the calcination temperature in step 2) is 400-600°C.

[0024] As a preferred technical solution, the calcination temperature in step 2) is 450-550°C.

[0025] As a preferred technical solution, the calcination time in step 2) is 30 to 120 minutes.

[0026] As a preferred technical solution, the calcination time in step 2) is 40 to 60 minutes. As the polymerization time increases, the degree of polymerization of phosphorus in the reaction product gradually increases. When the time is less than 20 minutes, the phosphoric acid polymerization rate is less than 60%. As the time increases, the polymerization rate increases slowly. After 40 minutes, it is basically maintained at 82%. If the reaction time continues to increase, the production cost will also increase. Obviously, it is unwise to increase the polymerization time in exchange for a small increase in the degree of polymerization. Therefore, the reaction time is selected to be 40 to 60 minutes.

[0027] As a preferred technical solution, in the step 1), yellow phosphorus slag and raffinate acid are added in proportion to obtain a reaction mixture, so that the molar ratio of (CaO+MgO): P2O5 in the reaction mixture is 1-1.1:1.2. In this step, the pH of the yellow phosphorus slag is neutralized or weakly acidic. As the alkali-acid ratio decreases, the pH gradually decreases, and the pH gradually decreases from 7.1 to 6.7. As the alkali-acid ratio decreases, the content of effective phosphorus, total phosphorus, and polyphosphorus gradually increases. When the alkali-acid ratio is 1:1.2, the polymerization rate reaches 80% and the pH is 6.7.

[0028] As a preferred technical solution, the mesh size of the yellow phosphorus slag in step 1) is 60 to 100 meshes. From 60 to 200 meshes, as the mesh size increases, the polymerized phosphorus gradually increases, and the polymerization rate gradually increases from 38 to 44%. Considering the industrial production cost, the polyphosphate content of the yellow phosphorus slag of 60 to 100 meshes remains basically unchanged, so this mesh size range is selected as the optimal condition.

[0029] As a preferred technical solution, in the yellow phosphorus slag in step 1), the mass percentage of phosphorus is 1-4% as calculated by P2O5; the mass percentage of magnesium is 1-4% as calculated by MgO; the mass percentage of calcium is 35-40% as calculated by CaO; and the mass percentage of silicon is 28-38% as calculated by SiO2.

[0030] As a preferred technical solution, in the step 1), the mass percentage of phosphorus in the raffinate is 25-40% in terms of P2O5.

[0031] The present invention also discloses a method for preparing polymerized calcium-magnesium fertilizer using yellow phosphorus slag. The polymerized calcium-magnesium fertilizer is prepared using yellow phosphorus slag and raffinate as raw materials. In terms of P2O5, MgO and CaO, the polymerized calcium-magnesium fertilizer comprises:

[0032] Total phosphorus 25-33%, effective phosphorus 25-31%, effective calcium 15-22%, effective magnesium 1-4%, effective silicon 28-35%, all are mass percentages.

[0033] As a preferred technical solution, the polymerization rate of the polymerized calcium-magnesium fertilizer is ≥80% based on P2O5.

[0034] As a preferred technical solution, the polymerized calcium-magnesium fertilizer also includes one or more of trace nutrient fertilizers, humic acid, and plant growth regulators.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) The present invention utilizes yellow phosphorus slag to react with raffinate acid to generate polymerized calcium and magnesium elements, thereby making full use of the effective elements of the yellow phosphorus slag. The present invention utilizes yellow phosphorus slag and raffinate acid for neutralization, thereby solving the problems of ammonia volatilization and phosphorus degradation caused by excessive alkalinity of the yellow phosphorus slag, and generating polymerized phosphorus, calcium and magnesium elements that are more conducive to absorption by crops. The present invention adopts a method of mixing and calcining yellow phosphorus slag with raffinate acid, which not only reduces the pH of the yellow phosphorus slag, but also produces polyphosphates to obtain polymerized phosphorus, calcium and magnesium. Compared with the traditional method of obtaining polyphosphates, this method has lower costs. It not only solves the problem of low utilization efficiency of yellow phosphorus slag, but also solves the phenomenon of ammonia volatilization and phosphorus degradation caused by yellow phosphorus slag when used as a fertilizer raw material, thereby obtaining polymerized phosphorus, calcium and magnesium nutrients with better effectiveness.

[0037] (2) The present invention utilizes the raffinate acid containing citric acid-soluble phosphorus, free acid and a large amount of iron and magnesium nutrients, and neutralizes the yellow phosphorus slag Ph through an initial reaction. The calcium and magnesium of the yellow phosphorus slag and the iron and magnesium of the raffinate acid are reacted to form fixed nutrients that can be slowly converted and absorbed by crops and are not easily lost.

[0038] (3) When this product is applied to the soil, the phosphorus in it will not be fixed quickly, but will slowly release orthophosphate to meet the needs of crops. Similarly, due to the effect of polyphosphate, magnesium and calcium are not easily leached by water in large quantities, making it particularly suitable for crops with high requirements for calcium and magnesium.

[0039] (4) The present invention effectively solves the problem of comprehensive utilization of yellow phosphorus slag and raffinate produced in the production process, recovers valuable elements in yellow phosphorus slag and raffinate, and complies with the comprehensive utilization principles of reduction, harmlessness, reuse and resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Effects of different fertilization treatments on nutrient absorption of eucalyptus. DETAILED DESCRIPTION

[0041] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments.

[0042] Embodiment 1:

[0043] A preparation method of polymerized calcium-magnesium fertilizer based on yellow phosphorus slag and residual acid, the raw material indicators used are as follows:

[0044] Raffinate: w(P2O5)38%, w(MgO)1.64%, w(CaO)0.15%;

[0045] Yellow phosphorus slag: w(P2O5)1%, w(MgO)3%, w(CaO)37%, w(SiO2)38%;

[0046] The steps include:

[0047] (1) mixing 10 kg of yellow phosphorus slag and 9.4 kg of raffinate acid in a reactor at room temperature to obtain a reaction mixture;

[0048] (2) The reaction mixture obtained above is calcined at 500° C. for 40 min to obtain an intermediate product.

[0049] (3) After grinding, polymerized calcium magnesium fertilizer can be obtained.

[0050] The product analysis results are shown in Table 1:

[0051] Total Phosphorus Available Phosphorus Available Calcium Effective Magnesium Effective Silicon Polyphosphate Polymerization rate pH 31.39 29.73 21.10 3.14 36.5％ 23.83 81.9 7.13

[0052] Embodiment 2:

[0053] A preparation method of polymerized calcium-magnesium fertilizer based on yellow phosphorus slag and residual acid, the raw material indicators used are as follows:

[0054] Raffinate acid: w(P2O5)35%, w(MgO)1.5%, w(CaO)0.12%;

[0055] Yellow phosphorus slag: w(P2O5)1%, w(MgO)3%, w(CaO)35%, w(SiO2)35%;

[0056] The steps include:

[0057] (1) mixing 10 kg of yellow phosphorus slag and 18.8 kg of raffinate acid in a reactor at room temperature to obtain a reaction mixture; (2) calcining the reaction mixture obtained at 500° C. for 40 minutes to obtain an intermediate product;

[0058] (3) After grinding, polymerized calcium magnesium fertilizer can be obtained.

[0059] The product analysis results are shown in Table 2:

[0060] Total Phosphorus Available Phosphorus Available Calcium Effective Magnesium Effective Silicon Polyphosphate Polymerization rate pH 38.37 37.65 18.90 3.36 33.7 31.50 83.68 5.97

[0061] Embodiment 3:

[0062] A preparation method of polymerized calcium-magnesium fertilizer based on yellow phosphorus slag and residual acid, the raw material indicators used are as follows:

[0063] Raffinate acid: w(P2O5)25%, w(MgO)1.4%, w(CaO)0.11%

[0064] Yellow phosphorus slag: w(P2O5)1%, w(MgO)2%, w(CaO)34%, w(SiO2)28%;

[0065] The steps include:

[0066] (1) mixing 10 kg of yellow phosphorus slag and 9.4 kg of raffinate acid in a reactor at room temperature to obtain a reaction mixture; (2) calcining the reaction mixture obtained at 200° C. for 50 min to obtain an intermediate product;

[0067] (3) After grinding, polymerized calcium magnesium fertilizer can be obtained.

[0068] The product analysis results are shown in Table 3:

[0069] Total Phosphorus Available Phosphorus Available Calcium Effective Magnesium Effective Silicon Polyphosphate Polymerization rate pH 20.14 19.78 18.19 2.64 24.6 11.31 38.83 7.13

[0070] Embodiment 4:

[0071] A preparation method of polymerized calcium-magnesium fertilizer based on yellow phosphorus slag and residual acid, the raw material indicators used are as follows:

[0072] Raffinate: w(P2O5)38%, w(MgO)1.64%, w(CaO)0.15%;

[0073] Yellow phosphorus slag: w(P2O5)1%, w(MgO)3%, w(CaO)37%, w(SiO2)38%;

[0074] The steps include:

[0075] (1) mixing 10 kg of yellow phosphorus slag and 26.9 kg of raffinate acid in a reactor at room temperature to obtain a reaction mixture;

[0076] (2) calcining the reaction mixture obtained above at 800° C. for 60 min to obtain an intermediate product;

[0077] (3) After grinding, polymerized calcium magnesium fertilizer can be obtained.

[0078] The product analysis results are shown in Table 4:

[0079] Total Phosphorus Available Phosphorus Available Calcium Effective Magnesium Effective Silicon Polyphosphate Polymerization rate pH 37.65 36.72 18.90 3.36 36.9 31.50 84.45 4.78

[0080] Embodiment 5:

[0081] A preparation method of polymerized calcium-magnesium fertilizer based on yellow phosphorus slag and residual acid, the raw material indicators used are as follows:

[0082] Raffinate: w(P2O5)38%, w(MgO)1.64%, w(CaO)0.15%;

[0083] Yellow phosphorus slag: w(P2O5)1%, w(MgO)3%, w(CaO)37%, w(SiO2)38%;

[0084] The steps include:

[0085] (1) mixing 10 kg of yellow phosphorus slag and 9.4 kg of raffinate acid in a reactor at room temperature to obtain a reaction mixture;

[0086] (2) The reaction mixture obtained above was calcined at 100° C. for 40 min to obtain an intermediate product.

[0087] (3) After grinding, polymerized calcium magnesium fertilizer can be obtained.

[0088] The product analysis results are shown in Table 5:

[0089] Total Phosphorus Available Phosphorus Available Calcium Effective Magnesium Effective Silicon Polyphosphate Polymerization rate pH 26.88 26.52 13.93 2.26 35.8 0.83 5.94 7.13

[0090] Compared with Example 4, Example 1 adds excessive raffinate acid, resulting in a decrease in the effective calcium content and too low pH acidity. Compared with Example 5, Example 5 reduces the reaction temperature, resulting in a significant decrease in the polyphosphorus content and polymerization rate.

[0091] Test example:

[0092] Raw materials: yellow phosphorus slag, raffinate, urea, calcium sulfate, potassium chloride

[0093] Test time and location: The test was conducted in August 2023 at the pilot base in Xishan District, Kunming City, Yunnan Province.

[0094] The test treatment is as follows:

[0095] Treatment 1: 0.18kg urea, 0.15kg general calcium, 0.075kg potassium chloride, and 0.039kg yellow phosphorus slag (crushed) were applied to the eucalyptus potted plants.

[0096] Treatment 2: 0.18kg urea; 0.15kg calcium sulfate; 0.075kg potassium chloride; add 0.039kg yellow phosphorus slag to the residual acid-base ratio of 1:1.5, the reaction temperature is 500℃, the reaction time is 40min, and the obtained neutralization product is applied to the eucalyptus potted plants.

[0097] Treatment 3: 0.18kg urea; 0.15kg calcium sulfate; 0.075kg potassium chloride; add 0.039kg yellow phosphorus slag to the residual acid-base ratio of 1:1.2, the reaction temperature is 500℃, the reaction time is 40min, and the obtained neutralization product is applied to the eucalyptus potted plants.

[0098] Treatment 4: 0.18kg urea; 0.15kg general calcium; 0.075kg potassium chloride; add 0.039kg yellow phosphorus slag and residual acid and alkali in a ratio of 1:1, reaction temperature of 500℃, reaction time of 40min to obtain the neutralization product, which is applied to the eucalyptus potted plants.

[0099] Treatment 5: 0.18kg urea; 0.15kg calcium sulfate; 0.075kg potassium chloride; add 0.039kg yellow phosphorus slag to the residual acid-base ratio of 1:1.2, the reaction temperature is 200℃, the reaction time is 40min, and the obtained neutralization product is applied to the eucalyptus potted plants.

[0100] The experiment used potted plants, each pot was filled with 30 kg of soil, and the above-mentioned fertilizers were evenly mixed with the soil before filling. Each treatment was set up with 5 replicates, and the average value was taken to measure the tree height and breast diameter.

[0101] Table 6 Effects of different fertilization treatments on eucalyptus growth

[0102] deal with Tree height (cm) Diameter at breast height (cm) Tree height growth ratio Growth ratio of breast diameter Process 1 17 0.2124 —— —— Process 2 14.5 0.2448 -14.71 15.25 Process 3 20.7 0.3606 21.76 69.77 Process 4 26.5 0.458 55.88 115.63 Process 5 17.6 0.2516 3.53 18.46

[0103] It can be clearly seen from Table 6 that the product of the present invention has obvious effects of improving quality and increasing yield. In addition, although the amount of effective phosphorus applied in treatment 3 is the same as that in treatment 5, due to the low polymerization rate of phosphorus in treatment 5, the tree height is 18.23% less than that in treatment 3, and the breast diameter is 51.34 less than that in treatment 3. It can be seen from treatments 2 to 4 that a suitable alkali-acid ratio can effectively increase the growth of eucalyptus crops. Figure 1 It can be seen that compared with the application of ordinary yellow phosphorus slag alone, the absorption of nitrogen, phosphorus, calcium and magnesium in treatment 4 is the largest. It is proved that the polyphosphate calcium magnesium raw material based on raffinate acid and yellow phosphorus slag proposed in this patent has different effects on crop growth under different process conditions. The preferred scheme proposed in this patent is most conducive to providing a variety of nutrients to crops, especially active Ca and Mg nutrients, which are generally lacking in the environment where eucalyptus grows, thereby significantly promoting the growth of eucalyptus.

[0104] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing polymerized calcium-magnesium fertilizer from yellow phosphorus slag, characterized in that: The steps include: 1) Initial reaction Yellow phosphorus slag and raffinate acid are used as raw materials and mixed evenly at room temperature to obtain a reaction mixture; 2) Calcination calcining the reaction mixture in a mixing reactor; 3) Reaction In the mixed reactor reaction, when the phosphoric acid polymerization rate is ≥80%, the reaction is stopped and the product is ground to obtain polymerized calcium magnesium fertilizer; the phosphoric acid polymerization rate is calculated as P2O5.

2. A method for preparing polymeric calcium-magnesium fertilizer using yellow phosphorus slag as claimed in claim 1, characterized in that: The calcination temperature in the step 2) is 400-600°C.

3. A method for preparing polymerized calcium-magnesium fertilizer using yellow phosphorus slag as claimed in claim 2, characterized in that: The calcination temperature in step 2) is 450-550°C.

4. A method for preparing polymerized calcium-magnesium fertilizer from yellow phosphorus slag as claimed in claim 1, characterized in that: The calcination time in step 2) is 30 to 120 minutes.

5. A method for preparing polymeric calcium-magnesium fertilizer using yellow phosphorus slag as claimed in claim 4, characterized in that: The calcination time in step 2) is 40 to 60 minutes.

6. A method for preparing polymerized calcium-magnesium fertilizer using yellow phosphorus slag as claimed in claim 1, characterized in that: In the step 1), the molar ratio of (CaO+MgO): P2O5 in the reaction mixture is 1-1.1:1.

2.

7. A method for preparing polymeric calcium-magnesium fertilizer using yellow phosphorus slag as claimed in claim 1, characterized in that: In the step 1), the particle size of the yellow phosphorus slag is 60 to 100 meshes.

8. A method for preparing polymeric calcium-magnesium fertilizer using yellow phosphorus slag as claimed in claim 1, characterized in that: In the step 1), the content of P2O5 in the yellow phosphorus slag is 1-4%; the content of MgO is 1-4%; the content of CaO is 35-40%; and the content of SiO2 is 28-38%.

9. A method for preparing polymeric calcium-magnesium fertilizer using yellow phosphorus slag as claimed in claim 1, characterized in that: The P2O5 content in the raffinate in step 1) is 25-40%.

10. A polymerized calcium-magnesium fertilizer prepared by the method for preparing polymerized calcium-magnesium fertilizer using yellow phosphorus slag as claimed in any one of claims 1 to 7, characterized in that: The polymerized calcium-magnesium fertilizer is prepared with yellow phosphorus slag and residual acid as raw materials. Calculated by P2O5, MgO and CaO, the total phosphorus is 25-33%, the effective phosphorus is 25-31%, the effective calcium is 15-22%, the effective magnesium is 1-4%, and the effective silicon is 28-35%, all of which are mass percentages.

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