Medium-low-grade phosphorite acidolysis product as well as preparation method and application thereof

Abstract

The invention relates to the technical field of low-grade phosphorite treatment, in particular to a medium-low-grade phosphorite acidolysis product as well as a preparation method and application thereof. According to the method, the raffinate acid is introduced to prepare the low-quality phosphate-based sulfur-phosphorus mixed acid urea to decompose the medium-low-grade phosphorite, so that the incremental utilization of the raffinate acid and the full-amount utilization of phosphorite resources are realized; the introduction of the raffinate acid creates good reaction conditions for the acidolysis process, is beneficial to relieving the generation of bubbles in the reaction process, reduces the foaming rate, and improves the conversion rate of elements in the medium-low grade phosphorite, and the highest conversion rate can reach 97.5% or above; and the fluidity of the acidolysis slurry is effectively improved by the raffinate acid, so that convenient conditions are provided for preparation of middle-low-grade phosphate ore acidolysis products.

Description

Technical Field

[0001] The invention relates to the technical field of low-grade phosphate ore processing, and in particular to a medium- and low-grade phosphate ore acid hydrolysis product and a preparation method and application thereof. Background Art

[0002] Due to the limitation of process conditions, the traditional production process of phosphate compound fertilizer cannot directly use medium and low-grade phosphate ore. It is necessary to form high-quality phosphate ore through ore dressing and enrichment, and then use the wet phosphoric acid process to produce phosphoric acid, and then produce phosphate compound fertilizer products. The flotation and wet phosphoric acid processes not only produce a large number of industrial by-products such as tailings, phosphogypsum, slag acid, and residual acid, but also due to the limitation of process conditions, industrial impurities such as calcium, magnesium, silicon, and sulfur need to be removed during the acid processing process; in order to meet the demand for medium and trace elements during the growth period of crops, the medium and trace elements required by crops need to be added in the subsequent stages of compound fertilizer production, which increases the difficulty of the process, causes environmental pollution and waste of resources and energy, and increases production costs.

[0003] As the contradiction between high-quality phosphate reserves and the demand for phosphate fertilizers becomes increasingly acute, the green and efficient utilization technology of medium and low-grade phosphate is an inevitable choice. However, due to the structural characteristics of phosphate ore, there are differences in its utilization methods, but it can be mainly divided into the following four categories, namely, mechanochemical activation of phosphate resources, acid activation of phosphate resources, organic resource utilization of phosphate resources, and thermal activation of phosphate resources. However, the conversion rate of phosphorus in the existing full utilization methods of phosphate resources is poor, and the utilization rate of elements such as calcium and magnesium is low, the energy consumption is high, and the biological effect of the product is poor, which cannot meet the needs of green and efficient production of crops. Therefore, reducing the waste of resources and energy in the full utilization process of medium and low-grade phosphate resources and improving the conversion rate and biological effectiveness of beneficial elements phosphorus, calcium and magnesium in medium and low-grade phosphate ores are crucial to achieving green development of industry and agriculture.

[0004] Patent CN 201310096516.6 and Patent CN 201810722694.8 both disclose the use of urea-sulfuric acid as an acidolysis agent to decompose medium- and low-grade phosphate ore, which can achieve full utilization of medium- and low-grade phosphate ore resources. The urea-sulfuric acid compound fertilizer production process can make full use of medium- and low-grade phosphate ore resources, and adopt a "one-step method" to produce compound fertilizers, that is, all acids are mixed and added. Compared with the traditional sulfuric acid decomposition of phosphate ore to prepare phosphoric acid, the urea-sulfuric acid compound fertilizer process has high phosphate ore conversion rate, short production cycle, and no unorganized emission of gas-phase fluorine. It can be directly produced by modifying the original compound fertilizer or superphosphate production device, saving energy and reducing consumption. The urea-sulfuric acid compound fertilizer product finally prepared contains not only nitrogen, phosphorus, and potassium, but also trace nutrients such as calcium, magnesium, sulfur, silicon, and iron, and has the advantages of high nutrient utilization rate, cleanliness, environmental protection, and high efficiency.

[0005] However, when urea-sulfuric acid is used to directly decompose medium- and low-grade phosphate ore, a large amount of foam is generated during the production process, and the foaming volume is large, which seriously hinders the reaction, resulting in incomplete reaction and reduced conversion rates of beneficial elements phosphorus, calcium and magnesium. The conversion rate of phosphorus is only about 80%. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a medium- and low-grade phosphate rock acid hydrolysis product and a preparation method and application thereof, which can effectively reduce the foaming amount and improve the reaction effect.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows.

[0008] The first aspect of the present invention provides a method for preparing a medium- and low-grade phosphate rock acid hydrolysis product, comprising the following steps:

[0009] The phosphate rock powder and the alkaline aqueous solution are mixed in a mass volume ratio of 1 kg: 0.4 L to 0.45 L to obtain an alkaline phosphate slurry;

[0010] At 70° C. to 90° C., firstly, the raffinate acid and the alkaline phosphate slurry are mixed and stirred in a mass ratio of 0.8 to 1:1 for 15 to 75 minutes to reduce the amount of foaming, and then urea-sulfuric acid aqueous solution is added and the mixture is stirred and reacted for 30 to 150 minutes to obtain the medium-low grade phosphate ore acid hydrolysis product;

[0011] The urea-sulfuric acid aqueous solution is obtained by mixing urea, sulfuric acid and water in a mass ratio of 0.8-4.2:1.0:1.0;

[0012] The mass ratio of the raffinate acid to the urea-sulfuric acid aqueous solution is 3.5-13.6:1.

[0013] The present invention adds the raffinate acid to the alkaline phosphate slurry at a mass ratio of 0.8 to 1:1 at 70°C to 90°C. The early addition of the raffinate acid is beneficial to improving the phosphate conversion rate. Since the raffinate acid has a low acidity, the foaming rate is low when reacting with the alkaline phosphate ore. Even if the urea-sulfuric acid solution is added later, the foaming rate of the system is still low, providing a good reaction environment for the reaction. This effectively avoids the problem of incomplete reaction caused by the one-time addition of urea-sulfuric acid in the prior art, serious foaming during the reaction, and the occurrence of problems that are not conducive to the reaction. The principle of the present invention is as follows: Fig.13 The method of the present invention can achieve a phosphorus conversion rate of up to 97.5% or more in medium and low grade phosphate ore.

[0014] In another preferred embodiment, the mixing and stirring speed is 100 r / min to 300 r / min.

[0015] In another preferred embodiment, the particle size of the phosphate rock powder is 60 mesh to 200 mesh.

[0016] In another preferred embodiment, the mass percentage of phosphoric acid in the raffinate acid is 38% to 45%.

[0017] In another preferred embodiment, the alkaline aqueous solution is a mixture of urea, sodium dodecyl sulfate / sodium dodecylbenzene sulfonate and water in a mass volume ratio of 1.3kg-13.9kg:1kg:14.6L-28.6L.

[0018] The second aspect of the present invention provides the acid hydrolysis product of the medium- and low-grade phosphate rock.

[0019] The third aspect of the present invention provides the use of the medium- and low-grade phosphate rock acid hydrolysis products in the preparation of raffinate acid-sulfuric acid mixed acid urea-based slow-release compound fertilizer for crop growth promotion.

[0020] In another preferred embodiment, the raffinate acid-sulfuric acid mixed acid urea-based slow-release compound fertilizer for crop growth promotion is prepared by mixing and granulating low- and medium-grade phosphate rock acidolysis products, alkaline materials, nitrogen fertilizers, phosphate fertilizers, granulation aids and potassium fertilizers in a mass ratio of 1:0-1.93:1.25-1.74:0.02-0.20:0.03-0.55:1.

[0021] In another preferred embodiment, ammonia is introduced during the granulation process. Ammonia is introduced during the granulation process to cause a neutralization reaction between the acid hydrolyzed slurry and the ammonia, so that the acid hydrolyzed slurry is nearly neutral or neutral to alkaline; during the granulation process, the granulation rate is improved by passing ammonia through the secondary neutralization method, the fertilizer granule strength is improved, and the yield is improved. The secondary neutralization method refers to first passing ammonia through the acid hydrolyzed slurry to partially neutralize it, and then adding a certain amount of alkaline material during the granulation process to completely neutralize it, and finally preparing a neutral to alkaline compound fertilizer with a pH of 7.0 to 7.8.

[0022] In another preferred embodiment, the alkaline material is calcium magnesium phosphate or ammonium bicarbonate;

[0023] The nitrogen fertilizer is at least one of urea, ammonium chloride, ammonium sulfate and ammonium bicarbonate;

[0024] The phosphate fertilizer is any one of monoammonium phosphate, diammonium phosphate, calcium magnesium phosphate, and molten potassium phosphate fertilizer;

[0025] The potash fertilizer is any one of potassium sulfate, potassium chloride and potassium nitrate;

[0026] The granulation aid is any one of bentonite, attapulgite and montmorillonite.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention can create favorable reaction conditions for the acid hydrolysis process by first adding raffinate acid during the preparation process, which helps to alleviate the generation of bubbles during the reaction, reduce the foaming rate, and improve the conversion rate of beneficial elements of phosphorus, calcium and magnesium in medium and low-grade phosphate ore. In addition, the use of raffinate acid effectively improves the fluidity of the acid hydrolysis slurry, enables more uniform stirring, more complete reaction, improves the effect of full utilization of phosphate rock powder, and provides convenient conditions for the preparation of medium and low-grade phosphate ore acid hydrolysis products. Using the method of the present invention, the conversion rate of phosphorus can reach more than 97.5%.

[0029] (2) The slow-release compound fertilizer obtained by granulating the acid hydrolysis products of medium- and low-grade phosphate ore in the present invention can significantly promote the growth of Chinese cabbage. Compared with the traditional fertilization treatment, the fresh weight and dry weight of the aboveground part of Chinese cabbage in the rapid growth period are significantly increased by 94.8% and 158.8%, respectively; the fresh weight and dry weight of the aboveground part of Chinese cabbage in the harvest period are significantly increased by 21.1% and 35.1%, respectively, the fresh weight of the root system is significantly increased by 29.7%, and the calcium and magnesium contents of the leaves are increased by 15.6% and 9.7%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The figures are the effects of different reaction temperatures on the conversion rates of phosphorus, calcium and magnesium in the acidolysis products of medium and low-grade phosphate rocks; A is the effect of different reaction temperatures on phosphorus, B is the effect of different reaction temperatures on calcium, and C is the effect of different reaction temperatures on magnesium.

[0031] Figure 2 The figures are the effects of different stirring speeds on the conversion rates of phosphorus, calcium and magnesium in the acidolysis products of medium and low-grade phosphate rocks; A is the effect of different stirring speeds on phosphorus, B is the effect of different stirring speeds on calcium, and C is the effect of different stirring speeds on magnesium.

[0032] Figure 3 The figures are the effects of different reaction times on the conversion rates of phosphorus, calcium and magnesium in the acidolysis products of medium and low-grade phosphate rocks; A is the effect of different reaction times on phosphorus, B is the effect of different reaction times on calcium, and C is the effect of different reaction times on magnesium.

[0033] Figure 4 The figures are the effect of different phosphate rock mesh sizes on the conversion rates of phosphorus, calcium and magnesium in the acidolysis products of medium and low-grade phosphate rocks; A is the effect of different phosphate rock mesh sizes on phosphorus, B is the effect of different phosphate rock mesh sizes on calcium, and C is the effect of different phosphate rock mesh sizes on magnesium.

[0034] Figure 5The figures are the effects of different acid dosages on the conversion rates of phosphorus, calcium and magnesium in the acidolysis products of medium and low-grade phosphate rocks; A is the effect of different acid dosages on phosphorus, B is the effect of different acid dosages on calcium, and C is the effect of different acid dosages on magnesium.

[0035] Figure 6 The figures are the effects of different urea-sulfuric acid aqueous solution ratios on the conversion rates of phosphorus, calcium and magnesium in the acidolysis products of medium and low-grade phosphate rocks; A is the effect of different urea-sulfuric acid aqueous solution ratios on phosphorus, B is the effect of different urea-sulfuric acid aqueous solution ratios on calcium, and C is the effect of different urea-sulfuric acid aqueous solution ratios on magnesium.

[0036] Figure 7 The response surface diagram of the effects of different preparation conditions on the phosphorus conversion rate in the acidolysis products of medium and low grade phosphate ore is shown in Figure 1, wherein A is the effect of the interaction between reaction temperature and reaction time on the phosphorus conversion rate in the acidolysis products of medium and low grade phosphate ore; B is the effect of the interaction between reaction time and the ratio of urea sulfuric acid aqueous solution on the phosphorus conversion rate in the acidolysis products of medium and low grade phosphate ore; C is the effect of the interaction between stirring speed and reaction temperature on the phosphorus conversion rate in the acidolysis products of medium and low grade phosphate ore; D is the effect of the interaction between reaction temperature and the ratio of urea sulfuric acid aqueous solution on the phosphorus conversion rate in the acidolysis products of medium and low grade phosphate ore; E is the effect of the interaction between stirring speed and reaction time on the phosphorus conversion rate in the acidolysis products of medium and low grade phosphate ore; and F is the effect of the interaction between the ratio of urea sulfuric acid aqueous solution and stirring speed on the phosphorus conversion rate in the acidolysis products of medium and low grade phosphate ore.

[0037] Figure 8 This is a schematic diagram of sowing and fertilizing Chinese cabbage.

[0038] Fig. 9 These are the results of fresh weight of the aboveground part of Chinese cabbage during its rapid growth period and harvest period.

[0039] Fig.10 This is a graph showing the dry weight of the aboveground part of Chinese cabbage during its rapid growth period and harvest period.

[0040] Fig.11 This is a graph showing the fresh weight and dry weight of the underground part of Chinese cabbage during the rapid growth period and harvest period.

[0041] Fig.12 This is the result chart of phosphorus, calcium and magnesium nutrient contents in Chinese cabbage leaves during the harvest period. Fig.13 The schematic diagram is a schematic diagram of the preparation of low-grade phosphate rock acid hydrolysis products in the present invention. DETAILED DESCRIPTION

[0042] The following will be combined with the specific embodiments of the present invention to clearly and completely describe the technical solutions in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] The methods described in the embodiments of the present invention are conventional methods unless otherwise specified. The materials, reagents, etc. used can be obtained from commercial sources unless otherwise specified.

[0044] Example 1

[0045] This example adopts a single factor test, with reaction temperature as the single factor value, to explore the optimal range of reaction temperature in the process of preparing medium and low grade phosphate rock acid hydrolysis products.

[0046] The specific steps include:

[0047] 1. Preparation of alkaline phosphate slurry

[0048] Accurately weigh 50g of phosphate rock powder that has passed a 200-mesh standard sieve and put it in beaker 1 for later use. The basic properties of the phosphate rock are shown in Table 1. Weigh 9.85g of urea B and 0.75g of sodium dodecyl sulfate in beaker 2, and add 11.58mL of water to beaker 2 and stir well to prepare an alkaline aqueous solution. Slowly add the alkaline aqueous solution in beaker 2 into beaker 1 and keep stirring to obtain an alkaline phosphate slurry with a water content of 19%. Add the alkaline phosphate slurry into a 2000mL three-necked flask, and place the three-necked flask in a water bath at 80°C for later use.

[0049] Table 1 Chemical composition of medium and low grade phosphate rock

[0050] Main Ingredients <![CDATA[P2O5]]> MgO CaO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> Loss on ignition Mass percentage (%) 19.00 7.59 38.48 1.06 1.46 13.61

[0051] 2. Preparation of Raffinate Acid and Urea-Sulfuric Acid Aqueous Solution

[0052] Preparation of raffinate acid (acid hydrolysis agent A): Accurately measure 68.71 mL of raffinate acid in a 250 mL beaker, heat to 78°C in a constant temperature water bath, and set aside. The raffinate acid used in the test is prepared by mixing the supernatant and the lower precipitate completely. The basic physical and chemical properties of the raffinate acid used in the test are shown in Table 2.

[0053] Preparation of urea-sulfuric acid aqueous solution (acidolysis agent B): Accurately measure 6.19 mL of 98% sulfuric acid in a 250 mL beaker, heat to 78 ° C in a constant temperature water bath, then slowly add 18.24 g of urea A and 2.09 mL of water, and stir at 300 r / min for 30 min. At this time, the molar mass ratio of urea A, sulfuric acid and water is 3.6:1.0:1.0.

[0054] Table 2 Basic physical and chemical properties of the raffinate used in the experiment

[0055]

[0056] 3. Acid hydrolysis products of medium and low grade phosphate rock

[0057] At the beginning of acid hydrolysis, first add distilled water to the absorption bottle, then cover it with a rubber stopper, and check the air tightness of the device. The raffinate acid (acid hydrolysis solution A) and the urea sulfuric acid acid hydrolysis agent aqueous solution (acid hydrolysis solution B) obtained in 2 are placed in water baths at 50°C, 60°C, 70°C, 80°C, and 90°C, respectively. At the beginning of the reaction, the acid hydrolysis solution A is quickly added to a 2000mL three-necked flask containing alkaline phosphate slurry, covered with a rubber stopper, and the vacuum pump switch is immediately turned on. The reaction is carried out at a set stirring speed of 400r / min and a stirring time of 30min. After the reaction is carried out for 15min, the acid hydrolysis solution B is added and the reaction is continued for 15min. After the reaction is completed, the stirrer switch is first turned off, and the vacuum pump switch is turned off after 10s to obtain a medium- and low-grade phosphate ore acid hydrolysis product. The reaction is repeated 3 times.

[0058] Determine the available phosphorus, total phosphorus, available calcium, available magnesium, total calcium and total magnesium in the acid hydrolysis products of medium and low grade phosphate rocks.

[0059] Phosphorus decomposition rate (%) = effective phosphorus / total phosphorus; calcium decomposition rate (%) = effective calcium / total calcium; magnesium decomposition rate (%) = effective magnesium / total magnesium.

[0060] Among them, the conversion rates of phosphorus, calcium and magnesium in the acid hydrolysis products of medium and low-grade phosphate ore are shown in Figure 1 .

[0061] from Figure 1 As can be seen from A in the figure, temperature has a significant effect on the conversion rate of phosphorus in medium and low-grade phosphate ore. As the temperature increases, the decomposition rate of phosphorus in phosphate ore shows a trend of first increasing and then decreasing. The results show that the increase in temperature promotes the decomposition of medium and low-grade phosphate ore by raffinate acid and urea-sulfuric acid aqueous solution. However, when the temperature reaches 90°C, the alkaline phosphate slurry loses water and becomes dry, which hinders the further progress of the reaction and reduces the conversion rate of phosphorus in phosphate ore. Figure 1 From B, we can see that the conversion rate of calcium in the acid hydrolysis products of medium and low-grade phosphate rocks has basically the same trend as the conversion rate of phosphorus, increasing with increasing temperature, and reaching the maximum conversion rate at 80°C. Figure 1 Figure C shows that the effect of temperature on the conversion rate of magnesium in the acid hydrolysis products of medium and low-grade phosphate ore is not significant, and all can reach more than 97.5%. In summary, combined with the conversion rates of phosphorus, calcium and magnesium in the acid hydrolysis products of medium and low-grade phosphate ore, the optimal reaction temperature is 80°C, and the optimal range of the reaction temperature is 70°C to 90°C.

[0062] Example 2

[0063] This example adopts a single factor test, with stirring speed as a single factor value, to explore the optimal value range of stirring speed in the preparation process of medium and low grade phosphate rock acid hydrolysis products.

[0064] The specific steps include:

[0065] 1. Preparation of alkaline phosphate slurry

[0066] Accurately weigh 50g of phosphate rock powder that has passed a 200-mesh standard sieve and put it into beaker 1 for later use. The basic properties of the phosphate rock are shown in Table 1. Weigh 9.85g of urea B and 0.75g of sodium dodecyl sulfate into beaker 2, and add 11.58ml of water into beaker 2 and stir well to prepare an alkaline aqueous solution. Slowly add the alkaline aqueous solution in beaker 2 into beaker 1 and keep stirring to obtain an alkaline phosphate slurry with a water content of 19%. Add the alkaline phosphate slurry into a 2000mL three-necked flask, and place the three-necked flask in a water bath at 80°C for later use.

[0067] 2. Preparation of Raffinate Acid and Urea-Sulfuric Acid Aqueous Solution

[0068] Preparation of raffinate acid (acid hydrolysis agent A): Accurately measure 68.71 mL of raffinate acid in a 250 mL beaker, heat to 78°C in a constant temperature water bath, and set aside. The raffinate acid used in the test is prepared by mixing the supernatant and the lower precipitate completely. The basic physical and chemical properties of the raffinate acid used in the test are shown in Table 2.

[0069] Preparation of urea-sulfuric acid aqueous solution (acidolysis agent B): Accurately measure 6.19 mL of 98% sulfuric acid in a 250 mL beaker, heat to 78 ° C in a constant temperature water bath, then slowly add 18.24 g of urea A and 2.09 mL of water, and stir at 300 r / min for 30 min. At this time, the molar mass ratio of urea A, sulfuric acid and water is 3.6:1.0:1.0.

[0070] 3. Acid hydrolysis products of medium and low grade phosphate rock

[0071] At the beginning of acid hydrolysis, first add distilled water to the absorption bottle, then cover it with a rubber stopper, and check the air tightness of the device. The raffinate acid (acid hydrolysis solution A) and urea sulfuric acid aqueous solution (acid hydrolysis solution B) obtained in 2 are added to a water bath at 80°C respectively. At the beginning of the reaction, the acid hydrolysis solution A is quickly added to a 2000mL three-necked flask containing alkaline phosphate slurry, covered with a rubber stopper, and the vacuum pump switch is immediately turned on. According to the set stirring speed of 100r / min, 200r / min, 300r / min, 400r / min, 500r / min, 600r / min, the reaction is carried out for 15min, and then the acid hydrolysis solution B is added to continue the reaction for 15min. After the reaction is completed, the stirrer switch is first turned off, and the vacuum pump switch is turned off after 10s to obtain a medium- and low-grade phosphate ore acid hydrolysis product. The reaction is repeated 3 times.

[0072] Determine the available phosphorus, total phosphorus, available calcium, available magnesium, total calcium and total magnesium in the acid hydrolysis products of medium and low grade phosphate rocks.

[0073] Phosphorus conversion rate (%) = effective phosphorus / total phosphorus; calcium decomposition rate (%) = effective calcium / total calcium; magnesium decomposition rate (%) = effective magnesium / total magnesium.

[0074] The conversion rates of phosphorus, calcium and magnesium in the acid hydrolysis products of medium and low-grade phosphate ore are shown in Figure 2 .

[0075] from Figure 2 As can be seen from A in the figure, the stirring speed has a significant effect on the conversion rate of phosphorus in medium and low-grade phosphate ore. Initially increasing the stirring speed will significantly increase the decomposition rate of phosphorus in the phosphate ore. Further increasing the stirring speed will have a negative impact on the decomposition rate of phosphorus. The reason may be that too low a stirring speed will lead to uneven mixing of the reactants and incomplete reaction, while a higher stirring speed will destroy the contact balance between the phosphate ore and the acid solution in the reaction system, hindering the further progress of the reaction. Figure 2 From B and C in Figure 1, it can be seen that the change trend of calcium and magnesium conversion rate in the acid hydrolysis products of medium and low-grade phosphate ore is basically consistent with the change trend of phosphorus. Under high stirring speed conditions, the calcium and magnesium conversion rate of the acid hydrolysis products of medium and low-grade phosphate ore shows a downward trend. Therefore, the optimal stirring speed is selected as 200r / min, and the optimal stirring speed range is 100r / min~300r / min.

[0076] Example 3

[0077] This example adopts a single factor test, with reaction time as the single factor value, to explore the optimal range of reaction time in the process of preparing medium and low grade phosphate rock acid hydrolysis products.

[0078] The specific steps include:

[0079] 1. Preparation of alkaline phosphate slurry

[0080] Accurately weigh 50g of phosphate rock powder that has passed a 200-mesh standard sieve and put it in beaker 1 for later use. The basic properties of the phosphate rock are shown in Table 1. Weigh 9.85g of urea B and 0.75g of sodium dodecyl sulfate in beaker 2, and add 11.58mL of water to beaker 2 and stir well to prepare an alkaline aqueous solution. Slowly add the alkaline aqueous solution in beaker 2 into beaker 1 and keep stirring to obtain an alkaline phosphate slurry with a water content of 19%. Add the alkaline phosphate slurry into a 2000mL three-necked flask, and place the three-necked flask in a water bath at 80°C for later use.

[0081] 2. Preparation of Raffinate Acid and Urea-Sulfuric Acid Aqueous Solution

[0082] Raffinate acid (acid hydrolysis agent A): Accurately measure 68.71 mL of raffinate acid into a 250 mL beaker, heat to 78°C in a constant temperature water bath, and set aside. The raffinate acid used in the test is the supernatant and the lower precipitate are completely mixed. The basic physical and chemical properties of the raffinate acid used in the test are shown in Table 2.

[0083] Preparation of urea-sulfuric acid aqueous solution (acidolysis agent B): Accurately measure 6.19 mL of 98% sulfuric acid in a 250 mL beaker, heat to 78 ° C in a constant temperature water bath, then slowly add 18.24 g of urea A and 2.09 mL of water, and stir at 300 r / min for 30 min. At this time, the molar mass ratio of urea A, sulfuric acid and water is 3.6:1.0:1.0.

[0084] 3. Acid hydrolysis products of medium and low grade phosphate rock

[0085] At the beginning of acid hydrolysis, first add distilled water to the absorption bottle, then cover it with a rubber stopper, and check the air tightness of the device. The raffinate acid (acid hydrolysis solution A) and urea sulfuric acid aqueous solution (acid hydrolysis solution B) obtained in 2 are added to a water bath at 80°C respectively. At the beginning of the reaction, the acid hydrolysis solution A is quickly added to a 2000mL three-necked flask containing alkaline phosphate slurry, covered with a rubber stopper, and the vacuum pump switch is immediately turned on. According to the set stirring speed of 200r / min, the stirring time is set to 15min, 30min, 45min, 60min, and 75min respectively. After 15min, 30min, 45min, 60min, and 75min, the acid hydrolysis solution B is added and the reaction is continued for 15min, 30min, 45min, 60min, and 75min. After the reaction is completed, the stirrer switch is first turned off, and the vacuum pump switch is turned off after 10s to obtain a medium- and low-grade phosphate ore acid hydrolysis product. The reaction is repeated 3 times.

[0086] Test items and calculation formula: Determination of available phosphorus, total phosphorus, available calcium, available magnesium, total calcium and total magnesium in the acid hydrolysis products of medium and low grade phosphate rock.

[0087] Phosphorus conversion rate (%) = effective phosphorus / total phosphorus; calcium decomposition rate (%) = effective calcium / total calcium; magnesium decomposition rate (%) = effective magnesium / total magnesium.

[0088] The conversion rates of phosphorus, calcium and magnesium in the acid hydrolysis product 3 are shown in Figure 3 .

[0089] from Figure 3It can be seen from A in that the reaction time has little effect on the decomposition rate of phosphorus in medium and low-grade phosphate ore. The reaction reaches its maximum at 120 minutes, and when the reaction time is 90 minutes, the conversion rate of phosphorus has a significant downward trend. The change trend of the decomposition rate of calcium and magnesium in the acid hydrolysis products of medium and low-grade phosphate ore is different from that of the phosphorus decomposition rate. For example, B and C in 3 both reach their maximum at 60 minutes, but the calcium decomposition rate at 120 minutes is not significantly different from that at 60 minutes. In order to maintain the stability of the phosphorus decomposition rate of the system, the reaction time is preferably 120 minutes, and the optimal stirring speed range is 90 minutes to 150 minutes.

[0090] Example 4

[0091] This example adopts a single factor test, with the fineness of the phosphate rock raw material as a single factor value, to explore the optimal value range of the fineness of the phosphate rock raw material in the preparation of medium- and low-grade phosphate rock acid hydrolysis products.

[0092] The specific steps include:

[0093] 1. Preparation of alkaline phosphate slurry

[0094] Accurately weigh 50g of phosphate rock powder that has passed through 60-80 mesh, 80-100 mesh, 100-120 mesh, 120-150 mesh, 150-200 mesh, and -200 mesh standard sieves into beaker 1 for later use. The basic properties of phosphate rock are shown in Table 1. Weigh 9.85g of urea B and 0.75g of sodium dodecyl sulfate into beaker 2, and add 11.58ml of water into beaker 2 and stir well to prepare an alkaline aqueous solution. Slowly add the alkaline aqueous solution in beaker 2 into beaker 1 and stir continuously to obtain an alkaline water phosphate slurry with a water content of 19%. Add the alkaline water phosphate slurry into a 2000mL three-necked flask, and place the three-necked flask in a water bath at 80°C for later use. Among them, -200 mesh represents the sieve undersize after sieving.

[0095] 2. Preparation of Raffinate Acid and Urea-Sulfuric Acid Aqueous Solution

[0096] Preparation of raffinate acid (acid hydrolysis agent A): Accurately measure 68.71 mL of raffinate acid in a 250 mL beaker, heat to 78°C in a constant temperature water bath, and set aside. The raffinate acid used in the test is prepared by mixing the supernatant and the lower precipitate completely. The basic physical and chemical properties of the raffinate acid used in the test are shown in Table 2.

[0097] Preparation of urea-sulfuric acid aqueous solution (acidolysis agent B): Accurately measure 6.19 mL of 98% sulfuric acid in a 250 mL beaker, heat to 78 ° C in a constant temperature water bath, then slowly add 18.24 g of urea A and 2.09 mL of water, and stir at 300 r / min for 30 min. At this time, the molar mass ratio of urea A, sulfuric acid and water is 3.6:1.0:1.0.

[0098] 3. Acid hydrolysis products of medium and low grade phosphate rock

[0099] At the beginning of acid hydrolysis, first add an appropriate amount of distilled water to the absorption bottle, then cover it with a rubber stopper, and check the air tightness of the device. Add the raffinate acid (acid hydrolysis solution A) and urea sulfuric acid aqueous solution (acid hydrolysis solution B) obtained in 2 to a water bath at 80°C. At the beginning of the reaction, quickly add acid hydrolysis solution A to a 2000mL three-necked flask containing alkaline phosphate slurry, cover it with a rubber stopper, and immediately turn on the vacuum pump switch. Respond according to the set stirring speed of 200r / min and stirring time of 60min. After 60min, add acid hydrolysis solution B and continue to react for 60min. After the reaction is completed, first turn off the stirrer switch, and then turn off the vacuum pump switch after 10s to obtain medium and low-grade phosphate acid hydrolysis products. The reaction is repeated 3 times.

[0100] Determine the available phosphorus, total phosphorus, available calcium, available magnesium, total calcium and total magnesium in the acid hydrolysis products of medium and low grade phosphate rocks.

[0101] Phosphorus conversion rate (%) = effective phosphorus / total phosphorus; calcium decomposition rate (%) = effective calcium / total calcium; magnesium decomposition rate (%) = effective magnesium / total magnesium.

[0102] Among them, the conversion rates of phosphorus, calcium and magnesium in the acid hydrolysis products of medium and low-grade phosphate ore are shown in Figure 4 .

[0103] from Figure 4 As can be seen from A in the figure, the fineness of the phosphate ore raw material has a significant impact on the conversion rate of phosphorus in medium and low-grade phosphate ore. The phosphorus decomposition rate in phosphate ore is negatively correlated with the fineness of the phosphate ore raw material, that is, as the raw material particle size decreases, the phosphorus conversion rate in phosphate ore increases. The decomposition rates of calcium and magnesium in the acid hydrolysis products of medium and low-grade phosphate ore are basically consistent with the decomposition rate of phosphorus, and both increase with the decrease of the fineness of the phosphate ore raw material, such as Figure 4 B and C in. Therefore, in order to achieve the best conversion rate in phosphate rock, the fineness of phosphate rock raw material should be -200 mesh.

[0104] Example 5

[0105] This example adopts a single factor test, with the theoretical acid dosage as the single factor value, to explore the optimal value range of the acid dosage in the preparation process of the acid hydrolysis products of medium and low-grade phosphate rocks.

[0106] The specific steps include:

[0107] 1. Preparation of alkaline phosphate slurry

[0108] Accurately weigh 50g of phosphate rock powder that has passed a 200-mesh standard sieve and put it into beaker 1 for later use. The basic properties of the phosphate rock are shown in Table 1. Weigh 9.85g of urea B and 0.75g of sodium dodecyl sulfate into beaker 2, and add 11.58ml of water into beaker 2 and stir well to prepare an alkaline aqueous solution. Slowly add the alkaline aqueous solution in beaker 2 into beaker 1 and keep stirring to obtain an alkaline phosphate slurry with a water content of 19%. Add the alkaline phosphate slurry into a 2000mL three-necked flask, and place the three-necked flask in a water bath at 80°C for later use.

[0109] 2. Preparation of Raffinate Acid and Urea-Sulfuric Acid Aqueous Solution

[0110] Preparation of raffinate acid (acid hydrolysis agent A): Accurately measure a certain amount of raffinate acid in a 250 ml beaker, heat it to 78°C in a constant temperature water bath, and set aside. The raffinate acid used in the test is the supernatant and the lower precipitate are completely mixed. The basic physical and chemical properties of the raffinate acid used in the test are shown in Table 2.

[0111] Preparation of urea-sulfuric acid aqueous solution (acidolysis agent B): Accurately measure a certain amount of 98% sulfuric acid in a 250 ml beaker, heat it to 78°C in a constant temperature water bath, then slowly add a certain amount of urea A and a certain amount of water, and stir at a speed of 300 r / min for 30 min. At this time, the molar mass ratio of urea A, sulfuric acid and water is 3.6:1.0:1.0.

[0112] The theoretical amounts of acid required to decompose medium and low-grade phosphate ore are 90%, 95%, 100%, 105% and 110%, respectively, that is, the amounts of raffinate acid added are 58.9g, 62.17g, 65.44g, 68.71g and 71.98g, respectively; under the condition that the ratio of urea, sulfuric acid and water in ureasulfuric acid is 3.6:1.0:1.0, the amounts of sulfuric acid added are 5.30mL, 5.60mL, 5.89mL, 6.19mL and 6.48mL, respectively; the amounts of urea added are 15.63g, 16.50g, 17.37g, 18.24g and 19.11g, respectively; the amounts of sulfuric acid added are 1.79mL, 1.89mL, 1.99mL, 2.09mL and 2.19mL, respectively.

[0113] The theoretical amount of acid used refers to the theoretical amount of acid used to completely acid-decompose 1g of low-grade phosphate ore, and then the acid addition amount is set to 90%, 95%, 100%, 105%, and 110% of 1g in the experiment. The specific calculation is as follows:

[0114] 1.61×19.00+0.61×1.06+0.96×1.46+2.23×13.6=62.99g sulfuric acid / 100g phosphate rock.

[0115] 3. Extraction of low-grade phosphate rock acid hydrolysis products

[0116] At the beginning of acid hydrolysis, first add distilled water to the absorption bottle, then cover it with a rubber stopper, and check the air tightness of the device. Add the raffinate acid (acid hydrolysis solution A) and urea sulfuric acid aqueous solution (acid hydrolysis solution B) obtained in 2 to a water bath at 80°C respectively. At the beginning of the reaction, quickly add acid hydrolysis solution A to a 2000mL three-necked flask containing alkaline phosphate slurry, cover it with a rubber stopper, immediately turn on the vacuum pump switch, and react at a set stirring speed of 200r / min and a stirring time of 60min. After 60min, add acid hydrolysis solution B and continue to react for 60min. After the reaction is completed, first turn off the stirrer switch, and then turn off the vacuum pump switch after 10s to obtain medium and low-grade phosphate ore acid hydrolysis products. The reaction is repeated 3 times.

[0117] Determine the available phosphorus, total phosphorus, available calcium, available magnesium, total calcium and total magnesium in the acid hydrolysis products of medium and low grade phosphate rocks.

[0118] Phosphorus conversion rate (%) = effective phosphorus / total phosphorus; calcium decomposition rate (%) = effective calcium / total calcium; magnesium decomposition rate (%) = effective magnesium / total magnesium.

[0119] The conversion rates of phosphorus, calcium and magnesium in the acid hydrolysis products of medium and low-grade phosphate rocks are shown in 5.

[0120] from Figure 5 It can be seen from A in that the acid dosage has a significant effect on the conversion rate of phosphorus in medium and low-grade phosphate ore. The phosphorus decomposition rate in phosphate ore is positively correlated with the theoretical acid dosage, that is, the phosphorus conversion rate in phosphate ore increases with the increase of acid dosage. When the acid dosage is 105% to 110%, the decomposition rate of phosphorus in the acid hydrolysis product no longer increases significantly. The calcium decomposition rate of the acid hydrolysis product of medium and low-grade phosphate ore has no significant difference when the acid dosage is 95% to 105%, and reaches 97.5%. Figure 5 The change trend of magnesium decomposition rate of acid hydrolysis products of medium and low-grade phosphate ore is negatively correlated with the change trend of phosphorus decomposition rate, and decreases with the increase of acid dosage, but the difference is not significant. Figure 5 Therefore, in order to achieve the best conversion rate of elements in phosphate rock and reduce resource waste, the acid dosage is selected to be 105%.

[0121] Example 6

[0122] This example adopts a single factor test, with the urea-sulfuric acid ratio as a single factor value, to explore the optimal value range of the urea-sulfuric acid ratio in the process of preparing medium and low-grade phosphate ore acid hydrolysis products.

[0123] The specific steps include:

[0124] 1. Preparation of alkaline phosphate slurry

[0125] Accurately weigh 50g of phosphate rock powder that has passed a 200-mesh standard sieve and put it in beaker 1 for later use. The basic properties of the phosphate rock are shown in Table 1. Weigh 9.85g of urea B and 0.75g of sodium dodecyl sulfate in beaker 2, and add 11.58mL of water to beaker 2 and stir well to prepare an alkaline aqueous solution. Slowly add the alkaline aqueous solution in beaker 2 into beaker 1 and keep stirring to obtain an alkaline phosphate slurry with a water content of 19%. Add the alkaline phosphate slurry into a 2000mL three-necked flask, and place the three-necked flask in a water bath at 80°C for later use.

[0126] 2. Preparation of Raffinate Acid and Urea-Sulfuric Acid Aqueous Solution

[0127] Preparation of raffinate acid (acid hydrolysis agent A): Accurately measure 68.71 mL of raffinate acid in a 250 mL beaker, heat to 78°C in a constant temperature water bath, and set aside. The raffinate acid used in the test is prepared by mixing the supernatant and the lower precipitate completely. The basic physical and chemical properties of the raffinate acid used in the test are shown in Table 2.

[0128] Preparation of urea-sulfuric acid aqueous solution (acid hydrolysis agent B): Accurately measure a certain amount of sulfuric acid with a concentration of 98% in a 250mL beaker, heat it to 78°C in a constant temperature water bath, then slowly add urea A and water, and stir at a speed of 300r / min for 30min. At this time, the molar mass ratios of urea A, sulfuric acid and water are 1.0:1.0:1.0, 1.6:1.0:1.0, 2.0:1.0:1.0, 2.5:1.0:1.0, 3.6:1.0:1.0 and 4.0:1.0:1.0, respectively. The specific addition amounts of raffinate acid, sulfuric acid, urea and water are shown in Table 3.

[0129] Table 3 Different urea-sulfuric acid ratio acidolysis agent raw material addition amount

[0130]

[0131] 3. Acid hydrolysis products of medium and low grade phosphate rock

[0132] At the beginning of acid hydrolysis, first add distilled water to the absorption bottle, then cover it with a rubber stopper, and check the air tightness of the device. The raffinate acid (acid hydrolysis solution A) and urea sulfuric acid acid hydrolysis solution (acid hydrolysis solution B) obtained in step 2 are added to a water bath at 80°C. At the beginning of the reaction, the acid hydrolysis solution A is quickly added to a 2000mL three-necked flask containing alkaline phosphate slurry, covered with a rubber stopper, and the vacuum pump switch is immediately turned on. According to the set stirring speed of 200r / min and stirring time of 60min, the reaction is responded. After 60min, the acid hydrolysis solution B is added and the reaction is continued for 60min. After the reaction is completed, the stirrer switch is first turned off, and the vacuum pump switch is turned off after 10s to obtain a medium- and low-grade phosphate acid hydrolysis product. The reaction is repeated 3 times.

[0133] Determine the available phosphorus, total phosphorus, available calcium, available magnesium, total calcium and total magnesium in the acid hydrolysis products of medium and low grade phosphate rocks.

[0134] Phosphorus conversion rate (%) = effective phosphorus / total phosphorus; calcium decomposition rate (%) = effective calcium / total calcium; magnesium decomposition rate (%) = effective magnesium / total magnesium.

[0135] The conversion rates of phosphorus, calcium and magnesium in the acid hydrolysis products of medium and low-grade phosphate ore are shown in Figure 6 .

[0136] from Figure 6 It can be seen from A in that different ratios of urea-sulfuric acid aqueous solution have different decomposition rates for phosphorus in medium and low-grade phosphate ore. With the increase of the proportion of urea A, the conversion rate of phosphorus in phosphate ore increases first and then decreases. When the ratio of urea A: sulfuric acid: water is 2.5:1.0:1.0, the phosphorus conversion rate in phosphate ore is the highest. When the proportion of urea A increases, the phosphorus conversion rate decreases. Basically consistent with the trend of phosphorus decomposition rate, when the ratio of urea-sulfuric acid is greater than 2.5:1.0:1.0, the decomposition of calcium and magnesium is reduced; when the ratio of urea-sulfuric acid is less than 2.5:1.0:1.0, the conversion rate of calcium and magnesium in the acidolysis product is not significantly different. Figure 6 B and C in. Therefore, in order to achieve the best conversion rate of phosphorus in phosphate rock and reduce the content of urea A in the reaction system and improve the granulation rate, the urea-sulfuric acid ratio is selected to be 2.5:1.0:1.0.

[0137] Example 7

[0138] According to the single factor response results of Examples 1 to 6, factors that significantly affect the decomposition rate of phosphorus in medium and low-grade phosphate ore are selected, namely: reaction temperature, stirring speed, reaction time, and ratio of urea-sulfuric acid aqueous solution. Design expert 13.0 software is used to perform response surface design according to the Box-Behnken model.

[0139] Through the RSM-BBD experiment with 4 factors and 3 levels, the reaction temperature (A), stirring speed (B), reaction time (C), urea-sulfuric acid aqueous solution (F) were used as independent variables, and the phosphorus decomposition rate of medium and low-grade phosphate rock (Y) was used as the dependent variable. The response design and results are shown in Table 4. After processing these data, the quadratic polynomial equation reflecting the relationship between the response variable (Y) and the independent variables (A, B, C, F) is shown in Formula (3).

[0140] Table 4 Box-Behnken response design and response results

[0141]

[0142]

[0143] Note: Std means standard deviation, Run means a complete test process

[0144] According to the response results, the model is established and the quadratic multiple regression model equation is fitted as follows:

[0145] Y=-0.0420873+0.0158095A-0.00145256B+0.00510732C+0.167539F+1.97343e - 5 AB-1.83581e -5 AC-0.000308407AF-3.29187e -6 BC+0.000207959BF-0.00030211CF-0.000110459A 2 -6.9962e-07B 2 -8.49376e-06C 2 -0.0251252F 2 ; Wherein: A, reaction temperature; B, stirring speed; C, reaction time; D, ratio of urea to sulfuric acid aqueous solution.

[0146] Variance analysis and significance analysis were performed on the quadratic multiple regression model equation. The variance analysis of phosphorus conversion rate of acid hydrolysis products of medium and low-grade phosphate rocks is shown in Table 5.

[0147] Table 5 Variance analysis of phosphorus conversion rate of low-grade phosphate ore

[0148]

[0149]

[0150] Note: df means degree of freedom, F-value means variance, p means significance, and - means no such item.

[0151] Data analysis, pairwise interaction analysis of reaction temperature, stirring speed, reaction time, and urea-sulfuric acid aqueous solution ratio, such as Figure 7 As shown, it can be seen that the optimal conditions for the best phosphorus conversion rate of medium and low-grade phosphate ore are: reaction temperature 73.78℃, stirring speed 138.49r / min, reaction time 140.15min, and uric acid ratio 2.88:1.0:1.0.

[0152] Example 8

[0153] According to the optimal process conditions screened by the response surface optimization method in Example 7, medium and low-grade phosphate rock acid hydrolysis products were prepared, compound fertilizer was prepared, and the performance of the compound fertilizer was evaluated.

[0154] 1. Preparation of alkaline phosphate slurry

[0155] Accurately weigh 50g of phosphate rock powder passed through a 200-mesh sieve and put it in beaker 1 for later use. The basic properties of the phosphate rock are shown in Table 1. Weigh 9.85g of urea B and 0.75g of sodium dodecyl sulfate in beaker 2, and add 11.58mL of water to beaker 2 and stir well to prepare an alkaline aqueous solution. Slowly add the alkaline aqueous solution in beaker 2 to beaker 1 to obtain an alkaline phosphate slurry with a water content of 19%, and add the alkaline phosphate slurry into a 2000mL three-necked flask, and place the three-necked flask in a water bath at 80°C for later use.

[0156] 2. Preparation of Raffinate Acid and Urea-Sulfuric Acid Aqueous Solution

[0157] Preparation of raffinate acid (acid hydrolysis agent A): Accurately measure 68.71 mL of raffinate acid in a 250 mL beaker, heat to 78°C in a constant temperature water bath, and set aside. The raffinate acid used in the test is the supernatant liquid and the lower precipitate are completely mixed. The basic physical and chemical properties of the raffinate acid used in the test are shown in Table 2.

[0158] Preparation of urea-sulfuric acid aqueous solution (acidolysis agent B): Accurately measure 6.19 mL of 98% sulfuric acid in a 250 mL beaker, heat to 78 ° C in a constant temperature water bath, then slowly add 14.60 g of urea A and 2.09 ml of water, and stir at 300 r / min for 30 min. At this time, the molar mass ratio of urea A, sulfuric acid and water is 2.88:1.0:1.0.

[0159] 3. Acid hydrolysis products of medium and low grade phosphate rock

[0160] At the beginning of acid hydrolysis, first add distilled water to the absorption bottle, then cover it with a rubber stopper, and check the air tightness of the device. The raffinate acid (acid hydrolysis solution A) and urea sulfuric acid acid hydrolysis solution (acid hydrolysis solution B) obtained in 2 are added to a water bath at 73.8°C respectively. At the beginning of the reaction, the acid hydrolysis solution A is quickly added to a 2000mL three-necked flask containing alkaline phosphate slurry, covered with a rubber stopper, and the vacuum pump switch is immediately turned on. According to the optimal response conditions obtained by the response surface analysis method, the stirring speed is set to 139r / min and the stirring time is 140min for response. After the reaction is carried out for 70min, the acid hydrolysis solution B is added and the reaction is continued for 70min. After the reaction is completed, the stirrer switch is first turned off, and the vacuum pump switch is turned off after 10s to obtain 108.49g of low-grade phosphate acid hydrolysis product.

[0161] 4. Granulation

[0162] Ammonia gas was introduced into the obtained 108.49g of low-grade phosphate ore acidolysis product, and the introduction rate was controlled to be 0.005L / min to form an ammoniation acidolysis slurry. Then 25.03g of montmorillonite powder with a mesh of 200 was added to the ammoniation slurry, and stirred at a rate of 139r / min for 5min to form a slow-release ammoniation acidolysis slurry. The slow-release ammoniation acidolysis slurry was added to a disc granulator, and 8.80g of calcium magnesium phosphate fertilizer, 104.29g of urea, 80g of potassium sulfate, and 12.0g of diammonium phosphate were added to the ammoniation slurry according to crop requirements to form granules, and after drying and screening, raffinate acid-sulfuric acid mixed acid urea-based slow-release compound fertilizer was formed. The mass ratio of calcium, magnesium, and phosphorus in the calcium magnesium phosphate fertilizer is 3:1:2.

[0163] Example 9

[0164] The raffinate-sulfuric acid mixed acid urea-based slow-release compound fertilizer obtained in Example 8 was tested on potted Chinese cabbage to clarify its effect on the yield and nutrient absorption of Chinese cabbage.

[0165] The response of pakchoi potted plants was conducted from November 18, 2023 to January 2, 2024 (45 days) at the Zhongqing Yilan pilot base of the research and development center of Yuntianhua Co., Ltd., Xishan District, Kunming, Yunnan Province, China. The pakchoi variety is "KY28" with a growth period of 45 days. There are three treatments in total, as shown in Table 6. Treatment CK is a control without fertilizer, treatment CF is traditional fertilization (N-P2O5-K2O is 17-10-11), and treatment GIF is a raffinate-sulfuric acid mixed acid urea-based slow-release compound fertilizer, and its nutrient content is N-P2O5-K2O+CaO+MgO is 17-10-11+3.6+1.1; the fertilizer application rate is 300mg / kg, 176mg / kg and 190mg / kg dry soil according to nitrogen, phosphorus and potassium, respectively. The diameter of the pot is 18.0cm at the top, 12.0cm at the bottom, and 13.5cm high. Each pot is filled with 2.0kg of soil. The fertilization method is layered fertilization, such as Figure 8 Each treatment was repeated 5 times, and the pots were randomly arranged. Except for the different fertilization, the daily management of the pots and the pest and disease control measures were the same.

[0166] Table 6 Design of compound fertilizer for Chinese cabbage

[0167] deal with Fertilization method CK No fertilizer CF Nitrogen, phosphorus and potassium compound fertilizer GIF Raffinate-sulfuric acid mixed acid urea based slow-release compound fertilizer

[0168] The leaf length, leaf width, leaf number, and leaf SPAD of Chinese cabbage were measured during the vigorous growth period of Chinese cabbage (25 days after sowing); the leaf number, leaf SPAD, aboveground fresh weight, aboveground dry weight, underground fresh weight, underground dry weight, leaf total phosphorus, available calcium, and available magnesium content were measured during the mature period (45 days after sowing). Figures 9 to 12 shown.

[0169] Compared with the traditional fertilization treatment, the raffinate-sulfuric acid mixed acid urea-based slow-release compound fertilizer can significantly promote the growth of Chinese cabbage. Compared with the CF treatment, the number of leaves, leaf length, leaf width and SPAD value of Chinese cabbage in the rapid growth period and mature period under the GIF treatment were significantly increased (Table 7).

[0170] Table 7 Effects of different fertilization treatments on the growth of Chinese cabbage

[0171]

[0172]

[0173] As can be seen from Table 7, in the rapid growth period (25 days), compared with the CF treatment, the aboveground fresh weight and dry weight of the pakchoi in the GIF treatment were significantly increased by 94.8% and 158.8%, respectively; in the harvest period (45 days), compared with the CF treatment, the aboveground fresh weight and dry weight of the pakchoi in the GIF treatment were significantly increased by 21.1% and 35.1%, the root fresh weight was significantly increased by 29.7%, and the calcium and magnesium contents in the leaves were increased by 15.6% and 9.7%. This is because the raffinate acid-based thiophosphate mixed acid urea prepared by the optimal process decomposes the low-grade phosphate ore, and the calcium and magnesium resources in the acid hydrolysis products are activated, which alleviates the current situation of calcium and magnesium nutrient deficiency in acidic soil, promotes the root growth of pakchoi, and then promotes the growth of the aboveground part of pakchoi and nutrient utilization.

[0174] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a medium- and low-grade phosphate ore acid hydrolysis product, characterized in that: The following steps are involved: The phosphate rock powder and the alkaline aqueous solution are mixed in a mass volume ratio of 1 kg: 0.4 L to 0.45 L to obtain an alkaline phosphate slurry; At 70° C. to 90° C., firstly, the raffinate acid and the alkaline phosphate slurry are mixed and stirred in a mass ratio of 0.8 to 1:1 for 15 to 75 minutes to reduce the amount of foaming, and then urea-sulfuric acid aqueous solution is added and the mixture is stirred and reacted for 30 to 150 minutes to obtain the medium-low grade phosphate ore acid hydrolysis product; The urea-sulfuric acid aqueous solution is obtained by mixing urea, sulfuric acid and water in a mass ratio of 0.8-4.2:1.0:1.0; The mass ratio of the raffinate acid to the urea-sulfuric acid aqueous solution is 3.5-13.6:

1.

2. The method for preparing the medium- and low-grade phosphate ore acid hydrolysis product according to claim 1, characterized in that: The mixing and stirring speed is 100 r / min to 300 r / min.

3. The method for preparing low- and medium-grade phosphate ore acid hydrolysis products according to claim 1, characterized in that: The particle size of the phosphate rock powder is 60 mesh to 200 mesh.

4. The method for preparing low- and medium-grade phosphate rock acid hydrolysis products according to claim 1, characterized in that: The alkaline aqueous solution is prepared by mixing urea, sodium dodecylsulfurate / sodium dodecylbenzenesulfonate and water in a mass volume ratio of 1.3kg-13.9kg:1kg:14.6L-28.6L.

5. A medium-low grade phosphate ore acid hydrolysis product prepared according to the method for preparing a medium-low grade phosphate ore acid hydrolysis product according to any one of claims 1 to 4.

6. Use of the medium- and low-grade phosphate rock acid hydrolysis product according to claim 5 in the preparation of raffinate acid-sulfuric acid mixed acid urea-based slow-release compound fertilizer for crop growth promotion.

7. The use according to claim 6, characterized in that: The raffinate acid-sulfuric acid mixed acid urea-based slow-release compound fertilizer for promoting crop growth is prepared by mixing and granulating low- and medium-grade phosphate rock acid hydrolysis products, alkaline materials, nitrogen fertilizers, phosphate fertilizers, granulation aids and potash fertilizers in a mass ratio of 1:0-1.93:1.25-1.74:0.02-0.20:0.03-0.55:

1.

8. The use according to claim 7, characterized in that: Ammonia gas was introduced during the granulation process.

9. The use according to claim 7, characterized in that: The alkaline material is calcium magnesium phosphate or ammonium bicarbonate; The nitrogen fertilizer is at least one of urea, ammonium chloride, ammonium sulfate and ammonium bicarbonate; The phosphate fertilizer is any one of monoammonium phosphate, diammonium phosphate, calcium magnesium phosphate, and molten potassium phosphate fertilizer; The potash fertilizer is any one of potassium sulfate, potassium chloride and potassium nitrate; The granulation aid is any one of bentonite, attapulgite and montmorillonite.

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