A method for preparing potassium sulfate fertilizer

Abstract

The application discloses a preparation method of potassium sulfate fertilizer, and particularly relates to the technical field of potassium sulfate fertilizer preparation, and the method comprises the following steps: mixing potash feldspar powder and a specific composite catalyst, and then introducing the mixture and pretreated industrial tail gas containing sulfur dioxide into a fluidized bed reactor to perform a catalytic oxidation-sulfation reaction at 380 DEG C to 430 DEG C, so that a solid product containing potassium sulfate is generated, and finally, the end product is obtained through separation, leaching, crystallization and drying. The method combines tail gas treatment with mineral resource utilization, treats waste with waste, has mild process conditions, and the prepared potassium sulfate product has high purity, low chlorine content, excellent anti-caking and anti-hygroscopic physical stability, and realizes efficient conversion of sulfur dioxide and high-yield extraction of potassium resources.

Description

Technical Field

[0001] This invention relates to the field of potassium sulfate fertilizer technology, and more specifically, to a method for preparing potassium sulfate fertilizer. Background Technology

[0002] Potassium sulfate, as an important chlorine-free potassium fertilizer, is widely used in cash crops. Its industrial production mainly relies on the Mannheim process and the sulfate metathesis process.

[0003] The Mannheim process uses potassium chloride and concentrated sulfuric acid as raw materials and reacts them at high temperatures. However, this method suffers from severe equipment corrosion, high energy consumption, and difficulties in treating the byproduct hydrochloric acid. While the sulfate metathesis process avoids the use of strong acids, it generally suffers from technical bottlenecks such as low reaction efficiency, complex mother liquor circulation, difficulty in stabilizing the chloride ion content in the product, and the tendency for the production system to experience a decline in yield and quality due to the accumulation of impurities during long-term operation.

[0004] On the other hand, a large amount of sulfur dioxide emissions from industrial processes require environmental treatment. Although the mainstream limestone-gypsum process can achieve emission standards, it converts sulfur resources into low-value gypsum solid waste, failing to achieve effective resource utilization. Meanwhile, my country has abundant potassium feldspar mineral resources, but its stable structure makes it difficult to extract potassium from it economically. Traditional potassium feldspar extraction processes usually require extremely high reaction temperatures or the use of large amounts of strong acids under high pressure, resulting in huge energy consumption, high equipment requirements, and heavy environmental pollution, making it difficult to achieve large-scale industrial application.

[0005] Therefore, it is of great significance to provide a potassium sulfate preparation process that can synergistically utilize industrial waste gas and mineral resources, produce efficiently under mild conditions, and produce products with stable and excellent performance. In the existing technology, there is no effective method disclosed that combines the purification of sulfur dioxide-containing tail gas with the resource utilization of potassium feldspar to directly prepare highly stable potassium sulfate fertilizer. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, the present invention provides a method for preparing potassium sulfate fertilizer to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing potassium sulfate fertilizer, comprising the following steps:

[0008] S1. Raw material pretreatment: The potassium feldspar ore is ground into mineral powder, and the industrial exhaust gas containing sulfur dioxide is treated for dust removal and temperature regulation.

[0009] S2. Catalytic reaction and synthesis: Potassium feldspar powder is mixed with a composite catalyst and then fed into a fluidized bed reactor along with pretreated sulfur dioxide-containing tail gas. The catalytic oxidation-sulfation reaction is carried out at 380℃ to 430℃ to generate a solid product containing potassium sulfate. The composite catalyst contains vanadium oxide, iron oxide and silica support.

[0010] S3. Product separation and purification: The gas-solid mixture generated in step S2 is separated to obtain a solid product. The solid product is then leached and filtered to obtain a potassium sulfate solution, which is then crystallized and dried to obtain the potassium sulfate product.

[0011] Preferably, in step S2, the composite catalyst contains, by mass percentage, 3% to 8% vanadium oxide (calculated as vanadium pentoxide), 5% to 15% iron oxide (calculated as ferric oxide), and the remainder is silicon dioxide.

[0012] Preferably, in step S2, the mass ratio of the composite catalyst to potassium feldspar powder is 1:10 to 1:30.

[0013] Preferably, in step S1, the grinding particle size of potassium feldspar powder is <75μm.

[0014] Preferably, in step S1, the temperature adjustment process involves adjusting the industrial exhaust gas containing sulfur dioxide to 300°C to 450°C.

[0015] Preferably, in step S2, the catalytic oxidation-sulfation reaction is carried out under normal pressure.

[0016] Preferably, in step S2, the volume concentration of sulfur dioxide in the sulfur dioxide-containing industrial tail gas is 1% to 4%.

[0017] Preferably, in step S2, the specific temperature of the catalytic oxidation-sulfation reaction is controlled within the range of 400°C to 420°C.

[0018] Preferably, in step S3, the insoluble residue generated after leaching and filtration is calcined at 500°C to 700°C and then recycled back to step S2 as a composite catalyst.

[0019] Preferably, in step S3, the crystallization process includes evaporating and concentrating the potassium sulfate solution, followed by cooling and crystallization.

[0020] The technical effects and advantages of this invention are as follows:

[0021] 1. This invention innovatively integrates the purification of industrial sulfur-containing tail gas and the development of non-water-soluble potassium mineral resources, completing them simultaneously in a single process. This achieves the goal of treating waste with waste and turning waste into treasure, thereby significantly reducing raw material costs and environmental governance costs. It realizes the synergy between waste gas treatment and mineral resource utilization, and has significant environmental and economic benefits.

[0022] 2. Through the design of the catalytic system, this invention enables the core reaction to proceed efficiently under relatively mild temperature and pressure conditions. Compared with traditional high temperature and high pressure or highly corrosive processes, it significantly saves energy consumption, reduces the stringent requirements on equipment materials, improves the inherent safety and economy of the production process, and greatly reduces the harshness of the reaction and production energy consumption, making the process green and safe.

[0023] 3. The potassium sulfate product prepared by this invention not only effectively controls the impurity content, but also has excellent anti-hygroscopic and anti-caking properties due to its unique formation mechanism, thereby greatly improving the storage stability and performance of the product, enhancing its commercial value and market competitiveness. The product has high purity and significantly improved physical stability, resulting in superior commercial performance. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the overall steps of the present invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Example 1

[0026] This invention provides a method for preparing potassium sulfate fertilizer, as shown in the attached figure. Figure 1 As shown, it includes the following steps:

[0027] S1. Raw material pretreatment: Potassium feldspar with a potassium oxide content of 10.5wt% is crushed and ground into mineral powder with an average particle size of about 60μm. To simulate the flue gas of a smelter, a mixed gas with a sulfur dioxide volume concentration of 2.5% is prepared (the carrier gas is nitrogen and air, and the oxygen content is 5%), and preheated to 400℃.

[0028] S2. Catalytic reaction and synthesis: 1000g of potassium feldspar ore powder and 50g of composite catalyst (composition: vanadium pentoxide 5wt%, ferric oxide 10wt%, silicon dioxide 85wt%) are mixed evenly in a mixer. The mixture is continuously added to a small circulating fluidized bed reactor. Preheated simulated flue gas is introduced into the bottom of the reactor at a certain space velocity. The reactor bed temperature is controlled at 410±5℃, the system pressure is atmospheric pressure, and the reaction residence time is about 60min.

[0029] S3. Product Separation and Purification: The gas after the reaction is discharged after passing through a cyclone separator and a bag filter. The solid product is collected and added to 3L of 80℃ hot water for stirring and soaking for 30min. Then it is filtered. The filter residue (mainly catalyst and silicon-aluminum residue) is regenerated by calcining at 650℃ for 2h and then reused. The filtrate (potassium sulfate solution) is evaporated and concentrated to saturation, then cooled to 20℃ for crystallization, centrifuged, and the crystals are dried at 110℃ to obtain potassium sulfate product. Example 2

[0030] This embodiment provides a method for preparing potassium sulfate fertilizer. The difference from Example 1 lies in adjusting the composition of the composite catalyst and the reaction temperature, as detailed below:

[0031] The composite catalyst composition in step S2 is: vanadium pentoxide 3wt%, ferric oxide 15wt%, and silicon dioxide 82wt%.

[0032] The reactor bed temperature in step S2 is controlled at 380±5℃;

[0033] The average particle size of the potassium feldspar powder in step S1 is 70 μm;

[0034] The remaining steps and parameters are the same as in Example 1. Example 3

[0035] This embodiment provides a method for preparing potassium sulfate fertilizer. The difference from Embodiment 1 lies in adjusting the raw material ratio and the concentration of the exhaust gas, as detailed below:

[0036] The mass ratio of the composite catalyst to potassium feldspar powder in step S2 is 1:25.

[0037] In step S1, the simulated sulfur dioxide volume concentration in the flue gas is 1%;

[0038] The calcination temperature of the filter residue in step S3 is 550℃;

[0039] The remaining steps and parameters are the same as in Example 1.

[0040] Comparative Example 1

[0041] The difference between the potassium sulfate fertilizer prepared in this comparative example and Example 1 is that no composite catalyst is added, and potassium feldspar ore powder is directly added to the fluidized bed reactor to react with simulated flue gas (sulfur dioxide concentration 2.5%) preheated to 410°C. The reaction temperature is the same as 410°C.

[0042] The remaining steps are the same as in Example 1.

[0043] Comparative Example 2

[0044] The potassium sulfate fertilizer prepared in this comparative example differs from that in Example 1 in that: a single-active-component catalyst is used, and the composite catalyst is replaced with: 5 wt% vanadium pentoxide, 95 wt% silicon dioxide, and no ferric oxide.

[0045] The remaining steps and parameters are the same as in Example 1.

[0046] Comparative Example 3

[0047] This comparative example of potassium sulfate fertilizer uses a typical potassium feldspar sulfuric acid leaching method as a process control. The specific steps are as follows:

[0048] 1000g of potassium feldspar powder (60μm) of the same grade was mixed with a 50% sulfuric acid solution at 1.2 times the theoretical amount. Then, the mixture was placed in a rotary kiln and roasted at 600℃ for 2 hours. The roasted clinker was leached and filtered with hot water. The filtrate was concentrated, cooled and crystallized, and dried to obtain potassium sulfate product. The tail gas was treated by alkali absorption.

[0049] The potassium sulfate fertilizers prepared in Examples 1-3 and Comparative Examples 1-3 were tested separately below. The specific test methods are as follows:

[0050] 1. Determination of potassium extraction rate: The total potassium content (calculated as potassium oxide) in the final product was determined by the sodium tetraphenylborate gravimetric method (GB / T8574-2010 Determination of Potassium Content in Compound Fertilizers), and the potassium extraction rate was calculated according to the following formula: Potassium extraction rate (%) = (Mass of total potassium oxide in the product / Mass of total potassium oxide in the raw material potassium feldspar) × 100%;

[0051] 2. Product purity determination: The main content of potassium sulfate was determined by gravimetric method;

[0052] 3. Determination of chloride ion content: Silver nitrate potentiometric titration method (GB / T3051-2000).

[0053] 4. Product stability test:

[0054] Hygroscopicity: Place 10g of dry sample in a constant temperature and humidity chamber (temperature 30±1℃, relative humidity 80±2%), weigh it after 24h, and calculate the moisture absorption weight gain rate.

[0055] Agglomeration: 100g of sample was placed in a plastic bag and sealed. It was then stored in a 50℃ oven for 7 days. After being removed, it was allowed to cool naturally to room temperature. A 1kg weight was dropped from a height of 10cm onto the center of the sample bag once. The agglomeration was observed and evaluated, and the agglomeration rate was calculated (agglomeration mass / total mass × 100%).

[0056] 5. Determination of sulfur dioxide conversion rate in exhaust gas: The sulfur dioxide concentration at the reactor inlet and outlet is monitored online using a flue gas analyzer, and the following calculation is performed: Sulfur dioxide conversion rate (%) = [(Inlet sulfur dioxide concentration - Outlet sulfur dioxide concentration) / Inlet thermal sulfur dioxide concentration] × 100%.

[0057] The test results of the potassium sulfate fertilizer products prepared in Examples 1-3 and Comparative Examples 1-3 are shown in the table below:

[0058]

[0059] From the test data of the above embodiments and comparative examples, it can be seen that:

[0060] 1. Examples 1-3 successfully prepared high-purity potassium sulfate products with low chlorine content using sulfur dioxide-containing tail gas and potassium feldspar. The potassium extraction rate reached over 82%, and the tail gas was purified efficiently (sulfur dioxide conversion rate > 97%), proving the feasibility of the technical route of the present invention.

[0061] 2. The potassium extraction rate of Comparative Example 1 (without catalyst) was extremely low (18.7%), and the sulfur dioxide conversion rate was only 15.4%, proving that under mild conditions, the reaction can hardly proceed effectively without the composite catalyst of this invention.

[0062] The potassium extraction rate (45.2%) and sulfur dioxide conversion rate (75.6%) of Comparative Example 2 (vanadium pentoxide only) were much lower than those of Example 1 (88.5%, 99.3%), which proves that the synergistic effect of ferric oxide and vanadium pentoxide is indispensable: ferric oxide is crucial for activating the potassium feldspar lattice, and the two work together to achieve a highly efficient catalytic oxidation-sulfation coupling reaction;

[0063] 3. Mild conditions and energy consumption advantages: The embodiments were carried out under mild atmospheric pressure conditions of around 410°C, while Comparative Example 3 (traditional process) requires a high temperature and strong acid environment of over 600°C and produces corrosive exhaust gas. Therefore, the present invention has a revolutionary advantage in terms of energy consumption, equipment requirements and environmental protection.

[0064] The product exhibits outstanding stability: the hygroscopicity and agglomeration rate of the product in the example are significantly better than those in Comparative Example 2 and Comparative Example 3, especially with a significant reduction in agglomeration rate. This confirms that the in-situ reaction-crystallization process of the present invention can generate potassium sulfate products with better physical stability, thus achieving the goal of improving stability.

[0065] Resource recycling and environmental protection: The example demonstrates the characteristics of green process through catalyst recycling, while Comparative Example 3 has problems with the treatment of waste acid gas and a large amount of residue.

[0066] In summary, the preparation method provided by this invention, through a specific composite catalyst and fluidized bed process, creatively transforms industrial waste gas and potassium feldspar into a highly stable potassium sulfate product under mild conditions. Compared with existing technologies, this method has achieved unexpected and significant progress in terms of technical approach, comprehensive performance, and environmental and economic benefits.

[0067] The above description is merely a preferred embodiment of the present invention and is 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 within the protection scope of the present invention.

Claims

1. A method of producing a potassium sulfate fertilizer, characterized by: Includes the following steps: S1. Raw material pretreatment: The potassium feldspar ore is ground into mineral powder, and the industrial exhaust gas containing sulfur dioxide is treated for dust removal and temperature regulation. S2. Catalytic reaction and synthesis: Potassium feldspar powder is mixed with a composite catalyst and then fed into a fluidized bed reactor along with pretreated sulfur dioxide-containing tail gas. The catalytic oxidation-sulfation reaction is carried out at 380℃ to 430℃ to generate a solid product containing potassium sulfate. The composite catalyst contains vanadium oxide, iron oxide and silica support. In the composite catalyst, by mass percentage, the content of vanadium oxide (calculated as vanadium pentoxide) is 3% to 8%, the content of iron oxide (calculated as ferric oxide) is 5% to 15%, and the remainder is silicon dioxide. S3. Product separation and purification: The gas-solid mixture generated in step S2 is separated to obtain a solid product. The solid product is then leached and filtered to obtain a potassium sulfate solution, which is then crystallized and dried to obtain the potassium sulfate product.

2. The method of claim 1, wherein: In step S2, the mass ratio of the composite catalyst to potassium feldspar powder is 1:10 to 1:

30.

3. The method of claim 1, wherein: In step S1, the grinding particle size of potassium feldspar powder is <75μm.

4. The method of claim 1, wherein: In step S1, the temperature adjustment process involves adjusting the industrial exhaust gas containing sulfur dioxide to 300°C to 450°C.

5. The method of claim 1, wherein: In step S2, the catalytic oxidation-sulfation reaction is carried out under normal pressure.

6. The method of claim 1, wherein: In step S2, the volume concentration of sulfur dioxide in the industrial tail gas containing sulfur dioxide is 1% to 4%.

7. The method of claim 1, wherein: In step S2, the specific temperature of the catalytic oxidation-sulfation reaction is controlled within the range of 400℃ to 420℃.

8. The method of claim 1, wherein: In step S3, the insoluble residue generated after leaching and filtration is calcined at 500°C to 700°C and then recycled back to step S2 as a composite catalyst.

9. The method for preparing potassium sulfate fertilizer according to claim 1, characterized in that: In step S3, the crystallization process includes evaporating and concentrating the potassium sulfate solution, followed by cooling and crystallization.

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