Method for preparing potassium sulfate fertilizer and co-producing cement raw material by using ardealite

Abstract

The invention provides a method for preparing a potassium sulfate fertilizer and co-producing a cement raw material by using ardealite. According to the method disclosed by the invention, the potassium sulfate fertilizer is prepared by a one-step potassium hydroxide leaching ardealite method, and meanwhile, the byproduct filter residue is subjected to low-temperature calcination, so that cement raw materials (SiO2 and CaO) can be obtained; the ardealite is directly leached through potassium hydroxide, high-purity potassium sulfate is obtained in one step, the cement raw material is directly obtained through low-temperature calcination of by-products, the process is simple, environment-friendly and efficient, and double-industry high-value utilization of solid waste is achieved. The prepared potassium sulfate fertilizer is high in purity, chloride ions and other elements unfavorable for soil are not introduced, and meanwhile a thought is provided for effectively absorbing a large amount of solid waste, namely ardealite; the calcining temperature is only 300-600 DEG C, compared with the prior art, the calcining temperature is lower, the energy consumption is lower, the cement raw materials (SiO2 and CaO) are obtained at the same time, and the maximum efficient utilization of the phosphogypsum is realized.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste resource utilization technology, and in particular relates to a method for preparing potassium sulfate fertilizer and cement raw materials using phosphogypsum. Background Technology

[0002] Phosphogypsum is a large-scale solid waste generated during the wet-process phosphoric acid production in the phosphate chemical industry. Its main component is CaSO4·2H2O. Its annual emissions are enormous, and its stockpiling not only occupies significant land resources but also easily pollutes soil and water bodies through rainwater leaching, causing serious ecological and environmental problems. Currently, the resource utilization of phosphogypsum is a critical issue that urgently needs to be addressed by the industry.

[0003] Potassium sulfate, as an important chloride-free potassium fertilizer and industrial raw material, enjoys strong market demand. Traditional processes for preparing potassium sulfate mostly use potassium chloride and sulfuric acid as raw materials, which have problems such as introducing chloride ion impurities, complex production processes, and difficult-to-treat by-products. At the same time, some comprehensive utilization technologies for phosphogypsum can only recover the gypsum component alone, or require multi-step reactions and special catalysts in the preparation of potassium sulfate, resulting in high process costs and difficulty in ensuring product purity.

[0004] In addition, cement production has a stable demand for calcium and silicon raw materials, while phosphogypsum is mainly composed of calcium sulfate and silicon dioxide. After processing, it can be used as a cement raw material. However, the current technology for processing phosphogypsum often cannot simultaneously achieve the efficient preparation of potassium sulfate and the high-quality co-production of cement raw materials, and it is easy to leave behind impurities such as chloride ions, which affects product quality and application scenarios.

[0005] Existing technology CN101580409A discloses a method for producing potassium sulfate fertilizer using phosphogypsum. This method involves thoroughly mixing 20%–80% by weight of phosphogypsum with 20%–80% of potassium carbonate powder, followed by calcination at a temperature of 800℃–1800℃. While this method also utilizes phosphogypsum to produce potassium sulfate fertilizer, its high calcination temperature (800℃–1800℃) results in significant energy consumption. Furthermore, this method does not prepare cement raw materials and does not maximize the utilization of phosphogypsum. Given the current shortcomings in the production of potassium sulfate fertilizer using phosphogypsum, it is necessary to improve this method. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum. This method involves a one-step leaching process of phosphogypsum with potassium hydroxide to produce potassium sulfate fertilizer, while simultaneously calcining the byproduct filter residue at low temperatures to obtain cement raw materials. The prepared potassium sulfate fertilizer has high purity and does not introduce harmful elements to the soil, such as chloride ions. This method also provides a new approach for the effective disposal of phosphogypsum, a major solid waste. Compared to existing technologies, this method uses a calcination temperature of only 300-600℃, resulting in lower energy consumption and the simultaneous production of cement raw materials, thus maximizing the utilization of phosphogypsum.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum, comprising the following steps:

[0009] Add phosphogypsum to potassium hydroxide solution and stir to obtain a slurry;

[0010] The slurry is filtered to obtain filtrate and filter residue;

[0011] The filtrate was evaporated and crystallized to obtain potassium sulfate;

[0012] The filter residue is calcined to obtain cement raw materials;

[0013] The calcination temperature is 300~600℃.

[0014] Preferably, in the step of calcining the filter residue, the calcination time is:

[0015] Preferably, phosphogypsum is added to a potassium hydroxide solution and stirred at 20~100℃ to obtain a slurry.

[0016] Preferably, phosphogypsum is added to potassium hydroxide solution and stirred at 20~100℃ for 10min~5h to obtain slurry.

[0017] Preferably, the concentration of the potassium hydroxide solution is 0.8~3 mol / L.

[0018] Preferably, the molar ratio of phosphogypsum to potassium hydroxide in the potassium hydroxide solution is 1:(1~3), based on CaSO4 in phosphogypsum.

[0019] Preferably, phosphogypsum is added to potassium hydroxide solution and stirred at 20-25°C for 0.5 hours to obtain a slurry;

[0020] The slurry is filtered to obtain filtrate and filter residue;

[0021] The filtrate was evaporated and crystallized to obtain potassium sulfate;

[0022] The filter residue is calcined to obtain cement raw materials;

[0023] The calcination temperature is 600℃;

[0024] The concentration of the potassium hydroxide solution is 1.2 mol / L;

[0025] Based on the CaSO4 content in phosphogypsum, the molar ratio of phosphogypsum to potassium hydroxide in the potassium hydroxide solution is 1:1.

[0026] Preferably, in the step of evaporating and crystallizing the filtrate, the evaporation temperature is 70~90℃.

[0027] The method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum according to the present invention has the following advantages compared with the prior art:

[0028] 1. The present invention provides a method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum. Potassium sulfate fertilizer is prepared by one-step leaching of phosphogypsum with potassium hydroxide, while the by-product filter residue is calcined at low temperature to obtain cement raw materials (SiO2, CaO). The potassium sulfate fertilizer prepared by the present invention has high purity and does not introduce elements harmful to the soil, such as chloride ions. It also provides a new approach for the effective disposal of phosphogypsum, a major solid waste. Existing technologies disclose the production of potassium sulfate fertilizer from phosphogypsum, but their calcination temperatures are as high as 800℃~1800℃, resulting in high energy consumption, and this method does not produce cement raw materials. In contrast, the calcination temperature of the present invention is only 300~600℃, which is lower than the existing technology, resulting in lower energy consumption, and simultaneously obtaining cement raw materials (SiO2, CaO). This maximizes the efficient utilization of phosphogypsum compared to the existing technology.

[0029] 2. This invention uses potassium hydroxide as an alkali source to react with phosphogypsum, without introducing harmful impurities such as chloride ions throughout the process, thus avoiding the problem of residual chloride ions in the product potassium sulfate from the source. High-purity, chloride-free potassium sulfate not only meets the agricultural sector's demand for high-quality potassium fertilizer but also extends to industrial-grade potassium sulfate applications. Compared to traditional conversion processes using potassium chloride as raw material, it eliminates the need for additional dechlorination and purification steps, reducing process complexity and minimizing the negative impact of impurities on product performance and subsequent applications, resulting in broader market applicability.

[0030] The core reaction of this invention requires only a direct reaction between phosphogypsum and potassium hydroxide. Solid potassium sulfate is obtained through solid-liquid separation, evaporation, and crystallization. The entire process involves no complex intermediate reactions and requires no stringent reaction conditions. This simplified process not only shortens the production cycle and reduces equipment investment costs (eliminating the need for dedicated catalytic reaction devices and complex separation and purification equipment), but also reduces energy and material consumption during production, thereby improving production efficiency. Compared to traditional processes involving multi-step conversion and graded purification, this solution has a lower operational threshold, is more suitable for large-scale continuous production, and can effectively reduce production costs and operational risks for enterprises.

[0031] 3. As a major solid waste in the phosphate chemical industry, phosphogypsum is utilized efficiently in this invention. The reaction product, potassium sulfate, is a high-value agricultural / industrial raw material, while the by-product filter residue (calcium hydroxide + silicon dioxide) can be directly used as a raw material for cement production without additional treatment. This design completely solves the problems of land occupation and environmental pollution (such as leachate pollution) caused by phosphogypsum stockpiling, realizing a closed-loop industrial chain of "raw materials-products-by-products". Compared with some processes that only recover a single product and require separate disposal of filter residue, this solution not only reduces solid waste treatment costs but also creates additional economic benefits through by-product resource utilization, aligning with the green production orientation under the "dual carbon" goal, combining environmental protection and economic value.

[0032] 4. The potassium sulfate produced by this invention, after evaporation and crystallization, exhibits high purity and uniform particle size, resulting in stable product quality. Crystallization process parameters can be adjusted according to requirements, adapting to the purity and particle size requirements of different fields. The ratio of calcium hydroxide to silicon dioxide in the byproduct filter residue is well-suited to cement-making raw materials, allowing for direct use without additional ratio adjustments. Furthermore, the filter residue contains no harmful impurities, ensuring no impact on cement product quality. Compared to some processes that suffer from large fluctuations in product purity and require secondary modification of byproducts for utilization, this solution ensures that both the product and byproduct quality meet downstream application needs without additional modification or purification costs, thus improving the overall efficiency and market acceptance of the process. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 The image shows the XRD pattern of the potassium sulfate fertilizer prepared in Example 2.

[0035] Figure 2The image shows the XRD patterns of calcium oxide and silicon dioxide, the cement raw materials generated after calcination in Example 2. Detailed Implementation

[0036] To facilitate understanding of the present invention, a more comprehensive description of the invention will be provided below in conjunction with specific embodiments. Preferred embodiments of the invention are given in the specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0037] The order in which the embodiments are described below is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0038] This invention provides a method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum, comprising the following steps:

[0039] S1. Add phosphogypsum to potassium hydroxide solution and stir to obtain a slurry;

[0040] S2. Filter the slurry to obtain filtrate and filter residue;

[0041] S3. Evaporate the filtrate to crystallize and obtain potassium sulfate;

[0042] S4. Calcine the filter residue to obtain cement raw materials;

[0043] The calcination temperature is 300~600℃.

[0044] This invention discloses a method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum. First, phosphogypsum and potassium hydroxide are dissolved and stirred in a specific ratio. After reacting for a period of time, the mixture is filtered. The filtered residue is then calcined at a low temperature to obtain cement raw materials. The filtrate is a potassium sulfate solution, which is evaporated and crystallized to obtain potassium sulfate fertilizer. This invention directly leaches phosphogypsum with potassium hydroxide to obtain high-purity potassium sulfate in one step. The byproduct is then directly calcined at a low temperature to obtain cement raw materials. The process is simple, environmentally friendly, and efficient, achieving high-value utilization of solid waste in two industries.

[0045] This invention prepares potassium sulfate fertilizer by one-step leaching of phosphogypsum with potassium hydroxide, while simultaneously calcining the by-product filter residue at low temperature to obtain cement raw materials (SiO2, CaO). The potassium sulfate fertilizer prepared by this invention has high purity and does not introduce elements harmful to the soil such as chloride ions. It also provides a new approach for the effective disposal of phosphogypsum, a major solid waste.

[0046] Existing technologies disclose the production of potassium sulfate fertilizer using phosphogypsum, but the calcination temperature is as high as 800℃~1800℃, which results in high energy consumption, and the method does not produce cement raw materials. In contrast, the calcination temperature of this invention is only 300~600℃, which is lower than the existing technology, resulting in lower energy consumption, and cement raw materials (SiO2, CaO) are obtained simultaneously. Compared with the existing technology, this method maximizes the efficient utilization of phosphogypsum.

[0047] Specifically, the working principle of the method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum according to the present invention is as follows:

[0048] When phosphogypsum is added to a potassium hydroxide solution, the following reaction occurs: CaSO4 + KOH = Ca(OH)2 + K2SO4. After filtration, the filtrate contains K2SO4. The filtrate is then evaporated, concentrated, and crystallized to obtain K2SO4 fertilizer. The filter residue is mainly composed of Ca(OH)2 (containing some SiO2). Calcination of Ca(OH)2 results in the following reaction: Ca(OH)2 = CaO + H2O, thus obtaining cement raw materials.

[0049] In some embodiments, the calcination time for the filter residue is 2 to 150 minutes.

[0050] In some embodiments, phosphogypsum is added to a potassium hydroxide solution and stirred at 20-100°C to obtain a slurry.

[0051] In some embodiments, phosphogypsum is added to a potassium hydroxide solution and stirred at 20~100°C for 10 min~5 h to obtain a slurry.

[0052] In some embodiments, the concentration of the potassium hydroxide solution is 0.8~3 mol / L.

[0053] In some embodiments, the molar ratio of phosphogypsum to potassium hydroxide in the potassium hydroxide solution is 1:(1~3), based on CaSO4 in phosphogypsum.

[0054] In some embodiments, phosphogypsum is added to a potassium hydroxide solution and stirred at 20-25°C for 0.5 hours to obtain a slurry;

[0055] The slurry is filtered to obtain filtrate and filter residue;

[0056] The filtrate was evaporated and crystallized to obtain potassium sulfate;

[0057] The filter residue is calcined to obtain cement raw materials;

[0058] The calcination temperature is 600℃;

[0059] The concentration of the potassium hydroxide solution is 1.2 mol / L;

[0060] Based on CaSO4 in phosphogypsum, the molar ratio of phosphogypsum to potassium hydroxide in potassium hydroxide solution is 1:2.

[0061] In some embodiments, the evaporation temperature is 70~90°C during the step of evaporating and crystallizing the filtrate.

[0062] The method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum according to the present invention has the following advantages:

[0063] This invention uses potassium hydroxide as an alkali source to react with phosphogypsum, without introducing harmful impurities such as chloride ions throughout the process, thus avoiding the problem of residual chloride ions in the finished potassium sulfate product from the source. High-purity, chloride-free potassium sulfate not only meets the agricultural sector's demand for high-quality potassium fertilizer but also extends to industrial-grade potassium sulfate applications. Compared to traditional conversion processes using potassium chloride as raw material, it eliminates the need for additional dechlorination and purification steps, reducing process complexity and minimizing the negative impact of impurities on product performance and subsequent applications, resulting in broader market applicability.

[0064] The core reaction of this invention requires only a direct reaction between phosphogypsum and potassium hydroxide. Solid potassium sulfate is obtained through solid-liquid separation, evaporation, and crystallization. The entire process involves no complex intermediate reactions and requires no stringent reaction conditions. This simplified process not only shortens the production cycle and reduces equipment investment costs (eliminating the need for dedicated catalytic reaction devices and complex separation and purification equipment), but also reduces energy and material consumption during production, thereby improving production efficiency. Compared to traditional processes involving multi-step conversion and graded purification, this solution has a lower operational threshold, is more suitable for large-scale continuous production, and can effectively reduce production costs and operational risks for enterprises.

[0065] As a major solid waste in the phosphate chemical industry, phosphogypsum is utilized efficiently in this invention. The reaction product, potassium sulfate, is a high-value agricultural / industrial raw material, while the by-product filter residue (calcium hydroxide + silicon dioxide) can be directly used as a raw material for cement production without additional treatment. This design completely solves the problems of land occupation and environmental pollution (such as leachate pollution) caused by phosphogypsum stockpiling, realizing a closed-loop industrial chain of "raw materials-products-by-products". Compared with some processes that only recover a single product and require separate disposal of filter residue, this solution not only reduces solid waste treatment costs but also creates additional economic benefits through by-product resource utilization, aligning with the green production orientation under the "dual carbon" goal, and combining environmental and economic value.

[0066] The potassium sulfate produced by this invention, after evaporation and crystallization, exhibits high purity and uniform particle size, resulting in stable product quality. Crystallization process parameters can be adjusted according to requirements, adapting to the purity and particle size requirements of different fields. The ratio of calcium hydroxide to silicon dioxide in the byproduct filter residue is highly compatible with cement-making raw materials, allowing for direct use without additional ratio adjustments. Furthermore, the filter residue contains no harmful impurities, ensuring no impact on cement product quality. Compared to some processes that suffer from large fluctuations in product purity and require secondary modification of byproducts for utilization, this solution ensures that both the product and byproduct quality meet downstream application needs without incurring additional modification or purification costs, thus improving the overall efficiency and market acceptance of the process.

[0067] The following specific embodiments further illustrate the method of preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum according to the present invention. This section further illustrates the content of the present invention with reference to specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0068] The chemical composition of phosphogypsum in the following examples is shown in the table below, with the remainder being unavoidable impurities.

[0069] Table 1 - Chemical Composition of Phosphogypsum

[0070]

[0071] Example 1

[0072] This embodiment provides a method for preparing potassium sulfate fertilizer and cement raw materials using phosphogypsum, including the following steps:

[0073] S1. Add phosphogypsum to 1L of 0.8 mol / L potassium hydroxide solution and dissolve and stir at room temperature (25℃) for 2 hours to obtain a slurry; based on CaSO4 in phosphogypsum, the molar ratio of phosphogypsum to potassium hydroxide in potassium hydroxide solution is 1:2.

[0074] S2. Filter the slurry to obtain filtrate and filter residue;

[0075] S3. Evaporate the filtrate at 70°C to crystallize and obtain potassium sulfate;

[0076] S4. Calcine the filter residue at 600℃ for 10 minutes to obtain cement raw materials.

[0077] Example 2

[0078] This embodiment provides a method for preparing potassium sulfate fertilizer and cement raw materials using phosphogypsum, including the following steps:

[0079] S1. Add phosphogypsum to 1L of 1.2 mol / L potassium hydroxide solution and dissolve and stir at room temperature (25℃) for 0.5h to obtain a slurry; based on CaSO4 in phosphogypsum, the molar ratio of phosphogypsum to potassium hydroxide in potassium hydroxide solution is 1:2.

[0080] S2. Filter the slurry to obtain filtrate and filter residue;

[0081] S3. Evaporate the filtrate at 70°C to crystallize and obtain potassium sulfate;

[0082] S4. Calcine the filter residue at 600℃ for 10 minutes to obtain cement raw materials.

[0083] Example 3

[0084] This embodiment provides a method for preparing potassium sulfate fertilizer and cement raw materials using phosphogypsum, including the following steps:

[0085] S1. Add phosphogypsum to 1L of 1.6 mol / L potassium hydroxide solution and dissolve and stir at room temperature (25℃) for 2 hours to obtain a slurry; based on CaSO4 in phosphogypsum, the molar ratio of phosphogypsum to potassium hydroxide in potassium hydroxide solution is 1:2.

[0086] S2. Filter the slurry to obtain filtrate and filter residue;

[0087] S3. Evaporate the filtrate at 70°C to crystallize and obtain potassium sulfate;

[0088] S4. Calcine the filter residue at 500℃ for 10 minutes to obtain cement raw materials.

[0089] Example 4

[0090] This embodiment provides a method for preparing potassium sulfate fertilizer and cement raw materials using phosphogypsum, including the following steps:

[0091] S1. Add phosphogypsum to 1L of 2.0 mol / L potassium hydroxide solution and dissolve and stir at room temperature (25℃) for 2 hours to obtain a slurry; based on CaSO4 in phosphogypsum, the molar ratio of phosphogypsum to potassium hydroxide in potassium hydroxide solution is 1:2.

[0092] S2. Filter the slurry to obtain filtrate and filter residue;

[0093] S3. Evaporate the filtrate at 70°C to crystallize and obtain potassium sulfate;

[0094] S4. Calcine the filter residue at 500℃ for 10 minutes to obtain cement raw materials.

[0095] Example 5

[0096] This embodiment provides a method for preparing potassium sulfate fertilizer and cement raw materials using phosphogypsum, including the following steps:

[0097] S1. Add phosphogypsum to 1L of 1.2 mol / L potassium hydroxide solution and dissolve and stir at room temperature (25℃) for 2 hours to obtain a slurry; based on CaSO4 in phosphogypsum, the molar ratio of phosphogypsum to potassium hydroxide in potassium hydroxide solution is 1:2.

[0098] S2. Filter the slurry to obtain filtrate and filter residue;

[0099] S3. Evaporate the filtrate at 70°C to crystallize and obtain potassium sulfate;

[0100] S4. Calcine the filter residue at 600℃ for 10 minutes to obtain cement raw materials.

[0101] Example 6

[0102] This embodiment provides a method for preparing potassium sulfate fertilizer and cement raw materials using phosphogypsum, including the following steps:

[0103] S1. Add phosphogypsum to 1L of 1.2 mol / L potassium hydroxide solution and dissolve and stir at 60℃ for 0.5h to obtain a slurry; based on CaSO4 in phosphogypsum, the molar ratio of phosphogypsum to potassium hydroxide in potassium hydroxide solution is 1:2.

[0104] S2. Filter the slurry to obtain filtrate and filter residue;

[0105] S3. Evaporate the filtrate at 70°C to crystallize and obtain potassium sulfate;

[0106] S4. Calcine the filter residue at 600℃ for 10 minutes to obtain cement raw materials.

[0107] Example 7

[0108] This embodiment provides a method for preparing potassium sulfate fertilizer and cement raw materials using phosphogypsum, including the following steps:

[0109] S1. Add phosphogypsum to 1L of 1.2 mol / L potassium hydroxide solution and dissolve and stir at room temperature (25℃) for 2 hours to obtain a slurry; based on CaSO4 in phosphogypsum, the molar ratio of phosphogypsum to potassium hydroxide in potassium hydroxide solution is 1:2.

[0110] S2. Filter the slurry to obtain filtrate and filter residue;

[0111] S3. Evaporate the filtrate at 70°C to crystallize and obtain potassium sulfate;

[0112] S4. Calcine the filter residue at 400℃ for 10 minutes to obtain cement raw materials.

[0113] Comparative Example 1

[0114] This embodiment provides a method for preparing potassium sulfate fertilizer and cement raw materials using phosphogypsum, including the following steps:

[0115] S1. Add phosphogypsum to 1L of 0.6 mol / L potassium carbonate solution and dissolve and stir at room temperature (25℃) for 0.5h to obtain a slurry; based on CaSO4 in phosphogypsum, the molar ratio of phosphogypsum to potassium carbonate in potassium carbonate solution is 1:1.

[0116] S2. Filter the slurry to obtain filtrate and filter residue;

[0117] S3. Evaporate the filtrate at 70°C to crystallize and obtain potassium sulfate;

[0118] S4. Calcine the filter residue at 1000℃ for 10 minutes to obtain cement raw material. Performance testing.

[0119] phosphogypsum leaching rate test

[0120] Leaching rate test of phosphogypsum: The filtrates obtained in Examples 1-6 (Example 7 was not performed because its phosphogypsum was stirred in potassium hydroxide solution with the same parameters as in Example 5) and Comparative Example 1 in step S2 were brought to a final volume of 250 mL. The sulfate content (X1) in the filtrate was tested according to HJ / T 342-2007 (Determination of sulfate in water by barium chromate spectrophotometry), and the calcium ion concentration (C1) was detected by ICP. According to GB / T 23456 (phosphogypsum), the sulfate ion content (X2) and calcium ion concentration (C2) were determined. The phosphogypsum leaching rate was calculated using the following formula:

[0121] The leaching rate of phosphogypsum, Q (%), is calculated as (X1 / X2) × 100%.

[0122] Calcium loss rate R (%) = (C1 / C2) × 100%

[0123] The test results are shown in Table 2 below:

[0124] Table 2 - Leaching rate of phosphogypsum in Examples 1-6 and Comparative Example 1

[0125]

[0126] This invention achieves efficient sulfate leaching and effective control of calcium loss in phosphogypsum by adjusting process parameters such as potassium hydroxide concentration, reaction time, and calcination temperature. For example, Example 2, using 1.2 mol / L potassium hydroxide and stirring at room temperature for 0.5 h, achieved a sulfate leaching rate of 99.82% and a calcium loss rate of only 1.86%, demonstrating optimal performance in balancing potassium sulfate preparation and cement raw material co-production. Example 4, using 2.0 mol / L potassium hydroxide, reduced the calcium loss rate to 2.38%, providing an option for scenarios requiring low calcium loss. In Comparative Example 1, the use of 0.6 mol / L potassium carbonate solution resulted in a sulfate leaching rate of only 76.73% and a calcium loss rate as high as 16.31%. Compared to Example 6, Examples 1-4 achieve efficient reactions at room temperature without additional heating, making the process more economical. Furthermore, parameter optimization significantly improves the efficiency and economy of phosphogypsum resource utilization, demonstrating outstanding technical advantages in the fields of potassium sulfate fertilizer preparation and cement raw material co-production.

[0127] Fertilizer quality testing

[0128] The potassium sulfate obtained in Examples 1-6 and Comparative Example 1 in step S3 was tested. Its water-soluble potassium oxide, sulfur, chloride ion, moisture and free acid were tested according to GB / T 20406—2017 (potassium sulfate for agricultural use). The results are shown in Table 3.

[0129] Table 3 - Detection results of potassium sulfate prepared in Examples 1-6

[0130]

[0131] The potassium sulfate product prepared by this invention meets the requirements of industrial qualified product standards in terms of water-soluble potassium oxide and sulfur content. Examples 2 and 4, and Examples 5 and 6, all meet the requirements of first-class product standards. Furthermore, no chloride ions are introduced into the raw materials, and the moisture and free acid contents are far below the standard limits. For example, the water-soluble potassium oxide content in Example 2 reaches 50.26%. The product quality is excellent and stable, fully demonstrating the outstanding advantages of the process in chloride-free properties, product purity, and stability, perfectly meeting the high-quality requirements of industrial-grade potassium sulfate. In Comparative Example 1, the water-soluble potassium oxide content is only 49.31%, and the free acid content is 0.32%, further indicating that the potassium sulfate obtained by using potassium hydroxide in this invention has higher purity than that obtained by using potassium carbonate.

[0132] XRF analysis was performed on the calcined cement raw material in Example 2 to detect its mass ratio of calcium oxide to silicon dioxide. The mass ratio was 3.58, which meets the requirement of GB / T 21372—2024 (Silicate Cement Clinker) that the mass ratio of calcium oxide to silicon dioxide is ≥2, indicating that the cement raw material generated by this process can be used for cement production.

[0133] Figure 1 The image shows the XRD pattern of the potassium sulfate fertilizer prepared in Example 2.

[0134] The potassium sulfate prepared in Example 2 of this invention was subjected to XRD testing, and the results were compared with those of the standard potassium sulfate card. Figure 1 As shown, the XRD pattern of the potassium sulfate product obtained by this invention completely matches the diffraction peaks of standard PDF#70-1488 K2SO4, indicating that the product is a high-purity potassium sulfate crystal without interference from impurity phase diffraction peaks. This result verifies at the crystal structure level that this process can efficiently prepare pure potassium sulfate, further confirming the high purity of the product and the reliability of the process. It has significant technical advantages in controlling the crystal purity of potassium sulfate, providing strong structural support for the high-quality application of the product in agriculture and industry.

[0135] Figure 2 The image shows the XRD patterns of calcium oxide and silicon dioxide, the cement raw materials generated after calcination in Example 2.

[0136] from Figure 2 As can be seen, the main components of the calcined filter residue are CaO (PDF#99-0070) and SiO2 (PDF#89-1961), and the diffraction peaks perfectly match those of the standard card, indicating high crystal purity and absence of impurity phase interference. Considering the quality requirements of cement raw materials, CaO and SiO2 are the core components of silicate cement clinker. The phase composition of CaO and SiO2 in the calcined product of this invention highly matches the compositional requirements of cement raw materials and can be directly used as calcareous and siliceous raw materials for cement production, meeting the quality standards for cement production. This further verifies the technical advantages of this process in the co-production of cement raw materials from solid waste resources.

[0137] It is understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0138] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum, characterized in that, Includes the following steps: Add phosphogypsum to potassium hydroxide solution and stir to obtain a slurry; The slurry is filtered to obtain filtrate and filter residue; The filtrate was evaporated and crystallized to obtain potassium sulfate; The filter residue is calcined to obtain cement raw materials; The calcination temperature is 300~600℃.

2. The method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum as described in claim 1, characterized in that, In the step of calcining the filter residue, the calcination time is 2~150min.

3. The method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum as described in claim 1, characterized in that, Add phosphogypsum to potassium hydroxide solution and stir at 20~100℃ to obtain a slurry.

4. The method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum as described in claim 1, characterized in that, Add phosphogypsum to potassium hydroxide solution and stir at 20~100℃ for 10min~5h to obtain slurry.

5. The method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum as described in claim 1, characterized in that, The concentration of the potassium hydroxide solution is 0.8~3 mol / L.

6. The method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum as described in claim 1, characterized in that, Based on CaSO4 in phosphogypsum, the molar ratio of phosphogypsum to potassium hydroxide in potassium hydroxide solution is 1:(1~3).

7. The method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum as described in claim 1, characterized in that, Add phosphogypsum to potassium hydroxide solution and stir at 20-25℃ for 0.5 hours to obtain a slurry; The slurry is filtered to obtain filtrate and filter residue; The filtrate was evaporated and crystallized to obtain potassium sulfate; The filter residue is calcined to obtain cement raw materials; The calcination temperature is 600℃; The concentration of the potassium hydroxide solution is 1.2 mol / L; Based on the CaSO4 content in phosphogypsum, the molar ratio of phosphogypsum to potassium hydroxide in the potassium hydroxide solution is 1:

1.

8. The method for preparing potassium sulfate fertilizer and co-producing cement raw materials using phosphogypsum as described in claim 1, characterized in that, In the step of evaporating and crystallizing the filtrate, the evaporation temperature is 70~90℃.

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