Modified ardealite based on semi-hydrated-dihydrated process byproduct and preparation method of modified ardealite
By combining three countercurrent washing processes, water washing, acid resizing, and wet modification, the problem of high impurity content in hemihydrate and dihydrate phosphogypsum has been solved, achieving efficient resource utilization of phosphogypsum. This process is applicable to roadbed and building materials industries.
Patent Information
- Application Number
- CN202511560825.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-29
- Publication Date
- 2026-01-13
AI Technical Summary
The phosphogypsum produced during the hemihydrate and dihydrate process of phosphoric acid production has a high content of impurities, especially fluorine and phosphorus, which are difficult to treat harmlessly through conventional methods, resulting in difficulties in resource utilization and becoming a bottleneck restricting the sustainable development of this process.
The process combines three countercurrent washing, water washing, acid resizing, and wet modification. The countercurrent washing removes soluble impurities, the water washing removes some impurities, the acid resizing dissolves fluorosilicates, and the wet modification fixes residual impurities, forming a highly efficient modified phosphogypsum.
It significantly reduces the total phosphorus and total fluorine content in phosphogypsum, improves the quality of phosphogypsum, and enables it to meet the Class I solid waste standard, thus achieving efficient resource utilization. It is suitable for applications such as roadbeds and building materials.
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Figure CN121317846A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of phosphorus chemical technology, specifically to a modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process and its preparation method. Background Technology
[0002] Phosphogypsum is a byproduct of wet-process phosphoric acid production. Approximately 4.5 to 5.5 tons of phosphogypsum are generated for every ton of phosphoric acid produced (calculated as P2O5). By the end of 2024, my country's annual phosphogypsum production had exceeded 78 million tons. Due to its high content of impurities such as phosphorus, fluorine, and heavy metals, phosphogypsum has been restricted from use in various fields such as building materials and agriculture. The stockpiling of phosphogypsum has brought enormous pressure to the environment and wasted resources.
[0003] The hemihydrate-dihydrate process of phosphogypsum differs significantly from that of the traditional dihydrate process, particularly in crystal morphology, impurity occurrence, and the difficulty of subsequent processing. The hemihydrate-dihydrate process byproduct phosphogypsum is mostly in flake form, generated under high temperature and high acid concentration conditions. This results in deep encapsulation and eutectic formation of impurities, leading to a higher impurity content in the phosphogypsum and making removal extremely difficult. Conventional water washing is insufficient to remove it. Furthermore, the fluorine content in hemihydrate-dihydrate phosphogypsum is predominantly SiF6. 2- It exists in the form of phosphogypsum, and its content is about an order of magnitude higher than that of phosphogypsum by-products of ordinary dihydrate processes. It is not possible to effectively prepare qualified harmless phosphogypsum products by simply washing with water or neutralizing with lime, and the harmless treatment is more difficult.
[0004] The ineffective and rational utilization of phosphogypsum has become a technical bottleneck restricting the sustainable development of the hemihydrate and dihydrate wet phosphoric acid process, a low-carbon and energy-saving process. How to efficiently utilize phosphogypsum through technological innovation and processing is a technical problem that urgently needs to be solved. Summary of the Invention
[0005] To address the above technical problems, this invention provides a modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process and its preparation method, which can effectively reduce total phosphorus, total fluorine, soluble phosphorus, etc. in phosphogypsum, and helps to achieve efficient resource utilization of phosphogypsum.
[0006] The technical solution is as follows:
[0007] The first aspect of this invention provides a modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process, the key point of which is that it comprises the following components, calculated by weight: 70-90 parts phosphogypsum, 10-30 parts water, and 0.3-3 parts modifier;
[0008] The phosphogypsum is a byproduct of phosphoric acid production from phosphate concentrate via a hemihydrate-dihydrate process. The phosphogypsum contains 0.2%-1.5% phosphorus and 0.1%-1.5% fluorine, and 40%-70% of its particles are smaller than 0.075mm.
[0009] Preferably, the modifier is one or more of lime, calcium hydroxide, polyaluminum chloride, or aluminum sulfate;
[0010] The particle size range of the modifier is 1~100μm, and the specific surface area is 10-40m². 2 / g.
[0011] A second aspect of the present invention provides a method for preparing modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process as described in the first aspect of the present invention, comprising the following steps:
[0012] S1: The phosphogypsum slurry, a byproduct of the hemihydrate-dihydrate process, is filtered, washed three times countercurrently with water, then washed with clean water, and filtered again to obtain product ①.
[0013] S2: Mix product ① with acidic reslurry at a certain liquid-solid ratio, stir evenly, filter, and rinse with clean water to obtain product ②;
[0014] S3: Mix product ② with the aqueous solution of the modifier at a certain liquid-solid ratio and stir evenly to obtain product ③;
[0015] S4: Continue to add a high-concentration modifier aqueous solution to product ③ until the pH stabilizes at 9.0-11.5. Stir evenly, filter and age to obtain the modified phosphogypsum product.
[0016] Preferably, the three countercurrent washings in step S1 are performed after the phosphogypsum slurry has been filtered on a filter press and then washed three times in a countercurrent manner.
[0017] The first wash water from the filter cake after filtration of the gypsum slurry is the filtrate from the second stage of gypsum washing; the second wash water is the filtrate from the third stage of gypsum washing; and the third wash water is the filtrate from the acidic reslurry of phosphogypsum. The filtrate from the first stage of phosphogypsum washing is collected and sent to the hemihydrate-dihydrate wet-process phosphoric acid as wash water.
[0018] Preferably, the temperature of the three countercurrent washing cycles is controlled between 40-90℃.
[0019] Preferably, in step S1, the water washing involves washing the phosphogypsum filter cake with hot water after countercurrent washing, and then sending the filtrate to a semi-water rinsing process, with the temperature controlled at 60-90℃.
[0020] Preferably, the acidic reslurry is the filtrate after acidic reslurry of product ①, mixed with a certain proportion of sulfuric acid, with a pH value of 1.0-1.6 and a temperature of 50-90℃, and the total phosphorus content of the acidic reslurry is 0.1-0.6% and the total fluorine content is 0.4-1.0%.
[0021] Preferably, the proportion of sulfuric acid added is 0.2-3.0%.
[0022] The liquid-to-solid ratio of the acidic re-slurry water to phosphogypsum is 1.2-3.0;
[0023] The re-sizing time between the acidic re-sizing water and phosphogypsum is 60-240 min.
[0024] Preferably, the liquid-to-solid ratio of the modifier to phosphogypsum in step S3 is 1.2-3.0;
[0025] The temperature for wet modification is 60-90℃.
[0026] In step S4, the wet modification temperature is 40-90℃, the pH value is 9.0-11.5, and the aging time is greater than 14 days.
[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0028] 1) This invention utilizes a process of "three countercurrent washing + water washing + acidic resizing + wet modification" to form a synergistic treatment process for phosphogypsum. Specifically, the three countercurrent washing processes use water to dissolve and remove soluble impurities from the phosphogypsum, and impurities trapped between crystals are slowly released; water washing removes some soluble impurities and impurities carried in the aqueous phase, further dissolving them; acidic resizing facilitates the dissolution of potassium fluorosilicate and sodium fluorosilicate in the gypsum; water washing removes the dissolved potassium fluorosilicate and sodium fluorosilicate; and wet modification effectively fixes the remaining and slowly released impurities in the phosphogypsum in the solid phase, significantly reducing leaching risk and improving the long-term environmental safety requirements of phosphogypsum.
[0029] 2) The process of this invention realizes the recycling of process water. The three-stage countercurrent washing water and the purified water washing are used for the washing water of the semi-aqueous filter cake. The acidic resizing water and the washing water are filtered and part of them are used for the washing water of the diaqueous process. The other part is acidified and returned to the acidic resizing process. The resizing water after wet modification is neutralized and used as wet modification water, which can save a lot of industrial water.
[0030] 3) Compared with existing technologies that use a single method (such as single water washing or neutralization), the "three-stage countercurrent washing + clean water washing + acidic resizing + clean water rinsing + wet modification" process of this invention has multiple functions. It can effectively reduce the total phosphorus, total fluorine, soluble phosphorus, and soluble fluorine in phosphogypsum, improve the quality of phosphogypsum, and have long-term stability. Through the innovative combination of the above key processes, while realizing energy saving in the hemihydrate and dihydrate wet phosphoric acid process, it also eliminates the technical problem of difficult treatment of its by-product phosphogypsum compared with traditional dihydrate phosphogypsum. The treated phosphogypsum can stably meet the index requirements of Class I solid waste and can be used in the fields of roadbed, building materials, and ecological restoration. Attached Figure Description
[0031] Figure 1 This is a schematic diagram of the process of the present invention.
[0032] Wherein, 1 is the first filter, 1.1 is the filtration section, 1.2 is the first washing section, 1.3 is the second washing section, 1.4 is the third washing section, 1.5 is the fourth washing section, 2 is the gypsum re-slurry tank, 3 is the second filter, 4 is the wet modification tank, 5 is the high-concentration modifier reaction tank, 6 is the third filter, 7 is the modified phosphogypsum storage silo, and 8 is the modifier reaction tank. Detailed Implementation
[0033] The present invention will be further described below with reference to the embodiments and accompanying drawings.
[0034] like Figure 1 As shown, a modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process comprises, by weight, 70-90 parts phosphogypsum, 10-30 parts water, and 0.3-3 parts modifier.
[0035] The phosphogypsum is made from phosphate rock as raw material. After beneficiation, phosphate concentrate is obtained. Phosphoric acid is prepared from the phosphate concentrate through a hemihydrate-dihydrate wet phosphoric acid process to obtain phosphoric acid as a byproduct. The phosphogypsum contains 0.2%-1.5% phosphorus and 0.1%-1.5% fluorine. The particles with a particle size of less than 0.075 mm account for 40%-70% of the phosphogypsum.
[0036] The modified phosphogypsum is prepared by washing phosphogypsum three times in countercurrent, then washing and filtering it with purified water, then re-slurrying it with acidic re-slurry, filtering and rinsing it with purified water, and finally mixing it with a solution containing a modifier at a certain liquid-solid ratio and filtering.
[0037] Its preparation method is as follows:
[0038] S1: The phosphogypsum slurry, a byproduct of the hemihydrate-dihydrate process, is filtered through the first filter 1 and then washed three times countercurrently with water (at a temperature of 40-90℃). It is then washed with clean water (at a temperature controlled at 60-90℃) and filtered to obtain product ①.
[0039] After the phosphogypsum slurry is filtered through the filtration section 1.1 of the first filter 1, the filter cake is washed three times in a countercurrent manner.
[0040] The first washing water of the filter cake is the filtrate from the second stage of gypsum washing, corresponding to... Figure 1 The first washing stage (section 1.2) and the second washing water are the filtrate from the third stage of gypsum washing. Figure 1 The second washing section 1.3, and the third washing water is the filtrate after acidic resizing of phosphogypsum, corresponding to... Figure 1 The third washing section, 1.4.
[0041] The filtrate from the first stage of phosphogypsum washing is sent to the hemihydrate-dihydrate wet-process phosphoric acid as washing water, and then washed with purified water (corresponding to...). Figure 1 The fourth washing section (1.5) sends its washing filtrate to the semi-aqueous process.
[0042] S2: The acidic resizing water and product ① are mixed and stirred evenly in the gypsum resizing tank 2 at a liquid-solid ratio of 1.2-3 for resizing. The resizing time is 60-240 min. After filtration in the second filter 3, the product ② is obtained by rinsing with clean water (temperature 60-90℃).
[0043] Among them, the acidic reslurry is the filtrate after product ① is reslurried in the gypsum reslurry tank 2 and filtered by the second filter 3, and 0.2-3.0% sulfuric acid is added to it to make the pH value 1.0-1.6 and the temperature 50-90℃. The total phosphorus content of the acidic reslurry is 0.1-0.6% and the total fluorine content is 0.4-1.0%.
[0044] S3: Mix product ② with the modified agent aqueous solution (0-1.2 parts) prepared in the modified agent reaction tank 8 in the wet modification tank 4 at a certain liquid-solid ratio (1.2-3) and stir evenly to obtain product ③;
[0045] S4: Continue to add high-concentration modifier solution (0-3 parts) from the high-concentration modifier reaction tank 5 to product ③ until the pH stabilizes (9.0-11.5), stir evenly, filter in the third filter 6, and age in the modified phosphogypsum storage bin 7 for more than 14 days to obtain the modified phosphogypsum product.
[0046] Among them, high-concentration modifier solution refers to a saturated solution containing undissolved solid modifier, which is a suspension or emulsion.
[0047] The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.
[0048] It should be noted that the modified phosphogypsum in the following examples or comparative examples was prepared using the preparation method proposed in this invention.
[0049] Example 1
[0050] A modified phosphogypsum, by weight, comprises 85 parts phosphogypsum, 0.63 parts modifier, and 15 parts water; the modified phosphogypsum is prepared by three countercurrent washings and washing with clean water, followed by re-slurrying with acidic re-slurry water, filtration, rinsing with clean water, and then wet modification, mixing evenly, filtration, and aging for a certain period of time.
[0051] The phosphogypsum was subjected to three countercurrent washings at 90°C, a water washing at 90°C, an acidic resizing at 90°C, a pH of 1.2, an acidic resizing liquid-to-solid ratio of 3:1, a resizing time of 4 hours, a wet modification liquid-to-solid ratio of 3:1, and a wet modification temperature of 80°C.
[0052] The phosphogypsum, after being rinsed with water, has a total phosphorus content of 0.2540%, a water-soluble phosphorus content of 0.1332%, a total fluoride content of 0.2806%, a water-soluble fluoride content of 0.2791%, and a pH of 3.31.
[0053] The modifier, calculated by weight, includes 60 parts lime and 40 parts calcium hydroxide. The modifier is added in two steps: first, 0.4 parts modifier are added to the wet modification slurry; second, 0.23 parts modifier are added during the wet modification. The pH of the slurry during modification is 11.2, and the modified phosphogypsum is aged for 14 days.
[0054] Example 2
[0055] A modified phosphogypsum, by weight, comprises 85 parts phosphogypsum, 0.79 parts modifier, and 15 parts water; the modified phosphogypsum is prepared by three countercurrent washings and washing with clean water, followed by re-slurrying with acidic re-slurry water, filtration, rinsing with clean water, and then wet modification, mixing evenly, filtration, and aging for a certain period of time.
[0056] The phosphogypsum was subjected to three countercurrent washings at 90°C, a water washing at 80°C, an acidic resizing at 80°C, a pH of 1.3, an acidic resizing liquid-to-solid ratio of 2.5:1, a resizing time of 3 hours, a wet modification liquid-to-solid ratio of 2.5:1, and a wet modification temperature of 70°C.
[0057] The phosphogypsum, after undergoing three countercurrent washings, water washings, acidic re-slurrying, and water rinsings, has a total phosphorus content of 0.2431%, a water-soluble phosphorus content of 0.1594%, a total fluoride content of 0.4172%, a water-soluble fluoride content of 0.3100%, and a pH of 3.25.
[0058] The modifier, calculated by weight, includes 50 parts lime and 50 parts calcium hydroxide. The modifier is added in two steps: first, 0.4 parts modifier are added to the wet modification slurry; second, 0.39 parts modifier are added during the wet modification. The pH of the slurry during modification is 11.4, and the modified phosphogypsum is aged for 14 days.
[0059] Example 3
[0060] A modified phosphogypsum, by weight, comprises 85 parts phosphogypsum, 0.83 parts modifier, and 15 parts water; the modified phosphogypsum is prepared by three countercurrent washings and washing with clean water, followed by re-slurrying with acidic re-slurry water, filtration, rinsing with clean water, and then wet modification, mixing evenly, filtration, and aging for a certain period of time.
[0061] The phosphogypsum was subjected to three countercurrent washings at 80°C, a water washing at 75°C, an acidic resizing at 75°C, a pH of 1.1, an acidic resizing liquid-to-solid ratio of 2:1, a resizing time of 2.5 hours, a wet modification liquid-to-solid ratio of 2:1, and a wet modification temperature of 70°C.
[0062] The phosphogypsum, after undergoing three countercurrent washings, water washings, acidic re-slurrying, and water rinsings, has a total phosphorus content of 0.2167%, a water-soluble phosphorus content of 0.1153%, a total fluoride content of 0.4782%, a water-soluble fluoride content of 0.4367%, and a pH of 3.11.
[0063] The modifier, calculated by weight, includes 70 parts lime and 30 parts calcium hydroxide. The modifier is added in two steps: first, 0.42 parts modifier are added to the wet modification slurry; second, 0.43 parts modifier are added during the wet modification. The pH of the slurry during modification is 10.7, and the modified phosphogypsum is aged for 14 days.
[0064] Example 4
[0065] A modified phosphogypsum, by weight, comprises 85 parts phosphogypsum, 0.98 parts modifier, and 15 parts water; the modified phosphogypsum is prepared by three countercurrent washings and washing with clean water, followed by re-slurrying with acidic re-slurry water, filtration, rinsing with clean water, and then wet modification, mixing evenly, filtration, and aging for a certain period of time.
[0066] The phosphogypsum was subjected to three countercurrent washings at 75°C, a water washing at 70°C, an acidic resizing at 70°C, a pH of 1.4, an acidic resizing liquid-to-solid ratio of 1.5:1, a resizing time of 2 hours, a wet modification liquid-to-solid ratio of 1.5:1, and a wet modification temperature of 60°C.
[0067] The phosphogypsum, after undergoing three countercurrent washings, water washings, acidic re-slurrying, and water rinsings, has a total phosphorus content of 0.1854%, a water-soluble phosphorus content of 0.1180%, a total fluoride content of 0.4476%, a water-soluble fluoride content of 0.3102%, and a pH of 3.10.
[0068] The modifier, calculated by weight, includes 70 parts lime and 30 parts calcium hydroxide. The modifier is added in two steps: first, 0.50 parts modifier is added to the wet modification slurry; second, 0.48 parts modifier is added during the wet modification. The pH of the slurry during modification is 10.3, and the modified phosphogypsum is aged for 14 days.
[0069] Comparative Example 1
[0070] A modified phosphogypsum, by weight, comprises 85 parts phosphogypsum, 0.66 parts modifier, and 15 parts water; the modified phosphogypsum is prepared by three countercurrent washings and washing with clean water, followed by re-sizing with acidic re-sizing water, filtration, rinsing with clean water, and then directly mixing with the modifier evenly.
[0071] The phosphogypsum was subjected to three countercurrent washings at 80°C, a water washing at 75°C, an acidic resizing at 70°C, a pH of 1.4, an acidic resizing liquid-to-solid ratio of 2:1, a resizing time of 2 hours, and a wet modification liquid-to-solid ratio of 2:1.
[0072] The phosphogypsum, after undergoing three countercurrent washings, water washings, acidic re-slurry re-slurryings, and water rinsings, has a total phosphorus content of 0.2898%, a water-soluble phosphorus content of 0.1379%, a total fluoride content of 0.4400%, a water-soluble fluoride content of 0.4431%, and a pH of 3.15.
[0073] The modifier, calculated by weight, includes 60 parts lime and 40 parts calcium hydroxide. The modifier is directly mixed with phosphogypsum, and the modified phosphogypsum is aged for 14 days.
[0074] Comparative Example 2
[0075] A modified phosphogypsum, by weight, comprises 85 parts phosphogypsum, 0.89 parts modifier, and 15 parts water; the modified phosphogypsum is prepared by three countercurrent washings and washing with purified water, followed by wet modification, uniform mixing, filtration, and aging for a certain period of time.
[0076] The phosphogypsum was subjected to three countercurrent washings at a temperature of 70°C, a water washing temperature of 70°C, a liquid-to-solid ratio of 2:1 for wet modification, and a wet modification temperature of 65°C.
[0077] The phosphogypsum, after three countercurrent washings and water washings, has a total phosphorus content of 0.4502%, a water-soluble phosphorus content of 0.3053%, a total fluorine content of 0.6100%, a water-soluble fluorine content of 0.5225%, and a pH of 3.07.
[0078] The modifier, calculated by weight, includes 60 parts lime, 39.5 parts calcium hydroxide, and 0.5 parts aluminum sulfate or polyaluminum chloride. The modifier is added in two steps: first, 0.48 parts of the modifier are added to the wet modification slurry; second, 0.41 parts of the modifier are added during the wet modification. The pH of the slurry during modification is 11.3, and the modified phosphogypsum is aged for 14 days.
[0079] Comparative Example 3
[0080] A modified phosphogypsum, by weight, comprises 85 parts phosphogypsum, 1.09 parts modifier, and 15 parts water; the modified phosphogypsum is prepared by three countercurrent washings, re-slurrying with acidic re-slurry water, filtration, rinsing with clean water, and then undergoing wet modification, mixing, filtration, and aging for a certain period of time.
[0081] The phosphogypsum was subjected to three countercurrent washings at 70°C, followed by acidic resizing at 70°C, with a pH of 1.2. The liquid-to-solid ratio for wet modification was 2:1, and the wet modification temperature was 65°C.
[0082] The phosphogypsum, after three countercurrent washings, acidic resizing, and rinsing with purified water, has a total phosphorus content of 0.3412%, a water-soluble phosphorus content of 0.2380%, a total fluoride content of 0.6952%, a water-soluble fluoride content of 0.6670%, and a pH of 3.07.
[0083] The modifier, calculated by weight, includes 60 parts lime, 39 parts calcium hydroxide, and 1 part aluminum sulfate or polyaluminum chloride. The modifier is added in two steps: first, 0.50 parts of the modifier are added to the wet modification slurry; second, 0.59 parts of the modifier are added during the wet modification. The pH of the slurry during modification is 10.3, and the modified phosphogypsum is aged for 14 days.
[0084] Comparative Example 4
[0085] A modified phosphogypsum, by weight, comprises 85 parts phosphogypsum, 2.46 parts modifier, and 15 parts water; the modified phosphogypsum is obtained by washing with clean water, re-slurrying with acidic re-slurry, filtering, rinsing with clean water, and then undergoing wet modification, mixing evenly, filtering, and aging for a certain period of time.
[0086] The phosphogypsum was washed with purified water at a temperature of 70°C, re-slurried with acidic water at a temperature of 60°C, with a pH of 1.1. The liquid-to-solid ratio for wet modification was 1.5:1, and the temperature for wet modification was 65°C.
[0087] The phosphogypsum, after being washed with water, has a total phosphorus content of 1.52%, a water-soluble phosphorus content of 1.24%, a total fluoride content of 1.33%, a water-soluble fluoride content of 1.15%, and a pH of 2.37.
[0088] The modifier, calculated by weight, comprises 60 parts lime, 37.5 parts calcium hydroxide, and 2.5 parts aluminum sulfate or polyaluminum chloride. The modifier is added in two steps: first, 0.55 parts of the modifier are added to the wet modification slurry; second, 1.91 parts of the modifier are added during the wet modification process. The pH of the slurry during modification is 10.8, and the modified phosphogypsum is aged for 14 days.
[0089] Test case
[0090] The above Examples 1-4 and Comparative Examples 1-4 were tested respectively, including testing the total phosphorus and total fluorine in the modified phosphogypsum aged for 14 days, and the phosphorus, fluorine and pH of the leachate of the modified phosphogypsum.
[0091] The specific process of the leachate is as follows: After mixing the above Examples 1-4 and Comparative Examples 1-4 evenly, weigh 100g of dry phosphogypsum modified for 14 days and place it in a 2L conical flask. According to the water content of the modified phosphogypsum, soak the modified phosphogypsum at a liquid-to-solid ratio of 10:1. After shaking in a water bath constant temperature shaker at room temperature for 8 hours, let it stand for 16 hours and test the phosphorus, fluorine and pH in the leachate.
[0092] The results for total phosphorus, total fluoride, phosphorus and fluoride in the leachate, and pH of the modified phosphogypsum in the examples and comparative examples are shown below:
[0093] Example 1: Modified phosphogypsum (14d): Total phosphorus 0.2266%, total fluorine 0.2355%;
[0094] Leachate (14d): P 0.0428 mg / L, F 7.48 mg / L, pH 7.49;
[0095] Example 2: Modified phosphogypsum (14d): Total phosphorus 0.2182%, total fluorine 0.3562%;
[0096] Leachate (14d): P 0.0504 mg / L, F 7.31 mg / L, pH 7.57;
[0097] Example 3: Modified phosphogypsum (14d): Total phosphorus 0.2088%, total fluorine 0.4554%;
[0098] Leachate (14d): P 0.0910 mg / L, F 8.00 mg / L, pH 7.42;
[0099] Example 4: Modified phosphogypsum (14d): Total phosphorus 0.1769%, total fluorine 0.4425%;
[0100] Leachate (14d): P 0.1323 mg / L, F 7.29 mg / L, pH 7.43;
[0101] Comparative Example 1: Modified phosphogypsum (14d): Total phosphorus 0.2942%, total fluorine 0.4517%;
[0102] Leachate (14d): P 0.1695 mg / L, F 11.46 mg / L, pH 7.80;
[0103] Comparative Example 2: Modified phosphogypsum (14d): Total phosphorus 0.4531%, Total fluorine 0.6084%;
[0104] Leachate (14d): P 0.1522 mg / L, F 14.73 mg / L, pH 7.56;
[0105] Comparative Example 3: Modified phosphogypsum (14d): Total phosphorus 0.3356%, Total fluorine 0.6891%;
[0106] Leachate (14d): P 0.1217 mg / L, F 15.91 mg / L, pH 7.21;
[0107] Comparative Example 4: Modified phosphogypsum (14d): Total phosphorus 1.5126%, Total fluorine 1.3257%;
[0108] Leachate (14d): P 0.2463 mg / L, F 24.31 mg / L, pH 7.98.
[0109] The test results of total phosphorus, total fluoride, phosphorus, fluoride and pH of the leachate of the modified phosphogypsum above show that the total phosphorus and total fluoride of the modified phosphogypsum in Examples 1-4 are significantly lower than those in Comparative Examples 1-4. The fluoride in the leachate of the modified phosphogypsum in Examples 1-4 is significantly lower than that in Comparative Examples 1-4. The phosphorus in the leachate is also relatively low. The pH of the leachate is weakly alkaline.
[0110] Examples 1 to 4 were all prepared by a process of “three countercurrent washing + clean water washing + acidic re-slurry + clean water rinsing + wet modification”, which can effectively reduce phosphorus and fluorine in the leachate of modified phosphogypsum.
[0111] Comparative Example 1 is a modified phosphogypsum that has been subjected to “three countercurrent washings + water washing + acidic resizing + water washing” and then directly mixed with a modifier. This shows that the wet modification process plays an important role in the preparation of qualified modified phosphogypsum.
[0112] Comparative Example 2 was prepared by "three countercurrent washing + water washing + wet modification" of phosphogypsum, which shows that the acid resizing and water rinsing process has the effect of reducing phosphorus and fluorine in phosphogypsum.
[0113] Comparative Example 3 was prepared by "three countercurrent washings + acid resizing + water washing + wet modification", which shows that water washing removes phosphogypsum and impurities in the liquid phase, and is an essential process.
[0114] The modified phosphogypsum in Comparative Example 4 was prepared by "washing with clean water + acidic re-slurrying + washing with clean water + wet modification". This indicates that phosphogypsum that has not undergone three countercurrent washings contains a large amount of impurities such as phosphorus and fluorine, making it difficult to prepare harmless phosphogypsum products through simple washing and modification.
[0115] The results show that phosphogypsum, a byproduct of phosphoric acid production via a hemihydrate-dihydrate process, can effectively reduce phosphorus and fluoride in its leachate through a process of "three countercurrent washings + water washing + acidic resizing + water washing + wet modification," resulting in a qualified, harmless phosphogypsum product. Specifically, the three countercurrent washings utilize water to dissolve and remove soluble impurities from the phosphogypsum, while impurities trapped between crystals are slowly released. Water washing removes some soluble impurities and impurities carried in the aqueous phase, further dissolving them. Acidic resizing facilitates the dissolution of potassium fluorosilicate and sodium fluorosilicate from the gypsum. Water rinsing removes the dissolved potassium fluorosilicate and sodium fluorosilicate. Wet modification effectively fixes the remaining and slowly released impurities in the phosphogypsum within the solid phase, significantly reducing leaching risk and improving the long-term environmental safety of phosphogypsum.
[0116] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention. Those skilled in the art, under the guidance of the present invention, can make various similar representations without departing from the spirit and claims of the present invention, and such modifications all fall within the protection scope of the present invention.
Claims
1. A modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process, characterized in that: It includes the following components, calculated by weight: 70-90 parts phosphogypsum, 10-30 parts water, and 0.3-3 parts modifier; The phosphogypsum is a byproduct of phosphoric acid production from phosphate concentrate via a hemihydrate-dihydrate process. The phosphogypsum contains 0.2%-1.5% phosphorus and 0.1%-1.5% fluorine, and 40%-70% of its particles are smaller than 0.075mm.
2. The modified phosphogypsum based on a hemihydrate-dihydrate process byproduct according to claim 1, characterized in that: The modifier is one or more of lime, calcium hydroxide, polyaluminum chloride, or aluminum sulfate; The particle size range of the modifier is 1~100μm, and the specific surface area is 10-40m². 2 / g.
3. A method for preparing modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process as described in claims 1-2, characterized in that: Includes the following steps: S1: The phosphogypsum slurry, a byproduct of the hemihydrate-dihydrate process, is filtered, washed three times countercurrently with water, then washed with clean water, and filtered to obtain product ①. S2: Mix product ① with acidic resizing water at a certain liquid-solid ratio and stir evenly for resizing. After filtration, rinse with clean water to obtain product ②. S3: Mix product ② with the aqueous solution of the modifier at a certain liquid-solid ratio and stir evenly to obtain product ③; S4: Continue to add a high-concentration modifier aqueous solution to product ③ until the pH is stable. After stirring evenly, filtering and aging, the modified phosphogypsum product is obtained.
4. The method for preparing modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process according to claim 3, characterized in that: The three countercurrent washings in step S1 refer to the phosphogypsum slurry being filtered on a filter and then washed three times in a countercurrent manner. The first wash water from the filter cake after filtration of the phosphogypsum slurry is the filtrate from the second stage of phosphogypsum washing; the second wash water is the filtrate from the third stage of phosphogypsum washing; and the third wash water is the filtrate from the acidic reslurry of the phosphogypsum. The filtrate from the first stage of phosphogypsum washing is collected and sent to the hemihydrate-dihydrate wet-process phosphoric acid as wash water.
5. The method for preparing modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process according to claim 4, characterized in that: The temperature of the three countercurrent washes is controlled between 40-90℃.
6. The method for preparing modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process according to claim 5, characterized in that: The water washing in step S1 involves washing the phosphogypsum filter cake with hot water after countercurrent washing, and then sending the filtrate to the semi-aqueous process, where the temperature is controlled at 60-90℃.
7. A modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process according to claim 6, characterized in that: The acidic resizing water is the filtrate after filtration and washing of product ① after resizing, with sulfuric acid added to bring the pH value to 1.0-1.6, the amount of sulfuric acid added is 0.2-3%, the temperature is 50-90℃, and the total phosphorus content of the acidic resizing water is 0.1-0.6%, and the total fluorine content is 0.4-1.0%.
8. The method for preparing modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process according to claim 7, characterized in that: In step S2, the liquid-to-solid ratio of acidic re-slurry water to phosphogypsum is 1.2-3. The re-sizing time between the acidic re-sizing water and phosphogypsum is 60-240 min; The temperature of the purified water rinse is 60-90℃.
9. The method for preparing modified phosphogypsum based on a byproduct of a hemihydrate-dihydrate process according to claim 8, characterized in that: In step S3, the liquid-to-solid ratio of the modifier to phosphogypsum is 1.2-3.
10. The method for preparing modified phosphogypsum based on a hemihydrate-dihydrate process byproduct according to claim 9, characterized in that: In step S4, the wet modification temperature is 40-90℃, the pH value is 9-11.5, and the aging time is greater than 14 days.