Optimization method for filtering performance of phosphogypsum and application of optimization method

Abstract

The invention discloses a method for optimizing filtering performance of phosphogypsum by using white fertilizer and application of the method, according to the method, phosphoric acid production by-product white fertilizer serves as seed crystal to be reused in a phosphoric acid-phosphate concentrate pulp system, and collaborative optimization of phosphogypsum crystal morphology, filtering performance and phosphorus occurrence state is achieved by regulating and controlling the addition amount and reaction conditions of the white fertilizer. The method comprises the following steps: according to an ion competitive adsorption and heterogeneous nucleation principle, when the addition amount of the white fertilizer is less than or equal to 10%, reducing phosphorus wrapping through Ca < 2 + > and SO4 < 2-> competitive active sites on the surface of gypsum; and when the addition amount is greater than or equal to 15%, inducing heterogeneous nucleation of the semi-hydrated gypsum to form a quasi-hexagonal or hexagonal crystal. According to the method, the filtering rate can be increased to 2.68 m < 3 > / (m < 2 >. H), the water-soluble phosphorus reduction amplitude reaches 94.3%, the operation is simple, the cost is low, and the method has an excellent application effect in the fields of phosphogypsum efficient filtering and phosphorus resource recovery.

Description

Technical Field

[0001] This invention relates to the field of phosphorus chemical solid waste treatment and resource recycling technology, specifically to a method for optimizing the filtration performance of phosphogypsum and its application. Background Technology

[0002] As a key industry supporting food security and the development of new energy materials, the phosphorus chemical industry faces a significant challenge in its green transformation: the production of phosphogypsum. Global phosphogypsum stockpiles not only consume vast amounts of arable land, but the soluble phosphorus (WP) it contains can also lead to eutrophication of soil and water bodies through leaching, with concentrations reaching 50-100 mg / L, posing a significant environmental risk.

[0003] In the phosphoric acid production process, the filtration performance of phosphogypsum directly determines the plant's capacity. Based on work experience and statistical analysis, for every 0.5 m³ / (m²h) decrease in filtration rate, the capacity of a single 500,000-ton / year plant will decrease by 8%-10%. Currently, wet-process phosphoric acid (PPA) pretreatment units use a phosphoric acid-phosphate concentrate slurry reaction system (phosphoric acid concentration 45%-48%, phosphate concentrate slurry P2O5 content ≥30%). After the reaction slurry is treated by four-stage series reaction tanks (A→D), an arsenic removal agent is added in tank D to reduce the arsenic content. It then enters a thickener for separation to obtain white fertilizer slurry (mainly composed of CaSO4·0.5H2O), which is finally filtered to obtain phosphogypsum (CaSO4·2H2O). In this process, phosphogypsum suffers from low filtration rates and significant phosphorus encapsulation loss, resulting in low phosphorus resource utilization and high costs for subsequent solid waste disposal and plant maintenance.

[0004] Existing methods for improving the filtration performance of phosphogypsum mainly rely on adding crystallization regulators, but this has two major drawbacks: first, the cost of the reagents is relatively high, approximately 20-30 yuan per ton of gypsum, increasing the production burden (e.g., publication number CN106395879B); second, it may introduce new impurities, affecting the resource utilization of phosphogypsum. Therefore, developing low-cost, pollution-free filtration performance optimization technologies has become an urgent need. Summary of the Invention

[0005] This invention addresses the problems of low phosphogypsum filtration rate, severe phosphorus encapsulation loss, and high cost and easy introduction of impurities by traditional regulators in existing PPA pretreatment devices. This invention provides an optimization method for phosphogypsum filtration performance, which significantly improves the phosphogypsum filtration rate and increases device capacity; reduces phosphorus resource encapsulation loss and lowers the risk of environmental leaching; and uses white fertilizer, a process byproduct, as raw material to reduce production costs and achieve resource recycling.

[0006] The technical solution of this invention: A method for optimizing the filtration performance of phosphogypsum is as follows: Add ≤25% (by volume) white fertilizer to a reaction system of phosphate concentrate slurry with a P2O5 content ≥30w% and phosphoric acid concentration 45w%-48w%, and react at a constant temperature and rate of 81℃-83℃ and a mechanical stirring rate of 180r / min for 10 hours to obtain phosphogypsum; the white fertilizer is the underflow product obtained by thickening after a four-stage series reaction of phosphoric acid and phosphate concentrate slurry.

[0007] The main component of the white fertilizer is CaSO4·0.5H2O, which accounts for more than 55% of its mass, with the remainder being water.

[0008] The amount of white fertilizer added is not zero.

[0009] The preferred amount of white fertilizer added is 10%-20% by volume of phosphate.

[0010] The filtration rate of the phosphogypsum is 2.25 m³ / (m²h)-2.70 m³ / (m²h), the total phosphorus content is 7.82%-9.21%, and the water-soluble phosphorus content is 1.42%-7.92%.

[0011] Another object of the present invention is to provide the application of the above-mentioned method for optimizing the filtration performance of phosphogypsum in the filtration of phosphogypsum in a wet phosphoric acid pretreatment unit.

[0012] This invention recycles the byproduct of wet phosphoric acid process, white fertilizer (CaSO4·0.5H2O), into the phosphoric acid-concentrate slurry system. By using white fertilizer as a precursor for hemihydrate gypsum, it can influence gypsum growth by inducing nucleation or changing the surface properties of crystals. This not only reveals the potential value of white fertilizer in regulating gypsum crystallization but also realizes resource recycling. Furthermore, through systematic research on its regulation of phosphogypsum crystallization and filtration performance, a set of efficient and economical process optimization schemes has been formed.

[0013] This invention achieves uniform crystal growth and complete structure through effective control of stirring speed, reaction temperature, and time, significantly improving filter cake permeability, ensuring reaction stability, facilitating continuous industrial operation and energy consumption control, and scientifically controlling reaction time to ensure full dissociation of phosphorus encapsulation, and scientifically controlling stirring speed to promote the desorption of soluble phosphorus, thus significantly reducing environmental risks.

[0014] The beneficial effects of this invention are: 1. Filtration performance is significantly improved.

[0015] Using the method of this invention, the filtration rate of phosphogypsum reaches 2.70 m³ / (m²h), which is 47.3% higher than that of traditional treatment (1.82 m³ / (m²h)). The filtrate exhibits a continuous stream flow, and the filtrate volume increases significantly within 60 seconds.

[0016] 2. Phosphorus loss was significantly reduced.

[0017] Using the method of this invention, the total phosphorus in phosphogypsum decreased from 30.15% to 7.98%, and the water-soluble phosphorus decreased from 26.60% to 1.50%, a reduction of 94.3%.

[0018] 3. Significant cost advantage.

[0019] Using by-product white fertilizer as raw material, no additional chemical agents are needed, and the cost per ton of gypsum can be reduced by 20-30 yuan. Based on an annual production of 1 million tons of phosphogypsum, the annual cost savings would be 20-30 million yuan.

[0020] 4. Outstanding environmental benefits.

[0021] The method of this invention reduces the leaching concentration from 50-100 mg / L to below 2 mg / L, thereby reducing leaching pollution from stockpiled phosphogypsum. At the same time, the full reaction significantly improves the purity of the gypsum, turning it from grayish-black to grayish-white, laying the foundation for its resource utilization as a building material and soil conditioner. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in further detail below, but the present invention is not limited to these embodiments. Any improvements or substitutions based on the basic spirit of these embodiments shall still fall within the scope of protection claimed by the claims of the present invention.

[0023] An optimization method for the filtration performance of phosphogypsum is as follows: white fertilizer is added to the reaction system of phosphate concentrate slurry and phosphoric acid in the PPA pretreatment device, and the reaction is carried out at a constant temperature and rate of 81℃-83℃ and a mechanical stirring rate of 180r / min for 10h to obtain phosphogypsum.

[0024] Among them, industrial phosphoric acid has a concentration of 45%-48% (mass fraction) and is derived from the wet phosphoric acid concentration process; phosphate concentrate slurry has a P2O5 content of ≥30% (mass fraction) and is pulped after flotation enrichment; white fertilizer is taken from the underflow of the thickener in the PPA pretreatment unit, and its main component is CaSO4·0.5H2O, which accounts for more than 55% of the mass, with the remainder being water, which is used as a crystallization regulator.

[0025] The amount of white fertilizer added is ≤25% by volume of phosphate and not zero, preferably 10%-20%.

[0026] Through experiments on the process and the amount of white fertilizer added, this invention has discovered that: When the white fertilizer is added at a low concentration (≤10%): under the conditions of 82℃±1℃ and 180r / min stirring, the white fertilizer reacts and releases Ca after 10 hours. 2+ SO4 2- , with PO4 3-Competitive active sites on the surface of gypsum dihydrate (Ca 2+ With SO4 2- The binding energy is higher, at -5.2 eV, which is higher than that of PO4. 3- The -4.8eV) reduces phosphorus adsorption and encapsulation; gentle stirring at 180r / min avoids crystal breakage and promotes uniform ion diffusion, making the filter cake structure loose and initially improving the filtration rate.

[0027] High addition level stage (≥15%): The long reaction time of 10 hours ensures that the hemihydrate gypsum seed crystals fully exert their heterogeneous nucleation effect. At 82℃±1℃, the surface energy of the seed crystals drops to 0.070 J / m², significantly lower than the homogeneous nucleation energy barrier of dihydrate gypsum (0.095 J / m²), inducing the formation of a large number of regular hexagonal hemihydrate gypsum crystals. The Ca in the hemihydrate gypsum lattice... 2+ The coordination number is 6, lower than the 8 coordination number of gypsum dihydrate, for PO4. 3- The encapsulation ability was significantly weakened, and the crystals grew in an orderly manner under stirring at 180 r / min, resulting in increased filter cake porosity and a significantly improved filtration rate.

[0028] Ultimately, through a series of single-factor and orthogonal experiments, the optimal process parameters were integrated. The white fertilizer addition amount was 10%-20% (based on phosphoric acid volume); temperature was 82℃±1℃; stirring speed was 180 r / min; and reaction time was 10 h. The temperature of 82℃±1℃, stirring speed of 180 r / min, and reaction time of 10 h used in this invention are all existing, mature production process parameters for the reaction of phosphate concentrate and sulfuric acid, and their rationality and applicability have been verified in long-term industrial practice. The core innovation of this invention lies in determining the optimal white fertilizer addition amount as 10%-20% (based on phosphoric acid volume), and verifying the compatibility of this addition amount with the aforementioned existing process parameters through single-factor and orthogonal experiments. The final integrated optimal process parameter combination meets the disclosure requirements of the patent technology solution.

[0029] Example 1: Effect of white fertilizer addition on filtration rate The phosphoric acid-concentrate slurry system of the PPA pretreatment unit was used as the research object. In this example, the phosphoric acid concentration was 46% (mass fraction), and the P2O5 content of the phosphate concentrate slurry was 32% (mass fraction). The reaction temperature was fixed at 82℃±1℃, the stirring intensity was 180r / min, and the reaction time was 10h. The amount of white fertilizer added was set to 0%, 5%, 10%, 15%, 20%, and 25% (based on the volume of phosphoric acid). The white fertilizer was taken from the underflow of the thickener in the PPA pretreatment unit, and its main component was CaSO4·0.5H2O, accounting for 55% by mass. The remainder was water. A vacuum filtration system (Buchner funnel ϕ=12cm, ultimate vacuum degree 0.09MPa) was used for filtration, and the filtration rate was measured. The results are shown in Table 1 below.

[0030] The results showed that under the conditions of reaction temperature 82℃±1℃, stirring intensity 180r / min, and reaction time 10h, the filtration rate increased significantly in a stepwise manner when the amount of white fertilizer added was 10%-20%, reaching the best effect at 20% addition. The increase slowed down with further increases in addition (25%), verifying the existence of a threshold effect. The 10h reaction time allowed the seed crystals to fully exert their effect, and the 180r / min stirring avoided crystal damage. Overall, the filtration rate was better than that of the short-time reaction group.

[0031] Example 2: Effect of white fertilizer addition on phosphorus content The experimental conditions were the same as in Example 1. The total phosphorus (TP) and water-soluble phosphorus (WP) contents in gypsum under different amounts of white fertilizer were determined using ICP-OES 7000DV. The results are shown in Table 2 below:

[0032] The results showed that, under the conditions of reaction temperature 82℃±1℃, stirring intensity 180r / min, and reaction time 10h, the reduction in water-soluble phosphorus reached 94.3% with a 20% white fertilizer addition, effectively controlling phosphorus resource loss and environmental risks. The long reaction time of 10h allowed for the complete dissolution of phosphorus encapsulation, and the 180r / min stirring promoted the competitive adsorption of phosphorus ions and white fertilizer ions, resulting in a significantly better phosphorus reduction effect than the short-time reaction group.

[0033] Example 3: Effect of white fertilizer addition on crystal morphology The experimental conditions were the same as in Example 1. A ZEISS Sigma 300 field emission scanning electron microscope was used to observe the crystal morphology under different amounts of white fertilizer. In the 0%, 5%, and 10% white fertilizer groups, the crystals were mainly gypsum dihydrate, exhibiting short columnar shapes. After 10 hours of sufficient growth, the crystals became coarser, with no significant morphological differences. In the 15%, 20%, and 25% white fertilizer groups, with increasing addition, hexagonal or quasi-hexagonal crystals appeared, consistent with the typical morphology of hemihydrate gypsum (JCPDS 33-0311). 10 hours of growth resulted in uniform crystal size. Stirring at 180 r / min prevented crystal aggregation, and the hexagonal structure remained complete and clear. With increasing addition, the number of hexagonal crystals increased and tended towards saturation.

[0034] Example 4: Three-phase composition of gypsum under different amounts of white fertilizer The experimental conditions were the same as in Example 1. The content of hemihydrate gypsum in gypsum was determined using an SGSX-Ⅲ gypsum three-phase analyzer. The results are shown in Table 3 below:

[0035] The results showed that a full reaction time of 10 hours allowed for the continuous induction of hemihydrate gypsum seed crystals. The hemihydrate gypsum content in the 20% white fertilizer addition group reached 11.70%, which significantly improved the filter cake permeability, consistent with the filtration rate data.

[0036] In summary, under the conditions of a constant temperature of 81℃-83℃, a constant stirring speed of 180r / min, and a constant reaction time of 10h, this invention can significantly optimize the filtration performance of phosphogypsum and reduce phosphorus loss by adjusting the amount of white fertilizer added, thus achieving significant economic and environmental benefits and making it suitable for promotion and application in the phosphorus chemical industry.

Claims

1. A method for optimizing the filtration performance of phosphogypsum, characterized in that: White fertilizer is added to the reaction system of phosphate concentrate slurry and phosphoric acid, and the reaction is carried out under constant temperature and rate conditions with mechanical stirring to obtain phosphogypsum; the white fertilizer is the underflow product obtained by thickening after phosphoric acid and phosphate concentrate slurry undergo a four-stage series reaction.

2. The method for optimizing the filtration performance of phosphogypsum according to claim 1, characterized in that: The main component of the white fertilizer is CaSO4·0.5H2O.

3. The method for optimizing the filtration performance of phosphogypsum according to claim 1, characterized in that: The concentration of phosphoric acid is 45%-48% by mass fraction, and the P2O5 content in the phosphate concentrate slurry is ≥30%.

4. The method for optimizing the filtration performance of phosphogypsum according to claim 1, characterized in that: The amount of white fertilizer added is ≤25% by volume of phosphate and is not zero.

5. The method for optimizing the filtration performance of phosphogypsum according to claim 4, characterized in that: The amount of white fertilizer added is 10%-20% by volume of phosphate.

6. The method for optimizing the filtration performance of phosphogypsum according to claim 1, characterized in that: The constant temperature and constant rate reaction conditions include: a reaction temperature of 81℃-83℃, a mechanical stirring rate of 180r / min, and a reaction time of 10h.

7. The method for optimizing the filtration performance of phosphogypsum according to claim 1, characterized in that: The filtration rate of the phosphogypsum is 2.25 m³ / (m²h)-2.70 m³ / (m²h), the total phosphorus content is 7.82%-9.21%, and the water-soluble phosphorus content is 1.42%-7.92%.

8. The application of the method for optimizing the filtration performance of phosphogypsum according to any one of claims 1-7 in the filtration of phosphogypsum in a wet phosphoric acid pretreatment unit.

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