A method for harmless treatment of phosphogypsum at the source

Abstract

The present invention relates to the technical field of solid waste treatment, and specifically relates to a method for the source harmless treatment of phosphogypsum. The end-stage water washing of the crystal-growing slurry filtration system is washed with clean water, and the amount of clean water used is in a ratio of 1:10 to 1:1 cubic meter / ton to the phosphogypsum. After washing, phosphogypsum is obtained; the filter cloth washing water in the crystal-growing slurry filtration system and the obtained phosphogypsum are adjusted to a phosphogypsum slurry with a concentration of 20wt% to 60wt%; the obtained phosphogypsum slurry is added with a harmless treatment agent A, stirred and mixed evenly, and reacted for 5-60 minutes to obtain a first-stage reaction slurry; the obtained first-stage reaction slurry is added with a harmless agent B, stirred and mixed evenly, and the reaction residence time is 20-60 minutes. After filtration, a filtrate and harmless phosphogypsum are obtained. The present invention realizes the comprehensive recovery rate of fluorine and phosphorus valuable components in the wet-process phosphoric acid industry through simple process improvement, and reduces the pollutant content of phosphogypsum after water washing and filtration; this harmless treatment of phosphogypsum utilizes the idea of "treating pollution with waste" for industrial solid waste. The raw materials for preparing the agent have a wide source and low cost, and it is a typical example of the coordinated control of solid waste pollution prevention and control and the synergistic increase of pollution reduction and carbon reduction.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste treatment, and particularly relates to a method for harmless treatment of phosphogypsum at the source. Background Art

[0002] Phosphogypsum is the main by-product generated in the wet production of phosphoric acid and the production process of phosphate fertilizers. The solid generated by the three-stage countercurrent water washing and filtration of the underflow slurry of the phosphoric acid reactor is phosphogypsum, and the filtrate is returned to the extraction to extract fluorine and phosphorus. Approximately 4.5 - 5.0 tons of phosphogypsum can be produced per ton of phosphoric acid produced. In 2022, the production volume of phosphogypsum in China was approximately 77 million tons, and the non-utilization rate exceeded 50%, with an accumulated stockpile of approximately 820 million tons. The solid waste attribute of phosphogypsum from most enterprises reaches that of hazardous waste, posing a relatively high environmental risk. Therefore, how to achieve harmless treatment of phosphogypsum at the source with low cost and on a large scale is the key and difficult problem that the current industry urgently needs to solve.

[0003] Currently, the methods for harmless treatment of phosphogypsum at the source are mainly divided into the method of adding agents and the water washing process method. CN117102219A discloses a method for harmless treatment of phosphogypsum by adding alkaline materials and neutral calcareous raw materials. In addition to adding a variety of agents, this method also requires high temperature and high pressure in a reaction kettle. CN112871457A discloses a method for purifying and removing impurities from phosphogypsum. The phosphogypsum is prepared into a slurry by adding water, and then quicklime is added to precipitate soluble phosphorus and fluorine. Under strong stirring, water glass is added to disperse the precipitated phosphorus and fluorine generated with lime, and then a decolorizing agent and an adsorbing agent are added to finally obtain gypsum concentrate. This method requires adding a large amount of agents, resulting in a high cost. CN106977123A discloses a method for removing impurity fluorine in phosphogypsum, that is, washing phosphogypsum with citric acid water added, then washing the phosphogypsum sample, and finally removing impurities through a water washing process. This method may carry out soluble organic matter in phosphogypsum during the water washing process, causing secondary pollution. At the same time, the water consumption for multiple water washings is large, and the treatment cost is high. Summary of the Invention

[0004] In view of the above technical problems, the present invention provides a method for harmless treatment of phosphogypsum at the source. Based on the problems existing in the three-stage countercurrent water washing of phosphogypsum in the wet-process phosphoric acid industry, the present invention makes technical improvements to the water washing and filtration section, thereby achieving the improvement of the comprehensive recovery rate of fluorine and phosphorus resources while reducing the content of harmful components in phosphogypsum; in addition, the improved phosphogypsum undergoes slurry preparation and two-stage dosing and stirring to achieve the goal of green, large-scale, and low-cost harmless treatment, so as to expand the comprehensive utilization channels of phosphogypsum. The present invention uses the industrial solid waste "treating waste with waste" for the solid hazardous waste phosphogypsum, and treats phosphogypsum without external temperature and pressure conditions, with low cost and on a large scale and harmlessly, which is a very effective environmental protection technology, enabling the harmlessly treated phosphogypsum to meet the requirements of Class I general solid waste.

[0005] A method for harmless treatment of phosphogypsum at the source, which comprises the following steps:

[0006] Step 1, reducing pollution at the source: Wash the last stage of the crystal-growing slurry filtration system with clean water. The ratio of the amount of clean water used to phosphogypsum is 1:10 to 1:1 cubic meter per ton. After washing, phosphogypsum is obtained. Generally, the last stage is the third stage. Reducing pollution at the source is not a necessary condition for the harmless treatment of phosphogypsum at the source. This section only helps to improve the recovery rates of fluorine and phosphorus and reduce the dosage of harmless agents in the subsequent section;

[0007] Step 2, mixing and stirring to adjust the slurry: Mix the filter cloth washing water in the crystal-growing slurry filtration system with the phosphogypsum obtained in Step 1 to adjust the slurry to a phosphogypsum slurry with a concentration of 20wt% - 60wt%;

[0008] Step 3, first-stage mixing and stirring reaction: Add harmless treatment agent A to the phosphogypsum slurry obtained in Step 2, stir and mix evenly, and react for 5 - 60 minutes to obtain a first-stage reaction slurry;

[0009] Step 4, second-stage mixing and stirring reaction: Add harmless agent B to the first-stage reaction slurry obtained in Step 3, stir and mix evenly, and the reaction residence time is 20 - 60 minutes. After filtration, a filtrate and harmless phosphogypsum are obtained.

[0010] The clean water in Step 1 is fresh water or reclaimed water with low fluoride and phosphate impurity contents after treatment of production wastewater.

[0011] The washing water after the last-stage water washing in Step 1 is sequentially returned to the previous-stage water washing, and after being filtered by the first-stage water washing, it is returned to the extraction section to recover fluorine and phosphorus.

[0012] The harmless treatment agent A in Step 3 is one or a mixture of any proportion of steel slag, coal gangue, yellow phosphorus slag, fly ash, boiler ash, building materials waste, water quenched slag, red mud, aluminum ash, and the addition amount is 0.5% - 2.5% of the mass of the treated phosphogypsum.

[0013] The harmless treatment agent B in Step 4 is one or a mixture of any proportion of carbide slag, lime, alkali residue, and the addition amount is 0.1% - 1.5% of the mass of the treated phosphogypsum.

[0014] The filtrate in Step 4 is returned to the crystal-growing slurry filtration system as filter cloth washing water, and after washing, it is mixed and adjusted with phosphogypsum to form a slurry.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] (1) The present invention realizes the comprehensive recovery rate of valuable components of fluorine and phosphorus in the wet-process phosphoric acid industry through simple process improvement, and reduces the pollutant content of phosphogypsum after water washing and filtration; the present invention reduces pollution at the source, significantly reduces the fluoride and phosphate contents in the phosphogypsum after reducing pollution at the source, and in the subsequent phosphogypsum treatment process, the dosage of the medicament is reduced by 50-70% compared with the case without reducing pollution at the source.

[0017] (2) The harmless treatment of this phosphogypsum utilizes the idea of "treating pollution with waste" of industrial solid waste, and the raw materials for preparing the medicament have wide sources and low costs; the harmless treatment process of the phosphogypsum of the present invention is simple in operation and short in process, and the harmless treatment reaction is completed in the slurry. The treatment scale is flexible and the reaction is sufficient. The properties of the phosphogypsum after harmless treatment are stable. It is a green, environmental protection and energy-saving phosphogypsum source harmless treatment technology. The phosphogypsum leaving the factory treated by this method meets the standards of Class I general industrial solid waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the process flow chart of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0020] Example 1

[0021] The method for harmless treatment of the phosphogypsum source includes the following steps:

[0022] Step 1, reducing pollution at the source: An enterprise A's wet-process phosphoric acid production line produces 200 t / h of phosphogypsum. The third-stage water washing of the crystal-growing slurry filtration system uses clean water for washing, and the ratio of the clean water consumption to the phosphogypsum is 1:10 cubic meters / ton, that is, the water washing consumption is 20 m 3 / h, and the phosphogypsum is obtained after washing; generally, the last stage is the third stage, and reducing pollution at the source is not a necessary condition for the harmless treatment of the phosphogypsum source. This section only helps to improve the recovery rates of fluorine and phosphorus and reduce the dosage of the harmless medicament in the subsequent section;

[0023] Step 2, mixing and stirring to adjust the slurry: The filter cloth washing water in the crystal-growing slurry filtration system and the phosphogypsum obtained in Step 1 are adjusted to a phosphogypsum slurry with a concentration of 45 wt%;

[0024] Step 3, first-stage mixing and stirring reaction: The phosphogypsum slurry obtained in Step 2 is pumped into the first-stage harmless mixing and stirring tank, and at the same time, medicament A (prepared from red mud, yellow phosphorus slag, and stone cutting waste in a ratio of 1:1:1) is added, and the addition amount is 3 t / h (1.5% of the mass of the treated phosphogypsum). The stirring speed is 70 r / min, and the mixture is stirred evenly. The reaction time at normal temperature is 30 min to obtain the first-stage reaction slurry;

[0025] Step 4: Secondary mixing and stirring reaction: The primary reaction slurry obtained in Step 3 is self-flowed or sent to the secondary mixing and stirring reaction tank, and at the same time, harmless chemical agent B (prepared by mixing carbide slag and lime in a ratio of 1:2) is added, with an addition amount of 2 t / h (1% of the mass of the treated phosphogypsum). It is stirred and mixed evenly at a stirring speed of 70 r / min. The reaction residence time at normal temperature is 40 min. After filtration, filtrate and harmless phosphogypsum are obtained. Before and after the harmless treatment, the phosphogypsum is leached according to the "Horizontal Oscillation Method for the Leaching Toxicity of Solid Wastes" (HJ557-2010). The characteristic pollution indicators of the leachate are shown in Table 1, and the pollutant content meets the requirements of Class I general industrial solid wastes.

[0026] Comparative Example 1

[0027] A method for the source harmless treatment of phosphogypsum, which includes the following steps (without implementing source pollution reduction improvement and directly implementing harmless treatment):

[0028] Step 1: Mixing, stirring and slurry adjustment: An enterprise A's wet-process phosphoric acid production line generates 200 t / h of phosphogypsum. The third-stage water washing of the crystal-growing slurry filtration system is the leachate generated from the phosphogypsum storage yard. The water washing water consumption ratio to phosphogypsum is 1:10 cubic meters per ton, that is, the water washing water consumption is 20 m 3 / h. After washing, wash water and phosphogypsum are obtained. The wash water is sequentially returned as the water for secondary and primary water washing. After filtration in the primary water washing, the filtrate is returned to the extraction section to recover fluorine and phosphorus. The generated phosphogypsum and the filter cloth flushing water are modulated into a slurry with a solid content of 45%.

[0029] Step 2: Primary mixing and stirring reaction: The phosphogypsum slurry obtained in Step 1 is pumped to the primary harmless mixing and stirring tank, and at the same time, chemical agent A (prepared by mixing red mud, yellow phosphorus slag, and stone cutting waste in a ratio of 1:1:1) is added, with an addition amount of 6 t / h (3% of the mass of the treated phosphogypsum). It is stirred and mixed evenly at a stirring speed of 70 r / min. The reaction time at normal temperature is 30 min to obtain the primary reaction slurry;

[0030] Step 3: Secondary mixing and stirring reaction: The primary reaction slurry obtained in Step 2 is self-flowed or sent to the secondary mixing and stirring reaction tank, and at the same time, harmless chemical agent B (prepared by mixing carbide slag and lime in a ratio of 1:2) is added, with an addition amount of 6 t / h (3% of the mass of the treated phosphogypsum). It is stirred and mixed evenly at a stirring speed of 70 r / min. The reaction residence time at normal temperature is 40 min. After filtration, filtrate and harmless phosphogypsum are obtained. Before and after the harmless treatment, the phosphogypsum is leached according to the "Horizontal Oscillation Method for the Leaching Toxicity of Solid Wastes" (HJ557-2010). The characteristic pollution indicators of the leachate are shown in Table 1, and the pollutant content meets the requirements of Class I general industrial solid wastes.

[0031] Table 1 Pollutant content in the leachate of phosphogypsum before and after harmless treatment in Example 1 and Comparative Example 1 (mg / L)

[0032]

[0033] It can be seen from the comparison between Example 1 and Comparative Example 1 that after source pollution reduction in Example 1, the dosage of chemicals added in the first-stage reaction decreased by 50%, and the dosage of chemicals added in the second-stage reaction decreased by 67%, significantly reducing the production cost of harmless treatment.

[0034] Comparative Example 2

[0035] A method for the source harmless treatment of phosphogypsum, which includes the following steps (only one-stage reaction is carried out):

[0036] The method for the source harmless treatment of phosphogypsum includes the following steps:

[0037] Step 1, source pollution reduction: An enterprise A's wet-process phosphoric acid production line generates 200 t / h of phosphogypsum. The third-stage water washing of the crystal-growing slurry filtration system is washed with clean water, and the ratio of the clean water consumption to phosphogypsum is 1:10 m³ / t, that is, the water washing consumption is 20 m 3 / h, and the phosphogypsum is obtained after washing; generally, the last stage is the third stage. Source pollution reduction is not a necessary condition for the source harmless treatment of phosphogypsum. This section only helps to improve the recovery rates of fluorine and phosphorus and reduce the dosage of harmless chemicals in the subsequent section;

[0038] Step 2, mixing and stirring for pulp adjustment: The filter cloth washing water in the crystal-growing slurry filtration system and the phosphogypsum obtained in Step 1 are adjusted to a phosphogypsum slurry with a concentration of 45 wt%;

[0039] Step 3, first-stage mixing and stirring reaction: The phosphogypsum slurry obtained in Step 2 is pumped into the first-stage harmless mixing and stirring tank, and at the same time, Chemical A (prepared by mixing red mud, yellow phosphorus slag, and stone cutting waste in a ratio of 1:1:1) is added, with an addition amount of 12 t / h (6% of the mass of the treated phosphogypsum). The stirring speed is 70 r / min, and the mixture is stirred evenly. The reaction time at normal temperature is 30 min to obtain the first-stage reaction slurry; after filtration, the filtrate and harmless phosphogypsum are obtained. The phosphogypsum before and after harmless treatment is leached according to the "Horizontal Oscillation Method for the Leaching Toxicity of Solid Wastes" (HJ557-2010), and the characteristic pollution indicators of the leachate are shown in Table 2.

[0040] Table 2 Pollutant content in the leachate of phosphogypsum before and after harmless treatment in Example 1 and Comparative Example 2 (mg / L)

[0041]

[0042] It can be seen from Example 1 and Comparative Example 2 that the pollutant content in Comparative Example 2 did not meet the requirements for Class I general industrial solid waste. That is, without undergoing the specific two-stage harmless treatment steps of the present invention, it is impossible to obtain the technical effects of the present invention.

[0043] Comparative Example 3

[0044] A method for the source harmless treatment of phosphogypsum, which includes the following steps (the same medicaments are added in the first-stage reaction and the second-stage reaction):

[0045] The method for the source harmless treatment of phosphogypsum includes the following steps:

[0046] Step 1, source pollution reduction: An enterprise A's wet-process phosphoric acid production line generates 200 t / h of phosphogypsum. The third-stage water washing of the crystal-growing slurry filtration system is washed with clean water, and the ratio of the clean water consumption to the phosphogypsum is 1:10 cubic meters per ton, that is, the water washing consumption is 20 m 3 / h, and the phosphogypsum is obtained after washing; generally, the last stage is the third stage. Source pollution reduction is not a necessary condition for the source harmless treatment of phosphogypsum. This section only helps to improve the recovery rates of fluorine and phosphorus and reduce the dosage of harmless medicaments in the subsequent section;

[0047] Step 2, mixing and stirring for slurry preparation: The filter cloth washing water in the crystal-growing slurry filtration system and the phosphogypsum obtained in Step 1 are mixed and stirred to prepare a phosphogypsum slurry with a concentration of 45 wt%;

[0048] Step 3, first-stage mixing and stirring reaction: The phosphogypsum slurry obtained in Step 2 is pumped into the first-stage harmless mixing and stirring tank, and at the same time, medicament A (prepared from red mud, yellow phosphorus slag, and stone cutting waste in a ratio of 1:1:1) is added, and the addition amount is 6 t / h (3% of the mass of the treated phosphogypsum). The stirring speed is 70 r / min, and the mixture is stirred evenly. The normal-temperature reaction time is 30 min to obtain the first-stage reaction slurry;

[0049] Step 4, second-stage mixing and stirring reaction: The first-stage reaction slurry obtained in Step 3 is self-flowed or pumped to the second-stage mixing and stirring reaction tank, and at the same time, harmless medicament B (prepared from red mud, yellow phosphorus slag, and stone cutting waste in a ratio of 1:1:1) is added, and the addition amount is 6 t / h (3% of the mass of the treated phosphogypsum). The mixture is stirred evenly at a stirring speed of 70 r / min, and the normal-temperature reaction residence time is 40 min. After filtration, the filtrate and harmless phosphogypsum are obtained. The phosphogypsum before and after the harmless treatment is leached according to the "Horizontal Oscillation Method for Solid Waste Leaching Toxicity Leaching Method" (HJ557-2010), and the characteristic pollution indexes of the leachate are shown in Table 3.

[0050] Table 3 Pollutant content (mg / L) of phosphogypsum leachate before and after harmless treatment in Example 1 and Comparative Example 3

[0051]

[0052] As can be seen from Example 1, the pollutant content in Comparative Example 3 did not meet the requirements of Class I general industrial solid waste. That is, without undergoing the harmless treatment steps with different types of agents in different reaction stages specific to the present invention, it is impossible to obtain the technical effects of the present invention.

[0053] Example 2

[0054] As Figure 1 shown, the method for harmless treatment at the source of phosphogypsum includes the following steps:

[0055] Step 1, source pollution reduction: Improve the third-stage water washing water of the crystallization-aiding slurry filtration system in wet-process phosphoric acid production to process water. The ratio of the water washing amount to phosphogypsum is 1:10 cubic meters per ton, that is, the water washing amount is 20 m 3 / h. The process water has a fluoride content of 5.6 mg / L and a phosphate content of 0.2 mg / L. After washing and filtration, wash water and phosphogypsum are obtained. The wash water is sequentially returned as the front-stage water washing water, and the filtrate after the first-stage water washing and filtration is returned to the extraction section to recover fluorine and phosphorus. The pollutant content of the phosphogypsum produced before and after the implementation of source pollution reduction is shown in Table 4.

[0056] Table 4 Comparison of phosphogypsum quality before and after the implementation of source pollution reduction

[0057]

[0058] Step 2, mixing and stirring for slurry adjustment: Adjust the filter cloth washing water in the crystallization-aiding slurry filtration system and the phosphogypsum obtained in Step 1 to a phosphogypsum slurry with a concentration of 45 wt%.

[0059] Step 3, first-stage mixing and stirring reaction: Pump the phosphogypsum slurry obtained in Step 2 into the first-stage mixing and stirring reaction tank, and simultaneously add Agent A (prepared by mixing yellow phosphorus slag and water quenched slag at a ratio of 1:1), with an addition amount of 5 t / h (3% of the treated phosphogypsum mass). The stirring speed is 70 r / min, and the mixture is stirred evenly. The reaction time at normal temperature is 40 min to obtain the first-stage reaction slurry.

[0060] Step 4: Secondary mixing and stirring reaction: The primary reaction slurry obtained in Step 3 is fed by gravity or pumped into a secondary mixing and stirring reaction tank. Meanwhile, reagent B (prepared from carbide slag and alkali residue in a ratio of 2:1) is added at a rate of 6 t / h (3% of the mass of the treated phosphogypsum). The mixture is stirred evenly at a stirring speed of 70 r / min and reacts at room temperature for 40 min. After filtration, filtrate and harmless phosphogypsum are obtained. The leaching of phosphogypsum before and after harmless treatment is carried out in accordance with the "Horizontal Oscillation Method for the Leaching Toxicity of Solid Wastes" (HJ557-2010). The characteristic pollution indicators of the leachate are shown in Table 5, and the pollutant content meets the requirements for Class I general industrial solid wastes.

[0061] Table 5 Analysis Results of Leachate before and after Source Harmless Treatment of Phosphogypsum

[0062]

[0063] Example 3

[0064] As Figure 1 shown, the method for source harmless treatment of phosphogypsum includes the following steps:

[0065] Step 1: Source pollution reduction: Improve the third-stage water washing water of the crystal-growing slurry filtration system in wet-process phosphoric acid production to process water. The ratio of water washing water consumption to phosphogypsum is 1:8 cubic meters per ton, that is, the water washing water consumption is 25 m 3 / h, where the clear and clean water has a fluoride content of 5.6 mg / L and a phosphate content of 0.2 mg / L. After washing and filtration, wash water and phosphogypsum are obtained. The wash water is sequentially returned as the water for the previous stage of water washing, and the filtrate after the first-stage water washing and filtration is returned to the extraction section to recover fluorine and phosphorus. The pollutant content of the phosphogypsum generated before and after the implementation of source pollution reduction is shown in Table 6.

[0066] Table 6 Comparison of Phosphogypsum Quality before and after the Implementation of Source Pollution Reduction

[0067]

[0068] Step 2: Mixing and stirring for slurry adjustment: Adjust the filter cloth washing water in the crystal-growing slurry filtration system and the phosphogypsum obtained in Step 1 to a phosphogypsum slurry with a concentration of 50 wt%.

[0069] Step 3: Primary mixing and stirring reaction: Pump the phosphogypsum slurry obtained in Step 2 into a primary mixing and stirring reaction tank. Meanwhile, reagent A (prepared from steel slag and fly ash in a ratio of 1:1) is added at a rate of 5 t / h (2.5% of the mass of the treated phosphogypsum). The mixture is stirred evenly at a stirring speed of 70 r / min and reacts at room temperature for 20 min to obtain a primary reaction slurry.

[0070] Step 4: Secondary mixing and stirring reaction: The primary reaction slurry obtained in Step 3 is fed by gravity or pumped to a secondary mixing and stirring reaction tank. Meanwhile, reagent B (prepared from carbide slag) is added at a rate of 8 t / h (4% of the mass of the treated phosphogypsum). The mixture is stirred evenly at a stirring speed of 70 r / min, and the reaction residence time at room temperature is 60 min. After filtration, filtrate and harmless phosphogypsum are obtained. Before and after the harmless treatment, the leaching of phosphogypsum is carried out according to the "Horizontal Oscillation Method for Leaching Toxicity of Solid Wastes" (HJ557-2010). The characteristic pollution indicators of the leachate are shown in Table 7, and the pollutant content meets the requirements of Class I general industrial solid wastes.

[0071] Table 7 Analysis Results of Leachate before and after Source Harmless Treatment of Phosphogypsum

[0072]

[0073] Example 4

[0074] As Figure 1 shown, the method for source harmless treatment of phosphogypsum includes the following steps:

[0075] Step 1: Source pollution reduction: The third-stage water washing water of the crystal-growing slurry filtration system in wet-process phosphoric acid production is improved to process water. The ratio of water washing water consumption to phosphogypsum is 1:6.7 cubic meters per ton, that is, the water washing water consumption is 30 m 3 / h, where the process water has a fluoride content of 1.6 mg / L and a phosphate content of 0.6 mg / L. After washing and filtration, wash water and phosphogypsum are obtained. The wash water is sequentially returned as the water for the previous stage of water washing, and the filtrate after the first-stage water washing and filtration is returned to the extraction section to recover fluorine and phosphorus. The pollutant content of the phosphogypsum generated before and after the implementation of source pollution reduction is shown in Table 8.

[0076] Table 8 Comparison of Phosphogypsum Quality before and after the Implementation of Source Pollution Reduction

[0077]

[0078]

[0079] Step 2: Mixing, stirring, and slurry adjustment: The filter cloth washing water in the crystal-growing slurry filtration system and the phosphogypsum obtained in Step 1 are adjusted to a phosphogypsum slurry with a concentration of 35 wt%.

[0080] Step 3: Primary mixing and stirring reaction: The phosphogypsum slurry obtained in Step 2 is pumped to a primary mixing and stirring reaction tank. Meanwhile, reagent A (prepared by mixing aluminum ash and construction waste at a ratio of 1:1) is added at a rate of 3 t / h (1.5% of the mass of the treated phosphogypsum). The mixture is stirred evenly at a stirring speed of 70 r / min, and the reaction time at room temperature is 40 min to obtain a primary reaction slurry.

[0081] Step 4: Secondary mixing and stirring reaction: The slurry obtained from the first-stage reaction in Step 3 is fed by gravity or pumped into a secondary mixing and stirring reaction tank. Meanwhile, reagent B (prepared from alkali residue) is added at a rate of 10 t / h (5% of the mass of phosphogypsum to be treated). The mixture is stirred evenly at a stirring speed of 70 r / min, and the reaction residence time at normal temperature is 60 min. After filtration, filtrate and harmless phosphogypsum are obtained. The leaching of phosphogypsum before and after harmless treatment is carried out in accordance with the "Horizontal Oscillation Method for Leaching Toxicity of Solid Wastes" (HJ557-2010). The characteristic pollution indicators of the leachate are shown in Table 9, and the pollutant content meets the requirements for Class I general industrial solid wastes.

[0082] Table 9 Analysis Results of Leachate of Phosphogypsum before and after Source Harmless Treatment

[0083]

[0084] The specific embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention.

Claims

1. A method for harmless treatment at the source of phosphogypsum, characterized in that It includes the following steps: Step 1, source pollution reduction: Wash the end section of the crystal cultivation slurry filtration system with clean water. The ratio of the amount of clean water used to phosphogypsum is 1:10 to 1:1 cubic meter / ton. After washing, phosphogypsum is obtained; Step 2, mixing and stirring for pulp preparation: Adjust the filter cloth flushing water in the crystal cultivation slurry filtration system and the phosphogypsum obtained in Step 1 into a phosphogypsum slurry with a concentration of 20wt% - 60wt%; Step 3, first-stage mixing and stirring reaction: Add the harmless treatment agent A to the phosphogypsum slurry obtained in Step 2, stir and mix evenly, and react for 5 - 60 minutes to obtain the first-stage reaction slurry; Step 4, second-stage mixing and stirring reaction: Add the harmless agent B to the first-stage reaction slurry obtained in Step 3, stir and mix evenly, and the reaction residence time is 20 - 60 minutes. After filtering the slurry, filtrate and harmless phosphogypsum are obtained; The harmless treatment agent A in Step 3 is one or a mixture of any proportion of steel slag, coal gangue, yellow phosphorus slag, fly ash, boiler ash, building materials waste, water quenched slag, red mud, aluminum ash, and the addition amount is 0.5% - 2.5% of the mass of the treated phosphogypsum; The harmless treatment agent B in Step 4 is one or a mixture of any proportion of carbide slag, lime, alkali slag, and the addition amount is 0.1% - 1.5% of the mass of the treated phosphogypsum.

2. The method for harmless treatment of phosphogypsum at the source according to claim 1, characterized in that: The clean water in Step 1 is fresh water or production wastewater or treated process water with fluoride and phosphate impurity contents less than 10mg / L and 1mg / L respectively.

3. The method for harmless treatment of phosphogypsum at the source according to claim 2, characterized in that: The washing water after the end-section water washing in Step 1 is sequentially returned to the previous-section water washing, and after being filtered by the first-section water washing, it is returned to the extraction section to recover fluorine and phosphorus.

4. The method for source harmless treatment of phosphogypsum according to claim 1, characterized in that: The filtrate in Step 4 is returned to the crystal cultivation slurry filtration system as filter cloth flushing water.

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