WO2024021235A1 - Method for preparing building gypsum by purifying and calcining phosphogypsum - Google Patents

Abstract

A method for preparing building gypsum by purifying and calcining phosphogypsum. The method comprises: leaching phosphogypsum in ammonia water, subjecting same to solid-liquid separation, washing filter residues with water, subjecting the resulting residues that are washed with water to ammonia distillation drying, first calcining the dried material, and then subjecting same to phase change for dehydration, so as to obtain the building gypsum. The phosphogypsum is leached by using ammonia water, such that the acidity of the phosphogypsum is neutralized, and aluminum in the phosphogypsum can be further dissolved, thereby reducing the content of metal impurities. Ammonia leaching can further inhibit the dissolution of calcium ions, reduce the loss of main elements in the gypsum, inhibit the generation of calcium phosphate and calcium fluoride, and further improve the removal of soluble substances in the phosphogypsum.

Description

Method for preparing building gypsum by purifying and calcining phosphogypsum Technical field

The invention belongs to the technical field of phosphogypsum treatment in phosphorus chemical industry, and specifically relates to a method for purifying and calcining phosphogypsum to prepare building gypsum.

Background technique

Phosphogypsum is a solid waste residue discharged by phosphorus chemical companies using wet processes to produce phosphoric acid. The main component is calcium sulfate dihydrate. In addition, it also contains undecomposed phosphate rock, organic matter, silica, fluoride, phosphate, sulfuric acid, and a small amount of Impurities such as metals (potassium, sodium, iron, aluminum) and heavy metals. Normally, 1 ton of phosphoric acid produced by wet process will produce 4.5-5.5 tons of phosphogypsum. At present, the annual emission of phosphogypsum in the world reaches more than 200 million tons, but the utilization rate of phosphogypsum does not exceed 10%. The treatment, disposal and comprehensive utilization of phosphogypsum have become a worldwide problem. So far, most of the phosphogypsum has been disposed of by building warehouses and stockpiling, which not only occupies a large amount of land, but also brings serious environmental problems to the surrounding environment due to the leakage and transfer of harmful substances in the phosphogypsum. Phosphogypsum is rich in calcium and sulfur and is a valuable resource. Modified phosphogypsum can be used to replace increasingly scarce natural gypsum resources. Therefore, from the perspective of environmental protection and resource utilization, the treatment and utilization of phosphogypsum waste residue is urgent.

The impurities contained in phosphogypsum are divided into soluble and insoluble. Among them, soluble P ₂ O ₅ makes phosphogypsum acidic and causes powdering and frosting of the dried gypsum surface; soluble fluorine contains fluoride ions, fluorosilicon They exist in the form of acid ions and slowly react with gypsum to release hydrogen ions; the main impact of soluble sodium and potassium ions on gypsum products is to cause them to pulverize and bloom. Residual insoluble organic matter will adhere to the surface of the gypsum and delay the setting of the gypsum, affecting the color of the product.

At present, the main methods for purifying and removing impurities from phosphogypsum include water washing, neutralization, flotation, acid leaching or a combination of the above methods.

The water washing method is used to remove water-soluble impurities in phosphogypsum, such as free sulfuric acid, phosphoric acid, water-soluble sulfates, phosphates and fluoride salts. This treatment process is relatively simple, but it can only remove soluble impurities, which is insufficient, consumes a lot of water, and the wastewater produced can easily cause secondary pollution. Although the neutralization method reduces the acidity of phosphogypsum, the metal impurities iron and aluminum in it will still have adverse effects. Flotation method can only screen out large particle size silica. The acid leaching method requires a large amount of acid, which further increases the acidity of phosphogypsum and leads to the dissolution of calcium ions.

Therefore, there is an urgent need for a method that can purify phosphogypsum and achieve comprehensive utilization.

Contents of the invention

The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a method for preparing building gypsum by purifying and calcining phosphogypsum. By purifying and calcining gypsum, harmful substances in phosphogypsum are removed and the availability of phosphogypsum is improved.

According to one aspect of the present invention, a method for purifying and calcining phosphogypsum to prepare building gypsum is proposed, which includes the following steps:

S1: Place phosphogypsum in ammonia water for leaching, and solid-liquid separation to obtain filtrate and filter residue;

S2: Wash the filter residue with water, and dry the resulting water-washed residue with evaporated ammonia to obtain dry material;

S3: The dry material is first calcined at 450-800°C, and then phase-change dehydrated at 150-190°C to obtain the building gypsum.

In some embodiments of the present invention, in step S1, the solid-liquid ratio of the phosphogypsum and the ammonia water is 30-50g/L, and the concentration of the ammonia water is 8-15 mol/L.

In some embodiments of the present invention, in step S1, the filtrate is subjected to deamination treatment. Further, the filtrate is deaminated to a nitrogen content lower than 10 mg/L.

In some embodiments of the present invention, in step S1, the stirring speed of the leaching process is controlled to be 150-300 r/min. Further, the leaching time is 2-4h.

In some embodiments of the present invention, in step S2, the liquid produced after water washing is recycled as wash water; when the nitrogen content in the wash water is enriched to a certain value, the wash water undergoes deamination treatment. Further, when the nitrogen content in the wash water is ≥8g/L, the wash water undergoes deamination treatment.

In some embodiments of the present invention, in step S2, during the water washing, the mass ratio of the filter residue to water is 1: (1-2).

In some embodiments of the present invention, in step S2, the steamed ammonia drying adopts an airflow drying method, controlling the inlet air temperature to 400-450°C, the outlet air temperature to 150-180°C, and the air inlet speed to 15-20m/s , the residence time is 5-10s.

In some embodiments of the present invention, in step S3, the calcination process is: blowing in hot air, controlling the inlet air temperature to 450-800°C, the outlet air temperature to 400-650°C, and the air inlet speed to 15-20m/ s, the residence time is 2-5s.

In some embodiments of the present invention, in step S3, the phase change dehydration process is: blowing in hot air, controlling the inlet air temperature to 150-190°C, the outlet air temperature to 150-180°C, and the air inlet speed to 15-190°C. 20m/s, residence time is 10-20min.

In some embodiments of the present invention, in step S3, the gas dehydrated through the phase change is mixed with the calcined gas and used as the heat source for the evaporated ammonia drying in step S2.

In some embodiments of the present invention, the deamination treatment is carried out using a deamination tower, and the gas dehydrated through the phase change in step S3 and/or the ammonia-containing gas dried by ammonia evaporation in step S2 enters the deamination tower for use. Deamination treatment.

In some embodiments of the present invention, the gas generated by the deamination tower is condensed to prepare new ammonia water, and the uncondensed non-condensable gas is directly discharged. When the nitrogen content of the solution in the deamination tower is lower than 10 mg/L, The solution is sent to the wastewater treatment system.

According to a preferred embodiment of the present invention, it has at least the following beneficial effects:

1. The present invention uses ammonia water to leaching phosphogypsum. On the one hand, it neutralizes the acidity of phosphogypsum. On the other hand, relatively concentrated ammonia water can dissolve aluminum in phosphogypsum and reduce the content of metal impurities in phosphogypsum; The phosphogypsum after ammonia leaching is further washed with water to take away most of the remaining ammonia and other soluble salts, thereby achieving the initial purification of phosphogypsum; and then through ammonia evaporation, calcination, and phase change, semi-hydrated gypsum is produced. Preferably, the process of the present invention can make full use of the waste heat generated in each process, introduce the waste heat in the calcination and phase change processes into the ammonia evaporation system and the deamination system, reduce heat consumption, and reuse the waste heat to prepare a new ammonia solution, achieving Resource utilization.

2. Use concentrated ammonia water to immerse phosphogypsum with ammonia. Part of the reaction is as follows:

6NH ₃ ·H ₂ O+P ₂ O ₅ →2(NH ₄ ) ₃ PO ₄ +3H ₂ O;

3NH ₃ ·H ₂ O+H ₃ PO ₄ →(NH ₄ ) ₃ PO ₄ +3H ₂ O;

NH ₃ ·H ₂ O+HF→NH ₄ F+H ₂ O;

SiF ₆ ^2- +4NH ₃ ·H ₂ O→6F ^- +4NH ₄ ⁺ +SiO ₂ +H ₂ O;

4NH ₃ ·H ₂ O+Al ³⁺ →4NH ₄ ⁺ +[Al(OH) ₄ ] ^- .

Concentrated ammonia water can not only neutralize the acidity of phosphogypsum and dissolve the aluminum metal impurities in it, but also 99% of the ammonia in the ammonia water system exists in the form of NH _3. The polarity of N in NH ₃ is strong, making H almost in the proton state. form, providing multiple sites for hydrogen bonding. On the CaSO ₄ ·2H ₂ O surface, N—H···O hydrogen bonds are formed with the O atoms in the adjacent Ca-O double layers, which increases the stability of the adjacent Ca-O double layers and creates new hydrogen bonds. This causes NH ₃ to adhere to the surface of the CaSO ₄ ·2H ₂ O crystal, increasing the potential barrier for interlayer dissolution and inhibiting the dissolution of calcium ions. Therefore, ammonia leaching can reduce the loss of main elements in gypsum, inhibit the generation of calcium phosphate and calcium fluoride, and further increase the removal of soluble substances in phosphogypsum.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and examples, wherein:

Figure 1 is a process flow diagram of Embodiment 1 of the present invention.

Detailed ways

The concept of the present invention and the technical effects produced will be clearly and completely described below with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without exerting creative efforts are all protection scope of the present invention.

Example 1

A method for preparing building gypsum by purifying and calcining phosphogypsum. Refer to Figure 1. The specific process is:

Step 1: Place phosphogypsum in ammonia water with a concentration of 15 mol/L according to a solid-liquid ratio of 50g/L, stirring at a speed of 300r/min, and leaching for 2 hours;

Step 2: Solid-liquid separation to obtain filtrate and filter cake. The filtrate enters the deamination tower for deamination treatment, and the filter cake enters the water washing process;

Step 3: Use primary water to clean the filter cake according to the mass ratio of phosphogypsum:water=1:2;

Step 4, solid-liquid separation, the obtained water washing residue enters the ammonia evaporation system, and the generated liquid can be recycled as washing water. When the nitrogen content in the washing water reaches 8g/L, the washing water and filtrate are sent to the deamination tower for treatment;

Step 5: Place the water-washed slag obtained in Step 4 into a pulse airflow dryer to evaporate ammonia and dry it. Control the inlet air temperature to 450°C, the outlet air temperature to 180°C, the air inlet speed to 20m/s, and the residence time to 5s. ;

Step 6: Place the ammonia-vaporized and dried material into a calciner for calcination, blow in high-temperature hot air, control the inlet air temperature to 800°C, the outlet air temperature to 600°C, the air inlet speed to 15m/s, and the residence time to 2s;

Step 7: Place the calcined material in a fluidized bed for phase change dehydration, blow in medium-temperature hot air, control the inlet temperature to 190°C, the outlet temperature to 180°C, the air inlet speed to 15m/s, and the residence time. is 10s;

Step 8: After the phase change reaction is completed, cool to room temperature to obtain hemihydrate gypsum;

Step 9. Part of the gas from the phase change system is mixed with the gas from the calcination system and then enters the ammonia evaporation system in step 5. It is used as the heat source of the ammonia evaporation system. The other part of the gas is mixed with the ammonia-containing gas from the ammonia evaporation system and enters the deamination tower. , and perform deamination treatment on the filtrate;

Step 10, as the heat exchange reaction in the deamination tower proceeds, the ammonia gas and water in the filtrate continue to evaporate, producing solid waste residue and sending it to the solid waste treatment plant. The generated gas is condensed by the condenser to prepare new ammonia water. The uncondensed gas is not The condensed gas is directly discharged. When the nitrogen content of the filtrate in the tower is lower than 10 mg/L, the filtrate is sent to the wastewater treatment system.

Example 2

A method for preparing building gypsum by purifying and calcining phosphogypsum. The specific process is:

Step 1: Place phosphogypsum in ammonia water with a concentration of 12 mol/L according to a solid-to-liquid ratio of 40g/L, stirring speed 200r/min, and leaching time 3h;

Step 2: Solid-liquid separation to obtain filtrate and filter cake. The filtrate enters the deamination tower for deamination treatment, and the filter cake enters the water washing process;

Step 3: Use primary water to clean the filter cake according to the mass ratio of phosphogypsum:water=1:1.5;

Step 4, solid-liquid separation, the obtained water washing residue enters the ammonia evaporation system, and the generated liquid can be recycled as washing water. When the nitrogen content in the washing water reaches 8g/L, the washing water and filtrate are sent to the deamination tower for treatment;

Step 5: Place the water-washed slag obtained in Step 4 into a pulse airflow dryer to evaporate ammonia and dry it. Control the inlet air temperature to 430°C, the outlet air temperature to 165°C, the air inlet speed to 17m/s, and the residence time to 7s. ;

Step 6: Place the ammonia-vaporized and dried materials into a calciner for calcination, blow in high-temperature hot air, control the inlet air temperature to 600°C, the outlet air temperature to 500°C, the air inlet speed to 16m/s, and the residence time to 3s;

Step 7: Place the calcined material in a fluidized bed for phase change dehydration, blow in medium-temperature hot air, control the inlet temperature to 170°C, the outlet temperature to 160°C, the air inlet speed to 18m/s, and the residence time. is 15s;

Step 8: After the phase change reaction is completed, cool to room temperature to obtain hemihydrate gypsum;

Step 9. Part of the gas from the phase change system is mixed with the gas from the calcination system and then enters the ammonia evaporation system in step 5. It is used as the heat source of the ammonia evaporation system. The other part of the gas is mixed with the ammonia-containing gas from the ammonia evaporation system and enters the deamination tower. , and perform deamination treatment on the filtrate;

Step 10, as the heat exchange reaction in the deamination tower proceeds, the ammonia gas and water in the filtrate continue to evaporate, producing solid waste residue and sending it to the solid waste treatment plant. The generated gas is condensed by the condenser to prepare new ammonia water. The uncondensed gas is not The condensed gas is directly discharged. When the nitrogen content of the filtrate in the tower is lower than 10 mg/L, the filtrate is sent to the wastewater treatment system.

Example 3

A method for preparing building gypsum by purifying and calcining phosphogypsum. The specific process is:

Step 1: Place phosphogypsum in ammonia water with a concentration of 8 mol/L according to a solid-to-liquid ratio of 30g/L, with a stirring speed of 150r/min and a leaching time of 4h;

Step 2: Solid-liquid separation to obtain filtrate and filter cake. The filtrate enters the deamination tower for deamination treatment, and the filter cake enters the water washing process;

Step 3: Use primary water to clean the filter cake according to the mass ratio of phosphogypsum:water=1:1;

Step 4, solid-liquid separation, the obtained water washing residue enters the ammonia evaporation system, and the generated liquid can be recycled as washing water. When the nitrogen content in the washing water reaches 8g/L, the washing water and filtrate are sent to the deamination tower for treatment;

Step 5: Place the water-washed slag obtained in Step 4 into a pulse airflow dryer to evaporate ammonia and dry it. Control the inlet air temperature to 400°C, the outlet air temperature to 150°C, the air inlet speed to 15m/s, and the residence time to 10s. ;

Step 6: Place the ammonia-vaporized and dried materials into a calciner for calcination, blow in high-temperature hot air, control the inlet air temperature to 450°C, the outlet air temperature to 400°C, the air inlet speed to 15m/s, and the residence time to 5s;

Step 7: Place the calcined material in a fluidized bed for phase change dehydration, blow in medium-temperature hot air, control the inlet temperature to 155°C, the outlet temperature to 150°C, the air inlet speed to 15m/s, and the residence time. for 20s;

Step 8: After the phase change reaction is completed, cool to room temperature to obtain hemihydrate gypsum;

Step 9. Part of the gas from the phase change system is mixed with the gas from the calcination system and then enters the ammonia evaporation system in step 5. It is used as the heat source of the ammonia evaporation system. The other part of the gas is mixed with the ammonia-containing gas from the ammonia evaporation system and enters the deamination tower. , and perform deamination treatment on the filtrate;

Step 10, as the heat exchange reaction in the deamination tower proceeds, the ammonia gas and water in the filtrate continue to evaporate, producing solid waste residue and sending it to the solid waste treatment plant. The generated gas is condensed by the condenser to prepare new ammonia water. The uncondensed gas is not The condensed gas is directly discharged. When the nitrogen content of the filtrate in the tower is lower than 10 mg/L, the filtrate is sent to the wastewater treatment system.

Comparative ratio

A method for preparing building gypsum by purifying and calcining phosphogypsum. This method does not perform ammonia leaching. The specific process is:

Step 1: Place phosphogypsum in primary water according to a solid-to-liquid ratio of 30g/L, with a stirring speed of 300r/min and a leaching time of 4h;

Step 2, solid-liquid separation to obtain filtrate and filter cake;

Step 3: Use primary water to clean the filter cake again according to the mass ratio of phosphogypsum:water=1:2;

Step 4, solid-liquid separation, the washed slag obtained is placed in a pulse air flow dryer for drying, the inlet air temperature is controlled to 450°C, the air outlet temperature is 180°C, the air inlet speed is 20m/s, and the residence time is 10s;

Step 5: Place the dried material in a calcining furnace for calcination, blow in high-temperature hot air, control the inlet air temperature to 800°C, the outlet air temperature to 650°C, the air inlet speed to 20m/s, and the residence time to 5s;

Step 6: Place the calcined material in a fluidized bed for phase change dehydration, blow in medium-temperature hot air, control the inlet temperature to 190°C, the outlet temperature to 180°C, the air inlet speed to 20m/s, and the residence time. for 20s;

Step 7: After the phase change reaction is completed, cool to room temperature to obtain hemihydrate gypsum.

According to "GB/T 5484-2012 Gypsum Chemical Analysis Method" and "JC/T 2073 Determination Method of Phosphorus and Fluorine in Phosphogypsum" and "GB/T 36141 Building Gypsum Phase Composition Analysis Method", the phosphogypsum raw materials and examples and comparisons were The semi-hydrated gypsum obtained in the proportion was tested, and the results are shown in Table 1.

Table 1

sample	Phosphogypsum raw materials	Example 1	Example 2	Example 3	Comparative ratio
BaiDu	58.76	93.74	92.62	91.87	86.33
CaSO 4 ·2H 2 O	87.51	1.13	1.26	1.29	1.57
CaSO 4 ·0.5H 2 O	-	90.37	89.96	89.83	87.04
Total phosphorus %	1.77	0.87	0.89	0.87	1.43
Water-soluble P 2 O 5 %	0.762	0.027	0.030	0.038	0.41
Water soluble F%	0.31	0.018	0.023	0.022	0.13
Organic matter%	1.12	-	-	-	-
SiO 2 %	7.11	7.08	7.06	7.09	7.10
Fe 2 O 3 %	0.233	0.196	0.181	0.202	0.198
Al 2 O 3 %	0.251	0.002	0.006	0.010	0.11
Na 2 O%	0.156	0.018	0.020	0.022	0.021
MgO%	0.11	0.037	0.031	0.033	0.034
Yield %	-	98.37	98.26	98.35	95.73

It can be seen from Table 1 that the impurity content of the examples is very low and the yield is very high. The comparative example has not been treated with ammonia leaching, the yield is slightly lower, and the impurity content is more than that of the example. This is because the comparative example only uses water washing and does not remove impurities. Sufficient, and the water washing process will cause the dissolution of a small amount of calcium, resulting in a reduction in the yield. The ammonia leaching process in the embodiment not only contributes to the leaching of impurities, but also inhibits the dissolution of CaSO ₄ ·2H ₂ O.

The embodiments of the present invention have been described in detail above with reference to 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 modifications can be made without departing from the purpose of the present invention. Variety. In addition, the embodiments of the present invention and the features in the embodiments may be combined with each other without conflict.

Claims (10)

1. A method for preparing building gypsum by purifying and calcining phosphogypsum, which is characterized by including the following steps:

   S1: Place phosphogypsum in ammonia water for leaching, and solid-liquid separation to obtain filtrate and filter residue;

   S2: Wash the filter residue with water, and dry the resulting water-washed residue with evaporated ammonia to obtain dry material;

   S3: The dry material is first calcined at 450-800°C, and then phase-change dehydrated at 150-190°C to obtain the building gypsum.
2. The method according to claim 1, characterized in that in step S1, the solid-liquid ratio of the phosphogypsum and the ammonia water is 30-50g/L, and the concentration of the ammonia water is 8-15 mol/L.
3. The method according to claim 1, characterized in that, in step S1, the filtrate is subjected to deamination treatment.
4. The method according to claim 1, characterized in that, in step S2, the liquid produced after washing is recycled as wash water; when the nitrogen content in the wash water is enriched to a certain value, the wash water undergoes deamination treatment.
5. The method according to claim 1, characterized in that, in step S2, the steamed ammonia drying adopts an airflow drying method, the inlet air temperature is controlled to 400-450°C, the air outlet temperature is 150-180°C, and the air inlet speed is 15 -20m/s, residence time is 5-10s.
6. The method according to claim 1, characterized in that in step S3, the calcination process is: blowing in hot air, controlling the inlet air temperature to 450-800°C, the outlet air temperature to 400-650°C, and the air inlet speed to 15-20m/s, residence time is 2-5s.
7. The method according to claim 1, characterized in that in step S3, the phase change dehydration process is: blowing in hot air, controlling the inlet air temperature to 150-190°C, the outlet air temperature to 150-180°C, and the inlet air temperature to 150-180°C. The speed is 15-20m/s and the residence time is 10-20min.
8. The method according to claim 1, characterized in that, in step S3, the gas dehydrated through the phase change is mixed with the calcined gas and used as the heat source for the evaporated ammonia drying in step S2.
9. The method according to claim 3 or 4, characterized in that the deamination treatment is carried out using a deamination tower, and the gas dehydrated through the phase change in step S3 and/or the ammonia-containing gas evaporated and dried by ammonia in step S2 Enter the deamination tower for deamination treatment.
10. The method according to claim 9, characterized in that the gas generated by the deamination tower is condensed to prepare new ammonia water, and the uncondensed non-condensable gas is directly discharged. When the nitrogen content of the solution in the deamination tower is less than 10 mg /L, the solution is sent to the wastewater treatment system.

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