A method for recovering phosphorus and fluorine from scale formed in a wet-process phosphoric acid production process

Abstract

The application provides a method for recovering phosphorus and fluorine from scaling substances in a wet-process phosphoric acid production process, and has the steps of: S1, crushing the scaling substances into powder, mixing the powder with dilute sulfuric acid, treating by microwave, and then filtering to obtain a clear liquid and a solid, the clear liquid being a phosphoric acid solution; S2, uniformly mixing the solid obtained in S1 with an activator, mixing the solid with concentrated sulfuric acid, and treating by microwave under negative pressure, and absorbing the escaped gas with cold water to obtain a fluorine-containing solution. The application takes solid waste in the production of phosphoric acid as raw material, recovers useful components in the solid waste by microwave decomposition, has a simple process, and the raw material is cheap and easy to obtain. In the meanwhile, the application protects the environment and realizes the recycling of solid waste resources.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of resource utilization of wet-process phosphoric acid solid waste, and particularly relates to a method for recovering phosphorus and fluorine from scaling substances in a wet-process phosphoric acid production process. BACKGROUND

[0002] In the process of producing wet-process phosphoric acid by the two-water method, there are many types of impurities in the raw material phosphate rock, such as F-, Ca2+, K+, Na+ and the like. In the extraction reaction stage, due to the high temperature of phosphoric acid, most of these impurities are dissolved in phosphoric acid and will not precipitate out of phosphoric acid. Although the content of this part of dissolved impurities is very small, it is extremely unstable. When the phosphoric acid enters the filtration stage, the temperature of the acid liquid will also decrease, and a large part of the impurities will crystallize and deposit, forming scaling on the system pipelines and equipment.

[0003] The scaling substances in the process of transporting dilute phosphoric acid mainly include calcium salts (calcium sulfate, calcium phosphate) and fluorosilicate (such as potassium fluorosilicate, sodium fluorosilicate). In recent years, with the decrease of phosphate rock grade, the clogging speed of the wet-process phosphoric acid production device is accelerated, and the scaling is cleaned frequently. The amount of scaling cleaned is large and cannot be reused, and is usually stored in solid form, which not only causes waste of resources, but also brings adverse effects to the environment. At present, the research on phosphoric acid scaling mainly focuses on scale inhibitors, and there is no related report on recycling useful components in phosphoric acid scaling. SUMMARY

[0004] The present application provides a method for recovering phosphorus and fluorine from scaling substances in a wet-process phosphoric acid production process.

[0005] The technical solution of the present application is a method for recovering phosphorus and fluorine from scaling substances in a wet-process phosphoric acid production process, comprising the following steps:

[0006] S1, crushing the scaling substances into powder, mixing with dilute sulfuric acid, treating with microwave, and then filtering to obtain clear liquid and solid, the clear liquid being a phosphoric acid solution;

[0007] S2, uniformly mixing the solid obtained in S1 with an activator, mixing with concentrated sulfuric acid, and treating with microwave under negative pressure, and absorbing the escaped gas with cold water to obtain a fluorine-containing solution.

[0008] Further, the scaling substances are crushed to a particle size of 0.15mm-0.5mm.

[0009] Further, the mass fraction of dilute sulfuric acid is 15%-30%, and the mass fraction of concentrated sulfuric acid is 90%-98%.

[0010] Further, the mass ratio of scaling substances to dilute sulfuric acid in S1 is 100:5-15.

[0011] Further, the power of microwave treatment in S1 is 100-400w, the radiation time is 0.5h-1h, and the temperature is 70-80℃.

[0012] Further, the activator in S2 is diatomite or silicon slag or white carbon black or one or a mixture of two of wollastonite, and the adding amount is 5-10% of the mass of the solid obtained in S1.

[0013] Further, the adding amount of concentrated sulfuric acid in S2 is 25-35% of the mass of the solid.

[0014] Further, the power of microwave treatment in S2 is 400-1000w, the radiation time is 0.5h-1.5h, and the temperature is 90-100℃.

[0015] Further, the negative pressure in S2 is-0.08--0.05MPa.

[0016] Further, the scaling comes from the pipeline and equipment after the filtration stage of the wet-process phosphoric acid.

[0017] The present application has the following beneficial effects:

[0018] The present application efficiently decomposes the phosphoric acid scaling in the microwave field and recovers phosphorus and fluorine therein, under the microwave condition, the ionization degree, ion activity and permeation ability to the reaction solid film of the liquid molecules are all improved, the diffusion speed between the solid phase and the liquid phase is accelerated, thereby accelerating the dissolution and reaction speed of the scaling. The dilute sulfuric acid can convert the calcium phosphate in the scaling into phosphoric acid and calcium sulfate, the dilute phosphoric acid can enter the industrial wet-process phosphoric acid reaction tank as the return acid, under the microwave and heating conditions, the fluorosilicate in the scaling is decomposed by the concentrated sulfuric acid to obtain silicon tetrafluoride and hydrogen fluoride, under the action of the activator, the hydrogen fluoride can be converted into silicon tetrafluoride gas, which is converted into fluorosilicic acid solution by water absorption, the solution can be used as the water supplement of the fluorine absorption device of the wet-process phosphoric acid, and the fluorine-containing compounds in the product are maximally recovered.

[0019] The present application uses the solid waste in the production of phosphoric acid as the raw material, and the useful components are recovered by microwave decomposition, the process is simple, the raw material is cheap and easy to obtain, the environment is protected, and the solid waste resource is reused. DETAILED DESCRIPTION

[0020] The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application.

[0021] The phosphatic scale used in the following examples was obtained from the inside of a dilute phosphoric acid pipeline in a wet-process phosphoric acid production plant. The main components of the phosphatic scale were determined to be 46.54% K2SiF6, 10.75% Na2SiF6, 14.78% CaSO4.2H2O, and 7.02% Ca(H2PO4)2.

[0022] Example 1

[0023] The phosphatic scale was first ground into powder having a particle size range of 0.15-0.5 mm. 1000 g of the powder was mixed with 100 g of dilute sulfuric acid having a mass fraction of 20%. The mixture was subjected to microwave treatment at a microwave radiation power of 300 w and a temperature of 70°C for 0.5 h. The mixture was then filtered to obtain a clear solution A and a solid A. The solid A was mixed with 25 g of diatomite and then mixed with 150 g of concentrated sulfuric acid having a mass fraction of 98%. The mixture was subjected to microwave treatment at a microwave radiation power of 800 w and a temperature of 90°C for 0.5 h under a pressure of -0.05 MPa. The evolved gas was absorbed by cold water to obtain a solution B. The P2O5 content of the clear solution A was determined to be 5% by gravimetric method, and the fluorine content of the solution B was determined to be 2.1% by a fluorine ion electrode.

[0024] Comparative Example 1

[0025] The phosphatic scale was first ground into powder having a particle size range of 0.15-0.5 mm. 1000 g of the powder was mixed with 100 g of dilute sulfuric acid having a mass fraction of 20%. The mixture was subjected to microwave treatment at a microwave radiation power of 300 w and a temperature of 70°C for 0.5 h. The mixture was then filtered to obtain a clear solution A and a solid A. The solid A was mixed with 25 g of diatomite and then mixed with 150 g of concentrated sulfuric acid having a mass fraction of 98%. The mixture was subjected to microwave treatment at a microwave radiation power of 800 w and a temperature of 90°C for 0.5 h under a pressure of -0.05 MPa. The evolved gas was absorbed by cold water to obtain a solution B. The P2O5 content of the clear solution A was determined to be 5% by gravimetric method, and the fluorine content of the solution B was determined to be 2.1% by a fluorine ion electrode.

[0026] Comparative Example 2

[0027] The phosphatic scale was first ground into powder having a particle size range of 0.15-0.5 mm. 1000 g of the powder was mixed with 100 g of dilute sulfuric acid having a mass fraction of 20%. The mixture was subjected to microwave treatment at a microwave radiation power of 300 w and a temperature of 70°C for 0.5 h. The mixture was then filtered to obtain a clear solution A and a solid A. The solid A was mixed with 25 g of diatomite and then mixed with 150 g of concentrated sulfuric acid having a mass fraction of 98%. The mixture was subjected to microwave treatment at a microwave radiation power of 800 w and a temperature of 90°C for 0.5 h under a pressure of -0.05 MPa. The evolved gas was absorbed by cold water to obtain a solution B. The P2O5 content of the clear solution A was determined to be 5% by gravimetric method, and the fluorine content of the solution B was determined to be 2.1% by a fluorine ion electrode.

[0028] Example 2

[0029] The phosphoric acid scale block is first ground into powder with a particle size range of 0.15-0.5 mm, 1000 g of the powder is mixed with 100 g of dilute sulfuric acid with a mass fraction of 20%, the microwave radiation power is 300 w, the temperature is 70°C, after 1 h, the mixture is filtered to obtain clear liquid A and solid A; 500 g of the above solid A is first mixed with 25 g of diatomite uniformly, then mixed with 150 g of concentrated sulfuric acid with a mass fraction of 98%, under -0.05 MPa, the microwave radiation power is 800 w, the temperature is 90°C, and the process is continued for 1.5 h, the escaped gas is absorbed by cold water to obtain solution B. The P2O5 content of the clear liquid A is 6.1% measured by gravimetric method, and the fluorine content of the solution B is 2.3% measured by a fluorine ion electrode.

[0030] Comparative Example 3

[0031] The phosphoric acid scale block is first ground into powder with a particle size range of 1.5-2.0 mm, 1000 g of the powder is mixed with 100 g of dilute sulfuric acid with a mass fraction of 20%, the microwave radiation power is 300 w, the temperature is 70°C, after 0.5 h, the mixture is filtered to obtain clear liquid A and solid A; 500 g of the above solid A is first mixed with 25 g of diatomite uniformly, then mixed with 150 g of concentrated sulfuric acid with a mass fraction of 98%, under -0.05 MPa, the microwave radiation power is 800 w, the temperature is 90°C, and the process is continued for 0.5 h, the escaped gas is absorbed by cold water to obtain solution B. The P2O5 content of the clear liquid A is 1.2% measured by gravimetric method, and the fluorine content of the solution B is 0.8% measured by a fluorine ion electrode.

[0032] Example 3:

[0033] The phosphoric acid scale block is first ground into powder with a particle size below 0.5 mm, 1000 g of the powder is mixed with 50 g of dilute sulfuric acid with a mass fraction of 30%, the mixture is subjected to microwave treatment, the microwave radiation power is 400 w, the temperature is 80°C, after 1 h, the mixture is filtered to obtain clear liquid A and solid A; 500 g of the above solid A is first mixed with 45 g of white carbon black uniformly, then mixed with 125 g of concentrated sulfuric acid with a mass fraction of 95%, under -0.05 MPa, the microwave radiation power is 1000 w, the temperature is 100°C, and the process is continued for 1.5 h, the escaped gas is absorbed by cold water to obtain solution B. The P2O5 content of the clear liquid A is 5.6% measured by gravimetric method, and the fluorine content of the solution B is 3.0% measured by a fluorine ion electrode.

[0034] Example 4:

[0035] The phosphoric acid scale block is first ground into powder with particle size below 0.5 mm, 1000 g of the powder is mixed with 150 g of dilute sulfuric acid with mass fraction of 25%, microwave treatment is performed, microwave radiation power is 200 w, temperature is 80°C, after 1 h, the mixture is filtered to obtain clear liquid A and solid A; 500 g of the above solid A is first mixed with 50 g of wollastonite uniformly, then mixed with 175 g of concentrated sulfuric acid with mass fraction of 90%, microwave radiation power is 600 w, temperature is 100°C, under -0.05 MPa, for 1.5 h, the escaped gas is absorbed by cold water to obtain solution B. The P2O5 content of the clear liquid A is 4.4% measured by gravimetric method, and the fluorine content of the solution B is 2.8% measured by fluorine ion electrode.

[0036] Comparative Example 4:

[0037] The phosphoric acid scale block is first ground into powder with particle size below 0.5 mm, 1000 g of the powder is mixed with 150 g of dilute sulfuric acid with mass fraction of 25%, microwave treatment is performed, microwave radiation power is 200 w, temperature is 80°C, after 1 h, the mixture is filtered to obtain clear liquid A and solid A; 500 g of the above solid A is first mixed with 50 g of wollastonite uniformly, then mixed with 175 g of concentrated sulfuric acid with mass fraction of 25%, microwave radiation power is 600 w, temperature is 100°C, under -0.05 MPa, for 1.5 h, the escaped gas is absorbed by cold water to obtain solution B. The P2O5 content of the clear liquid A is 4.1% measured by gravimetric method, and the fluorine content of the solution B is 0.2% measured by fluorine ion electrode.

[0038] Example 5:

[0039] The phosphoric acid scale block is first ground into powder with particle size below 0.5 mm, 1000 g of the powder is mixed with 100 g of dilute sulfuric acid with mass fraction of 15%, microwave treatment is performed, microwave radiation power is 100 w, temperature is 75°C, after 1 h, the mixture is filtered to obtain clear liquid A and solid A; 500 g of the above solid A is first mixed with 25 g of wollastonite and 25 g of diatomite uniformly, then mixed with 175 g of concentrated sulfuric acid with mass fraction of 95%, microwave radiation power is 800 w, temperature is 100°C, under -0.05 MPa, for 1.5 h, the escaped gas is absorbed by cold water to obtain solution B. The P2O5 content of the clear liquid A is 4.5% measured by gravimetric method, and the fluorine content of the solution B is 3.0% measured by fluorine ion electrode.

[0040] Comparative Example 5:

[0041] Firstly, the phosphoric acid scale block is ground into powder with particle size below 0.5 mm, 1000 g of the powder is mixed with 100 g of dilute sulfuric acid with mass fraction of 15%, microwave treatment is performed, microwave radiation power is 100 w, temperature is 75 ℃, after 1 h, the mixture is filtered to obtain clear liquid A and solid A; 500 g of the above-mentioned solid A is mixed with 175 g of concentrated sulfuric acid with mass fraction of 95%, without adding activator, microwave radiation power is 800 w, temperature is 100 ℃, and the process lasts for 1.5 h, the escaped gas is absorbed by cold water to obtain solution B. The P2O5 content of the clear liquid A is 4.5% measured by gravimetric method, and the fluorine content of the solution B is 0.8% measured by fluorine ion electrode.

[0042] The above examples are only for illustrating the technical ideas and characteristics of the present application, and the content is only the preferred embodiments of the present application, but the protection scope of the present application is not limited to this. Within the technical scope disclosed by the present application, equivalent changes or improvements according to the technical solutions and inventive concept of the present application should be covered in the protection scope of the present application.

Claims

1. A method of recovering phosphorus and fluorine from scale in a wet-process phosphoric acid production process, characterized in that, The method comprises the following steps: S1, crushing the fouling into powder, mixing with dilute sulfuric acid, treating with microwave, and then filtering to obtain a clear liquid and a solid, the clear liquid being a phosphoric acid solution; the microwave treatment is performed at a power of 100-400 W, a radiation time of 0.5-1 h, and a temperature of 70-80 ℃; S2, uniformly mixing the solid obtained in S1 with an activating agent, the activating agent being one or a mixture of two of diatomite, silicon slag, white carbon black, and wollastonite, and the adding amount being 5-10% of the mass of the solid obtained in S1; further mixing with concentrated sulfuric acid, the adding amount of the concentrated sulfuric acid being 25-35% of the mass of the solid, and performing microwave treatment under negative pressure, the microwave treatment being performed at a power of 400-1000 W, a radiation time of 0.5-1.5 h, and a temperature of 90-100 ℃; and absorbing the escaped gas with cold water to obtain a solution containing fluorine.

2. The method of claim 1, wherein: The fouling is crushed to a particle size of 0.15-0.5 mm.

3. The method of claim 1, wherein: The mass fraction of the dilute sulfuric acid is 15-30%, and the mass fraction of the concentrated sulfuric acid is 90-98%.

4. The method of claim 1, wherein: The mass ratio of the fouling to the dilute sulfuric acid in S1 is 100:5-15.

5. The method of claim 1, wherein: The negative pressure in S2 is -0.08 to -0.05 MPa.

6. The method of claim 1, wherein: The fouling is derived from pipelines and equipment after the filtration stage of wet-process phosphoric acid.