Process for purifying phosphoric acid and removing TOC (Total Organic Carbon) by solvent extraction method

Abstract

The invention is applied to the technical field of wet-process phosphoric acid refining, and particularly relates to a novel post-extraction phosphoric acid deoiling process which comprises the following steps: removing and recovering suspended oil, dispersed oil and part of emulsified oil in acid by adopting an air flotation technology, introducing ozone into the air-floated acid, pumping the acid containing ozone microbubbles into a mixed packed column of activated carbon phase silicon carbide and boron carbide, and carrying out deoiling on the acid. Phosphoric acid containing ozone microbubbles is catalyzed in a silicon carbide and boron carbide packed column, the ozonolysis rate is increased, more hydroxyl radicals are generated, the deoiling purpose can be achieved, oxidized acid enters an activated carbon adsorption column to adsorb oxidized short-carbon-chain organic matter, and finally deoiled phosphoric acid liquid is obtained. Wherein high-concentration oleic acid which can be collected after air flotation can flow back to the extraction system to be recycled, so that the extraction agent is recycled and reused.

Description

Technical Field

[0001] The present invention belongs to the technical field of wet-process phosphoric acid purification, and particularly relates to a new process for removing extractant from phosphoric acid after extraction. Background Art

[0002] Metal ions contained in wet-process phosphoric acid, such as Ca 2+ , Mg 2+ , Al 3+ , Fe 3+ , will cause a large amount of phosphorus loss in subsequent use. Therefore, it is necessary to use extraction to purify the metal ion content in wet-process acid, improve the phosphorus recovery rate and high-quality utilization of subsequent wet-process phosphoric acid.

[0003] After wet-process phosphoric acid is extracted, the acid contains some extractant. Most extractants exist in the acid in the form of suspended oil, dispersed oil, emulsified oil and dissolved oil. According to different extraction processes and extraction agents, the content of various oils in the acid will vary. Among them, emulsified oil and dissolved oil are the most difficult to treat in the acid. At present, existing oil removal technologies include oxidation method, electrolytic decomposition method, demulsification method, adsorption method, etc. Because of the high viscosity and strong acidity of phosphoric acid, simple oil removal technologies cannot meet the requirements of deep oil removal in acid (TOC is lower than 100 ppm), and multiple oil removal technologies need to be combined to achieve better results.

[0004] Based on this, the present invention proposes a new process for phosphoric acid oil removal. Summary of the Invention

[0005] In view of the above, the present invention provides a new phosphoric acid oil removal process, which uses a flotation device to remove dispersed oil, suspended oil and most of the emulsified oil and recover them. A small part of the dissolved oil is oxidized and decomposed, and then a packing column is used for deep oil removal to remove a small part of the dissolved oil and short-chain organic compounds that have not been completely decomposed, so as to achieve deep oil removal of phosphoric acid solution and recovery of extractant.

[0006] The process route adopted by the present invention is as follows: An oil removal process for reducing the TOC of phosphoric acid pressurizes phosphoric acid with a flotation device to mix small air bubbles into the phosphoric acid. The organic matter in the acid enters the upper liquid surface with the bubbles. The phosphoric acid after flotation at the lower layer is pumped into an ozone mixing tank to obtain phosphoric acid containing ozone microbubbles. The phosphoric acid containing ozone microbubbles is pumped into a packing column from bottom to top for catalytic oxidation, and the oxidized phosphoric acid is then adsorbed by activated carbon to obtain purified phosphoric acid.

[0007] Bubbles are added to phosphoric acid by a flotation device at a rate of 30 - 50 L / h and a pressure of 0.4 - 0.6 Mpa, and then it enters the flotation tank for static settlement. After the bubbles float to the surface, the valve in the middle of the flotation tank is opened, and the acid is pumped into the ozone mixing tank at a rate of 30 - 50 L / h by a magnetic pump. Finally, the phosphoric acid containing ozone micro - bubbles is pumped from the bottom to the top into a mixing packing column of silicon carbide and boron carbide by a magnetic pump. The oxidized acid is then adsorbed by activated carbon, and finally purified phosphoric acid is obtained.

[0008] The flotation device consists of an air compressor, a micro - bubble generator, a flotation column and a metering pump. When operating the flotation device, all valves of the device are closed, the metering pump is started, the inlet valve of the metering pump is adjusted, and the pressure gauge on the metering pump is controlled at about 0.4 Mpa. Then the air compressor is turned on, and the outlet valve of the metering pump is slightly opened to control the pressure gauge on the flotation column at 0.4 - 0.6 Mpa. Phosphoric acid is filled into the flotation device at a rate of 40 - 50 L / h. At this time, the bubble size in the phosphoric acid is 10 - 100 nm, and the proportion of bubbles in the phosphoric acid reaches 40 - 50%.

[0009] In the present invention, further, for the flotation tank, the internal volume of the flotation tank is 100 L, and the inside of the flotation tank is divided into a flotation area and a clear liquid area. Among them, the flotation area is provided with a partition board and a high - TOC phosphoric acid collection tank, which divides the flotation tank into a flotation area and a clear liquid area. The clarified phosphoric acid after flotation enters the clear liquid area from below the partition board. The phosphoric acid containing micro - bubbles enters the flotation tank at a speed of 40 - 50 L / h. The phosphoric acid containing bubbles stays in the flotation tank for 2 - 3 hours. The phosphoric acid oil droplets therein float to the surface of the flotation tank with the bubbles and enter the collection tank. The clarified liquid after flotation enters the clear liquid area and waits for further adsorption treatment. In the present invention, further, for the oxidation mixing tank, it is divided into an ozone generator, a micro - bubble generator and a stirring paddle. Ozone is pumped into phosphoric acid by the ozone generator. Among them, the amount of ozone is 4 - 6 g / h, and micro - bubbles are formed in the phosphoric acid. The volume of the oxidation mixing tank is only a 25 - L container.

[0010] In the present invention, further, for the mixing packing column, the internal volume is 100 L, and the mixed packing material of silicon carbide and boron carbide with a volume ratio of 2 - 10:1 is filled. Another packing column is a 100 - L activated carbon packing column, and the intermediate buffer tank is a 25 - L container. Phosphoric acid enters the mixing packing column from below at a flow rate of 30 - 50 L / h and flows out from the top into the buffer tank, with a residence time of 1 - 2 h. The buffer tank then passes through a magnetic pump and enters the activated carbon packing column from below at a flow rate of 30 - 50 L / h and flows out from the top to obtain purified phosphoric acid. The residence time of phosphoric acid in the activated carbon packing column is 1 - 2 h.

[0011] In the preferred embodiment, the volume ratio of silicon carbide to boron carbide is 3 - 5:1.

[0012] In the present invention, further, the specific surface area of silicon carbide is 50-100 m 2 / g of β-type silicon carbide, and the specific surface area of boron carbide is 40-50 m 2 / g.

[0013] The present invention has the following beneficial effects: The air flotation equipment used in the present invention can effectively recover the extractant in the acid solution, and can be reused without introducing new substances, and the removal effect is obvious.

[0014] In the present invention, both the air and ozone used in air flotation play their roles in phosphoric acid in the form of nanoscale bubbles. The nanoscale bubbles are bubbles with a diameter of 50-100 nm. The microbubbles have a large specific surface area, a long floating time, and a long reaction time, and have higher efficiency compared with conventional bubbles.

[0015] In the present invention, ozone has a good degradation effect in acid during oxidation, reducing the TOC value in the acid, and after ozone is reduced, it overflows in the form of oxygen without introducing new impurities.

[0016] The ozone used in the present invention is prepared from pure oxygen. There is an air separation system in the wet-process phosphoric acid plant, so the cost of preparing ozone is relatively low and there is no need for separate oxygen production.

[0017] The silicon carbide and boron carbide catalysts used in the present invention are made of non-metallic materials themselves, can have good chemical stability in phosphoric acid, and have a relatively large internal specific surface area, and have a good catalytic effect on ozone, further promoting the degradation of organic matter by ozone into small-molecule materials.

[0018] The activated carbon used in the present invention has a large adsorption capacity for macromolecular oil droplets, a high cycle number, and a good regeneration effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the process flow chart of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] To make the above objects, features, and advantages of the present invention better understood, the following detailed description of the specific embodiments of the present invention is provided.

[0021] In this embodiment, the raffinate acid after extraction is purified, and the purification process is carried out in the following manner: In the raffinate acid deoiling process, air bubbles are added to phosphoric acid at a rate of 50 L / h and a pressure of 0.4-0.6 Mpa using an air flotation device. At this time, the bubble density reaches 30%, and the bubble size is about 50 nm.

[0022] Phosphoric acid with bubbles enters the air flotation tank at a rate of 50 L / h. The phosphoric acid containing bubbles is left standing in the air flotation tank for 2 hours. The phosphoric acid oil droplets float to the surface of the air flotation tank along with the bubbles and enter the collection tank. The clarified liquid after air flotation enters the clarified liquid area to wait for adsorption. The phosphoric acid in the clarified liquid area is pumped into the ozone mixing tank at a rate of 50 L / h by a magnetic pump. Ozone is injected into the phosphoric acid by an ozone generator. Among them, the amount of ozone is 4 - 6 g / h, and microbubbles are formed in the phosphoric acid. The phosphoric acid containing microbubbles and ozone enters from the bottom of the mixed packing column at a flow rate of 50 L / h and flows out from the top and enters the buffer tank. The mixed packing column is a mixture of β-type silicon carbide and boron carbide formed in a volume ratio of 2:1. The specific surface area of silicon carbide is 75 - 85 m 2 / g, and the specific surface area of boron carbide is 40 - 50 m 2 / g.

[0023] The phosphoric acid in the buffer tank is then pumped from the bottom to the top into the activated carbon adsorption column by a magnetic pump, and finally the purified raffinate acid is obtained.

[0024] The defatting effect of each stage of this process changes with time (starting to record time when acid comes out from the top of the last activated carbon adsorption column). The results are shown in Table 1: Table 1

[0025] It can be seen from the results in Table 1 that this defatting process can reduce the TOC in the raffinate acid to about 50 ppm through air flotation, catalytic oxidation and adsorption, and has a good removal effect.

[0026] Comparing with the above embodiments, the process used in this embodiment is as follows. Catalytic oxidation is not carried out with a mixed packing column, and only adsorption of activated carbon is carried out. The defatting effect of each stage of this process changes with time (starting to record time when acid comes out from the top of the last activated carbon adsorption column). The results are shown in Table 2: Table 2

[0027] It can be seen from the results in Tables 1 and 2 that after only ozone oxidation and then adsorption, the TOC of phosphoric acid is as high as 500 ppm, and the purification effect is not obvious. If through air flotation, oxidation, catalysis and activated carbon adsorption, the TOC in the raffinate acid can be reduced to about 50 ppm, indicating that the catalytic oxidation efficiency of ozone can be improved and the TOC can be reduced through the catalysis of silicon carbide and boron carbide, meeting the requirements of deep defatting.

[0028] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it cannot be understood as a limitation to the scope of the present invention.

Claims

1. A deoiling process for reducing phosphoric acid TOC, characterized in that: The phosphoric acid is pressurized by flotation equipment to mix small air bubbles in the phosphoric acid. Organic matter in the acid enters the upper liquid surface with the bubbles. The phosphoric acid after flotation in the lower layer is pumped into the ozone mixing tank to obtain phosphoric acid containing ozone microbubbles. The phosphoric acid containing ozone microbubbles is pumped from bottom to top into the packing column for catalytic oxidation. The oxidized phosphoric acid is then adsorbed by activated carbon to obtain purified phosphoric acid.

2. The process for reducing phosphoric acid TOC by deoiling according to claim 1, characterized in that: Air bubbles are added to phosphoric acid at a rate of 40-50 L / h and a pressure of 0.4-0.6 MPa using an air flotation device.

3. The process for reducing phosphoric acid TOC by deoiling according to claim 2, characterized in that: The size of bubbles in phosphoric acid is 10-100nm, and the proportion of bubbles in phosphoric acid reaches 40-50%.

4. The process for reducing phosphoric acid TOC by deoiling according to claim 1, characterized in that: The flotation tank is divided into a flotation zone and a clear liquid zone, which are separated by a middle partition. After flotation, the lower phosphoric acid enters the clear liquid zone through the bottom channel, and the organic matter is taken away by the bubbles to form the flotation zone. The uppermost layer containing high TOC phosphoric acid and extractant enters the collection tank.

5. The process for reducing phosphoric acid TOC by deoiling according to claim 4, characterized in that: The phosphoric acid containing bubbles enters the flotation tank at a speed of 30-50L / h. The phosphoric acid containing bubbles stays in the flotation tank for 2-3 hours. The phosphoric acid oil droplets float to the surface of the flotation tank with the bubbles and enter the collection tank. The clear liquid after flotation enters the clear liquid area.

6. The process for reducing phosphoric acid TOC by deoiling according to claim 5, characterized in that: The ozone mixing tank comprises an ozone generator, a microbubble generator and a stirring paddle. Ozone is injected into phosphoric acid through the ozone generator, wherein the amount of ozone is 4-6 g / h, and microbubbles are formed in the phosphoric acid.

7. The process for reducing phosphoric acid TOC by deoiling according to claim 1, characterized in that: The filler column is a mixed filler material of silicon carbide and boron carbide, wherein the volume ratio of silicon carbide to boron carbide is 2-10:

1.

8. The process for reducing phosphoric acid TOC by deoiling according to claim 7, characterized in that: The volume ratio of silicon carbide to boron carbide is 3-5:

1.

9. The process for reducing phosphoric acid TOC by deoiling according to claim 7, characterized in that: The specific surface area of ​​silicon carbide is 50-100m 2 / g of β-type silicon carbide and boron carbide with a specific surface area of ​​40-50m 2 / g.

10. The process for reducing phosphoric acid TOC by deoiling according to claim 7, characterized in that: Phosphoric acid enters from the bottom of the packing column at a flow rate of 30-50L / h, flows out from the top into the buffer tank, stays in the packing column for 1-2 hours, and then enters the activated carbon column for adsorption at the same flow rate to obtain purified phosphoric acid.

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