A process for purifying and removing arsenic from concentrated phosphoric acid by wet process

Abstract

The invention discloses a process for purifying and removing arsenic from concentrated phosphoric acid by a wet process, comprising the following steps: step 1: concentrated phosphoric acid after desulfurization and defluorination treatment enters a pipeline mixer and reacts with a novel arsenic removal agent; step 2: after the reacted acid is pumped into a thickener through a micro-negative pressure storage tank for thickening, the upper clear acid enters a concentration workshop through a centrifugal pump, and the bottom arsenic slag is filtered through a belt filter and enters a phosphogypsum re-slurry tank; the novel arsenic removal agent in step 1 is a polysulfide, the reaction temperature of the arsenic removal reaction is 70 to 80 degrees, and the residence time in the pipeline reactor is 5 to 10 minutes. Arsenic removal is carried out by combining polysulfide with a pipeline reactor. The polysulfide is stable in nature and is not easy to release hydrogen sulfide gas under acidic conditions. Arsenic impurities in phosphoric acid can be safely removed. The pipeline reactor can quickly and safely remove arsenic from 45-50% phosphoric acid, and can greatly reduce the use of polysulfide, while solving the problem of rapid decomposition of sodium sulfide.

Description

Technical Field

[0001] The invention belongs to the technical field of wet-process phosphoric acid purification, and in particular relates to a process for purifying and removing arsenic from wet-process concentrated phosphoric acid. Background Art

[0002] The purity of wet-process phosphoric acid is an important factor affecting the quality of intermediate products in phosphorus chemical industry. The pretreatment stage cannot make the purity of phosphoric acid meet the production requirements of fine chemicals, and the pretreated phosphoric acid needs to be further purified. Based on the existing wet-process phosphoric acid purification technology, one-step purification cannot achieve the expected purification effect, especially when the target product is food-grade and electronic-grade phosphoric acid, which requires segmented treatment to achieve the requirements of deep purification. Usually, wet-process phosphoric acid is first subjected to desulfurization, decolorization, defluorination, and dearsenicization treatment. This step is called the pretreatment stage, and the phosphoric acid obtained is pretreated phosphoric acid.

[0003] The Chinese invention patent with the publication number CN102515125B discloses a method for filtering arsenic removal of high-concentration polyphosphoric acid. The method uses industrial polyphosphoric acid as a raw material, adds a water-soluble phosphorus pentasulfide emulsion as a dearsenicating agent, causes the arsenic contained in the polyphosphoric acid to form a sulfide precipitate under acidic conditions, and purifies and refines the polyphosphoric acid by filtering, aeration and other means, thereby producing a method for producing low-arsenic polyphosphoric acid. The polyphosphoric acid dearsenicating filtering method provided by the present invention first forms a filter cake on a filter medium through dilute polyphosphoric acid containing arsenic slag, and then filters the polyphosphoric acid added with the dearsenicating agent to produce a low-arsenic polyphosphoric acid product, solves the filtration technology problem in the process of preparing low-arsenic polyphosphoric acid, enables the production of low-arsenic polyphosphoric acid to be industrialized, and has low operating costs and simple operating processes, and can provide a low-arsenic polyphosphoric acid product with a concentration of 105%-118%, that is, a P2O5 percentage of 76.1%-85.5%, and an arsenic content of no more than 10ppm that cannot be obtained by conventional methods. The Chinese invention patent with publication number CN101676201A discloses a polyphosphoric acid arsenic removal process, which generates a precipitate at a certain temperature by introducing hydrogen sulfide or adding a sulfide (such as sodium sulfide, phosphorus pentasulfide) into a phosphoric acid solution, and then obtains low-arsenic phosphoric acid by filtration and separation. The arsenic content of the products prepared by the above two inventions is still high and cannot meet the requirements of refined production. Summary of the invention

[0004] In order to solve the above problems, the present invention aims to provide a process for purifying and removing arsenic from wet concentrated phosphoric acid.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme: a process for purifying and removing arsenic from concentrated phosphoric acid by wet process, comprising the following steps:

[0006] Step 1: After desulfurization and defluorination treatment, concentrated phosphoric acid enters the pipeline mixer and undergoes arsenic removal reaction with the new phosphoric acid purifier;

[0007] Step 2: The reacted acid is pumped into the thickener after passing through a slightly negative pressure storage tank. The upper clear acid enters the concentration workshop through a centrifugal pump, and the bottom arsenic slag enters the phosphogypsum re-slurry tank;

[0008] The novel phosphoric acid purifier in step 1 is modified polysulfide, the reaction temperature of the arsenic removal reaction is 70 to 80 degrees, and the residence time in the pipeline reactor is 5 to 10 minutes.

[0009] Preferably, the novel phosphoric acid purifier is added by a dosing method.

[0010] Preferably, the novel phosphoric acid purifier and concentrated phosphoric acid in step 1 are transported to a pipeline mixer via a pump.

[0011] Preferably, in step 1, the pipeline mixer is connected to a flow meter and a dosing pump, and the flow meter is connected to a sampling port of the phosphoric acid storage tank through a pipeline.

[0012] Preferably, the novel arsenic removal agent in step 1 is added in two times, and each time is reacted in a different pipeline mixer.

[0013] Preferably, the concentration of phosphoric acid used in step 1 is 45-50wt%, and the arsenic content in the phosphoric acid is 40-60ppm.

[0014] A pipeline mixer is provided with a spiral stirrer inside the pipeline mixer. The spiral stirrer is composed of spiral stirring blades, and the outer diameter of the spiral stirrer is adapted to the inner diameter of the pipeline.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. By controlling the type and dosage of phosphoric acid purifier, the pump volume of the pipeline reactor, the addition method, the residence time, the reaction temperature and other conditions, the impurity arsenic and some metal ions in the wet-process phosphoric acid can be removed, and the arsenic impurity content is less than 0.50ppm.

[0017] 2. A special pipeline mixer is used for arsenic removal test. After the concentrated phosphoric acid and the arsenic removal agent pass through the special pipeline mixer, the arsenic in the concentrated phosphoric acid and the arsenic removal agent can fully react to achieve the best arsenic removal effect.

[0018] 3. Utilize modified polysulfide and pipeline reactor to jointly cooperate in arsenic removal. The modified polysulfide is stable in nature and is not easy to release hydrogen sulfide gas under acidic conditions. It can safely remove arsenic impurities in phosphoric acid. The pipeline reactor can quickly and safely remove 45-50% of arsenic in phosphoric acid, and can greatly reduce the use of modified polysulfide. At the same time, it solves the disadvantage of rapid decomposition of sodium sulfide, so that the product can slow down the decomposition rate of H2S by the arsenic removal agent in the arsenic removal of phosphoric acid. It can quantitatively control the decomposition amount of H2S according to the arsenic ion content in phosphoric acid, control the decomposition rate of the arsenic removal agent, and reduce H2S overflow. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a schematic diagram of pipeline arrangement in the present invention;

[0021] Figure 2 is an internal schematic diagram of a pipeline mixer in the present invention;

[0022] Figure 3 for Figure 2 A magnified image of FIG4 is a process flow chart of the wet-process concentrated phosphoric acid purification and arsenic removal in the present invention;

[0023] In the figure, A-feed port; B-discharge port; 1-first dosing port; 2-second dosing port. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but it should not be understood that the scope of the subject matter described in the present invention is limited to the following embodiments. Without departing from the above-mentioned technical ideas of the present invention, various modifications, substitutions and changes made according to the common technical knowledge and customary means in the field are included in the scope of the present invention.

[0025] The present invention utilizes a method combining a chemical precipitant with a pipeline reactor to remove arsenic impurities in wet-process phosphoric acid, thereby achieving the purpose of product purification. The method is mainly based on the principle of mixing chemical precipitants with physical turbulence, and uses chemical precipitants in conjunction with pipeline reactors. By controlling the type, dosage, pump volume, addition method, residence time, reaction temperature and other conditions of the arsenic removal precipitant, the removal of impurity arsenic and some metal ions in wet-process phosphoric acid is achieved. The method is suitable for wet-process purified phosphoric acid pretreatment production, is simple to operate, has high safety and economy, and is of great significance for the efficient and high-quality development of phosphorus chemical enterprises.

[0026] Reference Figure 2 and Figure 3The specific pipeline mixing device is a highly efficient fluid mixing device. Its basic working mechanism is to use the spiral fixed in the pipe to change the flow state of the fluid in the pipe to increase the contact surface between phosphoric acid and the arsenic removal agent, so as to achieve the purpose of fully mixing different fluids. To this end, by using a special pipeline mixer to carry out arsenic removal tests, after the concentrated phosphoric acid and the new phosphoric acid purifier pass through the special pipeline mixer, the arsenic in the concentrated phosphoric acid can fully react with the arsenic removal agent, achieving the best arsenic removal effect.

[0027] The sampling port of the phosphoric acid storage tank is connected to a flow meter through a pipeline, the flow meter is connected to a special pipeline mixing device through a pipeline, and the dosing pump is connected to a special pipeline mixer. Concentrated phosphoric acid and phosphoric acid purifier enter the special pipeline mixer for arsenic removal reaction, and the phosphoric acid purifier adopts a two-step sample addition method to carry out arsenic removal reaction before entering the micro-negative pressure storage tank.

[0028] The invention utilizes modified polysulfide and a pipeline reactor to jointly cooperate in arsenic removal. The modified polysulfide is stable in nature, is not easy to release hydrogen sulfide gas under acidic conditions, and can safely remove arsenic impurities in phosphoric acid. The pipeline reactor can quickly and safely remove 45-50% of arsenic in phosphoric acid, and can greatly reduce the use of modified polysulfide, and solve the disadvantage of rapid decomposition of sodium sulfide, so that the product can slow down the decomposition speed of arsenic removal agent in phosphoric acid arsenic removal, and can quantitatively control the decomposition amount of H2S according to the arsenic ion content in phosphoric acid, control the decomposition speed of arsenic removal agent, and reduce H2S overflow.

[0029] A process for purifying and removing arsenic from concentrated phosphoric acid by a wet process comprises the following steps:

[0030] Step 1: After desulfurization and defluorination treatment, concentrated phosphoric acid enters the pipeline mixer and undergoes arsenic removal reaction with the new phosphoric acid purifier;

[0031] Step 2: The reacted acid is pumped into the thickener after passing through a slightly negative pressure storage tank. The upper clear acid enters the concentration workshop through a centrifugal pump, and the bottom arsenic slag enters the phosphogypsum re-slurry tank;

[0032] The addition method of the novel arsenic removal agent includes a dosing method. The novel phosphoric acid purifier and the concentrated phosphoric acid obtained in step 1 are transported to a pipeline mixer by a pump. The novel phosphoric acid purifier is added twice, and each of the two times reacts in a pipeline mixer at a different position. A spiral stirrer is arranged inside the pipeline mixer, and the spiral stirrer is composed of a spiral stirring blade, and its outer diameter is adapted to the inner diameter of the pipeline.

[0033] The specific process flow is as follows Figure 4 shown.

[0035] After desulfurization and defluorination, the raw phosphoric acid enters the pipeline mixer through the acid supply pump, and undergoes arsenic removal reaction with polysulfide in the pipeline mixing reactor. The acid after the reaction is concentrated in the thickener through the storage tank. The clear acid on the upper layer of the thickener enters the concentration workshop through the centrifugal pump; the arsenic slag at the bottom of the thickener is pumped into the belt filter through the sludge pump and filtered into the phosphogypsum re-slurry tank.

[0036] The technical parameters are as follows: Medium: phosphoric acid; Medium density: 80kg / m 3 ; Working temperature: 80℃; Working pressure: 0.9MPa; Medium flow: 100m 3 / h; residence time: 10min.

[0037] Example 1

[0038] The concentrated phosphoric acid after desulfurization and defluorination treatment was taken as the research object, and modified sodium thiosulfate was selected as the dearsenicizing agent. The addition method was a dosing method, and modified sodium thiosulfate was added from the first dosing port 1. Figure 1 , the modified sodium thiosulfate and concentrated phosphoric acid are pumped to the feed port A of the pipeline reaction tank, and the reverse production load is controlled at 100m 3 / h, the reaction residence time is 10min, the reaction temperature is 80℃, with the addition of phosphoric acid purifier, the arsenic impurity content gradually decreases to 0.10ppm, and the removal filter is 99.8%. This result fully utilizes the synergistic effect of polysulfide and pipeline reactor to remove arsenic from concentrated phosphoric acid.

[0039] Example 2

[0040] The concentrated phosphoric acid after desulfurization and defluorination treatment was taken as the research object, and modified sodium thiosulfate was selected as the dearsenicizing agent. The addition method was a two-step dosing method, which was added from the first dosing port 1 and the second dosing port 2 respectively. Figure 1 The polysulfide and concentrated phosphoric acid are pumped to the feed port A of the pipeline reaction tank, and the reverse production load is controlled at 100m 3 / h, the reaction residence time is 10min, the reaction temperature is 70℃, with the addition of precipitant, the arsenic impurity content gradually decreases to 0ppm, and the removal rate is 100%. This result fully utilizes the synergistic effect of polysulfide and pipeline reactor to remove arsenic from concentrated phosphoric acid.

[0041] Example 3

[0042] The concentrated phosphoric acid after desulfurization and defluorination treatment was taken as the research object, and modified sodium thiosulfate was selected as the dearsenicizing agent. The addition method was a dosing method, and polysulfide was added from the first dosing port 1. Figure 1 The polysulfide and concentrated phosphoric acid are pumped to the feed port of the pipeline reaction tank, and the reverse production load is controlled at 100m 3 / h, the reaction residence time is 5min, the reaction temperature is 70℃, with the addition of precipitant, the arsenic impurity content gradually decreases to 0.20ppm, and the removal filter is 99.6%. This result fully utilizes the synergistic effect of polysulfide and pipeline reactor to remove arsenic from concentrated phosphoric acid.

[0043] The present invention adopts a pipeline reactor to improve the intrinsic safety of the equipment from the perspective of the equipment of the process route and reduce safety risks. The invention has a high degree of automation, reduces labor costs, responds quickly, and improves production efficiency. The use of a pipeline reactor can reduce the consumption of arsenic removal agents and reduce production costs.

[0044] By adjusting the dosage of the precipitant, reaction temperature, residence time, addition method and other conditions, rapid removal of arsenic from wet-process concentrated phosphoric acid can be achieved, which is more economical.

[0045] The above is a detailed introduction to a wet concentrated phosphoric acid purification and arsenic removal process provided by the present invention. The structure and working principle of the present invention are described in detail using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, the present invention can also be improved and modified without departing from the principle of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A process for purifying and removing arsenic from concentrated phosphoric acid by a wet process, characterized in that: The following steps are involved: Step 1: concentrated phosphoric acid after desulfurization and defluorination treatment enters the pipeline mixer and undergoes arsenic removal reaction with the new arsenic removal agent; Step 2: The reacted acid is pumped into the thickener after passing through a slightly negative pressure storage tank. The upper clear acid enters the concentration workshop through a centrifugal pump, and the bottom arsenic slag enters the phosphogypsum re-slurry tank; The novel arsenic removal agent in step 1 is polysulfide, the reaction temperature of the arsenic removal reaction is 70-80° C., and the residence time in the pipeline mixer is 5-10 minutes.

2. The process for purifying and removing arsenic from concentrated phosphoric acid by wet process according to claim 1, characterized in that: The polysulfide includes but is not limited to modified sodium thiosulfide.

3. The process for purifying and removing arsenic from concentrated phosphoric acid by wet process according to claim 1, characterized in that: The adding method of the novel arsenic removal agent includes a dosing method.

4. The process for purifying and removing arsenic from concentrated phosphoric acid by wet process according to claim 1, characterized in that: The novel phosphoric acid purifier and concentrated phosphoric acid in step 1 are transported to the pipeline mixer through a pump.

5. The process for purifying and removing arsenic from concentrated phosphoric acid by wet process according to claim 1, characterized in that: In step 1, the concentrated phosphoric acid and the novel phosphoric acid purifier enter a special pipeline mixer for reaction, and then enter a pipeline reactor for secondary addition of arsenic removal agent for reaction before entering a sedimentation tank.

6. The process for purifying and removing arsenic from concentrated phosphoric acid by wet process according to claim 1, characterized in that: The pipeline mixer is connected with a flow meter and a dosing pump, and the flow meter is connected with a sampling port of the phosphoric acid storage tank through a pipeline.

7. The process for purifying and removing arsenic from concentrated phosphoric acid by wet process according to claim 1, characterized in that: The novel arsenic removal agent in step 1 is added in two times, and each of the two times reacts in a pipeline mixer at a different position.

8. The process for purifying and removing arsenic from concentrated phosphoric acid by wet process according to claim 1, characterized in that: The concentration of concentrated phosphoric acid in step 1 is 45-50wt%, and the arsenic content in the phosphoric acid is 40-60ppm.

9. A pipeline mixer used in the process for purifying and removing arsenic from wet concentrated phosphoric acid according to any one of claims 1 to 8, characterized in that: A spiral stirrer is arranged inside the pipeline mixer. The spiral stirrer is composed of spiral stirring blades, and the outer diameter of the spiral stirrer is adapted to the inner diameter of the pipeline.

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