Method for efficient removal of arsenic from wet-process phosphoric acid and device for using same

Abstract

This invention discloses a wet-process high-efficiency arsenic removal method and its application apparatus using phosphoric acid, comprising the following steps: 1) preparing an arsenic removal agent and water in a certain proportion to form a solution; 2) adding the arsenic removal agent solution prepared in step 1) from the bottom of the arsenic removal reaction tank through a slurry pump; 3) reacting the arsenic removal agent added in step 2) with phosphoric acid; 4) introducing the H2S gas generated by the reaction of the arsenic removal agent and phosphoric acid in step 3) through an induced draft fan from the bottom of a scrubbing tower; 5) absorbing the H2S gas in step 4) by countercurrent scrubbing to form a sulfide solution; 6) adding the sulfide solution in step 5) to the phosphoric acid feed pipe by a slurry pump in a multi-point feeding manner. This invention makes the reaction more complete; after the unreacted H2S is absorbed with an alkaline solution and added to the phosphoric acid feed pipe by a multi-point feeding manner, the contact time and contact area between the sulfide and phosphoric acid are significantly increased, making the arsenic removal reaction of phosphoric acid more thorough.

Description

Technical Field

[0001] This invention relates to the field of phosphoric acid purification technology, and in particular to a wet phosphoric acid high-efficiency arsenic removal method and its application apparatus. Background Technology

[0002] Wet-process phosphoric acid is mainly used to prepare various phosphides, which are widely used in agriculture, medicine, chemicals, and electronics. Wet-process phosphoric acid is generally prepared by decomposing phosphate rock with sulfuric acid. Because phosphate rock contains various impurities, a large number of these impurities dissolve into the phosphoric acid along with the sulfuric acid. Arsenic is the main heavy metal impurity in wet-process phosphoric acid; excessive arsenic intake poses a serious threat to human and animal health. Precipitation removal of arsenic involves adding sulfides to wet-process phosphoric acid to form insoluble arsenic sulfide, which is then separated from the phosphoric acid. Precipitation has advantages such as low investment, low equipment requirements, and good arsenic removal efficiency, making it the main method for arsenic removal from phosphoric acid.

[0003] However, the arsenic removal reactors used in wet-process phosphoric acid production enterprises are large in volume, require high investment, have low mass transfer efficiency, and require large amounts of arsenic removal agent. This results in high arsenic removal agent consumption, low arsenic removal efficiency, and high costs in the actual production process. Therefore, it is necessary to develop an efficient, low-cost, and widely applicable arsenic removal method. Summary of the Invention

[0004] This invention provides a wet-process phosphoric acid high-efficiency arsenic removal method and apparatus to solve the problems in the background art.

[0005] The solution of the present invention is:

[0006] A highly efficient wet-process method for arsenic removal from phosphoric acid includes the following steps:

[0007] 1) Prepare a 2% to 10% arsenic removal agent solution by mixing the arsenic removal agent and water in the arsenic removal preparation tank according to the specified ratio;

[0008] 2) Add the arsenic removal agent solution prepared in 1) from the bottom of the arsenic removal reaction tank using a slurry pump at a rate of 1 m / s. 3 / h~4m 3 / h;

[0009] 3) React the arsenic removal agent solution added in 2) with phosphoric acid. Control the solution in the arsenic removal reaction tank at 60-90°C by electric heating, and the reaction time is 5-240 min.

[0010] 4) The H2S gas generated by the reaction of the arsenic removal agent solution in 3) with phosphoric acid is introduced from the bottom of the scrubbing tower through the first induced draft fan;

[0011] 5) The H2S gas described in 4) is absorbed by countercurrent scrubbing to form a sulfide solution. The volume of countercurrent scrubbing liquid used is 50m³. 3 / h~200m 3 / h;

[0012] 6) The sulfide solution described in 5) is added to the phosphoric acid feed pipe through a washing circulation pump in a multi-point feeding manner.

[0013] As a preferred technical solution, the arsenic removal agent in step 1) is one or more of Na2S, K2S, and P2S5.

[0014] As a preferred technical solution, the arsenic removal agent solution configured in step 2) is added from the bottom of the arsenic removal reaction tank through the arsenic removal agent feed pipe via a slurry pump. The arsenic removal agent feed pipe is connected to 10 to 40 feed ports at the bottom of the arsenic removal reaction tank.

[0015] As a preferred technical solution, the countercurrent washing solution is one or more of KOH, NaOH, Na2CO3, and K2CO3.

[0016] The present invention also discloses an apparatus for a high-efficiency arsenic removal method for wet phosphoric acid, comprising an arsenic removal agent preparation tank, an arsenic removal reaction tank, and a washing tower connected in sequence. The arsenic removal reaction tank is also connected to a gas recovery device. The gas recovery device is used to guide the overflow gas in the arsenic removal reaction tank into the washing tower, and the washing liquid is added back to the phosphoric acid feed pipe for reuse in a multi-point feeding manner.

[0017] As a preferred technical solution, a spray pipe is provided at the top of the washing tower; the spray pipe is connected to a washing circulation pump; a tail gas absorption pipe is connected to the top of the washing tower; the washing circulation pump pipeline is connected to the phosphoric acid feed pipe through a control valve; the washing circulation pump pipeline is connected from the bottom of the phosphoric acid feed pipe; the washing circulation pump pipeline and the phosphoric acid feed pipe have 2 to 10 connection ports; the distance between adjacent connection ports is 0.5 to 5 meters.

[0018] As a preferred technical solution, the gas recovery device includes a first induced draft fan and an H2S detector; the air inlet of the first induced draft fan is connected to the arsenic removal reaction tank; and the air outlet of the first induced draft fan is connected to the H2S detector.

[0019] As a preferred technical solution, the H2S detector is connected to the arsenic removal reaction tank through a control valve.

[0020] As a preferred technical solution, the H2S detector is connected to the washing tower via a control valve.

[0021] A highly efficient wet-process phosphoric acid arsenic removal method, employing the aforementioned technical solution, includes the following steps: 1) preparing an arsenic removal agent solution of 2% to 10% with water in an arsenic removal preparation tank; 2) adding the arsenic removal agent solution prepared in step 1) from the bottom of the arsenic removal reaction tank via a slurry pump at a rate of 1 m / s. 3 / h~4m 3 / h; 3) React the arsenic removal agent solution added in 2) with phosphoric acid, and control the solution in the arsenic removal reaction tank at 60-90℃ by electric heating, with a reaction time of 5-240 min; 4) Introduce the H2S gas generated by the reaction of the arsenic removal agent solution with phosphoric acid in 3) from the bottom of the scrubbing tower through the first induced draft fan; 5) Absorb the H2S gas mentioned in 4) to form a sulfide solution by countercurrent scrubbing, with a countercurrent scrubbing liquid volume of 50 m³ / h. 3 / h~200m 3 / h; 6) Add the sulfide solution described in 5) to the phosphoric acid feed pipe through a washing circulation pump in a multi-point feeding manner.

[0022] Advantages of this invention:

[0023] 1. The arsenic removal agent is added from multiple points at the bottom of the arsenic removal reaction tank. The arsenic removal agent reacts with phosphoric acid at the bottom of the arsenic removal reaction tank to generate a large number of H2S bubbles. Compared with the traditional method, the generated H2S has a longer residence time in the reaction tank, which makes the arsenic removal reaction more complete.

[0024] 2. The H2S generated by the arsenic removal agent inlet is evenly distributed at the bottom of the arsenic removal reaction tank. The H2S bubbles rise evenly from the bottom to the liquid surface, which fully agitates the phosphoric acid, improves the mass transfer rate, and optimizes the kinetic conditions of the arsenic removal reaction.

[0025] 3. After the unreacted H2S is absorbed with an alkaline solution, it is added to the phosphoric acid feed pipe at multiple points, which significantly increases the contact time and contact area between the sulfide and the phosphoric acid, making the arsenic removal reaction of the phosphoric acid more thorough.

[0026] 4. Because the arsenic removal agent reacts more fully with phosphoric acid, the amount of arsenic removal agent used is significantly reduced. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the present invention;

[0028] Figure 2 This is a schematic diagram of the apparatus used in the wet-process phosphoric acid high-efficiency arsenic removal method of the present invention;

[0029] Figure 3 This is a schematic diagram showing the distribution of the bottom feed inlet of the arsenic removal reactor in the apparatus used in the wet-process high-efficiency arsenic removal method for phosphoric acid of the present invention;

[0030] Figure 4 This is a schematic diagram of the multi-point feeding of washing liquid in the wet phosphoric acid high-efficiency arsenic removal method of the present invention;

[0031] Wherein: 1-Arsenic removal reaction tank; 2-Arsenic removal agent preparation tank agitator; 3-Slurry pump; 4-Arsenic removal agent feed control valve; 5-Arsenic removal agent feed pipe; 6-Arsenic removal reaction tank agitator; 7-H2S escaping control valve; 8-First induced draft fan; 9-H2S feed control valve; 10-Washing circulation pump; 100-Washing circulation pump pipeline; 11-Second induced draft fan; 12-Washing tower; 13-Control valve; 14-Arsenic removal reaction tank; 140-Inlet; 15-Phosphoric acid feed pipe; 16-Arsenic removal agent; 17-Slurry filter; 18-Tail gas absorption; 19-Phosphoric acid; 20-Washing liquid. Detailed Implementation

[0032] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0033] Example 1:

[0034] Na2S and water were mixed in a certain proportion to prepare a 6% Na2S solution, which was added from the bottom and top of the arsenic removal reaction tank respectively. The solution in the arsenic removal reaction tank was controlled at 65°C by electric heating, and the reaction time was 60 minutes. The H2S gas generated by the reaction of Na2S solution with phosphoric acid was introduced from the bottom of the scrubbing tower by an induced draft fan. NaOH solution was added to the top of the scrubbing tower. The Na2S solution formed by the reaction of H2S and NaOH was added to the phosphoric acid feed pipe by a slurry pump in a multi-point feeding manner.

[0035] Table 1. Experimental Results

[0036]

[0037] As shown in Table 1, before the improvement, the amount of Na2S used as the arsenic removal agent was 11 times the theoretical amount. After the improvement to bottom feeding and multi-point feeding into the phosphoric acid feed pipe, the amount of Na2S used was significantly reduced to only 3 times the theoretical amount, greatly reducing the production cost. At the same time, after changing to bottom feeding and multi-point feeding into the phosphoric acid feed pipe, the residence time of the arsenic removal agent in the phosphoric acid was extended and the mass transfer rate was improved, thus improving the arsenic removal reaction kinetics. The As and Pb contents in the phosphoric acid were only 0.0006% and 0.0003%, respectively, which were 40% and 25% lower than before the improvement, showing significant effects.

[0038] Example 2:

[0039] Na2S and water were mixed in a certain proportion to prepare a 9% Na2S solution, which was added from the bottom and top of the arsenic removal reaction tank. The solution in the arsenic removal reaction tank was controlled at 75°C by electric heating, and the reaction time was 30 minutes. The H2S gas generated by the reaction of the Na2S solution with phosphoric acid was introduced from the bottom of the scrubbing tower by an induced draft fan. NaOH solution was added to the top of the scrubbing tower. The Na2S solution formed by the reaction of H2S and NaOH was added to the phosphoric acid feed pipe by a slurry pump in a multi-point feeding manner.

[0040] Table 2 Experimental Results

[0041]

[0042] As shown in Table 2, before the improvement, the amount of Na2S used as the arsenic removal agent was 11 times the theoretical amount. After the improvement to bottom feeding and multi-point feeding into the phosphoric acid feed pipe, the amount of Na2S used was significantly reduced to only 3 times the theoretical amount, greatly reducing the production cost. At the same time, after changing to bottom feeding and multi-point feeding into the phosphoric acid feed pipe, the residence time of the arsenic removal agent in the phosphoric acid was extended and the mass transfer rate was improved, thus improving the arsenic removal reaction kinetics. The As and Pb contents in the phosphoric acid were only 0.0007% and 0.0003%, respectively, which were 22% and 25% lower than before the improvement, showing significant effects.

[0043] Example 3:

[0044] Na2S and water were mixed in a certain proportion to prepare a Na2S solution with a mass concentration of 11%, which was added from the bottom and top of the arsenic removal reaction tank. The solution in the arsenic removal reaction tank was controlled at 80°C by electric heating, and the reaction time was 90 min. The H2S gas generated by the reaction of the Na2S solution with phosphoric acid was introduced from the bottom of the scrubbing tower by an induced draft fan. NaOH solution was added to the top of the scrubbing tower. The Na2S solution formed by the reaction of H2S and NaOH was added to the phosphoric acid feed pipe by a slurry pump in a multi-point feeding manner.

[0045] Table 3. Experimental Results

[0046]

[0047] As shown in Table 3, before the improvement, the amount of Na2S used as the arsenic removal agent was 11 times the theoretical amount. After the improvement to bottom feeding and multi-point feeding into the phosphoric acid feed pipe, the amount of Na2S used was significantly reduced to only 3 times the theoretical amount, greatly reducing the production cost. At the same time, after changing to bottom feeding and multi-point feeding into the phosphoric acid feed pipe, the residence time of the arsenic removal agent in the phosphoric acid was extended and the mass transfer rate was improved, thus improving the arsenic removal reaction kinetics. The As and Pb contents in the phosphoric acid were only 0.0005% and 0.0003%, respectively, which were 37.5% and 25% lower than before the improvement, showing significant effects.

[0048] Example 4:

[0049] like Figure 2 , Figure 3 and Figure 4 As shown, the arsenic removal agent preparation tank 1, the arsenic removal reaction tank 14, and the washing tower 12 are connected in sequence; the arsenic removal reaction tank 14 is also connected to a gas recovery device; the gas recovery device is used to guide the overflow gas in the arsenic removal reaction tank 2 into the washing tower 12, and the washing liquid is added back into the phosphoric acid feed pipe 15 for reuse.

[0050] The discharge pipe of the arsenic removal agent preparation tank 1 is connected to the bottom of the arsenic removal reaction tank 2 through a control valve; one end of the discharge pipe of the arsenic removal agent preparation tank 1 is connected to 10 to 40 feed ports 140 at the bottom of the arsenic removal reaction tank 14; the 10 to 40 feed ports 140 are distributed in a ring at the bottom of the arsenic removal reaction tank 14, and the distance between two adjacent feed ports 140 is 300mm to 500mm;

[0051] The arsenic removal agent is one or more of Na2S, K2S, and P2S5. The arsenic removal agent and water are mixed in an arsenic removal agent preparation tank to form an arsenic removal agent solution. The arsenic removal agent solution reacts with phosphoric acid in the arsenic removal reaction tank 14 to generate H2S bubbles. The large number of H2S bubbles increases the reaction area between phosphoric acid and H2S, and the rising of the bubbles agitates the phosphoric acid, making the reaction more complete.

[0052] The gas recovery device consists of a first induced draft fan 8 and an H2S detector; the air inlet of the first induced draft fan 8 is connected to the arsenic removal reaction tank 14; and the air outlet of the first induced draft fan 8 is connected to the H2S detector.

[0053] The H2S detector is connected to the arsenic removal reaction tank 14 via a control valve.

[0054] The H2S detector is connected to the scrubbing tower via a control valve.

[0055] The negative pressure of the gas phase in the arsenic removal reaction tank 14 is -5 kPa to -2 kPa.

[0056] The washing tower 12 is equipped with a spray pipe at its upper part; the spray pipe is connected to a washing circulation pump 10;

[0057] The washing liquid 20 selected for the washing tower 12 is one or more of KOH, NaOH, Na2CO3, and K2CO3; the top of the washing tower 12 is connected to a tail gas absorption pipe;

[0058] The washing circulation pump 100 pipeline 100 is connected to the phosphoric acid feed pipe 15 through the control valve 13; the circulation pump pipeline 100 and the phosphoric acid feed pipe 15 have 2 to 20 connection ports; the distance between each connection port is 0.5 to 5 meters.

[0059] The arsenic removal reaction tank 14 is equipped with a stirring paddle.

[0060] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A highly efficient wet-process method for arsenic removal from phosphoric acid, characterized in that, Includes the following steps: 1) Prepare a 2% to 10% arsenic removal agent solution by mixing the arsenic removal agent and water in the arsenic removal preparation tank according to the specified ratio; 2) The arsenic removal agent solution prepared in 1) is added from the bottom of the arsenic removal reaction tank using a slurry pump. The arsenic removal agent feed pipe is connected to 10-40 feed ports at the bottom of the arsenic removal reaction tank, and the addition rate is 1 m. 3 / h ~4m 3 / h; 3) React the arsenic removal agent solution added in 2) with phosphoric acid. Control the solution in the arsenic removal reaction tank at 60-90°C by electric heating, and the reaction time is 5-240 min. 4) The H2S gas generated by the reaction of the arsenic removal agent solution in 3) with phosphoric acid is introduced from the bottom of the scrubbing tower through the first induced draft fan; 5) The H2S gas described in 4) is absorbed by countercurrent scrubbing to form a sulfide solution. The volume of countercurrent scrubbing liquid used is 50m³. 3 / h ~200m 3 / h; 6) The sulfide solution described in 5) is added to the phosphoric acid feed pipe through a washing circulation pump in a multi-point feeding manner. The washing circulation pump pipe and the phosphoric acid feed pipe have 2 to 10 connection ports; the distance between adjacent connection ports is 0.5 to 5 meters.

2. The wet-process phosphoric acid high-efficiency arsenic removal method as described in claim 1, characterized in that: The arsenic removal agent in 1) is one or more of Na2S, K2S, and P2S5.

3. The wet-process phosphoric acid high-efficiency arsenic removal method as described in claim 1, characterized in that: The countercurrent washing solution is one or more of KOH, NaOH, Na2CO3, and K2CO3.

4. An apparatus for using the wet-process phosphoric acid high-efficiency arsenic removal method as described in any one of claims 1 to 3, characterized in that: The system includes a dearsenic removal agent preparation tank, a dearsenic removal reaction tank, and a washing tower connected in sequence. The dearsenic removal reaction tank is also connected to a gas recovery device. The gas recovery device is used to guide the overflow gas from the dearsenic removal reaction tank into the washing tower. A spray pipe is installed at the top of the washing tower. The spray pipe is connected to a washing circulation pump. A tail gas absorption pipe is connected to the top of the washing tower. The washing circulation pump pipeline is connected to the phosphoric acid feed pipe through a control valve. The washing circulation pump pipeline is connected from the bottom of the phosphoric acid feed pipe. The washing circulation pump pipeline and the phosphoric acid feed pipe have 2 to 10 connection ports. The distance between adjacent connection ports is 0.5 to 5 meters. The washing liquid is added back to the phosphoric acid feed pipe for reuse in a multi-point feeding manner.

5. The apparatus for the wet-process phosphoric acid high-efficiency arsenic removal method as described in claim 4, characterized in that: The gas recovery device includes a first induced draft fan and an H2S detector; the air inlet of the first induced draft fan is connected to the arsenic removal reaction tank; and the air outlet of the first induced draft fan is connected to the H2S detector.

6. The apparatus for the wet-process phosphoric acid high-efficiency arsenic removal method as described in claim 5, characterized in that: The H2S detector is connected to the arsenic removal reaction tank via a control valve.

7. The apparatus for the wet-process phosphoric acid high-efficiency arsenic removal method as described in claim 5, characterized in that: The H2S detector is connected to the scrubbing tower via a control valve.

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