A wet-process arsenic removal system and method for phosphoric acid

Abstract

This invention discloses an arsenic removal system and method for wet-process phosphoric acid. The arsenic removal system includes an arsenic removal reactor, a hydrogen sulfide scrubbing tower, an arsenic removal acid tank, a waste acid tank, and a desulfurization tank. The hydrogen sulfide outlet of the arsenic removal reactor is connected to both the hydrogen sulfide inlet of the arsenic removal reactor and the inlet of the hydrogen sulfide scrubbing tower. The outlet of the hydrogen sulfide scrubbing tower is connected to the inlet of the waste acid tank. The overflow outlet of the waste acid tank is connected to the inlet of the desulfurization tank. The outlets of the waste acid tank and the desulfurization tank are connected to the hydrogen sulfide inlet of the arsenic removal reactor. The acid outlet of the arsenic removal reactor is connected to the inlet of the arsenic removal acid tank. The arsenic removal system and method provided by this invention fully utilize hydrogen sulfide flue gas, greatly reducing the arsenic removal cost of wet-process phosphoric acid. Furthermore, it has the advantages of simple reaction equipment structure, small size, easy availability, low production and operating costs, and safe and reliable operation, making it suitable for promotion and application in industrial production.

Description

Technical Field

[0001] This invention relates to the field of phosphoric acid production technology in the phosphate chemical industry, specifically to an arsenic removal system and method for wet-process phosphoric acid. Background Technology

[0002] Phosphoric acid, a crucial raw material in the phosphate chemical industry, is produced through two methods: the thermal process and the wet process. The thermal process uses yellow phosphorus as raw material, undergoing high-temperature oxidation, hydration, and demisting to produce phosphoric acid. Its advantages include high purity and mature technology, but its disadvantages include high energy consumption (due to yellow phosphorus), high cost, and heavy pollution (producing toxic gases and dust). The wet process uses inorganic acids such as sulfuric acid, nitric acid, or hydrochloric acid to decompose phosphate rock powder into crude phosphoric acid, which is then purified to obtain the final phosphoric acid product. Its advantages include low cost (20-25% lower than the thermal process) and low energy consumption (approximately one-third of the thermal process), but its disadvantages include insufficient purity and the production of phosphogypsum pollutants. Due to the energy crisis of the 1970s, developed countries restricted, phased out, or shut down the energy-intensive production of yellow phosphorus, while increasing research into the purification of wet-process phosphoric acid. In recent years, purified wet-process phosphoric acid has accounted for 85% of phosphoric acid production abroad, while the thermal process accounts for only 15%. Currently, 90% of my country's industrial phosphoric acid is produced using the thermal process (mainly concentrated in mountainous areas of Yunnan, Guizhou, Sichuan, and Hubei, where high-energy-consuming yellow phosphorus is produced using small hydropower plants), with only 10% being purified wet-process phosphoric acid. With the increasing emphasis on energy consumption control, the purification of wet-process phosphoric acid to replace the thermal process is imperative.

[0003] Currently, arsenic removal from wet-process phosphoric acid is one of the requirements for its purification. The arsenic in wet-process phosphoric acid mainly originates from arsenic contained in phosphate rock (arsenic content typically ranges from 20-150 mg / kg). In wet-process phosphoric acid, arsenic exists in the form of arsenic acid (H3AsO4) and arsenous acid (H3AsO3). Methods for arsenic removal from wet-process phosphoric acid mainly include chemical precipitation, electrochemical methods, crystallization, and extraction. Among these, chemical precipitation involves adding a precipitant (such as Na2S or P2S5) to the phosphoric acid raw material, causing it to precipitate as a sparingly soluble or insoluble compound. This compound is then separated by filtration to obtain low-arsenic sulfuric acid. Because chemical precipitation requires simple steps and equipment and has good arsenic removal efficiency, it is the primary method used in industrial production for arsenic removal from wet-process phosphoric acid.

[0004] The reaction principle of using Na2S as an arsenic removal agent is as follows:

[0005] Na₂S + 2H₃PO₄ → H₂S + 2NaH₂PO₄

[0006] H3AsO4+ H2S → H3AsO3+ H2O + S↓

[0007] 2H3AsO3+3H2S → As2S3↓+6H2O

[0008] The reaction principle of using P2S5 as an arsenic removal agent is as follows:

[0009] 2 P2S5+ 16 H2O → 4H3PO4+ 10H2S↑

[0010] H3AsO4+ H2S → H3AsO3+ H2O + S↓

[0011] 2H3AsO3+ 3H2S → 6H2O + As2S3↓

[0012] When sodium sulfide solution is used as a arsenic removal agent to remove arsenic from phosphoric acid, the addition of sodium sulfide solution introduces sodium ions, thus affecting the quality of industrial or food-grade phosphoric acid. Although using P2S5 as a arsenic removal agent overcomes the introduction of sodium ions in the phosphoric acid solution, the solubility of hydrogen sulfide generated by P2S5 and water in phosphoric acid is not high in the micro-negative pressure system formed inside the arsenic removal tower. In order to ensure that the arsenic content reaches the quality requirement of very low arsenic content, the arsenic removal agent P2S5 is usually added in excess, resulting in excessive consumption of arsenic removal agent P2S5 and high arsenic removal costs. At the same time, the excessive addition of arsenic removal agent will also generate excess hydrogen sulfide flue gas discharged from the arsenic removal tower, resulting in the inefficient use of hydrogen sulfide gas. The discharged hydrogen sulfide flue gas needs to be treated before being discharged. Moreover, in the existing chemical precipitation method of arsenic removal, some excess unreacted hydrogen sulfide will always be mixed in with phosphoric acid during arsenic removal. The excess hydrogen sulfide gas in the phosphoric acid needs to be blown out after arsenic removal filtration, and the blown hydrogen sulfide gas also needs to be treated before being discharged. Currently, many production enterprises use alkali recovery towers to treat hydrogen sulfide gas. Sodium hydroxide or sodium carbonate alkali solutions are circulated and sprayed to absorb the hydrogen sulfide flue gas discharged from the arsenic removal tower and the hydrogen sulfide gas blown out of phosphoric acid. However, the recovered sodium sulfide solution needs to be sent to a chemical plant for further processing. This undoubtedly increases production costs because a recovery device needs to be installed for the large amount of excess, unreacted hydrogen sulfide, wasting equipment, power, and chemicals. The recovered solution still requires further treatment, all of which increase costs. Summary of the Invention

[0013] In view of the above-mentioned shortcomings of the prior art, the purpose of this invention is to provide a wet phosphoric acid arsenic removal system and method to solve the problem of underutilization of hydrogen sulfide flue gas and reduce the cost of wet phosphoric acid arsenic removal.

[0014] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0015] A wet-process phosphoric acid arsenic removal system includes an arsenic removal reactor, a hydrogen sulfide scrubbing tower, an arsenic removal acid tank, a waste acid tank, and a desulfurization tank. The arsenic removal reactor includes a reactor body with a hydrogen sulfide outlet at the top and an arsenic removal acid outlet at the bottom. A raw material acid inlet is located above the reactor body, and a hydrogen sulfide inlet is located below it. The hydrogen sulfide outlet of the arsenic removal reactor is connected to both the hydrogen sulfide inlet and the inlet of the hydrogen sulfide scrubbing tower. The outlet of the hydrogen sulfide scrubbing tower is connected to the inlet of the waste acid tank. The overflow outlet of the waste acid tank is connected to the inlet of the desulfurization tank. The outlets of the waste acid tank and the desulfurization tank are connected to the hydrogen sulfide inlet of the arsenic removal reactor. The acid outlet of the arsenic removal reactor is connected to the inlet of the arsenic removal acid tank. A nitrogen purging pipe is installed inside the desulfurization tank, and the inlet of the waste acid tank is connected to a waste phosphoric acid delivery pipe.

[0016] The workflow of the arsenic removal system provided by the above technical solution is as follows: First, a certain amount of sodium sulfide solution and waste phosphoric acid are added to the waste acid tank. The generated hydrogen sulfide gas enters the arsenic removal reactor and reacts countercurrently with the raw acid to complete the arsenic removal of the raw acid. Excess hydrogen sulfide gas is partially discharged from the hydrogen sulfide outlet of the arsenic removal reactor and returned to the arsenic removal reactor via the hydrogen sulfide inlet to continue participating in the arsenic removal reaction of the raw acid, forming an internal circulation loop for hydrogen sulfide gas. The other part is discharged from the hydrogen sulfide outlet of the arsenic removal reactor and enters the hydrogen sulfide scrubbing tower to react with the hydrogen sulfide absorbent (sodium carbonate solution or sodium hydroxide solution) to generate sodium sulfide solution, which overflows into the waste acid tank and reacts with the waste phosphoric acid in the waste acid tank to generate hydrogen sulfide gas, which is then supplied to the arsenic removal reactor. If sodium carbonate absorbent is used to absorb hydrogen sulfide, the generated carbon dioxide gas is discharged through the chimney. The phosphate formed after the reaction in the waste acid tank overflows into the desulfurization tank. Nitrogen purging removes the hydrogen sulfide gas from the phosphate and transports it to the arsenic removal reactor to participate in the arsenic removal reaction. The phosphate after purging is then discharged for use.

[0017] The reactions involved in the above workflow include:

[0018] In the waste acid tank: Na₂S + 2H₃PO₄ → H₂S + 2NaH₂PO₄

[0019] Inside the arsenic removal reactor: H3AsO4 + H2S → H3AsO3 + H2O + S↓

[0020] 2H3AsO3+3H2S → As2S3↓+6H2O

[0021] Inside the hydrogen sulfide scrubbing tower: 2NaOH + 2H₂S → Na₂S + 2H₂O

[0022] Na2CO3+H2S → Na2S+H2O+CO2↑

[0023] Furthermore, a hydrogen sulfide fan is installed on the connecting pipeline between the gas outlet of the waste acid tank and the gas outlet of the desulfurization tank and the hydrogen sulfide inlet of the arsenic removal reactor. The hydrogen sulfide gas in the waste acid tank and the desulfurization tank is transported to the arsenic removal reactor by the hydrogen sulfide fan. The flow rate of hydrogen sulfide gas entering the arsenic removal reactor is controlled by controlling the speed of the fan, thereby adjusting the reaction rate between hydrogen sulfide and raw acid.

[0024] Furthermore, the raw acid inlet of the arsenic removal reactor is fixed with an acid inlet pipe located inside the reactor body. The outlet end of the acid inlet pipe is connected to a nozzle, which includes a spray chamber and a nozzle communicating with the spray chamber. The atomization effect of the raw acid sprayed through the nozzle is good, ensuring the uniformity of the raw acid spraying in the arsenic removal reactor. Preferably, depending on the size of the arsenic removal reactor body, the number of nozzles is set to two or more, so that the raw acid can be sprayed more dispersedly in the reactor, further improving the uniformity of the raw acid spraying and strengthening the countercurrent contact area between the raw acid and hydrogen sulfide gas. The orifice diameter of the nozzle is designed to be 50-100mm, which not only ensures that the sprayed raw acid liquid particles are fine and uniform, but also avoids the raw acid with a high solid content (1-30%) from clogging the orifice and affecting the arsenic removal reaction.

[0025] Furthermore, the hydrogen sulfide inlet of the arsenic removal reactor is connected to a gas inlet pipe, which is connected to a gas distribution pipe located inside the reactor body. The gas distribution pipe has several outlet holes with a diameter of 20–100 mm. More preferably, the outlet holes are evenly spaced, with a spacing of 20–100 mm between adjacent outlet holes. Using a gas distribution pipe enhances the dispersion of hydrogen sulfide gas and increases the countercurrent contact area between the hydrogen sulfide gas and the raw material acid. The gas distribution pipe can be snowflake-shaped, annular, quadrilateral, etc., arranged to maximize gas dispersion.

[0026] Furthermore, a compressed air pipe is connected to the gas inlet pipe. The compressed air entering the compressed air pipe is charged and discharged at a frequency of 1500–3000 ms, and the compressed air pressure is 15–30 kPa. By controlling the compressed air pressure and charging / discharging pressure of the compressed air pipe, hydrogen sulfide gas is made to react countercurrently with the raw material acid in a pulsed manner. This allows for efficient reaction between hydrogen sulfide and arsenic acid in the raw material acid, improving the utilization rate of hydrogen sulfide and avoiding the residue of hydrogen sulfide gas in the arsenic removal process.

[0027] Furthermore, the bottom of the reactor body of the arsenic removal reactor is connected to a liquid collecting cone, and the bottom of the liquid collecting cone is connected to an arsenic removal acid outlet pipe, which is connected to the inlet of the arsenic removal acid tank. The liquid collecting cone can increase the arsenic removal reaction time of the raw material acid, improve the arsenic removal rate of the raw material acid, and avoid the residue of hydrogen sulfide gas in the arsenic removal acid.

[0028] Based on the aforementioned arsenic removal system, the present invention further provides an arsenic removal method for wet-process phosphoric acid using the aforementioned arsenic removal system, wherein the arsenic removal method includes controlling the liquid-to-gas ratio of the raw material acid to hydrogen sulfide gas in the arsenic removal reactor to be 20–80 L / m³. 3 The method involves controlling the concentration of the raw acid (35-86%) and the arsenic content (10-100 mg / kg), the feed flow rate of the hydrogen sulfide absorbent in the hydrogen sulfide scrubbing tower (10-150 L / h), and the residence time of the de-arsenic acid in the collecting cone (5-60 min). Controlling the liquid-to-gas ratio in the de-arsenic reactor further ensures efficient reaction between hydrogen sulfide and the raw acid, improves hydrogen sulfide utilization, and avoids hydrogen sulfide residue in the de-arsenic acid. Controlling the concentration and arsenic content of the raw acid ensures the solubility of hydrogen sulfide gas in the raw acid, guaranteeing de-arsenic efficiency. Controlling the residence time of the de-arsenic acid in the collecting cone further avoids hydrogen sulfide residue. Controlling the feed flow rate of the hydrogen sulfide absorbent in the hydrogen sulfide scrubbing tower controls the amount of hydrogen sulfide gas generated in the waste acid tank, ensuring stable system operation. This invention, by controlling the above parameters, further improves the de-arsenic efficiency of the raw acid.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) The present invention uses hydrogen sulfide gas generated from waste phosphoric acid and sodium sulfide solution as an arsenic removal agent, which can utilize the waste phosphoric acid generated in the phosphoric chemical production process, realize the efficient utilization of phosphoric acid resources, and reduce production costs;

[0031] (2) In this invention, a portion of the hydrogen sulfide gas discharged from the arsenic removal reactor is recycled back into the arsenic removal reactor, which reduces the consumption of hydrogen sulfide absorbent in the hydrogen sulfide scrubbing tower and lowers production costs.

[0032] (3) The present invention returns the sodium sulfide solution generated after the hydrogen sulfide washing tower absorbs hydrogen sulfide to the waste acid tank for use, which reduces the consumption of sodium sulfide in the front-end production, makes full use of hydrogen sulfide gas, and reduces production costs.

[0033] (4) The arsenic removal reactor provided by the present invention strengthens the countercurrent contact between the gas and liquid phases by setting up the acid inlet pipe and the gas distribution pipe. It replaces the traditional mixing and stirring, liquid phase circulation, and rotating spraying methods with pulse form to carry out the arsenic removal operation, which enhances the mass transfer effect between the gas and liquid phases, enables hydrogen sulfide to react efficiently with trace amounts of arsenic in the raw acid, improves the utilization rate of hydrogen sulfide, avoids the residue of hydrogen sulfide gas in the arsenic removal acid, and improves the arsenic removal efficiency.

[0034] In summary, the arsenic removal system and method provided by this invention make full use of hydrogen sulfide flue gas, greatly reduce the arsenic removal cost of wet phosphoric acid, and have the advantages of simple reaction equipment structure, small size, easy availability, low production and operating costs, and safe and reliable operation, making them suitable for promotion and application in industrial production. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the arsenic removal system provided by the present invention;

[0036] Figure 2 This is a schematic diagram of the arsenic removal reactor provided by the present invention;

[0037] Figure 3 for Figure 2 A top view of the gas distribution pipe.

[0038] Legend:

[0039] 1-Arsenic removal reactor; 2-Hydrogen sulfide scrubbing tower; 201-Chimney; 202-Absorbent inlet pipe; 3-Desulfurization tank; 301-Nitrogen purging pipe; 4-Waste acid tank; 5-Arsenic acid removal tank; 6-Hydrogen sulfide blower; 7-Waste phosphoric acid conveying pipe; 8-Arsenic acid removal conveying pump;

[0040] 101-Reactor body; 102-Collecting cone; 103-Hydrogen sulfide outlet; 104-Raw material acid inlet; 105-Acid inlet pipe; 106-Nozzle; 1061-Spray chamber; 1062-Nozzle; 107-Hydrogen sulfide inlet; 108-Gas inlet pipe; 109-Gas distribution pipe; 110-Arsenic acid removal outlet; 111-Arsenic acid removal outlet pipe; 112-Compressed air pipe; 113-Outlet. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0042] See Figure 1This invention provides a wet-process phosphoric acid arsenic removal system, comprising an arsenic removal reactor 1, a hydrogen sulfide scrubbing tower 2, an arsenic removal acid tank 5, a waste acid tank 4, and a desulfurization tank 3. The hydrogen sulfide outlet of the arsenic removal reactor 1 is connected to both the hydrogen sulfide inlet of the arsenic removal reactor and the inlet of the hydrogen sulfide scrubbing tower 2. The outlet of the hydrogen sulfide scrubbing tower 2 is connected to the inlet of the waste acid tank 4. The overflow outlet of the waste acid tank 4 is connected to the inlet of the desulfurization tank 3. The outlets of the waste acid tank 4 and the desulfurization tank 3 are connected to the hydrogen sulfide inlet of the arsenic removal reactor 1. A hydrogen sulfide fan 6 is installed on their connecting pipelines. The arsenic removal acid outlet of the arsenic removal reactor 1 is connected to the inlet of the arsenic removal acid tank 5. An arsenic removal acid transfer pump 8 is connected to the outlet of the arsenic removal acid tank. A nitrogen purging pipe 301 is installed inside the desulfurization tank 3. The inlet of the waste acid tank is connected to a waste phosphoric acid transfer pipe 7.

[0043] See Figure 2 The arsenic removal reactor 1 provided by the present invention includes a reactor body 101 and a liquid collecting cone 102 connected to the bottom of the reactor body 101. The bottom of the liquid collecting cone 102 is connected to an arsenic removal acid outlet pipe 111, which is connected to the inlet of the arsenic removal acid tank 5. A hydrogen sulfide outlet 103 is provided at the top of the reactor body 101, and an arsenic removal acid outlet 110 is provided at the bottom. A raw material acid inlet 104 is provided above the reactor body 101. An acid inlet pipe 105 is inserted into the reactor body 101 from the raw material acid inlet 104. The acid inlet pipe 105 is located 0.2 meters below the hydrogen sulfide outlet 103. A nozzle 106 is welded to the outlet end of the acid inlet pipe 105. The nozzle 106 includes a spray cavity 1061 and a nozzle 1062 communicating with the spray cavity. The spray cavity 1061 is a rectangular cavity. There are two nozzles 1062, symmetrically arranged on both sides of the spray cavity 1061. The nozzle 1062 has several spray holes with a diameter of 50-100 mm. A hydrogen sulfide inlet 107 is provided below the reactor body 101. One end of the hydrogen sulfide inlet 107 is connected to a gas inlet pipe 108 located outside the reactor body 101, and the other end is connected to a gas distribution pipe 109 located inside the reactor body 101. A compressed air pipe 112 is connected to the gas inlet pipe 108. The compressed air entering the compressed air pipe has a charging and discharging frequency of 1500–3000 ms and a compressed air pressure of 15–30 kPa. See also Figure 3 The gas distribution pipe 109 is arranged in a cross shape inside the reactor body 101. Several gas outlet holes 113 are opened on the gas distribution pipe 109, and the diameter of the gas outlet holes is 20-100mm.

[0044] The reactor body 101, liquid collecting cone 102, acid inlet pipe 105, nozzle 106, gas inlet pipe 108, gas distribution pipe 109, arsenic removal acid outlet pipe 111, and compressed air pipe 112 are all made of stainless steel.

[0045] The arsenic removal system provided by this invention performs arsenic removal operations on raw acid, including the following steps:

[0046] 1. A certain amount of sodium sulfide solution is added to waste acid tank 4 through the inlet. Waste phosphoric acid is pumped into waste acid tank 4 through waste phosphoric acid conveying pipe 7 using a centrifugal pump. The waste phosphoric acid reacts with the sodium sulfide solution to generate hydrogen sulfide flue gas, which is then conveyed to arsenic removal reactor 1 by hydrogen sulfide fan 6. The chemical reaction involved is: Na2S + 2H3PO4 → H2S + 2NaH2PO4.

[0047] 2. Hydrogen sulfide flue gas reacts with the raw material acid in arsenic removal reactor 1 to generate arsenic sulfide. The arsenic-removed phosphoric acid overflows into the arsenic removal acid tank 5 through the arsenic removal acid outlet pipe 111. The arsenic removal acid is then transported to the filtration device via the arsenic removal acid transfer pump 8. The chemical reactions involved are: H3AsO4 + H2S → H3AsO3 + H2O + S↓; 2H3AsO3 + 3H2S → As2S3↓ + 6H2O.

[0048] 3. The hydrogen sulfide outlet 103 and hydrogen sulfide inlet 107 of the arsenic removal reactor are connected to form an internal circulation system for hydrogen sulfide flue gas. Excess hydrogen sulfide flue gas enters the hydrogen sulfide scrubbing tower 2, reacts with the hydrogen sulfide absorbent to produce sodium sulfide. The sodium sulfide solution overflows into the waste acid tank 4, while the carbon dioxide gas produced in the reaction is emitted through the chimney 201. The hydrogen sulfide absorbent is pumped into the hydrogen sulfide scrubbing tower 2 through the absorbent inlet pipe 202 using a metering pump. The hydrogen sulfide absorbent can be selected as sodium hydroxide solution or sodium carbonate alkaline solution depending on the actual production situation. The chemical reaction formulas involved are: 2NaOH + 2H2S → Na2S + 2H2O; Na2CO3 + H2S → Na2S + H2O + CO2↑.

[0049] 4. The phosphates after the reaction in waste acid tank 4 overflow into desulfurization tank 3. The hydrogen sulfide in the phosphates is blown off by nitrogen. The hydrogen sulfide gas is transported to the arsenic removal reactor 1 by hydrogen sulfide blower 6 for recycling. The blown-off phosphates are discharged for use.

[0050] The term "waste phosphoric acid" refers to the collective term for discarded samples of acid, experimental acid, etc.

[0051] The compressed air pressure is 15-30 kPa, and the compressed air charging and discharging frequency is 1500-3000 ms.

[0052] The arsenic content of the raw acid is 10-100 mg / kg. After the raw acid reacts with hydrogen sulfide flue gas in the arsenic removal reactor, the resulting solid-liquid mixture containing arsenic slag enters the arsenic removal acid tank. The arsenic content of the removed acid is 0.1-1 mg / kg.

[0053] The hydrogen sulfide blower speed is 100-2500 rpm, and the liquid-to-gas ratio of the arsenic removal reactor is 20-80 L / m³. 3 The concentration of hydrogen sulfide absorbent is 2-20%, and the feed flow rate of hydrogen sulfide absorbent is 10-150 L / h.

[0054] The acid concentration of the raw materials used is 35-86% (calculated as P2O5).

[0055] The residence time for arsenic removal in the liquid collecting cone is 5-60 minutes.

[0056] The arsenic removal system and method provided by the present invention will be described in detail below with reference to specific embodiments.

[0057] Example 1:

[0058] like Figure 1 As shown, a measured amount of sodium sulfide solution is added to waste acid tank 4. Waste phosphoric acid with a flow rate of 5 L / h is pumped into waste acid tank 4 via a centrifugal pump. The waste phosphoric acid reacts with the sodium sulfide solution for 10 minutes to generate hydrogen sulfide. The hydrogen sulfide flue gas is then transported to arsenic removal reactor 1 via hydrogen sulfide blower 6, with the blower speed at 1000 rpm. The compressed air pressure in compressed air pipe 112 of arsenic removal reactor 1 is controlled at 15 kPa, and the charging / discharging frequency is 1500 ms, so that the hydrogen sulfide gas contacts the raw acid in a countercurrent manner in a pulsed form. The hydrogen sulfide flue gas and the raw acid in the arsenic removal reactor are mixed at a liquid-to-gas ratio of 80 L / m³. 3 The reaction produces arsenic sulfide, with a raw acid concentration of 55% (calculated as P2O5) and an arsenic content of 50 mg / kg. The residence time of the liquid in the collecting cone 102 is 20 min. After arsenic removal, the de-arsenic acid overflows through the de-arsenic acid outlet pipe 11 into the de-arsenic acid tank 5. The de-arsenic acid is then transported to the filtration device by the de-arsenic acid transfer pump 8. Testing shows that the de-arsenic acid in the de-arsenic acid tank 5 has no residual hydrogen sulfide gas, and the arsenic content is 0.5 mg / kg, meeting the requirements for raw acid arsenic removal production. The phosphate from the reaction in the waste acid tank 4 overflows into the desulfurization tank 3. Nitrogen purging removes hydrogen sulfide from the phosphate in the desulfurization tank 3, and the hydrogen sulfide is then transported to the de-arsenic reactor 1 for recycling via the hydrogen sulfide blower 6. The hydrogen sulfide gas outlet of the arsenic removal reactor 1 is connected to the inlet to form an internal circulation. Excess hydrogen sulfide enters the hydrogen sulfide scrubbing tower 2, where it reacts with sodium carbonate solution for 10 minutes to produce sodium sulfide. The sodium sulfide solution overflows into the waste acid tank 4, and the remaining gas enters the chimney 201. The sodium carbonate solution has a concentration of 5% and is pumped to the hydrogen sulfide scrubbing tower 2 at a flow rate of 50 L / h via a metering pump.

[0059] The consumption quotas for each raw material were calculated based on the operation of acid removal of arsenic from 1 ton of raw material. The results are shown in Table 1 below.

[0060] Example 2:

[0061] The arsenic removal operation of the raw acid was carried out according to the existing chemical precipitation method. The arsenic removal method uses sodium sulfide solution as the arsenic removal agent and sodium carbonate solution as the hydrogen sulfide absorbent. The concentration and arsenic content of the raw acid are the same as in Example 1. The consumption quota of each raw material is calculated based on the arsenic removal operation of 1 ton of raw acid. The results are shown in Table 1 below.

[0062] Table 1. Raw material consumption quota

[0063]

[0064] As can be seen from the data in the table above, after using the arsenic removal system and method provided in Example 1, the consumption of sodium sulfide and sodium carbonate is only 40% of that in the prior art, which significantly reduces costs. Furthermore, Example 1 also utilizes waste phosphoric acid, achieving efficient recycling of phosphorus resources.

[0065] Example 3:

[0066] The specific operation is the same as in Example 1, except that the following parameters are changed: compressed air is stopped from flowing into the compressed air pipe; the hydrogen sulfide flue gas and the raw acid in the arsenic removal reactor are mixed at a liquid-to-gas ratio of 15 L / m³. 3 The reaction proceeds to produce arsenic sulfide; the residence time of the liquid in the collecting cone 102 is 2 minutes.

[0067] Testing revealed that the arsenic content in the arsenic-removing acid in tank 5 was 10 mg / kg, and the residual hydrogen sulfide gas was 12 ml / kg, which did not meet the requirements for arsenic removal from raw acid.

[0068] Example 4:

[0069] like Figure 1 As shown, a measured amount of sodium sulfide solution is added to waste acid tank 4. Waste phosphoric acid with a flow rate of 6 L / h is pumped into waste acid tank 4 via a centrifugal pump. The waste phosphoric acid reacts with the sodium sulfide solution for 8 minutes to generate hydrogen sulfide. The hydrogen sulfide flue gas is then transported to arsenic removal reactor 1 via hydrogen sulfide blower 6, with the blower speed at 1500 rpm. The compressed air pressure in compressed air pipe 112 of arsenic removal reactor 1 is controlled at 20 kPa, and the charging / discharging frequency is 2000 ms, so that the hydrogen sulfide gas contacts the raw acid in a countercurrent manner in a pulsed form. The hydrogen sulfide flue gas and the raw acid in the arsenic removal reactor are mixed at a liquid-to-gas ratio of 60 L / m³. 3The reaction produces arsenic sulfide, with a raw acid concentration of 57% (calculated as P2O5) and an arsenic content of 40 mg / kg. The residence time of the liquid in the collecting cone 102 is 30 min. After arsenic removal, the de-arsenic acid overflows into the de-arsenic acid tank 5 through the de-arsenic acid outlet pipe 11. The de-arsenic acid is then transported to the filtration device by the de-arsenic acid transfer pump 8. Testing shows that the de-arsenic acid in the de-arsenic acid tank 5 has no residual hydrogen sulfide gas, and the arsenic content is 0.4 mg / kg, meeting the requirements for raw acid arsenic removal production. The phosphate from the waste acid tank 4 overflows into the desulfurization tank 3. Nitrogen purging removes hydrogen sulfide from the phosphate in the desulfurization tank 3, and the hydrogen sulfide is then transported to the de-arsenic reactor 1 for recycling via the hydrogen sulfide blower 6. The hydrogen sulfide gas outlet of the arsenic removal reactor 1 is connected to the inlet to form an internal circulation. Excess hydrogen sulfide enters the hydrogen sulfide scrubbing tower 2, where it reacts with sodium carbonate solution for 10 minutes to produce sodium sulfide. The sodium sulfide solution overflows into the waste acid tank 4, and the remaining gas enters the chimney 201. The sodium carbonate solution has a concentration of 8% and is pumped to the hydrogen sulfide scrubbing tower 2 at a flow rate of 35 L / h via a metering pump.

[0070] Example 5:

[0071] like Figure 1 As shown, a measured amount of sodium sulfide solution is added to waste acid tank 4. Waste phosphoric acid with a flow rate of 7 L / h is pumped into waste acid tank 4 via a centrifugal pump. The waste phosphoric acid reacts with the sodium sulfide solution for 6 minutes to generate hydrogen sulfide. The hydrogen sulfide flue gas is then transported to arsenic removal reactor 1 via hydrogen sulfide blower 6, with the blower speed at 1800 rpm. The compressed air pressure in compressed air pipe 112 of arsenic removal reactor 1 is controlled at 25 kPa, and the charging / discharging frequency is 2500 ms, so that the hydrogen sulfide gas contacts the raw acid in a countercurrent manner in a pulsed form. The hydrogen sulfide flue gas and the raw acid in the arsenic removal reactor are reacted at a liquid-to-gas ratio of 40 L / m³. 3 The reaction produces arsenic sulfide, with a raw acid concentration of 58% (calculated as P2O5) and an arsenic content of 30 mg / kg. The residence time of the liquid in the collecting cone 102 is 35 min. After arsenic removal, the de-arsenic acid overflows through the de-arsenic acid outlet pipe 11 into the de-arsenic acid tank 5. The de-arsenic acid is then transported to the filtration device by the de-arsenic acid transfer pump 8. Testing shows that the de-arsenic acid in the de-arsenic acid tank 5 has no residual hydrogen sulfide gas, and the arsenic content is 0.3 mg / kg, meeting the requirements for raw acid arsenic removal production. The phosphate from the waste acid tank 4 overflows into the desulfurization tank 3. Nitrogen purging removes hydrogen sulfide from the phosphate in the desulfurization tank 3, and the hydrogen sulfide is then transported to the de-arsenic reactor 1 for recycling via the hydrogen sulfide blower 6. The hydrogen sulfide gas outlet of the arsenic removal reactor 1 is connected to the inlet to form an internal circulation. Excess hydrogen sulfide enters the hydrogen sulfide scrubbing tower 2, where it reacts with sodium carbonate solution for 10 minutes to produce sodium sulfide. The sodium sulfide solution overflows into the waste acid tank 4, and the remaining gas enters the chimney 201. The sodium carbonate solution has a concentration of 13% and is pumped to the hydrogen sulfide scrubbing tower 2 at a flow rate of 25 L / h via a metering pump.

[0072] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for removing arsenic from wet-process phosphoric acid, characterized in that: The application discloses a dearsenification system for dearsenifying wet-process phosphoric acid, which comprises a dearsenification reactor, a hydrogen sulfide washing tower, a dearsenification acid tank, a waste acid tank and a desulfurization tank. The dearsenification reactor comprises a reactor body, a hydrogen sulfide outlet is arranged at the top of the reactor body, a dearsenification acid outlet is arranged at the bottom of the reactor body, a raw material acid inlet is arranged above the reactor body, and a hydrogen sulfide inlet is arranged below the reactor body. The hydrogen sulfide outlet of the dearsenification reactor is communicated with the hydrogen sulfide inlet of the dearsenification reactor and the gas inlet of the hydrogen sulfide washing tower. The liquid outlet of the hydrogen sulfide washing tower is communicated with the inlet of the waste acid tank. The overflow port of the waste acid tank is communicated with the inlet of the desulfurization tank. The gas outlets of the waste acid tank and the desulfurization tank are communicated with the hydrogen sulfide inlet of the dearsenification reactor. The dearsenification acid outlet of the dearsenification reactor is communicated with the inlet of the dearsenification acid tank. A nitrogen purging pipe is arranged in the desulfurization tank. The liquid inlet of the waste acid tank is communicated with a waste phosphoric acid conveying pipe. The raw material acid inlet of the dearsenification reactor is fixed with an acid inlet pipe arranged in the reactor body. The outlet end of the acid inlet pipe is connected with a spray head. The spray head comprises a spray cavity and a nozzle communicated with the spray cavity. The hydrogen sulfide inlet of the dearsenification reactor is connected with a gas inlet pipe. The gas inlet pipe is connected with a gas distribution pipe arranged in the reactor body. A plurality of gas outlets are arranged on the gas distribution pipe. The diameter of the gas outlets is 20-100 mm. A compressed air pipe is connected with the gas inlet pipe. The compressed air in the compressed air pipe is filled and discharged at a frequency of 1500-3000 ms. The compressed air pressure is 15-30 kPa. A liquid collecting cone is connected with the bottom of the reactor body of the dearsenification reactor. A dearsenification acid outlet pipe is connected with the bottom of the liquid collecting cone. The dearsenification acid outlet pipe is communicated with the inlet of the dearsenification acid tank. The liquid-gas ratio of raw material acid and hydrogen sulfide gas in the dearsenification reactor is controlled to be 20-80 L / m 3 The concentration of raw material acid is controlled to be 35-86%, the arsenic content of raw material acid is controlled to be 10-100 mg / kg, the hydrogen sulfide absorbent feeding flow of hydrogen sulfide washing tower is controlled to be 10-150 L / h, and the residence time of dearsenification acid in the liquid collecting cone is controlled to be 5-60 min.

2. The method for removing arsenic from wet-process phosphoric acid according to claim 1, characterized in that: A hydrogen sulfide fan is arranged on the communication pipeline between the gas outlets of the waste acid tank and the desulfurization tank and the hydrogen sulfide inlet of the dearsenification reactor.

3. The method for removing arsenic from wet-process phosphoric acid according to claim 1, characterized in that: The number of the nozzles is more than two.

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