Positive-pressure arsenic removal process for wet-process phosphoric acid

Abstract

The invention provides an arsenic removal process for wet-process phosphoric acid, which comprises the following steps: firstly, mixing and pre-reacting crude phosphoric acid and a sodium sulfide aqueous solution to obtain a primary reaction product; feeding the primary reaction product obtained in the previous step into a closed reaction device, continuously reacting the primary reaction product in the closed reaction device with gradually increased pressure, and carrying out solid-liquid separation on the reacted slurry to obtain arsenic-removed acid; and finally, atomizing the arsenic-removed acid obtained in the previous step in a stripping tower, and releasing residual H2S after gas stripping to obtain a phosphoric acid product. The technology is simple, the arsenic removal effect is good, the removal efficiency of H2S in the acid liquor is high, the washing efficiency of H2S-containing tail gas is high, the reaction is totally closed, and the technology is a wet-process phosphoric acid arsenic removal and arsenic acid removal efficient stripping washing technology which is free of waste water and tail gas emission, environmentally friendly, low in safety risk and low in production cost.

Description

Technical Field

[0001] The invention belongs to the technical field of arsenic removal from wet phosphoric acid, and relates to a arsenic removal process for wet phosphoric acid, and in particular to a positive pressure arsenic removal process for wet phosphoric acid. Background Art

[0002] Arsenic in phosphoric acid generally exists in the form of H3AsO3 or H3AsO4. Arsenic removal methods include chemical precipitation, electrochemistry, extraction and crystallization. Among them, chemical precipitation is one of the most commonly used arsenic removal technologies today because of its simple operation and low investment cost.

[0003] The chemical precipitation method is to precipitate and separate As in phosphoric acid in the form of As2S3, usually by adding Na2S aqueous solution and P2S5 solid to phosphoric acid. The generated H2S reacts with As in phosphoric acid to generate As2S3. The H2S partial pressure generated by the reaction of P2S5 solid and Na2S aqueous solution with phosphoric acid is low, the arsenic removal effect is poor, the reagent consumption is large, the removal rate of H2S remaining in phosphoric acid is low, the washing efficiency of tail gas containing H2S is low, and the environmental pollution and safety risks are high.

[0004] At present, the main equipment in industrial production includes reaction tanks, sedimentation tanks, filters, etc. Among them, the reaction tank adopts a cylindrical reaction tank with a stirring device. The reaction tank cannot be completely closed for production, which is easy to cause leakage of hydrogen sulfide gas, pollute the environment, and threaten the safety of operators. At the same time, the reaction efficiency of the reaction tank is low, and the reaction time is more than 30 minutes. Combined with the sedimentation time, the time from adding the arsenic removal agent to completing the filtration is as long as more than 2 hours, and the production efficiency is low.

[0005] For example, patent CN209759039U discloses a wet phosphoric acid sulfidation arsenic removal purification device, which adds a venturi mixer in front of the stirred reaction tank to reduce the reaction amount in the stirred reaction tank, but the problems of low production efficiency, high operating risk, and difficulty in deep arsenic removal still exist. For another example, patent CNI08910850 discloses a thermal electronic grade phosphoric acid arsenic removal method, which is to directly react the hydrogen sulfide gas generated by sodium sulfide solution with phosphoric acid in a dearsenication tower, and the arsenic content in phosphoric acid after the reaction can be as low as 10ppb or less. The good dearsenication effect of this method is related to the high initial arsenic content of the raw material being thermal phosphoric acid (often >500ppm, even 1000ppm), and the easy growth and filtration of dearsenication slag. Moreover, the dearsenication tower has a large volume, high investment, low mass transfer efficiency, poor controllability of the reaction process, and the excess hydrogen sulfide gas blown out needs to be absorbed by alkali solution and cannot be recycled. There are still large safety hazards in actual production.

[0006] In addition, CN102701165A discloses a method for removing arsenic from electronic-grade phosphoric acid produced by wet phosphoric acid, and the steps are as follows: ① adding H2S and phosphoric acid to the dearsenication reactor, and maintaining the reaction temperature at 80°C and stirring; ② filtering the concentrated solution from the dearsenication reactor through a filter to separate the arsenic slag and the clear liquid; ③ after the clear liquid is heated to a certain temperature, it is pumped into the de-H2S tower with a pump, and the hydrogen sulfide gas remaining in the acid is blown off by air bubbling and negative pressure suction; ④ the acid obtained after removing H2S enters the storage tank through a microfilter for standby use, ensuring that the arsenic content of the low arsenic acid is less than 1μg / g, and the particle size is controlled at less than 5μm; ⑤ the hydrogen sulfide (H2S) gas blown out during the dearsenication process is absorbed by a sodium carbonate (Na2CO3) solution, and the resulting sodium sulfide (Na2S) solution is used to produce other phosphates that do not require high sulfur content. This invention can effectively remove arsenic from phosphoric acid and meet industry standards.

[0007] The above schemes have the following problems: 1) The reaction tank adopts a cylindrical reaction tank with a stirring device, which cannot be completely closed for production, resulting in leakage of hydrogen sulfide gas, environmental pollution, threat to the safety of operators, and low arsenic removal efficiency; 2) The phosphoric acid clear liquid needs to be heated before stripping, which consumes a lot of energy; 3) The air bubbling, negative pressure suction and gas stripping methods are used to strip the residual H2S gas in the acid. Since the contact area between air and the phosphoric acid clear liquid is small, the stripping effect is poor, and the H2S gas dissolved in the phosphoric acid cannot be effectively replaced, causing H2S to be reduced to elemental S in the phosphoric acid, reducing the product quality; 4) The H2S-containing tail gas cannot be effectively and fully contacted with the alkali solution, the washing effect is poor, and the tail gas after washing still contains a small amount of H2S gas, which is directly discharged to pollute the environment and has low safety.

[0008] Therefore, how to find a more suitable arsenic removal method for wet phosphoric acid process and solve the above-mentioned problems existing in the arsenic removal process in the existing wet phosphoric acid process has become one of the urgent problems to be solved by many front-line researchers in the industry. Summary of the invention

[0009] In view of this, the technical problem to be solved by the present invention is to provide a dearsenification process for wet-process phosphoric acid, in particular, a positive pressure dearsenification process for wet-process phosphoric acid. The present invention has a simple process, high dearsenification efficiency, high H2S removal efficiency in acid solution, high H2S tail gas washing efficiency, and fully closed reaction. It is a wet-process phosphoric acid dearsenification and dearsenic acid efficient air stripping and washing process with zero wastewater, zero tail gas emission, environmental friendliness, low safety risk, and low production cost.

[0010] The present invention provides a process for removing arsenic from wet-process phosphoric acid, comprising the following steps:

[0011] 1) Pre-reacting crude phosphoric acid and sodium sulfide aqueous solution by mixing to obtain a primary reaction product;

[0012] 2) feeding the primary reaction product obtained in the above step into a closed reaction device, the primary reaction product continues to react in the closed reaction device with gradually increasing pressure, and the slurry after the reaction is subjected to solid-liquid separation to obtain dearsenic acid;

[0013] 3) The dearsenic acid obtained in the above step is atomized in a stripping tower, and after gas stripping, the residual H2S is released to obtain a phosphoric acid product.

[0014] Preferably, the crude phosphoric acid includes crude phosphoric acid prepared by a wet phosphoric acid process;

[0015] The mass content of P2O5 in the crude phosphoric acid is 38% to 45%;

[0016] The mass content of As in the crude phosphoric acid is 15 to 100 ppm.

[0017] Preferably, the molar ratio of Na2S to As in the crude phosphoric acid is (0.67-3.67):1;

[0018] The mixing pre-reaction time is 15 to 30 seconds;

[0019] The temperature of the mixed pre-reaction is 50-95°C;

[0020] The pressure is specifically the gas phase pressure.

[0021] Preferably, the gradually increasing pressure is specifically increasing the first pressure to the second pressure;

[0022] The first pressure is 30-60 kPa;

[0023] The second pressure is 80-90 kPa;

[0024] The temperature of the continued reaction is 50-95°C.

[0025] Preferably, the step 2) further comprises the following process: after the pressure in the closed reaction device is reduced to the first pressure, the discharging is stopped, and the initial reaction product is fed again and the reaction in the closed reaction device is carried out, and the cycle is repeated;

[0026] The reaction process in the closed reaction device is specifically controlled by the change of pressure.

[0027] The separation specifically comprises solid-liquid separation in a closed device;

[0028] After the separation, dearsenicated acid and dearsenicated slag are obtained.

[0029] Preferably, the atomization is specifically performed by using a multi-stage high-efficiency atomizer;

[0030] The multi-stage high-efficiency atomizer is specifically 2 to 4 layers of vertically distributed atomizing nozzles;

[0031] The number of the atomizing nozzles in a single layer is multiple.

[0032] Preferably, the spray angle of the atomizing nozzle is 20° to 55°;

[0033] The size of the atomized droplets is 5 to 10 μm;

[0034] The liquid-to-gas ratio of the dearsenic acid to the gas is 5‰ to 20‰.

[0035] Preferably, the stripping further includes a washing step;

[0036] The stripping gas of the gas stripping comprises a mixed gas of air and washing tail gas;

[0037] The gas stripping is specifically that the atomized droplets are in countercurrent contact with the gas from bottom to top in the stripping tower from top to bottom to perform gas stripping;

[0038] Phosphoric acid is obtained at the bottom of the stripping tower and discharged from the bottom.

[0039] Preferably, the washing step comprises the following process:

[0040] The stripped tail gas after the gas stripping is sent to the bottom of the washing tower, and the tail gas is countercurrently contacted with the atomized alkaline solution from bottom to top for washing, thereby obtaining a sodium sulfide washing liquid and a washed tail gas;

[0041] The washing tail gas is returned to the bottom of the stripping tower as stripping gas;

[0042] The sodium sulfide washing liquid is returned to step 1) for mixing pre-reaction.

[0043] Preferably, the arsenic content in the phosphoric acid product is ≤0.05ppm;

[0044] The arsenic removal rate of the arsenic removal process is ≥99.9%.

[0045] The present invention provides a dearsenication process for wet phosphoric acid, comprising the following steps: first, crude phosphoric acid and sodium sulfide aqueous solution are mixed and pre-reacted to obtain a primary reaction product; then the primary reaction product obtained in the above step is fed into a closed reaction device, the primary reaction product continues to react in the closed reaction device with gradually increasing pressure, and the slurry after the reaction is subjected to solid-liquid separation to obtain dearsenic acid; finally, the dearsenic acid obtained in the above step is atomized in a stripping tower, and after gas stripping, the residual H2S is released to obtain a phosphoric acid product. Compared with the prior art, the present invention believes that the reaction tank of the existing wet phosphoric acid chemical precipitation method dearsenication process adopts a cylindrical reaction tank with a stirring device, which cannot be completely closed for production, has a low H2S partial pressure, low dearsenication efficiency, and hydrogen sulfide gas is easy to leak, pollutes the environment, and threatens the safety of operators. At the same time, the dearsenication H2S stripping effect of the existing wet phosphoric acid chemical precipitation method dearsenication process is poor, the process is complex, the energy consumption is high, and the system sealing is poor, which easily causes the risk of H2S poisoning of operators. Moreover, the H2S scrubbing efficiency is low, the exhaust gas contains a certain amount of H2S gas and the equipment is prone to clogging, which directly discharges and pollutes the environment, posing a safety risk.

[0046] Based on this, the present invention creatively designs a dearsenification process for wet-process phosphoric acid, which is a positive pressure dearsenification process for wet-process phosphoric acid and a dearsenic acid H2S efficient blowing and washing process. The dearsenication process provided by the present invention has low energy consumption for positive pressure dearsenication, good dearsenication effect, simpler process and no risk of hydrogen sulfide leakage; at the same time, the dearsenic acid does not need to be heated before blowing, and the energy consumption is low; and the dearsenic acid is efficiently atomized into tiny droplets through multi-stage efficient atomization, and the H2S gas remaining in the acid is efficiently blown off by countercurrent contact, which can effectively replace the H2S gas dissolved in phosphoric acid and improve product quality; and the H2S-containing tail gas is fully contacted with the atomized alkali solution, and the washing efficiency is high. There is almost no residual H2S gas in the tail gas after washing, and the tail gas generated by washing is used in the blowing process to achieve zero tail gas emission; the generated sodium sulfide solution returns to the dearsenication system to achieve zero wastewater emission. In addition, the dearsenication process provided by the present invention is in a fully closed circulation state, and the safety risk of hydrogen sulfide leakage is effectively controlled.

[0047] The arsenic removal process provided by the present invention has the advantages of simple process, good arsenic removal effect, high H2S removal efficiency in acid solution, high H2S tail gas washing efficiency, and fully closed reaction. It is a wet phosphoric acid arsenic removal and arsenic acid removal efficient stripping and washing process with zero wastewater, zero tail gas emission, environmental friendliness, low safety risk, and low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The present invention provides a schematic diagram of the positive pressure arsenic removal and H2S efficient air stripping and washing process of wet phosphoric acid. DETAILED DESCRIPTION

[0049] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention.

[0050] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0051] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses industrial pure materials or materials of conventional purity used in the wet-process phosphoric acid process.

[0052] The present invention provides a process for removing arsenic from wet-process phosphoric acid, comprising the following steps:

[0053] 1) Pre-reacting crude phosphoric acid and sodium sulfide aqueous solution by mixing to obtain a primary reaction product;

[0054] 2) feeding the primary reaction product obtained in the above step into a closed reaction device, the primary reaction product continues to react in the closed reaction device with gradually increasing pressure, and the slurry after the reaction is subjected to solid-liquid separation to obtain dearsenic acid;

[0055] 3) The dearsenic acid obtained in the above step is atomized in a stripping tower, and after gas stripping, the residual H2S is released to obtain a phosphoric acid product.

[0056] The invention firstly mixes crude phosphoric acid and sodium sulfide aqueous solution for pre-reaction to obtain a primary reaction product.

[0057] In the present invention, the crude phosphoric acid preferably includes crude phosphoric acid prepared by a wet phosphoric acid process.

[0058] In the present invention, the mass content of P2O5 in the crude phosphoric acid is preferably 38% to 45%, more preferably 39% to 44%, more preferably 40% to 43%, and more preferably 41% to 42%.

[0059] In the present invention, the mass content of As in the crude phosphoric acid is preferably 15 to 100 ppm, more preferably 35 to 80 ppm, and even more preferably 55 to 60 ppm.

[0060] In the present invention, the molar ratio of Na2S to As in the crude phosphoric acid is preferably (0.67-3.67):1, more preferably (1-3):1, and more preferably (1.5-2.5):1.

[0061] In the present invention, the time of the mixing pre-reaction is preferably 15 to 30 seconds, more preferably 18 to 27 seconds, and more preferably 21 to 24 seconds.

[0062] In the present invention, the temperature of the mixed pre-reaction is preferably 50 to 95°C, more preferably 60 to 85°C, and more preferably 70 to 75°C.

[0063] In the present invention, the primary reaction product obtained in the above steps is fed into a closed reaction device, and the primary reaction product continues to react in the closed reaction device with gradually increasing pressure, and the slurry after the reaction is subjected to solid-liquid separation to obtain dearsenic acid.

[0064] In the present invention, the pressure is preferably gas phase pressure.

[0065] In the present invention, the gradual increase in pressure is preferably from the first pressure to the second pressure.

[0066] In the present invention, the first pressure is preferably 30-60 kPa, more preferably 35-55 kPa, more preferably 40-50 kPa, specifically 50 kPa.

[0067] In the present invention, the second pressure is preferably 80-90 kPa, more preferably 80-86 kPa, more preferably 80-82 kPa, specifically 80 KPa.

[0068] In the present invention, the temperature of the continued reaction is preferably 50 to 95°C, more preferably 60 to 85°C, and more preferably 70 to 75°C.

[0069] In the present invention, the step 2) also preferably includes the following process: after the pressure in the closed reaction device drops to the first pressure, the discharging is stopped, the initial reaction product is fed again and the reaction in the closed reaction device is carried out, and the cycle is performed.

[0070] In the present invention, the reaction process in the closed reaction device is preferably controlled by changes in pressure.

[0071] In the present invention, the separation is preferably carried out by performing solid-liquid separation in a closed device.

[0072] In the present invention, after the separation, dearsenicated acid and dearsenicated slag are preferably obtained.

[0073] Finally, the dearsenic acid obtained in the above steps is atomized in a stripping tower, and after gas stripping, the residual H2S is released to obtain a phosphoric acid product.

[0074] In the present invention, the atomization is preferably performed by using a multi-stage high-efficiency atomizer.

[0075] In the present invention, the multi-stage high-efficiency atomizer is preferably a vertically distributed 2 to 4 layers of atomizing nozzles, more preferably a 2, 3 or 4 layers of atomizing nozzles.

[0076] In the present invention, the number of the atomizing nozzles in a single layer is preferably multiple.

[0077] In the present invention, the spray angle of the atomizing nozzle is preferably 20° to 55°, more preferably 25° to 50°, more preferably 30° to 45°, and more preferably 35° to 40°.

[0078] In the present invention, the size of the atomized droplets is preferably 5 to 10 μm, more preferably 6 to 9 μm, and more preferably 7 to 8 μm.

[0079] In the present invention, the liquid-to-gas ratio of the dearsenic acid to gas is preferably 5‰ to 20‰, more preferably 8‰ to 17‰, and more preferably 11‰ to 14‰.

[0080] In the present invention, a high-efficiency atomizer is used for multi-stage atomization, and 2 to 4 layers of atomizing nozzles are vertically distributed in the stripping tower and the washing tower. Specifically, 6 nozzles are installed on each layer, the spray angle is 20 to 55 degrees, and the droplet particle size is 5.016 to 10 μm.

[0081] In the present invention, the stripping step preferably further includes a washing step.

[0082] In the present invention, the stripping gas of the gas stripping preferably comprises a mixed gas of air and washing tail gas.

[0083] In the present invention, the gas stripping is preferably carried out by the atomized droplets contacting from top to bottom with the gas from bottom to top in a countercurrent manner in a stripping tower to carry out the gas stripping.

[0084] In the present invention, phosphoric acid is preferably obtained at the bottom of the stripping tower and discharged from the bottom.

[0085] In the present invention, the washing step preferably includes the following process: the stripping tail gas after the gas stripping is sent to the bottom of the washing tower, and the tail gas is countercurrently contacted with the atomized alkaline solution from bottom to top for washing to obtain Na2S washing liquid and washing tail gas.

[0086] In the present invention, the scrubber tail gas is preferably returned to the bottom of the stripping tower as stripping gas.

[0087] In the present invention, the sodium sulfide washing liquid is preferably returned to step 1) for mixing pre-reaction.

[0088] In the present invention, the arsenic content in the phosphoric acid product is preferably ≤0.05 ppm, more preferably ≤0.045 ppm, and more preferably ≤0.04 ppm.

[0089] In the present invention, the arsenic removal rate of the arsenic removal process is preferably ≥99.9%, more preferably ≥99.92%, and more preferably ≥99.95%.

[0090] The arsenic removal process for wet phosphoric acid provided by the present invention adopts positive pressure arsenic removal, controls the normal operation of the arsenic removal process by pressure, has low energy consumption, high arsenic removal efficiency, automatic process and no risk of hydrogen sulfide leakage. In addition, an efficient gas distribution system is set for the air intake, the solution is forced to circulate, and the solution is atomized into tiny droplets by the atomizer and fully countercurrently contacts with the gas, so that the H2S in the dearsenic acid is efficiently and thoroughly blown away. The H2S gas enters the scrubbing tower and fully contacts the atomized sodium carbonate solution in countercurrent, and the H2S gas reacts with sodium carbonate to generate sodium sulfide, water and carbon dioxide. The main component of the tail gas is carbon dioxide, and the tail gas returns to the blow-off tower for continuous recycling, and the sodium sulfide solution enters the arsenic removal system for use. In the process provided by the present invention, the positive pressure arsenic removal, efficient blow-off and washing are all carried out under closed conditions, achieving zero tail gas and zero wastewater discharge, so that the safety risk of hydrogen sulfide leakage is effectively controlled and the arsenic content of the finished phosphoric acid is ≤0.05ppm.

[0091] The present invention is to complete and refine the overall technical solution, better ensure the stability and controllability of the above-mentioned arsenic removal process for wet-process phosphoric acid, and further improve the arsenic removal efficiency and H2S removal efficiency of the arsenic removal process. The above-mentioned positive pressure arsenic removal process for wet-process phosphoric acid and the arsenic acid H2S efficient air stripping and washing process can specifically include the following contents:

[0092] The principle of removing As ions from wet phosphoric acid by Na2S is as follows:

[0093] Main reaction:

[0094] Na2S+2H3PO4→H2S+2NaH2PO4

[0095] H2S→S 2- +2H +

[0096] 2As 3+ +3S 2- →As2S3↓

[0097] Side effects:

[0098] Pb 2+ +H2S→PbS↓+2H +

[0099] As 5+ +S 2- →As 3+ +S

[0100] Tail gas washing reaction formula:

[0101] H2S+Na2CO3→Na2S+H2O+CO2.

[0102] See also Figure 1 , Figure 1 The present invention provides a schematic diagram of the positive pressure arsenic removal and H2S efficient air stripping and washing process of wet phosphoric acid. In which, 1-reactor; 2, 5, 7, 16-pump; 3-positive pressure arsenic removal tower; 4-gas control valve; 6-plate and frame filter press; 8-efficient air stripping tower; 9, 13-circulating pump; 10, 14-efficient atomizer; 11, 15-induced draft fan; 12-washing tower; E1-crude phosphoric acid; E2-sodium sulfide aqueous solution; E3-non-condensable gas; E4-slurry; E5-arsenic removal slag; E6-arsenic removal acid; E7-qualified phosphoric acid; E8-air; E9-sodium carbonate aqueous solution; E10-air stripping tail gas; E11-non-condensable gas; E12-washing tower tail gas; E13-sodium sulfide aqueous solution.

[0103] Brief description of the process:

[0104] (1) Crude phosphoric acid and sodium sulfide aqueous solution are contacted in 1 for initial reaction and then pumped into 3 through pump 2 to continue the reaction under positive pressure.

[0105] (2) 3 is a fully enclosed device. The gas in the container is compressed as the liquid level in 3 continues to rise, and the pressure increases. The hydrogen sulfide gas can fully dissolve in the mixed liquid and react with As. 3+ After sufficient reaction, when the pressure in the container increases from 50 kPa to 80 kPa, close 2 and open 5, and the slurry is separated into solid and liquid at 6, and 6 is a closed device.

[0106] (3) Since 5 is opened and 2 is closed, the liquid level in 3 drops. When the pressure drops to 50 kPa, 5 is closed and 2 is opened, and this cycle is repeated. The operation of the entire process is controlled by the change in pressure.

[0107] (4) Dearsenic acid is pumped into 8 from 7. The dearsenic acid passes through a high-efficiency atomizer 10, and after being atomized, it contacts with the mixed gas (air and tail gas generated by washing) in countercurrent. The H2S in the dearsenic acid is blown off and released, and qualified phosphoric acid is discharged from the bottom of 8.

[0108] (5) The gas in 8 is introduced into 12 through 11 and fully contacted with the small alkaline liquid particles that have been efficiently atomized in 14 for countercurrent washing. The sodium sulfide solution obtained by washing is pumped into 1 through 16 to continue to react with the crude phosphoric acid.

[0109] (6) The tail gas from 12 is introduced into 8 through 15 and mixed with air to blow off the H2S in the dearsenic acid.

[0110] (7) Non-condensable gases should be discharged regularly at E3 and E11.

[0111] The above content of the present invention provides a positive pressure arsenic removal process for wet phosphoric acid, which is a positive pressure arsenic removal process for wet phosphoric acid and an efficient blowing and washing process for arsenic acid H2S. The arsenic removal process provided by the present invention has low energy consumption for positive pressure arsenic removal, good arsenic removal effect, simpler process and no risk of hydrogen sulfide leakage; at the same time, the arsenic acid does not need to be heated before blowing, and the energy consumption is low; and the arsenic acid is efficiently atomized into tiny droplets through multi-stage high efficiency, and the H2S gas remaining in the acid is efficiently blown off by countercurrent contact, which can effectively replace the H2S gas dissolved in phosphoric acid and improve product quality; and the H2S-containing tail gas is fully contacted with the atomized alkali solution, and the washing efficiency is high. There is almost no residual H2S gas in the tail gas after washing, and the tail gas generated by washing is used in the blowing process to achieve zero tail gas emission; the generated sodium sulfide solution is returned to the arsenic removal system to achieve zero wastewater emission. In addition, the arsenic removal process provided by the present invention is in a fully closed circulation state, and the safety risk of hydrogen sulfide leakage is effectively controlled.

[0112] The wet-process phosphoric acid positive pressure arsenic removal and arsenic acid removal efficient air stripping and washing process provided by the present invention has compact system design, reasonable layout, simple process, low operation difficulty, high air stripping efficiency of H2S residual in acid solution, high washing efficiency of H2S in tail gas, the system is in a fully enclosed state, the degree of automation is high, the safety risk of hydrogen sulfide leakage is effectively controlled, the system realizes zero tail gas and zero wastewater discharge, and effectively solves the problems in the prior art that the arsenic removal reaction tank, arsenic acid stripping and washing cannot be produced in a completely closed manner, and the air stripping and washing efficiency is low.

[0113] In order to further illustrate the present invention, a dearsenicization process for wet-process phosphoric acid provided by the present invention is described in detail below in combination with examples. However, it should be understood that these examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following examples.

[0114] A factory uses the technology of the present invention to remove arsenic from crude phosphoric acid in the production process of wet phosphoric acid. The specific scheme is as follows:

[0115] Example 1

[0116] (1) E1 and E2 were contacted in 1 for the initial reaction, the molar ratio of Na2S to As was 0.67:1, the premixing time was 15 s, and the premixing temperature was 50 °C.

[0117] (2) After the initial reaction, the crude phosphoric acid is pumped into the sealed chamber 3 from chamber 2. As the mixture of crude phosphoric acid and sodium sulfide aqueous solution is continuously pumped in, the gas in chamber 3 is continuously compressed. When the pressure in chamber 3 reaches 80 kPa, the feeding is stopped.

[0118] (3) Open 5, and the slurry after full reaction is discharged from the bottom of 3. The pressure in 3 continues to drop. When the pressure drops to 30 kPa, stop discharging.

[0119] (4) While continuously discharging the material, the slurry is pumped from step 5 into step 6 for filtration to obtain E6 and E5.

[0120] (5) E6 is injected from 7 into 8 and atomized multiple times by forced circulation from 9, and contacts with the blow-off gas from bottom to top in countercurrent, and the residual H2S is blown away. The liquid-gas ratio of 3 is 5‰, among which 3 has 4 layers of atomizing nozzles vertically distributed, and 6 nozzles are installed on each layer. The spray angle is 35°, and the droplet particle size is 5μm.

[0121] (6) The stripped E10 is introduced from 11 to 12 for countercurrent contact reaction with the atomized E9 droplets to obtain E13 and E12, wherein the concentration of E9 is 15 wt %. There are three layers of atomizing nozzles vertically distributed in 12, with four nozzles installed on each layer, the spray angle is 55°, and the droplet particle size is 5 μm.

[0122] (7) The generated E13 is returned to 1 to continue reacting with E1.

[0123] (8) The generated E12 is introduced into 8 through 15 and mixed with E8, and then the arsenic acid is stripped again.

[0124] Through the application of positive pressure arsenic removal technology in production, the arsenic in the product is compared with the conventional arsenic removal process. The data are shown in Tables 1 to 3.

[0125] Table 1 shows the technical indicators of the arsenic removal process in Example 1 of the present invention and the conventional arsenic removal process before and after arsenic removal.

[0126] Table 1

[0127]

[0128] Table 2 shows the main indicators of arsenic acid removed by the air stripping process in Example 1 of the present invention and the conventional air stripping process.

[0129] Table 2

[0130]

[0131] Table 3 shows the main indicators of the tail gas after washing in Example 1 of the present invention and the tail gas after the conventional washing process.

[0132] Table 3

[0133] Process Type Analyze Project unit Before washing After washing Conventional washing process Hydrogen sulfide vol% 0.4 0.18 High efficiency atomization washing Hydrogen sulfide vol% 0.44 0.08

[0134] Example 2

[0135] (1) E1 and E2 were contacted in 1 for the initial reaction, the molar ratio of Na2S to As was 3.67:1, the premixing time was 30 s, and the premixing temperature was 95 °C.

[0136] (2) After the initial reaction, the crude phosphoric acid is pumped into the sealed chamber 3 from chamber 2. As the crude phosphoric acid and the sodium sulfide aqueous solution mixture are continuously pumped in, the gas in chamber 3 is continuously compressed. The pressure in chamber 3 is 90 kPa, and the feeding is stopped at this time.

[0137] (3) Open 5, and the slurry after full reaction is discharged from the bottom of 3. The pressure in 3 continues to drop. When the pressure drops to 60 kPa, stop discharging.

[0138] (4) While continuously discharging the material, the slurry is pumped from step 5 into step 6 for filtration to obtain E6 and E5.

[0139] (5) E6 is pumped from 7 into 8 and atomized multiple times by forced circulation from 9, where it contacts the stripping gas from bottom to top in countercurrent flow, and the residual H2S is blown away. The liquid-gas ratio in the stripping tower is 20‰, and there are 4 layers of atomizing nozzles vertically distributed in the stripping tower. Six nozzles are installed on each layer, with a spray angle of 55° and a droplet particle size of 8 μm.

[0140] (6) The stripped E10 is introduced from 11 to 12 for countercurrent contact reaction with the atomized E9 droplets to obtain E13 and E12, wherein the E9 concentration is 15 wt %. The washing tower has three layers of atomizing nozzles vertically distributed, and four nozzles are installed on each layer. The spray angle is 55°, and the droplet particle size is 8 μm.

[0141] (7) The generated E13 is returned to reactor 1 to continue reacting with E1.

[0142] (8) The generated E12 is introduced into 8 through 15 and mixed with E8, and then the arsenic acid is stripped again.

[0143] Through the application of positive pressure arsenic removal technology in production, the arsenic in the product is compared with the conventional process. The data are shown in Tables 4 to 6.

[0144] Table 4 shows the technical indicators of the arsenic removal process in Example 2 of the present invention and the conventional arsenic removal process before and after arsenic removal.

[0145] Table 4

[0146]

[0147] Table 5 shows the main indicators of the arsenic acid removed by the air stripping process in Example 2 of the present invention and the conventional air stripping process.

[0148] Table 5

[0149]

[0150] Table 6 shows the main indicators of the tail gas after washing in Example 2 of the present invention and the tail gas after the conventional washing process.

[0151] Table 6

[0152] Process Type Analyze Project unit Before washing After washing Conventional washing process Hydrogen sulfide vol% 0.4 0.18 High efficiency atomization washing Hydrogen sulfide vol% 0.32 0.06

[0153] Example 3

[0154] (1) E1 and E2 were contacted in 1 for the initial reaction, the molar ratio of Na2S to As was 1.8:1, the premixing time was 23 seconds, and the premixing temperature was 73°C.

[0155] (2) After the initial reaction, crude phosphoric acid is pumped into 3 from 2. As the crude phosphoric acid and sodium sulfide aqueous solution mixture is continuously pumped in, the gas in 3 is continuously compressed. The pressure in 3 is 80 kPa, and the feeding is stopped at this time.

[0156] (3) Open 5, and the slurry after full reaction is discharged from the bottom of 3. The pressure in 3 continues to drop. When the pressure drops to 50 kPa, stop discharging.

[0157] (4) While continuously discharging the material, the slurry is pumped into a plate and frame filter press from step 5 for filtration to obtain dearsenicated acid E6 and dearsenicated slag E5.

[0158] (5) E6 is pumped from 7 into 8 and atomized multiple times by forced circulation from 9, where it contacts the stripping gas from bottom to top in countercurrent flow, and the residual H2S is blown away. The liquid-gas ratio in the stripping tower is 12‰, and there are 4 layers of atomizing nozzles vertically distributed in the stripping tower. Six nozzles are installed on each layer, with a spray angle of 38° and a droplet particle size of 7 μm.

[0159] (6) The stripped gas E10 is introduced from 11 to 12 for countercurrent contact reaction with the atomized E9 droplets to obtain E13 and E12, wherein the concentration of E9 is 15 wt %. There are three layers of atomizing nozzles vertically distributed in the washing tower, and four nozzles are installed on each layer. The spray angle is 38°, and the droplet particle size is 7 μm.

[0160] (7) The generated E13 is returned to 1 to continue reacting with E1.

[0161] (8) The generated E12 is introduced into 8 through 15 and mixed with E8, and then the arsenic acid is stripped again.

[0162] Through the application of positive pressure arsenic removal technology in production, the arsenic in the product is compared with the conventional process. The data are shown in Tables 7 to 9.

[0163] Table 7 shows the technical indicators of the arsenic removal process in Example 3 of the present invention and the conventional arsenic removal process before and after arsenic removal.

[0164] Table 7

[0165]

[0166] Table 8 shows the main indicators of arsenic acid removed by the air stripping process in Example 3 of the present invention and the conventional air stripping process.

[0167] Table 8

[0168]

[0169] Table 9 shows the main indicators of the tail gas after washing in Example 3 of the present invention and the tail gas after the conventional washing process.

[0170] Table 9

[0171] Process Type Analyze Project unit Before washing After washing Conventional washing process Hydrogen sulfide vol% 0.4 0.18 High efficiency atomization washing Hydrogen sulfide vol% 0.38 0.02

[0172] The above is a detailed introduction to a wet phosphoric acid positive pressure arsenic removal process provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enables any technician in the field to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements that are not different from the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A process for removing arsenic from wet-process phosphoric acid, characterized in that: The following steps are involved: 1) Pre-reacting crude phosphoric acid and sodium sulfide aqueous solution by mixing to obtain a primary reaction product; 2) feeding the primary reaction product obtained in the above step into a closed reaction device, the primary reaction product continues to react in the closed reaction device with gradually increasing pressure, and the slurry after the reaction is subjected to solid-liquid separation to obtain dearsenic acid; 3) The dearsenic acid obtained in the above step is atomized in a stripping tower, and after gas stripping, the residual H2S is released to obtain a phosphoric acid product.

2. The arsenic removal process according to claim 1, characterized in that: The crude phosphoric acid includes crude phosphoric acid prepared by a wet phosphoric acid process; The mass content of P2O5 in the crude phosphoric acid is 38% to 45%; The mass content of As in the crude phosphoric acid is 15 to 100 ppm.

3. The arsenic removal process according to claim 1, characterized in that: The molar ratio of Na2S to As in the crude phosphoric acid is (0.67-3.67):1; The mixing pre-reaction time is 15 to 30 seconds; The temperature of the mixed pre-reaction is 50-95°C; The pressure is specifically the gas phase pressure.

4. The arsenic removal process according to claim 1, characterized in that: The gradual increase in pressure specifically refers to the increase from the first pressure to the second pressure; The first pressure is 30-60 kPa; The second pressure is 80-90 kPa; The temperature of the continued reaction is 50-95°C.

5. The arsenic removal process according to claim 4, characterized in that: The step 2) further comprises the following process: after the pressure in the closed reaction device drops to the first pressure, the discharge is stopped, and the initial reaction product is fed again and the reaction in the closed reaction device is carried out, and the cycle is repeated; The reaction process in the closed reaction device is specifically controlled by the change of pressure. The separation specifically comprises solid-liquid separation in a closed device; After the separation, dearsenicated acid and dearsenicated slag are obtained.

6. The arsenic removal process according to claim 1, characterized in that: The atomization is specifically performed by using a multi-stage high-efficiency atomizer; The multi-stage high-efficiency atomizer is specifically 2 to 4 layers of vertically distributed atomizing nozzles; The number of the atomizing nozzles in a single layer is multiple.

7. The arsenic removal process according to claim 6, characterized in that: The spray angle of the atomizing nozzle is 20° to 55°; The size of the atomized droplets is 5 to 10 μm; The liquid-to-gas ratio of the dearsenic acid to the gas is 5‰ to 20‰.

8. The arsenic removal process according to claim 1, characterized in that: The stripping step also includes a washing step; The stripping gas of the gas stripping comprises a mixed gas of air and washing tail gas; The gas stripping is specifically that the atomized droplets are in countercurrent contact with the gas from bottom to top in the stripping tower from top to bottom to perform gas stripping; Phosphoric acid is obtained at the bottom of the stripping tower and discharged from the bottom.

9. The arsenic removal process according to claim 8, characterized in that: The washing step comprises the following steps: The stripped tail gas after the gas stripping is sent to the bottom of the washing tower, and the tail gas is countercurrently contacted with the atomized alkaline solution from bottom to top for washing, thereby obtaining a sodium sulfide washing liquid and a washed tail gas; The washing tail gas is returned to the bottom of the stripping tower as stripping gas; The sodium sulfide washing liquid is returned to step 1) for mixing pre-reaction.

10. The arsenic removal process according to claim 1, characterized in that: The phosphoric acid product has an arsenic content of ≤0.05 ppm; The arsenic removal rate of the arsenic removal process is ≥99.9%.

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