Process method and system for preparing calcium hydroxide from ardealite recovered acid

Abstract

The invention belongs to the technical field of chemical engineering, and discloses a process method for preparing calcium hydroxide from ardealite recovered acid, the production process of the invention mainly comprises seven procedures: ardealite pulping and mixing, reaction defluorination, impurity removal and recovery, ammonification, silicon dioxide recovery, calcium hydroxide recovery and ammonium sulfate distillation. The filtrate filtered and dehydrated in the arsenic removal and impurity removal working section is subjected to ultrafiltration concentration and then enters an ionization reaction tank, ammonia gas is introduced into the reaction tank to convert sulfate of magnesium in the reaction liquid into magnesium hydroxide and ammonium sulfate, the reacted material is subjected to ultrafiltration concentration and then is subjected to dehydration filtration, and a solid non-magnesium hydroxide wet material obtained through filtration is obtained; drying the wet material in a dryer to obtain magnesium hydroxide; and the filtrate enters an ammonium sulfate ammonia distillation system after ultrafiltration. The quality of calcium hydroxide prepared from ardealite recovered acid is greatly improved; and secondary pollution is avoided through a recovery process.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and in particular relates to a process method and system for recovering acid from phosphogypsum to prepare calcium hydroxide. Background Art

[0002] The phosphogypsum acid production process is mainly based on phosphogypsum, a solid waste in the wet phosphoric acid production process. The large accumulation of phosphogypsum not only occupies land resources, but also may pollute the environment. The technical background of this process mainly comes from the effective utilization of calcium sulfate resources in phosphogypsum. Through high-temperature decomposition or other chemical methods, the calcium sulfate in phosphogypsum is converted into sulfur dioxide, and then further converted into sulfuric acid. This process not only reduces the emission of phosphogypsum, but also produces valuable sulfuric acid products.

[0003] The quality of calcium hydroxide made from the existing phosphogypsum acid recovery is poor; at the same time, in the process of phosphogypsum acid production, waste gas, waste liquid and other pollutants may be generated. If these pollutants are not properly handled, they may cause secondary pollution to the environment.

[0004] Through the above analysis, the problems and defects of the prior art are as follows:

[0005] The quality of calcium hydroxide made from the existing phosphogypsum acid recovery is poor; at the same time, in the process of phosphogypsum acid production, waste gas, waste liquid and other pollutants may be generated. If these pollutants are not properly handled, they may cause secondary pollution to the environment. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a process for recovering acid from phosphogypsum to prepare calcium hydroxide.

[0007] The present invention is achieved in that a process for recovering acid from phosphogypsum to prepare calcium hydroxide comprises:

[0008] Step 1, phosphogypsum slurry preparation and slurry mixing process;

[0009] The phosphogypsum raw materials transported by trucks are unloaded into the primary discharge tank after being weighed. Recycled water and dilute sulfuric acid are added to the primary discharge tank to make the phosphogypsum slurry into liquid: solid = 2.5:1, medium density 1.85g / cm 3 , Bulk density 2.67g / cm 3 The slurry is stirred in the feeding tank to keep the solids suspended, and the slurry of phosphogypsum flows into the secondary feeding tank through overflow;

[0010] The phosphogypsum slurry in the secondary pulping tank is pumped into the screening machine through a slurry pump for screening and then enters the slurry mixing tank. The coarse particles screened out are crushed and finely ground before entering the secondary pulping tank; 98% sulfuric acid is added to the slurry mixing tank to acidify the phosphogypsum slurry. During the acidification process, trace amounts of hydrogen sulfide, sulfuric acid mist, fluorine-containing gas and other waste gases are generated. The waste gas is firstly absorbed by 7580℃ 5% lime water in a washing tower to absorb hydrogen sulfide and sulfuric acid mist, and then low-temperature lime water is used to absorb fluorine-containing gas; the acidified slurry is adjusted to pH value again with sulfuric acid through a dual-channel pipeline mixer and then enters the ionization reaction tank for reaction;

[0011] Step 2, reaction defluorination process;

[0012] The slurry reacted in the ionization reaction tank first passes through the aeration system to remove hydrogen fluoride, and the hydrogen fluoride is washed in the washing tower in three stages, and the calcium slurry is sprayed and combined with hydrofluoric acid to form calcium fluoride for storage; the slurry passing through the aeration system enters the flow separation system to separate the heavy slag and the light slurry, and the separated heavy slag is returned to the pulping tank. The separated light slurry enters the filter for filtration and dehydration after ultrafiltration to concentrate most of the water. The water concentrated by ultrafiltration is used as recycled water for phosphate ore pulping. The solid phase after filtration and dehydration enters the ammoniation process, and the liquid phase after filtration and dehydration is sent to the impurity removal and calcium hydroxide recovery system;

[0013] Step 3, impurity removal and recycling process;

[0014] Step 4, amination;

[0015] Step 5, silicon dioxide recovery;

[0016] Step 6, calcium hydroxide recovery;

[0017] Step 7, distilling ammonia from ammonium sulfate.

[0018] Further, the impurity removal and recovery process:

[0019] (1) Aluminum oxide recovery;

[0020] The filtrate after filtration and dehydration is concentrated by ultrafiltration and then enters into the impurity removal and slurry mixing tank. A magnesium hydroxide suspension is added into the impurity removal and slurry mixing tank to carry out a de-hybridization reaction. The aluminum sulfate in the reaction liquid reacts to generate aluminum hydroxide. The reacted material is concentrated by ultrafiltration and then dehydrated and filtered. The filtrate obtained by filtration enters into the arsenic removal and impurity removal system. The solid phase obtained by dehydration and filtration is aluminum hydroxide wet material. The wet material is dried in a dryer and then enters into a calcining kiln for calcination. After calcination, aluminum oxide is obtained.

[0021] (2) arsenic removal and impurity removal;

[0022] The filtrate from the aluminum oxide recovery section after filtration and dehydration is concentrated by ultrafiltration and then enters the impurity removal slurry tank, and magnesium hydroxide suspension and hydrogen peroxide are added to the impurity removal slurry tank for secondary impurity removal reaction, and the arsenic compounds in the reaction liquid are oxidized to arsenic trioxide. The reacted material is concentrated by ultrafiltration and then dehydrated and filtered to obtain arsenic trioxide wet material, and the wet material is recovered by drying and sublimation to obtain arsenic trioxide;

[0023] (3) magnesium hydroxide recovery;

[0024] The filtrate after filtration and dehydration in the arsenic removal and impurity removal section is concentrated by ultrafiltration and then enters the ionization reaction tank. Gaseous ammonia is introduced into the reaction tank to convert the magnesium sulfate in the reaction liquid into magnesium hydroxide and ammonium sulfate. The reacted material is concentrated by ultrafiltration and then dehydrated and filtered. The solid non-magnesium hydroxide wet material obtained by filtration is dried in a dryer to obtain magnesium hydroxide; the filtrate is ultrafiltered and then enters the ammonium sulfate ammonia distillation system.

[0025] Further, the amination:

[0026] The solid phase filtered and dehydrated from the defluorination process is added with recycled water in a pulping tank with stirring, and then ammonia is introduced for pulping. After the pulping is completed, the slurry is adjusted in a double-channel pipeline mixer by adding nitric acid and then enters an ionization reaction tank for reaction. After the reaction, a mixed slurry of calcium hydroxide, calcium sulfate and silicon dioxide is generated. The calcium hydroxide suspension and silicon dioxide heavy solid liquid obtained by separation of the slurry through aeration, fractionation and gravity selection are pumped into the calcium hydroxide recovery process and the silicon dioxide recovery process respectively.

[0027] Further, the silicon dioxide is recovered:

[0028] The silica heavy solid liquid from the ammoniation process is dehydrated and filtered to obtain a filtrate which is then concentrated by ultrafiltration and then fed into an ammonium sulfate ammonia distillation system. The solid wet material obtained by dehydration and filtration is dried in a dryer to obtain silica.

[0029] Further, the calcium hydroxide is recovered:

[0030] The calcium hydroxide suspension from the ammoniation process is concentrated by ultrafiltration, and the recycled water obtained by concentration is used for ammoniation pulping. The filtrate obtained after the concentrate is dehydrated and filtered is sent to the ammonium sulfate ammonia distillation system after ultrafiltration and concentration. The solid wet material obtained by dehydration and filtration is dried in a dryer to obtain calcium hydroxide.

[0031] Further, the ammonium sulfate distillation ammonia:

[0032] The ammonium sulfate solution generated from the recovery of magnesium hydroxide, silicon dioxide and calcium hydroxide is sent to the negative pressure ammonia evaporator for low-temperature ionization, decomposition and evaporation. The low-temperature evaporated ammonia gas and water vapor are washed with chilled water in the washing tower to obtain ammonia water, which is sent to the ammonia water tank for temporary storage. The residual liquid from the ammonia evaporation is sent to the sulfuric acid concentration device and phosphogypsum pulping.

[0033] Another object of the present invention is to provide a process system for recovering acid from phosphogypsum to produce calcium hydroxide, comprising:

[0034] The slurry preparation and mixing module is used to unload the phosphogypsum raw materials transported by cars into the first-level unloading tank after being weighed. Recycled water and dilute sulfuric acid are added to the first-level unloading tank to make the phosphogypsum slurry into liquid: solid = 2.5:1, medium density 1.85g / cm3, bulk density 2.67g / cm3 slurry. The unloading tank is set with stirring to keep the solid suspended. The slurry of phosphogypsum slurry enters the second-level unloading tank through overflow; the phosphogypsum slurry in the second-level slurry tank is pumped into the screening machine through the slurry pump for screening and then enters the slurry mixing tank. The coarse particles screened out are crushed and finely ground before entering the secondary pulping tank; 98% sulfuric acid is added to the slurry mixing tank to acidify the phosphogypsum slurry. During the acidification process, trace amounts of hydrogen sulfide, sulfuric acid mist, fluorine-containing gas and other waste gases are generated. The waste gas is firstly absorbed by 7580℃ 5% lime water in the washing tower to absorb hydrogen sulfide and sulfuric acid mist, and then low-temperature lime water is used to absorb fluorine-containing gas; the acidified slurry is adjusted with sulfuric acid again through a dual-channel pipeline mixer to enter the ionization reaction tank for reaction;

[0035] The reaction defluorination process module is used for the slurry reacted in the ionization reaction tank to first remove hydrogen fluoride through the aeration system, and the hydrogen fluoride is washed in the washing tower in three stages, and the calcium slurry is sprayed and combined with hydrofluoric acid to form calcium fluoride for storage; the slurry passing through the aeration system enters the flow separation system to separate the heavy slag and the light slurry, and the separated heavy slag is returned to the pulping tank. The separated light slurry is concentrated by ultrafiltration to concentrate most of the water and then enters the filter for filtration and dehydration. The concentrated water from the ultrafiltration is used as recycled water for phosphate ore pulping. The solid phase after filtration and dehydration enters the ammoniation process, and the liquid phase after filtration and dehydration is sent to the impurity removal and calcium hydroxide recovery system;

[0036] The impurity removal module is used for impurity removal and recycling processes;

[0037] The ammoniation module is used to add recycled water to the solid phase filtered and dehydrated from the defluorination process in a slurrying tank with stirring, and then introduce gas ammonia to make slurry. After the slurrying is completed, the slurry is adjusted in a double-channel pipeline mixer by adding nitric acid and then enters an ionization reaction tank for reaction. After the reaction, a mixed slurry of calcium hydroxide, calcium sulfate and silicon dioxide is generated. The calcium hydroxide suspension and silicon dioxide heavy solid liquid obtained by separation of the slurry through aeration, fractionation and gravity selection are pumped into the calcium hydroxide recovery process and the silicon dioxide recovery process respectively;

[0038] The silicon dioxide recovery module is used to extract the silicon dioxide heavy solid liquid from the ammoniation process through dehydration and filtration, and then the filtrate is concentrated by ultrafiltration and sent to the ammonium sulfate ammonia distillation system. The solid wet material obtained by dehydration and filtration is dried in a dryer to obtain silicon dioxide;

[0039] The calcium hydroxide recovery module is used to concentrate the calcium hydroxide suspension from the ammoniation process through ultrafiltration. The recycled water obtained by concentration is used for ammoniation pulping. The filtrate obtained after the concentrated liquid is dehydrated and filtered is sent to the ammonium sulfate ammonia distillation system after ultrafiltration and concentration. The solid wet material obtained by dehydration and filtration is dried in a dryer to obtain calcium hydroxide;

[0040] The ammonium sulfate ammonia distillation module is used to feed the ammonium sulfate solution generated from magnesium hydroxide recovery, silicon dioxide recovery and calcium hydroxide recovery into the negative pressure ammonia distillation device for low-temperature ionization, decomposition and evaporation. The low-temperature evaporated ammonia gas and water vapor are washed with chilled water in the washing tower to obtain ammonia water, which is then sent to the ammonia water tank for temporary storage. The residual liquid from ammonia distillation is sent to the sulfuric acid concentration device and phosphogypsum pulping.

[0041] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0042] In the process of preparing calcium hydroxide from phosphogypsum, the existing technology generally faces the problems of high impurity content in phosphogypsum, insufficient efficiency of defluorination and arsenic removal, etc., resulting in unstable product quality. In addition, the recycling of water resources and by-products often lacks a perfect separation and recovery mechanism, which easily leads to resource waste and increased system complexity.

[0043] The present invention gradually separates impurities in phosphogypsum through a series of unit operations such as multi-stage pulping, screening, acidification, ionization reaction and ammoniation, and adopts step-by-step addition and multiple concentration methods in the impurity removal and recovery stages to achieve graded control of fluorine, arsenic and other soluble or insoluble impurities. At the same time, the present invention introduces ionization aeration and multi-stage washing in the defluorination and impurity removal process to ensure that key impurities are effectively separated at different stages.

[0044] In the ammoniation and subsequent ammonia evaporation process, the present invention extracts byproducts such as ammonium sulfate and calcium fluoride in stages, and constructs a relatively complete closed-loop system through water reuse and gas circulation. This method helps to separate multiple resources in different operating units, thereby achieving comprehensive processing and diversified recovery of phosphogypsum raw materials on the same production line.

[0045] Through the integrated design of the steps of phosphogypsum pulping, impurity separation and calcium hydroxide preparation, the present invention forms a synergistic system structure in terms of raw material processing, impurity removal and by-product recovery. With the help of multi-stage pulping and multiple filtration and concentration strategies, each step can be stably operated within a relatively clear parameter range, thereby achieving deep utilization of phosphogypsum and efficient output of multiple products in the overall process flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The present invention provides a flow chart of a process for recovering acid from phosphogypsum to produce calcium hydroxide.

[0047] Figure 2 The present invention provides a block diagram of a process system for recovering acid from phosphogypsum to produce calcium hydroxide.

[0048] Figure 3 The present invention provides a detailed process flow chart for recovering acid from phosphogypsum to produce calcium hydroxide. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0050] like Figure 1 As shown, a process for recovering acid from phosphogypsum to produce calcium hydroxide provided by an embodiment of the present invention comprises the following steps:

[0051] S101, phosphogypsum slurry preparation and slurry mixing process;

[0052] The phosphogypsum raw materials transported by trucks are unloaded into the primary discharge tank after being weighed. Recycled water and dilute sulfuric acid are added to the primary discharge tank to make the phosphogypsum slurry into liquid: solid = 2.5:1, medium density 1.85g / cm 3 , Bulk density 2.67g / cm 3 The slurry is stirred in the feeding tank to keep the solids suspended, and the slurry of phosphogypsum flows into the secondary feeding tank through overflow;

[0053] The phosphogypsum slurry in the secondary pulping tank is pumped into the screening machine through a slurry pump for screening and then enters the slurry mixing tank. The coarse particles screened out are crushed and finely ground before entering the secondary pulping tank; 98% sulfuric acid is added to the slurry mixing tank to acidify the phosphogypsum slurry. During the acidification process, trace amounts of hydrogen sulfide, sulfuric acid mist, fluorine-containing gas and other waste gases are generated. The waste gas is firstly absorbed by 7580℃ 5% lime water in a washing tower to absorb hydrogen sulfide and sulfuric acid mist, and then low-temperature lime water is used to absorb fluorine-containing gas; the acidified slurry is adjusted to pH value again with sulfuric acid through a dual-channel pipeline mixer and then enters the ionization reaction tank for reaction;

[0054] S102, reaction defluorination process;

[0055] The slurry reacted in the ionization reaction tank first passes through the aeration system to remove hydrogen fluoride, and the hydrogen fluoride is washed in the washing tower in three stages, and the calcium slurry is sprayed and combined with hydrofluoric acid to form calcium fluoride for storage; the slurry passing through the aeration system enters the flow separation system to separate the heavy slag and the light slurry, and the separated heavy slag is returned to the pulping tank. The separated light slurry enters the filter for filtration and dehydration after ultrafiltration to concentrate most of the water. The water concentrated by ultrafiltration is used as recycled water for phosphate ore pulping. The solid phase after filtration and dehydration enters the ammoniation process, and the liquid phase after filtration and dehydration is sent to the impurity removal and calcium hydroxide recovery system;

[0056] S103, impurity removal and recycling process;

[0057] S104, amination;

[0058] S105, silica recovery;

[0059] S106, calcium hydroxide recovery;

[0060] S107, distilling ammonia from ammonium sulfate.

[0061] In the embodiment of the present invention, after the phosphogypsum is transported by car, it is first mixed with recycled water and dilute sulfuric acid in a primary feed tank to form a liquid-solid ratio of about 2.5:1 and a medium density of about 1.85 g / cm 3 , Bulk density about 2.67g / cm 3 The first-stage feeding tank is equipped with a stirring device to ensure that the phosphogypsum remains fully suspended in the slurry. Subsequently, the slurry that overflows into the second-stage feeding tank is screened to remove coarse particles; the screened coarse particles need to be further crushed and finely ground before being sent back to the second-stage feeding tank. This process can make the particle size of the phosphogypsum uniform and effectively reduce problems such as incomplete acidification or reduced dissolution efficiency caused by excessively large particles in the subsequent reaction process.

[0062] In the slurry mixing tank, 98% sulfuric acid is added to acidify the phosphogypsum slurry, so that the pH value of the slurry drops to about 1.0-2.0 to ensure that impurities such as fluoride and sulfide in the phosphogypsum can be fully dissolved or converted. In this process, a small amount of waste gas such as hydrogen sulfide, sulfuric acid mist and fluorine-containing gas will be released. After using lime water at about 75-80°C and a concentration of about 5% to gradedly absorb hydrogen sulfide and sulfuric acid mist in the washing tower, low-temperature lime water is used to remove fluorine-containing gases. The multi-stage absorption process can significantly improve the efficiency of waste gas purification while ensuring the safety and stability of subsequent reactions. The acidified slurry is further adjusted in pH through a dual-channel pipeline mixer and enters the ionization reaction tank for deep reaction.

[0063] In the ionization reaction tank, the aeration system is used to fully mix the reaction slurry, so that hydrogen fluoride can be precipitated from the liquid phase and enter the washing tower for tertiary washing. During the washing process, calcium slurry is sprayed in, and hydrogen fluoride and calcium ions form calcium fluoride precipitation, which is enriched in the storage tank. This process can effectively remove the fluorine element in phosphogypsum and recover the available fluorine resources to a certain extent. The aerated slurry enters the flow separation system to separate the heavy slag from the light slurry. The heavy slag returns to the pulping tank for further recycling, and the light slurry recovers most of the water through the ultrafiltration concentration device to reduce the energy consumption of subsequent processes.

[0064] The water concentrated by ultrafiltration can be used as recycled water again in the front-end phosphate ore pulping or other links, forming a closed-loop water system for recycling. Subsequently, the concentrated slurry is sent to the filter for solid-liquid separation: the filtrate part enters the impurity removal and calcium hydroxide recovery system, and the filter cake part enters the ammoniation process. At this time, the main components of the filter cake are the acidified phosphogypsum residue and a small amount of impurities; the filter cake reacts with ammonia water in the subsequent ammoniation process to further transform or dissolve some impurities, thus laying the foundation for the next step of recovering silicon dioxide and calcium hydroxide.

[0065] The filtrate enters the impurity removal section, where specific impurity removers (such as appropriate amounts of aluminum salts or iron salts) are added to precipitate phosphates or other soluble impurities, reducing the impurity concentration in the solution to a controllable range. Subsequently, the silicon dioxide is deposited or enriched under specific conditions and then separated using appropriate pH and temperature control conditions, thereby obtaining a silicon dioxide product with a higher purity. The solution after impurity removal and silicon dioxide separation is reacted by adding alkaline reagents such as lime milk or sodium hydroxide to eventually generate calcium hydroxide precipitate, which is then centrifuged or filtered to obtain the target calcium hydroxide product.

[0066] The filter cake enters the ammoniation process and contacts and reacts with ammonia water or ammonia gas, so that some of the residual acidic components or impurities in the phosphogypsum residue are neutralized or replaced. At this time, the ammonium sulfate solution generated in the system enters the ammonia distillation section, and the ammonium sulfate crystals are separated by evaporation and concentration to achieve the reuse of by-products. The ammonia gas produced by ammonia distillation can be recycled back to the ammoniation process, further reducing the loss of raw materials and forming a closed-loop comprehensive resource utilization system. Through the linkage and parameter control of the above processes, the present invention realizes the efficient treatment of phosphogypsum raw materials, successfully recovers various resources such as calcium hydroxide, silicon dioxide and calcium fluoride, and significantly improves the overall economic benefits and environmental protection level.

[0067] The impurity removal and recycling process provided by the embodiment of the present invention is as follows:

[0068] (1) Aluminum oxide recovery;

[0069] The filtrate after filtration and dehydration is concentrated by ultrafiltration and then enters into the impurity removal and slurry mixing tank. A magnesium hydroxide suspension is added into the impurity removal and slurry mixing tank to carry out a de-hybridization reaction. The aluminum sulfate in the reaction liquid reacts to generate aluminum hydroxide. The reacted material is concentrated by ultrafiltration and then dehydrated and filtered. The filtrate obtained by filtration enters into the arsenic removal and impurity removal system. The solid phase obtained by dehydration and filtration is aluminum hydroxide wet material. The wet material is dried in a dryer and then enters into a calcining kiln for calcination. After calcination, aluminum oxide is obtained.

[0070] (2) arsenic removal and impurity removal;

[0071] The filtrate from the aluminum oxide recovery section after filtration and dehydration is concentrated by ultrafiltration and then enters the impurity removal slurry tank, and magnesium hydroxide suspension and hydrogen peroxide are added to the impurity removal slurry tank for secondary impurity removal reaction, and the arsenic compounds in the reaction liquid are oxidized to arsenic trioxide. The reacted material is concentrated by ultrafiltration and then dehydrated and filtered to obtain arsenic trioxide wet material, and the wet material is recovered by drying and sublimation to obtain arsenic trioxide;

[0072] (3) magnesium hydroxide recovery;

[0073] The filtrate after filtration and dehydration in the arsenic removal and impurity removal section is concentrated by ultrafiltration and then enters the ionization reaction tank. Gaseous ammonia is introduced into the reaction tank to convert the magnesium sulfate in the reaction liquid into magnesium hydroxide and ammonium sulfate. The reacted material is concentrated by ultrafiltration and then dehydrated and filtered. The solid non-magnesium hydroxide wet material obtained by filtration is dried in a dryer to obtain magnesium hydroxide; the filtrate is ultrafiltered and then enters the ammonium sulfate ammonia distillation system.

[0074] The amination provided by the embodiment of the present invention:

[0075] The solid phase filtered and dehydrated from the defluorination process is added with recycled water in a pulping tank with stirring, and then ammonia is introduced for pulping. After the pulping is completed, the slurry is adjusted in a double-channel pipeline mixer by adding nitric acid and then enters an ionization reaction tank for reaction. After the reaction, a mixed slurry of calcium hydroxide, calcium sulfate and silicon dioxide is generated. The calcium hydroxide suspension and silicon dioxide heavy solid liquid obtained by separation of the slurry through aeration, fractionation and gravity selection are pumped into the calcium hydroxide recovery process and the silicon dioxide recovery process respectively.

[0076] Silicon dioxide recovery provided by the embodiment of the present invention:

[0077] The silica heavy solid liquid from the ammoniation process is dehydrated and filtered to obtain a filtrate which is then concentrated by ultrafiltration and then fed into an ammonium sulfate ammonia distillation system. The solid wet material obtained by dehydration and filtration is dried in a dryer to obtain silica.

[0078] Calcium hydroxide recovery provided by the embodiment of the present invention:

[0079] The calcium hydroxide suspension from the ammoniation process is concentrated by ultrafiltration, and the recycled water obtained by concentration is used for ammoniation pulping. The filtrate obtained after the concentrate is dehydrated and filtered is sent to the ammonium sulfate ammonia distillation system after ultrafiltration and concentration. The solid wet material obtained by dehydration and filtration is dried in a dryer to obtain calcium hydroxide.

[0080] The ammonium sulfate distillation method provided by the embodiment of the present invention is as follows:

[0081] The ammonium sulfate solution generated from the recovery of magnesium hydroxide, silicon dioxide and calcium hydroxide is sent to the negative pressure ammonia evaporator for low-temperature ionization, decomposition and evaporation. The low-temperature evaporated ammonia gas and water vapor are washed with chilled water in the washing tower to obtain ammonia water, which is sent to the ammonia water tank for temporary storage. The residual liquid from the ammonia evaporation is sent to the sulfuric acid concentration device and phosphogypsum pulping.

[0082] like Figure 2 As shown, a process system for recovering acid from phosphogypsum to produce calcium hydroxide provided by an embodiment of the present invention comprises:

[0083] The slurry preparation and mixing module is used to unload the phosphogypsum raw materials transported by cars into the first-level unloading tank after being weighed. Recycled water and dilute sulfuric acid are added to the first-level unloading tank to make the phosphogypsum slurry into liquid: solid = 2.5:1, medium density 1.85g / cm3, bulk density 2.67g / cm3 slurry. The unloading tank is set with stirring to keep the solid suspended. The slurry of phosphogypsum slurry enters the second-level unloading tank through overflow; the phosphogypsum slurry in the second-level slurry tank is pumped into the screening machine through the slurry pump for screening and then enters the slurry mixing tank. The coarse particles screened out are crushed and finely ground before entering the secondary pulping tank; 98% sulfuric acid is added to the slurry mixing tank to acidify the phosphogypsum slurry. During the acidification process, trace amounts of hydrogen sulfide, sulfuric acid mist, fluorine-containing gas and other waste gases are generated. The waste gas is firstly absorbed by 7580℃ 5% lime water in the washing tower to absorb hydrogen sulfide and sulfuric acid mist, and then low-temperature lime water is used to absorb fluorine-containing gas; the acidified slurry is adjusted with sulfuric acid again through a dual-channel pipeline mixer to enter the ionization reaction tank for reaction;

[0084] The reaction defluorination process module is used for the slurry reacted in the ionization reaction tank to first remove hydrogen fluoride through the aeration system, and the hydrogen fluoride is washed in the washing tower in three stages, and the calcium slurry is sprayed and combined with hydrofluoric acid to form calcium fluoride for storage; the slurry passing through the aeration system enters the flow separation system to separate the heavy slag and the light slurry, and the separated heavy slag is returned to the pulping tank. The separated light slurry is concentrated by ultrafiltration to concentrate most of the water and then enters the filter for filtration and dehydration. The concentrated water from the ultrafiltration is used as recycled water for phosphate ore pulping. The solid phase after filtration and dehydration enters the ammoniation process, and the liquid phase after filtration and dehydration is sent to the impurity removal and calcium hydroxide recovery system;

[0085] The impurity removal module is used for impurity removal and recycling processes;

[0086] The ammoniation module is used to add recycled water to the solid phase filtered and dehydrated from the defluorination process in a slurrying tank with stirring, and then introduce gas ammonia to make slurry. After the slurrying is completed, the slurry is adjusted in a double-channel pipeline mixer by adding nitric acid and then enters an ionization reaction tank for reaction. After the reaction, a mixed slurry of calcium hydroxide, calcium sulfate and silicon dioxide is generated. The calcium hydroxide suspension and silicon dioxide heavy solid liquid obtained by separation of the slurry through aeration, fractionation and gravity selection are pumped into the calcium hydroxide recovery process and the silicon dioxide recovery process respectively;

[0087] The silicon dioxide recovery module is used to extract the silicon dioxide heavy solid liquid from the ammoniation process through dehydration and filtration, and then the filtrate is concentrated by ultrafiltration and sent to the ammonium sulfate ammonia distillation system. The solid wet material obtained by dehydration and filtration is dried in a dryer to obtain silicon dioxide;

[0088] The calcium hydroxide recovery module is used to concentrate the calcium hydroxide suspension from the ammoniation process through ultrafiltration. The recycled water obtained by concentration is used for ammoniation pulping. The filtrate obtained after the concentrated liquid is dehydrated and filtered is sent to the ammonium sulfate ammonia distillation system after ultrafiltration and concentration. The solid wet material obtained by dehydration and filtration is dried in a dryer to obtain calcium hydroxide;

[0089] The ammonium sulfate ammonia distillation module is used to feed the ammonium sulfate solution generated from magnesium hydroxide recovery, silicon dioxide recovery and calcium hydroxide recovery into the negative pressure ammonia distillation device for low-temperature ionization, decomposition and evaporation. The low-temperature evaporated ammonia gas and water vapor are washed with chilled water in the washing tower to obtain ammonia water, which is then sent to the ammonia water tank for temporary storage. The residual liquid from ammonia distillation is sent to the sulfuric acid concentration device and phosphogypsum pulping.

[0090] Another object of the present invention is to provide a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the process method for recovering acid from phosphogypsum to produce calcium hydroxide.

[0091] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to execute the steps of the process method for recovering acid from phosphogypsum to produce calcium hydroxide.

[0092] Another object of the present invention is to provide an information data processing terminal, which is used to implement the process system for recovering acid from phosphogypsum to produce calcium hydroxide.

[0093] The present invention is specifically implemented:

[0094] Overview of the process flow of acid production from phosphogypsum

[0095] Process description

[0096] The production process is mainly divided into seven steps: phosphogypsum slurry preparation and adjustment, reaction defluorination step, impurity removal and recovery step, amination step, silica recovery step, calcium hydroxide recovery step, and ammonium sulfate distillation step.

[0097] like Figure 3 The process is briefly described as follows:

[0098] 1. Phosphogypsum slurry preparation and slurry mixing process

[0099] The phosphogypsum raw materials transported by trucks are unloaded into the primary discharge tank after being weighed. Recycled water and dilute sulfuric acid are added to the primary discharge tank to make the phosphogypsum slurry into liquid: solid = 2.5:1, medium density 1.85g / cm 3 , Bulk density 2.67g / cm 3 The slurry is prepared in the feeding tank and a stirring device is set to keep the solids suspended. The slurried phosphogypsum slurry flows into the secondary feeding tank (slurry making tank) through overflow.

[0100] The phosphogypsum slurry in the secondary pulping tank is pumped into the screening machine through a slurry pump for screening and then enters the slurry mixing tank. The coarse particles screened out are crushed and finely ground before entering the secondary pulping tank. 98% sulfuric acid (from the sulfuric acid concentration device) is added to the slurry mixing tank to acidify the phosphogypsum slurry. During the acidification process, trace amounts of hydrogen sulfide, sulfuric acid mist, fluorine-containing gas and other waste gases will be generated. The waste gas is firstly absorbed by 7580℃ 5% lime water in the washing tower to absorb hydrogen sulfide and sulfuric acid mist, and then the fluorine-containing gas is absorbed by low-temperature lime water. The acidified slurry is adjusted to pH value again with sulfuric acid through a dual-channel pipeline mixer and then enters the ionization reaction tank for reaction.

[0101] 2. Reaction defluorination process

[0102] The slurry reacted in the ionization reaction tank first passes through the aeration system to remove hydrogen fluoride, and the hydrogen fluoride is washed in the washing tower in three stages, and the calcium slurry is sprayed and combined with hydrofluoric acid to form calcium fluoride for storage. The slurry passing through the aeration system enters the flow separation system (cyclone, oblique vibration, flow trough, screening equipment) to separate the heavy slag and light slurry. The separated heavy slag returns to the pulping tank, and the separated light slurry enters the filter for filtration and dehydration after ultrafiltration and concentration of most of the water. The water concentrated by ultrafiltration is used as recycled water for phosphate ore pulping. The solid phase after filtration and dehydration enters the ammoniation process, and the liquid phase after filtration and dehydration is sent to the impurity removal and calcium hydroxide recovery system.

[0103] 3. Impurity removal and recycling process

[0104] (1) Aluminum oxide recovery

[0105] The filtrate after filtration and dehydration is concentrated by ultrafiltration and then enters the impurity removal and slurry mixing tank. Magnesium hydroxide suspension is added to the impurity removal and slurry mixing tank for a de-impurity reaction. Aluminum sulfate in the reaction liquid reacts to form aluminum hydroxide. The reacted material is concentrated by ultrafiltration and then dehydrated and filtered (the water recovered after ultrafiltration and concentration is used for magnesium hydroxide slurrying). The filtrate obtained by filtration enters the arsenic removal and impurity removal system. The solid phase obtained by dehydration and filtration is wet aluminum hydroxide. The wet material is dried in a dryer and then enters a calcining kiln for calcination. Alumina is obtained after calcination.

[0106] (2) Arsenic removal and impurity removal

[0107] The filtrate from the alumina recovery section after filtration and dehydration is concentrated by ultrafiltration and then enters the impurity removal and slurry mixing tank (the recycled water concentrated by ultrafiltration is used for phosphogypsum slurrying). Magnesium hydroxide suspension and hydrogen peroxide are added to the impurity removal and slurry mixing tank for secondary impurity removal reaction. Arsenic compounds in the reaction liquid are oxidized to arsenic trioxide. The reacted materials are concentrated by ultrafiltration and then dehydrated and filtered to obtain arsenic trioxide wet material (the recycled water concentrated by ultrafiltration is used to prepare magnesium hydroxide suspension). The wet material is recovered by drying and sublimation to obtain arsenic trioxide.

[0108] (3) Magnesium hydroxide recovery

[0109] The filtrate after filtration and dehydration in the arsenic removal and impurity removal section enters the ionization reaction tank after ultrafiltration concentration. Ammonia gas is introduced into the reaction tank to convert magnesium sulfate in the reaction liquid into magnesium hydroxide and ammonium sulfate. The reacted material is concentrated by ultrafiltration and then dehydrated and filtered. The solid non-magnesium hydroxide wet material obtained by filtration is dried in a dryer to obtain magnesium hydroxide. The filtrate enters the ammonium sulfate ammonia distillation system after ultrafiltration.

[0110] 4. Amination

[0111] The solid phase (mainly calcium sulfate and silicon-containing impurities) filtered and dehydrated from the defluorination process is added with recycled water in a pulping tank with stirring, and then ammonia gas is introduced for pulping. After the pulping is completed, the slurry is adjusted in a double-channel pipeline mixer by adding nitric acid and then enters an ionization reaction tank for reaction. After the reaction, a mixed slurry of calcium hydroxide, calcium sulfate and silicon dioxide is generated. The calcium hydroxide suspension and silicon dioxide heavy solid liquid obtained by separation of the slurry through aeration, fractionation and gravity selection are pumped into the calcium hydroxide recovery process and the silicon dioxide recovery process respectively.

[0112] 5. Silica recovery

[0113] The silica heavy solid liquid from the ammoniation process is dehydrated and filtered to obtain a filtrate which is then concentrated by ultrafiltration and then sent to the ammonium sulfate distillation system (the recycled water produced by ultrafiltration and concentration is returned to the ammoniation pulping water), and the solid wet material obtained by dehydration and filtration is dried in a dryer to obtain silica.

[0114] 6. Calcium hydroxide recovery

[0115] The calcium hydroxide suspension from the ammoniation process is concentrated by ultrafiltration, and the recycled water obtained by concentration is used for ammoniation pulping. The filtrate obtained after dehydration and filtration of the concentrated liquid is sent to the ammonium sulfate ammonia distillation system after ultrafiltration and concentration (the recycled water produced by ultrafiltration and concentration is returned to the water for ammoniation pulping). The solid wet material obtained by dehydration and filtration is dried in a dryer to obtain calcium hydroxide.

[0116] 7. Ammonium sulfate distillation

[0117] The ammonium sulfate solution generated from the recovery of magnesium hydroxide, silicon dioxide and calcium hydroxide is sent to the negative pressure ammonia evaporator for low-temperature ionization, decomposition and evaporation. The low-temperature evaporated ammonia gas and water vapor are washed with chilled water in the washing tower to obtain ammonia water, which is sent to the ammonia water tank for temporary storage. The residual liquid from the ammonia evaporation is sent to the sulfuric acid concentration device and phosphogypsum pulping.

[0118] Consumption of raw materials

[0119] Appendix 4.21 Consumption of raw materials, auxiliary materials and fuel for acid production from phosphogypsum (phosphogypsum 800,000t)

[0120]

[0121] Example 1: Application in a phosphate fertilizer production plant

[0122] In this embodiment, the process of recovering acid from phosphogypsum to produce calcium hydroxide is applied to a large phosphate fertilizer production plant. First, the phosphogypsum is transported to the factory by a transport vehicle and unloaded into a primary discharge tank after being weighed. In the primary discharge tank, recycled water and dilute sulfuric acid are added according to a liquid: solid ratio of 2.5:1, and a stirring device is used to keep the solid suspended to form a medium with a density of 1.85g / cm 3 , bulk density is 2.67g / cm 3 The slurry flows into the secondary discharge tank through overflow for further processing.

[0123] Next, the phosphogypsum slurry in the secondary pulping tank is transported to the screening machine for screening through a slurry pump. The coarse particles screened out are crushed and finely ground before re-entering the secondary pulping tank for recycling. 98% sulfuric acid is added to the slurry mixing tank to acidify the slurry. The waste gas generated during the acidification process is passed through a washing tower to absorb hydrogen sulfide, sulfuric acid mist and fluorine-containing gas with lime water of different concentrations. The acidified slurry is adjusted to a pH value through a dual-channel pipeline mixer and then enters an ionization reaction tank for further reaction.

[0124] In the reactive defluorination process, the slurry in the ionization reaction tank is deionized by the aeration system to remove hydrogen fluoride, and the hydrogen fluoride reacts with the calcium spray slurry and hydrofluoric acid in the three-stage washing tower to generate calcium fluoride for storage. The defluorinated slurry enters the flow separation system to separate the heavy slag from the light slurry. The heavy slag is returned to the pulping tank for recycling, and the light slurry is concentrated by ultrafiltration and filtered and dehydrated. The solid phase enters the ammoniation process, and the liquid phase enters the impurity removal and calcium hydroxide recovery system.

[0125] Finally, the slurry after the impurity removal and recovery process is subjected to an ammoniation reaction to generate calcium hydroxide, calcium sulfate and silicon dioxide. Calcium hydroxide is concentrated by ultrafiltration and dehydrated and filtered to obtain a pure calcium hydroxide product, and silicon dioxide is recovered by drying and sublimation. In this embodiment, the process method effectively realizes the resource utilization of phosphogypsum, reduces environmental pollution, and improves the economic value of the product.

[0126] Example 2: Process verification in a pilot plant

[0127] This example verifies the process of recovering acid from phosphogypsum to produce calcium hydroxide in a pilot plant of environmental protection technology. First, the phosphogypsum raw material is unloaded into the primary feeding tank after being weighed, and recycled water and dilute sulfuric acid are added at a liquid: solid ratio of 2.5:1. An efficient stirring device is set in the feeding tank to ensure the uniformity of the slurry and the suspension of solid particles. The prepared phosphogypsum slurry enters the secondary feeding tank by overflow for preliminary treatment.

[0128] In the secondary pulping tank, the slurry is transported to the screening machine through the slurry pump for coarse screening. The coarse particles screened out are processed by the crusher and fine grinder and then returned to the secondary pulping tank to form a circulation system. High-concentration sulfuric acid is added to the slurry mixing tank for acidification. The waste gas generated during the acidification process is purified by the double scrubber with lime water of different concentrations. After the acidified slurry is adjusted in pH value by the mixer, it enters the ionization reaction tank for chemical reaction.

[0129] In the reaction defluorination process, the slurry in the ionization reaction tank is deionized by the aeration system to remove hydrogen fluoride gas, and the hydrogen fluoride reacts with the calcium spray slurry and hydrofluoric acid in the three-stage washing tower to generate calcium fluoride. The treated slurry enters the flow separation system to separate the heavy slag and light slurry. The heavy slag returns to the pulping tank. After the light slurry is concentrated by ultrafiltration and filtered and dehydrated, the solid phase enters the ammoniation process, and the liquid phase enters the impurity removal and calcium hydroxide recovery system.

[0130] In the impurity removal and recovery process, the filtrate after filtration and dehydration enters the impurity removal slurry tank after ultrafiltration concentration, and magnesium hydroxide suspension is added to carry out impurity removal and chemical reaction to generate aluminum hydroxide. Subsequently, after further ultrafiltration concentration and dehydration filtration, the obtained solid phase material enters the calcining kiln to generate aluminum oxide. At the same time, the filtrate after treatment in the arsenic removal and impurity removal section is converted into magnesium hydroxide and ammonium sulfate through an ionization reaction tank. Finally, the calcium hydroxide and silicon dioxide generated by the ammoniation process are respectively obtained through a special recovery system to obtain pure products. This embodiment proves the feasibility and efficiency of the process method at a pilot scale, laying a foundation for large-scale application.

[0131] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A process for preparing calcium hydroxide from phosphogypsum, comprising the following steps: (1) Phosphogypsum slurry preparation and slurry adjustment: slurry the phosphogypsum raw materials to form a slurry and transport it to the slurry adjustment or secondary slurry preparation process; (2) reactive defluorination: subjecting the slurry to ionization reaction and aeration treatment to separate heavy residue from light slurry, and concentrating and filtering the light slurry to obtain filtrate and filter cake; (3) Impurity removal and recovery: The filtrate is subjected to impurity removal and enters the subsequent recovery system; (4) Ammoniating: contacting the filter cake with ammonia water or ammonia gas to make pulp and adjust the pH value; (5) Silica recovery: separation of the silica-containing solid and liquid produced in the ammoniation process and subsequent drying or concentration; (6) Calcium hydroxide recovery: concentrating the suspension containing calcium hydroxide and performing solid-liquid separation to obtain calcium hydroxide; (7) Distillation of ammonium sulfate: The ammonium sulfate solution produced in the recovery process is subjected to distillation treatment and ammonia gas or ammonia water is recovered.

2. The process according to claim 1, characterized in that: Step (1) includes: Unloading the phosphogypsum raw materials into the primary discharge tank; Add recycled water and dilute sulfuric acid to the first-stage feed tank to form a liquid-solid ratio of about 2.5:1 and a medium density of about 1.85g / cm 3 , Bulk density about 2.67g / cm 3 of slurry; A stirring device is arranged in the first-level feeding tank; The prepared slurry is transported to the secondary discharge tank by overflow.

3. The process according to claim 1, characterized in that: Step (2) includes: The phosphogypsum slurry in the secondary slurry tank is transported to the screening machine for screening by using a slurry pump; The coarse particles screened out are crushed and finely ground and then returned to the secondary pulping tank; About 98% sulfuric acid is added into the slurry mixing tank to acidify the phosphogypsum slurry, and after the pH value is adjusted through a double-channel pipeline mixer, the slurry is transported to the ionization reaction tank for reaction.

4. The process according to claim 1, characterized in that: Step (3) includes: The filtrate after filtration and dehydration is subjected to ultrafiltration and concentration; A magnesium hydroxide suspension is added to the impurity removal slurry mixing tank to perform an impurity removal operation to generate aluminum hydroxide; After ultrafiltration concentration and dehydration filtration, the obtained filtrate is subjected to arsenic removal and impurity removal treatment to generate arsenic trioxide; In the further impurity removal stage, gaseous ammonia is introduced to convert the magnesium salt in the reaction solution into magnesium hydroxide and ammonium sulfate, and the magnesium hydroxide is dehydrated and dried to obtain a solid product, and the filtrate is sent to the ammonium sulfate ammonia distillation system.

5. The process according to claim 1, characterized in that: Step (4) includes: The solid phase obtained by filtering and dehydrating in the defluorination process is mixed with the recycled water in a pulping tank; Ammonia gas is introduced to form an ammoniated slurry; The pH value was adjusted by adding nitric acid in a dual-channel pipeline mixer; The adjusted slurry is sent to an ionization reaction tank for reaction to obtain a mixed slurry containing calcium hydroxide, calcium sulfate and silicon dioxide; The mixed slurry is separated by aeration, flow fractionation and sorting operations to obtain a calcium hydroxide suspension and a silica heavy solid liquid.

6. The process according to claim 1, characterized in that: Step (5) includes: Dehydrating and filtering the silica heavy solid liquid; The filtrate is concentrated by ultrafiltration and then sent to the ammonium sulfate distillation system; The solid wet material obtained by dehydration and filtration is dried to obtain silicon dioxide.

7. The process according to claim 1, characterized in that: Step (6) includes: The calcium hydroxide suspension is ultrafiltered and concentrated, and the recovered water is used for ammoniation pulping; The concentrated calcium hydroxide material is dehydrated and filtered, and the filtrate is concentrated again and then sent to the ammonium sulfate distillation system; The solid wet material obtained by dehydration and filtration is dried to obtain calcium hydroxide.

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