Semi-hydrated wet-process phosphoric acid production system and production method

Abstract

The invention relates to the technical field of phosphorus chemical industry, in particular to a semi-hydrated wet-process phosphoric acid production system and a production method. The semi-hydrated wet-process phosphoric acid production system comprises a production module and a semi-hydrated ardealite purification module arranged at an ardealite discharging position, and the purification module comprises a repulping tank, a flotation device, a gravity separation device, a high-frequency vibrating screen and a filtering device which are sequentially arranged. According to the method, dissociation of phosphoric acid, organic matters and siliceous black slag wrapped in the phosphogypsum is realized by utilizing in-situ phase change and recrystallization during water dissolution of the semi-hydrated phosphogypsum, the organic black slag and the siliceous black slag in the phosphogypsum are removed through flotation and gravity separation, and calcium sulfate dihydrate with high whiteness and high purity is obtained; the method lays a foundation for purifying ardealite recycling, also greatly improves the washing efficiency of residual phosphorus in gypsum, reduces the water consumption of the system, and fundamentally solves the production problem that the water consumption of a semi-water system is not easy to balance.

Description

Technical Field

[0001] The present application relates to the field of phosphorus chemical technology, and in particular to a semi-aqueous wet-process phosphoric acid production system and production method. Background Art

[0002] The wet phosphoric acid production process is mainly an industrial process in which phosphate rock reacts with sulfuric acid to produce phosphoric acid, which can be divided into two-water and half-water processes. The two-water process has become the mainstream process for phosphoric acid production due to its low reaction temperature, infrequent system scaling, and large washing water capacity. However, the disadvantages of the two-water process are also obvious. The initial concentration of the obtained phosphoric acid is low (about 21%), and the cost of later concentration is high. In order to obtain phosphoric acid with a higher concentration in one step, the half-water process came into being. Although the half-water process can obtain phosphoric acid with a higher initial concentration due to the high reaction temperature, phosphogypsum is half-water gypsum (CaSO4·0.5H2O). Half-water gypsum is easy to scale due to hydration, which affects production. More importantly, the half-water system has a limited acceptance of washing water. If the washing is not enough, high phosphorus will remain in the phosphogypsum. Therefore, it is difficult to balance the washing water and production water, resulting in difficulties in production. In order to solve these problems, the half-water + two-water process has emerged in the phosphorus chemical industry. The characteristic of this process is to conduct a two-water reaction on the half-water phosphogypsum in the traditional half-water system. The main purpose is to recover the residual phosphorus in the phosphogypsum. However, with this transformation process, the organic matter and black siliceous impurities in the phosphogypsum are still not eliminated, the morphology of the gypsum is not controlled, and the gypsum is still piled up as a solid waste.

[0003] In view of the above problems in the prior art, the present application provides a semi-aqueous wet-process phosphoric acid production system and production method that fundamentally solves the difficulties in production start-up and purification of phosphogypsum, and can efficiently recover phosphorus. This technology can not only efficiently recover phosphorus but also convert semi-aqueous phosphogypsum into dihydrate gypsum with a purity of more than 90% and a whiteness of more than 80. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems existing in the existing semi-aqueous wet phosphoric acid production technology, and to provide a semi-aqueous wet phosphoric acid production system and production method that fundamentally solves the difficulties in production start-up and purification of phosphogypsum, and can efficiently recover phosphorus. The production system and production method described in the present application fully utilize the water dissolution process of semi-aqueous phosphogypsum, the principle of isotopic dissolution and recrystallization of phosphogypsum, greatly reducing the residual phosphorus in phosphogypsum and washing efficiency, and using less water. The production system and production method described in the present application achieve efficient recovery of phosphorus in phosphogypsum while also solving the problem of difficult balance of water in semi-aqueous system production; in addition, the entire process performs decolorization, desiliconization and other purification treatments on the phosphogypsum, and finally obtains dihydrate gypsum with high whiteness and high purity, reducing the cost of resource utilization of phosphogypsum.

[0005] In a first aspect, the present application provides a semi-aqueous wet-process phosphoric acid production system, which includes a semi-aqueous wet-process phosphoric acid production module and a semi-aqueous phosphogypsum purification module arranged at the gypsum unloading place of the semi-aqueous wet-process phosphoric acid production module, wherein the semi-aqueous phosphogypsum purification module includes a re-slurry tank, a flotation device, a gravity separation device, a high-frequency vibrating screen and a filtering device arranged in sequence.

[0006] Among them, the re-slurry tank is used to realize the process of isotopic dissolution and recrystallization of the rapid hydration of hemihydrate phosphogypsum to form dihydrate gypsum. During the isotopic dissolution and recrystallization, the phosphogypsum is dissociated, and the phosphoric acid, organic matter and siliceous black slag contained in the original hemihydrate phosphogypsum are separated instantly, the phosphoric acid is transferred to the liquid phase, and the organic matter is captured by the flotation capture agent added in advance and removed from the top of the flotation device. The separated siliceous black slag and the dissociated dihydrate gypsum remain in the flotation device. The bottom flow of the flotation device enters the gravity separation device again. The different specific gravity of dihydrate gypsum and siliceous black slag are used to separate the siliceous black slag in a physically separated state from the dihydrate gypsum through a gravity separation device (such as a cyclone separator), and the siliceous black slag is separated at the bottom of the gravity separation device. The upstream containing dihydrate gypsum is filtered through a high-frequency vibrating screen and a filtering device to obtain purified dihydrate gypsum with high whiteness and good purity. The filtrate of the filtering device is used as return water in this system for recycling.

[0007] In one embodiment, the reslurry tank is provided with a stirring and feeding device; the volume of the reslurry tank is ≤5m 3 , 2 or more reslurry tanks can be connected in parallel, such as 2-10, 2-5 reslurry tanks. The feeding device is used to add water, hydration aid and flotation capture agent to the reslurry tank.

[0008] In one set of embodiments, the bottom of the flotation device is connected to the gravity separation device to introduce the underflow into the gravity separation device; two or more flotation devices can be used in series, such as 2-5 flotation devices, the underflow of the previous flotation device enters the next flotation device for flotation, and the bottom of the last flotation device is connected to the gravity separation device. The flotation device is preferably a flotation column or a flotation machine.

[0009] In one embodiment, the gravity separation device is preferably a cyclone separator, which can more effectively separate the siliceous black slag and dihydrate gypsum with different densities. The upper part of the cyclone separator is connected to a high-frequency vibrating screen, and the lower part of the high-frequency vibrating screen is connected to the first filtering device. The high-frequency vibrating screen can control the particle size distribution of dihydrate gypsum. The mesh number of the high-frequency vibrating screen is ≥100 mesh, such as 200-400 mesh. The filtrate of the first filtering device is used as return water in this system.

[0010] In one embodiment, a second filtering device is further included for filtering the top flow of the flotation device, the bottom flow of the gravity separation device, and the material on the high-frequency vibration screen. The filtrate of the second filtering device is circulated in the system as return water.

[0011] In one set of embodiments, as required, a dehydration and / or drying and calcining device may be provided after the first filtering device to process and purify the gypsum product required for the production of dihydrate gypsum.

[0012] In one embodiment, the first and second filter devices (including the first and second filter devices) are preferably plate-frame filter presses or belt filters. Preferably, a concentrate tank is provided in front of the first filter device, and a buffer tank is provided in front of the second filter device.

[0013] In one embodiment, a membrane treatment device is further provided after the first and second filtering devices; used for filtrate concentration. The filtrates of all filtering devices are recycled as return water in the purification module (such as recycled to the re-slurry tank). When the P2O5 content in the filtrate is greater than 0.3%, the filtrate stops recycling. After membrane concentration, the obtained concentrated liquid enters the semi-aqueous wet phosphoric acid production module as recycled phosphorus water, and the clear liquid is recycled to the semi-aqueous phosphogypsum purification module for recycling (such as recycled to the washing water of the first filtering device).

[0014] In one set of embodiments, the semi-aqueous wet-process phosphoric acid production module includes a dissolution tank, a decomposition tank, a crystallization tank and a filtration device arranged in sequence.

[0015] Among them, phosphate rock and phosphorus water recycled from the purification system are mixed and slurried in a dissolution tank, and then sulfuric acid is added to a temperature-controlled decomposition tank to control the temperature. The phosphate rock reacts with sulfuric acid to produce phosphoric acid and hemihydrate phosphogypsum at the same time. The excess sulfuric acid is controlled in the crystallization tank to make the hemihydrate phosphogypsum crystals grow. Finally, the phosphoric acid solution and hemihydrate phosphogypsum are separated in the filtration device of the production module.

[0016] In a second aspect, the present application provides a method for producing semi-aqueous wet-process phosphoric acid, using the semi-aqueous wet-process phosphoric acid production system described in the present application, which comprises:

[0017] 1) Production: obtaining phosphoric acid solution and semi-hydrated phosphogypsum through a semi-aqueous wet phosphoric acid production module;

[0018] 2) Reslurry hydration: The semi-hydrated phosphogypsum is introduced into the reslurry tank, water, hydration aid and flotation capture agent are added into the reslurry tank, the semi-hydrated phosphogypsum undergoes isotopic dissolution and recrystallization in the reslurry tank, the intercrystalline phosphorus, organic matter and siliceous black slag in the phosphogypsum are dissociated, the organic matter is captured by the flotation capture agent, and the semi-hydrated phosphogypsum is converted into dihydrate gypsum;

[0019] 3) Flotation: The mixture in the reslurry tank is introduced into the flotation device, and the flotation capture agent is added again to remove the black slag foam containing organic matter at the top of the flotation device;

[0020] 4) Sorting: The bottom flow containing dihydrate gypsum and siliceous black slag in the flotation device is introduced into the gravity sorting device. By utilizing the density difference between the siliceous black slag and dihydrate gypsum, the bottom flow containing the siliceous black slag is removed at the bottom, and the top flow containing the dihydrate gypsum is introduced into the high-frequency vibrating screen;

[0021] 5) Filtration: The undersize solution containing dihydrate gypsum after passing through the high-frequency vibration screen is introduced into the first filtering device to obtain purified dihydrate gypsum, and the filtrate is circulated in the system as return water.

[0022] In one embodiment, in step 2), the re-slurry tank quickly receives hemihydrate phosphogypsum to form a 10-50 wt% slurry solution, preferably a 20-40 wt% slurry solution. The slurry is rapidly dissolved and recrystallized in situ under the action of the hydration aid.

[0023] In one set of embodiments, in step 2), the hydration aid is selected from one or more of sulfuric acid, nitric acid or formic acid; and the amount thereof is 0.5%-10%, preferably 1-5%, of the weight of the anhydrous gypsum.

[0024] In one set of embodiments, in step 2-3), the flotation capture agent comprises xanthate, alcohols and surfactants; preferably, the flotation capture agent comprises the following components in mass ratio: xanthate 5-35%, surfactant 30-90%, alcohol 5-35%; more preferably, the flotation capture agent comprises the following components in mass ratio: xanthate 10-20%, surfactant 60-80%, alcohol 10-20%. The xanthate, i.e., xanthate, can be selected from one or both of sodium ethyl xanthate or sodium butyl xanthate, the surfactant is selected from a mixture of sodium fatty alcohol polyoxyethylene ether sulfate (AES) and sodium dodecyl sulfate (SDS), the AES:SDS (mass ratio) is preferably 1:1-5, more preferably 1:2-1:3, and the alcohol is selected from isopropanol or n-butanol. The amount of the flotation capture agent is 0.01-0.5, preferably 0.02-0.2, more preferably 0.05-0.1% of the weight of anhydrous gypsum. The weight ratio of the flotation capture agent in step 2) to that in step 3) is 1:4-1, preferably 1.5-3:1.

[0025] In one set of embodiments, two or more flotation devices are used in series, such as 2-5 flotation devices are used in series. Preferably, the flotation capture agent is added to the first flotation device, or the flotation capture agent is added to the underflow of the first flotation device.

[0026] In one embodiment, as required, the dihydrate gypsum obtained by the first filtering device is treated by a dehydration and / or drying and calcining device to obtain purified dihydrate gypsum. The obtained dihydrate gypsum can be used as a filling material for papermaking or plastics.

[0027] In one set of embodiments, the top flow of the flotation device, the bottom flow of the gravity separation device and the high-frequency vibration screen are introduced into the second filtering device, and black slag is obtained after dehydration, and the filtrate is circulated in this system as return water. Preferably, the undersize of the high-frequency vibration screen is introduced into the concentrate tank for storage, and then introduced into the first filtering device (preferably introduced by a pump); the top flow of the flotation device, the bottom flow of the gravity separation device and the high-frequency vibration screen are introduced into the buffer tank, and then introduced into the second filtering device.

[0028] In one set of embodiments, the filtrates of the first and second filtering devices are first collected and recycled in the purification module. When the P2O5 content in the filtrate is greater than 0.3%, the filtrate stops recycling. After membrane concentration, the concentrated liquid enters the semi-aqueous wet-process phosphoric acid production module, and the clear liquid is recycled to the semi-aqueous phosphogypsum purification module for recycling. Preferably, the filtrates of the first and second filtering devices are first collected and recycled to the re-slurry tank. When the P2O5 content in the filtrate is greater than 0.3%, the filtrate stops recycling. After membrane concentration, the concentrated liquid enters the phosphoric acid system as recycled phosphorus water, and the clear liquid is recycled to the first filtering device as washing water.

[0029] In one set of embodiments, step 1) specifically includes mixing and dissolving phosphate ore and phosphorus water recycled from a purification system in a dissolution tank, and then controlling the temperature in a decomposition tank to add sulfuric acid to decompose the phosphate ore. While the phosphate ore reacts with sulfuric acid to produce phosphoric acid, stable calcium sulfate hemihydrate crystals are formed, which are then introduced into a crystallization tank. The amount of sulfuric acid and the temperature in the crystallization tank are controlled to allow hemihydrate phosphogypsum to crystallize and grow, and finally a filtration device is used to separate the phosphoric acid solution and the hemihydrate phosphogypsum.

[0030] In a third aspect, the present application provides a purified dihydrate gypsum prepared using the semi-aqueous wet phosphoric acid production system or production method described in the present application.

[0031] In a fourth aspect, the present application provides an application of purified dihydrate gypsum prepared using the semi-aqueous wet phosphoric acid production system or production method described in the present application, which can be used as papermaking and plastic filling materials after dehydration, drying and calcination.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The semi-aqueous wet-process phosphoric acid production system and production method described in the present application rapidly dissolves and recrystallizes the semi-aqueous phosphogypsum produced by the production module in a re-slurry tank, and utilizes the characteristics of isotopic dissolution and recrystallization to release the phosphorus, siliceous black slag and organic matter remaining in the phosphogypsum during the rapid dissolution and recrystallization process. In the flotation device, the organic black slag is promptly removed from the gypsum purification system using the flotation capture agent added in advance, thereby achieving a decolorization effect; at the same time, the siliceous black slag and the hydrated dihydrate gypsum are converted from the previous wrapped state to a separated state. Due to the large difference in density between the two, the siliceous black slag and the pure dihydrate gypsum can be separated under the action of a gravity sorting device and a high-frequency vibrating screen. The purified gypsum can be used as a raw material for gypsum products, providing a guarantee for the resource utilization of phosphogypsum.

[0034] (2) Through research, the present applicant has found that due to the efficient dissociation of hemihydrate phosphogypsum, the residual lattice phosphorus in the gypsum can be well released. The present system and method do not require a large amount of washing water to remove the residual phosphorus in the hemihydrate phosphogypsum. In addition, the filtered water of the semi-hydrated phosphogypsum treatment system can be recycled and used. It is suitable for the current semi-hydrated wet system and solves the problem of the traditional semi-hydrated system that the residual phosphorus in the washing phosphogypsum is difficult to balance the system water.

[0035] (3) The semi-hydrated phosphogypsum purification module of the present application adds a hydration aid in the re-slurry tank and adds a flotation capture agent in two stages in the re-slurry tank and the flotation device, which can better separate organic matter and siliceous black slag and improve the purity and whiteness of the dihydrate gypsum.

[0036] (4) The purified hemihydrate phosphogypsum produced as a by-product of the present application has a whiteness (dried at 120°C) greater than 80, a CaSO4·2H2O content greater than 92%, and an average particle size greater than 600 meshes. The product can be used as a filling material for papermaking and plastics after dehydration and / or drying and calcination. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of a traditional semi-aqueous wet process phosphoric acid production system.

[0038] Figure 2 It is a schematic diagram of a specific implementation of the semi-aqueous wet-process phosphoric acid production system described in the present application. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0040] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] The terms "and / or", "or / and", and "and / or" used in this article include any one of two or more related listed items, and also include any and all combinations of related listed items, and the arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that in this application, the technical solution undoubtedly includes technical solutions that are all connected by "logical and", and undoubtedly includes technical solutions that are all connected by "logical or". For example, "A and / or B" includes three parallel solutions of A, B and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, the technical solution that is all connected by "logical OR"), and also includes any and all combinations of A, B, C, and D, that is, the combination of any two or any three of A, B, C, and D, and also includes the combination of four of A, B, C, and D (that is, the technical solution that is all connected by "logical AND").

[0042] As used in this application, the terms "comprising," "including," and "comprising" are synonymous and are inclusive or open-ended and do not exclude additional, unrecited members, elements, or method steps.

[0043]

[0013] The use of numerical ranges as endpoints herein includes all numbers and fractions subsumed within that range, as well as the recited endpoints.

[0044] The concentration values ​​involved in this application include fluctuations within a certain range. For example, fluctuations can be allowed within a corresponding accuracy range. For example, 2% can allow fluctuations within ±0.1%. For values ​​that are large or do not require too fine control, their meanings are also allowed to include greater fluctuations. For example, 100mM can allow fluctuations within the range of ±1%, ±2%, ±5%, etc.

[0045] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0046] In this application, "preferred", "better", "more preferred", and "suitable" are only used to describe implementation methods or examples with better effects. It should be understood that they do not constitute a limitation on the scope of protection of this application. In this application, "optionally", "optional", and "optional" refer to being optional, that is, any one of the two parallel schemes of "yes" or "no". If multiple "optional" items appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" item is independent of each other.

[0047] Figure 1 A traditional semi-aqueous wet phosphoric acid production system is shown. The phosphoric acid production module includes a dissolving tank, a decomposition tank, a crystallization tank and a filtering device in sequence. The phosphate ore is mixed and dissolved in the dissolving tank. Then, in the decomposition tank, sulfuric acid is added to control the temperature to decompose the phosphate ore. While the phosphate ore reacts with sulfuric acid to produce phosphoric acid, stable semi-hydrated calcium sulfate crystals are formed. Then, the crystallization tank is introduced. The amount of sulfuric acid and the temperature are controlled in the crystallization tank to make the semi-hydrated phosphogypsum crystals grow. Finally, a filtering device is used to separate the phosphoric acid solution and the semi-hydrated phosphogypsum. In order to fully wash and remove the residual phosphorus in the semi-hydrated phosphogypsum, a large amount of water is required for washing. However, the semi-hydrated wet phosphoric acid production module requires limited water, and can only accept part of the washing water for reuse in the dissolving tank, and the water cannot be balanced. It is not easy to balance the semi-hydrated phosphogypsum washing water and production water, which is the main reason why the traditional semi-hydrated wet phosphoric acid system is difficult to start.

[0048] In order to overcome the problems existing in the traditional semi-aqueous wet-process phosphoric acid production, the present application provides a semi-aqueous wet-process phosphoric acid production system and production method that fundamentally solves the difficulties in production start-up and purification of phosphogypsum, and can efficiently recover residual phosphorus in gypsum.

[0049] Figure 2 A specific embodiment of the semi-aqueous wet-process phosphoric acid production system described in the present application is shown, which includes a semi-aqueous wet-process phosphoric acid production module and a semi-aqueous phosphogypsum purification module.

[0050] The phosphoric acid production module includes a dissolution tank, a decomposition tank, a crystallization tank and a filtering device in sequence. The phosphate rock and the phosphorus water recycled from the purification system are mixed and dissolved in the dissolution tank. Then, in the decomposition tank, sulfuric acid is added to control the temperature to decompose the phosphate rock. While the phosphate rock reacts with sulfuric acid to produce phosphoric acid, stable hemihydrate calcium sulfate crystals are formed. The crystallization tank is then introduced, and the amount of sulfuric acid and the temperature are controlled in the crystallization tank to allow the hemihydrate phosphogypsum to crystallize and grow. Finally, a filtering device is used to separate the phosphoric acid solution and the hemihydrate phosphogypsum.

[0051] The phosphogypsum purification module includes a re-slurry tank, a flotation device, a gravity separation device, a high-frequency vibrating screen, a first and a second filtering device, which are arranged in sequence, and a membrane treatment device is also arranged after the filtering device.

[0052] Among them, the semi-hydrated phosphogypsum purification module is set at the semi-hydrated phosphogypsum unloading place of the production module. The semi-hydrated phosphogypsum is introduced into the re-slurry tank with a stirring device, and water, hydration aid and a part of flotation capture agent are added. Under the action of the hydration aid, the semi-hydrated phosphogypsum quickly undergoes isotopic dissolution and recrystallization. During the dissolution-recrystallization process, the intercrystalline residual phosphorus, organic matter and siliceous black slag in the phosphogypsum will be dissociated, and the semi-hydrated gypsum will complete the transformation into dihydrate gypsum. The residual phosphorus released in the phosphogypsum is transferred to the liquid phase in the form of phosphoric acid, and the organic matter is captured by the flotation capture agent added in advance. A flotation capture agent is further added to the flotation device, and the captured organic matter is removed from the system as upstream black slag, and the bottom flow containing dihydrate gypsum and siliceous black slag enters the gravity separation device (preferably a cyclone separator) again. After being released, the siliceous black slag and the dihydrate gypsum form a state of physical separation from the previous mutual wrapping. The density difference between the siliceous black slag and the dihydrate gypsum is utilized to separate the siliceous black slag at the bottom of the gravity separation device, and the upstream of the gravity separation device passes through a high-frequency vibrating screen, and the screened material passes through the first filtering device to obtain purified dihydrate gypsum with high whiteness and good purity. The upstream black slag on the top of the flotation device, the bottom siliceous black slag of the gravity separation device and the material on the high-frequency vibration screen are separated from the slag and water by the second filtering device. The filtrates of all the filtering devices are collected together and first circulated in the purification module. When the P2O5 content in the filtrate is greater than 0.3%, the filtrate stops circulating. After membrane concentration, the concentrated liquid enters the semi-aqueous wet process; phosphoric acid production module, and the clear liquid is recycled to the semi-aqueous phosphogypsum purification module for circulation.

[0053] Example 1

[0054] After the semi-hydrated phosphogypsum of the production module is discharged from the belt filter, it quickly enters the re-slurry tank under stirring conditions, and water is added to prepare a gypsum solution with a solid content of 30%. At the same time, sulfuric acid (1% relative to the amount of anhydrous gypsum) and 300 g / ton (relative to the weight of anhydrous gypsum) of flotation collector (xanthate 10%, AES 20%: SDS 60%: isopropanol 10%) are added respectively. The gypsum slurry is pumped into the primary flotation column, and the flotation collector is added again in the primary flotation column, and the amount is 200 g / ton (relative to the weight of anhydrous gypsum). Under the action of the flotation capture agent, the organic matter at the top of the flotation column overflows the flotation column in the form of foam and enters the filter press buffer tank, and finally achieves solid-liquid separation through plate and frame filter press; the bottom flow of the primary flotation column enters the secondary flotation column, and the flotation capture agent foam carries the dissociated organic matter and further overflows at the top of the flotation column. The bottom flow solution is desiliconized by the cyclone separator, and the bottom flow silicon slag enters the filter press buffer tank. After the top flow of the cyclone separator passes through a 200-mesh high-frequency vibrating screen, the underscreen solution enters the concentrate tank for storage and then enters the filter press through a pump. After filtration, purified dihydrate gypsum is obtained. The material on the high-frequency vibrating screen enters the filter press buffer tank, and finally passes through a filter press to complete the separation together with the top flow foam of the flotation column and the bottom flow silicon slag of the cyclone separator. The concentrate filter press and black slag filter press solutions are collected and then enter the re-slurry tank for recycling. When the P2O5 content in the circulating filtrate is greater than 0.3%, the filtrate stops recycling. After membrane concentration, the concentrated liquid enters the semi-aqueous wet phosphoric acid production module, and the clear liquid is reused as gypsum washing water for the concentrate filter press.

[0055]

[0056] Example 2

[0057] After the semi-hydrated phosphogypsum of the production module is discharged from the belt filter, it quickly enters the re-slurry tank under stirring conditions, and water is added to prepare a gypsum solution with a solid content of 40%. At the same time, 1.5% of concentrated sulfuric acid relative to the amount of anhydrous gypsum and 400 g / ton (relative to the weight of anhydrous gypsum) of flotation capture agent (xanthate 20%, AES 15%: SDS 45%: n-butanol 20%) are added respectively. The gypsum slurry is pumped into the primary flotation machine (scraper type). Under the action of the flotation capture agent, the organic matter in the top flow of the flotation machine is scraped out of the flotation machine in the form of foam and enters the filter press. The buffer tank is used, and finally the solid-liquid separation is achieved through plate and frame filter pressing; the flotation capture agent is added again at the outlet of the first-stage flotation machine, and the dosage is 150 g / ton (relative to the weight of anhydrous gypsum). The bottom flow of the first-stage flotation column enters the second-stage flotation machine, and the flotation capture agent foam carrying the dissociated organic matter is further scraped out at the top of the flotation machine. The bottom flow solution passes through the cyclone separator for desiliconization, and the bottom flow silicon slag enters the filter press buffer tank. After the top flow of the cyclone separator passes through a 200-mesh high-frequency vibrating screen, the underscreen solution enters the concentrate tank for storage and then enters the filter press through a pump. After filtration, purified dihydrate gypsum is obtained. The material on the high-frequency vibrating screen enters the filter press buffer tank, and finally passes through a filter press to complete the separation together with the top flow foam of the flotation machine and the bottom flow silicon slag of the cyclone separator. The concentrate filter press and black slag filter press solutions are collected and then enter the re-slurry tank for recycling. When the P2O5 content in the circulating filtrate is greater than 0.3%, the filtrate stops recycling. After membrane concentration, the concentrated liquid enters the semi-aqueous wet phosphoric acid production module, and the clear liquid is reused as gypsum washing water for the concentrate filter press.

[0058]

[0059] In the description of this specification, the description with reference to the terms "a specific embodiment", "a set of embodiments", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0060] The protection scope of the present application is not limited to the above-mentioned embodiments. Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the scope and spirit of the present invention. If these changes and modifications fall within the scope of the claims of the present application and their equivalents, the intention of the present application also includes these changes and modifications.

Claims

1. A semi-aqueous wet-process phosphoric acid production system, characterized in that: It includes a semi-aqueous wet phosphoric acid production module and a semi-aqueous phosphogypsum purification module arranged at the gypsum unloading place of the semi-aqueous wet phosphoric acid production module, wherein the semi-aqueous phosphogypsum purification module includes a re-slurry tank, a flotation device, a gravity separation device, a high-frequency vibrating screen and a filtering device which are arranged in sequence.

2. The semi-aqueous wet-process phosphoric acid production system according to claim 1, characterized in that: The reslurry tank is provided with stirring and feeding devices; preferably, two or more reslurry tanks are connected in parallel.

3. The semi-aqueous wet-process phosphoric acid production system according to claim 1 or 2, characterized in that: The bottom of the flotation device is connected to a gravity separation device to introduce the underflow into the gravity separation device; preferably, two or more flotation devices are used in series, the underflow of the previous flotation device enters the next flotation device for flotation, and the bottom of the last flotation device is connected to the gravity separation device.

4. The semi-aqueous wet-process phosphoric acid production system according to any one of claims 1 to 3, characterized in that: The gravity separation device is a cyclone separator, the upper part of the cyclone separator is connected to a high-frequency vibration screen, and the lower part of the high-frequency vibration screen is connected to the first filtering device; preferably, the aperture of the high-frequency vibration screen is ≥100 meshes.

5. The semi-aqueous wet-process phosphoric acid production system according to any one of claims 1 to 4, characterized in that: The invention also comprises a second filtering device which can be used for filtering the top flow of the flotation device, the bottom flow of the gravity separation device and the material on the high-frequency vibration screen.

6. The semi-aqueous wet-process phosphoric acid production system according to any one of claims 1 to 5, characterized in that: A dehydration and / or drying calcination device is also provided after the first filtering device.

7. The semi-aqueous wet-process phosphoric acid production system according to any one of claims 4 to 6, characterized in that: The first and second filtering devices are plate-and-frame filter presses or belt filters.

8. The semi-aqueous wet-process phosphoric acid production system according to any one of claims 4 to 7, characterized in that: A membrane treatment device is also provided after the first and second filtering devices; the filtrate of all filtering devices is circulated in the purification module as return water. When the P2O5 concentration in the filtrate is greater than 0.3%, the filtrate stops circulating and is concentrated by the membrane. The concentrated liquid enters the semi-aqueous wet phosphoric acid production module, and the clear liquid is recycled to the semi-aqueous phosphogypsum purification module for circulation.

9. A method for producing semi-aqueous wet-process phosphoric acid, characterized in that: The semi-aqueous wet-process phosphoric acid production system according to any one of claims 1 to 8 comprises the following steps: 1) Production: A phosphoric acid solution and semi-hydrated phosphogypsum are obtained through a semi-aqueous wet phosphoric acid production module; 2) Reslurry hydration: The semi-hydrated phosphogypsum is introduced into the reslurry tank, water, hydration aid and flotation capture agent are added into the reslurry tank, the semi-hydrated phosphogypsum undergoes isotopic dissolution and recrystallization in the reslurry tank, the intercrystalline phosphorus, organic matter and siliceous black slag in the semi-hydrated phosphogypsum are dissociated, the organic matter is captured by the flotation capture agent, and the semi-hydrated phosphogypsum is converted into dihydrate gypsum; 3) Flotation: The mixture in the reslurry tank is pumped into the flotation device, and the flotation capture agent is added again, and the black slag foam containing organic matter is removed from the top of the flotation device; 4) Sorting: The bottom flow containing dihydrate gypsum and siliceous black slag in the flotation device is introduced into the gravity sorting device. The bottom flow containing siliceous black slag is removed at the bottom by utilizing the density difference between the siliceous black slag and dihydrate gypsum, and the top flow solution containing dihydrate gypsum is introduced into the high-frequency vibrating screen; 5) Filtration: The undersize solution containing dihydrate gypsum after passing through the high-frequency vibration screen is introduced into the first filtering device, filtered to obtain purified dihydrate gypsum, and the filtrate is circulated in the system as return water.

10. The method for producing semi-aqueous wet-process phosphoric acid according to claim 9, characterized in that: In step 2), the re-slurry tank quickly receives the hemihydrate phosphogypsum to form a slurry solution of 10-50 wt%, and the slurry is rapidly dissolved and recrystallized in situ under the action of the hydration aid.

11. The method for producing semi-aqueous wet-process phosphoric acid according to claim 9 or 10, characterized in that: In step 2), the hydration aid is selected from one or more of sulfuric acid, nitric acid or formic acid; preferably, the amount thereof is 0.5%-10% of the weight of the anhydrous gypsum.

12. The method for producing semi-aqueous wet-process phosphoric acid according to any one of claims 9 to 11, characterized in that: In step 2-3), the flotation capture agent comprises xanthate, alcohols and surfactants; preferably, the flotation capture agent comprises the following components in mass ratios: 5-35% xanthate, 30-90% surfactant, and 5-35% alcohols.

13. The method for producing semi-aqueous wet-process phosphoric acid according to claim 12, characterized in that: The xanthate is selected from one or both of sodium ethyl xanthate and sodium butyl xanthate, the surfactant is selected from a mixture of sodium fatty alcohol polyoxyethylene ether sulfate (AES) and sodium dodecyl sulfate (SDS), and the alcohol is selected from isopropanol or n-butanol.

14. The method for producing semi-aqueous wet-process phosphoric acid according to claim 12 or 13, characterized in that: The amount of the flotation capture agent used is 0.01%-0.5% of the weight of the anhydrous gypsum, and the weight ratio of the flotation capture agent in step 2) to that in step 3) is 1:4-1.

15. The method for producing semi-aqueous wet-process phosphoric acid according to any one of claims 9 to 14, characterized in that: Two or more flotation devices are used in series, preferably, a flotation capture agent is added to the first flotation device, or a flotation capture agent is added to the underflow of the first flotation device.

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