Method for purifying and preparing phosphoric acid by wet process

Abstract

A wet phosphoric acid purification and preparation method, comprising the following steps: extraction: removing impurity ions in the phosphoric acid solution by using selective solubility of extractant; fine desulfurization: the extraction phase obtained from the extraction section is subjected to fine desulfurization treatment, and sulfate in the extraction phase is completely removed; the extraction phase containing suspended matter generated by the fine desulfurization is subjected to separation of the acid solution and the extraction phase by a second phase separator; washing: the extraction phase separated by the second phase separator enters a washing section; back extraction: the organic phase obtained after the washing sequentially enters secondary back extraction and tertiary back extraction for further recovery of phosphoric acid, the back extraction liquid of the secondary back extraction is back extraction acid generated by the tertiary back extraction; the raffinate phase, washing acid and back extraction acid are subjected to phase separation to recover the organic solvent and reuse to the extraction section. The present application realizes efficient preparation of phosphoric acid by combining phase separation technology and extraction technology.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wet-process phosphoric acid, and particularly relates to a wet-process phosphoric acid purification and preparation method. BACKGROUND

[0002] There are two main methods for producing phosphoric acid: wet-process and thermal process. The wet-process uses inorganic acid to decompose phosphate rock to produce phosphoric acid. Due to the characteristics of raw materials and processes, the wet-process phosphoric acid contains a large amount of impurities. The main process route of the wet-process phosphoric acid is as follows: acidolysis -> filtration -> pre-desulfurization -> defluorination -> dearsenication -> filtration -> extraction -> refined desulfurization / arsenic removal -> washing -> back extraction -> concentration -> decolorization -> rectification -> bleaching -> refined phosphoric acid. The "pre-desulfurization -> defluorination -> dearsenication" is the pretreatment section of the phosphoric acid refining; the "filtration -> extraction -> refined desulfurization / arsenic removal -> washing -> back extraction" is the purification section of the phosphoric acid refining; and the "decolorization -> rectification -> bleaching" is the post-treatment section of the phosphoric acid refining.

[0003] Current problems in the preparation of phosphoric acid include:

[0004] 1. The phosphoric acid refining is limited by the insufficient filtration accuracy of the phosphoric acid, which causes part of the suspended solids in the phosphoric acid to enter the extraction section, resulting in a low extraction efficiency of the phosphoric acid and a low quality of the prepared phosphoric acid.

[0005] 2. The separation accuracy of the extractant and the raffinate in the extraction phase is low, and the raffinate phase is directly discharged in the prior art, resulting in a large amount of extractant loss and a high production cost of the traditional method. SUMMARY

[0006] In view of the above technical problems, the present application aims to provide a wet-process phosphoric acid purification and preparation method. By combining the phase separation technology and the extraction technology, on the one hand, the recovery rate of the extractant in the raffinate phase in the extraction section and the recovery rate of the organic phase in the back extraction section are improved, the loss of the extractant in the whole process and the pollution of the extractant to the environment are reduced, and the production cost of the phosphoric acid preparation is reduced; on the other hand, the purity of the extraction phase entering the back extraction section is improved, and the back extraction efficiency is improved.

[0007] In order to achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0008] According to one aspect of the present application, a wet-process phosphoric acid purification method is provided, which comprises the following steps:

[0009] Extraction: impurity ions in the phosphoric acid solution are removed by using the selective solubility of the extractant. The raffinate phase obtained in the extraction section is separated into the extractant and the raffinate acid by the first phase separator. The recovered extractant is returned to the extraction section to continue participating in the extraction reaction, and the obtained raffinate acid is used for phosphate fertilizer.

[0010] Fine desulfurization: the extraction phase obtained from the extraction section is subjected to fine desulfurization treatment to completely remove sulfate in the extraction phase, and the extraction phase containing suspended solids generated by fine desulfurization is subjected to separation of acidic solution and extraction phase by a second phase separator;

[0011] Washing: the extraction phase separated by the second phase separator enters the washing section, and the washing acid obtained after washing is subjected to recovery of organic solvents in the washing acid by a third phase separator and reuse to the extraction section;

[0012] Stripping: the organic phase obtained after washing enters the second stripping and the third stripping in sequence for further recovery of phosphoric acid, the stripping solution of the second stripping is the stripping acid generated by the third stripping, the stripping solution of the third stripping is desalted water, the organic solvent generated by the third stripping is reused to the extraction section, and the stripping acid generated by the second stripping is subjected to recovery of organic solvents in the stripping acid by a fourth phase separator and reuse to the extraction section.

[0013] In some technical solutions, the first phase separator and the second phase separator adopt a loose fiber bed + special plate group type phase separator; and the third phase separator and the fourth phase separator adopt a dense fiber bed type phase separator.

[0014] In some technical solutions, the material treated by each step of the phase separator contains a dispersed phase of less than one ten-thousandth in the main phase, and the main phase of less than one ten-thousandth in the dispersed phase.

[0015] In some technical solutions, the acid phase separated by the second phase separator is subjected to complete removal of suspended solids in the acid phase by a third membrane filtration, and the filtrate of the third membrane filtration enters the extraction section and the concentrated solution is subjected to recovery of barium sulfate.

[0016] In some technical solutions, the method further comprises the following steps:

[0017] Pretreatment: a purification agent is added to the crude phosphoric acid for pretreatment of desulfurization, defluorination and dearsenication, and the acid solution is subjected to complete interception of suspended solids and solid particles by a second membrane filtration, and the pretreated phosphoric acid obtained enters the extraction section.

[0018] In some technical solutions, the second membrane filtration and the third membrane filtration adopt an ultrafiltration membrane.

[0019] The material of the ultrafiltration membrane is one or a combination of several of PTFE, PVDF, PS, silicon carbide, zirconium oxide and aluminum oxide corrosion-resistant materials; and / or,

[0020] The filtration precision of the ultrafiltration membrane is between 10 nm and 1000 nm; and / or,

[0021] The operating temperature of the ultrafiltration membrane is 20-70°C, the operating pressure is 0.1-0.8 MPa, and the operating membrane surface flow rate is 2-6 m / s; and / or,

[0022] The clear liquid turbidity of the filtrate of the ultrafiltration membrane is less than 1 NTU.

[0023] According to another aspect of the present application, a method for preparing wet-process phosphoric acid is further provided, comprising the following steps:

[0024] acidolysis: decomposing phosphate rock by using organic acid to obtain acidolysis solution, and then removing phosphogypsum by the first membrane filtration to obtain crude phosphoric acid; and

[0025] The specific steps involved in the wet-process phosphoric acid purification method are as described above.

[0026] In some technical solutions, the method further comprises the following steps:

[0027] concentration: inputting the washed acid and the back-extracted acid after the second back-extraction into a concentration section to perform evaporation concentration.

[0028] In some technical solutions, the method further comprises the following steps:

[0029] post-treatment: inputting the concentrated purified phosphoric acid into a post-treatment section, and then sequentially performing decolorization, fourth membrane filtration, rectification and bleaching treatment to obtain refined phosphoric acid.

[0030] In some technical solutions, the third membrane filtration and the fourth membrane filtration adopt ultrafiltration membranes, the filtration precision of the ultrafiltration membranes is between 10 nm and 1000 nm, and the clear liquid turbidity of the filtrate is less than 1 NTU.

[0031] The present application has at least the following beneficial effects by adopting the above technical solutions:

[0032] 1. The present application provides a wet-process phosphoric acid purification and preparation method, which combines extraction technology with phase separation technology, on the one hand, can improve the recovery rate of the extractant in the extraction section and the recovery rate of the organic phase in the back-extraction acid in the back-extraction section, reduces the loss of the extractant and the environmental pollution caused by the extractant in the whole process, and reduces the production cost of phosphoric acid preparation; on the other hand, improves the purity of the extraction phase entering the back-extraction section, and further improves the back-extraction efficiency.

[0033] 2. The present application provides a wet-process phosphoric acid purification and preparation method, the first phase separator and the second phase separator adopt a loose fiber bed + special plate group type phase separator; the third phase separator and the fourth phase separator adopt a dense fiber bed type phase separator; the loose fiber bed + special plate group type phase separator can tolerate a certain amount of solid suspensions, but the separation precision is low; the material treated by the phase separator can ensure that the dispersed phase contained in the main phase is less than one ten-thousandth, and the main phase contained in the dispersed phase is also less than one ten-thousandth.

[0034] 3.The present application provides a wet-process phosphoric acid purification and preparation method, further combined with membrane filtration technology, realizing efficient preparation of phosphoric acid, the membrane filtration technology can completely intercept the suspended solids and solid particles in the phosphoric acid, improving the subsequent extraction efficiency of the phosphoric acid and improving the quality of the phosphoric acid product;

[0035] 4.The present application provides a wet-process phosphoric acid purification and preparation method, using ultrafiltration membrane to filter the suspended solids and precipitates in the wet-process phosphoric acid, the turbidity of the filtered clear liquid is less than 1 NTU; meanwhile, using extraction, desulfurization, washing and back extraction means to effectively remove magnesium, calcium, manganese, aluminum, chromium and zinc impurity ions in the phosphoric acid, and the number of back extractions can be designed according to the specific impurity ion content in the phosphoric acid produced by different phosphorite reactions;

[0036] 5.The present application provides a wet-process phosphoric acid purification and preparation method, through the reuse of the raffinate acid and desulfuric acid in the purification process, the loss of phosphoric acid is reduced; and through the efficient recovery of by-products phosphogypsum and barium sulfate, the resource utilization rate is improved, and the accumulation of impurity ions in the system is reduced;

[0037] 6.The present application provides a wet-process phosphoric acid purification and preparation method, the phosphoric acid entering the concentration section is treated by phosphoric acid concentration and post-treatment, and 85% concentration high-purity refined phosphoric acid is obtained, the post-treatment includes phosphoric acid decolorization, fourth membrane filtration, rectification and bleaching, the phosphoric acid after decolorization will mix a small amount of decolorizing agent, which needs to be further removed by the fourth membrane filtration;

[0038] 7.The present application provides a wet-process phosphoric acid purification and preparation method, a purification agent is added to the crude phosphoric acid for pre-desulfurization, defluorination and dearsenication treatment, the suspended solids and solid particles in the acid liquid are completely intercepted by the second membrane filtration, and the obtained pretreated phosphoric acid enters the extraction section; the utilization rate of the extractant is improved. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings and their labels used in the embodiments will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0040] Figure 1 The wet-process phosphoric acid purification and preparation process flowchart described in the embodiments of the present application. DETAILED DESCRIPTION

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0042] To keep the drawings concise, each figure only schematically shows the parts relevant to the invention, and these do not represent the actual structure of the product. Furthermore, to facilitate understanding, in some figures, only one of components with the same structure or function is schematically depicted, or only one is labeled. In this document, "one" not only means "only one," but can also mean "more than one."

[0043] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0044] In this document, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0045] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0046] In one embodiment, a wet-process phosphoric acid purification method is provided; please refer to [link to relevant documentation]. Figure 1 The steps include:

[0047] Extraction: The selective solubility of the extractant is used to remove impurity ions from the phosphoric acid solution. These impurity ions include magnesium, calcium, manganese, aluminum, chromium, and zinc. The raffinate obtained from the extraction section is separated from the extractant and raffinate acid by the first phase separator. The recovered extractant is returned to the extraction section to continue the extraction reaction, and the raffinate acid is used to make phosphate fertilizer.

[0048] Fine desulfurization: the extraction phase obtained in the extraction section is subjected to fine desulfurization treatment to completely remove sulfate in the extraction phase. Specifically, barium sulfate suspension is generated by adding precipitants such as barium carbonate and barium chloride to separate the suspension; the extraction phase containing the suspension generated in the fine desulfurization is first subjected to high-efficiency separation of the acid solution and the extraction phase in the second phase separator, the acid phase separated in the second phase separator is subjected to complete removal of the suspended matter in the acid phase in the third membrane filtration, and the third membrane filtration clear liquid enters the extraction section to further reuse the phosphoric acid in the acid phase, and the concentrated liquid is subjected to barium sulfate recovery.

[0049] Washing: the extraction phase separated in the second phase separator enters the washing section (washing is equivalent to the first reverse extraction) to contact with desalted water in countercurrent, the washing liquid in the washing section can be desalted water or the reverse extraction acid generated in the second reverse extraction to make the impurity ions in the organic phase enter the washing acid; the washing acid obtained after the washing is subjected to recovery of the organic solvent in the washing acid in the third phase separator and then enters the concentration section, and the recovered organic solvent is reused to the extraction section.

[0050] Reverse extraction: the organic phase obtained after the washing enters the second reverse extraction to further recover the phosphoric acid, the reverse extraction liquid in the second reverse extraction is the reverse extraction acid generated in the third reverse extraction, the organic phase generated in the second reverse extraction enters the third reverse extraction to further recover the phosphoric acid, the reverse extraction liquid in the third reverse extraction is desalted water, the organic solvent generated in the third reverse extraction is reused to the extraction section, and the reverse extraction acid generated in the second reverse extraction is subjected to recovery of the organic solvent in the reverse extraction acid in the fourth phase separator and then enters the concentration section together with the washing acid, and the recovered organic solvent is reused to the extraction section.

[0051] The embodiment combines the extraction technology with the phase separation technology, which can improve the recovery rate of the extraction agent in the extraction section and the recovery rate of the organic phase in the reverse extraction acid in the reverse extraction section, reduce the loss of the extraction agent and the pollution of the extraction agent to the environment in the whole process, and reduce the production cost of the phosphoric acid preparation; on the other hand, the purity of the extraction phase entering the reverse extraction section is improved, and the reverse extraction efficiency is improved.

[0052] The embodiment can ensure that the material treated by the phase separator in each step contains less than one ten-thousandth of the dispersed phase in the main phase, and the main phase contains less than one ten-thousandth of the dispersed phase.

[0053] In the above embodiment, the specific process further includes a pretreatment step: adding a purifying agent to the crude phosphoric acid to perform pre-desulfurization, defluorination and dearsenication treatment, the purifying agent can be phosphorite slurry, NaOH and Na2S, etc.; the pretreated phosphoric acid obtained by completely intercepting the suspended matter and solid particles in the acid liquid in the second membrane filtration enters the extraction section.

[0054] In a preferred embodiment, the second membrane filtration and the third membrane filtration both use ultrafiltration membranes, the filtration accuracy is between 10nm and 1000nm, and the turbidity of the filtrate is less than 1NTU.

[0055] Specifically, the material of the ultrafiltration membrane is PTFE, PVDF, PS or other corrosion-resistant organic materials, or silicon carbide, zirconia, alumina or other corrosion-resistant inorganic materials; the operating temperature is 20-70℃, the operating pressure is 0.1-0.8MPa, and the operating membrane surface flow rate is 2-6m / s.

[0056] The embodiment further combines the membrane filtration technology to achieve efficient preparation of phosphoric acid. The membrane filtration technology can completely intercept the suspended solids and solid particles in the phosphoric acid, improve the subsequent extraction efficiency of the phosphoric acid, and improve the quality of the phosphoric acid product.

[0057] The second membrane filtration filters the phosphoric acid solution to ensure the purity of the phosphoric acid entering the extraction section and improve the extraction efficiency (the extraction efficiency is improved by more than 30%).

[0058] The first phase separator recovers the extractant in the raffinate phase, improves the extractant recovery rate (the extractant recovery rate is improved by more than 90%), protects the environment, reduces production costs, and improves the quality of phosphate fertilizer.

[0059] The third membrane filtration completely intercepts barium sulfate in the desulfurization acid, avoids the loss of barium sulfate, improves the production capacity of the byproduct barium sulfate (the production capacity of barium sulfate is improved by more than 20%), and increases the enterprise benefit.

[0060] The second phase separator efficiently separates the material after the fine desulfurization, not only improves the purity of the organic phase and the stripping efficiency of the stripping section (the stripping efficiency is improved by more than 30%), but also improves the acid recovery rate of the material after the fine desulfurization.

[0061] The third phase separator recovers the organic solvent in the washing acid, improves the extractant recovery rate (the extractant recovery rate is improved by more than 90%), improves the purity of the phosphoric acid, and reduces production costs.

[0062] The fourth phase separator recovers the organic solvent after the stripping of the phosphoric acid, improves the extractant recovery rate (the extractant recovery rate is improved by more than 90%), improves the purity of the phosphoric acid, and reduces production costs.

[0063] In another embodiment, a wet-process phosphoric acid preparation method is provided. Please refer to Figure 1 On the basis of the above embodiment, the method further includes an acidolysis section, and the specific steps are as follows:

[0064] Acidolysis: After the phosphate ore is acidolysed by sulfuric acid (or nitric acid, hydrochloric acid), phosphoric acid and phosphogypsum are produced by the acidolysis reaction. The acidolysis solution is filtered by the first membrane to absolutely intercept the phosphogypsum in the acidolysis solution, and to obtain crude phosphoric acid. The phosphogypsum intercepted by the first membrane filtration is purified, and the first membrane filtration clear solution enters the pretreatment section.

[0065] In the embodiment, the first membrane filtration is used to efficiently recover the byproduct phosphogypsum, thereby improving the resource utilization rate and reducing the accumulation of impurity ions in the system.

[0066] In the above embodiment, the concentration section and the post-treatment section are further included, and the specific steps are as follows:

[0067] Concentration: The washed acid and the stripping acid after the second stripping are input into the concentration section to be evaporated and concentrated.

[0068] Post-treatment: The purified phosphoric acid after the concentration is input into the post-treatment section, and after being subjected to decolorization, fourth membrane filtration, rectification and bleaching treatment in sequence, refined phosphoric acid is obtained. The purity of the refined phosphoric acid can reach more than 85%.

[0069] The first membrane filtration in the above embodiment filters the acidolysis solution to ensure the complete interception of the phosphogypsum, to improve the production capacity of the byproduct phosphogypsum (the production capacity of the phosphogypsum is increased by more than 20%), and to increase the enterprise benefit.

[0070] The fourth membrane filtration in the above embodiment removes the decolorizing agent from the phosphoric acid after the decolorization, to improve the quality of the phosphoric acid and to reduce the loss of the decolorizing agent (the loss of the decolorizing agent is reduced by more than 30%).

[0071] The membrane filtration process in the present application mainly includes a membrane filtration circulating tank, a membrane filtration circulating pump, a membrane assembly and pipelines connected with each other, and the operation mode of the membrane assembly can be static or dynamic, which is not specifically limited in the present application.

[0072] The phase separator in the present application mainly includes a phase separator shell, a fiber bed and a special plate group. The first phase separator and the second phase separator are loose fiber bed + special plate group type phase separators, which are especially suitable for separating materials containing part of solid particles. The third phase separator and the fourth phase separator are dense fiber bed type phase separators, which have higher separation precision and are especially suitable for materials not containing solid particles.

[0073] The loose fiber bed + special plate group type phase separator specifically uses a product with a model number of AFBP of Shanghai Ansi Environmental Protection Technology Co., Ltd., wherein the special plate group is a third generation improved plate group. The dense fiber bed specifically uses a product with a model number of AFB of Shanghai Ansi Environmental Protection Technology Co., Ltd. Of course, other products that meet the requirements of a cross-sectional flow rate of the loose fiber bed being not greater than 0.006 m / s and a surface flow rate of the dense fiber bed being not greater than 0.11 m / s can also be applied to the present application.

[0074] In order to have a clearer understanding of the technical solutions of the present application and their technical effects, a specific example is provided below for illustration:

[0075] The phosphorite and sulfuric acid are reacted to produce a phosphoric acid solution with a mass concentration of 35%, and the obtained phosphoric acid solution contains a large amount of undissolved slag. The slag is first separated by a settling tank, and the overflow liquid of the settling tank is filtered by a first membrane filter. The mass concentration of the suspended matter in the overflow liquid of the settling tank is 0.02%, and the first membrane filter can completely remove the suspended particles in the overflow liquid to ensure the purity of the phosphoric acid solution entering the pretreatment section. The turbidity of the first membrane filter liquid is less than 1 NTU, and the concentrated liquid produced by the first membrane filter is removed together with the sediment at the bottom of the settling tank for purification treatment. The solid material after the purification treatment is phosphogypsum;

[0076] The crude phosphoric acid entering the pretreatment section is pretreated by a phosphorite slurry, sodium hydroxide, sodium sulfide and the like, and a small amount of calcium phosphate, calcium fluoride, sulfide and the like are produced in the phosphoric acid solution. The mass concentration of the suspended matter accounts for 0.1% to 0.5%;

[0077] The pretreated phosphoric acid is filtered by a second membrane filter, which can completely remove the suspended matter produced in the pretreatment section. The turbidity of the second membrane filter liquid is less than 1 NTU, and the second membrane filter liquid enters an extraction section for further impurity removal of the phosphoric acid. The mass concentration of the suspended matter in the second membrane filter concentrated liquid is about 10% to 20%, which is returned to the acidolysis section for adjustment of the acidity of the acidolysis section;

[0078] The raffinate acid produced after the extraction section is separated by a first phase separator, and the raffinate acid contains suspended matter with a mass concentration of 0.01% and an extractant with a mass concentration of about 1%. Since the raffinate acid contains a small amount of suspended matter and an extractant, a loose fiber bed + special plate group type phase separator is selected here. After the raffinate acid is separated by the first phase separator, the raffinate acid contains an extractant with a mass concentration of 0.05% and suspended matter with a mass concentration of 0.01%. The organic phase contains phosphoric acid with a mass concentration of 0.05%. The raffinate acid containing a small amount of extractant is used for phosphate fertilizer, and the extractant containing a small amount of phosphoric acid is returned to the extraction section;

[0079] After the phosphoric acid solution is extracted by the extraction section, it enters a fine desulfurization section, and barium carbonate is added to further remove sulfate radicals in the extracted organic phase (at this time, the organic phase is an extractant containing phosphoric acid, and the phosphoric acid exists in the organic phase). The organic phase after fine desulfurization enters a second phase separator. Since the organic phase after fine desulfurization contains water introduced by barium carbonate and suspended barium sulfate produced, a loose fiber bed + special plate group type phase separator is selected here. After the organic phase is separated by the second phase separator, the mass concentration of water in the organic phase is 0.05%, the mass concentration of suspended matter in the aqueous phase is 0.01%, and the mass concentration of the extractant is 0.05%.

[0080] The aqueous phase produced by the second phase separator enters the third membrane filter, where the barium sulfate suspension is completely removed from the aqueous phase to achieve barium sulfate recovery. The clear liquid from the third membrane filter is returned to the extraction section.

[0081] The organic phase produced by the second phase separator is washed and back-extracted with demineralized water. The phosphoric acid in the organic phase is back-extracted into the aqueous phase to form a washing acid with a phosphoric acid concentration of approximately 30%. The washing acid contains 0.5% extractant. After efficient separation by the third phase separator, the mass concentration of extractant in the washing acid is <0.025%. The washing acid here does not contain any suspended solids, so a dense fiber bed phase separator with higher analytical precision is selected here. The water content in the organic phase from the third phase separator is <0.025%, and the organic phase is returned to the extraction section.

[0082] After washing, the organic phase undergoes a second and third back-extraction process, and the resulting extractant is entirely returned to the extraction section. The back-extracting acid from the third back-extraction is reused in the second back-extraction to increase its acidity. The final back-extracting acid enters the fourth phase separator. This back-extracting acid contains 0.5% extractant by mass. After efficient separation in the fourth phase separator, the extractant content in the back-extracting acid is <0.025%. Since this back-extracting acid does not contain suspended solids, a dense fiber bed phase separator with higher analytical precision is selected. The organic phase water content exiting the fourth phase separator is <

[0083] 0.025%, organic phase returned to the extraction section;

[0084] The washing acid and back-extraction acid are combined to form a 22% (w / w) phosphoric acid solution, which is then fed into the concentration section. The 22% (w / w) phosphoric acid solution is concentrated by steam to a concentration of 45-55% (w / w) before entering the post-processing section. First, activated carbon is used to decolorize the phosphoric acid, further removing the extractant entrained in the phosphoric acid. During the decolorization process, some activated carbon particles will be worn into the phosphoric acid. At this point, the solid suspended matter in the phosphoric acid is finally removed by a fourth membrane filtration. The removed phosphoric acid is then distilled and bleached to finally produce a high-quality phosphoric acid product with a (w / w) concentration of 85%.

[0085] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A wet-process phosphoric acid purification method, characterized in that, Includes the following steps: Extraction: The selective solubility of the extractant is used to remove impurity ions from the phosphoric acid solution. The raffinate obtained from the extraction section is separated from the extractant and raffinate by the first phase separator. The recovered extractant is returned to the extraction section to continue to participate in the extraction reaction, and the raffinate obtained is used to make phosphate fertilizer. Fine desulfurization: The extract phase obtained from the extraction section undergoes fine desulfurization treatment to completely remove sulfate ions from the extract phase. The extract phase containing suspended solids produced by fine desulfurization is separated from the acidic solution by a second phase separator. Washing: The extract phase separated by the second phase separator enters the washing section. The washing acid obtained after washing is recycled to the third phase separator to recover the organic solvent in the washing acid and reused in the extraction section. Back-extraction: The organic phase obtained after washing is sequentially fed into the second and third back-extraction processes for further recovery of phosphoric acid. The back-extraction solution of the second back-extraction is the back-extraction acid produced by the third back-extraction, and the back-extraction solution of the third back-extraction is demineralized water. The organic solvent produced by the third back-extraction is recycled to the extraction section. The back-extraction acid produced by the second back-extraction is recycled to the extraction section via the fourth phase separator to recover the organic solvent in the back-extraction acid. The first and second phase separators are loose fiber bed and special plate type phase separators, while the third and fourth phase separators are dense fiber bed type phase separators. Furthermore, the content of dispersed phase entrained in the main phase obtained after separation by each phase separator is less than one ten-thousandth, and the content of main phase entrained in the dispersed phase is less than one ten-thousandth.

2. The wet-process phosphoric acid purification method according to claim 1, characterized in that, After separation by the second phase separator, the acid phase is filtered through the third membrane to completely remove suspended solids. The clarified liquid from the third membrane filter enters the extraction section, and the concentrated liquid is used for barium sulfate recovery.

3. The wet-process phosphoric acid purification method according to claim 2, characterized in that, It also includes the following steps: Pretreatment: Purifying agent is added to crude phosphoric acid for pre-desulfurization, defluorination and dearsenic removal. After passing through a second membrane filter, suspended solids and solid particles in the acid solution are completely removed. The resulting pretreated phosphoric acid enters the extraction section.

4. The wet-process phosphoric acid purification method according to claim 3, characterized in that, The second and third membrane filtrations use ultrafiltration membranes; The ultrafiltration membrane is made of one or a combination of several of the following corrosion-resistant materials: PTFE, PVDF, PS, silicon carbide, zirconium oxide, and alumina; and / or, The ultrafiltration membrane has a filtration precision between 10 nm and 1000 nm; and / or, The ultrafiltration membrane operates at a temperature of 20~70℃, an operating pressure of 0.1~0.8MPa, and a flow velocity of 2~6m / s at the membrane surface; and / or, The turbidity of the supernatant in the filtered material from the ultrafiltration membrane is <1 NTU.

5. A wet-process method for preparing phosphoric acid, characterized in that, Includes the following steps: Acid hydrolysis: Phosphate rock is decomposed using organic acids to obtain an acid hydrolysis solution, which is then filtered through a first membrane to remove phosphogypsum, yielding crude phosphoric acid; and The specific steps involved in the wet phosphoric acid purification method as described in any one of claims 1-4.

6. The wet-process phosphoric acid preparation method according to claim 5, characterized in that, It also includes the following steps: Concentration: The washing acid after washing and the back-extraction acid after the second back-extraction are fed into the concentration section for evaporation and concentration.

7. The wet-process phosphoric acid preparation method according to claim 5, characterized in that, It also includes the following steps: Post-processing: The concentrated purified phosphoric acid is fed into the post-processing section, where it undergoes decolorization, fourth membrane filtration, distillation, and bleaching in sequence to obtain refined phosphoric acid.

8. The wet-process phosphoric acid preparation method according to claim 7, characterized in that, The third and fourth membrane filtrations use ultrafiltration membranes with a filtration accuracy between 10 nm and 1000 nm, and the turbidity of the clear liquid in the filtered material is <1 NTU.

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