Method for producing industrial-grade phosphoric acid from wet-process phosphoric acid raffinate acid

Abstract

The invention relates to a method for producing industrial-grade phosphoric acid from wet-process phosphoric acid raffinate acid, and belongs to the technical field of wet-process phosphoric acid. The technical problem to be solved by the invention is to provide a low-cost method for producing industrial-grade phosphoric acid from wet-process phosphoric acid raffinate. The method comprises the steps of pretreatment, metal ion extraction, pretreatment, phosphoric acid extraction, washing, phosphoric acid reverse extraction, concentration and the like, and finally industrial-grade phosphoric acid is obtained. The method adopts the raffinate acid as the raw material to prepare the industrial grade phosphoric acid, perfects and improves the wet-process phosphoric acid purification process, can utilize the original production equipment of a phosphorus purification enterprise, does not need to add new equipment, and is low in production cost. According to the method, phosphoric acid loss is avoided, all extracting agents can be recycled, associated metal elements in the raffinate acid can be recycled in a cascade classification mode, and cost is saved. The method is high in extraction efficiency, the content of metal impurity ions in the obtained product phosphoric acid is low, and the requirement of industrial grade phosphoric acid is met.

Description

Technical Field

[0001] The invention relates to a method for producing industrial-grade phosphoric acid by raffinate acid from wet-process phosphoric acid, belonging to the technical field of wet-process phosphoric acid. Background Art

[0002] Wet-process phosphoric acid is produced by using inorganic acid to decompose phosphate rock powder, separate crude phosphoric acid, and then use crude phosphoric acid as raw material to extract and purify the phosphoric acid product. In this process, raffinate acid is produced, which is characterized by complex composition, high impurity content, high concentration, and viscous phase. The recycling of raffinate acid has always been a technical problem that has plagued phosphoric acid purification companies.

[0003] At present, there are many methods for utilizing the raffinate acid of wet phosphoric acid, and the more mature one is to use the raffinate acid to produce fertilizer ammonium phosphate such as monoammonium phosphate and diammonium phosphate, such as patents CN110371939A, CN102674284A, CN112624074A, CN101613094A, etc. However, most of these treatment methods require the addition of phosphoric acid, which still consumes a large amount of original acid, and for wet phosphoric acid production enterprises that originally did not have ammonium phosphate production equipment, they need to build a new ammonium phosphate workshop, which increases a lot of costs.

[0004] Wet-process phosphoric acid raffinate can be used to produce heavy superphosphate. For example, the invention patent with application number 201210029255.1 discloses a method for producing heavy superphosphate using raffinate acid from purified phosphoric acid. The raffinate acid is used as the raw acid for producing heavy superphosphate. However, due to the high content of cationic impurities in the raffinate acid, which affects its hydrogen ion concentration, it needs to go through a series of treatments before it can produce heavy superphosphate. The method is complicated and is prone to a series of problems during the production process, such as low strength, poor granulation, and inability to balance moisture and output.

[0005] The raffinate acid from wet phosphoric acid can also be returned to the phosphoric acid production process. The invention patent application with application number 201610514424.9 discloses a combined extraction method for producing high-quality phosphoric acid, which first removes metal ions through primary extraction and then performs a refined phosphoric acid extraction operation. The extract after refined extraction produces high-quality phosphoric acid, and the raffinate is directly mixed with crude phosphoric acid as the primary extraction raw material for circulation. This method is to mix the raffinate acid into crude phosphoric acid for further extraction. Since the extraction after mixing will produce raffinate acid with a higher impurity content, a higher concentration, and a more viscous phase, the requirements for equipment will be very high, and more extractants and an increase in the number of extraction stages will be required. The greater the amount of extractant used, the greater the cost of regenerating the extractant; increasing the number of extraction stages means that larger tower equipment is required when applied to industrial production, and the cost will increase. Summary of the invention

[0006] In view of the above defects, the technical problem solved by the present invention is to provide a method for producing industrial-grade phosphoric acid from wet-process phosphoric acid raffinate at a low cost.

[0007] The method for producing industrial-grade phosphoric acid by wet-process phosphoric acid raffinate of the present invention comprises the following steps:

[0008] a. Pretreatment: dilute the raffinate with a concentration of 40wt.% to 60wt.% to a concentration of 20wt.% to 60wt.%, and then filter, the filtrate is treated by steam stripping, and after standing and stratification, the lower layer of liquid is taken, which is the aqueous phase 0;

[0009] b. Extraction of metal ions: After adding the extractant A to the aqueous phase 0 to extract the metal ions, an organic phase 1 and an aqueous phase 1 are obtained;

[0010] c. Pretreatment: The aqueous phase 1 is concentrated and defluorinated to obtain the aqueous phase 3, and the aqueous phase 3 is subjected to raffinate centrifugal separation, activated carbon adsorption, and hydrogen peroxide oxidation to obtain purified concentrated phosphoric acid; wherein the raffinate centrifugal separation is performed by using a centrifugal extractor;

[0011] d. Extraction of phosphoric acid: extractant B is added to the purified concentrated phosphoric acid for extraction to obtain an organic phase 5 and a raffinate acid; the raffinate acid is returned to step a for use as a wet phosphoric acid raffinate acid;

[0012] e. Washing 1: The organic phase 5 is washed with water to recover the phosphoric acid and impurities entrained therein, and then allowed to stand for phase separation to obtain an organic phase 6 and an aqueous phase 4;

[0013] f. phosphoric acid stripping: stripping the organic phase 6 with water, and then standing the phases to obtain an organic phase 7 and an aqueous phase 7; the organic phase 7 is centrifuged and separated by centrifugation using a centrifugal extractor and returned to step d as an extractant B;

[0014] g. Concentration: The aqueous phase 7 is concentrated to obtain industrial grade phosphoric acid.

[0015] In one embodiment, the method for producing industrial-grade phosphoric acid by wet-process phosphoric acid raffinate of the present invention further comprises the following steps:

[0016] h. Washing 2: After diluting the aqueous phase 4 to obtain an aqueous phase 5, the aqueous phase 5 is used as a washing liquid to wash the organic phase 1, and the phases are allowed to stand to obtain an organic phase 2 and an aqueous phase 6. After diluting the aqueous phase 6, the aqueous phase 6 is returned to this step as a washing liquid;

[0017] i. Stripping of metal ions: After stripping 1 of the organic phase 2 with stripping agent 1, an organic phase 3 and stripping solution 1 are obtained; after stripping 2 of the organic phase 3 with stripping agent 2, the obtained organic phase is the regenerated extractant A, which is returned to step b and used as the extractant A; the obtained aqueous phase is the stripping solution 2;

[0018] The stripping agent 1 is potassium sulfate and sulfuric acid solution, and the stripping agent 2 is oxalic acid solution.

[0019] Furthermore, the method for producing industrial-grade phosphoric acid from raffinate of wet-process phosphoric acid of the present invention further comprises the following steps:

[0020] The metal ions in the crude phosphoric acid are extracted with extractant A to obtain aqueous phase 2, organic phase 4 and raffinate acid. The aqueous phase 2 is combined with the aqueous phase 1 to perform step c. The organic phase 4 is combined with the organic phase 1 to perform step h. The raffinate acid is subjected to step a.

[0021] In one embodiment of the present invention, in step a, the temperature of the aqueous phase 0 is ensured to be 30-60°C.

[0022] In one embodiment of the present invention, in step b, several stages of countercurrent extraction are used, the number of stages is 1 to 5; preferably, the number of stages is 3, each stage has three stages, the extraction temperature of each stage is 25 to 85°C, and the volume ratio O / A is 1 to 10:1.

[0023] In one embodiment of the present invention, extractant A is at least one of P204, P507, Cynex272, DNNSA, cyclopentane acid and tert-butyl carboxylic acid; extractant B is at least one of TBP, MIBK, DBBP, DAMP, P-311, organic alcohols, ethers and sulfoxides.

[0024] In one embodiment of the present invention, in step c, the activated carbon adsorption is that the aqueous phase 3 obtained after the raffinate centrifugal separation flows through an activated carbon layer having a height of 1 to 6 cm; the hydrogen peroxide oxidation is that hydrogen peroxide is added to the aqueous phase obtained after the activated carbon adsorption and stirred, the amount of hydrogen peroxide is 1% to 5% of the weight of the aqueous phase, the temperature is 100 to 120° C., and the oxidation time is 10 to 30 min.

[0025] In a specific embodiment of the present invention, in step d, the extraction is a three-stage countercurrent extraction, the extraction temperature is 25 to 85° C., and the volume ratio O / A is 1 to 10:1.

[0026] In a specific embodiment of the present invention, in step e, the organic phase 5 is washed with water at a temperature of 25 to 85° C., and the volume ratio of O / A is 1 to 10:1; the obtained aqueous phase 4 is diluted and then enters step h.

[0027] In one embodiment of the present invention, in step f, the organic phase 6 is countercurrently stripped with water, the stripping temperature is 25 to 85° C., and the volume ratio O / A is 1 to 10:1.

[0028] In one embodiment of the present invention, in step g, the aqueous phase 7 is concentrated under reduced pressure to a phosphoric acid concentration (in terms of H3PO4) of 70 wt.% to 85 wt.%, and the concentration temperature is 75 to 85°C.

[0029] In one embodiment of the present invention, in step h, two-stage countercurrent washing with washing liquid is adopted, the phosphoric acid concentration in the washing liquid is 1wt.% to 8wt.% in terms of P2O5, the washing temperature is 25 to 85°C, and the volume ratio of O / A is 1 to 10:1.

[0030] In a specific embodiment of the present invention, in the stripping agent 1, the concentration of potassium sulfate is 5wt.% to 60wt.%, and the concentration of sulfuric acid is ≤15wt.%; the temperature of stripping 1 is 25 to 85°C, and the volume ratio O / A is 1 to 10:1; in the stripping agent 2, the concentration of oxalic acid is 5wt.% to 45wt.%, and the temperature of stripping 2 is 30 to 70°C, and the volume ratio O / A is 1 to 10:1.

[0031] In a specific embodiment of the present invention, in step i, stripping solution 1 is heated and concentrated, cooled and crystallized, and filtered to obtain calcium sulfate, potassium magnesium sulfate and potassium aluminum sulfate; stripping solution 2 is precipitated by light to obtain ferrous oxalate.

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

[0033] 1) The present invention uses raffinate as a raw material to prepare industrial-grade phosphoric acid, thereby improving and enhancing the wet-process phosphoric acid purification process. Moreover, the method can utilize the original production equipment of the phosphorus purification enterprise without adding new equipment, and has low production cost.

[0034] 2) The method of the present invention has no phosphoric acid loss, all extractants can be recycled, and the associated metal elements in the residual acid can be recovered in a step-by-step classification manner, thus saving costs.

[0035] 3) The method of the present invention has high extraction efficiency, and the content of metal impurity ions in the obtained phosphoric acid product is small, which meets the requirements of industrial-grade phosphoric acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a process flow chart for producing industrial-grade phosphoric acid from wet-process phosphoric acid raffinate.

[0037] Figure 2 This is a flow chart of the extraction process of step b1 in Examples 1-6 of the present invention. DETAILED DESCRIPTION

[0038] The method for producing industrial-grade phosphoric acid by wet-process phosphoric acid raffinate of the present invention comprises the following steps:

[0039] a. Pretreatment: dilute the raffinate with a concentration of 40wt.% to 60wt.% to a concentration of 20wt.% to 60wt.%, and then filter, the filtrate is treated by steam stripping, and after standing and stratification, the lower layer of liquid is taken, which is the aqueous phase 0;

[0040] b. Extraction of metal ions: After adding the extractant A to the aqueous phase 0 to extract the metal ions, an organic phase 1 and an aqueous phase 1 are obtained;

[0041] c. Pretreatment: The aqueous phase 1 is concentrated and defluorinated to obtain the aqueous phase 3, and the aqueous phase 3 is subjected to raffinate centrifugal separation, activated carbon adsorption, and hydrogen peroxide oxidation to obtain purified concentrated phosphoric acid; wherein the raffinate centrifugal separation is performed by using a centrifugal extractor;

[0042] d. Extraction of phosphoric acid: extractant B is added to the purified concentrated phosphoric acid for extraction to obtain an organic phase 5 and a raffinate acid; the raffinate acid is returned to step a for use as a wet phosphoric acid raffinate acid;

[0043] e. Washing 1: The organic phase 5 is washed with water to recover the phosphoric acid and impurities entrained therein, and then allowed to stand for phase separation to obtain an organic phase 6 and an aqueous phase 4;

[0044] f. phosphoric acid stripping: stripping the organic phase 6 with water, and then standing the phases to obtain an organic phase 7 and an aqueous phase 7; the organic phase 7 is centrifuged and separated by centrifugation using a centrifugal extractor and returned to step d as an extractant B;

[0045] g. Concentration: The aqueous phase 7 is concentrated to obtain industrial grade phosphoric acid.

[0046] The method for producing industrial-grade phosphoric acid by wet-process phosphoric acid raffinate of the present invention further comprises the following steps:

[0047] h. Washing 2: After diluting the aqueous phase 4 to obtain an aqueous phase 5, the aqueous phase 5 is used as a washing liquid to wash the organic phase 1, and the phases are allowed to stand to obtain an organic phase 2 and an aqueous phase 6. After diluting the aqueous phase 6, the aqueous phase 6 is returned to this step as a washing liquid;

[0048] i. Stripping of metal ions: After stripping 1 of the organic phase 2 with stripping agent 1, an organic phase 3 and stripping solution 1 are obtained; after stripping 2 of the organic phase 3 with stripping agent 2, the obtained organic phase is the regenerated extractant A, which is returned to step b and used as the extractant A; the obtained aqueous phase is the stripping solution 2;

[0049] The stripping agent 1 is potassium sulfate and sulfuric acid solution, and the stripping agent 2 is oxalic acid solution.

[0050] Furthermore, the method for producing industrial-grade phosphoric acid from raffinate of wet-process phosphoric acid of the present invention further comprises the following steps:

[0051] The metal ions in the crude phosphoric acid are extracted with extractant A to obtain aqueous phase 2, organic phase 4 and raffinate acid. The aqueous phase 2 is combined with the aqueous phase 1 to perform step c. The organic phase 4 is combined with the organic phase 1 to perform step h. The raffinate acid is subjected to step a.

[0052] The wet-process phosphoric acid raffinate of the present invention is a byproduct after wet-process phosphoric acid purification and extraction. During the production process of purified phosphoric acid, phosphoric acid accounting for about half of the feed acid remains in the raffinate and is not extracted into the organic phase. The raffinate contains relatively high impurities such as P2O5, Fe, Al, Mg, and Ca. Among them, the content of P2O5 is 40wt.% to 50wt.%, the content of Al2O3 is 2 to 4wt.%, the content of MgO is 2 to 5wt.%, the content of Fe2O3 is 0.1 to 0.5wt.%, and the content of CaO is 0.1 to 0.4wt%.

[0053] Step a is pretreatment, diluting the raffinate with a concentration of 40wt.% to 60wt.% to a concentration of 20wt.% to 60wt.%, and then filtering to remove obvious particulate matter; the filtrate is treated by steam stripping, and the pretreated raffinate in the lower layer is separated after standing and stratification, and the resulting liquid is the aqueous phase 0.

[0054] In one embodiment of the present invention, the pretreated raffinate acid is transported to a raffinate acid storage tank by a pump, and the resulting liquid is the pretreated raffinate acid, i.e., the aqueous phase 0.

[0055] In one embodiment of the present invention, in step a, the temperature of the aqueous phase 0 is maintained at 30-60°C to prevent the impurity metal cations from forming phosphate precipitation. Specifically, the raffinate storage tank can be heated and insulated so that the temperature control range is 30-60°C.

[0056] Step b is to extract metal ions, using extractant A to perform extraction and phase separation to obtain an organic phase 1 rich in metal impurity ions and an aqueous phase 1 containing phosphorus.

[0057] The extractant A can be commonly used in the art, including but not limited to at least one of P204 (chemical name di(2-ethylhexyl) phosphate), P507 (chemical name 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester), Cynex272 (chemical name di(2,4,4-trimethylpentyl) hypophosphorous acid), DNNSA (chemical name dinonylnaphthalenesulfonic acid), cycloalkane acid and tertiary carbonic acid.

[0058] In one embodiment of the present invention, in step b, several stages of countercurrent extraction are used, the number of stages is 1 to 5; preferably, the number of stages is 3, each stage has three stages, the extraction temperature of each stage is 25 to 85°C, and the volume ratio O / A is 1 to 10:1.

[0059] In one embodiment of the present invention, in step b, the following method is specifically used for extraction: during extraction, the flow rates of aqueous phase 0 and extractant A are controlled by a peristaltic pump according to the designed flow rate, and aqueous phase 0 and extractant A enter the reaction tank at the same time and start stirring. When the mixed liquid in the reaction tank reaches about 3 / 4 of the volume of the reaction tank and the stirring time is greater than 30 minutes, the mixed liquid is extracted, and during this period, aqueous phase 0 and extractant A are continuously added in proportion to ensure that the extracted flow rate is equal to the sum of the flow rates of the two phases entering; the extracted mixed liquid enters the phase separation tank for phase separation to obtain aqueous phase 1 and organic phase 1.

[0060] Step c is pretreatment, the aqueous phase 1 is concentrated and defluorinated to obtain the aqueous phase 3, the aqueous phase 3 is subjected to raffinate centrifugal separation, activated carbon adsorption, and hydrogen peroxide oxidation to obtain purified concentrated phosphoric acid, the concentration of which is 40-60wt.% in terms of P2O5.

[0061] The centrifugal separation of the extract is carried out using a centrifugal extractor. In this centrifugal field, due to the different densities of oil and water, the centrifugal forces they are subjected to are also different, thus producing a stratification phenomenon, which can better separate the water phase and the oil phase.

[0062] In one embodiment of the present invention, activated carbon adsorption is to pass the aqueous phase 3 obtained after the raffinate centrifugal separation through an activated carbon layer with a certain height (1 to 6 cm), and this process can further adsorb the entrained organic phase; hydrogen peroxide oxidation is to add hydrogen peroxide to the aqueous phase obtained after the activated carbon adsorption and stir, the amount of hydrogen peroxide is 1% to 5% of the weight of the aqueous phase, the temperature is 100 to 120°C, and the oxidation time is 10 to 30 minutes.

[0063] Step d is to extract phosphoric acid, and extractant B is added to the purified concentrated phosphoric acid for extraction to obtain an organic phase 5 and raffinate acid; the raffinate acid is returned to step a and used as wet-process phosphoric acid raffinate acid.

[0064] Extractant B may be commonly used in the art, including but not limited to TBP (chemical name tributyl phosphate), MIBK (chemical name 4-methyl-2-pentanone), DBBP (chemical name dibutyl butylphosphonate), DAMP (chemical name diisoamyl methylphosphonate), P-311 (diisomethylphosphonate), organic alcohols, ethers and sulfoxides, and at least one phosphorus-type extractant.

[0065] In a specific embodiment of the present invention, in step d, the extraction is a three-stage countercurrent extraction, the extraction temperature is 25 to 85° C., and the volume ratio O / A is 1 to 10:1.

[0066] Step e is washing, in which the organic phase 5 is washed with water to recover phosphoric acid and impurities carried therein, and then allowed to stand for phase separation to obtain an organic phase 6 and an aqueous phase 4.

[0067] In a specific embodiment of the present invention, in step e, the temperature is 25-85° C., and the volume ratio of O / A is 1-10:1; the obtained aqueous phase 4 is diluted and then enters step h.

[0068] Step f is to strip phosphoric acid, strip the organic phase 6 with water, and then stand the phases to obtain an organic phase 7 and an aqueous phase 7; the organic phase 7 is centrifuged and returned to step d as an extractant B.

[0069] In one embodiment of the present invention, in step f, the organic phase 6 is countercurrently stripped with water, the stripping temperature is 25 to 85° C., and the volume ratio O / A is 1 to 10:1.

[0070] In step g, the aqueous phase 7 is concentrated under reduced pressure to obtain industrial-grade phosphoric acid. In one embodiment of the present invention, in step g, the aqueous phase 7 is concentrated to a phosphoric acid concentration (in terms of H3PO4) of 70 wt.% to 85 wt.%, and the concentration temperature is 75 to 85°C.

[0071] Step h and step i are for recovering the extractant A in step b, and the regenerated extractant A is recovered from the organic phase 1 in step b.

[0072] Step h is washing, using a washing liquid to wash the organic phase 1, standing for phase separation to obtain an organic phase 2 and an aqueous phase 6, and the aqueous phase 6 is diluted and returned to this step for use as a washing liquid; and the washing liquid can come from the aqueous phase 4 of step e, and the aqueous phase 4 is diluted to obtain the aqueous phase 5, and the aqueous phase 5 is used as the washing liquid.

[0073] In one embodiment of the present invention, in step h, two-stage countercurrent washing with washing liquid is adopted, the phosphoric acid concentration in the washing liquid is 1wt.% to 8wt.% in terms of P2O5, the washing temperature is 25 to 85°C, and the volume ratio of O / A is 1 to 10:1.

[0074] Step i is to strip the metal ions, after removing the metal ions in the organic phase 2, obtain the regenerated extractant A, and return to step b for use.

[0075] The stripping operation adopts two specific stripping operations. The first time, stripping agent 1 is used to strip the organic phase 2 to obtain organic phase 3 and stripping liquid 1. The second time, stripping agent 2 is used to strip the organic phase 3 to obtain regenerated extracting agent A and stripping liquid 2.

[0076] In a specific embodiment of the present invention, in the stripping agent 1, the concentration of potassium sulfate is 5wt.% to 60wt.%, and the concentration of sulfuric acid is ≤15wt.%; the temperature of stripping 1 is 25 to 85°C, and the volume ratio O / A is 1 to 10:1; in the stripping agent 2, the concentration of oxalic acid is 5wt.% to 45wt.%, and the temperature of stripping 2 is 30 to 70°C, and the volume ratio O / A is 1 to 10:1.

[0077] In a specific embodiment of the present invention, the stripping solution 1 is heated and concentrated, cooled and crystallized, and filtered to obtain calcium sulfate, potassium magnesium sulfate, and potassium aluminum sulfate; and the stripping solution 2 is precipitated by light to obtain ferrous oxalate. In this way, the metal ions in the extractant A can be recovered, and the associated metal elements in the raffinate acid can be recovered by step-by-step classification.

[0078] The specific implementation modes of the present invention are further described below in conjunction with embodiments, but the present invention is not limited to the scope of the embodiments.

[0079] Example 1

[0080] A method for producing industrial-grade phosphoric acid by extracting raffinate from wet phosphoric acid, the process of which is as follows Figure 1 As shown, the following steps are included:

[0081] a. Pretreatment: dilute the raffinate with a concentration of 60wt.% to a concentration of 30wt.%, and then filter to remove obvious particulate matter; the filtrate is treated by steam stripping, and the pretreated raffinate in the lower layer is separated after standing and stratification, and the resulting liquid is water phase 0, which is pumped to a raffinate storage tank, and the storage tank is heated and insulated, and the temperature is controlled at 40°C to prevent impure metal cations from forming phosphate precipitation.

[0082] b. Extraction of metal ions: After adding extractant A (specifically P204) to aqueous phase 0 to extract metal ions, an organic phase 1 and an aqueous phase 1 are obtained; during extraction, the flow rate is designed according to the phase ratio (the volume ratio O / A is 5:1), and the flow rates of aqueous phase 0 and extractant A are controlled by a peristaltic pump. After aqueous phase 0 and extractant A enter the reaction tank at the same time, stirring begins. When the mixed liquid in the reaction tank reaches about 3 / 4 of the volume of the reaction tank and the stirring time is greater than 30 minutes, the mixed liquid is extracted, and during this period, aqueous phase 0 and extractant A are continuously added in proportion to ensure that the extracted flow rate is equal to the sum of the flow rates of the two phases entering; the extracted mixed liquid enters the phase separation tank for phase separation to obtain aqueous phase 1 and organic phase 1.

[0083] A three-stage three-level countercurrent extraction was adopted, the extraction temperature of each stage was 55°C, and the volume ratio of O / A was 5:1.

[0084] b1. Extraction of metal ions from crude phosphoric acid: Extracting metal ions from crude phosphoric acid with extractant A to obtain aqueous phase 2, organic phase 4 and raffinate acid. The aqueous phase 2 is combined with the aqueous phase 1 to proceed to step c. The organic phase 4 is combined with the organic phase 1 to proceed to step h. The raffinate acid is subjected to step a. The process flow is shown in Figure 2 Continuous three-stage extraction is adopted, and after the reaction stops, the phosphoric acid remaining in the first-stage extraction tank and the second-stage extraction tank that has not passed through the third-stage extraction tank is the residual acid.

[0085] c. Pretreatment: The aqueous phase 1 is concentrated and defluorinated to obtain the aqueous phase 3, and the aqueous phase 3 is subjected to raffinate centrifugal separation, activated carbon adsorption, and hydrogen peroxide oxidation to obtain purified concentrated phosphoric acid. The aqueous phase and the organic phase are separated by raffinate centrifugal separation using a centrifugal extractor; the aqueous phase is passed through a 3 cm high activated carbon layer to further adsorb the entrained organic phase; 1% hydrogen peroxide by weight is added to the aqueous phase, and stirred at 100°C for 10 minutes to obtain purified concentrated phosphoric acid.

[0086] d. Extraction of phosphoric acid: Extractant B (specifically TBP) is added to the purified concentrated phosphoric acid for extraction to obtain an organic phase 5 and raffinate acid; the raffinate acid is returned to step a and used as wet phosphoric acid raffinate acid. The extraction adopts a one-stage three-stage process, the extraction temperature is 55°C, and the phase volume ratio O / A is 5:1.

[0087] e. Washing 1: The organic phase 5 is washed with water to recover the phosphoric acid and impurities carried therein, and then allowed to stand for phase separation to obtain an organic phase 6 and an aqueous phase 4; the temperature is 55°C, and the volume ratio of O / A is 5:1; the obtained aqueous phase 4 is diluted and enters step h.

[0088] f. Re-extraction of phosphoric acid: The organic phase 6 is extracted with water, and then allowed to stand for phase separation to obtain an organic phase 7 and an aqueous phase 7; the organic phase 7 is centrifuged and returned to step d as an extractant B; the stripping temperature is 55°C, and the volume ratio O / A is 5:1.

[0089] g. Concentration: The aqueous phase 7 was concentrated under reduced pressure to a phosphoric acid concentration (in terms of H3PO4) of 70wt.%, and the concentration temperature was 80°C to obtain industrial grade phosphoric acid.

[0090] h. Washing 2: After diluting the aqueous phase 4 in step e, an aqueous phase 5 is obtained, and the aqueous phase 5 is used as a washing liquid to wash the organic phase 1. The organic phase 2 and the aqueous phase 6 are allowed to stand for phase separation, and the aqueous phase 6 is diluted and returned to this step for use as a washing liquid.

[0091] i. Stripping of metal ions: After stripping 1 of the organic phase 2 using stripping agent 1, an organic phase 3 and stripping solution 1 are obtained; after stripping 2 of the organic phase 3 using stripping agent 2, the obtained organic phase is the regenerated extractant A, which is returned to step b for use as the extractant A; the obtained aqueous phase is the stripping solution 2.

[0092] The stripping agent 1 is a potassium sulfate and sulfuric acid solution, the potassium sulfate concentration is 5wt.%, the sulfuric acid concentration is 15wt.%, the stripping temperature 1 is 60°C, and the volume ratio O / A is 5: 1. The stripping solution 1 obtained after stripping is heated and concentrated, cooled and crystallized, and filtered to obtain calcium sulfate, potassium magnesium sulfate and potassium aluminum sulfate.

[0093] The stripping agent 2 is an oxalic acid solution, the oxalic acid concentration is 10 wt.%, the stripping temperature 2 is 50° C., and the volume ratio O / A is 5: 1. The stripping solution 2 obtained after stripping is precipitated by light to obtain ferrous oxalate.

[0094] Comparative Example 1

[0095] The method for producing industrial-grade phosphoric acid by extracting raffinate from wet-process phosphoric acid comprises the following steps:

[0096] a. Mixing: diluting the raffinate having a concentration of 60wt.% to a concentration of 30wt.%, and mixing with crude phosphoric acid to obtain a mixed solution 1;

[0097] b1. Extraction of metal ions: Extracting the metal ions in the mixed solution 1 with an extractant A to obtain an aqueous phase 1, an organic phase 1 and a raffinate acid. The aqueous phase 1 is subjected to step c, the organic phase 1 is subjected to step h, and the raffinate acid is returned to step a and mixed with the crude phosphoric acid. The process flow is shown in Figure 2 Continuous three-stage extraction is adopted, and after the reaction stops, the phosphoric acid remaining in the first-stage extraction tank and the second-stage extraction tank that has not passed through the third-stage extraction tank is the residual acid.

[0098] c. Pretreatment: The aqueous phase 1 is concentrated and defluorinated to obtain the aqueous phase 3, and the aqueous phase 3 is subjected to raffinate centrifugal separation, activated carbon adsorption, and hydrogen peroxide oxidation to obtain purified concentrated phosphoric acid. The aqueous phase and the organic phase are separated by raffinate centrifugal separation using a centrifugal extractor; the aqueous phase is passed through a 3 cm high activated carbon layer to further adsorb the entrained organic phase; 1% hydrogen peroxide by weight is added to the aqueous phase, and stirred at 100°C for 10 minutes to obtain purified concentrated phosphoric acid.

[0099] d. Extraction of phosphoric acid: Extractant B (specifically TBP) is added to the purified concentrated phosphoric acid for extraction to obtain an organic phase 5 and raffinate acid; the raffinate acid is returned to step a and used as wet phosphoric acid raffinate acid. The extraction adopts a one-stage three-stage process, the extraction temperature is 55°C, and the phase volume ratio O / A is 5:1.

[0100] e. Washing 1: The organic phase 5 is washed with water to recover the phosphoric acid and impurities carried therein, and then allowed to stand for phase separation to obtain an organic phase 6 and an aqueous phase 4; the temperature is 55°C, and the volume ratio of O / A is 5:1; the obtained aqueous phase 4 is diluted and enters step h.

[0101] f. Re-extraction of phosphoric acid: The organic phase 6 is extracted with water, and then allowed to stand for phase separation to obtain an organic phase 7 and an aqueous phase 7; the organic phase 7 is centrifuged and returned to step d as an extractant B; the stripping temperature is 55°C, and the volume ratio O / A is 5:1.

[0102] g. Concentration: The aqueous phase 7 was concentrated under reduced pressure to a phosphoric acid concentration (in terms of H3PO4) of 70wt.%, and the concentration temperature was 80°C to obtain industrial grade phosphoric acid.

[0103] h. Washing 2: After diluting the aqueous phase 4 in step e, an aqueous phase 5 is obtained, and the aqueous phase 5 is used as a washing liquid to wash the organic phase 1. The organic phase 2 and the aqueous phase 6 are allowed to stand for phase separation, and the aqueous phase 6 is diluted and returned to this step for use as a washing liquid.

[0104] i. Stripping of metal ions: After stripping 1 of the organic phase 2 using stripping agent 1, an organic phase 3 and stripping solution 1 are obtained; after stripping 2 of the organic phase 3 using stripping agent 2, the obtained organic phase is the regenerated extractant A, which is returned to step b for use as the extractant A; the obtained aqueous phase is the stripping solution 2.

[0105] The stripping agent 1 is a potassium sulfate and sulfuric acid solution, the potassium sulfate concentration is 5wt.%, the sulfuric acid concentration is 15wt.%, the stripping temperature 1 is 60°C, and the volume ratio O / A is 5: 1. The stripping solution 1 obtained after stripping is heated and concentrated, cooled and crystallized, and filtered to obtain calcium sulfate, potassium magnesium sulfate and potassium aluminum sulfate.

[0106] The stripping agent 2 is an oxalic acid solution, the oxalic acid concentration is 10 wt.%, the stripping temperature 2 is 50° C., and the volume ratio O / A is 5: 1. The stripping solution 2 obtained after stripping is precipitated by light to obtain ferrous oxalate.

[0107] Table 1 Effect Differences between Examples and Comparative Examples

[0108]

[0109] Example 2

[0110] a. Pretreatment: dilute the raffinate with a concentration of 60wt.% to a concentration of 30wt.%, and then filter to remove obvious particulate matter; the filtrate is treated by steam stripping, and the pretreated raffinate in the lower layer is separated after standing and stratification, and the resulting liquid is water phase 0, which is pumped to a raffinate storage tank, and the storage tank is heated and insulated, and the temperature is controlled at 60°C to prevent impure metal cations from forming phosphate precipitation.

[0111] b. Extraction of metal ions: After adding extractant A (specifically P204) to aqueous phase 0 to extract metal ions, an organic phase 1 and an aqueous phase 1 are obtained; during extraction, the flow rates of aqueous phase 0 and extractant A are controlled by a peristaltic pump according to the designed flow rate, and aqueous phase 0 and extractant A enter the reaction tank at the same time and begin to stir. When the mixed liquid in the reaction tank reaches about 3 / 4 of the volume of the reaction tank and the stirring time is greater than 30 minutes, the mixed liquid is extracted, and during this period, aqueous phase 0 and extractant A are continuously added in proportion to ensure that the extracted flow rate is equal to the sum of the flow rates of the two phases entering; the extracted mixed liquid enters the phase separation tank for phase separation to obtain aqueous phase 1 and organic phase 1.

[0112] A three-stage three-level countercurrent extraction was adopted, the extraction temperature of each stage was 85°C, and the volume ratio of O / A was 10:1.

[0113] b1. Extraction of metal ions from crude phosphoric acid: Extracting metal ions from crude phosphoric acid with extractant A to obtain aqueous phase 2, organic phase 4 and raffinate acid. The aqueous phase 2 is combined with the aqueous phase 1 to proceed to step c. The organic phase 4 is combined with the organic phase 1 to proceed to step h. The raffinate acid is subjected to step a. The process flow is shown in Figure 2 Continuous three-stage extraction is adopted, and after the reaction stops, the phosphoric acid remaining in the first-stage extraction tank and the second-stage extraction tank that has not passed through the third-stage extraction tank is the residual acid.

[0114] c. Pretreatment: The aqueous phase 1 is concentrated and defluorinated to obtain the aqueous phase 3, and the aqueous phase 3 is subjected to raffinate centrifugal separation, activated carbon adsorption, and hydrogen peroxide oxidation to obtain purified concentrated phosphoric acid. The raffinate centrifugal separation of the aqueous phase and the organic phase is performed by a centrifugal extractor; the aqueous phase is passed through a 6-cm high activated carbon layer to further adsorb the entrained organic phase; 5% hydrogen peroxide by weight is added to the aqueous phase, and stirred at 120°C for 30 minutes to obtain purified concentrated phosphoric acid.

[0115] d. Extraction of phosphoric acid: Extractant B (specifically TBP) is added to the purified concentrated phosphoric acid for extraction to obtain an organic phase 5 and raffinate acid; the raffinate acid is returned to step a and used as wet phosphoric acid raffinate acid. The extraction adopts a one-stage three-stage process, the extraction temperature is 85°C, and the phase volume ratio O / A is 10:1.

[0116] e. Washing 1: The organic phase 5 is washed with water to recover the phosphoric acid and impurities carried therein, and then allowed to stand for phase separation to obtain an organic phase 6 and an aqueous phase 4; the temperature is 85°C, and the volume ratio of O / A is 10:1; the obtained aqueous phase 4 is diluted and enters step h.

[0117] f. Re-extraction of phosphoric acid: The organic phase 6 is extracted with water, and then allowed to stand for phase separation to obtain an organic phase 7 and an aqueous phase 7; the organic phase 7 is centrifuged and returned to step d as an extractant B; the stripping temperature is 85°C, and the volume ratio O / A is 10:1.

[0118] g. Concentration: The aqueous phase 7 was concentrated under reduced pressure to a phosphoric acid concentration (in terms of H3PO4) of 85wt.%, at a concentration temperature of 85°C, to obtain industrial grade phosphoric acid.

[0119] h. Washing 2: After diluting the aqueous phase 4 in step e, an aqueous phase 5 is obtained, and the aqueous phase 5 is used as a washing liquid to wash the organic phase 1. The organic phase 2 and the aqueous phase 6 are allowed to stand for phase separation, and the aqueous phase 6 is diluted and returned to this step for use as a washing liquid.

[0120] i. Stripping of metal ions: After stripping 1 of the organic phase 2 using stripping agent 1, an organic phase 3 and stripping solution 1 are obtained; after stripping 2 of the organic phase 3 using stripping agent 2, the obtained organic phase is the regenerated extractant A, which is returned to step b for use as the extractant A; the obtained aqueous phase is the stripping solution 2.

[0121] The stripping agent 1 is a potassium sulfate and sulfuric acid solution, the potassium sulfate concentration is 25wt.%, the sulfuric acid concentration is 15wt.%, the stripping temperature 1 is 85°C, and the volume ratio O / A is 10: 1. The stripping solution 1 obtained after stripping is heated and concentrated, cooled and crystallized, and filtered to obtain calcium sulfate, potassium magnesium sulfate and potassium aluminum sulfate.

[0122] The stripping agent 2 is an oxalic acid solution, the oxalic acid concentration is 10 wt.%, the stripping temperature 2 is 70° C., and the volume ratio O / A is 10: 1. The stripping solution 2 obtained after stripping is precipitated by light to obtain ferrous oxalate.

[0123] Example 3

[0124] a. Pretreatment: dilute the raffinate with a concentration of 55wt.% to a concentration of 28wt.%, and then filter to remove obvious particulate matter; the filtrate is treated by steam stripping, and the pretreated raffinate in the lower layer is separated after standing and stratification, and the resulting liquid is water phase 0, which is pumped to a raffinate storage tank, and the storage tank is heated and insulated, and the temperature is controlled at 55°C to prevent the impurity metal cations from forming phosphate precipitation.

[0125] b. Extraction of metal ions: After adding extractant A (specifically P204) to aqueous phase 0 to extract metal ions, an organic phase 1 and an aqueous phase 1 are obtained; during extraction, the flow rates of aqueous phase 0 and extractant A are controlled by a peristaltic pump according to the designed flow rate, and aqueous phase 0 and extractant A enter the reaction tank at the same time and begin to stir. When the mixed liquid in the reaction tank reaches about 3 / 4 of the volume of the reaction tank and the stirring time is greater than 30 minutes, the mixed liquid is extracted, and during this period, aqueous phase 0 and extractant A are continuously added in proportion to ensure that the extracted flow rate is equal to the sum of the flow rates of the two phases entering; the extracted mixed liquid enters the phase separation tank for phase separation to obtain aqueous phase 1 and organic phase 1.

[0126] A three-stage three-level countercurrent extraction was adopted, the extraction temperature of each stage was 75°C, and the volume ratio of O / A was 8:1.

[0127] b1. Extraction of metal ions from crude phosphoric acid: Extracting metal ions from crude phosphoric acid with extractant A to obtain aqueous phase 2, organic phase 4 and raffinate acid. The aqueous phase 2 is combined with the aqueous phase 1 to proceed to step c. The organic phase 4 is combined with the organic phase 1 to proceed to step h. The raffinate acid is subjected to step a. The process flow is shown in Figure 2 Continuous three-stage extraction is adopted, and after the reaction stops, the phosphoric acid remaining in the first-stage extraction tank and the second-stage extraction tank that has not passed through the third-stage extraction tank is the residual acid.

[0128] c. Pretreatment: The aqueous phase 1 is concentrated and defluorinated to obtain the aqueous phase 3, and the aqueous phase 3 is subjected to raffinate centrifugal separation, activated carbon adsorption, and hydrogen peroxide oxidation to obtain purified concentrated phosphoric acid. The aqueous phase and the organic phase are separated by raffinate centrifugal separation using a centrifugal extractor; the aqueous phase is passed through a 5 cm high activated carbon layer to further adsorb the entrained organic phase; 4% hydrogen peroxide by weight is added to the aqueous phase, and stirred at 120°C for 25 minutes to obtain purified concentrated phosphoric acid.

[0129] d. Extraction of phosphoric acid: Extractant B (specifically TBP) is added to the purified concentrated phosphoric acid for extraction to obtain an organic phase 5 and raffinate acid; the raffinate acid is returned to step a and used as wet phosphoric acid raffinate acid. The extraction adopts a one-stage three-stage process, the extraction temperature is 75°C, and the phase volume ratio O / A is 8:1.

[0130] e. Washing 1: The organic phase 5 is washed with water to recover the phosphoric acid and impurities carried therein, and then allowed to stand for phase separation to obtain an organic phase 6 and an aqueous phase 4; the temperature is 75°C, and the volume ratio of O / A is 8:1; the obtained aqueous phase 4 is diluted and enters step h.

[0131] f. Re-extraction of phosphoric acid: The organic phase 6 is extracted with water, and then allowed to stand for phase separation to obtain an organic phase 7 and an aqueous phase 7; the organic phase 7 is centrifuged and returned to step d as an extractant B; the stripping temperature is 75°C, and the volume ratio O / A is 8:1.

[0132] g. Concentration: The aqueous phase 7 was concentrated under reduced pressure to a phosphoric acid concentration (in terms of H3PO4) of 81wt.%, and the concentration temperature was 83°C to obtain industrial grade phosphoric acid.

[0133] h. Washing 2: After diluting the aqueous phase 4 in step e, an aqueous phase 5 is obtained, and the aqueous phase 5 is used as a washing liquid to wash the organic phase 1. The organic phase 2 and the aqueous phase 6 are allowed to stand for phase separation, and the aqueous phase 6 is diluted and returned to this step for use as a washing liquid.

[0134] i. Stripping of metal ions: After stripping 1 of the organic phase 2 using stripping agent 1, an organic phase 3 and stripping solution 1 are obtained; after stripping 2 of the organic phase 3 using stripping agent 2, the obtained organic phase is the regenerated extractant A, which is returned to step b for use as the extractant A; the obtained aqueous phase is the stripping solution 2.

[0135] The stripping agent 1 is a potassium sulfate and sulfuric acid solution, the potassium sulfate concentration is 20wt.%, the sulfuric acid concentration is 12wt.%, the stripping temperature 1 is 75°C, and the volume ratio O / A is 8: 1. The stripping solution 1 obtained after stripping is heated and concentrated, cooled and crystallized, and filtered to obtain calcium sulfate, potassium magnesium sulfate and potassium aluminum sulfate.

[0136] The stripping agent 2 is an oxalic acid solution, the oxalic acid concentration is 8 wt.%, the stripping temperature 2 is 60° C., and the volume ratio O / A is 8: 1. The stripping solution 2 obtained after stripping is precipitated by light to obtain ferrous oxalate.

[0137] Example 4

[0138] a. Pretreatment: dilute the raffinate with a concentration of 50wt.% to a concentration of 26wt.%, and then filter to remove obvious particulate matter; the filtrate is treated by steam stripping, and the pretreated raffinate in the lower layer is separated after standing and stratification, and the resulting liquid is water phase 0, which is pumped to a raffinate storage tank, and the storage tank is heated and insulated, and the temperature is controlled at 50°C to prevent the impurity metal cations from forming phosphate precipitation.

[0139] b. Extraction of metal ions: After adding extractant A (specifically P204) to aqueous phase 0 to extract metal ions, an organic phase 1 and an aqueous phase 1 are obtained; during extraction, the flow rates of aqueous phase 0 and extractant A are controlled by a peristaltic pump according to the designed flow rate, and aqueous phase 0 and extractant A enter the reaction tank at the same time and begin to stir. When the mixed liquid in the reaction tank reaches about 3 / 4 of the volume of the reaction tank and the stirring time is greater than 30 minutes, the mixed liquid is extracted, and during this period, aqueous phase 0 and extractant A are continuously added in proportion to ensure that the extracted flow rate is equal to the sum of the flow rates of the two phases entering; the extracted mixed liquid enters the phase separation tank for phase separation to obtain aqueous phase 1 and organic phase 1.

[0140] A three-stage three-level countercurrent extraction was adopted, the extraction temperature of each stage was 65°C, and the volume ratio of O / A was 6:1.

[0141] b1. Extraction of metal ions from crude phosphoric acid: Extracting metal ions from crude phosphoric acid with extractant A to obtain aqueous phase 2, organic phase 4 and raffinate acid. The aqueous phase 2 is combined with the aqueous phase 1 to proceed to step c. The organic phase 4 is combined with the organic phase 1 to proceed to step h. The raffinate acid is subjected to step a. The process flow is shown in Figure 2 Continuous three-stage extraction is adopted, and after the reaction stops, the phosphoric acid remaining in the first-stage extraction tank and the second-stage extraction tank that has not passed through the third-stage extraction tank is the residual acid.

[0142] c. Pretreatment: The aqueous phase 1 is concentrated and defluorinated to obtain the aqueous phase 3, and the aqueous phase 3 is subjected to raffinate centrifugal separation, activated carbon adsorption, and hydrogen peroxide oxidation to obtain purified concentrated phosphoric acid. The aqueous phase and the organic phase are separated by raffinate centrifugal separation using a centrifugal extractor; the aqueous phase is passed through a 4 cm high activated carbon layer to further adsorb the entrained organic phase; 3% hydrogen peroxide by weight is added to the aqueous phase, and stirred at 110°C for 20 minutes to obtain purified concentrated phosphoric acid.

[0143] d. Extraction of phosphoric acid: Extractant B (specifically TBP) is added to the purified concentrated phosphoric acid for extraction to obtain an organic phase 5 and raffinate acid; the raffinate acid is returned to step a and used as wet phosphoric acid raffinate acid. The extraction adopts a one-stage three-stage process, the extraction temperature is 65°C, and the phase volume ratio O / A is 6:1.

[0144] e. Washing 1: The organic phase 5 is washed with water to recover the phosphoric acid and impurities carried therein, and then allowed to stand for phase separation to obtain an organic phase 6 and an aqueous phase 4; the temperature is 65°C, and the volume ratio O / A is 6:1; the obtained aqueous phase 4 is diluted and enters step h.

[0145] f. Re-extraction of phosphoric acid: The organic phase 6 is extracted with water, and then allowed to stand for phase separation to obtain an organic phase 7 and an aqueous phase 7; the organic phase 7 is centrifuged and returned to step d as an extractant B; the stripping temperature is 65°C, and the volume ratio O / A is 6:1.

[0146] g. Concentration: The aqueous phase 7 was concentrated under reduced pressure to a phosphoric acid concentration (in terms of H3PO4) of 77wt.%, and the concentration temperature was 81°C to obtain industrial grade phosphoric acid.

[0147] h. Washing 2: After diluting the aqueous phase 4 in step e, an aqueous phase 5 is obtained, and the aqueous phase 5 is used as a washing liquid to wash the organic phase 1. The organic phase 2 and the aqueous phase 6 are allowed to stand for phase separation, and the aqueous phase 6 is diluted and returned to this step for use as a washing liquid.

[0148] i. Stripping of metal ions: After stripping 1 of the organic phase 2 using stripping agent 1, an organic phase 3 and stripping solution 1 are obtained; after stripping 2 of the organic phase 3 using stripping agent 2, the obtained organic phase is the regenerated extractant A, which is returned to step b for use as the extractant A; the obtained aqueous phase is the stripping solution 2.

[0149] The stripping agent 1 is a potassium sulfate and sulfuric acid solution, the potassium sulfate concentration is 15wt.%, the sulfuric acid concentration is 9wt.%, the stripping temperature 1 is 65°C, and the volume ratio O / A is 6: 1. The stripping solution 1 obtained after stripping is heated and concentrated, cooled and crystallized, and filtered to obtain calcium sulfate, potassium magnesium sulfate and potassium aluminum sulfate.

[0150] The stripping agent 2 is an oxalic acid solution, the oxalic acid concentration is 6 wt.%, the stripping temperature 2 is 50° C., and the volume ratio O / A is 6: 1. The stripping solution 2 obtained after stripping is precipitated by light to obtain ferrous oxalate.

[0151] Example 5

[0152] a. Pretreatment: dilute the raffinate with a concentration of 45wt.% to a concentration of 24wt.%, and then filter to remove obvious particulate matter; the filtrate is treated by steam stripping, and the pretreated raffinate in the lower layer is separated after standing and stratification, and the resulting liquid is water phase 0, which is pumped to a raffinate storage tank, and the storage tank is heated and insulated, and the temperature is controlled at 45°C to prevent impure metal cations from forming phosphate precipitation.

[0153] b. Extraction of metal ions: After adding extractant A (specifically P204) to aqueous phase 0 to extract metal ions, an organic phase 1 and an aqueous phase 1 are obtained; during extraction, the flow rates of aqueous phase 0 and extractant A are controlled by a peristaltic pump according to the designed flow rate, and aqueous phase 0 and extractant A enter the reaction tank at the same time and begin to stir. When the mixed liquid in the reaction tank reaches about 3 / 4 of the volume of the reaction tank and the stirring time is greater than 30 minutes, the mixed liquid is extracted, and during this period, aqueous phase 0 and extractant A are continuously added in proportion to ensure that the extracted flow rate is equal to the sum of the flow rates of the two phases entering; the extracted mixed liquid enters the phase separation tank for phase separation to obtain aqueous phase 1 and organic phase 1.

[0154] A three-stage three-level countercurrent extraction was adopted, the extraction temperature of each stage was 55°C, and the volume ratio of O / A was 4:1.

[0155] b1. Extraction of metal ions from crude phosphoric acid: Extracting metal ions from crude phosphoric acid with extractant A to obtain aqueous phase 2, organic phase 4 and raffinate acid. The aqueous phase 2 is combined with the aqueous phase 1 to proceed to step c. The organic phase 4 is combined with the organic phase 1 to proceed to step h. The raffinate acid is subjected to step a. The process flow is shown in Figure 2 Continuous three-stage extraction is adopted, and after the reaction stops, the phosphoric acid remaining in the first-stage extraction tank and the second-stage extraction tank that has not passed through the third-stage extraction tank is the residual acid.

[0156] c. Pretreatment: The aqueous phase 1 is concentrated and defluorinated to obtain the aqueous phase 3, and the aqueous phase 3 is subjected to raffinate centrifugal separation, activated carbon adsorption, and hydrogen peroxide oxidation to obtain purified concentrated phosphoric acid. The aqueous phase and the organic phase are separated by raffinate centrifugal separation using a centrifugal extractor; the aqueous phase is passed through a 3 cm high activated carbon layer to further adsorb the entrained organic phase; 2% hydrogen peroxide by weight is added to the aqueous phase, and stirred at 105°C for 15 minutes to obtain purified concentrated phosphoric acid.

[0157] d. Extraction of phosphoric acid: Extractant B (specifically TBP) is added to the purified concentrated phosphoric acid for extraction to obtain an organic phase 5 and raffinate acid; the raffinate acid is returned to step a and used as wet phosphoric acid raffinate acid. The extraction adopts one stage and three stages, and the extraction temperature of each stage is 55°C, and the volume ratio O / A is 4:1.

[0158] e. Washing 1: The organic phase 5 is washed with water to recover the phosphoric acid and impurities carried therein, and then allowed to stand for phase separation to obtain an organic phase 6 and an aqueous phase 4; the temperature is 55°C, and the volume ratio of O / A is 4:1; the obtained aqueous phase 4 is diluted and enters step h.

[0159] f. Re-extraction of phosphoric acid: The organic phase 6 is extracted with water, and then allowed to stand for phase separation to obtain an organic phase 7 and an aqueous phase 7; the organic phase 7 is centrifuged and returned to step d as an extractant B; the stripping temperature is 55°C, and the volume ratio O / A is 4:1.

[0160] g. Concentration: The aqueous phase 7 was concentrated under reduced pressure to a phosphoric acid concentration (in terms of H3PO4) of 74 wt.%, and the concentration temperature was 79°C to obtain industrial grade phosphoric acid.

[0161] h. Washing 2: After diluting the aqueous phase 4 in step e, an aqueous phase 5 is obtained, and the aqueous phase 5 is used as a washing liquid to wash the organic phase 1. The organic phase 2 and the aqueous phase 6 are allowed to stand for phase separation, and the aqueous phase 6 is diluted and returned to this step for use as a washing liquid.

[0162] i. Stripping of metal ions: After stripping 1 of the organic phase 2 using stripping agent 1, an organic phase 3 and stripping solution 1 are obtained; after stripping 2 of the organic phase 3 using stripping agent 2, the obtained organic phase is the regenerated extractant A, which is returned to step b for use as the extractant A; the obtained aqueous phase is the stripping solution 2.

[0163] The stripping agent 1 is a potassium sulfate and sulfuric acid solution, the potassium sulfate concentration is 10wt.%, the sulfuric acid concentration is 6wt.%, the stripping temperature 1 is 55°C, and the volume ratio O / A is 4: 1. The stripping solution 1 obtained after stripping is heated and concentrated, cooled and crystallized, and filtered to obtain calcium sulfate, potassium magnesium sulfate and potassium aluminum sulfate.

[0164] The stripping agent 2 is an oxalic acid solution, the oxalic acid concentration is 4 wt.%, the stripping temperature 2 is 40° C., and the volume ratio O / A is 4: 1. The stripping solution 2 obtained after stripping is precipitated by light to obtain ferrous oxalate.

[0165] Example 6

[0166] a. Pretreatment: dilute the raffinate with a concentration of 40wt.% to a concentration of 22wt.%, and then filter to remove obvious particulate matter; the filtrate is treated by steam stripping, and the pretreated raffinate in the lower layer is separated after standing and stratification, and the resulting liquid is water phase 0, which is pumped to a raffinate storage tank, and the storage tank is heated and insulated, and the temperature is controlled at 40°C to prevent impure metal cations from forming phosphate precipitation.

[0167] b. Extraction of metal ions: After adding extractant A (specifically P204) to aqueous phase 0 to extract metal ions, an organic phase 1 and an aqueous phase 1 are obtained; during extraction, the flow rates of aqueous phase 0 and extractant A are controlled by a peristaltic pump according to the designed flow rate, and aqueous phase 0 and extractant A enter the reaction tank at the same time and begin to stir. When the mixed liquid in the reaction tank reaches about 3 / 4 of the volume of the reaction tank and the stirring time is greater than 30 minutes, the mixed liquid is extracted, and during this period, aqueous phase 0 and extractant A are continuously added in proportion to ensure that the extracted flow rate is equal to the sum of the flow rates of the two phases entering; the extracted mixed liquid enters the phase separation tank for phase separation to obtain aqueous phase 1 and organic phase 1.

[0168] A three-stage three-level countercurrent extraction was adopted, the extraction temperature of each stage was 45°C, and the volume ratio of O / A was 2:1.

[0169] b1. Extraction of metal ions from crude phosphoric acid: Extracting metal ions from crude phosphoric acid with extractant A to obtain aqueous phase 2, organic phase 4 and raffinate acid. The aqueous phase 2 is combined with the aqueous phase 1 to proceed to step c. The organic phase 4 is combined with the organic phase 1 to proceed to step h. The raffinate acid is subjected to step a. The process flow is shown in Figure 2 Continuous three-stage extraction is adopted, and after the reaction stops, the phosphoric acid remaining in the first-stage extraction tank and the second-stage extraction tank that has not passed through the third-stage extraction tank is the residual acid.

[0170] c. Pretreatment: The aqueous phase 1 is concentrated and defluorinated to obtain the aqueous phase 3, and the aqueous phase 3 is subjected to raffinate centrifugal separation, activated carbon adsorption, and hydrogen peroxide oxidation to obtain purified concentrated phosphoric acid. The aqueous phase and the organic phase are separated by raffinate centrifugal separation using a centrifugal extractor; the aqueous phase is passed through a 2 cm high activated carbon layer to further adsorb the entrained organic phase; 1% hydrogen peroxide by weight is added to the aqueous phase, and stirred at 100°C for 10 minutes to obtain purified concentrated phosphoric acid.

[0171] d. Extraction of phosphoric acid: Extractant B (specifically TBP) is added to the purified concentrated phosphoric acid for extraction to obtain an organic phase 5 and raffinate acid; the raffinate acid is returned to step a and used as wet phosphoric acid raffinate acid. The extraction adopts a one-stage three-stage process, the extraction temperature is 45°C, and the phase volume ratio O / A is 2:1.

[0172] e. Washing 1: The organic phase 5 is washed with water to recover the phosphoric acid and impurities carried therein, and then allowed to stand for phase separation to obtain an organic phase 6 and an aqueous phase 4; the temperature is 45°C, and the volume ratio of O / A is 2:1; the obtained aqueous phase 4 is diluted and enters step h.

[0173] f. Re-extraction of phosphoric acid: The organic phase 6 is extracted with water, and then allowed to stand for phase separation to obtain an organic phase 7 and an aqueous phase 7; the organic phase 7 is centrifuged and returned to step d as an extractant B; the stripping temperature is 45°C, and the volume ratio O / A is 2:1.

[0174] g. Concentration: The aqueous phase 7 was concentrated under reduced pressure to a phosphoric acid concentration (in terms of H3PO4) of 70wt.%, and the concentration temperature was 77°C to obtain industrial grade phosphoric acid.

[0175] h. Washing 2: After diluting the aqueous phase 4 in step e, an aqueous phase 5 is obtained, and the aqueous phase 5 is used as a washing liquid to wash the organic phase 1. The organic phase 2 and the aqueous phase 6 are allowed to stand for phase separation, and the aqueous phase 6 is diluted and returned to this step for use as a washing liquid.

[0176] i. Stripping of metal ions: After stripping 1 of the organic phase 2 using stripping agent 1, an organic phase 3 and stripping solution 1 are obtained; after stripping 2 of the organic phase 3 using stripping agent 2, the obtained organic phase is the regenerated extractant A, which is returned to step b for use as the extractant A; the obtained aqueous phase is the stripping solution 2.

[0177] The stripping agent 1 is a solution of potassium sulfate and sulfuric acid, the concentration of potassium sulfate is 5wt.%, the concentration of sulfuric acid is 3wt.%, the temperature of stripping 1 is 45°C, and the volume ratio O / A is 2: 1. The stripping solution 1 obtained after stripping is heated and concentrated, cooled and crystallized, and filtered to obtain calcium sulfate, potassium magnesium sulfate and potassium aluminum sulfate.

[0178] The stripping agent 2 is an oxalic acid solution, the oxalic acid concentration is 2 wt.%, the stripping temperature 2 is 30° C., and the volume ratio O / A is 2: 1. The stripping solution 2 obtained after stripping is precipitated by light to obtain ferrous oxalate.

Claims

1. A method for producing industrial-grade phosphoric acid from raffinate of wet-process phosphoric acid, characterized in that: The following steps are involved: a. Pretreatment: dilute the raffinate with a concentration of 40wt.% to 60wt.% to a concentration of 20wt.% to 60wt.%, and then filter, the filtrate is treated by steam stripping, and after standing and stratification, the lower layer of liquid is taken, which is the aqueous phase 0; b. Extraction of metal ions: After adding the extractant A to the aqueous phase 0 to extract the metal ions, an organic phase 1 and an aqueous phase 1 are obtained; c. Pretreatment: The aqueous phase 1 is concentrated and defluorinated to obtain the aqueous phase 3, and the aqueous phase 3 is subjected to raffinate centrifugal separation, activated carbon adsorption, and hydrogen peroxide oxidation to obtain purified concentrated phosphoric acid; wherein the raffinate centrifugal separation is performed by using a centrifugal extractor; d. Extraction of phosphoric acid: Extraction agent B is added to the purified concentrated phosphoric acid to obtain an organic phase 5 and a raffinate; The raffinate acid is returned to step a and used as wet-process phosphoric acid raffinate acid; e. Washing 1: The organic phase 5 is washed with water to recover the phosphoric acid and impurities entrained therein, and then allowed to stand for phase separation to obtain an organic phase 6 and an aqueous phase 4; f. phosphoric acid stripping: stripping the organic phase 6 with water, and then standing the phases to obtain an organic phase 7 and an aqueous phase 7; the organic phase 7 is centrifuged by a centrifugal extractor and returned to step d as an extractant B after the raffinate is centrifuged; g. Concentration: The aqueous phase 7 is concentrated to obtain industrial grade phosphoric acid.

2. The method for producing industrial-grade phosphoric acid from raffinate acid of wet-process phosphoric acid according to claim 1, characterized in that: The following steps are also included: h. Washing 2: After diluting the aqueous phase 4 to obtain an aqueous phase 5, the aqueous phase 5 is used as a washing liquid to wash the organic phase 1, and the phases are allowed to stand to obtain an organic phase 2 and an aqueous phase 6. After diluting the aqueous phase 6, the aqueous phase 6 is returned to this step as a washing liquid; i. Stripping of metal ions: After stripping 1 of the organic phase 2 with stripping agent 1, an organic phase 3 and stripping solution 1 are obtained; after stripping 2 of the organic phase 3 with stripping agent 2, the obtained organic phase is the regenerated extractant A, which is returned to step b and used as the extractant A; the obtained aqueous phase is the stripping solution 2; The stripping agent 1 is potassium sulfate and sulfuric acid solution, and the stripping agent 2 is oxalic acid solution.

3. The method for producing industrial-grade phosphoric acid from raffinate acid of wet-process phosphoric acid according to claim 2, characterized in that: The following steps are also included: The metal ions in the crude phosphoric acid are extracted with extractant A to obtain aqueous phase 2, organic phase 4 and raffinate acid. The aqueous phase 2 is combined with the aqueous phase 1 to perform step c. The organic phase 4 is combined with the organic phase 1 to perform step h. The raffinate acid is subjected to step a.

4. The method for producing industrial-grade phosphoric acid from raffinate acid of wet-process phosphoric acid according to claim 1, characterized in that: In step a, the temperature of the aqueous phase 0 is ensured to be 30-60°C.

5. The method for producing industrial-grade phosphoric acid from raffinate acid of wet-process phosphoric acid according to claim 1, characterized in that: In step b, several stages of countercurrent extraction are adopted, the number of stages is 1 to 5; preferably the number of stages is 3, each stage has three stages, the extraction temperature of each stage is 25 to 85°C, and the volume ratio O / A is 1 to 10:

1.

6. The method for producing industrial-grade phosphoric acid from raffinate acid of wet-process phosphoric acid according to claim 1, characterized in that: Extractant A is at least one of P204, P507, Cynex272, DNNSA, cyclohexane acid and tert-butyl carboxylic acid; extractant B is at least one of TBP, MIBK, DBBP, DAMP, P-311, organic alcohols, ethers and sulfoxides; In step c, the activated carbon adsorption is that the water phase 3 obtained after the raffinate centrifugal separation flows through an activated carbon layer with a height of 1 to 6 cm; the hydrogen peroxide oxidation is that hydrogen peroxide is added to the water phase obtained after the activated carbon adsorption and stirred, the amount of hydrogen peroxide is 1% to 5% of the weight of the water phase, the temperature is 100 to 120° C., and the oxidation time is 10 to 30 minutes.

7. The method for producing industrial-grade phosphoric acid from raffinate acid of wet-process phosphoric acid according to claim 1, characterized in that: In step d, the extraction is a three-stage countercurrent extraction, the extraction temperature is 25 to 85° C., and the volume ratio O / A is 1 to 10:

1.

8. The method for producing industrial-grade phosphoric acid from raffinate acid of wet-process phosphoric acid according to claim 1, characterized in that: In step e, the organic phase 5 is washed with water at a temperature of 25 to 85° C., with a volume ratio of O / A of 1 to 10:1; the obtained aqueous phase 4 is diluted and then enters step h.

9. The method for producing industrial-grade phosphoric acid from raffinate acid of wet-process phosphoric acid according to claim 1, characterized in that: In step f, the organic phase 6 is counter-extracted with water at a temperature of 25 to 85° C., and the volume ratio O / A is 1 to 10:1; In step g, the aqueous phase 7 is concentrated under reduced pressure to a phosphoric acid concentration (in terms of H3PO4) of 70 wt.% to 85 wt.%, and the concentration temperature is 75 to 85°C.

10. The method for producing industrial-grade phosphoric acid from raffinate acid of wet-process phosphoric acid according to claim 2, characterized in that: In step h, two-stage countercurrent washing with washing liquid is adopted, the concentration of phosphoric acid in the washing liquid is 1wt.% to 8wt.% in terms of P2O5, the washing temperature is 25 to 85°C, and the volume ratio of O / A is 1 to 10:

1. In the stripping agent 1, the concentration of potassium sulfate is 5wt.% to 60wt.%, and the concentration of sulfuric acid is ≤15wt.%; the temperature of the stripping 1 is 25 to 85°C, and the volume ratio of O / A is 1 to 10:1; In the stripping agent 2, the oxalic acid concentration is 5wt.% to 45wt.%, the stripping temperature 2 is 30 to 70°C, and the volume ratio O / A is 1 to 10:1; In step i, stripping solution 1 is heated and concentrated, cooled and crystallized, and filtered to obtain calcium sulfate, potassium magnesium sulfate and potassium aluminum sulfate; stripping solution 2 is precipitated by light to obtain ferrous oxalate.

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