Process for the recovery of metal cations from wet-process phosphoric acid

Abstract

The present application relates to a method for recovering metal cations from wet-process phosphoric acid, and belongs to the technical field of wet-process phosphoric acid. The present application solves the technical problem of providing a method for recovering metal cations from wet-process phosphoric acid. The method comprises steps of extraction, washing 1, back extraction, recovery of metal ions and washing 2. The present application adopts a specific back extraction method to recover metal cations from wet-process phosphoric acid, various metal ions can be effectively separated, the recovery rate of each metal element is high, and the product value is high. And a kind of back extraction agent can classify and recover associated metal elements in wet-process phosphoric acid, the method is simple, the cost is relatively low, and the recovered associated metal elements can be effectively separated and high-quality utilization.

Description

Technical Field

[0001] This invention relates to a method for recovering metal cations from wet-process phosphoric acid, specifically a method for recovering metal cations from wet-process phosphoric acid using back-extraction during solvent extraction, belonging to the field of wet-process phosphoric acid technology. Background Technology

[0002] Wet-process phosphoric acid is an important intermediate product in the production of phosphate fertilizers such as diammonium phosphate, monoammonium phosphate, and superphosphate, and is also a raw material for food-grade and industrial-grade phosphoric acid. However, in recent years, with the large-scale development and utilization of phosphate rock resources, the quality of phosphate rock has been continuously depleted, resulting in a gradual increase in metal cation impurities such as Fe, Al, Mg, and Ca in wet-process phosphoric acid. This has led to more complex processing of subsequent products from wet-process phosphoric acid, making it difficult for the product quality to meet the requirements of superior grades, and increasing costs.

[0003] Common methods for removing metal cations from phosphoric acid include: 1. Organic solvent extraction; 2. Chemical precipitation; 3. Ion exchange; 4. Membrane separation. Chemical precipitation has low impurity removal efficiency, introduces alkaline ions which weaken the acidity of the acidic system, and makes separation difficult. Ion exchange requires a large amount of resin, resulting in high regeneration costs. Membrane separation utilizes the difference in membrane pore size to selectively allow impurities to pass through, achieving separation and purification; however, this method is relatively expensive. Organic solvent extraction yields high-purity products, has a simple production process and equipment, low energy consumption, good separation effect, high recovery rate, and can be used continuously.

[0004] Solvent extraction is the mainstream process for wet-process phosphoric acid purification. Both domestic and international researchers have conducted extensive work on removing metal ions from phosphoric acid using organic solvent extraction. However, most methods suffer from problems such as the need for multi-step back-extraction, low metal ion recovery rates, and difficulties in classifying and recovering metal ions for high-value utilization. Therefore, exploring a one-step extraction and classified recovery method for metal ions from the extractant is of practical significance.

[0005] Patent application number 201610514424.9 discloses a combined extraction method for producing high-quality phosphoric acid. It uses extractants such as P204 to extract metal cations from crude phosphoric acid. The raffinate, i.e., the aqueous phase, is used to prepare high-quality phosphoric acid. However, the extract phase contains a variety of metal cations. When strong acid is used for back-extraction, the metal cations obtained cannot be separated and can only be used to produce fertilizers or flame retardants. The product has low application value and the recovery rate of metal ions is also low. Summary of the Invention

[0006] To address the above deficiencies, the technical problem solved by this invention is to provide a method for recovering metal cations from wet-process phosphoric acid.

[0007] The present invention provides a method for recovering metal cations from wet-process phosphoric acid, comprising the following steps:

[0008] (1) Extraction: Extract wet phosphoric acid, the resulting organic phase is the extractant loaded with metal ions, and the aqueous phase is purified phosphoric acid;

[0009] (2) Washing 1: The metal ion-loaded extractant is washed with dilute phosphoric acid to obtain the washed extractant;

[0010] (3) Back-extraction: Using ammonium oxalate solution or a mixed solution of ammonium oxalate and ammonium sulfate as back-extraction agent, the washed extractant is back-extracted to obtain aqueous phase 1 and organic phase 1;

[0011] (4) Recovery of metal ions: Recovery of metal ions from aqueous phase 1;

[0012] (5) Washing 2: Wash organic phase 1 to recover ammonium oxalate and ammonium sulfate entrained in organic phase 1 to obtain regenerated extractant, which is returned to step (1) as an extractant for the extraction of wet phosphoric acid.

[0013] In one specific embodiment of the present invention, in step (4), the recovery of metal ions is performed using method 1, method 2, method 3, or method 4, wherein,

[0014] Method 1 includes the following steps:

[0015] a. Cooling crystallization: Aqueous phase 1 is cooled and crystallized, and solid-liquid separation is performed to obtain a mixed salt of iron, aluminum and magnesium sulfates and aqueous phase 2;

[0016] Method 2 includes the following steps:

[0017] a. Cooling crystallization 1: Cool the aqueous phase 1 to crystallize, and separate the solid and liquid phases to obtain magnesium ammonium sulfate crystals and aqueous phase 2;

[0018] b. Cooling crystallization 2: Cool the aqueous phase 2 to crystallize, and separate the solid and liquid phases to obtain ammonium aluminum sulfate crystals and aqueous phase 3;

[0019] c. Cooling crystallization 3: Cool the aqueous phase 3 to crystallize, and separate the solid and liquid phases to obtain ferric ammonium sulfate crystals and aqueous phase 4;

[0020] Method 3 includes the following steps:

[0021] a. Precipitation: Ammonia gas is passed into aqueous phase 1 to adjust the pH. Precipitation occurs. Solid-liquid separation is performed to obtain iron, aluminum and magnesium hydroxide precipitate and aqueous phase 2.

[0022] b. Ammonia distillation: Heat aqueous phase 2 to distill off the ammonia gas. The collected ammonia gas is returned to step I, and aqueous phase 3 is returned as a back-extraction agent.

[0023] Method 4 includes the following steps:

[0024] a. Precipitation 1: Add ammonia to aqueous phase 1 to adjust the pH. A red precipitate appears. Separate the solid and liquid phases to obtain Fe(OH)3 precipitate and aqueous phase 2.

[0025] b. Precipitation 2: Ammonia water was added dropwise to aqueous phase 2 to adjust the pH. A white precipitate appeared. Solid-liquid separation was performed to obtain Al(OH)3 precipitate and aqueous phase 3.

[0026] c. Precipitation 3: Add aqueous phase 3 dropwise to ammonia water, adjust the pH, and a white precipitate will appear. Separate the solid and liquid phases to obtain Mg(OH)2 precipitate and aqueous phase 3.

[0027] In one embodiment of the present invention, in step (1), the extraction is a multi-stage three-stage countercurrent extraction, with 1 to 5 stages. Preferably, there are 3 stages, and the extraction temperature of each stage is 25 to 85°C, with a volume ratio of O / A of 1 to 10:1.

[0028] In one embodiment of the present invention, in step (2), a two-stage countercurrent washing with dilute phosphoric acid is used. The concentration of dilute phosphoric acid is 1 wt.% to 8 wt.% based on P2O5, the temperature is 25 to 85°C, and the O / A ratio is 1 to 10:1 by volume.

[0029] In one embodiment of the present invention, in step (3), the back-extraction is a multi-stage three-stage countercurrent back-extraction, with 1 to 5 stages. In a preferred embodiment, the back-extraction has 3 stages, and the back-extraction temperature of each stage is 25 to 90°C, with a volume ratio of O / A of 1 to 10:1.

[0030] In one embodiment of the present invention, in the stripping agent of step (3), the concentration of ammonium oxalate is 1 wt.% to 20 wt.% and the concentration of ammonium sulfate is 0 wt.% to 35 wt.%.

[0031] Preferably, in step (4) of method 1, the crystallization temperature is -10 to 50°C; in step (4) of method 2, the crystallization temperature of magnesium ammonium sulfate is 20 to 50°C; the crystallization temperature of aluminum ammonium sulfate is 1 to 15°C; and the crystallization temperature of ferric ammonium sulfate is -10 to 0°C.

[0032] As a preferred embodiment, in method 3 of step (4), in step a, the pH is adjusted to 3.3 to 12.4; in step b, the temperature for ammonia stripping is -10 to 0℃; in method 4 of step (4), in step a, the pH is adjusted to 3.3 to 3.8; in step b, the pH is adjusted to 4 to 5; and in step c, the pH is adjusted to 9 to 12.4.

[0033] In one embodiment of the present invention, in step (5), organic phase 1 is washed in a two-stage countercurrent process with ammonium oxalate and ammonium sulfate. The concentration of ammonium oxalate is 0.1 wt.% to 5 wt.%, the concentration of ammonium sulfate is 0.1 wt.% to 5 wt.%, the temperature is 30 to 70°C, and the volume ratio of O / A is 1 to 10:1.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. This invention employs a specific back-extraction method to recover metal cations from wet-process phosphoric acid. Various metal ions can be effectively separated, resulting in high recovery rates for each metal element and high product value.

[0036] 2. This invention uses a back-extraction agent to classify and recover associated metal elements in wet-process phosphoric acid. The method is simple and low-cost, and the recovered associated metal elements can be effectively separated and utilized in a high-quality manner. Attached Figure Description

[0037] Figure 1 This is a process flow diagram of the method for recovering metal cations from wet-process phosphoric acid in Embodiment 1 of the present invention.

[0038] Figure 2 This is a process flow diagram of the method for recovering metal cations from wet-process phosphoric acid in Examples 2-4 and 9 of the present invention.

[0039] Figure 3 This is a process flow diagram of the method for recovering metal cations from wet-process phosphoric acid in Embodiment 5 of the present invention.

[0040] Figure 4 This is a process flow diagram of the method for recovering metal cations from wet-process phosphoric acid in Examples 6-8 of the present invention. Detailed Implementation

[0041] The present invention provides a method for recovering metal cations from wet-process phosphoric acid, comprising the following steps:

[0042] (1) Extraction: Extract wet phosphoric acid, the resulting organic phase is the extractant loaded with metal ions, and the aqueous phase is purified phosphoric acid;

[0043] (2) Washing 1: The metal ion-loaded extractant is washed with dilute phosphoric acid to obtain the washed extractant;

[0044] (3) Back-extraction: Using ammonium oxalate solution or a mixed solution of ammonium oxalate and ammonium sulfate as back-extraction agent, the washed extractant is back-extracted to obtain aqueous phase 1 and organic phase 1;

[0045] (4) Recovery of metal ions: Recovery of metal ions from aqueous phase 1;

[0046] (5) Washing 2: Wash organic phase 1 to recover ammonium oxalate and ammonium sulfate entrained in organic phase 1 to obtain regenerated extractant, which is returned to step (1) as an extractant for the extraction of wet phosphoric acid.

[0047] In one specific embodiment of the present invention, in step (4), the recovery of metal ions is performed using method 1, method 2, method 3, or method 4, wherein,

[0048] Method 1 includes the following steps:

[0049] a. Cooling crystallization: Aqueous phase 1 is cooled and crystallized, and solid-liquid separation is performed to obtain a mixed salt of iron, aluminum and magnesium sulfates and aqueous phase 2;

[0050] Method 2 includes the following steps:

[0051] a. Cooling crystallization 1: Cool the aqueous phase 1 to crystallize, and separate the solid and liquid phases to obtain magnesium ammonium sulfate crystals and aqueous phase 2;

[0052] b. Cooling crystallization 2: Cool the aqueous phase 2 to crystallize, and separate the solid and liquid phases to obtain ammonium aluminum sulfate crystals and aqueous phase 3;

[0053] c. Cooling crystallization 3: Cool the aqueous phase 3 to crystallize, and separate the solid and liquid phases to obtain ferric ammonium sulfate crystals and aqueous phase 4;

[0054] Method 3 includes the following steps:

[0055] a. Precipitation: Ammonia gas is passed into aqueous phase 1 to adjust the pH. Precipitation occurs. Solid-liquid separation is performed to obtain iron, aluminum and magnesium hydroxide precipitate and aqueous phase 2.

[0056] b. Ammonia distillation: Heat aqueous phase 2 to distill off the ammonia gas. The collected ammonia gas is returned to step I, and aqueous phase 3 is returned as a back-extraction agent.

[0057] Method 4 includes the following steps:

[0058] a. Precipitation 1: Add ammonia to aqueous phase 1 to adjust the pH. A red precipitate appears. Separate the solid and liquid phases to obtain Fe(OH)3 precipitate and aqueous phase 2.

[0059] b. Precipitation 2: Ammonia water was added dropwise to aqueous phase 2 to adjust the pH. A white precipitate appeared. Solid-liquid separation was performed to obtain Al(OH)3 precipitate and aqueous phase 3.

[0060] c. Precipitation 3: Add aqueous phase 3 dropwise to ammonia water, adjust the pH, and a white precipitate will appear. Separate the solid and liquid phases to obtain Mg(OH)2 precipitate and aqueous phase 3.

[0061] Step (1) is an extraction process, and conventional methods for extracting metallic impurities from wet-process phosphoric acid are applicable to this invention. In one embodiment of this invention, the extraction is a multi-stage countercurrent extraction, with 1 to 5 stages; preferably, there are 3 stages, and each stage has three levels.

[0062] In one specific embodiment, the extraction temperature of each segment is 25–85°C, compared to a volume ratio of O / A of 1–10:1.

[0063] Extractants for metal cations can be those 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)phosphine), DNNSA (chemical name: dinonylnaphthalenesulfonic acid), cycloalkanoic acid, and tertiary carbonate.

[0064] Step (2) is washing 1, in which the metal ion-loaded extractant is washed with dilute phosphoric acid to recover the phosphoric acid entrained in the extractant.

[0065] In one embodiment of the present invention, in step (2), a two-stage countercurrent washing with dilute phosphoric acid is used. The concentration of dilute phosphoric acid is 1 wt.% to 8 wt.% based on P2O5, the temperature is 25 to 85°C, and the O / A ratio is 1 to 10:1 by volume.

[0066] Step (3) is back-extraction, in which various metal ions are back-extracted from the extractant loaded with metal ions, so as to realize the separate recovery of metal ions and improve the product value.

[0067] Step (3) Use ammonium oxalate solution or a mixed solution of ammonium oxalate and ammonium sulfate as the back-extraction agent to back-extract the washed extractant to obtain back-extraction solution 1 and organic phase 1;

[0068] In one embodiment of the present invention, in step (3), the back-extraction is a multi-stage three-stage countercurrent back-extraction, with 1 to 5 stages. In a preferred embodiment, the back-extraction has 3 stages, and the back-extraction temperature of each stage is 25 to 90°C, with a volume ratio of O / A of 1 to 10:1.

[0069] In one embodiment of the present invention, the concentration of ammonium oxalate in the back-extraction agent is 1 wt.% to 20 wt.%, and the concentration of ammonium sulfate is 0 wt.% to 35 wt.%.

[0070] Step (4) is to recover various metal ions from aqueous phase 1, preferably using method 1, method 2, method 3, or method 4.

[0071] In one specific embodiment, method 1 is used to recover metal ions, and method 1 includes the following steps:

[0072] a. Cooling crystallization: Aqueous phase 1 is cooled and crystallized, and solid-liquid separation is performed to obtain a mixed salt of iron, aluminum and magnesium sulfates and aqueous phase 2;

[0073] Preferably, in method 1, the crystallization temperature is -10 to 50°C.

[0074] In another specific embodiment, method 2 is used to recover metal ions, which includes the following steps:

[0075] a. Cooling crystallization 1: Cool the aqueous phase 1 to crystallize, and separate the solid and liquid phases to obtain magnesium ammonium sulfate crystals and aqueous phase 2;

[0076] b. Cooling crystallization 2: Cool the aqueous phase 2 to crystallize, and separate the solid and liquid phases to obtain ammonium aluminum sulfate crystals and aqueous phase 3;

[0077] c. Cooling crystallization 3: Cool the aqueous phase 3 to crystallize, and separate the solid and liquid phases to obtain ferric ammonium sulfate crystals and aqueous phase 4;

[0078] Preferably, in method 2, the crystallization temperature of magnesium ammonium sulfate is 20–50°C; the crystallization temperature of aluminum ammonium sulfate is 1–15°C; and the crystallization temperature of ferric ammonium sulfate is -10–0°C.

[0079] The solid-liquid separation in methods 1 and 2 can be performed using conventional separation methods in the field, as long as the purpose of separating the crystal from the aqueous phase is achieved. For example, filtration can be used.

[0080] In another specific embodiment, method 3 is used to recover metal ions, which includes the following steps:

[0081] a. Precipitation: Ammonia gas is passed into aqueous phase 1 to adjust the pH. Precipitation occurs. Solid-liquid separation is performed to obtain iron, aluminum and magnesium hydroxide precipitate and aqueous phase 2.

[0082] b. Ammonia distillation: Heat aqueous phase 2 to distill off the ammonia gas. The collected ammonia gas is returned to step I, and aqueous phase 3 is returned as a back-extraction agent.

[0083] Preferably, in step a of method 3, the pH is adjusted to 3.3 to 12.4; and in step b, the temperature for ammonia stripping is -10 to 0°C.

[0084] In another specific embodiment, method 4 is used to recover metal ions, which includes the following steps:

[0085] a. Precipitation 1: Add ammonia to aqueous phase 1 to adjust the pH. A red precipitate appears. Separate the solid and liquid phases to obtain Fe(OH)3 precipitate and aqueous phase 2.

[0086] b. Precipitation 2: Ammonia water was added dropwise to aqueous phase 2 to adjust the pH. A white precipitate appeared. Solid-liquid separation was performed to obtain Al(OH)3 precipitate and aqueous phase 3.

[0087] c. Precipitation 3: Add aqueous phase 3 dropwise to ammonia water, adjust the pH, and a white precipitate will appear. Separate the solid and liquid phases to obtain Mg(OH)2 precipitate and aqueous phase 3.

[0088] Preferably, in step a of method 4, the pH is adjusted to 3.3–3.8; in step b, the pH is adjusted to 4–5; and in step c, the pH is adjusted to 9–12.4.

[0089] The solid-liquid separation described in this invention employs conventional methods in the art. In one specific embodiment, the solid-liquid separation uses a high-speed centrifuge with a rotation speed of 5000-8000 rpm and a time of 15-30 min.

[0090] Step (5) is washing 2, washing and recovering ammonium oxalate and ammonium sulfate entrained in organic phase 1, which can obtain regenerated extractant, which is returned to step (1) and recycled as extractant.

[0091] In one embodiment of the present invention, organic phase 1 is washed in a two-stage countercurrent process with a solution of dilute ammonium oxalate and dilute ammonium sulfate. The concentration of dilute ammonium oxalate is 0.1 wt.% to 5 wt.%, the concentration of dilute ammonium sulfate is 0.1 wt.% to 5 wt.%, the temperature is 30 to 70°C, and the volume ratio of O / A is 1 to 10:1.

[0092] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0093] Example 1

[0094] like Figure 1 As shown, a method for recovering metal cations from wet-process phosphoric acid includes the following steps:

[0095] (1) Extraction: Wet phosphoric acid was subjected to three-stage countercurrent extraction, with the extraction temperature of each stage being 60℃ and the O / A ratio being 4:1 (volume ratio).

[0096] (2) Washing 1: The metal ion-loaded extractant is first washed in two stages of countercurrent washing with dilute phosphoric acid with a concentration of 1 wt.% P2O5 at a temperature of 50°C and a ratio of O / A of 3:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0097] (3) Back-extraction: A mixed solution of ammonium oxalate and ammonium sulfate was used as the back-extraction agent, wherein the concentration of ammonium oxalate was 4.5 wt.% and the concentration of ammonium sulfate was 35 wt.%. The extractant loaded with metal ions was subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage was 60℃, and the O / A ratio was 1:3 (volume ratio) to obtain aqueous phase 1 and organic phase 1.

[0098] (4) Recovery of metal ions: The aqueous phase 1 is cooled to 0°C to obtain a mixed salt of iron, aluminum and magnesium sulfate and aqueous phase 2. This step simultaneously recovers magnesium, aluminum and iron ions.

[0099] (5) Washing 2: Use a 0.1 wt.% dilute ammonium oxalate solution and a 0.1 wt.% dilute ammonium sulfate solution to wash the organic phase 1 in two countercurrent stages at a temperature of 30°C. The O / A ratio is 3:1 (volume ratio). The ammonium oxalate and ammonium sulfate entrained in the organic phase 1 are recovered to obtain a regenerated extractant that can be recycled.

[0100] In this embodiment, metal cations were recovered, and the back-extraction rate and recovery rate are shown in Table 1.

[0101] Example 2

[0102] like Figure 2 As shown, a method for recovering metal cations from wet-process phosphoric acid includes the following steps:

[0103] (1) Extraction: Wet phosphoric acid was subjected to three-stage countercurrent extraction, with the extraction temperature of each stage being 60℃ and the O / A ratio being 4:1 (volume ratio).

[0104] (2) Washing 1: The metal ion-loaded extractant is first washed in two stages of countercurrent washing with dilute phosphoric acid with a concentration of 1 wt.% P2O5 at a temperature of 50°C and a ratio of O / A of 3:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0105] (3) Back-extraction: A mixed solution of ammonium oxalate and ammonium sulfate was used as the back-extraction agent, wherein the concentration of ammonium oxalate was 4.5 wt.% and the concentration of ammonium sulfate was 35 wt.%. The extractant loaded with metal ions was subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage was 60℃, and the O / A ratio was 1:3 (volume ratio) to obtain aqueous phase 1 and organic phase 1.

[0106] (4) Recovery of metal ions: Cooling aqueous phase 1 to 20°C yields magnesium ammonium sulfate and aqueous phase 2; cooling aqueous phase 2 to 0°C yields aluminum ammonium sulfate and aqueous phase 3; cooling aqueous phase 3 to -10°C yields ferric ammonium sulfate; this step recovers magnesium, aluminum and iron ions separately.

[0107] (5) Washing 2: Use a 0.1 wt.% dilute ammonium oxalate solution and a 0.1 wt.% dilute ammonium sulfate solution to wash the organic phase 1 in two countercurrent stages at a temperature of 30°C. The O / A ratio is 3:1 (volume ratio). The ammonium oxalate and ammonium sulfate entrained in the organic phase 1 are recovered to obtain a regenerated extractant that can be recycled.

[0108] In this embodiment, metal cations were recovered, and the back-extraction rate and recovery rate are shown in Table 1.

[0109] Comparative Example 1

[0110] A method for recovering metal cations from wet-process phosphoric acid includes the following steps:

[0111] (1) Extraction: Wet phosphoric acid was subjected to three-stage countercurrent extraction, with the extraction temperature of each stage being 60℃ and the O / A ratio being 4:1 (volume ratio).

[0112] (2) Washing 1: The metal ion-loaded extractant is first washed in two stages of countercurrent washing with dilute phosphoric acid with a concentration of 1 wt.% P2O5 at a temperature of 50°C and a ratio of O / A of 3:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0113] (3) Back-extraction: Using a 35 wt.% ammonium sulfate solution as the back-extraction agent, the extractant loaded with metal ions is subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage is 60℃, and the O / A ratio is 1:3 (volume ratio) to obtain aqueous phase 1 and organic phase 1.

[0114] (4) Recovery of metal ions: Aqueous phase 1 is cooled to 20°C to obtain magnesium ammonium sulfate and aqueous phase 2; aqueous phase 2 is cooled to 0°C to obtain aluminum ammonium sulfate and aqueous phase 3; aqueous phase 3 is cooled to -10°C to obtain ferric ammonium sulfate; this step recovers magnesium, aluminum and iron ions separately.

[0115] (5) Washing 2: Use a 0.1 wt.% dilute ammonium oxalate solution and a 0.1 wt.% dilute ammonium sulfate solution to wash the organic phase 1 in two countercurrent stages at a temperature of 30°C. The O / A ratio is 3:1 (volume ratio). The ammonium oxalate and ammonium sulfate entrained in the organic phase 1 are recovered to obtain a regenerated extractant that can be recycled.

[0116] The back-extraction rate and recovery rate of the metal cations recovered in this comparative example are shown in Table 1.

[0117] Example 3

[0118] like Figure 2 As shown, a method for recovering metal cations from wet-process phosphoric acid includes the following steps:

[0119] (1) Extraction: Wet phosphoric acid was subjected to three-stage countercurrent extraction, with the extraction temperature of each stage being 60℃ and the O / A ratio being 4:1 (volume ratio).

[0120] (2) Washing 1: The metal ion-loaded extractant is first washed in two stages of countercurrent washing with dilute phosphoric acid with a concentration of 1 wt.% P2O5 at a temperature of 50°C and a ratio of O / A of 3:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0121] (3) Back-extraction: A mixed solution of ammonium oxalate and ammonium sulfate was used as the back-extraction agent, wherein the concentration of ammonium oxalate was 4.5 wt.% and the concentration of ammonium sulfate was 25 wt.%. The extractant loaded with metal ions was subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage was 60℃, and the O / A ratio was 1:3 (volume ratio) to obtain aqueous phase 1 and organic phase 1.

[0122] (4) Recovery of metal ions: Cooling aqueous phase 1 to 30°C yields magnesium ammonium sulfate and aqueous phase 2; cooling aqueous phase 2 to 5°C yields aluminum ammonium sulfate and aqueous phase 3; cooling aqueous phase 3 to -7°C yields ferric ammonium sulfate; this step recovers magnesium, aluminum and iron ions separately.

[0123] (5) Washing 2: Use a 0.1 wt.% dilute ammonium oxalate solution and a 0.1 wt.% dilute ammonium sulfate solution to wash the organic phase 1 in two countercurrent stages at a temperature of 30°C. The O / A ratio is 3:1 (volume ratio). The ammonium oxalate and ammonium sulfate entrained in the organic phase 1 are recovered to obtain a regenerated extractant that can be recycled.

[0124] In this embodiment, metal cations were recovered, and the back-extraction rate and recovery rate are shown in Table 1.

[0125] Example 4

[0126] like Figure 2 As shown, a method for recovering metal cations from wet-process phosphoric acid includes the following steps:

[0127] (1) Extraction: Wet phosphoric acid was subjected to three-stage countercurrent extraction, with the extraction temperature of each stage being 60℃ and the O / A ratio being 4:1 (volume ratio).

[0128] (2) Washing 1: The metal ion-loaded extractant is first washed in two stages of countercurrent washing with dilute phosphoric acid with a concentration of 1 wt.% P2O5 at a temperature of 50°C and a ratio of O / A of 3:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0129] (3) Back-extraction: A mixed solution of ammonium oxalate and ammonium sulfate was used as the back-extraction agent, wherein the concentration of ammonium oxalate was 4.5 wt.% and the concentration of ammonium sulfate was 15 wt.%. The extractant loaded with metal ions was subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage was 60℃, and the O / A ratio was 1:3 (volume ratio) to obtain aqueous phase 1 and organic phase 1.

[0130] (4) Recovery of metal ions: Cooling aqueous phase 1 to 40°C yields magnesium ammonium sulfate and aqueous phase 2; cooling aqueous phase 2 to 10°C yields aluminum ammonium sulfate and aqueous phase 3; cooling aqueous phase 3 to -5°C yields ferric ammonium sulfate; this step recovers magnesium, aluminum and iron ions separately.

[0131] (5) Washing 2: Use a 0.1 wt.% dilute ammonium oxalate solution and a 0.1 wt.% dilute ammonium sulfate solution to wash the organic phase 1 in two countercurrent stages at a temperature of 30°C. The O / A ratio is 3:1 (volume ratio). The ammonium oxalate and ammonium sulfate entrained in the organic phase 1 are recovered to obtain a regenerated extractant that can be recycled.

[0132] In this embodiment, metal cations were recovered, and the back-extraction rate and recovery rate are shown in Table 1.

[0133] Example 5

[0134] like Figure 3 As shown, a method for recovering metal cations from wet-process phosphoric acid includes the following steps:

[0135] (1) Extraction: Wet phosphoric acid was subjected to three-stage countercurrent extraction, with the extraction temperature of each stage being 60℃ and the O / A ratio being 4:1 (volume ratio).

[0136] (2) Washing 1: The metal ion-loaded extractant is first washed in two stages of countercurrent washing with dilute phosphoric acid with a concentration of 1 wt.% P2O5 at a temperature of 50°C and a ratio of O / A of 3:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0137] (3) Back-extraction: Ammonium oxalate solution was used as the back-extraction agent, wherein the concentration of ammonium oxalate was 4.5 wt.%, and the extractant loaded with metal ions was subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage was 60℃, and the O / A ratio was 1:3 (volume ratio) to obtain aqueous phase 1 and organic phase 1.

[0138] (4) Recovery of metal ions: Ammonia gas is passed into aqueous phase 1 to adjust the pH to 11. Precipitation occurs. Solid-liquid separation is performed to obtain iron, aluminum and magnesium hydroxide precipitates and aqueous phase 2. Aqueous phase 2 is heated to evaporate the ammonia gas. The collected ammonia gas is returned to step a.

[0139] (5) Washing 2: Use a 0.1 wt.% dilute ammonium oxalate solution and a 0.1 wt.% dilute ammonium sulfate solution to wash the organic phase 1 in two countercurrent stages at a temperature of 30°C. The O / A ratio is 3:1 (volume ratio). The ammonium oxalate and ammonium sulfate entrained in the organic phase 1 are recovered to obtain a regenerated extractant that can be recycled.

[0140] In this embodiment, metal cations were recovered, and the back-extraction rate and recovery rate are shown in Table 1.

[0141] Example 6

[0142] like Figure 4 As shown, a method for recovering metal cations from wet-process phosphoric acid includes the following steps:

[0143] (1) Extraction: Wet phosphoric acid was subjected to three-stage countercurrent extraction, with the extraction temperature of each stage being 60℃ and the O / A ratio being 4:1 (volume ratio).

[0144] (2) Washing 1: The metal ion-loaded extractant is first washed in two stages of countercurrent washing with dilute phosphoric acid with a concentration of 1 wt.% P2O5 at a temperature of 50°C and a ratio of O / A of 3:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0145] (3) Back-extraction: Ammonium oxalate solution was used as the back-extraction agent, wherein the concentration of ammonium oxalate was 4.5 wt.%, and the extractant loaded with metal ions was subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage was 60℃, and the O / A ratio was 1:3 (volume ratio) to obtain aqueous phase 1 and organic phase 1.

[0146] (4) Recovery of metal ions: Add ammonia to aqueous phase 1 and adjust the pH to 3.7. A red precipitate appears. After solid-liquid separation, Fe(OH)3 precipitate and aqueous phase 2 are obtained. Add ammonia to aqueous phase 2 and adjust the pH to 5. A white precipitate appears. After solid-liquid separation, Al(OH)3 precipitate and aqueous phase 3 are obtained. Add ammonia to aqueous phase 3 and adjust the pH to 12.4. A white precipitate appears. After solid-liquid separation, Mg(OH)2 precipitate and aqueous phase 3 are obtained.

[0147] (5) Washing 2: Use a 0.1 wt.% dilute ammonium oxalate solution and a 0.1 wt.% dilute ammonium sulfate solution to wash the organic phase 1 in two countercurrent stages at a temperature of 30°C. The O / A ratio is 3:1 (volume ratio). The ammonium oxalate and ammonium sulfate entrained in the organic phase 1 are recovered to obtain a regenerated extractant that can be recycled.

[0148] In this embodiment, metal cations were recovered, and the back-extraction rate and recovery rate are shown in Table 1.

[0149] Example 7

[0150] like Figure 1 As shown, a method for recovering metal cations from wet-process phosphoric acid includes the following steps:

[0151] (1) Extraction: Wet phosphoric acid was subjected to three-stage countercurrent extraction, with the extraction temperature of each stage being 60℃ and the O / A ratio being 4:1 (volume ratio).

[0152] (2) Washing 1: The metal ion-loaded extractant is first washed in two stages of countercurrent washing with dilute phosphoric acid with a concentration of 1 wt.% P2O5 at a temperature of 50°C and a ratio of O / A of 3:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0153] (3) Back-extraction: A mixed solution of ammonium oxalate and ammonium sulfate was used as the back-extraction agent, wherein the concentration of ammonium oxalate was 8.0 wt.%, and the extractant loaded with metal ions was subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage was 60℃, and the O / A ratio was 1:3 (volume ratio), to obtain aqueous phase 1 and organic phase 1.

[0154] (4) Recovery of metal ions: Add ammonia to aqueous phase 1 to adjust the pH to 3.5. A red precipitate appears. After solid-liquid separation, Fe(OH)3 precipitate and aqueous phase 2 are obtained. Add ammonia to aqueous phase 2 to adjust the pH to 4.7. A white precipitate appears. After solid-liquid separation, Al(OH)3 precipitate and aqueous phase 3 are obtained. Add ammonia to aqueous phase 3 to adjust the pH to 10. A white precipitate appears. After solid-liquid separation, Mg(OH)2 precipitate and aqueous phase 3 are obtained.

[0155] (5) Washing 2: Use a 0.1 wt.% dilute ammonium oxalate solution and a 0.1 wt.% dilute ammonium sulfate solution to wash the organic phase 1 in two countercurrent stages at a temperature of 30°C. The O / A ratio is 3:1 (volume ratio). The ammonium oxalate and ammonium sulfate entrained in the organic phase 1 are recovered to obtain a regenerated extractant that can be recycled.

[0156] In this embodiment, metal cations were recovered, and the back-extraction rate and recovery rate are shown in Table 1.

[0157] Example 8

[0158] like Figure 1 As shown, a method for recovering metal cations from wet-process phosphoric acid includes the following steps:

[0159] (1) Extraction: Wet phosphoric acid was subjected to three-stage countercurrent extraction, with the extraction temperature of each stage being 60℃ and the O / A ratio being 4:1 (volume ratio).

[0160] (2) Washing 1: The metal ion-loaded extractant is first washed in two stages of countercurrent washing with dilute phosphoric acid with a concentration of 1 wt.% P2O5 at a temperature of 50°C and a ratio of O / A of 3:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0161] (3) Back-extraction: Ammonium oxalate solution was used as the back-extraction agent, wherein the concentration of ammonium oxalate was 12.0 wt.%, and the extractant loaded with metal ions was subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage was 60℃, and the O / A ratio was 1:3 (volume ratio), to obtain aqueous phase 1 and organic phase 1.

[0162] (4) Recovery of metal ions: Add ammonia to aqueous phase 1 and adjust the pH to 3.3. A red precipitate appears. After solid-liquid separation, Fe(OH)3 precipitate and aqueous phase 2 are obtained. Add ammonia to aqueous phase 2 and adjust the pH to 4. A white precipitate appears. After solid-liquid separation, Al(OH)3 precipitate and aqueous phase 3 are obtained. Add ammonia to aqueous phase 3 and adjust the pH to 9. A white precipitate appears. After solid-liquid separation, Mg(OH)2 precipitate and aqueous phase 3 are obtained.

[0163] (5) Washing 2: Use a 0.1 wt.% dilute ammonium oxalate solution and a 0.1 wt.% dilute ammonium sulfate solution to wash the organic phase 1 in two countercurrent stages at a temperature of 30°C. The O / A ratio is 3:1 (volume ratio). The ammonium oxalate and ammonium sulfate entrained in the organic phase 1 are recovered to obtain a regenerated extractant that can be recycled.

[0164] In this embodiment, metal cations were recovered, and the back-extraction rate and recovery rate are shown in Table 1.

[0165] Example 9

[0166] A method for recovering metal cations from wet-process phosphoric acid includes the following steps:

[0167] (1) Extraction: Wet phosphoric acid was subjected to three-stage countercurrent extraction, with the extraction temperature of each stage being 60℃ and the O / A ratio being 4:1 (volume ratio).

[0168] (2) Washing 1: The metal ion-loaded extractant is first washed in two stages of countercurrent washing with dilute phosphoric acid with a concentration of 1 wt.% P2O5 at a temperature of 50°C and a ratio of O / A of 3:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0169] (3) Back-extraction: Using a 4.5 wt.% ammonium oxalate solution as the back-extraction agent, the extractant loaded with metal ions is subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage is 60℃, and the O / A ratio is 1:3 (volume ratio), to obtain aqueous phase 1 and organic phase 1.

[0170] (4) Recovery of metal ions: Aqueous phase 1 is cooled to 20°C to obtain magnesium ammonium sulfate and aqueous phase 2; aqueous phase 2 is cooled to 0°C to obtain aluminum ammonium sulfate and aqueous phase 3; aqueous phase 3 is cooled to -10°C to obtain ferric ammonium sulfate; this step recovers magnesium, aluminum and iron ions separately.

[0171] (5) Washing 2: Use a 0.1 wt.% dilute ammonium oxalate solution and a 0.1 wt.% dilute ammonium sulfate solution to wash the organic phase 1 in two countercurrent stages at a temperature of 30°C. The O / A ratio is 3:1 (volume ratio). The ammonium oxalate and ammonium sulfate entrained in the organic phase 1 are recovered to obtain a regenerated extractant that can be recycled.

[0172] In this embodiment, metal cations were recovered, and the back-extraction rate and recovery rate are shown in Table 1.

[0173] Table 1 shows the back-extraction rate and recovery rate of metal ions in each example and comparative example.

[0174]

[0175]

[0176] In the table above, the back-extraction rate is calculated as the ratio of the mass of the back-extracted substance to the mass of the substance previously extracted into the organic phase. The recovery rate is calculated as the ratio of the mass of the substance recovered after extraction and back-extraction to the mass of the substance in the initial feedstock.

[0177] It can be seen that using ammonium oxalate and ammonium sulfate as stripping agents in step (3) can improve the stripping rate and recovery rate of metal ions, which is higher than that of the example using only ammonium oxalate as stripping agent. However, the stripping rate gradually increases with the increase of ammonium oxalate concentration. In contrast, in Comparative Example 1, where only ammonium sulfate is used as stripping agent, iron ions are basically not stripped. When ammonium oxalate and ammonium sulfate are used as stripping agents, the stripping rate of metal ions is significantly improved and increases with the increase of ammonium sulfate addition.

Claims

1. A method for recovering metal cations from wet-process phosphoric acid, characterized in that, Includes the following steps: (1) Extraction: Extraction of wet phosphoric acid, the resulting organic phase is an extractant loaded with metal ions, and the aqueous phase is purified phosphoric acid; (2) Washing 1: The metal ion-loaded extractant is washed with dilute phosphoric acid to obtain the washed extractant; (3) Back-extraction: Use ammonium oxalate solution or a mixed solution of ammonium oxalate and ammonium sulfate as back-extraction agent to back-extract the washed extractant to obtain aqueous phase 1 and organic phase 1; (4) Recovery of metal ions: Recovery of metal ions from aqueous phase 1; (5) Washing 2: The organic phase 1 is washed in two countercurrent stages with dilute ammonium oxalate and dilute ammonium sulfate to recover the ammonium oxalate and ammonium sulfate entrained in the organic phase 1 and obtain the regenerated extractant. The regenerated extractant is returned to step (1) as the extractant for the extraction of wet phosphoric acid.

2. The method for recovering metal cations from wet-process phosphoric acid as described in claim 1, characterized in that: In step (4), the metal ions are recovered using method 1, method 2, method 3, or method 4, wherein, Method 1 includes the following steps: a. Cooling crystallization: Cool the aqueous phase 1 to crystallize, and separate the solid and liquid phases to obtain a mixed salt of iron, aluminum and magnesium sulfates and aqueous phase 2; Method 2 includes the following steps: a. Cooling crystallization 1: Cool the aqueous phase 1 to crystallize, and separate the solid and liquid phases to obtain magnesium ammonium sulfate crystals and aqueous phase 2; b. Cooling crystallization 2: Cool the aqueous phase 2 to crystallize, and separate the solid and liquid phases to obtain ammonium aluminum sulfate crystals and aqueous phase 3; c. Cooling crystallization 3: Cool the aqueous phase 3 to crystallize, and separate the solid and liquid phases to obtain ferric ammonium sulfate crystals and aqueous phase 4; Method 3 includes the following steps: a. Precipitation: Ammonia gas is passed into aqueous phase 1 to adjust the pH. Precipitation occurs. Solid-liquid separation is performed to obtain iron, aluminum and magnesium hydroxide precipitate and aqueous phase 2. b. Ammonia distillation: Heat aqueous phase 2 to distill off the ammonia gas. The collected ammonia gas is returned to step a, and aqueous phase 3 is returned as a back-extraction agent. Method 4 includes the following steps: a. Precipitation 1: Add ammonia to aqueous phase 1 to adjust the pH. A red precipitate appears. Separate the solid and liquid phases to obtain Fe(OH)3 precipitate and aqueous phase 2. b. Precipitation 2: Add ammonia to aqueous phase 2 to adjust the pH. A white precipitate appears. Separate the solid and liquid phases to obtain Al(OH)3 precipitate and aqueous phase 3. c. Precipitation 3: Add aqueous phase 3 dropwise to ammonia water, adjust the pH, and a white precipitate appears. Separate the solid and liquid phases to obtain Mg(OH)2 precipitate and aqueous phase 3.

3. The method for recovering metal cations from wet-process phosphoric acid as described in claim 1, characterized in that: In step (1), the extraction is a three-stage countercurrent extraction with 1 to 5 stages; the extraction temperature of each stage is 25 to 85°C, and the volume ratio O / A is 1 to 10:

1.

4. The method for recovering metal cations from wet-process phosphoric acid as described in claim 3, characterized in that: In step (1), there are 3 segments.

5. The method for recovering metal cations from wet-process phosphoric acid as described in claim 1, characterized in that: In step (2), a two-stage countercurrent washing with dilute phosphoric acid is used. The concentration of dilute phosphoric acid, calculated as P2O5, is 1 wt.% to 8 wt.%, and the temperature is 25 to 85℃. The O / A ratio is 1 to 10 : 1 by volume.

6. The method for recovering metal cations from wet-process phosphoric acid as described in claim 1, characterized in that: In step (3), the back-extraction is a multi-stage three-stage countercurrent back-extraction with 1 to 5 stages; the back-extraction temperature of each stage is 25 to 90°C, and the volume ratio O / A is 1 to 10:

1.

7. The method for recovering metal cations from wet-process phosphoric acid as described in claim 6, characterized in that: In step (3), there are 3 segments.

8. The method for recovering metal cations from wet-process phosphoric acid as described in claim 1, characterized in that: In step (3), the concentration of ammonium oxalate in the stripping agent is 1 wt.% to 20 wt.%, and the concentration of ammonium sulfate is 0 wt.% to 35 wt.%.

9. The method for recovering metal cations from wet-process phosphoric acid as described in claim 2, characterized in that: In step (4) of method 1, the crystallization temperature is -10 to 50℃; in step (4) of method 2, the crystallization temperature of magnesium ammonium sulfate is 20 to 50℃, the crystallization temperature of aluminum ammonium sulfate is 1 to 15℃, and the crystallization temperature of ferric ammonium sulfate is -10 to 0℃.

10. The method for recovering metal cations from wet-process phosphoric acid as described in claim 2, characterized in that: In step (4) of method 3, in step a, the pH is adjusted to 3.3 to 12.4; in step b, the temperature for ammonia stripping is -10 to 0℃; in step (4) of method 4, in step a, the pH is adjusted to 3.3 to 3.8; in step b, the pH is adjusted to 4 to 5; in step c, the pH is adjusted to 9 to 12.

4.

11. The method for recovering metal cations from wet-process phosphoric acid as described in claim 1, characterized in that: In step (5), the concentration of dilute ammonium oxalate is 0.1 wt.% to 5 wt.%, the concentration of dilute ammonium sulfate is 0.1 wt.% to 5 wt.%, the temperature is 30 to 70℃, and the volume ratio of O / A is 1 to 10:1.

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