Method for stepwise recovering metal cations from wet-process phosphoric acid

Abstract

The invention relates to a method for stepwise recovering metal cations from wet-process phosphoric 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 method for stepwise recovering metal cations from wet-process phosphoric acid. The method comprises the following steps: extracting wet-process phosphoric acid to obtain an organic phase which is an extracting agent loaded with metal ions and a water phase which is purified phosphoric acid; and washing the extraction agent loaded with the metal ions with dilute phosphoric acid, and recovering metal cations such as magnesium, calcium, aluminum, iron and the like in a gradient manner by using a specific reverse extraction method. The specific reverse extraction method is adopted, the metal cations are recycled from the wet-process phosphoric acid in a stepped mode, various metal ions can be effectively separated, and no byproduct raffinate acid is generated. According to the method, associated metal elements and phosphoric acid in wet-process phosphoric acid can be recovered in a cascade classification manner by adopting different stripping agents, the recovery rate of each metal element is high, the recovered associated metal elements can be effectively separated and utilized in a high-quality manner, and the product value is high.

Description

Technical Field

[0001] The invention relates to a method for stepwise recovery of metal cations from wet-process phosphoric acid, in particular to a method for stepwise recovery of metal cations from wet-process phosphoric acid using a stripping method in a solvent extraction process, and belongs to the technical field of wet-process phosphoric acid. Background Art

[0002] Wet-process phosphoric acid is an important intermediate product for the production of phosphate fertilizers such as diammonium phosphate, monoammonium phosphate, and triple superphosphate, and is also the raw material for food-grade phosphoric acid and industrial-grade phosphoric acid. However, in recent years, with the substantial development and utilization of phosphate resources, the quality of phosphate ore has been continuously depleted, resulting in an increase in metal cation impurities such as Fe, Al, Mg, Mn, and Ca in wet-process phosphoric acid, which has complicated the processing of subsequent products of wet-process phosphoric acid, and the quality of the products is difficult to meet the requirements of high-quality products, resulting in increased costs.

[0003] The common methods for removing metal cations from phosphoric acid are as follows: 1. Organic solvent extraction. 2. Chemical precipitation. 3. Ion exchange. 4. Membrane separation. The chemical precipitation method has low impurity removal efficiency, introduces alkaline ions to weaken the acidity of the acidic system, and is difficult to separate. The ion exchange method requires a large amount of resin and has high recycling costs. The method uses the difference in the pore size of the separation membrane to selectively pass impurities to achieve the purpose of separation and purification. The cost of this method is relatively high. The product obtained by the organic solvent extraction method has high purity, simple production process and equipment, low energy consumption, good separation effect, high recovery rate, and can be applied continuously.

[0004] Solvent extraction is the mainstream process for wet phosphoric acid purification. Both at home and abroad, a lot of work has been done on the removal of metal ions from phosphoric acid by organic solvent extraction. However, most of them have problems such as low metal ion recovery rate, difficulty in classified recovery and high-value utilization. Therefore, it is of practical significance to explore the cascade classification recovery of metal ions from extractants.

[0005] The invention patent application with application number 201610514424.9 discloses a combined extraction method for producing high-quality phosphoric acid, in which metal cations in crude phosphoric acid are extracted using extractants such as P204, and the raffinate, i.e., the aqueous phase, is used to prepare high-quality phosphoric acid. The extract phase contains a variety of metal cations, and strong acid back extraction is used. The obtained metal cations cannot be separated and can only be used to produce fertilizers or flame retardants. The product application value is not high, and the recovery rate of metal ions is not high. 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 stepwise recovery of metal cations from wet-process phosphoric acid, which can classify and recover metal ions and improve the recovery rate and product value.

[0007] The method for stepwise recovery of metal cations from wet-process phosphoric acid of the present invention comprises the following steps:

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

[0009] (2) washing: washing the metal ion-loaded extractant with dilute phosphoric acid to obtain a washed extractant;

[0010] (3) Stripping 1: Using a mixed solution of sulfuric acid and sulfate as stripping agent 1, stripping the washed extractant to obtain stripping solution 1 and organic phase 1; the stripping solution 1 is concentrated by evaporation and filtered to obtain calcium sulfate; the filtrate is continuously cooled to obtain crystals of manganese sulfate and magnesium sulfate, and the crystallization mother liquor is recycled as stripping agent 1;

[0011] (4) Washing 1: washing the organic phase 1 with a dilute sulfate solution to recover sulfate entrained in the organic phase 1;

[0012] (5) Stripping 2: using sulfuric acid solution as stripping agent 2 to perform stripping to obtain stripping solution 2 and organic phase 2; adding sulfate solid to stripping solution 2, cooling and crystallizing to obtain aluminum sulfate, and the crystallization mother liquor is recycled as stripping agent 2;

[0013] (6) Washing 2: washing the organic phase 2 with dilute sulfuric acid to recover the sulfuric acid entrained in the organic phase 2;

[0014] (7) Stripping 3: using oxalic acid solution as stripping agent 3 to strip the organic phase 2 to obtain stripping solution 3 and organic phase 3, and treating the stripping solution 3 with ultraviolet light to obtain ferrous oxalate precipitate;

[0015] (8) Washing 3: Wash the organic phase 2 with dilute oxalic acid to recover the oxalic acid entrained in the organic phase 2 to obtain a regenerated extractant, which is returned to step (1) for recycling.

[0016] In one embodiment of the present invention, in step (1), the extraction is a multi-stage countercurrent extraction, the number of stages is 1 to 5; preferably the number of stages is 3, each stage has 3 levels, the extraction temperature of each stage is 25 to 85°C, and the volume ratio O / A is 1 to 10:1.

[0017] In one embodiment of the present invention, in step (2), two-stage countercurrent washing is performed using dilute phosphoric acid, the concentration of which is 1 wt.% to 8 wt.% in terms of P2O5, the temperature is 25 to 85°C, and the volume ratio of O / A is 1 to 10:1.

[0018] In one embodiment of the present invention, in step (3), the sulfate includes but is not limited to at least one of potassium sulfate, ammonium sulfate, cesium sulfate, etc.; the concentration of the sulfate solution is 5wt.% to 60wt.%, the temperature is 25 to 85°C, and the volume ratio O / A is 1 to 10:1;

[0019] In one embodiment of the present invention, in step (3), the stripping solution 1 is evaporated and concentrated, and filtered to obtain calcium sulfate; the filtrate is continuously cooled, and then the manganese sulfate salt and the magnesium sulfate salt are separated under different cooling conditions.

[0020] In a specific embodiment, the sulfate is ammonium sulfate, and manganese ammonium sulfate, magnesium sulfate, potassium magnesium sulfate and sodium magnesium sulfate are separated by different cooling conditions, wherein the cooling crystallization temperature of manganese ammonium sulfate is 55-80°C, the cooling crystallization temperature of magnesium ammonium sulfate is 15-50°C, and when cooled to 0-10°C, mixed crystals of potassium magnesium sulfate and sodium magnesium sulfate are precipitated simultaneously.

[0021] In one embodiment of the present invention, in step (4), the organic phase 1 is washed in two-stage countercurrent with a dilute sulfate solution, the concentration of the dilute sulfate solution is 0.1wt.% to 8wt.%, the temperature is 30 to 80°C, and the volume ratio O / A is 1 to 10:1.

[0022] In one embodiment of the present invention, in step (5), two-stage countercurrent stripping is performed with a sulfuric acid solution, the sulfuric acid concentration is 10 wt.% to 60 wt.%, the temperature is 25 to 65° C., and the volume ratio of O / A is 1 to 10:1;

[0023] In one embodiment of the present invention, in step (5), solid ammonium sulfate is added to the stripping solution 1 and cooled for crystallization, wherein the cooling crystallization temperature of cesium aluminum sulfate is 60-80°C, the cooling crystallization temperature of potassium aluminum sulfate is 25-55°C, and the cooling crystallization temperature of ammonium aluminum sulfate is 0-20°C, and a nano-scale aluminum hydroxide flame retardant is prepared using ammonium aluminum sulfate.

[0024] In one embodiment of the present invention, in step (6), the organic phase 1 is washed in two-stage countercurrent with dilute sulfuric acid, the concentration of the dilute sulfuric acid is 1 wt.% to 10 wt.%, the temperature is 25 to 65°C, and the volume ratio O / A is 1 to 10:1.

[0025] In one embodiment of the present invention, in step (7), two-stage countercurrent stripping is performed with oxalic acid solution, the oxalic acid concentration is 5wt.% to 20wt.%, the temperature is 30 to 70°C, and the volume ratio O / A is 1 to 10:1.

[0026] In one embodiment of the present invention, in step (8), the organic phase 2 is washed in two-stage countercurrent with dilute oxalic acid, the concentration of the dilute oxalic acid is 0.1wt.% to 3wt.%, the temperature is 30 to 70°C, and the volume ratio O / A is 1 to 10:1.

[0027] The present invention adopts a specific stripping method to recover metal cations from wet-process phosphoric acid in a stepwise manner, various metal ions can be effectively separated, the recovery rate of each metal element is high, and the product value is high. Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The method adopted by the present invention does not produce by-product raffinate acid; 2. Different stripping agents can be used to recover associated metal elements and phosphoric acid in wet-process phosphoric acid in a step-by-step classified manner; 3. The recovered associated metal elements can be effectively separated and utilized in a high-quality manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a process flow chart of the method for stepwise recovery of metal cations from wet-process phosphoric acid according to Examples 1 to 8 of the present invention. DETAILED DESCRIPTION

[0030] The method for stepwise recovery of metal cations from wet-process phosphoric acid of the present invention comprises the following steps:

[0031] (1) Extraction process: Extract wet-process phosphoric acid, the resulting organic phase is the extractant loaded with metal ions, and the aqueous phase is the purified phosphoric acid;

[0032] (2) washing: washing the metal ion-loaded extractant with dilute phosphoric acid to obtain a washed extractant;

[0033] (3) Stripping 1: Using a mixed solution of sulfuric acid and sulfate as stripping agent 1, stripping the washed extractant to obtain stripping solution 1 and organic phase 1; the stripping solution 1 is concentrated by evaporation and filtered to obtain calcium sulfate; the filtrate is continuously cooled to obtain crystals of manganese sulfate and magnesium sulfate, and the crystallization mother liquor is recycled as stripping agent 1;

[0034] (4) Washing 1: washing the organic phase 1 with a dilute sulfate solution to recover sulfate entrained in the organic phase 1;

[0035] (5) Stripping 2: using sulfuric acid solution as stripping agent 2 to perform stripping to obtain stripping solution 2 and organic phase 2; adding sulfate solid to stripping solution 2, cooling and crystallizing to obtain aluminum sulfate, and the crystallization mother liquor is recycled as stripping agent 2;

[0036] (6) Washing 2: washing the organic phase 2 with dilute sulfuric acid to recover the sulfuric acid entrained in the organic phase 2;

[0037] (7) Stripping 3: using oxalic acid solution as stripping agent 3 to strip the organic phase 2 to obtain stripping solution 3 and organic phase 3, and treating the stripping solution 3 with ultraviolet light to obtain ferrous oxalate precipitate;

[0038] (8) Washing 3: Wash the organic phase 2 with dilute oxalic acid to recover the oxalic acid entrained in the organic phase 2 to obtain a regenerated extractant, which is returned to step (1) for recycling.

[0039] Step (1) is an extraction process, and conventional methods for extracting metal impurities in wet-process phosphoric acid in the art are applicable to the present invention. In one embodiment of the present invention, the extraction is a multi-stage countercurrent extraction, the number of stages is 1 to 5; preferably the number of stages is 3, and each stage has three stages.

[0040] In a specific embodiment, the extraction temperature of each stage is 25-85° C., and the volume ratio O / A is 1-10:1.

[0041] The extractant for extracting metal cations 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.

[0042] Step (2) is washing, using dilute phosphoric acid to wash the extractant loaded with metal ions and recover the phosphoric acid entrained in the extractant.

[0043] In one embodiment of the present invention, two-stage countercurrent washing is performed using dilute phosphoric acid, the concentration of which is 1 wt.% to 8 wt.% in terms of P2O5, the temperature is 25 to 85°C, and the volume ratio of O / A is 1 to 10:1.

[0044] Steps (3) to (8) are stripping steps, which strip various metal ions from the extractant loaded with metal ions in a stepwise manner, thereby achieving separate recovery of metal ions and improving product value.

[0045] Step (3) using a mixed solution of sulfuric acid and sulfate as a stripping agent 1 to strip the washed extractant to obtain a stripping solution 1 and an organic phase 1;

[0046] In step (3), the sulfate includes but is not limited to at least one of potassium sulfate, ammonium sulfate, cesium sulfate, etc.; the concentration of the sulfate solution is 5wt.% to 60wt.%, the concentration of sulfuric acid is ≤15wt.%, the temperature is 25 to 85°C, and the volume ratio O / A is 1 to 10:1;

[0047] In step (3), the stripping solution 1 is evaporated and concentrated, and filtered to obtain calcium sulfate; the filtrate is continuously cooled, and then the manganese sulfate salt and the magnesium sulfate salt are separated under different cooling conditions.

[0048] In a specific embodiment, when the sulfate is ammonium sulfate, manganese ammonium sulfate, magnesium sulfate, potassium magnesium sulfate and sodium magnesium sulfate can be separated by different cooling conditions. The cooling crystallization temperature of manganese ammonium sulfate is 55-80°C, and the cooling crystallization temperature of magnesium ammonium sulfate is 15-50°C. When cooled to 0-10°C, mixed crystals of potassium magnesium sulfate and sodium magnesium sulfate are precipitated simultaneously. High-quality cement retarder is prepared with the obtained calcium sulfate, high-purity manganese carbonate is prepared with manganese ammonium sulfate, nano-grade magnesium hydroxide flame retardant is prepared with magnesium ammonium sulfate, and potassium magnesium sulfate fertilizer is prepared with potassium magnesium sulfate and sodium magnesium sulfate.

[0049] Step (4) is washing 1, washing the organic phase 1 with a dilute sulfate solution to recover the sulfate entrained in the organic phase 1; in one embodiment of the present invention, in step b1, the concentration of the dilute sulfate solution is 0.1wt.% to 8wt.%, the temperature is 30 to 80°C, and the volume ratio O / A is 1 to 10:1.

[0050] Step (5) using sulfuric acid solution as stripping agent 2 to perform two-stage countercurrent stripping on organic phase 1 to obtain stripping solution 2 and organic phase 2;

[0051] In step (5), the concentration of sulfuric acid is 10 wt.% to 60 wt.%, the temperature is 25 to 65° C., and the volume ratio of O / A is 1 to 10:1;

[0052] In step (5), solid ammonium sulfate is added to the stripping solution 1, and cooled and crystallized, wherein the cooling and crystallization temperature of cesium aluminum sulfate is 60-80° C., the cooling and crystallization temperature of potassium aluminum sulfate is 25-55° C., and the cooling and crystallization temperature of ammonium aluminum sulfate is 0-20° C., and a nano-scale aluminum hydroxide flame retardant is prepared using ammonium aluminum sulfate;

[0053] Step (6) is washing 2, using dilute sulfuric acid to wash the organic phase 1 in two-stage countercurrent to recover the sulfuric acid entrained in the organic phase 2; in one embodiment of the present invention, in step b2, the concentration of dilute sulfuric acid is 1wt.%~10wt.%, the temperature is 25~65°C, and the volume ratio O / A is 1~10:1.

[0054] In step (7), oxalic acid solution is used as the stripping agent 3 to perform two-stage countercurrent stripping on the organic phase 2 to obtain a stripping solution 3 and an organic phase 3, which are then irradiated with ultraviolet light to obtain a ferrous oxalate precipitate. In one embodiment of the present invention, in step (7), the oxalic acid concentration is 5wt.% to 20wt.%, the temperature is 30 to 70°C, and the volume ratio O / A is 1 to 10:1;

[0055] Step (8) is washing 3, using dilute oxalic acid to wash the organic phase 3 in two-stage countercurrent, recovering the oxalic acid entrained in the organic phase 3, and obtaining a regenerated extractant that can be recycled; in one embodiment of the present invention, in step b3, the concentration of dilute oxalic acid is 0.1wt.%~3wt.%, the temperature is 30~70°C, and the volume ratio O / A is 1~10:1.

[0056] 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.

[0057] Example 1

[0058] like Figure 1 As shown, a method for stepwise recovery of metal cations from wet-process phosphoric acid comprises the following steps:

[0059] (1) Extraction: The wet-process phosphoric acid was subjected to three-stage three-stage countercurrent extraction. The extraction temperature of each stage was 60° C. and the O / A ratio was 4:1 (volume ratio).

[0060] (2) Washing: The metal ion-loaded extractant is first subjected to two-stage countercurrent washing with dilute phosphoric acid having a concentration of 1 wt.% P2O5 at a temperature of 50°C and an O / A ratio 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.

[0061] (3) Stripping 1: Using 35wt.% ammonium sulfate solution and 1wt.% sulfuric acid solution as stripping agent 1, the metal ion-loaded extractant is subjected to two-stage three-stage countercurrent stripping, the stripping temperature of each stage is 30°C, and the ratio O / A is 2:1 (volume ratio), to obtain stripping solution 1 and organic phase 1. Stripping solution 1 is evaporated and concentrated, filtered, and calcium sulfate is obtained; the filtrate is continuously cooled to 80°C to obtain ammonium manganese sulfate; the filtrate is cooled to 50°C to obtain ammonium magnesium sulfate; the filtrate is cooled to 10°C to obtain mixed crystals of potassium magnesium sulfate and sodium magnesium sulfate; this step classifies and recovers calcium, manganese, magnesium, potassium, and sodium ions.

[0062] (4) Washing 1: The organic phase 1 is washed with a dilute ammonium sulfate solution having a concentration of 0.1 wt.% in two stages in countercurrent at a temperature of 30° C. and a phase O / A ratio of 3:1 (volume ratio) to recover the ammonium sulfate entrained in the organic phase 1.

[0063] (5) Stripping 2: Using a sulfuric acid solution with a concentration of 30 wt.% as stripping agent 2, stripping the metal ions in the organic phase 1, the temperature is 30°C, the phase O / A is 1:1 (volume ratio), and stripping solution 2 and organic phase 2 are obtained; ammonium sulfate solid is added to the stripping solution 2, and the temperature is reduced to 80°C to obtain cesium aluminum sulfate; the temperature is reduced to 55°C to obtain potassium aluminum sulfate; the temperature is reduced to 20°C to obtain ammonium aluminum sulfate; the crystallization mother liquor is recycled as stripping agent 2.

[0064] (6) Washing 2: The organic phase 2 is washed with dilute sulfuric acid having a concentration of 5 wt.% in two-stage countercurrent at a temperature of 30° C. and a phase O / A ratio of 3:1 (volume ratio). The sulfuric acid entrained in the organic phase 2 is recovered and returned to the stripping agent 1 for recycling.

[0065] (7) Stripping 3: Using 10 wt.% oxalic acid solution as stripping agent 3, the organic phase 2 is subjected to two-stage countercurrent stripping at a temperature of 50° C. and a phase O / A ratio of 1:1 (volume ratio) to obtain stripping solution 3 and organic phase 3. The stripping solution 3 is treated with ultraviolet light to obtain ferrous oxalate precipitate.

[0066] (8) Washing 3: Wash the organic phase 3 with dilute oxalic acid of 1 wt.% in two-stage countercurrent at a temperature of 50°C and a phase O / A ratio of 3:1 (volume ratio) to recover the oxalic acid entrained in the organic phase 3 and obtain a regenerated extractant that can be recycled.

[0067] This example recovers metal cations, and its stripping rate and recovery rate are shown in Table 1.

[0068] Example 2

[0069] like Figure 1 As shown, a method for stepwise recovery of metal cations from wet-process phosphoric acid comprises the following steps:

[0070] (1) Extraction: The wet-process phosphoric acid was subjected to three-stage three-stage countercurrent extraction. The extraction temperature of each stage was 60° C. and the O / A ratio was 4:1 (volume ratio).

[0071] (2) Washing: The metal ion-loaded extractant is first subjected to two-stage countercurrent washing with dilute phosphoric acid having a concentration of 2 wt.% P2O5 at a temperature of 55°C and an O / A ratio of 4:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0072] (3) Stripping 1: Using 35wt.% ammonium sulfate solution and 3wt.% sulfuric acid solution as stripping agent 1, the metal ion-loaded extractant is subjected to two-stage three-stage countercurrent stripping, the stripping temperature of each stage is 30°C, and the ratio O / A is 3:1 (volume ratio), to obtain stripping solution 1 and organic phase 1. Stripping solution 1 is evaporated and concentrated, filtered, and calcium sulfate is obtained; the filtrate is continuously cooled to 75°C to obtain ammonium manganese sulfate; the filtrate is cooled to 45°C to obtain ammonium magnesium sulfate; the filtrate is cooled to 8°C to obtain mixed crystals of potassium magnesium sulfate and sodium magnesium sulfate; this step classifies and recovers calcium, manganese, magnesium, potassium, and sodium ions.

[0073] (4) Washing 1: The organic phase 1 is washed with a dilute ammonium sulfate solution having a concentration of 1 wt.% in two stages in countercurrent at a temperature of 35° C. and a phase O / A ratio of 4:1 (volume ratio) to recover the ammonium sulfate entrained in the organic phase 1.

[0074] 5) Stripping 2: Using a sulfuric acid solution with a concentration of 35 wt.% as the stripping agent 2, stripping the metal ions in the organic phase 1, the temperature is 25°C, the phase O / A is 2:1 (volume ratio), and a stripping solution 2 and an organic phase 2 are obtained; ammonium sulfate solid is added to the stripping solution 2, and the temperature is reduced to 75°C to obtain cesium aluminum sulfate; the temperature is reduced to 50°C to obtain potassium aluminum sulfate; the temperature is reduced to 15°C to obtain ammonium aluminum sulfate; the crystallization mother liquor is recycled as the stripping agent 2.

[0075] (6) Washing 2: The organic phase 2 is washed with dilute sulfuric acid having a concentration of 6 wt.% in two-stage countercurrent at a temperature of 25° C. and a phase O / A ratio of 4:1 (volume ratio). The sulfuric acid entrained in the organic phase 2 is recovered and returned to the stripping agent 1 for recycling.

[0076] (7) Stripping 3: Using 12 wt.% oxalic acid solution as stripping agent 3, the organic phase 2 is subjected to two-stage countercurrent stripping at a temperature of 55° C. and a phase O / A ratio of 2:1 (volume ratio) to obtain stripping solution 3 and organic phase 3. The stripping solution 3 is treated with ultraviolet light to obtain ferrous oxalate precipitate.

[0077] (8) Washing 3: Wash the organic phase 3 with dilute oxalic acid at a concentration of 0.1 wt.% in two-stage countercurrent at a temperature of 55°C and a phase O / A ratio of 4:1 (volume ratio) to recover the oxalic acid entrained in the organic phase 3 and obtain a regenerated extractant that can be recycled.

[0078] This example recovers metal cations, and its stripping rate and recovery rate are shown in Table 1.

[0079] Example 3

[0080] like Figure 1 As shown, a method for stepwise recovery of metal cations from wet-process phosphoric acid comprises the following steps:

[0081] (1) Extraction: The wet-process phosphoric acid was subjected to three-stage three-stage countercurrent extraction. The extraction temperature of each stage was 60° C. and the O / A ratio was 4:1 (volume ratio).

[0082] (2) Washing: a. The metal ion-loaded extractant is first subjected to two-stage countercurrent washing with dilute phosphoric acid having a concentration of 3 wt.% P2O5 at a temperature of 60°C and an O / A ratio of 5:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0083] (3) Stripping 1: Using 35wt.% ammonium sulfate solution and 5wt.% sulfuric acid solution as stripping agent 1, the metal ion-loaded extractant is subjected to two-stage three-stage countercurrent stripping, the stripping temperature of each stage is 35°C, and the ratio O / A is 4:1 (volume ratio), to obtain stripping solution 1 and organic phase 1. Stripping solution 1 is evaporated and concentrated, filtered, and calcium sulfate is obtained; the filtrate is continuously cooled to 70°C to obtain ammonium manganese sulfate; the filtrate is cooled to 40°C to obtain ammonium magnesium sulfate; the filtrate is cooled to 6°C to obtain mixed crystals of potassium magnesium sulfate and sodium magnesium sulfate; this step classifies and recovers calcium, manganese, magnesium, potassium, and sodium ions.

[0084] (4) Washing 1: The organic phase 1 is washed with a 2 wt.% dilute ammonium sulfate solution in two stages in countercurrent at a temperature of 40° C. and a phase O / A ratio of 5:1 (volume ratio) to recover the ammonium sulfate entrained in the organic phase 1.

[0085] 5) Stripping 2: Using a sulfuric acid solution with a concentration of 40 wt.% as the stripping agent 2, stripping the metal ions in the organic phase 1, the temperature is 35°C, the phase O / A is 3:1 (volume ratio), and a stripping solution 2 and an organic phase 2 are obtained; ammonium sulfate solid is added to the stripping solution 2, and the temperature is reduced to 70°C to obtain cesium aluminum sulfate; the temperature is reduced to 45°C to obtain potassium aluminum sulfate; the temperature is reduced to 10°C to obtain ammonium aluminum sulfate; the crystallization mother liquor is recycled as the stripping agent 2.

[0086] (6) Washing 2: The organic phase 2 is washed with dilute sulfuric acid having a concentration of 7 wt.% in two-stage countercurrent at a temperature of 35° C. and a phase O / A ratio of 5:1 (volume ratio). The sulfuric acid entrained in the organic phase 2 is recovered and returned to the stripping agent 1 for recycling.

[0087] (7) Stripping 3: Using 14 wt.% oxalic acid solution as stripping agent 3, the organic phase 2 is subjected to two-stage countercurrent stripping at a temperature of 60°C and a phase O / A ratio of 3:1 (volume ratio) to obtain stripping solution 3 and organic phase 3. The stripping solution 3 is treated with ultraviolet light to obtain ferrous oxalate precipitate.

[0088] (8) Washing 3: Wash the organic phase 3 with dilute oxalic acid at a concentration of 0.5 wt.% in two-stage countercurrent at a temperature of 60°C and a phase O / A ratio of 5:1 (volume ratio) to recover the oxalic acid entrained in the organic phase 3 to obtain a regenerated extractant that can be recycled.

[0089] This example recovers metal cations, and its stripping rate and recovery rate are shown in Table 1.

[0090] Example 4

[0091] like Figure 1 As shown, a method for stepwise recovery of metal cations from wet-process phosphoric acid comprises the following steps:

[0092] (1) Extraction: The wet-process phosphoric acid was subjected to three-stage three-stage countercurrent extraction. The extraction temperature of each stage was 60° C. and the O / A ratio was 4:1 (volume ratio).

[0093] (2) Washing: a. The metal ion-loaded extractant is first subjected to two-stage countercurrent washing with dilute phosphoric acid having a concentration of 4 wt.% P2O5 at a temperature of 65°C and an O / A ratio of 6:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0094] (3) Stripping 1: Using 35wt.% ammonium sulfate solution and 7wt.% sulfuric acid solution as stripping agent 1, the metal ion-loaded extractant is subjected to two-stage three-stage countercurrent stripping, the stripping temperature of each stage is 45°C, and the ratio O / A is 5:1 (volume ratio), to obtain stripping solution 1 and organic phase 1. Stripping solution 1 is evaporated and concentrated, filtered, and calcium sulfate is obtained; the filtrate is continuously cooled to 65°C to obtain ammonium manganese sulfate; the filtrate is cooled to 35°C to obtain ammonium magnesium sulfate; the filtrate is cooled to 4°C to obtain mixed crystals of potassium magnesium sulfate and sodium magnesium sulfate; this step classifies and recovers calcium, manganese, magnesium, potassium, and sodium ions.

[0095] (4) Washing 1: The organic phase 1 is washed with a 3 wt.% dilute ammonium sulfate solution in two stages in countercurrent at a temperature of 45° C. and a phase O / A ratio of 6:1 (volume ratio) to recover the ammonium sulfate entrained in the organic phase 1.

[0096] 5) Stripping 2: Using a sulfuric acid solution with a concentration of 25 wt.% as the stripping agent 2, stripping the metal ions in the organic phase 1, the temperature is 40°C, the phase O / A is 4:1 (volume ratio), and a stripping solution 2 and an organic phase 2 are obtained; ammonium sulfate solid is added to the stripping solution 2, and the temperature is reduced to 65°C to obtain cesium aluminum sulfate; the temperature is reduced to 40°C to obtain potassium aluminum sulfate; the temperature is reduced to 5°C to obtain ammonium aluminum sulfate; the crystallization mother liquor is recycled as the stripping agent 2.

[0097] (6) Washing 2: The organic phase 2 is washed with 8 wt.% dilute sulfuric acid in two stages in countercurrent at a temperature of 40°C and a phase O / A ratio of 6:1 (volume ratio). The sulfuric acid entrained in the organic phase 2 is recovered and returned to the stripping agent 1 for recycling.

[0098] (7) Stripping 3: Using 16 wt.% oxalic acid solution as stripping agent 3, the organic phase 2 is subjected to two-stage countercurrent stripping at a temperature of 65° C. and a phase O / A ratio of 4:1 (volume ratio) to obtain stripping solution 3 and organic phase 3. The stripping solution 3 is treated with ultraviolet light to obtain ferrous oxalate precipitate.

[0099] (8) Washing 3: Wash the organic phase 3 with dilute oxalic acid at a concentration of 1.5 wt.% in two-stage countercurrent at a temperature of 65°C and a phase O / A ratio of 6:1 (volume ratio) to recover the oxalic acid entrained in the organic phase 3 to obtain a regenerated extractant that can be recycled.

[0100] This example recovers metal cations, and its stripping rate and recovery rate are shown in Table 1.

[0101] Example 5

[0102] like Figure 1 As shown, a method for stepwise recovery of metal cations from wet-process phosphoric acid comprises the following steps:

[0103] (1) Extraction: The wet-process phosphoric acid was subjected to three-stage three-stage countercurrent extraction. The extraction temperature of each stage was 60° C. and the O / A ratio was 4:1 (volume ratio).

[0104] (2) Washing: a. The metal ion-loaded extractant is first subjected to two-stage countercurrent washing with dilute phosphoric acid having a concentration of 1 wt.% P2O5 at a temperature of 50°C and an O / A ratio 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) Stripping 1: Using a 35wt.% potassium sulfate solution and a 3wt.% sulfuric acid solution as stripping agent 1, the metal ion-loaded extractant is subjected to two-stage three-stage countercurrent stripping, the stripping temperature of each stage is 30°C, and the ratio O / A is 2:1 (volume ratio), to obtain stripping solution 1 and organic phase 1. Stripping solution 1 is evaporated and concentrated, filtered, and calcium sulfate is obtained; the filtrate is continuously cooled to 80°C to obtain potassium manganese sulfate; the filtrate is cooled to 10°C to obtain mixed crystals of potassium magnesium sulfate and sodium magnesium sulfate; this step classifies and recovers calcium, manganese, magnesium, potassium, and sodium ions.

[0106] (4) Washing 1: The organic phase 1 is washed with a dilute potassium sulfate solution having a concentration of 0.1 wt.% in two stages in countercurrent at a temperature of 30° C. and a phase O / A ratio of 3:1 (volume ratio) to recover the potassium sulfate entrained in the organic phase 1.

[0107] 5) Stripping 2: Using a sulfuric acid solution with a concentration of 30 wt.% as stripping agent 2, stripping the metal ions in the organic phase 1, the temperature is 30°C, the phase O / A is 1:1 (volume ratio), and stripping solution 2 and organic phase 2 are obtained; adding ammonium sulfate solid to the stripping solution 2, cooling to 80°C, obtaining cesium aluminum sulfate; cooling to 55°C, obtaining potassium aluminum sulfate; cooling to 20°C, obtaining ammonium aluminum sulfate; the crystallization mother liquor is recycled as stripping agent 2.

[0108] (6) Washing 2: The organic phase 2 is washed with dilute sulfuric acid having a concentration of 5 wt.% in two-stage countercurrent at a temperature of 30° C. and a phase O / A ratio of 3:1 (volume ratio). The sulfuric acid entrained in the organic phase 2 is recovered and returned to the stripping agent 1 for recycling.

[0109] (7) Stripping 3: Using 10 wt.% oxalic acid solution as stripping agent 3, the organic phase 2 is subjected to two-stage countercurrent stripping at a temperature of 50° C. and a phase O / A ratio of 1:1 (volume ratio) to obtain stripping solution 3 and organic phase 3. The stripping solution 3 is treated with ultraviolet light to obtain ferrous oxalate precipitate.

[0110] (8) Washing 3: Wash the organic phase 3 with dilute oxalic acid of 1 wt.% in two-stage countercurrent at a temperature of 50°C and a phase O / A ratio of 3:1 (volume ratio) to recover the oxalic acid entrained in the organic phase 3 and obtain a regenerated extractant that can be recycled.

[0111] This example recovers metal cations, and its stripping rate and recovery rate are shown in Table 1.

[0112] Example 6

[0113] like Figure 1 As shown, a method for stepwise recovery of metal cations from wet-process phosphoric acid comprises the following steps:

[0114] (1) Extraction: The wet-process phosphoric acid was subjected to three-stage three-stage countercurrent extraction. The extraction temperature of each stage was 60° C. and the O / A ratio was 4:1 (volume ratio).

[0115] (2) Washing: a. The metal ion-loaded extractant is first subjected to two-stage countercurrent washing with dilute phosphoric acid having a concentration of 2 wt.% P2O5 at a temperature of 55°C and an O / A ratio of 4:1 (volume ratio) to recover the phosphoric acid entrained in the extractant and improve the yield of P2O5 in the phosphoric acid purification process.

[0116] (3) Stripping 1: Using a 35wt.% potassium sulfate solution and a 5wt.% sulfuric acid solution as stripping agent 1, the metal ion-loaded extractant is subjected to two-stage three-stage countercurrent stripping, the stripping temperature of each stage is 30°C, and the ratio O / A is 3:1 (volume ratio), to obtain stripping solution 1 and organic phase 1. Stripping solution 1 is evaporated and concentrated, filtered, and calcium sulfate is obtained; the filtrate is continuously cooled to 75°C to obtain potassium manganese sulfate; the filtrate is cooled to 8°C to obtain mixed crystals of potassium magnesium sulfate and sodium magnesium sulfate; this step classifies and recovers calcium, manganese, magnesium, potassium, and sodium ions.

[0117] (4) Washing 1: The organic phase 1 is washed with a 1 wt.% dilute potassium sulfate solution in two stages in countercurrent at a temperature of 35° C. and a phase O / A ratio of 4:1 (volume ratio) to recover the potassium sulfate entrained in the organic phase 1.

[0118] 5) Stripping 2: Using a sulfuric acid solution with a concentration of 35 wt.% as the stripping agent 2, stripping the metal ions in the organic phase 1, the temperature is 25°C, the phase O / A is 2:1 (volume ratio), and a stripping solution 2 and an organic phase 2 are obtained; ammonium sulfate solid is added to the stripping solution 2, and the temperature is reduced to 75°C to obtain cesium aluminum sulfate; the temperature is reduced to 50°C to obtain potassium aluminum sulfate; the temperature is reduced to 15°C to obtain ammonium aluminum sulfate; the crystallization mother liquor is recycled as the stripping agent 2.

[0119] (6) Washing 2: The organic phase 2 is washed with dilute sulfuric acid having a concentration of 6 wt.% in two-stage countercurrent at a temperature of 25° C. and a phase O / A ratio of 4:1 (volume ratio). The sulfuric acid entrained in the organic phase 2 is recovered and returned to the stripping agent 1 for recycling.

[0120] (7) Stripping 3: Using 12 wt.% oxalic acid solution as stripping agent 3, the organic phase 2 is subjected to two-stage countercurrent stripping at a temperature of 55° C. and a phase O / A ratio of 2:1 (volume ratio) to obtain stripping solution 3 and organic phase 3. The stripping solution 3 is treated with ultraviolet light to obtain ferrous oxalate precipitate.

[0121] (8) Washing 3: Wash the organic phase 3 with dilute oxalic acid at a concentration of 0.1 wt.% in two-stage countercurrent at a temperature of 55°C and a phase O / A ratio of 4:1 (volume ratio) to recover the oxalic acid entrained in the organic phase 3 and obtain a regenerated extractant that can be recycled.

[0122] This example recovers metal cations, and its stripping rate and recovery rate are shown in Table 1.

[0123] Example 7

[0124] like Figure 1 As shown, a method for stepwise recovery of metal cations from wet-process phosphoric acid comprises the following steps:

[0125] (1) Extraction: The wet-process phosphoric acid was subjected to three-stage three-stage countercurrent extraction. The extraction temperature of each stage was 60° C. and the O / A ratio was 4:1 (volume ratio).

[0126] (2) Washing: The metal ion-loaded extractant is first subjected to two-stage countercurrent washing with dilute phosphoric acid having a concentration of 1 wt.% P2O5 at a temperature of 50°C and an O / A ratio 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.

[0127] (3) Stripping 1: Using 20wt.% ammonium sulfate solution and 5wt.% sulfuric acid solution as stripping agent 1, the metal ion-loaded extractant is subjected to two-stage three-stage countercurrent stripping, the stripping temperature of each stage is 30°C, and the ratio O / A is 2:1 (volume ratio), to obtain stripping solution 1 and organic phase 1. Stripping solution 1 is evaporated and concentrated, filtered, and calcium sulfate is obtained; the filtrate is continuously cooled to 80°C to obtain ammonium manganese sulfate; the filtrate is cooled to 50°C to obtain ammonium magnesium sulfate; the filtrate is cooled to 10°C to obtain mixed crystals of potassium magnesium sulfate and sodium magnesium sulfate; this step classifies and recovers calcium, manganese, magnesium, potassium, and sodium ions.

[0128] (4) Washing 1: The organic phase 1 is washed with a dilute ammonium sulfate solution having a concentration of 0.1 wt.% in two stages in countercurrent at a temperature of 30° C. and a phase O / A ratio of 3:1 (volume ratio) to recover the ammonium sulfate entrained in the organic phase 1.

[0129] 5) Stripping 2: Using a sulfuric acid solution with a concentration of 30 wt.% as stripping agent 2, stripping the metal ions in the organic phase 1, the temperature is 30°C, the phase O / A is 1:1 (volume ratio), and stripping solution 2 and organic phase 2 are obtained; adding ammonium sulfate solid to the stripping solution 2, cooling to 80°C, obtaining cesium aluminum sulfate; cooling to 55°C, obtaining potassium aluminum sulfate; cooling to 20°C, obtaining ammonium aluminum sulfate; the crystallization mother liquor is recycled as stripping agent 2.

[0130] (6) Washing 2: The organic phase 2 is washed with dilute sulfuric acid having a concentration of 5 wt.% in two-stage countercurrent at a temperature of 30° C. and a phase O / A ratio of 3:1 (volume ratio). The sulfuric acid entrained in the organic phase 2 is recovered and returned to the stripping agent 1 for recycling.

[0131] (7) Stripping 3: Using 10 wt.% oxalic acid solution as stripping agent 3, the organic phase 2 is subjected to two-stage countercurrent stripping at a temperature of 50° C. and a phase O / A ratio of 1:1 (volume ratio) to obtain stripping solution 3 and organic phase 3. The stripping solution 3 is treated with ultraviolet light to obtain ferrous oxalate precipitate.

[0132] (8) Washing 3: Wash the organic phase 3 with dilute oxalic acid of 1 wt.% in two-stage countercurrent at a temperature of 50°C and a phase O / A ratio of 3:1 (volume ratio) to recover the oxalic acid entrained in the organic phase 3 and obtain a regenerated extractant that can be recycled.

[0133] This example recovers metal cations, and its stripping rate and recovery rate are shown in Table 1.

[0134] Comparative Example 1

[0135] A method for stepwise recovery of metal cations from wet-process phosphoric acid comprises the following steps:

[0136] (1) Extraction: The wet-process phosphoric acid was subjected to three-stage three-stage countercurrent extraction. The extraction temperature of each stage was 60° C. and the O / A ratio was 4:1 (volume ratio).

[0137] (2) Washing: a. The metal ion-loaded extractant is first subjected to two-stage countercurrent washing with dilute phosphoric acid having a concentration of 1 wt.% P2O5 at a temperature of 50°C and an O / A ratio 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.

[0138] (3) Stripping 1: Using 35 wt.% ammonium sulfate solution as stripping agent 1, the metal ion-loaded extractant is subjected to two-stage three-stage countercurrent stripping, the stripping temperature of each stage is 30°C, and the phase O / A ratio is 2:1 (volume ratio), to obtain stripping solution 1 and organic phase 1. Stripping solution 1 is evaporated and concentrated, filtered, and calcium sulfate is obtained; the filtrate is continuously cooled to 80°C to obtain ammonium manganese sulfate; the filtrate is cooled to 50°C to obtain ammonium magnesium sulfate; the filtrate is cooled to 10°C to obtain mixed crystals of potassium magnesium sulfate and sodium magnesium sulfate; this step classifies and recovers calcium, manganese, magnesium, potassium, and sodium ions.

[0139] (4) Washing 1: The organic phase 1 is washed with a dilute ammonium sulfate solution having a concentration of 0.1 wt.% in two stages in countercurrent at a temperature of 30° C. and a phase O / A ratio of 3:1 (volume ratio) to recover the ammonium sulfate entrained in the organic phase 1.

[0140] 5) Stripping 2: Using a sulfuric acid solution with a concentration of 30 wt.% as stripping agent 2, stripping the metal ions in the organic phase 1, the temperature is 30°C, the phase O / A is 1:1 (volume ratio), and stripping solution 2 and organic phase 2 are obtained; adding ammonium sulfate solid to the stripping solution 2, cooling to 80°C, obtaining cesium aluminum sulfate; cooling to 55°C, obtaining potassium aluminum sulfate; cooling to 20°C, obtaining ammonium aluminum sulfate; the crystallization mother liquor is recycled as stripping agent 2.

[0141] (6) Washing 2: The organic phase 2 is washed with dilute sulfuric acid having a concentration of 5 wt.% in two-stage countercurrent at a temperature of 30° C. and a phase O / A ratio of 3:1 (volume ratio). The sulfuric acid entrained in the organic phase 2 is recovered and returned to the stripping agent 1 for recycling.

[0142] (7) Stripping 3: Using 10 wt.% oxalic acid solution as stripping agent 3, the organic phase 2 is subjected to two-stage countercurrent stripping at a temperature of 50° C. and a phase O / A ratio of 1:1 (volume ratio) to obtain stripping solution 3 and organic phase 3. The stripping solution 3 is treated with ultraviolet light to obtain ferrous oxalate precipitate.

[0143] (8) Washing 3: Wash the organic phase 3 with dilute oxalic acid of 1 wt.% in two-stage countercurrent at a temperature of 50°C and a phase O / A ratio of 3:1 (volume ratio) to recover the oxalic acid entrained in the organic phase 3 and obtain a regenerated extractant that can be recycled.

[0144] This comparative example recovers metal cations, and its stripping rate and recovery rate are shown in Table 1.

[0145] Table 1 Stripping rate and recovery rate of metal ions in each embodiment and comparative example

[0146]

[0147] In the above table, the stripping rate is calculated as: the ratio of the mass of the substance stripped out 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 stripping to the mass of the substance in the previous raw material.

[0148] It can be seen that in step (3), using a certain proportion of sulfate and sulfuric acid as the stripping agent 1 can improve the stripping rate and recovery rate of metal ions. In comparative example 1, which uses only ammonium sulfate as the stripping agent 1, the stripping rate of metal ions is not high; when sulfate and sulfuric acid are used as the stripping agent 1, the stripping rate of metal ions is significantly improved, and increases with the increase of the amount of sulfuric acid added, but when the amount of sulfuric acid added exceeds a certain amount, the stripping rate of metal ions will begin to decrease again. The reason is that when the hydrogen ion content of the solution is low, the hydrogen ions will only affect the equilibrium relationship between ammonium ions and hydrogen ions in the extractant; when the hydrogen ion content reaches a certain amount, the hydrogen ions will synergistically strip metal ions with ammonium ions; when the hydrogen ion content is higher, the stripping solution will strip metal ions with hydrogen ions as the core, and ammonium sulfate will serve as a precipitant for metal ions. In addition, as the concentration of ammonium sulfate increases, the stripping rate of metal ions will also increase accordingly, and increasing the concentration of ammonium sulfate will improve the regeneration effect of the extractant.

[0149] In summary, the present invention adds an appropriate amount of sulfate and sulfuric acid as the stripping agent 1 in step (3), which can improve the stripping rate and recovery rate of metal ions.

Claims

1. A method for stepwise recovery of metal cations from wet-process phosphoric acid, characterized in that: The following steps are involved: (1) Extraction: Extraction of wet-process phosphoric acid, the resulting organic phase is the extractant loaded with metal ions, and the aqueous phase is the purified phosphoric acid; (2) washing: washing the metal ion-loaded extractant with dilute phosphoric acid to obtain a washed extractant; (3) Stripping 1: using a mixed solution of sulfuric acid and sulfate as a stripping agent 1 to strip the washed extractant to obtain a stripping solution 1 and an organic phase 1, and the stripping solution 1 is concentrated by evaporation and filtered to obtain calcium sulfate; The filtrate is continuously cooled to obtain crystals of manganese sulfate and magnesium sulfate, and the crystallization mother liquor is recycled as stripping agent 1; (4) Washing 1: washing the organic phase 1 with a dilute sulfate solution to recover sulfate entrained in the organic phase 1; (5) Stripping 2: using sulfuric acid solution as stripping agent 2 to perform stripping to obtain stripping solution 2 and organic phase 2; adding sulfate solid to stripping solution 2, cooling and crystallizing to obtain aluminum sulfate, and the crystallization mother liquor is recycled as stripping agent 2; (6) Washing 2: washing the organic phase 2 with dilute sulfuric acid to recover the sulfuric acid entrained in the organic phase 2; (7) stripping 3: using oxalic acid solution as stripping agent 3 to strip the organic phase 2 to obtain stripping solution 3 and organic phase 3, and treating the stripping solution 3 with ultraviolet light to obtain ferrous oxalate precipitate; (8) Washing 3: Wash the organic phase 2 with dilute oxalic acid to recover the oxalic acid entrained in the organic phase 2 to obtain a regenerated extractant, which is returned to step (1) for recycling.

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

1.

3. The method for stepwise recovery of metal cations from wet-process phosphoric acid according to claim 1, characterized in that: In step (2), two-stage countercurrent washing is performed using dilute phosphoric acid, the concentration of which is 1 wt.% to 8 wt.% in terms of P2O5, the temperature is 25 to 85°C, and the volume ratio of O / A is 1 to 10:

1.

4. The method for stepwise recovery of metal cations from wet-process phosphoric acid according to claim 1, characterized in that: In step (3), the sulfate includes at least one of potassium sulfate, ammonium sulfate and cesium sulfate.

5. The method for stepwise recovery of metal cations from wet-process phosphoric acid according to claim 1, characterized in that: In step (3), the concentration of the sulfate solution is 5wt.% to 60wt.%, the concentration of sulfuric acid is ≤15wt.%, the temperature is 25 to 85°C, and the volume ratio O / A is 1 to 10:

1.

6. The method for stepwise recovery of metal cations from wet-process phosphoric acid according to claim 1, characterized in that: In step (3), in step (3), the stripping solution 1 is evaporated and concentrated, filtered, and calcium sulfate is obtained; the filtrate is continuously cooled, and then the manganese sulfate salt and the magnesium sulfate salt are separated by different cooling conditions; Preferably, the sulfate is ammonium sulfate, and manganese ammonium sulfate, magnesium ammonium sulfate, potassium magnesium sulfate and sodium magnesium sulfate are separated by different cooling conditions, wherein the cooling crystallization temperature of manganese ammonium sulfate is 55-80°C, the cooling crystallization temperature of magnesium ammonium sulfate is 15-50°C, and when cooled to 0-10°C, mixed crystals of potassium magnesium sulfate and sodium magnesium sulfate are precipitated simultaneously.

7. The method for stepwise recovery of metal cations from wet-process phosphoric acid according to claim 1, characterized in that: In step (4), in step (4), the organic phase 1 is washed in two-stage countercurrent with a dilute sulfate solution, the concentration of the dilute sulfate solution is 0.1wt.% to 8wt.%, the temperature is 30 to 80°C, and the volume ratio O / A is 1 to 10:1; In step (6), the organic phase 1 is washed with dilute sulfuric acid in two-stage countercurrent, the concentration of the dilute sulfuric acid is 1 wt.% to 10 wt.%, the temperature is 25 to 65° C., and the volume ratio O / A is 1 to 10:1; In step (8), the organic phase 2 is washed in two-stage countercurrent with dilute oxalic acid, the concentration of the dilute oxalic acid is 0.1wt.% to 3wt.%, the temperature is 30 to 70°C, and the volume ratio O / A is 1 to 10:

1.

8. The method for stepwise recovery of metal cations from wet-process phosphoric acid according to claim 1, characterized in that: In step (5), two-stage countercurrent stripping is performed with a sulfuric acid solution, the sulfuric acid concentration is 10wt.% to 60wt.%, the temperature is 25 to 65°C, and the volume ratio of O / A is 1 to 10:

1.

9. The method for stepwise recovery of metal cations from wet-process phosphoric acid according to claim 1, characterized in that: In step (5), solid ammonium sulfate is added to the stripping solution 2 and cooled to crystallize, wherein the cooling crystallization temperature of cesium aluminum sulfate is 60 to 80° C., the cooling crystallization temperature of potassium aluminum sulfate is 25 to 55° C., and the cooling crystallization temperature of ammonium aluminum sulfate is 0 to 20° C.

10. The method for stepwise recovery of metal cations from wet-process phosphoric acid according to claim 1, characterized in that: In step (7), two-stage countercurrent stripping is performed with oxalic acid solution, the oxalic acid concentration is 5wt.% to 20wt.%, the temperature is 30 to 70°C, and the volume ratio O / A is 1 to 10:1.

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