Process for producing high-purity calcium sulfate by extraction method

Abstract

The invention belongs to the technical field of wet-process phosphoric acid purification, and relates to a process for producing high-purity calcium sulfate by extracting calcium ions from wet-process phosphoric acid purification byproduct raffinate acid through a solvent extraction method. The main process comprises the following steps: fully reacting in an extraction device by utilizing a high-selectivity extraction agent, extracting and enriching impurity cations of iron, magnesium, aluminum and calcium in raffinate acid, then carrying out reverse extraction by utilizing sulfuric acid with a certain concentration, and enabling the cations of iron, magnesium, aluminum and calcium to enter reverse extraction liquid sulfuric acid; through concentration control, calcium ions and sulfate radicals are combined to produce high-purity calcium sulfate crystals, and the high-purity calcium sulfate is obtained after filtering and drying.

Description

Technical Field

[0001] The invention belongs to the technical field of wet-process phosphoric acid purification and relates to a process technology for removing impurities from wet-process phosphoric acid and utilizing them in a high-value manner. Background Art

[0002] Metal ions contained in wet-process phosphoric acid, such as Ca 2+ Mg 2+ 、Al 3+ , Fe 3+ Such metals will cause a large amount of phosphorus loss in subsequent use, so it is necessary to use extraction methods to purify the metal ion content in wet-process acid, improve the phosphorus yield of subsequent wet-process phosphoric acid use and high-quality utilization.

[0003] After wet phosphoric acid is extracted, the loaded solvent contains Ca 2+ Mg 2+ 、Al 3+ , Fe 3+ Impurity ions, during the solvent stripping regeneration process, use sulfuric acid to strip Ca 2+ Mg 2+ 、Al 3+ Impurity ions: Conventional centrifugal extraction equipment will precipitate a large amount of calcium sulfate during the reaction process, which will adhere to the reaction drum, causing large vibrations during the system operation and reduced reaction efficiency. At the same time, the presence of a large amount of calcium ions has a significant impact on the crystallization of ammonium aluminum sulfate and ammonium magnesium sulfate, resulting in poor crystallization effects, low magnesium aluminum crystallization rates, and affecting the circulation of the sulfuric acid solution system. Summary of the invention

[0004] In view of the above, combined with the low solubility and easy crystallization characteristics of calcium sulfate, the present invention provides a process scheme for generating high-purity calcium sulfate using extraction technology.

[0005] The process route adopted by the present invention is: using a highly selective solvent and wet-process phosphoric acid to purify byproduct raffinate acid, fully mixing and extracting, and then separating oil from water.

[0006] The highly selective organic solvent is a mixture of an organic phosphonate and a thiol, wherein the organic phosphonate is selected from ethyl (2-(diethylamino)-2-oxyethyl)(phenyl)phosphinate and ethyl 1-(ethoxy(phenyl)phosphoryl)butyrate; and the thiol is selected from any one of pyrithiol, panthenethiol, sec-butyl mercaptan, 2-pyrimidinethiol and 1-phenyl-1H-tetrazol-5-thiol.

[0007] The volume ratio of the organic phosphonate to the thiol is 0.1:1-10.

[0008] The separated aqueous phase of the solvent loaded with iron, magnesium, aluminum and calcium enters the stripping process, and a certain concentration of sulfuric acid is used for a full stripping reaction. Based on the principle of low solubility of calcium sulfate, sulfuric acid and calcium ions combine to form calcium sulfate crystals, in which magnesium and aluminum enter the sulfuric acid solution in the form of ions.

[0009] The calcium sulfate crystal mixture is sent to a thickener for enrichment, and the calcium sulfate crystals are filtered and washed to obtain high-purity phosphogypsum.

[0010] In the present invention, further, the process extraction reaction adopts a centrifugal extractor, and its working principle is that the extractant and the raffinate enter the centrifugal extractor and realize the extraction reaction under the high-speed shear dispersion of the internal mixing drum, and then the oil-water separation is realized by using the relative gravity difference between the two under the action of centrifugation. The reaction ratio (O / A) is 2:1-4:1, the rotation speed is 800-1000 rpm, and the temperature is 42-45°C.

[0011] In the present invention, further, the crystallization separation operation is that the solvent loaded with cations reacts with 30-35% dilute sulfuric acid in a high-speed extractor, enters a concentrated mass for crystallization and solid-liquid separation, the reaction ratio is 1:1, and the temperature is 8-15°C.

[0012] In the present invention, further, the slurry with high solid content in the lower part of the thickener contains 5-10% calcium sulfate crystals, the slurry is pumped to a plate and frame filter press for filtration, and washed with process water to obtain high-purity calcium sulfate, the ratio of slurry to washing water is 8-10:1, and then blown with compressed air for 15-20 minutes.

[0013] In the present invention, further, the calcium sulfate crystallization clarified liquid and the filtered clear liquid are sent to the aluminum magnesium ammonium sulfate crystallization process for treatment, and then the dilute sulfuric acid is returned to the sulfuric acid preparation tank for treatment.

[0014] Beneficial effects of the present invention The present invention has the following beneficial effects: The invention makes full use of the difference in solubility of calcium, magnesium, aluminum and iron ions after they are combined with sulfate ions, firstly separates the calcium ions, and reduces the influence of the calcium ions on the crystallization of aluminum sulfate and magnesium sulfate.

[0015] This process uses a combination of emulsification extraction and dense sedimentation process, which can effectively prevent calcium sulfate crystallization from adhering to the centrifugal extraction drum, resulting in reduced system extraction efficiency and poor production stability.

[0016] The calcium sulfate product produced by this process has high purity and can increase the added value of the calcium sulfate product in terms of operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0018] In order to make the above-mentioned objects, features and advantages of the present invention more easily understood, the specific implementation modes of the present invention are described in detail below.

[0019] Example 1 The phosphoric acid concentration in the raffinate is 40-45%, 2 O 5 The wet-process phosphoric acid inevitably contains impurity components, wherein the iron oxide content in the sesquioxide in the impurity components is 0.25-0.28%, the magnesium oxide content is 1.5-1.8%, the aluminum oxide content is 1.5-1.8%, and the calcium oxide content is 1.5-1.8%.

[0020] The above raffinate was treated with 2m 3 / h flow rate, the organic phosphonate is selected from a mixture of ethyl (2-(diethylamino)-2-oxoethyl)(phenyl)phosphinate and sec-butyl mercaptan in a volume ratio of 0.1:4 0.1m 3 / h, feed temperature 40-50℃, extraction centrifuge speed 900 rpm for full extraction.

[0021] After extraction, the separated solvent loaded with iron, magnesium, aluminum and calcium is transported to an emulsification pump through a centrifugal pump to fully react with 35% dilute sulfuric acid, and then sent to a thickener for reaction, crystallization and separation. The flow rate is 4m3 / h, the flow rate of dilute sulfuric acid is 4m3 / h, and the temperature is 15°C.

[0022] The results of this process are shown in Table 1: Table 1 Preparation of high-purity calcium sulfate by extraction of 26% dilute acid

[0023] The three-stage extraction means: using the solvent and the residual acid extraction reaction to adopt a three-stage countercurrent contact extraction process, that is, after the extraction, the extract is collected again and extracted again, and the extraction is continuously recovered for 3 times.

[0024] Six-stage extraction means: using solvent and raffinate extraction reaction to adopt a six-stage countercurrent contact extraction process, that is, after extraction, the extract is collected again and extracted again, and the extraction is continuously recovered for 6 times.

[0025] Crystalline product specifications: dihydrate calcium sulfate content 99.5%, anhydrous calcium sulfate content 0.22%, product whiteness 95.6%.

[0026] Example 2 The raffinate after purification and extraction contains 26% dilute phosphoric acid, and 45-48% concentrated phosphoric acid after concentration. It also contains impurities, among which the iron oxide content in the sesquioxide is 0.25-0.28%, the magnesium oxide content is 1.5-1.8%, the aluminum oxide content is 1.5-1.8%, and the calcium oxide content is 1.5-1.8%. The concentrated raffinate after extraction is filtered twice, and the solid content is treated to less than 0.5%. 3 / h flow rate, 0.5m3 of a mixture of 1-(ethoxy(phenyl)phosphoryl)butyric acid ethyl ester and pyritinol in a volume ratio of 1:6 3 / h, feed temperature 40-50℃, extraction centrifuge speed 1000 rpm for full extraction.

[0027] After extraction, the solvent loaded with iron, magnesium, aluminum and calcium is separated and transported to the emulsification pump through a centrifugal pump to fully react with 35% dilute sulfuric acid, and then sent to the thickener for reaction, crystallization and separation. The flow rate is 8m 3 / h, dilute sulfuric acid flow rate is 8m 3 / h, temperature is 15℃.

[0028] The results of this process are shown in Table 2: Table 2 Extraction method for preparing high purity calcium sulfate from raffinate

[0029] The three-stage extraction means: using the solvent and the residual acid extraction reaction to adopt a three-stage countercurrent contact extraction process, that is, after the extraction, the extract is collected again and extracted again, and the extraction is continuously recovered for 3 times.

[0030] Six-stage extraction means: using solvent and raffinate extraction reaction to adopt a six-stage countercurrent contact extraction process, that is, after extraction, the extract is collected again and extracted again, and the extraction is continuously recovered for 6 times.

[0031] Crystalline product specifications: dihydrate calcium sulfate content 99.7%, anhydrous calcium sulfate content 0.3%, product whiteness 95.1%.

[0032] From the results in Table 1 and Table 2, it can be seen that the process has good extraction and removal capabilities for impurity ions for both dilute and concentrated acids, and the characteristic selection is magnesium, aluminum, and calcium. The sulfuric acid stripping has poor selectivity for iron, which is more conducive to the subsequent separation of iron ions. The calcium sulfate output quality is stable and the purity is high.

[0033] The above-mentioned implementation cases only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they should not be understood as limiting the scope of the present invention.

Claims

1. A process for producing high-purity calcium sulfate by extraction, the method comprising: using a highly selective solvent and wet-process phosphoric acid to purify by-product raffinate acid, fully mixing and extracting, and then separating oil from water; The separated solvent aqueous phase loaded with iron, magnesium, aluminum and calcium enters the stripping process, and a certain concentration of sulfuric acid is used for full stripping reaction. The sulfuric acid and calcium ions combine to form calcium sulfate crystals, in which magnesium and aluminum enter the sulfuric acid solution in the form of ions. The calcium sulfate crystal mixture is sent to a thickener for enrichment, and the calcium sulfate crystals are filtered and washed to obtain high-purity phosphogypsum.

2. The process according to claim 1, characterized in that The phosphoric acid concentration in the raffinate is 40-45%, calculated as P2O5. The wet-process phosphoric acid inevitably contains impurity components, wherein the iron oxide content in the sesquioxide in the impurity components is 0.25-0.28%, the magnesium oxide content is 1.5-1.8%, the aluminum oxide content is 1.5-1.8%, and the calcium oxide content is 1.5-1.8%.

3. The process according to claim 2, characterized in that The highly selective organic solvent is a mixture of an organic phosphonate and a thiol, wherein the organic phosphonate is selected from ethyl (2-(diethylamino)-2-oxyethyl)(phenyl)phosphinate and ethyl 1-(ethoxy(phenyl)phosphoryl)butyrate; and the thiol is selected from any one of pyrithiol, panthenethiol, sec-butyl mercaptan, 2-pyrimidinethiol and 1-phenyl-1H-tetrazol-5-thiol.

4. The process according to claim 3, characterized in that The volume ratio of the organic phosphonate to the thiol is 0.1:1-10.

5. The process according to claim 3, characterized in that The centrifugal extraction equipment is one of the forms of an emulsified extraction phase separation tank combination, a centrifugal extraction separator, and a tank-type stirring thickener.

6. The process according to claim 1, characterized in that The stripping agent used in the stripping crystallization process is a 30-35% dilute sulfuric acid solution. The dilute sulfuric acid and the solvent loaded with iron, magnesium, aluminum and calcium are fully mixed and reacted in a ratio of 1:

1. The reaction temperature is 25-35°C, the reaction residence time is 3-5min, and the phase separation residence time is 30-50min.

7. The process according to claim 1, characterized in that The solid-liquid separation device used in the filtering and washing process is a plate-frame filter press, and the washing liquid is 5% dilute sulfuric acid.

8. A high-purity calcium sulfate, characterized in that: The calcium sulfate dihydrate is prepared according to claim 1-6, and the content of calcium sulfate dihydrate is ≥99% and the whiteness is ≥95%.

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