Method for reducing aluminum and extracting phosphorus in a semi-hydro-dihydrate wet-process phosphoric acid process

Abstract

The application discloses a method for extracting phosphorus and reducing aluminum in a hemihydrate-dihydrate wet-process phosphoric acid process, and belongs to the technical field of the wet-process phosphoric acid. The method is characterized in that: after phosphorite and return acid are uniformly mixed, hemihydrate acidolysis reaction is carried out in the presence of concentrated sulfuric acid, a mixed slurry of stable hemihydrate calcium sulfate crystals and intermediate acid is obtained, then a hydroxyquinoline compound is added, and after continuous reaction, hemihydrate gypsum and intermediate acid with low Al2O3 content can be obtained by filtration; dihydrate gypsum can be obtained by carrying out dihydrate conversion reaction of the hemihydrate gypsum in the presence of concentrated sulfuric acid. The method couples a chemical precipitation method in the hemihydrate-dihydrate wet-process phosphoric acid acidolysis process, can reduce the Al2O3 content in the intermediate acid by the chemical precipitation method, the generated precipitate can be filtered together with the phosphogypsum, and the separation of impurities is easy to realize; meanwhile, the generated precipitate can promote crystal growth in the dihydrate conversion reaction of the hemihydrate gypsum, uniform and bulky dihydrate calcium sulfate crystals are obtained, the washing and filtering performance of the filter cake is improved, and the phosphorus yield is increased.

Description

TECHNICAL FIELD

[0001] The application relates to a method for removing aluminum and reducing aluminum content in a semi-hydro-dihydro process wet-process phosphoric acid, and belongs to the technical field of wet-process phosphoric acid. BACKGROUND

[0002] Metal impurity ions such as iron, magnesium and aluminum existing in wet-process phosphoric acid have been an important factor restricting the industrial application breadth and depth of the wet-process phosphoric acid and limiting the added value of products. In particular, the semi-hydro-dihydro process of the wet-process phosphoric acid often has the problem of high aluminum content in the semi-hydro acid, which seriously affects the production of the wet-process phosphoric acid and the quality of downstream phosphorus chemicals. The removal of aluminum ions in the wet-process phosphoric acid has become a difficult problem to be solved in the industry.

[0003] In view of the problem of removing aluminum ions in the wet-process phosphoric acid, many research works have been carried out in the industry, and many purification and impurity removal methods for the wet-process phosphoric acid have also been proposed, such as organic solvent extraction, ion exchange, membrane separation, electrodialysis and chemical precipitation. However, these methods are carried out in the finished product acid of the wet-process phosphoric acid, and the organic solvent extraction, ion exchange, membrane separation and electrodialysis have problems of complex process, tedious process and high cost, and are difficult to realize industrial application. The chemical precipitation method is simple in process and low in treatment cost, and is the preferred method for purification and impurity removal of the wet-process phosphoric acid, but has the problems of fine precipitation and difficult separation.

[0004] Patent CN103523764A discloses a method for reducing magnesium and aluminum impurities in the wet-process phosphoric acid, which adds an ammonium compound containing fluorine into the wet-process phosphoric acid, and removes the magnesium and aluminum impurities through aging and natural sedimentation. However, the removal rate of the magnesium and aluminum impurity ions in the wet-process phosphoric acid is only 5-40% by using the method, the magnesium and aluminum impurity content in the phosphoric acid after impurity removal is still high, and the obtained crystal particles are fine and difficult to separate, and need to be aged and naturally settled for a long time.

[0005] Patent CN109809377A discloses a method for efficiently removing impurities in the sulfuric acid method wet-process phosphoric acid, which adds one or more of calcium-containing inorganic substances, aluminum-containing inorganic substances, silicon-containing inorganic substances, sulfur-containing inorganic substances or fluorine-containing inorganic substances into the wet-process phosphoric acid, adjusts the molar ratio of Ca, Al, Si, S and F in the sulfuric acid method wet-process phosphoric acid, and makes the Ca, Al, Si, S and F impurity elements in the wet-process phosphoric acid form complex inorganic salt precipitates to be precipitated and separated. The method can simultaneously remove the Ca, Al, Si, S and F impurities in the wet-process phosphoric acid. However, the method needs to additionally add multiple reagents, the reagent consumption is large, the reagent cost is high, and the generated precipitates still need to be separated from the liquid phase, and additional solid-liquid separation equipment and process are needed, and the treatment cost is high.

[0006] Therefore, there is an urgent need in the field to develop a new purification and impurity removal method which can efficiently remove aluminum ions in the wet-process phosphoric acid and is low in cost and simple in process. SUMMARY

[0007] In view of the deficiencies in the existing impurity removal technology of wet-process phosphoric acid purification, the application provides a method for phosphorus extraction and aluminum reduction in a hemihydrate-dihydrate wet-process phosphoric acid process.

[0008] The technical scheme of the application is as follows: after the phosphate ore and return acid are uniformly mixed, a hemihydrate acidolysis reaction is performed in the presence of concentrated sulfuric acid, a mixture slurry of stable hemihydrate calcium sulfate crystals and intermediate acid is obtained, then a hydroxyquinoline compound is added, and after continuous reaction and filtration, hemihydrate gypsum and intermediate acid with low Al2O3 content are obtained; the hemihydrate gypsum is subjected to a dihydrate conversion reaction in the presence of concentrated sulfuric acid to obtain dihydrate gypsum.

[0009] In the above technical scheme, in the hemihydrate acidolysis reaction, the return acid is dilute phosphoric acid with a P2O5 content of 36-42wt%, the phosphate ore is phosphate concentrate powder with a P2O5 content of ≥31.5wt% obtained after crushing, grinding and flotation of phosphate ore, and the concentrated sulfuric acid is 98wt% sulfuric acid.

[0010] In the above technical scheme, in the hemihydrate acidolysis reaction, the mass ratio of return acid to phosphate ore in the reaction system is controlled to be 1-10:1, the solid content is 25-40wt%, the liquid-phase sulfate ion concentration is 2-10wt%, and the reaction temperature is 90-100℃, and the reaction time is 1-2 hours.

[0011] Preferably, the mass ratio of return acid to phosphate ore is 2-4:1.

[0012] Preferably, the solid content is 28-37wt%.

[0013] Preferably, the liquid-phase sulfate ion concentration is 2-5wt%.

[0014] Preferably, the reaction temperature is 95-100℃.

[0015] Preferably, the reaction time is 1.5-2 hours.

[0016] In the technical scheme, the hydroxyquinoline compound is one of 1-hydroxyquinoline, 2-hydroxyquinoline, 3-hydroxyquinoline, 4-hydroxyquinoline, 5-hydroxyquinoline, 6-hydroxyquinoline, 7-hydroxyquinoline, 8-hydroxyquinoline or a combination of at least two of them; the added amount of the hydroxyquinoline compound is 0.5-5wt% of the return acid mass; and the reaction time after adding the hydroxyquinoline compound is 0.5-2 hours.

[0017] Preferably, the added amount of the hydroxyquinoline compound is 0.5-2wt% of the return acid mass.

[0018] In the technical scheme, in the dihydrate conversion reaction of the hemihydrate gypsum, the liquid phase sulfate ion concentration in the conversion zone is controlled to be 5-10wt%, the phosphoric acid concentration is controlled to be 20-30wt% P2O5, the solid content is controlled to be 30-40wt%, the reaction temperature is controlled to be 60-80℃, and the reaction time is controlled to be 0.5-1 hour.

[0019] Preferably, the liquid phase sulfate ion concentration in the conversion zone is 5-8wt%.

[0020] Preferably, the phosphoric acid concentration is 25-30wt% P2O5.

[0021] Preferably, the solid content is 35-40wt%.

[0022] Preferably, the reaction temperature is 60-70℃.

[0023] As a preferred technical scheme of the present application, the method comprises the following steps:

[0024] The return acid with a P2O5 content of 36-42wt% is heated to 95-100℃, then the phosphate concentrate powder with a P2O5 content of ≥31.5wt% obtained by crushing, grinding and flotation and 98wt% concentrated sulfuric acid are added into the return acid, the mass ratio of the return acid to the phosphate concentrate in the system is controlled to be 2-4:1, the solid content is controlled to be 28-37wt%, the liquid phase sulfate ion concentration is controlled to be 2-5wt%, and after 1.5-2 hours of reaction, the hydroxyquinoline compound with a mass of 0.5-2wt% of the return acid is added into the mixed slurry, and after 0.5-2 hours of continuous reaction, the hemihydrate gypsum and the intermediate acid with a low Al2O3 content are obtained by filtration; the hemihydrate gypsum obtained by filtration is added with the phosphoric acid with a P2O5 content of 20-30wt% and 98wt% concentrated sulfuric acid, the solid content in the conversion zone is controlled to be 35-40wt%, the liquid phase sulfate ion concentration is controlled to be 5-8wt%, and the temperature is controlled to be 60-70℃, and after 0.5-1 hours of reaction, the dihydrate gypsum is obtained.

[0025] The present application has the following beneficial effects:

[0026] (1) The present application couples a chemical precipitation method in the semi-hydro-dihydrate wet-process phosphoric acid hydrolysis process, which can be directly carried out on the existing wet-process phosphoric acid device without changing the existing process and equipment, is simple to operate and low in cost.

[0027] (2) The present application uses hydroxyquinoline compounds as a precipitant to combine with aluminum ions to form stable complex precipitates in the strong acidic and strongly corrosive complex reaction environment of the semi-hydro-dihydrate wet-process phosphoric acid hydrolysis process, effectively removes the aluminum impurities from the wet-process phosphoric acid liquid phase, has good aluminum removal effect, and the generated hydroxyquinoline aluminum precipitate can be filtered together with the phosphogypsum, the impurities are separated quickly, no additional solid-liquid separation equipment and process are needed, and the time cost and economic cost are low.

[0028] (3) In the dihydrate conversion reaction of semi-hydrated gypsum, the complex precipitate hydroxyquinoline aluminum can promote the growth of dihydrate gypsum crystals, obtain uniform and bulky calcium sulfate dihydrate crystals, and improve the washing and filtering performance of the filter cake and increase the phosphorus yield. BRIEF DESCRIPTION OF DRAWINGS

[0029] Fig. 1 The X-ray diffraction pattern of the dihydrate gypsum obtained after adding hydroxyquinoline compounds to Example 1;

[0030] Fig. 2 The X-ray diffraction pattern of the dihydrate gypsum obtained without adding hydroxyquinoline compounds to Comparative Example 1. DETAILED DESCRIPTION

[0031] In order to deepen the understanding of the present application by those skilled in the art, the present application will be further described in detail below in conjunction with specific examples, which are only used to explain the present application and do not constitute a limitation on the scope of protection of the present application.

[0032] Example 1

[0033] The return acid with a P2O5 content of 37.0wt% was heated to 97℃, then the phosphate concentrate powder with a P2O5 content of 32.0wt% obtained by crushing, grinding and flotation was added, and 98wt% concentrated sulfuric acid was added, the mass ratio of return acid to phosphate concentrate in the system was controlled to be 2:1, the solid content was 30wt%, and the liquid phase sulfate ion concentration was 4wt%, after 90min of reaction, 1.0wt% hydroxyquinoline compounds were added to the mixed slurry, and after 60min of continuous reaction, semi-hydrated gypsum and intermediate acid with low Al2O3 content were obtained by filtration; P2O5 content of 25wt% phosphoric acid and 98wt% concentrated sulfuric acid were added to the semi-hydrated gypsum obtained by filtration, the solid content in the conversion zone was controlled to be 35wt%, the liquid phase sulfate ion concentration was 6wt%, and the temperature was 65℃, after 30min of reaction, dihydrate gypsum was obtained, which was washed and dried, and the phosphorus yield was calculated and detected.

[0034] Comparative Example 1

[0035] The acid retort with a P2O5 content of 37.0 wt% was heated to 97°C. Then, phosphate concentrate powder with a P2O5 content of 32.0 wt% (obtained through crushing, grinding, and flotation) and concentrated sulfuric acid with a P2O5 content of 98 wt% were added. The mass ratio of acid retort to phosphate ore was controlled at 2:1, the solid content was 30 wt%, and the liquid phase sulfate ion concentration was 4 wt%. After reacting for 150 min, the mixture was filtered to obtain hemihydrate gypsum and intermediate acid. Phosphoric acid with a P2O5 content of 25 wt% and concentrated sulfuric acid with a P2O5 content of 98 wt% were added to the filtered hemihydrate gypsum. The solid content in the conversion zone was controlled at 35 wt%, the liquid phase sulfate ion concentration was 6 wt%, and the temperature was 65°C. After reacting for 30 min, dihydrate gypsum was obtained. The dihydrate gypsum was washed, dried, and the phosphorus yield was calculated.

[0036] The chemical composition analysis and phosphorus yield calculation results of the raw material acid return, phosphate concentrate powder and product intermediate acid in Example 1 and Comparative Example 1 are shown in Table 1.

[0037] Table 1 Comparison of raw material and product composition in Example 1 and Comparative Example 1

[0038]

[0039] Table 1 shows that after adding 1 wt% hydroxyquinoline compounds in the hemihydrate-dihydrate wet phosphoric acid process, the phosphorus yield was 95.4%, an increase of 5.1% compared to the unadded result; the content of intermediate acid Al2O3 decreased by 72.6% compared to the unadded result; and the filtration efficiency of dihydrate gypsum was 916.12 kg dry gypsum / (m 2 ·h), which increased the yield of dry gypsum by 30.4 kg / (m³) compared to when no gypsum was added. 2 ·h).

[0040] from Figs. 1-2 It can be seen that, compared with the dihydrate gypsum obtained by adding hydroxyquinoline compounds in the hemihydrate-dihydrate wet process of phosphoric acid, the crystal form of the dihydrate gypsum obtained by adding hydroxyquinoline compounds is coarse and elongated, with a larger aspect ratio, and the crystal surface is relatively smooth with less crystal agglomeration. The dihydrate calcium sulfate crystals are also coarser and more uniform.

[0041] Example 2

[0042] The P2O5 content of 38.7wt% of the return acid is heated to 98℃, then the P2O5 content of 33.4wt% of the phosphate concentrate powder obtained by crushing, grinding and flotation is added to the return acid and 98wt% of concentrated sulfuric acid, the mass ratio of return acid to phosphate concentrate in the system is controlled to be 3:1, the solid content is 33wt%, the liquid phase sulfate ion concentration is 3wt%, after 100min of reaction, 1.5wt% of hydroxyquinoline compound of the return acid mass is added to the mixed slurry, after 90min of continuous reaction, the semihydrate gypsum and the intermediate acid with low Al2O3 content can be obtained by filtration; the P2O5 content of 27.3wt% of phosphoric acid and 98wt% of concentrated sulfuric acid is added to the semihydrate gypsum obtained by filtration, the solid content in the conversion zone is controlled to be 36wt%, the liquid phase sulfate ion concentration is 7wt%, the temperature is 69℃, after 40min of reaction, the dihydrate gypsum can be obtained, and the dihydrate gypsum is washed and dried to detect and calculate the phosphorus yield.

[0043] Comparative Example 2

[0044] The P2O5 content of 38.7wt% of the return acid is heated to 98℃, then the P2O5 content of 33.4wt% of the phosphate concentrate powder obtained by crushing, grinding and flotation is added to the return acid and 98wt% of concentrated sulfuric acid, the mass ratio of return acid to phosphate concentrate in the system is controlled to be 3:1, the solid content is 33wt%, the liquid phase sulfate ion concentration is 3wt%, after 190min of reaction, the semihydrate gypsum and the intermediate acid can be obtained by filtration; the P2O5 content of 27.3wt% of phosphoric acid and 98wt% of concentrated sulfuric acid is added to the semihydrate gypsum obtained by filtration, the solid content in the conversion zone is controlled to be 36wt%, the liquid phase sulfate ion concentration is 7wt%, the temperature is 69℃, after 40min of reaction, the dihydrate gypsum can be obtained, and the dihydrate gypsum is washed and dried to detect and calculate the phosphorus yield.

[0045] The chemical composition analysis comparison of the raw materials return acid, phosphate concentrate powder and the product intermediate acid in Example 2 and Comparative Example 2, and the phosphorus yield calculation results are shown in Table 2.

[0046] Table 2 Comparison of raw material and product composition in Example 2 and Comparative Example 2

[0047]

[0048]

[0049] As shown in Table 2, after adding 1.5wt% of hydroxyquinoline compound in the process of semihydrate-dihydrate wet-process phosphoric acid, the phosphorus yield is 94.5%, which is increased by 4.9% compared with that without adding; the Al2O3 content of the intermediate acid is reduced by 72.4% compared with that without adding; the dihydrate gypsum filtration intensity is 919.23kg dry gypsum / (m 2 ·h), which is increased by 46.88kg dry gypsum / (m2 ·h).

[0050] Example 3

[0051] The return acid with P2O5 content of 40.4wt% was heated to 95℃, then the phosphate concentrate powder with P2O5 content of 31.7wt% and 98wt% concentrated sulfuric acid were added into the return acid, the mass ratio of return acid to phosphate concentrate was controlled to be 4:1, the solid content was 35wt%, the liquid phase sulfate ion concentration was 5wt%, after 110min reaction, 2.0wt% hydroxyquinoline compound was added into the mixture slurry, after 70min reaction, the hemihydrate gypsum and the intermediate acid with low Al2O3 content were obtained by filtration; the hemihydrate gypsum obtained by filtration was added into 24.7wt% phosphoric acid and 98wt% concentrated sulfuric acid, the solid content was controlled to be 38wt% in the conversion zone, the liquid phase sulfate ion concentration was 8wt%, the temperature was 63℃, after 50min reaction, the dihydrate gypsum was obtained, which was washed and dried, then the phosphorus yield was calculated.

[0052] Comparative Example 3

[0053] The return acid with P2O5 content of 40.4wt% was heated to 95℃, then the phosphate concentrate powder with P2O5 content of 31.7wt% and 98wt% concentrated sulfuric acid were added into the return acid, the mass ratio of return acid to phosphate concentrate was controlled to be 4:1, the solid content was 35wt%, the liquid phase sulfate ion concentration was 5wt%, after 180min reaction, the hemihydrate gypsum and the intermediate acid were obtained by filtration; the hemihydrate gypsum obtained by filtration was added into 24.7wt% phosphoric acid and 98wt% concentrated sulfuric acid, the solid content was controlled to be 38wt% in the conversion zone, the liquid phase sulfate ion concentration was 8wt%, the temperature was 63℃, after 50min reaction, the dihydrate gypsum was obtained, which was washed and dried, then the phosphorus yield was calculated.

[0054] The chemical composition analysis comparison of the raw materials return acid, phosphate concentrate powder and the product intermediate acid, and the phosphorus yield calculation results in Example 3 and Comparative Example 3 are shown in Table 3.

[0055] Table 3 Comparison of raw materials and product composition in Example 3 and Comparative Example 3 As shown in Table 3, after adding 2.0wt% hydroxyquinoline compound in the hemihydrate-dihydrate wet-process phosphoric acid process, the phosphorus yield was 94.7%, which was increased by 5.8% compared with that without adding; the Al2O3 content of the intermediate acid was reduced by 76.5% compared with that without adding; the dihydrate gypsum filtration intensity was 928.15kg dry gypsum / (m 2 ·h), which was increased by 50.8kg dry gypsum / (m2 • h).

[0056] Example 4-1

[0057] The return acid with P2O5 content of 39.1wt% was heated to 96℃, then P2O5 content of 31.5wt% phosphate concentrate powder obtained by crushing, grinding and flotation was added into the return acid, and 98wt% concentrated sulfuric acid was added, the mass ratio of return acid to phosphate concentrate in the system was controlled to be 2.5:1, the solid content was 29wt%, and the liquid phase sulfate ion concentration was 2wt%, after 120min reaction, 0.5wt% hydroxyquinoline compound was added into the mixed slurry, after 100min continuous reaction, the semihydrated gypsum and the intermediate acid with low Al2O3 content were obtained by filtration, then P2O5 content of 21.8wt% phosphoric acid and 98wt% concentrated sulfuric acid were added into the semihydrated gypsum obtained by filtration, the solid content in the conversion zone was controlled to be 37wt%, the liquid phase sulfate ion concentration was 5wt%, and the temperature was 64℃, after 60min reaction, the dihydrate gypsum was obtained, and the dihydrate gypsum was washed and dried, then the phosphorus yield was calculated and detected.

[0058] Example 4-2

[0059] The return acid with P2O5 content of 39.1wt% was heated to 96℃, then P2O5 content of 31.5wt% phosphate concentrate powder obtained by crushing, grinding and flotation was added into the return acid, and 98wt% concentrated sulfuric acid was added, the mass ratio of return acid to phosphate concentrate in the system was controlled to be 2.5:1, the solid content was 29wt%, and the liquid phase sulfate ion concentration was 2wt%, after 120min reaction, 0.2wt% hydroxyquinoline compound was added into the mixed slurry, after 100min continuous reaction, the semihydrated gypsum and the intermediate acid with low Al2O3 content were obtained by filtration, then P2O5 content of 21.8wt% phosphoric acid and 98wt% concentrated sulfuric acid were added into the semihydrated gypsum obtained by filtration, the solid content in the conversion zone was controlled to be 37wt%, the liquid phase sulfate ion concentration was 5wt%, and the temperature was 64℃, after 60min reaction, the dihydrate gypsum was obtained, and the dihydrate gypsum was washed and dried, then the phosphorus yield was calculated and detected.

[0060] Example 4-3

[0061] The P2O5 content of 39.1wt% of the return acid is heated to 96℃, then the P2O5 content of 31.5wt% of the phosphate concentrate powder obtained after crushing, grinding and flotation is added to the return acid, and 98wt% of concentrated sulfuric acid is added, the mass ratio of return acid to phosphate in the system is controlled to be 2.5:1, the solid content is 29wt%, and the liquid phase sulfate ion concentration is 2wt%, after 120min of reaction, 5.0wt% of hydroxyquinoline compounds of the return acid mass is added to the mixed slurry, and after 100min of continuous reaction, the semihydrated gypsum and the intermediate acid with low Al2O3 content are obtained by filtration; the semihydrated gypsum obtained by filtration is added with P2O5 content of 21.8wt% of phosphoric acid and 98wt% of concentrated sulfuric acid, the solid content in the conversion zone is controlled to be 37wt%, the liquid phase sulfate ion concentration is 5wt%, and the temperature is 64℃, after 60min of reaction, the dihydrate gypsum is obtained, and the dihydrate gypsum is washed, dried and detected to calculate the phosphorus yield.

[0062] Example 4-4

[0063] The P2O5 content of 39.1wt% of the return acid is heated to 96℃, then the P2O5 content of 31.5wt% of the phosphate concentrate powder obtained after crushing, grinding and flotation is added to the return acid, and 98wt% of concentrated sulfuric acid is added, the mass ratio of return acid to phosphate in the system is controlled to be 2.5:1, the solid content is 29wt%, and the liquid phase sulfate ion concentration is 2wt%, after 120min of reaction, 5.0wt% of hydroxyquinoline compounds of the return acid mass is added to the mixed slurry, and after 100min of continuous reaction, the semihydrated gypsum and the intermediate acid with low Al2O3 content are obtained by filtration; the semihydrated gypsum obtained by filtration is added with P2O5 content of 21.8wt% of phosphoric acid and 98wt% of concentrated sulfuric acid, the solid content in the conversion zone is controlled to be 37wt%, the liquid phase sulfate ion concentration is 5wt%, and the temperature is 64℃, after 60min of reaction, the dihydrate gypsum is obtained, and the dihydrate gypsum is washed, dried and detected to calculate the phosphorus yield.

[0064] Example 4-5

[0065] The P2O5 content of 39.1wt% of the return acid is heated to 96℃, then the P2O5 content of 31.5wt% of the phosphate concentrate powder obtained after crushing, grinding and flotation is added into the return acid, and 98wt% of concentrated sulfuric acid is added, the mass ratio of return acid to phosphate concentrate in the system is controlled to be 2.5:1, the solid content is 29wt%, and the liquid phase sulfate ion concentration is 2wt%, after 120min of reaction, 0.5wt% of hydroxyquinoline compound of the return acid mass is added into the mixed slurry, and after 150min of continuous reaction, the semihydrated gypsum and the intermediate acid with low Al2O3 content can be obtained by filtration; the P2O5 content of 21.8wt% of phosphoric acid and 98wt% of concentrated sulfuric acid is added into the semihydrated gypsum obtained by filtration, the solid content in the conversion zone is controlled to be 37wt%, the liquid phase sulfate ion concentration is 5wt%, and the temperature is 64℃, after 60min of reaction, the dihydrate gypsum can be obtained, and the phosphorus yield is calculated after washing and drying the dihydrate gypsum.

[0066] Comparative Example 4

[0067] The P2O5 content of 39.1wt% of the return acid is heated to 96℃, then the P2O5 content of 31.5wt% of the phosphate concentrate powder obtained after crushing, grinding and flotation is added into the return acid, and 98wt% of concentrated sulfuric acid is added, the mass ratio of return acid to phosphate concentrate in the system is controlled to be 2.5:1, the solid content is 29wt%, and the liquid phase sulfate ion concentration is 2wt%, after 220min of reaction, the semihydrated gypsum and the intermediate acid can be obtained by filtration; the P2O5 content of 21.8wt% of phosphoric acid and 98wt% of concentrated sulfuric acid is added into the semihydrated gypsum obtained by filtration, the solid content in the conversion zone is controlled to be 37wt%, the liquid phase sulfate ion concentration is 5wt%, and the temperature is 64℃, after 60min of reaction, the dihydrate gypsum can be obtained, and the phosphorus yield is calculated after washing and drying the dihydrate gypsum.

[0068] The chemical composition analysis comparison of the raw materials return acid, phosphate concentrate powder and product intermediate acid in Example 4 and Comparative Example 4, and the phosphorus yield calculation results are shown in Table 4.

[0069] Table 4 Comparison of raw material and product composition in Example 4 and Comparative Example 4

[0070]

[0071] As shown in Table 4, compared with the preferred technical scheme (Example 4-1) of the present application, when the addition amount of the hydroxyquinoline compound is less than 0.5 wt% (Example 4-2), the phosphorus yield, the removal rate of intermediate acid Al2O3 and the filtration intensity of dihydrate gypsum are all obviously reduced; when the addition amount of the hydroxyquinoline compound is greater than 2.0 wt% (Example 4-3), the phosphorus yield, the removal rate of intermediate acid Al2O3 and the filtration intensity of dihydrate gypsum are similar to those of Example 4-1, and are not obviously increased; when the continued reaction time after adding the hydroxyquinoline compound is less than 0.5 h (Example 4-4), the phosphorus yield, the removal rate of intermediate acid Al2O3 and the filtration intensity of dihydrate gypsum are all obviously reduced; when the continued reaction time after adding the hydroxyquinoline compound is greater than 2 h (Example 4-5), the phosphorus yield, the removal rate of intermediate acid Al2O3 and the filtration intensity of dihydrate gypsum are similar to those of Example 4-1, and are not obviously increased; when no hydroxyquinoline compound is added (Comparative Example 4), the phosphorus yield, the removal rate of intermediate acid Al2O3 and the filtration intensity of dihydrate gypsum are all obviously reduced. The above examples are only the preferred technical scheme of the present application, and should not be regarded as the limitation of the present application. The examples in the present application and the features in the examples can be combined with each other in the case of no conflict. The protection scope of the present application should be the technical scheme recited in the claims, and the equivalent replacement scheme of the technical features recited in the claims is the protection scope. That is, the equivalent replacement improvement in this range is also within the protection scope of the present application.

Claims

1. A method for reducing aluminum and extracting phosphorus in a semi-hydro-dihydrate wet-process phosphoric acid process, characterized by, The method comprises the following steps: 1) uniformly mixing phosphate ore with return acid, and then performing a semi-hydrated acidolysis reaction in the presence of concentrated sulfuric acid to obtain a mixed slurry of stable semi-hydrated calcium sulfate crystals and intermediate acid; 2) adding a hydroxyquinoline compound, continuing to react, and then filtering to obtain semi-hydrated gypsum and intermediate acid with low Al2O3 content, wherein the hydroxyquinoline compound is one or a combination of at least two of 1-hydroxyquinoline, 2-hydroxyquinoline, 3-hydroxyquinoline, 4-hydroxyquinoline, 5-hydroxyquinoline, 6-hydroxyquinoline, 7-hydroxyquinoline and 8-hydroxyquinoline; the addition amount of the hydroxyquinoline compound is 0.5-5 wt% of the mass of the return acid, and the reaction time after adding the hydroxyquinoline compound is 0.5-2 hours; 3) performing a dihydrate conversion reaction on the semi-hydrated gypsum in the presence of concentrated sulfuric acid to obtain dihydrated gypsum; The method completes the phosphorus extraction and aluminum reduction operation in the semi-hydrated-dihydrated wet-process phosphoric acid process.

2. The method for reducing aluminum and extracting phosphorus in a hemi-di wet-process phosphoric acid process according to claim 1, characterized in that, In the step 1), in the semi-hydrated acidolysis reaction, the return acid is dilute phosphoric acid with a P2O5 content of 36-42 wt%, the phosphate ore is phosphate concentrate powder with a P2O5 content of ≥31.5 wt% obtained by crushing, grinding and flotation of phosphate ore, and the concentrated sulfuric acid is 98 wt% sulfuric acid.

3. The method for reducing aluminum and extracting phosphorus in a hemi-di wet-process phosphoric acid process according to claim 1, characterized in that, In the step 1), in the semi-hydrated acidolysis reaction, the mass ratio of the return acid to the phosphate ore in the reaction system is controlled to be (1-10):1, the solid content is 25-40 wt%, the liquid-phase sulfate ion concentration is 2-10 wt%, the reaction temperature is 90-100℃, and the reaction time is 1-2 hours.

4. The method for reducing aluminum and extracting phosphorus in a hemi-di wet-process phosphoric acid process according to claim 3, characterized in that, In the step 1), the mass ratio of the return acid to the phosphate ore is (2-4):

1. The solid content is 28-37 wt%. The liquid-phase sulfate ion concentration is 2-5 wt%. The reaction temperature is 95-100℃. The reaction time is 1.5-2 hours.

5. The method for phosphorus extraction and aluminum reduction in the hemihydrate-dihydrate wet phosphoric acid process according to claim 1, characterized in that, In the step 2), the addition amount of the hydroxyquinoline compound is 0.5-2 wt% of the mass of the return acid.

6. The method for phosphorus extraction and aluminum reduction in the hemihydrate-dihydrate wet phosphoric acid process according to claim 1, characterized in that, The method comprises the following steps: In the step 2), the Al2O3 content in the intermediate acid with low Al2O3 content is <1.0 wt%.

7. The method for phosphorus extraction and aluminum reduction in the hemihydrate-dihydrate wet phosphoric acid process according to claim 1, characterized in that, In the step 3), in the dihydrate conversion reaction of the semi-hydrated gypsum, the liquid-phase sulfate ion concentration in the conversion zone is controlled to be 5-10 wt%, the phosphoric acid concentration is 20-30 wt% P2O5, the solid content is 30-40 wt%, the reaction temperature is 60-80℃, and the reaction time is 0.5-1 hour.

8. The method for reducing aluminum and extracting phosphorus in a hemi-di wet-process phosphoric acid process according to claim 7, characterized in that, In the step 3), the liquid-phase sulfate ion concentration in the conversion zone is 5-8 wt%. The phosphoric acid concentration is 25-30 wt% P2O5. The solid content is 35-40 wt%. The reaction temperature is 60-70℃.

9. The method for reducing aluminum and extracting phosphorus in a hemi-di wet-process phosphoric acid process according to claim 1, characterized in that, The method comprises the following specific steps: a) heating return acid with a P2O5 content of 36-42 wt% to 95-100℃, and then adding phosphate concentrate powder with a P2O5 content of ≥31.5 wt% obtained by crushing, grinding and flotation and 98 wt% concentrated sulfuric acid into the return acid, controlling the mass ratio of the return acid to the phosphate ore in the system to be 2-4:1, the solid content to be 28-37 wt%, and the liquid-phase sulfate ion concentration to be 2-5 wt%, and reacting for 1.5-2 hours, b) adding 0.5-2wt% of hydroxyquinoline compound to the mixed slurry, and continuing to react for 0.5-2h to obtain hemihydrate gypsum and intermediate acid with low Al2O3 content, and then filtering; c) adding 20-30wt% of phosphoric acid and 98wt% of concentrated sulfuric acid to the hemihydrate gypsum obtained by filtering, and controlling the solid content in the conversion zone to be 35-40wt%, the liquid-phase sulfate ion concentration to be 5-8wt%, and the temperature to be 60-70℃, and then reacting for 0.5-1h to obtain dihydrate gypsum.

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