Method for preparing semi-hydrated gypsum through desulfurization and acid returning

Abstract

The invention relates to the technical field of wet-process phosphoric acid, and particularly discloses a method for preparing semi-hydrated gypsum by desulfurization and acid return, which comprises the following steps: S1, adding phosphorite into intermediate acid in the production process of semi-hydrated wet-process phosphoric acid for desulfurization treatment to obtain desulfurized slurry, cooling the slurry, and aging to obtain bottom ore pulp and top overflow desulfurized phosphoric acid; and S2, part of the desulfurized phosphoric acid obtained in the S1 returns to a semi-hydrated wet-process phosphoric acid reaction tank to fully react with phosphorite, then excessive sulfuric acid is added for reaction, and finally solid-liquid separation is performed to obtain semi-hydrated intermediate acid and semi-hydrated gypsum. According to the method disclosed by the invention, the desulfurized intermediate acid is used for decomposing the phosphate ore, so that the phenomenon of phosphate ore passivation easily caused by too high concentration of liquid-phase sulfate radicals in the semi-hydrated process is reduced, the phosphate ore acidolysis is more complete, the decomposition efficiency is higher, and the yield of phosphorus can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of wet-process phosphoric acid, and particularly relates to a method for preparing hemihydrate gypsum by desulfurization and acid return. Background Art

[0002] The wet-process phosphoric acid production process can be divided into an anhydrous process, a semi-hydrate process, and a dihydrate process for one-step acid production, as well as a semi-hydrate-dihydrate process and a dihydrate-semi-hydrate process for two-step acid production, according to the morphology of the calcium sulfate crystals generated. Among them, the dihydrate gypsum generated by the mainstream dihydrate process is characterized by flaky rhombus crystals. During the solid-liquid separation process, solid calcium sulfate crystals are easily stacked, which makes filtering and washing difficult, and the residual phosphorus content in the gypsum increases, resulting in a low phosphorus yield. Compared with the dihydrate process, the semi-hydrate process can obtain high-concentration phosphoric acid, and uniform semi-hydrate calcium sulfate crystals can be obtained under the condition of controlling the concentration of liquid sulfate ions, further improving the solid-liquid separation rate and the phosphorus yield. The by-product semi-hydrate phosphogypsum can achieve high added value utilization of calcium sulfate.

[0003] A large number of studies have shown that because the hemihydrate process is carried out under high phosphoric acid concentration and high reaction temperature conditions, the excessively high concentration of sulfate in the liquid phase during the decomposition of phosphate ore can easily lead to the passivation of phosphate ore, disrupting the smooth progress of the hemihydrate reaction process. Therefore, in view of the problems existing in the existing hemihydrate process, it is necessary to seek a method with simple and easy control process, low production cost, and by-product high-quality hemihydrate phosphogypsum, so as to solve the problems of phosphorus yield and comprehensive utilization of phosphogypsum. Summary of the invention

[0004] The invention provides a method for preparing hemihydrate gypsum by desulfurization and acid return, which can improve the phosphorus yield of the wet-process phosphoric acid hemihydrate process and improve the quality of gypsum.

[0005] The technical solution of the present invention is to provide a method for preparing hemihydrate gypsum by desulfurization and acid return, comprising the following steps: S1. Adding phosphate rock to the intermediate acid in the semi-aqueous wet phosphoric acid production process for desulfurization treatment to obtain a desulfurized slurry, which is cooled and aged to obtain a bottom slurry and a top overflow of desulfurized phosphoric acid; The desulfurized phosphoric acid obtained in S2 and S1 is partially returned to the semi-aqueous wet phosphoric acid reaction tank to fully react with the phosphate rock, and then excess sulfuric acid is added to react, and finally solid-liquid separation is performed to obtain semi-aqueous intermediate acid and semi-aqueous gypsum.

[0006] Optionally, the intermediate acid in S1 is P 2 O 5 Concentrated phosphoric acid with a concentration of 36-45%; including but not limited to 36%, 38%, 40%, 42% or 45%.

[0007] Optionally, the phosphate ore in S1 is a post-flotation phosphate concentrate with a grade greater than 31.5%, including but not limited to 31.5%, 32%, 32.5%, 33% or 33.5%.

[0008] Optionally, during the desulfurization treatment in S1, the mass ratio of the intermediate acid added to the phosphate rock is controlled at (45~55):1; including but not limited to 45:1, 47:1, 50:1, 53:1 or 55:1.

[0009] Optionally, during the desulfurization treatment in S1, the desulfurization temperature is controlled at 60-100°C; including but not limited to 60°C, 70°C, 80°C, 90°C or 100°C.

[0010] Optionally, when cooling in S1, a high-position flash cooler is used to cool the temperature to 50-80°C; including but not limited to 50°C, 57°C, 65°C, 73°C or 80°C.

[0011] Optionally, the bottom slurry in S1 enters the reaction tank for further acid hydrolysis; part of the desulfurized phosphoric acid overflowing from the top enters the concentration or downstream production system, and part is returned to the semi-aqueous wet phosphoric acid reaction tank.

[0012] Optionally, the solid content of the bottom slurry entering the reaction tank is controlled at 50-70%, including but not limited to 50%, 55%, 60%, 65% or 70%.

[0013] Optionally, the solid content of the desulfurized phosphoric acid overflowing from the top is below 1%, including but not limited to 0.1%, 0.3%, 0.5%, 0.7% or 0.9%.

[0014] Optionally, in the S2 semi-aqueous wet phosphoric acid reaction tank, the mass ratio of desulfurized phosphoric acid to phosphate rock is 1.5-2:1, including but not limited to 1.5:1, 1.6:1, 1.7:1, 1.8:1 or 2:1. The mixing reaction time is 1.5-2.5h, including but not limited to 1.5h, 1.7h, 2h, 2.3h or 2.5h.

[0015] Optionally, the amount of sulfuric acid added controls the supersaturated concentration of sulfate in the system to be 2.8-3.2%, including but not limited to 2.8%, 2.9%, 3%, 3.1% or 3.2%.

[0016] Optionally, after sulfuric acid is added to S2, the reaction temperature is 95-100°C, including but not limited to 95°C, 96°C, 97°C, 98°C or 100°C, and the reaction time is 1-3h, including but not limited to 1h, 1.5h, 2h, 2.5h or 3h.

[0017] The present invention has the following beneficial effects: The inventors have found that in the production process of semi-aqueous wet-process phosphoric acid, since phosphate rock and sulfuric acid are continuously added in a constant ratio, if the acidolysis of the phosphate rock is incomplete, the normal growth of the semi-hydrated calcium sulfate crystals will be destroyed, and passivation will occur, disrupting the entire semi-hydrate reaction process. In the method provided by the present invention, by desulfurizing the intermediate acid, the aged overflowed desulfurized phosphoric acid reacts with the phosphate rock, the pre-decomposition efficiency of the phosphate rock is enhanced, and sulfate is added to regulate the crystallization of the semi-hydrated calcium sulfate, uniform rod-shaped semi-hydrated gypsum crystals can be generated, the phosphorus content in the semi-hydrated gypsum is greatly reduced, and the whiteness and purity are significantly improved.

[0018] The present invention utilizes the intermediate acid after desulfurization treatment to decompose phosphate ore, thereby reducing the occurrence of phosphate ore passivation phenomenon easily caused by excessively high liquid phase sulfate concentration in the semi-aqueous process, making the phosphate ore acid decomposition more complete, the decomposition efficiency higher, and the phosphorus yield capable of improving. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A process flow chart of the method is provided for the present invention.

[0020] Figure 2 This is the crystal form diagram of the semi-hydrated gypsum obtained in Example 3. DETAILED DESCRIPTION

[0021] The present invention is described in detail below in conjunction with specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0022] Example 1 For semi-water method P 2 O 5 The intermediate acid with a concentration of 37% is subjected to desulfurization treatment, and the mass ratio of the intermediate acid to the phosphate rock is controlled at 47:1 to obtain a desulfurized slurry; the obtained desulfurized slurry is treated by a high-level flash cooler and the temperature is reduced to 60°C and then transferred to an aging tank, in which bottom slurry and top overflow desulfurized intermediate acid are separated; the solid content of the bottom slurry is controlled at 50% and enters the reaction tank for further acidolysis, and the solid content of the top desulfurized intermediate acid is controlled at 0.5%, a part of which enters the concentration or downstream production system, and a part is recycled to the reaction tank as desulfurized return acid, and the amount recycled to the reaction tank is 1.5 times the amount of the semi-hydrated reaction phosphate rock; the desulfurized return acid is first fully mixed with the phosphate rock, and the mixing time is controlled at 2h, and then sulfuric acid is added to adjust to obtain semi-hydrated calcium sulfate, and the supersaturated concentration of sulfate is adjusted to 2.9%, the reaction temperature is 96°C, and the reaction time is 1.5h. After solid-liquid separation, semi-hydrated intermediate acid and semi-hydrated gypsum are obtained.

[0023] Example 2 For semi-water method P 2 O 5The intermediate acid with a concentration of 40% is subjected to desulfurization treatment, and the mass ratio of the intermediate acid to the phosphate rock is controlled at 51:1 to obtain a desulfurized slurry; the obtained desulfurized slurry is treated by a high-level flash cooler, and the temperature is reduced to 75°C and then transferred to an aging tank, in which the bottom slurry and the top overflow desulfurized intermediate acid are separated; the solid content of the bottom slurry is controlled at 67% and enters the reaction tank for further acidolysis, and the solid content of the top desulfurized intermediate acid is controlled at 0.2%, a part of which enters the concentration or downstream production system, and a part is recycled to the reaction tank as desulfurized return acid, and the amount recycled to the reaction tank is 1.7 times the amount of the semi-hydrated reaction phosphate rock; the desulfurized return acid is first fully mixed with the phosphate rock, and the mixing time is controlled at 2.5h, and then sulfuric acid is added to adjust to obtain semi-hydrated calcium sulfate, and the sulfate supersaturation concentration is adjusted to 3.0%, the reaction temperature is 97°C, and the reaction time is 2h. After solid-liquid separation, semi-hydrated intermediate acid and semi-hydrated gypsum are obtained.

[0024] Example 3 For semi-water method P 2 O 5 The intermediate acid with a concentration of 38% is subjected to desulfurization treatment, and the mass ratio of the intermediate acid to the phosphate rock is controlled at 45:1 to obtain a desulfurized slurry; the obtained desulfurized slurry is treated by a high-level flash cooler, and the temperature is reduced to 80°C and then transferred to an aging tank, in which the bottom slurry and the top overflow desulfurized intermediate acid are separated; the solid content of the bottom slurry is controlled at 59% and enters the reaction tank for further acidolysis, and the solid content of the top desulfurized intermediate acid is controlled at 0.7%, a part of which enters the concentration or downstream production system, and a part is recycled to the reaction tank as desulfurized return acid, and the amount recycled to the reaction tank is twice the amount of the semi-hydrated reaction phosphate rock; the desulfurized return acid is first fully mixed with the phosphate rock, and the mixing time is controlled at 1.8h, and then sulfuric acid is added to adjust to obtain semi-hydrated calcium sulfate, and the sulfate supersaturation concentration is adjusted to 3.1%, the reaction temperature is 95°C, and the reaction time is 2.5h. After solid-liquid separation, semi-hydrated intermediate acid and semi-hydrated gypsum are obtained.

[0025] Example 4 For semi-water method P 2 O 5The intermediate acid with a concentration of 39% is subjected to desulfurization treatment, and the mass ratio of the intermediate acid to the phosphate rock is controlled at 52:1 to obtain a desulfurized slurry; the obtained desulfurized slurry is treated by a high-level flash cooler, and the temperature is reduced to 77°C and then transferred to an aging tank, in which bottom slurry and top overflow desulfurized intermediate acid are separated; the solid content of the bottom slurry is controlled at 60% and enters the reaction tank for further acidolysis, and the solid content of the top desulfurized intermediate acid is controlled at 0.9%, a part of which enters the concentration or downstream production system, and a part is recycled to the reaction tank as desulfurized return acid, and the amount recycled to the reaction tank is 1.6 times the amount of the semi-hydrated reaction phosphate rock; the desulfurized return acid is first fully mixed with the phosphate rock, and the mixing time is controlled at 1.5h, and then sulfuric acid is added to adjust to obtain semi-hydrated calcium sulfate, and the supersaturated concentration of sulfate is adjusted to 2.7%, the reaction temperature is 100°C, the reaction time is 1h, and semi-hydrated intermediate acid and semi-hydrated gypsum are obtained after solid-liquid separation.

[0026] Example 5 For semi-water method P 2 O 5 The intermediate acid with a concentration of 44% is subjected to desulfurization treatment, and the mass ratio of the intermediate acid to the phosphate rock is controlled at 50:1 to obtain a desulfurized slurry; the obtained desulfurized slurry is treated by a high-level flash cooler and the temperature is reduced to 65°C and then transferred to an aging tank, in which the bottom slurry and the top overflow desulfurized intermediate acid are separated; the solid content of the bottom slurry is controlled at 70% and enters the reaction tank for further acidolysis, and the solid content of the top desulfurized intermediate acid is controlled at 1%, a part of which enters the concentration or downstream production system, and a part is recycled to the reaction tank as desulfurized return acid, and the amount recycled to the reaction tank is 1.6 times the amount of the semi-hydrated reaction phosphate rock; the desulfurized return acid is first fully mixed with the phosphate rock, and the mixing time is controlled at 2h, and then sulfuric acid is added to adjust to obtain semi-hydrated calcium sulfate, and the sulfate supersaturation concentration is adjusted to 3.2%, the reaction temperature is 96°C, and the reaction time is 2.7h. After solid-liquid separation, semi-hydrated intermediate acid and semi-hydrated gypsum are obtained.

[0027] Comparative Example 1 This comparative example provides a method for preparing high-quality hemihydrate gypsum by desulfurization and returning acid. The method is the same as Example 1 except that the intermediate acid is not desulfurized.

[0028] Comparative Example 2 This comparative example provides a method for preparing high-quality hemihydrate gypsum by desulfurization and acid return. The method is the same as Example 1 except that the desulfurization slurry is not subjected to high-level flash cooling.

[0029] Comparative Example 3 This comparative example provides a method for preparing high-quality hemihydrate gypsum by using desulfurized acid. In the method, sulfuric acid is added after the desulfurized acid is mixed with phosphate rock without being fully mixed. The rest is the same as Example 1.

[0030] The high-quality hemihydrate gypsum was prepared by the methods provided in Application Examples 1-5 and Comparative Examples 1-3. The residual P in the hemihydrate gypsum after treatment was 2 O 5 Content and desulfurization intermediate acid P 2 O 5 The concentrations are shown in Table 1. 2 O 5 The content is in accordance with GB / T5484-2012, P in phosphoric acid 2 O 5 The content is in accordance with GB 1866.15-2015.

[0031] Table 1

[0032] It can be seen from Table 1 that the intermediate acid after desulfurization treatment can decompose phosphate ore more efficiently, reducing the passivation of phosphate ore caused by excessive concentration of sulfate ions in the liquid phase during the semi-water process, making the acid decomposition of phosphate ore more complete and the growth of semi-hydrated gypsum more uniform. Figure 2 It can be seen that the semi-hydrated gypsum presents uniform coarse needle-shaped crystals, the crystals grow evenly, there is no obvious agglomeration and wrapping, and the gypsum washing and filtration performance is significantly improved, and the phosphorus yield after the semi-hydrated reaction is increased to 98.5%. Under the process conditions of preparing semi-hydrated gypsum using desulfurized acid, the efficiency of phosphoric acid hydrolysis is improved, and the purity and whiteness of the by-product semi-hydrated phosphogypsum are improved, which solves the problem of phosphorus yield in the semi-hydrated reaction and comprehensive utilization of phosphogypsum.

[0033] After the desulfurized slurry is cooled, a part of the solid phase in the slurry is the incompletely dissolved phosphate rock, and the other part is the calcium dihydrogen phosphate precipitated after cooling, and both are returned to the reaction tank for a more complete reaction, effectively improving the yield of phosphorus. When the desulfurized phosphoric acid overflowing from the top of the aging tank after aging returns to the reaction tank, it is difficult to control the solid content, which can be achieved by single-stage or multi-stage aging as needed.

[0034] The improved scheme of the present invention is especially for hemihydrate gypsum. Generally speaking, dihydrate gypsum has low acid concentration and coarse crystals that are easy to filter. In order to obtain a higher phosphorus yield, hemihydrate gypsum will be converted into crystals for a second time, that is, hemihydrate dihydrate. The present invention does not change the original hemihydrate production device, but adds desulfurization and cooling aging sections. After the returned acid decomposes the phosphate rock again to produce a hemihydrate reaction, it has the advantages of 1) high acid concentration of the produced product, 2) good crystal form of hemihydrate reaction gypsum, and good washing and filtering effect.

[0035] The above embodiments describe the preferred implementation of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing hemihydrate gypsum by desulfurization and acid return, characterized in that: The following steps are involved: S1. Adding phosphate rock to the intermediate acid in the semi-aqueous wet phosphoric acid production process for desulfurization treatment to obtain a desulfurized slurry, which is cooled and aged to obtain a bottom slurry and a top overflow of desulfurized phosphoric acid; The desulfurized phosphoric acid obtained in S2 and S1 is partially returned to the semi-aqueous wet phosphoric acid reaction tank to fully react with the phosphate rock, and then excess sulfuric acid is added to react, and finally solid-liquid separation is performed to obtain intermediate acid and semi-hydrated gypsum.

2. The method according to claim 1, characterized in that: The intermediate acid in S1 is concentrated phosphoric acid with a P2O5 mass concentration of 36~45%; the phosphate rock grade is above 31.5%.

3. The method according to claim 1, characterized in that: During the desulfurization treatment in S1, the mass ratio of the intermediate acid added to the phosphate rock is controlled at (45~55):1, and the desulfurization temperature is controlled at 60~100℃.

4. The method according to claim 1, characterized in that: When cooling S1, a high-level flash cooler is used to cool the temperature to 50~80℃.

5. The method according to any one of claims 1 to 4, characterized in that: The desulfurized slurry after desulfurization treatment in S1 is cooled by a high-level flash cooler and then enters the aging tank. After aging, the slurry at the bottom enters the semi-aqueous wet phosphoric acid reaction tank in S2 for further acid hydrolysis; part of the desulfurized phosphoric acid overflowing from the top enters the concentration or downstream production system, and part returns to the semi-aqueous wet phosphoric acid reaction tank.

6. The method according to claim 5, characterized in that: The solid content of the bottom slurry entering the reaction tank is controlled at 50~70%.

7. The method according to claim 5, characterized in that: The solid content of the desulfurized phosphoric acid overflowing from the top is less than 1%.

8. The method according to claim 1, characterized in that: In the S2 semi-aqueous wet phosphoric acid reaction tank, the mass ratio of desulfurized phosphoric acid to phosphate rock is 1.5~2:1; the mixing reaction time is 1.5~2.5h.

9. The method according to claim 1 or 9, characterized in that: The amount of sulfuric acid added controls the supersaturated concentration of sulfate in the system to be 2.8~3.2%.

10. The method according to claim 9, characterized in that: After sulfuric acid is added to S2, the reaction temperature is 95~100℃ and the reaction time is 1~3h.

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