Method for producing wet-process phosphoric acid and by-producing alpha-hemihydrate gypsum and high-purity and high-whiteness alpha-hemihydrate gypsum
10696552 ยท 2020-06-30
Assignee
Inventors
- Zhaoping Hu (Shandong, CN)
- Hualong Yao (Shandong, CN)
- Hongkun Chen (Shandong, CN)
- Shihua Pang (Shandong, CN)
- Yongxiu Liu (Shandong, CN)
- Chengzhi Li (Shandong, CN)
Cpc classification
International classification
Abstract
Provided is a method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as well as high-purity and high-whiteness alpha-hemihydrate gypsum, including: mixing phosphoric acid and phosphate rock powder and performing extraction reaction; adding sulfuric acid solution to continue the reaction so that 30% to 50% of calcium ions are generated into dihydrate gypsum; transferring the dihydrate gypsum to a crystal transformation tank; adding a crystal transformation agent and controlling the crystal transformation conditions to obtain 30% to 50% of normal hemihydrate gypsum; after separation, introducing phosphoric acid extraction solution containing other 30% to 50% of calcium ions in a form of calcium dihydrogen phosphate into decalcification reaction tank; adding sulfuric acid solution diluted by washing liquid and performing decalcification reaction; controlling the crystal transformation conditions and performing crystal transformation reaction to convert the solid into high-purity and high-whiteness alpha-hemihydrate gypsum.
Claims
1. A method for producing wet-process phosphoric acid and at the same time obtaining an alpha-hemihydrate gypsum I as well as an alpha-hemihydrate gypsum II as by-products, comprising the following steps: (1) mixing phosphoric acid and phosphate rock powder, performing an extraction reaction under stirring; after completion of the extraction reaction, adding sulfuric acid solution, continuing the reaction under stirring to obtain an extraction slurry; separating solid and liquid of the extraction slurry to obtain a phosphoric acid extraction solution A and a slag slurry B; wherein the amount of the sulfuric acid solution added is controlled, so that 10% to 50% of calcium ions are transformed into dihydrate gypsum and the other 50% to 90% of calcium ions exist in a form of calcium dihydrogen phosphate; (2) mixing the phosphoric acid extraction solution A obtained in step (1) and the sulfuric acid solution, performing a decalcification reaction; after completion of the reaction, separating solid and liquid to obtain a solid C and a filtrate D; (3) performing a crystal transformation reaction with the solid C obtained in step (2), part of the filtrate D obtained in step (2), a sulfuric acid solution and a crystal transformation agent; after completion of the reaction, separating solid and liquid to obtain the alpha-hemihydrate gypsum II as well as a filtrate F; (4) performing crystal transformation reaction with the slag slurry B obtained in step (1), part of the filtrate D obtained in step (2), a sulfuric acid solution and a crystal transformation agent; after completion of the reaction, separating solid and liquid to obtain the alpha-hemihydrate gypsum I and a filtrate J, wherein a purity of the alpha-hemihydrate gypsum II is higher than that of the alpha-hemihydrate gypsum I.
2. The method according to claim 1, comprising the following steps: (1) mixing phosphoric acid and phosphate rock powder, performing an extraction reaction under stirring; after completion of the extraction reaction, adding sulfuric acid solution, continuing the reaction under stirring to obtain an extraction slurry; separating solid and liquid of the extraction slurry to obtain a phosphoric acid extraction solution A and a slag slurry B; wherein the amount of the sulfuric acid solution added is controlled, so that 30% to 50% of calcium ions are transformed into dihydrate gypsum and the other 50% to 70% of calcium ions exist in a form of calcium dihydrogen phosphate; (2) mixing the phosphoric acid extraction solution A obtained in step (1) and the sulfuric acid solution, performing a decalcification reaction; after completion of the reaction, separating solid and liquid to obtain a solid C and a filtrate D; (3) performing a crystal transformation reaction with the solid C obtained in step (2), part of the filtrate D obtained in step (2), a sulfuric acid solution and a crystal transformation agent; after completion of the reaction, separating solid and liquid to obtain the alpha-hemihydrate gypsum II as well as a filtrate F; (4) performing crystal transformation reaction with the slag slurry B obtained in step (1), part of the filtrate D obtained in step (2), a sulfuric acid solution and a crystal transformation agent; after completion of the reaction, separating solid and liquid to obtain the alpha-hemihydrate gypsum I and a filtrate J.
3. The method according to claim 2, comprising the following steps: (1) mixing phosphoric acid and phosphate rock powder, performing an extraction reaction under stirring; after completion of the extraction reaction, adding sulfuric acid solution, wherein the amount of the sulfuric acid solution added is controlled, so that 30% to 50% of calcium ions are transformed into dihydrate gypsum and the other 50% to 70% of calcium ions exist in a form of calcium dihydrogen phosphate; continuing the reaction under stirring to obtain an extraction slurry; separating solid and liquid of the extraction slurry to obtain a phosphoric acid extraction solution A and a slag slurry B; (2) mixing the phosphoric acid extraction solution A obtained in step (1) and the sulfuric acid solution, performing a decalcification reaction; after completion of the reaction, separating solid and liquid to obtain a solid C and a filtrate D; dividing the filtrate D into four parts, which are used for the extraction reaction of step (1), the crystal transformation reaction of step (3), the crystal transformation reaction of step (4), and used as phosphoric acid final product, respectively; (3) performing crystal transformation reaction with the solid C, the filtrate D obtained in step (2), a sulfuric acid solution and a crystal transformation agent; after completion of the reaction, separating solid and liquid to obtain a solid E and a filtrate F; mixing the obtained filtrate F and the solid C and performing a circular crystal transformation reaction; washing the solid E with 80 to 100 C. hot water to obtain a solid G and a washing liquid H; using the washing liquid H to dilute concentrated sulfuric acid to provide the sulfuric acid solution; drying the solid G to obtain the alpha-hemihydrate gypsum II; (4) performing crystal transformation reaction with the slag slurry B obtained in step (1), the filtrate D, a sulfuric acid solution and a crystal transformation agent; after completion of the reaction, separating solid and liquid to obtain a solid I and a filtrate J; dividing the filtrate J into two parts, which is used for the extraction reaction of step (1) and mixing with the slag slurry B for circular crystal transformation reaction, respectively; washing the solid I with 80 to 100 C. hot water to obtain a solid K and a washing liquid L which is used to dilute concentrated sulfuric acid to provide the sulfuric acid solution; drying the solid K to obtain the alpha-hemihydrate gypsum I.
4. The method according to claim 3, wherein in step (1), the fineness of the phosphate rock powder is from 80 to 100 meshes; the concentration of phosphoric acid counted by H.sub.3PO.sub.4 is from 20 to 35 wt %; and the solid-liquid mass ratio of the phosphate rock powder to the phosphoric acid is from 1:15 to 1:45.
5. The method according to claim 3, wherein in step (1), the reaction temperatures for the extraction reaction and the reaction after the addition of sulfuric acid solution are both from 50 to 80 C.; the extraction duration is from 1.5 to 4.5 h; after adding sulfuric acid solution, and reaction is continued under stirring for 1 to 2 h.
6. The method according to claim 3, wherein in step (1), the concentration of phosphoric acid in the phosphoric acid extraction solution A is from 2 to 3 mol/L and the concentration of calcium ion is from 0.5 to 1.0 mol/L.
7. The method according to claim 3, wherein in step (2), the temperature for decalcification reaction is from 60 to 130 C. and the reaction duration is from 1.5 to 7.5 h.
8. The method according to claim 3, wherein in step (2), the volume ratio of the sulfuric acid solution to the phosphoric acid extraction solution A is from 1:3 to 1:5.
9. The method according to claim 3, wherein in both step (3) and step (4), the liquid-solid mass ratio of crystal transformation reaction is (2 to 6):1; preferably, mixed acid comprising sulfuric acid and phosphoric acid is included in the crystal transformation system, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 in the mixed acid is from 8 to 12% and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 in the mixed acid is from 16 to 25%.
10. The method according to claim 3, wherein in both steps (3) and (4), the temperature for the crystal transformation reaction is from 60 to 130 C. and the reaction duration of the crystal transformation reaction is from 1.5 to 7.5 h.
11. The method according to claim 3, wherein in steps (3) and (4), the crystal transformation agent is selected from cation-containing water-soluble phosphate, cation-containing sulfate, cation-containing nitrate, cation-containing citrate, cation-containing alkylbenzenesulfonate, cation-containing alkyl fatty acid salt or a mixture thereof, and wherein the cation is selected from Al.sup.3+, Fe.sup.3+, Mg.sup.2+, K.sup.+, Na.sup.+ and NH.sub.4.sup.+, or a mixture thereof.
12. The method according to claim 3, wherein in steps (3) and (4), the addition amount of the crystal transformation agent is from 0.1 to 1.0% of the mass of the crystal transformation system.
13. The method according to claim 3, comprising placing the solid G obtained in step (3) in the air and allowing water to be absorbed to give a dihydrate gypsum.
14. The method according to claim 3, comprising placing the solid G obtained in step (3) in the air and allowing water to be absorbed; performing calcination to give a beta-hemihydrate gypsum.
15. The method according to claim 14, wherein the temperature for calcination is from 140 to 180 C.
Description
BRIEF DESCRIPTION OF DRAWINGS
(1)
(2)
DETAILED DESCRIPTION
(3) In order to understand the present disclosure better, the preferred embodiments of the present disclosure are described hereinafter in conjunction with the examples of the present disclosure. It is to be understood that the description is merely illustrating the characters and advantages of the present disclosure, and is not intended to limit the claims of the present application.
(4) All of the chemical agents used in the examples of the present disclosure are commercially available.
Example 1
(5) Raw material 1: phosphate rock, collection site: Guizhou Province;
(6) Raw material 2: sodium citrate, commercially available;
(7) Raw material 3: aluminum sulfate, commercially available;
(8) Raw material 4: sodium dodecyl sulfonate, commercially available;
(9) Raw material 5: sulfuric acid, concentration 97 wt %, commercially available.
(10) All of the sulfuric acid solutions used in the example were obtained by diluting the concentrated sulfuric acid of 97 wt % in sulfuric acid diluting tank.
(11) A method for producing by-products of wet-process phosphoric acid, alpha-hemihydrate gypsum as well as high-purity and high-whiteness alpha-hemihydrate gypsum as by-products, comprising the following steps:
(12) (1) Phosphate rock powder and excess amount of phosphoric acid were added to the extraction tank, wherein the solid-liquid mass ratio of the phosphate rock powder to the phosphoric acid was 1:18 and the concentration of phosphate acid was 25 wt %. The extraction reaction was carried out under the condition of continuous stirring. After the completion of the extraction, sulfuric acid solution with a concentration of 30 wt % was added. The addition amount of sulfuric acid was controlled and the reaction was carried out continuously to obtain an extraction slurry. About 30% of the calcium ions were transformed into dihydrate gypsum and the other 70% of calcium ions existed in the extraction slurry in a form of calcium dihydrogen phosphate. Thereafter, solid and liquid phases of the extraction slurry were separated by passing the extraction slurry through a filter to obtain a phosphoric acid extraction solution A and a slag slurry B. Therein, phosphoric acid in the phosphoric acid extraction solution was 2.5 mol/L and the calcium ion concentration was 0.6 mol/L.
(13) (2) The phosphate acid extraction solution A obtained in the step (1) was introduced into the decalcification reaction tank. Sulfuric acid solution with a concentration of 30 wt %, which was diluted with phosphoric acid of 25 wt %, was added to the decalcification reaction tank. The temperature was maintained at 85 C. and the reaction was carried out for 2 h with stirring. The resulting gypsum whiskers suspended in the phosphoric acid. Solid and liquid of the gypsum whisker suspension was separated by filter to obtain a solid C and a filtrate D. The filtrate D was divided into four parts: one part was introduced into the crystal transformation tank I for crystal transformation reaction, another part was introduced into the crystal transformation tank II for crystal transformation reaction, another part was introduced into the extraction tank for phosphoric rock extraction and the other part was transferred to acid pool as the phosphoric acid product.
(14) (3) The solid C was transferred to the crystal transformation tank I, part of the filtrate D and part of the sulfuric acid solution in the sulfuric acid diluting tank were added, and the liquid-solid mass ratio in the crystal transformation tank I was controlled to be 2:1. The crystal transformation tank I contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 10% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 20% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: sodium citrate 0.12%, sodium dodecyl sulfonate 0.02% and aluminum sulfate 0.25%. Crystal transformation reaction was carried out for 2 h at a temperature maintained at 100 C. After the completion of the reaction, the solid and the liquid were separated by filter to obtain a solid E and a filtrate F. The obtained filtrate F was introduced into the crystal transformation tank I and subjected to crystal transformation reaction continuously. The solid E obtained was washed by 80 to 100 C. hot water to obtain a solid G and a washing liquid H. The solid G not only can be made into high-purity and high-whiteness alpha-hemihydrate gypsum after drying, but also can be made into high-quality gypsum products, such as gypsum board, gypsum block, gypsum components and so on, by adding water directly without drying. The washing liquid H was introduced into the sulfuric acid diluting tank to dilute concentrated sulfuric acid. One part of the diluted sulfuric acid solution was introduced into the extraction tank for continuing the extraction of phosphate rock, another part was introduced into the decalcification reaction tank for continuing the decalcification reaction, another part was introduced into the crystal transformation tank I for crystal transformation reaction, and the other part was introduced into the crystal transformation tank II for crystal transformation reaction. The vapor generated during dilution process provided heat for the crystal transformation tank I and the crystal transformation tank II.
(15) (4) The slag slurry B obtained in the step (1) was transferred to the crystal transformation tank II, and part of the filtrate D, part of the filtrate J and part of the sulfuric acid solution in the sulfuric acid diluting tank were introduced. The liquid-solid mass ratio in the crystal transformation tank II was controlled to be 2:1. The crystal transformation tank II contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 9% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 21% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: sodium citrate 0.15%, sodium dodecyl sulfonate 0.03% and aluminum sulfate 0.37%. Crystal transformation reaction was carried out for 2 h at a temperature maintained at 100 C. After the reaction, the solid and the liquid were separated by belt filter to obtain a solid I and a filtrate J. One part of the filtrate J was introduced into the extraction tank for continuing extraction of the phosphate rock powder, and another part was introduced into the crystal transformation tank II for continuing the crystal transformation reaction. The solid I was washed with hot water to obtain a solid K and a washing liquid L. The solid K not only can be made into normal alpha-hemihydrate gypsum after drying by a drying machine, but also can be made into gypsum products, such as gypsum board, gypsum block, gypsum components and so on, by adding water directly without drying process. The washing liquid L was introduced into the sulfuric acid diluting tank for diluting the concentrated sulfuric acid.
(16) Implementation Results:
(17) Quimociac gravimetric method was used to test the phosphoric acid liquid product and the concentration was 20% wt; P.sub.2O.sub.5 content of the normal alpha-hemihydrate gypsum product was 0.06% wt; P.sub.2O.sub.5 content of the high-purity and high-whiteness alpha-hemihydrate gypsum product was 0.07% wt.
(18) The normal alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short cylindrical shape, with an aspect ratio of 1 to 2. The alpha-hemihydrate gypsum showed a 2 h bending strength of 8.0 MPa, a dry bending strength of 15 MPa, a dry compressive strength of 93 MPa, an initial setting time of 9 min and a final setting time of 18 min. The mass percentage of the alpha-hemihydrate gypsum was 87%.
(19) The high-purity and high-whiteness alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 1 to 2. The high-purity and high-whiteness alpha-hemihydrate gypsum showed a 2 h bending strength of 9.0 MPa, a dry bending strength of 16 MPa, a dry compressive strength of 90 MPa, an initial setting time of 8 min and a final setting time of 17 min, a whiteness value of 95.6. The mass percentage of the alpha-hemihydrate gypsum was 99.98%.
Example 2
(20) Raw material 1: phosphate rock, collection site: Guizhou Province;
(21) Raw material 2: sodium citrate, commercially available;
(22) Raw material 3: ferric sulfate, commercially available;
(23) Raw material 4: sulfuric acid, concentration 97 wt %, commercially available.
(24) All of the sulfuric acid solutions used in the example were obtained by diluting the concentrated sulfuric acid of 97 wt % in sulfuric acid diluting tank.
(25) A method for producing by-products of wet-process phosphoric acid, alpha-hemihydrate gypsum as well as high-purity and high-whiteness alpha-hemihydrate gypsum as by-products, comprising the following steps:
(26) (1) Phosphate rock powder and excess amount of phosphoric acid were added to the extraction tank, wherein the solid-liquid mass ratio of the phosphate rock powder to the phosphoric acid was 1:25 and the concentration of phosphate acid was 30 wt %. The extraction reaction was carried out under the condition of continuous stirring. After the completion of the extraction, sulfuric acid solution with a concentration of 26 wt % was added. The addition amount of sulfuric acid was controlled and the reaction was carried out continuously to obtain an extraction slurry. About 50% of the calcium ions were transformed into dihydrate gypsum and the other 50% of calcium ions existed in the extraction slurry in a form of calcium dihydrogen phosphate. Thereafter, solid and liquid phases of the extraction slurry were separated by passing the extraction slurry through a filter to obtain a phosphoric acid extraction solution A and a slag slurry B. Therein, phosphoric acid in the phosphoric acid extraction solution was 3.0 mol/L and the calcium ion concentration was 0.8 mol/L.
(27) (2) The phosphate acid extraction solution A obtained in the step (1) was introduced into the decalcification reaction tank. Sulfuric acid solution with a concentration of 26 wt %, which was diluted with phosphoric acid of 30 wt %, was added to the decalcification reaction tank. The temperature was maintained at 90 C. and the reaction was carried out for 2 h with stirring. The resulting gypsum whiskers suspended in the phosphoric acid. Solid and liquid of the gypsum whisker suspension was separated by filter to obtain a solid C and a filtrate D. The filtrate D was divided into four parts: one part was introduced into the crystal transformation tank I for crystal transformation reaction, another part was introduced into the crystal transformation tank II for crystal transformation reaction, another part was introduced into the extraction tank for phosphoric rock extraction and the other part was transferred to acid pool as the phosphoric acid product.
(28) (3) The solid C was transferred to the crystal transformation tank I, part of the filtrate D and part of the sulfuric acid solution in the sulfuric acid diluting tank were added, and the liquid-solid mass ratio in the crystal transformation tank I was controlled to be 3:1. The crystal transformation tank I contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 11% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 18% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: sodium citrate 0.14%, ferric sulfate 0.25%. Crystal transformation reaction was carried out for 3 h at a temperature maintained at 110 C. After the completion of the reaction, the solid and the liquid were separated by filter to obtain a solid E and a filtrate F. The obtained filtrate F was introduced into the crystal transformation tank I and subjected to crystal transformation reaction continuously. The solid E obtained was washed by 80 to 100 C. hot water to obtain a solid G and a washing liquid H. The solid G not only can be made into high-purity and high-whiteness alpha-hemihydrate gypsum after drying, but also can be made into high-quality gypsum products, such as gypsum board, gypsum block, gypsum components and so on, by adding water directly without drying. The washing liquid H was introduced into the sulfuric acid diluting tank to dilute concentrated sulfuric acid. One part of the diluted sulfuric acid solution was introduced into the extraction tank for continuing the extraction of phosphate rock, another part was introduced into the decalcification reaction tank for continuing the decalcification reaction, another part was introduced into the crystal transformation tank I for crystal transformation reaction, and the other part was introduced into the crystal transformation tank II for crystal transformation reaction. The vapor generated during dilution process provided heat for the crystal transformation tank I and the crystal transformation tank II.
(29) (4) The slag slurry B obtained in the step (1) was transferred to the crystal transformation tank II, and part of the filtrate D, part of the filtrate J and part of the sulfuric acid solution in the sulfuric acid diluting tank were introduced. The liquid-solid mass ratio in the crystal transformation tank II was controlled to be 3:1. The crystal transformation tank II contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 10% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 18% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: sodium citrate 0.19%, ferric sulfate 0.30%. Crystal transformation reaction was carried out for 3 h at a temperature maintained at 110 C. After the reaction, the solid and the liquid were separated by belt filter to obtain a solid I and a filtrate J. One part of the filtrate J was introduced into the extraction tank for continuing extraction of the phosphate rock powder, and another part was introduced into the crystal transformation tank II for continuing the crystal transformation reaction. The solid I was washed with hot water to obtain a solid K and a washing liquid L. The solid K not only can be made into normal alpha-hemihydrate gypsum after drying by a drying machine, but also can be made into gypsum products, such as gypsum board, gypsum block, gypsum component and so on, by adding water directly without drying process. The washing liquid L was introduced into the sulfuric acid diluting tank for diluting the concentrated sulfuric acid.
(30) Implementation Results:
(31) Quimociac gravimetric method was used to test the phosphoric acid liquid product and the concentration was 29% wt; P.sub.2O.sub.5 content of the normal alpha-hemihydrate gypsum product was 0.05% wt; P.sub.2O.sub.5 content of the high-purity and high-whiteness alpha-hemihydrate gypsum product was 0.06% wt.
(32) The normal alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 2 to 3. The alpha-hemihydrate gypsum has a 2 h bending strength of 7.0 MPa, a dry bending strength of 13 MPa, a dry compressive strength of 91 MPa, an initial setting time of 9 min and a final setting time of 19 min. The mass percentage of the alpha-hemihydrate gypsum was 88%.
(33) The high-purity and high-whiteness alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 2 to 3. The high-purity and high-whiteness alpha-hemihydrate gypsum showed a 2 h bending strength of 8.0 MPa, a dry bending strength of 14 MPa, a dry compressive strength of 90 MPa, an initial setting time of 9 min and a final setting time of 20 min, a whiteness value of 96.6. The mass percentage of the alpha-hemihydrate gypsum was 99.99%.
Example 3
(34) Raw material 1: phosphate rock, collection site: Guizhou Province;
(35) Raw material 2: ferric sulfate, commercially available;
(36) Raw material 3: sodium dodecyl sulfonate, commercially available;
(37) Raw material 4: sulfuric acid, concentration is 97 wt %, commercially available;
(38) All of the sulfuric acid solutions used in the example were obtained by diluting the concentrated sulfuric acid of 97 wt % in sulfuric acid diluting tank.
(39) A method for producing by-products of wet-process phosphoric acid, alpha-hemihydrate gypsum as well as high-purity and high-whiteness alpha-hemihydrate gypsum as by-products, comprising the following steps:
(40) (1) Phosphate rock powder and excess amount of phosphoric acid were added to the extraction tank, wherein the solid-liquid mass ratio of the phosphate rock powder to the phosphoric acid was 1:30 and the concentration of phosphate acid was 28 wt %. The extraction reaction was carried out under the condition of continuous stirring. After the completion of the extraction, sulfuric acid solution with a concentration of 25 wt % was added. The addition amount of sulfuric acid was controlled and the reaction was carried out continuously to obtain an extraction slurry. About 60% of the calcium ions were transformed into dihydrate gypsum and the other 40% of calcium ions existed in the extraction slurry in a form of calcium dihydrogen phosphate. Thereafter, solid and liquid phases of the extraction slurry were separated by passing the extraction slurry through a filter to obtain a phosphoric acid extraction solution A and a slag slurry B. Therein, phosphoric acid in the phosphoric acid extraction solution was 2.7 mol/L and the calcium ion concentration was 0.7 mol/L.
(41) (2) The phosphate acid extraction solution A obtained in the step (1) was introduced into the decalcification reaction tank. Sulfuric acid solution with a concentration of 25 wt %, which was diluted with phosphoric acid of 28 wt %, was added to the decalcification reaction tank. The temperature was maintained at 95 C. and the reaction was carried out for 2.5 h with stirring. The resulting gypsum whiskers suspended in the phosphoric acid. Solid and liquid of the gypsum whisker suspension was separated by filter to obtain a solid C and a filtrate D. The filtrate D was divided into four parts: one part was introduced into the crystal transformation tank I for crystal transformation reaction, another part was introduced into the crystal transformation tank II for crystal transformation reaction, another part was introduced into the extraction tank for phosphoric rock extraction and the other part was transferred to acid pool as the phosphoric acid product.
(42) (3) The solid C was transferred to the crystal transformation tank I, part of the filtrate D and part of the sulfuric acid solution in the sulfuric acid diluting tank were added, and the liquid-solid mass ratio in the crystal transformation tank I was controlled to be 4:1. The crystal transformation tank I contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 12% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 19% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: ferric sulfate 0.25%, sodium dodecyl sulfate 0.05%. Crystal transformation reaction was carried out for 4 h at a temperature maintained at 100 C. After the completion of the reaction, the solid and the liquid were separated by filter to obtain a solid E and a filtrate F. The obtained filtrate F was introduced into the crystal transformation tank I and subjected to crystal transformation reaction continuously. The solid E obtained was washed by 80 to 100 C. hot water to obtain a solid G and a washing liquid H. The solid G not only can be made into high-purity and high-whiteness alpha-hemihydrate gypsum after drying, but also can be made into high-quality gypsum products, such as gypsum board, gypsum block, gypsum components and so on, by adding water directly without drying. The washing liquid H was introduced into the sulfuric acid diluting tank to dilute concentrated sulfuric acid. One part of the diluted sulfuric acid solution was introduced into the extraction tank for continuing the extraction of phosphate rock, another part was introduced into the decalcification reaction tank for continuing the decalcification reaction, another part was introduced into the crystal transformation tank I for crystal transformation reaction, and the other part was introduced into the crystal transformation tank II for crystal transformation reaction. The vapor generated during dilution process provided heat for the crystal transformation tank I and the crystal transformation tank II.
(43) (4) The slag slurry B obtained in the step (1) was transferred to the crystal transformation tank II, and part of the filtrate D, part of the filtrate J and part of the sulfuric acid solution in the sulfuric acid diluting tank were introduced. The liquid-solid mass ratio in the crystal transformation tank II was controlled to be 4:1. The crystal transformation tank II contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 12% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 19% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: ferric sulfate 0.25%, sodium dodecyl sulfate 0.05%. Crystal transformation reaction was carried out for 4 h at a temperature maintained at 100 C. After the reaction, the solid and the liquid were separated by a filter to obtain a solid I and a filtrate J. One part of the filtrate J was introduced into the extraction tank for continuing extraction of the phosphate rock powder, and another part was introduced into the crystal transformation tank II for continuing the crystal transformation reaction. The solid I was washed with hot water to obtain a solid K and a washing liquid L. The solid K not only can be made into normal alpha-hemihydrate gypsum after drying by a drying machine, but also can be made into gypsum products, such as gypsum board, gypsum block, gypsum component and so on, by adding water directly without drying process. The washing liquid L was introduced into the sulfuric acid diluting tank for diluting the concentrated sulfuric acid.
(44) Implementation Results:
(45) Quimociac gravimetric method was used to test the phosphoric acid liquid product and the concentration was 26% wt; P.sub.2O.sub.5 content of the normal alpha-hemihydrate gypsum product was 0.06% wt; P.sub.2O.sub.5 content of the high-purity and high-whiteness alpha-hemihydrate gypsum product was 0.04% wt.
(46) The normal alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 3 to 4. The alpha-hemihydrate gypsum has a 2 h bending strength of 8.0 MPa, a dry bending strength of 17 MPa, a dry compressive strength of 89 MPa, an initial setting time of 12 min and a final setting time of 15 min. The mass percentage of the alpha-hemihydrate gypsum was 87%.
(47) The high-purity and high-whiteness alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 3 to 4. The high-purity and high-whiteness alpha-hemihydrate gypsum has a 2 h bending strength of 10.0 MPa, a dry bending strength of 20 MPa, a dry compressive strength of 91 MPa, an initial setting time of 10 min and a final setting time of 14 min, a whiteness value of 97.6. The mass percentage of the alpha-hemihydrate gypsum was 99.99%.
Example 4
(48) Raw material 1: phosphate rock, collection site: Guizhou Province;
(49) Raw material 2: magnesium nitrate, commercially available;
(50) Raw material 3: ferric citrate, commercially available;
(51) Raw material 4: sulfuric acid, concentration 97 wt %, commercially available;
(52) All of the sulfuric acid solutions used in the example were obtained by diluting the concentrated sulfuric acid of 97 wt % in sulfuric acid diluting tank.
(53) A method for producing by-products of wet-process phosphoric acid, alpha-hemihydrate gypsum as well as high-purity and high-whiteness alpha-hemihydrate gypsum as by-products, comprising the following steps:
(54) (1) Phosphate rock powder and excess amount of phosphoric acid were added to the extraction tank, wherein the solid-liquid mass ratio of the phosphate rock powder to the phosphoric acid was 1:40 and the concentration of phosphate acid was 35 wt %. The extraction reaction was carried out under the condition of continuous stirring. After the completion of the extraction, sulfuric acid solution with a concentration of 27 wt % was added. The addition amount of sulfuric acid was controlled and the reaction was carried out continuously to obtain an extraction slurry. About 50% of the calcium ions were transformed into dihydrate gypsum and the other 50% of calcium ions existed in the extraction slurry in a form of calcium dihydrogen phosphate. Thereafter, solid and liquid phases of the extraction slurry were separated by passing the extraction slurry through a filter to obtain a phosphoric acid extraction solution A and a slag slurry B. Therein, phosphoric acid in the phosphoric acid extraction solution was 2.9 mol/L and the calcium ion concentration was 0.9 mol/L.
(55) (2) The phosphate acid extraction solution A obtained in the step (1) was introduced into the decalcification reaction tank. Sulfuric acid solution with a concentration of 27 wt %, which was diluted with phosphoric acid of 35 wt %, was added to the decalcification reaction tank. The temperature was maintained at 90 C. and the reaction was carried out for 2 h with stirring. The resulting gypsum whiskers suspended in the phosphoric acid. Solid and liquid of the gypsum whisker suspension was separated by filter to obtain a solid C and a filtrate D. The filtrate D was divided into four parts: one part was introduced into the crystal transformation tank I for crystal transformation reaction, another part was introduced into the crystal transformation tank II for crystal transformation reaction, another part was introduced into the extraction tank for phosphoric rock extraction and the other part was transferred to acid pool as the phosphoric acid product.
(56) (3) The solid C was transferred to the crystal transformation tank I, part of the filtrate D and part of the sulfuric acid solution in the sulfuric acid diluting tank were added, and the liquid-solid mass ratio in the crystal transformation tank I was controlled to be 5:1. The crystal transformation tank I contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 10% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 23% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: magnesium nitrate 0.10%, iron citrate 0.12%. Crystal transformation reaction was carried out for 3 h at a temperature maintained at 90 C. After the completion of the reaction, the solid and the liquid were separated by filter to obtain a solid E and a filtrate F. The obtained filtrate F was introduced into the crystal transformation tank I and subjected to crystal transformation reaction continuously. The solid E obtained was washed by 80 to 100 C. hot water to obtain a solid G and a washing liquid H. The solid G not only can be made into high-purity and high-whiteness alpha-hemihydrate gypsum after drying, but also can be made into high-quality gypsum products, such as gypsum board, gypsum block, gypsum components and so on, by adding water directly without drying. The washing liquid H was introduced into the sulfuric acid diluting tank to dilute concentrated sulfuric acid. One part of the diluted sulfuric acid solution was introduced into the extraction tank for continuing the extraction of phosphate rock, another part was introduced into the decalcification reaction tank for continuing the decalcification reaction, another part was introduced into the crystal transformation tank I for crystal transformation reaction, and the other part was introduced into the crystal transformation tank II for crystal transformation reaction. The vapor generated during dilution process provided heat for the crystal transformation tank I and the crystal transformation tank II.
(57) (4) The slag slurry B obtained in the step (1) was transferred to the crystal transformation tank II, and part of the filtrate D, part of the filtrate J and part of the sulfuric acid solution in the sulfuric acid diluting tank were introduced. The liquid-solid mass ratio in the crystal transformation tank II was controlled to be 5:1. The crystal transformation tank II contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 10% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 23% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: magnesium nitrate 0.10%, iron citrate 0.12%. Crystal transformation reaction was carried out for 3 h at a temperature maintained at 90 C. After the reaction, the solid and the liquid were separated by a filter to obtain a solid I and a filtrate J. One part of the filtrate J was introduced into the extraction tank for continuing extraction of the phosphate rock powder, and another part was introduced into the crystal transformation tank II for continuing the crystal transformation reaction. The solid I was washed with hot water to obtain a solid K and a washing liquid L. The solid K not only can be made into normal alpha-hemihydrate gypsum after drying by a drying machine, but also can be made into gypsum products, such as gypsum board, gypsum block, gypsum component and so on, by adding water directly without drying process. The washing liquid L was introduced into the sulfuric acid diluting tank for diluting the concentrated sulfuric acid.
(58) Implementation Results:
(59) Quimociac gravimetric method was used to test the phosphoric acid liquid product and the concentration was 28% wt; P.sub.2O.sub.5 content of the normal alpha-hemihydrate gypsum product was 0.06% wt; P.sub.2O.sub.5 content of the high-purity and high-whiteness alpha-hemihydrate gypsum product was 0.05% wt.
(60) The normal alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 2 to 3. The alpha-hemihydrate gypsum has a 2 h bending strength of 10.0 MPa, a dry bending strength of 20 MPa, a dry compressive strength of 91 MPa, an initial setting time of 10 min and a final setting time of 13 min. The mass percentage of the alpha-hemihydrate gypsum was 88%.
(61) The high-purity and high-whiteness alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 2 to 3. The high-purity and high-whiteness alpha-hemihydrate gypsum has a 2 h bending strength of 11.0 MPa, a dry bending strength of 20 MPa, a dry compressive strength of 90 MPa, an initial setting time of 11 min and a final setting time of 14 min, a whiteness value of 95.6. The mass percentage of the alpha-hemihydrate gypsum was 99.99%.
Example 5
(62) Raw material 1: phosphate rock, collection site: Guizhou Kailin;
(63) Raw material 2: ferric nitrate, commercially available;
(64) Raw material 3: sodium citrate, commercially available;
(65) Raw material 4: sulfuric acid, concentration 97 wt %, commercially available;
(66) All of the sulfuric acid solutions used in the example were obtained by diluting the concentrated sulfuric acid of 97 wt % in sulfuric acid diluting tank.
(67) A method for producing by-products of wet-process phosphoric acid, alpha-hemihydrate gypsum as well as high-purity and high-whiteness alpha-hemihydrate gypsum as by-products, comprising the following steps:
(68) (1) Phosphate rock powder and excess amount of phosphoric acid were added to the extraction tank, wherein the solid-liquid mass ratio of the phosphate rock powder to the phosphoric acid was 1:45 and the concentration of phosphate acid was 20 wt %. The extraction reaction was carried out under the condition of continuous stirring. After the completion of the extraction, sulfuric acid solution with a concentration of 27 wt % was added. The addition amount of sulfuric acid was controlled and the reaction was carried out continuously to obtain an extraction slurry. About 40% of the calcium ions were transformed into dihydrate gypsum and the other 60% of calcium ions existed in the extraction slurry in a form of calcium dihydrogen phosphate. Thereafter, solid and liquid phases of the extraction slurry were separated by passing the extraction slurry through a filter to obtain a phosphoric acid extraction solution A and a slag slurry B. Therein, phosphoric acid in the phosphoric acid extraction solution was 2.1 mol/L and the calcium ion concentration was 0.8 mol/L.
(69) (2) The phosphate acid extraction solution A obtained in the step (1) was introduced into the decalcification reaction tank. Sulfuric acid solution with a concentration of 27 wt %, which was diluted with phosphoric acid of 20 wt %, was added to the decalcification reaction tank. The temperature was maintained at 80 C. and the reaction was carried out for 2 h with stirring. The resulting gypsum whiskers suspended in the phosphoric acid. Solid and liquid of the gypsum whisker suspension was separated by filter to obtain a solid C and a filtrate D. The filtrate D was divided into four parts: one part was introduced into the crystal transformation tank I for crystal transformation reaction, another part was introduced into the crystal transformation tank II for crystal transformation reaction, another part was introduced into the extraction tank for phosphoric rock extraction and the other part was transferred to acid pool as the phosphoric acid product.
(70) (3) The solid C was transferred to the crystal transformation tank I, part of the filtrate D and part of the sulfuric acid solution in the sulfuric acid diluting tank were added, and the liquid-solid mass ratio in the crystal transformation tank I was controlled to be 6:1. The crystal transformation tank I contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 12% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 25% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: ferric nitrate 0.22%, sodium citrate 0.07%. Crystal transformation reaction was carried out for 3 h at a temperature maintained at 100 C. After the completion of the reaction, the solid and the liquid were separated by filter to obtain a solid E and a filtrate F. The obtained filtrate F was introduced into the crystal transformation tank I and subjected to crystal transformation reaction continuously. The solid E obtained was washed by 80 to 100 C. hot water to obtain a solid G and a washing liquid H. The solid G not only can be made into high-purity and high-whiteness alpha-hemihydrate gypsum after drying, but also can be made into high-quality gypsum products, such as gypsum board, gypsum block, gypsum components and so on, by adding water directly without drying. The washing liquid H was introduced into the sulfuric acid diluting tank to dilute concentrated sulfuric acid. One part of the diluted sulfuric acid solution was introduced into the extraction tank for continuing the extraction of phosphate rock, another part was introduced into the decalcification reaction tank for continuing the decalcification reaction, another part was introduced into the crystal transformation tank I for crystal transformation reaction, and the other part was introduced into the crystal transformation tank II for crystal transformation reaction. The vapor generated during dilution process provided heat for the crystal transformation tank I and the crystal transformation tank II.
(71) (4) The slag slurry B obtained in the step (1) was transferred to the crystal transformation tank II, and part of the filtrate D, part of the filtrate J and part of the sulfuric acid solution in the sulfuric acid diluting tank were introduced. The liquid-solid mass ratio in the crystal transformation tank II was controlled to be 6:1. The crystal transformation tank II contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 12% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 25% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: ferric nitrate 0.22%, sodium citrate 0.07%. Crystal transformation reaction was carried out for 3 h at a temperature maintained at 100 C. After the reaction, the solid and the liquid were separated by a filter to obtain a solid I and a filtrate J. One part of the filtrate J was introduced into the extraction tank for continuing extraction of the phosphate rock powder, and another part was introduced into the crystal transformation tank II for continuing the crystal transformation reaction. The solid I was washed with hot water to obtain a solid K and a washing liquid L. The solid K not only can be made into normal alpha-hemihydrate gypsum after drying by a drying machine, but also can be made into gypsum products, such as gypsum board, gypsum block, gypsum component and so on, by adding water directly without drying process. The washing liquid L was introduced into the sulfuric acid diluting tank for diluting the concentrated sulfuric acid.
(72) Implementation Results:
(73) Quimociac gravimetric method was used to test the phosphoric acid liquid product and the concentration was 20% wt; P.sub.2O.sub.5 content of the normal alpha-hemihydrate gypsum product was 0.07% wt; P.sub.2O.sub.5 content of the high-purity and high-whiteness alpha-hemihydrate gypsum product was 0.06% wt.
(74) The normal alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 4 to 5. The alpha-hemihydrate gypsum has a 2 h bending strength of 12.0 MPa, a dry bending strength of 20 MPa, a dry compressive strength of 89 MPa, an initial setting time of 13 min and a final setting time of 16 min. The mass percentage of the alpha-hemihydrate gypsum was 89%.
(75) The high-purity and high-whiteness alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 4 to 5. The high-purity and high-whiteness alpha-hemihydrate gypsum has a 2 h bending strength of 12.0 MPa, a dry bending strength of 20 MPa, a dry compressive strength of 89 MPa, an initial setting time of 14 min and a final setting time of 18 min, a whiteness value of 95.8. The mass percentage of the alpha-hemihydrate gypsum was 99.98%.
Example 6
(76) Raw material 1: phosphate rock, collection site: Guizhou Province;
(77) Raw material 2: magnesium nitrate, commercially available;
(78) Raw material 3: ferric citrate, commercially available;
(79) Raw material 4: sulfuric acid, concentration 97 wt %, commercially available;
(80) All of the sulfuric acid solutions used in the example were obtained by diluting the concentrated sulfuric acid of 97 wt % in sulfuric acid diluting tank.
(81) A method for producing by-products of wet-process phosphoric acid, alpha-hemihydrate gypsum as well as high-purity and high-whiteness alpha-hemihydrate gypsum as by-products, comprising the following steps:
(82) (1) Phosphate rock powder and excess amount of phosphoric acid were added to the extraction tank, wherein the solid-liquid mass ratio of the phosphate rock powder to the phosphoric acid was 1:40 and the concentration of phosphate acid was 35 wt %. The extraction reaction was carried out under the condition of continuous stirring. After the completion of the extraction, sulfuric acid solution with a concentration of 27 wt % was added. The addition amount of sulfuric acid was controlled and the reaction was carried out continuously to obtain an extraction slurry. About 50% of the calcium ions were transformed into dihydrate gypsum and the other 50% of calcium ions existed in the extraction slurry in a form of calcium dihydrogen phosphate. Thereafter, solid and liquid phases of the extraction slurry were separated by passing the extraction slurry through a filter to obtain a phosphoric acid extraction solution A and a slag slurry B. Therein, phosphoric acid in the phosphoric acid extraction solution was 2.9 mol/L and the calcium ion concentration was 0.9 mol/L.
(83) (2) The phosphate acid extraction solution A obtained in the step (1) was introduced into the decalcification reaction tank. Sulfuric acid solution with a concentration of 27 wt %, which was diluted with phosphoric acid of 35 wt %, was added to the decalcification reaction tank. The temperature was maintained at 90 C. and the reaction was carried out for 2 h with stirring. The resulting gypsum whiskers suspended in the phosphoric acid. Solid and liquid of the gypsum whisker suspension was separated by filter to obtain a solid C and a filtrate D. The filtrate D was divided into four parts: one part was introduced into the crystal transformation tank I for crystal transformation reaction, another part was introduced into the crystal transformation tank II for crystal transformation reaction, another part was introduced into the extraction tank for phosphoric rock extraction and the other part was transferred to acid pool as the phosphoric acid product.
(84) (3) The solid C was transferred to the crystal transformation tank I, part of the filtrate D and part of the sulfuric acid solution in the sulfuric acid diluting tank were added, and the liquid-solid mass ratio in the crystal transformation tank I was controlled to be 5:1. The crystal transformation tank I contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 10% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 23% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: magnesium nitrate 0.10%, iron citrate 0.12%. Crystal transformation reaction was carried out for 3 h at a temperature maintained at 90 C. After the completion of the reaction, the solid and the liquid were separated by filter to obtain a solid E and a filtrate F. The obtained filtrate F was introduced into the crystal transformation tank I and subjected to crystal transformation reaction continuously. The solid E obtained was washed by 80 to 100 C. hot water to obtain a solid G and a washing liquid H. The solid G not only can be made into high-purity and high-whiteness alpha-hemihydrate gypsum after drying, but also can be made into high-purity and high-whiteness dihydrate gypsum by drying naturally in the air. The high-purity and high-whiteness dihydrate gypsum can be calcined in a calcining furnace at 150 C. and ground to a particle size of 90-110 m to obtain a high-purity and high-whiteness beta-gypsum powder. The washing liquid H was introduced into the sulfuric acid diluting tank to dilute concentrated sulfuric acid. One part of the diluted sulfuric acid solution was introduced into the extraction tank for continuing the extraction of phosphate rock, another part was introduced into the decalcification reaction tank for continuing the decalcification reaction, another part was introduced into the crystal transformation tank I for crystal transformation reaction, and the other part was introduced into the crystal transformation tank II for crystal transformation reaction. The vapor generated during dilution process provided heat for the crystal transformation tank I and the crystal transformation tank II.
(85) (4) The slag slurry B obtained in the step (1) was transferred to the crystal transformation tank II, and part of the filtrate D, part of the filtrate J and part of the sulfuric acid solution in the sulfuric acid diluting tank were introduced. The liquid-solid mass ratio in the crystal transformation tank II was controlled to be 5:1. The crystal transformation tank II contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 10% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 23% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: magnesium nitrate 0.10%, iron citrate 0.12%. Crystal transformation reaction was carried out for 3 h at a temperature maintained at 90 C. After the reaction, the solid and the liquid were separated by a filter to obtain a solid I and a filtrate J. One part of the filtrate J was introduced into the extraction tank for continuing extraction of the phosphate rock powder, and another part was introduced into the crystal transformation tank II for continuing the crystal transformation reaction. The solid I was washed with hot water to obtain a solid K and a washing liquid L. The solid K not only can be made into normal alpha-hemihydrate gypsum after drying by a drying machine, but also can be made into gypsum products, such as gypsum board, gypsum block, gypsum component and so on, by adding water directly without drying process. The washing liquid L was introduced into the sulfuric acid diluting tank for diluting the concentrated sulfuric acid.
(86) Implementation Results:
(87) Quimociac gravimetric method was used to test the phosphoric acid liquid product and the concentration was 28% wt; P.sub.2O.sub.5 content of the normal alpha-hemihydrate gypsum product was 0.06% wt; P.sub.2O.sub.5 content of the high-purity and high-whiteness alpha-hemihydrate gypsum product was 0.05% wt.
(88) The normal alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 2 to 3. The alpha-hemihydrate gypsum has a 2 h bending strength of 10.0 MPa, a dry bending strength of 20 MPa, a dry compressive strength of 91 MPa, an initial setting time of 10 min and a final setting time of 13 min. The mass percentage of the alpha-hemihydrate gypsum was 88%.
(89) The high-purity and high-whiteness alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 2 to 3. The high-purity and high-whiteness alpha-hemihydrate gypsum has a 2 h bending strength of 11.0 MPa, a dry bending strength of 20 MPa, a dry compressive strength of 90 MPa, an initial setting time of 11 min and a final setting time of 14 min, a whiteness value of 95.6. The mass percentage of the alpha-hemihydrate gypsum was 99.99%.
(90) The high-purity and high-whiteness beta-hemihydrate gypsum products conformed to the national standard Building Gypsum Plaster GB/T 9776-2008, which have an initial setting time of 7 min 20 sec and a final setting time of 1 min 15 sec, a 2 h wet bending strength of 3.3 MPa and a whiteness value of 95. The mass percentage of the beta-hemihydrate gypsum was higher than 99.9%.
(91) The mass percentage of calcium sulfate in dihydrate gypsum product was higher than 99.8%, and the mass percentage of adhesive water was below 0.2%.
Example 7
(92) Raw material 1: phosphate rock, collection site: Guizhou Kailin;
(93) Raw material 2: ferric nitrate, commercially available;
(94) Raw material 3: sodium citrate, commercially available;
(95) Raw material 4: sulfuric acid, concentration 97 wt %, commercially available;
(96) All of the sulfuric acid solutions used in the example were obtained by diluting the concentrated sulfuric acid of 97 wt % in sulfuric acid diluting tank.
(97) A method for producing by-products of wet-process phosphoric acid, alpha-hemihydrate gypsum as well as high-purity and high-whiteness alpha-hemihydrate gypsum as by-products, comprising the following steps:
(98) (1) Phosphate rock powder and excess amount of phosphoric acid were added to the extraction tank, wherein the solid-liquid mass ratio of the phosphate rock powder to the phosphoric acid was 1:45 and the concentration of phosphate acid was 20 wt %. The extraction reaction was carried out under the condition of continuous stirring. After the completion of the extraction, sulfuric acid solution with a concentration of 27 wt % was added. The addition amount of sulfuric acid was controlled and the reaction was carried out continuously to obtain an extraction slurry. About 40% of the calcium ions were transformed into dihydrate gypsum and the other 60% of calcium ions existed in the extraction slurry in a form of calcium dihydrogen phosphate. Thereafter, solid and liquid phases of the extraction slurry were separated by passing the extraction slurry through a filter to obtain a phosphoric acid extraction solution A and a slag slurry B. Therein, phosphoric acid in the phosphoric acid extraction solution was 2.1 mol/L and the calcium ion concentration was 0.8 mol/L.
(99) (2) The phosphate acid extraction solution A obtained in the step (1) was introduced into the decalcification reaction tank. Sulfuric acid solution with a concentration of 27 wt %, which was diluted with phosphoric acid of 20 wt %, was added to the decalcification reaction tank. The temperature was maintained at 80 C. and the reaction was carried out for 2 h with stirring. The resulting gypsum whiskers suspended in the phosphoric acid. Solid and liquid of the gypsum whisker suspension was separated by filter to obtain a solid C and a filtrate D. The filtrate D was divided into four parts: one part was introduced into the crystal transformation tank I for crystal transformation reaction, another part was introduced into the crystal transformation tank II for crystal transformation reaction, another part was introduced into the extraction tank for phosphoric rock extraction and the other part was transferred to acid pool as the phosphoric acid product.
(100) (3) The solid C was transferred to the crystal transformation tank I, part of the filtrate D and part of the sulfuric acid solution in the sulfuric acid diluting tank were added, and the liquid-solid mass ratio in the crystal transformation tank I was controlled to be 6:1. The crystal transformation tank I contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 12% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 25% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: ferric nitrate 0.22%, sodium citrate 0.07%. Crystal transformation reaction was carried out for 3 h at a temperature maintained at 100 C. After the completion of the reaction, the solid and the liquid were separated by filter to obtain a solid E and a filtrate F. The obtained filtrate F was introduced into the crystal transformation tank I and subjected to crystal transformation reaction continuously. The solid E obtained was washed by 80 to 100 C. hot water to obtain a solid G and a washing liquid H. The solid G not only can be made into high-purity and high-whiteness alpha-hemihydrate gypsum after drying, but also can be made into high-purity and high-whiteness dihydrate gypsum by drying naturally in the air. The high-purity and high-whiteness dihydrate gypsum can be calcined in a calcining furnace at 170 C. and ground to a particle size of 75-90 m to obtain a high-purity and high-whiteness beta-gypsum powder. The washing liquid H was introduced into the sulfuric acid diluting tank to dilute concentrated sulfuric acid. One part of the diluted sulfuric acid solution was introduced into the extraction tank for continuing the extraction of phosphate rock, another part was introduced into the decalcification reaction tank for continuing the decalcification reaction, another part was introduced into the crystal transformation tank I for crystal transformation reaction, and the other part was introduced into the crystal transformation tank II for crystal transformation reaction. The vapor generated during dilution process provided heat for the crystal transformation tank I and the crystal transformation tank II.
(101) (4) The slag slurry B obtained in the step (1) was transferred to the crystal transformation tank II, and part of the filtrate D, part of the filtrate J and part of the sulfuric acid solution in the sulfuric acid diluting tank were introduced. The liquid-solid mass ratio in the crystal transformation tank II was controlled to be 6:1. The crystal transformation tank II contained a mixed acid comprising sulfuric acid and phosphoric acid, wherein the mass percentage of sulfuric acid counted by H.sub.2SO.sub.4 was 12% of the mixed acid and the mass percentage of phosphoric acid counted by P.sub.2O.sub.5 was 25% of the mixed acid. According to mass percentage of the crystal transformation system, the following crystal transformation agents were added: ferric nitrate 0.22%, sodium citrate 0.07%. Crystal transformation reaction was carried out for 3 h at a temperature maintained at 100 C. After the reaction, the solid and the liquid were separated by a filter to obtain a solid I and a filtrate J. One part of the filtrate J was introduced into the extraction tank for continuing extraction of the phosphate rock powder, and another part was introduced into the crystal transformation tank II for continuing the crystal transformation reaction. The solid I was washed with hot water to obtain a solid K and a washing liquid L. The solid K not only can be made into normal alpha-hemihydrate gypsum after drying by a drying machine, but also can be made into gypsum products, such as gypsum board, gypsum block, gypsum component and so on, by adding water directly without drying process. The washing liquid L was introduced into the sulfuric acid diluting tank for diluting the concentrated sulfuric acid.
(102) Implementation Results:
(103) Quimociac gravimetric method was used to test the phosphoric acid liquid product and the concentration was 20% wt; P.sub.2O.sub.5 content of the normal alpha-hemihydrate gypsum product was 0.07% wt; P.sub.2O.sub.5 content of the high-purity and high-whiteness alpha-hemihydrate gypsum product was 0.06% wt.
(104) The normal alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 4 to 5. The alpha-hemihydrate gypsum has a 2 h bending strength of 12.0 MPa, a dry bending strength of 20 MPa, a dry compressive strength of 89 MPa, an initial setting time of 13 min and a final setting time of 16 min. The mass percentage of the alpha-hemihydrate gypsum was 89%.
(105) The high-purity and high-whiteness alpha-hemihydrate gypsum products conformed to the industrial standard JC/T 2038-2010. Under optical microscope of 200 magnification, the alpha-hemihydrate gypsum showed a short hexagonal cylindrical shape, with an aspect ratio of 4 to 5. The high-purity and high-whiteness alpha-hemihydrate gypsum has a 2 h bending strength of 12.0 MPa, a dry bending strength of 20 MPa, a dry compressive strength of 89 MPa, an initial setting time of 14 min and a final setting time of 18 min, a whiteness value of 95.8. The mass percentage of the alpha-hemihydrate gypsum was 99.98%.
(106) The high-purity and high-whiteness beta-hemihydrate gypsum products conformed to the national standard Building Gypsum Plaster GB/T 9776-2008, which have an initial setting time of 6 min 50 sec and a final setting time of 10 min 30 sec, a 2 h wet bending strength of 3.2 MPa and a whiteness value of 95.2. The mass percentage of the beta-hemihydrate gypsum was higher than 99.9%.