METHOD FOR PRODUCING PHOSPHORIC ACID AND BY-PRODUCING ALPHA-HEMIHYDRATE GYPSUM BY WET-PROCESS

Abstract

Provided is a method for producing phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum including: adding a phosphate rock powder and a part of dilute sulfuric acid into an extraction tank, carrying out an extraction reaction on same, separating a clear liquid from the obtained mixed slurry, sending the clear liquid, as a finished product phosphoric acid, into an acid storeroom, and transferring a separated solid, together with the rest mixed slurry, into a crystal transformation tank; and adding sulfuric acid and a crystal transformation agent into the crystal transformation tank, carrying out a crystal transformation reaction for 1.5-7.5 h at 60? C.-130? C., and solid-liquid separating the obtained mixed acid slurry, wherein the solid can be dried into a gypsum powder, or may be not subjected to a drying step and made into gypsum products such as gypsum boards, gypsum building blocks and gypsum members by directly adding water.

Claims

1. A method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product, comprising the following steps: S1) mixing phosphate rock powder with diluted sulfuric acid and performing an extraction reaction to obtain a mixed slurry A; S2) taking a fraction of 0 to ? volume of the mixed slurry A obtained in step S1) and performing a solid and liquid separation to obtain a supernatant B and a solid C; S3) mixing the solid C and the rest mixed slurry with diluted sulfuric acid; adding a crystal transformation agent; performing a crystal transformation reaction under heating to obtain a mixed slurry D; S4) filtering the mixed slurry D obtained in step S3) to obtain an alpha-hemihydrate gypsum.

2. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 1, wherein in step S1), the solid-liquid mass ratio of the phosphate rock powder to the diluted sulfuric acid is from 1:2 to 1:10.

3. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 1, wherein in step S1), the temperature of the extraction reaction is from 30 to 95? C. and the duration of the extraction reaction is from 15 to 60 minutes.

4. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 1, wherein the crystal transformation agent is one selected from water-soluble phosphate, water-soluble sulfate, water-soluble nitrate, water-soluble citrate, water-soluble alkylbenzenesulfonate, water-soluble alkyl fatty acid salt and water-soluble organic carboxylate, or a combination thereof; the water-soluble phosphate, water-soluble sulfate, water-soluble nitrate, water-soluble citrate, water-soluble alkylbenzenesulfonate, water-soluble alkyl fatty acid salt and water-soluble organic carboxylate each independently contain one or more ion(s) of Al.sup.3+, Fe.sup.3+, Mg.sup.2+, Na.sup.+ and NH.sub.4.sup.+.

5. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 1, wherein in step S3), the temperature of the crystal transformation reaction is from 60 to 130? C. and the duration of the crystal transformation reaction is from 1.5 to 7.5 hours.

6. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 1, wherein in step S3), the solid-liquid mass ratio of a mixture of solid C and the rest mixed slurry to the diluted sulfuric acid is from 2:1 to 6:1.

7. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 1, wherein in step S3), in the liquid phase resulting from mixing the solid C and the rest mixed slurry with diluted sulfuric acid, the mass fraction of phosphoric acid in terms of P.sub.2O.sub.5 is from 16% to 25%, and the mass fraction of sulfuric acid in terms of H.sub.2SO.sub.4 is from 8% to 12%.

8. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 1, comprising the following steps: (1) adding phosphate rock powder and diluted sulfuric acid in a solid-liquid mass ratio of 1:2 to 1:10 into an extraction tank; performing extraction reaction for 15 to 60 minutes under controlling the temperature of the extraction tank at 30 to 95? C. to obtain a mixed slurry A; (2) taking a fraction of 0 to ? volume of the mixed slurry A obtained in step S1) and performing a solid and liquid separation to obtain a supernatant B and a solid C; transferring the supernatant B to an acid storage as final phosphoric acid and transferring the solid C to a crystal transformation tank together with the rest mixed slurry; (3) adding diluted sulfuric acid to the crystal transformation tank; controlling the liquid-solid ratio as well as the content of P.sub.2O.sub.5 and H.sub.2SO.sub.4 in the liquid phase of phosphoric acid after decalcification to obtain a mixed slurry; adding a crystal transformation agent and performing a crystal transformation reaction for 1.5 to 7.5 hours to obtain a mixed acid slurry D, wherein the temperature of the crystal transformation tank is maintained at 60 to 130? C.; (4) separating solid and liquid in the mixed acid slurry D obtained in step (3) to obtain a solid E and a filtrate F; washing the solid E with hot water to obtain a washing liquid H and a solid G; and drying the solid G to obtain an alpha-hemihydrate gypsum; (5) introducing the filtrate F in step (4) into the extraction tank of step (1) to continue the extraction of phosphate rock powder; introducing the washing liquid H into a sulfuric acid diluting tank to dilute concentrated sulfuric acid, which is used for the extraction process of step (1) and the crystal transformation reaction of step (3).

9. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 8, wherein the fineness of the phosphate rock powder in step (1) is from 80 to 100 meshes and the phosphorus pentoxide content in the phosphate rock powder is from 10 to 40% by mass fraction.

10. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 8, wherein the mass concentration of diluted sulfuric acid in steps (1) and (3) is from 20 to 40%, more preferably from 20 to 35%.

11. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 8, wherein the mass fraction of sulfate ions in the mixed slurry A in step (1) is less than 1%.

12. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 8, wherein in step (3), the liquid-solid mass ratio of the mixed acid solution after decalcification and the rest slurry is from 2:1 to 6:1, wherein the liquid phosphoric acid in terms of P.sub.2O.sub.5 accounts for 16% to 25% by mass fraction of the mixed acid, and the sulfuric acid in terms of H.sub.2SO.sub.4 accounts for 8% to 12% by mass fraction of the mixed acid; preferably, in step (3), the liquid-solid mass ratio of the mixed acid solution after decalcification and the rest slurry is from 3:1 to 5:1, wherein the liquid phosphoric acid in terms of P.sub.2O.sub.5 accounts for 18% to 23% by mass fraction of the mixed acid, and the sulfuric acid in terms of H.sub.2SO.sub.4 accounts for 9% to 10% by mass fraction of the mixed acid.

13. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 8, wherein the crystal transformation agent in step (3) is one selected from a water-soluble phosphate, water-soluble sulfate, water-soluble nitrate, water-soluble citrate, water-soluble alkylbenzenesulfonate, water-soluble alkyl fatty acid salt and water-soluble organic carboxylate, or a combination thereof, which contains Al.sup.3+, Fe.sup.3+, Mg.sup.2+, K.sup.+, Na.sup.+, NH.sub.4.sup.+ ions.

14. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 13, wherein the crystal transformation agent added in step (3) is a combination of sodium citrate, ferric sulfate and sodium lignosulfonate; or a combination of sodium nitrate, magnesium sulfate and sodium dodecyl sulfonate; or a combination of sodium phosphate, aluminum sulfate and sodium lignosulfonate; or a combination of ammonium nitrate, magnesium sulfate and sodium chloride; wherein the total amount of the crystal transformation agent added in step (3) is from 0.1% to 1.0% by mass of the mixed slurry; wherein the combination of the crystal transformation agent is one of the following combinations by mass ratio: a. sodium citrate:ferric sulfate:sodium lignosulfonate=1.00:1.50?2.00:0.30?0.90; b. sodium nitrate:magnesium sulfate:sodium dodecyl sulfonate=1.00:1.50?2.00:0.30?0.90; c. sodium phosphate:aluminum sulfate:sodium lignosulfonate=1.00:1.50?2.00:0.40?0.90; d. ammonium nitrate:magnesium sulfate:sodium chloride=1.00:1.60?2.20:0.50?0.80.

15. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 8, wherein the temperature of the hot water in step (4) is from 80 to 90? C.; wherein the drying temperature in step (4) is from 110 to 180? C., more preferably from 110 to 130? C.

16. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 8, wherein vapor generated in the dilution process in step (5) is introduced into the crystal transformation tank in step (3) to provide heat for reaction.

17. The method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product according to claim 8, comprising the following steps: (1) adding phosphate rock powder and diluted sulfuric acid with a mass concentration of 20% into an extraction tank according to a solid-liquid mass ratio of 1:4, wherein the fineness of the phosphate rock powder is 100-mesh and the phosphorus pentoxide content in the phosphate rock is 32%; performing an extraction reaction for 30 minutes under controlling the temperature of the extraction tank at 80? C. under stirring to obtain a mixed slurry A; (2) taking a fraction of ? volume of the mixed slurry A obtained in step S1) and performing a solid and liquid separation to obtain a supernatant B and a solid C; transferring the supernatant B to an acid storage as final phosphoric acid and transferring the solid C to a crystal transformation tank together with the rest mixed slurry; (3) adding diluted sulfuric acid with a mass concentration of 20% to the crystal transformation tank; controlling the liquid-solid mass ratio of mixed acid solution after decalcification and slag slurry at 6:1 to obtain a mixed slurry, wherein the liquid phosphoric acid in terms of P.sub.2O.sub.5 is 20% by mass fraction of the mixed acid and the sulfuric acid in terms of H.sub.2SO.sub.4 is 9% by mass fraction of the mixed acid; then, adding crystal transformation agents: iron sulfate accounted for 0.23% of the mass of the mixed slurry, sodium citrate accounted for 0.12% of the mass of the mixed slurry, and sodium lignosulfonate accounted for 0.08% of the mass of the mixed slurry; performing crystal transformation reaction for 3 h under maintaining the temperature of crystal transformation tank is maintained at 110? C. to obtain a mixed acid slurry D; (4) separating solid and liquid in the mixed acid slurry D obtained in step (3) to obtain a solid E and a filtrate F; washing the solid E with 85? C. hot water to obtain a washing liquid H and a solid G; and drying the solid G by a blow-dryer at a drying temperature of 110? C. to obtain an alpha-hemihydrate gypsum; (5) introducing the filtrate F in step (4) into the extraction tank of step (1) to continue the extraction of phosphate rock powder; introducing the washing liquid H into a sulfuric acid diluting tank to dilute concentrated sulfuric acid, which is used for the extraction process of step (1) and the crystal transformation process of step (3); introducing vapor generated during the dilution process into the crystal transformation tank to provide heat for reaction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIG. 1 is the schematic of technical flow chart of a method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product.

DETAILED DESCRIPTION

[0062] For further understanding of the present disclosure, the preferred embodiments of the present disclosure are described below with reference to examples. However, it is to be understood that these descriptions are only for further illustrating the features and advantages of the present disclosure, rather than limiting the claims of the present disclosure.

[0063] The chemical reagents used in the examples of the present disclosure are all commercially available, and the concentration of the reagent and the content of the mineral components are both in mass percentage.

EXAMPLES

Example 1

[0064] Phosphate rock mining site: Kailin, Guizhou; phosphorus pentoxide content of the phosphate rock: about 32%.

[0065] A method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product, comprising the following steps:

[0066] (1) phosphate rock powder and diluted sulfuric acid with a mass concentration of 20% were added into an extraction tank according to a solid-liquid mass ratio of 1:4, wherein the fineness of the phosphate rock powder was 100 meshes and the phosphorus pentoxide content in the phosphate rock was 32%; extraction reaction was performed for 30 minutes under stirring to obtain a mixed slurry A, wherein the temperature of the extraction tank was controlled at 80? C.;

[0067] (2) solid and liquid in ? volume of the mixed slurry A obtained in step (1) were separated by a filter machine to obtain a supernatant B and a solid C; the supernatant B was transferred to an acid storage as final phosphoric acid and the solid C was transferred to a crystal transformation tank together with the rest mixed slurry;

[0068] (3) diluted sulfuric acid with a mass concentration of 20% was added to the crystal transformation tank; the liquid-solid mass ratio of the mixed acid solution after decalcification and slag slurry was controlled at 6:1 to obtain a mixed slurry, wherein the liquid phosphoric acid in terms of P.sub.2O.sub.5 was 20% by mass of the mixed acid and the sulfuric acid in terms of H.sub.2SO.sub.4 was 9% by mass of the mixed acid; after obtaining the mixed slurry, crystal transformation agents were added: iron sulfate accounted for 0.23% of the mass of the mixed slurry, sodium citrate accounted for 0.12% of the mass of the mixed slurry, and sodium lignosulfonate accounted for 0.08% of the mass of the mixed slurry; crystal transformation reaction was performed for 3 h to obtain a mixed acid slurry D, wherein the temperature of crystal transformation tank was maintained at 110? C.;

[0069] (4) solid and liquid in the mixed acid slurry D obtained in step (3) were separated to obtain a solid E and a filtrate F; the solid E was washed with 85? C. hot water to obtain a washing liquid H and a solid G; and the solid G was dried by a blow-dryer at a drying temperature of 110? C. to obtain an alpha-hemihydrate gypsum;

[0070] (5) the filtrate F in step (4) was introduced into the extraction tank of step (1) to continue the extraction of phosphate rock powder; the washing liquid H was introduced into a sulfuric acid diluting tank to dilute concentrated sulfuric acid with a mass percentage of 97%, which was used for the extraction process of step (1) and the crystal transformation process of step (3); vapor generated during the dilution process was introduced into the crystal transformation tank to provide heat for reaction.

[0071] Detection Results:

[0072] Quimociac gravimetric method was used to test the phosphoric acid product and the concentration was 27% wt. The alpha-hemihydrate gypsum product has a P.sub.2O.sub.5 content of 0.06 wt %. The alpha-hemihydrate gypsum product conformed to the industry 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 alpha-hemihydrate gypsum has a 2 h bending strength of 9.5 MPa, a dry bending strength of 17 MPa, a dry compressive strength of 95 MPa, an initial setting time of 8 min and a final setting time of 17 min.

Example 2

[0073] Phosphate rock mining site: Lufa, Guizhou; phosphorus pentoxide content of the phosphate rock: 27%.

[0074] A method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product, comprising the following steps:

[0075] (1) phosphate rock powder and diluted sulfuric acid with a mass concentration of 30% were added into an extraction tank according to a solid-liquid mass ratio of 1:3, wherein the fineness of the phosphate rock powder was 100 meshes and the phosphorus pentoxide content in the phosphate rock was 27%; extraction reaction was performed for 50 minutes under stirring to obtain a mixed slurry A, wherein the temperature of the extraction tank was controlled at 70? C.;

[0076] (2) solid and liquid in ? volume of the mixed slurry A obtained in step (1) were separated by a filter machine to obtain a supernatant B and a solid C; the supernatant B was transferred to an acid storage as final phosphoric acid and the solid C was transferred to a crystal transformation tank together with the rest mixed slurry;

[0077] (3) diluted sulfuric acid with a mass concentration of 30% was added to the crystal transformation tank; the liquid-solid mass ratio of the mixed acid solution after decalcification and slag slurry was controlled at 5:1 to obtain a mixed slurry, wherein the liquid phosphoric acid in terms of P.sub.2O.sub.5 was 20% by mass of the mixed acid and the sulfuric acid in terms of H.sub.2SO.sub.4 was 12% by mass of the mixed acid; after obtaining the mixed slurry, crystal transformation agents were added: aluminum sulfate accounted for 0.25% of the mass of the mixed slurry, sodium citrate accounted for 0.09% of the mass of the mixed slurry, and sodium lignosulfonate accounted for 0.06% of the mass of the mixed slurry; crystal transformation reaction was performed for 2 h to obtain a mixed acid slurry D, wherein the temperature of crystal transformation tank was maintained at 100? C.;

[0078] (4) solid and liquid in the mixed acid slurry D obtained in step (3) were separated to obtain a solid E and a filtrate F; the solid E was washed with 90? C. hot water to obtain a washing liquid H and a solid G; and the solid G was dried by a blow-dryer at a drying temperature of 110? C. to obtain an alpha-hemihydrate gypsum;

[0079] (5) the filtrate F in step (4) was introduced into the extraction tank of step (1) to continue the extraction of phosphate rock powder; the washing liquid H was introduced into a sulfuric acid diluting tank to dilute concentrated sulfuric acid, which was used for the extraction process of step (1) and the crystal transformation process of step (3); vapor generated during the dilution process was introduced into the crystal transformation tank to provide heat for reaction.

[0080] Detection Results:

[0081] Quimociac gravimetric method was used to test the phosphoric acid product and the concentration was 22% wt. The alpha-hemihydrate gypsum product has a P.sub.2O.sub.5 content of 0.08 wt %. The alpha-hemihydrate gypsum product conformed to the industry 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 8.0 MPa, a dry bending strength of 15 MPa, a dry compressive strength of 75 MPa, an initial setting time of 9 min and a final setting time of 18 min.

Example 3

[0082] A method for producing wet-process phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum as by-product was carried out in the same manner as described in Example 1, except that the components and contents of the crystal transformation agent used were different, as shown in Table 1:

TABLE-US-00001 TABLE 1 Components and contents of crystal transformation agent, as well as performances of the resulting product Combination of crystal transformation Components and contents agent (wt %) Performances of alpha-hemihydrate gypsum product 1 sodium nitrate 0.10 Exhibiting a short hexagonal cylindrical shape with an aspect magnesium sulfate 0.20 ratio of 1 to 2 under an optical microscope at 200 X sodium dodecyl magnification; a 2 h bending strength of 8.0 MPa, a dry bending benzenesulfonate 0.07 strength of 16 MPa, a dry compressive strength of 89 MPa, an initial setting time of 8 min and a final setting time of 17 min. 2 ferric sulfate 0.22 Exhibiting a short hexagonal cylindrical shape with an aspect sodium dodecyl ratio of 2 to 4 under an optical microscope at 200 X benzenesulfonate 0.07 magnification; a 2 h bending strength of 7.0 MPa, a dry bending strength of 14 MPa, a dry compressive strength of 65 MPa, an initial setting time of 7 min and a final setting time of 17 min. 3 sodium phosphate 0.10 Exhibiting a short hexagonal cylindrical shape with an aspect aluminum sulfate 0.20 ratio of 1 to 2 under an optical microscope at 200 X aluminum lignosulfonate magnification; a 2 h bending strength of 7.0 MPa, a dry bending 0.07 strength of 15 MPa, a dry compressive strength of 90 MPa, an initial setting time of 6 min and a final setting time of 19 min. 4 sodium phosphate 0.12 Exhibiting a short hexagonal cylindrical shape with an aspect aluminum lignosulfonate ratio of 3 to 5 under an optical microscope at 200 X 0.14 magnification; a 2 h bending strength of 7.0 MPa, a dry bending strength of 14 MPa, a dry compressive strength of 62 MPa, an initial setting time of 6 min and a final setting time of 18 min. 5 ammonium nitrate 0.11 Exhibiting a short hexagonal cylindrical shape with an aspect magnesium sulfate 0.21 ratio of 1 to 2 under an optical microscope at 200 X sodium chloride 0.08 magnification; 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 7 min and a final setting time of 19 min. 6 ammonium sulfate 0.33 Exhibiting a short hexagonal cylindrical shape with an aspect sodium citrate 0.18 ratio of 4 to 5 under an optical microscope at 200 X magnification; a 2 h bending strength of 7.0 MPa, a dry bending strength of 13 MPa, a dry compressive strength of 60 MPa, an initial setting time of 8 min and a final setting time of 20 min. 7 potassium nitrate 0.10 Exhibiting a short hexagonal cylindrical shape with an aspect ferric sulfate 0.21 ratio of 7 to 8 under an optical microscope at 200 X sodium acetate0.12 magnification; a 2 h bending strength of 6.0 MPa, a dry bending strength of 10 MPa, a dry compressive strength of 50 MPa, an initial setting time of 3 min and a final setting time of 10 min. 8 potassium nitrate 0.19 Exhibiting a short hexagonal cylindrical shape with an aspect sodium acetate0.10 ratio of 5 to 7 under an optical microscope at 200 X magnification; a 2 h bending strength of 5.0 MPa, a dry bending strength of 9 MPa, a dry compressive strength of 45 MPa, an initial setting time of 4 min and a final setting time of 13 min.

[0083] From the above table, it can be seen that gypsum powder prepared by the present disclosure has an aspect ratio of <10 can be obtained, indicating that the morphology of the alpha-hemihydrate gypsum prepared in the present disclosure can be controlled, and the alpha-hemihydrate gypsum having different aspect ratios can be prepared by adjusting the formulation of the crystal transformation agent, which can apply to different market demands.

Example 4

[0084] The amount of vapor (t) generated from per production of 1 ton of alpha-hemihydrate gypsum in the actual production process of examples 1 to 3 was detected and shown in Table 2.

TABLE-US-00002 TABLE 2 Results of vapor generated by a vapor recycling process from concentrated sulfuric acid diluting tank in examples 1-3 Example 3 Example 1 Example 2 (Combination 1) Average value 0.0436 0.0420 0.0422 0.0426

[0085] As shown in Table 2, by using the vapor recycling process from sulfuric acid diluting tank, 0.0426 ton of vapor in average is produced per production of 1 ton of alpha-hemihydrate gypsum. An alpha-hemihydrate gypsum production line having an annual output of 100,000 tons can produce a benefit of 639,000 Yuan, as calculated according to the price of 150 Yuan per ton of vapor.