Method of curing a gypsum calcination product

Abstract

A method of conditioning stucco comprises the steps of supplying a quantity of stucco particles to a reaction vessel, the stucco particles comprising calcium sulphate hemihydrate and/or calcium sulphate anhydrite, as well as calcium sulphate dihydrate; and conditioning the stucco particles at a temperature of at least 100? C. and a humidity of at least 70%. During the step of conditioning the stucco particles, the bulk density of the stucco particles within the reaction vessel is at least 1 g/cm.sup.3.

Claims

1. A method of conditioning stucco comprising the steps of: supplying a quantity of stucco particles to a reaction vessel, the stucco particles comprising calcium sulphate dihydrate and at least one of calcium sulphate hemihydrate and calcium sulphate anhydrite; and conditioning the stucco particles at a temperature of at least 100? C. and a humidity of at least 70%, wherein during the step of conditioning the stucco particles, the stucco particles are held statically within the reaction vessel, such that the bulk density of the stucco particles within the reaction vessel is at least 1 g/cm.sup.3; and further wherein the humidity of at least 70% is provided by the release of chemically-bound water molecules from the dihydrate particles.

2. A method according to claim 1, wherein the bulk density of the stucco particles within the reaction vessel is at least 1.5 g/cm.sup.3.

3. A method according to claim 1, wherein the conditioning time of the stucco particles is at least 30 minutes.

4. A method according to claim 1, wherein the conditioning temperature is at least 130? C.

5. A method according to claim 1, wherein the pressure inside the reaction vessel during the step of conditioning the stucco particles is less than 2 bar.

6. A method according to claim 1, wherein the stucco particles supplied to the reaction vessel comprise calcium sulphate anhydrite.

7. A method according to claim 6, wherein the stucco particles supplied to the reaction vessel comprise calcium sulphate anhydrite III.

8. A method according to claim 7, wherein the stucco particles supplied to the reaction vessel comprise calcium sulphate anhydrite III in an amount of up to 70 wt %.

9. A method according to claim 8, wherein the stucco particles supplied to the reaction vessel comprise calcium sulphate anhydrite III in an amount of between 10-15 wt %.

10. A method according to claim 1, wherein the stucco particles supplied to the reaction vessel comprise calcium sulphate dihydrate in an amount of 3-20 wt %.

11. A method according to claim 10, wherein the stucco particles supplied to the reaction vessel comprise calcium sulphate dihydrate in an amount of 5-10 wt %.

12. A method according to claim 1, further comprising the step of calcining gypsum material in a calcination vessel to provide the stucco particles for supplying to the reaction vessel.

13. A method according to claim 12, wherein the calcium sulphate dihydrate present in the stucco particles comprises residual calcium sulphate dihydrate resulting from incomplete calcination of the gypsum material.

14. A method according to claim 1, wherein the calcium sulphate dihydrate and the calcium sulphate hemihydrate are provided from separate sources.

15. A method according to claim 1, wherein the stucco particles are supplied to the reaction vessel in an amount such that a bulk volume of the stucco particles occupies at least 80% of an internal volume of the reaction vessel.

Description

EXAMPLES 1-5

(1) Gypsum (calcium sulphate dihydrate) was calcined in a calcination kettle at a temperature of 190? C. for about 1 hour. After calcining, further gypsum (calcium sulphate dihydrate) was added to the calcination product to provide a gypsum-enriched calcination product. This mixture was then transferred to a steam pressure vessel. The steam pressure vessel was sealed and placed in an oven at 130? C. for 4 hours to condition the stucco. After this treatment, the conditioned stucco was immediately placed into a metallic bucket and allowed to cool.

(2) Table 1 shows the anhydrite and dihydrate contents, water demand and specific surface area of the gypsum-enriched calcination product before and after conditioning in the steam pressure vessel. Each example was prepared from a different grade of gypsum, the d50 value of each gypsum grade being indicated in the Table.

(3) The specific surface area was measured through BET.

(4) TABLE-US-00001 TABLE 1 Residual gypsum Water BET Example D50 AIII (%) (%) demand (m.sup.2/g) 1 50 ?m Before 30 15.4 85 10.4 After 2.4 4.3 65 7.9 2 25 ?m Before 20 14.5 90 11.4 After 4.4 4.6 80 10.9 3 61 ?m Before 10.1 8.6 87 10.9 After 0 3.8 68 8.2 4 8 ?m Before 22 10.4 92 12.9 After 2.3 3.9 80 9.5 5 13 ?m Before 21.7 11.8 91 10.1 After 0.3 4.1 73 8.0

(5) As shown by Table 1, the conditioning treatment decreases the levels of anhydrite and dihydrate in the stucco, and additionally decreases the water demand and the specific surface area.

Examples 6 and 7, and Comparative Example 1

(6) Gypsum (calcium sulphate dihydrate) was calcined in a calcination kettle at a temperature of 190? C. for about 1 hour, to provide a calcination product. After calcining, further gypsum (calcium sulphate dihydrate) was added to the calcination product in an amount corresponding to 5 wt % of the calcination product, to provide a gypsum-enriched calcination product. This mixture was then transferred to a steam pressure vessel. The steam pressure vessel was sealed and placed in an oven for 2 hours to condition the stucco. After this treatment, the conditioned stucco was immediately placed into a metallic bucket and allowed to cool.

(7) Table 2 shows the anhydrite and dihydrite contents, water demand and specific surface area of the conditioned stucco as a function of oven temperature. Corresponding parameters for the direct calcination product (that is, without gypsum enrichment) are also given, for reference.

(8) The specific surface area was measured through BET.

(9) TABLE-US-00002 TABLE 2 Conditioning AIII Gypsum Water BET Example temperature (%) (%) demand (%) (m.sup.2/g) Comparative Not applicable 8.3 4.4 80 12.1 example 1 Example 6 120? C. 2.2 4.4 72 10.1 Example 7 130? C. 0.8 4 65 9.6

Examples 8-10 and Comparative Example 1

(10) Gypsum (calcium sulphate dihydrate) was calcined in a calcination kettle at a temperature of 190? C. for about 1 hour, to provide a calcination product. After calcining, further gypsum (calcium sulphate dihydrate) was added to the calcination product in an amount corresponding to 8 wt % of the direct calcination product, to provide a gypsum-enriched calcination product. This mixture was then transferred to a steam pressure vessel. The steam pressure vessel was sealed and placed in an oven at 130? C. to condition the stucco.

(11) After this treatment, the conditioned stucco was immediately placed into a metallic bucket and allowed to cool.

(12) Table 3 shows the anhydrite and dihydrite contents, water demand and specific surface area of the conditioned stucco as a function of conditioning time. Corresponding parameters for the direct calcination product (that is, without gypsum enrichment) are also given, for reference.

(13) TABLE-US-00003 TABLE 3 Conditioning AIII Gypsum Water BET Example time (%) (%) demand (%) (m.sup.2/g) Comparative Not applicable 8.3 4.4 80 12.1 example 1 Example 8 1 h 0 3.9 65 7.4 Example 9 2 h 0 3.5 62 6.4 Example 10 4 h 0 3.2 63 6.5

Examples 11-13 and Comparative Example 1

(14) Gypsum (calcium sulphate dihydrate) was calcined in a calcination kettle at a temperature of 190? C. for about 1 hour, to provide a calcination product. After calcining, further gypsum (calcium sulphate dihydrate) was added to the calcination product to provide a gypsum-enriched calcination product. This mixture was then transferred to a steam pressure vessel. The steam pressure vessel was sealed and placed in an oven at 130? C. for 2 hours to condition the stucco. After this treatment, the conditioned stucco was immediately placed into a metallic bucket and allowed to cool.

(15) Table 4 shows the anhydrite and dihydrite contents, water demand and specific surface area of the conditioned stucco as a function of the level of gypsum enrichment. Corresponding parameters for the direct calcination product (that is, without gypsum enrichment) are also given, for reference.

(16) TABLE-US-00004 TABLE 4 Gypsum addition (relative to the direct calcination AIII Gypsum Water BET Example product) (%) (%) demand (%) (m.sup.2/g) Comparative Not applicable 8.3 4.4 80 12.1 Example 1 Example 11 15 wt % 1.8 5.9 74 7.6 Example 12 8 wt % 0 3.5 62 6.4 Example 13 5 wt % 0.8 4 65 9.6

Examples 14-16 and Comparative Example 1

(17) Gypsum (calcium sulphate dihydrate) was calcined in a calcination kettle at a temperature of 190? C. for about 1 hour, to provide a calcination product. After calcining, further gypsum (calcium sulphate dihydrate) was added to the calcination product to provide a gypsum-enriched calcination product. This mixture was then transferred to a steam pressure vessel. The steam pressure vessel was sealed and placed in an oven at 130? C. for 4 hours to condition the stucco. After this treatment, the conditioned stucco was immediately placed into a metallic bucket and allowed to cool.

(18) Table 5 shows the anhydrite and dihydrite contents, water demand and specific surface area of the conditioned stucco as a function of extent to which the stream pressure vessel was filled with the gypsum-enriched calcination product. Corresponding parameters for the direct calcination product (that is, without gypsum enrichment) are also given, for reference.

(19) TABLE-US-00005 TABLE 5 Extent of AIII Gypsum Water BET Example filling (%) (%) demand (%) (m.sup.2/g) Comparative Not applicable 8.3 4.4 80 12.1 Example 1 Example 14 70% 1.8 4.4 75 8.7 Example 15 77% 0.6 3.5 76 8.8 Example 16 90% 0 3.2 63 6.5

Examples 17 and 18, and Comparative Example 1

(20) Gypsum (calcium sulphate dihydrate) was calcined in a calcination kettle at a temperature of 190? C. for about 1 hour, to provide a calcination product. After calcining, further gypsum (calcium sulphate dihydrate) was added to the calcination product to provide a gypsum-enriched calcination product. This mixture was then transferred to a steam pressure vessel. The steam pressure vessel was sealed and placed in an oven at 130? C. for 1 hour to condition the stucco. After this treatment, the conditioned stucco was immediately placed into a metallic bucket and allowed to cool.

(21) Table 6 shows the anhydrite and dihydrite contents, water demand and specific surface area of the conditioned stucco as a function of the pressure within the steam vessel. Corresponding parameters for the direct calcination product (that is, without gypsum enrichment) are also given, for reference.

(22) TABLE-US-00006 TABLE 6 Pressure within AIII Gypsum Water BET Example steam vessel (%) (%) demand (%) (m.sup.2/g) Comparative Not applicable 8.3 4.4 80 12.1 example 1 Example 17 1.5 bars 0 3.9 65 7.4 Example 18 Atmospheric 1.1 4.3 63 10.6 pressure