We Claim:
1. An improved process for the preparation of boehmite from aluminium hydroxide of
Bayer process comprising the steps of:
(a) pre-calcining aluminium hydroxide to remove chemically bound water partially;
(b) subjecting the pre~calcined powder in an autoclave, to which water is added
followed by stirring to make a slurry;
(c) treating the slurry to a hydrothermal reaction for a period of 1-15 hours;
(d) removing the slurry from the autoclave and filtering of the water to produce
boehmite.
2. The process as claimed in claim 1 wherein the pre-calcining is carried out in a batch type or rotary furnace.
3. The process as claimed in claim 1 wherein the pre-calcining is performed at a temperature of 150 °C to 350 °C.
4. The process as claimed in claim 3 wherein the pre-calcining is performed at a temperature of 200 °C to 300 °C.
5. The process as claimed in claim 1 wherein the pre-calcining is done for a residence time of 30 minutes to 10 hours.
6. The process as claimed in claim 5 wherein the pre-calcining is done for a residence time of 30 minutes to 5 hours.
7. The process as claimed in claim 1 wherein the removal of chemically bound water in the pre-calcining step is 10-30 weight percent.
8. The process as claimed in claim 7 wherein the removal of chemically bound water in the pre-calcining step is 15-25 weight percent.

9. The process as claimed in claim 1 wherein in step (b) the ratio of water to pre-calcined powder is 1:1 to 1:8.
10. The process as claimed in claim 9 wherein in step (b) the ratio of water to pre-calcined powder is 1:3 to 1:5.
11. The process as claimed in claim 1 wherein the hydrothermal reaction in step (c) is carried out for a period of 5 to 10 hours.
12. The process as claimed in claim 1 wherein the hydrothermal reaction in step (c) is carried out at a temperature of 120 °C to 250 °C.
13. The process as claimed in claim 12 wherein the hydrothermal reaction in step (c) is carried out at a temperature of 150 °C to 200 °C.
14. The process as claimed in claim 1 wherein filtered slurry in step (d) is washed multiple times.
15. A process for preparing sintered alumina abrasives from the boehmite obtained by the process as claimed in claim 1.