A NEW PROCESS TO PRODUCE GRANULAR BORIC OXIDE BY HIGH-TEMPERATURE DEHYDRATION OF BORIC-ACID IN A FLUIDIZED-BED

The production of boric oxide has only been achieved as a hard, compac t or spongy mass that requires crushing and grinding operations before utilization. This paper represents the production of pure and granula r boric oxide by high temperature dehydration of boric acid in a fluid ized bed. Such dehydration is incomplete since agglomeration starts at 603 K, and to avoid agglomeration the boric oxide particles have been covered with a material that has a higher melting point than boric ox ide itself. In order to achieve this high melting cover, a mixture of boric acid and alkali berate has been fed into a fluidized bed. During dehydration, the proper percentage of alkali berate has been determin ed by examining the behaviour of different mixtures. As the percentage of alkali berate increases, a more homogeneous cover has been formed on the surface of boric oxide particles. This causes the agglomeration temperature of the end-product to shift to 728 K. A two stage dehydra tion process has been investigated to reduce the dehydration residence time and to make the process continuous. As a result, granular boric oxide of 99.85%-99.90% purity and containing 0.10%-0.15% Na2O has been produced.