BigPatents India

In the Bayer process for the production of alumina, problems are caused by silica dissolving in the caustic liquor. This silica arises from the presence of kaolin in the bauxite. A process for removing this kaolin comprises contacting the bauxite with sodium hydroxide solution to form a mixture, and subjecting the mixture to intense ultrasonic irradiation to cause cavitation; this can be carried out at temperatures below 100 DEG C. This enhances both the dissolution of kaolin and the precipitation of sodium aluminium silicate. Silica remaining in solution in spent Bayer liquor (after digestion and then precipitation of gibbsite) can be removed by a similar ultrasonic irradiation treatment to cause it to precipitate before it forms scale in heat exchangers.