PROCESS FOR EXTRACTION OF ALUMINA FROM ORES BY SOLUTION OF CAUSTIC SODA AND SODIUM ALUMINATE

摘要

Bauxite is treated (to achieve a dissolution of the alumina content of the bauxite) with an aqueous solution of caustic soda and sodium aluminate in suspension in a series of pressure stages of increasing temperature, the final pressure stage being heated by live steam. The suspension is then passed through a series of expansion stages in which the suspension is cooled by partial vaporization. The first and each intermediate pressure stage comprises a mixing exchanger 44 and reservoir 45, suspension passing from the preceding stage into mixing exchanger 44 where it is heated to near its boiling point by direct injection of steam from a corresponding expansion stage 41. The reheated suspension remains in reservoir 45 until the solubility equilibria are reached, when an amount of suspension equal to that received from the preceding stage is passed via 46 to the next pressure stage, the excess being pumped via 47 to evaporator 42 wherein it is partially vaporized by the steam from 41, the remaining unvaporized suspension returning to the reservoir by gravity. In a modification of the process only the aqueous solution of NaOH and NaAlO 2 is passed through the initial pressure stage or stages and the bauxite is added in a later stage.