Image Number 2 for United States Patent #5653947.
The present invention is a method for producing alumina trihydrate with a low silica content from Gibbsite-containing bauxite of low reactive silica content. The present method involves two desilication steps: one step before extraction of alumina from the bauxite, i.e., a pre-desilication, and an additional desilication step following alumina extraction, i.e., a post-desilication. The present method comprises the steps of:(a) heating a suspension of ground bauxite in an aqueous solution comprising sodium hydroxide at a temperature greater than 80.degree. C.; and(b) increasing the sodium hydroxide concentration of the suspension from (a); and(c) heating the suspension from (b) at a temperature greater than 80.degree. C.; and(d) diluting the suspension from (c) with an aqueous solution; and(e) heating the suspension from (d) at a temperature greater than 80.degree. C., affording a suspension comprising a supersaturated, desilicated sodium aluminate liquor and insoluble solid.