This paper describes in-depth studies conducted by the Bureau of Mines on the recovery of alumina from kaolinitic clay in order to provide technology for alumina production from domestic raw materials. The hyrochloric acid (hcl) process consists of the following steps: (1) clay calcination at 750 deg c, (2) clay leaching with 26-pct hcl, (3) removal of iron from pregnant liquor by solvent extraction, (4) crystallization of aluminum chloride hexahydrate from pregnant liquor by hcl gas injection, and (5) calcination of aluminum chloride hexahydrate to al203 with hcl recovery. All unit operations except 5 were run on a semicontinuous basis in a pilot plant. Research also investigated process alternatives, such as leaching of uncalcined clay, changes in leaching acid concentration and stoichiometry, elimination of solvent extraction for iron removal, and formation of aluminum oxychloride instead of aluminum chloride hexahydrate as an intermediate product.
Paper in Chemeca '88. Institution of Engineers, Australia, 1988, PP. 316-322