The control of phosphate contamination in an acid alumina process

Abstract

In concentrated aluminium sulphate solutions, such as are used in an acid alumina process, phosphate is very powerfully complexed and no satisfactory methods for its removal from solution have been previously described. The procedure herein uses zirconium sulphate to precipitate phosphate from acid solutions containing up to 50 g/l. Al₂O₃. Faster precipitation is achieved by prior heating of the aluminium solutions to 100º for a short period and a residual liquor containing less than 50 p.p.m. P₂O₅ is readily obtained. The procedure has been successfully applied to the preparation of specification-grade alumina from an Argentine laterite (0.1 % P₂O₅) using the CSIRO acid alumina process.