The Bureau of Mines conducted laboratory studies to investigate methods for desilicating sodium aluminate solution derived from leaching a limestone-anorthosite sinter with 10-pct na2co3 solution. Desilication tests were made at atmospheric pressure to determine the effects of time and additions of lime and desilication residues. A two-stage, countercurrent desilication procedure was developed to reduce the sio2 content sufficiently to meet specifications for cell- grade al2o3. Both stages were conducted at boiling temperatures at atmospheric pressure. Reagent lime was charged as desilication seed to the partially desilicated solution in the second stage, and a product (desilication residue) precipitated by the lime addition was charged to the freshly leached solution in the first stage. Average al2o3 loss in the desilication circuit was 5.8 pct, and the product solution contained less than 0.04 G/l sio2. Complete precipitation of al2o3 by carbonation resulted in a hydrate containing less than 0.01 pct sio2. Calcination of this hydrate would produce al2o3 meeting the 0.015 pct sio2 specification for cell-grade materials.