As part of its program to lessen dependence of foreign bauxite as the nation's primary source of cell-grade alumina, the Bureau of Mines is investigating sulfuric acid (h2so4) leaching procedures for the recovery of alumina from domestic aluminous materials. The successful application of a h2so4 leaching process depends on the recovery of the aluminum values in an easily washed and filtered form, containing a minimum of water to be driven off in the subsequent calcination step. This goal was met by the high- temperature hydrolysis of simulated aluminum sulfate [al2(so4)3] leach liquor. Crystalline, insoluble aluminum hydroxy sulfate [al(oh)so4], which had a water-to-alumina mole ratio of 1:1, was produced. Eighty-six percent of a solution containing 127 g of al2(so4)3 per liter and 76 pct of a solution containing 336 g of al2(so4)3 per liter was hydrolyzed to insoluble aluminum hydroxy sulfate by autoclaving for 1 hr at 320 deg. C and rapidly quenching to room temperature. Higher operating temperatures were precluded by corrosion of the autoclave. The yield of aluminum in the hydrolysis product increased with the increasing hydrolysis temperature and decreasing al2(so4)3 concentration.