A method comprising (a) reacting aluminum metal with an acid in the presence of water to provide a first aluminum salt solution comprising an aluminum salt in water, wherein the aluminum salt comprises a reaction product of the acid and the aluminum metal, (b) heating the first aluminum salt solution to provide a mother liquor and solid aluminum salt, (c) optionally, separating the solid aluminum salt from the mother liquor, (d) optionally, dissolving at least a portion of the separated solid aluminum salt with water to provide a second aluminum salt solution, (e) spray roasting the first, or second (if produced), aluminum salt solution to provide an aluminum oxide powder, and (f) washing the aluminum oxide powder, wherein the washed aluminum oxide powder comprises less than about 30 ppmw total metallic and alkyl impurities.