Al is extracted with high yield in a clear solution from which sulfate readily convertible to useful al2o3 can be crystallized, from mixtures of various minerals by fusion, quenching to an amorphous solid, crushing, and leaching with h2so4. The melt can be poured into h2o, atomized with steam, or chilled on a cold metal plate, and the frit pulverized to 35-65 mesh. This is preferably leached with 8-17 vol pct h2so4, in an amount providing 1.26-1.68X as much acid as frit by weight, for 15-30 min at close to the boiling temperature; longer time and more concentrated acid decreases the solubility of sio2 and cao. A solution of 95-99 pct of the al is thus obtained that can be readily clarified by filtration or settling. By evaporating the clear solution or treating it at high temperature and pressure in an autoclave, crystals of naal3(so4)3(oh)6 can be precipitated and converted to al2o3. If hcl is used for the extraction, too much ca is dissolved with the al. If the sio2/ca proportion is not 3-8 by weight, the al solution is difficult to clarify and filter. When 50-g mixtures of anorthite with 50-60 pct albite having a 6.2-7.9 Sio2/cao weight ratio were leached 15 min with 288 ml of 16 vol pct h2so4 at >90 deg c, 92.7 pct of the al2o3 was extracted in solutions containing 0.37- 1.47 pct sio2 and 3.59-4.08 pct fe2o3; but with 67 pct albite only 2.6 pct of the al2o3 was extracted and with 20 pct the sio2 and fe2o3 in the solution were >17 pct each under the same conditions.
U.S. Pat. 3,507,629; Apr. 21, 1970; Chem. Abstr. 73:5,514N