Alumina Extraction by Autoclave Precipitation of Basic Sodium Aluminum Sulfate

摘要

An investigation was conducted on the conditions affecting the precipitation of aluminum by autoclaving synthetic solutions containing Na2SO4, Al2(SO3)3, H2SO4, and H2O. Virtually all of the alumina could be precipitated as natroalunite (NaAl3(SO4)2(OH)6). This product could be readily filtered and dried. Results are reported in terms of alumina precipitated in this compound and not in terms of alumina itself. Solutions of approximately 0.30, approximately 0.60, and approximately 0.80 mole/liter Al2O3 and various concentrations of H2SO4 and Na2SO4 were investigated. The optimum time and temperature for autoclaving were 20 to 30 minutes at 200C. The highest yields of natroalunite were obtained from solutions containing little H2SO4 and approximately 2 moles Na2SO4 per mole Al2O3. Acid in quantities of 0.3 to 0.5 mole/mole of alumina in solution depressed the yield to 90 percent or less. In differential thermal analysis, at 1,000C the natroalunite precipitate decomposed without melting to yield SO3 and SO2 gases, a solid composed of Na2SO4, and gamma and alpha Al2O3. Continued heating to 1,200C produced Na2SO4 and alpha Al2O3. Water-leaching of this product removed the Na2SO4 and left a final residue of alpha Al2O3. (Author)