Acid sulfation of alunite

"The U.S. Bureau of Mines conducted laboratory studies on sulfuric acid (h2so4) digestion of alunite [kal3(so4)2(oh)6] as a means for treating domestic deposits of this mineral. Digesting alunite ore in boiling h2so4 at concentrations of 88-wt-pct acid or higher breaks down the alunite and permits a convenient separation of potassium and aluminum. The digestion reaction is a complex sulfation reaction occurring in two stages. In this reaction, the potassium component extracts into the h2so4 for eventual recovery as potassium sulfate (k2so4) in a separate unit operation. Aluminum is left as acid-insoluble aluminum sulfate [al2(so4)3], which can be extracted by a 95 deg. C water leach. Additional purification of al2(so4)3 produced in this study is needed to meet cell-grade alumina (al203) purity specifications. Extraction and separation of potassium and aluminum from the alunite ore were consistently above 90 pct." - NIOSHTIC-2NIOSHTIC no. 10006814198