"This research simplified an earlier hydrogen chloride (HC1) leach-sparge process developed by the U.S. Bureau of Mines to recover reduction-grade alumina from domestic kaolin clay. Improvements were made by decreasing the initial leaching acid concentration from 25 to 20 pct, decreasing the leaching time from 1-2 h to 15-30 min, eliminating the solvent extraction step for Fe removal, and eliminating the step to recover the Al content of the bleedstream circuit. A 10-cycle bench-scale experiment of the simplified process showed that the FeCl3 concentration built up to 9.3 g/L in the recycle stream. This did not interfere with any of the unit operations or final alumina product purity because Fe forms stable soluble chloride complexes when sparged with HC1 and is easily washed from the large aluminum chloride hexahydrate (ACH) crystals. The reduced leaching time and acid concentration did not decrease Al extraction." - NIOSHTIC-2 NIOSHTIC no. 20039176

National Institute for Occupational Safety and Health