Pressure Leaching Alumina from Raw Kaolinitic Clay Using Hydrochloric Acid

摘要

The Bureau of Mines studied alumina extraction from uncalcined, kaolinitic clay at temperatures from 100 to 250C using 20- or 27- wt-pct-HCl concentrations and with an acid-to-clay ratio of from 0.8 to 1.4 times stoichiometric. A combination of high temperature and 20 wt pct excess HCl promoted rapid and almost quantitative extraction of alumina (99 pct in some tests). Additional Bureau data obtained with 35-mL tantalum bombs and leaching tests with added fluoride are also provided. At high temperatures, the addition of fluoride did not result in a significant improvement over HCl alone and was deleterious to the filtering properties of the digest residue.