The second step in the hydrochloric acid process for the production of alumina from clay as carried out in the pilot plant constructed at the National Bureau of Standards to test the process. The digester is shown, in which, after preliminary roasting, the clay is stirred with hot dilute hydrochloride acid until soluble material is dissolved. Thus the aluminum content is dissolved out as alumina, whereas the silicon remains as insoluble silica.
National Institute of Standards and Technology
National Institute of Standards and Technology