Method for producing solutions of high alumina concentration by alkaline extraction.
MacMillan-RT; Jackson-J Jr.
U S Pat 3 700 766 1972 Oct; :
Intermittent addition of predetermined amounts of naoh to the leach solution increases the tendency toward dissolution of al and minimizes the dissolution of si and other impurities, giving a higher concentration of al2o3 in the product. The 0.5-1N naoh solution is present in a sufficient amount that the mole ratio between na in the solution and al in the shale is in the range 2- 2.5:1 (Calculated as na2o-al2o3). The ph is kept at >12 during the extraction by addition of more naoh. The mole ratio between the additional naoh and undissolved al, expressed as na2o-al2o3, is 1.3:1. Thus, <8-mesh retorted oil shale containing 2.85 pct al was stirred 20 min at 30 deg. C with 100 ml of 0.8N naoh solution (na2o- al2o3 mole ratio was 3.2:1). The extract solution was fortified with additional naoh and water and used to extract another sample of retorted shale. After 4 or more cycles the al concentration was 46.4 G/l.
U.S. Pat. 3,700,766; Oct. 24, 1972; Chem. Abstr. 78:60,302V