Abstract: There is provided a flash activated hydrotalcite which, when extruded to sizes of about 1/16 inch or more, has a crush load strength of at least about 7 pounds. The process for making this extrudate includes: (a) providing a hydrotalcite compound; (b) heating said compound for less than two seconds to one or more temperatures above about 482.degree. C. (900.degree. F.); (c) cooling said heated compound; (d) collecting said cooled compound; (e) forming said compound into an extrudate; and (f) reactivating said extrudate by heating to one or more temperatures above about 400.degree. C. (752.degree. F.) for about 20 minutes or more. Further strength improvements are achieved by exposing these extrudates to steam for at least about 8 hours prior to step (f).

Abstract: Back reactions of dissolved alumina from a high caustic-lime digest of anorthosite and other alumina-containing siliceous materials can be eliminated or mitigated by control of particle size of digestible material; and time and temperature of separation of the alumina-bearing liquid from the solid residues. In one embodiment the back reaction is further controlled by adjustment of the caustic concentration of the digest effluent.