The mechanism of the sodalite-to-cancrinite phase transformation in synthetic spent Bayer liquor

The precipitation of zeolite, sodalite and cancrinite and subsequent phase transformations were investigated under a variety of conditions in sodium a luminate liquor. At sufficiently high SiO2 relative supersaturation, amorph ous sodium aluminosilicate and zeolite precipitated at temperatures as high as 160 degrees C. They subsequently transformed to sodalite and finally to cancrinite. Thus the sequence of the transformation of phases is: [Aluminosilicate species] --> Amorphous phase --> Zeolite (Linde A) --> Sod alite --> Cancrinite. It was found that sodalite did not transform to cancrinite in the absence o f a liquid medium. The transformation of sodalite to cancrinite was demonst rated to involve a solution-mediated mechanism with sodalite dissolution an d subsequent cancrinite precipitation. Neither the amorphous phase nor the zeolite phase precipitates at typical spent Bayer liquor SiO2 supersaturati on. (C) 1999 Elsevier Science B.V. All rights reserved.