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 aluminate liquor. At sufficiently high SiO2 relative supersaturation, amorphous 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) --> Sodalite --> Cancrinite. It was found that sodalite did not transform to cancrinite in the absence of a liquid medium. The transformation of sodalite to cancrinite was demonstrated to involve a solution-mediated mechanism with sodalite dissolution and subsequent cancrinite precipitation. Neither the amorphous phase nor the zeolite phase precipitates at typical spent Bayer liquor SiO2 supersaturation. (C) 1999 Elsevier Science B.V. All rights reserved.