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°C. They subsequently transformed to sodalite and finally to cancrinite. Thus the sequence of the transformation of phases is:\ud \ud [Aluminosilicate species] → Amorphous phase → Zeolite (Linde A) → Sodalite → Cancrinite\ud \ud 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