Smith, P., Wingate, C. and De Silva, L.

Bayer sodalite is the main form of desilication product. Its zeolite type cage structure contains included ions, and the leaching of these ions is a possible way to recover “fixed soda”. The ions leach through the windows of the sodalite cage structure and thus recovery should be restricted to those anions that are smaller than the cage openings. This paper examines the mobility of different ions within the structure of sodalite by water washing and re-digestion of the sodalite in water.

Whether dominated by sulphate, carbonate or hydroxide, soda leaches from sodalite with cold water washing only sparingly, and to a maximum of ~15% under a “standard” washing procedure used. When re-digested in water the sodalites leached soda more extensively. In particular all included soda can be removed from a hydroxide dominated sodalite by re-digestion and washing. Both “standard” washing and enhanced washing by re-digestion showed evidence of carbonate leaching despite the carbonate ion being too large to pass through the sodalite cage window. In addition, washed samples sometimes showed an imbalance of included soda and total included anions. This has led to the proposal that neutral CO2 forms from carbonate during washing, a portion of which can exit through the sodalite cage openings.