CATION EXCHANGE IN FELDSPATHOID FORMED IN CARBONATE-CONTAINING BAYER LIQUORS

The application of bauxite residue has been a long-lasting problem in the aluminium refinery industry using the Bayer-process. Two common feldspathoids in desilication products, sodalite and cancrinite, have high theoretical cation and anion exchange capacity. This implied their potential to serve as possible nutrient carriers and nutrient reservoirs. In this study, sodium feldspathoids were synthesized at 100 and 230 °C in carbonate-containing Bayer liquors and their cation exchange behaviours were studied. Four cations were selected for the exchange experiment at 80 °C: K+, NH4+, Ca2+, and Mg2+. The synthesized and cation exchanged feldspathoids were analyzed with XRD, FTIR, TGA-DSC, SEM, and ICP-OES. The obtained feldspathoid, Bayer-SOD, at 100 °C showed similar features as an intermediate phase between sodalite and cancrinite, while a cancrinite-like material, Bayer-CAN, was found at 230 °C. Bayer-SOD generally has higher cation exchange capacity up to 500 cmolc/kg than Bayer-CAN and both of them have the following cation exchange order: K+> NH4+ > Mg2+ > Ca2+. Tthe unit cells of K+, NH4+, and Ca2+ exchanged Bayer-SOD and Baer-CAN were expanded. After the cation exchange, parts or all of the carbonate were released from the structure and replaced by water molecules.