Effect of iron minerals on formation of hydroandradite during alkali-thermal process

The hydroandradite (HA) is an efficient and ideal desilication product to deal with the bauxite and red mud based on the alkali-thermal process, while the selection of iron source is crucial for the HA generation. This work investigates the effects of various natural iron minerals on the alkali-thermal formation HA in aluminate solution by comparing with synthetic sodium ferrate. The Gibbs free energy changes of HA formation with different iron oxides were calculated based on the complex silicate theory, and the preferential conversion order for HA formation was obtained thermodynamically. The solubility data of various iron minerals in aluminate solution were determined and correlated by the Apelblat model. The contribution order of iron minerals for HA formation was obtained, and the goethite is the best alternative to replace sodium ferrite by comparing to hematite and magnetite. The phase transformation of HA is above 80% in the presence of goethite, and the alkali content in reaction product is as low as 0.20%. Moreover, the effect mechanism of goethite on HA formation was discussed and established.