Calcification-Carbonation Method for Bayer Red Mud Treatment: Carbonation Performance of Hydrogarnets

Hydrogarnets are vital intermediate products in the calcification- carbonation method, which is designed for Bayer red mud treatment. Their carbonation performance greatly depends on SiO₂ substitution. In this study, different SiO₂-substituted hydrogarnets were synthesized and characterized. Then, batch experiments were performed to evaluate the potential effects of important parameters such as CO₂ pressure, and SiO₂ substitution degree (x) on the carbonation process. The SiO₂ substitution degrees of the hydrogarnets synthesized at 60, 120, 180, and 240°C were 0.27, 0.36, 0.70, and 0.73, respectively. As the SiO₂ substitution degree increased, the hydrogarnet carbonation extents gradually declined. With an increase in CO₂ pressure, the hydrogarnet carbonation percentages increased gradually and rose from 80.33% to 98.19% within 120 min. The phases detected in the carbonized products were strip-like aragonite as well as some calcite; the Al-rich and Si-rich phases in the carbonized products were amorphous.