A green method for solidification and recovery of soluble sodium in red mud via super-gravity

Red mud produced in the Bayer process is an ultrafine solid waste containing various metallic elements, which is hazardous to the environment because of its high alkalinity caused by the soluble sodium (Na). In this study, a green method for efficiently solidification and recovery of soluble sodium to eliminate high alkalinity of red mud via super-gravity was developed. Iron-slag melting separation from red mud was firstly conducted at 1523 K, where the Fe was fully recovered into metallic iron and almost all the Na was enriched into the Na-rich slag. Subsequently, the Na was selectively solidified into a stable phase of anorthite at 1373–1323 K, all of which were efficiently separated from the Na-rich slag at 1323 K via super-gravity, where the recovery ratio of Na in anorthite was up to 97.09%. Compared to the red mud, the leaching rates of Na+ in the anorthite and residue were significantly decreased to 0.01% and 0.05%, and the pH of both products was decreased to 8.1–8.4. It was confirmed that the high soluble sodium in red mud was efficiently solidified and recovered into a stable phase of anorthite, and the high alkalinity was fully eliminated in both products which are environmentally friendly.