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 supergravity, 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. (c) 2022 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

Automated summary

In this study, a green method was developed to solidify and recover soluble sodium in red mud using a super-gravity process, effectively eliminating its high alkalinity. The process involved iron-slag melting separation to recover metallic iron and enrich sodium in a Na-rich slag, followed by selective solidification of sodium into anorthite and subsequent separation using supergravity. The recovery ratio of sodium in anorthite was up to 97.09%. The pH of both anorthite and residue products decreased, and the leaching rates of Na+ significantly decreased compared to red mud.