Rare Earth Recovery from Indian Bauxite Residue: Approach Towards Valorization

Bauxite residue or red mud is the alkaline waste generated during the production of alumina through Bayer process. Per year almost 170 million tonnes of bauxite residue will be generated adding to the 4 billion tonnes stockpiled globally. India holds the fifth position globally by generating ~10 million tonnes annually.  Hindalco, Nalco, Vedanta and Balco are the major alumina producers in India. There are no large volumes applications of the bauxite residue generated other than some minor uses in construction products and cement industry. One of the promising applications of bauxite residue is that it can serve as a secondary resource for many metal ions. It contains oxides of major components like iron, aluminium, calcium and titanium along with minor components like oxides of Rare earth elements. The composition of red mud is highly regiocentric. Red mud samples were collected from four different major alumina producers in India, Hindalco, Nalco and Vedanta. The study aimed to develop a selective recovery process for rare earth oxides from various Indian red mud samples. The first step in the developed process is the sulphation, which is done by heating the dried red mud and concentrated H₂SO₄ at 120 ºC and is then roasted at 700 ºC, the roasted sample is then leached with distilled water at room temp. Calcium sulphate which has low water solubility also will remain in the residue. The sample was then leached with distilled water. The selective precipitations of REEs were tested at different pH using various precipitating agents like NaOH and NH₃. The developed process aims at environment remediation while reducing the reliability on natural resources for mining of valuable metals. The chemical composition precipitated rare earth oxide was analyzed using ICP, UV and EDX. The morphological characterization was done using SEM, and XRD.