Recovery of lanthanides and yttrium from red mud by selective leaching

This study presents a rapid and selective method for the recovery of lanthanides and yttrium, existing in economically interesting concentrations, from red mud, the byproduct of the alumina production. The leaching process is based on the extraction of these elements with diluted nitric acid from red mud under moderate conditions and without using any preliminary treatment. Several parameters such as leaching agents, contact time, temperature, pressure and solid to liquid ratio were investigated in order to achieve an optimum recovery. The process followed here was selected taking into account its efficiency for the selective recovery of yttrium and lanthanides, but also its suitability for the subsequent liquid-liquid extraction of the leaching solution for the separation of the individual lanthanides. The achieved recovery percentages were for Y about 90%, for the investigated heavy lanthanides (Dy, Er, Yb) up to 70%, for the middle ones (Nd, Sm, Eu, Gd) up to 50% and for the group of light lanthanides (La, Ce, Pr) up to 30%. Most of the main elements of the red mud and especially iron are hardly dissolved by this leaching process, leading to an interference free determination of the lanthanides and yttrium in the leachate by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).