Separation and Purification of some Lanthanides from Aqueous Solution using Continuous Counter-Current Technique

Abstract

This work has been carried out to investigate the separation of some lanthanides from Egyptian monazite sand using solvent extraction technique. The ore was opened using the usual alkaline digestion method. Rare earths were extracted from aqueous solution usingbis(2,4,4-trimethyl-pentyl) monothiophosphinic acid, commonly known as Cyanex 302, in kerosene. The various parameters affecting on the extraction of La3+, Nd3+, Sm3+, Eu3+ and Gd3+ were studied in detail for each element, such asthe effect of shaking time, PH, metal ion concentrations, extractant concentrations, nitrate ions, phase ratio and temperature. The results obtained show that ten minutes is quite sufficient for the extraction equilibrium of the investigated elements with pH = 3 as the best pH for extraction. Nitrate ions slightly decrease the extraction percent. As the organic:aqueous phase ratio increases the [Ln (III)]org increases. Extraction percent increases with increasing the extractant concentrate and the metals concentrate have a reverse effect on [Ln (III)]org in high concentration range. The extraction of the investigated elements is endothermic with an increase in the random nature of the species involved. Stripping investigations using different stripping agents indicated that nitric acid is the best strippant for all the investigated elements. Based on bench scale results, a continuous counter-current extraction flow sheet was developed and tested using a 16 stage horizontal type mixer-settler.