Removal of Trace Aluminum Impurity for High-Purity GdCl₃ Preparation using an Amine-Group-Functionalized Ionic Liquid

Abstract

Aluminum, as an associated metal with rare-earth resources, is a common impurity in rare-earth separation products. In the traditional P507-kerosene-HCl system, tremendous aluminum impurity (8875 mg/L herein) is often enriched in GdCl 3 solutions because of the similar extraction sequence during rare-earth separation. In this work, a new amine-groupfunctionalized ionic liquid (IL) was developed to remove trace aluminum impurity from high-purity GdCl 3 solutions, overcoming the drawbacks of strong hydrophilicity and complicated compositions of the organic phase, as well as other impurities introduced and tremendous saline wastewater produced inevitably. Methyltrioctylammonium hydroxide (N1888OH), instead of the water soluble ammonium hydroxide (NH 4 OH), was used to dissociate the dimer of sec-octylphenoxy acetic acid (CA12) and synthesize cation-and anion-bifunctionalized IL [N1888][CA12]. The separation factor of Al/Gd was as high as 36. The influences of pH, saltingout agent, extraction time, temperature, and stripping efficiency on the extraction efficiency were evaluated. The result showed that high-purity GdCl 3 solution was obtained with low aluminum impurity of 10 ppm after five-stage countercurrent extraction. Due to the weak interaction between the metal and IL, very dilute HCl solution (0.07 mol/L) and NaOH solution (0.07 mol/L) were in favor of metal stripping and IL regeneration.

Experimental and Theoretical Studies on Selective Separation of Nd from La/Ce/Pr Using [Omim][DOP]

“…Dai et al synthesized several ILs like trihexyl­(tetradecyl)­phosphonium di­(2-ethylhexyl)­phosphate ([THTP]­[DEHP]) for extraction separation of Nd­(III) in nitrate media with the Nd­(III) loading of 0.0007 mol·L –1 , but the high viscosity of the quaternary phosphine-based ILs required diluents. Our group has been engaged in the research on selective separation and purification of REEs − and found that the Nd­(III) loading of phosphate IL [N 1,1, n ,H ]­[DEHP] ( n = 8, 10, 12) could reach 0.008 mol·L –1 , and the β of Nd/Pr was 3.4, which is higher than 2 of the conventional industrial system. However, the dosage of [N 1,1, n ,H ]­[DEHP] ( n = 8, 10, 12) was high during the extraction process, and the β was not high enough for selective separation of Nd from LREEs.…”