Extraction Of Rare Earth Elements With Mixtures Of Sec-octylphenoxyacetic Acid And Cyanex923, Cyanex925 In Hydrochloric Acid

Rare earth elements(REEs) have excellent magnetic, optical, and electrical properties, which have become a category of extremely important strategic resource. Solvent extraction is the main method for separation and purification of REEs. As a branch of solvent extraction, synergistic extraction(extraction with two more kinds of extraction agents) has been successfully widely applied to the isolation, purification, and analysis of various elements, including nuclear fuel, rare metals and transition metals, and other aspects of hydrometallurgy. Within this research field, current work mainly focuses on the selection of new extraction systems, synergistic extraction mechanism and structures of the compounds formed in the synergetic extraction process.In this study,an acidic extractant, sec-octylphenoxyacetic acid(CA12) and its mixtures with two organic phosphine oxide extractants, Cyanex923 and Cyanex 925, have been employed as the extraction solvent extraction agent of REEs. The synergistic extraction effects and mechanism of REEs CA12+Cyanex923, CA12+Cyanex 925, are investigated in detail.Firstly, the extraction behaviours of REEs by CA12, Cyanex923, Cyanex925 are respectively studied with La(III), Nd(III), Eu(III), Gd(III), Er(III) and Y(III) as representatives. The results showed that the extraction of rare earth elements by CA12 is greatly affected by the aqueous phase acidity. CA12(H2A2) molecules are involved in the formation of the extracted complex with a ratio of 2:1 to RE(III). In addition, CA12 can be used for the separation of Y from light REEs. Extraction mechanisms of Cyanex923 and Cyanex925 are similar and the REs are extracted as complexs of RECl3·2.5B(Cyanex923) and RECl3·B(Cyanex925), respectively. Secondly, the extraction of CA12+Cyanex923 system for rare earth elements are studied. It is found that synergistic extraction effects decrease with the decrease of ionic radius of the rare earth elements. By adjusting the pH value, Cl?concentration and other experimental factors, the synergistic extraction effects and mechanisms of CA12+Cyanex923 and CA12+Cyanex925 to La are discussed. The organic phosphine oxide molecule is able to replace organic carboxylic acid molecules, forming a more complex molecule LaA3·nB,(Cyanex923, n=3; Cyanex925, n=1). According to the thermodynamic analysis, the synergistic extraction reactions of La3+ with both CA12+Cyanex923 and CA12+Cyanex925 systems are endothermic processes.