The application of biodiesel and sec-octylphenoxyacetic acid (CA-12) for the yttrium separation

Soybean oil methyl ester (SBME), better known as biodiesel was used as diluent for the rare earth ions (RE (III))(La (III), Pr (III), Nd (III), Eu (III), Gd (III), Er (III), Yb (III), Lu (III) and Y (III)) extraction in the presence of sec-octylphenoxyacetic acid (CA-12) in this paper. The effects of extractant concentration, the equilibrium pH of aqueous phase and temperature etc. were examined in the chloride medium. The slope analysis technique was used to investigate the extraction mechanism, and it was found that the extraction mechanism was a cation-exchange mechanism in CA-12-SBME system. Y (III) extraction in the nitrate medium was also investigated, and the extraction mechanism in the nitrate medium was similar to the chloride medium. The separation factors (β) amongst RE (III) pairs have also been evaluated. It showed that Y (III) was the most difficult RE (III) to be extracted in the CA-12-SBME system, implying CA-12-SBME system could be employed to extract and separate Y (III). To examine the suitability of this extraction system, a fractional extraction (4 stages for extraction and 2 stages for scrubbing) was studied in a real sample, and the percentage of Y (III) in the raffinate was enhanced from 30.5% to 76.9% when the recovery of Y (III) was 36.5%. The results were consistent with the data calculated by Xu model, which were 75.0% and 40.0% respectively. This implied the purity of Y (III) and the percentage of recovery could be improved by increasing the stages for extraction and scrubbing.

Research Highlights
► A systematic investigation was carried out by using SBME as diluent for the RE(III) extraction in the presence of CA-12.
► Y(III) was the most difficult RE(III) to be extracted in the CA-12-SBME extraction system.
► A fractional extraction (4 stages for extraction and 2 stages for scrubbing) was studied in a real sample.