Solvent extraction behavior of metal ions and selective separation Sc3+ in phosphoric acid medium using P204

Acid leaching-solvent extraction is an effective process to extract scandium from scandium-bearing resources. This study was aimed to investigate the extraction behavior of metal ions, including Sc3+, Fe3+, Al3+and Ca2+, in phosphoric acid medium using P204. More than 95% of scandium was selectively extracted under the conditions of pH value of 1.5–1.8, aqueous-organic ratio of 3 and oscillation for 15 min. The impurity elements like Fe3+, Al3+ and Ca2+, were separated via the solvent extraction process using P204 (e.g., separation coefficient of scandium to iron is 298). In stripping process, the majority of co-extracted metal ions can be removed from the organic phase with hydrochloric acid solution. The scandium-bearing organic phase was stripped with 4 mol/L NaOH, wherein the recovery of scandium attained about 95% while that of the co-extracted iron and aluminum were only 3.1% and 1.2%, respectively. It was also confirmed that both P204 and H3PO4 played roles in extraction reaction, and the desirable extraction of scandium in P204 was attributed to the ion exchange between hydrogen ion of PO(OH) and Sc3+ on acidic condition (pH = 0.4–1.5). Impurity elements (Fe3+ and Al3+) also reacted with phosphate anion to form hydrophilic ions, and in turn result in selective extraction of scandium in phosphoric acid leachate using P204.