Application of annular centrifugal contactors in the extraction flowsheet for producing high purity yttrium

Compared with mixer-settlers applied widely in the hydrometallurgical industry of rare earths (RE), centrifugal contactors have several advantages such as low hold-up volume, excellent phase separation, high mass transfer efficiency, compact and short pieces of equipment, etc., and have been successfully used in some industrial fields. Yttrium (Y) is an important element and in great demand in many industries. For a variety of uses in many specialized areas, the high purity Y is often required. However, the separation and purification of Y by solvent extraction from RE mixture is widely known to be difficult due to their similar chemical properties. This paper studied both the separation factors of RE ions in the 32% HA (naphthenic acid) − 20% iso-octylalcohol–48% kerosene–RECl system and the distribution ratios of RE ions in the 32% HEHEHP (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) − 68% kerosene–RECl system. Based on these studies, an extraction flowsheet for producing high purity Y with HA and HEHEHP as extractants has been developed. Both the bench scale test and the pilot-plant test of the flowsheet have been performed with ϕ20 mm and ϕ120 mm centrifugal contactors respectively. It is shown that Y₂O₃ with 99.99% purity was obtained, and the total recovery of Y was about 95%.