Continuous ion exchange processes for separating rare earth elements

A process for separating rare earth metals comprising:

• a) receiving a purified feed solution comprising a mixture of cations of two or more rare earth metals, wherein each of the two or more rare earth metals is selected from the group consisting of the elements having atomic numbers 57-71, scandium (atomic no. 21), and yttrium (atomic no. 39), and wherein the purified feed solution is substantially free of non-rare earth elements;
• b) loading the cations contained in the purified feed solution onto a first cation resin;
• c) eluting the cations loaded onto the first cation resin with a first eluent to form one or more eluates of rare earth metals complexed with an anion of a chelating agent, wherein the chelating agent is a salt solution of an organic acid;
• d) separately providing each of the one or more eluates as a feed input to a respective first instance of a continuous ion exchange process implemented on a continuous ion exchange device, wherein the continuous ion exchange process comprises:
• i) continuously contacting the feed input over a second cation resin by passing the feed input countercurrent to the second cation resin in a series of columns, wherein the second cation resin has been acidified and rinsed;
• ii) continuously producing a raffinate stream comprising cations of a first set of one or more faster-eluting rare earth metals;
• iii) continuously introducing a pure chelating second eluent free of rare earth metals or cations thereof in countercurrent fashion over the second cation resin, wherein the second eluent desorbs rare earth metals present in the feed input to produce an extract stream comprising cations of a second set of one or more slower-eluting rare earth metals;
• iv) continuously recovering the second cation resin for reuse in a subsequent cycle of the continuous ion exchange process, wherein said second cation resin is recycled via an acidification process;
• and
• v) and recycling a non-excess portion of the raffinate stream and a non-excess portion of the extract stream;
• e) providing an excess portion of the raffinate stream produced by the first instance of the continuous ion exchange process as the feed input to a second instance of the continuous ion exchange process;
• f) providing an excess portion of the extract stream produced by the first instance of the continuous ion exchange process as the feed input to a third instance of the continuous ion exchange process;
• and
• g) providing each of the excess portion of the raffinate stream and the excess portion of the extract stream produced by each of the second and third instances of the continuous ion exchange process as the feed input to respective additional instances of the continuous ion exchange process until each of the raffinate and extract streams produced by such additional instances consists essentially of cations of a single rare earth metal or cations of a third set of rare earth metals.