Useful method for separating light rare earth elements and heavy rare earth elements

A method for obtaining a light rare earth element-rich inclusion and a heavy rare earth element-rich inclusion from a workpiece containing a light rare earth element and a heavy rare earth element in order to separate the two, characterized by including at least:

• (1) a step of obtaining, from a workpiece containing a light rare earth element and a heavy rare earth element, a composite oxide of the light rare earth element and the heavy rare earth element or a mixture of an oxide of the light rare earth element and an oxide of the heavy rare earth element;
• (2) a step of dissolving the obtained composite oxide of the light rare earth element and the heavy rare earth element or the mixture of an oxide of the light rare earth element and an oxide of the heavy rare earth element in hydrochloric acid and/or nitric acid;
• (3) a step of adding a precipitant to the obtained solution to give a precipitate;
• (4) a step of calcining the obtained precipitate;
• (5) a step of adding the obtained calcine in an amount of 1.1 times to 3.0 times the upper solubility limit to hydrochloric acid and/or nitric acid having a concentration of 0.7 mol/L or more to give a solution and a residue;
• and
• (6) a step of separating the obtained solution and residue, thereby giving the solution as a light rare earth element-rich inclusion and the residue as a heavy rare earth element-rich inclusion, wherein the term “rich” means that the content ratio of the concerned rare earth element to the other rare earth element is higher than the content ratio in the workpiece.