Hidden Nature of the Conversion Reaction from Rare Earth Chloride to Oxychloride and the Application to Novel Separation

A mutual separation process that uses rare‐earth oxychloride in a proactive way was developed. In particular, the heat‐treatment conditions under which DyCl3 is converted into DyOCl (without causing such conversion of NdCl3) in dry oxygen with 6.5 ppm of H2O (dew point: 209 K) at a relatively low temperature (around 573 K) were determined. A difference between conversion reactions of the two kinds of rare‐earth chlorides into rare‐earth oxychlorides appeared in the case of an oxygen atmosphere with ultra‐low H2O content, although this difference is usually hidden in the presence of atmospheric humidity. Under these conditions, high separability of a NdCl3 and DyCl3 mixture was demonstrated. A mutual separation process that uses rare earth oxychloride in a proactive way is developed. The heat treatment conditions under which DyCl3 can be converted into DyOCl without causing such conversion of NdCl3 in dry oxygen with 6.5 ppm of H2O at around 573 K. The DyOCl and NdCl3 mixture obtained dissolves into water, then NdCl3 solves into water and DyOCl remain as residue. After filtering, we can separate Nd solution and DyOCl residue.