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 DyCl 3 is converted into DyOCl (without causing such conversion of NdCl 3 ) in dry oxygen with 6.5 ppm of H 2 O (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 H 2 O content, although this difference is usually hidden in the presence of atmospheric humidity. Under these conditions, high separability of a NdCl 3 and DyCl 3 mixture was demonstrated.