A more comprehensive interpretation of distinct discontinuity in rare-earth element dissolution by HCl-HNO₃ from silicate rock powder

Abstract

Discussions are given to a step-wise discontinuity between Nd and Gd observed in acid extraction or dissolution of REE from silicate rock powder. It is concluded that, aside from polymorphism of REE sesquioxides, the change of hydration number from 9 to 8 in the primary hydration sphere surrounding lanthanide cations is a significant parameter responsible for the observed fact, although attention has been paid only to effect of polymorphism of sesquioxides of REE in the previous communication. There appears to be a parallel relationship between these two parameters.