A hydrometallurgical method of energy saving type for separation of rare earth elements from rare earth polishing powder wastes with middle fraction of ceria

This study described a hydrometallurgical method to investigate the separation of rare earth elements (REEs) from rare earth polishing powder wastes (REPPWs) containing large amounts of rare earth oxides with a major phase of CeO2 and minor phases of La2O3, Pr2O3, and Nd2O3 using a process devised by the authors. The suggested approach consisted of five processes: the synthesis of NaRE(SO4)2·xH2O from rare earth oxides in Na2SO4-H2SO4-H2O solutions (Process 1), the conversion of NaRE(SO4)2·xH2O into RE(OH)3 using NaOH (Process 2), and the oxidation of Ce(OH)3 into Ce(OH)4 using air with O2 injection (Process 3), followed by Processes 4 and 5 for separation of REEs by acid leaching using HCl and H2SO4, respectively. To confirm the high yield of NaRE(SO4)2·xH2O in Process 1, experiments were carried out under various Na2SO4 concentrations (0.4–2.5 mol/L), sulfuric acid concentrations (6–14 mol/L), and reaction temperatures (95–125 °C). In addition, the effect of the pH value on the separation of Ce(OH)4 in HCl-H2O solutions with Ce(OH)4, La-, Pr-, and Nd(OH)3 in Process 4 was also investigated. On the basis of above results, the possibility of effective separation of REEs from REPPWs could be confirmed.

Graphical AbstractSchematic flow diagram for separation of rare earth elements from rare earth polishing powder wastes via a devised hydrometallurgical processFigure optionsDownload as PowerPoint slide