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 CeO_2 and minor phases of La_2O_3,Pr_2O_3,and Nd_2O_3 using a process devised by the authors.The suggested approach consisted of five processes:the synthesis of NaR E(SO_4)_2·xH_2O from rare earth oxides in Na_2SO_4-H_2SO_4-H_2 O solutions(Process 1),the conversion of NaR E(SO_4)_2·xH_2O into RE(OH)_3 using NaO H(Process 2),and the oxidation of Ce(OH)_3 into Ce(OH)_4 using air with O_2 injection(Process 3),followed by Processes 4 and 5 for separation of REEs by acid leaching using HCl and H_2SO_4,respectively.To confirm the high yield of NaR E(SO_4)_2·xH_2O in Process 1,experiments were carried out under various Na_2SO_4 concentrations(0.4–2.5 mol/L),sulfuric acid concentrations(6–14 mol/L),and reaction temperatures(95–125 oC).In addition,the effect of the pH value on the separation of Ce(OH)_4 in HCl-H_2 O 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. This study describes a 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 CeO 2 and minor phases of La 2 O 3, Pr 2 O 3, and Nd 2 O 3 using a process devised by the authors. Suggested suggestions consisted of five processes: the synthesis of NaR E (SO 4) 2 · xH 2 O from rare earth oxides in Na 2 SO 4 -H 2 SO 4 -H 2 O solutions (Process 1), the conversion of NaR E (SO 4 ) _2 · xH_2O into RE (OH) _3 using NaO H (Process 2), and the oxidation of Ce (OH) _3 into Ce (OH) _4 using air with O_2 injection (Process 3), followed by Processes 4 and 5 for separation of REEs by acid leaching using HCl and H 2 SO 4, respectively. To confirm the high yield of NaR E (SO 4) 2 · xH 2 O in Process 1, experiments were carried out under various Na 2 SO 4 concentrations (0.4-2.5 mol / L), sulfuric acid concentrations (6-14 mol / L), and reaction temperatures (95-125 oC) .In addition, the effect of the pH value on the separation of Ce (OH) _4 in HCl-H_2 O 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.