Separation of Ce, La and Nd in rare earth hydroxide (REOH) by oxidation with potassium permanganate and precipitation

Abstract

The present work describes the development of an efficient and relatively simple process to obtain high grade Ce(OH)4 from REOH (Rare earth hydroxide). The Rare earth hydroxide was obtained through base digestion of monazite. The steps investigated in the process for obtaining Ce(OH)4 were: (i) dissolution RE hydroxide (REOH) with HNO3 and oxidation of Ce+3 to Ce+4, (ii) selective precipitation of Ce(OH)4 with Na2CO3, (iii) selective precipitation of Nd(OH)3 with ammonium hydroxide (iv) precipitation of La with oxalic acid. The main variables affecting the cerium oxidation were: the ratio of the KMnO4 / REOH, temperature and oxidation time. A ratio of 1.25/10 of KMnO4 / REOH was necessary for full cerium recovery. The recovery of cerium increases as temperature and oxidation time rises, the purity of the product Ce(OH)4 at the pH above 4. The process conditions were achieved in the use of 1.25/10, KMnO4/REOH ratio, at the 120 °C and the oxidation time of 75 minutes. The composition of the final product Ce(OH)4 was 97.98 wt.% Ce(OH)4, in a process yielding a recovery of Ce greater than 93%, were obtained. The composition of the final product Nd(OH)3 was 37 wt.% Nd(OH)3, in a process yielding a recovery of Nd greater than 98%, were obtained. The composition of the final product La2(C2O4)3 was 90 wt.% La2(C2O4)3, in a process yielding a recovery of La greater than 93%, were obtained. The oxidation of Ce3+ to Ce4+ using KMnO4 follows first order reaction. The value of reaction rate constant of Ce was 0.0291 minutes−1.