THE RECOVERY OF RARE-EARTH-OXIDES FROM A PHOSPHORIC-ACID BY-PRODUCT .3. THE SEPARATION OF THE MIDDLE AND LIGHT RARE-EARTH FRACTIONS AND THEPREPARATION OF PURE EUROPIUM OXIDE

The development and operation of a continuous solvent extraction proce ss for the separation of the middle (Sm, Eu, Gd, Tb) and light rare ea rth fractions (La, Ce, Pr, Nd) from a nitrate feed liquor is described . The process consists of extraction of the middle rare earths into a 15 vol% solution of D2EHPA in Shellsol AB in 8 counter-current stages, followed by scrubbing with 1 M nitric acid in 2-4 stages, and strippi ng with 1.5 M hydrochloric acid in 6-8 stages. Residual rare earth val ues in the organic phase (mainly Dy, with some Tb and Gd) were removed in a secondary stripping circuit using 2.5 M hydrochloric acid in 4 s tages. More than 1000 l of feed liquor were processed in two continuou s counter-current trials lasting a total of 630 h. From a feed contain ing Sm 3.5, Gd 2.4, Eu 0.8 and Nd 20 g l(-1) (together with 4-8 g l(-1 ) each of the lighter rare earths), strip liquors containing Sm 35, Gd 20 and Eu 8 g l(-1) were obtained, with neodymium (5 g l(-1)) as the main impurity. Recoveries of the middle rare earths to the strip liquo rs were high (95-100%), whereas losses of the light rare earths were l ow (0-4%). Addition of oxalic acid to the strip liquors, followed by c alcination of the precipitated oxalate, gave a middle rare earth oxide containing 45% Sm2O3, 29% Gd2O3, 13% Eu2O3 and 6% Nd2O3. This oxide w as dissolved in acetic acid and electrolysed in 1 M potassium citrate solution, using a mercury cathode and a platinum anode, to give a euro pium amalgam containing a small amount of samarium (Eu:Sm approximate to 66:1). The amalgam was treated with acetic acid, and the resulting acetate solution was again electrolysed to give a purified amalgam fro m which was recovered a final europium oxide product containing only t races of other rare earths (< 25 mg kg(-1) Sm, < 6 mg kg(-1) Nd and < 3 mg kg(-1) each of Gd, Pr, Ce and La).