Studies on europium separation from a middle rare earth concentrate by in situ zinc reduction technique

Stability of europium(ii) in aqueous nitrate solutions

“…Ce 3+ (E 0 (Ce 4+ /Ce 3+ ) = +1.72 V) and Tb 3+ (E 0 (Tb 4+ /Tb 3+ ) = +3.10 V) can be oxidized to the +IV oxidation state, by which they are stabilized by an empty 4f subshell ([Xe] 4f 0 ) and by a halffilled 4f subshell ([Xe] 4f 7 ), respectively. Sm 3+ (E 0 (Sm 3+ /Sm 2+ ) = -1.55 V), Eu 3+ (E 0 (Eu 3+ /Eu 2+ ) = -0.34 V) and Yb 3+ (E 0 (Yb 3+ /Yb 2+ ) = -1.05 V) can be reduced to the +II oxidation state because of a stabilizing effect of a near-half filled ([Xe] 4f 6 ), a half-filled ([Xe] 4f 7 ) and a filled 4f subshell ([Xe] 4f 14 ), respectively. However, Sm 2+ and Yb 2+ in aqueous solutions tend to be 4 very short-lived because of their high oxygen-sensitivity and their high tendency to reduce water.…”

“…Eu 3+ can be selectively reduced using chemical, electrochemical or photochemical techniques. [9][10][11][12][13][14][15] Oxidizing agents, such as dissolved oxygen (E 0 (O 2 /H 2 O) = +1.23 V), H + (E 0 (H + / H 2 ) = 0.00 V) or nitrate anions (E 0 (NO 3 -/NO) = +0.95 V, in presence of H + ), are usually avoided because of the high possibility for back-oxidation of Eu 2+ . Consequently, reduction of Eu 3+ is usually performed in media that are insensitive to reducing conditions, most often containing chlorides.…”

“…Consequently, reduction of Eu 3+ is usually performed in media that are insensitive to reducing conditions, most often containing chlorides. 9,11,[14][15][16][17][18][19] Nevertheless, our research group recently observed that Eu 3+ could also be successfully reduced in nitrate media at quasi-neutral pH. 20,21 Reducibility of Eu 3+ in aqueous nitrate media opens new perspectives to isolate europium from other trivalent lanthanides.…”

O‐carboxymethyl chitosan entrapped by silica: preparation and adsorption behaviour toward neodymium (III) ions

“…Separation of REEs has become a bottleneck for their application since they have similar chemical properties . Traditional REEs separation processes include chemical precipitation, oxidation‐reduction,, adsorption, and solvent extraction . Among them, adsorption is a green technology for the separation of metal ions, and is a simple process, which can be performed in a single‐stage operation within a packed column and is environmentally benign, not using any organic solvents.…”

Study on separation of Eu(II) from trivalent rare earths via electro-reduction and ion exchange

“…However, in contrast to other rare earths, Eu(III) can be relatively easily reduced to divalent state (E 0 = −0.43 V). Chemical reduction of Eu(III) with zinc powder followed by Eu(II) sulfate precipitation [2] is preferred way of Eu separation at an industrial scale. However, the presence of zinc would complicate Eu(II) separation by means of ion exchange or solvent extraction.…”