[en] Trivalent europium can be reduced selectively to the divalent state by subjecting a mixed solution containing Eu³⁺ and other rare earth ions to electrolytic reduction on a solid conductive cathode in a separated cathode chamber. The pH must be held within the pH 3-6 range. At higher pH, rare earth hydroxides separate, whereas at lower pH, hydrogen is evolved, whereupon the Eu³⁺ reduction current decreases. At a suitable current density, which depends on the concentration of Eu³⁺ in the solution and on the flow rate of the solution in the vicinity of the cathode, Eu solely is reduced and virtually no hydrogen evolves. The re-oxidation of Eu²⁺ by hydrogen ions is slower than during the reduction with zinc in acid medium. As the electrolysis proceeds, the concentration of Eu³⁺ decreases as does the limiting current density of Eu³⁺ reduction, and hydrogen starts to evolve. The pH must therefore be controlled or else the current density must be reduced during the electrolysis. Chloride solutions are suitable for the process whereas nitrate and sulfate solutions cannot be used. The active surface of the cathode consists of graphite, alloys, oxides or elements of Cu, Ag, Au, Pt, Ir, Ru, Rh, Pd, Co or Ni. Diaphragm or membrane electrolyzers with vertical electrode arrangement suit well. (P.A.)