EUROPIUM RECOVERY BY PHOTOCHEMICAL REDUCTION FROM Eu AND Eu–Gd CHLORIDE SOLUTIONS

Abstract

The recovery of europium in aqueous chloride solution by photochemical reduction/precipitation was evaluated in the presence of sulfate ions and a radical scavenger. A commercial low-pressure mercury lamp with an emission peak at 253.7 nm was used as an irradiation source. The influencing factors were investigated in detail with a pure europium (III) chloride solution and then applied to a solution containing a Gd/Eu molar ratio of 27. Europium recovery was shown to increase with an increase in SO₄ ²⁻/Eu molar ratio up to 7, which corresponds to a stoichiometric excess of 600%. Similarly, high scavenger requirements (formic acid/Eu ratio of 500) were needed to achieve high yields. Faster reaction rate in the presence of formic acid, as compared with 2-propanol (2 and 15 hr, respectively, at 99% Eu recovery), used as scavengers, was observed. This was related to the photoactivation of formic acid, demonstrated by a strong absorption in the near-UV region, not observed with 2-propanol, and a ready drop of the solution Eh. Measurements of redox potential indicated the reducing character in the formic acid system. This reducing character, that was not observed with 2-propanol, increases with the irradiation at 253.7 nm. The increase in rare earth concentration led to either Eu(III) precipitation prior to irradiation, in pure Eu solutions, or Eu–Gd coprecipitation, in multicomponent solutions. Europium recovery reached 99% when the experiments were carried out with pure, dilute europium chloride solutions. High yields could not be achieved in the presence of high gadolinium concentration, owing to the Eu–Gd coprecipitation.

Keywords:

• Europium
• Europium reduction
• Photochemical reduction

ACKNOWLEDGMENTS

The authors would like to thank “INB—Industrias Nucleares do Brasil S.A.” for supplying the sample and the technical support of the CDTN chemical laboratory, specially Eugênio M. Oliveira, José dos Santos J. Pereira, Liliane P. Tavares, Luiz Carlos da Silva, and Marcos A. Evangelista. V. Ciminelli thanks the sponsorship of the Brazilian Research Council-CNPq.