A study on the photo-reductive precipitation rate of europium sulfate from rare earth mixture by addition of hydrogen peroxide

The influence of H₂O₂ on the photo-reductive precipitation of Eu³⁺ from a solution containing Sm³⁺, Eu³⁺ and Gd³⁺ was investigated. The solution contains isopropanol as a reduction agent, ammonium sulfate as a precipitation agent, and hydrogen peroxide as an acceleration agent of precipitation rate. A mercury lamp emitting a wavelength of 254 nm was used as a light source. Adding a small amount of H₂O₂ considerably increased the photo-reductive precipitation rate of Eu³⁺. OH radicals obtained from the photodecomposition of H₂O₂ oxidized isopropanol into the radical (CH₃)₂C’OH and the resulting radicals reduced Eu³⁺ rapidly. It was found that the organic radical has the ability to reduce only Eu³⁺ in the solution containing Sm³⁺, Eu³⁺ and Gd³⁺. The precipitation yields of Eu, Sm and Gd were about 99%, 10% and 4%, respectively. It was also found that the Sm and Gd were not photo-reduced and co-precipitated with Eu.