Book Description

Cerium- and 144 promethium-147, accompanied by rare earths resulting from fission or decay can be removed from Purex 1WW in>90% yield as an insoluble, crystalline sodium-rare earth double sulfate. Precipitation is initiated by a one-to-three hour equilibration at 90 deg C and centrifugation at 90 deg C to take advantage of the lower solubility of the double sulfate salt at a higher temperature. The sulfate concentration should be one molar and the solution pH at the time of precipitation should be 0.5 to 1.5. The addition of tartrate ion to complex the iron allows the use of a higher pH and sulfate concentration, gives a more complete separation from iron, and a quantitative recovery of the rare earths. The double sulfate precipitate can be dissolved in dilute nitric acid or converted to the carbonate and then dissolved to yield a solution for further processing. The double sulfate precipitation of the rare earths, with tartrate added, gives a good separation from impurities. One-cycle decontamination factors of 150 for Zr-Nb and 1100 for Ru-Rh have been achieved in laboratory tests. Tests in the Purex head-end equipment with up to twomegacurie batches of cerium have corroborated the laboratory results. Decontamination factors of 70 for iron, 10 for zirconium, 20 for niobium and 25 for ruthenium have been obtained. It was found wise to limit the batch size because decay heat leads to partial calcination in the centrifuge and to difficulty in redissolution. (auth).