In cooperation with the Ministry of Research and Technology we investigated the influence of hydroxylapatite (HAP) added to the backfill material of a radioactive waste disposal located in a salt dome. The time dependence of the sorption and precipitation of radionuclides has been studied in three different praxisrelevant salt brines under variation of temperature and pH-value.
Performing batch experiments uranium and thorium phosphates were precipitated from UO2(NO3)2 and Th(NO3)4 solutions at 75°C, the amounts of the relevant actinide compounds also exceeding that of HAP. The isolated precipitates were investigated by use of X-ray-powder-diffractometry and SEM. For the various uranium systems two mineral phases were obtained. From solution II and also from Q-brine the mineral saléeite Mg(UO2)2 (PO4)2 · 9H2O was formed. From solution III meta-autunite Ca(UO2)2(PO4)2 · 6H2O, a dehydration product of autunite, was precipitated.