Cesium sorption on studtite (UO 2 O 2 ·4H 2 O)

• Published in: Radiochimica acta Vol. 98; no. 8; pp. 479 - 483
• Main Authors: Giménez, Javier, Martínez-Lladó, Xavier, Rovira, Miquel, de Pablo, Joan, Casas, Ignasi, Sureda, Rosa, Martinez-Esparza, Aurora
• Format: Journal Article
• Language: English
• Published: 01.08.2010
• ISSN: 0033-8230
• DOI: 10.1524/ract.2010.1742

Abstract One of the mechanisms that may decrease the mobility of cesium released from spent fuel in a high level nuclear waste repository (HLNW) is its sorption onto uranyl-containing alteration phases formed on the spent fuel surface such as studtite (UO 2 O 2 ·4H 2 O). The results obtained in this work show that sorption is a very fast process; cesium in solution is sorbed in less than one hour at pH 5. Sorption as a function of initial concentration in solution was also studied between initial cesium concentrations ranging from 7.6×10 −9  mol dm −3 to 1.0×10 −3  mol dm −3 . The data have been modelled considering a Freundlich isotherm, with K F and n values of 10±1, and 1.4±0.1, respectively ( r 2 =0.998). Sorption is very dependent on ionic strength, suggesting that cesium sorbs onto studtite by forming an outer-sphere complex involving electrostatic interactions. Sorption is observed to be very low at acidic pH, while relatively high at alkaline pH ( i.e. , almost 60% of the total cesium concentration in solution is sorbed at pH>9). The results point to the importance of sorption processes on uranyl alteration phases on the retention of radionuclides.