Investigation of the interactions of uranium and plutonium with Boom clay organic matter

The solubility of uranium (IV) oxide, UO2, was investigated. Uranium (VI) was reduced to uranium (IV) using sodium dithionite and iron granules at high pH (NaOH). A solubility enhancement of UO2 in the presence of Boom clay humic acid (BCHA) was found to be approximately one order of magnitude, where the solubility of UO2 (10-9 to 10-8 mol dm-3) was increased to 10-7 mol dm-3 by BCHA. The solubility product (Ksp) of aqueous U(OH)4 and stability constant (β141) for BCHA-U(OH)4 were calculated from experimental data using a novel approach utilising the side reaction coefficient theory ('A' term). A log Ksp value of -54.51 for U(OH)4, and a log β141 value of 51.36 for BCHA-U(OH)4 were calculated. [Continues.

Stability constants of U(VI) and U(IV)-humic acid complexes

Conditional stability constants have been determined for U(IV) and U(VI) Boom Clay humic acid (BCHA) and Aldrich humic acid (AHA) complexes, under anaerobic and carbonate free conditions. The constants are needed for nuclear waste repository performance assessment purposes. The U(IV) constants were obtained by developing an approach based on the solubility product of amorphous U(OH)4. The U(VI) constants were obtained by applying the Schubert ion exchange approach