PNNL

Abstract

Single-pass flow-through (SPFT) tests were conducted to study the effects of aqueous organic material on the dissolution kinetics of synthetic sodium meta-autunite, Na[sub]2[/sub][(UO[sub]2[/sub])[sub]2[/sub](PO[sub]4[/sub])[sub]2[/sub]] 3H[sub]2[/sub]O, as a function of pH ( 7 -10) and temperature (25 – 70[sup]o[/sup]C). System conditions were identical except for the chemical composition of the buffer which consisted of either the organic 0.05 M tris(hydroxymethyl)aminomethane (TRIS) buffer, or the inorganic 0.1M ammonium hydroxide (NH[sub]4[/sub]OH) buffer solution. Both systems exhibited an increase in the release rates of uranium with increasing pH and temperature. However, the release of uranium was 10-1000X greater in the presence of aqueous organic material. Additionally, saturation limits for secondary uranyl-phases were typically met under inorganic conditions, but rarely achieved within the organic environment. The results highlight the importance of aqueous organic material and secondary uranyl-phases on the long-term fate of uranium in the environment.