On silica's roles in controlling americium migration in contaminated sediments

Journal Article · 19 May 2023 · Applied Geochemistry

DOI: https://doi.org/10.1016/j.apgeochem.2023.105690 · OSTI ID:1998058

Delegard, Calvin H.  ^[1]; Pearce, Carolyn I. ^[2]; Emerson, Hilary P.  ^[2]

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1. TradeWind Services, LLC, Richland, WA (United States)
2. Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)

Two studies in the early 1980s described the leaching behavior of americium (Am) disposed as part of acidic high-salt processing wastes from the Hanford Site’s Plutonium Finishing Plant to nearby ground sediments. Here these batch leach experiments showed that the Am concentrations followed a linear log [Am] versus pH relationship with a slope of –1. Column leach experiments in the second study, however, did not follow this relationship and only ~30% of the americium desorbed even after extensive column leaching. Here, the 1980s research is re-examined along with previously unpublished information and, in light of recent published work, a plausible mechanism is proposed to explain these phenomena. Amorphous silica in the contaminated sediments is postulated to be the substrate responsible for both the exchangeable Am available for leaching and the retained low-leachable Am made evident in the column leach experiments. The exchangeable Am³⁺ in the contaminated sediment leach experiments behaves with pH dependence similar to that observed for uptake onto amorphous silica of sodium (Na⁺), calcium (Ca²⁺), barium (Ba²⁺), cadmium (Cd²⁺), uranyl (UO₂²⁺), ferric (Fe³⁺), chromic (Cr³⁺), cupric (Cu²⁺), plumbous (Pb²⁺), uranium(IV) (U⁴⁺), plutonium(IV) (Pu⁴⁺), zirconium (Zr⁴⁺), analogue lanthanide (gadolinium, Gd³⁺, europium, Eu³⁺, and lutetium, Lu³⁺) and curium (Cm³⁺) ions as well as other studies with Am³⁺. Correspondingly, the residual low-leachable Am³⁺ revealed in the column leach experiments is attributed to incorporation of Am³⁺ within amorphous silica by dynamic Am³⁺ sorption and silica precipitation processes.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC05-76RL01830; AC06-77RL01030
• OSTI ID: 1998058
• Alternate ID(s): OSTI ID: 1983502
• Report Number(s): PNNL-SA-178865
• Journal Information: Applied Geochemistry, Vol. 154; ISSN 0883-2927
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English