Sorption of Neptunium on Clays and Clay Minerals — A Review

Abstract

During recent decades, the search for possible repositories for high-level nuclear waste has yielded large amounts of sorption data for actinides on different minerals. Clays and clay minerals are of special interest as potential host-rock formations and backfill materials, by virtue of their good retardation properties. Neptunium (Np) is one of the actinides which is considered in long-term scenarios due to its long-lived nuclide 237Np (t1/2 = 2.1 × 106 y). Because neptunium sorption is heavily dependent on the experimental conditions, comparison of sorption data from different experiments is challenging. Normalizing reported data with respect to the surface area of the sorbent enables conversion of conventional distribution coefficients (Kd) to normalized (Ka) values, which improves comparability among the results of different experiments. The present review gives a detailed summary of sorption data of Np on clays and clay minerals and examines critically the applicability of the Ka approach.

X‐ray spectral characteristics of typical clays in China and their application in clay classification

“…1,2 It is also an important catalyst for petroleum cracking and refining. 3,4 The application of clay in remediating environmental pollution 5,6 and dealing with nuclear waste [7][8][9] has also achieved great progress. In addition, research on clays and the origin of life has also aroused great interest.…”

Oxidation State and Structure of Fe in Nontronite: From Oxidizing to Reducing Conditions

“…Thereby, Fe-bearing clay minerals act as redox batteries, playing important roles e.g. in the natural carbon cycle, for nutrient availability, and for the mobility and toxicity of organic and inorganic pollutants. , Ferric iron in minerals potentially limits organic matter mineralization in floodplains and thus sustains the ecosystem. , Fe-bearing clay minerals efficiently retain pesticides, , phosphates, , organic contaminants, − and heavy metals. − Fe-bearing clay minerals used as engineered barriers and backfill in radioactive waste repositories are critical for immobilizing redox sensitive radionuclides, such as uranium, − neptunium, , technetium, − and selenium. , Iron redox reactions are involved in all these processes. The Fe­(II)/Fe­(III) ratio in clay minerals, its structural position, and the ability to participate in redox-reactions are the key parameters necessary for the understanding and modeling the redox-controlled retention processes .…”

“… 5 , 6 Fe-bearing clay minerals efficiently retain pesticides, 7 , 8 phosphates, 9 , 10 organic contaminants, 11 − 13 and heavy metals. 14 − 17 Fe-bearing clay minerals used as engineered barriers and backfill in radioactive waste repositories are critical for immobilizing redox sensitive radionuclides, such as uranium, 18 − 22 neptunium, 23 , 24 technetium, 25 − 28 and selenium. 29 , 30 Iron redox reactions are involved in all these processes.…”