Neptunium and Americium Speciation in Selected Basalt, Granite, Shale, and Tuff Ground Waters

Abstract
Neptunium and americium are relatively insoluble in ground waters containing high sulfate concentrations, particularly at 90°C. The insoluble neptunium species is Np(IV); hence reducing waters should enhance its formation. Americium can exist only in the trivalent state under these conditions, and its solubility also should be representative of that of curium.