Oxyhydroxy Silicate Colloids: A New Type of Waterborne Actinide(IV) Colloids

At the near-neutral and reducing aquatic conditions expected in undisturbed ore deposits or in closed nuclear waste repositories, the actinides Th, U, Np, and Pu are primarily tetravalent. These tetravalent actinides (An^IV) are sparingly soluble in aquatic systems and, hence, are often assumed to be immobile. However, An^IV could become mobile if they occur as colloids. This review focuses on a new type of An^IV colloids, oxyhydroxy silicate colloids. We herein discuss the chemical characteristics of these colloids and the potential implication for their environmental behavior. The binary oxyhydroxy silicate colloids of An^IV could be potentially more mobile as a waterborne species than the well-known mono-component oxyhydroxide colloids.