Abstract
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.