O 2 0 ( O H ) 1 6 ) . Adsorption is a major fate process for actinides in natural systems. These results have implications for industry, especially with regards to deep geological repositories for radioactive waste. Also, acid mine drainage in uranium mining areas releases actinides directly into surface and groundwaters. Goethite was chosen for this study as it is amongst the most common of iron oxyhydroxides, and is found to have a strong affinity for adsorption of the uranyl (UO~ +) ion (Hsi and Langmuir, 1985). Goethite has a well characterized crystal structure, and is easily prepared under laboratory conditions (Schwertmann and Cornell, 1991). The clinochlore was studied to investigate adsorption onto clay minerals present within the Borrowdale Volcanic group, the rock sequence into which the proposed NIREX repository was to be placed. The clinochlore used was prepared from a single crystal, which was crushed and sieved to give the grain size fraction 63-125 p. Both minerals were characterized by BET surface area analysis (N 2 adsorption), SEM and XRD. The goethite surface area was 35 m2/g and clinochlore was 14 m2/g. Reaction conditions were varied in order to discover the effect of changing mineral type, pH,