Several clays of extremely high cation exchange capacity were synthesized and characterized for their cation exchange selectivity properties. The selectivity studies clearly indicated that soils or ground water contaminated with Sr-90 and Ra-226 could be remediated using these clays. Three different novel swelling mica-type clays were synthesized using various cost-effective precursors by solid-state processes. Synthetic fluorinated clays of nominal compositions of Na2Si6Al2Mg6O20F4.xH2O (Na-2-mica), Na3Si5Al3Mg6O20F4.xH2O (Na-3-mica) and Na4Si4Al4Mg6O20F4.xH2O (Na-4-mica) were prepared and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Al-27 and Si-29 solid-state magic angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. Cation exchange equilibria with Sr and Ba (as simulator for Ra) revealed that these synthetic micas exhibited extreme selectivity for these less hydrated divalent cations. Tests with actual ground waters contaminated with Sr-90 at the Hanford site clearly indicated the superiority of these novel clays when compared to the best commercially available materials. Selectivity of these clays was also determined for Sr and Ra-226 using 0.5 to 2 M NaCl and expressed as distribution coefficients, Kds. For an example, Na-4- mica and Na-2-mica showed very high Kd values of 20680±1280 and 15740±840 for Ra-226 from 0.5 M NaCl. In addition to radioactive species, other metals such as Cu, Pb etc could be remediated from soils using these clays.