Although direct disposal to the ground has provided an effective means for the disposal of low- and intermediate-level waste streams, there is concern regarding the lack of control of the radionuclides once the wastes have been discharged to the ground. The use of a mineral-filled column is regarded as an inexpensive, yet efficient, alternative method for waste decontamination. For this purpose the cesium-exchange properties of various grades of commercially available vermiculite were investigated and compared to other natural ion-exchange materials. Elucidation of the reaction mechanism has led to improvement of the cesium-sorptive properties, either by potassium treatment or heat treatment of the vermiculite or by addition of potassium to the waste stream. Studies of the kinetics and the thermodynamics of the exchange reaction permit extrapolation of the data for consideration of the extended use of vermiculite columns for decontaminating other waste streams. Data obtained from bench-scale and field-scale (10-ft long, 2-in. i.d.) column studies compare closely with those obtained by slurry studies. The breakthrough curves obtained were sufficiently steep to indicate that the partial cesium-sorptive capacity of a vermiculite column would be completely utilized if two columns were operated in series. A column 10 ft long and 10 ft in diameter filled with Na-treated vermiculite is estimated to be capable of decontaminating more than 5 × 105 gal of ORNL intermediate-level waste. Larger volumes of waste streams having lower concentrations of stable salts could be decontamined with respect to cesium and strontium.