Hydrocarbon evolution from a montmorillonite clay-soil was studied at three scales and at temperatures ranging from 300 to 650°C in order to develop a thermal treatment assessment procedure for contaminated soils in rotary kilns. The two components of the assessment procedure included experimental evaluation of the soil at bench- or pilot-scale in conjunction with data fitting using an appropriate mathematical desorption model. The results of the experiments have been embodied in the model which can be used for scaling and correlative purposes. Performing experiments at three scales permitted a clear delineation of intraparticle and interparticle effects and it also allowed the testing of the model's ability to correctly scale results. In addition to reactor size, the key parameters examined included hydrocarbon volatility, temperature, moisture levels, and soil particle size.