The results of muffle furnace calcination experiments, in which the temperature of the bed of colliery tailings was measured as a function of the nominal furnace temperature, are presented. ΔT, the increase in the bed temperature due to oxidation of the coal particles in the tailings was found to increase with increasing calorific value of the tailings and with increasing bed depth. ΔT values up to 150 K were measured at a bed loading of 5.6 kg m-2. The results of differential thermal analysis (DTA) and thermogravimetric (TG) analysis of the tailings, in both oxidising and inert atmospheres, and of reference clay mineral samples are also presented. The dependence of the leaching properties of the tailings and clay mineral samples on their thermal history was investigated. There was a marked increase in the rates of extraction of both aluminium and iron in the temperature range 823-1123 K. Above 1173 K the rate of extraction of aluminium decreased sharply. These results have been interpreted in terms of the various phase changes and chemical reactions undergone by the clay and non-clay minerals present in the tailings. Practical aspects of the controlled calcination of colliery tailings are discussed, and it is concluded that calcination in a fluidised bed combustor is the only suitable method on an industrial scale. © 1983.