The present invention constitutes a heat treatment apparatus like a fluidized-bed dryer for heat treating a particulate material in a low temperature, open-air process. Preferably, available waste heat sources within the surrounding industrial plan operation are used to provide heat to the dryer. Moreover, conveyor means contained within the dryer can remove larger, denser particles that could otherwise impede the continuous flow of the particulate material through the dryer or plug the fluidizing dryer. This invention is especially useful for drying coal for an electricity generation plant.