Abstract: Disclosed is a method and an apparatus for the heat treatment of lime sludge (CaCO.sub.3) to form burnt lime (CaO). In the method of the present invention a lime sludge feed is entrained in and thereafter dried in a gas flash dryer means to produce a dried lime sludge. The dried lime sludge is separated from the gases and thereafter is fed to a rotary kiln in which the dried lime sludge is converted to active burnt lime. In order to maintain the flow of gas in the flash dryer means at a predetermined velocity in order to entrain all the lime sludge feed in the gas flow, an adjustable portion of the separated gases are recycled through the flash dryer means.