Processes considered are the lime/limestone, magnesium oxide, sodium carbonate, aqueous carbonate, double alkali, Wellman-Lord/Allied Chemical and Chiyoda Thoroughbred 101. Of these, the lime/limestone process has received by far the most study and use, and is the popular choice for flue gas desulphurization installations. Consequently, large quantities of waste sludge from these units will be produced and the need for landfill sites will become critical. Government regulation and the high cost of disposal may eventually increase the feasibility of utilizing such wastes as raw materials, most probably for the construction industry.