Massive quantities of sulfite-rich flue gas desulfurization (FGD) scrubber sludge have been generated by coal burning power plants. Utilization of the sulfite-rich sludge for preparing alpha-calcium sulfate hemihydrate (alpha-HH), an important kind of cementitious material, is of particular interest to electric utilities and environmental preservation. In the experiment, calcium sulfite hemihydrate was directly transformed to alpha-HH without the occurrence of calcium sulfate dihydrate (DH). The transformation was performed in a concentrated CaCl(2) solution containing Mg(2+) and Mn(2+) at 95 degrees C, atmospheric pressure and low pH. The oxidation of calcium sulfite and the subsequent crystallization of alpha-HH constitute the whole conversion, during which the oxidation turns out to be the rate controlling step. Solid solution comprised of calcium sulfite hemihydrate and calcium sulfate was found to coexist with alpha-HH in the suspension. Calcium sulfate increases and calcium sulfite decreases spontaneously until the solid solution disappears. Thus, it is a potential alternative to utilize sulfite-rich FGD scrubber sludge for the direct preparation of alpha-HH. (C) 2010 Elsevier Ltd. All rights reserved.