Flue gas desulfurization (FGD) is a classic low-cost absorption process based on the limestone-gypsum process. This process involves the separation of sulfur oxides (SOxs such as SO2 and SO3) from flue gases containing medium or high sulfur oxides. Among the advantages of this process are the high SO2 recovery in wet type FGD systems, the wide applicability of absorption chemicals and the need for large-scale knowledge in the management of the chemical process. For this reason, it is the most common flue gas treatment system used. The wet FGD system by-product is a dry, powdery solid residue and can also be used as fill material (eg road building) after stabilization, depending on its components.