A tremendous amount of wet flue-gas desulfurization scrubber sludge (estimated 20 million metric tons per year in the United States) is currently being landfilled at a huge cost to utility companies. Scrubber sludge is the solid precipitate produced during desulfurization of flue-gas from burning high sulfur coal. The amount of this sludge is expected to increase in the near future due to ever increasing governmental regulation concerning the amount of sulfur emissions. Scrubber sludge is a fine, grey colored powder that contains calcium sulfite hemihydrate (CaSO{dollar}sb3cdot{dollar}1/2H{dollar}sb2{dollar}O), calcium sulfate dihydrate (CaSO{dollar}sb4cdot{dollar}2H{dollar}sb2{dollar}O), limestone (CaCO{dollar}sb3{dollar}), silicates, and iron oxides.; This material can continue to be landfilled at a steadily increasing cost, or an alternative for utilizing this material can be developed. This thesis explores the characteristics of a naturally oxidized wet flue-gas desulfurization scrubber sludge and uses these characteristics to develop alternatives for recycling this material.; In order for scrubber sludge to be used as a feed material for various markets, it was necessary to process it to meet the specifications of these markets. A physical separation process was therefore needed to separate the components of this sludge into useful products at a low cost. There are several physical separation techniques available to separate fine particulates. These techniques can be divided into four major groups: magnetic separation, electrostatic separation, physico-chemical separation, and density-based separation. The properties of this material indicated that two methods of separation were feasible: water-only cycloning (density-based separation), and froth flotation (physico-chemical separation). These processes could be used either separately, or in combination. The goal of this study was to reduce the limestone impurity in this scrubber sludge from 5.6% by weight to below 2.0% by weight. The resulting clean calcium sulfite/sulfate material can be oxidized into a synthetic gypsum that can be used in several markets which include: wallboard manufacturing, plaster, portland cement, and as a soil conditioner.; Single stage water-only cycloning removed nearly 50% of the limestone by weight from the scrubber sludge and maintained a weight recovery of 76%. Froth flotation produced a calcium sulfite/sulfate that contained 4.30% limestone by weight with a 71% weight recovery. These methods were successful in removing some of the limestone impurity, but were not able to meet the specifications needed. However, the combination of water-only cycloning and froth flotation provided a clean, useful calcium sulfite/sulfate material with a limestone grade of 1.70% by weight and a total weight recovery of nearly 66%.
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