The Bureau of Mines developed a flue gas desulfurization process as part of its goal of minimizing the undesirable environmental impacts associated with energy and mineral-processing plants. The modified citrate process involves absorption of sulfur dioxide (so2) in a buffered citric acid solution. The so2-loaded solution is regenerated by countercurrent contact with steam in a packed tower. The wet so2 product is then dried and can be liquefied or further processed to make sulfuric acid. Test data from process investigation unit studies are presented. Material balances, flowsheets, and cost estimates are given for recovering so2 from copper smelter reverberatory gas, led smelter sintering machine tail gas, and powerplant stack gas. Operating cost estimates show the process will add $0.04 Per pound of copper, $0.01 Per pound of lead, and $0.015 Per kwhr to the cost of the respective operations. These costs could be substantially reduced if a source of waste heat was available to provide the process steam requirements.