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High-calcium quicklime [calcium oxide (CaO)] is presently the major chemical used for controlling environmental pollutants. Areas of application for water include domestic water, industrial waste water, including acid mine drainage, and sewage and hazardous wastes. Domestic water is included because lime can remove metals in source waters which might be considered as pollutants. The area of application in air pollution control is the reduction of sulfur oxides in the stack gases of coal-fired boilers or other operations producing sulfur dioxide as a potential air pollutant. While the foregoing do not cover all of the environmental uses for lime, they are the major ones, an understanding of which should be helpful in almost any environmental application of lime.
The behavior of lime in these applications is discussed. Reference is also made to the use of dolomitic lime [calcium oxide; magnesium oxide (CaO; MgO)]. The magnesium content of this material gives rise to special considerations—for example, the solubility of magnesium sulfate as contrasted with that of calcium sulfate. This paper also calls attention to materials which are competitive with lime as a chemical in the environmental program.
The discussions include lime as the chemical for pH control of the liquid phase in sewage treatment, as well as for sludge dewatering and sludge stabilization prior to ultimate sludge disposal. Waste acids which favor the use of lime are contrasted with those which do not. Potential uses for lime in stabilizing tailings and in the construction of barrier walls around hazardous waste dumps are called to attention. In the field of sulfur oxides control, both wet and dry lime scrubbing procedures are covered, including reference to direct lime or limestone injection into coal-fired boilers.
The paper concludes with a review of the more important engineering considerations which must be taken into account when designing lime handling systems. These include storage, lime slaking, and lime slurry transport.
calcium, sulfur, lime, environment, oxides, coal-fired boiler, stack gases
Director, National Lime Association, Lakewood, CO