Limestone fines and lime sludge: from by-product waste to potential beneeficial use--a key to sustainability

Limestone fines and lime residue waste (lime sludge) may contain more than 95 wt% calcium carbonate (CaCO3), making them highly desirable for many beneficial uses. In this paper, we explore the sustainable utilization of by-product waste materials that are normally disposed of, namely, fines from limestone quarries or lime sludge from water treatment plants that are converted into a potentially effective flue gas desulfurization sorbent. Each year, millions of tons of by-product fines are produced during the crushing and processing of limestone and dolomite quarried in the United States. Similarly, a large amount of lime sludge is produced in the United States from water treatment plants that use lime softening to reduce the calcium and magnesium hardness of the source water. Because these by-products currently have limited uses, large portions end up in landfills or, in the case of fines, are used to backfill mined-out areas. Some of the fines and a small portion of the lime sludge materials are used in agriculture to control soil pH. Our recent studies, funded by the Illinois Clean Coal Institute, demonstrate that these potentially valuable, yet largely unknown, resources could provide an affordable and highly reactive sorbent for desulfurization in coal-fired power plants.