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black lung continued PA coal dust or calcite alone, but not following exposure to PA coal dust mixed with calcite. In theory, calcite neutralizes acid, producing nontoxic calcium ions and carbon dioxide. These results suggest that, even inhalation of pure calcite is toxic. When mixed with BAI-containing coal, calcite and BAI neutralize each other's level and diminish the toxic effects of the mixed dusts. Further laboratory investigations should confirm this observation. To turn the scientific research finding into a CWP mitigation technology, proper amount of calcite should be introduced to the BAI-containing coal or coal dust in efficient and practical means. In a mining setting, three potential technologies to introduce calcite into coal mines could be explored. First, a potential calcite-based technology might be especially applicable in Appalachian coalfields, which have much higher methane content than other U.S. coalfields. To prevent methane explosions and to reduce the ventilation requirement, large underground coal mines employ various degasification technologies to remove the major portion of methane content in the coal bed before it is extracted. The modern degasification technology includes drilling long horizontal degas holes in the coal bed and then hydraulically fracturing the coal bed for improved methane recovery. Both of these might provide an ideal avenue for calcite introduction, particularly because the calcite-BAI contact time would be relatively long, allowing for extended neutralization (Figure 1). The hydraulic fracturing process used to degasify coal beds might be an ideal time to 56 www.coalage.com introduce calcite to the coal seam. A predetermined amount of calcite (e.g., 20-30 mesh size) could be added along with sand to the fracturing water to serve as a proppant to keep the coal seam fractures open. Degas holes normally have a service time ranging from a few months to two years or even longer before the degassed coal is extracted. Assuming diffusion of the calcite suspension throughout the coal seam, this would allow sufficient time for the injected calcite to neutralize the BAI in the coal. If such an approach proves feasible, the toxicity of dust produced in cutting the calcite-treated coal might be greatly reduced. Yet, much preliminary research should be done in a laboratory environment before attempting any large-scale calcite injection in coal seams. Also, the implementation of advanced drilling techniques, including surface to horizontal multilateral degasification wells, and in-mine horizontal wells could allow for even more targeted introduction of calcite to mining areas. These methods are well documented and allow for high seam contact. These wells are generally flooded or filled with a specialized gel prior to mining to avoid mining into pressurized wells. They could instead be filled with a calcite mixture. Third, when degasing is not feasible in small coal mines, it may be possible to introduce respirable calcite during mining through a secondary water spray system. The primary water spray currently in use is to wet the airborne dust particles and make the contacted particles larger and heavier, causing them to quickly settle out of the ventilation air so that they are no longer respirable. A secondary water spray system with respirable calcite may be used to target the escaped respirable coal particles. Future research should assess whether adding calcite to these water sprays can be done safely and effectively, with the intent of not only reducing dust levels but also neutralizing adverse health effects of BAI and quartz contained in the respirable coal dust. In conclusion, calcite holds promise for reducing CWP prevalence among Appalachian coal miners, regardless of the pneumoconiotic effects caused by either BAI or quartz or both. Thus, while efforts to identify causative compounds and to reduce respirable dust levels in underground coal mines must continue to be pursued, further research is warranted to explore the potential use of calcite as a novel strategy for preventing CWP. Acknowledgments The concept has been developed through grant support by the National Institute for Occupational Safety and Health; grant number: 1R01 OH009771. About the Authors Huang is with the Department of Environmental Medicine at the NYU School of Medicine and can be reached at Xi.Huang@nyumc.org; Luo is with the WVU Mining Engineering Deptartment, Zhang is with the School of Public Health, Soochow University, Suzhou, China; Dong is with China Coal Technology & Engineering Group Corp.-Xi'an Research Institute, Xi'an in China; and Luxbacher is with Virginia Tech's Department of Mining & Minerals Engineering. April 2013