Fly Ash as a Sealing Material for Spontaneous Combustion and Acid Rock Drainage Prevention and Control

Abstract

Oxidation processes result in a number of environmentally adverse phenomenons such as spontaneous combustion of coal in piles, coal mining waste dumps and coal seams, as well as ARD generation in sulfide-bearing coal and ore mining waste dumps. The most efficient way to prevent, attenuate or intercept both adverse processes is to effectively cut off air penetration into the coal- or/and sulfite-bearing material with use of abundant, cost-effective, efficient and easy-to-handle material of high sealing properties against air penetration. Fly ash (FA) from coal-fired power plants in the form of a dense mixture with water (≤1:1 wt.) appeared to be an excellent sealing/insulation material against air penetration that has no competing natural materials in this respect and fulfills all the conditions of efficiency and availability. A series of experiments carried out to evaluate these properties of different FA: Water mixtures showed that penetration resistance of solidified FA: Water mixtures to air is 1–2 orders of magnitude higher than that of the natural sealing materials, while hydraulic conductivity qualifies this material as permeable to water. Full-scale applications of FA: Water dense mixtures for spontaneous ignition control at coal mining waste dumps confirmed high efficiency of this material. Pending projects and potential application fields of dense mixtures of FA with water for these purposes were also discussed, among them the most promising and not yet sufficiently utilized areas of use such as potential for fire control in burning coal seams (exemplified in Jharia Coalfield, India) and prevention of ARD generation in coal/ore mining waste dumps with use of FA: mine water mixtures.