Chapter 7 - Phytoreclamation of abandoned acid mine drainage site after treatment with fly ash

Abstract

Mining and drilling are two methods used for extracting underground fossil fuels. While mining extracts solid fossil fuels and other economically important buried solid resources by way of digging and scraping, drilling extracts liquid (e.g., conventional oil) or gaseous (e.g., natural gas) fossil fuels that are forced to flow to the earth surface. Both processes are equally hazardous and cause serious health and environmental impacts like landscape degradation, vegetation and biodiversity loss, habitat fragmentation, and generation of acid mine drainage (AMD). AMD is formed when water draining through deep mines, surface mines, and mine waste materials come in direct contact with the pyrite (iron sulfide) containing exposed rocks, causing sulfuric acid production that further dissolves other rocks, and heavy metals present in them polluting waterways and groundwater with acid, dissolve ions and heavy metals. The threats of AMD pollution continue even long after the closure of the mine and abandoned mining sites are difficult to restore without treatment due to this acidic AMD effect. Unlike mining and drilling that cause direct damage to natural ecosystems, burning coal for thermal energy produces a huge quantity of coal combustion products (CCPs), disposal of which poses another challenge. Five major types of CCPs (bottom ash; boiler slag; fly ash; fluidized bed combustion ash or FBC; flue gas desulfurization ash or FGD) are used in mine reclamation either in a single form or in various combinations. Among the different utilizations of CCPs, mine reclamation is one of the most important beneficiations as the lime content of CCPs can easily neutralize acidic water and prevent or minimize AMD. While the placement of fly ashinto deep mines give structural support to abate subsidence, placement of fly ash into surface mines or other open pits or mine overburdens help in fights against AMD as the strong packing and absorbing nature of the fly ash reduces the permeability of mine strata and divert away water from acid-generating materials. The final step of reclamation is covering the fly ash treated underground and surface mining lands with the plantations that aid in the containments of the pollutants or phytostabilize them and accelerate phytorestoration of the pre-mining habitat. Therefore, scientifically sound rehabilitation of the mines through proper phytomanagement with native plants should be designed to produce a sustainable fuelwood or bioenergy crop plantation and contribute to the prevention of climate change through encouraging clean green energy.