Environmental risk of mining - Environmental Deterioration and Contamination: Problems and their Management - page 118

drainage (AMD) and from leachate from acids added during beneficiation processes.
AMD and ARD occur when the overburden is excavated to expose the materials of
interest (i.e., coal, metal ores, nonmetallic ores) or the waste rock or tailings formed
during the processing of valuable minerals that contain sulfide minerals such a pyrite
(FeS 2 ), which when exposed to air and water will oxidize and release large quantities of
iron and sulfate into solution. In addition, H + ions are liberated during the oxidation
process producing an acidic solution that readily weathers and releases other trace min-
erals (i.e., copper and zinc) into solution (EPA, 2000; Younger, 2006; Wolkersdorfer
et al. , 2012).
Water quality can be severely impaired also by discharges from other beneficiation
processes: cyanide, solvents, flotation agents (sulfur dioxide, sulfuric acid, cyanide
compounds, cresols, hydrocarbons, copper compounds and zinc dust), flocculants
(aluminum sulfate, lime, iron, calcium salts, starches). The cyanide-contaminated solu-
tion that remains after valuable minerals have been removed is placed in a tailings pond
or solution retention basin. These ponds and basins have proven to attract unsuspect-
ing waterfowl and wildlife that suffer from both acute and chronic poisoning as a result
of direct contact with and ingestion of cyanide-contaminated solutions. Leakage from
the piles of waste that are leached with cyanide can release cyanide and other toxic
constituents directly into the environment via surface water and groundwater flow.
The general environmental impacts of mining are associated with resource con-
sumption and resource degradation. Subsidence of mined-out areas can create surface
impact. Unstable rock and tailings ponds, vegetation and habitat destruction, soil and
water contamination by runoff and spills of fuels, lubricants and hydraulic oils lead to
resource degradation. The large disturbances caused by mining can disrupt the environ-
ment, adversely affecting aquatic habitats (i.e., lakes, ponds, streams, rivers), terrestrial
habitats (i.e., deserts, grasslands, forests), and wetlands that many organisms rely on
for survival. The disruption of site hydrology by large consumption or release of water,
manipulation of topography and the release of particulates and chemicals can all have
indirect impacts on various habitats (EPA, 2000; Younger, 2007).
Erosion and sedimentation present another environmental issue for mine sites.
When surface material is disturbed by the mining process, large quantities of sediment
are transported by water erosion. The sediment eventually drops out of solution and
sedimentation occurs at some point downstream from the erosive source. The degree
of erosion and sedimentation depends on the degree to which the surface has been
disturbed, the prevalence of vegetative cover, the type of soil, the slope length and
the degree of the slope. Erosion and sedimentation affect surface water and wetlands
more than any other media. Erosion can adversely affect soil organisms, vegetation and
revegetation efforts because it results in the movement of soil, including topsoil and
nutrients, from one location to another (EPA, 2000).
4 MINING PRODUCTION DATA
The annual mine production statistics of countries at world and European levels were
compiled based on the comprehensive database maintained by the British Geologi-
cal Survey covering the years 2005-2009 (BGS, 2011) and 2007-2011 (BGS, 2013).
Data on mineral resources and reserves are still highly variable based on different