Page 267 - Advances In Productive, Safe, and Responsible Coal Mining

246 Advances in Productive, Safe, and Responsible Coal Mining

size fractions leading to two coal refuse products on the output side: (1) coarse coal
processing waste (CCPW) and (2) fine coal processing waste (FCPW). Generally,
CCPW is material larger than 150μm (100 mesh) in size [2]. CCPW includes reject
streams from jigs, heavy media vessels, and heavy media cyclones. FCPW includes
reject streams from spirals, flotation columns and cells, desliming cyclones, and efflu-
ent streams of filter presses, screenbowl centrifuges, and other dewatering equipment.
All FCPW streams are typically concentrated in a thickener whose output is a waste
slurry.
Most extraction and beneficiation wastes from coal mining (i.e., mine spoils and
coal refuse) are categorized as “special wastes” that are exempted from regulation
by hazardous waste rules and laws (e.g., Subtitle C of the US Resource Conservation
and Recovery Act). However, coal utilization generates another type of waste known
as coal combustion residuals (CCRs), which are regulated to some degree (e.g.,
Subtitle D of the US Resource Conservation and Recovery Act). CCRs are categorized
into four groups based on physical and/or chemical forms that derive from the com-
bustion method and the emission control system used. A brief description of each
group follows [3]:
Fly ash is a very fine, powdery material composed mostly of siliceous mineral matter left
l
over from the burning of finely ground coal in a boiler. It comprises 60% of all CCRs.
l Bottom ash is a coarse, angular, gritty material with similar chemical composition to fly ash.
It is too large to be carried up by the smokestack, so it collects in the bottom of the coal
furnace. It comprises 12% of all CCRs.
l Boiler slag is molten bottom ash that forms into pellets in the bottom of slag tap and cyclone
type furnaces. It has a smooth glassy appearance after it is cooled with water. Boiler slag
comprises 4% of all CCRs.
l Flue gas desulfurization (FGD) material is residue from the sulfur dioxide emission scrub-
bing process. It can be a wet sludge consisting of calcium sulfite or calcium sulfate, or it can
be a dry powdery material that is a mixture of sulfites and sulfates. FGD material comprises
24% of all CCRs.

13.1.2 Sustainability defined
Because no other industry has such a direct impact on the environment in which it
operates, no other industry is as focused on maintaining its environment than the min-
ing industry. That focus may not have always been there, but as society increasingly
recognizes the need for balance between life and lifestyle, the mining community has
responded by becoming much better stewards of the land where it conducts business.
Although mining is one of the world’s oldest industries, the concept of environ-
mental stewardship as it relates to mining is relatively young [4]. For example, in
the United States, the Environmental Protection Agency (EPA) was not formed until
1970. In 1977, the US Congress passed the Surface Mining Control and Reclamation
Act, which remains the primary federal law regulating environmental impacts of coal
mining. In 1983, the United Nations appointed the World Commission on Environ-
ment and Development to unite its member countries in an effort to pursue sustainable
development, which it defined as “the advance of human prosperity in a way that does