Page 272 - Advances In Productive, Safe, and Responsible Coal Mining

Sustainable coal waste disposal practices 251

13.2 Sustainable coal waste disposal practices
of the future

13.2.1 Eliminating slurry impoundments with codisposal
Following a 2000 incident in Martin County, Kentucky, the United States, in which an
impoundment containing >300 million gallons of fine coal processing waste failed
allowing slurry to flow through an underground mine into surrounding creeks and riv-
ers, the US Mine Safety and Health Administration (MSHA) and the Office of Surface
Mining recommended that research be conducted to identify and evaluate alternative
methods of coal waste disposal [15]. The need for alternative methods is due to mul-
tiple hazards associated with conventional coal refuse disposal facilities. Such facil-
ities have a history of geotechnical failures, although the risk for this has diminished
significantly with the development of regulatory performance standards (e.g., the US
Surface Mine Control and Reclamation Act passed in 1977). Additionally, these facil-
ities have been identified as principal sources of elevated sulfate and chloride dis-
charges resulting from pyrite weathering due to infiltration of oxygen- and ferric
iron-bearing water.
In response to the above recommendation and additional concerns regarding efforts
to regulate coal mine discharges at the same level as the general use of water quality
standard, the authors became involved in a series of studies to develop good manage-
ment practices restricting pyrite oxidation thereby reducing sulfate levels in coal mine
discharges to levels that comply with present and future regulatory standards. The
studies culminated in long-term, field-scale column leaching experiments showing
that codisposal of coarse and fine coal refuse provides both the geotechnical stability
needed to lower refuse facility liabilities and the geochemical environment necessary
to minimize sulfate and chloride discharges. The primary objectives of these studies
were to reduce water treatment costs during mining and prevent long-term problem-
atic discharges that could hinder reclamation and bond release.

13.2.1.1 Experimental set up
FCPW and CCPW samples were collected from a large coal preparation plant
cleaning ROM coal from two underground mines and one surface mine all operating
in commonly mined seams in the Illinois Basin. A complete physical and chemical
characterization of these samples and some limestone material was performed includ-
ing particle size distribution, moisture content, acid-base accounting (pH), total and
pyritic sulfur content, key trace element concentrations in a high-temperature ash
(HTA) product, and X-ray fluorescence (XRF). Potential acidity (PA), neutralization
potential (NP), and net neutralization potential (NNP) were calculated.
After this characterization, samples were mixed according to three waste disposal
options to be considered: disposal practice (DP) 1 consisting of 100% CCPW (con-
trol), DP 2 consisting of codisposal of blended CCPW (90%) and FCPW (10%),