Limestone has been used for decades to raise pH
and precipitate metals in AMD. It has the lowest material cost and is
the safest and
easiest to handle of the AMD chemicals. Unfortunately, its successful
application has been limited due to its low solubility and
tendency to develop an external coating, or armor, of ferric hydroxide
when added to AMD. In cases where pH is low and mineral
acidity is also relatively low (low metal concentrations), finely-ground
limestone may be dumped in streams directly or the limestone
may be ground by water-powered rotating drums and metered into the stream.
These applications have been tried recently in West
Virginia in AMD-impacted streams with great success. Limestone has also
been used to treat AMD in anaerobic (anoxic limestone
drains) and aerobic environments (open limestone channels). These latter
two techniques are especially useful in situations where
specific discharge limits do not have to be met. They are both being
installed on abandoned mine land reclamation projects and by
operators wishing to reduce chemical treatment costs and improve compliance
(Faulkner 1996).
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