tech n ica I
f,:l::1t 1Jres
.
.
.
water 1n m1n1ng
ACID AND METALLIFEROUS DRAINAGE (AMD) J Taylor, S Pape Abstract Acid and Metallifero us Drainage (AMD) is the biggest environmental issue facing the mining industry. T his paper reviews the causes and impacts of AMD, and provides techniques for its minimisation , control and rreacmenc.
Overview Acid and Metalli ferous Drainage (AMD), from both existing and historic mines, is the biggest environmental issue facing the mining industry worldwide. AMD has traditionally been referred co as "acid mine drainage" or "acid rock drainage". Any type of mining operatio n chat affects common sulfid e minerals such as pyrite has the potential co generate water pollution associated with AMD. The effects of AMD often continue lo ng after mine closure, when the mine operators have disbanded. AMD affects all sectors of mining, including precious metal, base metal, coal, mineral sand and uranium mines and even quarries. A prime example in Australia is the discharge of AMD fro m the Mr Lyell mine into the King River in Tasmania. Curren cly some 80 tonnes per day of sulfuri c acid, along with iron and copper, is still entering Macquarie Harbour via the King River. World-wide, the Rio Tineo (lie. 'Red River') in Spain gees its name from the iron content of the outflow from copper mi nes char were worked by the Romans, over 2000 years ago (see Figure I).
Figure 1. Th is historic mine site on the Rio Tinto ('Red River') in Spain has been discharging iron-rich AMD for over 2000 years.
Types of AMD "Acid drainage" is formed by the exposure of sulfidic minerals (usually pyrite) co air and water. This process produces a precipitate of ferr ic hydroxide (o range in
colour) and sulfuric acid. Figure 2 is a dramatic illustration of what can happen. Due to natural buffering reactions, it is possib le for AMD co be near-neutral , bu r with a high acidi ty due co elevated metal
AM D can occur whenever pyrite is exposed co air, either in underground workings, in open cues, waste rock piles, ore stockpiles, or railings storages. Some mines uti lise the phenomenon co extract metal from heaps of ore or old railings deposits.
It is crucial to assess AMD risks as ea¡r ly as possible. This article has been drafted based on the author's presentation to the AWA Conference 'Warer in Mining', Adelaide, September, 2006.
132
FEBRUARY 2007
Water
Figure 2. Iron-rich a nd acidic drainage from underground mine workings in western Tasmania.
Journal of the Australian Water Association