The potential use of exhausted open pit mine voids as sinks for atmospheric CO2: insights from natural reedbeds and mine water treatment wetlands

摘要

Abandoned surface mine voids are often left to flood, forming pit lakes. Drawing simple but important lessons from experiences with compost-based passive remediation systems for acidic mine waters, an alternative end-use for open pit mine voids is proposed: gradual infilling with organic material, which can serve as a long-term sink for atmospheric CO2, whilst ameliorating or eventually eliminating sustained evaporative water loss and acidic water pollution. Key to the success of this approach is the suppression of methane release from organic sediments flooded with sulfate-rich mine waters: the presence of modest amounts of sulfate (which is typically abundant in mine waters) inhibits the activity of methanogenic bacteria. This explains why gas release studies of mine water treatment wetlands never report methane emissions; CO2 is the only greenhouse gas emitted, and this is clearly not at levels sufficient to undo the benefits of wetlands as net CO2 sinks. While the compete infilling of open pits with organic sediments might take a very long time, only minimal maintenance would be needed, and if carbon trading markets finally mature, a steady income stream could be obtained to cover the costs, thus extending the economic life of the mine site far beyond cessation of mining.