ACID MINE
DRAINAGE IN PERMAFROST REGIONS: ISSUES, CONTROL STRATEGIES AND
RESEARCH REQUIREMENTS
Mine Environment Neutral Drainage at CANMET-MMSL |
MEND Project 1.61.2
July 1996
EXECUTIVE
SUMMARY
This report
provides perspectives on issues, strategies, and research requirements
for disposing of potentially acid generating mine tailings and mine
waste rock in a permafrost environment. It is important to distinguish
between the continuous and the discontinuous permafrost environment.
Within the discontinuous region the warm permafrost conditions are
very susceptible to thaw degradation.
Acid generation
within mine tailings has been noted at two minesites in Canada's
permafrost regions. Acidic seepage and runoff have also been documented
in the natural permafrost environment. Cold temperature leach column
testing shows that acid generation is slowed down but not necessarily
reduced to negligible levels at temperatures approaching freezing.
Processes related
to acidic drainage in cold climates have been reviewed. Important
processes that require further study include the influence of sulphide
minerals and process chemicals on unfrozen water content, thaw degradation
due to oxidation, reaction rates at low temperatures, and frozen
hydraulic conductivity of saturated and unsaturated mine waste materials.
Control strategies
that take advantage of permafrost conditions include freeze control
and climate control. Freeze control of tailings would appear to
be a viable strategy however there is a need for more cost effective
insulating cover designs and a more thorough understanding of frozen
tailings thermal properties. There is potential for using the beneficial
permafrost climate for achieving modest engineering control strategies
in waste rock dumps using zoning of different material types.
Implementation
of reliable and economic AMD control strategies are impeded by a
lack of understanding of important cold weather processes and demonstrated
performance. A program for researching freeze control of mine tailings
is scoped out. Development of freeze control and climate control
strategies for mine waste rock requires a much better understanding
of mass transfer and geochemical processes acting within waste rock
dumps. A fairly substantial effort will be required to achieve this
level of knowledge. A general program of research in this area should
be considered.
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