Polymer-Modified
Clay as Impermeable Barriers for Acid Mining Tailings
Mine Environment Neutral Drainage at CANMET-MMSL |
MEND
Report 6.2
April 1994
Executive
Summary
Acidic drainage
resulting from the oxidation of sulphide minerals is the single
largest environmental problem facing the Canadian mining industry
today. Sulphide oxidation, which generally occurs at shallow depths
above the water table, can result in the production of highly acidic
pore water containing elevated levels of many heavy metals and other
deleterious constituents. It is generally agreed that the production
of acid is controlled by the availability of the oxygen at the sulphide
surface. In tailings the primary mode of oxygen transport is diffusion
through porous spaces. An impermeable cover can eliminate or significantly
alleviate the problems related to the acid mine wastes.
The Alberta
Research Council (ARC) proposed to use its newly-developed super
absorbent polymer (SAP) for the abatement of acid mine drainage.
SAP is a patented product and is made of polyacrylamide-modified
clay. When fully hydrated, one gram of SAP can adsorb more than
650 grams of fresh water and increases its volume significantly
during the process. This very property of SAP could be very useful
in the area of acid tailing abatement.
Preliminary
tests with the SAP/sands mixture show a significant potential for
SAP application in acid mine tailing abatement. Addition of 1 wt%
of SAP into a medium sand can lower its hydraulic conductivity by
four orders of magnitude. Moisture retention capability can also
be increased significantly.
The use of
SAP in a bottom liner of a tailings pond is not a viable option
because the poisoning effect of multi-valent cations on the SAP.
However, a SAP-bearing cover should be an effective hydraulic barrier.
Essentially, the cover would be an impermeable barrier and would
retain its water saturation. If used in 0.2 wt% concentration, the
cost of SAP will be about 1/20 of the total cost for the construction
of the cover. The cost for this material may be offset by the savings
on the transportation of another barrier material and construction
of the cover.
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