Compatibility of slurry wall backfill soils with acid mine drainage.pdf

Advances in Environmental Research 4Ž. 2000 251᎐268
Compatibility of slurry wall backfill soils with acid mine
drainage
U
Mansor Kashira, Ernest K. Yanfulb,
aAGRA Earth and En¨ironmental Limited, 160 Traders Bl¨d. East, Suite 110, Mississauga, Ontario, Canada L4Z 3K7
bGeotechnical Research Center, Department of Ci¨il and En¨ironmental Engineering, The Uni¨ersity of Western Ontario,
London, Ontario, Canada N6A 5B9.
Accepted 5 June 2000
Abstract
The use of slurry walls to contain oxidized tailings and provide cutoff below tailings dams is generally a
cost-effective way of preventing environmental degradation due to seepage of acid water from tailings areas.
Long-term environmental protection dictates that the slurry wall materials patible with the acid water. Six
percent Avonseal bentonite by weight was added separately to two natural soils to represent slurry wall backfill
materials, which were then permeated with several pore volumes of acid mine drainageŽ. AMD in the laboratory.
Results using both flexible wall and fixed wall permeameters were similar. The carbonate-rich backfill gave an
y
average hydraulic conductivity of 1=109 cmrs, buffered the AMD at circumneutral pH, and kept effluent
metal concentrations to very low valuesŽ. for example, less than mgrl zinc . Although the carbonate-free backfill
y
also maintained low K Žaverage 3=108 cmrs. during AMD permeation, it could not neutralize the AMD as
effluent pH decreased to approximately , and metal concentrations reached those of the influent or permeant
after approximately 17 pore volumes. ᮊ 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Sulfide mineral oxidation; Containment; Hydraulic conductivity; Hydraulic gradient; Effective stress; Effluent chemistry;
Secondary minerals; Gypsum
1. plex, but can be represented by the following reac-
tions, using pyrite as the surrogate sulfide mineral:
Acid drainage is produced when sulfide mine waste
q 7 q ª 2q