Specialized Services
Mine
Waste Management at CANMET-MMSL |
The
objective of the Innovations in Mine Waste Management Program at CANMET
Mining and Mineral Sciences Laboratories (MMSL) is to develop technologies
or apply existing technologies to reduce the potential environmental
liabilities of mine waste in a cost-effective manner. Important program
areas include:
Other areas of
expertise:
- Abandoned
mines;
- Environmental
technologies for cold (northern) climates;
- Leaching
characteristics of key metals (As, Sb, Se);
- Tailings
dam stability;
- Novel prediction
methods for acid generation;
- Investigation
of alternative disposal methods;
- Total suspended/dissolved
solids;
- Microbial
characterization for natural processes;
- Transport,
fate and impact of emissions;
- Chronic
toxicity and metal mixture toxicology.
For more information,
please contact us.
Waste
Characterization
Waste characterization
is the first step in assessing a potential liability and defining
environmentally sound waste management practices. In terms of acid
generation, proponents must be able to adequately assess the potential
for acid generation via chemical and mathematical prediction methods.
These predictions form the basis for waste management plans and
numerous methodologies are readily available for this purpose. For
more information, please contact
us.
Prevention
of Acidic Drainage
CANMET-MMSL's
Environment Group has considerable expertise in prevention of acidic
drainage, particularly in the areas of subaqueous disposal, wet
barriers and permafrost. Laboratory studies on sub-aqueous tailings
disposal have shown oxygen ingress to the tailings interstitial
water appears to be limited to the first 10 cm. In addition, secondary
barriers consume dissolved oxygen, preventing or significantly reducing
oxygen ingress into the mine waste. Additional studies are being
completed on the resuspension of tailings and secondary barrier
materials under various water-depth and wave-energy scenarios.
For more information,
please contact us.
Chemical
Treatment of Acidic Drainage
At present,
the "best available technology economically achievable" (BATEA)
for the treatment of acidic drainage is lime neutralization. CANMET-MMSL
is investigating ways to improve the lime neutralization process
through plant modifications to reduce reagent/operating costs and
improve effluent quality. In addition, work is ongoing to further
enhance sludge stability and density through novel treatment processes.
Field and laboratory studies allow CANMET-MMSL to assess and optimize
various aspects related to chemical treatment. For
more information, please contact
us.
Optimization
of Lime Treatment Systems
Several treatment
parameters have a significant impact on sludge production and the
geochemical stability of the sludge. Through minor modifications
to the treatment process, the properties of the sludge generated
can be tailored to the plant or site operating priorities.
CANMET-MMSL's
Environment Group has studied the effect of various process parameters
for their effect on lime consumption, energy requirements, sludge
density and stability. The database of field and laboratory information
provides a basis to optimize existing treatment operations from
the simple on-line systems to more sophisticated High Density Sludge
(HDS) processes. Modification in operating parameters can result
in considerable cost savings as well as reduction in long term environmental
liabilities associated with sludge disposal. For
more information, please contact
us.
Staged-Neutralization
Treatment Technology to Produce Super Dense Sludges
The staged-neutralization
process applies crystallization principles to enhance precipitate
crystallinity and reduce sludge volume. This process has been patented
in the United States and the Canadian patent is pending.
The staged-neutralization
process involves neutralizing in a series of steps to control the
level of supersaturation during metal precipitation. Preliminary
results indicate that in this process chemical overgrowth, not mechanical
aggregation, is the primary precipitation mechanism. In laboratory
tests, the physical properties of the sludge were greatly improved:
densification increased from 25% solids with recycling to 55-67%
solids under supersaturation controlled recycling. The settleability
of the sludge was extremely fast, 12 m/h, as compared to 4 m/h observed
with most sludges. This ability to rapidly dewater allows the sludge
to reach its maximum densification much fast than typical sludges.
The mean true particle size (not aggregate) triples to 20 micrometres.
Unlike most treatment plants in operation, the sludge produced contained
crystalline iron compounds rather than an amorphous phase. For more
information, please contact us.
Sludge
Disposal Options
Despite recent
improvements to the traditional neutralization method, it is estimated
that as much as 6.7 million cubic metres of lime treatment sludge
is produced annually in Canada. In addition, the minerals industry
is faced with questions related to the long-term stability of acid
mine drainage (AMD) treatment sludges and their environmentally
acceptable disposal. Recent studies have indicated that lime sludge
is stable, as defined by waste regulations, if disposed of in a
pond-type environment. However, the majority of the lime treatment
sludge produced is voluminous and consists of an amorphous hydroxyl-carbonate-sulphate-hydrate
thatserves to scavenge metal species. Many mine sites choose to
dispose of lime sludge with mill tailings to reduce the waste disposal
resources required to dispose of tailings and sludge separately.
While there is some perception that the addition of lime sludge
to a tailings impoundment area may provide buffering capacity, this
has yet to be validated. CANMET-MMSL is current investigating various
options for sludge disposal to limit metal mobility and to reduce
liability and costs associated with sludge disposal. For more information,
please contact us.
Mobile
Lime Treatment Pilot Plant Facility
CANMET-MMSL's
Environmental Group is investigating ways to improve the lime neutralization
process for the treatment of acid mine drainage (AMD) and has developed
a modular-mobile test facility. The pilot plant configuration consists
of a gravity-fed cascade of tanks that utilize stepwise neutralization,
aeration, flocculation and sludge recycle processes to produce a
high-density sludge and is based on similar industrial plant processes.
The treatment facility has a flexible design, allowing it to be
reconstructed to simulate and optimize a variety of treatment processes.
Presently, the plant is running in HDS mode while plans are under
way to use the facility to evaluate the staged-neutralization process.
For more information,
please contact us.
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