Tailings
Tailings are the waste materials produced from the extraction
process used for obtaining ore. In the process of extracting the
ore, the waste material is ground into particles with a typical
grain-size distribution that ranges from medium sand to clay size
particles. If the tailings are not treated or isolated, exposure
to air and water will likely produce acid mine drainage. Tailings
near the surface of an exposed pile will oxidize most readily, while
tailings at depth will remain unoxidized.
For proposed operations, tailings samples are typically obtained
from pilot plants which are small scale milling plants implemented
before the large scale plant in order to test operational methods
and to predict environmental impacts. Samples from pilot plants
can be used for predictive testing (i.e. static and kinetic testing)
to determine the acid generation potential of the tailings. For
more information on predictive testing, click
here. During mining operations, samples may be taken from designated
tailings piles to predict their acid generating potential, similar
to that done before mining. After mining is complete, tailings samples
are commonly taken during the following steps of the reclamation
process: site assessment, removal
and disposal, waste
treatment, and monitoring and assessment (soil,
vegetation, and water).
For abandoned mines, the tailings are often found distributed around
a site and are not consolidated in designated piles. The tailings
are found in stream bottoms and floodplains, in downstream lakes
and rivers, near areas where mining took place, in areas where ore
bodies were processed, and anywhere in between. It is often necessary
to do intensive sampling during the site assessment phase at abandoned
mine locations since often times, tailings are spatially widespread.
In addition, site assessment sampling is important to characterize
the site since there is often a lack of information available on
abandoned mine sites from when mining activities were taking place.
Samples are typically analyzed for chemical and physical parameters
such as metals (water
or solids),
acidity,
alkalinity,
pH (water or
solids), carbonate,
water content,
soil texture and structure,
rock content, bulk
density, and porosity.
Since a representative sample of tailings is challenging to obtain,
a statistically-based number of tailings samples are typically collected.
Chosen sample locations should give an accurate representation of
the entire waste volume with samples being taken both vertically
and laterally. To establish background soil concentrations, multiple
background soil samples should be taken. For more information on
determining sampling numbers, sample locations, replication, etc.,
see the data quality section.
Numerous sampling methods are available and different methods are
employed based on the necessary depth of the sample, whether the
sample is submerged, and limitations of equipment access to certain
areas (i.e. steep slopes, remote areas). The sampling methods chosen
should result in a low degree of sample disturbance. For samples
on or near the surface, sampling methods such as shoveling, hand
auguring, or hand-driven coring can be used. For subsurface samples,
various drilling techniques can be employed such as split spooning
with a hollow stem auger, vibrating core (sonic), or solid stem
augering. Also trenching may be an option. For submerged samples,
methods such as gravity coring, grab sampling, and surface water
grabbing can be used. Isolation from the atmosphere is desired in
many cases which may entail the use of liners when drilling for
a sample core. Liners may also be used for collection of submerged
samples (MEND,
2001).
If you are not familiar with the different sampling methods, check
out these websites for some more info:
Solid stem and hollow stem augering and vibrating core drilling:
http://www.frtr.gov/site/samplematrix.html?
http://www.geoscience.org.za/geohydro/drill.html
http://www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-2-1908/a-b.pdf
Gravity coring:
http://home.swipnet.se/valter/ct.html
General Subsurface Sampling:
http://www.deq.state.mt.us/ppa/mdm/SOP/pdf/11-08.pdf
It is important to document the sampling program so that the location
sampled can be identified with confidence at some later date, and
the sample collection and analysis procedure can be reassessed should
the need arise.
Check out the following websites to learn more about mine tailings:
Problem | Compliance
| Health & Safety | Sampling
| Analytical | Data
Quality
Site Assessment | Prediction
| Construction | GIS
| Monitoring & Assessment
|
