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Solids Sampling

TECH GUIDE

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:

 

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