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Prediction of acid rock drainage Red mountain project

University of British Columbia

Mine waste planning and management is essential to minimize the environmental impacts resulting from the deposition of mine and milling wastes, particularly with respect to acid rock drainage (ARD). Kinetic tests such as humidity cells are widely used in an attempt to predict the rates of acid generation and neutralization, water quality and time to onset of acidity. Results from a kinetic prediction program to assist in the development of a waste management plan for the Red Mountain project in North-western British Columbia have been used to evaluate the effects of testing under a variety of controlled conditions and to make long term predictions. Results of laboratory tests conducted on samples with masses of 1 to 50 kg were compared to large scale (20-tonne) test results conducted at the mine site. Non-aerated cells provided rates of weathering that were similar to the standard humidity cells. The advantages of the non-aerated test protocol over the standard humidity cell include: • improved repeatability of results, • less expensive apparatus, • easier to operate, and • require less time to obtain rates of weathering. Increasing the volume of leach water did not influence the sulfate release rate, yet it increased the rate of neutralization potential (NP) depletion. The results indicate that water addition to kinetic tests must be sufficient to remove weathering products but must not be excessive that may artificially inflate NP depletion. The cumulative amount of Mg and Ca released at the point of acidity was greater for column tests than for humidity cells, which was attributed to the test protocol. Therefore, predicting time to acidity from estimates of NP depletion are questionable. Based on the testwork, time to acidity seems to relate better to measurements of cumulative sulfate release (acid production). Laboratory oxidation rates, corrected for surface area and temperature, could not be scaled up to predict the field results. Therefore extensive laboratory kinetic test programs that attempt to account for variations in waste pile rock types are considered unwarranted until the models used to scale-up laboratory data are validated. The large scale field tests produced results that were difficult to interpret and inconsistent when compared to the laboratory tests. In addition, field tests are prohibitively expensive and time consuming. Therefore, before conducting field tests, careful consideration of the expected results and test protocols is required.

Thesis/Dissertation

application/pdf

2009-06-16

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http://hdl.handle.net/2429/9333

Materials Engineering

University of British Columbia

UBCV

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