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The design, construction, instrumentation and initial response of a field-scale waste rock test pile Corazao Gallegos, Juan Carlos

Abstract

The geochemical and hydrological behavior of waste rock systems is usually predicted by conducting laboratory scale tests such as humidity cells and small-scale barrel tests. While these test procedures for the prediction of geochemical behavior are well developed and widely adopted in practice, little is known if the results obtained from these small scale tests can be used to describe and predict the full-scale behavior of waste rock impoundments under natural field conditions. Direct observations and measurements of water movement through waste rock dumps are necessary to improve the understanding of the hydrology of the dump and its influence on the geochemistry of full-scale waste rock dumps. These observations of oxygen and water movement are possible through the implementation of field-scale experiments. Some field-scale experiments have been developed in the last few decades; all of them focus primarily on studying waste rock geochemistry and hydrology in acid production environments. However, some ore bodies are hosted in rock with high neutralization capacity such as carbonates, generating alkaline/neutral drainage from the waste rock dumps. This type of drainage can also produce adverse effects on the environment. The alkaline/neutral drainage from waste rock dumps can limit the dissolution and mobility of some metals although other environmentally hazardous elements are not strongly attenuated at high pH. This thesis is part of an extensive research program currently undertaken by the University of British Columbia in Vancouver, Canada in collaboration with Teck Cominco Limited, the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Antamina mine in Peru to investigate waste rock hydrology and geochemistry in a neutral drainage environment. The field experimentation includes five field-scale waste rock test piles, a number of barrel-sized field cells and a cover study. The scope of this research involved the design, construction and instrumentation of a field-scale waste rock test pile constructed at the Antamina mine, which is hosted in rock with high ii neutralization capacity. The experimental data was used to analyze the initial hydrological and geochemical response of the constructed pile. The general conclusions are that: the test pile construction sequence and the meteorological conditions at the site during the construction and subsequent operation of the pile had a significant influence on the initial hydrological response of the test pile; the infiltration and drainage conditions in the test pile reached a semi-steady state in relatively short period of time; the effect of material segregation, heterogeneity and the presence of preferential flow paths appear to be evident; and, that the levels of electrical conductivity measured and the sulfates released along with concentrations of metals such as Cu and Zn suggests that oxidation is taking place within the pile.

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