Executive Summary

Oxidation of pyritic waste rock and the subsequent generation of acid mine drainage (AMD) is controlled to a large extent by the availability and transport of oxygen to the reaction sites. An understanding of the interaction of the gas transfer mechanisms within a waste rock pile is key to developing cost effective management strategies to control AMD.

The purpose of this document is to provide the rationale and description of the various techniques and procedures proven to be effective for measuring the bulk physical parameters of:

1. thermal conductivity;
2. gas diffusion; and
3. gas permeability

which are recognized as being the principal parameters required to define gas transfer. Measurement of thermal conductivities provides a means for determining oxidation rates from measured temperature distributions since oxidation, being exothermic, leads to a temperature rise, which in turn relates to the thermal conductivity of the bulk material. To reach oxidation sites within the waste rock piles, oxygen must flow through available pore spaces. There are two mechanisms that lead to this flow through gas filled pore space. The first is diffusion where the flux results from the oxygen gradient consequent on oxygen consumed in the oxidation process. The second, addressed through the measurement of gas permeability, is advection where the flux results from a pressure gradient set up in the pile.

In addition, techniques and procedures are provided in the report for monitoring temperature and oxygen concentrations within the pile. Since the pyritic oxidation reaction consumes oxygen and generates heat measurement of oxygen concentrations and temperature profiles within a waste rock pile can provide insight into the oxidation process and the pollution potential from waste rock material.

This document provides details of field installations and procedural guidelines for the measurement and monitoring of these principal gas transfer mechanisms associated with waste rock oxidation. Section l provides a general introduction. Section 2 provides the scientific background to the techniques used for in situ measurements of the key bulk physical parameters (thermal conductivity, gas diffusion, and gas permeability). Section 3 outlines the field installation techniques and instrumentation required while Section 4 outlines how the measurements are carried out and gives general guidance to data interpretation. The details of the measurement techniques, instrumentation and data reduction to obtain the bulk parameters are contained in the appendices. These appendices are sufficiently detailed to be used in the field as selfstanding guides.

Computer models such as FIDHELM (developed by Australian Nuclear Science and Technology

Organization, ANSTO) can be used to predict the impact of pyritic waste rock oxidation processes as well as evaluate various options for controlling acid drainage contamination. The measured field parameters described in this report are required as inputs to the model

Last Modified: 2003-11-26		Important Notices

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