Tuesday, 11 July 2006

The Importance of Understanding Possible Chemical Interactions in the Routine Testing Used to Assess the Acid Producing Potential and the Acid Neutralization Potential of Soils.

Joan Elizabeth Thomas1, Roger St C. Smart2, Andrea Gerson2, Paul Weber3, Russell Schumann4, George Levay4, Stuart Miller5, Warwick Stewart5, and William M. Skinner2. (1) Jefferson Lab, 12000 Jefferson ave, Mail stop 6A, Newport News, VA 23606, (2) University of South Australia, Mawson lakes, South Australia, 5095, Australia, (3) Solid Energy NZ Ltd., 2 show Place, Christchurch, New Zealand, (4) Levay & Co. Environmental Services, University of South Australia, Mawson Lakes, 5095, Australia, (5) Environmental Geochemistry International Pty. Ltd., 81A College St., Balmain, NSW, 2041, Australia

Routine testing of the capacity of soils to produce or neutralize acid can produce anomalous results. Failure to recognize such results can lead to costly over engineering or even more costly remediation. Two Australian Research Council / Australian Mining Industry Research Association projects (P387A, P387B) focused on developing an understanding of chemical factors operating in the testing of acid production from pyrite in mine waste and in accessing the neutralizing capacity of naturally occurring materials. The result was improvement in test methodologies and a greater understanding of factors which indicate that further more complex testing may be needed. The presence of organic matter and / or non iron sulfides were found to have significant influence on acid produced by testing using peroxide oxidation. It was also found that pyrite morphology could have significant influence. In testing for readily available neutralization capacity, as from carbonate, the nature of the carbonate can have a major influence on the result, Also, the presence of framboidal pyrite can have a negative influence when determining the quantity of neutralizing material present. Modification to the design of the long used Sobek test, can overcome these problems. Routinely used testing for carbonate does accommodate rapid neutralization from silicate minerals but does not identify slower sources of neutralization, as from silicate minerals. Such sources may have significant effect in situations of low acid release and slow percolation of moisture through the material.

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