Abstract:

Determining the quantity of metals that can be solubilized in acid drainage events is a critical yet challenging piece of information for incorporation into geochemical models in the mining industry. Presently, the predominant methods used by researchers and practitioners to estimate worst-case scenarios involve the use of the extract from the Net Acid Generating (NAG) assay and the results from the EPA 1313 test, which evaluates leaching in relation to pH. This study compares the efficacy of these two approaches across various samples, including those with and without acid drainage generation potential and different mineralogies.

The study was meticulously structured to assess the applicability and accuracy of both methods in different geological and mineralogical contexts. The findings indicated that the mineralogy of the samples plays a crucial role in determining the most suitable method. It was observed that, depending on the mineralogical composition, the kinetics of the reactions involved in metal solubilization can vary significantly, directly affecting the accuracy and relevance of the data obtained by each testing method.

A key discovery was that while the NAG extract provides valuable insights into metal release under sulfide oxidation conditions, the EPA 1313 test, with its pH-based leaching approach, offers a more detailed and nuanced perspective, especially in samples with varied mineralogical complexities. This distinction is particularly pertinent when considering the interaction between various types of minerals and how they influence the release and mobility of metals in the environment.

The study also highlighted the importance of an integrated approach, suggesting that combining data from both tests can offer a more accurate and comprehensive representation of the potential risks associated with acid mine drainage. This combined approach allows for a better understanding of geochemical processes and significantly improves the reliability of predictive models used for planning mitigation and remediation measures.

In conclusion, this research provides valuable insights into the effectiveness of the NAG and EPA 1313 tests in assessing the risks of toxic metal release in different mineralogical contexts. The results emphasize the need for careful assessment of sample mineralogy when choosing the most appropriate testing methodology, highlighting the complexity and significance of adopting a holistic and integrated approach in monitoring and managing acid mine drainage.

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Dr. Fernando J. Vilela