Application Note: Acid Mine/Rock Drainage Potential

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Assessing acid rock (ARD) and acid mine (AMD) drainage potential has never been easier, with new technology developments allowing field portable X-ray fluorescence spectrometry (pXRF) to achieve lab comparable data in-field.

Traditional approaches to assessing for ARD/AMD potential has required the collection of hundreds of samples for laboratory analysis. With the latest pXRF technology, you can reduce the number of samples for laboratory analysis, while reducing job time and cost.

Assessments of ARD/AMD often involve assessing the field pH of the matrix (soil, rock or waste) by dilution in de-ionised water. The oxidised pH of the matrix is often assessed by adding an oxidiser (e.g. hydrogen peroxide) to the solution. This tells us how the matrix will behave under oxidising conditions and the acid-forming potential of the matrix. Generally, a pH around 4 will indicate ARD/AMD forming potential.

The next step is to understand the composition of the matrix, and this is where a pXRF can be a powerful tool. Traditionally, hundreds of samples from a site of ARD/AMD concern would need to be collected and analysed in a laboratory. Using the pXRF, we can determine the elemental composition of the sample. This is important in understanding what potentially undesirable elements may be held in the matrix and liberated when ARD/AMD forms.

We then want to know what minerals the elements are bound in. In ARD/AMD assessment we are particularly interested in sulphide minerals. The Fe, Pb and Zn bearing sulphides are the most common sulphides. As water and oxygen interact with the various sulphide minerals, they can lead to ARD/AMD formation. Using a pXRF equipped with a sulphide mode, we can quantify the sulphide components. Ensuring the pXRF is appropriately calibrated and that certified reference material (i.e. NIST 2780) are analysed routinely throughout the analysis period we can achieve laboratory comparable results in a fraction of the time for laboratory analysis. A small number of samples (e.g. 10%) should be laboratory for confirmed, which can be used to adjust the calibration of the pXRF.

Applying pXRF for ARD/AMD has gained popularity in recent years, and a number of pXRF users have documented their experience. You can find some examples of applications here:

– Parbhakar-Fox, A., Aalders, J., Jackson, L., Lottermoser, B. (2016). Prediction of Acid Rock Drainage Using Field-Based Testing Tools. Environmental Indicators in Metal Mining, pp. 115-138.
– Simon, A., Ussath, M., Hoth, N., Drebenstedt, C., Rascher, J. (2014). Short Method for Detection of Acidifying and Buffering Sediments in Lignite Mining by Portable XRF-Analysis. Proceedings of the 12th International Symposium Continuous Surface Mining – Aachen 2014, pp. 329-338.
– Lee, J., Jeon, J., Chon, C., Nam, I., Cho, Y., Ryu, J., Song, Y., Kim, J. (2018). Development of assessment method for acid rock drainage generation potential using handheld XRF. Geophysical Research Abstracts, 20, 3224.
– Tuff, J., Usher, B. (2017). Field testing methods to improve sampling for acid rock drainage assessments. AusIMM Bulletin April 2017.