A Test of Two Methods for Waste Rock Drainage Quality Prediction: Aqua Regia Extraction and Single‑addition Net‑acid Generation Test Leachate Analysis

The mobility of contaminants from mine waste can be assessed using different extraction methods. Aqua regia (AR) extraction is the most commonly used method in Finland. Another method is the analysis of leachate from net acid generation (NAG) tests, primarily designed for acid production potential assessment. This study investigated the performance of single-addition NAG test leachate analysis and AR extraction in predicting drainage quality, utilizing waste rock and drainage water samples from several Finnish waste rock sites. The primary objective was to enhance the interpretation of results from both methods in drainage quality prediction. Findings revealed that AR extraction effectively reflected the elevated concentrations of certain elements in drainage water, although it over-predicted levels of Al, As, Cd, Co, Cu, and Ni under certain circumneutral conditions, as well as Cr in general. Conversely, the single-addition NAG test leachate analysis performed well in assessing the mobility of contaminants, particularly Al and Cr in acid mine drainage contexts. However, due to precipitation of contaminants in neutral NAG test solutions, the applicability of this method in neutral mine drainage cases necessitates further exploration. Limitations of this study include the focus on surface samples from waste rock piles, warranting future examinations to encompass waste rock histories and drainage quality shifts.