Prediction of acid rock drainage in waste rock piles part 2: Water flow patterns and leaching process

• Published in: Journal of contaminant hydrology Vol. 242; p. 103862
• Main Authors: Ma, Liang, Huang, Cheng, Liu, Zhong-Sheng, Morin, Kevin A., Aziz, Mike, Meints, Cody
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2021
• Subjects: Acid rock drainage; Heterogeneity; Leaching process; Probability density functions; Waste rock pile; Water flow pattern; Heterogeneity; Leaching process; Acid rock drainage; Probability density functions; Waste rock pile; Water flow pattern
• ISSN: 0169-7722; 1873-6009
• DOI: 10.1016/j.jconhyd.2021.103862

In waste rock piles, the leaching process involved in acid rock drainage is mainly controlled by water flow. This paper (Part 2) investigates the effects of heterogeneities on the water flow patterns by applying probability density functions to hydrogeological properties. In this study, a piecewise constant distribution is proposed to describe the permeability inside waste rock piles, which reflects the effect of both finer and coarser pores. Compared with uniform water flow obtained from traditional homogeneous modeling, various water flow patterns and their pathways inside waste rock piles can be simulated by the proposed model. In addition, the leaching process is also investigated by coupling the calculated water flow with the geochemical reaction based on the water film model proposed in part 1. For demonstration, these models are integrated and applied to the full-scale waste rock pile at Equity Silver mine in British Columbia, Canada. Because the iron loading is highly correlated to the acidity at this site, it is found that the fluctuation of annual lime consumption for neutralization at this site can be well predicted by the integrated model. In addition, the results indicate that waste rock piles with different spatial patterns of permeability distribution, but with the same probability density function, may have different water flow patterns and spatial distributions of iron concentrations inside the pile. However, the total water flow discharge rate and iron loading profiles from the pile are almost the same on the temporal scale. •Heterogeneities of permeability and water flow in waste rock piles are investigated.•A piecewise constant distribution for permeability in waste rock piles is proposed.•Combination of streamlines can be simulated, which is consistent to test observations.•Probability distribution function rather than its spatial pattern controls the output.•The fluctuation of lime consumption for full-scale waste rock piles can be simulated.