Weathering of unsaturated waste rocks from Kevitsa and Hitura mines: Pilot-scale lysimeter experiments and reactive transport modeling

Muhammad Muniruzzaman,Teemu Karlsson,Navid Ahmadi,Päivi M Kauppila,Tommi Kauppila,Massimo Rolle

doi:10.1016/j.apgeochem.2021.104984

Abstract

The fundamental understanding of hydrogeochemical processes leading to toxic drainage in mining environments is of utmost importance to predict the impact of mining activities in waste facilities and to design effective measures for the mitigation of environmental risk. This study investigates the weathering behavior of different types of mine waste rocks, with considerably different mineralogical and textural properties, by performing long-term (>3 years) pilot-scale lysimeter experiments combined with multiphase and multicomponent reactive transport modeling. The experiments were carried out in a series of five lysimeter setups, packed with unsaturated waste rocks collected from the Kevitsa and Hitura mine sites in Finland, under the influence of outdoor atmospheric conditions. We focus on the temporal dynamics of the waste rock effluents’ chemistry showing remarkably different compositions in different experiments. The low-sulfide containing Kevitsa pyroxene and Hitura serpentinite waste rocks lead to alkaline drainage, characterized by higher pH (up to 9.5) and lower dissolved constituents (e.g., up to 420 mg/L SO4, 89 μg/L Ni). In contrast, the effluents from the Hitura mica schist waste rocks, which have relatively higher sulfide abundance, show characteristics of acidic drainage with lower pH (~4.3) and orders of magnitude higher aqueous concentrations (e.g., up to 3100 mg/L SO4, 130 mg/L Ni). The results also show that the presence of a higher fraction of finer particles leads to a faster dissolution rate and thus relatively higher drainage concentrations. The experimental results were quantitatively interpreted with multiphase and multicomponent reactive transport modeling, which allowed capturing the complex dynamic trends and the concentration levels observed in the effluents of the different pilot-scale lysimeters.

Highlights

Mine waste management represents a key challenge in the mining sector because improper waste disposal can result in liability for mine operators with the risk of severe environmental pollution, financial consequence and reputational damage (e.g., INAP-GUARD, 2014; Blowes et al, 2014; MEND, 2017)
This study investigates the weathering behavior of different types of mine waste rocks, with considerably different mineralogical and textural properties, by performing longterm (>3 years) pilot-scale lysimeter experiments combined with multiphase and multicomponent reactive transport modeling
The performed simulations could reproduce the experimental behavior of the drainage chemistry by adopting a net water influx equal to 30% of the measured precipitation rate in different setups

Summary

Introduction

Mine waste management represents a key challenge in the mining sector because improper waste disposal can result in liability for mine operators with the risk of severe environmental pollution, financial consequence and reputational damage (e.g., INAP-GUARD, 2014; Blowes et al, 2014; MEND, 2017). Sulfide minerals are prone to oxidation once exposed to atmospheric oxygen and water, and can lead to the production of acidity, mobilization of toxic elements and release of polluted drainage containing high con centrations of dissolved metals and metalloids (e.g., Blowes and Jambor, 1990; Nordstrom et al, 2000; Parbhakar-Fox and Lottermoser, 2015; Dold et al, 2017) The transport of such low-quality drainage from mine wastes into receiving surface- and groundwater bodies may severely deteriorate water quality and harm aquatic ecosystem (e.g., Moncur et al, 2005; Amos et al, 2015). A thorough understanding of the governing physical, chemical and microbial processes occurring within the mine waste systems, and their complex interplay is of utmost importance for sustainable mine waste management (e.g., Singer and Stumm, 1970; Gunsinger et al, 2006; Heikkinen and Raisanen, 2009; Bailey et al, 2013; Neuner et al, 2013; Blowes et al, 2014; Haberer et al, 2015; Nordstrom et al, 2015; Dangelmayr et al, 2017; Munir uzzaman et al, 2018a; Bao et al, 2020a,b; Vriens et al, 2020a)

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