Abstract
Water substantially but differently influences the physical versus geochemical stability of mine waste materials. The impact of water content on weathering dynamics at a microscale level and subsequent bulk leachate quality remains incompletely understood. We conducted controlled, 13-week weathering experiments, manipulating water saturation levels to quantitatively assess mineral dissolution, precipitation reactions, and their implications for leachate quality. Our findings reveal leachate hydrochemistry was significantly different across water content, closely related to the mineral composition and texture. The pH consistently decreased with lower water saturation, ranging from a final average of 6.14 at full saturation to 5.37 at 5% saturation. Simultaneously, mineralogical analyses show a reduction in the size of carbonate phases, diminishing from 200µm to 145µm as water content increases from 5% to 100%. Furthermore, total concentrations of iron (Fe) and copper (Cu) rise as moisture levels decrease, with Cu concentrations surging 24-fold in samples at 5% saturation compared to full saturation. These correlate the controls of specific sulfide and carbonate mineral dissolution dynamics on bulk drainage acidification versus neutralization, respectively, as well as metal mobilization rates. Our findings highlight the value of diligent mineralogical sample preparation, and quantitative analysis for mine waste management.