Investigating the spatial heterogeneity impact on the geochemical and mineralogical controlling factors framing acid generation at a closed tailings facility

Mineral industry is increasingly generating massive amounts of tailings, usually deposited in tailings storage facilities (TSF). To highlight the spatial variability effect on the geoenvironmental outcomes, five samples were collected from a closed TSF from different locations. The characterization findings were used to investigate the heterogeneous physical, geochemical, and mineralogical properties depending on the sample location. For instance, the pyrite content spans the interval between 0.02 and 8 wt%. Likewise, the carbonate content varies from 0.05 wt% to 43 wt%. Static tests performed to assess the potential of acid generation yielded various findings regarding the acid generation potential. Therefore, each static test should be interpreted without overlooking its limitations and the mineralogical implications under the test operating conditions. Hence, a thorough mineralogical characterization was undertaken for the selected samples to highlight their inherent mineralogical differences. Additionally, kinetic testing using weathering cell tests, highlighted that the samples C1 and C2 are acid generating, whereas C3, C4 and C5 maintain circumneutral to alkaline pH throughout the testing period. Iron release was negligible for the samples C2, C3, C4 and C5 due to its precipitation as secondary iron-oxyhydroxides that coated pyrite in circumneutral conditions. A kinetic model was established using PHREEQC to perform a parametric analysis regarding the neutralization lag time of silicates as well as the effect of calcite depletion on iron and sulfate release. The main outcome of the model underline that at least 20 wt% albite should be included in a calcite-based amendment to prevent iron release upon calcite depletion or passivation.