Improvement in pH and Total Iron Concentration of Acid Mine Drainage after Backfilling: A Case Study of an Underground Abandoned Mine in Japan

Abstract

If the excavated underground veins are not backfilled, they may be a factor in the continued outflow of acid mine drainage (AMD). The flow rate of AMD can be reduced by backfilling underground drifts from abandoned mines. In addition, the quality of AMD may be improved as the flow rate of AMD reduces. In this paper, the quality of the AMD after backfilling was evaluated by a three-dimensional geochemical analysis model when the groundwater level was recovered after backfilling. The measured dissolved iron (Fe) and sulfate ion (SO42−) concentrations and pH before backfilling the drift were reproduced by the calibration of the simulation. Using the calibrated model, the pH at the outlet of the drift was changed from about pH 3 before backfilling to about pH 4 to 5 after backfilling. When calcite was contained in the filling materials of the drift, the pH approached neutral. However, when gypsum was formed, the neutralization was inhibited. The Fe concentration discharged from the drift was calculated at approximately 0.002 mol/L before backfilling. The total Fe concentration was calculated at 0.0004 mol/L or less after backfilling, and the dissolved Fe concentration decreased by several orders of magnitude after backfilling. A geochemical model quantitatively evaluated the improvement in water quality after backfilling the drifts. This method can be applied to the other abandoned mines with similar hydrogeological conditions.

Study on Rock and Surface Subsidence Laws of Super-High Water Material Backfilling and Mining Technology: A Case Study in Hengjian Coal Mine

“…The dry backfilling of solid waste material mainly refers to the use of chemical waste, coal gangue, coal fly ash, smelting slag, and other solid accumulation of mining areas for backfilling, among which underground gangue backfilling is one of the main directions of research [29,30]. Paste backfilling is a method of processing solid waste into a toothpaste-like slurry, which is transported by gravity and pressure to the backfilling position [31][32][33][34][35]. Hydraulic sand backfilling refers to the use of a mortar pump or self-flow method, the tailing plant sand, smelter slag, crushed stone gravel, and other solid-liquid two-phase slurries that are transported to the well as a backfilling material to backfill the mining area.…”

Real-Time Electrical Conductivity Monitoring and Correlation with Sulfate Release and Acid Mine Drainage Potential from a Gold/Silver Paste Tailing Storage

“…AMD is produced by the oxidation of sulfur minerals and is characterized by the generation of runoff with low pH and high concentrations of heavy metals and metalloids [4][5][6]. Various studies have focused efforts on establishing tailings stabilization processes with several techniques [7][8][9]. Likewise, different technological alternatives have been addressed to treat AMD, including active and passive methods [10][11][12][13][14].…”