Metal Transport in Groundwater Contaminated by Acid Mine Drainage

Abstract

Acid mine drainage from a rock dump at an abandoned mine in Dalarna, Sweden, has contaminated the groundwater and created a leachate plume characterized by low pH and high concentrations of Fe, SO4, and heavy metals. Groundwater samples have been collected in order to explain the observed spatial variations in groundwater chemistry. The mineralogy of soil samples collected at the water table has been identified by X-ray diffraction analysis In order to determine which processes may be controlling the evolution of the leachate plume, the geochemical mass-transfer model PHREEQE is used to evaluate a possible reaction pathway controlling the reaction of the leachate plume with uncontaminated groundwater and the till aquifer. The results suggest that silicate weathering and goethite precipitation are the processes primarily controlling observed pH, pe, and Fe concentrations in groundwater direct down-gradient of the rock dump. Increases in K, Na, and Al concentrations along the flow path can be attributed to the feldspar weathering while Al and SO4 concentrations further down-gradient can be controlled by the precipitation of AlOHSO4. The attenuation of heavy metal concentrations may be the result of adsorption and coprecipitation with goethite and other Fe xides.

Properties of Goethite and Jarosite Precipitated from Acidic Groundwater, Dalarna, Sweden

“…Previous mineral equilibria studies (Herbert 1994(Herbert , 1995a(Herbert , 1995b, using geochemical conditions observed near well B1 (Table 1), have concluded that goethite is the most stable secondary Fe mineral forming in the groundwater. Lepidocrocite reaches saturation in the groundwater only during snowmelt when groundwater pH increases (Herbert 1995b).…”

“…The glacial till has developed from the gneissic bedrock, and it is consequently noncalcareous with a low acid neutralization capacity. Groundwater occurs in the unconfined till unit, and has been investigated in geochemical studies by Herbert (1994Herbert ( , 1995b. The studies indicate that the atmospheric oxidation of primarily pyrite (FeS2) and pyrrhotite (Fe7S8), along with the percolation of water through the unsaturated rock dump, has led to the contamination of the groundwater.…”

Poorly humified peat as an adsorbent for metals in wastewater

“…However, the metal concentrations were low related to leachates from other acid mine areas (e.g. [25,26]). Wastewater was collected from the KM laundry in Gammelstad after washing of overalls used by mine workers from LKAB in 1995.…”

Combined effects of dissolution kinetics, secondary mineral precipitation, and preferential flow on copper leaching from mining waste rock

“…However, as copper may also adsorb on, for example, goetite, which may be continuously formed at the prevailing p H conditions, new sites would become available. Third, copper may substitute for iron in, for example, goetite leading to coprecipitation [Herbert, 1994]. To distinguish and discriminate among these processes is a delicate task, as they may yield quite similar results with regard to limiting copper leaching at neutral p H.…”