Effects of estuarine water mixing on the mobility of trace elements in acid mine drainage leachates

This research reports the effects of pH increase on contaminant mobility in acid mine drainage from the Iberian Pyrite Belt by seawater mixing in the laboratory, simulating the processes occurring in the Estuary of Huelva (SW Iberian Peninsula). Concentrations of Al, Fe, As, Cu and REY in mixing solutions significantly decreased with increasing pH. Schwertmannite precipitation at pH 2.5???4.0 led to the total removal of Fe(III) and As. Subsequently, iron-depleted solutions began to be controlled by precipitation of basaluminite at pH 4.5???6.0, which acted as a sink for Al, Cu and REY. Nevertheless, as the pH rises, schwertmannite becomes unstable and releases back to solution the previously retained As. Moreover, other elements (S, Zn, Cd, Ni and Co) behaved conservatively in mixing solutions with no participation in precipitation processes. Some toxic elements finally end up to the Atlantic Ocean contributing to the total pollutant loads and environmentally threatening the coastal areas.

Automated summary

This research investigates the impact of pH increase on contaminant mobility in acid mine drainage. The study finds that higher pH levels result in significant decrease of Al, Fe, As, Cu, and REY concentrations in the mixing solutions. Precipitation of schwertmannite and basaluminite plays a crucial role in removing Fe(III), As, and other elements. However, as the pH rises, schwertmannite becomes unstable and releases back the previously retained As, while other elements exhibit conservative behavior. The presence of toxic elements in the Atlantic Ocean poses a threat to coastal areas.