Totsche, O., Pothig, R., Uhlmann, W., Buttcher, H., & Steinberg, C. E. (2004). Buffering Mechanisms in Acidic Mining Lakes -- A Model-Based Analysis. Aquatic Geochemistry, 9, by Alex Stalboerger NDSU Geol 628 Geochemistry 2010

Introduction Extensive open cast lignite mining was done in eastern Germany for several decades before German reunification After the mines were closed approximately 200 acid mine lakes were formed through natural inflow of groundwater, surface runoff, and man-controlled flooding

Introduction cont. The weathering of sulfide minerals and low carbonate content of the soil resulted in extreme acidification of many of the lakes These lakes are not suitable sources for drinking water, fishing or recreational purposes due to the high acidity It is also possible that the highly acidic water in these lakes could potentially contaminate neutral groundwater

Buffering Mechanisms The main problem with neutralizing these lakes is the extremely high acidity produced by very strong buffering systems Hydrogen sulfate buffering Iron buffering Aluminum buffering Buffer based on ion exchange and mineral transformation

Buffering Mechanisms I will be focusing on neutralizing one of the major buffering mechanisms that is characterized by the formation of Goethite (FeOOH (s) ), from Schwertmannite (Fe 16 O 16 (OH) 16-2x (SO 4 ) x(s) ): Fe 16 O 16 (OH) 16-2x (SO 4 ) x(s) + 2xH 2 O  16 FeOOH + xSO xH +

Theoretical Situation To neutralize the buffering mechanism I will propose a theoretical situation I will assume that near the acid mine lakes there is a farming community The farmers use traditional fertilizers that contain N and P. Also within the soil there are sulfate compounds Water containing N, P, and Sulfate have spilled into acid mine lakes

Objective Using data for standard farm runoff concentrations of N and P of mmol/L and mmol/L respectively (Mitsch & Gosselink 2007), I will attempt to find a concentration of Sulfate that will begin to neutralize the Schwertmannite/Goethite buffering mechanism

Input File SOLUTION 1 pH 2.55 temp 25 pe units mmol/L Al 1.05 Ca 4.64 Cl 0.25 Fe(2) Fe(3) 2.68 Mg 1.14 Mn 0.05 K 0.08 Na 0.31 S as SO4-2 SAVE solution 1 END TITLE Untitled SOLUTION 2 pH 7.0 charge temp 25 pe units mmol/L N P S as SO4-2 SAVE solution 2 END TITLE MIX END

Solution 1 Output Phase SI log IAP log KT Goethite FeOOH pH = 2.55 Within normal acid mine lake conditions Goethite is supersaturated and present in mineral form

Solution 1 &2 Mixed Output Phase SI log IAP log KT Goethite FeOOH pH = 2.45 At a Sulfate concentration of mmol/L, the SI of Goethite drops to and is undersaturated and begins to dissolve in solution

SI Trends

Conclusion When acid mine lake water is mixed with water containing N, P and Sulfate it can affect the buffering mechanisms within the water creating such highly acidic conditions. When water containing a Sulfate concentration of mm0l/L, along with N and P concentrations of mmol/L and mmol/L the Schwetmannite/Goethite buffering mechanism is effectively reversed.

Conclusion cont. Even though the buffering mechanism appears to be reversed the system still maintains highly acidic conditions. In fact the pH move from 2.55 to 2.45 Efforts are still being made to understand the mechanisms and strength of the buffer systems