Buffering of Acidic Mine Lakes: The Relevance of Surface Exchange and Solid- Bound Sulphate
Buffering mechanisms in an acidic mine lake in Lusatia, Germany were investigated. The titration curve has four sections with different buffering mechanisms: (1) buffering by free hydrogen ions and hydrogen sulphate (pH = 2.55-2.9), (2) buffering by Fe with bound SO4 (pH = 2.9-4.3), (3) buffering by Al with bound SO4 (pH = 4.3-5.5), and (4) buffering by surface exchange of SO4 and basic cations (pH > 5.5). Three different phase models were applied to simulate the titration curve: (1) an iron and aluminium hydroxide model, (2) an iron and aluminium hydroxysulphate model, and (3) an iron hydroxide model with surface exchange for SO4, Ca, and Mg, coupled with an aluminium hydroxysulphate model. The uncertainty of model input parameters was accounted for in a sensitivity analysis. Only the third model, which considers surface exchange, was able to adequately reproduce the measured titration curve.