Modeling of titration experiments by a reactive transport model

Acid mine drainage (AMD) is commonly treated by neutralization with alkaline substances. This treatment is supported by titration experiments that illustrate the buffering mechanisms and estimate the base neutralization capacity (BNC) of the AMD. Detailed explanation of titration curves requires modeling with a hydro-chemical model. In this study the titration curves of water samples from the drainage of the As Pontes mine and the corresponding dumps have been investigated and six buffers are selected by analyzing those curves. Titration curves have been simulated by a reactive transport model to discover the detailed buffering mechanisms. These simulations show seven regions involving different buffering mechanism. The BNC is primarily from buffers of dissolved Fe, Al and hydrogen sulfate. The BNC can be approximated by: BNC = 3(CFe + CAl) + 0.05Csulfate, where the units are mol/L. The BNC of the sample from the mine is 9.25 × 10−3 mol/L and that of the dumps sample is 1.28 × 10−2 mol/L.