Buffering Mechanisms in Acidic Mining Lakes – A Model-Based Analysis

Abstract

Buffering mechanisms of acidic mining lakes were studied on an acidic open cast lignite mining lake (Plessa 111) in Lusatia, eastern Germany. The investigations were based upon laboratory experiments, hydrochemical modelling and mineralogical structure determination. The experiments were carried out as titrations of the lake water. The modelling was done using the hydrogeochemical simulator PHREEQC. Three different phase models were applied:(1) an iron- and aluminium hydroxide precipitation model, (2) an iron- and aluminium hydroxysulphate precipitation model and (3) an iron hydroxide and aluminium hydroxysulphate precipitation model with sorption on iron hydroxide. As a result of this study four different buffers in four successive sections of the titration curve could be detected in acidic mining lake water:(1) hydrogen sulphate buffering, (2) iron buffering, (3) aluminium buffering and (4) an additional buffering (solid phase buffer) which is based on ion exchange and mineral transformation. Mineralogical analysis showed that iron precipitates as schwertmannite, an iron hydroxysulphate. Aluminium precipitates are also hydroxysulphates. These results allow formulation of process-oriented description of the buffering processes in acidic mine waters. This could lead to better reliability in lake water quality and pH-development predictions of acidic mining lakes.