Sediment Conditioning with Organic and/or Inorganic Carbon Sources as a First Step in Alkalinity Generation of Acid Mine Pit Lake Water (pH 2−3)

Abstract

Laboratory scale microcosm studies were conducted to determine the efficacy of controlled in situ saprobization of lake sediments as one opportunity for deacidification of artificial shallow lakes resulting from open cast lignite mining located in southeast Germany. Under lasting anoxic conditions iron and sulfate were removed from the lake water as a result of microbial iron- and sulfate reduction together with a subsequent precipitation of insoluble sulfide minerals to the lake sediment. The 2 L closed system microcosms were made up of a model of the sediment/water interface. They were filled with lake water and sediment and treated subsequently with different organic and/or inorganic carbon sources in combination with wheat straw. Just the water was characterized initially and finally 8 weeks later. The rise of pH together with acidity consumption was observed. In the microcosms treated with wheat straw and pyruvate, ethanol, Carbokalk, or Pfezi-granula the pH rose to 5.5 and 7.0, respectively, and iron- and sulfate reduction were observed. With wheat straw and ethanol or Pfezi-granula sulfate concentrations decreased from initial concentrations of 11.5−13.5 mmol L-1 to final concentrations of < 3 mmol L-1. However, the iron concentration decreased significantly to a value of 0.01 mmol L-1 exclusively with Pfezi-granula and wheat straw. For the most reactive microcosms geochemical equilibrium calculations suggest precipitation of different sulfide minerals. The critical revision of the results obtained from this study indicate that ethanol or Carbokalk together with wheat straw are suitable for further upscaling in larger-scale microcosms.