Bioleaching of Indium-Containing Sphalerite and Biological Mine–Water Treatment: Two Steps Towards Greener Mining

While large-scale mining activities necessarily will considerably interfere with nature, there is clear need to make them more ecologically compatible. Bioleaching by its nature offers chances to save energy and avoid pollution by smelters, but it does not automatically result in “green” mining. One additional aspect to be considered is the question whether only the major element of an ore is won or whether trace elements which may be of strategic importance for industry are obtained in addition. Experiments with ore material and with mixed cultures from the research and teaching mine “Reiche Zeche” showed that depending on the medium used ca. 40 to 60% of the available zinc was obtained in solution. Most of the indium could also be leached, but the indium concentration found did not correlate with the loading of the solids in suspension. In order to optimize processes making use of acidophilic iron oxidizers, it is helpful to have a simple method for biomass determination. Therefore a method employing the fluorescent dye PicoGreen in microplate format was developed and found to correlate well with cell numbers per unit volume. A second aspect of green mining is the treatment of acidic waters generated. In a pilot plant for mine water treatment by iron oxidation at ca. pH 3 representatives of the new genus Ferrovum appear to dominate. Community analyses and cultures obtained show a considerable diversity of the Ferrovum relatives. Physiological experiments and genome analyses suggest that biomass yields may be improved by phosphate and/or urea addition.