Some important developments in biomining during the past thirty years
A selection of significant discoveries in the general field of biomining over the past thirty years with which the author has been directly or indirectly involved will be reviewed. Early steps in the development of the Biox® stirred tank process for the recovery of gold from arsenopyrite ores from laboratory work carried out in the early 1980s up to construction of the first full-scale processes will be described. This will include the development and adaptation of microbial inocula for such processes and that besides selection for arsenic resistance, selection for rapid growth in a continuous-flow system was almost certainly an important, though little recognized, time-consuming adaptation requirement. How the use of molecular techniques led to the discovery that Acidithiobacillus ferrooxidans did not play a major role in continuous-flow biooxidation tanks and why this is so will be discussed. Molecular techniques also clarified our understanding that some of the microorganisms that were initially recognized as being major role players in many bioleaching operations, such as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans consisted of more than one species and that the species initially identified were, in many cases, not the main role players. The track record for the development of genetic systems for some of the main microbial role players in bioleaching will be briefly described as well as some of what has been learned during this development. This includes evidence that families of plasmids with similar DNA backbones exist within isolates of certain bacterial species even though the isolates originated from different continents. However, the accessory genes that they carry may be very different. The view that genetically manipulated microorganisms are likely to play a very limited role in tank and heap leaching operations that are open to the environment will be defended. In conclusion, some of the history of the debate concerning the direct vs indirect mechanisms of bioleaching will be briefly reviewed, the possibility of nanowires as well as how the idea of ‘contact’ vs ‘non-contact’ leaching has helped to resolve that debate.