Microbial population dynamics of inoculated low-grade chalcopyrite bioleaching columns

This study investigates the effect of temperature on the population dynamics of microorganisms in bioleaching columns charged with a low-grade chalcopyrite ore. A mixed culture containing ten known bioleaching microorganisms was used to inoculate four bioleaching columns operated at 60, 50, 40 or 30 °C. Subsequently, Terminal Restriction Fragment Length Polymorphism (T-RFLP) was used to examine the diversity of bacterial and archaeal populations in the leachates and ores of the four columns. Similar results from samples collected from different locations in the columns give confidence in the reproducibility of the methods used. 10 microbial inoculants, only Acidithiobacillus caldus, Leptospirillum ferriphilum and Ferroplasma acidiphilum were identified from the leachate and the column solids. However, adventitious growth of a number of other species resulted in different microbial populations in the leachate and on the ore. The results bring into question the effectiveness of heap inoculation, a strategy proposed to overcome the paucity of thermophilic organisms occurring naturally, even in very long-term sulfide-leaching operations. The anticipated impact of temperature on the leachate population was ameliorated by the solution management regime used for the columns, which was chosen to imitate heap leach practice.