Dynamic microbial populations in heap leaching of zinc sulphide ore

Polymerase chain reaction (PCR) technology was used to monitor the microbial population within two 6-m-high sulphide ore heaps where zinc was bioleached. Genomic DNA was isolated from microorganisms attached to the ore particles. The microbial population varied in diversity at different heap heights and at different stages of the leaching cycle. Nine bioleaching microorganisms were identified, including iron oxidizers, sulphur oxidizers, whether mesophiles, or moderate thermophiles. No bioleaching extreme thermophiles were detected. Moderate thermophiles were present at average heap temperatures of 40 °C or higher. No moderate thermophiles were present in the top 2 m of the heaps. Mesophiles were present throughout the lifetime of the heaps and at all heap depths. Cultures of Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans originally introduced to inoculate the heaps did not proliferate but were instead displaced by other species; no benefits were obtained from heap inoculation. The most predominant species were Acidithiobacillus thiooxidans and Acidithiobacillus albertensis. Leptospirillum sp. was not predominant in the heaps, in contrast to the dominant role this organism plays in tank bioleaching operations.