Investigating the geochemistry and microbial ecology of heap bioleaching systems at the agglomerate scale
Cox, Alison
Date: 10 March 2018
Thesis or dissertation
Publisher
University of Exeter
Degree Title
MbyRes in Mining & Minerals Engineering
Abstract
Heap bioleaching is an alternative processing method for low-grade copper ores. Microbial iron oxidation produces ferric iron which solubilises copper-bearing minerals while microbially generated acid maintains a pH consistent with copper solubility. The microorganisms can inhabit the liquid within the heap or attach to the ore particles. ...
Heap bioleaching is an alternative processing method for low-grade copper ores. Microbial iron oxidation produces ferric iron which solubilises copper-bearing minerals while microbially generated acid maintains a pH consistent with copper solubility. The microorganisms can inhabit the liquid within the heap or attach to the ore particles. Temperature, pH, and iron content of the heap effluent (leachate) are typically monitored to examine heap health, however, the leachate has recently been disproven as an accurate analogue of the cell distribution within the ore-bed during microbial colonisation. Three ore-associated phases are now recognised, the interstitial, weakly attached and strongly attached. This dissertation examined the cell distribution, community structure, and the distribution of iron and copper between the four phases past heap colonisation. 150 g samples of non-sterile low-grade enargite ore were used to create agglomerate-scale ore-beds that were inoculated with a mixed mesophilic culture and monitored over 192 days at 27ºC. Cell distribution was at least 2500x higher in the ore-associated phases in comparison to the leachate. Leptospirillum ferriphilum was the dominant species in every phase. Iron and copper concentrations were 10x and 100x higher in the ore-associated phases compared to the leachate, respectively. Batch bioreactor tests using enargite-concentrate provided an analogue to potential conditions in the ore-associated phases in a functional heap, as only 6% of the total copper was solubilised from the agglomerate-scale beds. Microbial growth and copper dissolution decreased with pH and growth rates decreased at iron concentrations over 20g/L. On a large scale, a better understanding of the microbial environment with regards to cell and metal distribution leads to improved heap modelling and sampling procedures which examine all phases within the heap instead of the leachate only. Improved bioleaching technology then has the potential to provide a feasible method for mining refractory low-grade, large-scale deposits.
MbyRes Dissertations
Doctoral College
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