Investigating the effect of acid stress on selected mesophilic micro-organisms implicated in bioleaching
Journal Article
2015-05-01
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Journal Title
Minerals Engineering
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Publisher
Elsevier
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University of Cape Town
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Abstract
During start-up of heap bioleaching, low grade ores are typically treated with acid for
agglomeration and to combat the acid neutralising capacity of the gangue minerals. This may
stress the bioleaching inocula, particularly upon inoculation during ore agglomeration. Acid
addition for agglomeration varies across operations, ore types and their neutralising capacity,
with limited information published on recommended concentrations. The initial pH in the
agglomeration mix is typically below pH 1.0 and may be as low as pH 0.5.
This paper investigates the effect of acid stress in terms of initial acid concentration and
exposure duration in submerged culture on mesophilic bacteria typically implicated in
mineral sulphide bioleaching and critical for heap colonisation at start-up. Following acid
stress, cultures were returned to standard operating conditions in batch stirred slurry reactors
and their performance assessed in terms of mineral leach rates, ferrous oxidation and the rate
of microbial growth. Increasing acid stress resulted in an increase in the lag period before
onset of microbial growth and iron oxidation. Following adaptation, typical growth and
ferrous iron oxidation rates were observed under low stress conditions while reduction in the
rate and extent of microbial growth and ferrous iron oxidation persisted at extreme
conditions. A reduction in yield (microbial cells produced per kg iron oxidised) was observed
with increased acid concentration over comparative times. Microbial speciation analysis
indicated a substantial decrease in the diversity of surviving bacterial species.
Description
Reference:
Ngoma IE, Ojumu TV, Harrison STL, 2015, Investigating the effect of acid stress on selected mesophilic micro-organisms implicated in bioleaching, Minerals Engineering, Volume 75, 1 May 2015, Pages 6-13