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Investigation of bacterial ferrous iron oxidation kinetics in a novel packed-column reactor: pH and jarosite management
Author(s)
Wanjiya, Mwema
Date Issued
2013
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
Jarosite formation is regarded as undesirable in the bioleaching processes as it depletes ferric
reagent; a critical reagent for the oxidation of most sulphide minerals, from bioleach solution. It
creates kinetic barriers and clogs on mineral surfaces, thereby retarding leach rates of most
minerals. However, jarosite has also been shown to serve as support for the attachment of
bioleaching microbes, facilitating a high ferric-iron generation rate. In this study, a series of
experiments on microbial ferrous-iron oxidation by a mesophilic microbe were carried out in a
novel packed-column bioreactor with a view to investigating the potential use of solution pH to
manage jarosite accumulation in the bioreactor. The kinetics of the oxidation was also
investigated to establish base case data for the novel bioreactor.
The bioreactor was packed with glass balls 15 mm in diameter. The experiments were
conducted at a constant temperature of 38.6 °C, residence time of 18 hrs, airflow rate of 20
mL.s-1 and at desired solution pHs (1.3, 1.5 and 1.7). The results showed that the amount of
jarosite accumulation is proportional to the operating solution pH and also to the duration of
operation of the bioreactor. Jarosite precipitate of 4.95, 5.89 and 7.08 g.L-1 were obtained after
10 days of continuous operation at solution pH of 1.3, 1.5 and 1.7 respectively, while after 15
days the precipitate concentration increased to 5.50, 7.90 and 9.98 g.L-1respectively. The
results also showed that a 33% and 52% reduction in jarosite accumulation could be achieved
by a gradual decrease of the bioreactor solution pH after being continuously operated for 10
days from pH 1.7 to 1.5 and pH 1.7 to 1.3, respectively, for an additional five days of continuous
operation. The results of the ferrous-iron biooxidation kinetics investigated at pH 1.3 show a
maximum ferrous oxidation rate ( max
2 Fe
r ) of 6.85 mmol.L-1.h-1 and apparent affinity kinetics
constants ( 2 Fe
K , 2 Fe
K ) of 0.001 mmol Fe2+.L-1 and 0.006 (dimensionless) using Hansford and
Monod equations, respectively. Although a direct relationship exists between jarosite formation
and solution pH, the results of this study may be relevant in bioleach heaps, or at least in
column bioreactors, to manage and control jarosite accumulation, thereby improving leach
kinetics of sulphide minerals.
reagent; a critical reagent for the oxidation of most sulphide minerals, from bioleach solution. It
creates kinetic barriers and clogs on mineral surfaces, thereby retarding leach rates of most
minerals. However, jarosite has also been shown to serve as support for the attachment of
bioleaching microbes, facilitating a high ferric-iron generation rate. In this study, a series of
experiments on microbial ferrous-iron oxidation by a mesophilic microbe were carried out in a
novel packed-column bioreactor with a view to investigating the potential use of solution pH to
manage jarosite accumulation in the bioreactor. The kinetics of the oxidation was also
investigated to establish base case data for the novel bioreactor.
The bioreactor was packed with glass balls 15 mm in diameter. The experiments were
conducted at a constant temperature of 38.6 °C, residence time of 18 hrs, airflow rate of 20
mL.s-1 and at desired solution pHs (1.3, 1.5 and 1.7). The results showed that the amount of
jarosite accumulation is proportional to the operating solution pH and also to the duration of
operation of the bioreactor. Jarosite precipitate of 4.95, 5.89 and 7.08 g.L-1 were obtained after
10 days of continuous operation at solution pH of 1.3, 1.5 and 1.7 respectively, while after 15
days the precipitate concentration increased to 5.50, 7.90 and 9.98 g.L-1respectively. The
results also showed that a 33% and 52% reduction in jarosite accumulation could be achieved
by a gradual decrease of the bioreactor solution pH after being continuously operated for 10
days from pH 1.7 to 1.5 and pH 1.7 to 1.3, respectively, for an additional five days of continuous
operation. The results of the ferrous-iron biooxidation kinetics investigated at pH 1.3 show a
maximum ferrous oxidation rate ( max
2 Fe
r ) of 6.85 mmol.L-1.h-1 and apparent affinity kinetics
constants ( 2 Fe
K , 2 Fe
K ) of 0.001 mmol Fe2+.L-1 and 0.006 (dimensionless) using Hansford and
Monod equations, respectively. Although a direct relationship exists between jarosite formation
and solution pH, the results of this study may be relevant in bioleach heaps, or at least in
column bioreactors, to manage and control jarosite accumulation, thereby improving leach
kinetics of sulphide minerals.
Additional information
Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2013
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