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Applied and Environmental Microbiology, August 1999, p. 3588-3593, Vol. 65, No. 8
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
A Novel Mineral Flotation Process Using
Thiobacillus ferrooxidans
Toru
Nagaoka,
Naoya
Ohmura,* and
Hiroshi
Saiki
Department of Bio-Science, Central Research
Institute of Electric Power Industry, 1646 Abiko, Abiko City,
Chiba, Japan
Received 2 March 1999/Accepted 20 May 1999
 |
ABSTRACT |
Oxidative leaching of metals by Thiobacillus
ferrooxidans has proven useful in mineral processing. Here, we
report on a new use for T. ferrooxidans, in which bacterial
adhesion is used to remove pyrite from mixtures of sulfide minerals
during flotation. Under control conditions, the floatabilities of five
sulfide minerals tested (pyrite, chalcocite, molybdenite, millerite,
and galena) ranged from 90 to 99%. Upon addition of T. ferrooxidans, the floatability of pyrite was significantly
suppressed to less than 20%. In contrast, addition of the bacterium
had little effect on the floatabilities of the other minerals, even
when they were present in relatively large quantities: their
floatabilities remained in the range of 81 to 98%. T. ferrooxidans thus appears to selectively suppress pyrite
floatability. As a consequence, 77 to 95% of pyrite was removed from
mineral mixtures while 72 to 100% of nonpyrite sulfide minerals was
recovered. The suppression of pyrite floatability was caused by
bacterial adhesion to pyrite surfaces. When normalized to the mineral
surface area, the number of cells adhering to pyrite was significantly
larger than the number adhering to other minerals. These results
suggest that flotation with T. ferrooxidans may provide a
novel approach to mineral processing in which the biological functions
involved in cell adhesion play a key role in the separation of minerals.
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INTRODUCTION |
Leaching metals from low-grade ores
is a well-established application of bacteria to mineral processing
(15). For instance, Thiobacillus ferrooxidans is
able to oxidize pyrite to ferric ions and sulfate, thereby contributing
to the extraction of many kinds of valuable metals from a low-grade
mineral. In contrast to this biological processing, physical-chemical
methods have heretofore been utilized to remove impurities from sulfide
minerals. Flotation is known as one of the methods which can separate
minerals on the basis of differences in the mineral surface properties. In the flotation process, mineral particles with hydrophobic surfaces attach to air bubbles generated at the bottom of a flotation column and
float up to form a froth at the top of the column. In contrast, particles with hydrophilic surfaces do not attach to bubbles and sink
to the bottom, forming a tailing. Because of its hydrophobicity, pyrite
present as an impurity may contaminate froths containing other more
desirable hydrophobic minerals. In many cases, chemical reagents (e.g.,
cyanide) have been added to flotation columns with the goal of altering
the floatability of pyrite. However, success has been limited, and
pyrite contamination continues to be a problem.
Recently, much attention has focused on an alternative approach
involving the use of bacteria to modify the floatability of mineral
particles. Many reports have suggested that certain types of bacteria,
including T. ferrooxidans, may suppress floatability (20). The postulated mechanism of this suppression is an
increase in surface hydrophilicity due to adhesion of bacterial cells
(12). If true, the ability of specific bacteria to
selectively adhere to and alter the surface properties of specific
minerals could be highly useful. In that regard, T. ferrooxidans appears able to adhere well to iron-bearing minerals.
If the bacterium adheres selectively to (iron-bearing) pyrite, its
addition to a mineral mixture in a flotation column should suppress
pyrite floatability without suppressing flotation of the other minerals
contained within the mixture.
In this report, the ability of T. ferrooxidans to adhere to
selected minerals was investigated with the aims of clarifying whether
the bacterium selectively adheres to pyrite and determining whether it
will effectively remove pyrite from mixtures of sulfide minerals.
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MATERIALS AND METHODS |
Microorganism, medium, and conditions of cultivation.
The
iron-oxidizing bacterium T. ferrooxidans ATCC 23270 was used
in this study. T. ferrooxidans was cultured in 9K medium containing (per liter of distilled water) 3.0 g of
(NH4)2SO4, 0.5 g of
MgSO4 · 7H2O, 0.1 g of KCl,
0.5 g of K2HPO4, 0.01 g of Ca(NO3)2, and 44.2 g of
FeSO4 · 7H2O; the pH was adjusted to 2.5 with 6 N H2SO4. The bacteria were cultivated
for 3 days in a 10-liter carboy containing 7 liters of 9K medium
aerated at 30°C.
Sulfide minerals.
Pyrite (Cerro mine, Peru), chalcocite
(Broken Hill mine, Australia), millerite (Nepean nickel mine,
Australia), molybdenite (Wolfram Camp mine, Australia), and galena
(Sweetwater mine, Missouri) were used in this study. The pyrite and
chalcocite were purchased from Nihon Chikagaku Co. Ltd., Kyoto, Japan,
and the other minerals were purchased from Iwamoto Mineral Co. Ltd.,
Tokyo, Japan. All of the minerals were museum grade and >90% pure.
With the exception of molybdenite, the minerals were ground with an
agate mortar; molybdenite was ground with an impeller mill. The crushed
particles were fractionated with 200- and 270-mesh sieves. The
fractions between minus 200 and plus 270 mesh were sonicated for
several minutes in acetone to dissociate the very fine particles from the larger ones. The detached fine particles were removed by decanting; the large particles were dried at room temperature and used in subsequent experiments.
Specific surface areas of sulfide minerals.
The surface
areas of sulfide mineral particles were determined by the BET method,
by surface area gas adsorption (Quantasorb 9S-13; Quantachrome, New
York, N.Y.), or by direct microscopic visualization. By the BET method,
1.5 g of each mineral was subjected to three nitrogen-helium gas
mixtures containing 9.92, 19.7, and 29.7% nitrogen; the surface area
was estimated as a function of nitrogen adsorption. The microscopy
entailed photographing each sulfide mineral under a stereoscopic
microscope (×750), digitizing the images with an image scanner
(GT-9000; Epson Co., Tokyo, Japan), and storing the digital images on a
computer for later analysis. The major and minor lengths of >100
randomly selected individual mineral particles were measured with an
image analyzer (IP Lab Spectrum; Signal Analytics Co., Vienna, Va.).
The average particle size was calculated by assuming the shapes were
rectangular parallelepipeds. The number of particles per mineral weight
was estimated from both the volume of the average particle and the
specific gravity. Surface area per mineral weight was then calculated
by multiplying the total particle number per mineral weight by the
surface area of a single particle.
Adhesion experiments.
Culture medium containing T. ferrooxidans was passed through filter paper (no. 2; Advantec Toyo
Co., Tokyo, Japan) to remove precipitated ferric compounds. The
filtrate was then centrifuged at 15,000 × g for 15 min
to collect the cells. The harvested cells were washed three times with
sulfuric acid solution (pH 2.0) and then resuspended in sulfuric acid
solution at various cell densities. Cell density was estimated from a
previously constructed calibration curve in which optical density at
610 nm was plotted as a function of the density of T. ferrooxidans cells.
Adhesion experiments were carried out using both individual minerals
and mineral mixtures. In the case of the former, 0.5 g of each
sulfide mineral was added to 2 ml of cell suspension (3.2 × 108 cells/ml). The suspension was then shaken for 1 min
with a vortex mixer and then allowed to settle for 5 min. At that
point, the optical density of the supernatant was measured to determine
the cell density. In the case of mineral mixtures, 0.2 g each of
four minerals (chalcocite, millerite, molybdenite, and galena) plus various amounts of pyrite (0.25, 0.5, and 0.8 g) was added to 2 ml
of cell suspension (1.7 × 108 cells/ml). The
suspensions were shaken and allowed to settle, and the optical density
of the supernatant was measured. The number of adherent cells was
determined by subtracting the number of cells in the supernatant from
the number initially added. As a control a mineral mixture lacking
pyrite and pyrite alone were also tested separately.
Flotation experiments.
The flotation experiments were
conducted with a microflotation column (working volume, 270 ml; height
and diameter, 38 by 3 cm). Sulfuric acid solution (pH 2.0) containing
methyl isobutyl carbinol (25 µl/liter) was used as the flotation
liquor. Air bubbles were generated with a porous glass filter situated
at the bottom of the column.
The floatabilities of the minerals were measured by adding 0.5 g
of each sulfide mineral to 2 ml of the cell suspension (3.2
× 10
8 cells/ml). The suspension was then shaken for about 1 min and
allowed to settle for 5 min. The settled mineral particles were
applied to the flotation column, which was then aerated for 10
min at a
rate of 100 ml/min. The particles that floated to the
top of the column
were collected as froth, while the particles
that sank to the bottom
were recovered as tailing. Froths and
tailings were dried at 80°C and
weighed. Floatability was calculated
as the proportion of the froth
weight in the total mineral weight
(i.e., froth plus
tailing).
The flotation experiments aimed at separating pyrite from a mineral
mixture were carried out with two groups of mineral-pyrite
mixtures.
The simpler mixtures contained 0.2 g each of pyrite
and a single
sulfide mineral. Prior to the flotation test, the
0.4-g amount of
mineral-pyrite mixture was added to 2 ml of cell
suspension (3.7 × 10
8 cells/ml) to induce bacterial adhesion. The more
complex mineral-pyrite
mixtures were composed of all five minerals. A
low-pyrite mixture
contained 0.2 g of pyrite and 0.2 g each
of the other four minerals,
yielding a 20% final pyrite content; a
high-pyrite mixture contained
0.8 g of pyrite and 0.05 g each
of the other four minerals, yielding
an 80% final pyrite content.
Totals of 0.4 g of low-pyrite mixture
and 1.0 g of
high-pyrite mixture were exposed to 7.3 × 10
8 and
17.7 × 10
8 cells, respectively, for 2 min. After
exposure to the bacteria,
the mineral-pyrite mixtures were
subjected to flotation. To remove
pyrite by flotation,
mineral-pyrite mixtures were fed directly
into the middle of the column
containing 230 ml of flotation liquor
and aerated at a rate of 500 ml/min at 0.1 MPa; 10 min of flotation
was allowed to complete the
separation.
Froths and tailings were recovered as described above and analyzed to
determine the distribution of minerals: they were dissolved
in nitric
and hydrochloric acids, and the elements in the solution
were
identified and quantitated with an inductively coupled plasma
atomic
emission spectrometer (model JY48P; Seiko Industry Co.,
Tokyo, Japan).
The absolute amounts of identified elements were
converted to mineral
weights on the basis of the chemical formula
of each mineral. Each
mineral's floatability was then calculated
from mineral weights in the
froths and the tailings as described
above.
Scanning electron microscopy.
To observe the roughness of
mineral surfaces, scanning electron micrographs were obtained (model
JFM-T300; Joel Co. Ltd., Tokyo, Japan) following standard critical
point fixation.
Contact angle.
Contact angles were measured with a contact
angle meter (type CA-A; Kyowa Surface Science Co. Ltd., Tokyo, Japan).
The minerals were first polished with a fine abrasive (C800, A1500, and
A3000 [Maruto Co., Ltd., Tokyo, Japan] and 6- and 0.25-µm-diameter
diamond pastes [Buehler Co. Ltd., Lake Bluff, Ill.]) to produce
mirror-like surfaces. Measurements were made after carefully dropping
sulfuric acid solution (pH 2.0) onto the mineral surfaces. At least
five droplets (10 µl/droplet) were measured for each mineral.
Zeta potentials.
Zeta potentials of sulfide minerals and
T. ferrooxidans were determined in a sulfuric acid solution
(pH 2.76) with a Plus Zeta potential analyzer (Brookhaven Instruments,
Inc., New York, N.Y.). The mineral particles used were further reduced
by dry grinding with an agate mortar. The fine particles were suspended in the sulfuric acid solution and dispersed by sonication for 1 min.
The suspension was then allowed to settle for 2 min, and the
supernatant was analyzed.
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RESULTS |
Adhesion of T. ferrooxidans to sulfide minerals.
For all five minerals tested, T. ferrooxidans adhesion
increased with the number of cells added, although there were
significant differences in the affinity of the bacteria for the various
minerals (Fig. 1A). By far the largest
number of cells adhered to pyrite, followed in descending order by
molybdenite, chalcocite, millerite, and galena. The relative
adhesiveness of the cells for each mineral was assessed by comparing
the numbers of adherent cells while taking into consideration the
mineral surface areas (Fig. 1B and C). In each case, the mineral
surface area estimated by the BET method was substantially larger than
that determined by direct microscopy (Table
1). However, for each method, the number
of cells adhering per unit of surface area of pyrite was substantially greater than the number of those adhering to other minerals over the
entire range of added cells.
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FIG. 1.
Adhesion of T. ferrooxidans to selected
minerals. (A) Numbers of cells adhering to 0.5 g of each mineral
expressed without regard to mineral surface area. (B and C) Numbers of
adherent cells normalized to mineral surface areas estimated by BET gas
adsorption and direct microscopy, respectively. Symbols:  , pyrite;
 , millerite;  , chalcocite;  , molybdenite;  , galena. The
data points express values obtained from independent experiments.
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The differences in estimated surface area between the BET and
microscopy methods were likely due to surface roughness that
could not
be detected by light microscopy. The surface roughness
of each mineral
was, therefore, assessed by scanning electron
microscopy (data not
shown). Pyrite, molybdenite, and galena particles
had smooth surfaces.
The surfaces of chalcocite and millerite
particles were not smooth.
However, not every mineral showed the
surface roughness on a micrometer
scale. The largest irregularities
on the surfaces were gaps between
molybdenite particle lamina
due to their laminar structures, but gap
sizes were still smaller
than a micrometer. The size of a single
T. ferrooxidans cell is,
comparatively, very large (0.5 µm
wide and 1.0 µm long). Consequently,
the contribution made by surface
roughness to the available area
for bacterial adhesion should be
negligible.
The apparent specificity of
T. ferrooxidans adhesion
suggests that the bacterium may selectively adhere to pyrite, even when
pyrite is mixed with other minerals. Therefore, the adhesiveness
of
T. ferrooxidans was assessed with mineral mixtures composed
of 0.2 g each of molybdenite, chalcocite, millerite, and galena
and selected quantities of pyrite; these findings were compared
to
pyrite adhesion in the absence of other minerals. When
T. ferrooxidans cells were added to pyrite alone, adhesion increased
linearly
with increases in added pyrite (Fig.
2); the number of adherent
cells reached
2.75 × 10
8 in the presence of 0.8 g of pyrite.
In contrast, in the absence
of pyrite, adherence of
T. ferrooxidans to 0.8 g of mineral mixture
was 3.7 times lower.
The affinity of
T. ferrooxidans for pyrite
was particularly
evident when pyrite was mixed with other minerals.
As with pyrite
alone, the number of adherent cells increased linearly
with the weight
of the added pyrite when 0.3, 0.5, or 0.8 g of
pyrite was added in
combination with 0.8 g of the mineral mixture
(Fig.
2). It was
evident from the results that
T. ferrooxidans selectively
adhered to pyrite within mineral mixtures.
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FIG. 2.
Selective adhesion of T. ferrooxidans to
pyrite in mixtures of sulfide minerals. Symbols: , the number of
cells adhering to a mineral mixture; , the number of cells adhering
to pyrite alone. The mineral mixtures were prepared by blending
0.2 g each of molybdenite, chalcocite, millerite, and galena with
the indicated quantities of pyrite (x axis). The data points
are means ± standard deviations of triplicate determinations.
Dashed line, increase in adhesion with increases in added pyrite; solid
line, increase in adhesion with weight of added pyrite in combination
with 0.8 g of mineral mixture.
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The effects of T. ferrooxidans on the floatability of
sulfide minerals.
The effect of the addition of T. ferrooxidans on mineral floatabilities was investigated by
exposing mineral mixtures to cell suspensions containing 6.5 × 108 cells (Table 2). In the
absence of bacteria, all of the minerals exhibited high floatability
(90.8 to 99.0%). Upon exposure to the bacteria, the floatability of
pyrite declined dramatically from 95.9 to 19.3%. Exposure to bacteria
also affected the floatabilities of millerite and galena, which
decreased from 95.5 to 83.8% and from 90.8 to 81.8%, respectively.
However, those decreases were much smaller than the decrease in pyrite
floatability. Thus, pyrite floatability was specifically suppressed by
exposure to T. ferrooxidans.
Pyrite removal from mixtures of sulfide minerals.
The specific
ability of T. ferrooxidans to suppress pyrite floatability
is potentially useful for selectively removing pyrite from mineral
mixtures. We initially tested this possibility by blending pyrite (0.5 g) with equal quantities of molybdenite, chalcocite, millerite, or
galena, exposing the mixtures to cell suspensions, and then subjecting
them to flotation (Table 3). In the
absence of T. ferrooxidans, >90.2% of the pyrite was
recovered as froth; i.e., flotation by itself was very effective for
separating pyrite from other minerals. Exposing of mineral mixture to
T. ferrooxidans dramatically reduced the pyrite content of
the froth: 83.7 to 95.1% of the pyrite in each mixture was found in
the tailings. In contrast, 72.3 to 100% of the other minerals remained
in the froth. Consequently, the purity of the other minerals increased from 50% to 84.3 (±3.0)% (millerite), 86.0 (±8.0)% (galena), 84.4 (±4.0)% (chalcocite), and 79.2 (±7.5)% (molybdenite).
We next examined the capacity of
T. ferrooxidans to
selectively remove pyrite from mixtures containing the five minerals,
including either large or small quantities of pyrite (Table
4).
In the latter case, 84.5 to 98.8% of
the minerals, including pyrite,
was recovered from the froth in the
absence of cells. Upon addition
of
T. ferrooxidans to the
mixture, pyrite was selectively rejected
from the mixture and was
recovered from the tailings; 76.9% of
the pyrite was removed from the
mixture even though the initial
pyrite content of the mineral mixture
was low. Conversely, 75.1
to 100% of the other minerals were recovered
as froth. With high-pyrite
mixtures, in the presence of
T. ferrooxidans, 94.3% of the pyrite
was rejected from the mixture
and recovered as tailing whereas
82.2 to 97.2% of the other minerals
remained as froth. Separation
by flotation with
T. ferrooxidans increased the purity of the
other minerals from
20.0% (added) to 89.6 (±11.0)% (froth). Thus,
by addition of the
bacterium, the pyrite content of flotation
froth can be substantially
reduced without diminishing mineral
recovery, even when the pyrite
content is high.
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DISCUSSION |
Mineral surfaces available for adhesion of T. ferrooxidans.
We employed two methods to estimate the surface
areas of the minerals used in this study. With the BET method, areas
were determined as a function of the amount of nitrogen adsorbed on the
mineral surfaces. This means that even if mineral surfaces contain
convexities and concavities (roughness) as small as a few nanometers,
the small size of nitrogen molecules allows for easy adsorbance to the
entire surface. T. ferrooxidans cells are, by contrast,
approximately 0.5 µm wide and 1.0 µm long and are much too large to
adhere within concavities in particle surfaces. Consequently, our
measurements of bacterial adhesion should have been unaffected by
surface roughness. Indeed, the surfaces of the minerals used in this
study were fairly smooth (data not shown), and it seemed reasonable to
consider the surfaces available for adhesion of T. ferrooxidans as flat and without roughness. As a result, the
surface areas estimated microscopically were probably closer to the
actual areas available for bacterial adhesion than the estimates
obtained by the BET method.
Selective adhesion of T. ferrooxidans to pyrite and its
interactions.
The selectivity of T. ferrooxidans
adhesion to pyrite was first suggested when it was observed that the
cells adhered to pyrite within coal particles (3, 8). The
same phenomenon was observed in iron-rich areas of sulfide ores
(9). Adhesion of T. ferrooxidans to pyrite has
been compared with its adhesion to other minerals (13), but
the selectivity was not definitively shown. In contrast, the present
study clearly demonstrates that T. ferrooxidans will selectively adhere to pyrite, despite the presence of large quantities of one or more other minerals.
Of particular interest to us were the interactions mediating
T. ferrooxidans' selective adhesion. It is generally understood
that
bacterial adhesion is governed by physical (e.g., electrostatic
and/or
hydrophobic) interactions (
5,
7,
18). Electrostatic
interactions depend on the charges present on the surfaces of
the cell
and the particle. Therefore, the zeta potentials of the
minerals used
in this study were estimated (Table
5).
All of
the minerals had negatively charged surfaces, and the surfaces
of
T. ferrooxidans cells are also negatively charged
(
4). Thus,
electrostatic interaction would not produce the
essential force
necessary for
T. ferrooxidans adhesion; in
fact, the negative
charges would repel one another (
6).
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TABLE 5.
Surface properties of selected sulfide minerals and
change in surface free energy upon adhesion
of T. ferrooxidans
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Adhesion driven by hydrophobic interactions can be modeled
thermodynamically, taking into consideration the surface tensions
of
adherent cells, the solid surfaces, and the suspending liquid
medium
(
1). The surface tension of each mineral used in this
study
could be calculated from contact angles determined experimentally
as
shown in Table
5. The angles were measured toward the sulfuric
acid
solution that served as the suspending liquid medium in the
cell
adhesion experiments and which has a surface tension of 71.4
dynes/cm.
The angle of
T. ferrooxidans cells to the same sulfuric
acid
solution was reported as 24.0° (
13). The above-mentioned
values for angles and liquid surface tension were incorporated
into a
thermodynamic model to determine the change of surface
free energy
(
Gadh) that occurs when
T. ferrooxidans adheres to
the minerals shown in Table
5 (
1,
10,
11). In general,
bacterial adhesion via hydrophobic interaction
with the mineral
can occur spontaneously when
Gadh is negative, and the adhesion
is more
extensive the more negative the value of
Gadh
(
5,
18). According to this model, cells are most likely to
adhere
to molybdenite, followed by chalcocite, pyrite, millerite, and
galena in descending order. In contrast, cells adhered to pyrite,
followed by molybdenite, chalcocite, millerite, and galena (Fig.
1).
With the exception of pyrite, this theoretical determination
approximates the actual tendency in the adhesion observed
experimentally.
The large number of cells which adhered to pyrite did
not merely
match the theoretical determination made on the basis of
adhesion
via hydrophobic interactions. The adhesion of
T. ferrooxidans to pyrite involves specific interactions other than
hydrophobic
interactions.
Research conducted over the past several years has frequently focused
on whether there is a specific mechanism involved when
T. ferrooxidans adheres to pyrite. For instance, Rojas et al.
suggested that an organic capsule covering the cell surface is
relevant
to pyrite adhesion (
16,
17). Devacia et al. and Arredondo
et
al. both suggested that cell surface proteins play an important
role in
the adhesion of
T. ferrooxidans to solid surfaces (
2,
6). Very recently, an apo form of rusticyanin was isolated
as a
surface protein responsible for
T. ferrooxidans adhesion
to
pyrite, which may provide the key to its selectivity (
14).
Application of microbial flotation to mineral processing.
When
pyrite is present as a contaminant in mixtures of sulfide minerals,
commercial flotation processors commonly use cyanide to suppress its
floatability (21). Because the suppressive effect of cyanide
on pyrite flotation is enhanced in solutions made alkaline by the
presence of Ca(OH)2, the separation efficiency of flotation in the presence of cyanide plus Ca(OH)2 was tested with a
pyrite-galena mixture (results not shown). The pH of the flotation
liquor was adjusted to 10.0 with Ca(OH)2, and then cyanide
(KCN) was added to a concentration of 1 mM. Under these conditions,
pyrite rejection and galena recovery were 76 and 68%, respectively,
which are less than the separation efficiency of T. ferrooxidans, which produced corresponding values of 91 and 91%
(results not shown).
There is a growing consensus that bacteria can significantly affect
mineral floatability; the present study showed that
T. ferrooxidans suppresses pyrite floatability. Conversely, bacterial
cells may also be able to function as collectors. For instance,
Smith
et al. reported that addition of the hydrophobic bacterium
Mycobacterium phlei increased the hydrophobicity of mineral
surfaces
and thereby improved floatability (
19). Thus, it
may soon be
possible to replace conventional collectors, such as fatty
acids
or cationic amines, with bacteria. In the past, oxidative metal
leaching by bacteria has contributed significantly to mineral
processing. It now appears that it may be useful to expand the
role
played by bacteria in mineral processing to include adhesive
control of
mineral
floatability.
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FOOTNOTES |
*
Corresponding author. Mailing address: Central Research
Institute of Electric Power Industry, 1646 Abiko, Abiko City, Chiba, Japan. Phone: 81-471-82-1181. Fax: 81-471-83-3347. E-mail:
ohmura{at}criepi.denken.or.jp.
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REFERENCES |
| 1.
|
Absolom, D. R.,
F. V. Lamberti,
Z. Policova,
W. Zingg,
C. J. van Oss, and A. W. Neumann.
1983.
Surface thermodynamics of bacterial adhesion.
Appl. Environ. Microbiol.
46:90-97[Abstract/Free Full Text].
|
| 2.
|
Arredondo, R.,
A. Garcia, and C. A. Jerez.
1994.
Partial removal of lipopolysaccharide from Thiobacillus ferrooxidans affects its adhesion to solids.
Appl. Environ. Microbiol.
60:2846-2851[Abstract/Free Full Text].
|
| 3.
|
Bagdigian, R. M., and A. S. Myserson.
1986.
The adsorption of Thiobacillus ferrooxidans on coal surfaces.
Biotechnol. Bioeng.
28:467-479.
|
| 4.
|
Blake, R. C.,
E. A. Shute, and G. T. Howard.
1994.
Solubilization of minerals by bacteria: electrophoretic mobility of Thiobacillus ferrooxidans in the presence of iron, pyrite, and sulfur.
Appl. Environ. Microbiol.
60:3349-3357[Abstract/Free Full Text].
|
| 5.
|
Busscher, H. J., and A. H. Weekamp.
1987.
Specific and non-specific interaction in bacterial adhesion to solid substrata.
FEMS Microbiol. Rev.
46:165-173.
|
| 6.
|
Devacia, P.,
K. A. Natarajan,
D. N. Sathyanarayana,
G. Ramananda, and R. Rao.
1993.
Surface chemistry of Thiobacillus ferrooxidans relevant to adhesion on mineral surfaces.
Appl. Environ. Microbiol.
59:4051-4055[Abstract/Free Full Text].
|
| 7.
|
Marshall, K. C.
1976.
Solid-liquid and solid-gas interfaces, p. 27-52.
In
K. C. Marshall (ed.), Interfaces in microbial ecology. Harvard University Press, London, England.
|
| 8.
|
McCready, R. G. L., and B. P. L. Gallais.
1984.
Selective adsorption of 32P-labelled Thiobacillus ferrooxidans in finely ground coal suspensions.
Hydrometallurgy
12:281-288.
|
| 9.
|
Murr, L. E., and V. K. Berry.
1976.
Direct observation of selective attachment of bacteria on low-grade sulfide ores and other mineral surfaces.
Hydrometallurgy
2:11-24.
|
| 10.
|
Neumann, A. W.,
R. J. Good,
C. J. Hope, and M. Sejpal.
1974.
An equation-of-state approach to determine surface tensions of low-energy solids from contact angles.
J. Colloid Interface Sci.
49:291-304.
|
| 11.
|
Neumann, A. W.,
O. S. Hum,
D. W. Francis,
W. Zingg, and C. J. van Oss.
1980.
Kinetic and thermodynamic aspects of platelet adhesion from suspension to various substrates.
J. Biomed. Mater. Res.
14:499-509[Medline].
|
| 12.
|
Ohmura, N.,
K. Kitamura, and H. Saiki.
1993.
Mechanism of microbial flotation using Thiobacillus ferrooxidans for pyrite suppression.
Biotechnol. Bioeng.
41:671-676.
|
| 13.
|
Ohmura, N.,
K. Kitamura, and H. Saiki.
1993.
Selective adhesion of Thiobacillus ferrooxidans to pyrite.
Appl. Environ. Microbiol.
59:4044-4050[Abstract/Free Full Text].
|
| 14.
|
Ohmura, N., and R. Blake, II.
1997.
Aporusticyanin mediates the adhesion of Thiobacillus ferrooxidans to pyrite, Proc. PB1.
In
International Biohydrometallurgy Symposium.
|
| 15.
|
Rawlings, D. E., and S. Silver.
1995.
Mining with microbes.
Bio/Technology
13:773-778.
|
| 16.
|
Rojas, J.,
M. Giersig, and H. Tributsch.
1995.
Sulfur colloids as temporary energy reservoirs for Thiobacillus ferrooxidans during pyrite oxidation.
Arch. Microbiol.
163:352-356.
|
| 17.
|
Rojas, J.,
M. Giersig, and H. Tributsch.
1996.
The path of sulfur during the bio-oxidation of pyrite by Thiobacillus ferrooxidans.
Fuel
75:923-930.
|
| 18.
|
Rosenberg, M., and R. J. Doyle.
1990.
Microbial cell hydrophobicity: history, measurement and significance, p. 1-37.
In
R. J. Doyle, and M. Rosenberg (ed.), Microbial cell hydrophobicity. American Society for Microbiology, Washington, D.C.
|
| 19.
|
Smith, R. W.,
M. Misra, and S. Chen.
1993.
Adsorption of a hydrophobic bacterium onto hematite: implications in the froth flotation of the mineral.
J. Industrial Microbiol.
11:63-67.
|
| 20.
|
Townsley, C. C., and A. S. Atkins.
1986.
Comparative coal fines desulphurisation using the iron-oxidising bacterium Thiobacillus ferrooxidans and the yeast Saccharomyces cerevisiae during simulated froth flotation.
Proc. Biochem.
1986:188-191.
|
| 21.
|
Wills, B. A.
1992.
Froth flotation-depressants, p. 514-517.
In
B. A. Wills (ed.), Mineral processing technology, 5th ed. Pergamon Press, Elmsford, N.Y.
|
Applied and Environmental Microbiology, August 1999, p. 3588-3593, Vol. 65, No. 8
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Copyright © 1999, American Society for Microbiology. All rights reserved.
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Abstract
Introduction
