Previous Article | Next Article 
Appl Environ Microbiol, April 1998, p. 1237-1241, Vol. 64, No. 4
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Development of a Laboratory-Scale Leaching Plant
for Metal Extraction from Fly Ash by Thiobacillus
Strains
Christoph
Brombacher,1
Reinhard
Bachofen,1 and
Helmut
Brandl2,*
Institute of Plant Biology, Department of
Microbiology, University of Zurich, CH-8008
Zurich,1 and
Institute of
Environmental Sciences, University of Zurich, CH-8057
Zurich,2 Switzerland
Received 23 September 1997/Accepted 5 January 1998
 |
ABSTRACT |
Semicontinuous biohydrometallurgical processing of fly ash from
municipal waste incineration was performed in a laboratory-scale leaching plant (LSLP) by using a mixed culture of Thiobacillus thiooxidans and Thiobacillus ferrooxidans. The LSLP
consisted of three serially connected reaction vessels, reservoirs for
a fly ash suspension and a bacterial stock culture, and a vacuum filter
unit. The LSLP was operated with an ash concentration of 50 g
liter
1, and the mean residence time was 6 days (2 days in
each reaction vessel). The leaching efficiencies (expressed as
percentages of the amounts applied) obtained for the economically most
interesting metal, Zn, were up to 81%, and the leaching efficiencies
for Al were up to 52%. Highly toxic Cd was completely solubilized
(100%), and the leaching efficiencies for Cu, Ni, and Cr were 89, 64, and 12%, respectively. The role of T. ferrooxidans in
metal mobilization was examined in a series of shake flask experiments.
The release of copper present in the fly ash as chalcocite
(Cu2S) or cuprite (Cu2O) was dependent on the
metabolic activity of T. ferrooxidans, whereas other
metals, such as Al, Cd, Cr, Ni, and Zn, were solubilized by biotically
formed sulfuric acid. Chemical leaching with 5 N H2SO4 resulted in significantly increased
solubilization only for Zn. The LSLP developed in this study is a
promising first step toward a pilot plant with a high capacity to
detoxify fly ash for reuse for construction purposes and economical
recovery of valuable metals.
| |
INTRODUCTION |
Biohydrometallurgy, an
interdisciplinary field involving geomicrobiology, microbial ecology,
microbial biochemistry, and hydrometallurgy (23), is a novel
promising technology for recovering valuable metals from industrial
waste materials (e.g., bottom and fly ash, galvanic sludge, and filter
dust) and for detoxifying these materials for environmentally safe
deposition. Biohydrometallurgical processing of solid waste allows
recycling of metals, similar to natural biogeochemical metal cycles,
and diminishes the demand for resources, such as ores, energy, and
landfill space. Fly ash from municipal waste incineration (MWI) is a
concentrate containing a wide variety of toxic heavy metals (e.g., Cd,
Cr, Cu, and Ni). The zinc concentrations in fly ash (3%, wt/wt) can be
similar to the concentrations in ores subjected to conventional mining
(16), which makes MWI fly ash a suitable candidate for
economical zinc recovery. The low acute and chronic toxicity of fly or
bottom ash for a variety of microorganisms (8) and the low
mutagenic effect (17) of this material have been
demonstrated previously. However, the deposition of materials
containing heavy metals results in a severe risk that spontaneous metal
leaching may occur due to natural weathering processes and uncontrolled
bacterial activities (18, 21, 23). Agenda 21 adopted at the
1992 Earth Summit in Rio de Janeiro, Brazil, established that there is
a strong requirement to support sustainable development, including
ecological treatment of wastes and safe disposal of wastes. Biological
metal leaching of fly ash is a step in this direction.
Biohydrometallurgy is a technology that is cleaner and consumes less
energy than technologies used in the pyro- and hydrometallurgical industries. The latter technologies are well-established, and many of
them are patented, whereas patents for biohydrometallurgical processing
of industrial wastes are rarely published (7). The first
effort to develop biohydrometallurgical treatment of industrial waste
was made 20 years ago, and greater efforts are necessary now. This is
an important subject of research and should result in a wide range of
investigations and applications in the future. However, the previous
data on biohydrometallurgical treatment of fly ash or other industrial
waste obtained with bacteria or fungi included residence times for
leaching of up to 50 days (4-6, 11, 25). Most of these
experiments were performed on a small scale with low amounts of
heavy-metal-containing material.
In this paper, a semicontinuous laboratory-scale leaching plant (LSLP)
is described; this LSLP achieved high leaching efficiencies, which
resulted in an elevated load of elements in the effluent. Treatment
times were found to be less than treatment times obtained with batch
extraction procedures. A mixture of Thiobacillus thiooxidans producing sulfuric acid and Thiobacillus ferrooxidans
oxidizing reduced metal compounds (19) was used to perform
the leaching experiments. The results were compared to chemical
(abiotic) leaching efficiencies. In addition, we investigated whether
T. ferrooxidans was needed for leaching of fly ash. Metals
can be biotically released from fly ash by mechanisms such as direct
enzymatic reduction, indirect action resulting from extracellular
metabolic products, or acid formation (nonenzymatic dissolution), as
previously shown in an anaerobic system (10). It was
possible to differentiate among these release mechanisms in an oxic
acidic fly ash-Thiobacillus system.
| |
MATERIALS AND METHODS |
Bacterial strains, medium, and culture conditions.
T.
thiooxidans DSM622 and T. ferrooxidans DSM2391 were
cultivated in a medium containing (per liter) 0.1 g of
K2HPO4, 0.25 g of MgSO4
· 7H2O, 2.0 g of
(NH4)2SO4, 0.1 g of KCl, and
8.0 g of FeSO4 · 7H2O. Elemental
sulfur (1%, wt/vol) was added, and the pH was adjusted with sulfuric
acid to 2.5 to 2.7. The mixed culture was grown under nonsterile
conditions either in 250-ml baffled Erlenmeyer flasks on a rotary
shaker (140 rpm) or in an aerated and stirred 1,000-ml beaker. Growth
was monitored by monitoring the pH (with a Hamilton single-pore
electrode), the cell counts (with a Neubauer counting chamber), and the
Fe(II) concentration (12).
Samples and sample preparation.
A 500-kg portion of fly ash
retained by electric filters at the MWI plant in Hinwil, Switzerland,
was collected by workers at Sulzer Chemtech (Winterthur, Switzerland)
at different times on one day and was homogenized in a cement mixer to
obtain representative homogeneous samples. The ash was washed with
water to remove water-soluble compounds and dried on a vacuum filter.
For experiments the ash was ground and dried at 80°C for 48 h.
The concentrations of selected elements are listed in Table
1. The value for loss of combustion at
950°C represents the inorganic carbon content.
Semicontinuous LSLP.
The LSLP consisted of three serially
connected reaction vessels (designated RV-A, RV-B, and RV-C), each
having a volume of 1 dm3 (Fig.
1). Pulp from the fly ash storage
solution (100 g liter1) and the bacterial stock culture
(109 cells/ml) were mixed in equal amounts and fed every
12 h semicontinuously into the first reaction vessel (RV-A) with a
peristaltic pump at an overall dilution rate of 0.021 h1
(0.5 day1). RV-A and RV-B were connected by an overflow
connector. The pulp was pumped from RV-B to RV-C with a peristaltic
pump at the same rate to flush settled fly ash particles. This resulted
in a pulp concentration in the LSLP of 50 g liter1
and a mean residence time of 6 days (2 days in each reaction vessel).
The bacterial stock culture and the three reaction vessels were aerated
at a rate of about 2 volumes of air per volume of reactor per min.
After RV-C, the pulp was transported by gravity flow into a 2-liter
vacuum glass filter unit, and the particle-free, metal-rich solution
was collected in a 5-liter collecting vessel.
View larger version (14K):
[in this window]
[in a new window]
|
FIG. 1.
Schematic diagram of the LSLP. A, B, and C, serially
connected RV-A, RV-B, and RV-C, respectively; 1, fly ash reservoir; 2, bacterial stock culture; 3, peristaltic pump; 4, filter unit; 5, collecting vessel; 6, to vacuum pump; solid lines, liquid flow; dashed
lines, air flow.
|
|
Determination of mobilization mechanisms.
Forty milliliters
of an 8% (wt/vol) fly ash suspension (acidified with sulfuric acid to
pH 5.4) was diluted with 40 ml of a Thiobacillus culture
(109 cells/ml) after different treatments (see below) and
incubated for 8 days on a rotary shaker (150 rpm) at room temperature
(23 to 24°C). All samples were incubated in triplicate. Several
mechanisms of metal mobilization were distinguished, as described
below.
The direct enzymatic effect on the release of metals was determined by
diluting the ash suspension with bacterial stock cultures
(pH 1.1). The
cells were in direct contact with the fly ash. Growth
of
T. ferrooxidans might have been stimulated by increased energy
available from oxidation of reduced solid particles.
Leaching with cell-free spent medium revealed that indirect
solubilization by extracellular metabolic products occurred. The
stock
culture was centrifuged at 23,700 ×
g, and the
supernatant
was filtered through a 0.22-µm-pore-size Teflon filter to
obtain
cell-free spent medium. The cell-free spent medium was checked
for viable cells by incubating a 5-ml sample in 80 ml of fresh
medium.
Cell-free spent medium (see above) was autoclaved (12 min, 121°C) to
obtain a sterile leaching solution without enzymatic
activities to
evaluate the leaching ability of the acid formed.
The solution was
checked for precipitates and for changes in redox
state after the heat
treatment.
Forty milliliters of fresh uninoculated medium was added to the fly ash
suspension and used as a control.
Elements such as Cd or Zn might have been chemically mobilized during
preparation of the ash suspension due to the acidification
to pH 5.4.
Chemical leaching with sulfuric acid.
Eighty milliliters of
the fly ash suspension was leached at a concentration of 5% (wt/vol)
with a maximum of 11 ml of 5 N sulfuric acid (final pH, pH 2) at the
following pH values: at an initial pH of 10, at pH 8 (corresponding to
the carbonate buffer pH), at pH 4 (corresponding to the
potassium-aluminum buffer pH) (2), and at pH 2 (a possible
end point of a leaching experiment). The concentrations of the
solubilized metals and the acid consumption were measured. The pH at
each value was controlled with a pH-Stat (Metrom Impulsomat model 614).
Fly ash was suspended in distilled water and stirred at a constant pH
for 24 h. A new suspension was prepared for each pH step.
Analytical procedures.
Metal analyses were performed by
using inductively coupled plasma atomic absorption spectroscopy
(ICP-AES; Spectro Analytical Instruments, Kleve, Germany) and standard
addition methods at the following wavelengths: Al, 396.2 nm; Cd, 228.8 nm; Cr, 267.7 nm; Cu, 324.8 nm; Fe, 261.2 nm; Mn, 294.9 nm; Ni, 352.5 nm; and Zn, 206.2 nm. Prior to the inductively coupled plasma analysis, the samples were centrifuged at 23,700 × g for 15 min,
acidified with 5 drops of concentrated HNO3 per 30 ml of
aqueous solution, passed through a glass fiber filter (Whatman type
GF/C) to guarantee particle-free suspensions, and stored at 4°C.
| |
RESULTS AND DISCUSSION |
LSLP.
A semicontinuous three-stage leaching plant for
extraction of heavy metals from MWI fly ash was developed.
Biohydrometallurgical processing of fly ash from MWI poses, especially
at high pulp densities, severe problems due to the high content of
toxic metals in the fly ash and the saline and strongly alkaline
environment. It is necessary to obtain reduced treatment times for high
pulp concentrations without additional acidification; this is important for reducing the capital and maintenance costs of a pilot plant.
RV-A of the LSLP (Fig.
1) was filled with 500 ml of a bacterial culture
(pH 1.5) and 250 ml of a fly ash suspension (10%,
wt/vol) for the
first adaptation phase. After 36 h, another 250-ml
aliquot of the
suspension was added to obtain the final 5% (wt/vol)
solution. When
the pH in RV-A dropped below 2, the LSLP was started.
After 48 h
(corresponding to four discontinuous feeding cycles)
the solution was
pumped to RV-C. After 48 h, the microorganisms
produced sufficient
amounts of sulfuric acid in each reaction
vessel to maintain
steady-state conditions despite the alkaline
pH of the fly ash pulp (pH
9 during the experiment). A distinct
pH cascade occurred from one
reaction vessel to the following
reaction vessel. The pH fluctuated
during the steady state depending
on the fly ash present; in RV-A the
pH fluctuated between 3.7
and 4, in RV-B the pH fluctuated between 2.7 and 3.2, and in RV-C
the pH fluctuated between 1.2 and 1.5. Before the
bacterial stock
was added to RV-A, growth parameters [pH, Fe(II)
concentration,
cell number] were monitored (Fig.
2). The medium was fully replenished
with
fresh medium every 72 h (corresponding to an overall dilution
rate
of 0.01 liter h
1) to avoid aging of the bacterial stock
culture.
View larger version (18K):
[in this window]
[in a new window]
|
FIG. 2.
Monitoring of growth and activity of a mixed culture of
T. thiooxidans and T. ferrooxidans (maximum
growth rate, 0.055 h1; doubling time, 12.7 h). The
experiment was performed in an aerated 2-liter beaker before the
culture was used as a stock culture in the LSLP. During the operation
of the LSLP the pH remained between 1.0 and 1.3, and the cell count
increased slightly to 4 × 109 cells per ml. Symbols:
 , pH;  , Fe(II) concentration;  , cell count.
|
|
Samples used for metal analysis were removed after 168 h from each
reaction vessel, from the collection vessel, and (as controls)
from the
fly ash storage vessel and the bacterial stock culture.
For all
elements, the concentrations of soluble metals increased
continuously
with increasing mean residence time in the LSLP (Fig.
3). In RV-C the following amounts of
metals were solubilized (per
kilogram of fly ash): Al, 37 g; Zn,
25 g; Fe, 3.1 g; Cu, 0.98
g; Mn, 0.53 g; Cd,
0.49 g; Ni, 0.09 g; and Cr, 0.08 g. Ferrous
iron added
to the bacterial stock culture as an electron source
for
T. ferrooxidans precipitated in the first two reaction vessels
(RV-A
and RV-B) in high amounts, resulting in a decrease in the
soluble iron
level. At higher pH values iron either precipitated
as hydroxide or
became adsorbed on fly ash particles. In addition,
ferric iron
coprecipitates with other metals (e.g., As, Cd, Cr,
Cu, Pb, and Zn)
(
10). In RV-A, up to 45% of the iron added to
the medium
precipitated; in RV-B about 32% of the iron added precipitated.
Only
at the very low pH in RV-C (pH 1 to 1.3) was 10% net iron
leaching
observed. Leaching of Pb with sulfur-oxidizing bacteria
like members of
the genus
Thiobacillus is not very effective,
because of the
low solubility of PbSO
4 in aqueous solutions (
15,
20). Sulfate was present in the medium at high levels. Ferrous
sulfate was added as an energy source for
T. ferrooxidans,
and
sulfate was produced by
T. thiooxidans as a metabolic
product
of sulfur oxidation. Therefore, mobilized Pb immediately
precipitated
as PbSO
4 and remained with the leached fly ash
in the glass filter
unit. To verify this result, ChemEQL (a computer
program used
to calculate thermodynamic equilibrium concentrations and
precipitation
conditions) was used. Precipitation was calculated for
the following
conditions: (i) the maximum expected Pb concentration,
445 ppm
(2.15 mM); (ii) the minimum expected sulfate concentration,
1,380
ppm (14.4 mM) (only the sulfate from the medium was considered;
the sulfate formed due to bacterial oxidation of S° was not taken
into account); and (iii) the maximum Cl
and
F
concentrations (Cl
and F
form soluble Pb complexes), 235 ppm (6.63 mM) and 400 ppm (21
mM),
respectively. Concentrations were chosen by using the method
of Vonmont
(
27). As shown in Table
2,
only 1.2 to 2.6% of the
Pb stayed in solution under very acidic
conditions. At pH values
between 1 and 4, the solubility was <1%.
Although Pb concentrations
close to 10 g kg
1 can be
found in fly ash (Table
1), the leaching efficiencies
(expressed as
percentages of the amounts applied) were very low
(usually <5%).
View larger version (23K):
[in this window]
[in a new window]
|
FIG. 3.
Amounts of solubilized metals obtained from MWI fly ash
(50 g liter1), expressed as percentages of the amounts
present in a LSLP with three serially connected reaction vessels (RV-A,
RV-B, RV-C). The mean reaction time in each vessel was 2 days. Negative
values indicate metal precipitation.  , RV-A;
&atyp0220;, RV-B;  ,
RV-C.
|
|
View this table:
[in this window]
[in a new window]
|
TABLE 2.
Dissolution equilibrium for Pb from MWI fly ash as
determined by ChemEQL at high sulfate concentrations (50 g of fly
ash liter1; maximum total Pb concentration, 445 mg
liter1; minimum H2SO4
concentration, 1,380 mg liter1; maximum Cl
concentration, 235 mg liter1; maximum F
concentration, 400 mg liter1)a
|
|
Determination of mobilization mechanisms.
X ray fluorescence
analyses carried out by workers at Amt für
Gewässerschutz und Wasserbau des Kantons Zürich in 1991 (1) indicated that reduced copper species (chalcocite
[Cu2S] and cuprite [Cu2O]) were present in
MWI fly ash, whereas zinc and other metals were present in their fully
oxidized forms. Thus, copper release from fly ash should be directly
affected and enhanced by T. ferrooxidans, whereas Zn, Al,
Cd, Cr, and Ni are released primarily due to the acidic environment.
These different mobilization mechanisms could be distinguished by a
series of batch experiments.
In batch cultures with inoculated medium the pH decreased within 8 days
from 3.6 to 1.6 as a result of biotically formed sulfuric
acid. In
freshly filtered cell-free spent medium and autoclaved
sterile spent
medium the pH remained constant at 3.6; in uninoculated
medium the pH
remained constant at 5, and the pH remained constant
at 5.4 in assays
in which distilled water was used instead of
medium. Acidification of
the fly ash pulp (chemical mobilization)
led to significant extraction
yields for Cd, Ni, and Zn (Fig.
4), which
could be slightly increased by using uninoculated sterile
medium as the
lixiviant (leaching solution) due to the sulfuric
acid present in the
culture medium. The level of Al dissolution
was low, whereas the Cr and
Cu concentrations in both experiments
were below the detection limits.
View larger version (33K):
[in this window]
[in a new window]
|
FIG. 4.
Amounts of solubilized metals obtained from MWI fly ash
(40 g liter1), expressed as percentages of the amounts
present with different lixiviants within 8 days. All samples were
incubated in triplicate. The release of metals due to acidification of
the fly ash pulp was defined as chemical mobilization. , inoculated
medium; &atyp0220;,
filtered cell-free spent medium;
&atyp0220;, autoclaved
sterile spent medium; , uninoculated medium;  , chemical
mobilization.
|
|
By comparing the amounts of leached copper in filtered cell-free spent
medium (0.89 g kg of fly ash
1; standard deviation
[
sx] = 0.03 g kg
1;
n = 3) and autoclaved sterile spent medium (0.70 g
kg
1;
sx = 0.04 g
kg
1;
n = 3), it was concluded that in
contrast to other elements
significant amounts of copper (as determined
by a paired
t test
[one sided],
P = 0.02)
were mobilized by metabolic products of
T. ferrooxidans.
Leaching with cell-free spent medium, which indicated
that a
solubilizing mechanism involving extracellular components
was present,
was significantly more effective than leaching with
autoclaved spent
medium, in which excreted enzymes were inactivated.
It is known that
several components involved in the electron transport
chain in the
genus
Thiobacillus (rusticyanin, cytochromes, iron-sulfur
proteins) are located in the periplasmic space (
3,
24) and
might, therefore, also be present in cell-free spent medium and
catalyze oxidation of reduced metal compounds. It is possible
that heat
treatment (autoclaving) of spent medium leads to aggregation
of
nonenzymatic compounds or changes in the redox state. The two
solutions
were checked for precipitates (
A
660 = 0.003) and for
their redox potentials (E
h) (the values for cell-free spent
medium
and autoclaved spent medium were 830 and 810 mV, respectively).
The results show that aggregation and altered redox conditions
due to
autoclaving did not occur.
In contrast, for all of the other elements examined (Al, Cd, Cr, Ni,
and Zn), the difference between filtered cell-free spent
medium and
autoclaved cell-free spent medium was not significant.
Therefore, it
was concluded that the mobilization of these metals
from fly ash was
caused only by the acidic environment.
The maximal extraction yields for all elements were obtained with
samples incubated with both
T. thiooxidans and
T. ferrooxidans.
The data indicate that there was efficient release
of most heavy
metals from fly ash due to biotically formed sulfuric
acid (the
pH decreased within 8 days from 3.6 to 1.6). Copper
solubilization
increased significantly (1.10 g kg of fly
ash
1;
sx = 0.05 g
kg
1;
n = 3; paired
t test
[one sided];
P = 0.002), as well did mobilization
of
Al (
n = 3;
P = 0.003), Cd
(
n = 3;
P = 0.03), Cr
(
n = 3;
P =
0.0005), and Zn
(
n = 3;
P = 0.03) compared to samples
incubated
with cell-free spent medium.
Chemical leaching with sulfuric acid.
The value for loss of
combustion at 950°C, of 12.6% (Table 1), indicates that considerable
amounts of inorganic carbon occurred as carbonates in the fly ash.
These carbonates, along with other constituents, caused the pH of the
fly ash suspension to be more than 10. Most of the metals were
mobilized due to sulfuric acid, the acid necessary to neutralize and
acidify MWI fly ash was determined, and the chemical (abiotic) leaching
efficiencies of sulfuric acid at different pH values were assessed.
The dissolution of metals in fly ash in alkaline environments (pH 8 and
10) was low. Less than 0.03 g of Al or Zn and less
than 0.01 g of Cd, Cr, Cu, Fe, or Ni were solubilized per kg of
fly ash. To lower
the pH of the fly ash suspension from >10 to
4, 175 ml of
H
2SO
4 (95 to 97% pure) per kg of fly ash had
to be
added. This resulted in release of 15 g of Al kg of fly
ash
1 (corresponding to 22% of the total amount present),
20 g of Zn
kg
1 (75%), 1.44 g of Fe
kg
1 (5%), 0.49 g of Cu kg
1 (53%),
0.38 g of Cd kg
1 (76%), 0.02 g of Ni
kg
1 (14%), and 0.01 g of Cr kg
1
(2%). Large amounts of Al (45 g kg
1; 64%) and Zn (32 g
kg
1; 100%) were solubilized at pH 2, along with 7.4 g of Fe kg
1 (26%), 0.96 g of Cu kg
1
(88%), 0.44 g of Cd kg
1 (89%), 0.03 g of Ni
kg
1 (22%), and 0.08 g of Cr kg
1
(11%), when 311 ml of H
2SO
4 (95 to 97% pure)
was added. The leaching
efficiencies were comparable to those of the
LSLP.
Conclusions.
The ability of microorganisms to leach and
mobilize metals from solid materials is based on the following three
mechanisms: (i) redox reactions, (ii) formation of inorganic acids, and
(iii) excretion of complexing agents (e.g., organic acids). T. ferrooxidans mobilizes metals from solids by redox reactions.
Electron transfer from minerals to microorganisms either occurs
directly in the case of physical contact between organisms and solids
or is based on the biotic oxidation of Fe+2 to
Fe+3 when ferric iron catalyzes metal solubilization as an
oxidizing agent (9, 14). For solubilization of the reduced
copper compounds (chalcocite [Cu2S] and cuprite
[Cu2O]) present in the fly ash, these release mechanisms
are important. The Ni leaching efficiency is also considerably
increased by biological activities compared with chemical leaching with
sulfuric acid due to the presence of Fe(III) in the leaching solution.
The results obtained for bacterial leaching of heavy metals from
anaerobically digested sludge also confirmed that the solubilization
rates of metals obtained with mixed cultures of T. thiooxidans and T. ferrooxidans were higher than the
solubilization rates obtained with single cultures (26).
The three-stage LSLP described here is a promising first step toward
the establishment of a semicontinuous or continuous bioleaching
leaching plant. The lab work showed the practicability of biotic
fly
ash leaching despite the presence of saline and strongly alkaline
material. When acidophilic autotrophic
Thiobacillus strains
are
used, no aseptic LSLP set-up is required. The possibility of
contaminants
which interfere with the
Thiobacillus strains
is minimal, due
to the very acidic environment and the absence of
organic compounds
as carbon sources. Such conditions should reduce the
capital and
maintenance costs of a pilot plant. A scaled-up version of
the
LSLP, a pilot plant with three or more reaction vessels for biotic
leaching of industrial waste, seems to be technically feasible.
Large-scale reactor leaching of this type has been used previously,
especially for gold recovery (
13,
22). A large-scale
bioleaching
plant should allow us to detoxify fly ash for reuse in
construction,
while valuable metals, especially zinc, should be
economically
recovered for recycling in metal-manufacturing industries.
| |
ACKNOWLEDGMENTS |
The statistical assistance of C. Luchsinger (Institute of Applied
Mathematics, University of Zurich) is acknowledged.
Financial support was provided by the Swiss National Science Foundation
within the Priority Program Environment.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Institute of
Environmental Sciences, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland. Phone: 41 1 635 61 25. Fax: 41 1 635 57 11. E-mail: HBRANDL{at}UWINST.UNIZH.CH.
| |
REFERENCES |
| 1.
|
Amt für Gewässerschutz und Wasserbau des Kantons Zürich.
1991.
.
Immobilisierung von Rauchgasreinigungsrückständen aus Kehrichtverbrennungsanlagen (Projekt IMRA). Schlussbericht.
Amt für Gewässerschutz und Wasserbau des Kantons Zürich, Zurich, Switzerland.
|
| 2.
|
Amt für Gewässerschutz und Wasserbau des Kantons Zürich.
1992.
.
Emissionsabschätzung für Kehrichtschlacke (Projekt EKESA). Schlussbericht.
Amt für Gewässerschutz und Wasserbau des Kantons Zürich, Zurich, Switzerland.
|
| 3.
|
Blake, R. C., and E. A. Shute.
1994.
Respiratory enzymes of Thiobacillus ferrooxidans. Kinetic properties of an acid-stable iron:rustcyanin oxidoreductase.
Biochemistry
33:9220-9228[Medline].
|
| 4.
|
Bosecker, K.
1987.
Microbial recycling of mineral waste products.
Acta Biotechnol.
7:487-497.
|
| 5.
|
Bosecker, K.
1997.
Bioleaching: metal solubilization by microorganisms.
FEMS Microbiol. Rev.
20:591-604.
|
| 6.
|
Bosshard, P. P.,
R. Bachofen, and H. Brandl.
1996.
Metal leaching of fly ash from municipal waste incineration by Aspergillus niger.
Environ. Sci. Technol.
30:3066-3070.
|
| 7.
|
Brombacher, C.,
R. Bachofen, and H. Brandl.
1997.
Biohydrometallurgical processing of solids: a patent review.
Appl. Microbiol. Biotechnol.
48:577-587.
|
| 8.
|
Brombacher, C., and H. Brandl.
1994.
Abschätzung der Oekotoxizität unbehandelter Elektrofilterasche einer Kehrichtverbrennungsanlage mit dem Pseudomonas-O2-Verbrauchstest, abstr. P6, p. 69.
Abstracts of the 53rd Annual Meeting of the Swiss Society for Microbiology 1994.
Swiss Society for Microbiology, Lucerne, Switzerland.
|
| 9.
|
Curutchet, G.,
C. Pogliani, and E. Donati.
1995.
Indirect bioleaching of covellite by Thiobacillus thiooxidans with an oxidant agent.
Biotechnol. Lett.
17:1251-1256.
|
| 10.
|
Francis, A. J., and C. J. Dodge.
1990.
Anaerobic microbial remobilization of toxic metals coprecipitated with iron oxide.
Environ. Sci. Technol.
24:373-378.
|
| 11.
|
Hahn, M.,
S. Willscher, and G. Straube.
1993.
Copper leaching from industrial wastes by heterotrophic microorganisms, p. 673-683. In
A. E. Torma, J. E. Wey, and V. I. Lakshmanan (ed.), Biohydrometallurgical technologies, vol. 1.
The Minerals, Metals & Materials Society, Warrendale Pa.
|
| 12.
|
Herrera, L.,
P. Ruiz,
J. C. Aguillon, and A. Fehrmann.
1989.
A new spectrophotometric method for the determination of ferrous iron in the presence of ferric iron.
J. Chem. Technol. Biotechnol.
44:171-181.
|
| 13.
|
Hoffmann, W.,
N. Katsikaros, and G. Davis.
1993.
Design of a reactor bioleach process for refractory gold treatment.
FEMS Microbiol. Rev.
11:221-230.
|
| 14.
|
Hughes, M. N., and R. K. Poole.
1989.
.
Metals and micro-organisms.
Chapman and Hall, London, United Kingdom.
|
| 15.
|
Karavaiko, G. I.,
S. I. Kuznetsov, and A. I. Golonizik.
1977.
.
The bacterial leaching of metals from ores.
Technicopy Ltd., Stonehouse, Great Britain.
|
| 16.
|
Krebs, W.,
C. Brombacher,
P. P. Bosshard,
R. Bachofen, and H. Brandl.
1997.
Microbial recovery of metals from solids.
FEMS Microbiol. Rev.
20:605-617.
|
| 17.
|
Lahl, U., and R. Struth.
1993.
Verwertung von Müllverbrennungsschlacken aus der Sicht des Grundwasserschutzes.
Vom Wasser
80:341-355.
|
| 18.
|
Ledin, M., and K. Pedersen.
1995.
.
The environmental impact of mine waste role of microorganisms and their significance in treatment of mine waste. Report 83.
Swedish Waste Research Council, Stockholm, Sweden.
|
| 19.
|
Madigan, M. T.,
J. M. Martinko, and J. Parker.
1997.
.
Biology of microorganisms, 8th ed.
Prentice Hall, Upper Saddle River, N.J.
|
| 20.
|
Mercier, G.,
M. Chartier, and D. Couillard.
1996.
Strategies to maximize the microbial leaching of lead from metal-contaminated aquatic sediments.
Water Res.
30:2452-2464.
|
| 21.
|
Notter, M.
1993.
.
Metals and the environment. Report 4245.
Swedish Environmental Protection Agency, Solna, Sweden.
|
| 22.
|
Pinches, T.,
J. Neale,
R. Huberts, and P. Dempsey.
1993.
Development of the Mintek bacterial oxidation process (MINbac), p. 221-229.
Proceedings of Randol Gold Forum '93.
Randol International Ltd., Golden, Colo.
|
| 23.
|
Rossi, G.
1990.
.
Biohydrometallurgy.
McGraw-Hill Book Company, New York, N.Y.
|
| 24.
|
Sand, W.,
T. Gerke,
R. Hallmann, and A. Schippers.
1995.
Sulfur chemistry, biofilm, and the (in)direct attack mechanisma critical evaluation of bacterial leaching.
Appl. Microbiol. Biotechnol.
43:961-966.
|
| 25.
|
Schäfer, W.
1982.
.
Bakterielle Laugung von metallhaltigen Industrierückständen. Ph.D. thesis.
University of Dortmund, Dortmund, Germany.
|
| 26.
|
Tyagi, R. D.,
D. Couillard, and Y. Grenier.
1991.
Effects of medium composition on the bacterial leaching of metals from digested sludge.
Environ. Pollut.
71:57-67.
[Medline] |
| 27.
|
Vonmont, H.
1994.
.
Untersuchungsbericht 146'601/7.
EMPA (Eidgenössische Materialprüfungs- und Forschungsanstalt), Dübendorf, Switzerland.
|
Appl Environ Microbiol, April 1998, p. 1237-1241, Vol. 64, No. 4
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
This article has been cited by other articles:
-
Ryu, H. W., Moon, H. S., Lee, E. Y., Cho, K. S., Choi, H.
(2003). Leaching Characteristics of Heavy Metals from Sewage Sludge by Acidithiobacillus thiooxidans MET. J. Environ. Qual.
32: 751-759
[Abstract]
[Full Text]
Top
Abstract
Introduction
