EJB Electronic Journal of Biotechnology ISSN: 0717-3458
© 2000 by Universidad Católica de Valparaíso -- Chile
Vol.3 No.3, Issue of December 15, 2000
Received November 9, 2000 / Accepted November 22, 2000
REVIEW ARTICLE
The use of reactors in biomining processes
Fernando Acevedo
Escuela de Ingeniería Bioquímica
Universidad Católica de Valparaíso
Avenida Brasil 2147, Valparaíso, Chile
Tel: 56-32-273644
Fax: 56-32-273803
E-mail: facevedo@ucv.cl
Financial support: FONDECYT Grants 1980338 and 1000284 UCV Projects 203.703/98 and 203.715/00.
Keywords: bacterial leaching, bioleaching, biooxidation, bioreactors, stirred tanks, Thiobacillus.
Microbial processes applied to mining operations are
gaining increasing interest in the last years. Potential
and current applications include the mining of gold,
copper and other heavy metals, desulfurization of coal
and oil, tertiary recovery of oil and biosorption of metal
ions. Currently, bacterial leaching of copper and
biooxidation of refractory gold concentrates are wellestablished large-scale processes that are carried on
using heaps and tank reactors. Heap operation is simple
and adequate to handle large volumes of minerals, but
their productivity and yields are limited because of the
severe difficulties in exerting an adequate process
control. On the other hand, reactors can economically
handle moderate volumes of material, but they allow for
a close control of the variables involved, rendering
significantly better performances. This paper reviews
the basis of reactor selection and design for bioleaching
processes. Special attention is given to the influence of
oxygen and carbon dioxide mass transfer, process
stoichiometry,
solids
suspension
and
slurry
homogeneity, and the use of bioreactors in gold mining.
It is concluded that the future of reactors in biomining
is promising and that new applications, such as the
bioleaching of copper concentrates, will soon be a
reality.
Microbial processes are gaining increasing interest in the
mining industry. Bioleaching of heavy metals, biooxidation
of gold ores, desulfurization of coal and oil, tertiary
recovery of oil and biosorption of metal ions are examples
of the wide variety of potential and actual applications of
microorganisms in mining and related fields (Karavaiko,
1985; Kelley and Tuovinen, 1988; Lawrence and Poulin,
1995; Rawlings, 1997; Brierley and Brierley, 1999).
Currently, bacterial leaching and biooxidation are largescale processes that are being successfully used in copper
and gold processing (Acevedo et al. 1993; Brierley, 1997).
The term biomining have been coined to refer to the use of
microorganisms in mining processes. Biomining
encompasses two related microbial processes that are useful
in the extractive metallurgy of heavy metals: bacterial
leaching, also known as bioleaching, and biooxidation.
Leaching is the solubilization of one or more components
of a complex solid by contact with a liquid phase. In
bacterial leaching, the solubilization is mediated by
bacteria. So bacterial leaching is a process by which the
metal of interest is extracted from the ore by bacterial
action, as in the case of bacterial leaching of copper. On the
other hand, biooxidation implies the bacterial oxidation of
reduced sulfur species accompanying the metal of interest,
as in the biooxidation of refractory gold minerals.
For many years bioleaching was thought as a technology
for the recovery of metals from low-grade ores, flotation
tailings or waste material (Torma, 1977; Gentina and
Acevedo, 1985). Today bioleaching is being applied as the
main process in large-scale operations in copper mining and
as an important pretreatment stage in the processing of
refractory gold ores.
The main advantages of bacterial leaching of copper and
other heavy metals as compared with pyrometallurgy lie in
its relative simplicity, mild operation conditions, low
capital costs, low energy input, and in its friendliness
towards the environment. The biooxidation of refractory
gold ores presents similar characteristics when compared
with roasting and pressure oxidation (Gentina and Acevedo,
1985; Acharya, 1990).
Bacterial leaching of copper is usually performed in heaps
of ground ore or in dumps of waste or spent material. Heaps
and dumps are irrigated in closed circuit with an acidic
liquor that contains a fraction of the bacterial population,
the rest being attached to mineral. When the desired metal
concentration is attained, the rich liquor is pumped to the
solvent extraction (SE) section and then sent to
electrowinning (EW), where the fine metal is recovered.
The raffinate from the SE section is recycled to the heap or
dump and the spent liquor of the EW section is recycled to
the SE operation (Montealegre et al. 1993; Avendaño and
Domic, 1994; Readett, 1999).
This paper is available on line at http://www.ejb.org/content/vol3/issue3/full/4
Acevedo, F.
Heaps and dumps present a number of advantages such
as simple equipment and operation, low investment and
operation costs and acceptable yields. On the other hand
it must be realized that the operation suffers from some
severe limitations: the piled material is very
heterogeneous and practically no close process control
can be exerted, except for intermittent pH adjustment
and the addition of some nutrients. Moreover, the rates
of oxygen and carbon dioxide transfer that can be
obtained are low, and extended periods of operation are
required in order to achieve sufficient conversions
(Acevedo and Gentina, 1989).
From a process engineering standpoint, the complex
network of biochemical reactions encompassed in
bioleaching would best be performed in reactors. The
use of reactors would allow a good control of the
pertinent variables, resulting in a better performance.
Parameters such as volumetric productivity and degree
of extraction can be significantly increased (Pinches et
al. 1988; Acevedo and Gentina, 1989; Gormely and
Brannion, 1989; Adamov et al. 1990). The main
limitation in the use of reactors in biomining is the very
large amounts of run-of-mine ore that in most cases is to
be treated. The Chuquicamata copper mine in Chile
produced 630,000 tons of fine copper in 1999. The
production of that amount of metal implied the
treatment of around 6 million tons of run-of-mine. If
such amount would to be treated in bioreactors, the
required equipment volume would of the order of 30
million cubic meters, an unthinkable figure. This limits
their application to the treatment of mineral
concentrates or when moderate volumes of ore are to be
processed. For instance, over 11,000 tons of gold
concentrates are biooxidized in reactors every year.
The discussion that follows will center on the use of
bioreactors in biomining, with emphasis in oxygen and
carbon dioxide transfer, the maintenance of an adequate
solids suspensions and the application of bioreactors to
commercial mining operations.
Reactors in bioleaching
The selection of a suitable reactor for a biomining
process and its design should be based in the physical,
chemical and biological characteristics of the system.
Adequate attention should be paid to the complex nature
of the reacting sludge, composed by an aqueous liquid,
suspended and attached cells, suspended solids, and air
bubbles (Gormely and Brannion, 1989). Because of the
very large volumes of material to be processed,
bioleaching and biooxidation are best performed in a
continuous mode of operation in which volumetric
productivity is high and reactor volumes can be kept
low. Considering the kinetic characteristics of microbial
growth, a continuous stirred tank reactor, CSTR,
appears as the first choice.
An important consideration in selecting a suitable
reactor refers to the autocatalytic nature of microbial
growth. This fact is common to all fermentation
operations, but in bioleaching there is an important
difference. In industrial fermentations the nutrients are
chosen by their high affinity with the microbial
population, while in biomining the mineral species
involved are usually recalcitrant to microbial action,
implying that the affinity is quite low. The substratemicroorganism affinity is related to Monod’s saturation
constant, KS (Monod, 1949). High affinities are reflected
in low KS values, of the order of a few milligrams per
liter, as in the case of most sugars. Some minerals have
saturation constants as high as 3 to 6 g/L, that is,
thousands of orders of magnitude higher. This situation
affects the selection of the reactor. If a high degree of
conversion is desired, a single agitated tank will require
a very large volume, so an arrangement of reactors will
be more suitable (Dew, 1995). It can be shown that a
CSTR followed by a tubular plug flow reactor, PFR,
gives the minimum reaction volume to attain a certain
conversion (Levenspiel, 1972). Because the need of
aeration and the presence of solid particles makes PFRs
unpractical, their performance can be approximated by a
series of CSTRs (González et al. 1999).
Other types of reactors that have been studied for their
application in biomining are the percolation column, the
Pachuca tank, the air-lift column, and some special
designs such as rotary reactors (Atkins and Pooley,
1983; Atkins et al. 1986; Nikolov et al. 1986; Acevedo
et al. 1988; Barrette and Couillard, 1993; Loi et al.
1995; Herrera et al. 1997; Acevedo et al. 1999; Canales
et al. 1999; Nedeltchev et al. 1999; Rossi, 1999).
Gas mass transfer
Several mass transfer operations occur in a biomining
operation. Nutrients have to reach the attached and
suspended cells, metabolic products have to migrate
from the cells to the liquid and solubilized species must
be transported from the surface of the mineral particles
to the liquid. In addition, two other important transport
processes are to be considered: the supply of oxygen
and carbon dioxide from the air to the cells. Carbon
dioxide is demanded by the cell population as carbon
source, while oxygen is needed as the final electron
acceptor of the overall oxidation process. In reactors
these gases are usually supplied by bubbling air into the
liquid. In order to be used by the cells, oxygen and
2
The use of reactors in biomining processes
carbon dioxide must dissolve in the liquid, a mass
transfer operation that presents a high resistance and can
become limiting for the overall process rate.
A gas mass balance around the bioreactor gives (Wang
and Humphrey, 1968):
(
)
*
transfer coefficient (h -1), C i is the gas equilibrium
concentration (g/L), CLi is the dissolved gas
concentration, and t is time (h).
)
The gas supply, k L a i C i − C Li , must equal the gas
demand in order to avoid growth limitation, so
(
N i = k L a i C *i − C Li
)
[2]
The gas demands can be calculated as
Ni =
1⋅ M c
= 0.064 g cells/g consumed
55.34 ⋅ M O 2
[1]
where i stands for oxygen or carbon dioxide, N is the
gas demand (g gas/l·h), kL ai is the volumetric gas
*
YO2 =
oxygen [6]
dC Li
= k L a i C*i − C Li − N i
dt
(
The oxygen and carbon dioxide cell yields can be
calculated from equation [5]:
µX
Yi
[3]
YCO 2 =
1⋅ M c
= 0.51 g cells/g consumed
5.0 ⋅ M CO 2
carbon dioxide
[7]
in which M c, M O2 M CO2 are the molecular masses of the
cells, oxygen and carbon dioxide, respectively.
In an actual bioleaching operation, a similar
stoichiometric representation can be made. For instance,
for the biooxidation of enargite (Cu 3 AsS4 ) from a
refractory gold concentrate the following equation
applies, considering an experimental value of 0.6 g
cell/g Cu (Garcia, 1997):
5.0CO2 + NH3 + Cu3 AsS4 + 4.5H2 O + 3.75O2 →
C5 H7 O2 N + 3.0CuSO4 + H3 AsO4 + H2 SO4
[8]
where µ is the specific growth rate of the cells (h ), X is
cell mass concentration (g/L), and Yi is the gas cell
yield (g cells/g gas).
-1
In this case the oxygen and carbon dioxide cell yields
are:
113
= 0.94 g/g
3.75 ⋅ 32
[9]
113
= 0.51 g/g
5 ⋅ 44
[10]
The bioleaching process can be represented by a
stoichiometric equation (Acevedo, 1987; Acevedo and
Gentina, 1989). In the case of a leaching organism such
as Thiobacillus ferrooxidans growing in a simple
defined culture media with ferrous iron as the energy
source, the following equation can be written:
YO2 =
1 ⋅ CO2 + m ⋅ NH3 + n ⋅ FeSO4 + o ⋅ H2 SO4 + p
⋅ O2 → C5 H7O2N + r ⋅ Fe2 (SO)3 + s ⋅ H2 O [4]
As could be expected, the carbon dioxide yield, related
only with cell growth, is the same in the defined soluble
medium and in the bioleaching of a mineral.
C5 H7 O2 N represents the biomass with an elemental
composition of 53.1% C, 6.2% H, 28.3% O, and 12.4%
N (Jensen and Webb, 1995). Elemental mass balances
on C, H, O and N, together with the experimental value
of the ferrous ion cell yield of 0.0086 g cells/g Fe2+,
allows for the calculation of the stoichiometric
coefficients:
Equations [2], [3], [6], [7], [9] and [10] can be used to
estimate the required mass transfer coefficients, as
shown in Table 1. When not enough experimental data
are available, the required coefficient for oxygen can be
estimated from the stoichiometry equation of the main
oxidation reaction. Oxygen transfer coefficients
estimated by such method are included for chalcocite
(Cu 2 S), covellite (CuS) and chalcopyrite (CuFeS). The
required kL a’s for oxygen are of the same order of
magnitude or less than those that have been obtained
experimentally in bioreactors (Acevedo et al. 1988; Liu
5.0CO2 + NH3 + 241.37FeSO4 + 120.67H2 SO4
+ 55.34O2 → C5 H7O2N + 120.67Fe2 (SO4 )3 +
118.67 H2 O
[5]
YCO 2 =
3
Acevedo, F.
et al. 1988; Boon and Heijen, 1998; Harvey et al. 1999;
Rossi, 1999; Veljkovic et al. 1999). This implies that at
the usual experimental conditions of 5 to 18% w/v pulp
density, the process is not limited by oxygen supply.
This situation may change at higher pulp densities
(Bailey and Hansford, 1993; Hansford and Bailey,
1993; Loi et al. 1995).
Table 1. Required kLa values for the biooxidation of
ferrous iron and an enargite gold concentrate a .
k La, h-1
O2
30
3
12
20
42
Ferrous iron
Enargite
Chalcocite
Covellite
Chalcopyrite
a
CO2
65
84
-
Based on data by García (1997) and Acevedo et al. (1988).
In fermentation technology it is usual to correlate kL a
with agitation power per unit volume and gas superficial
velocity (Wang and Humphrey, 1968; Boon and
Heijnen, 1998; Harvey et al. 1999):
α
k La O
Pg
= K ⋅ vβs
V
[11]
In leaching bioreactors, the transfer coefficient may be
influenced by the presence of solids (Mills et al. 1987),
so the equations derived specifically for bioleaching are
required. Table 2 shows some correlations of this type.
Because of its very low concentration in air, 0.03% v/v,
the equilibrium concentration of carbon dioxide is also
very low, 0.00039 g/L at 30ºC. The magnitude of the
transfer potential, C*-CL , is severely limited, leading to
CO2 limited growth, as air flow rate is commonly
determined based in the oxygen demand. Carbon
dioxide limitation has been demonstrated by several
authors (Torma et al. 1972; Norris, 1989; Boogard et al.
1990; Haddadin et al. 1993; Nagpal et al. 1993; Jensen
and Webb, 1995; Jaworska and Urbanek, 1997;
Acevedo et al. 1998; Boon and Heijen, 1998), but more
work is required on this topic.
The CO2 transfer coefficient can be experimentally
determined by a dynamic method on the exit gas (André
et al. 1981) or estimated from de oxygen transfer
coefficient (Liu et al. 1983; Nagpal et al. 1993):
k LC
D
= k L O O
DC
−2 / 3
[12]
Suspension of solids
The CSTR is an ideal conception that implies a
completely mixed content that presents no gradients, so
the value of each variable is the same at every point
within the liquid. That being the case, the exit stream
has the same composition as the fluid within the reactor.
As stated previously, tank bioleaching is a three-phase
system composed by the incoming air and the outlet gas,
the acidic aqueous liquor, and the microbial cells and
mineral particles. The complex nature of this slurry
makes the attainment of homogeneity especially
difficult (Brucato and Brucato, 1998).
Agitation has a double purpose: to increase the rate of
transfer operations, such as oxygen and carbon dioxide
transfer and heat transfer, and to mix the reactor
content. Under conditions of insufficient agitation the
transfer operations may become limiting and the overall
reaction performance will decline because of the
appearance of zones of the fluid with insufficient
nutrients or inadequate temperature or pH (Namdev et
al. 1994). For several decades the use of disk turbines
(or Rushton turbines) have been common in industrial
fermentors.
Back in the fifties investigators were mainly looking for
impellers that specifically enhanced oxygen transfer, but
they neglected other important factors such as mixing,
impeller gas flooding and power consumption, which
are all negative assets for the disk turbine (Humphrey,
1998). The high shear stress exerted by the disk turbine
on the fluid may also produce metabolic stress and cell
growth inhibition (Toma et al. 1991). When mixing is
specially important, axial flow impellers such as the
hydrofoils become an advantageous alternative
(Nienow, 1997; Junker et al. 1998; Myers and Bakker,
1998).
This is the case of bioleaching, where the oxygen
demands are modest but the presence of fine solid
particles impose an additional difficulty in obtaining
homogeneous slurries. Table 3 lists the most commonly
used type of impellers. It can be seen that the power
required by disk turbines is very high compared with the
requirements of other impellers. NP , the power number,
is a dimensionless number defined as P/ρ·N3·D5 .
Some of the hydrofoil designs developed in the mideighties (Lally, 1987) present convenient characteristics
for their use in bioleaching reactors. Their power
requirement is low, the mixing and solids suspension
capabilities are good and oxygen and carbon dioxide
transfer coefficients are comparable with those of the
disk turbine (Kubera and Oldshue, 1992; Kaufman et al.
1997).
4
The use of reactors in biomining processes
Table 2. Correlations for the volumetric oxygen transfer coefficient in bioleaching processes.
Correlation
Remarks
Stirred tank with ferrous ion as Gormely
energy source
1989
0 .93
Pg
k L a O = K ⋅ v .s0. 8
V
k L a O = K ⋅ ρ −2. 8 N 2. 65 v 0s .57
kLaO
Pg
= K ⋅
V
P
k LaO = K ⋅ a
V
0 .09
v1s.13
and
Branion,
20-L stirred tank. Model system with Liu et al. 1988
0.5 to 20% w/v glass beads. The
density ρ of the suspension
accounts for the influence of the
solids
7-L stirred tank with 15% w/v Acevedo et al. 1988
chalcopyrite concentrate and air
enriched with 1% CO2
7-L Pachuca tank with 15% w/v Acevedo et al. 1988
chalcopyrite concentrate and air
enriched with 1% CO2
0 .33
Pg
k L a O = (a − bφ ) ⋅
V
Reference
o . 67
v
. 0. 31
s
18-L stirred tank, model system with Mills et al. 1987
0 to 40% w/v solids
k L a O = K· v (s0.72 −0.011 φ)
k La O = K
4-L air-lift column with 0 to 24% w/v Canales, 1999
gold concentrate
−0 .0015 2.8 1. 49 14-L rotating drum reactor with 50% Herrera et al. 1997
⋅φ
F N
w/w gold concentrate
Table 3. Impeller types used in bioreactors a .
Impeller
Disk turbine
Flat blade turbine
Pitched blade turbine
Curved blade turbine
Hydrofoil
Gas dispersing hydrofoil
Marine helix
Bar turbine
a
Flow
radial
radial
axial
radial
axial
axial
axial
radial
NP
6.0
2.8
1.2
2.8
0.3
0.8
0.3
0.7
Dickey and Fenic, 1976; Kubera and Oldshue, 1992.
The problem of solids suspension in agitated vessels has
been addressed by several investigators. An important
early work was that of Zwietering (1958), who studied
the minimum required stirrer speed (referred afterwards
as critical speed) and the stirrer dimensions for the
complete suspension of solids. In this work the main
objective was to avoid solids deposition on the bottom
of the tank, but the homogeneity of the slurry was not of
special concern. Different expressions for the critical
speed have been proposed since then (Oldshue, 1983;
Tatterson, 1996).
The concept of critical speed was developed for
solid/liquid systems and does not consider the effect of
bubble aeration. In this respect, some early work by
Oldshue (1969, 1983) can be cited. This author points
out that air bubbling has a negative effect in solids
suspension and homogeneity, because the bubbles tend
to disturb the flow pattern established by each type of
impeller. In the specific field of tank bioleaching,
Acevedo and Aroca (1986) present a comparative study
of the effect of pulp density and aeration rate on the
critical agitation speed when using three type of
turbines: flat blade, curved blade and pitched blade. The
critical speed increased with aeration and the pulp
density showed a minor effect. The pitched blade
turbine gave the lowest critical speeds, pointing to the
fact that that the presence of an axial component in the
flow is positive for solids suspension.
In the last few years a number of interesting papers have
been published on agitation of slurries in bioreactors for
the biooxidation of gold concentrates (Fraser, 1992;
Kubera and Oldshue, 1992; Fraser, 1993; Oolman,
1993; Dew, 1995; Howk et al. 1995, Dew et al. 1997;
Spencer et al. 1997; Greenhalgh and Ritchie, 1999;
Harvey et al. 1999).
5
Acevedo, F.
Table 4. Large-scale plants for the biooxidation of refractory gold minerals a .
Start-up
Technology
Capacity
Fairview, South Africa
1986
Tank leaching
35 tons gold concentrate/day
Sao Bento, Brazil
1990
Tank leaching
150 tons gold concentrate/day
Harbour Lights, Australia
1992
Tank leaching
40 tons gold concentrate/day
Wiluna, Australia
1993
Tank leaching
115 tons gold concentrate/day
Ashanti, Ghana
1994
Tank leaching
1,000 tons gold concentrate/day
Youanmi, Australia
1994
Tank leaching
120 tons gold concentrate/day
Sansu, Ghana
1994
Tank leaching
1,000 tons gold concentrate/day
Tamboraque, Peru
1999
Tank leaching
260,000 tons of zinc flotation tailings
Mount Leyshon, Australia
1992
Heap leaching
1,370 tons of copper-gold ore/day
Newmont-Carlin, USA
1995
Heap leaching
10,000 tons gold ore/day
Plant
a
Brierley, 1997; Loayza and Ly, 1999.
Bioreactors and gold mining
Gold is usually obtained from ores by solubilization
with a cyanide solution and recovery of the metal from
the solution. In ores known as refractory, small particles
of gold are covered by insoluble sulfides.
These sulfides difficult the contact between cyanide
and gold, resulting in low metal recoveries. In that case,
a pre-treatment stage must be considered. Several
alternative technologies are available, such as pressure
oxidation, chemical oxidation, roasting and biooxidation, the latter currently being the alternative of
choice.
In the biooxidation process, bacteria partially oxidize
the sulfide coating covering the gold microparticles in
ores and concentrates. Microorganisms belonging to the
Thiobacillus and Leptospirillum genera are commonly
used, although an increasing interest exists in
thermophilic archeons (Dew et al. 1999; Howard and
Crundwell, 1999). Gold recovery from refractory
minerals can increase from 15-30% to 85-95% after
biooxidation.
In the last 15 years several large-scale commercial gold
processing units have been established. As shown in
Table 4, most of them use stirred tank reactors to
process flotation concentrates, although a few use heaps
for low-grade ores and tailings.
For the reasons already discussed, the tank leaching
plants listed in Table 4 uses several tanks connected in
series. The Fairview plant operates with a total
residence time of four days and a gold recovery of 94%.
The Sao Bento plant was originally designed for
pressure oxidation. Nevertheless, a biooxidation reactor
was added afterwards that allowed for a significant
improvement in overall performance. The Ashanti plant
has three biooxidation modules, each one consisting in
six 900 m3 reactors (Dew et al. 1997).
The Youanmi plant consists in two 500 m3 tanks
operated in parallel as a first stage, followed by a series
of two 500 m3 tanks (Bell and Quan, 1999). Although
the oldest plants were designed using disk turbine
agitators, the newer ones use hydrofoil axial impellers,
resulting in a better solids suspension and reduced
power requirement (Dew et al. 1997).
Future applications
The future of bioreactors in mining appears promising.
Gold biooxidation operations tend to increase in number
and size in several countries the world over. The use of
reactors will most probably extended to the bioleaching
of other metals, such as copper. Currently studies are
being carried on for the development of processes for
the bioleaching of copper concentrates.
The experience gained in the heap leaching of copper
and in the biooxidation of gold concentrates is being
used in these studies. The bioleaching of chalcopyritic
copper concentrates in the next few years will constitute
a big breakthrough in biomining. The application of
these technologies to the processing of nickel, zinc, and
other heavy metals may also become a reality in the
near future.
6
The use of reactors in biomining processes
Nomenclature
a, b
*
Ci
CLi
DC
CST
R
DO
EW
F
K
k LaC
k Lai
k LaO
k LC
k LO
MC
MCO2
MO2
N
Ni
NP
P
Pa
Pg
PFR
SE
t
vs
V
X
YCO2
Yi
YO2
α, β
φ
ρ
µ
constants
equilibrium concentration of gas i g/L
dissolved concentration of gas i
g/L
2
diffusivity of carbon dioxide in m /s
water
continuous stirred tank reactor
diffusivity of oxygen in water
electrowinning
air flow
constant
volumetric carbon dioxide transfer
coefficient
volumetric
mass
transfer
coefficient of gas i
volumetric
oxygen
transfer
coefficient
carbon dioxide transfer coefficient
oxygen transfer coefficient
cell molecular mass
carbon dioxide molecular mass
oxygen molecular mass
impeller rotational speed
gas i demand
power number
ungassed agitation pòwer
aeration power
gassed agitation power
plug flow reactor
solvent extraction
Time
superficial gas velocity
liquid volume
cell concentration
carbon dioxide cell yield
cell yield of nutrient i
oxygen cell yield
Exponents
Pulp density
Density of the slurry
Specific growth rate
2
m /s
3
Acevedo, F. and Gentina, J.C. (1989). Process engineering
aspects of the bioleaching of copper ores. Bioprocess
Engineering 4:223-229.
Acevedo, F., Cacciuttolo, M.A. and Gentina, J.C. (1988).
Comparative performance of stirred and Pachuca tanks in
the bioleaching of a copper concentrate. In: Norris, P.R.
and Kelly, D.P., eds. Biohydrometallurgy: Proceedings
of the International Biohydrometallurgy Symposium,
Warwick. Science and Technology Letters, Kew Surrey,
U.K., 12th – 16th July. pp. 385-394.
m /s
-1
h
-1
h
-1
h
m/s
m/s
-1
s
g/L·h
W
W
W
h
m/s
3
m
g/L
g/g
g/g
g/g
%w/v
g/mL
-1
h
References
Acevedo, F. (1987). Mass balancing: an effective tool
for fermentation process optimization. CRC Critical
Reviews in Biotechnology 4:309-322.
Acevedo, F. and Aroca, G. (1986). Studies on the
agitation and power characteristics of mineral slurries. In:
Lawrence, R.W., Branion, R.M. and Ebner, H.G., eds.
Fundamental and Applied Biohydrometallurgy. Elsevier,
Amsterdam, The Netherlands. pp. 255-261.
Acevedo, F., Canales, C. and Gentina, J.C. (1999).
Biooxidation of an enargite-pyrite gold concentrate in
aerated columns. In: Amils, R. and Ballester, A., eds.
Biohydromatallurgy and the Environment Toward the
Mining of the 21st Century, Part A. Elsevier,
Amsterdam, The Netherlands. pp. 301-308.
Acevedo, F., Gentina, J.C. and Bustos, S. (1993).
Bioleaching of minerals – a valid alternative for
developing countries. Journal of Biotechnology 31:115123.
Acevedo, F., Gentina, J.C. and García, N. (1998). CO2
supply in the biooxidation of an enargite-pyrite gold
concentrate. Biotechnology Letters 20:257-259.
Acharya, R. (1990). Bacterial leaching: a potential for
developing countries. Genetic Engineering and
Biotechnology Monitor 27:57-58.
Adamov, E.V., Po’lkin, S.I., Koreshkov, N.G. and
Karavaiko, G.I. (1990). State of the art and prospects of
bacterial tank leaching in the production of non-ferrous
and rare metals. In: Karavaiko, G.I., Rossi, G. and
Avakyan, Z.A., eds. International Seminar on Dump and
Underground Bacterial Leaching Metals from Ores.
Centre for International Projects-GKNT, Moscow,
USSR, 1st – 6th June. pp. 235-248.
André, G., Moo-Young, M. and Robinson, C.W. (1981).
Improved method for the dynamic measurement of mass
transfer coefficient for application to solid-substrate
fermentation. Biotechnology and Bioengineering
23:1611-1622.
Atkins, A.S. and Pooley, F.D. (1983). Comparison of
bacterial reactors employed in the oxidation of sulphide
concentrates. In: Rossi, G. and Torma, A.E., eds. Recent
Progress
in
Biohydrometallurgy.
Associazione
Mineraria Sarda, Iglesias, Italy. pp. 111-125.
Atkins, A.S., Pooley, F.D. and Townsley, C.C. (1986).
Comparative mineral sulphide leaching in shake flasks,
percolation columns and pachuca reactors using
7
Acevedo, F.
Thiobacillus ferrooxidans. Process Biochemistry 21:310.
Avendaño, C. and Domic, E. (1994). Engineering
design of LX-SX-EW plants. In: Wilkomirsky, I.,
Sánchez, M. and Hecker, C., eds. Chemical Metallurgy,
Vol. II. Universidad de Concepción, Concepción, Chile.
pp. 21-31.
Bailey, A.D. and Hansford, G.S. (1993). Factors
affecting bio-oxidation of sulfide minerals at high
concentration of solids: a review. Biotechnology and
Bioengineering 42:1164-1174.
Barrette, L-M. and Couillard, D. (1993). Bacterial
leaching of sulfide tailings in an airlift reactor. In:
Torma, A.E., Wey, J.E. and Laksman, V.L., eds.
Biohydrometallurgical Technologies, Vol.I. The
Minerals, Metals and Materials Society, Warrendale,
Pennsylavania, USA. pp. 205-215.
Bell, N. and Quan, L. (1999). The application of
Bactech (Australia) Ltd. technology for processing
refractory gold ores at Youanmi gold mine. In: IBS’97–
BIOMINE’97: Biotechnology comes of age. Conference
Proceedings. Sydney, Australia, 4th – 6th August. Paper
M2.3.
Boogard, F.C., Kuenen, J.G., Heijen, J.J. and Van der
Lans, R.G.J.M. (1990). Oxygen and carbon diooxide
mass transfer and the aerobic, autotrophic cultivation of
moderate and extreme thermophiles: a case study
related to the microbial desulfurization of coal.
Biotechnology and Bioengineering 35:1111-1119.
Boon, M. and Heijen, J.J. (1998). Gas-liquid mass
transfer phenomena in bio-oxidation experiments of
sulphide minerals: a critical review of literature data.
Hydrometallurgy 48:187-204.
Brierley, C.L. (1997). Mining biotechnology: research
to commercial development and beyond. In: Rawlings,
D.E., ed. Biomining: Theory, Microbes and Industrial
Processes. Springer Verlag, Berlin, Germany. pp. 3-17.
Canales, C. (1999). Biooxidación de concentrados
refractarios de oro en reactores de columna agitados por
aire. Master’s Thesis. Escuela de Ingeniería Bioquímica,
Universidad Católica de Valparaíso, Valparaíso, Chile.
pp. 81-86.
Canales, C., Acevedo, F. and Gentina, J.C. (1999).
Biooxidación de Concentrados de oro a elevada
densidad de pulpa: efecto de la suspensión de sólidos.
In: Memorias IV Congreso Latinoamericano de
Biotecnología, Vol.1. Huatulco, México, 12th -17th
September. p. 150.
Dew, D.H. (1995). Comparison of performance for
continuous bio-oxidation of refractory gold ore flotation
concentrates. In: Vargas, T., Jerez, C.A., Wiertz, J.V.
and Toledo, H., eds. Biohydrometallurgical Processing,
Vol.1. Universidad de Chile, Santiago, Chile. pp. 239251.
Dew, D.W., Lawson, E.N. and Broadhurst, J.L. (1997).
The BIOX process for biooxidation of gold-bearing
ores or concentrates. In: Rawlings, D.E., ed. Biomining:
Theory, Microbes and Industrial Processes. Springer
Verlag, Berlin, Germany. pp. 45-80.
Dew, D.W., Van Buren, C., McEwan, K. and Bowker,
C. (1999). Bioleaching base metal sulphide
concentrates: a comparison of mesophile and
thermophile bacterial cultures: In: Amils, R. and
Ballester, A., eds. Biohydromatallurgy and the
Environment Toward the Mining of the 21st Century, Part
A. Elsevier, Amsterdam, The Netherlands. pp. 229-238.
Dickey, D.S. and Fenic, J.G. (1976). Dimensional
analysis for fluid agitation systems. Chemical
Engineering 83:139-145.
Fraser, G. (1992). Gas dispersion and mixing for
mineral oxidation reactors. In: Extractive Metallurgy of
Gold and Base Metals. Conference Proceedings.
Kalgoorlie, Australia, 26th – 28th October. pp. 293-301.
Fraser, G.M. (1993). Mixing and oxygen transfer in
mineral bioleaching. Lightnin Technical Article Nº
177.00.
Brierley, J.A. and Brierley, C.L. (1999). Present and
future commercial applications of biohydrometallurgy.
In: Amils, R. and Ballester, A., eds. Biohydromatallurgy
and the Environment Toward the Mining of the 21st
Century, Part A. Elsevier, Amsterdam, The Netherlands.
pp. 81-89.
García, N. (1997). Efecto del CO2 en la biooxidación de
concentrados refractarios de oro de alto contenido de
enargita. Master’s Thesis. Escuela de Ingeniería
Bioquímica, Universidad Católica de Valparaíso,
Valparaíso, Chile. pp. 15, 92-96.
Brucato, A. and Brucato, V. (1998). Unsuspended mass
of solid particles in stirred tanks. The Canadian Journal of
Chemical Engineering 76:420-427.
Gentina, J.C. and Acevedo, F. (1985). Microbial ore
leaching in developing countries. Trends in
Biotechnology 3:86-89.
8
The use of reactors in biomining processes
González, R., Gentina, J.C. and Acevedo, F. (1999).
Modelo matemático y configuración óptima de un
sistema continuo para la biooxidación de un mineral de
oro refractario. In: Actas del XIII Congreso Nacional de
Ingeniería Química, Antofagasta, 18 – 21 Octubre de
1998.
Gormely, L.S. and Brannion, R.M.R. (1989).
Engineering design of microbiological leaching
reactors. In: Biohydrometallurgy 1989: Proceedings of
the International Biohydrometallurgy Symposium.
Jackson Hole, Wyoming. 13th -18th August. pp. 499-518.
Greenhalgh, P. and Ritchie, I. (1999). Advancing
reactor designs for the gold bioleaching process. In:
Biomine ’99: Conference Proceedings, Perth, Australia,
23rd -24th August. pp. 52-60.
Haddadin, J., Dagot, C. and Fick, M. (1993). Models of
bacterial leaching. Enzyme and Microbial Technology
17:290-305.
Hansford, G.S. and Bailey, A.D. (1993). Oxygen
transfer limitation of bio-oxidation at high solids
concentration. In: Torma, A.E., Wey, J.E. and Laksman,
V.L., eds. Biohydrometallurgical Technologies, Vol.I.
The Minerals, Metals and Materials Society,
Warrendale, Pennsylvania, USA. pp. 469-478.
Harvey, P.I., Batty, J.D., Dew, D.W. Slabbert, W. and
Van Buuren C. (1999). Engineering considerations in
bioleach reactor design. In: Biomine ’99: Conference
Proceedings. Perth, Australia, 23 th – 24th August. pp.
88-97.
Herrera, M.N., Escobar, B., Parra, N., González, C. and
Vargas, T. (1997). Bioleaching of refractory gold
concentrates at high pulp densities in a nonconventional
rotating-drum reactor. In: The SME Annual Meeting.
Denver, Colorado, USA, 24th – 27th February. Preprint
Nº 97-145.
Howard, D. and Crundwell, F.K. (1999). A kinetic study
of the leaching of chalcopyrite with Sulfolobus
metallicus. In: Amils, R. and Ballester, A., eds.
Biohydromatallurgy and the Environment Toward the
Mining of the 21st Century, Part A. Elsevier, Amsterdam,
The Netherlands. pp. 209-217.
Howk, R.A., Kelly, J.R. and Kubera, P.M. (1995). The
effect of mixing impeller geometry and pumping
direction on solids suspension homogeneity. Lightnin
Technical Article Nº 184.00.
Humphrey, A.E. (1998). Shake flask to fermentor: what
have we learned? Biotechnology Progress 14:3-7.
Jaworska, M. and Urbanek, A. (1997). The influence of
carbon dioxide concentration in liquid medium on
elemental
sulphur
oxidation
by
Thiobacillus
ferrooxidans. Bioprocess Engineering 16:361-365.
Jensen, A.B. and Webb, C. (1995). Ferrous sulphate
oxidation using Thiobacillus ferrooxidans: a review.
Process Biochemistry 30:225-236.
Junker, B.H., Stanik, M., Barna, C., Salmon, P. and
Buckland, B.C. (1998). Influence of impeller type on
mass transfer in fermentation vessels. Bioprocess
Engineering 19:403-413.
Karavaiko, G.I. (1985). Microbiological Processes for
the Leaching of Metals from Ores: State-of-the-Art
Review.
Centre for International Projects-GKNT,
Moscow, USSR. 69 p.
Kaufman, P., Kubera, P. and Post, T. (1997).
Fermentation: critical process phenomena and new
technology developments that affect yield and
productivity. Pharmaceutical Engineering 17:1-6.
Kelley,
B.C.
and
Tuovinen,
O.H.
(1988).
Microbiological oxidation of minerals in tailings. In:
Salomons, W. and Foerstner, U., eds. Chemistry and
Biology of Solid Waste: Dregded Material and Mine
Tailings. Springer-Verlag, New York, USA. pp. 33-53.
Kubera, P.M. and Oldshue, J.Y. (1992). Advanced
impeller technologies match mixing performance to
process needs. Lightnin Technical Article 171.00
Lally, K.S. (1987). A-315 axial flow impeller for gas
dispersion. Lightnin Technical Article 144.00.
Lawrence, R.W. and Poulin, R. (1995). The demand for
biotechnology in mining in the 21st century. In: Vargas,
T., Jerez, C.A., Wiertz, J.V. and Toledo, H., eds.
Biohydrometallurgical Processing, Vol.1. Universidad
de Chile, Santiago, Chile. pp. 185-195.
Levenspiel, O. (1972). Chemical Reaction Engineering.
2nd Edition. J. Wiley and Sons, New York, USA. 578 p.
Liu, M.S., Brannion, R.M.R. and Duncan, D.W. (1988).
Oxygen transfer to Thiobacillus cultures. In: Norris,
P.R. and Kelly, D.P., eds. Biohydrometallurgy:
Proceedings of the International Biohydrometallurgy
Symposium, Warwick. Science and Technology Letters,
Kew Surrey, U.K. 12th – 16th July. pp. 375-384.
Liu, M.S, Branion, R.M.R. and Duncan, D.W. (1983).
Effects of ferrous iron, dissolved oxygen, and inert
solidas concentrations on the growth of Thiobacillus
9
Acevedo, F.
ferrooxidans. The Canadian Journal of Chemical
Engineering 66:445-451.
18th –23rd
May.
Available
on
the
http://hugroup.cems.umn.edu/Archive.htm
Loi, G., Trois, P. and Rossi, G. (1995). Biorotor: a new
development for biohydrometallurgical processing. In:
Vargas, T., Jerez, C.A., Wiertz, J.V. and Toledo, H.,
eds.
Biohydrometallurgical
Processing,
Vol.1.
Universidad de Chile, Santiago, Chile. pp. 263-271.
Nikolov, L., Mehochev,D. and Dimitrov, D. (1986).
Continuous bacterial ferrous iron oxidation by
Thiobacillus ferrooxidans in rotating biological
contactors. Biotechnology Letters 8:707-710.
Loayza, C. and Ly, M.E. (1999). Biooxidation of
arsenopyrite
concentrate
for
industrial
plant
Tamboraque using acid mine drainage. In: Biomine’99:
Conference Proceedings. Perth, Australia, 23rd – 25th
August, pp. 162-167.
Mills, D.B., Bar, R. and Kirwan, D.J. (1987). Effect of
solids on oxygen transfer in agitated three-phase
systems. American Institute of Chemical Engineering
Journal 33:1542-1549.
Monod, J. (1949). The growth of bacterial cultures.
Annual Reviews in Microbiology 3:371-394.
Montealegre, R., Bustos, S., Rojas, J., Neuburg, H.,
Araya, C., Yáñez, H., Tapia, R. and Rauld. J. (1993).
Application of the bacterial thin layer process to
Quebrada Blanca ores. In: Torma, A.E., Wey, J.E. and
Laksman,
V.L.,
eds.
Biohydrometallurgical
Technologies, Vol.I. The Minerals, Metals and
Materials Society, Warrendale, Pennsylvania, USA. pp.
1-14.
Myers, K.J. and Bakker, A. (1998). Solids suspension
with
up-pumping
pitched-blade
high-efficiency
impellers. Canadian Journal of Chemical Engineering
76:433-440.
Nagpal, S., Dahistrom, D. and Oolman, T. (1993).
Effect of carbon dioxide concentration on the
bioleaching of a pyrite-arsenopyrite ore concentrate.
Biotechnology and Bioengineering 41:459-464.
Namdev, P.K., Dunlop, E.H., Wenger, K. and
Villeneuve, P. (1994). Role of turbulence in
fermentations. In: Galindo, E. and Ramírez, O.T., eds.
Advances in Bioprocess Engineering. Kluwer Academic
Publishers, Dordrecht, The Netherlands. pp. 149-156.
Web:
Norris, P.R. (1989). Factors affecting bacterial mineral
oxidation: the example of carbon dioxide in the context
of bacterial diversity. In: Biohydrometallurgy:
Proceedings of the International Biohydrometallurgical
Symposium. Jakson Hole, Wyoming, 13th – 18th August.
pp.3-14.
Oolman, T. (1993). Bioreactor design and scaleup
applications in mineral bioleaching. In: Torma, A.E.,
Wey,
J.E.
and
Laksman,
V.L.,
eds.
Biohydrometallurgical Technologies, Vol.I. The
Minerals, Metals and Materials Society, Warrendale,
Pennsylvania, USA. pp. 401-415.
Oldshue, J.Y. (1969). Suspending solids and dipersing
gases in mixing vessel. Industrial and Engineering
Chemistry 61:79-89.
Oldshue, J.Y. (1983). Fluid Mixing Technology.
McGraw-Hill Publications C., New York, N.Y., USA.
574 p.
Pinches, A., Chapman, J.T., Te Riele, W.A.M. and Van
Staden, M. (1988). The performance of bacterial leach
reactors for the pre-oxidation of refractory gold-bearing
sulphide concentrates. In: Norris, P.R. and Kelly, D.P.,
eds. Biohydrometallurgy: Proceedings of the
International
Biohydrometallurgy
Symposium,
Warwick. Science and Technology Letters, Kew Surrey,
U.K. 12th – 16th July. pp. 329-344.
Rawlings, D.E., ed. (1997). Biomining: Theory,
Microbes and Industrial Processes. Springer Verlag,
Berlin, Germany. 302 p.
Readett, D.J. (1999). Heap leaching. In: Biomine ’99:
Conference Proceedings, Perth, Australia. 23rd–24th
August. pp.61-80.
Nedeltchev, S., Ookawara, S. and Ogawa, K. (1999). A
fundamental approach to bubble column scale-up based
on quality of mixedness. Journal of Chemical
Engineering of Japan 32:431-439.
Rossi, G. (1999). The design of bioreactors. In: Amils,
R. and Ballester, A., eds. Biohydromatallurgy and the
Environment Toward the Mining of the 21st Century,
Part A. Elsevier, Amsterdam, The Netherlands. pp. 6180.
Nienow, A.W. (1997). A status review of mixing in
bioreactors. In: Engineering Foundation Conference on
Biochemical Engineering X . Kananaskis, Canada,
Spencer, P.A., Satalic, D.M., Baxter, K.G., and Pinches,
T. (1997). Key aspects in the design of a bacterial
oxidation
reactor.
In:
IBS’97–BIOMINE’97:
10
The use of reactors in biomining processes
Biotechnology comes of age. Conference Proceedings.
Sydney, Australia, 4th – 6th August. Paper M14.1.
Tatterson, G.B. (1996). Scaleup and Design of
Industrial Mixing Processes. McGraw-Hill, Inc., New
York, New York, USA. pp. 107-201.
Toma, M.K., Ruklisha, M.P., Vanags, J.J., Zeltina,
M.O., Leite, M.P., Galinina, N.I., Viesturs, U.E. and
Tengerdy, R.P. (1991). Inhibition of microbial growth
and metabolism by excess turbulence. Biotechnology
and Bioengineering 38:552-556.
Torma, A.E. (1977). The role of Thiobacillus
ferrooxidans in hydrometallurgical processes. Avances
in Biochemical Engineering 6:1-37.
Torma, A.E., Walden, C.C., Duncan, D.W. and Branion,
R.M.R. (1972). The effect of carbon dioxide and
particle surface area on the microbiological leaching of
a zinc sulfide concentrate. Biotechnology and
Bioengineering 14:777-786.
Veljkovic, V.B., Savic, D.S., Lazic, M.L. and Vrvic,
M.M. (1999). Oxygen mass transfer requirements
during ferrous iron oxidation by Thiobacillus
ferrooxidans under controlled pH conditions. In: Amils,
R. and Ballester, A., eds. Biohydromatallurgy and the
Environment Toward the Mining of the 21st Century, Part
A. Elsevier, Amsterdam, The Netherlands. pp. 617-623.
Wang, D.I-C. and Humphrey, A.E. (1968).
Developments in agitation and aeration of fermentation
systems. Progress in Industrial Microbiology 8:1-33.
Zwietering, T.N. (1958). Suspending of solid particles
in liquid by agitators. Chemical Engineering Science
8:244-253.
11