U.S. patent application number 15/316605 was filed with the patent office on 2017-06-22 for bioleaching method and facility.
This patent application is currently assigned to L'AIR LIQUIDE, SOCIETE ANONYME POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE. The applicant listed for this patent is BRGM, L'AIR LIQUIDE, SOCIETE ANONYME POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE, MILTON ROY EUROPE. Invention is credited to Patrick D'HUGUES, Anne-Gwenaelle GUEZENNEC, Dominique IBARRA, Marie JAILLET, Yannick MENARD, Dominique MORIN, Anna PUBILL MELSIO, Frederic SAVREUX.
Application Number | 20170175223 15/316605 |
Document ID | / |
Family ID | 50976562 |
Filed Date | 2017-06-22 |
United States Patent
Application |
20170175223 |
Kind Code |
A1 |
GUEZENNEC; Anne-Gwenaelle ;
et al. |
June 22, 2017 |
BIOLEACHING METHOD AND FACILITY
Abstract
A method for the lagoon-based bioleaching of a metallic ore,
wherein the temperature of the suspension containing the metallic
ore to be bioleached, a bioleaching consortium and a nutritive
substrate of the microorganisms of the consortium is controlled by
regulating the flows and the composition of a gas containing oxygen
and optionally also CO2 injected into the suspension, the
temperature of the suspension being controlled such that it can be
maintained within a pre-determined range suitable for
bioleaching.
Inventors: |
GUEZENNEC; Anne-Gwenaelle;
(Orleans, FR) ; IBARRA; Dominique;
(Gif-sur-Yvette, FR) ; JAILLET; Marie; (Juvisy sur
Orge, FR) ; MENARD; Yannick; (Mezieres Les Clery,
FR) ; MORIN; Dominique; (Olivet, FR) ; PUBILL
MELSIO; Anna; (Paris, FR) ; SAVREUX; Frederic;
(Saint Mammes, FR) ; D'HUGUES; Patrick; (Olivet,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L'AIR LIQUIDE, SOCIETE ANONYME POUR L'ETUDE ET L'EXPLOITATION DES
PROCEDES GEORGES CLAUDE
BRGM
MILTON ROY EUROPE |
Paris
Orleans
PONT-SAINT-PIERRE |
|
FR
FR
FR |
|
|
Assignee: |
L'AIR LIQUIDE, SOCIETE ANONYME POUR
L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE
Paris
FR
BRGM
Orleans
FR
MILTON ROY EUROPE
Pont-Saint-Pierre
FR
|
Family ID: |
50976562 |
Appl. No.: |
15/316605 |
Filed: |
June 5, 2015 |
PCT Filed: |
June 5, 2015 |
PCT NO: |
PCT/EP2015/062592 |
371 Date: |
December 6, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22B 3/18 20130101; C22B
23/0407 20130101; C22B 15/0065 20130101; C22B 1/24 20130101; C22B
3/20 20130101; C22B 11/04 20130101; C22B 3/02 20130101; Y02P 10/234
20151101; Y02P 10/20 20151101 |
International
Class: |
C22B 3/18 20060101
C22B003/18; C22B 1/24 20060101 C22B001/24; C22B 3/02 20060101
C22B003/02; C22B 3/20 20060101 C22B003/20; C22B 3/00 20060101
C22B003/00; C22B 15/00 20060101 C22B015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2014 |
EP |
14305865.9 |
Claims
1-15. (canceled)
16. Method for bioleaching of a metalliferous ore, said method
comprising the following steps: a) adding, into a basin, a ground
metalliferous ore, a medium comprising a bioleaching microbial
consortium, and a nutritive medium for the microorganisms of the
microbial consortium, b) obtaining a suspension in the basin via at
least one stirring system for placing and maintaining the
metalliferous ore in suspension in a liquid phase, c) injecting,
into the suspension, a gas containing oxygen and optionally carbon
dioxide, d) in the suspension, bioleaching of the metalliferous ore
by the microbial consortium in order to obtain a released metal, e)
recovering a liquid product containing the released metal and
consisting of (a) a liquor and (b) a solid residue, wherein the
temperature of the suspension is controlled by regulating the flow
rates and the composition of the gas injected, as well as
optionally the concentration of solids in the suspension, the
temperature of the suspension being controlled in such a way as to
be maintained in a predetermined range suitable for
bioleaching.
17. Method according to claim 16, wherein the basin is an open-air
basin.
18. Method according to claim 16, wherein the gas injected has an
O.sub.2 concentration of at least 21% vol O.sub.2, preferably at
least 40% vol and more preferably 50% vol to 100% vol, and
optionally a CO.sub.2 concentration from 0% vol to 5% vol,
preferably from 1% vol to 3% vol.
19. Method according to claim 16, wherein said microbial consortium
comprises microorganisms chosen from the species Leptospirillum
ferriphilum, Acidithiobacillus caldus and Sulfobacillus benefaciens
and the combinations of at least two of said species.
20. Method according to claim 16, wherein the suspension is
maintained at a pH from 0.8 to 2.5, preferably 1.0 to 1.5.
21. Method according to claim 16, wherein the suspension comprises
from 15 to 40% solid by weight with respect to the total weight of
the suspension, preferably 22 to 38% and more preferably 25 to
35%.
22. Method according to claim 16, wherein the stirring system
comprises at least one stirrer, preferably at least one floating
stirrer, said at least one stirrer being provided with at least one
injector for the injection of the gas into the suspension.
23. Facility for bioleaching via lagooning, comprising: a basin,
preferably an open-air basin, containing a suspension comprising a
liquid phase, a ground metalliferous ore, a bioleaching microbial
consortium, and a nutritive medium for the microorganisms of the
microbial consortium; a stirring system for placing and/or
maintaining the metalliferous ore in suspension in the liquid
phase, said stirring system comprising a plurality of floating
stirrers; at least one injector or the injection of a gas into the
suspension, wherein said at least one injector is connected to a
source of an oxygenated gas having an O.sub.2 concentration of at
least 50% vol and more preferably of at least 85% vol; to a source
of a dilution gas having an O.sub.2 concentration from 0 to 21%
vol; optionally to a source of carbon gas that can be metabolised,
having a CO.sub.2 concentration of at least 50% vol, preferably of
at least 75% vol and more preferably of at least 85% vol; the
facility also comprising a gas regulator for regulating the flow
rate of the oxygenated gas and a dilution-gas regulator for
regulating the flow rate of the dilution gas to the at least one
injector and optionally also a regulator for regulating the flow
rate of the carbon gas that can be metabolised to the at least one
injector.
24. Facility according to claim 23, wherein the source of dilution
gas is a source of nitrogen or a source of air, said source of air
being preferably an air compressor.
25. Facility according to claim 23, comprising a control unit for
the control of the regulator of the oxygenated gas and of the
regulator of the dilution gas and optionally also of the regulator
of the carbon gas that can be metabolised, in order to regulate the
overall gaseous flow rate, the flow rate of O.sub.2 and optionally
the flow rate of CO.sub.2 supplied to said at least one
injector.
26. Facility according to claim 25, comprising at least one system
for measuring temperature, for measuring the temperature of the
suspension in the basin, the control unit being connected to said
system for measuring temperature, the control unit regulating the
flow rate of the oxygenated gas and the flow rate of the dilution
gas, as well as optionally also the flow rate of carbon gas that
can be metabolised, directed to the at least one injector according
to the temperature measured by the system for measuring temperature
in order to maintain the temperature of the suspension in a
predetermined range.
27. Facility according to one of claim 23, wherein the basin does
not comprise heating or cooling elements.
28. Facility according to claim 23, wherein the at least one
injector is integrated into the floating stirrers.
29. Facility according to claim 23, wherein the microbial
consortium comprises microorganisms chosen from the species
Leptospirillum ferriphilum, Acidithiobacillus caldus and
Sulfobacillus benefaciens and the combinations of said species.
30. Method for regulating temperature, for a bioleaching
suspension, said suspension comprising a metalliferous ore, a
bioleaching microbial consortium, and a nutritive medium for the
microorganisms of the consortium, wherein in said method, the
temperature of the suspension is controlled by regulating the flow
rate and the composition of a gas, containing oxygen and optionally
carbon dioxide, that is injected into said suspension, as well as
optionally by regulating the concentration of solids in the
suspension, in such a way that the temperature of the suspension is
maintained in a predetermined range.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a bioleaching method and facility
that allow the extraction of metals and the reuse of these metal
resources thus extracted.
PRIOR ART
[0002] Since the demand for metal compounds is constantly
increasing, the reuse of resources formerly deemed as not very
accessible now poses a growing economic interest. These resources
can be old deposits of mining waste containing residual quantities
of metals or ores having lower concentrations of metal and/or of a
more complex nature, comprising various metals and/or comprising a
high level of impurities. Moreover, these metals are often in the
form of sulphide compounds, the treatment of which is technically
complex and requires heavy investments.
[0003] One of the methods most frequently used to treat such ores
is pyrometallurgy. After concentration of the sulphides via a
physico-chemical treatment of the ore, this method involves a
thermal treatment that allows the sulphides to be "burned" via an
oxidation reaction and generates a calcine rich in iron and a solid
product with a high concentration of metals of value (matte). Such
methods involve the emission of toxic gases, the treatment of which
can be very disadvantageous, and are only slightly effective for
the treatment of ores comprising a high level of carbonate.
[0004] With respect to pyrometallurgy, hydrometallurgical methods
in general require less investment and are particularly suited to
the treatment of metal resources having a complex composition
and/or having a low concentration of the metal of interest. Among
the hydrometallurgical methods, a solution that is generally very
satisfactory from the environmental and economic points of view,
called biohydrometallurgy, involves extracting the metals by using
microorganisms. In particular, this solution allows both mining
waste and sulphide ores having low concentrations to be
treated.
[0005] The process of degradation of the sulphide ores by
microorganisms forms the basis of the bioleaching method used in
biohydrometallurgy. These microorganisms draw the energy necessary
for the functioning of their metabolisms from the reactions of
oxidation, in a highly acidic medium, of iron and sulphur, major
components of sulphide ores that contain significant quantities of
metals of high economic value (copper, nickel, cobalt, zinc, gold,
molybdenum, silver . . . ). Bioleaching also allows the
extremophilic metabolic capabilities of certain microbes such as
Sulfolobus metallicus, Acidithiobacillus ferrooxidans,
Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans to be
used to extract these metals of interest.
[0006] Heap bioleaching is a particular technique involving the
rough crushing of the ore to be treated and then the storage
thereof in heaps on impermeable pads. These heaps can reach a
height of more than 100 m. Then, a solution containing
microorganisms and a suitable nutritive medium is scattered at the
top of the heap. While the solution percolates through the heap,
the solution is progressively enriched with metal. After
percolation through the heap, this enriched solution is recovered
at the base of the heap. Heap bioleaching has slow or even very
slow kinematics (sometimes years of continuous treatment) and
yields that are variable (between 30 and 90%) and thus sometimes
low, and is difficult to implement for the treatment of
polymetallic ores and/or ores containing carbon. The slow
kinematics of this method are in particular linked to the
difficulty of applying and maintaining the optimal conditions
(temperatures, concentration and dispersion of the nutritive
medium, concentration and dispersion of the oxygen) homogeneously
inside the heap.
[0007] In order to achieve high yields and more attractive
operation times, bioleaching can be carried out in a reactor that
is mechanically stirred and thermally regulated. After grinding of
the ore to be treated and concentration of the sulphide phase via
physico-chemical means, the ore is mixed in reactors with an
aqueous phase containing microorganisms and a nutritive medium, and
thus a suspension is obtained. The reactors, manufactured from
non-oxidisable materials, comprise means for stirring, injection of
air and heat exchange, respectively allowing the ore to be
maintained in suspension and the gas to be dispersed in the
suspension, oxygen to be supplied for the reactions and for the
microorganisms, and the temperature of the suspension to be
controlled in order to maintain the fastest possible bioleaching
kinematics.
[0008] These reactors are therefore necessarily limited in size and
only allow the treatment of suspensions having limited
concentrations of ore (approximately 15 to 20% solid mass with
respect to the total mass of the suspension). Despite these
advantages, the investment in equipment and the operational cost in
terms of energy required for the implementation of such facilities
are only justified for the treatment of metal ores having high
value, such as gold-containing ores.
DESCRIPTION OF THE INVENTION
[0009] The present invention thus relates to a method for
bioleaching a metalliferous ore, the investment costs and the
environmental constraints of which are limited, as well as to a
bioleaching facility suitable for implementing said method.
[0010] The method according to the invention is particularly suited
to the treatment of metalliferous ores having low value and/or a
complex composition, but is also advantageous for the treatment of
metalliferous ores that are rich, have high value and/or have a
simple composition.
[0011] In the description of the invention, metalliferous ore
designates: an ore extracted from a mine, mining waste, or a
concentrate resulting from the mineralurgical treatment of an ore
and/or of mining waste.
[0012] Such a metalliferous ore can comprise one or more metals to
be released from the mineral matrix via bioleaching. Thus, the
references hereinafter to a "metal", in the singular, present in
the metalliferous ore or released via bioleaching can refer to both
a single metal or to (a combination of) several metals.
[0013] In the present context, suspension is understood as: any
liquid continuous phase comprising a solid phase dispersed in the
liquid phase.
[0014] A first object of the invention is a method for bioleaching,
for example via "lagooning", a metalliferous ore, said method
comprising the following steps:
[0015] a) a ground metalliferous ore, a medium comprising a
bioleaching microbial consortium, and a nutritive medium for the
microorganisms of the microbial consortium are added into a
basin,
[0016] b) a suspension is obtained in the basin via at least one
stirring system for placing and/or maintaining the metalliferous
ore in suspension in a liquid phase,
[0017] c) a gas containing oxygen and optionally carbon dioxide
that can be metabolised by the microorganisms is injected into the
suspension,
[0018] d) the metalliferous ore is bioleached by the microbial
consortium in such a way as to obtain released metal,
[0019] e) a liquid product containing the released metal and
consisting of (a) a liquor and (b) a solid residue is
recovered.
[0020] According to the invention, the temperature of the
suspension is controlled by regulating the flow rates and the
composition of the gas, as well as optionally the concentration of
solids in the suspension. More particularly, the temperature of the
suspension is controlled in such a way as to be maintained in a
predetermined range suitable for bioleaching.
[0021] The metal released via bioleaching of the metalliferous ore
that made said metal inaccessible for direct treatment may be
(partially or totally) in dissolved form and thus present in the
liquor of the product recovered at the end of the bioleaching. The
released metal may also be (partially or totally) in solid form
(that is to say, not dissolved) and thus present in the solid
residue of the recovered product.
[0022] The temperature of the suspension is considered suitable for
bioleaching when said temperature allows sufficient activity of the
microorganisms of the consortium and thus efficient bioleaching
kinematics.
[0023] In practice, the thermal regulation is not only related to
the microbial activity, but also to the geometry of the bioleaching
basins, and in particular to the volume to surface ratio, as well
as to the ambient conditions and the variability of said
conditions.
[0024] Thus, according to the invention, the temperature of the
suspension can be controlled without using an external thermal
regulation system such as heat exchangers or other heating and/or
cooling elements.
[0025] By allowing the temperature of the suspension to be
maintained in an optimal range for bioleaching without the need for
heating or cooling elements, the present invention not only allows
energy to be saved, but also allows optimal bioleaching kinematics
to be obtained in basins of a large size or even open air
basins.
Ore
[0026] The metalliferous ore that is used as a substrate in the
method according to the invention can, for example, come from
mining waste or be an ore with a low concentration of metals to be
recovered.
[0027] The invention is particularly useful for a sulphide ore
and/or an ore with a complex composition, for example a
polymetallic ore or an ore containing carbon (for example
carbonate). One advantage of the invention is to allow, under
acceptable economic conditions, the treatment of a metalliferous
ore for which the concentration of metal of interest is relatively
low. The types of sulphide ores used can comprise, for example,
pyrite, copper sulphides, galena or sphalerite. For example,
Kupferschiefer copper-containing black shales are ores having a
complex composition that could be used as substrates. The
metalliferous ore to be treated can also contain a high proportion
of carbon, for example 5% carbonate.
[0028] The ore used is ground. The corresponding particles can have
a particle size (corresponding to D90) from 10 .mu.m to 300 .mu.m,
preferably from 10 .mu.m to 200 .mu.m, and typically of
approximately 50 .mu.m; D90 indicates that 90%, by weight, of the
particles considered have a size less than D90, the remaining 10%
by weight having a size of at least D90.
Consortium and Nutritive Medium
[0029] The microbial consortium used in the method according to the
invention preferably comprises autotrophic and acidophilic
microorganisms. In a useful manner, the microbial consortium is
mesophilic and/or moderately thermophilic.
[0030] A mesophilic consortium is a consortium that grows at
temperatures from 20.degree. C. to 40.degree. C. A moderately
thermophilic consortium is a consortium that grows at temperatures
from 40 to 60.degree. C.
[0031] The consortium advantageously comprises microorganisms of
the species Leptospirillum ferriphilum, Acidithiobacillus caldus
and/or Sulfobacillus benefaciens, which can be found in the DSMZ
strain collection (Deutsche Sammlung von Mikroorganismen and
Zellkulturen). The consortium can be, for example, the microbial
consortium BRGM-KCC, which is described in the article Morin, D.,
d'Hugues, P. (2007). "Bioleaching of a cobalt-containing pyrite in
stirred reactors: a case study from laboratory scale to industrial
application" in: Rawlings, D. E., Johnson, D. B. (Eds), Biomining,
Chapter 2, Springer-Verlag, Berlin, pp. 35-55.
[0032] The specific composition of the consortium can vary
according to the metalliferous ore to be leached. A nutritive
medium adapted to the consortium is advantageously inserted into
the medium to allow the development of the microorganisms and thus
promote the bioleaching. This medium can be advantageously derived
from a "9K" medium described by Silverman and Lundgren in "Studies
on the chemoautotrophic iron bacterium Ferrobacillus ferrooxidans.
I. An improved medium and harvesting procedure for securing high
cell yields.", Silverman, M. P. and Lundgren, D. G., J. Bacteriol.,
77: 642-647. (1959) and adapted to the specific consortium. Thus, a
medium having the composition (NH.sub.4).sub.2SO.sub.4, 3.70
gL.sup.-1; H.sub.3PO.sub.4, 0.80 gL.sup.-1; MgSO.sub.4.7H.sub.2O,
0.52 gL.sup.-1; KOH, 0.48 gL.sup.-1 is particularly suited to the
growth of a microbial consortium as previously described when the
mineral substrate is cobalt-containing pyrite. The specific
composition of the nutritive medium can vary according to the
species present in the microbial consortium and according to the
ore to be treated.
pH
[0033] The suspension is generally an aqueous suspension.
[0034] In the basin, it is preferred that the suspension be
maintained at a pH greater than 0.8. Preferably, the pH of the
medium is maintained in a range from 0.8 to 2.5; advantageously,
the pH is maintained between 1 and 1.5.
[0035] To lower or raise the pH to the preferred values, for
example sulphuric acid or calcite, calcium carbonate, quick lime or
slaked lime, respectively, can be added to the suspension.
[0036] The pH range can vary according to the species present in
the microbial consortium and according to the composition of the
ore to be treated.
Solid Concentration
[0037] The invention has the particular advantage of allowing not
only the treatment of suspensions having a low concentration of
solid particles, but also of suspensions having a high
concentration of solid particles of metalliferous ore.
[0038] Indeed, in the conventional methods for bioleaching in a
stirred reactor, the use of air to supply the oxygen requires the
injection of a very large volume of gas, the dispersion of which
requires high power in the dispersion system, which correspondingly
reduces the power available to place the solid particles in
suspension via the stirrer. The use of a gas with a higher oxygen
content allows more oxygen to be supplied with a lower total gas
flow rate while also promoting the dissolution of the oxygen in the
liquid. Moreover, the possibility of using a plurality of gas
dispersion systems allows the flow rate of gas injected at each
system to be lowered accordingly.
[0039] The power available for stirring the medium, in particular
in order to place and maintain the solid particles in homogeneous
suspension, is therefore increased because of the reduction of the
power required for the dispersion of the gas.
[0040] If the stirring system consists of stirrers, the fact that
the geometry of a lagoon is such that the ratio of the diameter of
the mobile element of the stirring system to the diameter of the
lagoon is in general lower than for a stirred reactor as used in
the known bioleaching methods is added to this. The lower this
ratio, the easier it is to create and maintain the suspension. In
other words, the stirring speed required to return the particles to
or maintain the particles in suspension is lower in large spaces
than in confined spaces. Thus, when the method according to the
invention is implemented in one or more basins of a large size, the
power necessary for placing the solid particles in suspension is
reduced.
[0041] According to the invention, the solid concentration by
weight in the suspension is advantageously from 15 to 40%,
preferably from 22 to 38%, and more preferably from 25 to 35%, for
example approximately 30%, with respect to the total weight of the
suspension.
[0042] The ground metalliferous ore can be dispersed in a liquid
before being inserted into the basin.
Stirring System
[0043] According to the invention, the stirring system can comprise
a circulator of the suspension or a stirrer, or even a combination
of the two. Preferably, the stirring system comprises at least one
stirrer. The stirring system advantageously comprises at least one
and preferably a plurality of floating stirrers.
[0044] The use of floating stirrers significantly increases the
flexibility of the method according to the invention and is in
particular useful for basins that are non-circular and/or have a
high surface area and/or are open-air. Indeed, the position of a
floating stirrer in the basin and the number of floating stirrers
in a basin can be easily modified.
[0045] The speed of rotation of the stirrers is chosen from a range
from 40 to 500 rpm, preferably 200 to 350 rpm. On the laboratory
scale, however, the speed of rotation can reach 1500 rpm.
[0046] A suspension circulator can, for example, have the following
form: the bioleaching suspension is sucked into a pipe outside of
the basin via a pump suitable for a liquid of this type. The gas is
injected (simple injection or the use of a venturi or of a porous
element, for example) into this pipe and mixed with the suspension
(for example via a static mixer). Downstream of the injection of
gas, a sufficient line length of the pipe ensures good transfer
efficiency. The suspension thus "enriched" with gas is then
re-injected into the basin, ideally at the bottom of the basin, in
several locations in order to ensure homogeneous transfer of the
gas throughout the basin. The pump can advantageously be a vortex
pump, known to not be "traumatic" to the microorganisms.
Injection of Gas
[0047] According to the invention, a gas containing oxygen is
injected into the suspension in order to supply the oxygen
necessary for the development of the microbial consortium and for
the microbial lysis reaction. If the metalliferous ore does not
contain enough carbon that can be metabolised by the microbial
consortium in order to ensure the growth of said consortium,
CO.sub.2 is advantageously also injected into the suspension,
preferably in the form of a gaseous mixture with the oxygen. In the
latter case, the gas containing oxygen thus also contains
CO.sub.2.
[0048] In general, the ambient temperature around the basin in
which the method is carried out is lower than the temperature
suitable for the activity of the microbial consortium and the
development thereof. In the absence of a heat exchange system and
particular constraints on the gas pipe (thermal insulation after
compression, short length of the pipes, etc.), the gas injected is
in general close to the ambient temperature. The injection of a
significant flow of gas can therefore lead, despite the exothermic
nature of the reaction, to the cooling of the suspension to
temperatures that do not allow the microbial activity to be
maintained at an adequate level.
[0049] According to the invention, this is prevented by adjusting
the flow rate of gas injected in order to maintain the temperature
of the suspension in a predetermined temperature range suitable for
bioleaching. The supply of oxygen necessary for the reaction is
then ensured by adjusting the composition of the gas, in particular
the concentration of oxygen in the gas.
[0050] In particular, if it is not possible to maintain both a flow
rate of gas that allows the temperature to be maintained in the
predetermined range and the supply of oxygen necessary for the
reaction, it is also possible to act on the quantity of
metalliferous ore injected into the basin, for example to dilute
the suspension by adding liquid or, on the contrary, to increase
the concentration of metalliferous ore by adding metalliferous ore
to the suspension.
[0051] According to yet another particularly advantageous aspect of
the invention, the stirring system comprises at least one device
for ejection/dispersion of a gas, in particular a gas containing
oxygen and/or carbon dioxide. Such a suspension circulator that
integrates a gas injector has already been described above.
Likewise, when the stirring system comprises a stirrer, and in
particular a floating stirrer, said stirrer is advantageously
provided with a gas injector.
[0052] A gaseous mixture suitable for the method according to the
invention can contain, for example, 1% carbon dioxide, 49% nitrogen
and 50% oxygen by volume.
[0053] Advantageously, a gas obtained by mixing an oxygenated gas
and a dilution gas is injected into the suspension. The oxygenated
gas has an O.sub.2 concentration greater than the O.sub.2
concentration in the air, typically an O.sub.2 concentration of 50
to 100% vol, preferably of at least 75% vol, and more preferably of
at least 85%. The dilution gas advantageously comprises between 0
and 21% O.sub.2 by volume. The dilution gas can be a gas that is
inert with respect to bioleaching reactions, such as nitrogen, and
does not contain any oxygen. However, it is also possible to use a
gas having a relatively low (and in any case lower than the oxygen
concentration of the oxygenated gas) concentration as a dilution
gas, namely air for example. The gas injected into the suspension
optionally contains carbon that can be metabolised, preferably in
the form of CO.sub.2.
Basin
[0054] Although the invention is suitable for being used on a small
scale, or even on the laboratory scale, the invention is, as
indicated above, particularly useful for the treatment of
metalliferous ores on a large scale.
[0055] The basin or basins used in the method according to the
invention are thus advantageously of dimensions suitable for the
industrial treatment of the ores, such as lagoons. These dimensions
are dependent, for example, on the flow rate of the supply of
suspension/slurry and on the residence time necessary for the
leaching of the ore. For example, such basins have a depth that can
reach 6 m and have a total surface area of up to 1500 m.sup.2.
[0056] The residence time necessary for the leaching of the
metalliferous ore varies according to the conditions of reactions
and the starting materials used. This residence time is generally
approximately 4 to 8 days, for example 6 days.
[0057] Via the present invention, it is possible to reach an
adequate bioleaching yield for a reduced residence time with
basins, without the need to use conventional heating and/or cooling
systems such as heat exchangers.
[0058] According to the invention, the bioleaching of the
metalliferous ore can in particular be carried out in a single
basin or in a plurality of basins in series.
Facility and Use
[0059] The invention also relates to a lagooning facility
comprising a bioleaching basin, preferably open-air, said basin
comprising a liquid phase, typically an aqueous phase, a ground
metalliferous ore, a bioleaching microbial consortium, a nutritive
medium for the microorganisms of the microbial consortium. The
facility further comprises a stirring system for placing and/or
maintaining the metalliferous ore in suspension in the liquid
phase. The stirring system of the facility comprises a plurality of
floating stirrers. The facility also comprises at least one
injector for the injection of a gas into the suspension of
metalliferous ore.
[0060] According to the invention, said at least one injector of
gas is connected to a source of oxygenated gas and a source of a
dilution gas. The oxygenated gas has an O.sub.2 concentration
greater than the O.sub.2 concentration of air. The oxygenated gas
typically has an O.sub.2 concentration of 50 to 100% vol,
preferably of at least 75% vol, and more preferably of at least
85%. The source of oxygenated gas can thus be a unit for separating
the gases in air, a pipeline of oxygenated gas (for example of
industrial oxygen), or a tank of liquefied oxygenated gas.
[0061] The dilution gas advantageously comprises between 0 and 21%
O.sub.2 by volume.
[0062] The dilution gas can be a gas that is inert with respect to
bioleaching reactions, such as nitrogen, and does not contain any
oxygen.
[0063] However, it is also possible to use a gas having a
relatively low (and in any case lower than the oxygen concentration
of the oxygenated gas) concentration as a dilution gas, namely such
as air.
[0064] In the first case, the source of dilution gas can be a
facility that produces the inert gas, namely such as a unit for
separating the gases in air that produces not only oxygen that can
be used as the oxygenated gas, but also nitrogen. The source of
dilution gas can also be a tank of the dilution gas, liquefied if
necessary.
[0065] In the second case, the source of dilution gas is
advantageously an air compressor.
[0066] The facility also comprises a regulator of oxygenated gas
and a regulator of dilution gas. The regulator of oxygenated gas
regulates the flow rate of oxygenated gas to the at least one
injector. The regulator of dilution gas regulates the flow rate of
dilution gas to said at least one injector.
[0067] The (at least) one injector of the facility is optionally
also connected to a source of carbon gas that can be metabolised.
The carbon gas that can be metabolised typically contains from 50
to 100% CO.sub.2 by volume, preferably at least 75% vol, and more
preferably at least 85% vol. Such a source of carbon gas that can
be metabolised is, for example, a tank of liquefied CO.sub.2. In
this case, the system advantageously also comprises a regulator for
regulating the flow rate of carbon gas that can be metabolised to
the at least one injector.
[0068] The gas regulators are, in a useful manner, regulator
valves. When the source of dilution gas is an air compressor, the
dilution gas regulator can form an integral portion of said
compressor, in particular in the case of a compressor having an
adjustable flow rate.
[0069] The facility according to the invention thus allows both the
flow rate of O.sub.2 injected into the basin and optionally the
flow rate of CO.sub.2 injected into the basin to be regulated
according to the needs of the bioleaching reactions, and allows the
overall flow rate of gas injected into the basin to be regulated
separately. According to an advantageous aspect of the invention,
this allows the use of a facility without a system for conventional
regulation of the temperature of the suspension in the basin, in
particular such as a heat exchanger.
[0070] When, according to the present invention, the temperature of
the suspension is controlled in such a way that the temperature of
the suspension is maintained in the predetermined range, this
control being carried out by regulating the flow rates and the
composition of the gas injected, as well as optionally the
concentration of solids in the suspension, and the dilution gas
contains no or very little O.sub.2, the oxygen concentration of the
gas injected is determined by the ratio on one hand of the flow
rate of the oxygenated gas and, on the other to the flow rate of
the dilution gas or to the sum of the dilution gas flow rate and
the flow rate of the carbon gas that can be metabolised. When the
dilution gas and/or the gas containing the CO.sub.2 has a
non-negligible concentration of O.sub.2, the supply of O.sub.2 by
the dilution gas and/or the gas containing the CO.sub.2 is taken
into account during the adjustment of the composition and in
particular of the O.sub.2 concentration of the gas injected into
the suspension.
[0071] The regulation of the composition and of the flow rate of
the gas injected can be manual or automatic, continuous or
interrupted (by intervals).
[0072] Thus, the facility according to the invention can comprise a
control unit for the control of the regulator of the oxygenated gas
and of the regulator of the dilution gas and optionally also of the
regulator of the carbon gas that can be metabolised, in order to
regulate the flow rate of said gases and thus also the overall flow
rate and the composition, and in particular the O.sub.2 and
CO.sub.2 concentration, of the gas provided to the injector of gas
and injected into the suspension.
[0073] The facility advantageously comprises at least one system
for measuring temperature, for measuring the temperature of the
suspension in the basin. In this case, the control unit is
advantageously connected to said system for measuring temperature
in such a way as to allow the regulation of the overall gaseous
flow rate and the oxygen concentration of the injected gas by the
control unit according to the temperature measured.
[0074] The basin can be a basin that does not comprise heating or
cooling elements. The facility according to the invention can
comprise a single basin or a plurality of basins, for example a
plurality of bioleaching basins in series.
[0075] The microbial consortium is typically an autotrophic
consortium. Said consortium is preferably mesophilic to moderately
thermophilic.
[0076] The elements of this facility can advantageously be as
described in reference with the method of the invention, for
example with respect to the stirring system. Likewise, the elements
included in the description of the facility also apply to the
method according to the invention.
Recovery
[0077] During the bioleaching, the metal present in the
metalliferous ore is progressively released. The released metal is
typically present in dissolved form. In this case, the liquid phase
of the medium is progressively charged with dissolved released
metal. As described above, the released metal can also be partially
or totally present in solid form. The suspension obtained at the
end of the bioleaching can be subjected to liquid/solid separation
(for example via decantation and/or filtration) and thus be
separated into a liquid phase and a solid residue. The liquid phase
thus obtained is also called liquor. When at least a fraction of
the released metal is present in dissolved form, the dissolved
released metal is present in the liquid phase that can be refined
via known methods in order to allow the recovery of the dissolved
metals of value. When at least a fraction of the released metal of
value is present in solid form, this fraction can also be recovered
via known methods. The solid residue can, for example, be recovered
in order to undergo a new bioleaching step in other conditions, for
example in order to allow another type of metal that can be reused
(precious metals) to be recovered. Said residue can also be stored
as waste or used for other purposes.
[0078] The present invention also relates to a method for
regulating temperature for a bioleaching suspension comprising a
metalliferous ore, a bioleaching microbial consortium and a
nutritive medium for the microorganisms of the consortium.
According to this method, the temperature of the suspension is
maintained in a predetermined range by regulating the flow rate and
the composition of a gas containing oxygen and optionally carbon
dioxide that is injected into said suspension, as well as
optionally by regulating the concentration of solids in the
suspension.
[0079] The invention also relates to the use of a ground
metalliferous ore, a bioleaching microbial consortium, and in
particular such a microbial consortium that is autotrophic and
mesophilic to moderately thermophilic, a nutritive medium of the
microorganisms of the consortium, and a stirring system, for
creating a facility or in a method for bioleaching via
lagooning.
[0080] Finally, the products resulting from the method and/or the
facility as previously described are also part of the invention, in
particular the suspension, the liquid product comprising the metal
released via bioleaching, the liquor containing the metal dissolved
via bioleaching, the solid residue, which can comprise
non-dissolved metal released from the metalliferous ore via
bioleaching, as well as the metals recovered from the
suspension/from the liquor, such as copper, zinc, molybdenum,
antimony, nickel, gold, silver and cobalt.
[0081] The invention will be better understood by reading the
examples and the drawings that follow, which are not in any way
limiting and in which:
[0082] FIG. 1 is a graph representing the change in the
oxidation/reduction potential (redox) and in the number of
microorganisms in the pulp over time in the first example of an
embodiment of the method according to the invention.
[0083] FIG. 2 represents the rates of dissolution of the metals via
bioleaching, obtained in the first example of an embodiment of the
method according to the invention.
[0084] FIG. 3 is a graph of the change in the temperature in the
reaction mediums used in the method according to the invention of
example 2.
[0085] FIG. 4 is a diagram of the method of the facility for
bioleaching in basins according to example 3.
[0086] FIG. 5 is a schematic view from above of a bioleaching
facility using a suspension circulator.
EXAMPLE 1
[0087] A pilot facility was created on the laboratory scale in
conditions that can be easily extrapolated to the industrial
scale.
[0088] The ore treated is cobalt-containing mining waste from a
European mine, containing approximately 60% (by weight) pyrite
(iron disulphide). This ore has a cobalt concentration of
approximately 800 ppm, as well as gold at 1 ppm and copper at 1900
ppm.
[0089] A quantity of 713 kg of ore was added to a quantity of 1318
kg of nutritive medium and 226 kg of inoculum in a 2 m.sup.3 tank
in order to obtain a pulp. This tank is thermally insulated in such
a way that the results obtained can be easily extrapolated to a
lagoon industrial use.
[0090] Indeed, the surface-to-volume ratio of such a tank is much
higher than for a lagoon, the thermal losses via the edges in such
a tank are therefore much greater in proportion to the volume of
the suspension, and the insulation of the edges of the tank thus
allows the thermal conditions reigning in the volume of a lagoon to
be approached.
[0091] This pulp was inoculated with a microbial consortium from
the BRGM-KCC culture, the main organisms of which are affiliated
with the genera Leptospirillum, Acidithiobacillus and
Sulfobacillus. This culture was transplanted several times in
"batch" mode while progressively increasing the volume of liquid
from 2 mL to 200 L.
[0092] The nutritive medium used is a medium called "9 Km". This is
a "9K" medium modified and optimised to allow microbial growth on
cobalt-containing pyrites. The composition of said medium is the
following: (NH.sub.4).sub.2SO.sub.4, 3.70 gL.sup.-1;
H.sub.3PO.sub.4, 0.80 gL.sup.-1; MgSO.sub.4.7H.sub.2O, 0.52
gL.sup.-1; KOH, 0.48 gL.sup.-1.
[0093] A floating stirrer provided by the company MILTON ROY Mixing
under the brand name TURBOXAL.RTM. is installed on the surface of
the pulp. The stirring speed is 1300 rpm. The pH at the beginning
of the reaction is adjusted to 1.8 by the addition of concentrated
sulphuric acid. During the reaction, the pH was controlled by the
addition of calcite in such a way that the pH was never lower than
0.8.
[0094] A single floating stirrer was used in the pilot facility on
the laboratory scale. In the case of facilities according to the
invention on the industrial scale, the basin comprises a plurality
of such floating stirrers.
[0095] FIG. 1 shows the change in the solution redox potential (Eh)
and in the microbe concentration in the pulp that were measured
during the bioleaching process. An increase in the redox potential,
accompanied by an increase in the microbe concentration (from 2.6
10.sup.9 to 3.4 10.sup.10 microorganisms/mL), were observed.
[0096] The Eh value reached in the solution (close to 900 mV)
indicates that the totality of the iron in solution is in the form
of ferric iron (Fe.sup.III), which demonstrates a good microbial
activity of oxidation, confirmed by the increase in the microbe
concentration.
[0097] Because of this strong microbial activity, high levels of
extraction of the metals are obtained. The level of cobalt in
solution after 6 testing days is 86%, which indicates that 86% of
the pyrite contained in the pulp was leached (see FIG. 2). These
results demonstrate, in a surprising manner, that it is possible to
obtain high levels of extraction by simply using a floating stirrer
operating at a high stirring speed, without damaging the
microorganisms (no inhibiting effect, no detrimental microbial
lysis) and under lagooning conditions.
EXAMPLE 2
[0098] A pilot bioleaching facility imitating lagooning via a
series of basins in cascade was created on the laboratory scale
under conditions that can be easily extrapolated to an industrial
case of lagoons in series.
[0099] The same sulphide ore, the same inoculum and the same
stirring conditions as described in example 1 were used in a
facility comprising a primary basin of 50 L (R1) and two secondary
basins of 20 L (R2 and R3). The basins are fed in cascade. In R1,
the gaseous mixture injected consists of 50% O.sub.2 and 1%
CO.sub.2, and the flow rate is set to 316 NL/h. In R2 and R3, the
flow rate and concentration of O.sub.2 were reduced since the
demand for oxygen is lower than in the secondary basins (74 NL/h
and 40% O.sub.2). FIG. 3 shows the change in the temperature in the
basins without the use of an external temperature regulation
system. It is observed that the temperature is always greater than
35.degree. C. in the three basins, which allows strong microbial
activity to be maintained. Indeed, when the temperature is lower
than 35.degree. C., the oxidising activity of the Leptospirillum,
Acidithiobacillus and Sulfobacillus microorganisms is greatly
reduced. Over the duration of the bioleaching, the microbial
concentration remains close to 2.times.10.sup.10 microoganisms/mL,
and the oxidation/reduction potential remains close to 900 mV. At
the output of R3, the level of extraction of the cobalt is between
80 and 85%. This set of data demonstrates the capability of the
system to self-regulate the temperature while maintaining good
microbial activity and thus effective bioleaching of the
sulphides.
[0100] These conditions (stirring speed, concentration of oxygen in
the gas) can vary to a certain degree according to the composition
of the material (sulphide and carbonate concentration, nature of
the mineral species . . . ). The adaptation of these conditions is
part of routine techniques.
EXAMPLE 3
[0101] An embodiment of the method according to the invention with
three lagoons in series (in cascade) is shown in FIG. 4 and
exemplified below.
[0102] A finely ground sulphide ore 1 is placed in a pulp at the
desired solid concentration (from 15 to 40% (by weight) and for
example 30% (by weight)), in a nutritive medium 2 suitable for the
development of the microorganisms used for the bioleaching. The pH
of the pulp is adjusted by the addition of concentrated sulphuric
acid 3 in order to reach a value of approximately 1.8 (and
typically from 0.8 to 1.8). The pulp is then injected into the
basins 10, 20, 30 previously inoculated with an autotrophic,
mesophilic to moderately thermophilic microbial consortium that
combines Leptospirillum ferriphilum, Acidithiobacillus caldus and
Sulfobacillus benefaciens microorganisms (for example the microbial
consortium from the culture BRGM-KCC). The three types of
microorganisms necessary for the bioleaching (Leptospirillum
ferriphilum, Acidithiobacillus caldus and Sulfobacillus
benefaciens) are available from the DSMZ strain collection.
[0103] The three lagoons are provided with floating stirrers 11,
21, 31 that carry out the mixing of the suspension and the
injection and the transfer of the oxygen and of the carbon dioxide
necessary for the functioning of the microorganisms and for the
oxidation of the sulphides. Such stirrers are available on the
market. Thus, the stirrers sold by the company MILTON ROY Mixing
under the brand name TURBOXAL.RTM. and described in the patent
application No. EP-A-2714256 can be used to carry out the method
according to the invention.
[0104] The process of bioleaching takes place in these lagoons 10,
20 30.
[0105] The use of lagoons in series allows the liquor to be
concentrated. The operation thereof is the following: [0106] the
lagoons 10, 20, 30 are stirred by the floating stirrers, [0107] the
lagoons 10, 20, 30 are arranged to operate in series, [0108] the
volume of the set of lagoons 10, 20, 30 is adapted to the flow rate
of suspension in order to guarantee a minimum residence time of 6
days in the entire facility, and [0109] the feeding of the lagoons,
and in particular the transfer of the pulp from one lagoon to the
next lagoon and the extraction of pulp from the last lagoon 30, is
carried out via pumps (not shown). The lagoons have a depth of 6
m.
[0110] At the output 32 of lagoons, a pulp consisting of a liquor
rich in released, dissolved metals 33 and a solid residue 34
containing the non-leachable mineral phases is obtained, the
totality of the metal released by leaching being present in
dissolved form. After a step of solid/liquid separation (via
decantation or filtration), the liquor is sent for refining in
order to recover the metals, while the solid residue can be either
recovered in order to undergo a new leaching step in other
conditions (for example in order to recover the precious metals) or
stored as waste.
[0111] The depth of the lagoons can vary from 2 to 10 m and the
total volume of said lagoons depends on the flow rate at which pulp
is fed and the residence time necessary for the leaching of the
sulphides contained in the material (approximately 4 to 8 days and
for example 6 days). The number of lagoons can vary, for example
from 2 to 10.
[0112] The stirring speed depends mainly on the concentration of
the pulp and the density of said pulp, said speed typically varies
in a range from 200 to 350 rpm.
[0113] The gas injected into the pulp via the floating stirrers 11,
21, 31 comprises, by volume, approximately 1% vol CO.sub.2
(typically from 1 to 3% vol) coming from the CO.sub.2 tank 5, a
variable concentration of nitrogen of less than 78% vol nitrogen,
the nitrogen coming from the nitrogen tank coming from the
liquefied nitrogen tank 6, and a variable concentration of oxygen
of more than 21% vol, the oxygen coming from the liquefied oxygen
tank 4. The gas can thus contain, for example, 49% vol nitrogen and
50% vol oxygen. The oxygen must be injected in a sufficient
quantity in order to ensure the dissolution of a quantity of oxygen
sufficient to allow the dissolution of the sulphides (e.g.: to
dissolve 1 kg of pyrite (FeS.sub.2), 1 kg of O.sub.2 must be
provided).
[0114] The oxygen can be injected in concentrated or
non-concentrated form. The composition of the gas injected and the
flow rate of said gas are also adjusted for each lagoon 10, 20, 30
via flow rate regulators (not shown) in order to compensate mainly
for the heat generated by the reaction of oxidation of the
sulphides (exothermic reaction), but also for the influence of the
environment on the temperature of the pulp in the lagoons, and
maintain the system at the temperature required for the functioning
of the microbial consortium (between 35.degree. C. and 48.degree.
C.)
EXAMPLE 4
[0115] FIG. 5 shows a bioleaching basin 51 containing an aqueous
suspension of metalliferous ore to be treated, a bioleaching
microbial consortium, and a corresponding nutritive medium.
[0116] The basin 51 is provided with a suspension circulator.
[0117] A portion of the suspension is extracted from the basin 51
by a perforated aspiration tube 52 via a pump 53.
[0118] Said portion is expelled into a recirculation circuit
56.
[0119] The circuit 56 is provided with a system 54 for the
injection of a gas into a liquid phase, such as a venturi injector
or a porous injector. A regulated flow of a gaseous mixture having
a controlled concentration of oxygen and optionally also of
CO.sub.2, from a device 55 for supplying gas, is mixed with the
suspension in the recirculation circuit 56 via the gas injector 54.
The gaseous mixture is carried by the suspension in the
recirculation circuit and injected into the basin 51 with this
suspension at reinjection points 57 distributed around the
circumference of the basin. Such a suspension recirculator with
integrated injection of gas can be combined with other stirring
systems such as (floating) stirrers.
[0120] In order to adapt the method to the variations in ore, to
the microbial activity, to the basins and to the environmental
conditions that can affect the method, the following should be
done: [0121] Increasing or decreasing the residence time of the
pulp in the basins in order to reach the desired level of
dissolution of the metals; [0122] Increasing or decreasing the gas
flow rate in order to lower or raise, respectively, the temperature
of the basins; [0123] Increasing the concentration of O.sub.2 in
the gas (for example increasing the O.sub.2/N.sub.2 ratio) in order
to increase the supply of oxygen without increasing the gas flow
rate; and [0124] Controlling the operating parameters of the
stirrer (in particular the speed of rotation, the diameter of the
mobile element, etc.) in order to improve the suspension of the
materials and homogenise the pulp.
[0125] For example, when the temperature of the system is not high
enough, the O.sub.2/N.sub.2 ratio increases and the flow rate
decreases. On the contrary, when the system needs to be cooled, the
O.sub.2/N.sub.2 ratio decreases and the flow rate increases.
[0126] The invention is not limited to the embodiments presented,
and other embodiments will be obvious to a person skilled in the
art.
* * * * *