U.S. patent application number 14/897224 was filed with the patent office on 2016-05-26 for process of isolating rare earth elements.
The applicant listed for this patent is B.R.A.I.N. BIOTECHNOLOGY RESEARCH AND INFORMATION NETWORK AG. Invention is credited to Marco Fiedler, Esther Gabor, Martin Langer, Guido Meurer, Joerg Reichert, Yvonne Tiffert.
Application Number | 20160145717 14/897224 |
Document ID | / |
Family ID | 48628243 |
Filed Date | 2016-05-26 |
United States Patent
Application |
20160145717 |
Kind Code |
A1 |
Gabor; Esther ; et
al. |
May 26, 2016 |
PROCESS OF ISOLATING RARE EARTH ELEMENTS
Abstract
A process of isolating a REE or a group of REE from a solution
or dispersion containing said REE or said group of REEs comprising
the following steps: (i) preparing a mixture comprising said
solution or dispersion and biomass comprising at least one organism
selected from any one of the following organism classes:
eubacteria, archaea, algae, and fungi, whereby the at least one
organism is capable of adsorbing or accumulating said REE or said
group of REEs; (ii) incubating said mixture of step (i) for
allowing the adsorption or accumulation of said REE or said group
of REEs by said biomass; (iii) separating the biomass having
adsorbed or accumulated REE(s) from the mixture of step (ii); and
(iv) isolating said REE or said group of REEs from said biomass
separated in step (iii).
Inventors: |
Gabor; Esther; (Zwingenberg,
DE) ; Meurer; Guido; (Seeheim-Jugenheim, DE) ;
Langer; Martin; (Karlsruhe, DE) ; Tiffert;
Yvonne; (Mannheim, DE) ; Reichert; Joerg;
(Chemnitz, DE) ; Fiedler; Marco; (Halle a.d.
Saale, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
B.R.A.I.N. BIOTECHNOLOGY RESEARCH AND INFORMATION NETWORK
AG |
Zwingenberg |
|
DE |
|
|
Family ID: |
48628243 |
Appl. No.: |
14/897224 |
Filed: |
June 12, 2014 |
PCT Filed: |
June 12, 2014 |
PCT NO: |
PCT/EP2014/062245 |
371 Date: |
December 9, 2015 |
Current U.S.
Class: |
435/262 |
Current CPC
Class: |
C22B 3/20 20130101; Y02P
10/234 20151101; Y02P 10/20 20151101; C22B 59/00 20130101; C12P
3/00 20130101; C22B 3/18 20130101 |
International
Class: |
C22B 59/00 20060101
C22B059/00; C22B 3/20 20060101 C22B003/20; C22B 3/18 20060101
C22B003/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 14, 2013 |
EP |
13003058.8 |
Claims
1. A process of isolating or enriching the rare earth clement (REE)
scandium from a solution or dispersion containing said REE,
comprising the following steps: (i) preparing a mixture comprising
said solution or dispersion and biomass comprising at least one
organism selected from any one of the following organism classes:
eubacteria, archaea, algae, and fungi, whereby the at least one
organism is capable of adsorbing or accumulating said REE; (ii)
incubating said mixture of step (i) for allowing the adsorption or
accumulation of said REE by said biomass; (iii) separating the
biomass having adsorbed or accumulated REE(s) from the mixture of
step (ii); and (iv) isolating said REE from said biomass separated
in step (iii).
2. The process according to claim 1, wherein said solution or
dispersion is obtained by treating a source material of said REE,
such as a mineral ore, a mineral mining waste material, or an
electronic or metal scrap, by an extraction or solubilizing agent,
such as an aqueous acid.
3. A process of isolating or enriching the rare earth element (REE)
scandium from a particulate material, comprising the following
steps: (i) preparing a mixture comprising a solution or dispersion
prepared from said particulate material and biomass comprising at
least one organism selected from any one of the following organism
classes: eubacteria, archaea, algae, and fungi, whereby the at
least one organism is capable of adsorbing or accumulating said
REE; (ii) incubating said mixture of step (i) for allowing
adsorption or accumulation of said REE by said biomass; (iii)
separating the biomass having adsorbed or accumulated REE(s) from
the mixture of step (ii); and (iv) isolating said REE from said
biomass separated in step (iii).
4. The process according to claim 3, wherein said particulate
material containing said REE is a particulate mineral ore, a
particulate mineral mining waste material or a particulate obtained
from electronic scrap or scrap metal.
5. The process according to claim 3, wherein said particulate
material contains said REE in the form of chemical compounds of the
REE, such as carbonates, sulfates, oxides, phosphates or
silicates.
6. The process according to claim 3, wherein said particulate
material has an average particle size of at most 5 mm, preferably
at most 1 mm, more preferably of at most 400 .mu.m, and moat
preferably of at most 100 .mu.m.
7. The process according to claim 3, wherein said solution or
dispersion is obtained by treating said particulate material by an
extraction or solubilising agent such as an aqueous acid,
optionally followed by adjusting the pH to a suitable pH for
adsorption or accumulation of said REE by said biomass.
8. The process according to claim 3, wherein preparing said
solution or dispersion from said particulate material comprises
pre-treating said particulate material with autotrophic or
heterotrophic bacteria tor bioleaching said REE from said
particulate material before or concurrently to step (i).
9. The process according to claim 1, wherein said solution or
dispersion is aqueous.
10. The process according to claim 9, wherein said aqueous solution
or dispersion has a pH of from 0 to 5, preferably of from 0.5 to 3,
more preferably of from 1.0 to 2.0; and/or said mixture of step
(ii) has a pH of from 0 to 5, preferably of from 0.5 to 3, more
preferably of from 1.0 to 2.0.
11.-12. (canceled)
13. The process according to claim 1, wherein said organism is from
genus Cupriavidus, such as Cupriavidus metallidurans, or said
organism is Citrobacter sp.
14. A process of isolating the REE scandium from a particulate
material, or a solution or dispersion containing said REE
comprising of contacting biomass selected from the following
organism classes: Eubacteria, Archaea, Algae, and Fungi with said
particulate material or a solution or dispersion containing said
REE.
15. A method of testing a sample microorganism for its ability to
bind the rare earth element scandium or of screening a plurality of
microorganisms for the ability of members of said plurality to bind
the rare earth element scandium, comprising the following steps:
(a) contacting a microorganism with a solution or dispersion
containing the rare earth element (REE); (b) incubating the mixture
of step (a) for a predetermined period of time; (c) separating
microorganisms from the mixture obtained in step (b); (d) analysing
the separated microorganism for bound REE.
16. The process according to claim 3, wherein said solution or
dispersion is aqueous.
17. The process according to claim 14, wherein said aqueous
solution or dispersion has a pH of from 0 to 5, preferably of from
0.5 to 3, more preferably of from 1.0 to 2.0; and/or said mixture
of step (ii) has a pH of from 0 to 5, preferably of from 0.5 to 3,
more preferably of from 1.0 to 2.0.
18. The process according to claim 3, wherein said organism is from
genus Cupriavidus, such as Cupriavidus metallidurans, or said
organism is Citrobacter sp.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a process of isolating a rare earth
element (REE) or a group of REEs from an aqueous solution or
dispersion containing the REE or the group of REEs. Rare earth
elements are isolated and concentrated from an aqueous solution by
adsorption or accumulation by microorganisms and are subsequently
released therefrom by separation procedures. The invention also
provides a method of testing a sample microorganism for its ability
to bind a rare earth element or of screening a plurality of
microorganisms for the ability of members of said plurality to bind
a rare earth element.
BACKGROUND OF THE INVENTION
[0002] According to a recent classification the rare earth elements
include the 17 elements scandium, lanthanium, cer, praseodym,
neodym, promethium, samarium, europium (light rare earth elements,
LREE) and yttrium, gadolinium, terbium, dysprosium, holmium, erbium
thulium, ytterbium, lutetium (heavy rare earth elements, HREE). The
demand for rare earth elements is growing steadily due to their
importance, particularly in the field of high-tech electronics and
displays. Further, a relevant share of the increasing demand is
caused by so-called "green technologies" which aim at the reduction
of energy consumption, development of renewable energy carriers and
air pollution control. For example, rare earths are used in wind
turbines, (hybrid) electric vehicles, automotive catalysts and
energy-efficient lighting systems. Due to the increasing demand
there is an urgent need for more efficient and sustainable mining
processes even from low grade ores as well as efficient methods for
recycling of rare earth metals, i.e. recycling them from waste
material such electronic or metal scrap. To date, there has been no
large scale recycling of REE from magnets, batteries, lighting and
catalysts although the amounts of waste are substantial. The
advantages of recycling REEs are amongst others the lack of
radioactive impurities and economic independence from supply from
primary sources. One reason for inadequate exploitation of these
valuable resources, sometimes termed "urban mining", is that
recycling processes for REEs are quite complex and
energy-consuming, comprising physical and chemical treatment and
generally the available know-how is still quite low.
Conventional Beneficiation Processes
[0003] In most of the processes for REE beneficiation, the ore is
mined in the deposit, broken down or milled and REE minerals are
concentrated using physical properties such as density, magnetism
and surface activities like electrostatic charge or flotation
efficiency. The thus concentrated ore is then leached and the
resulting REE-bearing solution is purified from undesired elements
such as Fe, Ca, thorium and uranium. The process is described in
e.g. Gupta, C. K. and Krishnamurthy, N. (2005): Extractive
Metallurgy of Rare Earths, CRC Press (Florida, USA), and Castor, S.
B. and Hedrick, J. B. (2006): Rare Earth Elements, In: Kogel, J.
E., Trivedi, N. C., and Krukowski, S. T. (eds.): Industrial
minerals and rocks: Commodities, markets, and uses. 7th edition,
SME, page 769-792, as well as references therein. However, this
leaching or `cracking` stage depends on the type of minerals and
other characteristics of the deposit. For instance at Mountain
Pass, the mineral concentrate was calcined to drive off CO.sub.2
and fluorine and leached with HCl to dissolve most of the trivalent
REEs. Whereas the REE-bearing liquid was used for the separation of
individual REEs, the residue (predominantly CeO.sub.2) was sold. In
contrast to that, the Bayan Obo REE mineral concentrate is baked
with sulphuric acid at 300.degree. C. too 600.degree. C. and
leached with water, taking REEs into solution and precipitating
other elements as waste REEs are then precipitated as double
sulphates and converted to hydroxides (representing a chemical
mixed rare earth concentrate), which are leached with HCl for the
separation of individual REE. The varying composition and
distribution of the individual REEs in the pregnant, REE-bearing
solution or in the precipitated chemical mixed rare earth
concentrate depends on the mineral deposit from which the ore
originates. Following the leaching stage subsequent processing is
required to separate individual REEs from each other. Separating
individual REEs is a very difficult process due to their similar
chemical properties. As a consequence the high value of REEs
depends on their effective separation into high purity compounds.
Cerium and europium can be separated by selective oxidation or
reduction whilst other REEs can be separated in small amounts using
fractional crystallisation or fractional precipitation. However,
commercial separation generally is done using solvent extraction
and, less common, ion exchange methods. Solvent extraction (SX), or
liquid-liquid extraction, is a method used to separate compounds on
the basis of their relative solubility's in two immiscible liquids,
commonly the REE-containing aqueous solution and an organic
solvent. On an industrial scale the solvent extraction is carried
out in a group of mixer settlers, which allows repetitive
fractionation during a continuously flowing process. Initially the
process is relatively ineffective. When the process is repeated
many times each REE can be separated from the others. However, the
solvent extraction method is most appropriate for separating the
LREEs, with the HREEs being more difficult to extract using this
method. This is especially true if the used ore consists
predominantly of the LREEs. Ion exchange is a process in which ions
are exchanged between a solution and an insoluble (usually
resinous) solid. The REEs from the solution displace the cations on
the resin surface, whereas the aqueous waste containing the
exchanged cations. Individual REEs are then separated using a
complexing agent which has different affinities for the various
REEs. The Ion exchange method produces highly pure REE in small
quantities. However, it is a time consuming and thus expensive
process. Consequently, only a small amount of HREEs are purified
commercially on a small scale using ion exchange.
Impact of Conventional Rare Earth Leaching on the Environment and
on Health
[0004] The main environmental risks of conventional processes are
due to tailings containing small-size particles, waste water and
flotation chemicals. The tailings typically remain in the
impoundment areas where they are continuously exposed to water e.g.
from rain. Toxic substances are washed out, producing steady
emissions to ground water. The composition of the polluting water
is site-specific depending on the host minerals and the chemicals
used for leaching and flotation. The tailings may contain
radioactive substances, arsenic, fluorides, sulfides, acids and
heavy metals. The refining of the rare earth concentrate is an
energy-intensive and water consuming process and causes serious air
emissions e.g. of SO.sub.2, HCl, dust. Additionally, the solvent
extraction method causes waste water, which is often extensively
polluted by organic solvents like kerosene. Additionally,
radioactive waste can arise, as the majority of rare earth deposits
also contain thorium and/or uranium, thus radionuclides may pollute
water and air. CO.sub.2-emissions are also significant.
Bioleaching
[0005] The possibility to use predominantly acidophilic,
autotrophic iron-oxidising sulfur-oxidizing prokaryotes to recover
precious and base metals from mineral ores and concentrates is
known, e.g. from Rawlings, D E and Johnson, D B (The microbiology
of biomining: development and optimization of mineral-oxidizing
microbial consortia, Microbiology 2007, 153: 315-24). The
development of this technology was inspired by the observation that
certain bacteria, especially Thiobacilli, are able to solubilise
heavy metal minerals by oxidizing Fe(II) to Fe(III) as well as
sulfidic compounds to sulfate. This process is the major cause of
natural weathering of sulfidic minerals.
[0006] By creating conditions that favour the growth of
ore-decaying microorganisms, leaching of heavy metals from sulfidic
minerals under aerobic conditions can be increased more than
100-fold compared to weathering without bacteria. However,
degradation of minerals such as pyrite enclosing precious metal
atoms or clusters can lead to the release of the trapped high-value
compounds. While cheap in situ or dump/heap set-ups are generally
used to bioleach base metals from low-grade rocks and minerals,
more expensive (and more controlled) stirred-tank reactors are
typically employed in the pre-treatment of mineral ores for the
recovery of metals. After the initial bacterial disintegration
step, ores are subjected to a conventional chemical leaching
process, hazarding the environmental and health problems mentioned
above.
Bioadsorption
[0007] A number of living microorganisms, but also nonviable,
inactivated cells have the ability to bind metal ions. In the first
case, metal binding can occur via adsorption to the cell surface or
via active intracellular accumulation of metal ions. In the latter
case of nonviable, inactivated cells--that is often referred to as
biosorption--metal ion binding is believed to occur exclusively via
surface adsorption. The biosorption capacity as a general
characteristic of biomass results from the presence of chelating
groups (e.g. carboxyl-, amide-, hydroxyl-, phosphate-, and
thiol-groups) contributed by carbohydrates, lipids and proteins
that are displayed on the cell surface. It has been described that
amounts of metals of up to 50% of the cell dry weight can be
accumulated by biomass (Vieira and Volesky, 2000). United States
Patent 1991/5055402 describes a process for removing metal ions
from aqueous solution, using a matrix prepared from metal-binding
microorganisms that have been heat-inactivated at temperatures of
300-500.degree. C. However, specific binding mechanisms by organic
surface structures are obviated by this procedure. EP 0673350 B1
describes the accumulation of metals, including some rare earth
elements such as lanthanium and yttrium, by reacting phosphate ions
generated by a microorganism and metals to polyphosphates.
Accumulation of the metal-poly phosphates by the microorganism of
the genus Acmetobacter makes the metals accessible to precipitation
and depletion thus enabling purification of metal-polluted water.
WO 1891/003424 describes a biomining procedure for leaching of
gallium and germanium from ores using an admixture of bacteria,
culture medium and crushed ore. However, no process has been
described to date that could be used to recover REEs in significant
amounts from ores or waste materials.
[0008] It is therefore an object of the present invention to
provide a process of recovering, enriching or isolating REEs from
source material, such as a mineral ore or a waste material
containing REEs. It is another object of the invention to provide a
process for modulating the composition of REEs in a solution, or
isolating a particular REE, such as scandium or lutetium, from a
solution. It is another object to provide organisms for these
processes. It is a further object to provide a screening method for
such organism.
SUMMARY OF THE INVENTION
[0009] These objects are accomplished by: [0010] (1) A process of
isolating a rare earth element (REE) or a group of REEs from a
solution or dispersion, comprising the following steps: [0011] (i)
preparing a mixture comprising a solution or dispersion containing
said REE or said group of REEs and biomass that comprises at least
one organism selected from any one of the following organism
classes: eubacteria, archaea, algae, and fungi, whereby the at
least one organism is capable of adsorbing or accumulating said REE
or said group of REEs; [0012] (ii) incubating said mixture of step
(i) for allowing the adsorption or accumulation of said REE or said
group of REEs by said biomass; [0013] (iii) separating the biomass
having adsorbed or accumulated REE(s) from the mixture of step
(ii); and [0014] (iv) isolating said REE or said group of REEs from
said biomass separated in step (iii). [0015] (2) The process
according to (1), wherein said solution or dispersion is obtained
by treating a source material of said REE or said group of REEs,
such as a mineral ore, a mineral mining waste material, or an
electronic or metal scrap, by an extraction or solubilising agent,
such as an aqueous acid. [0016] (3) The process according (2),
wherein obtaining said solution or dispersion from said source
material comprises pre-treating said source material with auto- or
heterotrophic bacteria for bioleaching said REE or group of REEs
from said source material before or concurrently to step (i).
[0017] (4) A process of isolating or enriching a rare earth element
(REE) or a group of REEs from a particulate material, comprising
the following steps: [0018] (i') preparing a mature comprising a
solution or dispersion prepared from said particulate material and
biomass comprising at least one organism selected from any one of
the following organism classes: eubacteria, archaea, algae, and
fungi, whereby the at least one organism is capable of adsorbing or
accumulating said REE or said group of REEs; [0019] (ii) incubating
said mixture of step (i) for allowing adsorption or accumulation of
said REE or said group of REEs by said biomass; [0020] (iii)
separating the biomass having adsorbed or accumulated REE(s) from
the mixture of step (ii); and [0021] (iv) isolating said REE or
said group of REEs from said biomass separated in step (iii).
[0022] (5) The process according to (4), wherein said particulate
material containing said REE or said group of REEs is a particulate
mineral ore, a particulate mineral mining waste material or a
particulate obtained from electronic scrap or scrap metal. [0023]
(6) The process according to (4) or (5), wherein said particulate
material contains said REE(s) in the form of chemical compounds of
the REE(s), such as carbonates sulfates, oxides, phosphates or
silicates. [0024] (7) The process according to any one of (4) to
(6), wherein said particulate material has an average particle size
of at most 5 mm, preferably at most 1 mm, more preferably of at
most 400 .mu.m, and most preferably of at most 100 .mu.m. [0025]
(8) The process according to any one of (4) to (7), wherein said
particulate material is pre-treated with sulfide-oxidising bacteria
for bioleaching said REE or group of REEs from said particulate
material before or concurrently to step (i). [0026] (9) The process
according to (3) or (8), wherein said sulfide-oxidising bacteria
are genetically-modified to express an S-layer on the surface of
said bacteria. [0027] (10) The process according to any one of (4)
to (9), wherein said solution or dispersion is obtained by treating
said particulate material by an extraction or solubilising agent
such as an aqueous acid, optionally followed by adjusting the pH to
a suitable pH for adsorption or accumulation of said REE or said
group of REEs by said biomass. [0028] (11) The process according to
any one of items (4) to (10), wherein preparing said solution or
dispersion from said particulate material composes pre-treating
said particulate material with autotrophic or heterotrophic
bacteria for bioleaching said REE or group of REEs from said
particulate material before or concurrently to step (i). [0029]
(12) The process according to any one of (1) to (11), wherein said
solution or dispersion is aqueous. [0030] (13) The process
according to (12), wherein said aqueous solution or dispersion has
a pH of from 0 to 5, preferably of from 0.5 to 3, more preferably
of from 1.0 to 2.0; and/or said mixture of step (ii) has a pH of
from 0 to 5, preferably of from 0.5 to 3, more preferably of from
1.0 to 2.0. [0031] (14) The process according to any one of (1) to
(13), wherein step (ii) comprises agitating said mixture for
bringing said biomass in close contact with REE(s) present in said
mixture. [0032] (15) The process according to any one of (1) to
(14), wherein said REE is selected from the group consisting of
scandium, lanthanium, cer, praseodym, neodym, promethium, samarium,
europium, yttrium, gadolinium, terbium, dysprosium, holmium,
erbium, thulium, ytterbium, and lutetium; or said group of REEs
comprises at least two REEs selected from the aforementioned list.
[0033] (16) The process according to any one of (1) to (14),
wherein said REE is selected from the group consisting of
lanthanium, cer, praseodym, neodym, promethium, samarium, and
europium; or said group of REEs comprises at least two REEs
selected from the aforementioned list. [0034] (17) The process
according to any one of items (1) to (14), wherein said REE is
selected from the group consisting of terbium, dysprosium, holmium,
erbium, thulium, ytterbium, lutetium, scandium, yttrium; or said
group of REEs comprises at least two REEs selected from the
aforementioned list. [0035] (18) The process according to any one
of (1) to (14), wherein said REE is selected from the group
consisting of scandium, yttrium, gadolinium, terbium, dysprosium,
holmium, erbium, thulium, ytterbium, lutetium; or said group of
REEs comprises at least two REEs selected from the aforementioned
list. [0036] (19) The process according to any one of (1) to (14),
wherein said REE is scandium. [0037] (20) The process according to
any one of (1) to (19), wherein the biomass is separated in step
(iii) by one of the methods selected from centrifugation,
filtration, flocculation and flotation. [0038] (21) The process
according to any one of (1) to (20), wherein step (iii) involves
blowing of air into said mixture for accumulating biomass having
bound REE at the surface of said mixture. [0039] (22) The process
according to any one of (1) to (21), wherein the incubation time of
step (ii) is between 0.5 hours and 96 hours, preferably between 0.5
hours and 48 hours, and most preferably between 1 hour and 24
hours. [0040] (23) The process according to any one of (1) to (22),
wherein said organism is from genus Cupriavidus, such as
Cupriavidus metallidurans, or said organism is Citrobacter sp.
[0041] (24) Use of biomass selected from the following organism
classes: Eubacteria, Archaea, Algae, and Fungi for isolating a REE
or group of REEs from a particulate material or a solution or
dispersion containing said REE or said group of REEs. In one
embodiment, the organism is from genus Cupriavidus, such as
Cupriavidus metallidurans, or said organism is Citrobacter sp.
[0042] (25) A method of testing a sample microorganism for its
ability to bind a rare earth element or of screening a plurality of
microorganisms for the ability of members of said plurality to bind
a rare earth element, comprising the following steps: [0043] (a)
contacting a microorganism with a solution or dispersion containing
a rare earth element (REE) or multiple REEs; [0044] (b) incubating
the mixture of step (a) for a predetermined period of time; [0045]
(c) separating microorganisms from the mixture obtained in step
(b); [0046] (d) analysing the separated microorganism for bound
REE. [0047] (26) The method of (25), wherein said organism is
selected from the following organism classes: Eubacteria, Archaea,
Algae, and Fungi. [0048] (27) The method of (25) or (26), wherein
said solution or dispersion used in step (a) is an acidic aqueous
solution or dispersion having a pH of from 0 to 5, preferably of
from 0.5 to 3, more preferably of from 1.0 to 20; and/or wherein
the mixture of step (b) has a pH of from 0 to 5, preferably of from
0.5 to 3, more preferably of from 1.0 to 2.0. [0049] (28) The
method according to any one of (25) to (27), wherein said
predetermined period of time is between 0.5 hours and 96 hours,
preferably between 0.5 hours and 48 hours, and most preferably
between 1 hour and 24 hours.
[0050] The inventors have found that REEs can be isolated or
enriched from a solution or dispersion, preferably an aqueous
solution or dispersion, using biomass comprising organisms that can
bind REEs. The invention provides a process for isolating REEs in a
simple and cost-effective way. The biomass binds the REE or a group
of REEs by cell components of the organisms. After separation of
the biomass from unbound material, the REEs can be isolated from
the biomass. The invention allows isolating REEs from sources that
contain only low amounts of REEs, reducing the number of steps
needed for REE separation compared to a conventional multistep
process (refining or raffination). Therefore, the processes of the
invention provide an environmentally innocuous access to valuable
REEs, that requires less energy and avoids pollution by
transferring the mining procedure to a controlled containment. The
present invention is a break-through in the sustainable
exploitation of low-grade REE-sources, allowing the recovery of
REEs in a simple process.
BRIEF DESCRIPTION OF THE FIGURES
[0051] FIG. 1. Microbial strains that selectively enrich Scandium.
(A) Enrichment factors A (black bars) were calculated by
A=[m.sub.BM(Sc)*m.sub.L(REE)]/[m.sub.BM(REE)*m.sub.L(Sc)]; m being
the mass of scandium (Sc) or total REE (REE) in biomass (BM) and
mineral leach (L), respectively. Recovery W (grey bars) was
calculated by W=100*m.sub.BM(Sc)/m.sub.L(Sc). Assays were carried
out as described in Example 2 using a sulphuric acid leach of
REE-containing bastnaesite. Designations on the x-axis refer to
different microbial isolates.
[0052] FIG. 2. Enrichment of specific REE from mineral leach by
exemplary microorganisms. REE composition of mineral leach as
obtained by the treatment described in example 1 (black bars).
Composition of REE extracted by the use of microbial biomass as
described in Example 2. The y-axis refers to fraction of total REE
in percent by weight. A. Strain S3_12G_D6 strongly enriches
scandium (A=438) Strain S3_8B_B2 enriches scandium to a lower
extent (A=61), but also significantly accumulates the heavy REE
lutetium (A=22). B. Composition of REE extracted by use of
Cupriavidus metallidurans and Citrobacter sp. from an equimolar
solution of 16 SEE.
DETAILED DESCRIPTION OF THE INVENTION
[0053] The REE that may be isolated or enriched in the process of
the invention is selected from lanthanium, cer, praseodym, neodym,
promethium, samarium, europium (light rare earth elements, LREE)
and scandium, yttrium, gadolinium, terbium, dysprosium, holmium,
erbium, thulium, ytterbium, and lutetium (HREE). In one embodiment,
the REE is selected from the group of light REEs, i.e. lanthanium,
cer, praseodym, neodym, promethium, samarium, europium. In another
embodiment, the REE is selected from the group of heavy REEs, i.e.
scandium, yttrium, gadolinium, terbium, dysprosium, holmium, erbium
thulium, ytterbium, lutetium. In a further embodiment, the REE is
selected from the group consisting of terbium, dysprosium, holmium,
erbium, thulium, ytterbium, lutetium, scandium, yttrium. Scandium
is most preferred as the REE.
[0054] In the processes of the invention, groups of two or more
REEs may be isolated or enriched. Such group may contain two or
more REEs from any of the above-mentioned lists of REEs. A group of
REEs may comprise two or more REEs from the light REEs or from the
above list of heavy REEs.
[0055] The abbreviation "REE" stands for rare earth element.
Multiple rare earth elements are abbreviated by "REEs". The term
"REE(s)" covers the meaning of "REE" and "REEs". Herein, the term
"REE" covers rare earth elements in elemental (metallic) form and
chemical compounds comprising ionically or covalently bound REE
ions or atoms. Dissolved ions of REEs e.g. in aqueous solution are
also covered by the term "REEs". In the processes of the invention,
the chemical form of the REE may change. The chemical form of the
REE isolated in step (iv) may be different from the chemical form
of the REEs in the source material of the REE. Frequently, the
chemical form of the REE(s) will also be different in the solution
of step (i) and in the form isolated in step (iv). The difference
may be in terms of oxidation state and/or in terms of counter ions
to cationic REE ions. It is possible that the solution or
suspension used in the process of the invention contains REE(s) to
be isolated in two or more different chemical states or compounds.
Similarly, the REE(s) isolated in step (iv) may contain said metal
in two or more different chemical states or compounds.
[0056] In natural resources such as in mineral ores, but also in
mineral mining wastes, REEs usually occur as REE compounds such as
complexes wherein the REE is present in oxidised form. As is known
to the skilled person, the most prevalent oxidation states of REEs
are the states +III and +IV. REEs in elemental (metallic) form are
easily oxidised to form oxidised compounds, and generally react
with mineral acids such as dilute sulfuric acid to form hydrogen
and REE ions. Due to the stability of the oxidised state of the
REEs, the REEs isolated in step (iv) of the present invention is
generally a REE compound wherein the REE is present in oxidised
form. Thus, the processes of the invention are, in one embodiment,
processes of isolating compounds of REE(s). Known techniques may be
used for preparing REE in elemental (metallic) form from REE
compounds isolated in step (iv).
[0057] In the processes of the invention, the REEs generally bind
to the biomass in the oxidised form of the REEs. Preferably, the
REEs are contained in the mixture prepared in step (i) or (i') in
dissolved form. This does not exclude that REE compounds finely
dispersed in the mixture as small or colloidal particles are also
adsorbed or bound by the biomass. Further, as soluble REE is
preferably bound by the biomass in step (ii), insoluble forms of
the REE may dissolve according to their equilibrium solubility
under the conditions used.
[0058] The solution or dispersion containing the REE or the group
of REEs is a liquid. The liquid phase is made up or comprises of a
solvent. The solvent of the solution or dispersion may be water or
an organic solvent or mixtures thereof. The organic solvent may be
a polar solvent or a non-polar solvent, but is preferably a polar
solvent. However, the solvent is preferably water or contains
water, i.e. is aqueous. The aqueous solvent contains water and may
additionally contain a polar organic solvent. Preferably, the
aqueous solvent contains at least 50% by mass water. The solvent is
chosen such that a desired degree of solubility of the REE
compounds to be isolated from the solution or dispersion is
obtained. Since the solubility of REE compounds in solvents such as
water and other aqueous solutions is generally higher in the acidic
range, the solvent may contain an acid. Inorganic (mineral) acids
such as sulfuric acid or hydrochloric acid are preferred, but
organic acids may also be used alone or together with inorganic
acids. In aqueous solutions or dispersions, the pH may be from 0 to
5, preferably from 0.5 to 3, more preferably from 1.0 to 2.0. Upon
addition of the biomass in step (i), the pH or acidity may change.
Accordingly, the pH or acid content may be readjusted after
addition of the biomass in order to maintain the desired acidity or
pH for step (i) of the process. The mixture of step (ii) may have a
pH of from 0 to 5, preferably of from 0.5 to 3, more preferably of
from 1.0 to 2.0.
[0059] The solution or dispersion containing said REE or group of
REEs to be used in step (i) may be obtained or prepared in
different ways that depend to the source material of the REE(s). In
one embodiment, the REE(s) are already present in the form of a
solution or dispersion in the source material, such as in liquid
tailings from mining industry or liquids that form from rain
falling on piles of solid mining waste material and washing out
REE(s) from the waste material. In such cases, the solutions or
dispersions may be used for step (i) as they are, optionally after
adjustment of conditions such as concentration and/or acidity.
[0060] In another embodiment, the source material of the REE(s) is
metal or electronic scrap that may contain the REE(s) in metallic
elemental form or chemically bound or both. Metallic REE(s) may be
separated and enriched mechanically. Metallic REE(s) to be isolated
using the process of the invention are generally transformed
chemically to soluble form, e.g. by treatment with aqueous organic
or mineral acids, such as sulfuric acid or hydrochloric acid to
form the respective REE salts of such acids, such as sulfates or
chlorides, respectively, in aqueous solution or dispersion. Also
REE compounds that are insoluble or poorly soluble in water at
neutral pH may be solubilised by such acids. The solutions or
dispersions of the REEs used in step (i) may be acidic as described
above, since the solubility of REE salts is generally higher in
acidic solutions. The pH and other conditions may be adjusted as
required for step (ii).
[0061] In other embodiments, the source material of the REE(s) are
mineral ores or solid mine waste material obtained from processes
of producing other desired components from ore. In these cases, the
source material is generally first ground to fine particulate
material for improving accessibility and leachability of REE(s)
contained therein. Examples of mineral ores containing REE(s) are
bastnaesite, thortveitite, monazite, loparite, gadolinite,
euxerite, eschynite, allanite, apatite, britholite, brockite,
cerite, fluorcerite, fluorite, parisite, stillwellite, synchisite,
titanite, xenotime, zircon, zirconolite, etc. The mineral ores
generally contain the REE(s) in the form of chemical compounds such
as carbonates, sulfates, oxides, phosphates or silicates. To ensure
efficient solubilisation and extraction of the REEs from the ores
or mining waste material, these should be finely ground to form
particulate material. The particulate material may have an average
particle size of at most 5 mm. Alternatively, the particulate
material may have an average particle size of at most 1 mm, of at
most 400 .mu.m, or of at moat 100 .mu.m, or of at most 50 .mu.m, or
of at most 30 .mu.m.
[0062] For preparing the solution or dispersion for step (i) from
mineral ores or mining waste material as source material, the
preferably comminuted particulate material may be extracted
(leached) with suitable solvents such as with organic solvents,
bases or organic or inorganic acids, preferably with inorganic
acids such as with dilute sulfuric acid or hydrochloric acid,
whereby the REE compounds are dissolved in the solvent. The acid
concentration in the dilute organic or mineral acid is not
particularly limited, but should be at least 2% by weight for
ensuring sufficient efficiency. The concentration may be from 5 to
20% by weight or from 7 to 15% by weight. Alternatively, other
methods suitable to facilitate REE release and solubilisation may
be employed, such as oxidative or heterotrophic bioleaching or
incubation with microorganisms that produce corrosive metabolites.
After the extraction, solid material may be removed e.g. by
filtration or sedimentation. Furthermore, bioleaching procedures
may be used to release the REE(s) of the invention from the
particulate material. Autotrophic or heterotrophic bacteria may be
used for pre-treating the source material or the particulate
material for bioleaching. For instance, if said particulate
material is a sulfidic ore such as pyrite, sulfide-oxidizing
bacteria such as Thiobacilli may be used for at least partially
degrading the sulfidic mineral. Such bioleaching is described by
Rawlings, D E and Johnson, D B (The microbiology of biomining:
development and optimization of mineral-oxidizing microbial
consortia. Microbiology 2007, 153: 315-24). Bioleaching may be
carried out before or after solvent extraction. If it is carried
out after solvent extraction such us with strong acid or bases, a
step of bringing the acid or base content of the particulate
material to a level suitable for the bacteria used for bioleaching
may be necessary. In step (i'), bioleaching may be done
concurrently with step (i') and subsequent step (ii) by adding the
bacteria for bioleaching to the biomass of step (i'). In one
embodiment, the sulfide-oxidising bacteria are genetically-modified
to express an S-layer on the surface of said bacteria.
[0063] In step (i) of the process of the invention, a mixture is
prepared from said solution or dispersion containing the REE or
group of REEs to be isolated and said biomass in step (i'), a
mixture is prepared from the biomass and a solution or dispersion
obtained from the particulate matter, whereby the particulate
matter may still be present in the mixture. If the particulate
matter is still present, extraction and/or bioleaching may take
place or continue to take place concomitantly with binding of the
REE(s) by the biomass in step (i') and subsequent step (ii). If the
acidity of the solution from a previous leaching step is too high,
the pH may be increased by addition of bases to reach a pH that is
compatible with the biomass used in steps (i), (i') and (ii).
Preferred pH ranges for these steps are given below.
[0064] Steps (i) and (i') and subsequent step (ii) may be conducted
in closed reactors that preferably contain an agitation system for
agitating the mixture. The reactor may be a stirred-tank reactor
and may be operated in a batch or continuous-flow mode. The reactor
is preferably equipped with devices for measuring and controlling
process parameters such as temperature, pH, etc.
[0065] The biomass used in step (i) or (i') comprises organisms,
preferably microorganisms, selected from Eubacteria, Archaea,
Algae, and Fungi. Among these, Eubacteria, Archaea and Algae are
preferred. Eubacteria and Archaea are more preferred and Eubacteria
are most preferred. The microorganisms used may naturally or by
state-of-the-art genetic engineering have the potential to bind
REEs. Generally, the REEs are bound in the oxidised term of the
REEs. This property is exploited to adsorb or accumulate REEs that
are present in the mixtures of stops (i), (i') and (ii). The
organism to be used depends on the type of REE or group of REEs to
be isolated. Other criteria for the choice of the biomass may be
the chemical state of the REE present in the mixtures. Suitable
organisms for a given REE or REE compound can be identified by
screening large strain collections using the procedure described
below and in Example 1. Screening may be done following the
procedure of Example 1 or Example 2. In the research that led to
the invention, microorganisms were assayed for their ability to
grow in the presence of REEs and, in a secondary screening, to bind
and/or accumulate REEs. An alternative to screening a broad
diversity of organisms is the pre-selection of microbes that belong
to phylogenetic groups that have turned out to have high
metal-binding potential. The biomass may bind the REEs by
adsorption to the cell surface or cell wall opponents, or via
active intracellular accumulation of ions of the REEs.
Microorganisms carrying homologous or heterologous metal-binding or
modifying structures such as S-layers, polysaccharides,
metal-reducing enzymes, metallothioneines, phytochelatins or
surface-bound natural metallophores are suitable organisms for the
present invention.
[0066] Microorganisms, particularly eubacteria and archaea, fungi
and algae that have the required REE-binding affinity and
specificity can be isolated from environmental sources, using known
microbiological techniques. Environmental sources (habitats) that
contain organisms suitable for the present invention are, however
not exclusively, sediments and waters exposed to heavy metal or
radionuclide contamination, such as acid mine drainages,
electroplating effluents, mining waste piles, industrial effluents,
and waste water treatment plants. Microorganisms viable and
competitive in these environments often have adopted strategies to
efficiently bind and immobilize heavy metals either on their
surface or in their interior in order to reduce their toxicity.
Typically, cell envelopes of microorganisms exhibit negative
charges, enabling the adsorption of cationic metals. The main
functional groups that contribute to this negative charge are
phosphate moieties and carboxylic groups.
[0067] Organisms that do not naturally have metal-binding
components can be provided with components allowing binding of the
REE of the invention by genetic engineering. For instance, DNA
fragments encoding genes or pathways that lead to the formation of
metal-binding or metal-immobilizing structures can be introduced
into wild-type strains, using techniques known to those skilled in
the art. The present invention makes use of microorganisms that
naturally--or by genetic engineering--have the potential to bind
REEs.
[0068] Examples of natural or genetically-engineered components of
organisms that may be used for binding the metal of the invention
are the following.
[0069] Metallothionines. These metal-chelating polypeptides have
been identified in many groups of organisms, including mammals,
nematodes, fungi, and bacteria. Metallothioneines are characterized
by an extremely high cysteine content of up to 33% arranged in
(Cys-X-X-Cys) or (Cys-X-Cys) clusters and the absence of aromatic
and hydrophobic amino acids.
[0070] Phytochelatins. Phytochelatins typically occur in plants and
algae and are short, non-translationally synthesized polypeptides
with variously repeating gamma-glutamylcysteine units
(.gamma.Glu-Cys).sub.nGly (n=2-11). Synthetic phytochelatins
[(glu-Cys)nGly] nave the advantage that they can be synthesized by
the ribosomal machinery and that in some cases they bind metals
even more effectively than the natural phytochelatins.
[0071] S-layers. Paracrystalline proteinaceous surface layers
(S-layers) occur as surface structures in almost all major
phylogenetic groups of bacteria and in almost all archaea (Sara and
Sleytr 2000). The proteins (40-200 kDa) are secreted and
subsequently self-assemble on the bacterial membrane, forming a
very regular nano-porous structure (30-70% porosity). S-layer
proteins constitute up to 20% of all cellular proteins. Due to
their high content in hydrophobic amino acids, S-layer lattices in
general render prokaryotic cell walls less hydrophillic, which can
lead to increased foaming during cultivation. Immobilization of
metals on S-layer templates has been used in nanotechnology to
synthesize metallic nanoclusters of the precious metals Au
(Dieluweit, Pum et al. 1998; Gyorvary, Schroedter et al. 2004) and
Pt and Pd (Wahl, Mertig et al. 2001).
[0072] Polysaccharides. Some microorganisms produce biopolymers,
e.g. polysaccharides that are able to bind 0.1 mg to 1.4 g metal/g
isolated polymer, depending on the microorganism under
investigation and the specific metal (Gutnick and Bach 2000).
Binding generally occurs via electrostatic interactions between
negatively charged groups in the biopolymer and the positively
charged metal or via chelation of the metal by hydroxyl groups.
[0073] Examples of suitable microorganisms to be used in the
present invention are microorganisms from genus Cupriavidus, such
as Cupriavidus metallidurans. An example of Cupriavidus
metallidurans is DSMZ Type strain 2839. Another example is
Citrobacter sp. These microorganisms are preferably used in the
methods and uses of the invention for isolating or enriching
scandium.
[0074] In the process of the invention, it is possible to combine
two or more microorganisms in the biomass. For example, different
microorganisms each preferentially binding a particular REE (or
groups thereof) may be combined for increasing the variety of REEs
that may be isolated in the process. Depending on the composition
of the particulate material, two or more microorganisms can be
combined in said biomass to recover different chemical forms of
REEs or different REEs in parallel.
[0075] In one embodiment, microorganisms for the processes of the
invention are eubacteria and archaea. Microorganisms of the genera
of Pseudomonas, Cupriavidus or Bacillus are preferred. A preferred
species from genus Cupriavidus is Cupriavidus metallidurans such as
DSMZ type strain 2839.
[0076] In another embodiment, the biomass used in the invention is
or contains an organism belonging to eubacteria or archaea for
adsorbing or accumulating scandium as the REE. For this purpose,
microorganisms of the genera of Pseudomonas, Cupriavidus or
Bacillus may be used. A preferred species from genus Cupriavidus is
Cupriavidus metallidurans such as DSMZ type strain 2839 for
scandium isolation.
[0077] The biomass used in the invention may be viable or dead.
Native cells as obtained by cultivation in growth media (wet
biomass) as well as dry biomass, e.g. obtained by freeze-drying or
by drying at elevated temperatures can be used. Temperatures
applied during drying should not exceed 100.degree. C. in order to
prevent thermal degradation of cell components that are involved in
specific REE adsorption. Preferably, however, the biomass used in
step (i) and (i') is viable, i.e. contains viable cells of the
organisms used. The conditions in the mixtures of steps (i), (i')
and (ii) may be such that the organisms in the mixture remain
viable to a large extent and may even grow further in the step
(ii). In an embodiment where the organisms of the biomass should
stay viable in step (ii), conditions have to support viability. For
this purpose, the mixtures may contain nutrients required for the
biomass. Further, air by be blown into the mixtures for providing
oxygen to the biomass. Suitable growth conditions and nutrient
requirements for the organisms can be obtained from the general
prior art on microbiology. Suitable growth conditions are also
provided by collections of microorganisms such as the American Type
Culture Collection (ATCC) or the German Collection of
Microorganisms and Cell Cultures (Deutsche Sammlung von
Mikroorganismen und Zellkulturen GmbH, DSMZ) where members of the
classes of microorganisms mentioned above can be obtained from.
[0078] In another embedment, the biomass added in step (i) or (i')
is viable, but is allowed to fully or partly die in the course of
the process. Generally, the biomass may at least partly die due to
unfavourable conditions in the mixture such as acidic pH.
[0079] In step (ii) of the processes of the invention, the mixture
of step (i) or (i') is incubated for allowing binding such as
adsorption or accumulation, of said REE or said group of REEs by
said biomass. Step (ii) should be conducted for a time period
sufficient to allow the biomass to adsorb and/or accumulate the
REE(s) from the solution. The incubation time may be chosen such
that no or little more REE(s) are absorbed or accumulated by the
biomass at the end of the incubation step. The incubation time
depends on the rate of binding. Generally, the incubation time is
between 0.5 hours and 96 hours, preferably between 0.5 hours and 48
hours, and more preferably between 1 hour and 24 hours. The
temperature of incubation depends mostly on the type of biomass
used and the REE that are to be recovered. Step (ii) may comprise
agitating said mixture for bringing said biomass in close contact
with particles of said particulate material. As indicated above
with respect to step (i), the reactor in which step (ii) is carried
out may be equipped with devices for measuring and controlling
process parameters such as temperature, pH, etc.
[0080] In step (iii), said biomass having bound REE(s) is separated
from the mixture of step (ii). Known methods may be used for the
separation. For example, the metal-loaded biomass may be separated
from the solution by centrifugation or filtration. Alternatively,
flocculation or flotation may be used. The separated biomass may,
depending on the subsequent step, be dried for facilitating storage
and/or transport and/or metal separation in step (iv).
[0081] In step (iv), the metal bound to the biomass is isolated
from said biomass. The metal may for example be desorbed from the
biomass in a liquid phase using acidic or basic conditions, or
elution with chemicals such as chelating agents that can form
soluble complexes with the REEs. Alternatively, the biomass may be
combusted to destroy and remove organic matter of said biomass,
whereby the REE can be isolated from ashes or fumes. Further,
mechanical means may be used for separating the REEs from the
biomass, such as sonication. The REE(s) may be purified from the
residues, ashes or fumes of the biomass. Preferably, the isolation
method allows recycling of the biomass for use in further
REE-extraction processes.
[0082] In one embodiment, the mixture from step (ii) may be poured
in step (iii) into chromatography columns that holds back the
biomass but allows removal of excess liquid from the column. In
this embodiment, step (iv) may be performed by eluting REEs from
the column using a liquid medium as eluent that weakens the binding
of the REEs to the biomass such as complexing agents. In this way,
the REEs, notably soluble compounds thereof, may be obtained in
concentrated eluent.
[0083] The processes of the invention may be combined with process
steps used for isolating specific REE(s) from metal solutions known
from prior art. For example, where a group of REEs was isolated in
step (iv), individual REEs or compounds thereof may be isolated. If
desired, REEs in elemental form may be generated from REE compounds
by known reduction methods.
[0084] The invention also provides a method of testing a sample
microorganism for its ability to bind a REE, and a method of
screening a plurality of microorganisms for the ability of members
of said plurality to bind a rare earth element comprising the
following steps: [0085] (a) contacting a microorganism with a
solution or dispersion containing a rare earth element or multiple
REEs; [0086] (b) incubating the mixture of step (a) for a
predetermined period of time; [0087] (c) separating microorganisms
from the mixture obtained in step (b); [0088] (d) analysing the
separated microorganism for bound REE.
[0089] In step (a), a microorganism is contacted with a solution or
dispersion containing a REE or multiple REEs. Similarly as
described above, the microorganism may be selected from the
following organism classes: Eubacteria, Archaea, Algae, and Fungi.
The REE may be solution, preferably an aqueous solution, of the REE
for which the binding ability of the microorganism is to be tested.
Preferably, the solution contains two or more REEs, since this
allows testing the binding ability of the microorganism to multiple
REEs in parallel if the separated microorganism is analysed in step
(d) for the multiple REEs.
[0090] For increased solubility of the REE in the solution, the
solution may contain an acid such as those mentioned above. The
solution or dispersion used in step (a) may be an acidic aqueous
solution or dispersion. The pH of the solution or dispersion may be
from 0 to 5, preferably of from 0.5 to 3, more preferably of from
1.0 to 2.0. The pH of the mixture of step (ii) may be from 0 to 5,
preferably from 0.5 to 3, more preferably from 1.0 to 2.0.
[0091] In incubation step (b) and the separation step (c) may be
carried out as described above for steps (ii) and (iii) of the
process of isolating a REE.
[0092] In step (d), the separated microorganism is analysed for
bound REE. This may involve extraction of metal compounds from the
separated microorganism e.g. using a mixture of concentrated nitric
acid and hydrochloric acid, preferably in combination with heating.
The extraction acid may then be diluted with pure water and
subjected to any generally known method for analysing REEs such as
atom absorption spectroscopy or inductively coupled plasma mass
spectroscopy (ICP-MS). These methods may be used for quantitative
analysis of REEs in the separated microorganism. If multiple REEs
are detected, their relative abundance may be compared with the
relative abundance of multiple REEs in the starting REE solution.
Thus, enrichment of one or more particular REEs compared to others
can also be detected. In this way, a suitable or optimal
microorganism for a particular purpose may be found.
EXAMPLES
Example 1
Preparation of Mineral Leach
[0093] Bastnaesit ore was leached using 10%-H.sub.2SO.sub.4 in a 15
(w/v) ratio of ore and acid. A 50-g sample of ore was incubated
under continuous stirring with 250 ml of 10%-H.sub.2SO.sub.4 for 3
days at room temperature. The leach solution was centrifuged to
remove non-dissolved particles and the supernatant was used as
so-called "mineral leach" for further experiments. Before each
experiment, the pH of mineral leach was adjusted to 1.3 by the
addition of 10N NaOH.
Example 2
Screening for Microorganisms that enrich Scandium from Mineral
Leach
[0094] Microbial strains that have the potential for
adsorbing/accumulating REE were selected by their ability to grow
on solid media (Luria Bertani (LB) medium 10 g/l tryptone and 5 g/l
yeast extract, with 1.5 g/l agar) containing amounts of 1 to 5 mM
REE (single elements or mixtures). REE-resistant microorganisms
were screened for their ability to enrich scandium (Sc) from
mineral leach. To this end, microbial strains were cultivated in LB
medium (without agar) at the 50-ml scale according to standard
microbiological techniques. Cells were collected in the stationary
phase by centrifugation. Amounts of 20 OD units were incubated for
1 h at room temperature (25.degree. C.) with 1 ml of mineral leach.
After incubation, cells were collected by centrifugation and washed
once with 100 .mu.l 10%-H.sub.2SO.sub.4. As a control for
spontaneous (chemical) precipitation of REE, 1-ml aliquots of
mineral leach without biomass were used. Cell pellets and
precipitates were extracted by nitrohydrochloric acid for 2 h at
100.degree. C. using a Digi-Prep sample preparation device (S-Prep,
Oberlingen, Germany). After dilution in ultrapure water, REE
contents of the cell pellets were determined by ICP-MS (Agilent,
7700 ICP-MS).
Results
[0095] A number of 36 microbial strains (hit candidates) were
detected that selectively bind Sc in their biomass. Enrichment
factors for Sc compared to the other REE of up to 438 were observed
(FIG. 1). Analysis of partial 16 S rDNA sequences suggested that
many hit candidates originate from the groups of Pseudomonas and
Bacillus.
Example 3
Scandium Recovery from Mineral Leach by Microbial Biomass
[0096] Strains S3_8B_D12 and S3_8B_B2 were used to determine Sc
recovery in an experimental set-up as described in Example 2. As
shown in FIG. 2 A, S3_8B_D12 was able to enrich Sc by a factor of
438 compared to the original mineral leach (black bars, REE=w/w),
leading to a REE mixture that contains more than 80% of the target
element. By the applied single-step extraction, 33% of the present
Sc could be recovered. With strain S3_8B_B2 only an enrichment
factor of 61 could be achieved for Sc (W=22%). On the other hand,
however, also Lutetium--a very underrepresented heavy REE--could be
enriched by a factor 22, leading to a recovery of 8% of the present
material.
[0097] We used DSMZ Type strain 2839 (Cupriavidus metallidurans)
and Citrobacter sp. to recover REE from an equimolar solution (1 mM
each, in 10%-H.sub.2SO.sub.4; pH adjusted to 2.2 by addition of
1N-NaOH) of all 16 stable REE (FIG. 2B, black bars=SEE-mix, percent
(w/w)). 20 OD units of cells originating from a stationary phase
(overnight) culture prepared in LB medium were incubated for 1 h
with 1 ml of said REE solution. After incubation, cells were
collected by centrifugation and washed once with 100 .mu.l
10%-H.sub.2SO.sub.4. ICP-MS analysis was carried out as described
above.
[0098] The content of European patent application No. 13 003 058.8,
filed on Jun. 14, 2013 is herewith incorporated by reference in its
entirety including entire description, claims and figures.
REFERENCES
[0099] Dieluweit S., D. Pum, et al. (1998). "Formation of a gold
superlattice on an S-layer with square lattice symmetry." Supramol
Sci 5: 15-19. [0100] Gyorvary. E., A. Schroedter, et al. (2004).
"Formation of nanoparticle arrays on S-layer protein lattices." J
Nanosci Nanotechnol 4(1-2): 115-20. [0101] Gutnick, D. L. and H.
Bach (2000). "Engineering bacterial biopolymers (or the biosorption
of heavy metals: new products and novel formulations." Appl
Microbiol Biotechnol 54(4): 451-60. [0102] Sara, M. and U. B.
Sleytr (2000). "S-Layer proteins." J Bacteriol 182(4): 859-68.
[0103] Vieira, R. H. and B. Volesky (2000). "Biosorption: a
solution to pollution?" Int Microbiol 3(1): 17-24. [0104] Wahl, R.,
M. Mertig, et al. (2001). "Electron-beam induced formation of
highly ordered palladium and platinum nanoparticle arrays on the
S-layer of Bacillus sphaericus NCTC 9602." Adv Mater 13:
736-740.
* * * * *