ADAPTATION OF BACTERIA FOR USE IN LEACHING

ADAPTATION DE BACTERIES DESTINEES A ETRE UTILISEES DANS UN PROCEDE DE LIXIVIATION

English Abstract

A method for the adaptation of bacteria for use in the leaching of ores and
concentrates, the method characterised by the steps of : a) Obtaining samples
of bacteria exhibiting one or more desired attributes; b) Combining bacterial
samples from step a) with a stock bacterial culture known to have the ability
to oxidise sulphide minerals, whereby the resulting combined bacterial culture
ultimately expresses both the one or more desired attributes and the ability
to oxidise sulphide minerals. The particular desired attribute is preferably
salt tolerance.

French Abstract

L'invention concerne une méthode d'adaptation de bactéries destinées à être utilisées dans un procédé de lixiviation de minerais ou de concentrés. La méthode consiste à: a) obtenir des échantillons de bactéries présentant un ou plusieurs attributs désirés; b) combiner les échantillons de bactéries de l'étape a) avec une culture bactérienne souche réputée avoir la capacité d'oxyder des minéraux sulfurés. La culture bactérienne combinée résultante exprime au final lesdits attributs désirés et la capacité d'oxyder des minéraux sulfurés. Un tel attribut désiré est, de préférence, la tolérance au sel.

Claims

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Claims
1. A method for the adaptation of bacteria for use in the leaching of ores and
concentrates, the method characterised by the steps of:
a) Obtaining samples of bacteria exhibiting salt tolerance;
b) Combining bacterial samples from step a) with a stock bacterial culture
known to have the ability to oxidise sulphide minerals; and
c) Grow the combined culture of step b) over time in saline conditions,
whereby the resulting combined bacterial culture ultimately expresses
both salt tolerance and the ability to oxidise sulphide minerals.
2. A method according to claim 1, wherein the bacterial samples of step a) are
obtained with water samples, these water samples being used as a template
to prepare 'synthetic' solutions which are then in turn used to prepare
nutrient
solutions for the stock bacterial culture of step b).
3. A method according to claim 1 or 2, wherein the bacterial samples of step
a)
are obtained from at least two locations and subsequently combined and
grown, this combined culture then being combined with the stock bacterial
culture in step b).
4. A method for the adaptation of bacteria for use in the leaching of ores and
concentrates in generally saline conditions, the method characterised by the
steps of:
a) Obtaining samples of water with salt tolerant bacteria;
b) Combining and growing bacterial samples of step a);
c) Combining a stock bacterial culture known to have the ability to oxidise
sulphide minerals with a nutrient solution prepared from one or more of

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the samples of step a) and thereby beginning the adaptation of the stock
bacterial culture to saline conditions;
d) Combining a bacterial sample from step b) with a sample of culture from
step c); and
e) Growing the combined samples of step d) and gradually increasing
salinity, whereby the combined bacterial culture ultimately expresses both
salt tolerance and the ability to oxidise sulphide minerals.
5. A method according to claim 4, wherein the samples of water of step a) are
used as a template to prepare 'synthetic' saline solutions which are in turn
used to prepare the 'synthetic' saline nutrient solutions used in step c).
6. A method according to claim 5, wherein the nutrient solution prepared from
the sample having the lowest chloride ion concentration of the samples of
step a) is used in Step c).
7. A method according to claim 6, wherein the lowest chloride concentration is
about 13 g/L.
8. A method according to any one of claims 4 to 7, wherein salinity levels are
increased to levels of at least 40 g/L in step e).
9. A method according to any one of claims 4 to 8, wherein salinity levels are
increased to levels of at least about 98 g/L in step e).
10. A method according to any one of claims 4 to 9, wherein the salinity
levels are
increased over a period of about eight months in step e).
11. A method according to any one of claims 4 to 10, wherein the levels of
total
dissolved solids (TDS) is increased to at least about 80,000 ppm.
12. A method according to any one of claims 4 to 11, wherein the levels of
total
dissolved solids (TDS) is increased to at least about 200,000 ppm.

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13. A method for the adaptation of bacteria for use in the leaching of ores
and
concentrates substantially as hereinbefore described with reference to the
example.

Description

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"Adaptation of Bacteria for Use in Leaching"
Field of the Invention
The present invention relates to a method for the adaptation of bacteria for
use in
the leaching of ores and concentrates. More particularly, the method of the
present invention relates to the adaptation of sulphide mineral oxidising
bacterial
cultures to operate effectively in specific environments, including saline
environments.
Background Art
The bacterial oxidation of sulphide minerals requires reasonable volumes of
process water whether leaching takes place in tanks, vats, dumps or heaps. The
bacterial cultures used in these leaches operate well in waters with low total
dissolved solids (TDS) and more importantly, low levels of chloride ions. In
some
areas of the world, particularly in Australia, good quality process water is
very
difficult to find and the cost of improving water quality through the use of
water
treatment plants is very high. In order to use bacterial leaching in these low
quality process waters it is essential that sulphide oxidising bacteria are
adapted
to saline environments.
Bacteria are ubiquitous in the environment and can be found in such diverse
environments as thermal vents in the ocean floor, sulphur springs and salt
crystals. It is known that plasmids are found in most bacterial species.
Plasmids
are extrachromosomal pieces of circular DNA. Genes within the plasmid are
often
essential for the growth of the bacteria in certain extreme environments
(FREIFELDER, David., Essentials of Molecular Biology. Jones and Bartlett
Publishers, Inc. USA. 19r35). Plasmids are known to be transferred frequently
and rapidly amongst bacteria.
It is possible that any bacteria living in saline environments may contain
plasmids
allowing them to do so. These plasmids could then be transferred naturally
into
sulphide oxidising bacteria.

PCT/AU02/00971
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A general method for the adaptation of bacteria for use in the leaching of
ores and
concentrates has been described by the present applicant in co-pending
International Patent Application PCT/AU02/00182, and the entire content
thereof
is incorporated herein by reference.
The preceding discussion of the background art is intended to facilitate an
understanding of the present invention only. It should be appreciated that the
discussion is not an acknowledgement or admission that any of the material
referred to was part of the common general knowledge in Australia as at the
priority date of the application.
Throughout the specification, unless the context requires otherwise, the word
"comprise" or variations such as "comprises" or "comprising", will be
understood to
imply the inclusion of a stated integer or group of integers but not the
exclusion of
any other integer or group of integers.
Disclosure of the Invention
In accordance with the present invention there is provided a method for the
adaptation of bacteria for use in the leaching of ores and concentrates, the
method characterised by the steps of:
a) Obtaining samples of bacteria exhibiting salt tolerance;
b) Combining bacterial samples from step a) with a stock bacterial culture
known to have the ability to oxidise sulphide minerals; and
c) Grow the combined culture of step b) over time in saline conditions,
whereby the resulting combined bacterial culture ultimately expresses
both salt tolerance and the ability to oxidise sulphide minerals.
In accordance with the present invention there is further provided a method
for the
adaptation of bacteria for use in the leaching of ores and concentrates in
generally
saline conditions, the method characterised by the steps of:
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a) Obtaining samples of water with salt tolerant bacteria;
b) Combining and growing bacterial samples of step a);
c) Combining a stock bacterial culture known to have the ability to oxidise
sulphide minerals with a nutrient solution prepared from one or more of
~ the samples of step a) and thereby beginning the adaptation of the stock
bacterial culture to saline conditions; and
d) Combining a bacterial sample from step b) with a sample of culture from
step c); and
e) Growing the combined samples of step d) and gradually increasing
salinity, whereby the combined bacterial culture ultimately expresses both
salt tolerance and the ability to oxidise sulphide minerals.
Preferably, the samples of water of step a) are used as a template to prepare
'synthetic' saline solutions which are in turn used to prepare the 'synthetic'
saline
nutrient solutions used in step c). Still preferably, the nutrient solution
prepared
from the sample having the lowest chloride ion concentration of the samples of
step a) is used in Step c).
Brief Description of the Drawings
The present invention will now be described, by way of example only, with
reference to one embodiment thereof and the accompanying drawing, in which:
Figure 1 is a schematic diagram of a process for the adaptation of bacteria
for
use in the leaching of ores and concentrates in generally saline conditions in
accordance with the present invention.
Best Models) for Carrying Out the Invention
Generally, the present invention is intended to collect bacteria capable of
operating in saline waters and mix these bacteria with sulphide oxidising
bacteria

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with the view that saline resistance would be transferred from the bacteria of
the
saline waters.to the sulphide oxidising bacteria through the transfer of DNA
from
one species to another.
The method of the present invention will now be described with reference to an
example and Figure 1. The example is not intended to limit the generality of
the
foregoing description. Figure 1 is to be read in conjunction with the
following
description.
The inventors determined that the best chance of the intended DNA transfer
taking place would be between bacteria from similar environments. Naturally
occurring bacteria samples were collected from "black smokers" from the sea.
Black smokers are sulphide deposits found on the ocean floor. Examination of
the smokers has revealed that they are teeming with bacteria. Additional
samples
were collected from puddles of process water within and around sulphide mines.
Also from the mines, samples of ore and liquor from saline environments were
collected, these samples consisted of liquors, sludges and dry solids. In all
cases,
samples of the water/liquor were removed from each location.
Each of the liquor/water samples collected were submitted for full ICP-OES
(induced coupled plasma optical emission spectrometry) analysis, including
sodium, chloride and TDS analysis, in order to determine the levels of the
various
salts within the samples. The pH's of the liquors and sludges were also
determined.
The samples containing liquors were examined under a microscope and bacterial
counts made.
The results from TDS and ICP analysis were used, much like a template, to make
up 'synthetic' saline solutions for the appropriate samples using aquarium
salts.
Calculations were based on the levels of CI- rather than TDS. The synthetic
saline solutions were used for making up 'synthetic' saline nutrient
solutions, as it
is often difficult to get sufficient water samples for testing.
Standard OK nutrient solutions are made using the synthetic saline solutions.

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Any solid samples were split in half, one half was ground and used as a
sulphide
feed source for the indigenous bacterial samples from that location, the other
half
of the sample was not ground, as bacteria would have been destroyed from the
shearing forces.
The unground solid sample was combined with the synthetic saline solution
similar to its' indigenous salt water and the bacteria present on the solids
grown
up in shake flasks.
Solids and liquor samples from the same location were combined and placed in a
shaker bath at 45°C. Yeast extract was added to these tests at a
concentration of
0.1 g/L. Yeast extract provides nutrients for heterotrophic bacteria.
The pH of all the slurries was adjusted to the natural pH of the samples taken
from the environments.
Every week the pH of the tests was adjusted down 0.5 of a unit until a pH of
<2.0
is maintained. All pH adjustments were carried out through the addition of
concentrated sulphuric acid.
The shake flasks were examined on a weekly basis for bacterial activity and
the
liquors sampled and assayed for metals reporting to solution.
A 'stock' bacterial culture capable of oxidising sulphide minerals was
adjusted
slowly to saline waters. The culture was grown in a sample of the synthetic
nutrient solution with the lowest levels of CI- (approximately 13 g/L). The CI-
levels
were gradually increased over time, in some cases to chloride levels of 98 g/L
over eight months.
Once the bacterial numbers from the indigenous salt samples were considered
high enough (>107 cells/mL), the cultures were divided into three. A first
sample
fed and stored, a second sample scaled up, fed and maintained, and the third
sample combined with an equal portion of the stock bacterial culture adapted
to
low levels of salinity as above.
The combined bacterial cultures were used as an inoculum for sulphide
amenability testing. The volume of the test was made up to 3L using the
appropriate saline nutrient media, and the tests were conducted in standard
stirred tank reactors at a temperature ranging between 40°C to
55°C. The test

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was fed with a sulphide ore/concentrate and yeast extract added to a
concentration of 0.1 g/L.
The test was monitored by assaying the levels of metals reporting to solution.
The transfer of genetic material from one bacterial species to another may
take
some time. However, the resulting bacterial culture is capable of both growing
in
saline environments and oxidising sulphide minerals.
The salinity of the test may be increased with each successive scale up to
chloride levels of at least 40 to 55 g/L, and up to about 98 g/L, or to TDS
levels of
at least 80,000 to 90,000 ppm, and up to about 200,000 ppm. The inventors
envisage that the chloride and TDS levels may be able to be taken higher than
these levels if required.
Modifications and variations such as would be apparent to the skilled
addressee
are considered to fall within the scope of the present invention.