WO2018202691A1

WO2018202691A1 - Method for performing a bioleaching process of chalcopyrite

Info

Publication number: WO2018202691A1
Application number: PCT/EP2018/061175
Authority: WO
Inventors: Jan Nygren; Mark DOPSON; Paul WILMES; Malte HEROLD; Igor PIVKIN; Antoine BUETTI-DINH; Olga ILIE; Ansgar POETSCH; Sören BELLENBERG; Wolfgang SAND; Mario Vera VÉLIZ; Stephan CHRISTEL
Original assignee: Universita Della Svizzera Italiana; Ruhr Universitaet Bochum; Universitaet Duisburg Essen; Universite du Luxembourg; Linnaeus University; TATAA BIOCENTER AB
Current assignee: Universita Della Svizzera Italiana; Ruhr Universitaet Bochum; Universitaet Duisburg Essen; Universite du Luxembourg; Linnaeus University; TATAA BIOCENTER AB
Priority date: 2017-05-02
Filing date: 2018-05-02
Publication date: 2018-11-08
Anticipated expiration: 2019-11-02

Abstract

The present invention relates to a method for performing a bioleaching process of chalcopyrite comprising the steps of: providing a chalcopyrite containing material; providing microorganisms, the microorganisms oxidizing iron(ll) at a rate such that the redox potential does not rise above 550 mV relative to a Ag⁺/AgCI electrode; adding said microorganisms to the chalcopyrite containing material; allowing reaction at said redox potential to provide copper ions.

Description

METHOD FOR PERFORMING A BIOLEACHING PROCESS OF

CHALCOPYRITE

Technical Field of the Invention

The present invention relates to a method for performing a bioleaching process of chalcopyrite.

Background of the Invention

Bioleaching of chalcopyrite is a process where copper is extracted from chalcopyrite, CuFeS2, with the help of bacteria. The role of the bacteria is to oxidize iron(ll) ions into iron(lll) ions which are needed for the degradation of chalcopyrite.

In conventional processes crushed chalcopyrite ore is put into heaps and provided with an acidic solution containing iron(ll) oxidizing bacteria. The hydrogen ions of the acid together with iron(lll) ions react with the

chalcopyrite, degrading it and leaching copper ions from it. The solution becomes rich with copper as it flows down through the heap. The copper rich solution is retrieved at the bottom of the heap and pure copper can then be extracted from the solution.

To extract copper from chalcopyrite, the chalcopyrite is most commonly provided with an acidic solution containing iron(ll) oxidizing bacteria. The chalcopyrite is degraded by reacting with iron(lll) ions and hydrogen ions, releasing copper ions into the solution. Iron(ll) ions are also released into the solution by the degraded chalcopyrite. The degradation reaction uses or consumes iron(lll) ions, which are reduced into iron(ll) ions, and hydrogen ions, which form a compound with the sulfur containing part of the degraded chalcopyrite. The hydrogen ions are regenerated in a subsequent reaction of the remaining sulfur containing compound. However, the iron(lll) ions are not regenerated by a subsequent reaction but are instead provided by said bacteria. By providing iron(lll) ions, enzymes produced by the bacteria function as catalysts to the degradation reaction of chalcopyrite, and thereby the copper extraction. By generating iron(lll) ions the redox potential of the system increases. A higher iron(lll) ion concentration has the effect of increasing the rate of chalcopyrite degradation and is commonly considered beneficial for the copper release. It therefore seems desirable to generate as much iron(lll) ions as possible, thereby increasing the redox potential and the reaction rate. However, consequences of a high redox potential have other effects as well, one being the hindered dissolution of the chalcopyrite. At high redox potentials the dissolution of chalcopyrite will become hindered, decreasing its reactivity.

There is a need to provide new methods of bioleaching of chalcopyrite, which have an improved copper retrieval and rate thereof.

Summary of the Invention

It is an object of the present invention to provide a method for performing a bioleaching process of chalcopyrite such that it results in an increased rate of copper generation.

According to one aspect of the present invention there is provided a method for performing a bioleaching process of chalcopyrite. The method comprises the steps of providing chalcopyrite containing material and providing microorganisms. The chalcopyrite containing material and microorganisms are allowed to react to provide copper ions. The copper ions may then be retrieved, thereafter the obtained material(s) may be processed further. The microorganisms oxidize iron(ll) at a rate such that the redox potential does not rise above 550 mV, relative to a AgVAgCI electrode with 3 M KCI electrolyte. All redox potentials mentioned in this application are measured relative to this type of electrode. Further the method comprises the steps of adding the microorganisms to the chalcopyrite containing material and allowing a reaction at a redox potential of at most 550 mV, relative to a AgVAgCI electrode. The microorganisms make sure that the redox potential is kept at a value of at most 550 mV, relative to a AgVAgCI electrode, at or below which the rate of chalcopyrite degradation has been found the highest.

According to one embodiment of the invention the microorganisms oxidize iron(ll) at a rate such that the redox potential rises to at least 400 mV relative to a AgVAgCI electrode. A combination of the above embodiments has the advantage of making sure that the redox potential will be between 400 mV and 550 mV relative to a AgVAgCI electrode, between which potentials the rate of chalcopyrite degradation has been found the highest.

According to one embodiment of the invention the microorganisms are able to oxidize sulfur at a rate such that sulfuric acid is regenerated from the degraded chalcopyrite, at redox potentials between 400 mV and 550 mV relative to a AgVAgCI electrode. This will enable and ensure a continuous provision of the hydrogen ions needed for the degradation of chalcopyrite and that the degradation of chalcopyrite will not be limited by the concentration of hydrogen ions.

According to one embodiment of the invention the microorganisms are bacteria and/or archaea.

According to one embodiment of the invention the microorganisms are provided in a solution.

According to one embodiment of the invention there is provided between 10⁶ to 10⁸ microorganisms per ml of microorganism containing solution.

According to one embodiment of the invention an acidic solution is provided to the chalcopyrite.

According to one embodiment of the invention the acidic solution has a pH between 0.5 and 5, preferably between 1 .5 and 3, most preferably between 2 and 3.

According to one embodiment of the invention the acidic solution comprises at least one inorganic acid, preferably selected from the group consisting of HCI, H₂SO , H₃PO₄ and HNO₃, preferably H₂SO₄.

According to one embodiment of the invention the microorganisms are bacteria selected from the group consisting of Acidithiobacillus,

Acidimicrobium, Ferrithrix and Sulfobacillus, and any combination thereof. The bacteria are preferably selected from the group consisting of

Acidimicrobium ferrooxidans, Acidithiobacillus caldus, Acidithiobacillus ferrivorans, Acidithiobacillus ferrooxidans, Acidithiobacillus ferridurans, Acidithiobacillus ferriphilus, Acidithiobacillus thiooxidans, Ferrithrix thermotolerans, Sulfobacillus acidophilus, Sulfobacillus sibiricus, Sulfobacillus thermosulfidooxidans and Sulfobacillus thermotolerans, and any combination thereof.

According to one embodiment the method is performed during the initiation of the bioleaching process.

These and other aspects of the invention will be apparent from and elucidated with reference to the claims and the embodiments described hereinafter. Short description of the drawings

Figure 1 shows the copper ion concentration over time for different degradation processes.

Figure 2 shows the redox potential over time for different degradation processes.

Detailed Description of Preferred Embodiments of the Invention

The method according to the invention is performed in the following manner. A chalcopyrite containing material is provided. This material may contain more than chalcopyrite but the higher the content thereof then the more copper is obtainable from the process. Microorganisms are also provided, which are able to oxidize iron(ll) at a rate such that the redox potential does not rise above 550 mV relative to a AgVAgCI electrode. The microorganisms are added to the chalcopyrite. Reaction between the microorganisms and chalcopyrite containing material is allowed at a redox potential of at most 550 mV relative to an AgVAgCI electrode.

The method may be performed as an initiation of a bioleaching process, or to improve an already ongoing bioleaching process. With initiation may herein mean the period of time between the start of a bioleaching process and the point of time when extraction of copper has been achieved, preferably when the maximum extraction rate of copper has been achieved. The present method may be performed to the point of time when all copper has been recovered.

The present method may be performed as an initial start of the bioleaching of the chalcopyrite containing material. However, it may also be possible to apply the present method to chalcopyrite containing material already being treated or that has been treated.

The chalcopyrite containing material can be provided in many ways. For example, it could be crushed and/or ground chalcopyrite, e.g. with the particles being about 1 to 2 cm in size. It could be run-of-mine chalcopyrite which is provided. The chalcopyrite may be collected into a heap. The heap may have a height of several meters, for instance between 6 and 10 meters high, and a width and length of several kilometers, for instance 5 km wide and 10 km long. The heap may also be more than a 100 meters high. The chalcopyrite could of course also be provided in a small amount, such as a few grams. The chalcopyrite may also be finely ground, with sizes of the particles being 1 mm or less in size.

The microorganisms may be provided in a solution. The solution may comprise nutrients which are suitable for the microorganisms but it does not have to. The microorganisms could instead just feed of the chalcopyrite containing material and/or the surroundings. The microorganisms are able to oxidize iron(ll) into iron(lll). The microorganisms are able to oxidize iron(ll) such that the redox potential does not rise above 550 mV, relative to a AgVAgCI electrode. It is also possible to use microorganisms which are able to oxidize iron(ll) such that the redox potential is at most 530 mV, relative to a AgVAgCI electrode. An upper limit of 500 mV or 450 mV, relative to a

AgVAgCI electrode, may also be possible. The microorganisms are also able to oxidize the iron(ll) such that the redox potential is at least 400 mV, relative to a AgVAgCI electrode. The microorganisms may oxidize iron(ll) such that the redox potential is about 400-550mV, such as 400-530 mV, 400-500vV or 400-450mV.

The adding of the microorganisms to the chalcopyrite can be done by providing the microorganisms in a solution and then providing this solution to the chalcopyrite containing material, for example by pouring it onto the chalcopyrite. Instead of pouring the solution onto the chalcopyrite it is possible to mix it together with the chalcopyrite. The microorganisms may also be mixed together with the chalcopyrite even if the microorganisms are not provided in a solution. If collecting the chalcopyrite into a heap, it may be possible to continuously or intermittently add microorganisms to the heap as the heap is being constructed. It might of course also be possible to just put the microorganisms on top of the heap, letting them migrate into the heap, by for example pouring a liquid onto the microorganism covered heap or by letting the microorganisms grow into the heap. The microorganism containing solution would preferably contain between 10⁶ to 10⁸ microorganisms per ml.

The reaction which may be allowed at a redox potential between 400 mV and 550 mV relative to an AgVAgCI electrode is preferably the

degradation of chalcopyrite by means of iron(lll) ions and hydrogen ions. Another reaction which may be allowed may be the oxidization of iron(ll) ions into iron(lll) ions. Or it could be one of the reactions which turn sulfur into sulfuric acid. It may be more than just one reaction being performed, e.g. several different reactions being allowed simultaneously. Any reaction which is allowed could also be allowed between a redox potential of 400 mV and an upper limit such as 530 mV, 500 mV or 450 mV, relative to a AgVAgCI electrode. The allowed reaction for these ranges may be the same as described above for a redox potential between 400 mV and 550 mV relative to an AgVAgCI electrode.

The microorganisms could also be able to oxidize sulfur at a rate such that the acid consumed in the degradation of chalcopyrite is regenerated as sulfuric acid from the degraded chalcopyrite. The oxidation of sulfur may be allowed at redox potentials between 400 mV and 550 mV relative to a AgVAgCI electrode. The oxidation of sulfur could also be allowed from 400mV to an upper limit such as 530 mV, 500 mV or 450 mV, relative to a AgVAgCI electrode.

Any type of microorganisms can be used, as long as it oxidizes iron(ll) at a rate such that the redox potential does not rise above 550 mV. In other embodiments of the invention any microorganism can be used as long as it oxidizes iron(ll) at a rate such that the redox potential is at most 530 mV, 500 mv or 450 mV, relative to a AgVAgCI electrode. One type of microorganisms which may be used is bacteria. Another type which can be used is archaea. The microorganisms may be selected from bacteria of a genus selected from the group consisting of Acidithiobacillus, Acidimicrobium, Ferrithrix and Sulfobacillus. It is also possible to use the microorganisms in any

combination. Preferably the microorganisms are bacteria selected from a species selected from the group consisting of Acidimicrobium ferrooxidans, Acidithiobacillus caldus, Acidithiobacillus ferrivorans, Acidithiobacillus ferrooxidans, Acidithiobacillus ferridurans, Acidithiobacillus ferriphilus, Acidithiobacillus thiooxidans, Ferrithrix thermotolerans, Sulfobacillus acidophilus, Sulfobacillus sibiricus, Sulfobacillus thermosulfidooxidans and Sulfobacillus thermotolerans. It is also possible to use said microorganisms in any combination.

In a preferred embodiment of the invention the microorganisms are a combination of microorganisms chosen only from the group consisting of Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans. In a more preferred embodiment the microorganisms are a 1 :1 combination of microorganisms from the group consisting of Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans.

Choosing microorganisms which are able to survive, and preferably grow, under acidic environments is preferable. The microorganisms are preferably thriving in environments with pH as low as 5, preferably as low as 3, more preferably as low as 2 and most preferably as low as 0.5. The pH during the bioleaching process may be in the range of 0.5-5, such as 0.5-4, or 0.5-3.

The microorganisms used in the method could also be able to survive and thrive in a solution with a high metal ion concentration. Preferably it should be able to survive iron ions concentrations of up to 20000 mg/l and copper ion concentrations of up to 20000 mg/l.

It is possible to provide the chalcopyrite containing material with an acidic solution. The acidic solution could be continuously supplied to the chalcopyrite. It could also be supplied intermittently to the chalcopyrite, for example once every hour, once every day or once every week. The acidic solution could also be provided to the chalcopyrite all at once in the beginning of the bioleaching process. The acidic solution could be poured onto or dripped onto the chalcopyrite. It could also be mixed together with the chalcopyrite. The acidic solution would preferably comprise H2SO₄ but it is possible to use other acids instead, e.g. inorganic acids such as HCI, H3PO₄, or HNO3. The acidic solution could comprise a mixture of different acids as well as just one acid. The pH of the acidic solution could be between 1 .5 and 3, preferably between 2 and 3. The pH of the acidic solution could be such that the pH of the bioleaching process will be between 0.5 and 5, preferably between 1 .5 and 3, more preferably between 2 and 3.

The solution in which the microorganisms can be provided to the material to be treated can be the acidic solution. The acidic solution can be provided to the chalcopyrite in the same manner as the previously described solution in which the microorganisms can be provided.

The amount of microorganisms provided could be dependent on the amount of provided chalcopyrite. The amount of microorganisms could be between 10⁵ and 10⁸ microorganisms per gram of chalcopyrite containing material, preferably between 10⁶ and 10⁸ per gram of chalcopyrite and more preferably between 10⁶ and 10⁷ microorganisms per gram of chalcopyrite.

It is realized by a person skilled in the art that features from various embodiments disclosed herein may be combined with one another in order to provide further alternative embodiments. Examples

All experiments were performed in the same manner with the only difference being the composition of the microorganisms used.

In a 250 ml Erlenmeyer flask, 100 ml of Mackintosh medium

((NH₄)S0₄ ²-, 1 .0 mM; KH₂P0₄, 200 μΜ; MgCI, 125 μΜ; CaCI, 1 .0 mM) was provided. The medium was provided with chalcopyrite (CuFeS2) such that the mineral content was 2 weight percent. The chalcopyrite had a grain size of 50 to 100 μιτι. The medium had an initial pH of 1 .8. The temperature of the medium was kept at 40 °C. There was no aeration performed of the medium apart from the aeration that may be obtained from the agitation disclosed hereinafter. The flask was agitated at a constant speed of 150 rpm. No baffles were used. The medium was provided with 10⁷ microorganism cells per ml of medium and per species. During the process measurements were taken of the pH, the redox potential relative to a AgVAgCI electrode, the concentration of copper ions, the concentration of soluble iron(ll) ions, the concentration of soluble iron(lll) ions, the total amount of iron, the concentration of soluble sulfur ions and the total amount of elemental sulfur.

Three experiments were done with different compositions of microorganisms in each experiment. In one of them a mixture of

Leptospirillum ferriphilum and Sulfobacillus thermosulfidooxidans was used. In another one a mixture of Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans was used. In another one no microorganisms were used, i.e. no microorganisms were added to the medium, a so called

"reference mixture". All three experiments were performed as described above. The redox potential and the copper ion concentration was measured during the experiments and are presented in Figure 1 and Figure 2.

In Figure 1 it is shown the copper ion concentration in mM dependent on time in days for the three experiments. The dotted line is for the mixture of Leptospirillum ferriphilum and Sulfobacillus thermosulfidooxidans. The dashed line is for Acidithiobacillus caldus and Sulfobacillus

thermosulfidooxidans. The line which is both dashed and dotted is for the reference experiment in which no microorganisms have been added to said medium. As can be seen from the graph the combination of Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans highly improve the amount of copper ion obtained. A reason for the reference experiment disclosing a copper retrieval is that a small amount for Fe(lll) are present at the start of the experiment and slow chalcopyrite breakdown by the protons present in the added sulfuric acid.

In figure 2 it is shown the redox potential relative a AgVAgCI electrode in mV dependent on time in days for the three experiments. The dotted line is for the mixture of Leptospirillum ferriphilum and Sulfobacillus

thermosulfidooxidans. The dashed line is for Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans. The line which is both dashed and dotted is for the reference experiment. As can be seen from the graph the

combination of Acidithiobacillus caldus and Sulfobacillus

thermosulfidooxidans discloses a redox potential within the desired range. As can clearly be seen in Figure 1 and Figure 2 the highest extraction of copper from chalcopyrite is gotten when the redox potential is in a range between 400 mV and 550 mV relative a AgVAgCI electrode. Outside of this range the copper extraction is much lower. This range can be achieved by using a mixture of Acidithiobacillus caldus and Sulfobacillus

thermosulfidooxidans.

Claims

1 . Method for performing a bioleaching process of chalcopyrite

comprising the steps of,

- providing a chalcopyrite containing material;

- providing microorganisms, the microorganisms oxidizing iron(ll) at a rate such that the redox potential does not rise above 550 mV relative to a AgVAgCI electrode;

- adding said microorganisms to the chalcopyrite containing

material;

- allowing reaction at said redox potential to provide copper ions.

2. The method according to claim 1 , wherein the microorganisms oxidize iron(ll) at a rate such that the redox potential is at least 400 mV relative to a AgVAgCI electrode.

3. The method according to claim 1 or 2, wherein the microorganisms oxidize sulfur at a rate such that sulfuric acid is regenerated from the degraded chalcopyrite, at redox potentials between 400 mV and 550 mV relative to a AgVAgCI electrode.

4. The method according to any of the preceding claims, wherein the microorganisms are bacteria and/or archaea.

5. The method according to any of the preceding claims, wherein the microorganisms are provided in a solution.

6. The method according to claim 5, wherein there is provided between 10⁶ to 10⁸ microorganisms per ml of microorganism containing solution.

7. The method according to any of the preceding claims, wherein an

acidic solution is provided to the chalcopyrite.

8. The method according to claim 7, wherein the acidic solution has a pH between 0.5 and 5, preferably a pH between 1 .5 and 3, most preferably a pH between 2 and 3.

9. The method according to any of claims 7 to 8, wherein the acidic

solution comprises an inorganic acid selected from the group consisting of HCI, H₃PO , H₂SO and HNO₃; preferably H₂SO .

10. The method according to any of the preceding claims, wherein said microorganisms are bacteria selected from the group consisting of

Acidithiobacillus, Acidimicrobium, Ferrithrix and Sulfobacillus, and any combination thereof; preferably from the group consisting of

1 1 .The method according to any of the previous claims, wherein the

method is performed during the initiation of said bioleaching process.