BIOLEACHING METHOD AND FACILITY

Abstract

A method for the lagoon-based bioleaching of a metallic ore, wherein the temperature of the suspension containing the metallic ore to be bioleached, a bioleaching consortium and a nutritive substrate of the microorganisms of the consortium is controlled by regulating the flows and the composition of a gas containing oxygen and optionally also CO2 injected into the suspension, the temperature of the suspension being controlled such that it can be maintained within a pre-determined range suitable for bioleaching.

Claims

1-15. (canceled)

16. Method for bioleaching of a metalliferous ore, said method comprising the following steps: a) adding, into a basin, a ground metalliferous ore, a medium comprising a bioleaching microbial consortium, and a nutritive medium for the microorganisms of the microbial consortium, b) obtaining a suspension in the basin via at least one stirring system for placing and maintaining the metalliferous ore in suspension in a liquid phase, c) injecting, into the suspension, a gas containing oxygen and optionally carbon dioxide, d) in the suspension, bioleaching of the metalliferous ore by the microbial consortium in order to obtain a released metal, e) recovering a liquid product containing the released metal and consisting of (a) a liquor and (b) a solid residue, wherein the temperature of the suspension is controlled by regulating the flow rates and the composition of the gas injected, as well as optionally the concentration of solids in the suspension, the temperature of the suspension being controlled in such a way as to be maintained in a predetermined range suitable for bioleaching.

17. Method according to claim 16, wherein the basin is an open-air basin.

18. Method according to claim 16, wherein the gas injected has an O.sub.2 concentration of at least 21% vol O.sub.2, preferably at least 40% vol and more preferably 50% vol to 100% vol, and optionally a CO.sub.2 concentration from 0% vol to 5% vol, preferably from 1% vol to 3% vol.

19. Method according to claim 16, wherein said microbial consortium comprises microorganisms chosen from the species Leptospirillum ferriphilum, Acidithiobacillus caldus and Sulfobacillus benefaciens and the combinations of at least two of said species.

20. Method according to claim 16, wherein the suspension is maintained at a pH from 0.8 to 2.5, preferably 1.0 to 1.5.

21. Method according to claim 16, wherein the suspension comprises from 15 to 40% solid by weight with respect to the total weight of the suspension, preferably 22 to 38% and more preferably 25 to 35%.

22. Method according to claim 16, wherein the stirring system comprises at least one stirrer, preferably at least one floating stirrer, said at least one stirrer being provided with at least one injector for the injection of the gas into the suspension.

23. Facility for bioleaching via lagooning, comprising: a basin, preferably an open-air basin, containing a suspension comprising a liquid phase, a ground metalliferous ore, a bioleaching microbial consortium, and a nutritive medium for the microorganisms of the microbial consortium; a stirring system for placing and/or maintaining the metalliferous ore in suspension in the liquid phase, said stirring system comprising a plurality of floating stirrers; at least one injector or the injection of a gas into the suspension, wherein said at least one injector is connected to a source of an oxygenated gas having an O.sub.2 concentration of at least 50% vol and more preferably of at least 85% vol; to a source of a dilution gas having an O.sub.2 concentration from 0 to 21% vol; optionally to a source of carbon gas that can be metabolised, having a CO.sub.2 concentration of at least 50% vol, preferably of at least 75% vol and more preferably of at least 85% vol; the facility also comprising a gas regulator for regulating the flow rate of the oxygenated gas and a dilution-gas regulator for regulating the flow rate of the dilution gas to the at least one injector and optionally also a regulator for regulating the flow rate of the carbon gas that can be metabolised to the at least one injector.

24. Facility according to claim 23, wherein the source of dilution gas is a source of nitrogen or a source of air, said source of air being preferably an air compressor.

25. Facility according to claim 23, comprising a control unit for the control of the regulator of the oxygenated gas and of the regulator of the dilution gas and optionally also of the regulator of the carbon gas that can be metabolised, in order to regulate the overall gaseous flow rate, the flow rate of O.sub.2 and optionally the flow rate of CO.sub.2 supplied to said at least one injector.

26. Facility according to claim 25, comprising at least one system for measuring temperature, for measuring the temperature of the suspension in the basin, the control unit being connected to said system for measuring temperature, the control unit regulating the flow rate of the oxygenated gas and the flow rate of the dilution gas, as well as optionally also the flow rate of carbon gas that can be metabolised, directed to the at least one injector according to the temperature measured by the system for measuring temperature in order to maintain the temperature of the suspension in a predetermined range.

27. Facility according to one of claim 23, wherein the basin does not comprise heating or cooling elements.

28. Facility according to claim 23, wherein the at least one injector is integrated into the floating stirrers.

29. Facility according to claim 23, wherein the microbial consortium comprises microorganisms chosen from the species Leptospirillum ferriphilum, Acidithiobacillus caldus and Sulfobacillus benefaciens and the combinations of said species.

30. Method for regulating temperature, for a bioleaching suspension, said suspension comprising a metalliferous ore, a bioleaching microbial consortium, and a nutritive medium for the microorganisms of the consortium, wherein in said method, the temperature of the suspension is controlled by regulating the flow rate and the composition of a gas, containing oxygen and optionally carbon dioxide, that is injected into said suspension, as well as optionally by regulating the concentration of solids in the suspension, in such a way that the temperature of the suspension is maintained in a predetermined range.

Description

[0081] The invention will be better understood by reading the examples and the drawings that follow, which are not in any way limiting and in which:

[0082] FIG. 1 is a graph representing the change in the oxidation/reduction potential (redox) and in the number of microorganisms in the pulp over time in the first example of an embodiment of the method according to the invention.

[0083] FIG. 2 represents the rates of dissolution of the metals via bioleaching, obtained in the first example of an embodiment of the method according to the invention.

[0084] FIG. 3 is a graph of the change in the temperature in the reaction mediums used in the method according to the invention of example 2.

[0085] FIG. 4 is a diagram of the method of the facility for bioleaching in basins according to example 3.

[0086] FIG. 5 is a schematic view from above of a bioleaching facility using a suspension circulator.

EXAMPLE 1

[0087] A pilot facility was created on the laboratory scale in conditions that can be easily extrapolated to the industrial scale.

[0088] The ore treated is cobalt-containing mining waste from a European mine, containing approximately 60% (by weight) pyrite (iron disulphide). This ore has a cobalt concentration of approximately 800 ppm, as well as gold at 1 ppm and copper at 1900 ppm.

[0089] A quantity of 713 kg of ore was added to a quantity of 1318 kg of nutritive medium and 226 kg of inoculum in a 2 m.sup.3 tank in order to obtain a pulp. This tank is thermally insulated in such a way that the results obtained can be easily extrapolated to a lagoon industrial use.

[0090] Indeed, the surface-to-volume ratio of such a tank is much higher than for a lagoon, the thermal losses via the edges in such a tank are therefore much greater in proportion to the volume of the suspension, and the insulation of the edges of the tank thus allows the thermal conditions reigning in the volume of a lagoon to be approached.

[0091] This pulp was inoculated with a microbial consortium from the BRGM-KCC culture, the main organisms of which are affiliated with the genera Leptospirillum, Acidithiobacillus and Sulfobacillus. This culture was transplanted several times in batch mode while progressively increasing the volume of liquid from 2 mL to 200 L.

[0092] The nutritive medium used is a medium called 9 Km. This is a 9K medium modified and optimised to allow microbial growth on cobalt-containing pyrites. The composition of said medium is the following: (NH.sub.4).sub.2SO.sub.4, 3.70 g.Math.L.sup.1; H.sub.3PO.sub.4, 0.80 g.Math.L.sup.1; MgSO.sub.4.7H.sub.2O, 0.52 g.Math.L.sup.1; KOH, 0.48 g.Math.L.sup.1.

[0093] A floating stirrer provided by the company MILTON ROY Mixing under the brand name TURBOXAL is installed on the surface of the pulp. The stirring speed is 1300 rpm. The pH at the beginning of the reaction is adjusted to 1.8 by the addition of concentrated sulphuric acid. During the reaction, the pH was controlled by the addition of calcite in such a way that the pH was never lower than 0.8.

[0094] A single floating stirrer was used in the pilot facility on the laboratory scale. In the case of facilities according to the invention on the industrial scale, the basin comprises a plurality of such floating stirrers.

[0095] FIG. 1 shows the change in the solution redox potential (Eh) and in the microbe concentration in the pulp that were measured during the bioleaching process. An increase in the redox potential, accompanied by an increase in the microbe concentration (from 2.6 10.sup.9 to 3.4 10.sup.10 microorganisms/mL), were observed.

[0096] The Eh value reached in the solution (close to 900 mV) indicates that the totality of the iron in solution is in the form of ferric iron (Fe.sup.III), which demonstrates a good microbial activity of oxidation, confirmed by the increase in the microbe concentration.

[0097] Because of this strong microbial activity, high levels of extraction of the metals are obtained. The level of cobalt in solution after 6 testing days is 86%, which indicates that 86% of the pyrite contained in the pulp was leached (see FIG. 2). These results demonstrate, in a surprising manner, that it is possible to obtain high levels of extraction by simply using a floating stirrer operating at a high stirring speed, without damaging the microorganisms (no inhibiting effect, no detrimental microbial lysis) and under lagooning conditions.

EXAMPLE 2

[0098] A pilot bioleaching facility imitating lagooning via a series of basins in cascade was created on the laboratory scale under conditions that can be easily extrapolated to an industrial case of lagoons in series.

[0099] The same sulphide ore, the same inoculum and the same stirring conditions as described in example 1 were used in a facility comprising a primary basin of 50 L (R1) and two secondary basins of 20 L (R2 and R3). The basins are fed in cascade. In R1, the gaseous mixture injected consists of 50% O.sub.2 and 1% CO.sub.2, and the flow rate is set to 316 NL/h. In R2 and R3, the flow rate and concentration of O.sub.2 were reduced since the demand for oxygen is lower than in the secondary basins (74 NL/h and 40% O.sub.2). FIG. 3 shows the change in the temperature in the basins without the use of an external temperature regulation system. It is observed that the temperature is always greater than 35 C. in the three basins, which allows strong microbial activity to be maintained. Indeed, when the temperature is lower than 35 C., the oxidising activity of the Leptospirillum, Acidithiobacillus and Sulfobacillus microorganisms is greatly reduced. Over the duration of the bioleaching, the microbial concentration remains close to 210.sup.10 microoganisms/mL, and the oxidation/reduction potential remains close to 900 mV. At the output of R3, the level of extraction of the cobalt is between 80 and 85%. This set of data demonstrates the capability of the system to self-regulate the temperature while maintaining good microbial activity and thus effective bioleaching of the sulphides.

[0100] These conditions (stirring speed, concentration of oxygen in the gas) can vary to a certain degree according to the composition of the material (sulphide and carbonate concentration, nature of the mineral species . . . ). The adaptation of these conditions is part of routine techniques.

EXAMPLE 3

[0101] An embodiment of the method according to the invention with three lagoons in series (in cascade) is shown in FIG. 4 and exemplified below.

[0102] A finely ground sulphide ore 1 is placed in a pulp at the desired solid concentration (from 15 to 40% (by weight) and for example 30% (by weight)), in a nutritive medium 2 suitable for the development of the microorganisms used for the bioleaching. The pH of the pulp is adjusted by the addition of concentrated sulphuric acid 3 in order to reach a value of approximately 1.8 (and typically from 0.8 to 1.8). The pulp is then injected into the basins 10, 20, 30 previously inoculated with an autotrophic, mesophilic to moderately thermophilic microbial consortium that combines Leptospirillum ferriphilum, Acidithiobacillus caldus and Sulfobacillus benefaciens microorganisms (for example the microbial consortium from the culture BRGM-KCC). The three types of microorganisms necessary for the bioleaching (Leptospirillum ferriphilum, Acidithiobacillus caldus and Sulfobacillus benefaciens) are available from the DSMZ strain collection.

[0103] The three lagoons are provided with floating stirrers 11, 21, 31 that carry out the mixing of the suspension and the injection and the transfer of the oxygen and of the carbon dioxide necessary for the functioning of the microorganisms and for the oxidation of the sulphides. Such stirrers are available on the market. Thus, the stirrers sold by the company MILTON ROY Mixing under the brand name TURBOXAL and described in the patent application No. EP-A-2714256 can be used to carry out the method according to the invention.

[0104] The process of bioleaching takes place in these lagoons 10, 20 30.

[0105] The use of lagoons in series allows the liquor to be concentrated. The operation thereof is the following: [0106] the lagoons 10, 20, 30 are stirred by the floating stirrers, [0107] the lagoons 10, 20, 30 are arranged to operate in series, [0108] the volume of the set of lagoons 10, 20, 30 is adapted to the flow rate of suspension in order to guarantee a minimum residence time of 6 days in the entire facility, and [0109] the feeding of the lagoons, and in particular the transfer of the pulp from one lagoon to the next lagoon and the extraction of pulp from the last lagoon 30, is carried out via pumps (not shown). The lagoons have a depth of 6 m.

[0110] At the output 32 of lagoons, a pulp consisting of a liquor rich in released, dissolved metals 33 and a solid residue 34 containing the non-leachable mineral phases is obtained, the totality of the metal released by leaching being present in dissolved form. After a step of solid/liquid separation (via decantation or filtration), the liquor is sent for refining in order to recover the metals, while the solid residue can be either recovered in order to undergo a new leaching step in other conditions (for example in order to recover the precious metals) or stored as waste.

[0111] The depth of the lagoons can vary from 2 to 10 m and the total volume of said lagoons depends on the flow rate at which pulp is fed and the residence time necessary for the leaching of the sulphides contained in the material (approximately 4 to 8 days and for example 6 days). The number of lagoons can vary, for example from 2 to 10.

[0112] The stirring speed depends mainly on the concentration of the pulp and the density of said pulp, said speed typically varies in a range from 200 to 350 rpm.

[0113] The gas injected into the pulp via the floating stirrers 11, 21, 31 comprises, by volume, approximately 1% vol CO.sub.2 (typically from 1 to 3% vol) coming from the CO.sub.2 tank 5, a variable concentration of nitrogen of less than 78% vol nitrogen, the nitrogen coming from the nitrogen tank coming from the liquefied nitrogen tank 6, and a variable concentration of oxygen of more than 21% vol, the oxygen coming from the liquefied oxygen tank 4. The gas can thus contain, for example, 49% vol nitrogen and 50% vol oxygen. The oxygen must be injected in a sufficient quantity in order to ensure the dissolution of a quantity of oxygen sufficient to allow the dissolution of the sulphides (e.g.: to dissolve 1 kg of pyrite (FeS.sub.2), 1 kg of O.sub.2 must be provided).

[0114] The oxygen can be injected in concentrated or non-concentrated form. The composition of the gas injected and the flow rate of said gas are also adjusted for each lagoon 10, 20, 30 via flow rate regulators (not shown) in order to compensate mainly for the heat generated by the reaction of oxidation of the sulphides (exothermic reaction), but also for the influence of the environment on the temperature of the pulp in the lagoons, and maintain the system at the temperature required for the functioning of the microbial consortium (between 35 C. and 48 C.)

EXAMPLE 4

[0115] FIG. 5 shows a bioleaching basin 51 containing an aqueous suspension of metalliferous ore to be treated, a bioleaching microbial consortium, and a corresponding nutritive medium.

[0116] The basin 51 is provided with a suspension circulator.

[0117] A portion of the suspension is extracted from the basin 51 by a perforated aspiration tube 52 via a pump 53.

[0118] Said portion is expelled into a recirculation circuit 56.

[0119] The circuit 56 is provided with a system 54 for the injection of a gas into a liquid phase, such as a venturi injector or a porous injector. A regulated flow of a gaseous mixture having a controlled concentration of oxygen and optionally also of CO.sub.2, from a device 55 for supplying gas, is mixed with the suspension in the recirculation circuit 56 via the gas injector 54. The gaseous mixture is carried by the suspension in the recirculation circuit and injected into the basin 51 with this suspension at reinjection points 57 distributed around the circumference of the basin. Such a suspension recirculator with integrated injection of gas can be combined with other stirring systems such as (floating) stirrers.

[0120] In order to adapt the method to the variations in ore, to the microbial activity, to the basins and to the environmental conditions that can affect the method, the following should be done: [0121] Increasing or decreasing the residence time of the pulp in the basins in order to reach the desired level of dissolution of the metals; [0122] Increasing or decreasing the gas flow rate in order to lower or raise, respectively, the temperature of the basins; [0123] Increasing the concentration of O.sub.2 in the gas (for example increasing the O.sub.2/N.sub.2 ratio) in order to increase the supply of oxygen without increasing the gas flow rate; and [0124] Controlling the operating parameters of the stirrer (in particular the speed of rotation, the diameter of the mobile element, etc.) in order to improve the suspension of the materials and homogenise the pulp.

[0125] For example, when the temperature of the system is not high enough, the O.sub.2/N.sub.2 ratio increases and the flow rate decreases. On the contrary, when the system needs to be cooled, the O.sub.2/N.sub.2 ratio decreases and the flow rate increases.

[0126] The invention is not limited to the embodiments presented, and other embodiments will be obvious to a person skilled in the art.