SYSTEM AND METHOD FOR ENHANCED METAL RECOVERY DURING ATMOSPHERIC LEACHING OF METAL SULFIDES

Abstract

A method of improving metal leach kinetics and recovery during atmospheric or substantially atmospheric leaching of a metal sulfide is disclosed. In some embodiments, the method may comprise the steps of: (a) producing a metal sulfide flotation concentrate; (b) processing the metal sulfide concentrate in a reductive activation circuit that operates at a first redox potential, to produce a reductively-activated metal sulfide concentrate; and, (c) subsequently processing the activated metal sulfide concentrate in an oxidative leach circuit to extract metal values. In some disclosed embodiments, reductive activation steps may be employed prior to oxidative leaching steps (including heap leap leaching or bio-leaching steps). In some embodiments, physico-chemical processing steps may be employed during reductive activation and/or oxidative leaching. Systems for practicing the aforementioned methods are also disclosed.

Claims

1. (canceled)

2. A method of improving metal leach kinetics and recovery during atmospheric or substantially atmospheric leaching of a metal sulfide, the method comprising: (a) producing a metal sulfide concentrate via flotation; (b) processing the metal sulfide concentrate in one or more reductive activation reactors which are held at a first redox potential, to produce a reductively-activated metal sulfide concentrate via a copper metathesis reaction; and, (c) subsequently processing the reductively-activated metal sulfide concentrate in an oxidative leach process to extract and recover metal values; wherein the reductively-processed metal sulfide concentrate comprises activated particles composed of chalcopyrite and a transitory, metastable non-stoichiometric binary metal sulfide phase with point defects substantially throughout the entirety of the activated particles.

3. A method of improving metal leach kinetics and recovery during atmospheric or substantially atmospheric leaching of a metal sulfide, the method comprising: (a) producing a metal sulfide concentrate via flotation; (b) processing the metal sulfide concentrate in one or more reductive activation reactors which are held at a first redox potential, to produce a reductively-activated metal sulfide concentrate via a copper metathesis reaction; and, (c) subsequently processing the reductively-activated metal sulfide concentrate in an oxidative leach process to extract and recover metal values; wherein the metal sulfide concentrate comprises chalcopyrite particles and wherein the reductively-processed metal sulfide concentrate comprises converted chalcopyrite particles having a transitionary metastable non-stoichiometric binary metal sulfide mineral phase which differs from covellite.

4. (canceled)

5. (canceled)

6. (canceled)

7. (canceled)

8. (canceled)

9. (canceled)

10. A method of improving metal leach kinetics and recovery during atmospheric or substantially atmospheric leaching of a metal sulfide, the method comprising: (a) producing a metal sulfide concentrate via flotation; (b) processing the metal sulfide concentrate in one or more reductive activation reactors which are held at a first redox potential, to produce a reductively-activated metal sulfide concentrate via a copper metathesis reaction; and, (c) subsequently processing the reductively-activated metal sulfide concentrate in an oxidative leach process to extract and recover metal values; wherein the step of processing the reductively-processed metal sulfide concentrate within a plurality oxidative leach reactors to extract a metal from said reductively-activated concentrate via dissolution further comprises moving the reductively-processed metal sulfide concentrate from a plurality of oxidative, stirred-tank reactors to one or more shear-tank reactors.

11. The method of claim 10, wherein the plurality of oxidative stirred-tank reactors are in series with said one or more shear-tank reactors.

12. The method of claim 10, wherein the plurality of oxidative stirred-tank reactors are in parallel with said one or more shear-tank reactors.

13. A method of improving metal leach kinetics and recovery during atmospheric or substantially atmospheric leaching of a metal sulfide, the method comprising: (a) producing a metal sulfide concentrate via flotation; (b) processing the metal sulfide concentrate in one or more reductive activation reactors which are held at a first redox potential, to produce a reductively-activated metal sulfide concentrate via a copper metathesis reaction; and, (c) subsequently processing the reductively-activated metal sulfide concentrate in an oxidative leach process to extract and recover metal values; further comprising converting an outer portion of a metal sulfide within the metal sulfide concentrate to a metastable non-stoichiometric binary metal sulfide mineral phase within the one or more reductive activation reactors so as to introduce point defects substantially throughout the entirety of the activated particle.

14. A method of extracting a metal from a metal sulfide particle, comprising: activating a metal sulfide particle by changing a portion of the metal sulfide particle from a primary metal sulfide to a non-stoichiometric, metastable binary metal sulfide phase to introduce point defects substantially throughout the entirety of the activated particle; and extracting a metal from the activated metal sulfide particle.

15. The method of claim 14, wherein extracting the metal from the activated metal sulfide particle comprises an oxidative leaching process.

16. (canceled)

17. (canceled)

18. The method of claim 14, wherein the portion of the metal sulfide particle changed to a non-stoichiometric, metastable binary metal sulfide phase is less than about one tenth of the metal sulfide particle by weight or less than about one tenth by volume.

19. The method of claim 14, wherein activating the metal sulfide particle is performed in a reductive environment ranging from about 200 to about 650 mV (SHE).

20. (canceled)

21. (canceled)

22. (canceled)

23. (canceled)

24. (canceled)

25. (canceled)

26. (canceled)

27. (canceled)

28. (canceled)

29. The method of claim 14, wherein the primary metal sulfide phase comprises chalcopyrite.

30. A method of leaching a metal sulfide concentrate, comprising: processing a metal sulfide concentrate in a reactor at a first redox potential to produce a reductively-processed metal sulfide concentrate comprising an activated particle having a non-stoichiometric metastable binary metal sulfide phase with point defects introduced substantially throughout the entirety of the activated particle; and leaching a metal from the reductively-processed metal sulfide concentrate via oxidative dissolution.

31. (canceled)

32. (canceled)

33. The method of claim 30, wherein the non-stoichiometric metastable binary metal sulfide phase comprises less than about 10 wt. % or less than about 10 vol. % of the activated particle.

34. The method of claim 30, wherein the oxidative dissolution occurs in an oxidative leach reactor at a second redox potential greater than a rest potential of the activated particle.

35. The method of claim 30, wherein the first redox potential ranges from about 200 to about 650 mV (SHE).

36. The method of claim 30, wherein the second redox potential ranges from about 600 to about 750 mV (SHE).

37. The method of claim 30, wherein the metal sulfide concentrate comprises chalcopyrite.

38. The method of claim 30, wherein the metal leached from the metal sulfide concentrate is copper.

39. A method of extracting a metal from a metal sulfide particle, comprising: activating a metal sulfide particle by changing a portion of the metal sulfide particle from a primary metal sulfide to a binary metal sulfide phase; and if there is a sufficient amount of activated binary metal sulfide present, extracting a metal from the metal sulfide by an oxidative leach process.

40. The method of claim 39, wherein the oxidative leach process substantially reduces the physical and electrochemical passivation of the activated metal sulfide particle by a physicochemical process.

41. The method of claim 39, wherein the binary metal sulfide phase comprises a non-stoichiometric metastable binary metal sulfide phase with point defects substantially throughout the entirety of the activated particle.

42. (canceled)

43. (canceled)

44. The method of claim 41, wherein the non-stoichiometric metastable binary metal sulfide phase comprises less than about 10 wt. % or less than about 10 vol. % of the activated metal sulfide particle.

45. A process for extracting a metal from a metal sulfide, comprising an oxidative leach of a metal sulfide particle that substantially reduces both the electrochemical passivation and mechanical passivation of a metal sulfide particle via a physicochemical mechanism.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] To complement the description which is being made, and for the purpose of aiding to better understand the features of the invention, a set of drawings illustrating preferred processing apparatus and methods of using the same is attached to the present specification as an integral part thereof, in which the following are depicted as illustrative and non-limiting character. It should be understood that like reference numbers used in the drawings (if any are used) may identify like components.

[0050] FIG. 1 is a schematic diagram illustrating a non-limiting, exemplary flowsheet which might employ certain embodiments of the invention.

[0051] FIG. 2 is a schematic diagram illustrating, in more detail, a portion of the non-limiting, exemplary flowsheet shown in FIG. 1, wherein a reductive activation/pretreatment step may be performed prior to an oxidative atmospheric (or substantially atmospheric) metal sulfide leach process.

[0052] FIG. 3 is a schematic diagram illustrating a system and method of providing a reductive activation step prior to an oxidative atmospheric (or substantially atmospheric) metal sulfide leach, according to some embodiments.

[0053] FIG. 4 is a schematic diagram illustrating a system and method of using a reductive activation and/or a reductive pre-treatment step which may be employed in heap leach operations.

[0054] FIG. 5 suggests a method for enhancing metal recovery from metal sulfides and/or for enhancing leach kinetics of metal sulfides according to some embodiments which may be utilized for various forms of leaching including, but not limited to, vat leaching, tank leaching, heap leaching, bio-leaching, and/or the like, without limitation.

[0055] FIG. 6 suggests a method for enhancing metal recovery from metal sulfides and/or for enhancing leach kinetics of metal sulfides according to some embodiments; particularly for leaching metal sulfide concentrates.

[0056] FIG. 7 suggests a method for enhancing metal recovery from metal sulfides and/or for enhancing leach kinetics of metal sulfides according to some embodiments; particularly for heap leaching metal sulfide ores.

[0057] FIG. 8 suggests several exemplary and non-limiting arrangements of shear-tank reactors and a plurality of stirred-tank reactors within an oxidative metal sulfide leach circuit. It should be understood that the particular arrangement depicted in FIG. 8 has been provided merely to illustrate several different possible cooperative structural relationships between shear-tank reactors and stirred-tank reactors within the same figure, and therefore, variant embodiments should not be limited to the particular configuration shown. Accordingly, anticipated embodiments may practice as little as one of the particular configurations shown; anticipated embodiments may practice more than one of the particular configurations shown; anticipated embodiments may contain any pattern or sequence of the particular configurations shown; and anticipated embodiments may contain one or more of the particular configurations redundantly, without limitation.

[0058] In the following, the invention will be described in more detail with reference to drawings in conjunction with exemplary non-limiting embodiments.

DETAILED DESCRIPTION OF THE INVENTION

[0059] The following description of the non-limiting embodiments shown in the drawings is merely exemplary in nature and is in no way intended to limit the inventions disclosed herein, their applications, or uses.

[0060] As schematically shown in FIG. 1, embodiments of the invention may comprise a metal recovery flowsheet 10 having a unit operation 12. The unit operation 12 may comprise an atmospheric or substantially atmospheric metal sulfide leach circuit 200 downstream of a sulfide concentrator circuit 100, without limitation. Peripheral flowsheet operations, typical to such processes known to those skilled in the art of minerals processing, are not shown.

[0061] In some preferred embodiments, most or all of the oxidative leaching may occur at atmospheric pressure conditions. In some embodiments, a small amount of oxidative leaching (e.g., leaching occurring within one or more optional, but preferred shear-tank reactors) may occur at atmospheric conditions or optionally above atmospheric conditions.

[0062] In some preferred embodiments, a majority of the cumulative leaching time may occur at atmospheric pressure conditions, and a minimal amount of cumulative leaching time may occur above atmospheric conditions. For example, in some non-limiting embodiments, an oxidative leach reactor 202, such as the one shown in FIGS. 2, 3, and 8, may comprise one or more continuous stirred-tank reactors (CSTRs). The shear-tank reactors may comprise one or more enclosed stirred media reactors which are preferably configured to be pressurized (e.g., to 1-20 bar, 1-10 bar, 1-5 bar, approximately 5 bar, or the like), receive oxygen, an oxygen containing gas, and/or contain grinding media, without limitation.

[0063] In some embodiments, a shear-tank reactor 212 may comprise one or more enclosed high shear stirred reactors configured to be pressurized (e.g., to 1-20 bar, 1-10 bar, 1-5 bar, approximately 5 bar, or the like), receive oxygen, and/or impart shear by using one or more high shear impellers and/or pumping blades, without limitation. In some embodiments, the high shear impellers may be selected from the group consisting of: a Cowles disperser blade, a sawblade mixing impeller, a dispersion blade, a saw tooth dispersion blade, an angled tooth blade, an ultra-shear dispersion blade, a high-flow dispersion blade, a rotor/stator, and a combination thereof, without limitation.

[0064] In some embodiments, the plurality of oxidative leach reactors 202 may be operatively coupled to a shear-tank reactor 212 in parallel, in series, or a combination thereof (as suggested in FIG. 8). In some preferred embodiments, a shear-tank reactor 212 is placed in series, i.e., interposed between two oxidative, stirred tank reactors 202.

[0065] In some preferred embodiments, the volume of a shear-tank reactor 212 may be relatively less than the volume of an oxidative stirred tank reactor 202. In some preferred embodiments, the energy consumed by a shear-tank reactor 212 may be relatively more than the energy consumed by an oxidative stirred tank reactor 202.

[0066] In some embodiments (not shown), the one or more shear-tank reactors 212 may be omitted from the atmospheric or substantially atmospheric metal sulfide leach circuit 200 altogether. This arrangement can be advantageously used in those cases where a high-grade concentrate is first ground to an ultra-fine size distribution prior to reductive activation and downstream oxidative leaching.

[0067] If one or more separate shear-tank reactors 212 are utilized in combination with a plurality of oxidative stirred-tank reactors 202, then slurry recycle may be employed within the oxidative leach process.

[0068] Dissolved copper is provided to enable the reductive activation process to proceed. The amount of dissolved copper provided should be sufficient to complete the desired degree of conversion from the primary metal sulfide to the metastable, non-stoichiometric binary metal sulfide. The residence time required to complete the activation processing is typically between approximately 5 and 60 minutes. For example, a residence time of approximately 10-45 minutes, or a residence time of approximately 15-30 minutes, such as 20 minutes, may be sufficient prior to moving on to a downstream oxidative leach step. The activated metal sulfide concentrate 116 may be optionally re-ground in step 216, or sent directly to an oxidative leach circuit 202.

[0069] Pregnant leach solution (PLS) 204 created during the atmospheric or substantially atmospheric leaching of the metal sulfide concentrate 116 may be sent from the oxidative leach circuit 200 to a downstream solvent extraction/electrowinning (SX/EW) circuit, or direct electrowinning (D/EW) process.

[0070] Raffinate 206 may be recycled from the respective downstream solvent extraction/electrowinning (SX/EW) circuit, or direct electrowinning (D/EW) processes, and sent back to the oxidative leach circuit 200. Leach residues formed within the atmospheric or substantially atmospheric metal sulfide leach circuit 200 may be sent to a precious metals recovery circuit and/or ultimately to a leach residues disposal area as suggested by FIG. 1. While not expressly shown, leach residue sulfur may be internally or externally processed/recovered/removed, in order to create sulfuric acid which can re-supply the leach processes within the metal recovery flowsheet 10, such as the activation circuit 220 and/or the oxidative 202 leach circuit. Manufactured sulfuric acid produced from the elemental sulfur may also be sent to another unit operation(s), or may be sold or distributed outside of the flowsheet 10, as a salable byproduct to help offset flowsheet 10 operating costs.

[0071] In some embodiments, a bleed stream 233 may be separated from the main flow of reductive activated product 231 as shown in FIG. 3. The bleed stream 233 enters a solid/liquid separation circuit 222 which may comprise equipment such as a filter, thickener, centrifuge, cyclone, dewatering screen, or the like, without limitation. The solid fraction 224 leaving the solid/liquid separation circuit 222 may be recombined with the activated concentrate to be processed in the oxidative leach circuit 202. The liquid fraction 226 leaving the solid/liquid separation circuit 222 may enter one or more downstream processes for recovering other metals, or impurities removal, without limitation.

[0072] “Reductive activation”, where described herein, may comprise any metathesis or pre-treatment step, process, system, or device which is capable of converting at least a portion of a leach particle from a first mineral phase to a transitionary mineral phase. For example, a “reductive activation” pretreatment step or circuit may be configured to change or convert an outer surface of a leach particle from a primary metal sulfide (e.g., chalcopyrite) to a metastable non-stoichiometric binary metal sulfide phase which differs from chalcopyrite and covellite. In some embodiments, a reductive activation step, may completely or partially modify, disturb, damage, or alter the crystal lattice sufficiently to enhance the oxidative dissolution process whereby the leach time to reach approximately 95% metal recovery can be achieved in about 6 hours or less.

[0073] In some instances, chalcopyrite leach particles may undergo a reductive activation/reductive pre-treatment step in the one or more reductive leach reactors 220, wherein at least a portion of the outer surface product layers of the chalcopyrite leach particles may be at least partially transformed to a transitionary mineral phase comprising a metastable non-stoichiometric binary metal sulfide phase, wherein the chalcopyrite leach particles are not fully converted to a secondary metal sulfide phase such as covellite. For example, less than about half of each particle may be converted to said transitionary mineral phase, and more preferably, less than about 10% of each particle, but more than 50% of each particle outer surface may be converted to said transitionary mineral phase, and therefore, residence time of the metal sulfide concentrate 116 within the reductive activation process may be kept to a minimum.

[0074] In some instances, the activation may require conversion of 0.01 to 50% of the primary sulfide; or alternatively may require conversion of 0.01 to 40% of the primary metal sulfide; or alternatively may require conversion of 0.01 to 30% of the primary sulfide; or alternatively may require conversion of 0.01 to 20% of the primary sulfide; or alternatively may require conversion of 0.01 to 10% of the primary sulfide; for example conversion of as little as 2 to 8% of the primary sulfide. The extent of conversion to a metastable non-stoichiometric binary metal sulfide phase is carried out so as to introduce point defects substantially throughout the entirety of the activated particle.

[0075] Redox potential may, in some instances, vary within the reductive activation process as a function of time or within various reductive leach reactors 220. In some instances, the reductive process may comprise a different pH than a pH maintained during the subsequent oxidative leach. In some instances, the reductive activation may comprise a different redox potential than the subsequent oxidative leach. For example, the measured redox potential within the activation circuit 220 may fall within the range of approximately 200 mV (SHE) to about 650 mV (SHE), wherein portions of the chalcopyrite leach particles may be converted to a transitionary, mineral phase comprising a metastable, non-stoichiometric binary metal sulfide phase. Measured redox potential within the oxidative leach circuit, may fall within the range of approximately 600 mV (SHE) to about 800 mV (SHE). These redox potentials may change or fluctuate with time or depending on the composition of concentrate and/or the metal value desired to be recovered from the concentrate.

[0076] In some embodiments, the metal sulfide concentrate 116 (e.g., copper sulfide concentrate) may comprise residual flotation reagents. In some preferred embodiments, the metal sulfide comprises copper in the form of Chalcopyrite (CuFeS.sub.2), and/or Covellite (CuS). However, it should be known that other metal-bearing minerals occurring in combination with metal sulfides (e.g., including Acanthite Ag.sub.2S, Chalcocite Cu.sub.2S, Bornite Cu.sub.5FeS.sub.4, Enargite Cu.sub.3AsS.sub.4, Tennantite Cu.sub.12As.sub.4S.sub.13, Tetrahedrite Cu.sub.3SbS.sub.3.x(Fe, Zn).sub.6Sb.sub.2S.sub.9, Galena PbS, Sphalerite ZnS, Chalcopyrite CuFeS.sub.2, Pyrrhotite Fe.sub.1-xS, Millerite NiS, Pentlandite (Fe,Ni).sub.9S.sub.8, Cinnabar HgS, Realgar AsS, Orpiment As.sub.2S.sub.3, Stibnite Sb.sub.2S.sub.3, Pyrite FeS.sub.2, Marcasite FeS.sub.2, Molybdenite MoS.sub.2, Malachite CuCO.sub.3.Cu(OH).sub.2, Azurite 2CuCO.sub.3.Cu(OH).sub.2, Cuprite Cu.sub.2O, Chrysocolla CuO.SiO.sub.2.2H.sub.2O) may be used with the disclosed systems and methods.

[0077] In some embodiments, portions of the atmospheric or substantially atmospheric metal sulfide leach circuit 200, such as the plurality of oxidative leach reactors 202, may be maintained below a pH of about 1.8 (e.g., between a pH of 0.5 and a pH of about 1.2).

[0078] In some preferred embodiments, the atmospheric or substantially atmospheric metal sulfide leach 200 may be maintained at a temperature which is below the melting point of elemental sulfur, to control passivation of the leaching particles.

[0079] It should be known that the particular features, processes, and benefits which are shown and described herein in detail are purely exemplary in nature and should not limit the scope of the invention. For example, where used herein, and in related co-pending applications referenced herein, the term “atmospheric leach” may comprise leaching under very small amounts of pressure which are close, but not exactly, ambient. In other words, while it is most preferred that “atmospheric” leaching is performed completely open to air, it is anticipated by the inventors that some best modes of leaching using the inventive concepts may incorporate the use of a plurality of stirred-tank reactors 202 which are open to air, and one or more smaller shear-tank reactors 212 which may be pressurizable (e.g., to 1-10 bar) to overcome oxygen transfer limitations. Accordingly, portions of the oxidative metal sulfide leach 200 may be performed under slight pressure (e.g., in a covered or pressurizable vessel) or completely atmospherically (e.g., in a plurality of non-pressurized stirred-tank reactors).

[0080] It is further anticipated that in preferred embodiments, most (e.g., up to approximately 95%) of the cumulative oxidative leach time of a metal sulfide leach particle may occur at atmospheric conditions, while less than approximately 10% of the cumulative oxidative leach time may occur at or above atmospheric conditions, giving rise to the term “substantially atmospheric” used throughout this description.

[0081] Without departing from the intent of the invention, reductive and/or oxidative reactor head space may be atmospheric or alternatively pressurized to above ambient pressure to enhance oxygen mass transfer. The pressure may be controlled by temperature and/or by an applied gas pressure that is above ambient pressure. It is anticipated that above-atmospheric pressures, where/if used, may approach as much as 20 bar, but are preferably kept between about 1 bar and about 10 bar, for example, approximately 5 bar, without limitation.

[0082] Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.