ACTIVATION SYSTEM AND METHOD FOR ENHANCING 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 step of processing a metal sulfide concentrate in a reductive activation circuit 220 that operates at a first redox potential, to produce a reductively-activated metal sulfide concentrate. The method may further comprise the step of subsequently processing the activated metal sulfide concentrate in an oxidative leach circuit 240 to extract metal values. In some disclosed embodiments, reductive activation steps and/or oxidative dissolution steps may employ mechano-chemical and/or physico-chemical processing of particles or agglomerates thereof. Reductive activation may be made prior to heap leaching or bio-leaching operations to improve metal extraction. Systems for practicing the aforementioned methods are also disclosed.

Claims

1) (canceled)

2) A metal sulfide leach circuit 200 having therein, a reductive activation circuit 220 configured for performing low-yield metathesis reactions which are capable of producing an iron-depleted metastable phase on metal sulfide leach particles, wherein the reductive activation circuit 220 is configured such that the low-yield metathesis reactions produce the iron-depleted metastable phase at outer surface portions of the metal sulfide leach particles.

3) The metal sulfide leach circuit 200 according to claim 2, wherein the reductive activation circuit 220 is configured such that the low-yield metathesis reactions produce the iron-depleted metastable phase at inner portions of the metal sulfide leach particles which are below outer surface portions of the metal sulfide leach particles.

4) The metal sulfide leach circuit 200 according to claim 2, wherein the reductive activation circuit 220 is configured such that the low-yield metathesis reactions produce point defects within a portion of each of the metal sulfide leach particles.

5) The metal sulfide leach circuit 200 according to claim 2, wherein the reductive activation circuit 220 is configured such that the low-yield metathesis reactions produce point defects substantially entirely throughout the metal sulfide leach particles.

6) The metal sulfide leach circuit 200 according to claim 2, wherein a portion of the iron-depleted metastable phase comprises an intermediate phase between chalcopyrite and covellite.

7) The metal sulfide leach circuit 200 according to claim 2, wherein a portion of the iron-depleted metastable phase is transitory, transitionary, or metastable.

8) The metal sulfide leach circuit 200 according to claim 2, further comprising means for controlling the low-yield metathesis reactions to limit the production of the iron-depleted metastable phase on the metal sulfide leach particles to between about 0.01% and about 10% by weight or volume of the metal sulfide leach particles.

9) (canceled)

10) (canceled)

11) (canceled)

12) (canceled)

13) (canceled)

14) (canceled)

15) (canceled)

16) The metal sulfide leach circuit 200 according to claim 2, wherein the reductive activation circuit 220 comprises at least one stirred-tank reactor 202.

17) The metal sulfide leach circuit 200 according to claim 2, wherein the reductive activation circuit 220 comprises at least one shear-tank reactor 212.

18) The metal sulfide leach circuit 200 according to claim 2, wherein at least one stirred-tank reactor 202 and at least one shear-tank reactor are configured in series within the reductive activation circuit 220.

19) The metal sulfide leach circuit 200 according to claim 2, wherein the at least one stirred-tank reactor 202 and at least one shear-tank reactor are configured in parallel within the reductive activation circuit 220.

20) The metal sulfide leach circuit 200 according to claim 2, wherein at least one shear-tank reactor 212 is disposed within at least one stirred-tank reactor within the reductive activation circuit 220.

21) The metal sulfide leach circuit 200 according to claim 2, further comprising an oxidative leach circuit 240 for leaching the metal sulfide leach particles comprising the iron-depleted metastable phase.

22) The metal sulfide leach circuit 200 according to claim 21, wherein the oxidative leach circuit 240 comprises at least one stirred-tank reactor 202.

23) The metal sulfide leach circuit 200 according to claim 21, wherein the oxidative leach circuit 240 comprises at least one shear-tank reactor 212.

24) The metal sulfide leach circuit 200 according to claim 22, wherein the at least one stirred-tank reactor 202 and at least one shear-tank reactor 212 are configured in series within the oxidative leach circuit 240.

25) The metal sulfide leach circuit 200 according to claim 22, wherein the at least one stirred-tank reactor 202 and at least one shear-tank reactor 212 are configured in parallel within the oxidative leach circuit 240.

26) The metal sulfide leach circuit 200 according to claim 22, wherein at least one shear-tank reactor 212 is disposed within the at least one stirred-tank reactor 202 within the oxidative leach circuit 240.

27) The metal sulfide leach circuit 200 according to claim 21, wherein oxidative dissolution within the oxidative leach circuit 240 is substantially independent of the degree of completion of the conversion of the metal sulfide particles to the iron-depleted metastable phase.

28) (canceled)

29) (canceled)

30) The metal sulfide leach circuit 200 according to claim 2, wherein a residence time of the metal sulfide leach particles in the reductive activation circuit 220 is less than 1 hour.

31) (canceled)

32) (canceled)

33) (canceled)

34) (canceled)

35) The metal sulfide leach circuit 200 according to claim 2, wherein a portion of the metal sulfide leach circuit 200 is maintained at a temperature which is less than the melt temperature of elemental sulfur.

36) (canceled)

37) (canceled)

38) (canceled)

39) The metal sulfide leach circuit 200 according to claim 2, wherein a portion of the reductive activation circuit 220 operates at solids concentrations exceeding 10% solids.

40) (canceled)

41) (canceled)

42) (canceled)

43) (canceled)

44) (canceled)

45) (canceled)

46) (canceled)

47) (canceled)

48) The metal sulfide leach circuit 200 according to claim 2, wherein the reductive activation circuit 220 operates at pH values between about 1 and about 6.

49) (canceled)

50) The metal sulfide leach circuit 200 of claim 21, wherein the metal sulfide leach circuit 200 is configured for achieving chalcopyrite dissolution levels in excess of 90% in 9 hours or less.

51) (canceled)

52) (canceled)

53) (canceled)

54) (canceled)

55) The metal sulfide leach circuit 200 according to claim 2, wherein an activation process within the reductive activation circuit 220 is substantially free of parasitic side reactions which consume Cu++.

56) The metal sulfide leach circuit 200 according to claim 17, wherein the at least one shear-tank reactor 212 operates at a mixing energy higher than a stirred-tank reactor 202 in the metal sulfide leach circuit 200.

57) The metal sulfide leach circuit 200 according to claim 56, wherein the at least one stirred-tank reactor 202 operates at a mixing energy between approximately 0.1 and 0.5 kW/m3.

58) The metal sulfide leach circuit 200 according to claim 17, wherein the at least one shear-tank reactor 212 operates at a mixing energy between approximately 5 and 100 kW/m3.

59) The metal sulfide leach circuit 200 according to claim 17, wherein the volumetric ratio of the at least one shear-tank reactor 212 to at least one stirred-tank reactor 202 in the metal sulfide leach circuit 200 is between approximately 1:2 and 1:200.

60) (canceled)

61) (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] 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 apparatus and methods of using the same is attached to the present specification as an integral part thereof, in which the following has been depicted with an 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.

[0038] FIG. 1 is a schematic diagram illustrating a non limiting, exemplary metal recovery flowsheet which might employ certain aspects of the invention, wherein a reductive activation circuit 220 is employed, for example, upstream of oxidative leach circuit 240. Novel shear-tank reactors 212 may optionally be employed to the reductive activation circuit 202 as shown, without limitation. One or more stirred-tank reactors 202 may be employed in the reductive activation circuit 220 as shown.

[0039] FIGS. 2-5 illustratively show results obtained via bench-scale testing using the circuit shown in FIG. 6, wherein feed concentrate was activated within a reductive activation circuit to produce particles comprising a transitory/transitionary metastable non-stoichiometric binary metal sulfide phase.

[0040] FIGS. 2 and 4 show results of oxidatively leaching activated concentrates, according to certain embodiments.

[0041] FIG. 3 shows copper uptake during activation within a reductive activation circuit, according to certain embodiments.

[0042] FIG. 5 suggests a range of reaction rates for leaching enargite according to certain embodiments.

[0043] FIG. 6 is a schematic diagram illustrating a non-limiting, exemplary circuit which may be used to obtain batch leach test measurements.

[0044] FIG. 7 is a schematic diagram illustrating a non-limiting, exemplary flowsheet which might employ certain embodiments of the invention.

[0045] FIG. 8 is a schematic diagram illustrating, in more detail, a portion of the non-limiting, exemplary flowsheet shown in FIG. 7, wherein a reductive activation/pretreatment step may be performed prior to an oxidative atmospheric (or substantially atmospheric) metal sulfide leach process.

[0046] FIG. 9 is a schematic diagram illustrating a system and method of providing a reductive activation step prior to an oxidative atmospheric, substantially atmospheric, or above-atmospheric metal sulfide leach, according to some embodiments.

[0047] In the following, the invention will be described in more detail with reference to drawings in conjunction with exemplary embodiments.

DETAILED DESCRIPTION OF THE INVENTION

[0048] 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.

[0049] FIG. 1 suggests a metal sulfide leach circuit 200 of a metal recovery flowsheet 110, wherein concentrate 1 (e.g., a flotation concentrate 116 from a sulfide concentrator 100) enters a re-pulp tank (labeled “Repulp”), wherein additional acid and/or oxygen (not shown) may be added to the re-pulp tank. Re-pulped concentrate 2 may enter a grinding operation. The grinding operation (labeled “Regrind”) may optionally comprise one or more shear-tank reactors 212 arranged in series, or it may comprise a number of mills, such as fine grinding mills. Re-ground slurry 3 leaving the grinding operation enters a reductive activation circuit 220 within the metal sulfide leach circuit 200. The reductive activation circuit 220 may comprise one or more stirred-tank reactors 202, which may optionally have sparging means equipped to sparge a reactant gas, liquid, or gas/liquid combination 301, 302 therein. As shown, more than one stirred-tank reactor 202 may be employed within the reductive activation circuit 220, without limitation. As shown, stirred-tank reactors 202 may be arranged in series, without limitation.

[0050] hi some embodiments, one, some, or all portions of the activation circuit 220 may be fed with a copper source. For example, in some embodiments, one or more stilted-tank reactors 202 within the reductive activation circuit 220 may be operatively fed by a feed stream 72 comprising copper. In some embodiments, one or more shear-tank reactors 212 within the reductive activation circuit 220 may be operatively fed by a feed stream 72 comprising copper. In some embodiments, the re-pulp tank may be operatively fed by a feed stream 72 comprising copper. In some embodiments, the grinding operation may be operatively fed by a feed stream 72 comprising copper. The source of the copper in the feed stream 72 may comprise, without limitation, copper sulfate derived from off-spec copper cathode, raffinate comprising copper, electrolyte comprising copper, pregnant leach solution comprising copper (e.g., pregnant leach liquor from a copper heap leach operation), or the like, without limitation.

[0051] Optionally, one or more shear-tank reactors 212 (labeled “SMRt”) may optionally be employed within the reductive activation circuit 220. While not shown, a shear-tank reactor 212 may be arranged in series between stirred-tank reactors 202, e.g., in an inter-stage configuration, without limitation. While not shown, a shear-tank reactor 212 may be arranged inside of a stirred-tank reactor 202, e.g., in an in-situ configuration, without limitation. In some embodiments, as shown, a shear-tank reactor 212 may be arranged in parallel with a stirred-tank reactor 202, in an intra-stage configuration, without limitation. In this regard, a shear-tank reactor 212 may process slurry 100 leaving, a stirred-tank reactor 202, and return shear-processed slurry 212 back to the same respective stirred-tank reactor 202. In some embodiments, a shear-tank reactor 212 may be arranged in series with another shear-tank reactor 212, without limitation.

[0052] Slurry 5 leaving the reductive activation circuit 220 may enter a filter (labeled “Filter”), where a liquid component 74 may be separated from a solid component 6. The liquid component 74 may comprise iron and processing solution used in the reductive activation circuit 220. The filter may, accordingly, be utilized to bleed iron from the metal sulfide leach circuit 200. Activated particles within the solid component 6 may then enter an oxidative leach circuit 240. As shown, the oxidative leach circuit 240 may comprise at least one stirred-tank reactor 202. The at least one stirred-tank reactor 202 may receive raffinate 73 (e.g., from a solvent/extraction process). The at least one stilled-tank reactor 202 may comprise sparging means equipped to sparge a reactant gas, liquid, or gas/liquid combination 303. Oxidatively-processed slurry 7 continues downstream. As suggested in FIG. 8, and taught in co-pending application PCT/US2015/061761, the oxidative leach circuit 240 may comprise one or more shear-tank reactors 212, without limitation.

[0053] Turning to FIG. 7, a metal recovery flowsheet 110 may comprise a unit operation 112 having therein, a sulfide concentrator 100 and a metal sulfide leach circuit 200. The metal sulfide leach circuit 200 may receive raffinate 206 from a solvent extraction operation, and may deliver pregnant leach solution 204 to a solvent extraction operation. Optionally, precious metals may be recovered from leach residue from the metal sulfide leach circuit 200.

[0054] Turning now to FIG. 8, concentrate 116 leaving the sulfide concentrator 100 may enter an optional re-grind step 216 in a metal sulfide leach circuit 200. The concentrate 116 or re-ground concentrate leaving the optional re-grind step 216 is processed in a reductive activation circuit 220 within the metal sulfide leach circuit 200. The reductive activation circuit 220 may comprise a number of stirred-tank reactors 202 and/or a number of shear-tank reactors 212 as shown, without limitation. Slurry 231 leaving the reductive activation circuit 220 may enter an optional re-grind step 216. The slurry 231 or re-ground slurry leaving the optional re-grind step 216 may then be processed in an oxidative leach circuit 240 within the metal sulfide leach circuit 200. The oxidative leach circuit 220 may comprise a number of stirred-tank reactors 202 and/or a number of shear-tank reactors 212 as shown, without limitation. A portion of raffinate 206 may optionally be sent back to one or more portions of the reductive activation circuit 220 as a copper source.

[0055] In the following, the invention will be described in more detail with reference to drawings in conjunction with exemplary embodiments.

EXAMPLE 1

[0056] In this Example we describe the use of a unique Physico-chemical activation process, involving the use of a shear-tank reactor 212, to enhance the oxidative leaching of chalcopyrite under atmospheric conditions to produce greater than 97% copper recoveries in under 4 hours.

[0057] Contrary to prior approaches which focused on high-yield metathesis reactions for complete conversions of chalcopyrite to other copper sulfides in order to facilitate secondary sulfide leaching, the inventors have unexpectedly discovered that low-yield metathesis reactions are much more effective and economical for leaching primary metal sulfides. These low-yield metatheses reactions may be advantageously utilized as a pre-activation process via a reductive activation circuit 220, prior to oxidative leaching in an oxidative leach circuit 240. Accordingly, it may be desirable to provide a reductive activation circuit 220 which is adequately configured to produce these low-yield metathesis products.

[0058] While not being held to any one particular theory, it is believed that the unexpectedly improved efficiency during oxidative leaching is achieved because embodiments of the inventive method have been shown to produce modified metal sulfide particles comprising a novel synthetic transitory/transitionary metastable non-stoichiometric binary metal sulfide phase which avoids parasitic side reactions found in prior art methods using high-yield metathesis reactions. Moreover, it is believed that the unexpectedly improved efficiency may be because with embodiments of the inventive method, leach kinetics and metal recovery during oxidative dissolution are, beyond a certain point, independent of the degree of solid state conversion of the modified metal sulfide particles. Preferred embodiments of the present inventive method, therefore, require only low-yield metathesis which can be conducted under atmospheric conditions, in short periods of time (e.g., from several hours to as little as only several minutes). This Example illustrates a two-stage process coupling Physico-Chemical activation with oxidative dissolution. In stage one, the primary sulfide (e.g., chalcopyrite) is treated reductively to only partially convert a small amount of chalcopyrite to an activated, non-stoichiometric product covellite, wherein iron is only partially exchanged by copper as illustrated by the equation:

Cu.sub.xFe.sub.yS.sub.2+ZCuSO.sub.4.fwdarw.Cu.sub.x+zFe.sub.y−zS.sub.2+ZFeSO.sub.4

[0059] The fractional extent of conversion to the activated product is calculated as (Z/X).

[0060] In the present method, exposed surfaces of the chalcopyrite mineral phases are at least partially converted to a meta-stable, non-stoichiometric binary metal sulfide with the avoidance of parasitic side reactions that are characteristic of prior art methods. Without being held to any particular theory, we believe that partial conversion leads to the generation of point defects and to extensive crystal lattice strain, both of which in turn lead to enhanced oxidative leaching of chalcopyrite during stage two of the inventive method. Evidence for lattice strain was clearly visible as peak broadening in the x-ray diffraction pattern of the activated product.

[0061] In this example, a setup such as that shown in FIG. 6 was utilized, wherein a shear-tank reactor 212 was operatively coupled to a stirred-tank reactor 202. The shear-tank reactor 212 was configured as a stirred media reactor comprising grinding media. The only copper-bearing mineral in the copper concentrate feed was chalcopyrite. The P80 of the copper concentrate was 61 μm. The Physico-Chemical activation was conducted at 8% solids, pH≈1.8 and 80° C. The concentrate slurry contained an initial 2 g L.sup.−1 total iron, 22.6 g L.sup.−1 copper as copper sulfate. During the course of the Physico-Chemical activation process, iron within the chalcopyrite lattice was exchanged by copper in solution. During the activation step, the slurry redox potential dropped from about 565 mV to about 540 mV due to the release of Fe.sup.2+. After 5.5 hours, the residual copper concentration in solution was about 16.8 g L.sup.−1, giving an estimated conversion of chalcopyrite to covellite. of approximately 29%. XRD analysis of the reaction product showed the absence of secondary, parasitic reaction products like Cu.sub.2S which are present in prior art metathesis processes.

[0062] Although prior art methods have employed high-yield chemical metathesis reactions in which chalcopyrite is converted to copper sulfides, such as CuS, Cu.sub.2S, etc., as a potential method for improving copper concentrate grades prior to treatment by pyrometallurgical processes (see for example R. D. Peterson and M. E. Wadsworth, “Solid, Solution Reactions in the Hydrothermal Enrichment of Chalcopyrite at Elevated Temperatures,” EPD Congress 1994, The Minerals, Metals & Materials Society, pp. 275-291), embodiments of the present invention require only partial amounts of metastatic conversion, with the unexpected benefits of a metathesis reaction that avoids parasitic side reactions, and enhances oxidative dissolution of even un-converted, but surface-modified, chalcopyrite.

EXAMPLE 2

[0063] In this Example we further describe the use of Physico-Chemical activation to enhance the oxidative leaching of chalcopyrite. In stage one, the chalcopyrite is treated reductively to partially convert chalcopyrite to a metastable, non-stoichiometric binary copper sulfide according to the following reaction stoichiometry:

Cu.sub.xFe.sub.yS.sub.2+ZCuSO.sub.4.fwdarw.Cu.sub.x+zFe.sub.y−zS.sub.2+ZFeSO.sub.4

[0064] The reductive activation was conducted completely within a shear-tank reactor 212 at 80° C., a solids concentration of 15%, pH≈1.8, and enough copper sulfate to yield approximately 6.5% conversion of chalcopyrite. In this example, the shear-tank reactor was configured as a stirred media reactor comprising grinding media. The molar ratio of the initial solution copper to soluble iron which was contained within the concentrate feed was 0.066. The chalcopyrite concentrate, having a particle size distribution with a P80 of 17.5 μm, along with 2.5 g L.sup.−1 copper sulfate and 2 g L.sup.−1 ferrous sulfate were charged into the shear-tank reactor and the chalcopyrite was reductively activated with Cu.sup.2° for one hour.

[0065] The total mixing energy during the activation step was 72 kW.Math.h/tonne. Concomitantly, the soluble-copper concentration dropped from about 2.5 g L.sup.−1 to below detection as a result of the solid-state exchange reaction between cupric ion and ferrous ion located within the chalcopyrite crystal lattice.

[0066] The theoretical yield of the exchange reaction was 6.5%, relative to the initial amount of chalcopyrite present. While the exchange reaction in this test as allowed to continue for about an hour, the soluble copper was depleted within about 15-20 min. This indicates that Shorter reaction films (i.e., less than about 5 min.) might be equally effective and suggests that the mixing energy in this step could be reduced from 72 kW.Math.h/tonne to under 25-100 kW.Math.h/tonne.

[0067] At the completion of the Physico-Chemical activation, the slurry was transferred to the stirred-tank 202 reactor and the copper was leached oxidatively with O.sub.2 sparging. The slurry Eh increased from less than 50 mV to approximately 650-655 mV during the course of the copper dissolution stage. The leach liquor was an acidic ferric sulfate lixiviant comprising 20 g L.sup.−1 iron and an initial acid concentration of 44 g L.sup.−1. The pH was allowed to rise during the course of the test. In this Example, the contents of the stirred-tank reactor 202 were recirculated through the shear-tank reactor 212 only during the oxidative leach stage.

[0068] The resulting leach data are shown in FIG. 2. Greater than 98% copper recovery was achieved in about 1.5 hours after the start of the oxidative leach. This Example demonstrates that only partial surface conversion of chalcopyrite to a non-stoichiometric, metastable copper binary sulfide through the Physico-Chemical activation process is sufficient and optimal for achieving rapid copper dissolution from refractory minerals like chalcopyrite.

[0069] The present inventive method significantly departs from prior art (e.g., “The Sherritt-Cominco Copper Process—Part I: The Process,” G. M. Swinkels and R. M. G. S. Berezowsky, CIM Bulletin, February, 1978, pp. 105-121 and U.S. Pat. No. 3,816,105) wherein the required high levels of iron removal (i.e., 50-70%) from chalcopyrite necessitates reaction temperatures in excess of 150° C. and activation reaction times in excess of an hour. At these prior art-required temperatures, the following reactions involving bornite and chalcopyrite occur:

Cu.sub.5FeSO.sub.4+CuSO.sub.4.fwdarw.2Cu.sub.2S+2CuS+FeSO.sub.4

CuFe.sub.2+CuSO.sub.4.fwdarw.2CuS+FeSO.sub.4

Along with the undesirable side reaction:

5CuS+3CuSO.sub.4+4H.sub.2O.fwdarw.4Cu.sub.2S+4H.sub.2SO.sub.4

[0070] In the Sherritt-Cominco Copper Process, an activated copper concentrate is subsequently pressure leached at temperatures above 100° C. A distinguishing drawback from such prior art methods, is the fact that unless the O.sub.2 overpressure is significant, copper dissolution from chalcopyrite within the activated copper concentrate is limited to reactions involving only chalcocite (Cu.sub.2S).

[0071] In the Sherritt-Cominco Copper Process, unreacted chalcopyrite from the activated copper concentrate is “not amenable to further treatment by either an activation leach or an oxidative leach” unless significant O.sub.2 overpressures are used. This is contrary to the present invention, wherein atmospheric pressures and temperatures below about 100° C. are sufficient to achieve greater than 97% copper recovery within about 1-5 hours.

[0072] Unlike prior art methods, embodiments of the present inventive low-yield metathesis methods require only a few percent conversion of chalcopyrite to CuS by a Physico-Chemical activation process, wherein the conversion process may be prematurely stopped with little detriment during oxidative dissolution. Furthermore, the Physico-Chemical activation process does not produce undesirable, parasitic side reactions, such as the production of chalcocite, which serve only to consume copper sulfate.

EXAMPLE 3

[0073] This Example illustrates the use of a Physico-Chemical activation process to enhance chalcopyrite dissolution by atmospheric, acidic ferric sulfate leaching. Test conditions were identical to Example 2, except the residence time in the shear-tank reactor 212 during Physico-Chemical activation was limited to the time it took for complete copper uptake by the chalcopyrite concentrate. The rate of copper uptake by the concentrate is shown in FIG. 3. Reduction of the soluble copper concentration to below the detection limit was complete within about 15-17 minutes. A total mixing energy for the shear-tank reactor 212 of about 20 kW.Math.h/tonne had been expended during the activation stage. After completing the Physico-Chemical activation, the slurry was transferred to a stirred-tank reactor 202 as shown in FIG. 6, with a lixiviant composition of 20 g L.sup.−1 ferric, and 49 g L.sup.−1 H.sub.2SO.sub.4 and the copper was leached oxidatively at 80° C. The activated slurry was recirculated between the stirred-tank reactor 202 and the shear-tank reactor 212 at the rate of 0.5 L min.sup.−1. Greater than 97% copper dissolution was achieved in about 2.5 hours after the start of the oxidative leach process (see FIG. 4).

[0074] An additional, unexpected possible benefit of Physico-Chemical activation is the marked absence of frothing during the oxidative leaching of chalcopyrite. This is in contrast to prior art methods Which have been plagued by frothing, which makes it difficult to control oxygen delivery and particle residence times within the leach vessel(s) (see, for example, U.S. Pat. No. 5,993,635).

[0075] In some preferred embodiments, most or all of the reductive processing may occur at atmospheric pressure conditions e.g., chemical, processing occurring within one or more stirred-tank reactors 202). Dissolved copper may be provided to enable or facilitate the reductive activation process. The amount of dissolved copper provided should preferably 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 may typically be 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 for a residence time of metal sulfide particles within a reductive activation circuit 220, prior to moving on to a downstream oxidative leach circuit 240. The activated metal sulfide concentrate may he optionally re-ground in step 216, or sent directly to an oxidative leach circuit 240.

[0076] Pregnant leach solution (PLS) created during the atmospheric or substantially atmospheric leaching of the metal sulfide concentrate may be sent from the oxidative leach circuit 240 to a downstream solvent extraction/electrowinning (SX/EW) circuit, direct electrowinning (D/EW) process, or continuous direct electrowinning (CD/EW) operation, without limitation.

[0077] Raffinate may be recycled from the respective solvent extraction/electrowinning (SX/EW) circuit, direct electrowinning (D/EW) process, or continuous direct electrowinning (CD/EW) operation, and sent back to the oxidative leach circuit 240. Leach residues formed within the atmospheric or substantially atmospheric metal sulfide leach circuit 200 may optionally be sent to a precious metals recovery circuit and/or ultimately to a leach residues disposal area. While not expressly shown, leach residue sulfur lay be internally or externally processed/recovered/removed, in order to create sulfuric acid for pH control or for re-supplying the leach processes within the metal recovery flowsheet 110, such as the reductive activation circuit 220 and/or the oxidative leach circuit 240. 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, as a salable byproduct to help offset flowsheet operating costs.

[0078] In some embodiments, a bleed stream may be separated from the main flow of reductively-activated product. The bleed stream may enter a solid/liquid separation circuit which may comprise equipment such as a filter, thickener, centrifuge, cyclone, dewatering screen, or the like, without limitation. The solid fraction leaving the solid/liquid separation circuit may be recombined with the activated concentrate to be processed in the oxidative leach circuit 240. The liquid fraction leaving the solid/liquid separation circuit may optionally enter one or more downstream processes for recovering other metals or impurities removal, without limitation.

[0079] “Reductive activation”, “reductive processing”, or “reductive (pre)treatment” 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 second transitory/transitionary mineral phase. For example, a reductive pretreatment step may be configured to change or convert an outer surface of a leach particle from a primary metal sulfide (e.g., chalcopyrite) to a synthetic 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 of a leach particle sufficiently to enhance the oxidative dissolution process whereby the leach time to reach approximately 95% metal recovery from a metal sulfide concentrate can be achieved in about 6 hours or less.

[0080] In some instances, chalcopyrite leach particles may undergo a reductive activation/pre-treatment step in the one or more stirred tank reactors 202 within the reductive activation circuit 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 transitory/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. For example, less than about half of each particle may be converted to said transformed transitory transitionary mineral phase, and more preferably, less than about 10% of each particle by weight, volume, or outer surface area may be converted to said transformed transitory/transitionary mineral phase, and therefore, residence time of the metal sulfide concentrate within the reductive activation circuit 270 may be kept to a minimum.

[0081] In some most preferred instances, the activation may require conversion of 0.01 to 5.0% of the primary sulfide; or alternatively may require conversion of 0.01 to 4.0% of the primary metal sulfide; or alternatively may require conversion of 0.01 to 3.0% of the primary sulfide; or alternatively may require conversion of 0.1 to 2.0% of the primary sulfide; or alternatively may require conversion of 0.1 to 1.0% of the primary sulfide; for example conversion of as little as 0.5 to 0.8% of the primary sulfide. The extent of conversion to the synthetic metastable non-stoichiometric binary metal sulfide phase is carried out so as to introduce a sufficient amount of point defects substantially throughout portions of an activated particle or substantially throughout the entirety of an activated particle, without incurring unnecessary operating expenditures (OPEX).

[0082] Redox potential may, in some instances, vary within the reductive activation process as a function of time or within various stirred-tank reactors 202. In some instances, reductive processing within portions of the reductive activation circuit 220 may comprise a different pH than a pH maintained during oxidative dissolution within portions of the subsequent oxidative leach circuit 240. Where redox potential within the reductive activation circuit 220 approaches an Eh regime of the oxidative leach circuit 240, then pH is a determining factor; wherein higher pH's (e.g., above a pKa of sulfate-bisulfate) will favor metathesis reactions activation processes, and lower pH's (e.g., below a pKa of sulfate-bisulfate) will favor oxidative dissolution reactions. However, in many cases, devices 202, 212 within the reductive activation circuit 220 will comprise a different redox potential than devices 202, 212 within the subsequent oxidative leach circuit 240. For example, the measured redox potential within devices 202, 212 of the reductive activation circuit 220 may fall within the range of approximately 200 mV (SHE) to about 650 mV (SHE), for example between about 200 mV and 450 mV (SHE), between about 400 mV and 650 mV (SHE) or between about 500 mV and 650 mV (SHE), without limitation; wherein portions of the metal sulfide particles (e.g., chalcopyrite leach particles) may be converted to a transitory/transitionary mineral phase comprising a metastable, nonstoichiometric binary metal sulfide phase. Measured redox potential within devices 202, 212 of the oxidative leach circuit 240, may fall within the range of approximately 600 mV (SHE) to about 800 mV (SHE), for example between about 650 mV and 750 mV (SHE) or between about 600 mV and 750 mV (SHE), without limitation. These redox potentials may change or fluctuate with time or depending on the composition of concentrate 1 and/or the metal value desired to be recovered from the concentrate 1. The reductive activation circuit 220 may maintain a reductive environment at a redox potential between 200 mV (SHE) and 650 mV (SHE) with simultaneous pH control, and the combination of pH and redox may be maintained in such a manner so as to produce a reductively-activated concentrate or metal sulfide product comprising a metastable non-stoichiometric binary metal sulfide phase.

[0083] In some embodiments, the metal sulfide concentrate (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, Tennamite 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−x, Millerite NiS, Pentiandite (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.

[0084] In some embodiments, portions of the atmospheric or substantially atmospheric metal sulfide leach circuit 200, such as the plurality of stirred-tank reactors within the oxidative leach circuit 240, 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).

[0085] 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, so as to control passivation of the leaching particles (e.g., prevent smearing of sulfur onto leach particle surfaces).

[0086] 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 metal sulfide leach 200 (including portions of the reductive activation circuit 220) 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).

[0087] 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.

[0088] Without departing from the intent of the invention, reductive and/or oxidative stirred-tank reactor head space may be atmospheric or alternatively pressurized to above ambient pressure to enhance 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.

[0089] 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.