REACTOR FOR EXTRACTING METALS FROM METAL SULFIDE CONTAINING MATERIALS AND METHODS OF USE

BACKGROUND

1. Field

[0001] This application relates to an apparatus and methods for the recovery of metals from metal containing materials, such as ores. In particular, this application relates to an apparatus for the bio-oxidation and bio-leaching of metal sulfide containing materials to produce soluble metal sulfates.

2. Related Art

[0002] Cost-efficient metal recovery is a primary focus of the mining industry and significantly impacts numerous related industries, including construction, manufacturing, and electronics. Consequently, ores and other mining materials that are refractory to conventional metal recovery techniques are often not processed due to cost restrictions. Typically, refractory materials are ores that contain metals in a form (e.g., metal sulfides or extremely hard ores) and/or concentration that makes it cost-inefficient to process using conventional mining techniques. Often, refractory ores are the byproducts of mining operations and may also be referred to as mine tailings. These waste ores, or mine tailings, may be left to languish at previous mining sites and may present a significant challenge to communities and governments. For example, mine tailings may be a barrier to redevelopment of mine sites and may even present an environmental hazard as a source of pollution, since metals and other chemicals found in the tailings may find their way into the land and water supply.

[0003] Recently, attention has been focused on the efficient processing of these refractory ores. The cost-efficient processing of refractory ores provides at least a two-fold benefit. First, precious, semiprecious, and base metals are valuable commodities. Second, processing of refractory ores or mine tailings removes a barrier to redevelopment and a potential environmental hazard.

[0004] Bio-oxidation and bio-leaching, particularly of metal sulfide containing materials, using bacteria provides one possible avenue for the cost-efficient recovery of metals from

mine tailings and other refractory materials. Bio-oxidation and bio-leaching, as they relates to metal sulfide processing, is the bacterially catalyzed (directly or indirectly) process by which insoluble metal sulfides are oxidized into soluble metal sulfates. Metals are thereby leached or bio-leached from the refractory ores. In one example of bio-oxidation, the chemical reaction can be summarized as follows, wherein M is a metal to be recovered and S ⁰ is elemental sulfur:

2(MS) + 2(H ₂ SO ₄ ) + O ₂ → 2(MSO ₄ ) + 2(H ₂ O) + S ⁰

For this exemplary reaction, bacteria such as Thiobacilli thooxidans may catalytically drive the reaction by oxidizing elemental sulfur to form sulfuric acid:

2S° + 3O ₂ + H ₂ O → 2(H ₂ SO ₄ )

Bio-oxidation provides a potentially cost-efficient and environmentally low impact method for processing refractory ores. Most bacteria involved in the bio-oxidation of metal sulfides are aerobic and temperature dependent (generally mesophilic or thermophilic).

[0005] Bio-oxidation and bio-leaching is currently implemented commercially in two primary forms: agitated tanks and substantially inert leaching heaps or dumps. However, both methods present problems which impact their desirability as a refractory ore processing method.

[0006] Agitated tank bio-oxidation is generally practiced by dissolving large quantities of gases (primarily oxygen and carbon dioxide) into a slurry consisting of a flotation concentrate of the refractory ore. Mechanical agitation is employed to dissolve the gases and optimize the bio-oxidation reaction. Agitated tank bio-oxidation is relatively high cost and energy intensive. The refractory ore must be finely ground (e.g., <100 Tyler mesh) prior to processing, and grinding, agitation, and gas introduction are energy intensive. Further, the tanks and associated apparatus for agitated tank processing are generally high cost.

[0007] In heap leaching, coarsely ground (e.g., >one quarter inch) refractory ores are heaped onto a leach pad and irrigated with a leaching solution. Heap leaching has low operating costs but is a relatively slow method for the processing of refractory ores. Limited diffusion of oxygen and carbon dioxide, necessary for bio-oxidation, into the heap and

temperature control issues both reduce the reaction rate leading to a process that often requires weeks to complete.

[0008] Accordingly, there remains a need for cost-effective and efficient method and apparatus for the recovery of valuable metals from refractory ores.

SUMMARY

[0009] Described herein are an apparatus and a method for extracting metal sulfide containing materials to produce soluble metal sulfates.

[0010] In one embodiment, the apparatus for extracting metal sulfides is a reactor formed of a containment vessel including a base member and a wall member, the reactor having a gas injection member and a liquid injection member for introducing a gas and a liquid, respectively, into the containment vessel. The reactor further includes a cellular-confinement medium having aggregate materials capable of affecting liquid-solid separation positioned to contact the base or bed of the containment vessel.

[0011] In another embodiment, the containment vessel further includes a frame member movably mounted within the containment vessel; the frame member containing the gas injection member and the liquid injection member.

[0012] In an alternative embodiment, the aggregate materials are sized from 10 mesh to 0.5 inches. In one embodiment, the aggregate materials have a density of at least 1.3 g/cc. In another embodiment, the aggregate materials are provided as a layer having a thickness of at least 6 inches.

[0013] In one embodiment, the cellular confinement medium is configured to provide an effective drainage rate equivalent to an average hydraulic conductivity of approximately 0.002 cm/sec.

[0014] In yet another embodiment, the reactor includes a heat exchanger or an insulating member configured to regulate the internal temperature of the containment vessel. In one embodiment, the reactor of includes a lid member removably connected to the containment vessel. In one embodiment of the reactor, the wall member has a height of at least 4.0 feet. In another embodiment, the reactor includes an overflow mechanism, a second containment

vessel, and a recirculation mechanism. In this embodiment, the overflow mechanism is connected to the containment vessel and is configured to remove any excess liquid from the containment vessel, and the second containment vessel is connected to the overflow mechanism and is configured to store the excess liquid. Further in this embodiment, the recirculation mechanism is connected to the containment vessel and the second containment vessel and is configured to introduce the stored excess liquid from the second containment vessel to the containment vessel.

[0015] In one embodiment of the method for extracting metals from metal sulfide- containing solids, the method includes the steps of placing within a reactor of any of the previously described embodiments solids comprising metal sulfides, a culture of autotrophic, sulfide-oxidizing bacteria, and water. The method of this embodiment further includes, introducing a gas and a liquid at a rate sufficient to liquidize or fluidize the solids and to form a solute and/or a slurry, and removing, at intervals, a portion of the solute and/or slurry from the containment vessel.

[0016] In another embodiment of the method, the gas is introduced at a rate and over an area and period of time sufficient to agitate a portion of the solids and retain the agitated portion of the solids in suspension for the period of time.

[0017] In one embodiment of the method, the solids are not agitated by a mechanical agitation member.

[0018] In yet another embodiment of the method, the solids are ores, with at least 80% of the ores having a Tyler mesh size of less than .25 inches. In an embodiment of the method where the solids are ores, at least 80% of the ores have a Tyler mesh size of greater than 325 mesh. In an embodiment of the method where the solids are ores, the ores have an average metal sulfide content of between 1% and 30%.

[0019] In an alternative embodiment of the method for extracting metals, the method further includes the step of rinsing the solids with water or a dilute acid solution.

DESCRIPTION OF DRAWING FIGURES

[0020] Figure 1 depicts an exemplary reactor for the extraction of metals from metal sulfide containing materials;

[0021] Figure 2 depicts an exemplary reactor, having a frame member, for the extraction of metals from metal sulfide containing materials;

[0022] Figure 3 depicts a block diagram of an exemplary free drained method for extracting metals from metal sulfide containing materials;

[0023] Figure 4 depicts a block diagram for an exemplary partially saturated method for extracting metals from metal sulfide containing materials;

[0024] Figure 5 depicts a block diagram for an exemplary flooded method for extracting metals from metal sulfide containing materials.

DETAILED DESCRIPTION

[0025] The following description sets forth numerous exemplary configurations, processes, parameters, and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present invention, but is instead provided as a description of exemplary embodiments.

1. Metal Extraction Reactor

[0026] With reference to Figure 1, in an exemplary embodiment, a reactor 100 for use in extracting metals from metal sulfide containing materials is shown. Reactor 100 includes a containment vessel 102 that provides an open volume in which the chemical and biological processes of metal extraction may occur. The containment vessel may be constructed from a range of possible materials or combination of materials, including concrete and geosynthetics, such as woven and unwoven plastics and/or polymers including those geosynthetics commonly employed as part of an in-ground system similar to a typical storage lagoon or pond. Preferably, the containment vessel is constructed of materials, such as high- density polyethylene, that are non-toxic to bacteria. Containment vessel 102 includes an opening 104 into which metal sulfide containing materials may be loaded and processed or

expended materials may be unloaded. Loading and/or unloading may be performed hydraulically.

[0027] Reactor 100 also includes a vat liner system 106. In the present embodiment, the vat liner system is designed to contain fluids and solids and to prevent excursions of fluids into the environment. In one various embodiments, the vat liner system may be constructed from a range of natural and synthetic materials such as compacted clay, geosynthetics such as high density polyethylene (HDPE), concrete and stainless steel. In one embodiment, the vat liner system may be configured in multiple layers for duplication of function and as a margin of safety to prevent leaks and to recover and contain solutions. The inner layer of the vat liner system is preferably constructed of materials that are substantially or completely nontoxic to bacterial species employed in the bio-oxidation processes occurring inside the vat system.

[0028] Containment vessel 102 also includes a base member 108. In the embodiment of Figure 1, base member 108 is in contact with a cellular confinement medium provided as a base layer 110. Base layer 110 includes a structural layer formed by a cellular confinement medium into which has been placed packed aggregates sized to provide a proper filtering relationship with the metal sulfide containing materials intended for use with reactor 100. In one embodiment, the cellular confinement medium is a commercial material such as Geoweb® manufactured by Alcoa®. The Geoweb® cellular confinement layer is typically constructed of high density polyethylene (HDPE) and may incorporate perforations to enhance lateral solution and air movement. The packed aggregate material may be placed in layers of varying size, depending upon the characteristics of the given ore/waste type and the specific operational mode. Base layer 110 may also be configured to allow for drainage of a solution contained within containment vessel 102. In one embodiment, drainage rate is controlled by size selection of the aggregate material of the cellular confinement medium which may be sized from 28 mesh to approximately 0.50 inches

[0029] Also in contact with base member 108 is gas injection member 112. During operation, gas injection member 112 functions as a source of oxygen and/or other gases to facilitate the bio-oxidation of metal sulfides or the oxidation of elemental sulfur to form sulfuric acid. Depending on the rate of gas injection, gas injection member 112 may also serve to fluidize or assist in the fluidization of materials placed in the reactor 100 or

otherwise facilitate the recovery of metals. The gas injection member may be provided in the form of a nozzle, vent, or perforated pipe or any other convenient format capable of injecting a gas at a rate adequate to meet the total reaction requirements of the vat contents and more preferably at a rate of from 4 to 10 times the stoichiometric requirements of all oxidation reactions at the optimized kinetic rates for the entire volume of the vat contents. Gas injection member 110 is configured to inject gases such as ambient air, oxygen-enriched air, carbon dioxide-enriched air, or other gas useful for facilitating the bacterial bio-oxidation of metal sulfides. Preferably, the gas injection member is configured to inject ambient air. In embodiments configured to inject a gas at high volume and low pressure, the gas injection member may be a relatively low cost ventilation system. In alternate embodiments, the gas injection member is not in contact with base member 108 but is still positioned to inject a gas into the containment vessel. Gas injection member 112 may be configured to inject a gas at a constant or a variable rate.

[0030] Base member 108 also contacts liquid injection member 114. During operation, liquid injection member 114 functions as a source of liquid or solution to facilitate the bio- oxidation of metal sulfides or the oxidation of elemental sulfur to form sulfuric acid. Depending on the rate of liquid injection, liquid injection member 114 may also serve to fluidize or assist in the fluidization of materials placed in the reactor 100 or otherwise facilitate the recovery of metals. The liquid injection member may be provided in the form of a nozzle, vent, perforated pipe or any other convenient format capable of injecting a liquid at a rate that, in combination with added air, is sufficient to fluidized the largest particles in the vat, and more preferably, at a rate that, in combination with added air, is sufficient to fluidized the largest particles in the vat while not allowing the smallest particle sizes to overflow out of the vat. An alternate preferred liquid injection rate achieves the desired bio- oxidation level of the smaller sized particles in the vat and, in combination with the added air, causes overflow of the desired fraction of smaller particle sizes from the vat to a subsequent solid liquid separation step. In the present embodiment, liquid will be injected through a fraction of the available injection points such that only that fraction of the vat contents are fluidized at any given time. Preferably, following a fluidization period in a given area adequate to mix the associated particles and remove reaction by-products and any other coatings from the particle surfaces, solution injection in the given area is discontinued and solution injection in the adjacent area is initiated. This process is continued until the entire vat contents have been sequentially fluidized. The percentage of injection points utilized for a

single fluidization column of material is determined through test work and economic evaluations of the capital and operating costs to achieve the most cost effective fluidization of the entire vat contents at the optimum frequency of fluidization. In one embodiment, liquid injection member 114 is configured to inject a liquid such as H ₂ O or an acidic solution. Preferably, the liquid injection member is configured to inject recirculated bio-oxidation solutions. In alternate embodiments, the liquid injection member is not in contact with base member 108 but is still positioned to inject a liquid into the containment vessel. Liquid injection member 114 may be configured to inject a liquid at a constant or a variable rate.

[0031] In the embodiment of Figure 1, liquid recovery member 116 is also provided in contact with base member 108. Liquid recovery member 116 may be configured as a down drain for the free drain recovery of solution, including solution containing soluble metal sulfates after the completion of bio-oxidation and/or bio-leaching. The liquid recovery member may be configured to operate in a continuous or periodic recovery mode.

[0032] Reactor 100 also includes an overflow member 118. Overflow member 118 is connected to a thickener (not shown) and a re-circulator (not shown). The overflow is included to allow added solutions and slurries to flow to the desired location from the vat.

[0033] Reactor 100 further includes a temperature control system 120. Temperature control system includes one or more temperature sensors (not shown), a cooling member (not shown), and a heating member (not shown). Temperature control system 120 is configured to regulate the temperature of containment vessel 102 at the desired operating temperatures of ambient, moderate and extreme thermophiles as desired for a given application.

[0034] Figure 2 depicts another exemplary embodiment of a reactor for use in extracting metals from metal sulfide containing materials is shown. Reactor 200 includes a first containment vessel 202 and a second containment vessel 204. Containment vessels 202 and 204 both include openings 104, vat liner systems 106, base members 108, base layers 110, gas injection members 112, liquid injection members 114 (not shown for vessel 204), liquid recovery members 116 (not shown for vessel 204), and overflow members 118 (not shown for vessel 202), as described with reference to Figure 1.

[0035] Reactor 200 further includes frame member 206. Frame member 206 is movably mounted within containment vessel 202 and includes one or more gas injection members 208.

Each of the one or more gas injection members 208 is substantially configured as per gas injection member 112 of Figure 1, except that the one or more gas injection members 208 are not in contact with base member 108 of containment vessel 202. Frame member 206 further includes one or more liquid injection members 210. Each of the one or more liquid injection members 210 may be substantially configured as per liquid injection member 114 of Figure

1, except that the one or more liquid injection members 210 are not in contact with base member 108 of containment vessel 202. Frame member 206 may also be configured to remain stationary, move continuously, or move intermittently, during operation.

2. Methods of Use

[0036] The reactors described herein may be employed in methods of extracting metals from metal sulfide contain materials.

A. Free Drained

[0037] The reactors described herein may be employed as free drained reactors. With reference to Figure 3, a block diagram of a possible method of use, an ore containing 15% copper sulfide, by weight, may be pre-treated in step 300. In the present embodiment, pre- treatment involves grinding the copper sulfide-containing ore to a particle size range of 10 Tyler mesh to 50 Tyler mesh. In alternative embodiments, the metal sulfide materials may include, but are not limited to, precious metal, semi-precious metal, or base metal sulfides, contained in rock, gravel, glass, synthetics, or other metal sulfide containing materials. In other embodiments, the sulfide can contain metals such as gold, platinum, silver, nickel, copper, zinc, cobalt, or other metals. Pre-treatment may also include cleaning, crushing, bacterial addition, and/or pH adjustment of the materials.

[0038] In step 302, the pre-treated ore may be hydraulically loaded into a reactor, such as the reactor of Figure 1. In the present embodiment, the containment vessel 102 of the reactor has an internal volume adequate to provide the required retention time and to achieve the desired level of bio-oxidation.

[0039] In step 304, bio-oxidation and bio-leaching may be initiated through the addition of a solution containing cultured bacteria and appropriate combinations of bacterial nutrients. Sufficient solution may be initially added to completely submerse the pre-treated ore and

form a slurry of ore and solution. In an alternative embodiment, the solution may be a bacteria solution that includes ambient temperature bacterial cultures and/or moderate temperature bacterial cultures and/or extreme temperature bacterial cultures.

[0040] In step 306, solution may be periodically pulsed from the base of the containment vessel at a rate adequate to fluidize the slurry. In alternate embodiments employing alternative materials and reactor sizes, the rate of solution introduction is selected to achieve fluidization. Without being limited by theory, fluidization may result in the re-arrangement of ore particles such that the inter-granular contact is interrupted and filled with solution, a process which may allow for the removal of reaction productions thereby substantially improving the bio-kinetics of the metal extraction process. Note that in the present embodiment, mechanical agitation is not employed to agitate the ore particles. In an alternative embodiment, mechanical agitation is employed.

[0041] In step 308, the slurry may be free-drained to allow for liquid-solid separation. The liquid recovery member 116 of the reactor of Figure 1 may be employed for drainage. Positioned between the liquid recovery member 116 and the open volume of the containment vessel 102 is base layer 110. In the present embodiment, base layer 110 includes aggregate materials having a range of particle sizes between 10 mesh and 0.5 inches. The aggregate materials function in a manner similar to a sand filter layer and are provided in a quantity sufficient to allow for free drainage of the slurry.

[0042] In step 310, ambient air may be added at a high volume and low pressure rate to the drained slurry. Gas addition may improve the bio-kinetics of anaerobic bacteria and the oxygen-dependent bio-oxidation and bio-leaching reactions. In alternative embodiments, the gas may be an oxygen-enriched gas. In the present embodiment, ambient air may be added at a constant rate.

[0043] Steps 306, 308, and 310 may be repeated or cycled for a period sufficient to bio- oxidize and bio-leach a desired quantity of metals from the metal sulfide containing materials. Using the exemplary method, soluble copper sulfate may be bio-leached from the copper sulfide containing ore.

B. Partially Saturated

[0044] The reactors described herein may be employed as partially saturated reactors. With reference to Figure 4, steps 302, 304, and 306 are employed as with a free drained reactor. In step 400, the slurry may be partially free-drained, using liquid recovery member 116 and base layer 110, to provide a partially saturated slurry.

[0045] In step 402, ambient air may be added to the partially saturated slurry. In an alternative embodiment, small quantities of solution may be added to the top of the partially saturated slurry to achieve an optimal level of partial saturation. Operation in a partially saturated mode may allow for the use of metal sulfate materials having a finer particle size, as the particles do not have to be coarse enough to relatively quickly achieve the free drained state and allows for improved air distribution throughout the partially saturated slurry due to increase back pressure.

[0046] Steps 306, 400, and 402 may be repeated or cycled for a period sufficient to bio- oxidize and bio-leach a desired quantity of metals from the metal sulfide containing materials.

C. Flooded

[0047] The reactors described herein may be employed as flooded reactors. With reference to Figure 5, steps 302 and 304 are employed as with a free drained reactor. Free drainage is not employed.

[0048] In step 500, solution may be added as a continuous low pressure up-flow, in one embodiment the continuous low pressure is 3.0 psi, interspaced with periodic higher pressure, in one embodiment the periodic higher pressure is 75 psi, up-flow.

[0049] In step 502, ambient air may be added to the flooded slurry at a desired rate. Due to the increased back pressure, relative to the free drained or partially saturated embodiments, air addition in a flooded reactor requires additional energy expenditure.

[0050] Steps 500 and 502 may be repeated or cycled for a period sufficient to bio-oxidize and bio-leach a desired quantity of metals from the metal sulfide containing materials.