Microorganism-assisted dump leaching

Abstract

Microorganism-assisted dump leaching of fragments or agglomerates of fragments of copper-containing sulfide ores such as chalcopyrite ores and copper-containing sulfide waste is disclosed. The dump leaching method comprises the step of controlling the sulfate concentration in the leaching solution. When dump leaching includes the use of agglomerates, the method of forming agglomerates includes adding feed material at or near the inlet end, typically at no more than 40%, typically no more than 30%, more typically no more than 20% of the length from the inlet end of the agglomerating unit.

Description

Technical Field

[0001] The present invention relates to microbiologically assisted heap leaching of base metals, such as copper or nickel or zinc or cobalt, from fragments of sulphide materials containing base metal sulphides, wherein the term "material" includes, for example, ores and waste materials, such as tailings.

[0002] The term "ore" is understood herein to mean a natural rock or deposit containing one or more valuable metals, which may be mined, recovered, processed and sold for profit.

[0003] The present invention particularly, although not exclusively, relates to microbial assisted heap leaching of fragments of copper-containing sulphide ores, such as sulphide ores containing copper minerals such as chalcopyrite (CuFeS2), chalcopyrite (Cu3AsS4), tetrahedrite (Cu,Fe,Zn,Ag 12 Sb4 13 ), chalcopyrite (Cu 12 A4S 13 ), bornite (Cu5FeS4), chalcocite (Cu2S) and covellite (CuS), or any combination thereof, or other copper-containing sulfide minerals, and noting that the fragments may be (a) run-of-mine ("ROM") ore or (b) fragments of ROM ore that has undergone intermediate processing, as the terms "ROM ore" and "intermediate processing" are understood herein.

[0004] The present invention also particularly, although not exclusively, relates to microbiologically assisted heap leaching of agglomerates of fragments of copper-containing sulphide ores such as those described in the preceding paragraphs, noting that the fragments may be (a) ROM ore or (b) fragments of ROM ore which has undergone intermediate processing.

[0005] The invention also relates particularly, although not exclusively, to microbiologically assisted heap leaching of fragments of copper-containing sulphide waste such as tailings containing the minerals mentioned above, noting that the fragments may be (a) ROM waste or (b) fragments of ROM waste that have undergone intermediate processing.

[0006] The invention also relates particularly, although not exclusively, to the construction of heaps (and constructed heaps) configured to optimize microbial activity. Background Art

[0007] In conventional heap leaching of copper-containing sulfide ores (including chalcopyrite ores), the ore is piled into a heap, ventilated by direct injection of air through a vent pipe extending into the heap and / or by natural convection through the exposed area of ​​the heap, and irrigated with an acid solution for extracting copper into the solution. The leaching process requires acid and an oxidant to dissolve the copper into the solution. Copper is then recovered from the acid solution through a series of recovery options, including, for example, solvent extraction and electrowinning (SX / EW), cementation to more active metals such as iron, hydrogen reduction, and direct electrowinning. The acid solution is regenerated and recycled through the heap to leach more copper from the ore in the heap. The ore in the heap may include agglomerates of fragments of the ore. Leaching can be aided by the addition of ferrous and sulfur-oxidizing microorganisms.

[0008] Typically, heap leaching (which is understood herein to include dump leaching) provides lower metal recoveries than other metallurgical process options for recovering copper from copper-containing ores, such as grinding and flotation to produce copper-containing concentrates, which are then smelted to produce copper metal.

[0009] Heap leaching therefore tends to be reserved for lower grade ore types which have at least some proportion of readily recoverable copper, but where the crushing / milling costs per unit of copper (or copper equivalent - i.e. when by-product credits from, for example, gold and silver are taken into account) are too high to support a concentrator approach, or where mineral release and other characteristics (e.g. arsenic content) will not support the production of a directly usable or marketable concentrate.

[0010] Standard best industry practice is to use agglomerates of mined and subsequently comminuted (e.g. crushed) piles of ore fragments. Typically, the mined ore is processed through multiple crushing steps such as primary and secondary crushing steps, and in some cases tertiary and other crushing steps, and the crushed ore fragments are agglomerated in an agglomeration step, typically with the use of an acid. The following description focuses on chalcopyrite ore.

[0011] The term "chalcopyrite ore" is understood herein to mean an ore comprising chalcopyrite. The ore may also contain other copper-containing minerals. The ore may also contain pyrite.

[0012] This description applies equally to other copper-containing minerals in ores or wastes, such as those mentioned under the heading "Technical Field", and is not limited to chalcopyrite ore.

[0013] It is known to be difficult to extract more than 20 wt.% - 40 wt.% of total copper from chalcopyrite by heap leaching.

[0014] Low copper recoveries are generally believed to be related to the formation of a passive film on the surface of chalcopyrite in chalcopyrite ore.

[0015] The applicant has carried out extensive research and development work into the leaching of chalcopyrite ore (and other copper-bearing sulphide ores) and has made a number of inventions, including those described and claimed in international applications PCT / AU2016 / 051024, PCT / AU2018 / 050316, PCT / AU2019 / 050383, PCT / US2021 / 043869, PCT / AU2008 / 000928 and PCT / US2021 / 43899 in the applicant’s name.

[0016] The disclosures in the International application are incorporated herein by cross-reference.

[0017] The disclosure herein is directed to solving at least some of the technical problems identified during research and development efforts.

[0018] The above description should not be taken as an admission of common general knowledge in Australia or elsewhere.

[0019] Summary of the Disclosure

[0020] Inventions made during research and development work

[0021] The applicant has identified a number of further inventions as a result of the research and development work referred to above.

[0022] The present invention generally relates to microbiologically assisted heap leaching of sulfide materials containing base metal sulfides, noting that copper is a base metal of particular interest to applicants, although not the only base metal.

[0023] In embodiments of particular interest to applicants, the present invention relates to microbially assisted heap leaching of fragments or agglomerates of fragments of copper-containing sulfide ores (such as chalcopyrite ore) and copper-containing sulfide waste materials.

[0024] In embodiments of particular interest to applicants, the present invention relates to:

[0025] (a) microbiologically assisted heap leaching of fragments of copper-containing sulfide ores and copper-containing sulfide waste materials having high sulfate concentrations in the leachate; and

[0026] (b) microbial assisted heap leaching of agglomerates of debris from item (a); and

[0027] (c) adding microbes (also referred to as microorganisms, bacteria or archaea) to the fragments of copper-containing sulfide ore and copper-containing sulfide waste.

[0028] The term "fragment" is understood herein to mean mined (i.e. run of ore "ROM") material or a portion of intermediately processed (such as comminuted, e.g. crushed) ROM material, wherein the term "material" includes ore and waste, which may be stockpiled ore and waste that has been recovered.

[0029] It should be noted that the term "chips" as used herein may be understood by some skilled in the art to be better described as "particles" and "broken rock." It is intended that these terms be used synonymously.

[0030] The fragments may be fragments of ROM material, which may be ROM ore or ROM waste, from the location of the mine from which the ROM material is mined:

[0031] i. Transfer directly to the heap; or

[0032] ii. directly to a stockpile, and then directly to a heap thereafter; or

[0033] iii. Transfer for intermediate processing as described herein and then to a stack; or

[0034] iv. transferred for intermediate processing as described herein, and then transferred to a stockpile, and then thereafter to a heap; or

[0035] v. directly transferred to a stockpile, and then transferred for intermediate processing as described herein, and then transferred to a heap; or

[0036] vi. A combination of the aforementioned options iv. and v., wherein intermediate processing is carried out before and after the stockpile.

[0037] The term "intermediate processing" refers to any type of processing of ROM material, including processing that falls under the general description of "ore processing", including but not limited to any one or more of the following: crushing, size separation into different size fractions, sorting into different grade fractions according to the grade of target base metal (e.g., the concentration of base metal), sorting according to other mineralogical composition of ROM material (such as contaminants), sorting according to other properties of ROM material, and agglomeration.

[0038] It should be noted that ROM material may be fragments that have been reduced in size from larger fragments as a result of mining the ROM material and transferring the ROM material from the mine to a heap, stockpile or intermediate processing plant, rather than as a result of a specific crushing or other intermediate processing step.

[0039] For example, size reduction may be the result of larger fragments breaking up during collapse to the pit floor in a drill and blast mining operation in an open pit, and the transfer of the collapsed fragments to a pile, stockpile, or intermediate processing equipment by excavators and other material handling equipment, rather than a specific crushing or other intermediate processing step.

[0040] As a further example, size reduction may be the result of fragmentation as the fragments are removed from a draw point in a block cave mine by a front-end loader or other excavator and transferred to a stockpile, stockpile or intermediate processing facility, rather than as a result of a specific crushing or other intermediate processing step.

[0041] The ROM material can have a particle size within any suitable range.

[0042] For example, the ROM material may have a particle size in the range between a P80 of 30 mm and a P80 of 2000 mm. The particle size range of the ROM material may be any suitable range within this broad range, taking into account the characteristics of a given ore. For example, the particle size range of the ROM material may be a broad range such as between a P80 of 50 mm and a P80 of 1000 mm. For example, the particle size range of the ROM material may be a narrower range, such as typically in the range between a P80 of 30 mm and a P80 of 60 mm.

[0043] The ROM material and intermediate processed material may have any suitable particle shape, noting that the specified particle size ranges are based on one dimension only.

[0044] In the case where the ROM material has been comminuted in an intermediate processing step, the comminuted ROM material may, by way of example only, have a particle size in the range between a P80 of 5 mm and a P80 of 30 mm.

[0045] Microbial assisted leaching from copper-containing sulfide materials

[0046] Extraction of copper from materials in the form of copper-containing sulfide ores and copper-containing sulfide wastes requires an oxidant and an acid. Industrially, ferric ions are used as the oxidant and sulfuric acid is used as the acid. During the process of mineral dissolution, the ferric ions are reduced to ferrous ions and the sulfuric acid is consumed during the reaction with the gangue minerals. Microorganisms oxidize the ferrous ions to produce ferric ions and oxidize available solid and soluble sulfur compounds to produce sulfuric acid.

[0047] Maintaining adequate rates of iron and sulfur oxidation to promote optimal copper extraction requires a microbial population and any required nutrients in a habitable environment.

[0048] The mechanism of mineral sulfide dissolution of copper-containing sulfide ores and copper-containing sulfide wastes relies on the presence of iron ions and acids to break down the mineral matrix and dissolve the metals. The iron ions and acids are consumed during mineral oxidation, and unless they are replenished, the dissolution rate will decrease.

[0049] Under aerobic conditions, microorganisms (such as acidophilic bacteria and archaea) regenerate ferric ions and acids by biological oxidation of ferrous ions and sulfur compounds (including elemental sulfur):

[0050] 2Fe 2+ +2H + +0.5O2→2Fe 3+ +H2O

[0051] 2S+3O2+2H2O→2H2SO4

[0052] The sulfur compound may be derived from the oxidation of a sulfide or as an addition (such as elemental sulfur). The sulfur compound may be an inorganic sulfur-containing compound such as a thiosulfate or polysulfate or polysulfide, or an organic sulfur-containing compound such as thiourea or other thiocarbamides.

[0053] Not only do these reactions ensure that iron and acid concentrations are maintained, they are also used to generate energy for the formation of additional cells, potentially making the process autocatalytic under ideal conditions for microbial proliferation.

[0054] During mineral dissolution of copper-containing sulfide ores and copper-containing sulfide wastes, changing solution conditions affect the activity of microorganisms present in the leaching environment.

[0055] Applicant's research and development work has found that the rate of ferrous ion and sulfur oxidation is affected by high metal sulfate concentrations, fluctuations in solution pH and temperature changes.

[0056] The applicant's research and development work has also found that sulphide mineral dissolution (and hence copper extraction) of copper-containing sulphide ores and copper-containing sulphide wastes is negatively affected if iron ions and acids are not regenerated at a sufficient rate by microbial activity.

[0057] Effect of stack aeration

[0058] Applicants have recognized during their research and development work that oxygen affects many operating parameters of the stack, including the oxidation rate of the feed material, temperature, microbial activity, and populations within the stack.

[0059] For example, increasing the air supply, and therefore the oxygen supply, into the pile increases microbial activity, which in turn increases the temperature of the pile, the oxidation of ferrous ions to ferric ions, and the oxidation of sulfur compounds to sulfuric acid.

[0060] The applicant has discovered during research and development work that controlling the sulfate concentration in the leachate is an important consideration in a process for microbiologically assisted heap leaching of copper-containing sulfide ores and copper-containing sulfide wastes, and that the air and / or oxygen flow rate during aeration of the heap can be used as one option to influence the sulfate concentration in the leachate.

[0061] Adding microorganisms during agglomeration

[0062] The applicant has also found during research and development work that the formation of agglomerates of fragments of copper-containing sulphide ore and copper-containing sulphide waste in the presence of micro-organisms in the agglomerates requires careful control of the agglomeration unit and that this can be achieved by ensuring that the feed material for agglomeration is provided at or close to the inlet of the agglomeration unit and that the agglomerates are formed over a short distance along the length of the unit as described herein.

[0063] It should be noted that the present invention is not limited to agglomerating fragments of material.

[0064] It should also be noted that the present invention extends to embodiments in which microorganisms are added to the agglomerates and the heap leaching operation is performed after the agglomerates have been formed.

[0065] Invention 1

[0066] The present invention is based on the above mentioned discovery that controlling the sulfate concentration in the leachate is an important consideration in a process for microbiologically assisted heap leaching of copper-containing sulfide ores and copper-containing sulfide wastes.

[0067] Embodiments of the present invention are also based on the discovery, although the invention is not limited to this discovery, that thermophilic microorganisms that are active at temperatures above 45°C are more sensitive to high sulfate concentrations than mesophilic microorganisms that are most active at temperatures in the range of 20°C-40°C.

[0068] These findings led the applicants to develop a high sulfate generating heap leach process that can be operated at elevated heap temperatures up to 85°C (eg, 60°C-65°C), with the advantages of high temperature operation.

[0069] The present invention provides a method for microbial assisted heap leaching of copper-containing sulfide ore or copper-containing sulfide waste, the method comprising: supplying an acidic leachate containing sulfate to a heap of fragments or agglomerates of fragments of the copper-containing sulfide ore or copper-containing sulfide waste, and allowing the leachate to flow through the heap and leach copper, collecting the leachate from the heap, and processing the collected leachate and recovering copper from the leachate, wherein any one or more of the fragments, agglomerates of fragments (when present) and the leachate contains microorganisms, and the method comprises controlling the sulfate concentration in the leachate so that it does not exceed a threshold concentration (described further below).

[0070] The present invention also provides a method as described in the preceding paragraphs, generally applicable to base metal-containing sulphide ores or base metal-containing sulphide wastes.

[0071] Importantly, Applicants have discovered that microbial assisted heap leaching of fragments of copper-containing sulphide ore or copper-containing sulphide waste, or agglomerates of such fragments, can be operated even with high sulphate concentrations (such as at least 60 g / L sulphate) in the leachate, i.e. up to a threshold concentration, both with and without intermediate processing as described herein.

[0072] Even when using thermophilic microorganisms with high sulfate concentrations, applicants have observed in their research and development work that iron ions and acids are regenerated at commercially viable rates. The observed production of iron ions and acids in turn facilitates leaching of ores and wastes.

[0073] This is a surprising result, since studies reported in the literature have shown that high sulfate concentrations have a negative impact on microbial activity, i.e., the biological oxidation of ferrous ions and sulfur compounds to regenerate iron ions and protons.

[0074] The method may include controlling the method by any one or more of dilution, chemical neutralization, electrochemical neutralization, solution percolation, and physical separation techniques including nanofiltration so that the sulfate concentration in the leachate does not exceed a threshold sulfate concentration.

[0075] The method may include monitoring the sulfate concentration in the leachate collected from the heap, and controlling the method as required so that the sulfate concentration in the leachate does not exceed a threshold concentration.

[0076] The method may include indirectly controlling sulfate concentration.

[0077] As an example, the method may include indirectly controlling a parameter other than sulfate that affects the sulfate production rate, such that changing the parameter causes a known change in sulfate concentration.

[0078] In one example, the method can include controlling aeration rate of the stack. The aeration rate can be set based on a predetermined oxygen utilization of the stack, such as based on feed composition.

[0079] In another example, the method can include controlling the pH in the heap to be within a range that induces precipitation of sulfates such as jarosite.

[0080] The method is not limited to monitoring sulfate concentration in leachate collected from a heap and extends to other options for monitoring sulfate concentration.

[0081] In one example, the method can include monitoring either or both of microbial activity and population.

[0082] The method may include measuring or simulating oxygen utilization of the stack.

[0083] The method may include controlling one or more of the operating parameters based on the measured data or the simulated data to maintain a predetermined oxygen utilization of the stack.

[0084] The method may include selecting a ventilation rate for the stack based on a desired parameter value.

[0085] Examples of operating parameter values ​​include heap oxygen concentration, heap carbon dioxide concentration, temperature of the leach liquor from the heap (i.e., pregnant leach liquor temperature), temperature of the leach liquor to be fed to the heap (raffinate), heap temperature, pregnant leach liquor metal content, pregnant leach liquor oxidation potential, ferric and ferrous iron concentrations, Eh value, heap oxygen absorption rate, and heap carbon dioxide absorption rate.

[0086] The method may include selecting an aeration rate for the stack based on a desired oxidation rate for the stack.

[0087] The method may include determining an oxidation rate of a copper-containing sulfide feed material as a function of any one or more of: heap oxygen concentration, heap carbon dioxide concentration, temperature of a leachate discharged from the heap (i.e., temperature of a rich leachate), raffinate feed temperature, heap temperature, rich leachate metal content, rich leachate oxidation potential, ferric and ferrous iron concentrations, Eh value, heap oxygen absorption rate, heap carbon dioxide absorption rate, simulation based on at least one of feed composition, sulfide mineral leach rate, heap geometry, environmental conditions external to the heap, and historical data from an existing heap.

[0088] One advantage of selecting the aeration rate based on the desired parameter value is that it provides better operational control. For example, it ensures sufficient oxygen supply to the microorganisms to achieve the desired parameter value and avoids oversupply of oxygen, which may cause unnecessary financial and energy costs, for example due to higher pumping or compressor (blower) requirements.

[0089] The method may include selecting an aeration rate for the stack based on a desired microbial population and / or activity.

[0090] The method may include selecting a ventilation rate for the stack based on a desired stack temperature.

[0091] The method may include monitoring the temperature of the stack at different locations in the stack, noting that there may be variations in the temperature of the stack at different sections of the stack.

[0092] Suitably, the method comprises monitoring the temperature at one or more points across the height of the pile, more suitably the temperature at a point in the range from 1% to 95% of the height of the pile below the surface of the pile.

[0093] Suitably, the method comprises monitoring the temperature at one or more points across the width of the stack, more suitably the temperature at a point in the range from 1% to 95% of the width of the stack below the surface of the stack.

[0094] The temperature of the heap may be similar to the temperature of the enriched leachate. Thus, the method may comprise measuring the enriched leachate temperature to indirectly measure the heap temperature.

[0095] The ventilation rate may be controlled by controlling the irrigation rate. Suitably, the irrigation rate may be controllable using a rest-rinse cycle or varying the flow rate of an irrigant (eg acid).

[0096] The rinse step of the rest-rinse cycle involves flowing the leachate through the heap. The rinse step may involve replacing the enriched leachate with fresh leachate.

[0097] The rest step of the rest-rinse cycle involves stopping the flow of leachate through the heap. The rest step can allow the microorganisms to equilibrate with other components in the leachate. This can enhance the dissolution of copper in the leachate and improve the overall leaching process. The duration of the rest step can be less than the duration of the rinse step. The duration of the rest step can be the same as or longer than the duration of the rinse step.

[0098] The method may comprise aerating one or more lifts of the stack. Suitably, the method comprises aerating each lift of the stack.

[0099] Aerating each lift of the pile minimizes the risk of uneven distribution of oxygen throughout the pile. If aeration is only performed at the bottom of the pile, it is believed that oxygen will be consumed closer to the bottom of the pile as the air travels upward. This will cause less oxygen to reach the lifts higher in the pile and may starve the microorganisms in those lifts of oxygen.

[0100] In any given case, the threshold sulfate concentration may depend on the microbial culture used. In some cases, mesophiles can tolerate higher sulfate levels than moderate and extreme thermophiles. The following threshold concentrations are mentioned in this context.

[0101] The threshold sulfate concentration may be 170 g / L sulfate in the leachate collected from the heap.

[0102] The threshold sulfate concentration may be 150 g / L sulfate in the leachate collected from the heap.

[0103] The threshold sulfate concentration may be 120 g / L sulfate in the leachate collected from the heap.

[0104] The threshold sulfate concentration may be 60 g / L sulfate in the leachate collected from the heap.

[0105] During the start-up phase of the process, the threshold sulfate concentration may be at least 2 g / L.

[0106] During the start-up phase of the process, the threshold sulfate concentration may be at least 20 g / L.

[0107] In the later post-start-up leaching stage of the process, the threshold sulfate concentration may be 50 g / L - 100 g / L.

[0108] During the post-startup leaching phase of the process, the threshold sulfate concentration may be 60 g / L - 130 g / L.

[0109] During the post-startup leaching phase of the process, the threshold sulfate concentration may be in the concentration range of 100 g / L - 130 g / L.

[0110] During the post-startup leaching phase of the process, the threshold sulfate concentration may be a concentration range of 110 g / L - 120 g / L.

[0111] The threshold sulfate concentration may be increased to the threshold concentration limits described previously.

[0112] Microorganisms may be added during agglomeration.

[0113] Microorganisms may be added to the extract.

[0114] Microorganisms can be added during agglomeration and in the leachate.

[0115] The microorganism may be any suitable microorganism.

[0116] The microorganism can be any microorganism that can oxidize ferrous and / or sulfur compounds, and includes, but is not limited to, members of the bacterial genera Acidithiobacillus, Leptospirillum, Sulfobacillus, and Ferrimicrobium, and the archaeal genera Acidianus, Acidiplasma, Ferroplasma, Metallosphaera, and Thermoplasma.

[0117] Typically, the microorganisms are a diverse group including microorganisms selected from mesophiles, moderately thermophilic and thermophilic, psychrophilic or mesophilic or thermophilic (moderate or extreme) bacteria or archaea. The microorganisms may be acidophilic bacteria or archaea. The microorganisms may be thermoacidophiles. The diverse groups allow activity under a range of operating conditions including high sulfate concentrations.

[0118] Heap leaching may include controlling the pH of the leachate to less than 3.2, typically less than 3.0, typically less than 2.5, typically less than 2.0, typically less than 1.8 and typically less than 1.5.

[0119] Heap leaching may involve controlling the pH of the leachate to be greater than 0.5, typically greater than 1.0.

[0120] Heap leaching may include controlling the temperature of the heap to below 85°C, typically below 75°C, typically below 65°C, typically below 60°C, typically below 55°C and more typically below 50°C. In a preferred embodiment, heap leaching includes controlling the temperature to below 65°C.

[0121] Heap leaching may include controlling the temperature of the leach solution to be above the freezing point of the leach solution, typically above 0°C, typically at least 10°C, typically at least 20°C, typically at least 30°C, typically at least 40°C and more typically at least 50°C.

[0122] Heap leaching may include controlling the aeration rate of the heap to a level from 0.01 Nm 3 / h / t ore to 0.1Nm 3 / h / tore (where t is metric tons or tons, and N is normal temperature and pressure at sea level). Typical rates may be near the lower end of this range.

[0123] Heap leaching may include controlling the aeration rate of the heap to at least 0.25 kg / m per lift. 2 / h, typically at least 0.25kg / m per lift 2 / h, typically at least 0.75kg / m per lift 2 / h, typically at least 1kg / m per lift 2 / h, typically at least 2kg / m per lift 2 / h, more typically ranging from 0.25kg / m per lift 2 / h to 1.0kg / m 2 / h, and typically 0.25kg / m 2 / h to 2.5kg / m 2 / h. Suitably, the height of each lift is about 10m.

[0124] Irrigation rates can range from 1 L / h / m 2 -50 L / h / m 2 In the range of 1L / h / m 2 -20 L / h / m 2 Deploying a sprinkler or oscillator generally results in an irrigation rate at the higher end of the range, while deploying a dripper generally results in an irrigation rate at the lower end of the range.

[0125] In one example, heap leaching includes maintaining a ratio of average aeration rate and average irrigation rate in a range of 0.125:1 to 5:1, typically in a range of 0.15:1 to 2:1, typically in a range of 0.175:1 to 1.5:1, and more typically in a range of about 0.2:1.

[0126] In another example, the heap leaching includes maintaining the instantaneous aeration rate and the instantaneous irrigation rate in a range of 0:1 to 5:1, typically in a range of 0:1 to 2:1, typically in a range of 0:1 to 1.5:1, and more typically about a 0.2:1 ratio.

[0127] The ventilation rate may be set to maintain a predetermined oxygen utilisation of the stack.

[0128] In one example, heap leaching includes controlling the aeration rate to maintain oxygen utilization of the heap in the range of 1% to 99%, typically in the range of 15% to 90%, and more typically in the range of 20% to 85%.

[0129] Heap leaching may include controlling the oxidation potential of the leachate during the active leaching stage to less than 1000 mV, typically less than 900 mV, typically less than 850 mV, typically less than 800 mV, typically in the range of 500 mV to 750 mV, more typically in the range of 600 mV to 750 mV, all potentials being relative to a standard hydrogen electrode.

[0130] The oxidation potential will change during leaching and may be higher when most of the copper has been leached, and reference to an "active leaching stage" is intended to acknowledge this potential change. The oxidation potential reached is also dependent on temperature and will generally be higher at lower temperatures.

[0131] The process may include an agglomeration step for forming agglomerates of fragments of the copper-bearing sulphide ore or copper-bearing sulphide waste material, said agglomerates being used for subsequent heap leaching in the process.

[0132] The agglomeration step may comprise simultaneously mixing and agglomerating fragments of the copper-containing sulphide ore or copper-containing sulphide waste.

[0133] The agglomeration step may include mixing the fragments in one step and then agglomerating the mixed fragments in a subsequent step.

[0134] There may be overlap between the mixing step and the agglomeration step.

[0135] The agglomeration step may comprise agglomerating fragments of the copper-bearing sulphide ore or copper-bearing sulphide waste in an agglomeration unit and may also comprise various combinations of feed materials which are typically introduced at or immediately adjacent to the inlet of the unit.

[0136] The agglomeration step may comprise agglomerating fragments of the copper-bearing sulphide ore or copper-bearing sulphide waste in an agglomeration unit and may also comprise various combinations of the following feed materials, which are typically introduced at or immediately adjacent to the inlet of the unit:

[0137] (a) sulfuric acid,

[0138] (b) microorganisms which oxidize ferrous ions and oxidize solid and soluble sulfur compounds, thereby regenerating ferrous ions and acid,

[0139] (c) silver having catalytic properties to enhance the leaching of copper from copper-bearing sulphide ores or copper-bearing sulphide wastes,

[0140] (d) optionally, an activator for activating silver selected from thiourea, chloride, bromide and iodide,

[0141] (e) optionally, a complexing agent additive that enhances the dissolution of copper from copper minerals in the copper-containing sulfide ore or copper-containing sulfide waste by forming a complex between (i) sulfur derived from the copper minerals in the ore and (ii) the additive,

[0142] (f) pyrite (or any other suitable material including elemental sulphur), which provides a source of ferrous ions and heat in the case of pyrite (and heat alone in the case of elemental sulphur), and

[0143] (g) water and / or other water sources and / or the enriched leach solution from a heap leaching operation or the raffinate formed in a solvent extraction operation on the enriched leach solution.

[0144] Elemental sulfur may be a partial or complete substitute for sulfuric acid and / or pyrite.

[0145] Elemental sulfur has many benefits, including:

[0146] (a) Easier to transfer and handle than pyrite;

[0147] (b) be readily available; and

[0148] (c) Usually cheaper than pyrite and sulfuric acid.

[0149] Applicants have discovered that deployment of elemental sulphur may allow for the processing of base metal sulphide-containing sulphide materials, particularly copper-containing sulphide materials, having low pyrite concentrations.

[0150] The collected leachate may be processed by any suitable processing option to recover copper from the leachate.

[0151] The present invention also provides a pile of material, wherein the material comprises fragments of the copper-containing sulphide ore or copper-containing sulphide waste material described above or agglomerates of fragments of the copper-containing sulphide ore or copper-containing sulphide waste material.

[0152] The heap of material may be configured for use in a microbially assisted heap leaching operation.

[0153] The present invention also provides a microbial assisted heap leaching operation for fragments of copper-containing sulfide ore or copper-containing sulfide waste, the heap leaching operation comprising:

[0154] (a) a pile of fragments of copper-containing sulphide ore or copper-containing sulphide waste (usually in the form of agglomerates of the fragments) and microorganisms and optionally other additives; and

[0155] (b) A system which (i) supplies an acidic leachate comprising sulfate to a heap so that the leachate flows downwardly through the heap and leaches copper from a copper sulfide-containing sulfide ore or a copper-containing sulfide waste, (ii) collects an enriched leachate comprising copper in solution from the heap wherein microorganisms oxidize ferrous iron to ferric iron, and (iii) controls the sulfate concentration in the leachate so that the sulfate concentration does not exceed a threshold concentration.

[0156] The present invention also provides a heap leaching operation as described in the preceding paragraphs, typically applied to a base metal-bearing sulphide ore or a base metal-bearing sulphide waste material.

[0157] The fragments may be in the form of agglomerates of the fragments, and the agglomerates may contain any one or more than one of the additives described above, including silver, sulfuric acid, pyrite, activators for silver, elemental sulfur, and complexing additives.

[0158] The agglomerates may contain other additives, such as surfactants, to facilitate contact of the additives with the solids.

[0159] When present, pyrite generates acid and heat in the heap which aids in leaching the metal from the copper-bearing sulfide ore or copper-bearing sulfide waste.

[0160] It should be noted that the generation of heat and acid is not limited to pyrite, and other sulfides (such as pyrrhotite, if present) may also generate heat and acid as by-products.

[0161] The copper-containing sulfide ore, the agglomerate of fragments of pyrite and the microorganism may be as described above.

[0162] Typically, heap leaching operations are started with low sulfate concentrations (typically 5 g / L) and increased over time.

[0163] The threshold concentration may be as described above.

[0164] The system for a heap leach operation may be configured to measure or simulate the oxygen utilization of the heap.

[0165] The system may be configured to control one or more of the operating parameters based on the measured data or the simulated data to maintain a predetermined oxygen utilization of the stack.

[0166] The system may be configured to select a ventilation rate for the stack based on a desired parameter value.

[0167] The system may be configured to select a stack aeration rate based on a desired oxidation rate of the stack.

[0168] The system can be configured to determine the oxidation rate of the copper-containing sulfide feed material as a function of any one or more of: oxygen content of the gas in the heap, enriched leach temperature, heap temperature, enriched leach metal content, enriched leach stream oxidation potential, enriched leach oxygen concentration, heap oxygen absorption rate, heap carbon dioxide absorption rate, and simulations based on at least one of feed composition, sulfide mineral leach rate, heap geometry, environmental conditions external to the heap, and historical values ​​of previously leached heaps.

[0169] The system may be configured to select a stack aeration rate based on desired microbial populations and / or activity.

[0170] The system can be configured to select a threshold sulfate concentration in the solution based on a desired microbial population and / or activity.

[0171] The system may be configured to select a stack ventilation rate based on a desired stack temperature.

[0172] The system may be configured to monitor the temperature at various locations in the stack.

[0173] Suitably, the system is configured to monitor the temperature at any point along the height of the pile, more suitably the temperature in the range from 1%-95% of the height of the pile below the surface of the pile.

[0174] The system may be configured to measure the temperature of the enriched leachate.

[0175] The system may be configured to control the rate at which the stack is flushed.

[0176] The system may be configured to aerate one or more lifts of the stack. Suitably, the system may be configured to aerate each lift of the stack.

[0177] Heap leaching operations may include units for processing the collected enriched leachate and recovering copper from the leachate.

[0178] The present invention also provides a heap of copper-containing sulfide ore or copper-containing sulfide waste, the heap being configured for use in a microbially assisted heap leaching operation, the heap comprising:

[0179] Support surface,

[0180] a layer of granular material located on a support surface,

[0181] a layer of copper-bearing sulphide ore or a layer of copper-bearing sulphide waste material, which is located on a layer of granular material,

[0182] an irrigation system configured to supply a solution, typically a hot solution, through the layer of granular material,

[0183] a collection system configured to collect an enriched leachate comprising copper in solution from the heap,

[0184] an aeration system configured to supply air to the heap to react with the copper-containing sulfide ore layer or the copper-containing sulfide waste layer, and

[0185] A control system that monitors and changes one or more operating parameters to maintain a predetermined sulfate concentration.

[0186] The present invention also provides a heap as described in the preceding paragraph, typically applied to a base metal-bearing sulphide ore or base metal-bearing sulphide waste.

[0187] Granular material may include crushed rock, sand or gravel.

[0188] The air blown by the ventilation system may be ambient air.

[0189] In some embodiments, air blown by the ventilation system is heated.

[0190] The ventilation system may be located on the support surface.

[0191] The support surface may include a liner.

[0192] The operating parameters may be any one or more of the following: heap oxygen concentration, heap carbon dioxide concentration, enriched leachate temperature, heap temperature, enriched leachate metal content, enriched leachate oxidation potential, heap oxygen absorption rate, heap carbon dioxide absorption rate, ambient conditions external to the heap, and sulfate concentration.

[0193] The stack may contain a carbon source for supporting cell growth. Suitable carbon sources may include inorganic carbon sources such as carbon dioxide and carbonates and / or organic carbon sources such as yeast. Carbon dioxide may be dissolved in the solution.

[0194] The heap may include a drainage system on the supporting surface. Adequate drainage of the heap is very important to minimize or avoid phreatic build up. Phreatic build up occurs when the leachate cannot flow through the heap, or flows through the heap inefficiently. This causes the heap to saturate from the bottom up and affects microbial activity.

[0195] The granular rock layer may have a P80 grain size in the range from 0.5 cm to 1 m, typically in the range from 0.5 cm-50 cm, and typically in the range from 0.5 cm-20 cm.

[0196] The stack may contain a sulphide-containing additive.

[0197] Suitable sulphide-containing additives may include pyrite or a suitable sulphide concentrate.The additive may generate heat and acid to facilitate the leaching process.

[0198] The stack may be configured into at least two process zones, ie lifts, wherein the leaching processes are at least partially independently controlled.

[0199] The aeration system may be configured to aerate one or more lifts of the stack. Suitably, the aeration system is configured to aerate each lift of the stack.

[0200] The pile may include a cover. The cover may be made of plastic such as polyethylene. The cover may include a biofilm (more for insulation than for other reasons). The cover may be applied on top of the pile. The cover may be applied within the pile. The cover may reduce air and heat loss. This may help minimize temperature gradients across the pile.

[0201] The collection system may be any suitable system known in the art. For example, the collection system may include ponds, tanks or barrels and their associated piping, suitably with pumps, to transfer the enriched leachate from the heap for further processing to recover copper from the enriched leachate.

[0202] The present invention also provides a method of constructing a heap of copper-containing sulfide ore or copper-containing sulfide waste, the heap being configured to maintain a predetermined sulfate concentration, the method comprising:

[0203] Provide a supporting surface for the pile,

[0204] forming a layer of granular material on a support surface,

[0205] A copper-containing sulfide ore layer or a copper-containing sulfide waste layer is formed on the granular material layer,

[0206] installing an irrigation system configured to supply a solution, typically a hot solution, through the layer of granular material,

[0207] installing a collection system configured to collect an enriched leachate comprising copper in solution from the heap,

[0208] installing an aeration system configured to blow air to react with the copper-containing sulfide ore layer or the copper-containing sulfide waste layer; and

[0209] A control system is installed to monitor the sulfate concentration of the stack and vary one or more operating parameters to maintain a predetermined sulfate concentration.

[0210] The present invention also provides a method as described in the preceding paragraphs, generally applicable to base metal-containing sulphide ores or base metal-containing sulphide wastes.

[0211] The method may include the step of embedding the carbon source in the heap.

[0212] A carbon source may be added to the leachate and / or the gas stream.

[0213] The method may include installing a drainage system on the support surface.

[0214] The method may include forming a layer of granular rock on a support surface.

[0215] The method may include adding elemental sulphur or a sulphide-containing additive to the pile.

[0216] The method may comprise configuring the stack into at least two process zones, wherein the leaching processes are at least partially independently controlled.

[0217] The method may include ventilating one or more lifts of the stack.

[0218] The method may include aerating each lift of the stack.

[0219] The method may include installing a cover on the pile.

[0220] The covering may comprise a plastic sheet.

[0221] The covering may be a biofilm.

[0222] Mulch can be applied on top of the pile.

[0223] Mulch can be applied to the pile.

[0224] In this manual:

[0225] • The expression "hot solution" refers to a solution at a temperature above ambient temperature. Suitably, the hot solution is at a temperature in the range from 30-85°C. Suitably, the hot solution is at 40°C.

[0226] • The term "take-off" means the point at which the power produced in the stack rises from a relatively low rate to a higher rate in a relatively short period of time; it is the system bifurcation point.

[0227] • The expression "average irrigation rate" means the total irrigation volume applied to the heap over the total duration of the leaching cycle, expressed as the average hourly irrigation rate per unit area.

[0228] The term "average aeration rate" means the total amount of gas that passes through the heap over the total duration of the leaching cycle. The rate may be expressed per unit mass (e.g. Nm 3 / h / t (metric tons).

[0229] • The expression "instantaneous irrigation rate" means the instantaneous irrigation rate applied to the heap during any period of time shorter than the total duration of a leaching cycle, expressed as the instantaneous hourly irrigation rate per unit area.

[0230] • The expression "instantaneous aeration rate" means the instantaneous gas flow rate applied during any period of time shorter than the total duration of a leaching cycle, expressed as the instantaneous hourly aeration rate per unit area.

[0231] • Unless otherwise indicated, the terms "irrigation rate" and "ventilation rate" refer to the instantaneous irrigation rate and the instantaneous ventilation rate, respectively.

[0232] • The term "stack oxygen utilization" means the total oxygen consumed within the stack expressed as a percentage of the total oxygen passing through the stack.

[0233] Invention 2

[0234] The present invention is based on the discovery that the formation of agglomerates of fragments of copper-containing sulphide ore or copper-containing sulphide waste in the presence of microorganisms in the agglomerates requires careful control of the agglomeration units.

[0235] The present invention provides a method of forming agglomerates for heap leaching copper-containing sulphide ore or copper-containing sulphide waste, the method comprising agglomerating fragments of copper-containing sulphide ore or waste and other feed materials in an agglomeration unit, the agglomeration unit having an inlet end and an outlet end, the inlet end and the outlet end being configured to move material along the length of the agglomeration unit from the inlet end to the outlet end, wherein the method comprises adding feed material at or near the inlet end, typically adding feed material no more than 40% of the length from the inlet end of the agglomeration unit, typically no more than 30%, more typically no more than 20%.

[0236] The present invention also provides a method as described in the preceding paragraphs, said method being generally applicable to a base metal-containing sulphide ore or a base metal-containing sulphide waste.

[0237] The method may comprise substantially completing the formation of agglomerates within a short distance from the inlet end of the agglomeration unit (typically no more than 40% of the length from the inlet end of the agglomeration unit).

[0238] Applicants have found that microorganisms attached to solids are more tolerant to high concentrations of sulfate than microorganisms in solution.

[0239] Importantly, applicants have found that the majority of microorganisms adhere to solids.

[0240] In one embodiment, approximately 90% of the microorganisms were found attached to the solid and 10% of the microorganisms were suspended in solution.

[0241] Thus, early formation of agglomerates provides a longer time for the microorganisms to attach to the solids (i.e., agglomerates) and to be evenly distributed within the agglomerates when in the agglomeration unit. Even distribution of the microorganisms provides the opportunity to reduce the "lag period" and to begin leaching more quickly during heap startup - the ramp-up period of the heap leaching operation is shorter. Reduced lag periods can also be achieved by using adapted microorganisms.

[0242] The applicant has also found during research and development work that, in particular when the base metal is copper, it is preferred to add the following feed materials in addition to the copper-containing sulphide ore and / or fragments of copper-containing sulphide waste ("ore / waste fragments") to the agglomeration unit:

[0243] (a) silver having catalytic properties to enhance the leaching of copper from copper-bearing sulphide ores or copper-bearing sulphide wastes,

[0244] (b) sulphuric acid,

[0245] (c) microorganisms which oxidize ferrous ions and oxidize solid and soluble sulfur compounds, thereby regenerating ferric ions and acid,

[0246] (d) optionally, an activator for activating silver selected from thiourea, chloride, bromide and iodide,

[0247] (e) optionally, a complexing additive that enhances the dissolution of copper from the copper mineral in the ore or waste by forming a complex between (i) sulfur derived from the copper mineral in the ore or waste and (ii) the additive,

[0248] (f) pyrite (or any other suitable material, such as elemental sulphur), which in the case of pyrite provides a source of ferrous ions and heat (and in the case of elemental sulphur, heat alone); and

[0249] (g) Water and / or an enriched leach solution from a heap leaching operation or a raffinate formed in a solvent extraction operation on an enriched leach solution.

[0250] Elemental sulfur may be a partial or complete substitute for sulfuric acid and / or pyrite.

[0251] Feed material may be added at the same location or at different locations along the length of the agglomeration unit.

[0252] For example, ore / waste fragments are typically added at the inlet of an agglomeration unit.

[0253] As a further example, the acid is typically added at multiple locations along a segment of the length of the agglomerated unit.

[0254] As a further example, typically the acid is added at one location and the microorganisms are added at another location further along the length of the agglomeration unit to minimize the effect of the acid on the microorganisms.

[0255] As a further example, adding pyrite (if used as feed material) near the end of a short distance, typically no more than 40% of the length from the inlet end of the agglomeration unit, makes it more likely that pyrite will form on exposed surfaces of the agglomerates.

[0256] Some feed materials may be added and mixed together in a pre-treatment step, and then the mixture is added to the agglomeration unit to ensure that the feed materials are fully mixed before agglomeration. For example, ore / waste fragments and silver (such as silver nitrate solution) may be pre-mixed before the mixture is added to the agglomeration unit to maximize the contact of the silver with the copper-containing minerals in the ore / waste fragments. For example, a pyrite concentrate slurry underflow from a concentrator may be pre-mixed with ore / waste fragments before being directed to agglomeration.

[0257] The pretreatment step may be performed in any suitable unit such as an agglomeration unit.

[0258] Suitably, the microorganisms are added last.

[0259] In one embodiment, the order of addition along a section of the length of the agglomerated unit is as follows:

[0260] - a mixture of ore / waste fragments and silver nitrate (or other suitable form of silver),

[0261] - then water, typically water from the raffinate,

[0262] - then acid, optionally at multiple locations,

[0263] - then pyrite or elemental sulfur,

[0264] -Then microbes.

[0265] It should be noted that the order of addition can be changed as desired. For example, pyrite and microorganisms can be added to the agglomeration unit together.

[0266] The copper-containing sulfide ore or copper-containing sulfide waste may include naturally occurring silver, which may have catalytic properties for copper leaching. Naturally occurring silver may be present in the copper-containing ore or copper-containing sulfide waste in one or more of a variety of forms, including but not limited to native silver, argentite (Ag2S), argillite (AgCl), as an inclusion of native silver in copper minerals and pyrites, and as thiosilver salts such as tetrahedrite (Cu,Fe,Zn,Ag 12 Sb4 13 ), pyrargyrite (Ag3SbS3) and proustite (Ag3AsS3).

[0267] The added silver may be added to the agglomeration step in any suitable form, such as in solid form or in solution.

[0268] The added silver may be added in the agglomeration step in solid form which becomes mobile when dissolved with the leachate.

[0269] The added silver may be precipitated or otherwise deposited onto the surface of the fragments of the copper-containing sulfide ore.

[0270] The added silver may be dispersed on the surface of fragments of the copper-containing sulfide ore or copper-containing sulfide waste.

[0271] The added silver may be dispersed in fragments of the copper-bearing sulfide ore or copper-bearing sulfide waste.

[0272] The added silver may be in soluble form in the agglomerates.

[0273] The added silver may be in an insoluble form or in a slightly soluble form in the agglomerates.

[0274] The agglomerates may have a low total silver concentration, both added silver and naturally occurring silver.

[0275] The concentration of added silver in the agglomerates may be less than 5 g silver / kg copper in the ore in the agglomerates, typically less than 3 g silver / kg copper in the ore in the agglomerates, more typically less than 1 g silver / kg copper in the ore in the agglomerates.

[0276] The acid dosage rate may be less than 100 kg H2SO4 / dry t ore, typically less than 50 kg H2SO4 / dry t ore, more typically less than 30 kg H2SO4 / dry t ore, and may be less than 10 kg H2SO4 / dry t ore or less than 5 kg H2SO4 / dry t ore. Typically, the acid dosage rate is 0.5-30 kg H2SO4 / dry t ore.

[0277] The microorganism may be any suitable microorganism.

[0278] The microorganism may be any microorganism having the ability to oxidize ferrous and / or sulfur compounds, and includes, but is not limited to, members of the bacterial genera Acidithiobacillus, Leptospira, Thiobacillus, and Ferrobacterium, and the archaeal genera Acidobacterium, Acidoplasma, Ferroplasma, Metallosphaera, and Pyrogenus.

[0279] Typically, the microorganisms are a diverse group including microorganisms selected from mesophiles, mesophiles and thermophiles, psychrophiles or mesophiles or thermophiles (moderate or extreme) bacteria or archaea. The microorganisms can be acidophiles or archaea. The microorganisms can be thermophiles and acidophiles. The diverse groups allow activity across a range of temperatures.

[0280] The complexing additive may be any suitable agent.

[0281] As an example, the complexing additive may be a nitrogen-containing agent that includes at least two nitrogen atoms separated by two carbon atoms to allow the additive to form a complex between sulfur derived from the copper mineral in the ore and the agent.

[0282] The pyrite may be in any suitable form, such as in solid form or in the form of a slurry.

[0283] Pyrite may be 1 wt.% - 25 wt.% of the total mass of the agglomerates.

[0284] Pyrite may be 1 wt.% - 20 wt.% of the total mass of the agglomerates.

[0285] Pyrite may be 1 wt.% - 10 wt.% of the total mass of the agglomerates.

[0286] Pyrite may be obtained from any suitable source. It may already be contained in ore or waste materials.

[0287] For example, pyrite may be in tailings from a mine tailings dam or an ore processing facility, ie, a slurry containing pyrite, wherein the slurry is used directly in the agglomeration step. In addition, for example, pyrite may be in a flotation concentrate produced from tailings.

[0288] The term "ore processing plant" is understood herein to mean any suitable plant for recovering metals from mined ore.

[0289] The pyrite particles may be of any suitable size.

[0290] The pyrite particles in the pyrite-containing material may have a particle size P80 of 1 mm or a value <1 mm.

[0291] The pyrite particles in the pyrite-containing material may have a particle size P80 of 250 μm or a value <250 μm.

[0292] The present invention also provides a pile of materials, wherein the materials include agglomerates of the above-mentioned copper-containing sulfide ore or fragments of copper-containing sulfide waste.

[0293] The present invention also provides a microbial assisted heap leaching operation for copper-containing sulfide ore or copper-containing sulfide waste, the heap leaching operation comprising:

[0294] (a) a pile of agglomerates of the above copper-containing sulphide ore or copper-containing sulphide waste; and

[0295] (b) A system which (i) supplies an acidic leachate to a heap so that the leachate flows downwardly through the heap and leaches copper from a copper sulfide-containing sulfide ore or a copper sulfide-containing waste material, and (ii) collects the enriched leachate containing copper in solution from the heap, wherein microorganisms oxidize ferrous iron to ferric iron.

[0296] The present invention also provides an operation as described in the preceding paragraphs, said operation being generally applied to a base metal-bearing sulphide ore or base metal-bearing sulphide waste.

[0297] General

[0298] The copper-containing sulphide ore or copper-containing sulphide waste may be derived from any suitable mined ROM material.

[0299] The term "mined ROM material" is understood herein to include fragments of ROM material, which may be ROM ore or ROM waste, which are obtained from the location of a mine from which the ROM material is mined:

[0300] i. directly transferred to the heap; or

[0301] ii. directly to a stockpile and then directly to a pile thereafter; or

[0302] iii. Transfer for intermediate processing as described herein and then to a stack; or

[0303] iv. transferred for intermediate processing as described herein, and then transferred to a stockpile, and then thereafter to a heap; or

[0304] v. directly transferred to a stockpile, and then transferred for intermediate processing as described herein, and then transferred to a heap; or

[0305] vi. A combination of the aforementioned options iv. and v., wherein intermediate processing is carried out before and after the stockpile.

[0306] As discussed above, ROM material may be fragments that are reduced in size as a result of mining the ROM material and transferring the ROM material from the mine to a stockpile, stockpile or intermediate processing facility rather than as a result of a specific comminution step.

[0307] An example of a copper-bearing sulfide ore is a rock that contains low concentrations of copper.

[0308] The copper-containing sulphide ore may be in the form of as-mined material or a stockpile of copper-containing sulphide ore having a low grade, ie a low concentration, of copper in the material.

[0309] The term "low grade" as used in relation to the "copper-bearing sulfide ore" referred to above is understood herein as a term that depends on currently available technology and the current price of copper, and depending on technological developments and future prices of copper, materials currently considered "low grade" may be considered valuable materials in the future.

[0310] In the context of the preceding paragraphs, the term "low concentration of copper" is understood to mean an average copper concentration of ≤1.5% by weight, typically ≤1.2 wt.%, more typically ≤1.0 wt.%, even more typically ≤0.7 wt.%, even more typically ≤0.5 wt.%, even more typically ≤0.3 wt.%, even more typically ≤0.1 wt.%.

[0311] The method may include reducing the size of as-mined or stockpiled copper-containing sulphide ore prior to agglomeration.

[0312] The method may comprise comminuting the as-mined or stockpiled copper-containing sulphide ore and producing a suitable particle size distribution for the agglomeration step.

[0313] The comminution step may comprise crushing the as-mined or stockpiled copper-bearing sulphide ore in one or more comminution circuits which reduce the size of the material.

[0314] The comminution step may include successively comminuting the as-mined or stockpiled copper-bearing sulphide ore in a primary comminution circuit, a secondary comminution circuit and a tertiary comminution circuit as these terms are understood by copper mining industry personnel.

[0315] The comminution step may comprise a single or multiple comminution steps delivering as-mined or stockpiled copper-bearing sulphide ore that has been comminuted to produce material having the desired particle size distribution for the agglomeration step.

[0316] As an example, the term "primary crushing" is understood herein to mean crushing a copper-containing sulphide ore to an upper size limit of 300 mm. It should be noted that the upper size limit may be different for ores containing different metal values.

[0317] The above description under the heading "General" with respect to copper-containing sulphide ores applies equally to copper-containing sulphide waste materials and ROM ores. BRIEF DESCRIPTION OF THE DRAWINGS

[0318] The present invention is further described with reference to the accompanying drawings, in which:

[0319] Figure 1 The figure shows the steps of a method for microbiologically assisted heap leaching of agglomerates of fragments of a copper-containing sulfide ore containing chalcopyrite (CuFeS2), arsenite (Cu3AsS4), tetrahedrite (Cu, Fe, Zn, Ag) with a leachate according to an embodiment of the present invention. 12 Sb4 13 ), chalcopyrite (Cu 12 A4S 13 ), chalcocite (Cu2S), covellite (CuS), bornite (Cu5FeS4) or any combination thereof, or other sulfide minerals containing copper,

[0320] Figure 2 is a schematic diagram of an agglomeration unit for producing agglomerates of fragments of a copper-containing sulfide ore according to an embodiment of the present invention,

[0321] Figure 3 is a graph of microbial counts of microorganisms in the enriched leachate and on the solids versus sulfate concentration, which shows the effect of solution sulfate concentration on the cell populations in solution and on the ore solids for moderately thermophilic microorganisms at 50°C,

[0322] Figure 4 is a graph of microbial counts of microorganisms versus sulfate concentration, which shows the maximum bacterial cell concentration versus sulfate concentration for extreme thermophilic microorganisms at 60°C,

[0323] Figure 5 is a graph of copper extraction versus time for leach solutions having different sulfate concentrations, the graph illustrating the effect of starting solution sulfate concentration (first value in the legend) and maximum sulfate operating level (second value) on the extraction of copper from a primary copper sulfide-dominated ore in a column test operated at 60°C,

[0324] Figure 6is a graph of the ratio of ferric to ferrous iron versus time for columns inoculated with the adapted inoculum solution (C218) and the adapted inoculum slurry during agglomeration (C227); and

[0325] Figure 7 is a graph of the ferric to ferrous iron ratio for columns inoculated with the adapted inoculum solution (C221) and the adapted inoculum slurry during agglomeration (C226).

[0326] Description of the implementation plan

[0327] The following description is in the context of heap leaching agglomerates of fragments of copper-containing sulphide ROM material in ore form.

[0328] The following description is in the context of microbially assisted heap leaching of copper-containing sulfide ores with a leachate.

[0329] Figure 1 The flow chart shows the steps in one embodiment of a method of microbially assisted heap leaching of agglomerates of fragments of a copper-containing sulfide ore comprising chalcopyrite and / or fusostrea with a leachate.

[0330] refer to Figure 1 , copper-containing sulfide ROM ore 5 from mine 3, such as ore containing chalcopyrite and / or arsenic copper ore, is crushed in a crusher 7. The ore is crushed into fragments with a suitable particle size distribution for downstream processing of the fragments. The crushed ore fragments 9 are transferred to the agglomeration unit 11 and formed into agglomerates 25 containing fragments of the crushed copper ore. Agglomerates 25 are transferred to a heap 27. Leaching solution 39 is supplied to the upper surface of the heap 27 and is allowed to penetrate through the heap 27 and bring copper into the solution. The enriched leachate 29 containing copper in the solution is collected from the heap and processed in a copper recovery circuit 31. Circuit 31 can be a solvent extraction and electrowinning circuit. Copper product 33 is produced in circuit 31. Spent leachate 35, i.e., raffinate in the case where circuit 31 is an SX circuit, is transferred to a regeneration circuit 37. Any one or more of water, acid, microorganisms, and other additives are added as needed to produce a regenerated leachate 39 that is returned to the heap 27 .

[0331] refer to Figure 1 and Figure 2 In this embodiment, the following feed materials are transferred to the agglomeration unit 11 and mixed together and form agglomerates in the unit 11, wherein the feed materials are added at or near the inlet of the unit 11 and agglomerates are formed at a short distance along the length of the unit (typically within 40% of the length of the unit 11):

[0332] (a) crushed fragments 9 of the above-mentioned copper-containing sulfide ore,

[0333] (b) silver 13 having catalytic properties to enhance the leaching of copper from copper-containing sulphide ores, in this embodiment provided as a silver solution (but may be in solid form) which typically has an added concentration of silver of less than 5 g silver / kg copper in the ore in the agglomerates, wherein added concentration means a concentration of silver in addition to the concentration of silver naturally present in the ore,

[0334] (c) an acid 15, typically sulfuric acid at any suitable concentration,

[0335] (d) microorganisms 17 of any suitable type and in any suitable concentration that oxidize ferrous ions and oxidize solid and soluble sulfur compounds, thereby regenerating iron ions and protons,

[0336] (e) a silver activator 19, typically thiourea, chloride, bromide or iodide,

[0337] (f) an additive 21 that enhances the dissolution of copper from the copper mineral in the ore by forming a complex between (a) sulfur derived from the copper mineral in the ore and (b) the additive,

[0338] (g) pyrite 23 (or any other suitable material) for providing a source of ferrous ions and heat, in this embodiment a pyrite-containing concentrate derived from tailings - typically in the range of 1% to 20% pyrite in the agglomerates 25, and

[0339] (h) Water from any suitable water source (not shown).

[0340] As described further below, the feed materials may be added simultaneously or in any suitable order.

[0341] Typically, the microorganisms are added last.

[0342] In some embodiments, the microorganisms are added last and farthest from the inlet of the agglomeration unit 11.

[0343] It should be noted that the present invention is not limited to the use of all the above additives.

[0344] Furthermore, it should be noted that the present invention extends to the use of other additives.

[0345] For example, an optional additive is a surfactant to facilitate contact of the additive with the solid.

[0346] The agglomeration unit 11 may be any suitable agglomeration unit, such as a drum having an inlet end and an outlet end mounted at an inclined angle for rotation about an elongated axis of the drum, wherein the inlet is located at a higher level than the outlet so that material added to the drum tends to move down the drum to the outlet.

[0347] The agglomeration unit feed materials mentioned above, i.e. crushed ore fragments 9, silver 13, acid 15, microorganisms 17, activator 19 and complexing additive 21, pyrite 23 and water (as required - typically raffinate or fresh water) are added at or near the inlet end of the agglomeration unit 11 along the length of the drum, typically at not more than 40%, typically not more than 30%, more typically not more than 20%.

[0348] Typically, the addition of the above feed materials results in substantially complete formation of agglomerates along a short distance (usually no more than 40%) along the length of the drum.

[0349] In one embodiment, the order of addition along a section of the length of agglomeration unit 3 is as follows:

[0350] - a mixture of ore / waste fragments and silver nitrate (or other suitable form of silver),

[0351] - then water, typically water from the raffinate, but it can be fresh water,

[0352] - then acid, optionally at multiple locations,

[0353] - then pyrite or elemental sulfur,

[0354] -Then microbes.

[0355] The order of addition can be changed as desired. For example, pyrite and microorganisms can be added together in agglomeration unit 3.

[0356] Agglomeration Unit Feed material may be added to the agglomeration unit 11 in any suitable manner.

[0357] For example, silver 13 may be added as a solution in a fine mist or spray or as solid particles in an aerosol. The applicant has found that this is a particularly suitable way to achieve the desired dispersion of silver on the ore fragments - see International Publication WO2017 / 070747 in the name of the applicant, and the disclosure is incorporated herein by cross-reference. The choice of mist / spray / aerosol as the medium for adding silver to the chalcopyrite ore fragments allows for maximizing the delivery of low concentrations of silver to substantially larger mass (and large surface area) and substantial proportions of chalcopyrite (or other copper sulfide mineral) ore fragments.

[0358] The agglomeration unit feed material may be added to the agglomeration unit 11 in any suitable concentration, taking into account a range of factors including, for example, the mineralogy of the ore, the particle size distribution of the ore fragments, the dimensions (length and diameter of the drum), the target throughput of the agglomeration unit 3, the expected attrition of the agglomerates in the drum and the required mechanical properties of the agglomerates.

[0359] For example, the complexing additive 21 may be added to the drum or leachate 39 at a concentration of up to 10 g / L, up to 5 g / L, up to 2.5 g / L, up to 1.5 g / L, up to 1.25 g / L, or up to 1 g / L in the leachate. When the additive is a polymer-like additive, such as a longer chain organic substance, such as polyethyleneimine (PEI), it may be preferred to add the additive while the agglomerates are being formed in the agglomeration unit 3, rather than adding the additive to the leachate.

[0360] Mixing the feed material for agglomerates 25 and agglomerating the feed material may occur simultaneously.

[0361] Alternatively, mixing of the feed materials may be performed first, and agglomeration may be performed after mixing has been completed to the desired extent (eg, initiated by addition of acid 15).

[0362] Furthermore, the times for adding the feed materials and then mixing and agglomerating the feed materials can be selected to meet the end-use requirements of the agglomerates 25. For example, in some cases, it may be preferred to start mixing the chalcopyrite-containing fragments, and then gradually add silver in solution or in solid form, acid, and microorganisms in that order at different start and end times in the agglomeration step. As a specific example, in some cases, it may be preferred to start mixing the chalcopyrite-containing fragments, and then add silver and acid together in solution or solid form, and then add microorganisms at different start and end times in the agglomeration step.

[0363] The feed material can be added at the same location or at different locations along a short distance of the length of the agglomeration unit (typically no more than 40% of the length from the inlet end of the agglomeration unit). For example, acid 15 is usually added at one location and microorganisms 17 are added at another location further along the length of the agglomeration unit to minimize the effect of the acid on the microorganisms. As a further example, pyrite 23 is added near the end of the short distance so that pyrite is more likely to form on the exposed surface of the agglomerates 25. In addition, there can be multiple locations for adding portions of the same additive.

[0364] Some additives may be pre-mixed with the ore just prior to agglomeration. This provides a more thorough mixing. In one example, the ore is mixed with pyrite concentrate thickener underflow slurry prior to agglomeration.

[0365] Agglomerates 25 produced in agglomeration unit 11 can be directly transferred to a building site for pile 27. Alternatively, agglomerates 25 can be stacked and used as needed for pile 27—for example, added to the continuous lifting of pile 27. Agglomeration unit 11 and pile 27 are usually in close proximity. However, this is not necessary and may not be the case.

[0366] The method of agglomerating mined ore fragments described above is suitable for forming agglomerates that can be used in a standard heap.

[0367] The present invention is not limited to a specific shape and size of the heap, and is not limited to a specific method of building the heap from the agglomerates, and is not limited to specific operating steps of the heap leaching process for the heap.

[0368] By way of example only, the heap 27 may be a heap of the type described in International Publication WO 2012 / 031317 in the name of the present applicant and the disclosure of the heap construction and heap leaching process in that International Publication is incorporated herein by cross reference.

[0369] The stack 27 may be of any suitable stack configuration and is provided with:

[0370] (a) a leachate storage and delivery system that supplies leachate 39 to the upper surface of the heap;

[0371] (b) an enriched leachate collection system for collecting a leachate 29 containing copper in solution extracted from the copper sulfide-containing material in the agglomerates 25 in the heap 27; and

[0372] (c) Another microorganism (such as bacteria or archaea) or other suitable oxidizing agent that oxidizes the ferrous iron to ferric iron, wherein the ferric iron and protons decompose the mineral matrix and dissolve the copper.

[0373] In one example, the heap 27 comprises a support surface, a layer of granular material comprising crushed rock having a P80 particle size in the range of from 30 mm to 2000 mm, and a layer of feed material containing chalcopyrite. The purpose of the crushed rock is to allow the leachate to drain. The feed material includes the agglomerates described above. The feed material may also include tailings produced by processing the chalcopyrite feed material in another copper recovery method.

[0374] The layer of feed material containing chalcopyrite forms the initial lift of the feed material to be leached.

[0375] In use, when leaching of an initial lift reaches a selected point, a new layer of feed material is added to the heap to form a new lift which is subsequently leached, and so on.

[0376] An aeration system located on the support surface is used to blow ambient air through each lift at or near the bottom of the first lift, and optionally through the bottom of subsequent lifts, to react with the feed material. In addition, an irrigation system located on top of the heap is configured to supply an irrigation solution, which may include nutrients for microorganisms and pyrite to facilitate the leaching process and maintain the heap at a temperature ranging from 40°C to 70°C.

[0377] The control system monitors and changes one or more operating parameters to maintain a predetermined sulfate concentration in the leachate. The operating parameters can be controlled to ensure that the sulfate concentration in the leachate does not exceed a threshold concentration of 170 g / L sulfate in the leachate collected from the pile. The irrigation solution can be dosed with a carbon source such as carbon dioxide, carbonates, or yeast. A covering composed of a plastic sheet or biofilm can be applied on top of the pile to reduce air and heat losses and minimize temperature gradients across the pile.

[0378] Drainage systems are also installed on the supporting surface to avoid submerged accumulation.

[0379] Heap operation includes controlling the operation so that the sulfate concentration in the leachate does not exceed a threshold concentration.

[0380] As mentioned above, the applicants have discovered that it is possible to operate microbially assisted heap leaching of agglomerates of fragments of copper-containing sulphide ore or copper-containing sulphide waste having high sulphate concentrations in the acidic leach solution.

[0381] Sulfate concentration can be controlled in a variety of ways.

[0382] One way is to control the aeration rate of the pile. This regulates the amount of oxygen entering the pile, and therefore the amount of oxygen supplied to the microorganisms. The aeration rate is controlled to provide a microbial population sufficient to ensure that the leachate collected from the pile does not exceed a threshold concentration of 170 g / L sulfate.

[0383] The above findings were Figures 3 to 7 The results of the experimental work summarized in are indicated.

[0384] Figure 3is a graph of microbial counts of microorganisms in enriched leachate and on solids versus sulfate concentration, which shows the effect of solution sulfate concentration on the cell population in solution and on ore solids for a 50°C moderately thermophilic microbial culture (typically containing up to 20 different species of microorganisms). Note that the logarithmic y-axis graph shows that the cell count of this culture decreases much more slowly with increasing sulfate concentration for the microorganisms on solids. There is a greater magnitude decrease in cell count for the microorganisms in the enriched leachate. This suggests that microorganisms attached to solids are more tolerant of sulfate than microorganisms in solution. Attachment of microorganisms to solids is important for maintaining sufficiently high cell counts at higher sulfate concentrations to enable heap leaching to proceed at commercially practical rates.

[0385] Figure 4 is a graph of microbial counts versus sulfate concentration for a culture of an extreme thermophilic microorganism at 60°C. Figure 3 Compared with the cultures Figure 4 The cultures had higher numbers of cells in the solution population over the entire range of sulfate concentrations. Comparison of these figures, and taking into account the different samples and growth techniques tested, indicates that Figure 4 The ratio of cells in the solution Figure 3 The cells in the solution at 50 °C were more tolerant to sulfate.

[0386] Figure 5 is a graph of copper extraction versus time in column tests operated at 60°C on a chalcopyrite-dominated copper ore using an extreme thermophilic microbial culture with different starting (first value in the legend) sulfate concentrations and maximum operating level (second value) sulfate concentrations for the leaching solution. Similar high copper extractions (86%-89%) were achieved for all three tests. The results demonstrate the excellent performance of the culture over a wide sulfate operating range and high sulfate threshold concentrations.

[0387] Figure 6 : is a graph of the ferrous to ferrous ratio versus time for columns operated on copper ore inoculated with an adapted inoculum solution (C218) and an adapted inoculum solution plus slurry (C227) added during agglomeration. The columns were leached with a starting solution containing ferric iron. The ferrous to ferrous ratio initially decreased due to the reaction of the iron with the sulfide minerals, followed by a lag period, after which the ferrous to ferrous ratio increased rapidly due to the onset of high microbial activity. The columns inoculated with the adapted inoculum solution plus slurry exhibited a shorter lag period than the columns inoculated with the adapted inoculum solution, indicating that high microbial activity occurred more quickly.

[0388] Figure 7is a graph of the ferrous to ferrous ratios for another set of columns inoculated with an adapted inoculum solution (C221) and an adapted inoculum slurry during agglomeration (C226), operating on different copper ores. The results obtained are consistent with Figure 6 The results are similar to those described in .

[0389] Many modifications may be made to the embodiments of the present invention as hereinabove described with reference to the accompanying drawings without departing from the spirit and scope of the invention.

[0390] As an example, although the embodiments are described in the context of intermediate processing of fragments of copper-bearing sulphide ROM ore 5 by crushing in a crusher 7 and then agglomerating in an agglomeration unit 15, the invention also extends to other intermediate processing steps, such as grade sorting or size separation (e.g. on a screen).

[0391] As an example, although embodiments have been described in the context of heap leaching agglomerates of fragments of copper-containing sulphide ROM material in ore form, the invention also extends to heap leaching non-agglomerated ore fragments.

[0392] As an example, while embodiments are described in the context of heap leaching agglomerates of fragments of copper-bearing sulphide ROM material in ore form, the invention also extends to heap leaching of agglomerated or non-agglomerated fragments of ROM material in waste form.

[0393] As an example, although an embodiment is described in the context of fragments of copper-containing sulfide ROM ore 5 being directly transferred for intermediate processing by being crushed in a crusher 7 and then agglomerated in an agglomeration unit 15, respectively, the present invention also extends to an embodiment in which the fragments of copper-containing sulfide ROM ore 5 are first transferred to a stockpile (not shown) and retained in the stockpile until (a) being transferred directly to a heap or (b) being transferred to intermediate processing, such as being crushed in a crusher 7 and then agglomerated in an agglomeration unit 15, respectively, and then being transferred to a heap.

[0394] As an example, the invention also extends to embodiments in which (a) there is intermediate processing of fragments of the copper-bearing sulphide ROM ore 5 (e.g. crushing), (b) the intermediate processed ROM ore is transferred to a stockpile and stored in the stockpile, (c) there is intermediate processing of the stockpiled intermediate processed ROM ore (such as agglomeration), and (d) the agglomerates are transferred to a heap and leached in the heap.

Claims

1. A method for microbial assisted heap leaching of a base metal-containing sulfide ore or a base metal-containing sulfide waste, the method comprising: Supplying an acidic leachate containing sulfate to a heap of fragments or agglomerates of fragments of a base metal-bearing sulfide ore or a base metal-bearing sulfide waste material and allowing the leachate to flow through the heap and leach base metals from the fragments, collecting the leachate from the heap, and processing the collected leachate and recovering base metals from the leachate, wherein any one or more of the fragments, the agglomerates of the fragments (when present) and the leachate contain microorganisms, and the method controls the sulfate concentration in the leachate so that the sulfate concentration does not exceed a threshold sulfate concentration.

2. The method of claim 1 , comprising monitoring the sulfate concentration in the leachate collected from the heap and controlling the method as required so that the sulfate concentration in the leachate does not exceed a threshold concentration.

3. A method according to claim 1 or claim 2, comprising indirectly controlling a parameter other than sulfate concentration that affects the sulfate generation rate, such that changing the parameter causes a known change in the sulfate concentration.

4. A method according to any one of the preceding claims, wherein the threshold sulfate concentration in the leachate collected from the heap is 170 g / L sulfate.

5. A method according to any one of the preceding claims, wherein during a start-up phase of the method, in a leachate collected from the heap, the threshold sulfate concentration is at least 20 g / L.

6. A process according to any one of the preceding claims, wherein in a later leaching stage after start-up of the process, in the leachate collected from the heap, the threshold sulphate concentration is 50 g / L - 100 g / L.

7. A method according to any preceding claim comprising controlling the temperature of the stack to below 85°C.

8. A process as claimed in any one of the preceding claims including an agglomeration step for forming agglomerates of fragments of the copper-bearing sulphide ore or copper-bearing sulphide waste material for use in subsequent heap leaching in the process.

9. A method of forming agglomerates for heap leaching of a base metal sulphide ore or base metal sulphide waste, the method comprising agglomerating broken pieces of the base metal sulphide ore or base metal sulphide waste and other feed materials in an agglomeration unit, the agglomeration unit having an inlet end and an outlet end, the inlet end and outlet end being configured to move material along the length of the agglomeration unit from the inlet end to the outlet end, wherein the method comprises adding the feed material at or near the inlet end.

10. A method according to claim 9, comprising adding the feed material over a short distance along the length of the agglomeration unit, the short distance typically not exceeding 40%, typically not exceeding 30%, more typically not exceeding 20% ​​of the length from the inlet end of the agglomeration unit.

11. A method according to claim 9, comprising substantially completing the formation of agglomerates within a short distance along the length of the agglomeration unit, the short distance typically not exceeding 40% of the length from the inlet end of the agglomeration unit.

12. The method of any one of the preceding claims, wherein when the base metal is copper, the other feed material comprises a combination selected from: (a) silver having catalytic properties to enhance the leaching of copper from copper-bearing sulphide ores or copper-bearing sulphide wastes, (b) sulphuric acid, (c) microorganisms which oxidize ferrous ions and oxidize solid and soluble sulfur compounds, thereby regenerating iron ions and protons, (d) optionally, an activator for activating silver selected from thiourea, chloride, bromide and iodide, (e) optionally, a complexing additive that enhances the dissolution of copper from the copper mineral in the ore or waste by forming a complex between (i) sulfur derived from the copper mineral in the ore and (ii) the additive, (f) pyrite or elemental sulfur, which provides a source of ferrous ions (pyrite), acid, and heat (both pyrite and elemental sulfur), and (g) one or more of water and / or other water sources, an enriched leach solution from a heap leach operation, a raffinate formed in a solvent extraction operation on the enriched leach solution.

13. A microbial assisted heap leaching operation for a base metal-containing sulfide ore or a base metal-containing sulfide waste, the heap leaching operation comprising: (a) a pile of fragments of the base metal-containing sulfide ore or base metal-containing sulfide waste and microorganisms; as well as (b) A system which (i) supplies an acidic leachate comprising sulfate to the heap such that the leachate flows downwardly through the heap and leaches base metals from the base metal-bearing sulfide ore or base metal-bearing sulfide waste, (ii) collects an enriched leachate from the heap, the enriched leachate comprising base metals in solution, wherein the microorganisms oxidize ferrous iron to ferric iron, and (iii) controls the process such that the sulfate concentration in the leachate does not exceed a threshold concentration.

14. A heap leaching operation as claimed in claim 12, wherein when the base metal is copper and the fragments are in the form of agglomerates of fragments, the agglomerates comprise: (a) silver having catalytic properties to enhance the leaching of copper from copper-bearing sulphide ores or copper-bearing sulphide wastes, (b) acid, (c) optionally, an activator for activating silver selected from thiourea, chloride, bromide and iodide, (d) optionally, a complexing additive that enhances the dissolution of copper from the copper mineral in the ore or waste by forming a complex between (i) sulfur derived from the copper mineral in the ore or waste and (ii) the additive, (e) pyrite or elemental sulfur, which provides a source of ferrous ions (pyrite), acid, and heat (pyrite and elemental sulfur); and (f) water and / or other water sources and / or an enriched leach solution from a heap leaching operation or a raffinate formed in a solvent extraction operation of said enriched leach solution.

15. A heap of base metal-bearing sulphide ore or base metal-bearing sulphide waste material configured for use in a microbially assisted heap leaching operation, the heap comprising: Support surface, a layer of granular material located on the support surface, a layer of base metal-containing sulphide ore or a layer of base metal-containing sulphide waste material, which is located on the layer of granular material, an irrigation system configured to supply a solution through the layer of granular material, a collection system configured to collect an enriched leachate from the heap, the enriched leachate comprising base metals in solution, an aeration system configured to blow air to react with the base metal-containing sulfide ore layer or the base metal-containing sulfide waste layer, and A control system that monitors and changes one or more operating parameters to maintain a predetermined sulfate concentration.

16. A method of constructing a heap of a base metal-containing sulphide ore or base metal-containing sulphide waste, the heap being configured to maintain a predetermined sulphate concentration, the method comprising: providing a support surface for the stack, forming a layer of granular material on the support surface, forming a base metal-containing sulfide ore layer or a base metal-containing sulfide waste layer on the granular material layer, installing an irrigation system configured to supply a solution through the layer of granular material to heat the layer of granular material, installing a collection system configured to collect an enriched leachate from the heap, the enriched leachate comprising base metals in solution, installing an aeration system configured to supply air to the heap to react with the base metal-bearing sulfide ore layer or base metal-bearing sulfide waste layer, and A control system is installed to monitor the sulfate concentration of the stack and vary one or more operating parameters to maintain a predetermined sulfate concentration.

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