Bioheap leach

Abstract

An inoculated sulphide concentrate comprising a pyrite-containing sulphide particulate composition, wherein the particle surfaces of the sulphide composition are coated with a microbial mix and a method of bioheap leaching of a sulphide ore in which the acidity and temperature of the heap are enhanced. The concentrate 14 is blended through a particulate ore to be leached 16; and the blended ore 18 is stacked in a heap 20 which is leached with an irrigation liquid to recover the contained values in the concentrate and the ore. 20 23 28 60 25 28 D ec 2 02 3 2 0 2 3 2 8 6 0 2 5 2 8 D e c 2 0 2 3 1 / 4 3.10 DAVID Fig. 2 Fig. 1 10 14 18 20 12 16 Rate of aeration Rate of irrigation Excessive heat loss in air flow Excessive heat loss in PLS A B C 1 / 4 10 14 12 18 20 16 Fig. ] Rate of Aaeration Excessive heat loss in air flow Excessive heat loss in PLS B Rate of irrigation C Fig. 2 20 23 28 60 25 28 D ec 2 02 3 2 8 D e c 2 0 2 3 2 0 2 3 2 8 6 0 2 5 B

Description

RELATED APPLICATIONS The present application claims priority to US Patent Application No. 63 / 436,161 dated 30 December 2022, the entire contents of which are herein incorporated. BACKGROUND OF THE INVENTION Bio-heap leaching of sulphidic copper or nickel or gold or uranium ores requires ore preparation to achieve the heap permeability to adequately distribute gas and liquid flows, and hence control the gas and liquid flow rates through the heap to maintain the conditions in a suitable range to promote the bacteria populations, and an acidity and oxidation potential and temperature in a reaction zone that is conducive to leaching of the values. The heap operating temperature is a consequence of the rate of the exothermic sulphide oxidation in the heap, and the heat losses in the gas and liquids exiting the heap. Hence, the achievable heap temperature is a function of the ore type, the heap design, and the management of these variables. The temperature management of the heap is particularly important when the minerals to be leached are refractory or slower reacting, such as chalcopyrite and pentlandite and sphalerite. Typically, temperatures of around 70°C, for periods of a few months or more, are desirable to achieve high extractions for these ores. The acidity in any part of the heap is also particularly important to the sulphide oxidation rates within the heap, including that of initiating pyrite oxidation as the main form of acid generation within most heaps. There is a critical acidity level required to maintain an active sulphide leaching zone, loosely approximating the pH where some ferric ion is soluble. Without 2023286025   28 Dec 2023 adequate acidity the ferric level and hence the sulphide oxidation is slow, and hence heat generation within the heap is also minimal. Acid from external sources can be dosed into the heap in two places. The first is the mixing that occurs during ore preconditioning, possibly in conjunction with agglomeration of the ore, and the second is by addition of acid to the irrigant. When added during ore preconditioning, the acid is distributed throughout the ore to be stacked. But unless the acid is added in uneconomic quantities, the acid is neutralised by the most reactive gangue components by the time the ore is stacked and irrigation to dissolve the values can commence. Typical pH values at the start of irrigation are well above the pH required to sustain soluble ferric ion. Acid added during irrigation is added from the top of a lift, and is consumed by reactive gangue as the leachant trickles down through the heap. This consumption makes it extremely difficult to simultaneously maintain all of the ore lift in the active leaching zone, even if excessive acid is added to the irrigant. This rate of gangue dissolution is also dependent on temperature within the heap. So as the oxidation of pyrite and other sulphides increases the temperature in the heap, rate of gangue consumption of acid also increases. The warming heap starts to consume additional acid, thus raising the pH and slowing the rate of sulphide oxidation in parts or all of the heap. As such, ores suitable for heap leaching at elevated temperatures are limited to those with low gangue reactivity, and to those with an adequate to high total sulphur concentration, and a suitably high sulphide reactivity to generate sufficient heat to sustain the oxidation. To maintain uniform flows of air and irrigant through the heap, the ores must be prepared prior to stacking by either removing fines by classification, or by 2023286025   28 Dec 2023 sticking the fines formed during crushing to other particles using agglomeration. In this way, suitable heap permeability can be maintained through the leach duration to allow an even transfer of acidity down through the heap profile, and an even profile of oxygen as it is consumed while flowing through the heap. The concept of utilising pyrite oxidation, assisted by microbial cultures, as a source of additional acid and heat for sulphide leaching is well known (Watling et. al. Extremophiles in Mineral Sulphide Heaps: Some Bacterial Responses to Variable Temperature, Acidity and Solution Composition, Microorganisms. 2015 Sep; 3(3): 364-390, and Bulaev et. al. Effect of Carbon Sources on Pyrite-Arsenopyrite Concentrate Bio-oxidation and Growth of Microbial Population in Stirred Tank Reactors, Microorganisms. 2021 Nov; 9(11): 2350, the contents of which are incorporated herein by reference). In one paradigm using this biologically enhanced leaching, a number of operational facilities, use a process termed Biox Technology. Stirred reactors enable a sulphide concentrate to be oxidised in an acidic microbial environment and the exothermic reaction maintains an elevated temperature. Similarly, various processes seek to agglomerate finely ground concentrates on ore or other substrates, as a method of heap leaching these concentrates (Peterson et. al. Competitive bioleaching of pyrite and chalcopyrite, Hydrometallurgy, Volume 83, Issues 1-4, September 2006, Pages 40-49, the content of which is incorporated herein by reference). And the heap leaching of sulphide ores containing sufficient sulphides has also been trialed. In heap leaching, the addition of microbial cultures to the ore, either directly into the leachants or into agglomeration of the ore prior to leaching, is also well known and commonly utilised commercially, as described in CA2073589 (Brierley) and in US20090061503 (Hunter), the content of which is incorporated herein by reference. WO2004 / 027099 (Crundwell) (the content 2023286025   28 Dec 2023 of which is incorporated herein by reference) describes the addition of pyrite to a heap to supplement the amount of sulphide in the ore, hence the generation of heat in the heap leach. WO2022 / 013824 (Filmer) (the content of which is incorporated herein by reference) also describes the addition of a sulphide flotation concentrate blended through a sand heap. This flotation concentrate containing pyrite, provides additional reactive source of sulphides and hence generates greater levels of acidity and soluble iron and heat within the heap. The sulphides in the flotation concentrate typically have a finer grain size than the sulphides in the original rock and are almost fully exposed around the circumference of each sulphide grain. The absolute reaction rate of the sulphide is proportional to the available surface area. Thus, the pyrite particle numbers, size and exposure all provide extra surface area for the microbial cultures to adhere, and enable a faster sulphide oxidation to occur. Filmer also teaches the additional recovery of copper or equivalent that can be achieved by combining flotation and heap leaching. This achieved by operating the flotation at a different location on the grade recovery curve and recovering extra copper into a lower grade concentrate containing mostly pyrite and blending this into the heap leach to dissolve the values. In US11286540 (Burley) describes a very similar process of adding back a sulphide containing concentrate to a heap leach, in which the source of the sulphide can be reclaimed from a tailings dam. This pyrite containing concentrate is blended with the ore and agglomerated together with sulphuric acid. This agglomeration reduces the fines content prior to stacking the ore. Similarly to Brierley, Burley teaches that a microbial solution can be added to the pyrite during the agglomeration of the ore prior to stacking. The amount of concentrate add-back into heap leaching is constrained by the need to maintain high liquid and gas permeability in the heap. Excessive fines content in the form of a pyrite concentrate reduces this permeability. Nominally, adequate heap permeability requires less than around 10% fines of size less than 75 micron in the heap. The pyrite generated from flotation 2023286025   28 Dec 2023 typically contains around 50% <75 micron. Hence the amount of concentrate that can be added back is constrained, particularly for the case of agglomerated ore, as the crush size is already selected such as to maintain acceptable levels of fines in a stacked heap. Filmer achieves the high heap permeability by removing most of the fines in normal crushed ore, thus providing a greater ceiling for the amount of fine pyrite containing concentrate that can be blended. Burley has the same objective, in agglomerating the sulphide concentrate fines, together with the fines formed in crushing, to the coarser particles. But in this process, the ceiling for fine sulphide addition is lower for any given crush size of the ore. The addition of pyrite to a heap leach, can be thought of as a source of kindling added into a preset log fire. The reactive sulphide concentrate can ‘burn’ to both provide extra heat, and simultaneously contribute acid which acts as an accelerant throughout the ‘fire’. The combustion of the logs is promoted. The more fully exposed pyrite grains provide a greater surface area to serve as a fast burning fuel source. But, if too much of the fines are added, the fire will not be able to breathe effectively, or will burn out to quickly. Benefits of adding back a sulphide concentrate to a heap leach are • increased heat generation through heap allowing the more refractory ores such as primary copper ores containing significant proportions of chalcopyrite to dissolve with high extractions. • reducing the need for external acid additions, thus broadening the range of ores for heap leaching, see US 8,491,701 (Uhrie). • producing acid throughout the vertical profile of the heap, thus avoiding the inefficiencies of acid injection from the top. This enables higher individual lifts for stacking of any particular ore type. The concept of sulphide add-back, as previously noted by Filmer, also enhances the ability to recover other values contained in the sulphide 2023286025   28 Dec 2023 concentrates, such as to improve metal recovery from flotation tails or historical tailings by producing a low-grade concentrate. Despite these benefits, the concept of concentrate add-back also has some constraints and shortfalls. The first of these is the induction time required for the oxidation of the pyrite. Because the pyrite oxidation accelerates rapidly when the pH is sufficiently acid to stabilise ferric ion in solution, the primary benefits of sulphide add-back are only obtained once the acid profile has overcome the fast-reacting gangue, and the zone of low pH has migrated down to the level in the lift at which the particular pyrite is to be oxidised. Furthermore, the microbial populations required to oxidise the sulphides are added through preconditioning of the ore, but by the time the ore is stacked the pH has increased and only a small proportion of the microbial species survive on the surface of the ore. This is particularly true of the thermophiles, which are ultimately necessary to sustain heap temperatures above around 60°C. This survival of the thermophiles is further complicated by the transition in microbial populations that occurs as a heap heats up, from various mesophiles which survive up to around 55°C, and then into thermophiles some of which only thrive at above 65°C. Managing this microbial transition is essential to get heap temperatures suited to dissolution of the more refractory minerals such as chalcopyrite. Conventionally some or most of the effective microbial additions are through the irrigation of the heap. The time taken for this microbial population to migrate down the heap through different acidity and temperature regimes in the heap profile, to create the growth of the mesophile then the thermophile populations necessary for leaching primary copper, is significant. And even if such a transition from mesophile to thermophile population did occur, 2023286025   28 Dec 2023 significant parts of the heap would already be depleted in pyrite content. At best, the duration to create a hot heap would be considerably slower than desirable. The delay and excessive sulphide consumption at temperatures below that ideal, occur because acid profile and the microbial profile are mutually reinforcing, as the microbes require acidic conditions to thrive, and the localised generation of acid requires a substantive microbial population to oxidise the sulphides, particularly pyrite, to acid. So the heating and acidity creation tend to occur in the parts but not all of the heap. Thus, the generation of heat through the heap is both delayed, and uneven in height, and possibly also affected by the differential permeability in the heap, and potentially patchy arising from the distribution of the gangue components in changing ore types that make up the heap. High recoveries of the refractory values are unlikely. In parallel to these concerns about achieving conditions conducive to heat generation, a hot heap requires the simultaneous conservation of heat that has been generated (Dixon, D.G., 2000, Analysis of heat conservation during copper sulphide heap leaching, Hydrometallurgy, 58, 27-41). The conditions under which heat is mostly retained in a heap requires a balance between the irrigation rate and aeration rate, effectively squashing most of the heat in the heap by countercurrent flows of heat upwards in the air, and downwards in the irrigant. But even when balanced, the total heat loss is proportional to the flow of moist oxygen depleted air out from the heap, and the warm PLS from the base of the heap. However, the previously mentioned acid and microbial profile in the heap complicates this goal of heat retention, due to the need to irrigate rapidly to get acidic irrigant and appropriate microbial populations down through the heap. Heat losses are incurred, just at the time that the heap is heating up and heat retention is critical. This heat loss is caused either by the high rate 2023286025   28 Dec 2023 of aeration required to balance the high irrigation rate, or the imbalance between irrigation and aeration rates. Heating of a heap is also a function of the heap volume (total heat generation) to heap surface area (radiative heat losses to the environment). Higher heaps provide a superior heat generation to heat loss. But there is a constraint on heap height due to the need to adjust the acid profile from above. At lower heap heights, acid profile is almost acceptable, but the heat losses are excessive. At higher heap heights, the heat losses are acceptable, but the acid and bacterial profile becomes problematic. The delays due to achieving the acid and bacterial profiles extend the duration for heap operation prior to rapid oxidation, and hence recovery of values. They also vary the acidity recovered from the base of the heap though the duration of the leach, also make it difficult to utilise external acid additions efficiently. Most importantly for leaching of primary copper, by the time that the correct conditions exist for the thermophile population to thrive within the heap, much of the sulphide heat source has already been oxidised by the slow but steady action of the mesophiles. Thus, a conversion of the heaps from a warm (around 50°C) to a hot (around 70°C) has proven problematic. The acceptable temperatures for high copper recovery are either not achieved, or are restricted to some zones within the heap. Whilst Filmer, and more recently Burley, claim the benefits in terms of total acidity and heat generation, of adding back pyrite, the delays caused by the acid and microbial profiles mean it is difficult to fully utilise this additional fuel value and hence achieve the additional copper recovery. In some parts of the heap the additional sulphides are only partially oxidised over the duration of the leach, whereas in other parts they are completely consumed. The problem still to be addressed, to fully capture these benefits of adding back a sulphide concentrate, is how to overcome the acidity and microbial 2023286025   28 Dec 2023 population profiles down through the heap, and hence enable the microbial transition from a mesophilic population to a thermophilic population. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of a bioleach process according to an embodiment of the invention; Figure 2 is a graph showing a control strategy for a bioleach process according to an embodiment of the invention; Figure 3 is a graph showing the impact on the pH of the PLS over time, of adding a sulphide particulate composition, at various sizes and after direct inoculation, to a 6m column leach of a Chilean ore; Figure 4 is a graph showing the impact on the temperature of the ore over time, of adding a sulphide particulate composition, at various sizes and after direct inoculation, to a 6m column leach of a Chilean ore; and Figure 5 is a graph showing the impact on the copper extraction over time, of adding a sulphide particulate composition, at various sizes and after direct inoculation, to a 6m column leach of a Chilean ore. SUMMARY OF THE INVENTION According to the present invention, there is provided an inoculated sulphide concentrate comprising a pyrite-containing sulphide particulate composition, wherein the particle surfaces of the sulphide composition are coated with a microbial mix, preferably containing a range of both mesophile and thermophile microbes, for use in the bioheap leaching of a sulphide ore in which the acidity and temperature of the heap are enhanced. 2023286025   28 Dec 2023 The mesophilic microorganisms may be selected from: Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Acidithiobacillus caldus and leptospirilli, Leptospirillum ferrooxidans and Leptospirillum ferriphilum Sulfobacillus thermosulfidooxidans, Acidiphilium, Ferroplasma-\\ke archaea. The moderate thermophilic microorganisms may be selected from: Acidithiomicrobium, Sulfuracidifex metallicus, Acidithiobacillus caldus species. The thermophilic microorganisms may be selected from the Sulfolobus, Metallosphaera, Acidianus species. Typically, the particulate composition has a particle size p80 of less than 150 micron, typically between 20 and 100 microns, and preferably to less than 75 micron and even more preferably less than 50 micron. The particle size distribution of particles in the particulate composition may be adjusted by grinding of part or all of the concentrate to provide a particulate composition in which some particles will react very rapidly and some less rapidly. The sulphide concentrate may be recovered from a current or historical flotation stream or residue, and some or all this concentrate may be ground further prior to inoculation. Preferably, the sulphide concentrate contains greater than 10% S and preferably greater than 20% S and even more preferably greater than 30% S. Preferably, the microbial mix is an acidic mix of mesophile and thermophile microbes, i.e. the mix has a pH of less than 7, preferably less than 5, more preferably less than 3, typically a pH of between 1 and 2. 2023286025   28 Dec 2023 The sulphide concentrate typically contains pyrite, and associated values of one or more of copper, nickel, zinc, uranium or gold. This invention also relates to a method of bioheap leaching of a sulphide ore in which the acidity and temperature of the heap are enhanced, wherein an inoculated sulphide concentrate as defined above is: blended through a particulate ore to be leached; and the blended ore is stacked in a heap which is leached to recover the contained values in the concentrate and the ore. Blending of the particulate composition may be direct addition into the ore, or by agglomeration together with the ore. The crushed ore may comprise agglomerated or deslimed particles, and have a particle size of less than a p80 of 20mm and preferably between 210 mm. Preferably, the blended inoculated sulphide concentrate (the particulate composition) and ore contains a combined fines content of less than 15% below 75 micron, and preferably less than 10% less than 75 micron. Blending may be achieved by addition during stacking or by mixing prior to stacking, for example in agglomeration together with acid and the ore to be leached. Preferably, the inoculated sulphide concentrate is added to the ore as a high-density slurry or wetted solids, in which the liquid phase is in the pH range between 1.0 and 2.5 and even more preferably between 1 and 2. The lift height of the stacked heap is typically greater than 5m and preferably greater than 10m and even more preferably around 15m. Heat may be retained in the heap by maintaining a balanced ratio of irrigation and aeration rates for most of the leach cycle. 2023286025   28 Dec 2023 The blended and stacked ore may be aerated at a rate such that the average 02 content of the air exiting the upper parts of the heap is maintained between 3 and 20%, and preferably around 10 to 15% 02 for much of the leach cycle. The rate of irrigation may be controlled to retain heat in the heap consistent with the aeration rate. The ore and inoculated sulphide concentrate may blended such that specific parts of a lift have greater levels of added the inoculated composition, such as to generate a specific acid profile or heat profile through the heap. The irrigation rate may be adjusted to balance the heat generation of the composition surfaces, with the transfer of heat to the surrounding heap, thus facilitating the growth of thermophiles. This process may be conducted without the need for high irrigation rates to control acidity and microbial flow down the heap. Typically, the ore to be leached contains chalcopyrite or pentlandite or sphalerite, or pyrite containing uranium or gold. The sulphide concentrate typically contains pyrite, and associated values of one or more of copper, nickel, zinc, uranium or gold The inoculated sulphide concentrate may used to extend the range of ores that can be heap leached, to include those with higher levels of soluble gangue, or lower levels of contained sulphur. The invention also relates to a stacked heap for heap leaching comprising a blend of inoculated sulphide concentrate as defined above, and a sulphide ore. The invention also covers a method of producing an inoculated sulphide concentrate as defined above, wheren: 2023286025   28 Dec 2023 a range of microorganisms are cultured independently at their optimum growth conditions; and each microbial mix is then combined with a sulphide concentrate under conditions to maximize their attachment and acclimatation to the sulphide surface, to produce the inoculated sulphide concentrate. Preferably, the microbial mix is an acidic mix of mesophile and thermophile microbes, i.e. the mix has a pH of less than 7, preferably less than 5, more preferably less than 3, typically a pH of between 1 and 2. Two or more inoculated sulphide concentrates each, with its own individual microbial mix and particle size may be prepared and blend with the ore. DESCRIPTION OF PREFERRED EMBODIMENTS The first key to overcoming the acidity and microbial profiles in a heap is to accelerate the rate at which the sulphide concentrate composition, which has been distributed through the heap, reacts to generate acid and soluble iron throughout the heap. The second key to leaching the more refractory sulphides with high extractions is to provide the conditions within the heap where thermophilic species are naturally favoured over mesophilic species, thus enabling heat generation and a transition to a thermophile dominant microbial mix, hence the increase of the temperature within the heap beyond that achievable by mesophiles alone, Once these two success factors are combined, the heap will create its own acidity and soluble iron internally, and transition through the mesophile to thermophile population mix to reach temperatures exceeding 65°C, prior to a substantive proportion of the sulphide fuel being exhausted. The current invention provides this method of significantly increasing the initial reactivity of the sulphide concentrate, and enhancing the survival of 2023286025   28 Dec 2023 thermophilic species during heap stacking, thus providing conditions for the rapid growth of thermophiles and acid and soluble iron generation to be sustained as the heap heats up. The novel and inventive step is to provide for a very high surface area of well inoculated sulphide particles coated with a suitable microbial mix; and distributing this composition within the stacked heap. The sulphide particles will preferably contain a majority of pyrite, but may also be other reactive sulphide minerals or a mix of sulphide minerals and elemental sulphur. In accordance with an embodiment of the invention, with reference to Figure 1, inoculant liquor or liquors 10 are added directly to ground sulphide concentrate or fractions of the concentrate 12, having a particle size with a p80 of less than 150 microns, typically between 20 microns and 100 microns, allowing the microbial population in the inoculant to establish itself on the surface of each sulphide particle providing a fine inoculated concentrate 14. The fine inoculated concentrate surface provides ideal conditions for survival of the microbial mix during heap construction. The fine inoculated concentrate 14 is added to crushed ore 16, either utilising ore with fines removed or added as part of an agglomeration process, with an ore particle size of less than a p80 of 20mm and preferably between 2-10mm, to form a mixture 18 to be stacked and heap leached 20. The microbial rich sulphide concentrate exists as discrete particles of sulphide minerals within the ore to be leached 20, and hence can create its own acidity and soluble iron around the surface of each sulphide particle, for transfer throughout the heap 20, and hence create a more uniform acidity and microbial population profile down the heap, almost independently of the acidity and iron and microbial profile migrating down from the irrigation system located near the top of the lift. The coated surfaces of the individual sulphide concentrate particles, provide an ideal growth environment for both mesophiles and thermophiles to survive 2023286025   28 Dec 2023 the stacking of the ore into a heap. The mesophiles maintain a low pH and increase the temperature of the heap up to their natural temperature limit. The thermophiles survive at lower temperatures and then promulgate as the temperature approaches their ideal temperature range. The surface area of the composition may be adjusted according to the demands of the particular ore to be leached, either through the quantity added, or the size distribution, or both. As the individual sulphide particles heat prior to and during the initial stages of leaching, the surface moisture surrounding the fine inoculated concentrate particles also acts as a microclimate to promote the transition from a mesophile to thermophile dominant population. The irrigation rate through this phase may be adjusted to balance the heat generation of the composition surfaces, with the transfer of heat to the surrounding heap, thus facilitating the growth of thermophiles. This process may be conducted without the need for high irrigation rates to control acidity and microbial flow down through the heap. During the initial stages of irrigation, the resultant heat and thermophiles are transferred from the sulphide concentrate surface to the remainder of the ore enabling the establishment of the surviving thermophile population throughout the ore. The mesophilic microorganisms may be selected from: Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Acidithiobacillus caldus and leptospirilli, Leptospirillum ferrooxidans and Leptospirillum ferriphilum Sulfobacillus thermosulfidooxidans, Acidiphilium, Ferroplasma-\\ke archaea The moderate thermophilic microorganisms may be selected from : Acidithiomicrobium, Sulfuracidifex metallicus, Acidithiobacillus caldus species. 2023286025   28 Dec 2023 The thermophilic microorganisms may be selected from the Sulfolobus, Metallosphaera, Acidianus species. This oxidation on the prepared surface of the sulphide particles generates heat at the surface and accelerates the transition from mesophilic temperatures in the heap to thermophilic, and also transfers the heat to the surrounding ore, thus rapidly providing the conditions for the leaching the more refractory sulphides present in the ore. Furthermore, by adjusting the surface area of the sulphide concentrate prior to inoculation and being blended with the ore, the acid and heat generation rates can be adjusted. Thus, the rate of acid generation can be independently controlled. And the quantity of thermophiles present in the heap can be adjusted to take over from the mesophiles and raise the temperature of the heap above say 65°C for the required duration. The need to force acid and the microbial mix of mesophiles and thermophiles down through the heap by high irrigation rates is much reduced by the addition of an inoculated composition, the proportion of which has been selected and sized to suit the particular ore requirements. With this extra degree of freedom available to adjust the amount and rate of acid generation throughout the heap, the primary purpose of the irrigation becomes the washing out of dissolved values, and the secondary purpose being provision of acid and transfer of microbes within the heap. This decoupling of the need for acid and microbial additions through the irrigant, enables controlled heat retention within the heap by balancing the aeration rate that is necessary to maintain acceptable oxygen concentrations within the heap, with the irrigation rate. At critical times in the temperature increase, low aeration and irrigation rates can be utilised to minimise total heat loss from the heap. In particular, the bridging of the microbial temperature transition from mesophile to thermophile dominant species is greatly enhanced. And at other times, the rates can be increased to maximise the total metal being recovered in the PLS. 2023286025   28 Dec 2023 Later in the leach cycle as much of the added pyrite and much of the readily soluble gangue is consumed, the control focus can shift to heat retention to allow time for the more refractory sulphides in the ore to dissolve. The increased reactivity of the crushed ore is achieved by • Increasing the surface area of the sulphide concentrate including by further grinding to the required particle size for a particular ore composition to be leached • Inoculating the surface of the ground sulphide concentrate with a microbial mix containing both mesophiles and thermophiles • Blending the ground and inoculated concentrate through the ore to be leached • Stacking and heap leaching the blended ore, to recover the contained values. The essence of the current invention arises from the faster reaction rate of the fine and inoculated concentrate; through one or preferably both of: further fine grinding the sulphide concentrate; and inoculating the concentrate with the microbial mix, prior to blending in the heap. Depending on the ore characteristics, the reaction rate of the inoculated concentrate may be sufficient with the grind size emanating from flotation. This sulphide concentrate is already at a particle size that individual grains in the concentrate are predominantly sulphides, and hence the external surface of the grain is mostly exposed to leaching, rather than being encompassed partially or mostly by gangue. The size of the grains in the sulphide concentrate in the current invention may also be reduced by further grinding of the concentrates, thus creating even greater surface area of exposed sulphides. Additionally, the specific preparation of the surfaces of the composition provides a greater opportunity for the temperature transition to occur throughout the heap. 2023286025   28 Dec 2023 The faster oxidation of the fine sulphide concentrate provided by the large and exposed surface area that is inoculated with the microbial mix, implies that acid and soluble iron are generated more rapidly in the heap by the oxidation of the sulphide concentrate, and this acid is evenly distributed throughout the heap. This faster oxidation reduces the requirement for the acid to be provided by irrigation from above. Typically, a pyrite containing sulphide concentrate produced by scavenging flotation of a tailings, either from freshly ground ore or historical tailings, has a size distribution averaging a p80 of say 100 microns. For each further halving of this particle diameter, the available surface area of the concentrate increases by a factor of 2. Thus, the leaching rate of the sulphide particles will increase by a factor of 2, for a given level of acidity and temperature and biological population mix on the surface of the concentrate. The second element of increasing the heap leaching effectiveness is the separate addition of a microbial mix on the sulphide concentrate that is blended through the ore to be leached. These concentrate particles provide a vehicle for ensuring the longevity and distributing the desired microbial populations throughout the heap, in conditions in which they will thrive at the different stages of the leach temperature cycle. The microbial mix that makes up the inoculum may be generated in multiple reactors, each designed to encourage oxidation of the concentrate in the temperature range at which the particular microbes operate most efficiently. Since the thermophiles will survive but not become active until the temperature in their surroundings reaches around 50°C, they can be introduced into the heap on the surface of the inoculated concentrate but remain dormant until the active mesophiles have increased the ambient temperature at the sulphide surface. By pretreating the pyrite with an acidic inoculum of microbes, each pyrite particle will have a coating of acidic liquor and an established microbial mix adhering to the sulphide particles. These conditions are ideally suited to 2023286025   28 Dec 2023 microbial survival during stacking and to ongoing mesophile sulphide oxidation of the ore during early stages of leaching. In particular, the microbial population impregnated on the surface can contain a mix of thermophiles and mesophiles. The mix of mesophiles and thermophiles may be generated by multiple bioreactors preparing multiple acidic inoculant mixes, each suited for particular temperature ranges, such that microbial growth is encouraged throughout the heap transition from ambient to hot temperatures. The multiple inoculant mixes may be added to the concentrate in combination or separately such that each sulphide grain has a mix of microbial species, or to different concentrate streams such that individual sulphide particles have a predominance of one inoculant or another. The inoculant mix can also be added in conjunction with the irrigant, and the sulphide surfaces can act in a similar way. The mesophiles are suitable for the transition of the heap temperature from ambient to warm temperatures (mesophilic species typically thrive between around 30-50°C) and assist the thermophiles to survive and then make the transition to a hot heap temperatures. The microbial species that thrive on the warm or hot surface of the oxidizing sulphide grains, can then transfer to the adjacent ore neutralising the reactive gangue and oxidising the sulphur content of the ore. The microbial populations exist within a microclimate, present in the inoculant which is coating the surface of the sulphide grains. The inoculant can be adjusted initially and by adjusting the rate of irrigation, to provide all the conditions necessary for ongoing microbial survival. As these inoculated sulphide grains are blended into the ore, and through the duration required for heap construction from the blended ore, the wetted coating on the surface of the individual sulphide particles provides an ideal warm and acidic environment for the microbes to survive and prosper. 2023286025   28 Dec 2023 Initially, ongoing oxidation of the sulphides maintains the acidity and the warmth on the sulphide surface. And the physically separate grains of sulphide reduce the adverse impact of the adjacent rock particles on microbial prosperity, either as a sink of acid consumption or as a large heat sink. The inoculant coating effectively forms a microclimatic zone in which the pyrite oxidation can commence, and then generate a mix of soluble iron and acid and heat on the surface of the sulphide concentrate, even before additional irrigant is added from above. And then, as the irrigant flows down through the heap, the acid and soluble iron and heat and microbial populations present on the surface of the sulphide particles are distributed over the nearby ore particles, rapidly bringing the whole of the solids in the heap into the zone of ideal leaching conditions, where leaching of even refractory sulphides in the ore is relatively fast. The control strategy for heat retention in a heap can be fundamentally altered by the addition of an inoculated sulphide composition having an enhanced surface area. One such control strategy being illustrated schematically in Figure 2. In conventional heap leaching, acid irrigation from the upper surface of the heap is required initially to lower the pH in the heap and introduce a microbial population, which in turn accelerates the rate of acid generation within the heap. Because the acid added from the surface, much of this acid is consumed by gangue in its passage down through the ore. Thus conventionally, the best heat control strategy is to irrigate rapidly to push the acid profile and microbial mix down the heap. However, the average sulphide oxidation rate through the heap is slow initially due to the poor acid and microbial profiles, so some or most of the heat generated in the early stages of rapid irrigation is lost in the PLS. It is only when most of the heap reaches the required acidity that higher aeration rates are required, and the microbial 2023286025   28 Dec 2023 growth has accelerated to provide additional oxygen that the optimum balance of heat exchange occurs to retain heat in the heap. The hiatus between start of conventional heap leaching and achieving the ideal acidic and iron containing conditions for fast leaching can be an extended period. During this time, reactive sulphides are being consumed, and the conditions on the surface of the rapidly irrigated ore are not ideal for growth of thermophiles to replace the mesophiles that predominate the heap. This situation has caused the failure of several historic efforts to heap leach primary copper ores at elevated heap temperatures. With the current invention the acid profile is not a concern, and hence the aeration and irrigation control strategy can be quite different. The optimum and relative flows of irrigant and aeration can be controlled independently of the need to push acid and microbes down the heap as illustrated in Figure 2. The irrigation rate can be controlled at quite low levels during the early stages of leaching, enabling the creation of a ‘microclimate’ of conditions on the sulphide surfaces, thus further accelerating the acid and soluble iron and heat generation throughout the heap, and encouraging the early promotion of the thermophiles added in inoculation. Typically, irrigation will be slow in the early stages of leaching to avoid destroying the ideal microclimate on the sulphide surfaces and can then be increased at a later stage to spread the acid and microbial populations faster. Thus, the use of finely ground and inoculated sulphides, combined with controlled irrigation rates, enables this acidic microbial rich microclimate to be promulgated from the sulphide surfaces through the heap, until microbial populations and acidities are well established in the ore as a whole. And in particular, the transition from a mesophile to a thermophile dominant population can occur rapidly on the hot surface of individual sulphide concentrate particles and be transferred to the ore as a whole. 2023286025   28 Dec 2023 For conventional heap leaching, the heap is relatively easily controlled to achieve a temperature of around 30-55°C, typical of mesophiles. However, the transition to the temperatures required for leaching of all sulphide values in an acceptable duration, a heap temperature of around 70°C is required. The conventional transition from mesophilic to thermophilic microbial cultures is difficult as any hot spots that arise within a conventional heap leach lose their heat to adjacent ore due to heat exchange with the irrigant and air flowing past, at a rate required to manage the acidity profile. The transition to a hot heap requires large zones in the heap to reach the maximum temperature that the mesophiles can survive, and then not slow in heat generation rate as the mesophile population declines and the thermophile population increases. Figure 2, “A” shows the ideal ratio of irrigation to aeration to retain heat within the heap; whilst “B” is a control strategy for a normal heap which requires fast irrigation to acidify the heap, then gradually balance the air flow as the ore reaction commences at different rates through the heap; and “C” is a control strategy with the current invention, where acid generation through the heap enables much better heat retention through closer adherence to the optimum irrigation and aeration ratio. The current invention allows a mix of thermophiles and mesophiles to be added to the surface of the sulphides, and the irrigation rate to be adjusted to manage heat transfer within the heap, hence creating a strong thermophile population within the heap and promoting the rapid transition to a thermophilic dominant species on the sulphide surface. The current invention also reduces the tendency for all of the iron to precipitate in the lower levels of the heap, causing permeability issues towards the latter part of the leach cycle. Because the pH profile down the lift height is much reduced due to the even oxidation of pyrite through all levels of the heap, the precipitation of iron in the heap is also much more evenly distributed through the lift profile. 2023286025   28 Dec 2023 The greater the surface area of the sulphides available to assist this microbial transition, the more quickly the desired heap temperature can be created, and the more efficiently the remaining sulphide fuel can be burnt to maintain the heap in the desirable temperature range. The quantities of fines formed by the addition of finely ground sulphide concentrate would normally be problematic, due to the reduced heap permeability that accompanies this increased proportion of fines. But as previously noted, in the initial stages of leaching in the current invention, rapid irrigation is not required to adjust the pH profile, so this permeability constraint caused by the fines content is less critical. Furthermore, because the fines in the concentrate are constituted mostly of sulphides, on leaching they are solubilised, with the iron component being reprecipitated elsewhere in the heap. Hence later in the leach cycle when faster irrigation may be desirable, the permeability constraint has been reduced. The proportion of the sulphide concentrate which is finely ground can be specifically adjusted according to the desired rate of acid and heat generation. Where a particular ore type needs a very rapid injection of heat and acid through the heap, a larger proportion of the concentrate will be ground. However, when an ore type needs a more prolonged generation of heat and acid, a greater proportion of the concentrate can be added in its original form, and the aeration and irrigation rates adjusted to conserve heat. The avoidance of the need for rapid irrigation to push the acid profile down through the heap, resulting from the finely ground sulphide concentrate has additional implications. Firstly, the aeration rate can be controlled through the duration of the leach cycle such that the oxygen content exiting the top of the heap is at just a sufficient quantity to sustain good microbial growth. The irrigation rate can be independently controlled, to minimise heat loss and shift heat fronts throughout the cycle. Thus, oxygen content exiting the heap can be adjusted according to the sulphide reaction rates, to ensure the microbial population can thrive, enabling a gradual increase in aeration rate as the sulphide 2023286025   28 Dec 2023 oxidation reaction is accelerating, then a slowing of aeration rate as most of the reaction is complete. This variation in aeration flow over the duration of the leach cycle enables effective heat retention. Secondly, the lift height of the heap can be substantively increased. Since the heap profiles are no longer totally dependent on irrigation from the top, the lift height can be increased from say 5m to 10m or even 20m, affected more by 02 profile through the heap rather than acid profile. The total heat generated vs. heat losses are thus enhanced. Thirdly, fresh blended ore can be over-stacked on a heap which is currently leaching. The air with a depleted oxygen content flowing up from the irrigation zone below carries heat, transferring it to fresh ore. The lower 02 content in this air allows the microbial population to survive but limits the premature oxidation of the sulphides. When ready to commence irrigation in the next lift, the aeration rate can be increased to complete the leaching of the lift below whilst also providing sufficient oxygen in the lift above. Exchange of heat between heaps is achieved, and the total time taken to leach the combined ore quantity to completion is decreased. As a consequence of the fine size and the high reaction rates of the inoculated sulphide composition, almost quantitative dissolution of the sulphide concentrate can be achieved in the time duration taken for heap leaching of the classified sand or agglomerated ore. This implies that various finely ground concentrates, in addition to pyrite with minor quantities of base metal values, can be leached quantitatively. This implies that heap leaching can become a means to recover values from any sulphide concentrate that is added to the ore. Examples of different sulphide concentrates that can be utilised are, but not limited to, primary copper concentrates of various grades, nickel concentrates including those containing high levels of pyrrhotite, or a platinum group metals concentrate. The system is also applicable to recovery of gold associated with pyrite, where the preleach of the concentrate 2023286025   28 Dec 2023 removes the pyrite and liberates the gold, for subsequent recovery under different leaching conditions. The first of the various forms of embodiments is the particle size of the sulphide concentrate which is finely ground, to accelerate its reactivity in the heap. This fine grinding of the sulphide concentrate can provide for a variety of particle size distributions, including bimodal distributions, preferably less than a p80 of 100 microns and even more preferably to a p80 of around 50 microns, and even down to a p80 of a fraction of the pyrite of say 25 microns. Since the sulphide concentrate will normally have a sulphur content of greater than 20% and up to around 50%, and the requisite quantity of additional sulphur to be added to the ore is normally between 0.5% and around 1% by weight, the proportion of sulphide concentrate is typically around 2-5% of the total ore to be leached. As such, the cost of the fine grinding of the concentrate per tonne of ore leached is not excessive, relative to the reduced leaching time and greater extractions achieved using the finely ground concentrate. And the quantity of fines < 75 microns in the added concentrate, even prior to their dissolution, is not excessive and the resulting decrease in gas and liquid permeability is manageable. The second form of embodiments is the proportion of the finely ground and inoculated sulphide concentrate to be added to the ore. The usual aim is to heat the heap quickly, and in the case of a refractory sulphide ore, enable the transition to a thermophilic reaction temperature. In this case some or all of the sulphide concentrate may be finely ground. However, there are times where an extension of the elevated temperature is required to achieve complete leaching of the values from the rock. In this case, a proportion, say half or more of the concentrate may be in its original particle size, with a finely ground proportion designed just to initiate the reaction. 2023286025   28 Dec 2023 The third form of embodiments is the type of concentrate used. The ideal concentrate from an acid generation perspective is pyrite due to the high levels of contained sulphur. The ideal concentrate from the perspective of recovering extra values by dissolution of the concentrate is one in which the values content, such as one where the nickel or copper or gold or PGMs, is high. Various blends between these two competing objectives are possible, thus maximising recovery and concentrate grade from flotation. The particular benefits of processing mixed concentrates which are not saleable in their own right is apparent, both as a source of metal from the heap leach and in increasing the overall recovery and product quality in sulphide flotation plant. Such low-grade concentrates may be relatively low in valuable metals but can be quite high in sulphide content such as pyrite or pyrrhotite or other sulphides. As such they can form part, or all of the sulphide concentrate feed to the heap. In particular, they could include low grade copper concentrates, or low-grade nickel concentrates where the nickel is in solid solution with pyrrhotite. The key to generating sufficient heat and acid is the oxidizable sulphur content in the sulphide concentrate which will be greater than 10% S, and preferably greater than 20% S and even more preferably greater than 30% S. The fourth form of embodiments is the method of preparing and blending the sulphide concentrate through the ore. The inoculation of the concentrate will usually be from a separate bioreactor or multiple bioreactors, designed to contain and grow the optimum mix of microbial populations. The concentrate used to prepare the microbial populations may the same as that used as the sulphide additive to the heap. 2023286025   28 Dec 2023 The acidic inoculant (pH of typically between 1 and 2) will be added to the concentrate under conditions such that the microbial populations can establish on the surface of the sulphide concentrate. This may be achieved by spray coating or immersion, or in an agglomeration drum or similar mixing vessel. The liquid phase may contain other species to enhance the subsequent growth of the microbes. This inoculated concentrate can then be added in a timely manner to the ore, such as in a mixing vessel or by distribution onto a conveyor belt, in such a way that the sulphide particles remain coated with inoculant and preferably within a temperature range where the survival of the microbes is high, whilst being stacked. Examples might be as a separate stream of slurry or of a wet cake of inoculated concentrate being sprayed onto the conveyor during stacking, or the coated particles being added to the ore before or after agglomeration, and prior to stacking. The microbial addition may also occur by simple irrigation of the heap with an inoculant, where the heap has been enhanced with appropriately sized concentrate. The fifth set of embodiments encompasses the heap design and method of heap operation made possible by the grinding and inoculation of the pyrite containing sulphide concentrate, and the consequential reduction in the impact of the acid and microbial profile. The lift height of the modified heap can be increased to the limit set by the depletion of oxygen in a single pass through the heap, and even further. The percentage of concentrate added to the heap can be adjusted according to position in the lift height, to enable heat and acid to be generated at desirable levels within each lift and balanced against the acid additions from above. 2023286025   28 Dec 2023 The irrigation rates can be adjusted from the initiation of irrigation to allow heat to be retained in the heap, and or to optimise the tenor of the pregnant liquor. Initially the irrigation and aeration rates may be low, to enable the build up of heat and transition to thermophiles within the heap, followed by a period of faster irrigation to wash out the dissolving values, and then a reduction in irrigation rate to reduce the heat losses as the remaining available sulphides in the heap decline. Experimental Results The effectiveness of some of the embodiments of the invention was evaluated in a series of 6 metre columns, by comparing different particle sizes and inoculation strategies of a pyrite concentrate formed from a conventional flotation residue. The particulate compositions were added to a Chilean primary copper ore, which was then leached in 6 m columns. Irrigation was with a simulated raffinate solution, with an inoculant containing a microbial mix of mesophiles and thermophiles being added to the irrigant once per week. Aeration was at a controlled rate from the base of the column. The selected ore is naturally refractory, with most of the copper being present as chalcopyrite, and has an acid consumption of around 30kg H2SO4 / tonne ore. Fines were removed from the ore prior to addition of the particulate composition. For purposes of testing the effectiveness of the particulate composition, no acid addition was made during the ore blending, relying only on the only external acid additions to the column being in the form of a simulated raffinate irrigant. Based on the daily measured oxygen concentration in the off gas from the columns, the thermal heat generation was estimated, and each column was artificially ramped in temperature to simulate what would happen in a 3dimensional heap. 2023286025   28 Dec 2023 Figure 3 illustrates the impact of inoculated pyrite addition on maintaining a consistent acid profile through the heap. The comparison was made by measuring the PLS pH, between a base case with no pyrite added back, a case with no pyrite addback but irrigation with very high (15gpl) acid, and two tests with a 2% concentrate blend, one at normal concentrate size (CB76) and the second concentrate that had been finely ground to a p80 approximating 50 micron (CB78). The pH of the PLS illustrates that fine grinding of the concentrate brings the pH into a stable zone for ferric ion, almost immediately after the irrigant emerges from the column. This is in comparison to the base case (CB72) where even after 100 days of irrigation, the PLS was still at a pH of around 2.5 where ferric ion solubility would be low. The impact of addition of finely ground particulate on the PLS pH through the leach cycle was found to be roughly the equivalent to continuous addition of 15 gpl acid to the irrigant (CB73). Without prior fine grinding, the composition reached a satisfactory PLS pH within around 30 days of irrigation, showing much better acid generation than the base case. Additional sampling and measurement of the irrigant pH at the 2m and 4m depths in each column reinforced the conclusion that the fine particulate composition reached a pH at which ferric was soluble, through most of the column, whereas the coarser particulate composition reached this condition rapidly in the upper part of the column but required some time for the acidity to migrate down through the profile. The impact of the various sulphide particulate compositions on estimated heap temperature was also assessed. This is reflected in Figure 4. The finely ground pyrite column (CB78) rapidly reaches the upper temperature tolerance of the mesophiles, then falls back slightly, presumably as the thermophile population is establishing. The temperature then increases again to temperatures where chalcopyrite will oxidize. This transition from 2023286025   28 Dec 2023 mesophiles to thermophiles occurs within a few days. The normal sized composition (CB76) follows a similar curve albeit more delayed; and seems to find it more difficult to bridge the microbial gap. Both these pyrite additions sustain an elevated temperature for an extended period. Neither the base case (CB72) nor the high acid leach (CB73), reach the temperatures required for extensive chalcopyrite dissolution. In both cases without the addition of the particulate composition to the ore, the mesophiles and thermophiles added in the regular irrigant inoculations, fail to make the transition into a hot heap paradigm. The impact of the fine and normal inoculated pyrite addback on the leaching of copper is illustrated in Figure 5. In the two cases where the composition has assisted the heap to reach temperatures above 60°C, the copper dissolution increased greatly relative to the base case and high acid case. The experiments illustrate the benefits of the finer inoculated pyrite (CB76) to rapidly get the ore into a pH and temperature zone where the copper will dissolve, while the coarser inoculated pyrite composition can extend the leaching time of the ore at temperatures above 60°C, and hence the total achievable copper dissolution.

Claims

1. An inoculated sulphide concentrate comprising a pyrite-containing sulphide particulate composition, wherein the particle surfaces of the sulphide composition are coated with a microbial mix, for use in the bioheap leaching of a sulphide ore where the acidity and temperature of the heap are enhanced.

2. The inoculated sulphide concentrate claimed in claim 1, wherein the microbial mix contains a range of both mesophile and thermophile microbes.

3. The inoculated sulphide concentrate claimed in claim 2, wherein: mesophilic microorganisms are selected from: Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Acidithiobacillus caldus and leptospirilli, Leptospirillum ferrooxidans and Leptospirillum ferriphilum, Sulfobacillus thermosulfidooxidans, Acidiphilium, Ferroplasma-\\ke archaea;moderate thermophilic microorganisms are selected from: Acidithiomicrobium, Sulfuracidifex metallicus, Acidithiobacillus caldus species; andthermophilic microorganisms are selected from the Sulfolobus, Metallosphaera, Acidianus species.

4. The inoculated sulphide concentrate claimed in claim 1, wherein the particulate composition has a particle size p80 of less than 150 micron.

5. The inoculated sulphide concentrate claimed in claim 4, wherein the particulate composition has a particle size p80 of between 20 and 100 microns.2023286025   28 Dec 20236. The inoculated sulphide concentrate claimed in claim 5, wherein the particulate composition has a particle size p80 of less than 75 micron.

7. The inoculated sulphide concentrate claimed in claim 6, wherein the particulate composition has a particle size p80 of less than 50 micron.

8. The inoculated sulphide concentrate claimed in claim 1, wherein the sulphide concentrate is from a current or historical flotation stream or residue, and some or all this concentrate is ground further prior to inoculation.

9. The inoculated sulphide concentrate claimed in claim 1, wherein the sulphide concentrate contains greater than 10% S.

10. The inoculated sulphide concentrate claimed in claim 9, wherein the sulphide concentrate contains greater than 20% S.

11. The inoculated sulphide concentrate claimed in claim 10, whereinthe sulphide concentrate contains greater than 30% S.

12. The inoculated sulphide concentrate claimed in claim 1, whereinmicrobial mix has a pH of less than 7.

13. The inoculated sulphide concentrate claimed in claim 12, whereinmicrobial mix has a pH of less than 5.

14. The inoculated sulphide concentrate claimed in claim 13, whereinmicrobial mix has a pH of less than 3.

15. The inoculated sulphide concentrate claimed in claim 14, whereinmicrobial mix has a pH of between 1 and 2.2023286025   28 Dec 202316. The inoculated sulphide concentrate claimed in claim 1, containing pyrite, and associated values of one or more of copper, nickel, zinc, uranium or gold.

17. A method of bioheap leaching of a sulphide ore in which the acidity and temperature of the heap are enhanced, wherein an inoculated sulphide concentrate as defined in claim 1 is: blended through a particulate ore to be leached; andthe blended ore is stacked in a heap which is leached with an irrigation liquid to recover the contained values in the concentrate and the ore.

18. The method claimed in claim 17, wherein the particulate ore comprises agglomerated or discrete particles, and has a particle size of less than a p80 of 20mm.

19. The method claimed in claim 18, wherein the particulate ore comprises agglomerated or discrete particles, and has a particle size between 2-10mm.

20. The method claimed in claim 17, wherein the blended inoculated sulphide concentrate and ore contains a combined fines content of less than 15% below 75 micron.

21. The method claimed in claim 20, wherein the blended inoculated sulphide concentrate and ore contains a combined fines content less than 10% less than 75 micron.

22. The method claimed in claim 21, wherein blending takes place by addition of the inoculated sulphide concentrate to the ore during stacking or by mixing prior to stacking.2023286025   28 Dec 202323. The method claimed in claim 17, wherein the inoculated sulphide concentrate is added to the ore as a slurry or wetted solids, in which the liquid phase is in the pH range between 1.0 and 2.5.

24. The method claimed in claim 23, wherein the liquid phase is in the pH range between 1.2 and 2.

25. The method claimed in claim 17, wherein the lift height of the stacked heap is greater than 5m.

26. The method claimed in claim 25, wherein the lift height of the stacked heap is greater than 10m.

27. The method claimed in claim 26, wherein the lift height of the stacked heap is around 15m.

28. The method claimed in claim 17, wherein heat is retained in the heap by maintaining a balanced ratio of irrigation and aeration rates for most of the leach cycle.

29. The method claimed in claim 17, wherein the blended and stacked ore is aerated at a rate such that the average 02 content of the air exiting the upper parts of the heap is maintained between 3 and 20%, for much of the leach cycle.

30. The method claimed in claim 29, wherein the blended and stacked ore is aerated at a rate such that the average 02 content of the air exiting the upper parts of the heap is maintained between 10 and 15%, for much of the leach cycle.

31. The method claimed in claim 17, wherein the ore and inoculated sulphide concentrate are blended such that specific parts of a lift have2023286025   28 Dec 2023greater levels of added the inoculated composition, such as to generate a specific acid profile or heat profile through the heap.

32. The method claimed in claim 17, wherein the irrigation rate is adjusted to balance the heat generation of the composition surfaces, with the transfer of heat to the surrounding heap, thus facilitating the growth of thermophiles.

33. The method claimed in claim 17, wherein the ore to be leached contains chalcopyrite or pentlandite or sphalerite, or pyrite containing uranium or gold.

34. A stacked heap for heap leaching comprising a blend of inoculated sulphide concentrate as defined in claim 1, and a sulphide ore.

35. A method of producing an inoculated sulphide concentrate as defined in claim 1, wherein:a range of microorganisms are cultured independently at their optimum growth conditions;and each microbial mix is then combined with a sulphide concentrate under conditions to maximize their attachment and acclimatation to the sulphide surface, to produce the inoculated sulphide concentrate.

36. The method claimed in claim 35, wherein the microbial mix is an acidic mix of mesophile and thermophile microbes mix has a pH of less than 7.

37. The method claimed in claim 36, wherein the mix has a pH of less than 5.

38. The method claimed in claim 37 wherein the mix has a pH of less than 3.2023286025   28 Dec 202339. The method claimed in claim 38, wherein the mix has a pH of between1 and 2.

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