Heap leaching

Abstract

The present invention relates to a method for recovering metal values such as gold, copper, nickel, zinc and uranium from an ore containing metal values. The method comprises the following steps: crushing the ore (10) to provide P 80 Sand containing metal values less than 5 mm but greater than 1 mm; the sand is classified (12) to remove the finer fraction to provide P 10 Greater than 0.15mm, P 90 / P 10 The invention also relates to a heap (18) formed from the ore treated in this manner, wherein the ore is classified into a graded sand having a ratio less than 25 but greater than 3; a heap (18) formed from the graded sand; and a leachant and air distributed in the heap to leach valuables from the sand in a parent leachate, the leached valuables being recoverable from the parent leachate.

Description

Background of the Invention

[0002] Conventional heap leaching offers a low-cost, water-efficient method for metal recovery, but has the disadvantage of low extraction of valuables due to

[0003] Areas within individual rocks that do not have adequate leaching conditions due to microscopic permeability within the rock mass;

[0004] Areas within the pile that do not provide adequate leaching conditions due to variations in macroscopic permeability within the pile; and

[0005] Reprecipitation of valuables due to problematic gangue that results in localized macro-permeability.

[0006] These low extractions mean that heap leaching can only be used to process low-grade ores where low cost is a more important factor than high recovery. For most of the world's production, finer grinding and flotation or agitation leaching are the preferred processing routes.

[0007] Micropermeability is a term used to describe the ease with which a leachant can reach the values contained within the solid particles, allowing these values to dissolve, and then remove the parent leachant from the particles again, ultimately recovering it by gravity at the bottom of the heap. This level of micropermeability can be estimated using X-ray tomography (Miller - Int. J. Miner. Process. 72 (2003) 331–340), the contents of which are incorporated herein by reference.

[0008] The greater the degree to which the mineralized particles are exposed to the leachate, either through fine-grain exposure on the surface of the gangue particles or through micro-fractures in the surrounding gangue, the more valuable minerals can be recovered.

[0009] The biggest determinant of microscopic permeability is particle size. Smaller diameters increase the likelihood that valuable mineral fines will be located on the particle surface, or at least accessible through cracks large enough to achieve acceptable leachate ingress rates. For example, in milling operations, copper ore showed over 90% exposure below 3 mm.

[0010] But microscopic permeability also depends on how the rock is broken. It also depends on the mineralogy that influences how the rock breaks under stress.

[0011] The ultimate extension of this micropermeability advantage is agitation leaching, in which finely ground ore can be leached at a rate and total extraction determined by chemical reaction rates rather than by intraparticle diffusion. However, agitation leaching requires considerable capital and operating costs for grinding and agitation leaching equipment; it is impractical for low-grade ores or for leach durations exceeding 24 hours or so.

[0012] For heap leaching, resolving microscopic permeability constraints through finer comminution creates a different set of constraints in the macroscopic permeability of the heap. Macroscopic permeability is the term used to describe the permeability of fluid flow through the bulk of the heap, i.e., at distances of centimeters or meters at different locations within the heap.

[0013] The macropermeability of the heap decreases with decreasing crush size because excessive fine particles hinder the flow of leachate and air through the heap. Even at reasonably coarse crush sizes, such as 100 mm, segregation can occur during heap formation and compaction in operation due to the wide particle size distribution.

[0014] Variable macropermeability can affect air and leachant flow within certain parts of the heap, such that low leach extraction is achieved in some areas due to localized flooding or leachant starvation in areas of low permeability, or due to "rain shadows" created by areas of low permeability, or poor aeration through said parts of the heap.

[0015] This variability exists because of the accumulation of fines in the ore, which results from fracture and segregation during heap preparation, or through excessive crushing. During heap stacking and leaching, they tend to consolidate further. The fines prevent the ongoing leachant from entering certain areas within the heap.

[0016] This factor is explained by the Hazen equation ( https: / / agupubs.onlinelibrary.wiley.com / doi / full / 10.1002 / 2017WR020888 ), which empirically relates the macroscopic permeability of any material to the tenth percentile of the particle size distribution in any region within the pile.

[0017] The macropermeability of a particle packing depends on the absolute particle size. It is also affected by particle shape and size distribution, which define the void fraction within the packing. Void fraction is important because mixtures of different particle sizes naturally consolidate to a higher packing density, with finer particles filling the interstices of coarser particles.

[0018] Another measure of macroscopic permeability is hydraulic conductivity. However, for a pile formed from very different particle sizes, this metric can vary significantly between different regions within the pile. Therefore, another useful metric is the time it takes for the pile to drain.

[0019] Therefore, in conventional heap leaching, the primary determinant of macroscopic permeability is the absolute size achieved during crushing. In practice, crushed size influences the proportion of fines produced during crushing. As particle size decreases, a layer of adherent liquid accumulates around the particles. When the thickness of this layer is similar to the interstices between sand grains, the flow of either liquid or gas phases is inhibited. A second determinant is the relative particle size distribution, where uniformly sized particles exhibit higher conductivity than particles with a wide size range because the latter can be more densely packed during heap consolidation.

[0020] For these reasons related to macro-permeability, the maximum crushing size in normal heap leaching is usually between 10mm and 500mm to avoid the formation of excessive fines.

[0021] To reduce the impact of fines in traditional heap leaching, fines are sometimes agglomerated before heap construction. Agglomeration firmly binds the fines to the coarser rock. Effectively controlled heap leaching to prevent excessive deagglomeration improves macropermeability between aggregates, but this negatively impacts micropermeability within each aggregate. Therefore, the leachate typically acts as a binder for the aggregates, reducing the significance of micropermeability issues caused by fines coating.

[0022] While finer crushing and agglomeration can improve extraction of some ores well-suited for heap leaching, the balance of cost and benefit does not make it feasible for all ores. Agglomeration also does not allow for changes in heap operating conditions, such as utilizing multiple leaching agents to treat different mineral species. Agglomeration also does not completely overcome the problem of leaching agents accessing valuable materials locked up in the coarser matrix pebbles that form the center of the agglomerates.

[0023] Therefore, a balance needs to be struck in conventional heap leaching involving either coarser crushing, accepting moderate extraction in the heap leach (typically around 65%), or crushing to a finer size of about 12.7 mm and agglomerating the fines before stacking to achieve slightly higher extraction (typically around 80%).

[0024] Although not in commercial practice, some have suggested physically removing fines before heap leaching. In order to optimize the processing of the fines content of the ore by beneficiation, WO2016 / 170437 and US6146444 remove fines for separate beneficiation before heap leaching the remaining ore.

[0025] Both patents involve finer grinding than is typically used in conventional heap leaching. They both address new processing routes from the finer fraction of the ore. Both recommend heap leaching the remaining coarser fraction of the ore (which contains a moderate proportion of the total value), following size classification for the primary mode of value recovery.

[0026] WO2016 / 170437 requires an upper limit of 1 mm on the particle size, thus limiting the proportion of valuables that can be recovered by heap leaching, making heap leaching a secondary method for valuables production. Heap leaching of ores larger than 1 mm is not considered.

[0027] In the case of US6146444, heap leaching is used to separate gold from pyrite, rather than to extract the gold directly. Therefore, quantitative extraction of pyrite is not a key objective of leaching, unlike when pyrite is the primary value.

[0028] Neither author considered the effect of fines removal on macro- and micro-permeability during heap leaching of the coarser fraction and on the extraction efficiency and flexibility in the heap leaching operation.

[0029] In US6146444, size separation is performed by wet or dry screening of ore crushed to between 6 and 20 mm. Screening is performed between 0.6 and 2 mm, and the fine fraction is distributed to other beneficiation methods to recover pyrite and leach gold. The oversize fraction (>0.6-2 mm), comprising approximately half the ore weight, up to a maximum size of 25 mm, is used for heap leaching to dissolve the pyrite. Heap leaching is supplemented by adding back pyrite recovered during flotation or gravity separation of the finer fraction. The additional pyrite not only releases more of the contained gold but also accelerates bioleaching in the heap. These combined effects result in higher gold extraction than would be achieved in a separate leaching process.

[0030] It is obvious to those skilled in the art that the removal of fines by US 6146444 will partially address the macropermeability problem in the heap, particularly the desludging noted in US 6146444. However, the quantitative effect of removing ore smaller than 0.6-2 mm on the macropermeability of the heap is not known.

[0031] In terms of micro-permeability, the upper crushing particle size of US6146444 is only slightly finer than the typical agglomerate particle size in conventional heap leaching, so the micro-permeability problem still exists.

[0032] In US6146444 Figure 2 The effect of micropermeability on pyrite leaching rates is clearly demonstrated in Figure 1, where dissolution of 0.25-inch material (the claimed optimal crushing size) was slow. Compared to the 55% extraction at 2 mm, only about 15% of the pyrite was biooxidized over 300 days. While these extractions may be sufficient to partially remove problematic elements, such as pyrite, from a portion of the total ore, they are insufficient to recover the primary value in a normal heap leach process.

[0033] WO2016 / 170437 takes a different comminution and beneficiation approach, grinding the ore to a finer size, with a p80 of less than 1 mm and most preferably less than 0.6 mm, before applying coarse flotation in a stirred-bed reactor. Coarse flotation recovery is effective up to about 0.5 mm, leaving a disposable residue. If the grind size is expanded to the claimed 1 mm limit, the coarse flotation process is split to produce a middling residue stream. Recovery from this 0.5-1 mm ore fraction is slightly lower due to reduced release of valuables during the comminution process. Therefore, the middling residue still contains a significant amount of valuables. WO2016 / 170437 indicates that this residue is of fairly low grade and suitable for storage or heap leaching.

[0034] According to these preferred upper sizes in the claims, the middlings residue from rougher flotation will represent 0-30% of the total weight of the ore crushed. Due to the natural behavior of the crushing process and the partial extraction of values by rougher flotation, it will usually contain less than 10-20% of the total metal values. Therefore, heap leaching is not a major component of the overall production.

[0035] WO2016 / 170437 does not provide any teaching on the impact of middling preparation on heap leaching conditions or heap preparation, nor does it provide guidance on methods for recovering the majority of the value from such middling fractions by heap leaching.

[0036] In a separate patent related to heap leaching after removal of fines below approximately 0.5 mm, WO 2018 / 234880 utilizes heap leaching as a removal mechanism for the low-grade ore fraction rejected during bulk sorting and coarse flotation. These fines-removed streams are combined into a heap for heap leaching. Optionally, further intermediate size classification can be introduced, with the coarser ore fraction added to the heap leach feed.

[0037] While WO2018 / 234880 suggests that removal of fines will improve macro-permeability, the particle sizes produced by bulk sorting and screening are typical of conventional heap leaching, so micro-permeability issues will remain.

[0038] The particle size distribution will be very wide and therefore there will also be macro permeability problems due to partial consolidation of the pile.

[0039] Returning to conventional heap leaching, a more complex situation exists for the richest copper ores, which contain large amounts of chalcopyrite, which reacts very slowly under normal heap leaching conditions.

[0040] Other conditions for leaching primary copper ores containing significant amounts of chalcopyrite have been identified. By controlling the leaching in a high-chloride acidic environment within a specific range of oxidation potentials for the formation of the copper-cuprous pair, it is possible to achieve acceptable chalcopyrite leaching rates for conventional heap leaching (Muller-WO 2007 / 134343 A2).

[0041] Likewise, leaching at temperatures above 60°C with ferric sulfate solutions, more typically those produced during heap biooxidation, can achieve acceptable chalcopyrite leaching yields for conventional heap leaching (Robertson-JSAfr. Inst. Min. Metall. Vol. 112 No. 12, Johannesburg, January 2012).

[0042] However, the macro- and micro-permeabilities of conventional heaps make these higher-cost leaching agents problematic in conventional heap leaching of primary copper ores. For example, the use of acidic copper chloride solutions over extended heap leaching cycles consumes large amounts of acid and locks up significant working capital, leading to excessive dilution of reagents and losses throughout the heap leaching cycle. In the case of high-temperature heap leaching, starting and maintaining the entire heap at temperatures exceeding 60°C over extended cycles of conventional heap leaching requires significant external heat input.

[0043] For all these reasons, commercial heap leaching of primary copper ores is limited to opportunistic leaching with copper extraction rates up to around 20%. The chalcopyrite component of these ores is largely unleached.

[0044] Therefore, despite many efforts to optimize conventional heap leaching, the overall extraction of metals using heap leaching technology remains lower than that obtained from the same ore using flotation or agitation leaching. Conventional heap leaching relies on lower application costs and is primarily used to treat easily soluble, low-grade ore resources.

[0045] In summary, macro- and micro-permeability limitations make conventional heap leaching a second-tier method for metal production. Summary of the Invention

[0046] The present invention relates to a method for recovering metal values such as gold, copper, nickel, zinc and uranium from ores containing said metal values, including gold ores (including pyritic gold ores and copper gold ores), copper ores (including copper sulfide, primary copper, secondary copper, transition copper and oxide copper ores), nickel ores (including nickel sulfide, magnesian nickel and ultramafic nickel ores), zinc ores and uranium ores, in sand piles having high macro- and micro-permeability.

[0047] The method comprises the following steps:

[0048] Crushing ore containing metal values to a size where at least 85% of the valuable mineral particles are exposed to provide P80 Sand containing metallic values that is smaller than 5 mm, preferably smaller than 3 mm, and even more preferably around 2 mm, but larger than 1 mm;

[0049] Classifying the sand (i.e., passing the sand through one or more screens) to remove the finer fraction (i.e., removing particles having a size of less than 0.1 mm, less than 0.2 mm, less than 0.3 mm, or less than 0.4 mm) to provide a classified sand having a P 10 Greater than 0.15mm, or greater than 0.25mm, or greater than 0.3mm, or greater than 0.4mm, P 90 / P 10 The ratio is less than 25, less than 20, less than 18 or less than 15 and greater than 3, greater than 5 or greater than 8, and the water permeability is preferably greater than 10 -5 m / s, more preferably greater than 5x10 -4 m / s;

[0050] · Pile the classified sand into piles, where the permeability of the pile is preferably greater than 10 -5 m / s, preferably greater than 5x10 -4 m / s; and

[0051] • Distributing leachant and air in the heap to leach values from the sand in a parent leachate from which the leached values can be recovered.

[0052] Sand heap leaching is generally used as the main recovery method, and more than 50%, preferably more than 60%, and more preferably about 70% of the ore is recovered as sand, which is then subjected to sand heap leaching.

[0053] Typically, the ore is allocated to the leaching step without prior beneficiation steps such as flotation, gravity separation or magnetic separation.

[0054] Sand heap leaching may be carried out in fixed or dynamic heaps with a residence time not exceeding 2 years, preferably not exceeding 6 months, more preferably not exceeding 3 months.

[0055] The pile is preferably free draining to achieve a moisture content of less than 15% within 2 weeks, preferably within 1 week, and more preferably within about 3 days of cessation of irrigation.

[0056] The pile may be subjected to more than one irrigation and drainage cycle to sequentially enhance aeration and leaching.

[0057] Multiple leaching agents can be used sequentially to remove problematic gangue and recover valuable components from the sand heap. For example, an ore containing both copper and gold can be heap leached to extract the copper, then washed and then leached with a different agent to extract the gold.

[0058] By effectively washing and draining the leach sand pile, the loss of leaching reagents and the management of the water balance can be reduced.

[0059] Sand is deposited on the heap by throwing it from a discharge point using hydraulic or mechanical means.

[0060] The sand can be stored in elevators higher than 5 meters, preferably higher than 10 meters, even higher than 20 meters and up to 40 meters.

[0061] Sand can be leached in a dynamic pile and then removed from the dynamic pad by hydraulic mining techniques. The term "dynamic pile" refers to a pile constructed on a fixed pad, leached, and then recovered for storage elsewhere, allowing the pad to be used for further leaching of ore.

[0062] The present invention also relates to a sand pile with high macro- and micro-permeability, wherein the sand in the sand pile comprises crushed ore containing metal values such as gold, primary copper, secondary copper, nickel, zinc, uranium, etc., and the particle size of the sand is P 10 Greater than 0.15mm, or greater than 0.25mm, or greater than 0.3mm, or greater than 0.4mm, P 90 / P 10 The particle size ratio is less than 25, less than 20, less than 18, or less than 15; and greater than 3, greater than 5, or greater than 8, and the permeability is preferably greater than 10 -5 m / s, more preferably greater than 5x10 -4 m / s.

[0063] The sand pile may be stored in an elevator higher than 5 meters, preferably higher than 10 meters, more preferably higher than 20 meters and up to 40 meters in height.

[0064] BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a flow chart of the heap leaching method of the present invention;

[0066] Figure 2 It is a diagram of the heap construction method;

[0067] Figure 3 is a graph showing copper extraction during column leaching of copper ore prepared to different particle sizes using acidic copper chloride or ferric sulfate. The straight line represents solution-based extraction, and the data points represent mass balance extraction.

[0068] Figure 4 is a graph showing inventory-corrected total copper extraction as a function of particle size and time;

[0069] Figure 5 is a graph showing mineral extraction as a function of particle size and time;

[0070] Figure 6is shown as the maximum particle size and P 90 / P 10 a plot of hydraulic permeability of a plurality of samples as a function of ratio or sorting coefficient;

[0071] Figure 7 is a graph illustrating the saturation as a function of application rate for a copper ore sample prepared into fractions of different sizes;

[0072] Figure 8 The air conductivity is shown to be Figure 7 a graph showing the dependence of the application rate of the copper ore sample on the application rate of the copper ore sample; and

[0073] Figure 9 It is displayed Figure 7 Figure 2 shows the drainage profile of a copper ore sample when irrigation was stopped. DETAILED DESCRIPTION

[0074] The present invention is a method in which sand is prepared and piled to form a pile with appropriate macro- and micro-permeabilities to allow for faster and higher extraction of the metal of interest.

[0075] The choice of particle size is critical to achieving the micro- and macro-permeabilities required for rapid and complete heap leaching.

[0076] Establishing the macro- and micro-permeability of the ore particles in the sand heap not only enables higher extractions during sand heap leaching, but also creates heap properties that enable the effective use of a wider range of leachants. Examples of such leachants are those with higher costs, such as using copper chloride as an oxidant, or glycine as a complexing agent, where working capital and reagent losses are too great in conventional heap leaching.

[0077] Macropermeability is achieved by preparing sands with high exposure of valuable minerals (at least 85%) and a narrow size distribution, and with low size restrictions to allow the leachant to drain freely from the heap.

[0078] The combination of these properties allows for sand deposition without excessive consolidation during heap formation. 90 / P 10 The size ratio ensures a satisfactory porosity. With this narrow size distribution, the leachant and air can flow evenly through the pile, and the leachant can contact the most valuable mineral species.

[0079] The lower limit of the size set (P 10 ) to produce a free-draining sand pile, i.e., the hydraulic conductivity will exceed 10 -5m / s, allowing the heap to drain to a moisture content below 15% within a few days. This lower size limit is necessary to achieve macroscopic permeability in the heap, which can be described by the Hazen equation. The result is the ability to drain the heap to achieve high and uniform leachate recovery. The void ratio must be such that air can flow between the particles even during irrigation to maintain the oxidation potential in the heap.

[0080] The optimum amount of relatively fine sand also depends on the balance between gravity and capillary forces, with sufficient fine sand to allow the leachate to be transferred laterally through the heap. This is typically greater than 5% by weight in the heap.

[0081] Set the upper limit of the sand particle size (P 90 ) is to ensure effective micropermeability, thereby achieving high extraction, and to ensure sufficient porosity within the heap. The inventors unexpectedly discovered that the micropermeability and macropermeability characteristics achieved by the process of the present invention allow extraction using heap sand leaching to be exponentially increased to levels achievable with fine grinding and extended agitation leaching, and even surpass extraction achieved by other recovery techniques such as flotation.

[0082] As previously mentioned, the upper size of the valuables that are sufficiently exposed to leach a particular ore will depend on the particle size of the valuable mineral and the fracture characteristics of the mineral and gangue. In practice, acceptable extraction will also depend on the head grade of the ore being leached to form a disposable residue.

[0083] For example, a coarse-grained, low-grade copper ore previously exposed in roughing may have an upper size of 5 mm with approximately 85% exposure, while a fine-grained, high-grade copper ore would require finer crushing to achieve a disposable residue after sand heap leaching. Above approximately 5 mm, differential fracture along grain boundaries is insufficient to produce the required microcracks.

[0084] Therefore, according to the present invention, the preferred upper dimension P of the crushed ore is 80 Less than 5 mm, preferably less than 3 mm, even more preferably around 2 mm, but greater than 1 mm.

[0085] To meet the macro permeability requirements, the diameter of the ore must be large enough to allow the pile to drain freely and the permeability to exceed 10 -5 m / s, preferably greater than 5x10 -4 m / s. This requires P 10 Greater than 0.15 mm, preferably greater than 0.25 mm. Achieving an effective porosity requires P 90 / P 10 Less than 20, preferably less than 15.

[0086] To achieve these macro- and micro-permeability standards, the crushed ore must be classified to remove fines before distributing the coarse fraction to sand heap leach. Through efficient crushing and classification, up to approximately 70% of the ore can be distributed to sand heap leach within the specified size limits.

[0087] The remaining finer ore must be processed separately by flotation or agitation leaching.Like conventional heap leaching, but unlike US6146444, WO2016 / 170437 or WO2018 / 234880, sand heap leaching can be the primary method of value production; with supplementary production from fines.

[0088] refer to Figure 1 In an embodiment of the present invention, the ore is crushed 10 (in a crusher such as an HPGR (High Pressure Grinding Roller), a SAG (Semi-Autogenous Grinding) mill, a VSI (Vertical Shaft Impactor) or a cone crusher), typically to a size of less than 5 mm, to provide a P less than 5 mm. 80 The crushed ore is then classified (ie screened) 12 to remove fine particles 14 with a size less than 0.4 mm and to provide particles with a size greater than 0.4 mm and P 90 / P 10 The sand 16 is about 12.5. The sand 16 is piled up into a pile 18, and its typical hydraulic conductivity is greater than 5×10 -4 The heap 18 is subjected to a heap leaching process using a leachate 22, from which a product 24 containing metal values is obtained, which is recycled to the heap leach 20. After the heap leach is completed, the sand 26 depleted of metal values can be processed.

[0089] Leaching elasticity produced by sand heap leaching

[0090] The macro- and micro-permeabilities achievable with sand heaps having this particle size distribution create several additional characteristics that are distinct from conventional heaps. Within the narrow sand heap particle size distribution, the distribution of leachant and airflow is very uniform; the time required to achieve high extractions in sand heap leaching is short; and the heap drains uniformly and rapidly to low moisture content.

[0091] These three unique characteristics of the sand pile provide flexibility in adjusting and controlling heap leaching conditions that is not achievable in conventional heap leaching.

[0092] The uniform distribution of leachant and air within the sand pile exposes all areas of the pile to effective leaching conditions. In fact, by adjusting the construction and operation of the pile, factors such as oxidation potential and pile temperature can be controlled to a greater level of uniformity in different areas of the pile.

[0093] This improved control of the oxidation potential within the heap is particularly relevant to the leaching of primary copper ores, where strict control of the oxidation potential in sulfate and chloride solutions avoids passivation of chalcopyrite (Watling-Hydrometallurgy 140 (2013) 163-180), the contents of which are incorporated herein by reference.

[0094] Higher extractions can be achieved due to improved lixiviant and air distribution.

[0095] A second source of flexibility induced by sand heap leaching is the high micropermeability, which results in much shorter residence times to achieve high metal extraction.

[0096] For minerals that dissolve chemically quickly (i.e., are completely leached within a few days of agitated leaching under ambient conditions), such as easily separated gold, secondary copper ores, and copper oxide ores, the leaching time in sand heap leaching can usually be reduced to less than 3 months, or even less than 1 month.

[0097] This allows sand heap leaching of this ore to be carried out on dynamic pads at rates and recoveries comparable to bucket or agitated leaching, and significantly higher than conventional heap leaching. These high extractions can be achieved without the infrastructure required for crushing to a fine particle size and material movement in bucket or agitated leaching.

[0098] The faster leach rates achievable with sand heap leaching also produce higher grade parent leachates, thereby reducing the volume of leachate that needs to be handled in subsequent metal recovery processes.

[0099] The leaching reaction of most ores is exothermic. Consequently, leaching can increase the temperature within the heap, particularly when sulfide oxidation occurs at a rate greater than the heat loss from the heap. For example, during conventional heap leaching of copper ores, temperatures as high as approximately 70°C have been recorded in certain areas of the heap. These temperature increases support more rapid biooxidation and increased diffusion rates, leading to greater micropermeability within the particles. Using sand heap leaching can accelerate the leaching of readily oxidizable secondary copper minerals, resulting in a greater increase in heap temperature.

[0100] This temperature increase contributes, in part, to the higher extractions achieved using heap leaching of secondary copper sands.

[0101] The faster temperature increase also provides a means for the chalcopyrite to oxidize during leaching, thereby generating further heat. Furthermore, the relatively short time required to overcome microscopic permeability constraints in the particles being leached reduces the time the heap must be maintained at elevated temperatures to leach the majority of the chalcopyrite. Thus, sand heap leaching, as described in the present invention, allows for heap leaching of primary copper ores.

[0102] In another option for high-temperature leaching of primary copper ores, external heat input can be provided through techniques such as solar heating of the leachate. Typically, the residence time the pile must be maintained at high temperature is too long, but as high micropermeability allows for shorter leaching durations, the potential for external heating increases.

[0103] A third source of flexibility in sand heap leaching is the free-draining nature of the sand.

[0104] This efficient drainage ensures a sharp tail of eluate at the completion of the heap leach. The low residual leachate concentration within the heap, coupled with microscopic permeability, allows for rapid release of the remaining leachate. This also means the heap can be cleaned without significant dilution of the leachate. This results in lower reagent losses and a more manageable water balance for the sand heap leach.

[0105] Sand piles therefore offer the opportunity to use expensive leachants that would be economically unsuitable with conventional heap leaching, where fluid flow is less consistent and leachate carryover within the heap is higher. An example might be the use of acid copper chloride to leach primary copper ores. Other examples include glycine to leach copper or nickel sulfide ores and more concentrated cyanide solutions to accelerate gold leaching.

[0106] The free-draining and homogeneous nature of the heap also enables the leachate to be applied intermittently, followed by a rest period during which most of the void space in the heap is filled with air without the risk of entering areas that are still flooded or depleted of leachate. This rest period has been found to be beneficial in many conventional heap leach operations.

[0107] The free-draining nature of the heap also allows for the sequential use of different leachants without significant cross-contamination between them. This allows for the use of dual leachants in a single heap, thereby first removing problematic gangue and then recovering the mineral of interest, such as pyrite-gold. It also provides the opportunity for sequential leaching of copper-gold ores.

[0108] Recent advances in conventional heap leaching of primary copper ores have shown that high chalcopyrite extraction can be achieved over several years using acidic copper chloride in a strong brine solution. However, the presence of gangue elements in the ore consumes significant amounts of acid, which represents a consumable cost because pyrite is not oxidized at the system's oxidation potential. Because the heap is free-draining, conventional heap leaching can be performed first, using acid generated by the pyrite in the ore to neutralize the alkaline gangue, followed by a conversion to a copper chloride system to leach the chalcopyrite content.

[0109] Similar pre-neutralization can also occur in nickel sulfide ores, using pyrite and pyrrhotite produced during fines flotation to supplement the acid produced during sand heap leaching.

[0110] Gold extraction, whether by agitation or conventional heap leaching, is generally limited to easily beneficiated gold ores. For those ores where the gold is locked up in pyrite, either very fine grinding is required or the pyrite needs to be oxidized beforehand to release the gold.

[0111] Biooxidation of pyrite is a well-known method for releasing gold, while heap leaching is a low-cost method for achieving this release. However, recovering the released gold using cyanide is complex. Biooxidation of pyrite is carried out in an acidic environment, while heap leaching is carried out in an alkaline environment containing cyanide. Mixing these two systems is dangerous, and the reagents required to neutralize the heap before leaching the gold are very demanding. Therefore, similar to the process of US6146444, heap leaching is used to release the gold, followed by grinding, neutralization, and agitated leaching to recover the released gold.

[0112] The well-drained sand heap achieved by the present invention enables this dual leachant approach with initial biological oxidation in an acidic environment followed by drainage and neutralization, and then non-hazardous cyanide heap leaching with minimal additional reagent costs and without the need for fine grinding and agitated leaching.

[0113] Similar opportunities exist in gold deposits with high soluble copper content.

[0114] Table 1 below provides examples of ore types, leachants, and in some cases, sequential leachants that can be treated according to the present invention.

[0115] Table 1

[0116]

[0117]

[0118]

[0119] Sand heap leaching creates heap structure flexibility

[0120] The sand size range of the present invention, as specified to meet the macro- and micro-permeability requirements of sand heap leaching, also creates opportunities for different heap construction methods and different heap designs.

[0121] Conventional piles are often constructed using dump trucks, but this leads to problems with over-compaction and fines generation caused by the pressure of heavy equipment moving through the pile before and after dumping. Another conventional method of pile formation is the back-conveyor piler. This technology is expensive, and the location of the infrastructure is fixed relative to the pile it creates. While both technologies can also be used for sand pile formation, uniformly sized sand can also be "thrown" in multiple dimensions hydraulically or mechanically from an easily repositionable discharge point. (See Figure 2), the figure shows the sand being hydraulically deposited using high-pressure water guns to transport the ore to be leached, and then drained before leaching begins.

[0122] This allows the formation of sand piles without vehicle access and equipment that limits the location and size of the pile during the heap cycle. Uniform sand size also enables hydraulic mining techniques to reclaim the waste pile and pump the resulting residue slurry to a location for permanent disposal. Therefore, in addition to the previously mentioned benefits of short residence times, the potential for dynamic heap leaching on permanent leach pads is further enhanced.

[0123] Conventional heap leaching typically has a lift height of 5-10m to maintain effective vertical irrigation through the heap. Due to the uniform particle size of sand, stable macro-permeability, reduced consolidation capacity, and ability to drain and settle, the lift height of sand heap leaching can be significantly increased, especially if under-heap channels are provided for forced air entry.

[0124] The relatively small size of the sand allows for the placement of air ducts within the pile, thereby reducing oxygen depletion in certain areas as air flows through the pile. This placement of air ducts can be accomplished by drilling holes into the forming pile to inject the ducts, or as a permanent fixture in a dynamic pile formed around fixed air ducts, with the sand subsequently removed by hydraulic mining. This approach allows for further extension of the pile's height.

[0125] The uniform sand size in sand heap leach creates an ideal distribution path for leachant and air flow through the heap. Isolation during construction is limited. Problems associated with "drilling skew holes" and "dead zones" in traditional heaps are avoided in sand heaps formed from smaller particles. This improved flow means that irrigation at the heap edges and aeration in the center of the heap are much less of a concern in sand heap leach.

[0126] test

[0127] Different size fractions of transition copper ore were prepared by crushing the ore to -2.4 mm, -6.7 mm and -25 mm. The crushed fractions were then screened to obtain a relatively narrow particle size distribution as shown in Table 2, which shows good macro-permeability. Within a few hours of stopping irrigation, the 1-meter long sand column was drained to a moisture content of less than 8%, as shown in Table 2. Figure 9 shown.

[0128] These fractions, containing 30-40% copper (chalcopyrite), were leached at 25°C in a 1 m column using acid copper chloride of varying pH, salt and copper ion concentrations. Figure 3 Copper extractions calculated from solution balances, uncorrected for inventory changes, and final extractions from mass balances when available are presented. The results show that high extractions of transition copper ores can be achieved, with finer ores dissolving faster and more completely. Figure 3The results for the chlorine system shown here have identical test conditions, except that intermittent irrigation was used for the -2.4 mm fraction. In these tests, the more soluble components of the ore were extracted at high rates within approximately 10 days, while the less soluble component, chalcopyrite, was largely extracted within 150 days. The decrease in the rate and extent of copper extraction with increasing particle size highlights the influence of micropermeability.

[0129] Table 2: Particle size characteristics of column leaching samples

[0130]

[0131]

[0132] To further demonstrate the effect of micropermeability on achievable extraction, the same ore sample was ground to less than 1.25 mm before recovering the concentrate using coarse particle flotation and rejecting the low-grade sand. The resulting sand, which was at the harder end of the size distribution for optimal macropermeability, exhibited acceptable hydraulic conductivity for leaching, but was significantly more saturated than the coarser sand fraction at equivalent flow rates, as shown in Figure 2. Figure 7 As shown, when the particle size P 80 When the diameter is greater than 1 mm, the saturation of the component increases exponentially. Figure 7 It can be clearly seen that in order to achieve the appropriate saturation, a particle size of P is required. 80 Greater than about 1 mm. This higher saturation can become increasingly problematic in leach systems where materials such as iron oxides or calcium and aluminum sulfates reprecipitate, or where elemental sulfur formation occurs. Precipitation of such materials in the heap is common in many heap leaching applications.

[0133] -1.25 mm sand was leached in acidic copper chloride and ferric sulfate leaching agents at 25 °C, and the leaching conditions were the same as those for the other parts. Figure 3 The results showed that in the chloride system, the extraction rate exceeded 85% after 100 days, with chalcopyrite being the slowest dissolving mineral species. In the sulfate system, the extraction rate reached 75% in the same time, with every copper mineral except chalcopyrite showing high solubility.

[0134] Figure 4 This more clearly illustrates the increase in total extraction with decreasing particle size, consistent with the previously cited work by Miller et al. on mineral exposure and particle size. Most surprisingly, there is also a significant increase in leaching rate associated with particle size, indicating greatly improved access of the leachant to the surface of the valuable mineral particles. Under relatively mild leaching conditions, the ideal size range for rapid and complete extraction is less than approximately 6 mm.

[0135] When considering Figure 5 The effect of particle size is further highlighted when the dissolution rates of different copper minerals in the solution are investigated.

[0136] To achieve extraction rates exceeding 85%, the more readily leachable minerals (in this case, chalcocite and bornite) are less dependent on particle size than the more refractory chalcopyrite. In both lixiviant systems, extraction rates of the oxide and secondary sulfide fractions (consisting primarily of dephosphorite, chalcocite, and bornite) were greater than 98% in the finest particle size fractions examined. The impact of increasing extraction rate and extent with particle size below approximately 6 mm is significant and unexpected. Operating an additional 6 m column on the -1.25 mm fraction under the same experimental conditions demonstrated extraction of almost 80% of the copper from chalcopyrite in approximately 190 days. Size is a critical parameter in order to scale up efficient heap leaching to recover more refractory minerals, such as chalcopyrite, from primary copper ores.

[0137] Further particle size reduction is advantageous only on the basis of micropermeability, the offsetting factor being macropermeability. Figure 6 It is shown how macropermeability decreases exponentially with decreasing particle size, even for very well sorted sands. Therefore, a finite value is set for the minimum particle size to ensure effective macropermeability for practical application of heap leaching as the primary method for recovering value from a particular ore and leachant system.

[0138] Figure 7 、 8 Figures 9 and 10 show the hydrodynamic measurements of the column leaching portion. Due to the narrow particle size distribution and the lack of obvious fine particles, the sample has the lowest degree of compaction, with the dry bulk density ranging from about 1.3 t / m 3 Increased to about 1.4t / m 3 , the compression applied was equivalent to a pile height of 40 m. These results indicate that while the finest components examined exhibit good micropermeability with correspondingly high extraction, a significant decrease in macropermeability is observed. Figure 8 As shown, higher saturations can create greater problems for effective air permeability at irrigation rates suitable for heap leaching. This can become even more problematic if additional fine sediment forms in the heap. The slightly coarser fraction exhibits good macropermeability, has acceptable saturation and good air permeability at application rates suitable for heap leaching, resists consolidation, and exhibits rapid and extensive desaturation after irrigation ceases.

[0139] In the context of heap leaching, the results showed that the selection of P 80 Less than 5mm and P 90 / P 10By properly adjusting the particle size distribution of the ore with a particle size ratio less than 20 but greater than 3, exponential micropermeability for rapid sand heap leaching can be achieved while maintaining sufficient macropermeability to form a free-draining heap with excellent leachant and air distribution.

[0140] With favorable mineralogy, or sufficient time for the slower-reacting mineral species to dissolve, sand extraction rates exceeding 90% can be achieved in sand heap leaching. Surprisingly, these extraction rates are higher than the 80-85% extraction rates typically achieved by flotation of the ores used in the trials, indicating that sand heap leaching is equally attractive for low-grade and high-grade ores, and is particularly attractive for leaching highly oxidized ores. In addition, P crushed to less than 5 mm 80 Much easier than flotation requires, heap leaching can produce cathodes directly, with a lower overall environmental footprint.

[0141] References (The contents of which are incorporated herein by reference)

[0142] Filmer and Alexander–WO2016 / 170437

[0143] Filmer and Alexander–WO2018 / 234880

[0144] Muller-WO2007 / 134343A2

[0145] Kohr–US6146444

[0146] Robertson-JSAfr.Inst.Min.Metall. Vol. 112 No. 12, Johannesburg, January 2012

[0147] Watling–Hydrometallurgy 140(2013)163-180

[0148] Miller-Int.J.Miner.Process.72(2003)331–340

[0149] https: / / agupubs.onlinelibrary.wiley.com / doi / full / 10.1002 / 2017WR020888

[0150] Beard and Weyl, 1973, Influence of texture on porosity and permeability of unconsolidated sand, The American Association of Petroleum Geologists Bulletin, Volume 57, Number 2, pp. 349-369

[0151] Guzman, 2013, Implications of hydrodynamic testing for heap leach design, Hydroprocess 2013, Conference Paper。

Claims

1. A method for preparing and leaching an ore containing metal values in a heap leach comprising the following steps: Crushing the ore containing metal value to provide a particle size P 80 Sand containing metallic values less than 5 mm but greater than 1 mm; · Classify the sand to provide graded sand with a particle size P 10 Greater than 0.15mm, particle size P 90 / P 10 The ratio is less than 25 and greater than 3; ·Pile the classified sand into piles; and Distributing leachants and air throughout the heap to leach metal values from the sand; Among them, the sand is stacked in elevators with a height of more than 5 meters.

2. The method according to claim 1, wherein the ore is crushed into P 80 Less than 3mm.

3. The method according to claim 2, wherein the ore is crushed into P 80 It is 2mm.

4. The method according to claim 1, wherein the P of the classified sand 10 Greater than 0.

15.

5. The method according to claim 4, wherein the P of the classified sand 10 Greater than 0.25mm.

6. The method according to claim 5, wherein the P of the classified sand 10 Greater than 0.3mm.

7. The method according to claim 6, wherein the P of the classified sand 10 Greater than 0.4mm.

8. The method according to claim 1, wherein the P of the classified sand 90 / P 10 The ratio is less than 20.

9. The method according to claim 8, wherein the P of the classified sand 90 / P 10 The ratio is less than 18.

10. The method according to claim 9, wherein the P of the classified sand 90 / P 10 The ratio is less than 15.

11. The method according to claim 1, wherein the P of the classified sand 90 / P 10 The ratio is greater than 5.

12. The method according to claim 11, wherein the P of the classified sand 90 / P 10 The ratio is greater than 8.

13. The method according to claim 1, wherein the water permeability of the graded sand and the pile formed by the graded sand is greater than 10 -5 m / s.

14. The method according to claim 7, wherein the water permeability of the graded sand and the pile formed by the graded sand is greater than 5x10 - 4 m / s.

15. The method of claim 1 wherein sand heap leaching is the primary method of recovering values from the ore, with greater than 50% of the ore being processed by sand heap leaching.

16. The process of claim 15 wherein sand heap leaching is the primary method of recovering values from the ore, with greater than 60% of the ore being processed by sand heap leaching.

17. The method of claim 16 wherein sand heap leaching is the primary method of recovering values from the ore, with greater than 70% of the ore being processed by sand heap leaching.

18. The method of claim 1 wherein the sand heap leaching is performed in a fixed or dynamic heap with a residence time of less than 2 years.

19. The method of claim 18, wherein the residence time is less than 6 months.

20. The method of claim 19, wherein the residence time is less than 3 months.

21. The method of claim 1, wherein the water content is less than 15% within 2 weeks of cessation of irrigation.

22. The method of claim 1 wherein the pile undergoes more than one irrigation and drainage cycle to sequentially enhance aeration and leaching.

23. The method of claim 1, wherein multiple leaching agents are used sequentially to remove gangue and then recover valuable components from the sand pile.

24. A method according to claim 23, wherein an ore containing both copper and gold is first heap leached to extract the copper, then washed with water and subsequently leached with a different reagent to extract the gold.

25. The method of claim 1, wherein the graded sand is deposited on the heap by throwing it from a discharge point using hydraulic or mechanical means.

26. The method of claim 1, wherein the sand is stacked in an elevator having a height greater than 10 meters.

27. The method according to claim 26, wherein the sand is stacked in an elevator having a height of even greater than 20 meters.

28. The method of claim 27, wherein the sand is stacked in an elevator of up to 40 meters.

29. The method of claim 1 wherein the sand is leached in the dynamic pile and then removed from the dynamic mat by hydraulic mining techniques.

30. The method of claim 29, wherein the stack is constructed with air injection points to control the redox potential and temperature of regions within the stack.

31. The method of claim 1, wherein the metal value is selected from the group consisting of gold, copper, nickel, zinc, and uranium, and the ore containing the metal value is selected from the group consisting of gold, copper, nickel, zinc, and uranium.

32. A sand pile for heap leaching comprising sand prepared from an ore containing metal values, the sand having a particle size P 80 Less than 5mm,P 10 Greater than 0.15mm,P 90 / P 10 The particle size ratio is less than 25 and greater than 3; in, The sand is stacked in elevators with a height of more than 5 meters.

33. The sand pile according to claim 32, wherein the sand particle size P 10 Greater than 0.15mm.

34. The sand pile according to claim 33, wherein the sand particle size P 10 Greater than 0.25mm.

35. The sand pile according to claim 34, wherein the sand particle size P 10 Greater than 0.3mm.

36. The sand pile according to claim 35, wherein the sand particle size P 10 Greater than 0.4mm.

37. The sand pile according to claim 32, wherein the sand has a P value of 90 / P 10 The particle size ratio is less than 20 and greater than 5.

38. The sand pile according to claim 37, wherein the sand has a P value of 90 / P 10 The particle size ratio is less than 15 and greater than 8.

39. The sand pile of claim 32, wherein the water permeability of the sand pile is greater than 10 -5 m / s.

40. The sand pile of claim 39, wherein the water permeability of the sand pile is greater than 5 x 10 -4 m / s.

41. The sand pile of claim 32, stacked in an elevator having a height greater than 10 meters.

42. A sand pile as claimed in claim 41 , stacked in an elevator exceeding 20 metres in height and up to 40 metres in height.

43. The sand pile of claim 32, wherein the metal values are selected from the group consisting of gold, copper, nickel, zinc, and uranium, and the ore containing the metal values is selected from the group consisting of gold, copper, nickel, zinc, and uranium.

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