Abstract:
The invention provides processes that significantly reduce acid consumption while maintaining efficient leach recovery of copper from oxide and acid consuming ores. The invention provides a hydrometallurgical process that reduces acid required for leaching in the presence of a solid ion exchange media. The presence of the ion exchanger leads to copper extraction from solution into the ion exchange phase, the removal of the copper from solution shifts the dissolved copper equilibrium, enabling additional copper dissolution at weak acidities where normally the leaching equilibrium would be hindered. In select embodiments, the process is not reliant on an external neutralising agent to control pH but rather on the acid consuming characteristic of the ore being processed and a limit to the amount of acid added. At the pH at which the leach is controlled, iron (if present) is predominantly present as the ferrous ion, which has a lower affinity for the resin than copper.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention is in the field of extractive hydrometallurgy, particularly methods for the leaching and recovery of copper from acid consuming ores using a controlled acid addition in the presence of an ion exchange media capable of taking up copper from weakly acidic slurries and solutions. 
       BACKGROUND OF THE INVENTION 
       [0002]    Copper containing rocks and minerals normally only contain a small percentage of copper. Most of the rock and/or mineral is unwanted material, commonly referred to as gangue. The copper containing material can be processed in alternative ways, depending largely upon the form or association of the copper within the host rock or mineral. The two main types of copper ore that are processed industrially are copper oxide ores and copper sulphide ores. 
         [0003]    Copper sulphide ores have historically been the predominant source of copper production, principally from chalcopyrite ore. Sulphide copper ores have often been more profitable to treat, as they typically contain higher amounts of copper than oxide ores and treatment processes such as flotation and smelting enable ready separation from gangue minerals. However, sulphide copper ores are not as abundant as oxide ores, and many of the large copper sulphide ore bodies have been discovered and exploited or are being developed. The lower grade copper oxide ores have typically been regarded as less commercially attractive than the sulphide ores, although they have been economically processed using alternative hydrometallurgical processes. These hydrometallurgical processing options have been applied to the treatment of oxide ores which commonly contain soluble copper carbonate minerals including azurite, malachite, chrysocolla, dioptase, antlerite, chalcanthite, tenorite, and atacamite. All of these minerals are soluble in sulphuric acid, additional oxide minerals such as cuprite and delafossite are also acid soluble but to a lesser degree. 
         [0004]    Hydrometallurgical processing of copper oxide ores commonly utilises sulphuric acid heap or tank leaching. The economic treatment of these ores can be adversely impacted through high acid consumption by gangue or acid consuming copper minerals, leading to excessive operating costs. 
         [0005]    Copper production from oxide ores is gaining increasing importance, and the ability to economically treat these types of ores is strongly dependent upon the acid consumption of the ore. This acid consumption is driven both by the percentage and type of copper mineralization with minerals such as delafossite, azurite, brochatite and malachite being higher acid consuming copper oxides; but also by the acid consumption of the gangue minerals especially those high in silicates, limonite, as well as clays such as montmorillinite, kaolinite and smectite which readily absorb acid. 
         [0006]    One low cost treatment approach applied to the treatment of copper oxide ores is acid leaching using a heap leach, in which the copper minerals are crushed and stacked, acidic solutions are applied to the top of the heap, and the solution permeates the heap-leaching copper from the ore. Ores high in clays and other fine or friable materials can render heap leaching impractical due to permeability issues, these clays and fines may also prove challenging for downstream processing steps, such as solvent extraction circuits where fine solids disrupt the process through the formation of liquid solid combinations commonly referred to as CRUD. Solid liquid separation of large volumes of leach solutions is capital intensive, and in lower grade ores is challenging to justify economically. 
         [0007]    The presence of some sulphide minerals within oxide ores may reduce overall acid consumption, but these minerals tend to be relatively slow to leach under acidic atmospheric conditions. Secondary sulphides such as chalcocite and digenite are resistant to acid leaching as is native copper. 
         [0008]    Resin in pulp (RIP) has been proposed as a treatment/recovery option for base metals. Typically, leach conditions are at a low pH, where uptake of copper by the resins is not optimal and large amounts of iron may be also be dissolved. The challenges associated with the low pH, are generally overcome by a pH adjustment step using a neutralising agent to increase the pH, precipitating ferric ions, and increasing the loading of dissolved copper onto the resin. This pH adjustment step increases processing costs, through the addition of the neutralising agent and the effective loss of acid that has been added but not utilised to leach target metals. 
         [0009]    Conventional copper leaching processes add an excess of acid to drive the leaching equilibrium, once the leach has reached a target or equilibrium level, the pH of the slurry is adjusted to facilitate efficient extraction of copper. The pulp may have ion exchange resin added directly to it in a resin in pulp process. The pH adjustment step may precipitate deleterious impurities such as ferric ions which may compete with the copper for uptake onto some ion exchange media. A range of alternative leaching processes that include the use of ion exchange media are for example disclosed in: US Patent Publication 2012/0186398, US Patent Publication 2007/0041884, U.S. Pat. No. 6,350,420 and US Patent Publication 20090056500. 
       SUMMARY OF THE INVENTION 
       [0010]    In alternative embodiments, the invention provides processes for the efficient leaching of copper from an acid consuming ore, using a mineral acid at a controlled pH with simultaneous extraction of the leached copper onto a solid ion exchange media which is mixed with the pulp while the leaching is in process. In select embodiments, the process makes use of sufficient mineral acid to leach copper, while avoiding an excess of acid addition, and in this way the process of the invention may be carried out so as to avoid the need for a subsequent additional of an alkali to elevate the pH—for example to precipitate deleterious non target elements. In effect, leaching is carried out at a controlled pH level that facilitates the efficient uptake of the target metal by the ion exchanger, while avoiding the need for a subsequent pH elevation. 
         [0011]    In select embodiments, the invention accordingly provides processes for extracting copper from a comminuted acid consuming copper ore. The process involves adding a controlled amount of mineral acid to the comminuted copper ore in the presence of an ion exchange medium, so as to reach a target leaching-and-resin-loading pH. The target pH for the resin-in-leach leaching solution may for example be greater than pH 1, for example a value or range between 2 and 4. At the target leaching-and-resin-loading pH, copper ions leached from the ore are bound with relatively high affinity by the ion exchange media. Leaching conditions in the resin-in-leach leaching solution may be maintained for a leaching time period, adding mineral acid so as to maintain the leaching-and-resin-loading pH, so that the ion exchange media is loaded with copper ions leached from the ore. This provides a copper-loaded ion exchange media in a relatively barren resin-in-leach solution. The copper-loaded ion exchange media may be separated from the barren resin-in-leach solution, and copper eluted from the copper-loaded ion exchange media to provide a regenerated ion exchange media and a copper eluate. The regenerated ion exchange media may be recycled to the resin-in-leach leaching solution, and copper recovered from the copper eluate. 
         [0012]    Aspects of the invention accordingly provide processes that enable the use of relatively low levels of acid to leach copper, with simultaneous extraction of the leached copper onto a solid ion exchange media which is mixed with the pulp while the leaching is in process. At higher pH levels of 3.0 to 3.5, ferric ion solubility is low and therefore does not interfere with copper loading onto chelating resins (such as IDA and other chelating resins with uptake capabilities for copper from acidic slurries and solutions). 
         [0013]    Aspects of the invention use resin in leach (RIL) to recover copper while minimizing acid consumption. In selected embodiments, processes of the invention address challenges arising from the low permeability of some ores in heap leaching, as well as avoiding difficult and expensive solid liquid separation steps. Significantly, processes of the invention may be adapted so as to facilitate a reduction in the amount of acid required for leaching, compared with extractions that involve an acid leaching step followed by a distinct resin in pulp step to load the resin. In particular, the invention may be implements so as to reduce or eliminate the need for additional reagent addition to neutralize or partially neutralize a strongly acidic leach solution so that it is within a higher pH range selected for efficient copper uptake by ion exchange media (such as iminodiacetic resins). 
         [0014]    In aspects of the invention, after the resin is loaded with copper in the RIL extraction, copper can be stripped from the resin using a stronger sulphuric acid, and the resulting copper solutions can be treated for copper recovery via techniques such as electrowinning or cementation or further upgraded via solvent extraction prior to electrowinning or the production of copper sulphate. The regenerated resin may be returned to the circuit for re-use. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a process flow schematic illustrating aspects of the processes of the invention. 
           [0016]      FIG. 2  is a graph illustrating acid consumption at varying pH for copper leaching from an oxide acid consuming ore in the presence of an iminodiacetic ion exchange resin. 
           [0017]      FIG. 3  is a graph illustrating increased removal of leached copper from solution onto ion exchange media at higher pH. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    In select embodiments, the invention involves the treatment of acid consuming copper ores. In alternative embodiments, the ores may for example be copper oxide ores such as, but not limited to, delafossite, chrysocolla, azurite, dioptase, brochatite, tennorite, atacamite and malachite and mixtures thereof. These ores are representative of higher acid consuming copper oxides ores. Other oxide ores may be present, that are not acid consumers, such as antlerite and chalcanthite 
         [0019]    Processes of the invention involve adding a controlled amount of mineral acid to the comminuted copper ore. In select embodiments, sulphuric acid may be used, hydrochloric acid may also be used, or mixtures thereof. In general, the ore is comminuted to a grind size less than the average diameter of the ion exchange resin beads. For example, the ore may be ground to an average grind size less than about 500 μm, or alternatively less than about 200 μm. In select embodiments, finer grind sizes, for example of less than 100 μm may facilitate separation of ion exchange resin from the ore solids, as well as enhancement of leaching kinetics. 
         [0020]    Leaching may be carried out in the presence of various ion exchange media, such as cross linked polystyrene or acrylic polymers functionalized with groups exhibiting preferential selectivity for copper from mildly acidic solutions. For example, polystyrene divinylbenzene crosslinked polymers functionalized with iminodiacetic (IDA) groups may be used, such as the commercially available Lanxess TP-207 &amp; TP-208, Rohm &amp; Hass IRC 748 or Purolite S-930. To facilitate screening from pulps and slurries, the resin beads may be selected to be of relatively large average diameter, for example compared with resin bead sizes used in packed columns, for example greater than about 500 μm in diameter or greater than about 700 μm in diameter. Alternative chelating resin functionalities may be suited to select embodiments, such as resins with phosphonate functionalities. These resins are normally thought to be unsuitable for copper leach applications, due to their strong loading and high selectivity for ferric ions. However, in the context of the present invention, using a reduced acid RIL leach at a pH of 3.0 and above, ferric ions will have only minimal solubility so that the loading of ferric ions on phosphonic functionalised resins is minimized. Resins of this type include, for example, Rohm &amp; Hass Amberlite IRC 747, Lanxess TP-260, Purolite S-940, S-950 &amp; S957. Other resin functionalities may be employed in this process such as those comprising of a mixture of chelating groups with combinations of nitrogen, oxygen or phosphorous donors. 
         [0021]    Commonly used bispicolylamine (BPA) resins, such as Dow M4195, may not be well suited for various aspects of this invention, due to their very high affinity for copper, which may make stripping of copper from the loaded resin challenging. Copper may be retained by resin of this kind so strongly that elution is not effective even with very high strength sulphuric or hydrochloric acid, and in practice elution may for example require the use of ammonia or ammonium carbonate. Elution using alternative solutions may however cause osmotic shock to the resin, for example in the course of the change from an acidic leach environment to an alkaline elution environment, thereby shortening resin lifespan. For these reasons, modified picolylamine resins such as N-(2-hydroxypropyl)-2-picolylamine (HPPA) may be more suited to alternative embodiments of the invention, in conjunction with elution of copper using high strength sulphuric acid solutions. 
         [0022]    Process of the invention may be carried out so as to reach a target leaching-and-resin-loading pH, being a pH selected to optimize the combined effect of mineral leaching and resin loading. The target pH for the resin-in-leach leaching solution may for example be greater than a selected minimum value, such as: pH 1 or pH 2, and may be less than a selected maximum value, such as: pH 3, 4 or 5. Accordingly, the target pH may be a value or range between selected thresholds, such as between about 2 and about 4, or any value with such a range. The target leaching-and-resin-loading pH is selected so that copper ions leached from the ore are bound with relatively high affinity by the ion exchange media. 
         [0023]    Leaching conditions in the resin-in-leach leaching solution may be maintained for a leaching time period sufficient to leach the majority of the acid soluble copper ores, these time may be relatively rapid requiring an hour or less or may more typically require 2-6 hours and in some cases will require 6-12 hours or longer. Longer leaching times are possible, for example to achieve very high recoveries from slow-to-leach ores. During the leaching time period, mineral acid may be added so as to maintain the leaching-and-resin-loading pH, so that the ion exchange media is loaded with copper ions leached from the ore. Leaching conditions and time periods may be selected so as to remove a particular proportion of the copper in the ore, such as: 50%, 75%, 80%, 90-95%, or 95-100%. Leaching time and acid consumption may be balanced to achieve an optimized outcome where lower copper recovery is offset by lower acid consumption associated with reduced contact time with acid consuming gangue materials. 
         [0024]    The copper-loaded ion exchange media may be separated from the barren resin-in-leach solution, for example using static screens having low energy requirements, or vibrating screens for more difficult to screen ores. Screens are typically metallic of suitable corrosion resistance or may be manufactured from polyurethane or re-enforced polyurethane for minimisation of wear and resin attrition. Copper may be eluted from the copper-loaded ion exchange media to provide a regenerated ion exchange media and a copper eluate, and the regenerated ion exchange media may be recycled to the resin-in-leach leaching solution. The resin may for example be regenerated using a higher strength sulphuric acid, or other mineral acid. Elution may advantageously be controlled to that the copper bearing eluate is largely free of excess free acid. After elution, the resin may contain residual acid in the pores of the resin, and the resin may accordingly be rinsed with water to displace residual acid, and this weakly acidic solution may in turn be used as part of the leach solution. 
         [0025]    Copper may be recovered from the copper eluate using a variety of alternative techniques, such as such as electrowinning or cementation. In select embodiments, the copper eluate may be upgraded via solvent extraction prior to electrowinning or the production of copper sulphate. 
       Examples 
       [0026]    In representative embodiments, 250 g of copper bearing ore was slurried in 750 g of water. The exemplified copper ore contained copper minerals that are not readily or totally leached using sulphuric acid under atmospheric conditions without aeration, such as cuprite, delafossite and or native copper. 
         [0027]    As a control, a leach was conducted using sufficient acid addition for the slurry to have a final free acid level of 5-7 g/L at the end of the leach. This required 50-60 Kg/t equivalent acid addition with an average copper recovery of 58%. 
         [0028]    A number of reduced acid leach embodiments were conducted using pulps of the same ratio (250 g of copper bearing ore was slurried in 750 g of water) however to this slurry was added only sufficient sulphuric acid such that the leaching was controlled at the target pH for 6 hours. These leaching tests were conducted in the presence of an iminodiacetic functionalized ion exchange resin mixed with the pulp at a volume concentration (wet settled resin) of 5%. These tests were conducted using lower acid additions with acid addition operating across a pH range of 2.0-3.0. The acid consumption ranged from 14.5-21 Kg/t equivalent acid addition, with an average copper recovery of 58%. In effect, the same copper recovery as the control was achieved, but acid consumption was reduced by a factor of between 2 and 4. At a controlled pH leach of 3.5 in the presence of resin the copper recovery decreased to 47%. The results are illustrated in the graphs of  FIG. 2  and  FIG. 3 . 
         [0029]    A further control test was conducted using identical leach conditions at a pH of 3.0 but without any resin present. Without the resin present during the leach the leaching of copper from the ore decreased to 39%. 
         [0030]    Slurries containing leached copper were contacted with resin to measure the optimal pH for copper uptake by an iminodiacetic resin. The percentage of resin was constant in each test, the results set out in Table 1 illustrate that leaching at a higher pH improves the uptake of copper onto the resin. Leaching at higher pH ranges reduces or eliminates the need for acid neutralization or partial neutralization and enables the operation to take place as a resin-in-leach process, rather than requiring a pH adjusted resin-in-pulp process. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Copper removal from weakly acidic leach solutions by 
               
               
                 iminodiacetic functionalized resin at varying pH. 
               
             
          
           
               
                   
                 pH 
                 Copper Removal 
               
               
                   
                   
               
             
          
           
               
                   
                 2.4 
                 56% 
               
               
                   
                 2.6 
                 65% 
               
               
                   
                 2.8 
                 71% 
               
               
                   
                 3.0 
                 76% 
               
               
                   
                 3.2 
                 82% 
               
               
                   
                 3.4 
                 86% 
               
               
                   
                   
               
             
          
         
       
     
         [0031]    Although various embodiments of the invention are disclosed herein, many adaptations and modifications may be made within the scope of the invention in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way. Numeric ranges are inclusive of the numbers defining the range. The word “comprising” is used herein as an open-ended term, substantially equivalent to the phrase “including, but not limited to”, and the word “comprises” has a corresponding meaning. As used herein, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a thing” includes more than one such thing. Citation of references herein is not an admission that such references are prior art to the present invention. Any priority document(s) and all publications, including but not limited to patents and patent applications, cited in this specification are incorporated herein by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein and as though fully set forth herein. The invention includes all embodiments and variations substantially as hereinbefore described and with reference to the examples and drawings.