Patent Publication Number: US-2023134310-A1

Title: System and method including multi-circuit solution extraction for recovery of metal values from metal-bearing materials

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of and claims priority to U.S. patent application Ser. No. 17/366,653, entitled “SYSTEM AND METHOD INCLUDING MULTI-CIRCUIT SOLUTION EXTRACTION FOR RECOVERY OF METAL VALUES FROM METAL-BEARING MATERIALS,” which was filed on Jul. 2, 2021 (the “&#39;653 application”). The &#39;653 application is a continuation of and claims priority to U.S. patent application Ser. No. 16/671,323, entitled “SYSTEM AND METHOD INCLUDING MULTI-CIRCUIT SOLUTION EXTRACTION FOR RECOVERY OF METAL VALUES FROM METAL-BEARING MATERIALS,” which was filed on Nov. 1, 2019, now U.S. Pat. No. 11,053,566, issued Jul. 6, 2021 (the &#39;323 application). The &#39;323 application is a continuation of and claims priority to U.S. patent application Ser. No. 16/020,405, entitled “SYSTEM AND METHOD INCLUDING MULTI-CIRCUIT SOLUTION EXTRACTION FOR RECOVERY OF METAL VALUES FROM METAL-BEARING MATERIALS,” which was filed on Jun. 27, 2018, now U.S. Pat. No. 10,501,821, issued Dec. 10, 2019 (the &#39;405 application). The &#39;405 application is a continuation application of and claims priority to U.S. patent application Ser. No. 14/920,768, entitled “SYSTEM AND METHOD INCLUDING MULTI-CIRCUIT SOLUTION EXTRACTION FOR RECOVERY OF METAL VALUES FROM METAL-BEARING MATERIALS,” which was filed on Oct. 22, 2015, now U.S. Pat. No. 10,036,080, issued Jul. 31, 2018 (the &#39;768 application). The &#39;768 application is a divisional application of and claims priority to U.S. patent application Ser. No. 13/331,717, entitled “SYSTEM AND METHOD INCLUDING MULTI-CIRCUIT SOLUTION EXTRACTION FOR RECOVERY OF METAL VALUES FROM METAL-BEARING MATERIALS,” which was filed on Dec. 20, 2011, now U.S. Pat. No. 9,169,533, issued Oct. 27, 2015. The aforementioned applications are hereby incorporated by reference herein in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to systems and methods for extraction of metal values from metal-bearing materials, and more specifically, to systems and methods for recovering metal values using solution extraction techniques. 
     BACKGROUND OF THE INVENTION 
     Hydrometallurgical treatment of metal-bearing materials, such as metal ores, metal-bearing concentrates, and other metal-bearing substances, has been well established for many years. Moreover, leaching of metal-bearing materials is a fundamental process utilized to extract metal value from metal-bearing materials. Typical leach processes comprise contacting a metal-bearing material with an aqueous solution containing a leaching agent which extracts the metal or metals from the metal-bearing material into solution. For example, in copper leaching operations, especially copper from copper minerals, such as chalcopyrite and chalcocite, aqueous sulfuric acid is contacted with a copper-bearing ore. During the leaching process, acid in the leach solution may be consumed and various soluble components are dissolved thereby increasing the metal content of the aqueous solution. 
     The aqueous leach solution containing the leached metal can then be treated by, for example, solution extraction, wherein the aqueous leach solution is contacted with an organic solution comprising a metal-specific extraction reagent, for example, an aldoxime and/or ketoxime, to form an aqueous phase and an organic phase. The metal-specific extraction reagent extracts the metal from the aqueous phase into the organic phase. During a solution extraction process for copper and certain other metals, a leaching agent may be regenerated in the aqueous phase. For example, when sulfuric acid is used as the leaching agent, sulfuric acid can be regenerated in the aqueous phase when copper is extracted into the organic phase by the extraction reagent. 
     After copper is removed from the aqueous phase into the organic phase, the diluted aqueous solution, now called the raffinate, may be recycled back to the leaching process, recycled to the front of a solid-liquid separation process, and/or forwarded to secondary metal extraction processes, such as, for example, cobalt recovery. 
     Numerous technical challenges exist with typical leaching and solvent extraction processes. For example, under current leaching and solution extraction processes, large concentrations of soluble metal and metal precipitate can be lost in the metal-depleted, acid-containing aqueous phase raffinate solutions. These losses lead to inefficiencies and relatively low overall process yields. Additionally, relatively high primary metal concentrations (such as copper) in the raffinate make recovery of secondary metals costly and possibly impractical. 
     Accordingly, systems and methods for more easily controlling process conditions, such as the concentration of a primary metal the raffinate solution, would be advantageous. Additionally, systems and methods for improved recovery of secondary metals from a raffinate solution are desirable. 
     SUMMARY OF THE INVENTION 
     The present invention generally relates to a system and method for recovery of metal values from metal-bearing materials using solvent extraction techniques. The system and method employ a solvent extraction plant that includes a first circuit and a second circuit in fluid communication. As set forth in more detail below, various advantages of the system and method of the present disclosure include improved primary metal recovery, improved secondary metal recovery, and/or improved plant utilization. 
     An exemplary method for extracting one or more metal values from a metal-bearing solution comprises providing a first portion of a first metal-bearing solution to a first circuit of a solution extraction plant, providing a second portion of the first metal-bearing solution to a second circuit of the solution extraction plant, wherein the first circuit of the solution extraction plant and the second circuit of the solution extraction plant are in fluid communication with each other, providing a second metal-bearing solution to the second circuit of the solution extraction plant, extracting a first circuit raffinate, extracting a first circuit electrolyte, and extracting a second circuit electrolyte. The first circuit raffinate may comprise a low-grade raffinate. In accordance with various aspects of these embodiments, the first circuit and the second circuit are fluidly coupled by coupling an output of a first extractor of the second circuit to an input of a first extractor of the first circuit. Additionally, an output of a second extractor of the second circuit may be coupled to an input of a second extractor of the first circuit. In this case, a low-grade raffinate can be extracted from the first extractor of the first circuit, a high-grade raffinate can be extracted from the second extractor of the first circuit, and another high-grade raffinate can be extracted from a third extractor of the first circuit. In accordance with further aspects, lean electrolyte is provided to a stripper of the first circuit. 
     An exemplary system for extracting one or more metal values from a metal-bearing material comprises a first metal-bearing solution, a second metal-bearing solution, a solution extraction plant comprising a first circuit and a second circuit, wherein the first circuit comprises at least two first circuit extractors and at least one first circuit stripping unit, the second circuit comprises at least two second circuit extractors and at least one second circuit stripping unit, and the first circuit and second circuit are in fluid communication with each other. A second circuit raffinate may be produced by the second circuit and provided to one of the first circuit extractors. In accordance with additional aspects of these embodiments, the first circuit additionally involves a third extractor and a fourth extractor, and a second stripping unit. 
     In accordance with additional embodiments of the invention, an exemplary process for recovering one or more metals from a metal-bearing material comprises preparing a metal-bearing material, performing a reactive process on the metal-bearing material, extracting metal value from the processed metal-bearing material using the solution extraction method described herein, and subjecting extracted the metal value to at least one metal recovery step, such as electrowinning. In accordance with various aspects of these embodiments, the solution extraction method involves the use of a solution extraction plant comprising a first circuit and second circuit. The first circuit and the second circuit are fluidly coupled by coupling an output of a first extractor of the second circuit to an input of a first extractor of the first circuit. Additionally, an output of a second extractor of the second circuit may be coupled to an input of a second extractor of the first circuit. In this case, a low-grade raffinate can be extracted from the first extractor of the first circuit, a high-grade raffinate can be extracted from the second extractor of the first circuit, and another high-grade raffinate can be extracted from a third extractor of the first circuit. In accordance with further aspects, a lean electrolyte is provided to a stripper of the first circuit. 
     An exemplary system for recovering one or more metals from a metal-bearing material comprises a grinding unit, a leach system, one or more solid-liquid separators, a solution extraction plant with a first circuit and a second circuit as described herein, and at least one electrowinning operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the drawing figures, wherein like numerals denote like elements and wherein: 
         FIG.  1    illustrates a flow diagram of a metal recovery process in accordance with exemplary embodiments of the invention; 
         FIG.  2    illustrates a flow diagram of a solution extraction step of a metal recovery process in accordance with exemplary embodiments of the invention; 
         FIG.  3    illustrates a flow diagram of a solution extraction system in accordance with an exemplary embodiment of the invention; 
         FIG.  4    illustrates a flow diagram of a solution extraction system in accordance with another exemplary embodiment of the invention; and 
         FIG.  5    illustrates a flow diagram of a solution extraction system in accordance with yet another exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description of various embodiments herein makes reference to the accompanying drawing figures, which show various embodiments and implementations thereof by way of illustration, and not of limitation. While these embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, it should be understood that other embodiments may be realized and that mechanical and other changes may be made without departing from the spirit and scope of the present disclosure. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component may include a singular embodiment. 
     A system and method of various exemplary embodiments of the present invention exhibit significant advancements over prior art processes, particularly with regard to metal recovery and process efficiency. Moreover, existing metal recovery systems and processes that utilize a reactive process and solution extraction for metal recovery may, in many instances, be easily retrofitted to exploit the many commercial benefits of the present invention. 
     In various exemplary embodiments, a metal recovery process comprises preparing a metal-bearing material, performing a reactive process on the metal-bearing material, extracting metal value from the processed metal-bearing material, and subjecting the extracted metal value to at least one metal recovery step, such as electrowinning. 
       FIG.  1    illustrates an exemplary metal recovery process  100  for recovering a metal from a metal-bearing material  101 , including the steps of preparing metal-bearing material step  10 , reactive processing step  20 , optional conditioning step  30 , solution extraction step  40 , primary metal recovery step  50  and optional secondary metal recovery step  60 . In various exemplary embodiments, metal recovery process  100  is configured to recover multiple metal values from metal-bearing material  101 . For example, metal recovery process  100  may be configured to recover a primary and a secondary metal, such as cobalt, from an ore and/or concentrate comprising a significant concentration of the primary metal. 
     Metal-bearing material  101  may be an ore, a concentrate, or any other material from which valuable and/or useful metal values may be recovered. Such metal values may include, for example, copper, gold, silver, zinc, platinum group metals, nickel, cobalt, molybdenum, rhenium, uranium, rare earth metals, and the like. By way of a specific example, metal recovery process  100  is configured to recover copper from copper-bearing material, such as, for example, ores and/or concentrates containing chalcopyrite (CuFeS 2 ), chalcocite (Cu 2 S), bornite (Cu 5 FeS 4 ), and covellite (CuS), malachite (Cu 2 CO 3 (OH) 2 ), pseudomalachite (Cu 5 [(OH) 2 PO 4 ] 2 ), azurite (Cu 3 (CO 3 ) 2 (OH) 2 ), chrysocolla ((Cu,Al) 2 H 2 Si 2 O 5 (OH) 4 .nH 2 0), cuprite (Cu 2 O), brochantite (CuSO 4 .3Cu(OH) 2 ), atacamite (Cu 2 [OH 3 Cl]) and other copper-bearing minerals or materials and mixtures thereof. 
     During preparation of metal-bearing material step  10 , metal-bearing material  101  is prepared for reactive processing step  20 . Metal-bearing material  101  may be prepared in any manner that facilitates the recovery of metal values from metal-bearing material  101 —such as, for example, manipulating a composition and/or component concentration of metal-bearing material  101 —for the chosen reactive processing method of step  20 . Desired composition and component concentration parameters can be achieved through a variety of chemical and/or physical processing stages, the choice of which will depend upon the operating parameters of the chosen processing scheme, equipment cost and material specifications. For example, metal-bearing material  101  may undergo comminution, flotation, blending, and/or slurry formation, as well as chemical and/or physical conditioning in preparation step  10  before metal extraction. Any processing of metal-bearing material  101  which improves the ability to recover metal value from the material is in within the scope of the present disclosure. 
     In various exemplary embodiments, step  10  comprises a controlled grinding step. Controlled grinding may be used to produce a uniform particle size distribution of metal-bearing material  101 . Additionally, liquid, such as process water, may be added to metal-bearing material  101  to create a pulp density which corresponds to desirable operating conditions of the controlled grinding unit. Acceptable techniques and devices for reducing the particle size of the metal-bearing material include, for example, ball mills, tower mills, grinding mills, attrition mills, stirred mills, horizontal mills and the like, and additional techniques may later be developed that may achieve the desired result of reducing the particle size of the copper-bearing material to be transported. 
     After metal-bearing material  101  has been suitably prepared for metal recovery processing, it may be combined with any number of liquid feed streams to form a metal-bearing inlet stream  103 . Preferably, in an exemplary embodiment of the present invention, the liquid feed stream comprises process water, but any suitable liquid may be employed, such as, for example, recycled raffinate, pregnant leach solution, lean electrolyte, and/or other recycled streams from the metal recovery processes, including but not limited to secondary metal, such as cobalt or iron, recovery process streams. 
     After step  10 , metal-bearing inlet stream  103  may be forwarded to a reactive processing step  20 . Step  20  may comprise any process or reaction which places metal-bearing inlet stream  103  in condition for later metal recovery processing. Such processes may include, for example, a leaching step. In such configurations, the leaching step may comprise atmospheric leaching, ammonia leaching, pressure leaching, whole ore leaching, agitation leaching, heap leaching, stockpile leaching, pad leaching, thin-layer leaching and/or vat leaching, at either ambient or elevated temperatures, or any suitable process or reaction that puts metal value in metal-bearing inlet stream  103  in a condition such that it may be subjected to later metal recovery processing, is within the scope of the present disclosure. 
     During step  20 , the metal value is solubilized or otherwise liberated in preparation for later recovery processes. Any substance that assists in solubilizing the metal value, and thus releasing the metal value from a metal-bearing material, may be used. For example, where copper is the metal being recovered, an acid, such as sulfuric acid, may be contacted with the copper-bearing material such that the copper is solubilized for later recovery steps. However, it should be appreciated that any suitable method of solubilizing metal value in preparation for later metal recovery steps is within the scope of the disclosure. 
     After step  20 , the metal-bearing product stream  105  may undergo one or more optional conditioning steps  30 . In an exemplary embodiment, product stream  105  of reactive processing step  20  is conditioned to adjust the composition, component concentrations, solids content, volume, temperature, pressure, and/or other physical and/or chemical parameters to desired values. Generally, a properly conditioned metal-bearing product stream  105  will contain a relatively high concentration of soluble metal, for example, copper sulfate, in an acid solution and may contain few impurities. Moreover, the conditions of the metal-bearing product stream  105  may be kept substantially constant to enhance the quality and uniformity of the copper product ultimately recovered. 
     By way of example, step  30  may comprise adjusting certain physical parameters of the product stream  105 . Step  30  may comprise, for example, reagent additions, flashing processes, and one or more solid-liquid phase separation steps. For example, in various exemplary embodiments, product stream  105  may be further conditioned in preparation for later metal value recovery steps by one or more solid-liquid phase separation steps for the purpose of separating solubilized metal solution from solid particles. This may be accomplished in any conventional manner, including use of filtration systems, CCD circuits, thickeners, clarifiers, and the like. A variety of factors, such as the process material balance, environmental regulations, residue composition, economic considerations, and the like, may affect the decision whether to employ a CCD circuit, a thickener, a filter, a clarifier, or any other suitable device in a solid-liquid separation apparatus. One or more solid-liquid phase separation steps may be carried out with a conventional CCD utilizing conventional countercurrent washing of the residue stream to recover leached metal values to one or more solution products and to minimize the amount of soluble metal values advancing with the solid residue to further metal recovery processes or storage. 
     In various exemplary embodiments, step  30  comprises a solid-liquid phase separation step to produce a first metal-bearing solution and a second metal-bearing solution. In such embodiments, the first metal-bearing solution comprises a high-grade pregnant leach solution (“HGPLS”)  102 , comprising relatively high concentrations of dissolved metal values, and the second metal-bearing solution comprises a low-grade pregnant leach solution (“LGPLS”)  106 , comprising a lower concentration of dissolved metal values than HGPLS  102 . While the concentration of a primary metal value of both HGPLS and LGPLS may vary on an absolute basis, in various embodiments, the HGPLS will have a higher concentration of a primary metal value than the LGPLS. Stated another way, HGPLS and LGPLS may contain very low, or very high, primary metal value concentrations. 
     In various exemplary embodiments, large amounts of wash water are utilized in a solid-liquid phase separation step  30 . This wash water collects the remaining dissolved metal values from product stream  105  and may become part of LGPLS  106 . The separated solids may further be subjected to later processing steps, including other metal recovery processes, such as, for example, recovery of gold, silver, platinum group metals, molybdenum, zinc, nickel, cobalt, uranium, rhenium, rare earth metals, and the like, by sulphidation, cyanidation, or other techniques. Alternatively, the separated solids may be subject to impoundment or disposal. 
     In various exemplary embodiments, at least one HGPLS (e.g., solution  102 ) and at least one LGPLS (e.g., solution  106 ) are forwarded to a solution extraction step  40 . Step  40  produces at least one primary metal value containing stream  192  and may produce one or more secondary metal value containing streams, e.g., low grade raffinate  146 . For example, as discussed in connection with  FIGS.  2  and  3   , two HGPLS streams and one LGPLS stream may be forwarded to solution extraction step  40 . In other aspects, a single HGPLS stream and a single LGPLS stream may be provided to solution extraction step  40 . 
     In many instances, due to variations in concentration and quality of the metal-bearing material  101 , it may be advantageous to mix one or more leach solutions prior to solution extraction to form a first metal-bearing solution and/or a second metal-bearing solution. Additionally or alternatively, it may be beneficial to process two or more separate leach solution streams produced by multiple leach processes in a single solution extraction process or system. For example, if an operation has both a heap leach operation and a pressure or agitated leach operation, then the heap leach solution, equivalent to the LGPLS, may need to be processed with a more concentrated pregnant leach solution, such as HGPLS. It is not required that the HGPLS and LGPLS are produced from the same step  20 ; the HGPLS, LGPLS, or both can be produced by one or more steps  20 . Additionally, multiple steps  30 , such as controlled grinding steps, flashing steps, and/or solid-liquid phase separation steps may be utilized to produce the HGPLS and/or the LGPLS. 
     In various exemplary embodiments, the LGPLS has a concentration of a primary metal value greater than about 20% of the concentration of the primary metal value in the HGPLS. Preferably, the LGPLS has a concentration of the primary metal value greater than about 40% of the concentration of the primary metal value in the HGPLS. Most preferably, the LGPLS has a concentration of the primary metal value greater than about 50% of the concentration of the primary metal value in the HGPLS. 
     In step  40 , at least one raffinate may be produced. The at least one raffinate can be low-grade raffinate with a relatively low primary metal concentration and a relatively high secondary metal concentration. The low-grade raffinate may be forwarded to secondary metal recovery processes, such as a secondary metal recovery step  60  (which is discussed in more detail below). The production of any number and/or type of raffinate is within the scope of the present disclosure. 
     With initial reference to  FIG.  2   , an exemplary solution extraction process  200 , suitable for step  40 , is illustrated. Although individual steps of process  200  may be described as occurring sequentially, in some instances, the steps may occur simultaneously, or in a different process order than described below. 
     Process  200  includes the steps of providing a first metal-bearing solution to a first and second solution extraction circuit (step  202 ), producing a first loaded organic stream (step  204 ), producing a first circuit enriched electrolyte (step  206 ), producing a first circuit raffinate (step  208 ), optionally producing additional first circuit raffinates (step  210 ), providing a second metal-bearing solution to the second circuit (step  212 ), producing a second circuit loaded organic stream and second circuit raffinate (step  214 ), producing a second second circuit raffinate (step  216 ), and producing a second circuit enriched electrolyte (step  218 ). 
     With initial reference to  FIG.  3   , in various exemplary embodiments, process  200  is performed using a single solution extraction plant  300  comprising a first solution extraction circuit  301  and a second solution extraction circuit  302 . In various embodiments, one or more process streams are forwarded from the second solution extraction circuit to the first solution extraction circuit. In this case, a system and method provide, inter alia, efficient and controllable metal solution extraction from at least two separate pregnant leach solution feed streams, which may be used to recover two or more recoverable metal values. Where two metal values may be recoverable, one metal value may be referred to as a primary metal value and the other referred to as a secondary metal value. 
     In the illustrated case, first circuit  301  is configured to receive HGPLS  102  and lean electrolyte  108  and produce a rich electrolyte  162  and one or more raffinates  126 ,  136 , and/or  146 . First circuit  301  includes at least two extractors and at least one stripping unit. In the illustrated case, first circuit  301  includes four extractors ( 310 ,  320 ,  330 , and  340 ) and two stripping units ( 350  and  360 ) which are fluidly coupled together. 
     Second circuit  302  is configured to receive a HGPLS  104  and a LGPLS  106 , and includes at least two extractors and at least one stripping unit. In the illustrated case, second circuit includes two extractors ( 370  and  380 ) and one stripping unit  390  which are fluidly coupled together. However, the use of additional extractors and stripping units in second circuit  302  is within the scope of the present disclosure. 
     With reference to  FIG.  2    and  FIG.  3   , step  202  includes providing a first metal-bearing solution to a first circuit and a second circuit. By way of example, step  202  comprises providing HGPLS  102  to a first circuit extractor  310  of first circuit  301  and HGPLS  104  to a second circuit extractor  370  of second circuit  302 . However, in various embodiments, HGPLS  102  may be provided to first circuit  301  and a second HGPLS  104  may be provided to second circuit  302 . It is not required that HGPLS  102  and second HGPLS  104  be equivalent or derived from the same prior reactive processing step or steps  20 . 
     In step  204 , a first loaded organic stream  114  is formed by contacting HGPLS  102  with a partially loaded organic stream  118 . In such configurations, extractor  310  produces a first loaded organic stream  114  and an aqueous stream  116 . 
     In step  206 , a first circuit enriched electrolyte  162  is formed by contacting first loaded organic stream  114  with an intermediate electrolyte  156 , which is aqueous stream comprising a lower concentration of primary metal than that of first circuit enriched electrolyte  162 , in stripping unit  360 . Stripping unit  360  further produces a partially stripped organic stream  158 , which may be forwarded for further processing in the first circuit  301 . 
     In such embodiments, intermediate electrolyte  156  is produced by a stripping unit  350 . Stripping unit  350  is configured to receive a lean electrolyte  108  and partially stripped organic stream  158  from stripping unit  360 . Intermediate electrolyte  156  is formed by contacting lean electrolyte  108  and partially stripped organic stream  158  in stripping unit  350 . Intermediate electrolyte  156  is then forwarded to stripping unit  360 . 
     In step  208 , first circuit raffinate  146  is produced by contacting barren organic stream  148  with second circuit raffinate  186  in extractor  340 . Barren organic stream  148  comprises a metal-specific extraction reagent, such as, for example, an aldoxime and/or ketoxime, which extracts a primary metal value from second circuit raffinate  186  into the organic phase to form a partially loaded organic stream  138  and first circuit raffinate  146 . Barren organic may be recycled from various other processes and solution extraction components. As such, the term “barren” means sufficiently low in concentration of a primary metal value. 
     In an aspect of various embodiments, first circuit raffinate  146  is a low-grade raffinate. As will be discussed in greater detail below, low-grade raffinate  146  may be forwarded to further processing for secondary metal recovery. (e.g., step  60  of process  100 ). 
     In step  210 , additional extractors may be added to first circuit  301  to produce at least one additional raffinate. These raffinates may be aqueous solutions with a relatively low primary metal concentration, such as low-grade raffinates, or aqueous solutions with a primary metal concentration higher than low-grade raffinates, such as high-grade raffinates. The use of any number or configuration of additional extractors in first circuit  301  is within the scope of the present disclosure. 
     For example, additional extractors  320  and  330  are configured to receive partially loaded organic streams  128  and  138  and metal-bearing aqueous solutions, such as  176  and  116 . In such embodiments, the partially loaded organic streams and aqueous solutions are contacted within extractors  320  and  330 , producing partially loaded organic streams  118  and  128  and aqueous high-grade raffinates  126  and  136 . 
     High-grade raffinates  126  and  136  may be used beneficially in a number of ways. For example, all or a portion of high-grade raffinates  126  and  136  may be recycled to step  10 . The use of high-grade raffinates  126  and  136  in leaching operations may be beneficial because the acid and ferric iron values contained in high-grade raffinates  126  and  136  may optimize the potential for leaching oxide and/or sulfide ores that commonly dominate many leaching operations. That is, the ferric and acid concentrations of high-grade raffinates  126  and  136  may be used to optimize the pH of heap leaching operations. It should be appreciated that the properties of high-grade raffinates  126  and  136 , such as component concentrations, may be adjusted in accordance with the desired use high-grade raffinates  126  and  136 . 
     Extractor  330  may be configured to receive a second circuit raffinate  176 . In such configurations, second circuit raffinate  176  is forwarded to first circuit  301  from second circuit  302 . Any number of second circuit raffinates may be forwarded from second circuit  302  to first circuit  301 , provided a first circuit extractor is configured to receive the second circuit raffinate. 
     Step  212  provides LGPLS  106  to second circuit  302  (e.g., extractor  380 ). LGPLS  106  may be provided by step  30  of metal recovery method  100  or from other sources. LGPLS  106  may comprise, for example, wash water collected from prior conditioning steps, such as a solid-phase separation and/or a flashing of the slurry. In other aspects, LGPLS  106  may comprise the liquid product of a leaching step performed on a lower grade metal-bearing material than the metal-bearing material used to produce HGPLS  102  and/or  104 . Any LGPLS  106  which includes primary metal value and is of a lower concentration than the HGPLS  104  is within the scope of the present disclosure. 
     In step  214 , a second raffinate is provided. In the illustrated embodiment, the second raffinate is produced by contacting HGPLS  104  with a partially loaded organic stream  178  in extractor  370  to produce second loaded organic stream  174  and second circuit raffinate  176 . Second circuit raffinate  176  may be provided to an extractor (such as extractor  330 ) of first circuit  301 . However, second circuit raffinate  176  may be provided to any component of first circuit  301  which is configured to receive the raffinate. In addition, second circuit raffinate  176  may be provided to other processes, as described above in relation to first circuit raffinates  126  and  136 . 
     In step  216 , another second circuit raffinate is formed by contacting LGPLS  106  with barren organic stream  188  in extractor  370  to produce a second circuit raffinate  186  and a partially loaded organic stream  178 . In an aspect of these embodiments, second circuit raffinate  186  may be provided to an extractor (such as extractor  340 ) of first circuit  301 . However, second circuit raffinate  186  may be provided to any component of first circuit  301  which is configured to receive the raffinate. In addition, second circuit raffinate  186  may be provided to other processes, as described above in relation to first circuit raffinates  126  and  136 . 
     When second circuit raffinate  176  or  186  is provided to first circuit extractor  340 , extractor  340  may produce a raffinate  146  containing a relatively low concentration of primary metal. This occurs because raffinate  146  is produced by contacting an aqueous stream with a barren organic stream in two consecutive stages. For example, in  FIG.  3   , raffinate  146  is formed by contacting LGPLS  106  with barren organic stream  188  in second circuit extractor  380 . The resulting aqueous stream (e.g., second circuit raffinate  186 ) is then contacted with barren organic stream  148  in first circuit extractor  340 . This double exposure to barren organic, which is very low in primary metal concentration, produces a raffinate  146  which has a very low concentration of primary metal. Raffinate  146  is therefore well suited to secondary metal recovery step  60 . 
     In the case where an aqueous stream is forwarded from second circuit  302  to first circuit  301  to produce a raffinate low in primary metal value, the operating conditions of second circuit  302  significantly impact the quality of the raffinate. For example, as illustrated in  FIG.  3   , the concentration of primary metal value in raffinate  146  is dependent upon the concentration of primary metal value in second circuit raffinate  186 . In such configurations, it may be desirable to control the process conditions such that second circuit raffinate  186  is low in primary metal value concentration. 
     With continued reference to  FIG.  2   , in step  218 , second circuit enriched electrolyte  192  is formed by, for example, contacting second loaded organic stream  174  with an aqueous solution in stripping unit  390 . In an aspect of these embodiments, the aqueous solution comprises lean electrolyte  112 . However, the use of any aqueous solution having a primary metal concentration lower than second circuit enriched electrolyte  192  is within the scope of the present disclosure. 
     Second circuit enriched electrolyte stream  192  may be combined with first circuit enriched electrolyte stream  162 . The combined rich electrolyte may be forwarded to primary metal value recovery processes (e.g., step  50  of process  100 ). In other embodiments, second circuit enriched electrolyte stream  192  is not combined with first circuit enriched electrolyte stream  162 , and may be processed independently. In yet other embodiments, either or both of first circuit enriched electrolyte stream  162  and second circuit enriched electrolyte stream  192  may be sent to an electrolyte recycle tank. The electrolyte recycle tank may suitably facilitate process control for an electrowinning circuit, as will be discussed in greater detail below. 
     The particular embodiment described in connection with  FIG.  3    merely illustrates an exemplary system for solution extraction in accordance with the present disclosure. Various other exemplary embodiments comprise multiple stripping units and extractors arranged in series, parallel, and/or split configurations. For example, various exemplary embodiments may utilize a first circuit and/or second circuit with additional or fewer stripping units and/or extractors than first circuit  301  and/or second circuit  302 . Additional exemplary embodiments are discussed in further detail below. The use of any suitable number of stripping units and extractors, in any suitable configuration, is within the scope of the present disclosure. 
     With initial reference to  FIG.  4   , another exemplary solution extraction plant  400  suitable for use in processes  100  and  200  is illustrated. Solution extraction plant  400  comprises a first circuit  401  and a second circuit  402 . Second circuit  402  may be the same or substantially similar to second circuit  302 . First circuit  401  is similar to first circuit  301 , as both comprise four extractors ( 310 ,  320 ,  330 , and  340 ) and two stripping units ( 350  and  360 ). However, the location of stripping unit  450  of first circuit  401  differs from the location of stripping unit  350  of first circuit  301 . 
     As illustrated in  FIG.  4   , stripping unit  360  of first circuit  401  receives first loaded organic stream  114  and lean electrolyte  108 , and produces first circuit enriched electrolyte stream  162  and barren organic stream  448 . 
     Extractor  340  of first circuit  401  is configured to receive barren organic stream  448  and second circuit raffinate  186 , and produces low-grade raffinate  146  and a partially loaded organic stream  438 . Extractor  330  is configured to receive partially loaded organic stream  438  and second circuit raffinate  176 , and produces high-grade raffinate  136  and a loaded organic stream  424 . 
     Stripping unit  450  of first circuit  401  is located between extractors  320  and  330 . Stripping unit  450  receives partially loaded organic stream  424  and a raffinate  426 , and produces a barren organic stream  428  and an enriched electrolyte  463 . Enriched electrolyte  463  can be combined with first circuit enriched electrolyte  162 , if desired. Barren organic stream  428  is forwarded to extractor  320 , which produces raffinate  426  and partially loaded organic stream  118 . 
     With initial reference to  FIG.  5   , yet another exemplary solution plant  500  suitable for use in processes  100  and  200  is illustrated. Solution extraction plant  500  comprises a first circuit  501  and a second circuit  502 . First circuit  501  may be the same or substantially similar to first circuit  301  of solution extraction plant  300 . Second circuit  502  is similar to second circuit  302 , and further comprises an additional stripping unit  592 . In such configurations, lean electrolyte  112  is contacted with a partially stripped organic stream  598  in stripping unit  592 , producing an intermediate electrolyte  596  and a barren organic  588 . Extractor  380  of second circuit  502  is configured to receive barren organic stream  588  and LGPLS stream  106 , and produces partially loaded organic stream  178  and second circuit raffinate  186 . 
     Stripping unit  390  of second circuit  502  produces second circuit enriched electrolyte  192  and partially stripped organic stream  598  by contacting the intermediate electrolyte  596  with loaded organic stream  174 . Although two stripping units are illustrated in second circuit  502 , the use of any suitable number of stripping units in second circuit  502  is within the scope of the present disclosure. 
     The present disclosure illustrates a number of exemplary solution extraction plants comprising a first circuit and a second circuit in fluid communication with each other. Although the illustrated embodiments disclose particular combinations of first circuits (such as  301 ,  401 , and  501 ) and second circuits (such as  302 ,  402 , and  502 ), any first circuit and second circuit may be used together in a solution extraction plant. Stated another way, any combination of circuits (such as first circuit  401  and second circuit  502 ) is within the scope of the present disclosure. 
     Referring again to  FIG.  1   , in an exemplary embodiment, metal recovery process  100  further comprises primary metal recovery step  50 , in which a solution containing a sufficiently high amount of primary metal is forwarded to a process to extract the primary metal from the solution. For example, first circuit enriched electrolyte  162  and/or second circuit enriched electrolyte  192  may be forwarded to further metal recovery processes. In accordance with various aspects of the embodiments, step  50  may comprise any metal recovery process, for example, electrowinning, sulphidation, precipitation, ion exchange or any other process suitable for recovery of metals. Primary metals to be recovered may include copper, silver, platinum group metals, molybdenum, zinc, nickel, cobalt, uranium, rhenium, rare earth metals, and the like. By way of an example, step  50  may comprise an electrowinning circuit suitably designed to carry out any electrowining process capable of producing a metal cathode product. However, any metal recovery process which results in a relatively pure metal product is within the scope of the present disclosure. 
     With continued reference to  FIG.  1   , an exemplary secondary metal recovery step  60  includes recovering metal from a low-grade raffinate. In various exemplary embodiments, step  60  may comprise any metal recovery process such as, for example, electrowinning, sulphidation, precipitation, ion exchange, cyanidation, or any other process suitable for recovery of secondary metals. Further, as discussed in some detail below, in various exemplary embodiments, precipitation processes are used, thus making it advantageous to have low concentrations of primary metals in low-grade raffinate  146 . Additionally, in various exemplary embodiments, secondary metals to be recovered in step  60  may include, silver, platinum group metals, molybdenum, zinc, nickel, cobalt, uranium, rhenium, rare earth metals, and the like. 
     As mentioned above, the quality of metal-bearing material  101  can vary widely over the course of a metal recovery process  100 . Due to this variation, both primary and secondary metal recovery processes can evidence losses in efficiency and overall processing yields. One reason for these losses is the inability to control and tune the quality and composition of low-grade raffinate  146  from the step  40 . For example, low-grade raffinate  146  may be subjected to a selective precipitation process wherein all metal ions except for those of the secondary metal to be recovered such as, for example, cobalt, are eliminated from the low-grade raffinate  146  by precipitating them as solids. These precipitated primary metal solids may be recycled to step  20 . These precipitated solids may have a high probability of being rendered unrecoverable, depending on the precipitating mechanism employed. In the instance where there is high primary metal concentration in low-grade raffinate  146 , the amount of precipitated primary metal solids recycled to step  20  may increase. This increase in precipitated metal solids may lead to process inefficiencies due to high circulating loads in various steps  30 . 
     Similarly, the inability to control and tune the quality and concentration of low-grade raffinate  146  directly affects the costs associated with step  60 . For instance, low primary metal quality and concentration in low-grade raffinate  146  may require less reagent to effect precipitation (operating cost savings). Thus smaller equipment can be used to recycle the copper precipitate (capital cost savings). 
     Various embodiments of the present metal recovery process advantageously allow for control and tuning of the low-grade raffinate  146 . Moreover, step  40  may allow for control and tuning of low-grade raffinate  146  by adjustment of parameters such as, for example, the barren organic flow rate, reagent content, feed material flow rate, and/or any combinations thereof. Additionally, in various exemplary embodiments, the overall efficiency of the metal recovery process may be influenced by blending the primary metal solids precipitated from the low-grade raffinate with high-grade raffinate prior to recycling to the reactive process step. 
     By making any of these adjustments to control and tune the quality and concentration in the low-grade raffinate, the low-grade raffinate should preferably contain very limited amounts of the primary metal, which allows for efficient secondary metal processing. Additionally, the metal recovery process and solution extraction system described above allows plant operators to maintain a substantially controlled metal concentration in the HGPLS stream, LGPLS stream, and the raffinate streams. 
     As discussed above, in various embodiments, the flow rate and concentration of the barren organic flow containing a metal-specific extraction reagent can be altered based on the incoming metal ore quality to maintain a constant concentration of metal in the low-grade raffinate, allowing for efficient secondary processing of other metals, including but not limited to cobalt recovery. In an aspect of these embodiments, because both the HGPLS and LGPLS streams are treated in one facility, the metal content of the LGPLS may be controlled and held constant by adjusting LGPLS rate according to grade, with the excess being blended with the HGPLS. 
     The present disclosure allows the extraction circuit for the primary metal value to be tuned and optimized, both in terms of metallurgical performance and capital and operating costs. There is a trade off between achieving optimum metallurgical performance and minimizing the capital costs of the operating facility. The decisions made regarding this trade off are based on the performance and cost of the metal-specific extraction reagent employed as well as the chemistry of the pregnant leach solution streams to be treated. For example, the use of a metal-specific extraction reagent which exhibits rapid extraction kinetics may minimize the number of sequential extractors needed to achieve a satisfactory level of metal recovery. The presence of iron, manganese, or chloride in the pregnant leach solution streams may require the use of a wash stage prior to stripping. The number and placement of stripping units may be decided based on the stripping kinetics of the extraction reagent as well as its maximum metal loading capacity. Accordingly, various configurations are within the scope of the present disclosure. 
     It is believed that the disclosure set forth above encompasses at least one distinct invention with independent utility. While the invention has been disclosed in the exemplary forms, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the invention includes all novel and non-obvious combinations and sub combinations of the various elements, features, functions and/or properties disclosed herein and their equivalents. 
     The method and system described herein may be implemented to recover copper and other metals in a controlled manner. Other advantages and features of the present systems and/or methods may be appreciated from the disclosure herein and the implementation of the method and system.