MXPA06000863A - Methods for improving the recovery of metal leaching agents - Google Patents

Abstract

Processes for metal leaching/solvent extraction are described which comprise:(a) providing a first aqueous leach pulp which comprises a mixture of leached solids and an aqueous leach solution comprising a metal, a leaching agent and water;(b) subjecting the first aqueous leach pulp to a first solid-liquid separation to provide a first clarified aqueous leach solution and a second aqueous leach pulp, wherein the second aqueous leach pulp comprises the leached solids at a%solids level greater than the first pulp;(c) subjecting the first clarified aqueous leach solution to a first solvent extraction prior to any significant dilution, whereby a first aqueous raffinate is obtained;(d) subjecting the second aqueous leach pulp to a second solid-liquid separation with dilution via an aqueous stream to obtain a second clarified aqueous leach solution;and (e) subjecting the second clarified aqueous leach solution to a second solvent extraction whereby a second aqueous raffinate is obtained.

Description

METHODS TO IMPROVE THE RECOVERY OF AGENTS OF LEACHING OF METAL REFERENCE TO RELATED REQUESTS This application claims priority, in accordance with 35 U.S.C. S119 (e), of the Provisional Patent Application of E.U.A. No. 60 / 491,311, filed July 30, 2003, the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION Most metals are obtained by removing those metal values from the ores in which they are found in the earth. Once the ore has been mined, the metal must then be separated from the rest of the ore. A method to separate the metal from the ore is known as leaching. In general, the first step in this process is to contact the mined mineral with an aqueous solution that contains a leaching agent that extracts the metal from the mineral in solution. For example, in copper leaching operations, such as, for example, in the agitation leaching of copper oxide ores, the sulfuric acid in an aqueous solution is contacted with copper oxide ores. During this leaching process, the acid in the leach solution is consumed and the copper dissolves thereby increasing the copper content of the aqueous solution. The aqueous leaching solution containing the leached metal can then be treated through a known process referred to as solvent extraction wherein the aqueous leaching solution is contacted with a non-aqueous solution containing a metal-specific extraction reagent. The specific metal extraction reagent extracts the metal from the aqueous phase into the non-aqueous phase. During the solvent extraction process for copper and certain other metals, the leaching agent regenerates in the aqueous phase. In the case where sulfuric acid is the leaching agent, the sulfuric acid is regenerated in the aqueous phase when the copper is extracted into the organic phase by the extraction reagent. Normally, for every ton of copper removed from the leach solution, approximately 1.5 tons of sulfuric acid are generated in the leach solution. The leaching agents are often recycled back to the leaching process to dissolve more metal and the more leaching agent can be recycled, the less it needs to be obtained from another source. In a conventional agitation leaching process for copper, followed by solvent extraction, the leaching solution is diluted to a lesser or greater degree with water in conjunction with the solid-liquid separation process necessary to provide the clarified leach liquor and the cuts. The diluted clarified leaching solution is then transferred to one or more solvent extraction plants depending on the volume of leaching solution and the capacity of each plant. The diluted leach solution is subjected to solvent extraction where the copper is removed from, and the concentration of sulfuric acid is increased, in the aqueous phase. A portion of this acid-containing aqueous phase, depleted in copper, now called refining, is recycled back to the leaching process. The other portion is recycled back to the front of the solid-liquid separation process where it dilutes the leaching solution that leaves the leaching process by agitation. Depending on the rest of the acid through the complete process part of this recycled aqueous phase can be partially neutralized. The leaching solution of an agitation leaching process is usually diluted during the solid-liquid separation step in order to maximize the washing of the leached solids so that the metal lost to the solids is minimized. During the extraction with solvent as the metal is extracted, the concentration of acid accumulates in the aqueous phase and the reaction becomes self-equilibrating. Nevertheless, due to the initial dilution to maximize the metal recovery of the leached solids, the amount of regenerated acid is lower in concentration than if the leaching solution had not been diluted in the washing of the leached solids. Unfortunately, the lower the acid concentration in the recycled refining, the more fresh acid that needs to be added and this increases the cost of the operation. Accordingly, there is a need in the art for improved processes for metal leaching and solvent extraction, where the recovery of leaching agents is improved without adversely affecting metal recovery. BRIEF SUMMARY OF THE INVENTION The present invention relates, in general, to metal leaching operations and methods for improving the recovery of leaching agents from solvent extraction operations. It has been surprisingly discovered that by dividing the aqueous leaching solution into two or more portions and subjecting at least one portion to solvent extraction before any significant dilution and also subjecting at least one other portion to solvent extraction after dilution, (also called herein as a "split circuit"), that good and even optimal metal extraction can be achieved while significantly improving the recovery of the leaching agent. One embodiment of the present invention includes processes comprising: (a) providing a first aqueous leaching pulp comprising a mixture of leached solids and an aqueous leaching solution comprising a metal, a leaching agent and water; (b) subjecting the first aqueous leaching pulp to a first solid-liquid separation to provide a first clarified aqueous leaching solution and a second aqueous leaching pulp, wherein the second aqueous leaching pulp comprises the solids leached at a level % solids greater than the first pulp; (c) subjecting the first clarified aqueous leach solution to a first solvent extraction before any significant dilution, whereby a first aqueous raffinate is obtained, (d) subjecting the second aqueous leach pulp to a second solid separation. liquid with significant dilution through an aqueous stream to obtain a second clarified aqueous leaching solution; and (e) subjecting the second clarified aqueous leach solution to a second solvent extraction whereby a second aqueous raffinate is obtained.

In many of the preferred embodiments of the present invention, the metal comprises copper. Also, in many preferred embodiments of the present invention, the leaching agent comprises sulfuric acid. In more preferred embodiments of the present invention, the metal comprises copper and the leaching agent comprises sulfuric acid. Another embodiment of the present invention includes processes comprising: (a) providing a first aqueous leaching pulp obtained from an agitation leaching process, wherein the first aqueous leaching pulp comprises a mixture of leached solids and an aqueous leaching solution comprising copper, sulfuric acid and water; (b) subjecting the first aqueous leaching pulp to a first solid-liquid separation to provide a first clarified aqueous leaching solution and a second aqueous leaching pulp, wherein the second aqueous leaching pulp comprises the solids leached at a level % solids greater than the first pulp; (c) subjecting the first clarified aqueous leach solution to a first solvent extraction at any significant dilution, whereby a first aqueous raffinate is obtained; (d) subjecting the second aqueous leach pulp to a second solid-liquid separation with significant dilution through an aqueous stream to obtain a second clarified aqueous leaching solution, wherein the concentration of the metal in the first aqueous leach solution clarified is greater than the concentration of the metal in the second clarified aqueous leach solution; (e) subjecting the second diluted portion to a second solvent extraction whereby a second aqueous raffinate is obtained; wherein the aqueous stream for diluting the second aqueous leach pulp comprises at least a portion of the second aqueous raffinate; and (f) recycling at least a portion of the first aqueous raffinate and at least a portion of the second aqueous raffinate to the leaching process. BRIEF DESCRIPTION OF THE DIVERSE VIEWS OF THE DRAWINGS Figure 1 is a process flow diagram representing a conventional leaching / solvent extraction operation in which all the aqueous leaching solution is treated in the same manner. Figure 2 is a process flow diagram representing a preferred embodiment of the present invention, wherein an aqueous leaching solution is divided into two portions and subjected to solvent extraction under two sets of different conditions. DETAILED DESCRIPTION OF THE INVENTION Other than in operation examples, or where indicated otherwise, all numbers expressing quantities of ingredients or reaction conditions used herein must be understood as being modified in all cases by the term "approximately". The aqueous leach pulps of agitated leaching operations comprise a mixture of leached solids (ie, mineral residues) and an aqueous leaching solution. Aqueous leaching solutions comprise water, a leaching agent and a metal. The aqueous leach solutions may additionally contain other metals, impurities and residual leached solids. The aqueous leaching pulps are obtained from the treatment of ground minerals with an aqueous solution of a leaching agent. The aqueous leach pulp then flows or is brought to further processing and solvent extraction. The manner in which the aqueous leach pulp, or any other solution, current or refined, is transported during the processes according to the present invention has no consequence. In general, pulps, solutions, streams and refined can be transported by pipe or any other natural or man-made conduit. In accordance with the present invention, a first aqueous leaching pulp is subjected to a solid-liquid separation to remove at least some of the leached solids that are present therein. The first aqueous leaching pulp is divided into two or more portions by subjecting the aqueous leaching pulp to a solid-liquid separation, such as a decant-clarifier or filtration, to provide a first portion or first clarified aqueous leach solution and a second portion or second aqueous leach pulp, wherein the second pulp contains solids leached at a higher% solids level than the first aqueous leaching pulp. Essentially, the solid-liquid separation is used to divide the solution into the two portions to separate the solvent by extraction. The first portion is a clarified or partially clarified leaching solution while the second portion is a combination of leached liquor and leached solids at a higher solids content than the first aqueous leaching pulp. The clarified or partially clarified leaching solution proceeds to solvent extraction while the second portion advances to a counter current decanting circuit or to another type of solid-liquid separation that includes some washing of the solids.

In general, each solid-liquid separation can be carried out in any known manner. Any method for separating solids from liquids can be employed. The manner in which solid-liquid extraction is carried out is not critical. For example, solids can be separated from liquids by methods, including, but not limited to decanting and / or filtration. Decanting is preferred. The processes according to the present invention can be used in any metal recovery operation employing an aqueous agitation leaching operation wherein the leaching agent is regenerated in the solvent extraction process. In this way, the processes according to the present invention can be applied to any metal leached by an aqueous solution. These metals include transition metals. The processes according to the present invention are preferably used in the leaching of naturally occurring metals such as oxide minerals and / or sulfide. The processes according to the present invention are more preferably used in the leaching of divalent metal ores. These metals include copper, zinc, cobalt and nickel. The processes according to the present invention are more preferably used in the leaching of copper. The aqueous leaching solutions treated in the processes according to the present invention contain a leaching agent which is capable of leaching the metal from the ore with which they are previously contacted. The processes according to the present invention are applicable to leaching operations where an aqueous leaching agent is employed. In certain preferred embodiments of the present invention, the leaching agent comprises sulfuric acid. In those preferred embodiments of the present invention wherein the metal comprises copper, it is further preferred that sulfuric acid be used as the leaching agent. Other leaching agents that can be used in processes in accordance with the present invention include, but are not limited to acids such as hydrochloric acid, nitric acid, organic acids and combinations thereof, and basic substances such as ammonia. Essentially, any leaching agent that is miscible in water, capable of leaching the metal from the ore and producing a water-metal soluble leaching agent compound can be used. In the processes according to the present invention, the first aqueous leaching pulp is divided into at least two portions before any solvent extraction, a first clarified leaching solution and a second aqueous leaching pulp containing a% higher solids than the first aqueous leaching pulp. The division of the first aqueous leach pulp can be achieved through any known processes of dividing a leach pulp into two or more separate streams or volumes. In general, the first aqueous leaching pulp is divided into two portions. The first clarified leach solution is subjected to solvent extraction before any significant dilution and the second aqueous leach pulp is taken through a dilution wash circuit to produce a second diluted clarified leach solution which is then subjected to extraction with solvent. However, clarified aqueous leaching solutions can be divided into two or more streams, for example, where multiple circuits are running in parallel. For example, the first clarified leach solution can be further divided into two portions that proceed to two solvent extraction plants without any significant dilution while the second leach pulp is subjected to a solid-liquid separation to provide a stream of liquid. a second clarified leaching solution that then proceeds to a solvent extraction plant or vice versa. In a similar way, the first clarified leach solution can be further divided into two portions proceeding to two separate solvent extraction plants, and the second clarified aqueous leach solution could also be divided into two separate streams that proceed to two solvent extraction plants separated. The way in which leaching solutions are divided will depend on many factors such as the metal content of the original leaching solution, the design of the plant by solvent extraction, the response of leaching solids to solid-liquid separation and the total flow of leaching solution is going to be treated. The important feature of the division of the leaching solution is to take so much metal that it leaches to the first solvent extraction plant, in order to maximize the regeneration of the leaching agent. The added division of the leaching solution can occur when volume and capacity require. The division of the aqueous leaching solution according to the processes of the present invention can be done uniformly or so that one portion contains a larger volume than the other. In certain preferred embodiments of the present invention, the division of the aqueous leach solution is carried out so that the volume of the leach solution present in the portion that is subjected to solvent extraction before any significant dilution is greater than the volume of leaching solution present in the portion that is diluted before solvent extraction. As used herein, the term "significant dilution" refers to the addition of a measurable amount of water or other aqueous solution to an aqueous leaching solution. Accordingly, the significant dilution of the second aqueous leaching pulp refers to the addition of water or other aqueous solution to the second aqueous leaching pulp in an amount such that the metal concentration of the first clarified aqueous leach solution is greater than the concentration of the metal in the second clarified aqueous leach solution. In preferred embodiments of the present invention, the concentration of metal in the first clarified aqueous leach solution is at least 10% greater than the concentration of the metal in the second aqueous leach solution. In increasingly more preferred embodiments of the present invention, the metal concentration in the first clarified aqueous leach solution is at least 20% higher, at least 305 higher, at least 40% higher, at least 50% higher, at least 60% higher % higher, at least 70% higher, at least 805 higher, at least 90% higher, at least 100% higher, at least 200% higher, at least 300% higher, at least 400% higher, at least 500% higher or even higher than the concentration of the metal in the second clarified aqueous leaching solution. In the preferred embodiments of the present invention, the first clarified aqueous leaching solution is subjected to solvent extraction without any dilution. However, it should be understood that the water or other aqueous solution may be added to the first clarified aqueous leach solution before the first solvent extraction, but only in such quantities as the concentration of metal in the first clarified aqueous leach solution. before solvent extraction allows greater than the concentration of the metal in the second clarified aqueous leach solution. However, as the dilution of the first clarified aqueous leach solution increases, the recovery of leach agent decreases, less dilution is preferred. The solvent extraction according to the processes of the present invention can be carried out in any known manner wherein the aqueous leaching solution is brought into contact with an organic phase containing a specific metal extraction reagent. Each extraction made in accordance with the present invention can be carried out by mixing the organic phase and the aqueous leaching agent and allowing the two phases to settle. This mixing-sedimentation can be carried out in multiple series of mixing-sedimentation tanks with countercurrent flow of the aqueous and non-aqueous phases. The aqueous phase resulting from a solvent extraction operation is referred to as a raffinate. In the processes according to the present invention, the first portion of the aqueous leaching solution is subjected to solvent extraction before any significant dilution and a first aqueous raffinate is obtained. In the processes according to the present invention, the second portion of the aqueous leaching solution is diluted with an aqueous stream and then subjected to a separate solvent extraction and a second aqueous raffinate is obtained. The first refining produced in accordance with the processes of the present invention will generally have a concentration of leaching agent that is greater than the concentration of leaching agent present in the second raffinate. In preferred embodiments of the present invention, the first raffinate will have a concentration of leaching agent that is at least 10% greater than the concentration of leaching agent present in the second raffinate. In certain increasingly preferred embodiments of the present invention, the first refining will have a concentration of leaching agent that is at least 20% higher, 30% higher, 405 higher, 505 higher, 60% higher, 70% higher, 80% greater, 90% higher, 100% higher, 2005 higher, or more than the concentration of leaching agent present in the second refining. In the processes according to the present invention, the second aqueous leach pulp is diluted before being subjected to solvent extraction. The second aqueous leaching pulp is diluted with an aqueous stream. The aqueous stream for diluting the second aqueous leach pulp may comprise fresh water introduced into the process, at least a portion of the aqueous raffinate from another solvent extraction plant, at least a portion of the second aqueous raffinate, or a combination thereof. In certain preferred embodiments of the present invention, the second aqueous leach pulp is diluted with at least a portion of the second aqueous raffinate. When the leaching agent comprises an acid, the second aqueous raffinate may be at least partially neutralized before use to dilute the second aqueous leaching pulp. Neutralization can be achieved through the addition of any basic substance. In those embodiments wherein the leaching agent comprises sulfuric acid, lime is preferred for neutralization. Neutralization does not need to be complete. An appropriate pH scale for the second partially neutralized aqueous raffinate before use for dilution is any pH up to about 8. In the processes according to the present invention, a portion of the second aqueous raffinate can be bled from the circuit to maintain equilibrium of water. Additionally, in certain preferred embodiments of the present invention, at least a portion of the first aqueous raffinate is recycled to a leaching operation wherein the leaching agent contained therein is used to leach more metal from the ore. In more preferred embodiments, at least a portion of the first aqueous raffinate is recycled to the same leaching operation from which an aqueous leaching solution is obtained. In certain other preferred embodiments of the present invention, at least a portion of the second aqueous raffinate is recycled to a leaching operation wherein the leaching agent contained therein is used to leach more metal from the ore. In more preferred embodiments, at least a portion of the second aqueous raffinate is recycled to the same leaching operation from which the aqueous leach solution was obtained. In still more preferred embodiments of the present invention, at least a portion of both, the first and second aqueous refiners are recycled to a leaching operation wherein the leaching agent contained therein is used to leach more metal from the ore. In still more preferred embodiments, at least a portion of both, the first and second aqueous refiners are recycled to the same leaching operation from which the aqueous leaching solution was obtained. Figure 1 illustrates a process flow diagram of a previous agitation leaching process, conventional for copper followed by solvent extraction. The leaching pulp coming out of leaching (LEACH), approximately 190 cubic meters / hour, is mixed in a countercurrent decanting (S / L SEPARATION) with approximately 630 cubic meters / hour of refined recycling from the solvent extraction plants. Double copper (SX 1 & SX 2). The neutralization of the recycled refining is optional. In this way the copper concentration is diluted from about 24 g / 1 Cu to about 6.0 g / 1 Cu before feeding into the solvent extraction circuit. The solvent extraction circuit consists of 2 separate plants or trains labeled SX 1 and SX 2, respectively, with each plant treating approximately 400 cubic meters / hour of aqueous solution flow. The raffinate leaving the solvent extraction plants is combined and then a portion of this solution (approximately 160 cubic meters / hour) is recycled to the leach vessel where the acid in the leach solution is used to dissolve the copper. A second portion of this solution is recycled to the countercurrent solid-liquid separation operation where it is used to wash the leached solids leaching solution in order to minimize the metal losses to the leached solids that eventually They have cuts. A small portion of fresh water can be added to the total leach / wash system or a small portion of the aqueous solution can be bled from the total leach / wash system to maintain water balance. Figure 2 illustrates a process flow diagram of a leaching process for copper followed by solvent extraction in accordance with a preferred embodiment of the present invention. The aqueous leaching pulp leaving the leaching vessel (LEACH), approximately 190 cubic meters / hour, passes through an initial solid-liquid separation (SEPARATION OF S / L). Then approximately 120 cubic meters / hour of this solution containing about 26.2 g / 1 of Cu is taken directly to extraction with solvent (SX 1) where the copper is extracted and sulfuric acid is produced. SX 1 will reasonably produce a raffinate containing approximately 4 g / 1 Cu. and 35 g / 1 of acid. This solution is then recycled back to leaching. The aqueous portion of the leaching solution left in the pulp of leaching solution that has left the initial solid-liquid separation that does not proceed to SX 1 (approximately 70 cubic meters / hour) is taken to a countercurrent decanting ( CCD) where it is mixed with about 350 cubic meters / hour of SX 2 refining that has been partially neutralized, optionally. Then approximately 400 cubic meters of leaching solution from the CCD circuit containing 4.94 g / 1 Cu is taken to SX 2 to provide a raffinate containing 0.4 g / 1 Cu and 8 g / 1 acid. A small portion of SX 2 refining can be bled from the circuit to maintain water balance. Additionally, around 40 cubic meters / hour of SX 2 refining are returned to the leach vessel. An advantage of the process according to the present invention is that much more acid is returned to leaching than with the conventional process. For example, by comparing the conventional process illustrated in Figure 1 with the preferred embodiment of the present invention illustrated in Figure 2, it can be seen that in the conventional process, 160 cubic meters / hour of refining containing about 9.5 g / 1 of sulfuric acid is returned to the leach container bringing with it about 1.52 metric tons of acid per hour. In the process according to a preferred embodiment of the invention 120 cubic meters / hour of refining of SX 1 and 40 cubic meters / hour of refining of SX 2, a total of about 4.54 tons of acid is returned to the filled leach vessel again to leaching. This represents a saving of approximately 3.02 tons of acid / hour or around 72.5 tons of acid / day. A second advantage of the process according to the present invention is carried out in the neutralization of the recirculation raffinate if the neutralization is needed. For example, comparing the conventional process illustrated in Figure 1 with the preferred embodiment of the present invention illustrated in Figure 2, it can be seen that in the conventional process approximately 630 cubic meters / hour of solution containing about 9.5 g / 1 of acid is neutralized while in process in accordance with a preferred embodiment of the present invention, about 350 cubic meters / hour of solution containing about 8 g / 1 of acid are neutralized. This results in the need for significantly less neutralizing agent for the practice of this invention over conventional practice. A third advantage of the process according to the present invention is that the bleeding with the process according to the invention can in fact contain less metal than the bleeding with the normal configuration. Figure 1 shows that the bleeding for the normal circuit will contain approximately 0.5 g / 1 Cu and 9.5 c / 1 H2S04 while the bleeding in the process according to the preferred embodiment of the invention illustrated therein will only contain about 0.4 g / 1 cu and 8 g / 1 H2S0. In fact because the feed to SX 1 and SX 2 in the conventional process has approximately 6.05 g / 1 Cu while the feed to SX 2 in the preferred embodiment of the inventive process illustrated in Figure 2 has approximately 4.94 g / 1 it is readily apparent to one skilled in the art that SX 2 in the process according to the invention will produce a lower refining in copper than either SX 1 or SX 2 in the conventional process. A fourth advantage of the split circuit design belongs to copper solvent extraction plants where a component of value in the bleeding is recovered, for example cobalt. In most cases the bleeding must be neutralized before cobalt recovery. Neutralization with a soluble base such as caustic or ammonia is very costly therefore the lower the acid content of the bleeding stream the lower the amount of base necessary for neutralization. In addition, the use of a caustic solution for neutralization adds water to the bleed stream thereby diluting the valuable cobalt stream. Alternatively neutralization can occur with lime or limestone which is a less expensive base. In this case, a smaller amount of acid in the bleed stream requires less lime or limestone for neutralization and in the process a smaller amount of gypsum precipitate occurs. The plaster must be removed from the system and all the solution containing the valuable metal must be recovered. A lower amount of gypsum allows the use of smaller equipment for solid-liquid separation. When finely divided solids are separated from a liquid, the solids will always contain some of the liquid. In the case under discussion the smaller amount of gypsum will contain a smaller volume of the neutralized bleed stream containing the second valuable component, for example cobalt. In this way, the final recovery of the valuable component in the bleeding stream is higher when the process according to the invention is used. The present invention will now be illustrated in greater detail by reference to the following specific, non-limiting examples. COMPARATIVE EXAMPLE A AND EXAMPLE B In Comparative Example A, based on Figure 1, an aqueous leaching solution is obtained from a leaching operation that produces approximately 190 cubic meters / hour of leaching solution containing 24 g / 1 Cu and about 1 g / 1 of sulfuric acid. This leaching solution is mixed with a high volume of recycled and optionally, partially neutralized, 630 cubic meters / hour containing 0.5 g / 1 of Cu and about 1 g / 1 of sulfuric acid, to produce an aqueous solution of approximately 800 cubic meters / hour containing about 6.05 g / 1 Cu and about 1 g / 1 sulfuric acid. The 800 cubic meters / hour of solution is divided into two equal currents and each current and then fed to the extraction plant with copper solvent. Isothermal copper extraction followed by computer modulation show that solvent extraction of copper can be expected to produce a raffinate containing approximately 0.5 g / 1 Cu and approximately 9.5 g / 1 sulfuric acid. This represents a copper recovery of 91.7% that is well within the recovery that can be expected in a commercial copper solvent extraction plant.

In Comparative Example A, 160 cubic meters of refining containing 9.5 g / 1 of sulfuric acid would return to leaching carrying 1.52 metric tons of acid per hour for leaching. In Example B, based on Figure 2, an aqueous leaching solution is obtained from a leaching operation that produces 190 cubic meters of leaching solution containing 26.2 g / 1 Cu and about 1.0 g / 1 sulfuric acid . This leaching solution goes directly to a solid-liquid separation that occurs in a clarifier using decantation. Then approximately 120 cubic meters of the clarified leaching solution is taken to a first solvent extraction plant where the copper is extracted and sulfuric acid is produced. The isothermal extraction and computer modeling show that a raffinate containing approximately 4 g / 1 Cu and approximately 35.2 g / 1 sulfuric acid can be easily produced by advancing 400 cubic meters of organic flow using a reagent concentration of approximately 25 to 30% in reagent volume. In this case, the acid is returned to leaching in the 120 cubic meters of refining is approximately 4.22 metric tons / hour. Also, in Example B, an additional 40 cubic meters of recycled aqueous solution containing approximately 8.0 g / 1 of sulfuric acid are returned to leaching. This takes around 0.32 additional tons of acid / hour to leach. In this manner, the total acid returned to leaching using a process in accordance with this preferred embodiment of the present invention is about 4.54 tons per hour. A simple calculation shows that for this example the acid savings using the split circuit are about 4.54 metric tons / hour minus 1.52 metric tons / hours = about 3.02 metric tons / hour or about 72.5 metric tons of acid / day. Acid costs vary widely from as low as US $ 15 / ton to over US $ 150 / ton depending on the location. For low cost acids, the savings would be approximately US $ 1088 / day, while for high cost acid the savings would be approximately US $ 10,880 / day or higher. In Comparative Example A, neutralization of the acid is carried out in a large portion of the recycled raffinate that did not proceed directly to leaching, but rather is used to dilute the leach solution before solvent extraction. Approximately 630 cubic meters of refining flow are taken for neutralization. Additionally, a refining bleed before neutralization is needed to maintain water balance in the circuit and can be as high as 20 to 25% or as low as only a low% of the flow of the leaching solution leaving the vessel of leaching. In Comparative Example A, there is a bleed of 10 cubic meters / hour and a refining stream that is going to be neutralized of 630 cubic meters / hour. The raffinate contains about 0.5 g / 1 Cu and about 9.5 sulfuric acid. When this raffinate is neutralized at a pH of about 1.8 it will contain about 1 g / 1 of sulfuric acid so that the neutralized total acid is about 5.36 metric tons / hour (630 cubic meters / hour x 8.5 kilos of acid / cubic meter ). In Example B, the total refining taken at neutralization is about 350 cubic meters / hour containing about 8.0 g / 1 of sulfuric acid. After neutralization of a pH of 1.8, the neutralized total acid is about 2.45 metric tons / hour (350 cubic meters / hour x 7.0 kilos of acid / cubic meter). The now in neutralization is around 2.91 metric tons of acid per hour (5.36 minus 2.45). This is a significant improvement because less acid needs to be neutralized. Less acid neutralization means that less equipment is needed for neutralization and less base is needed for neutralization. Using lime as the neutralizing agent in Comparative Example A produces more than twice the amount of precipitated gypsum as the neutralization of acid with lime in Example B. In this way, the equipment needed for neutralization and the equipment needed for solid-liquid separation after neutralization will be more than twelve in size in Comparative Example A as in Example B. In Example B, additional savings in neutralization are realized that the leached slurry residue leaving the solid-liquid separation should be neutralized at a pH of about 7 to 7.5. In Comparative Example a, the water contained in the leached residues may contain up to about 7.5 g / 1 of sulfuric acid. In Example B, the water contained in the leached waste may contain up to about 6.5 g / 1 of sulfuric acid. In addition, the water leaving the CCD circuit with the solids washed (40 cubic meters per hour) contains 0.8 g / 1 Cu in normal practice while the same amount of water in the practice of this invention only contains 0.67 g / 1 of Cu. In this way for the exact same amount of leached copper ore the practice of the present invention will produce around 192 kilos of copper more per day (40 x 0.2 x 24). The bleeding of the example under consideration is 10 cubic meters / hour. In conventional practice this bleeding contains approximately 0.5 g / 1 Cu while the bleeding in the practice of this invention only contains about 0.4 g / 1 Cu. In this way, the copper lost in the bleeding for conventional practice is approximately 1 kilogram of copper per hour more than the copper lost in the bleeding for the practice of this invention. For small bleeding, the difference in copper lost in conventional practice compared to the practice of this invention is very small, but for a plant that has a bleeding of 20% to 25% the difference in lost copper can be significant. With reference to the optional neutralization of recycled refining it will be appreciated by those skilled in the art that the level of neutralization depends on the acid consumed by the leached solids as the leached solids continue through the solid-liquid separation. In some cases considerable acid will be consumed during the solid-liquid separation and little or no neutralization of the recycled refining will be needed. In other cases only small amounts of acid can be consumed during the solid-liquid separation and the neutralization of the recycled refining can be more extensive. It will be observed by those experts in the field that changes could be made to the modalities described above without abandoning the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments described, but is intended to cover the modifications within the spirit and scope of the present invention as defined by the appended claims.

Claims (20)

1. CLAIMS 1. A process comprising: (a) providing a first aqueous leaching pulp comprising a mixture of leached solids and an aqueous leaching solution comprising a metal, a leaching agent and water; (J_) subjecting the first aqueous leaching pulp to a first solid-liquid separation to provide a first clarified aqueous leaching solution and a second aqueous leaching pulp, wherein the second aqueous leaching pulp comprises the solids leached to a level of% solids greater than the first pulp; (c) subjecting the first clarified aqueous leaching solution to a first solvent extraction before any significant dilution, whereby a first aqueous raffinate is obtained; (d) subjecting the second aqueous leach pulp to a second solid-liquid separation with significant dilution through an aqueous stream to obtain a second clarified aqueous leach solution; and (e) subjecting the second clarified aqueous leaching solution to a second solvent extraction, whereby a second aqueous raffinate is obtained.
2. 2. - The process according to claim 1, wherein the metal is copper.
3. 3. The process according to claim 1, wherein the leaching agent is sulfuric acid.
4. 4. The process according to claim 1, wherein the volume of the aqueous leaching solution in the first clarified aqueous leaching solution is greater than the volume of the aqueous leaching solution in the second aqueous leaching pulp.
5. 5. The process according to claim 1, wherein the aqueous stream for diluting the second aqueous leaching pulp comprises the second aqueous raffinate.
6. 6. The process according to claim 5, wherein the aqueous stream comprising the second aqueous raffinate is at least partially neutralized before dilution of the second aqueous leach pulp.
7. 7. The process according to claim 1, wherein the second aqueous leaching pulp is subjected to the second solid-liquid separation before dilution.
8. 8. - The process according to claim 1, wherein the second aqueous leaching pulp is subjected to the second solid-liquid separation simultaneously with the dilution.
9. 9. The process according to claim 8, wherein the second solid-liquid separation comprises countercurrent decanting.
10. 10. The process according to claim 1, wherein the concentration of the metal in the first clarified aqueous leach solution is at least 10% greater than the concentration of the metal in the second clarified aqueous leach solution.
11. 11. The process according to claim 1, wherein the concentration of the metal in the first clarified aqueous leach solution is at least 50% greater than the concentration of the metal in the second clarified aqueous leach solution.
12. 12. The process according to claim 1, wherein the concentration of the metal in the first clarified aqueous leach solution is at least 100% greater than the concentration of the metal in the second clarified aqueous leach solution.
13. 13. The process according to claim 1, wherein at least a portion of the first aqueous raffinate is recycled to a leaching process.
14. 14. - The process according to claim 1, wherein the first aqueous leaching pulp is obtained from a leaching process and wherein at least a portion of the first aqueous raffinate is recycled to the leaching process.
15. 15. The process according to claim 1, wherein at least a portion of the second aqueous raffinate is recycled to a leaching process.
16. 16. The process according to claim 1, wherein the first aqueous leaching pulp is obtained from a leaching process and wherein at least a portion of the second aqueous raffinate is recycled to the leaching process.
17. 17. The process according to claim 1, wherein the first aqueous leaching pulp is obtained from a leaching process and wherein at least a portion of the first aqueous raffinate and at least a portion of the second aqueous raffinate are recycled to the leaching process.
18. 18. A process comprising: (a) providing a first aqueous leaching pulp obtained from an agitation leaching process, wherein the first aqueous leaching pulp comprises a mixture of leached solids and an aqueous leaching solution comprising copper , sulfuric acid and water; (b) subjecting the first aqueous leaching pulp to a first solid-liquid separation to provide a first clarified aqueous leaching solution and a second aqueous leaching pulp, wherein the second aqueous leaching pulp comprises the solids leached at a level % solids greater than the first pulp; (c) subjecting the first clarified aqueous leach solution to a first solvent extraction before any significant dilution, whereby a first aqueous raffinate is obtained; (d) subjecting the second aqueous leach pulp to a second solid-liquid separation with significant dilution through an aqueous stream to obtain a second clarified aqueous leaching solution, wherein the concentration of the metal in the first aqueous leach solution clarified is at least 10% greater than the concentration of the metal in the second clarified aqueous leach solution; (e) subjecting the second diluted portion to a second solvent extraction, whereby a second aqueous raffinate is obtained; wherein the aqueous stream for diluting the second aqueous leach pulp comprises at least a portion of the second aqueous raffinate; and (f) recycling at least a portion of the first aqueous raffinate and at least a portion of the second aqueous raffinate to the leaching process.
19. 19. The process according to claim 18, wherein the concentration of the metal in the first clarified aqueous leach solution is at least 50% greater than the concentration of the metal in the second clarified aqueous leach solution.
20. 20. The process according to claim 18, wherein the concentration of the metal in the first clarified aqueous leach solution is at least 100% greater than the concentration of the metal in the second clarified aqueous leach solution.