BR112020012757B1 - METHOD FOR MAXIMIZING THE AMOUNT OF WATER AVAILABLE FOR WASHING IN A LEACHING OPERATION IN HIGH CHLORIDE CONTENT STACKS - Google Patents

Abstract

A method for maximizing the amount of water available for rinsing in a high chloride heap leach operation that includes the step of using process make-up water in the range of 0.05 to 0.35 m3/ton for a ore wash leach residue, in the heap, to displace therewith an aqueous liquor containing chloride from the leachate ore.

Description

FUNDAMENTALS OF THE INVENTION

[0001] The present invention relates to a method of leaching with high chloride content of copper ores.

[0002] The bioleaching of low grade copper sulfide ores using acid sulfate solutions with bacteria is an established commercial process applied worldwide.

[0003] More recently, chloride leaching methods have been developed to allow the leaching of copper sulfide ores, including chalcopyrite, with high potential without the use of bacteria. The disclosures in WO2015/059551 and WO2014/030048 teach the use of high chloride concentrations to overcome chalcopyrite passivation, allowing operation at solution oxidation potentials above 700 mV vs. higher copper recoveries.

[0004] A high concentration of chloride increases the rate at which oxidants, such as cupric ions (Cu(II)) and ferric ions (Fe(III)), are formed in the presence of an oxygen-containing gas. These oxidants react with copper sulfide minerals to release copper into solution.

[0005] In practice, leaching in piles of copper ores in chloride solutions on a commercial scale is limited by restrictions that, if ignored, will limit the economic viability of the process. A specific restriction on heap leaching at high chloride concentrations (100 - 230g/L chloride) is the loss of chloride from the circuit in the solution contained in the leached residue as moisture.

[0006] An object of the present invention is to address, at least in part, the aforementioned issue, i.e. to maximize the amount of water that is available and that is suitable for rinsing the solids from leachate waste, thus allowing the recovery of chlorides and a reduction in losses of chlorides from the process.

SUMMARY OF THE INVENTION

[0007] The invention provides a method for maximizing the amount of water available for rinsing (or washing) the residue ore leached in a heap leaching operation with high chloride content, the method including the step of using make-up water process for rinsing the leachate ore in the heap, thereby displacing an aqueous liquor containing chloride from the leachate ore.

[0008] “Water balance” refers to the difference between a volume of water flowing into a system and a volume of water flowing out of the system.

[0009] Process make-up water, which contains little or no chloride, is used to displace the chloride-containing aqueous liquor, which is then recovered and recycled to the heap leaching operation, thereby decreasing the make-up salt added to the operation .

[0010] Soluble copper in the leachate ore or aqueous liquor containing chloride can be recovered in the rinse water, thus increasing the overall copper recovery.

[0011] To maximize the amount of make-up water available for rinsing and to avoid inadvertent purging and a corresponding loss of chloride and copper, methods for increasing the amount of make-up water and utilizing the make-up water can be implemented as follows : a) a water deficit can be created by increasing evaporation from the heap leaching operation, for example using aerial sprayers or not placing evaporation reducing devices such as covers on tanks or solar films on piles, i.e. leaving these devices exposed to the atmosphere; b) rainwater can be diverted from the pile; c) the volume of wash water in a copper solvent extraction circuit can be reduced using a countercurrent, multistage charged organic solvent wash approach; and d) a demand for electroplating bleed make-up water can be reduced by effective washing of the charged organic, in a way that is related to the above.

[0012] The concentration of chloride in the organic phase can be reduced to below 50 ppm.

[0013] The rinsing step can be carried out for a period of 5 to 100 days. Preferably, the period is 20 days.

[0014] The residual soluble copper that remained in the leachate residue ore and that is recovered in the rinsing step can be returned to the leaching operation and can be recovered subsequently through the use of a solvent extraction step and an electrodeposition step.

[0015] The amount of replacement water in the process, in the rinsing step, may be in the range of 0.05 to 0.35 m3/ton of ore and preferably is between 0.1 and 0.15 m3/ton of ore.

[0016] The chloride and copper recovered in the aqueous liquor displaced in the rinsing step by the process make-up water can be expressed as a fraction of the total content in the residue ore before rinsing and can be defined as an “efficiency of washing”. Wash efficiency is typically between 40% and 85% for the indicated wash volume (ie in the range of 0.05 to 0.35 m3/ton of ore). A desired fraction (or proportion) is on the order of 60%.

[0017] The chloride level can be in the above range and is normally 150 g/L; but this is only exemplary and not limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention is further described by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of a conventional heap leaching process; Figure 2 is a “black box” diagram of the inputs and outputs of the heap leaching process in Figure 1; Figure 3 is a schematic representation of a solvent extraction process and an electrodeposition process forming part of the process in Figure Figure 4 shows an optimized heap leaching process according to the invention; Figure 5A is a wash efficiency curve graphically showing the recovery of soluble ions on a percentage basis during a rinse stage, as a function of the amount of wash water addition per ton of ore; Figure 5B graphically shows the reduction in replacement salt addition in kg/L required as a function of the amount of washing water addition per ton of ore; Figure 6 is a schematic representation of an organic wash process loaded by solvent extraction of optimized copper, using a countercurrent loop, which forms part of the process in Figure 4; Figures 7A, 7B and 7C show, respectively, different countercurrent washing circuits that can be used in the washing process of Figure 6, operated in order to reduce the chloride concentration in an electrolyte that refers to an electrodeposition process at downstream; Figure 8 is a flowchart of an integrated pilot plant used to treat low-grade chalcopyrite ore; Figure 9 is a simplified diagram showing the inputs and outputs of the pilot plant mentioned in connection with Figure 8; Figure 10 shows copper recovery curves as a function of irrigation period for a number of berths during different operating phases of the pilot plant; Figure 11 is a curve of wash efficiency (salt recovery) versus addition of wash water to a berth in the pilot plant during a second phase of operation; Figure 12 graphically represents the amount of salt required for recovery as a function of the wash water added, for the cradle referred to in connection with Figure 11; and Figure 13 shows how impurity metals (aluminum, magnesium and iron) and sulfates accumulate in raffinate in the pilot plant as a function of time.

DESCRIPTION OF PREFERRED MODALITIES

[0019] Figure 1 of the accompanying drawings shows a generic heap leaching process 10 that includes a single-stage heap leaching. In general, the chloride heap leaching process is applied using a pile construction and operation method known as “race tracks”. In a racetrack-type pile, ore 12 is agglomerated (13) using acid 14 and salt 16 and is stacked in pile 18 into a block (not shown). The pile 18 is irrigated with an aqueous leach liquor 20 for a defined period of time. This liquor 20 is recycled over heap 18. Copper released from ore 12 is mobilized into a pregnant leach solution 22 which drains from the heap 18 into a tank of pregnant leach solution 24.

[0020] Through a combination of an organic solvent extraction step 26 and an electrodeposition step 28, the copper metal 29 is recovered from the solution.

[0021] At the end of the leaching period, irrigation is stopped and the leached ore can run off. The leachate ore residue 30 (also known as ripios) and any entrained aqueous liquor are removed and sent to a disposal facility.

[0022] Figure 2 shows various inputs and outputs of pile 18. The inputs include: a) ore 12: extracted mineral deposit that carries a mineral or metallic value, in this case copper; b) acid 14: it is usually sulfuric acid that is added to ore 12 to maintain an acidic environment and provide acid for reacting with gangue minerals and for dissolving copper minerals and generating Fe(III) and Cu(II) oxidants ), and for the release of soluble copper and other metallic ions in the pregnant leach solution 22; c) rain or precipitation 32: that is, the rain that falls on the pile 18 and associated tanks and that later joins the solution that circulates in the process; d) air 34: air is activated in the process to supply oxygen as an oxidant for the generation of Cu(II) and Fe(III) and for the leaching of sulphide minerals; e) process replacement water 36: this water is used to compensate for any deficit in which the amount of water at the outlet is greater than the amount of water at the inlet; process make-up water is added to compensate for water lost to evaporation (42), water lost as moisture in the leachate ore residue (30) and water lost in purge stream 45 taken from the leaching circuit, as and when Requested. f) Copper 38 solvent wash water: this water is used during solvent extraction to remove the chloride entrained in an organic phase, thus avoiding the transfer of the chloride to an electrolyte that reports to a subsequent electrodeposition process; g) electrolyte bleed replacement water 40: this water is used to replace the electrolyte bleed removed from the circuit to control a level of impurities in it; and h) salt 16: to introduce chloride. i) water 37: comprises replacement water 36, washing water 38 and electroplating replacement water 40.

[0023] The outputs shown in Figure 2 are as follows: a) the ore leachate (ripios) 30 which includes moisture as entrained solution 31 in the ore leachate residue 30 (ie ripios). This is the residual aqueous solution that remains with the leach ore 30 once irrigation with the leach liquor 20 has been stopped, the ore leach 30 drained, and the pregnant leach solution 22 collected; b) evaporation 42 from the stack and associated tanks, i.e. water that is lost to the atmosphere; c) copper 29, ie the target metal that is recovered from ore 12; and d) a purge stream 45 which is used as needed to remove impurities from the circuit or to lower the acid concentration in the leach liquor 20. A purge stream 45 may be drawn from any stream or tank of suitable solution in the leaching process in piles 10, in order to remove impurities. It is preferred that the flux contain a low concentration of copper to avoid a significant loss of copper from the leaching process in piles 10.

[0024] The air 34 which is introduced into the stack 18 exits the sides and top of the stack as air currents (not shown) which are depleted of oxygen.

[0025] Figure 3 is a simplified flow diagram of copper solvent extraction step 26 and electroplating process step 28. Pregnant leach solution 22X is passed from tank 24 through an organic solvent extraction facility 44 which includes an extraction process 46 followed by a scrubbing process 58 and then a pickling process 48.

[0026] During the extraction process 46, dissolved copper ions are taken from the pregnant leach solution 22X to an organic phase 51 and a spent copper solution 50 is then directed to a raffinate tank 52 for recycling in the stack 18 during the irrigation. During the washing process 58, the organic phase 51 is washed using the low chloride wash water 38 to remove chloride contained in small amounts of aqueous solution entrained within the organic phase. The 38X wash water, after use, is recirculated in the PLS 24 tank.

[0027] During the pickling process 48, dissolved copper is taken from the organic phase 51 into an electrolyte 54 which is directed to an electrodeposition step 56 in process 28, in which dissolved copper ions are reduced and then removed as the copper metal 29. The spent electrolyte 55 is returned to the etching process 48. An electroplating purge 35 may be recycled from the electroplating stage 56 to the heap leaching process 10, preferably to the PLS tank 24.

[0028] The only water leaving the process 10, shown in Figure 2, is the moisture 31 in the leachate ore 30, in the evaporation 42 and in the purge stream 45, in which the solution is removed from the circuit to limit the accumulation of impurities in circuit solutions or to lower the acid concentration. The moisture level in the leachate ore 30 can vary from 5% to 25% volume by mass, or more typically from 8% to 20%, depending on the characteristics of the ore material.

[0029] The chloride in the leach liquor 20 within the process 10 may come from the ore 12 itself, but mostly needs to be added in the form of the salt 16. This is because most ores normally contain very little soluble chloride. By way of comparison, the amount of chloride needed in the leach process 10 ranges from 100 - 230g/L in the leach liquor 20.

[0030] The amount of chloride added to the heap leaching operation must equal the amount lost. The only mechanism by which chloride-containing salt is removed from the process is through precipitated salts and chloride-containing moisture in the leachate pile residue, i.e., in the ripios 30. If the purge is removed from the circuit (not recycled internally), this will contribute to the loss of chloride, acid and copper and to the removal of dissolved metals and saline impurities from the circuit. Normally, a high copper solution purge would not be removed from the circuit. Therefore, a purge is only used as a last resort.

[0031] The lost chloride must be replaced. Chloride can be added as sodium chloride or through the use of a similar salt. This salt needs to be purchased and transported to the processing site. Overall, under average conditions, there is usually a net decrease in ore solids mass of about 5%, due to the loss of gangue and minerals through the leaching process, which compensates for a small gain in precipitated salts. Briefly, it is pointed out that the precipitation of Fe adds mass, since the precipitated iron salts contain sulfate, hydroxy ions and Na or K, so the mass of the precipitate is greater than the mass of metal and iron sulfide leached due to addition of S and oxygen to the solution. The mass addition of precipitates compensates for mass loss due to dissolution of copper and gangue minerals, but generally a net mass loss of about 5% can be expected.

[0032] The cost of salt and its transport depends on the location of the processing site. Costs can be as low as US$2.5/T or as high as US$40/T (sample numbers only). A high chloride leach operation typically starts production at a rate of 10,000,000 tons of ore per year and can increase substantially beyond that. Thus, the costs of purchasing and transporting salt can be substantial.

[0033] Figure 4 shows a process 10A in accordance with the invention which in many respects is similar to that shown in Figure 1. Water 37A comprises make-up water 36A, wash water 38A and make-up water electrodeposition 40A.

[0034] Salt 16A comprises salt added at the beginning of the process and the additional salt (replacement salt) necessary to maintain the required chloride concentration in the process solution, for example, in liquor 20A.

[0035] The make-up water 36A is directed to the ore leachate residue 30A to rinse the ore and displace the entrained solution with a high chloride concentration in a rinse stream solution 60A. 36A Makeup Water is low in chloride, while 60A Rinse Stream Solution is high in chloride. The 60A rinse current solution is routed to the 24A Pregnant Leach Tank, or any other suitable tank in the stack leaching circuit. Thus, a significant portion of the original salt content is retained in the process.

[0036] After irrigation with aqueous leach liquor 20A, a rest period of 5 to 50 days, typically 20 days, is preferred before the start of rinsing the pile 18A with make-up water 36A, to allow most of the entrained irrigation solution is drained from the stack 18A so that a residual moisture level of 8% to 20%, typically 10%, is achieved. Washing a drained pile improves the wash efficiency.

[0037] The washing period for applying make-up water 36A to the leachate ore residue 30A ranges from 5 to 100 days, preferably 10 to 50 days, or typically 20 days.

[0038] Process 10A refers to saving salt, but there is an added benefit in that a portion of any residual soluble copper remaining in the leachate ore 30A is put back into process 10A where it can subsequently be recovered through of using a solvent extraction step 26A and an electrodeposition step 28A.

[0039] Figure 5A shows a wash efficiency curve calculated using the displacement of soluble copper from the leachate ore. Percent displaced copper would apply to any soluble species including chloride - copper was used as an indicator due to the accuracy of the solution assay. The curve indicates a probable operating range R in which the expected demand for process make-up water (36A), expressed per ton of ore, is balanced with the recovery of soluble ions (expressed as a percentage). This interval may vary according to circumstances. The R range is between 0.05 and 0.35 m3/ton of ore and preferably is between 0.1 and 0.15 m3/ton of ore. The curve in Figure 5A indicates that an optimal wash efficiency in the R range is between 50% and 70%. A desired recovery with a wash water addition of 0.1 m3/ton is 60%.

[0040] Figure 5B indicates the reduction in the addition of replacement salt in kg/T as a function of the addition of wash water 36A. The reduction in make-up salt, which is directly related to salt recovery, is achieved by washing the ore residue with the indicated amount of make-up water 36A as wash water.

[0041] An effective way to maximize the amount of 36A make-up water available for rinsing is to reduce the amount of water entering the process through other streams. Water enters the process via precipitation 32A, acid 14A, acid reaction, solvent extraction wash water 38A, and electroplating bleed make-up water 40A. A water deficit is generated by evaporation 42A.

[0042] The following can be considered to maximize the amount of water that can be directed to the rinse stage. The wash water 38A can be reduced using a multi-stage countercurrent approach 70, as shown in Figure 6, which allows a larger amount of make-up water 36A to be used to rinse the leachate ore 30A (or ripides).

[0043] The process 70 comprises a first stage 70A, a second stage 70B and a third stage 70C. More steps could be added, but there would be diminishing gains and rising capital costs. Optimum performance for process 70 is expected in 3 stages. The loaded organic phase 51 is directed from the extraction process 46 to a mixer 72a for mixing with a first high chloride intermediate wash water 38Xb obtained from a decanter 74b in the second stage 70B of a previous cycle and subsequently directed to a decanter 74a to separate into a clean organic 49a and a high chloride spent wash water 38Xc.

[0044] The organic phase 49a reports to a mixer 72b (in the current second stage 70B) to mix with a second intermediate wash water with a high hydrochloric acid content 38Xa (obtained from the water used in the third stage 70C of a previous cycle ) and then to a decanter 74b to separate into a high chloride organic intermediate 49b and the spent water wash intermediate 38Xb (to be directed to the first stage 70A of a subsequent cycle).

[0045] The organic phase 49b goes to a mixer 72c (from the current third stage 70C) to mix with the fresh wash water 38A and then to a decanter 74c to separate into a washed organic 49c and a spent wash water with high 38Xa intermediate chloride content (to be directed to second stage 70B of a subsequent cycle). The washed organic 49c reports to pickling process 48.

[0046] Solvent extraction plants use mixers/decanters for contacting and separating aqueous and organic respectively. The two fluids are combined in a mixer to form a dispersion with the aqueous fluid forming a continuous phase, while the organic fluid is dispersed within it as a discontinuous phase. The aqueous/organic dispersion is fed to a decanter, where the two fluids separate into an organic phase and an aqueous phase. Separation is not perfect and each phase carries part of the other fluid entrained within it.

[0047] The resulting organic 51 that comes from the extraction or loading step in a solvent extraction process 46, reports to the washing step 58.

[0048] Figures 7A, 7B and 7C show, respectively, a single-stage countercurrent scrubbing circuit, a two-stage countercurrent scrubbing circuit and a three-stage countercurrent scrubbing circuit, used to reduce the concentration of organic phase chloride 51.

[0049] The organic phase 51 entering the wash stage 58 has a pregnant leach entrained solution with a chloride content typically around 150 000 ppm. It is generally desirable to reduce this level to about 50 ppm before the copper is stripped in electrolyte 54.

[0050] In the single cycle wash stage 58A, Figure 7A, the organic phase 51 from the extraction stage 46 is combined with a low concentration aqueous solution of chloride 38A in a mixer. The washing is not perfect and part of the entrained chloride passes through the final organic phase entrained solution 49a.

[0051] Figure 7B shows a two-cycle countercurrent wash stage 58A, 58B. The resulting organic phase 49b has a lower entrained chloride content than the organic phase 49a resulting from the single cycle wash stage 58A. However, in a high chloride leaching operation, a two-cycle wash stage may not be sufficient to reduce the chloride content of the resulting organic phase unless copious wash water is used.

[0052] In process 10A, a three-stage countercurrent washing circuit 58A, 58B, 58C is used (Figure 7C. In this circuit, the chloride concentration in the organic phase 49c of the final stage 58C is reduced to below 50 ppm, with wash flows of only about 1/75 of the organic resulting from extraction stage 46.

[0053] The wash water in a multi-cycle countercurrent wash stage is reduced to less than a third of that used in a typical single-stage conventional wash circuit. The water that is saved here can be used as wash water 36A, in Figure 4, which can be used to rinse the leachate ore. This maximizes the washing efficiency in terms of chloride recovery and decreases the loss of soluble copper in the leachate ore.

[0054] The following description refers to the test work carried out to validate the inventive principles that have been described.

[0055] Experimental Evaluation - Integrated Pilot Plant Example

[0056] An integrated pilot plant incorporating 9 berths and a solvent extraction plant was established to replicate the application of the method of the invention on a pilot scale. The plant is designed to treat various low grade chalcopyrite ores using a dynamic “race track” style leaching operation. This is a stack made up of multiple sectors where new sectors are stacked and older sectors are removed from a block that is reused.

[0057] Each berth has a cross-sectional area of 4 m2, an operating height of 7.5m, a total height of 10m and contained approximately 40T of ore. The berths were operated to simulate a commercial operation with 9 sectors. The process was dynamic, with periodic removal of leaching residue from a leached berth and replacement of the leached residue with fresh ore in a vacant berth.

[0058] Three separate phases of operation were carried out. The range in composition of the main copper sulfide and gangue minerals contained in the ore samples tested and a brief description of the operation are summarized in Table 1. Table 1 Pilot Plant Operational Phases *CSR - Copper Source Ratio (percentage of total copper contained in this mineral)

[0059] The ore samples were crushed in a 3-stage crushing circuit. The crushed ore was agglomerated before being loaded into the berths. Sodium chloride (salt), acid and raffinate (or other process liquor containing copper, iron and acid) were added to the ore in the agglomeration process. The agglomerated ore was then placed into an empty berth; for a period, after which irrigation began. At the end of the irrigation cycle, each berth was drained, irrigated with water to wash, drained again and finally emptied. The empty berth was then readied to accept a new load of lump ore.

[0060] Phases I and II were related to the beginning of the operation and data collection.

[0061] In the Phase III operation, low-grade ores were included with copper grades as low as 0.3% Cu and with up to 75% of the contained copper associated with chalcopyrite (CSR of chalcopyrite 75%). The operation consisted of a period of 45 days of curing, 20 days of wetting, 360 days of irrigation, 20 days of washing and 30 days of drainage (total of 475 days), before unloading and sample processing.

[0062] The phase III operating schedule was designed to allow the loading and unloading of a berth every 45 days, thus simulating a commercial dynamic block operation and handling of industrial liquids. This closure was essential to obtain steady-state concentrations of impurities and to identify possible operational problems. The operation was maintained in a closed circuit and the wash water was reintroduced to generate raffinate to compensate for the loss due to moisture and evaporation of the residues. The water addition rate was maintained at 0.11 m3/t of ore. Fresh make-up water was used to wash loaded organics to remove chlorides and to wash ore residues according to the method of the invention.

[0063] The pilot plant was operated as a closed system with carefully controlled inlets and outlets to mimic a commercial heap leaching operation, i.e. fresh water addition was limited to balance water lost to evaporation, moisture loss in the leachate residues (or sludge) and the replacement of water lost in the purge of the process solution (if necessary to reduce impurities). The pilot plant process flowchart is shown in Figure 8. The main components and operation of the pilot plant are summarized below: • Refining Tank 1: Storage of return raffinate from solvent extraction (SX) 7. Provides feed to separate 1m3 of raffinate from the 2A-I feed tanks for each 3A-I berth. Makeup acid can be added to the raffinate tank as needed to meet the process' operational acid demand. • Pregnant Leaching Solution (PLS) 4 and 5: The PLS solution from each berth (3A-I) is collected in 1m3 of PLS in tanks 4A-I. PLS is transferred from tanks 4A-I to the PLS 5 holding tank. • High Cu 6 Content PLS: The first PLS collected from the initial irrigation of the berths after the ore has cured has a high copper content. This initial PLS collects in holding tank 6. Makeup acid can be added to the high copper PLS in tank 6. SX purge water can be added to the high copper PLS in tank 6. • Ore Agglomeration 8: The ore is agglomerated into an agglomeration cylinder. Raffinate from tank 1 is added to the ore. Solid acid and salt are added to meet the desired acid addition and total salt addition as needed. High copper PLS 6 can be used in ore agglomeration to allow direct return of copper and acid (contained in high Cu PLS) to the ore agglomeration. A high copper content in acid-agglomerated ore can improve copper dissolution during ore curing in the initial rest stage. Agglomerated ore is transferred to loading berths (3A-I) when required. • Ore is leached in berths 3A-I: Agglomerated ore is stacked in berths. Healing is allowed (initial rest period). Irrigation is then started. Irrigation starts slowly to ensure the ore is wetted. Irrigation is accomplished by pumping the low copper raffinate from the solvent extraction process to the top of the cradles. The liquor is distributed over the surface of the cradle by application through a network of drippers. The solution seeps into the ore inside each berth. Simultaneously, air is introduced at the base of each cradle. Copper is solubilized by the combination of acid in the process liquor and oxygen in the air. The irrigation liquor reports to the base of the cradle. It now has a high copper content and is called PLS (pregnant leach solution). It is collected and reported to the solvent extraction process. • After ore leaching, irrigation of the ore with raffinate is stopped. The ore bed is allowed to drain and then the ore is washed with wash water to recover entrained chloride (salt) and dissolved copper. The washed ore leach residue is then removed from the berth for disposal. • Solvent Extraction (SX) 7: Copper is recovered from PLS by solvent extraction. Copper is loaded into the organic in two extraction stages, E1 and E2. The loaded organic is then washed with water in a two-stage wash L1 and L2. Washing is necessary to remove the entrained aqueous solution so that the chloride content of the advanced electrolyte after removal of the loaded organic material is <50 ppm. After the wash step, the loaded organic material is then pickled in S1 to recover the copper in advanced electrolyte 7b. Spent electrolyte for charged organic pickling is supplied in holding tank 7c. If necessary, make-up acid may be added to the spent electrolyte in holding tank 7c to increase the acid concentration to the amount necessary for complete removal of the loaded organic. The advanced electrolyte is removed from the copper recovery circuit and the spent electrolyte is returned to the circuit. Washing efficiency of loaded organic material can be improved by increasing the number of washing stages to three (see Figure 7C). Increased washing efficiency reduces the volume of washing water required for washing loaded organics, allowing increased water for washing leached ore residues, resulting in greater recovery of chloride and copper, by displacing the solution entrained in the residue of ore. Table 2 Pilot Plant Operating Parameters for Phase I, Phase II and Phase III

[0064] The simplified mass balance diagram for the pilot pile showing the inlets and outlets is shown in Figure 9. Typical values for the balance of ore, acid, salt and water are shown in Table 3. The results of Table 3 demonstrate that the salt recovered by washing the ore with the operational target of 0.11 m3/t of water was equal to 9 kg/t, representing a significant saving in terms of necessary make-up salt. For ore treated in Phase II, the total copper recovered, including copper recovered by washing the ore (as shown in Example 2), was equal to 60% of the copper in the original ore feed. Table 3 Summary of the Pilot Plant Mass Balance Showing Inputs and Outputs Phase II - Pilot Plant Mass Balance

[0065] Table 3 shows that the wash water for solvent extraction was 4.3 m3 for the 348 tons of ore treated during the process over a period. The wash water used to wash the ore, after leaching, was ~8x more than the 34.9m3, so there is very little scope to improve the ore wash, further reducing the solvent extraction wash in this case. However, solvent extraction wash performance was not satisfactory at this wash volume with a two-stage setup. The chloride concentration of the solution entrained in the organic loaded after washing is around 600 ppm. The wash water allocated for solvent extraction could be increased, but this would be detrimental to the amount of water that could be used to wash the leachate ore and would hardly sufficiently reduce the chloride content of the washed organic. The consequence of this would be an increase in the loss of soluble copper and an increase in the demand for salt. The other option, as described above, is to increase the number of stages of the countercurrent solvent wash stages to 3 or more (Figure 7C). This would significantly reduce the chloride in the organic after washing without the need to increase the wash water.

[0066] This example shows the interaction between the general process water balance and the configuration of the SX washing stage in the overall performance of the plant. The example demonstrates that efficient washing of loaded organics requires multiple washing stages to minimize the wash water addition volume and to achieve the desired chloride levels in the advanced electrolyte. This result is in line with the principles described above, as the water available to wash the residue is maximized.

Example 2: Copper and Chloride Washing and Recovery Efficiency Curves

[0067] Copper Recovery: The results shown in Figure 10 show the copper concentration profile for recovery of copper and PLS (or irrigation drainage solution) as a function of the operating time of two berths, berth 1 in phase I ( A ore; 0.5% Cu and 60% Chalcopyrite from CSR) and berth 5 in phase II (B ore; 0.65% Cu and 75% chalcopyrite from CSR) of pilot plant operation.

[0068] In berth 1 of phase I, the irrigation solution, or refined, contained 5 g/L of copper. The results show that, for the treated ore sample, copper recovery at the end of the leaching cycle was 59%. The leached residue was allowed to drain and then washed with water to recover the entrained dissolved copper. Displacement of copper from waste ore by water washing increased copper recovery to 70%, as shown in Figure 10.

[0069] In berth 5, phase II, the irrigation solution, or refined, contained 0.5 g/L of copper. The results show that, for the treated ore sample, copper recovery at the end of the leaching cycle was 59.5%. The leached residue was allowed to drain and then washed with process water to recover the entrained dissolved copper. Displacement of copper by washing with water increased copper recovery to 60%, as shown in Figure 10.

[0070] The reason why in berth 1 the copper recovery increased by 11% and in berth 5 it only increased by 0.6% is because berth 1 was irrigated with a solution containing a high copper content (5g/l) and, therefore, there was considerable retention of soluble copper in the cradle at the end of the leaching. In the case of cradle 5, it was irrigated with a continuous solution 1/10° the copper concentration of the solution used in cradle 1. Therefore, the amount of soluble copper retained in the cradle before washing was much smaller.

[0071] Careful operation of the solvent extraction process can reduce the loss of soluble copper by providing a low refined copper with which to irrigate the process.

[0072] Chloride Recovery: As stated, careful operation of the solvent extraction process can reduce the loss of soluble copper by providing a refined copper base with which to irrigate the process. This is not the case with chloride. The process requires a high chloride content in the irrigation liquor (~150g/l) to maximize chalcopyrite leaching. Any residual chloride that is left entrained in the leachate ore (ripios) that is removed from the pile must be compensated for by adding sodium chloride or an alternative source of chloride (HCl, MgCl, etc.).

[0073] The efficiency of washing in relation to the recovery of chloride is shown in Figure 11. These data come from the results of washing with process water from berth 5, phase II. The results show an increased recovery of chloride as the amount of applied rinse water volume is increased. The water balance of the pilot plant process flowsheet requires that the water used to wash the waste ore be limited to match the process water lost, minus other fresh water inputs. Water is lost as moisture from waste ore removed from the pilot plant, through evaporation and can be removed if the liquor is purged from the circuit. The other fresh water input to the loop is the fresh water used in the organic wash step loaded with solvent extraction to remove entrained chloride.

[0074] The maximum volume of water available to wash the residual ore is of the order of 0.1 m3 per ton of ore. The results presented in the example shown in Figure 11 indicate that, at this volume of wash water per ton of ore, the wash efficiency (or chloride recovery) was equal to about 60%.

[0075] The chloride recovery obtained by washing with water can also be expressed as the chloride equivalent that must be added to compensate for the chloride lost in the moisture of the ore residue. The salt (NaCl) for the cradle 5 phase II wash curve indicates that, at the wash ratio of 0.1 m3/T the salt composition (NaCl) is about 18 kg/T, as shown in Figure 12 .

Example 3: Accumulation of Impurities

[0076] Washing is considered to retain chloride and marginally increase recovered copper. The downside is that potentially unwanted species arising from the reaction of the acid with the gangue minerals will also be retained in the process.

[0077] The reaction of gangue minerals with acid will result in the dissolution of metals such as Ca, Si, Al, Mg, Fe and K. These dissolved species will accumulate in solution until they reach a concentration such that the mass of the dissolved species in the washed ore after leaching is equivalent to the mass that dissolved minus any of the species that re-precipitated after leaching.

[0078] The accumulation of impurities in the raffinate of the pilot plant under operation in a closed circuit with washing is shown in Figure 13. The concentration of aluminum and magnesium (dissolved by acid dissolution of gangue mineral silicates, such as biotite and chlorite) clearly increases with the period of closed-circuit operation and reaches concentrations of about 10 g/L and 5 g/L, respectively. The total iron concentration is in the range of 2-4 g/L. The total sulfate concentration is about 80 g/L.

[0079] In general, the accumulation of these species plus the addition of sodium chloride result in saturated solutions. It is already known that sulfate will precipitate out of solution as insoluble iron jarosites (Na or K jarosite, for example), as metasideronatrite [Na2Fe3+(SO4)2(OH)^(H2O)], and also at low temperatures and high levels of saturation, possibly as sodium sulfate, aluminum sulfate and/or magnesium sulfate. Precipitation of Na, Al or Mg or Fe sulfates will depend on temperature (increase in precipitation at lower temperature) and acidity, where precipitation of jarosite and metasideronatrite will increase at low acidity levels, i.e. at higher values of pH of the solution.

[0080] The precipitation of iron sulfates and other metal sulfates can cause problems in the operating circuit, especially when ambient temperatures are low (<20oC) and salt precipitation is increased. Potential problems include: • precipitation of sulfate salts in drip lines used to irrigate the piles, causing blockage of the lines and failure to effectively irrigate the piles; • precipitation of salts in solution tanks containing effective volume reduction; and • precipitation in layers within the pile causing pore space blockage and poor solution flow and distribution through the ore bed, possibly reducing copper recovery.

[0081] The amount of precipitation will be a function of the degree of washing. There may be a point in the process where optimizing chloride recovery is offset by costs generated by process issues resulting from the accumulation and precipitation of unwanted species. If this occurs, a reduction in the degree of washing may be necessary.

Claims (10)

1. Method for maximizing the amount of water available for washing in a leaching operation in high chloride heaps, that is, a leaching operation in chloride heaps with chloride concentrations of 100 to 230g/L, characterized by the fact that that the method includes the step of using process make-up water in the range of 0.05 to 0.35 m3/ton of ore to rinse the ore leachate residue in the heap to thereby displace an aqueous liquor containing ore chloride ore leachate, in which an amount of process make-up water available for rinsing is increased using a multi-stage countercurrent charged organic solvent scrubbing loop to reduce the chloride concentration in the organic phase. 2. Method, according to claim 1, characterized by the fact that the amount of process replacement water in the rinsing step is between 0.1 and 0.15 m3/ton of ore. 3. Method, according to claim 1, characterized in that it includes the step of increasing the amount of process replacement water available for washing by means of at least one of the following: increasing the evaporation of water from the leaching circuit ; divert rainwater from the pile; and reduce the demand for make-up water for bleeding by electrolysis by washing the loaded organic. 4. Method, according to claim 2, characterized by the fact that the chloride concentration in the organic phase is reduced to below 50 ppm. 5. Method, according to claim 1, characterized in that the aqueous liquor containing displaced chloride is recovered and recycled to the heap leaching operation, thereby decreasing the amount of replacement salt that is added to the heap leaching operation. heap leaching. 6. Method, according to claim 1, characterized by the fact that the rinsing step is carried out for a period of 5 to 100 days. 7. Method, according to claim 6, characterized by the fact that said period is 20 days. 8. Method, according to claim 1, characterized in that the copper recovered in the aqueous liquor displaced in the rinsing step is returned to the leaching operation and is subsequently recovered through the use of a solvent extraction step and a step of electrolysis. 9. Method, according to claim 1, characterized by the fact that the ratio of chloride recovered in the aqueous liquor, displaced in the rinsing step by the process recovery water, to the total content of the same in the residue ore before washing , is between 40 and 85%. 10. Method, according to claim 9, characterized in that said ratio is 60%.