Method for extracting copper in solution from concentrates, with retention of iron in solids

Abstract

The present invention aims to obtain a high recovery of copper from primary copper sulphide concentrates through the hydrometallurgical route via a quick, clean, reusable and water-efficient process. The invention relates to methods for extracting metals from concentrates via wet processes, and particularly to a highly efficient method in which a primary copper sulphide concentrate is pretreated and dissolved, using sodium persulphate and sodium chloride in an acid medium to extract copper in solution, the iron being retained in the solid.

Description

[0001] METHOD FOR EXTRACTING COPPER IN SOLUTION FROM CONCENTRATES, WITH IRON RETENTION IN SOLIDS

[0002] FIELD OF INVENTION

[0003] The present invention relates to methods for extracting metals from concentrates by wet processes, and in particular to a method that employs pretreatment and dissolution of a primary copper sulfide concentrate, using sodium persulfate and sodium chloride in an acidic medium, for the extraction of copper in solution, leaving the iron retained in the solid.

[0004] BACKGROUND OF THE INVENTION

[0005] The mining industry is experiencing a change in the production matrix of fine copper, focusing its initiatives on the production of copper concentrates; however, there are no projections aimed at using the large installed capacity available in hydrometallurgical plants.

[0006] It is internationally known that the largest processing of sulfide copper is through pyrometallurgy, and there has recently been a trend in which the largest copper (Cu) exports in Chile are of Cu concentrate, surpassing for the first time refined copper, which is sold mainly as cathodes.

[0007] On the other hand, the amount of copper oxides available in the country is decreasing, resulting in idle capacity in hydrometallurgical plants that are operating at reduced capacity and could become obsolete in the future. This shift in the production matrix also projects an increase in water consumption in mining, since sulfide minerals are primarily processed through flotation, a much more water-intensive process. Furthermore, the decline in ore grades requires a greater volume of water to obtain one ton of fine copper. Therefore, the use of seawater over continental water in copper mining at the national level is projected for the future. Some hydrometallurgical research has addressed the pretreatment of copper sulfide minerals or mineral concentrates prior to leaching, with the aim of improving copper solubilization.Pretreatments have been investigated in acid sulfate medium, acid chloride medium, and recently pretreatments with sodium persulfate.

[0008] For example, the publication by J. Ipinza et al. (Ipinza J, Ibañez J, Flaquer J, Engdahl O. Identification of compounds formed during the pretreatment of chalcopyrite with sulfuric acid-sodium chloride. Arequipa, Peru: PERUMIN Convention. 2015) describes a pretreatment of chalcopyrite minerals that consists of wetting them with water and adding the optimal amount of sodium chloride and concentrated sulfuric acid, followed by a resting period according to the mineral's characteristics. This allows for copper extraction of approximately 70% in about 120 days. The pretreatment preceding heap leaching is the key stage for the success of this technique, which has already been applied at a semi-industrial level for the beneficiation of secondary copper sulfides.

[0009] The document by Ricardo Andrés Soto Mellado (Leaching of low-grade copper sulfides pretreated with NaCl - H2SO4 along with NaNO3 or Fe(NO3)3, in sulfate-chloride medium with NaNOa or Fe(NOa)3, in sulfate-chloride medium (2018); Federico Santa María Technical University) describes pretreatments using both sodium chloride and nitrated salts. In this document, the pretreatment of copper sulfide ore, with a copper grade of 0.12%, is carried out by dosing solid sodium chloride, concentrated sulfuric acid relative to its standard consumption (20, 50, 80, and 100%), and 50% of the impregnation moisture. The solid mixture is left to stand for 7, 14, and 21 days, and then the pretreated ore is subjected to agitated leaching under conditions of pH 1, 25% solids, 370 rpm, 4 hours, chloride concentrations of 0, 35, and 70 g / L, and temperatures at both ambient and 25 and 35 °C. The maximum copper extraction obtained by this method is 27%.

[0010] The document by Cecilia P. Cerda (Cerda CP, Taboada ME, Jamett NE, Ghorbani Y, Hernández PC. Effect of Pretreatment on Leaching Primary Copper Sulfide in Acid-Chloride Media. Minerals. 2018; 8(1):1) proposed improving the dissolution of copper sulfide ore, composed mainly of chalcopyrite and bornite, through pretreatment before leaching. This article investigated the effect of pretreatment on copper sulfide dissolution using different leaching methods. The results obtained in this study show how copper sulfide ore leaching could be improved with pretreatment and an appropriate settling time using concentrated acid and the addition of chloride.

[0011] The publication by Paulina Moneada Benavides (Moneada Benavides P. Effect of a Chemical Pre-Treatment Based on NaCl-H2SO4 and Resting Time in the Leaching Process of a Low-Grade Chalcopyrite Ore. Federico Santa María Technical University. 2017) studied chemical pretreatment in a NaCl-H2SO4 medium. This document indicates that chemical pretreatment is a fundamental step, since almost all of the recovered copper comes from its effect on the ore. The in-situ formation of hydrochloric acid through the addition of sodium chloride and sulfuric acid, along with proper homogenization and aeration, allows, in part, the transformation of copper sulfide species such as chalcopyrite and secondary sulfides into species that dissolve rapidly in acidic media.

[0012] Furthermore, the document by Claudio Alberto Vásquez Valdenegro (Vázquez Valdenegro CA. Digestion of Chalcopyrite Concentrate Using Sodium Persulfate in Acid Medium, University of Santiago, Chile. 2022) describes the effect of sodium persulfate (Na2S2Os) on the acid digestion of a chalcopyrite concentrate, through the dissolution of copper and iron. The digestion system using Na2S2Os / H2SO4 is described to study the degree of copper and iron dissolution through the variables of temperature and digestion time of the concentrate, maintaining fixed parameters of mass ratio of sodium persulfate to concentrate (661 kg Na2S2Os / ton of concentrate), sulfuric acid to concentrate (30 kg H2SO4 / ton of concentrate), and a moisture content of 15%.It is concluded that sodium persulfate is an effective oxidizing agent for copper dissolution in an acid / oxidative pretreatment process of a predominantly chalcopyrite concentrate, involving sequential galvanic reactions within a solid-solid digestion system. However, as can be seen in this document, an excessively high quantity of sodium persulfate is used to achieve the desired copper dissolution, which makes the proposed method not very economically viable.

[0013] Therefore, within the state of the art there is still a need for new, more efficient and environmentally friendly procedures, where small volumes of water are used and copper is recovered in solution with few impurities, objectives towards which the present invention is directed.

[0014] SUMMARY OF THE INVENTION

[0015] The present invention aims to provide a method for the efficient extraction of copper from copper sulfide mineral concentrates, the method comprising the steps of: a) providing a mass of primary copper sulfide mineral concentrate with its natural moisture; b) adding to the mass of copper sulfide mineral concentrate a mixture of sodium persulfate and sodium chloride salts in the following mass ratios: between 80 and 330 kg of sodium persulfate / ton of concentrate and between 65 and 100 kg of sodium chloride / ton of concentrate; c) gradually adding water to the concentrate being pretreated with the salt mixture to moisten it; d) adding acid in a mass ratio of between 30 and 60 kg / ton of concentrate; e) diluting the pretreated concentrate with water; and f) separating the concentrated copper solution from the solid material, which retains the iron.

[0016] In a preferred embodiment of the invention, water is added to the concentrate being pretreated until a moisture content of between 10 and 25% is reached relative to the concentrate with its natural moisture content (which is also considered to be the concentrate on a dry basis). In yet another preferred embodiment of the invention, the water added to the concentrate is selected from either fresh water or seawater.

[0017] In another preferred embodiment of the invention, the acid added to the concentrate is selected from the group consisting of sulfuric acid, hydrochloric acid, or a mixture of these.

[0018] In another preferred embodiment of the invention, the pretreated concentrate is heated to a temperature between 25 and 75°C for 5 to 7 days, ensuring that the moisture content remains between 10 and 25%. Even more preferably, the pretreated concentrate is heated to a temperature between 55 and 75°C, and most preferably, it is heated to a temperature of 60°C.

[0019] In another preferred embodiment of the method of the invention, the concentrate, once subjected to heat, is diluted at room temperature in a ratio of approximately 30:1 mass of water / mass of concentrate, for 10 to 60 minutes and at a pH between 1.0 and 2.2.

[0020] Throughout the method of the invention, and preferably when the mixture of salts, water, and acid is added to the pretreated concentrate, the mixture is completely homogenized.

[0021] The method of the invention can be applied to primary and secondary copper sulfide mineral concentrates, and preferably to primary chalcopyrite concentrates.

[0022] BRIEF DESCRIPTION OF THE FIGURES

[0023] FIG. 1 is a representative diagram of preliminary pretreatment tests with a persulfate mass ratio of 330 and 170 kg / ton of concentrate (te), varying the concentration of NaCl (65, 80, 100 kg / tc) and H2SO4 (40, 50 kg / tc), with moisture of 18% and 20%, resting at 25°C and 60°C.

[0024] Figure 2 shows the iron and copper solutions in preliminary pretreatment tests with persulfate mass ratios of 330 and 170 kg / t, varying the concentrations of NaCl (65, 80, 100 kg / t) and H2SO4 (40, 50 kg / t), with moisture content of 18% and 20%, and incubated at 25°C and 60°C for 6 days. Figure 3 shows the effect of sodium persulfate dosage on the copper solution in pretreatments for copper concentrate with 100 kg / t [NaCl], 40 kg / t [H2SO4], at 60°C for 6 days, with a moisture content of 18%.

[0025] FIG. 4 shows the effect of sodium persulfate dosage on iron dissolution in pretreatments for copper concentrate with 100 kg / tc [NaCl], 40 kg / tc [H2SO4], at 60°C for 6 days, with a humidity of 18%.

[0026] FIG. 5 shows the copper dissolution per day of treatment, with 10, 30, and 60 minute solutions, in pretreatments with 120 kg / tc [Na2S20s], 100 kg / tc [NaCl], 40 kg / tc [H2SO4], at 60°C, with a humidity of 18%.

[0027] FIG. 6 shows the iron dissolution per day of treatment, with 10, 30, and 60 minute solutions, in pretreatments with 120 kg / tc [Na2S20s], 100 kg / tc [NaCl], 40 kg / tc [H2SO4], at 60°C, with a humidity of 18%.

[0028] FIG. 7 shows the temperature profile during the initial hydration of water and acid, according to persulfate dosage, treatments C1 (0kg / tc), C2 (80kg / tc), C3 (120kg / tc), C4 (250kg / tc), each with three water dosages, and one acid dosage.

[0029] FIG. 8 shows the mass loss in pretreatments with respect to the initial mass of concentrate, according to the dosage of persulfate, 0-330 kg / tc [Na2S20s], 100 kg / tc [NaCl], 40 kg / tc [H2SO4], with 6 days of rest at 60°C and humidity of 18%, and subsequent dissolution with acidic solution pH 1.8 for 10 minutes.

[0030] Figure 9 shows photographic records of the concentrate during pretreatment. Pretreatment begins at 60°C for samples C1, C2, C3, C4 (0, 80, 120, 250 kg / tc Na2S2O8 respectively).

[0031] FIG. 10 shows the evolution of sample C3 at the beginning of the second day (C3 2.0), third day (C3 3.0), fourth day (C3 4.0) and end of the sixth day (C3 6.0) of treatment at 60°C.

[0032] Figure 1 shows copper leached from a concentrate pretreated with 120 kg / t [Na2S20s], 100 kg / t [NaCl], and 40 kg / t [H2SO4] at 60°C for 6 days, with a moisture content of 18%. Figure 12 shows iron leached from a concentrate pretreated with 120 kg / t [Na2S20s], 100 kg / t [NaCl], and 40 kg / t [H2SO4] at 60°C for 6 days, with a moisture content of 18%.

[0033] FIG. 13 shows the dissolution of Fe and Cu from a concentrate with continuous double pretreatment at 60°C for 6 days with 120 kg / tc [Na2S20s], 100 kg / tc [NaCl], 40 kg / tc [H2SO4].

[0034] FIG. 14 shows the dissolution of Fe and Cu from a concentrate with two pretreatments cut for 30 days, at 60°C for 6 days with 120 kg / tc [Na2S20s], 100 kg / tc [NaCl], 40 kg / tc [H2SO4].

[0035] DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention aims to optimize the extraction of copper from copper sulfide mineral concentrate, providing a method that includes a pretreatment of a primary copper sulfide mineral concentrate with sodium persulfate and sodium chloride salts, in an acidic medium.

[0037] The main advantages of the present invention are the effectiveness of the method with respect to the high extraction of copper from a concentrate of primary copper sulfides, composed of chalcopyrite and bornite, with a high content of chalcopyrite and traces of bornite, where the extraction is achieved in a shorter time, that is, between 5 and 7 days and with little use of water, unlike other hydrometallurgical methods, which are far below in terms of copper extraction and with very long working times, and high water consumption, which makes them not very feasible from an economic point of view.

[0038] To the applicant's knowledge, there is no prior art solution directly related to this process, given the conditions employed, the variables studied, and the results obtained. However, it could be compared to laboratory studies, where pretreatment times could reach up to 30 days, with maximum copper dissolutions on the order of 50% (Ávila M. Study of copper solubilization from a bornitic concentrate using different pretreatments. University of Santiago, Chile. 2020). Furthermore, at an industrial level, copper sulfides are treated hydrometallurgically as low-grade sulfide ores, and leaching times can reach up to a year with copper recoveries on the order of 35%, which entails high water consumption.

[0039] The method proposed in the present invention, being hydrometallurgical, yields a solution with a high copper concentration (recovery between 70 and 80%) in which, unlike traditional processes, the iron present in the initial concentrate does not dissolve and remains as a stable solid in the final tailings. This is a highly significant advantage of the present invention, since iron is one of the main impurities in the process, and keeping it out of the resulting pregnant leaching solution (PLS) is extremely beneficial for subsequent copper extraction processes by solvent and electrowinning. This opens a new avenue for efficiently addressing the overall process of obtaining copper cathodes.

[0040] Given the characteristics of this invention, the amount of water to be used is very low compared to any other hydrometallurgical process, since the objective of this method is not to leach the concentrate, but to pretreat it with minimal moisture and, subsequently, extract the soluble copper through a dissolution process in very short times, where the process water is reused due to the characteristics of the subsequent copper concentration stages, such as solution purification and electrodeposition.

[0041] The economic potential of this invention lies in its application to the mining process on an industrial scale, where the aim is to process a percentage of the copper concentrates produced in the country and subsequently exported. Initially, the idle capacity of existing hydrometallurgical plants could be utilized, producing high-purity copper cathodes at the end of the processing line.

[0042] As explained, the invention provides a method that employs the pretreatment of a concentrate of primary copper sulfide minerals to efficiently obtain a high copper recovery.

[0043] To achieve the described advantageous results, the reagents are added, the concentrate is moistened and acidified, and the mixture is placed in a temperature-controlled oven (between 20°C and 75°C) for a specific period. The higher the temperature within this range, the faster the extraction process will occur. Throughout the process, the moisture content of the material should ideally be maintained between 10% and 25% relative to the dry weight of the concentrate, and the mixture should be homogenized to ensure the copper dissolves and the iron remains in the solid residue.

[0044] The composition of the concentrate used in the trials carried out as part of this invention is detailed in Table 1 and Table 2.

[0045] Table 1. Cu-Fe composition of the concentrate

[0046] Table 2. Mineralogical composition of the concentrate

[0047] EXAMPLES OF IMPLEMENTATION

[0048] Example 1. Optimization of copper recovery using pretreatment with sodium persulfate (Na2S20s), sodium chloride (NaCl) and sulfuric acid (H2SO4).

[0049] An objective of the present invention was to optimize the method of obtaining copper by pretreatment with salts, in particular sodium persulfate (Na2S20s), sodium chloride (NaCl), and sulfuric acid (H2SO4), in order to improve the copper dissolution efficiency and thereby reduce the dosage of Na2S20s. To determine the important parameters to consider in the method of the invention, pretreatments were carried out with a persulfate mass ratio of 330 and 170 kg / tc, varying the concentration of NaCl (65, 80, 100 kg / tc) and H2SO4 (40, 50 kg / tc), with humidity of 18% and 20%, at 25°C and 60°C, for 6 days. The mixture is kept at rest and is only homogenized each time the reactants or water are incorporated into the system to replace what evaporated with the heat to which it is subjected, and thus to maintain the humidity within the desired range.

[0050] Based on these results, subsequent tests were planned by adjusting the mass ratio of the persulfate reagent, with a suitable combination of NaCl and acid.

[0051] Figure 1 schematically shows the preliminary tests performed, with the respective reagent concentrations. Each of the eight samples (A1-A4 and B1-B4) was duplicated; the first group was treated at 25°C with 20% humidity, and the remaining group was treated at 60°C with 18% humidity. To distinguish the samples, those treated at 60°C were designated as raw samples, i.e., AT through B4'. Table 3 characterizes the samples used in the preliminary tests.

[0052] Table 3. Characterization of samples for preliminary tests

[0053] PRELIMINARY TESTS

[0054] Sample A0 A1 A2 A3 A4 B1 B2 B3 B4 AT A2' A3' A4' BT B2' B3' B4'

[0055] Na2S2O8[kg / tc] 330 330 330 330 330 170 170 170 170 330 330 330 330 170 170 170 170

[0056] NaCI [kg / tc] 65 65 80 100 65 65 80 100 65 65 80 100 65 65 80 100 65

[0057] H2SO4 [kg / tc] 40 40 40 40 50 40 40 40 50 40 40 40 50 40 40 40 50

[0058] Humidity [%] 20 20 20 20 20 20 20 20 20 18 18 18 18 18 18 18 18

[0059] Temperature [°C] 25 25 25 25 25 25 25 25 25 60 60 60 60 60 60 60 60

[0060] Time [days] 10 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6

[0061] Samples treated at 60°C were rehydrated daily to compensate for water loss through evaporation, and additional rehydration was performed during nighttime and weekend periods. Samples treated at 25°C did not require daily rehydration; evaporated water was only replenished on the third day.

[0062] Once the digestion period was complete—which is simply the impregnation of the copper concentrate with sodium persulfate and sodium chloride in an acidic medium, resulting in changes to the concentrate's morphology and the formation of more soluble solid species—the pretreated concentrate was dissolved. For this, 300 ml of acidic solution (water acidified with sulfuric acid, pH 1.8) was prepared and homogenized with the concentrate in a beaker for 10 minutes at 25°C. The pH was maintained at 1.8 by adding drops of sulfuric acid (concentrated and / or 50% diluted) during dissolution. In these solutions, the pH trend was consistently upward, so only drops of acid were added, and it was not necessary to add sodium hydroxide.

[0063] Additionally, an extra pretreatment was performed with another sample (A0) identical to A1, but treated at 25°C with 20% humidity for 10 days, without humidity control, followed by dissolution in water for 10 minutes at room temperature. This was done to analyze the effect of humidity control during the 25°C pretreatment and to compare the copper solutions obtained by dissolving in water and in an acidified solution at pH 1.8 with sulfuric acid.

[0064] It is important to note that the treatments at 25°C were not carried out in a controlled environment, so they may have suffered thermal fluctuations throughout the day, especially lower temperatures during nighttime periods.

[0065] Figure 2 shows the results of iron and copper solutions obtained from the pretreatments carried out in the preliminary tests.

[0066] Of the pretreatments carried out at 25°C (from A0 to B4) (FIG. 2); those with 330 kg of Na2S20s / ton of concentrate (te) (from A0 to A4) reached a copper dissolution of -48%, invariant to a higher dosage of NaCl and H2SO4. The pretreatments with 170 kg / tc of Na2S20s (from B1 to B4) show a maximum copper dissolution of 35% (B1 ) with variations of -4% and -8% approximately against higher dosages of NaCl and H2SO4 respectively. Of the pretreatments at 60°C (from AT to B4') (FIG. 2), AT with 330 kg / tc of Na2S2C>8 dissolved 69% of the copper. When the Na2S20s was decreased to 170 kg / tc (BT), the copper dissolution fell by 14%. However, in the pretreatments with less Na2S20s, copper dissolution was encouraged with higher dosages of NaCl, reporting a 12% increase in copper dissolution when the NaCl dosage was increased from 65 to 100 kg / tc (BT-B3').

[0067] Furthermore, increasing the dosage of H2SO4 from 40 to 50 kg / tc did not result in any improvements in copper dissolution.

[0068] Based on the evidence presented in FIG. 2, a considerable increase of -20% in copper dissolution was observed when the pretreatment temperature was raised from 25°C to 60°C. An immediate exothermic reaction occurs upon contact of the water with the concentrate, sodium chloride, and sodium persulfate, with the emission of gases, reaching in some cases a temperature sufficient for the thermal activation of the persulfate to occur in micro reaction cells.

[0069] However, the thermal activation of persulfate is not the sole cause of the method's reactivity. Concentrate pretreatments in NaCl-H2SO4 methods alone showed improvements in copper dissolution, so the reactivity of this new Na2S20s-NaCl-H2SO4 method should be considered as the independent effect of each reagent on the concentrate, as well as a synergistic effect between them, further enhanced by favorable temperature conditions.

[0070] Although the copper solutions in pretreatments at 25°C were lower than at 60°C, 48% dissolved copper (in pretreatments with 330 kg / tc Na2S20s) is still an important figure and demonstrates the oxidative capacity of the method even without the thermal activation of the persulfate.

[0071] In the present embodiment of the invention, these reagents were combined in a single pretreatment, with 330 kg / tc of Na2S2O8 and 65 kg / tc of NaCl, at 25°C it dissolved 48% of the copper (A1) and at 60°C 69% of the copper (AT) (FIG. 2).

[0072] From the above, a synergistic effect can be seen when combining the reagents Na2S20s and NaCl in a pretreatment of copper concentrate in an acidic medium, presenting higher copper dissolutions both at room temperature and at 60°C.

[0073] Comparing the best results by persulfate concentration, A3' and B3' (FIG. 2) yielded copper solutions of 71% and 67%, respectively. Based on this, the best combination of sodium chloride and acid for treating the concentrate was determined to be 100 kg / t of NaCl and 40 kg / t of H2SO4.

[0074] Comparing samples A0 and A1, both treated with equal reagent dosages at 25°C, copper dissolutions of 48% were obtained. A0 was left to stand for 10 days without humidity control and then dissolved in water for 10 minutes, while A1 was left to stand for 6 days with humidity control and then dissolved in acid with H2SO4 at pH 1.8 for 10 minutes. These results indicate that in the 25°C treatments, copper solubilization from the pretreatment transformations is primarily limited by the reagent dosage and temperature. From the sixth day onward, additional treatment days did not improve copper dissolution, nor did humidity control. Evaporation losses within the treatment period at 25°C were negligible.Furthermore, using an acidic solution to dissolve the pretreated concentrate at 25°C did not improve the copper dissolution compared to dissolution with water, showing that the copper species formed during pretreatment at 25°C are soluble in water.

[0075] While humidity control is not influential in pretreatments at 25°C, this is not the case in pretreatments at 60°C, where, logically, evaporation losses are greater. Humidity control in pretreatments at 60°C is key for this constantly evolving method, as it transforms the morphology of the concentrate, making it apparently more porous, less dense, and more hygroscopic. It was observed that, over time, the initial amount of water, defined as the constant moisture percentage of the concentrate to maintain hydration in the method, was insufficient, resulting in a heterogeneous distribution of the added water.

[0076] Water dosage and humidity control could even be the method's limitations at some point. Meanwhile, the solubilized iron remained low in all tests performed, both at room temperature and at 60°C, hovering around 1% dissolved iron at 60°C regardless of the salt and acid dosage. This low iron dissolution in the treatments could indicate that the iron species formed during pretreatment are thermodynamically stable under acidic dissolution conditions with H₂SO₄ at pH 1.8, and / or have a very low solubility product constant (Ksp), as is generally the case with iron sulfides. Therefore, these species would not enter aqueous solution, at least not within the 10 minutes of dissolution at 25°C.

[0077] In order to compare the preliminary results obtained (FIG. 2), with the previous experimental results, presented above (Osorio Henriquez KY. Study of pretreatment in a chalcopyrite concentrate using sodium chloride and sodium persulfate in acidic medium. Graduation work to obtain the Title of Execution Engineer in Metallurgy. University of Santiago de Chile. 2023. Document reserved by USACH), Table 4 is presented, where the conditions of each pretreatment and their respective iron and copper solutions are shown.

[0078] Table 4. Comparison of results for each pretreatment and their respective iron and copper solutions Analyzing the copper solutions obtained, with respect to the concentrate pretreatments with Na2S20s - NaCl - H2SO4 carried out previously (Osorio Henriquez KY. Study of pretreatment in a chalcopyrite concentrate using sodium chloride and sodium persulfate in acidic medium. Graduation work to obtain the Title of Execution Engineer in Metallurgy. University of Santiago de Chile. 2023, Document reserved by USACH), in the first instance the dosage of persulfate was reduced by 50% (samples A) and 75% (samples B), keeping the dosage of the other reagents constant.

[0079] Of the treatments at 60°C, comparing OT with AT (Table 4), it was found that by decreasing the persulfate dosage by 50%, and extending the resting time by two days, the copper dissolution only drops by 5%. While by decreasing the persulfate by 75% (OT - BT), with two more days of treatment, the copper dissolution drops by 19%, however, this drop can be partially compensated for with a higher dosage of sodium chloride.

[0080] Comparing OT (Table 4) with B3' (FIG. 2), it can be deduced that it is possible to decrease the dosage of persulfate by 75%, increasing the sodium chloride by 54%, and obtain a copper solution only 7% lower.

[0081] Based on the concentrate pretreatment tests using the Na2S20s-NaCl-H2SO4 method, it can be concluded that the treatment is most effective at 60°C, the optimal combination of NaCl and H2SO4 for the treatment is 100 kg / tc and 40 kg / tc respectively, and it is also possible to reduce the Na2S20s dosage by 75% compared to the previous study (Osorio Henriquez KY. Pretreatment study in a chalcopyrite concentrate using sodium chloride and sodium persulfate in acidic medium. Undergraduate thesis to obtain the title of Metallurgical Engineer. University of Santiago, Chile. 2023, Document reserved by USACH) from 661 to 170 kg / tc, compensating with an extra 54% of NaCl (from 65 to 100 kg / tc), and the copper dissolution is only 7% lower (from 74% to 67%).

[0082] Example 2. Persulfate dosage

[0083] From the preliminary tests at 60°C, similar copper and iron solutions were obtained in the treatments with 170 and 330 kg / tc of Na2S20s, so it was proposed to further decrease the dosage of persulfate, setting the sodium chloride and acid concentrations according to the best results obtained in the preliminary stage, that is, 100 kg / tc of NaCl and 40 kg / tc of H2SO4.

[0084] Four treatments were carried out with 0, 80, 120, and 250 kg / tc of Na2S20s, with a resting period of 6 days at 60°C, with a concentrate moisture content of 18%, and subsequent dissolution with an acidic solution pH 1.8 for 10 minutes (same dissolution conditions as preliminary tests). Table 5 characterizes the samples processed in this stage.

[0085] Table 5. Characterization of samples for persulfate dosage tests

[0086] Sample C1 C2 C3 C4

[0087] Na2S2O8[kg / tc] 0 80 120 250

[0088] NaCI [kg / tc] 100 100 100 100

[0089] H2SO4[kg / tc] 40 40 40 40

[0090] Humidity [%] 18 18 18 18

[0091] Temperature [°C] 60 60 60 60

[0092] Time [days] 6 6 6 6

[0093] Figures 3 and 4 show the effect of persulfate reagent dosage in the treatment on the dissolution of copper and iron respectively.

[0094] Figure 3 shows a clear upward trend in copper dissolution from concentrates pretreated with higher dosages of Na₂S₂Os, reaching a maximum of 71% solubilized copper in pretreatments with 250 to 330 kg / t of persulfate. With a pretreatment without persulfate, a copper dissolution of 24% is obtained, attributable to the effect of NaCl and H₂SO₄. As mentioned previously, sodium chloride can react with sulfuric acid to generate hydrochloric acid gas in situ, which, in addition to being highly corrosive, diffuses through the concentrate particles, promoting the formation of cracks and micropores, and facilitating the infiltration of oxidizing agents into the concentrate particles. Furthermore, at temperatures above 50°C, sodium sulfate is generated according to the reaction that could settle on the surface of the mineral, thus reducing the formation of elemental sulfur on the surface and mitigating the passivation of chalcopyrite.Then, by adding Na2S20s to the pretreatment, in addition to its already mentioned oxidative capacity on the method, a synergistic effect between persulfate and sodium chloride on the surface of the mineral could be considered when it comes into contact with water, evidenced by the aforementioned initial exothermic reaction when hydrating the method.

[0095] Figure 3 shows that with a dosage of 120 kg / tc of Na2S20s, a copper dissolution of 66% was obtained, only 5% less than the maximum copper dissolution obtained with 250 kg / tc of Na2S20s. Based on these results, this persulfate dosage was established for subsequent treatments.

[0096] From FIG. 4, a very low tendency to form soluble iron species was observed in pretreatments with Na2S20s - NaCl - H2SO4, with a rest of 6 days at 60°C, reaching a maximum iron dissolution of approximately 1% in pretreatments with 120 to 330 kg / tc of persulfate, and a base dissolution of 0.5% in pretreatments without sodium persulfate.

[0097] This showed that in pretreatments of chalcopyrite concentrate (28.5% Fe) with NaCl and H2SO4 with 6 days of rest at 60°C, iron tends to remain stable in solid state, without entering into solution at least in solutions acidified with H2SO4 at pH 1.8 for 10 minutes with agitation, from where only 0.5% of the iron dissolved.

[0098] The above opened up two possibilities: one option could be that the iron does not react at all, or the iron could react and transform into highly stable species under the solution conditions studied.

[0099] Figure 4 shows that adding Na₂S₂Os to the 6-day pretreatment at 60°C resulted in a slight tendency to dissolve an additional 0.5% of iron. This could be directly attributed to the oxidative effect of persulfate or to a synergistic effect between the reagents. While this 1% of dissolved iron is low compared to the copper dissolutions in the same pretreatment (Figure 3), this difference could be partly due to the reaction of the bornite present in the concentrate (11%). Given that bornite has a copper-to-iron mass ratio of 5:1 and is less refractory than chalcopyrite, it could have reacted preferentially, releasing a greater amount of copper relative to iron. However, this difference is not sufficient to explain the low iron dissolution obtained compared to copper.On the other hand, a galvanic couple is likely occurring between the chalcopyrite and pyrite, where the chalcopyrite is dissolving more rapidly, protecting the pyrite from releasing iron into the sample. Furthermore, the possibility should be considered that, during the days of incubation at 60°C, with periods of overhydration, some iron may have solubilized and subsequently precipitated, for example, as jarosite or other thermodynamically stable iron precipitates under the imposed dissolution conditions. Alternatively, the iron compounds formed may have low solubility and not readily dissolve (iron sulfides are known to have low Ksp).

[0100] Example 3. Days of treatment

[0101] Based on the results obtained previously, the reagent dosages for the pretreatment were defined (Na2S20s 120 kg / tc, NaCl 100 kg / tc, H2SO4 40 kg / tc). In this stage, nine pretreatments were carried out under identical conditions with different resting periods at 60°C, followed by dissolution for 1 hour with sampling at 10, 30, and 60 minutes, in order to study the dissolution behavior of the species with longer agitation times.

[0102] Figures 5 and 6 show the copper and iron solutions respectively, with respect to the days of treatment.

[0103] Figure 5 shows the increase in copper dissolution during the first three days of treatment. The copper dissolution rate was 34% on the first day, 17% on the second, and 15% on the third, reaching 66% dissolution after 30 and 60 minutes. After the third day, copper dissolution increased slightly at a rate of approximately 1%, maintaining a copper dissolution close to 70% by the seventh day of treatment. The maximum copper dissolution, 76%, was obtained on the ninth day of treatment. The dissolution time showed that the copper species formed during pretreatment dissolved rapidly after 10 minutes. After 30 minutes of dissolution, an average of 4% more copper dissolved, and between 30 and 60 minutes, an additional 1% more copper dissolved.This could indicate that the copper solubilized during pretreatment would have good solubility in an acidified medium at pH 1.8 with H2SO4, at 25°C, while the remaining copper could be found forming stable compounds under the working conditions or passivated by reaction products.

[0104] Figure 5 clearly shows the increase in copper dissolution on the first day of pretreatment at 60°C, reaching -35% dissolved copper. The method evolved over several days, even in the first few hours, in terms of evaporation and gas emissions, morphological transformations, and apparent moisture content of the pretreated concentrate, becoming more hygroscopic as the days passed. In the first hours of treatment, the concentrate has a higher apparent moisture content, exhibiting qualitative characteristics more similar to those of a pulp. Under these conditions of high initial moisture, solid-liquid reactions similar to leaching could occur, such as the direct oxidation of chalcopyrite by the persulfate anion, releasing copper and ionic iron into the medium. This could happen in micro-leach heaps and thus partially explain the method's ability to dissolve copper on the first day of standing at 60°C.

[0105] Additionally, the effect of sodium chloride and sulfuric acid present in the method must be considered, since, on the one hand, under high humidity conditions, chlorine could dissolve and stabilize the cupric ion, forming complexes that could then act as oxidants of chalcopyrite. Furthermore, these reagents could react with each other, generating highly corrosive gaseous HCl, which readily diffuses through the concentrate particles, promoting the formation of cracks and micropores and facilitating the penetration of oxidizing agents to the mineral surface.

[0106] Furthermore, above 50°C, the formation of sodium sulfate is promoted, which could settle on the mineral surface, reducing the formation of elemental sulfur and passivating the mineral. In addition to the effects produced by each reagent individually, the synergistic effect between NaCl and Na₂S₂Os must be considered. As previously mentioned, upon contact with the concentrate and water, an immediate exothermic reaction occurs, which could be gradually related over time to the rapid copper dissolution from the first day of treatment to the third day, compared to the copper dissolution rate from the third day onward. The trend of the curves in Figure 5 could be due to the effect of the initial exothermic reaction and the effect of the reagents described in an initial stage of high hydration, each acting both individually and synergistically.Also occurring on the same day are solid-solid reactions between the concentrate and the dehydrated reagents, which could morphologically transform the concentrate, helping to prevent mineral passivation. This is followed by a nighttime overhydration stage, during which solid-liquid reactions could again become relevant. This behavior could be responsible for the high copper dissolution rate up to the third day, by which time a morphologically different concentrate is observed, becoming more porous, qualitatively less dense, and more hygroscopic.From the third day onwards, it is evident that the copper dissolution rate decreases, possibly due to the depletion of reagents, passivation of particles, or the limiting factor could be the humidity of the treatment, since as the days go by, the concentrate appears qualitatively drier (adding the necessary water to maintain the same initial humidity percentage), leaving areas that may not be reacting due to lack of humidity.

[0107] Meanwhile, the solubilized iron was low compared to the copper dissolution levels achieved in the pretreatment. Figure 6 shows that the maximum iron dissolution was approximately 6%, obtained with a one-day pretreatment and dissolution times of 30 and 60 minutes.

[0108] The iron solubilization trend then decreased, falling to 1% dissolved iron on the second day of treatment and remaining stable until the tenth day. Iron dissolution barely increased with longer dissolution times, reaching an additional 0.3% dissolved iron from 10 to 30 minutes of dissolution, and another approximately 0.3% from 30 to 60 minutes. These results suggest that the low iron dissolution after pretreatment may not be due to a solubility (Ksp) issue of the formed species, since dissolved iron barely increases with longer dissolution times. However, these results could indicate that the iron species formed during pretreatment are highly stable under the dissolution conditions used (acidic solution, pH 1.8) and do not dissolve.The possibility that at some point during the dissolution the iron was in solution and then precipitated was ruled out, since the pH was kept controlled at 1.8, a range in which iron is stable in its ionic form.

[0109] Figure 6 shows that the highest iron dissolution was evident on the first day of treatment compared to subsequent days, with a difference of approximately 5% dissolved iron. The higher iron dissolution on the first day could be related to the exothermic reaction during the initial hydration stage of the method, where the pyrite present in the concentrate (21.6%) might be reacting with the persulfate and sodium chloride in solid-solid reactions in the presence of moisture, releasing iron into the process. The decrease in iron dissolution on the second day could be related to the dehydration stages, where the iron might have precipitated, for example, in jarosite or formed other iron compounds that are thermodynamically more stable under the dissolution conditions used.One of the possible reasons why the iron remains low from the second day onwards could be due to micro-battery reactions that would be forming thermodynamically more stable compounds under the pretreatment conditions.

[0110] According to the evidence presented in Figures 5 and 6, during the treatment period, thermodynamically more stable compounds could be forming under the given conditions, which would apparently remain in solid form, making up the transformed concentrate. These compounds could be high in iron and sulfur, and may even contain chlorine, non-stoichiometric chalcopyrites with a significant copper deficiency, mixed with passivated mineral particles.

[0111] Example 4. Temperature profile at initial hydration of the treatment

[0112] To demonstrate the initial exothermic reaction upon contact of the concentrate with sodium persulfate, sodium chloride and water, whose cause and effect is still unknown, the temperature was recorded during the initial hydration process of the treatments, which included three doses of water and subsequent dosage of sulfuric acid.

[0113] Figure 7 shows the temperature profiles for the pretreatments performed, C1, C2, C3, and C4, with 0, 80, 120, and 250 kg / t of Na2S20s respectively, and 100 kg / t of NaCl each. In each case, three data labels are shown, representing the start of a dosage. That is, from the beginning until the first label, the first water dosage and homogenization of the method occurs; then the second water dosage and homogenization begin; from the second label onward, the third water dosage begins; and finally, the third label represents the acid dosage.

[0114] Figure 7 shows the reactivity of the method, specifically between the concentrate, NaCl, and Na₂S₂Os, upon contact with water, reacting exothermically. The temperature profile of C1, the treatment without Na₂S₂Os and with 100 kg / tc of NaCl, shows that the temperature remains constant at around 20°C throughout the water dosing, indicating that no exothermic reaction occurs in the absence of Na₂S₂Os. Upon adding H₂SO₄, a temperature increase to approximately 35°C is observed, immediately accompanied by bubbling and visible gas release, which could be related to the formation of gaseous HCl and possible physical entrainment of H₂SO₄.In the temperature profiles of C2, C3, and C4, treatments with 80, 120, and 250 kg / t of Na₂S₂Os respectively and 100 kg / t of NaCl, it was observed that upon adding the first dose of water, an exothermic reaction immediately occurred. The effect of this reaction was proportional to the amount of persulfate added, reaching temperatures of 30°C, 40°C, and 70°C in the treatments with 80, 120, and 250 kg / t of Na₂S₂Os respectively. The reaction was immediate, reaching its maximum temperature within the first minute of contact with water. The temperature then tended to decrease during homogenization, but the reaction resumed with the second and third doses of water, reaching progressively lower temperatures. This reaction is accompanied by the release of gases perceptible to the smell, apparently gases containing sulfur, perhaps chlorine, or possibly a mixture of them; this effect is also proportional to the amount of persulfate.The addition of sulfuric acid in all cases generates an exothermic reaction that raises the temperature by approximately 10 to 15°C, but this effect is negligible in treatments with higher quantities of persulfate. It is important to note that this reaction only occurs in the presence of these four compounds: concentrated persulfate, sodium persulfate, sodium chloride, and water. The reaction does not occur in the absence of any of them. The reaction mechanism and its effects are still unknown, but the release of heat energy and the emission of gases with a distinct sulfur odor, possibly associated with chloride species, have been observed.

[0115] Example 5. Concentrate mass losses in the treatments

[0116] The mass loss of the concentrate was quantified in each pretreatment after dissolution. Figure 8 shows the mass loss of the pretreatments performed, as a function of the persulfate dosage.

[0117] Table 6 shows the mass losses of the tailings in the pretreatments according to the Na2S20s dosage. It also shows the percentage of dissolved copper and iron relative to the initial mass of concentrate.

[0118] Table 6. Mass losses in concentrate pretreatments, according to sodium persulfate dosage. Percentages with respect to the initial mass of concentrate.

[0119] Na2S20s dosage [kg / tc] 0 80 120 250

[0120] Loss of gravel mass 4.74% 1 1.65% 16.22% 16.37%

[0121] Copper loss in solution 6.30% 14.89% 17.55% 19.14%

[0122] Fe loss in solution 0.13% 0.20% 0.30% 0.30%

[0123] Regarding mass losses in concentrate pretreatments using the Na₂S₂O₃-NaCl-H₂SO₄ method, Figure 8 shows a clear trend toward mass loss in concentrate pretreatments with persulfate. Without persulfate, the total mass loss after dissolution is only 5% of the initial concentrate mass, and the dissolved copper represents 6% of the initial concentrate mass (Table 6). In other words, the dissolved copper practically accounts for the entire mass of concentrate lost during pretreatment. With the addition of persulfate, mass losses increase, reaching 15% in pretreatments with 120 kg / t of persulfate, where the dissolved copper represents 18% of the initial concentrate mass (Table 6).With higher persulfate dosages, mass losses remain practically constant, reaching 17% mass loss in pretreatments with 330 kg / t of persulfate, with dissolved copper representing 19% of the initial concentrate mass (Table 6). In all cases, dissolved copper accounts for virtually all of the mass loss during pretreatment. Although the mass of dissolved copper is greater than the mass loss relative to the initial concentrate in all pretreatments, this 2% to 4% mass difference can be attributed to experimental errors, or simply to the fact that some reagent mass remains in the tailings even after dissolution.

[0124] The mass losses presented in Table 6 could support the aforementioned transformation of the concentrate into thermodynamically stable species under the given conditions, apparently high in iron, sulfur, along with chlorine compounds, and sodium, mixed with unreacted concentrate particles, since according to the balance in Table 4, practically all the mass of concentrate lost in the treatment is equivalent to the mass of dissolved copper, this would indicate that the iron, sulfur, chlorine and sodium would be part of the tailings, according to the balance they would not be in solution, so the product of the dissolution would be a concentrated copper solution with a very low amount of iron.

[0125] Example 6. Evolution of the concentrate during pretreatment

[0126] The evolutionary behavior of the concentrate over the treatment period has been previously mentioned. To illustrate this behavior, Figures 9 and 10 present a series of photographic records of the concentrate during the pretreatment. Specifically, the treatments carried out with different dosages of persulfate are shown: C1 (0 kg / tc), C2 (80 kg / tc), C3 (120 kg / tc), and C4 (250 kg / tc), for 6 days at 60°C, with a concentrate moisture content of 18%.

[0127] Figure 9 shows samples C1, C2, C3, and C4 at the beginning of the pretreatment, before entering the oven to undergo temperature.

[0128] Figure 9 shows a tendency for the method to start with a slightly wetter consistency as the amount of persulfate added decreases. When dosing the same amount of water, defined from a constant concentrate moisture content, C1 (without Na2S20s) exhibits pulp-like characteristics, while C4 (with 250 kg / tc of Na2S20s) initially appears less wet, even forming clumps. This could be partly due to the hygroscopic properties of the salts. Based on this observation, the concentrate moisture content was reduced from 20% to 18% in the preliminary tests for the 60°C treatments, as conditions favoring solid-solid reactions were sought. With less persulfate, the samples initially exhibit pulp-like characteristics.

[0129] FIG. 10 shows the evolution of sample C3 at the beginning of the second day (C3 2.0), third day (C3 3.0), fourth day (C3 4.0) and end of the sixth day (C3 6.0) of treatment at 60°C.

[0130] Figure 10 shows the evolution of the concentrate during the days of treatment at 60°C. It should be noted that this photographic record corresponds to the first moment of the day observed, and it should be considered that the sample was overhydrated the previous day to compensate for the losses due to evaporation during the night period, and at this point the sample is already in a dehydration stage.

[0131] From the first day, a surface layer with a distinct color forms, which could be related to the formation of more soluble copper-associated species. This surface layer is observed in the record from the second day of treatment (C3 2.0 in FIG. 10). At this point, beneath the surface layer, the sample still has a graphite color characteristic of the concentrate (similar to C3 1.0 in FIG. 9), but with a more pasty texture. The fact that the layer is only superficial suggests that its formation could be due to the action of oxygen; furthermore, this surface layer apparently dissolves upon contact with water.

[0132] On the third day (C3 3.0), as shown in Figure 10, the change in the morphology of the concentrate is noticeable, exhibiting a more porous, less dense structure with a greater capacity to absorb water. The formation of reaction products similar to the previously mentioned surface layer, but less intense, can be observed on the surface of the glomeruli. On the fourth day, the evolution of the method continues, showing less density and more hygroscopicity. When the samples are hydrated (maintaining the same initial moisture content of the concentrate), the water distribution is no longer uniform, likely leaving unreacted areas due to a lack of a moist environment. On the sixth day of treatment (C3 6.0), the sample has just undergone a two-day period of overhydration followed by dehydration in the final hours. At this point, some of the drawbacks of overhydrating the method for extended periods without homogenization become apparent.With excessive hydration the method acquires characteristics of a pulp; without homogenization the particles will settle and when the method has dehydrated it will be a compact, low porosity and hardened method.

[0133] Based on the aforementioned observations, it is clear that humidity control and homogenization are highly relevant factors for optimizing pretreatment, ensuring a conductive humid environment favorable for transformation reactions and proper aeration that apparently favors copper solubilization.

[0134] Example 7. Study for the optimization of pretreatment.

[0135] Studies were conducted to optimize the pretreatment, which include pretreatment with subsequent leaching and, on the other hand, a double pretreatment.

[0136] Pretreatment and subsequent leaching

[0137] Figures 11 and 12 show the copper and iron solutions, respectively, from a pretreated mineral concentrate according to the preferred embodiment of the invention. This involves treating the concentrate with 120 kg / t of persulfate, 100 kg / t of NaCl, and 40 kg / t of acid at 60°C for 6 days. Leaching is then carried out with a leaching solution containing 60 g / L of persulfate anion, acidified with sulfuric acid to pH 1.8 for 70 hours at 25°C.

[0138] Figure 1 shows that the maximum copper dissolution achieved in the leaching of the pretreated concentrate is 70%, obtained after 40 hours of agitation and remaining stable until 70 hours, compared to the copper dissolved at 10 and 30 minutes, which were 64% and 67%, respectively. Considering that in previous pretreatments (under the same conditions), with dissolutions of 10, 30, and 60 minutes, copper dissolutions of 65%, 68%, and 69% were obtained, respectively, the effect of this leaching condition on the copper dissolution after pretreatment could be considered minimal, contributing only about 2% extra copper from the third hour of leaching onward. This low extra copper dissolution obtained by leaching could be due to the remaining copper being passivated, or perhaps the copper is thermodynamically stable under the leaching conditions used.Leaching was carried out at 25°C, and probably, higher copper recoveries would be obtained by leaching at higher temperatures, especially above 50°C where thermal activation of the persulfate would occur (Acevedo, P. Study of copper and iron dissolution from a concentrate in acidic medium using sodium persulfate as an oxidizing agent. Undergraduate thesis for a degree in Metallurgy. University of Santiago de Chile, Santiago. 2022).

[0139] Iron, for its part, showed a clear tendency to dissolve under the leaching conditions following pretreatment, reaching a maximum iron dissolution of approximately 37% after 70 hours of leaching. It is worth noting that in previous pretreatments (under the same conditions) with dissolution times of 10, 30, and 60 minutes, the respective iron dissolutions were approximately 0.4%, 0.7%, and 0.9%, while under leaching conditions, 0.8% of the iron dissolved after 10 minutes of agitation, and approximately 4% dissolved after 3 hours.

[0140] The behavior of the iron could be due to the oxidizing conditions of the leaching process releasing iron from the transformed concentrate. Additionally, the presence of pyrite could be reacting. The dissolution of some iron precipitates that may have formed during pretreatment could also be considered. It is believed that a higher leaching temperature could improve the iron dissolution kinetics.

[0141] double pretreatment of the concentrate

[0142] Two double pretreatments were performed, one continuous and the other with a 30-day delay, to verify if there was any change in the dissolving behavior of copper with respect to the drying time between pretreatments. In both cases, the first and second pretreatments were carried out under the conditions of the preferred embodiment of the invention. That is, with 120 kg / t of persulfate, 100 kg / t of NaCl, and 40 kg / t of acid, at 60°C for 6 days. Figures 13 and 14 show the copper and iron solutions for the continuous and split pretreatments, respectively. For the split double pretreatment, the tailings from sample C3, which were treated under the same conditions (Table 5), were used, and after 30 days, a second pretreatment, identical to the first, was performed.

[0143] Figures 13 and 14 show that, in both the continuous and the cut-off pretreatments, the copper solutions were of equal magnitude, 66% copper dissolved in the first pretreatment, and 39% in the second, resulting in a total dissolution of 79% of the copper with two pretreatments.

[0144] Iron dissolutions show slight differences between continuous and batch treatments, but in both cases, the dissolved iron content remains low, around 2%, after two pretreatments. This suggests that, once the tailings are washed and dried after dissolution, no further reactions occur that promote the dissolution of copper or iron during the resting period (at least 30 days) between pretreatments.

[0145] Example 8. Pretreatment with hydrochloric acid

[0146] The concentrate was pretreated with Na₂S₂O₈-NaCl-HCl. Sulfuric acid was replaced with hydrochloric acid, adding the same quantity (40 kg / tc), at 60°C for 4 days of standing, in order to explore the dissolving behavior of copper in a much more corrosive acidic medium such as HCl compared to H₂SO₄. For comparison, another pretreatment was carried out with both acids, 20 kg / tc of each under the same conditions. Table 7 shows the copper solutions obtained from the pretreatments and after 30 minutes of dissolution in an acidified solution at pH 1.8 with HCl.

[0147] Table 7. Copper solutions in pretreatment with HCI and mixed HCI with H2SO4

[0148] HCl + H2SO4

[0149] Copper solution 70% 66%

[0150] The treatments with HCl resulted in a 5% increase in copper dissolution compared to the treatments with H₂SO₄, and required two fewer days of treatment at 60°C. This positive effect on copper dissolution compared to sulfuric acid could be due to the greater corrosive power of hydrochloric acid. It may even be further modifying the morphology of the concentrate through the formation of gaseous HCl between the concentrate particles, promoting the formation of cracks and micropores. Furthermore, mixing the acids in the treatment process accelerates copper solubilization compared to treatment with H₂SO₄ alone, yielding similar solutions but with two fewer days of treatment. Although the same mass ratio of hydrochloric acid to sulfuric acid was used in the previous treatments, the HCl has a considerably lower purity (34%), so theoretically, the effective mass of HCl used was less than the mass of H₂SO₄.

[0151] Projecting the pretreatment process to an industrial level, the conditions in a chlorinated medium could be compatible with the use of seawater in the treatment, thus encouraging its use over freshwater. Alternatively, the waste salts produced during seawater desalination could be used if solid-solid reactions are preferred in the pretreatment.

[0152] Based on the studies conducted, it was possible to design a preferred embodiment of the invention that reduced the Na2S20s dosage by 82%, compensating with an additional 54% of NaCl. This resulted in a copper solution only 9% lower than the pretreatment method using 661 kg Na2S20s / tc, 65 kg NaCl / tc, 40 kg H2SC / tc, 20% humidity, at 60°C with 4 days of resting.

Claims

CLAIMS 1. A method for extracting metals from copper sulfide mineral concentrates, the method comprising the steps of: a) providing a mass of primary copper sulfide mineral concentrate with its natural moisture; b) adding to the mass of copper sulfide mineral concentrate a mixture of sodium persulfate and sodium chloride salts in the following mass ratios: between 80 and 330 kg of sodium persulfate / ton of concentrate and between 65 and 100 kg of sodium chloride / ton of concentrate; c) gradually adding water to the concentrate being pretreated with the salt mixture to moisten it; d) adding acid in a mass ratio of between 30 and 60 kg / ton of concentrate; e) diluting the pretreated concentrate with water; and f) separating the copper-concentrated solution from the solid material, which retains the iron.

2. The method of claim 1, CHARACTERIZED in that water is added to the concentrate being pretreated until a moisture content of between 10 and 25% is reached with respect to the concentrate with its natural moisture content.

3. The method of claim 1 or 2, CHARACTERIZED in that the water added is selected from fresh water and seawater.

4. The method of claim 1, CHARACTERIZED in that the acid is selected from the group consisting of sulfuric acid, hydrochloric acid or a mixture thereof.

5. The method of claim 1, CHARACTERIZED in that the pretreated concentrate is subjected to heat at a temperature between 25 and 75°C for 5 to 7 days, ensuring that the moisture content is maintained between 10 and 25%.

6. The method of claim 4, CHARACTERIZED in that the pretreated concentrate is subjected to heat at a temperature between 55 and 75°C.

7. The method of claim 5, CHARACTERIZED in that the pretreated concentrate is heated to a temperature of 60°C.

8. The method of claim 1, CHARACTERIZED in that the concentrate is diluted at room temperature in a ratio of approximately 30:1 mass of water / mass of concentrate, for 10 to 60 minutes and at a pH between 1.0 and 2.

2.

9. The method of any of claims 1 to 7, CHARACTERIZED in that the copper sulfide mineral concentrate is selected from primary and secondary copper sulfide mineral concentrates.

10. The method of claim 8, CHARACTERIZED in that it is a chalcopyrite concentrate.

Images