Heap leaching process with semi -autogenous heating

Abstract

Heap leaching process in chloride environments that uses chemical reactions and minimizes heat losses with the aim of achieving an operating temperature for the leaching of primary and secondary sulfides in ranges from 30°C to 40°C. The process includes semi-autogenous heating of leach heaps, from an initial saline-acid curing with hot brine and subsequent resting of the ore where the temperature increases as a result of the exothermic reactions, followed by thermal activation and subsequent intermittent irrigation, ending with chemical leaching. The combined effect of operating in temperature ranges higher than the ambient condition together with solutions concentrated in chloride ion allow significant improvement in the extraction kinetics of primary and secondary copper sulfides.

Description

[0001] PRO CE SO DE LIXIVIA CI ÓN DE MINERALE S EN PILA CON N CALEN TAMIENTS OS EMI -A UT Ó GENO

[0002] CRYPTIVE MEMORY

[0003] THE PREVIOUS RTE

[0004] Chloride leaching processes are currently used for the hydrometallurgical treatment of sulfide minerals. Leaching of oxidized copper minerals involves extracting copper ions from the mineral by stockpiling the crushed material to a desired size and then agglomerating it to form a leach pad. Finally, the pad is irrigated with acid solutions to obtain a copper-laden solution (PLS). This solution, in subsequent concentration and purification stages, is subjected to solvent extraction (SX) and electrowinning (EW). However, leaching is not simple in the case of sulfide minerals, since the dissolution times are longer.Various phenomena that could lead to the lethargy of copper dissolution in the sulfide state when leached have been studied, involving multiple variables, such as the particle size of the heap material, the shape and time of agglomeration, the redox potential and acidity, among others.

[0005] Significant levels of copper recovery have been achieved in prior art chloride leaching processes, ranging from 65% to 80%, in which copper sulfides are essentially transformed into more soluble compounds.

[0006] One of the widely used processes in the mining world is the process known as “Cuprochlor” ® from the Antofagasta Minerals company, which is a process for leaching primary sulfides with recoveries of up to 70%.This process contemplates the addition in the agglomeration stage of a first solution containing calcium ion, in a proportion of 1 to 10 kilos of calcium ion per ton of mineral, in concentrations between 10 and 200 grams of calcium ion per liter of solution; b) in the agglomeration stage, a second solution containing sulfate ion is added, in a proportion of 5 to 60 kilos of sulfate ion per ton of mineral, in concentrations of 150 to 1800 grams of sulfate ion per liter of solution; c) the final agglomerate has a water content between 35 and 130 kilos of water per ton of mineral; d) in the agglomeration stage, a stream of water is added when the combination of the first and second solutions does not comply with the range of point c).

[0007] Patent application CL 201701589 describes a method for recovering one or more copper, uranium, and precious metal minerals from a mineral material, characterized in that it includes: (a) forming a pile of the mineral material; (b) during irrigation of the active pile, contacting the mineral material pile with an acidified leaching liquid containing high chloride iron in the presence of an oxygen-containing gas, producing a charged leaching solution; and (c) recovering one or more copper, uranium, and precious metal elements from the charged leaching solution; wherein the solution potential of the leaching liquid exceeds 450 mv Ag / AgCl; the total iron concentration of the leaching liquid is greater than 0.1 g / l and the chloride ion concentration of the leaching liquid is between 20 and 230 g / l.

[0008] Patent registration CL 63,104 teaches a method of leaching copper from a heap of crushed chalcopyrite ore or chalcopyrite mixed with refractory oxide minerals or secondary sulfide minerals such as chalcosite, covellite, enargite and bomite which is irrigated with a leaching solution including at least a resting stage followed by an irrigation stage, wherein during the irrigation stage a leaching solution containing chloride ions is applied to the ore at a higher rate than during the resting stage, and during the irrigation stage the chloride ion concentration of the leaching solution is between 100 grams per liter and 190 grams per liter, and wherein the resting stage has a duration of 20 hours to 50 days in order to increase the dissolution of the mineral.

[0009] The present application differs from the prior art mainly due to the fact that a semi-autogenous heating of the heap is carried out, which is subjected to leaching from an initial saline-acid curing with hot brine and a subsequent resting of the mineral in which the temperature increases as a result of the exothermic reactions of the mineral, then follows a stage of thermal activation, a subsequent stage of irrigation with intermittence ending with a chemical leaching.

[0010] The combined effect of operating at temperature ranges higher than ambient conditions, together with concentrated chloride ion solutions, allows for a significant improvement in the extraction kinetics of primary and secondary sulfides.

[0011] In addition, the operating ranges of the process stages allow for improved copper recovery from the mineral, where: • The process applies to both copper sulfide minerals and mixed or mixtures of oxides and sulfides.

[0012] • Salt dosage in curing between 0 and 18 kg / t.

[0013] • Acid dosage in curing between 0 and 12 kg / t

[0014] • Cured mineral humidity between 6 and 8%

[0015] • Average operating temperature between 30° and 40° C.

[0016] • For saline-acid curing, aqueous solutions containing chloride ion are used.

[0017] • Generation of a pseudo-adiabatic system that minimizes heat loss with the environment (ground and air).

[0018] BRIEF DESCRIPTION OF THE FIGURES

[0019] Figures 1 and 2 correspond to graphs showing the recovery of copper according to the process of the present invention.

[0020] D ES C RIPTI ON OF THE INVENTION

[0021] The invention involves a heap leaching process for minerals in chlorinated environments that utilizes chemical reactions and minimizes heat loss. This process achieves semi-autogenous heating of leaching heaps with low external heat input. The process includes the following stages:

[0022] Salt-acid curing of minerals: Curing is carried out with acidified brine, which allows for an initial increase in mineral temperature. The acidified brine is heated to temperatures ranging from 30°C to 60°C autogenously by adding concentrated acid to the brine in a stirred tank or mixing reactor.

[0023] Resting of the stacked ore: The stacked ore is kept at rest in an aerated pile covered with a plastic cover ("thermofilm") to promote exothermic reactions and the consequent increase in ore temperature to values ​​between 25° and 60° C at the end of the resting period. The final temperature reached will depend strongly on the copper grade of the ore to be processed. The ore in the pile is covered with thermofilm—on its surface and sides—or a layer of bischofite, or both, and / or similar elements to reduce heat losses due to radiation and evaporation.

[0024] Thermal Activation: Once the resting period is over, irrigation begins with leaching solutions at temperatures between 40°C and 60°C. This leaching cycle is characterized by irrigation cycles aimed at increasing temperature to maintain chemical reactions above the Activation Energy threshold. This irrigation is carried out continuously for a period of 15 to 30 days, with irrigation rates between 6 and 12 L / hm. 2 , preferably 20 days or up to a leaching ratio (volume of solution [m 3 ] which irrigates a unit mass of mineral [ton]) between 0.25 to 0.35 m 3 / ton (thermal activation stage). At this stage, the mineral must be covered with thermofilms or similar coverings to minimize heat loss.

[0025] Resting followed by irrigation at a low leaching rate: Once the target temperature is reached within the heap, a new resting stage begins, followed by irrigation. Resting strategies can be 10, 15, 20 to 25 days of rest, each alternating with irrigation stages of 2 to 5 days. The irrigation stages allow the copper that dissolves during the resting stages to be "collected." The alternating irrigation is carried out with low-temperature solutions (between 15 and 25 °C) to prevent cooling in the heap.

[0026] Chemical Leaching: It has been observed that during the standing-irrigation stage, given the long standing periods, the solutions may be deficient in sulfuric acid, generating a re-precipitation of Cu (possibly as copper hydroxides, copper oxysulfates and / or copper oxychlorides). The objective of this stage is to dissolve these re-precipitated copper compounds; this is carried out through an acid leaching stage, the objective of which is to dissolve compounds soluble in acidic environments.

[0027] The acid-saline mineral curing stage involves adding an acidified brine at a temperature between 30 and 60°C, applied either directly to the mineral on a conveyor belt or using agglomerating drums to mix the mineral and the hot brine. The brine is prepared by mixing salt (NaCl, KCl, MgCl, or any salt with high chloride ion concentrations), sulfuric acid, and process leaching solutions (PLS, ILS, Refining). Mixing is carried out in stirred dissolution tanks, where all feed streams are incorporated at ambient temperature. The heat of mixing of these elements allows a brine temperature between 40°C and 60°C to be reached. To prevent heat loss during the preparation of acid brine, thermally insulated preparation tanks and pipelines are used.

[0028] The mixing ratio of each of the reactants (salt, acid, and process solutions) is adjusted to achieve chloride ion concentrations ranging from 250 to 350 g / L and sulfuric acid concentrations ranging from 150 to 250 g / L. The acidified brine is mixed with the mineral to be leached to achieve a moisture content ranging from 6% to 8%. This mineral-brine mixture can be carried out on conveyor belts or in agglomerating drums.

[0029] The final mixture reaches temperatures between 25°C and 30°C, which is achieved without the addition of external heat.

[0030] The resting stage involves installing the irrigation system immediately after stacking the mineral, and covering the pile with thermofilm or a similar covering to preserve the mineral's temperature. The mineral is covered with thermofilm or a layer of bischofite, or both, or similar elements to reduce heat loss due to radiation and evaporation, and to promote the absorption of solar radiation. Throughout the resting period, aeration is provided with atmospheric air or oxygen-enriched air at temperatures between 40 and 70 °C. The temperature of this air is increased to reduce heat loss due to conduction between the pile and the ground and to create a pseudo-adiabatic barrier at the base of the mineral. This stage involves enriching the air to values ​​up to an OI:N2 ratio of 90:10.The amount of enrichment is selected depending on the grade of the feed ore and to favor the oxidation reactions of the primary and secondary sulfide minerals.

[0031] Under the conditions described, during the mineral resting stage, chemical reactions of sulfide minerals occur, allowing temperature increases to between 25° and 40°C. The temperature at the end of the process will depend on the copper grade and characteristics of the mineral being treated. The resting time varies between 20 and 60 days. No external heat is added during this stage.

[0032] The thermal activation stage involves starting irrigation with leaching solutions at a temperature between 35°C and 50°C once the resting stage is complete. This irrigation is carried out continuously for a period of 15 to 30 days, preferably 20 days, or until a leaching rate of between 0.25 and 0.35 m is reached. 3 / ton. At this stage the mineral must be covered by thermofilms or similar coverings.

[0033] Continuous irrigation, carried out with an ILS solution, an intermediate leaching solution that collects the solution produced by the partial leaching of copper from the ore in the leaching piles during the leaching cycle, ends when the average temperature of the heap reaches values ​​​​higher than 40°C, but lower than 50°C. The leaching of the mineral can consider an initial wetting ramp, prior to continuous irrigation. It also considers a strategy to minimize heat losses through the base of the heap, heating the air injected into the base. The irrigation solution must contain a concentration of between 10 and 25 g / L of sulfuric acid and a chloride ion concentration between 50 and 90 g / L.The main chemical reactions, in a simplified way, that would take place in the pile for the case of chalcopyrite, catalyzed by the combined effect of temperature and chloride concentrations, would be the following (for other sulfide species they are analogous):

[0034] CuFeS2+ 4Fe(III) Cu(II) + 5 Fe(II) + 2 S

[0035] CuFeS2+ 4Cu(II) Cu(I) + 5 Fe(II) + 2 S

[0036] The incorporation of air at temperature is considered with the objective of maintaining the semi-adiabatic system and incorporating oxygen to ensure the oxidation reactions of ferrous and cuprous ions to favor the extension of the previous reactions.

[0037] In this single stage, external heat is added to the pile using previously heated irrigation solutions.

[0038] The low-leach-rate irrigation resting stage involves a period of time between 10, 15, 20, or 25 days between the target heap temperature reached in the previous stage. A new resting stage begins, where leaching is carried out interspersed with extended resting periods. Resting strategies can be 10, 15, 20, or 25 days. Between resting stages, irrigation is performed for periods of 2 to 5 days to collect the copper dissolved during the resting stages.

[0039] The refining solution is introduced at room temperature around 20°C and does not require heating.

[0040] The resting stage with pulse irrigation can extend between 60 and 150 days.

[0041] The total leaching rate of this stage (considering all pulse irrigations) varies between 0.25 and 0.45 m 3of leaching solution per ton of ore. The objective of irrigating at a low leaching rate is justified to avoid heat loss due to convection of the effluent solution. Under these conditions (adiabatic isolation, standing, pulse irrigation), the temperature of the heap, although decreasing compared to the previous stage, manages to remain at levels between 30°C and 40°C.

[0042] The main chemical reactions would be very similar to the previous ones, that is: CuFeS2+ 4 Fe(III) Cu(II) + 5 Fe(II) + 2 S

[0043] CuFeS2+ 4 Cu(II) Cu(I) + 5 Fe(II) + 2 S

[0044] Refining irrigation is maintained under the same acid and chloride conditions as in the thermal activation stage. Air is added to maintain the semi-adiabatic system and to incorporate oxygen to ensure the oxidation reaction of ferrous and cuprous ions. No external heat is added during this stage.

[0045] The chemical leaching stage is justified by the fact that, although the largest amount of copper is transferred to the PLS solution, high levels of rest can generate sulfuric acid deficits that do not allow the total solubilization of the reacted copper.

[0046] It has been observed that a portion of the copper re-precipitates on the mineral in the form of copper oxysulfates and / or copper oxychlorides according to the following simplified reactions (for other sulfide species they are analogous):

[0047] Once the resting process with pulse irrigation is complete, a leaching process is carried out with sulfuric acid concentrations ranging from 10 to 25 g / L. The final pH of the solution should be between 1.8 and 2.0.

[0048] This acid leaching can be performed in the primary heap itself or, depending on the cycles, in a waste disposal site equipped for secondary leaching. Acid leaching lasts between 30 and 90 days.

[0049] At this stage there is NO addition of external heat and it is carried out at room temperature.

[0050] EXAMPLE

[0051] Mineral: An ore containing mostly primary copper sulfides with a total copper grade of 0.52% was used as an example for this application. The copper content in the sample can be approximated as: 49% as chalcopyrite; 48% as bornite; 1% as chalcocite; and 2% as copper oxides. The ore was crushed to achieve a size distribution of 80% to 90%. Experimental leaching tests were carried out in tubular columns 10 m high and 27.4 cm in internal diameter, with a capacity of 945 kg of ore with a bulk density of 1.60 ton / m. 3 .

[0052] Acidified brine: The acidified brine added to the ore was prepared by previously dissolving the salt and acid in an ILS solution, considering doses of 16 kg / t and 8 kg / t respectively, in which the ILS volume was determined in such a way as to achieve an agglomeration humidity of 8% wet basis in the agglomerated ore. The acidified brine is heated autogenously by mixing the concentrated sulfuric acid, the salt and the ILS solution.

[0053] Agglomeration: The mineral was agglomerated using 65 L of hot acidified brine (8% moisture content) with concentrations of total copper 2 g / L, total iron 5 g / L, acid 132 g / L and chloride 148 g / L. The unagglomerated mineral had a temperature of 20°C. After this mixture, the temperature of the agglomerated mineral was increased to 24°C, measured after being loaded into the 10m column, an operation that was carried out immediately after agglomeration to minimize temperature losses.

[0054] Rest: The agglomerated and loaded mineral was subjected to a 30-day rest period. During this period, the column was covered with thermofilm on top and the walls were insulated with thermal blankets to achieve an adiabatic effect. During the rest period, aeration was carried out at a rate of 1 Nm. 3 / h / m 2 using enriched air at a ratio of OI:N2 = 60%:40%.

[0055] Thermal activation leaching: After the resting period, leaching was initiated, considering irrigation with ILS solution at 40 °C for thermal activation of the column, with concentrations of total copper 1.3 g / L, total iron 3 g / L, acid 14 g / L and chloride 90 g / L, for a period of 30 days under continuous irrigation. Aeration was carried out at a rate of 0.25 Nm³. 3 / h / m 2 .

[0056] Irrigation-rest leaching: Subsequently, leaching was started considering intermittent irrigation with ILS solution at 22 °C, with concentrations of total copper 1.3 g / L, total iron 3 g / L, acid 14 g / L and chloride 90 g / L, for a period of 45 days of intermittent regime of 10 days of rest followed by 5 days of continuous irrigation. Aeration was maintained at a rate of 0.25 Nm 3 / h / m 2 .

[0057] Acid leaching: The column continued with acid leaching with refining at 20-22°C, with concentrations of total copper 0.3 g / L, total iron 3 g / L, and acid 20 g / L, for a period of 45 days under intermittent conditions consisting of 10 days of rest followed by 5 days of continuous irrigation. Finally, 5 days of drainage were performed to complete a total cycle of 155 days.

[0058] Results :

[0059] The results obtained are presented in Figures 1 and 2.

[0060] These results demonstrate that by maintaining a temperature between 35°C and 45°C during the initial resting period and continuous irrigation of the mineral in the pile, an average bed temperature above 35°C is maintained for most of the irrigation cycle. Starting on day 60, intermittent irrigation at 22°C begins, gradually cooling the pile. The final copper recovery achieved after 155 days of irrigation is 70.2%.

[0061] The effect of higher temperatures during the initial resting and irrigation period of the mineral in the pile increases copper extraction by at least 10 percentage points compared to the case where the mineral is irrigated at a temperature of 22°C throughout the entire irrigation cycle.

Claims

CLAIMS 1. A heap leaching process for minerals in chlorinated environments that utilizes chemical reactions and minimizes heat loss, where semi-autogenous heating of the leaching piles is achieved - with low incorporation of external heat. CHARACTERIZED in that it comprises the following stages: a. agglomerating the mineral using an acidified brine, increasing the initial temperature of the mineral; b. letting the stacked mineral rest, where the pile is aerated and covered with thermofilm (plastic cover), to promote exothermic reactions and reduce heat loss; c. thermally activating the mineral once the resting stage is complete, where said activation comprises irrigation with leaching solutions with temperatures between 40 ° C and 60 ° C; d. letting the mineral rest again with irrigation at a low leaching rate, where the leaching is carried out alternating extended rest periods - no irrigation; and e.a chemical leaching stage in which a dissolution of re-precipitated copper compounds is carried out, which includes an acid leaching stage to dissolve compounds soluble in acidic environments.

2. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 1, CHARACTERIZED in that said saline-acid curing stage of the mineral comprises incorporating said acidified brine at a temperature between 30 to 60 C onto the mineral on a conveyor belt or using agglomerating drums to mix the mineral and the hot acid brine.

3. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 2, CHARACTERIZED in that said brine comprises a mixture of salt (NaCl, KC1, MgC12 or any salt with high concentrations of chloride ion), sulfuric acid and process solutions (PLS, ILS, Refining), all streams at room temperature.

4. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 3, CHARACTERIZED in that said acidified brine is heated to temperatures in a range of 30°C to 60°C in an autogenous manner - by heat of dilution - by mixing in stirred tanks of concentrated acid, salt and process solutions.

5. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 1, CHARACTERIZED in that said resting stage comprises an increase in the temperature of the mineral to values ​​between 25° and 40° C at the end of said resting stage.

6. Mineral leaching process in a heap in chlorinated environments that uses the heat of chemical reactions according to claim 1, CHARACTERIZED because said resting stage lasts for a period of between 20 to 60 days.

7. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 1, CHARACTERIZED in that said resting stage comprises that the mineral is covered with thermofilm and / or bischofite.

8. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 1, CHARACTERIZED in that in the thermal activation stage, said irrigation is carried out continuously for a period of 15 to 30 days or up to a leaching rate between 0.25 to 0.35 m 3 / ton.

9. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 1, CHARACTERIZED in that in the resting stage with a low leaching rate, said resting fluctuates in a range of 10, 15, 20 to 25 days of resting, each one alternated by irrigation stages of 2 to 5 days.

10. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 9, CHARACTERIZED in that said mixture comprises a mixing proportion of each of the reagents, in chloride ion concentrations that vary between 250 to 350 g / L and sulfuric acid between 150 and 250 g / L.

11. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 1, CHARACTERIZED in that said saline-acid curing stage comprises a mixture of said acidified brine with the mineral to be leached to reach a humidity that varies between 6% to 8%.

12. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 1, CHARACTERIZED in that in said stage b) of mineral resting, aeration is carried out with air or air enriched in oxygen at temperatures between 40° and 70 °C.

13. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 12, CHARACTERIZED in that said enriched air comprises values ​​of up to a ratio OI:N2 = 90:

10.

14. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 1, CHARACTERIZED in that said thermal activation stage comprises continuous irrigation with ILS solution which corresponds to an intermediate leaching solution that collects the solution produced by the partial leaching of copper from the mineral in the leaching piles during the leaching cycle, until reaching an average temperature of the heap with values ​​greater than 40°C but less than 50°C.

15. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 14, CHARACTERIZED in that said continuous irrigation comprises a solution with a concentration of between 10 to 25 g / L of sulfuric acid and a chloride ion concentration between 50 to 90 g / L.

16. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 1, CHARACTERIZED in that said stage d) resting stage with pulse irrigation (irrigation-no irrigation) extends between 60 and 150 days.

17. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 16, CHARACTERIZED in that the total leaching ratio of the irrigation-non-irrigation stage varies between 0.25 and 0.

45.

18. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 16, CHARACTERIZED in that the irrigation is carried out with a solution at room temperature.

19. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 1, CHARACTERIZED in that said chemical leaching stage comprises sulfuric acid ranges of 10 to 25 g / L and a final pH of the solution must be between 1.8 and 2.

0.

20. Mineral leaching process in a heap in chlorinated environments that uses chemical reactions according to claim 19, CHARACTERIZED in that the irrigation is carried out with a solution at room temperature.

21. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 18, CHARACTERIZED in that said chemical leaching stage comprises leaching in the same primary heap.

22. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 18, CHARACTERIZED in that said chemical leaching stage comprises leaching in a final disposal dump of gravel conditioned to carry out secondary leaching.

23. Mineral leaching process in a heap in chlorinated environments that uses the chemical reactions according to claim 18, CHARACTERIZED in that said chemical leaching stage is carried out over a period of 30 to 90 days.