Complexation leaching copper and nickel from low-grade sulfide mineral resources with co2 mineralization

Abstract

It is provided a process to selectively extract critical metals including copper and nickel from low-grade sulfide resources for enhanced critical metal recovery and to simultaneously achieve CO2 mineralization for carbon-neutrality production, comprising the steps of heap leaching the feedstock comprising at least one of chalcopyrite, pentlandite and gangue minerals in a leach solution producing a metals-containing leach solution, wherein the sulfide from the chalcopyrite sequester CO2 as bicarbonate ions, the iron from chalcopyrite and pentlandite or the magnesium from the gangue minerals sequester CO2 into iron and magnesium carbonates into the leach residue as stable CO2 storage; recovering copper and nickel from the metals-containing leach solution producing high-value copper and nickel products and a copper and nickel depleted solution; optionally regenerating the copper and nickel depleted solution by removing iron and magnesium as stable metal carbonates at elevated CO2 pressure producing a regenerated solution; and recycling the regenerated solution to the heap leaching step.

Description

COMPLEXATION LEACHING AND NICKEL FROM LOW-GRADE SULFIDE MINERAL RESOURCES WITH CO2MINERALIZATION CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application is claiming priority from U.S. Provisional Application No.63 / 611,988 filed December 19, 2023, the content of which is hereby incorporated by reference in their entirety. TECHNICAL FIELD

[0002] It is provided a process to selectively extract critical metals from low-grade sulfide resources and CO2mineralization for carbon-neutrality production. BACKGROUND

[0003] With the global transition to clean energy, there are considerably increasing demands on critical metals for electrification, especially for copper and nickel. Nearly 90% of the world copper reserves are in chalcopyrite (CuFeS2) while around 40% of the world nickel reserves are in pentlandite ((Ni,Fe)9S8). The increasing supply of the copper and nickel will continue to be produced significantly from sulfide mineral resources. However, the average ore grade of copper and nickel has been gradually decreased to less than 0.6%. More than 95% of the mined natural resources for production of copper, nickel, and cobalt becomes tailings as wastes. The conventional mining-mineral processing-beneficiation-smelting processes are becoming much less energy-efficient and emit excessive CO2gas into atmosphere. The conventional processes cannot meet the current requirements of carbon-neutrality and clean-energy production. The majority of energy are consumed to pulverize gangue minerals for the production of the minority- target sulfide minerals or metals. It is unreasonable due to the low energy efficiency. The most energy-consumption steps lie in the mineral processing and beneficiation where the particle size of the mined mineral resources is significantly reduced through energy- intensive crushing and grinding. To meet the increasing supply of critical metals, especially copper and nickel, and the carbon-neutrality production, it is significant to bypass the energy-intensive steps.

[0004] Therefore, it is desired to develop and be provided with a novel and energy- saving process to enhance production of copper and nickel from low-grade sulfide mineral sources and wastes with CO2mineralization.SUMMARY

[0005] It is provided a process for recovering metals from a sulfide containing feedstock comprising the steps of leaching the feedstock comprising at least one of chalcopyrite, pentlandite and gangue minerals in a leach solution producing a metals- containing leach solution, wherein the sulfide from the chalcopyrite sequester CO2as bicarbonate ions and the iron from chalcopyrite and pentlandite or the magnesium from the gangue minerals sequester CO2into iron and magnesium carbonates into the leach residue as stable CO2storage; recovering copper and nickel from the metals-containing leach solution producing high-value copper and nickel products and a copper and nickel depleted solution; optionally regenerating the copper and nickel depleted solution by removing iron and magnesium as stable metal carbonates at elevated CO2pressure producing a regenerated solution; and recycling the regenerated solution to the leaching step.

[0006] In an embodiment, the feed stock is leached by heap leaching or agitation leaching.

[0007] In another embodiment, the feedstock is a low-grade sulfide resource.

[0008] In a further embodiment, the feedstock is raw ores, waste rocks or tailing.

[0009] In another embodiment, the feedstock is low-grade copper, nickel, zinc and lead sulfide waste rocks or tailings.

[0010] In another embodiment, the feedstock is metal-oxide resources or residues.

[0011] In an embodiment, the process described herein further comprises a step of recovering cobalt, cadmium, zinc, and lead.

[0012] In an embodiment, the copper and nickel are recovered by precipitation, or by solvent extraction followed by electrowinning to produce high-purity copper cathode.

[0013] In a further embodiment, the process further comprises the step of further regenerating the copper and nickel depleted solution to remove iron and magnesium by CO2mineralization precipitation at elevated CO2pressure.

[0014] In an embodiment, the low-grade, copper, nickel, zinc, and lead sulfide resource is selectively leached at weakly alkaline, neutral, or weakly acidic leaching by applying a suitable complexing ligand.

[0015] In a further embodiment, further comprises applying the suitable complexing ligand with or without sodium bicarbonate.

[0016] In an embodiment, the heap or agitation leaching is carried out at a temperature of less than 90oC.

[0017] In a further embodiment, the heap leaching is carried out at a pH between 2.5-11.

[0018] In an embodiment, the copper and nickel are recovered from the leach solution by sulfide precipitation.

[0019] In a further embodiment, a sulfide reagent is used to precipitate the copper and nickel.

[0020] In an embodiment, the sulfide reagent is H2S, NaHS, Na2S or a gas mixture of H2S and CO2.

[0021] In a further embodiment, the copper is recovered by solvent extraction followed by electrowinning to produce a high-purity copper cathode.

[0022] In an embodiment, the feedstock is chalcopyrite and pentlandite concentrate.

[0023] In a further embodiment, an elemental sulfur is produced as by-product during leaching of sulfide metals.

[0024] In an embodiment, CO2gas from air or flue gas is directly captured as bicarbonate ions into the leach solution followed by precipitation as mineral carbonates.

[0025] In a further embodiment, a potential of acid mine drainage from sulfides is removed.

[0026] In a further embodiment, the process further comprises using the iron from sulfide minerals and magnesium from waste minerals to store CO2as stable carbonates.

[0027] In an embodiment, the regenerating step at elevated CO2pressure is optional and dependent on surrounding CO2sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Reference will now be made to the accompanying drawings.

[0029] Fig.1 illustrates a of the process described herein in accordance to an embodiment.

[0030] Fig.2 illustrates complexation leaching copper results from pure chalcopyrite with comparison to conventional acid leaching.

[0031] Fig.3 illustrates complexation leaching copper results from pure chalcopyrite by a complexing ligand w / wo sodium bicarbonate.

[0032] Fig.4 illustrates complexation leaching copper results from pure chalcopyrite by a complexing ligand at initial pH=7.0 and room temperature and atmospheric pressure.

[0033] Fig.5 illustrates complexation leaching copper results from pure chalcopyrite by a complexing ligand at initial pH=4.0 and room temperature and atmospheric pressure.

[0034] Fig.6 illustrates complexation leaching copper results from pure chalcopyrite by various complexing ligand and sodium bicarbonate at initial pH=9.2 and room temperature and atmospheric pressure.

[0035] Fig. 7 illustrates complexation leaching copper and zinc from low-grade chalcopyrite raw ores by a complexing ligand and sodium bicarbonate at initial pH=8.5 and room temperature and atmospheric pressure.

[0036] Fig. 8 illustrates complexation leaching copper and nickel from coarse chalcopyrite and pentlandite raw ores by a complexing ligand and sodium bicarbonate at initial pH=8.5 and room temperature and atmospheric pressure.

[0037] Fig.9 illustrates complexation leaching copper and nickel from chalcopyrite and pentlandite raw ores by a complexing ligand at initial pH=7.0 and room temperature and atmospheric pressure.

[0038] Fig.10 illustrates complexation leaching nickel results from pure nickel sulfide by a complexing ligand and sodium bicarbonate at initial pH=8.5 and room temperature and atmospheric pressure.

[0039] Fig. 11 illustrates atmospheric complexation leaching copper and nickel results from flotation tailings by a complexing ligand with sodium bicarbonate.

[0040] Fig. 12 illustrates complexation leach solution results from flotation tailings by a complexing ligand with sodium bicarbonate.

[0041] Fig. 13 illustrates atmospheric complexation leaching copper and nickel results from flotation tailings by a complexing ligand only.

[0042] Fig. 14 illustrates atmospheric complexation leach solution results from flotation tailings by a complexing ligand only.

[0043] Fig. 15 illustrates a histogram showing the recovery of copper and nickel results from leach solution of flotation tailings by sulfide precipitation.

[0044] Fig.16 illustrates a histogram showing indirect CO2mineralization of iron from chalcopyrite complexation leaching.

[0045] Fig.17 illustrates solvent extraction recovery of copper from leach solution.

[0046] Fig. 18 illustrates lead recovery from galena concentrate by a complexing ligand and sodium bicarbonate at initial pH=8.5 and room temperature and atmospheric pressure.

[0047] Fig.19 illustrates critical metal recovery from oxide residues from a zinc plant by a complexing ligand at initial pH=9 and elevated temperature and atmospheric pressure. DETAILED DESCRIPTION

[0048] It is provided a sustainable process to selectively extract critical metals including copper and nickel from low-grade sulfide resources for enhanced critical metal recovery and to simultaneously achieve CO2mineralization for carbon-neutrality production.

[0049] Heap leaching of chalcopyrite or pentlandite from low-grade resources and wastes without beneficiation steps is a promising method for enhanced copper and nickel production and reduced CO2emissions. Bio-heap leaching is the dominant approach through using suitable bacteria to accelerate the leaching kinetics. However, the suitability of bacteria is a great concern in that the activity of bacteria is highly affected by fluctuation of climates and temperatures, mineral compositions, and surrounding ecosystems. Robust technology in heap leaching is necessary and can potentially beachieved through complexation by ligand. In addition, the iron from chalcopyrite and pentlandite and the magnesium from the gangue minerals may be used to sequester CO2into iron and magnesium carbonates for permanent CO2storage while conventionally they are considered as an impurity and rejected as waste. In addition, the sulfide minerals in waste stockpiles usually induce a concern of potential acid mine drainage (AMD). In fact, the sulfur from sulfide minerals can be utilized to directly capture CO2from air while maintaining the stockpiles in neutral to weakly alkaline conditions. Therefore, the enhanced copper and nickel recovery through complexation and CO2mineralization can make significant contributions to enhanced copper supply, clean energy transition, and carbon neutrality.

[0050] The encompassed process selectively recovers copper and nickel from low- grade sulfide resources and simultaneously achieving CO2mineralization for CO2storage.

[0051] As seen in Fig.1, in the process for recovering critical metals as described herein, there is no need for an enrichment step (like comminution, flotation, smelting, converting, refining or electrorefining) between feedstock and final product. The process 10 comprises a first step of heap leaching 12 the sulfide containing resource producing a critical metals-containing leach solution. The critical metals are recovered 14 from the critical metals-containing leach solution by precipitation (recovering copper and nickel) or by solvent extraction, followed by electrowinning to produce high-purity copper cathode. Once the critical metals are recovered, the remaining copper and nickel depleted solution can be regenerated to remove iron and magnesium as stable metal carbonates at elevated CO2pressure. CO2storage can be achieved as in-direct CO2mineralization 16 during the regeneration step. The in-direct CO2mineralization is optional. The regenerated solution can be recycled to the heap leaching.

[0052] The encompassed process can be suitable for low-grade copper sulfide waste rocks or tailings. The mined low-grade natural copper sulfide resources can be directly utilized for heap leaching without treatments of energy-intensive comminution. The heap leaching is at ambient temperature and atmospheric pressure and is accelerated by a solution matrix of sodium bicarbonate and a suitable ligand as weakly alkaline leaching or simply by a suitable ligand as neutral leaching. The copper is the priority to be leached from the copper sulfide minerals into aqueous solution, followed by iron and impurity magnesium. During the complexation heap leaching, the sulfide from chalcopyrite can be oxidized by air to elemental sulfur and simultaneously sequester CO2directly from air as bicarbonate ions leach solution. Then the leach solution can directly go through a metal recovery step to selectively recover copper as a final product for sale. The solution after metal recovery can be regenerated to remove iron and magnesium through an optional step by CO2mineralization precipitation at elevated CO2pressure as stable mineral carbonates. The regenerated solution can be recycled to the heap leaching.

[0053] This process described herein is suitable for low-grade zinc and lead sulfide waste rocks or tailings. The low-grade zinc and lead sulfide resources can be also selectively leached at weakly alkaline or neutral leaching by applying a suitable complexing ligand with or without sodium bicarbonate.

[0054] Furthermore, the process described herein is also suitable for chalcopyrite and pentlandite concentrates. The complexation leaching for the copper and nickel concentrates can be carried out at elevated temperature less than 90 C to accelerate leaching kinetics. Complexation leaching involves dissolving target elements (e.g., cooper and / or nickel) by forming a stable complex with a suitable complexing reagent.

[0055] The process utilizes the strong competition between complex ions formation and carbonate and hydroxide precipitation and maintain a part of the ligand as free ligand ions in aqueous solution. The fast kinetics and high selectivity are important for application. Maintaining a part of the ligand in aqueous solution through the competition can keep the continuous dissolution of chalcopyrite or pentlandite and thus can significantly accelerate the leaching kinetics.

[0056] The suitable pH values for the heap leaching can vary from 2.5 – 11. As encompassed herein, the heap leaching is suitable for weakly acidic, neutral, and weakly alkaline leaching.

[0057] As encompassed the process described herein can be utilized to prevent potential acid mine drainage (AMD).

[0058] The aqueous solution for the heap leaching of low-grade sulfide mineral resources contains a suitable ligand and / or sodium bicarbonate.

[0059] The suitable ligand as encompassed herein has slightly greater stability with metal ions than the corresponding metal carbonates and has lower stability with metalions than the corresponding metal as shown in Table 1. The priority of the ligand for complex is copper and nickel over iron, magnesium, and calcium. Table 1: Stability constant of suitable ligands with metal ions to the corresponding metal carbonatesions Me- trisodium Carbonateanitrilotriacetate glutamate methylnitrilotriacetate iminodisuccinate (CHNO diacetate (C7H8NO6Na3) (C8H7NO8Na4) 6 6 6Na3) (C9H9NO8Na4) Mg2+5.1 6.1 5.8 6.1 11.3 Ca2+8.3 5.2 7.0 5.2 5.3 Mn2+9.1 7.6 8.4 7.7 12.7 Al3+- - - 14.1 3.2 Cr3+- - - 9.6 30 Fe2+8.3 8.7 8.1 8.2 16.3 Fe3+- 11.7 16.5 15.2 38.6 Co2+9.3 10.0 - 10.5 14.5 Ni2+11.0 10.9 (12.7e) 12.0 12.2 15.3 Cu2+9.813.1 13.9 13.1 21.6

[0060] The following reactions can happen during the heap leaching where L represents the suitable ligand: CuFeS2+ 2HL2-= CuL- + FeL- + 2HS- Ni9Fe9S16+ 18HL2-+ 0.5O2(g) = 9NiL- + 9FeL- + 16HS- + H2O 2HS- + O2= 2S0+ 2OH- OH- + CO2(g) = HCO3- FeL- + HCO3- = FeCO3 + HL2-CuFeS2 + FeL- + 2HCO3- = CuL- + 2FeCO3 + 2HS- 4FeL- + 8OH- + O2 + 2H2O = 4Fe(OH)3 + 4L3-L3-+ H2O = HL2-+ OH- Mg2SiO4 + 2HL2-= 2MgL- + SiO2 + 2OH-

[0061] During heap leaching, the from air (or flue gas) can be sequestered by the basic solution as bicarbonate ions (HCO3-) as a direct air capture (DAC) and then further precipitate with impurity ions as stable carbonates including MgCO3and FeCO3. This approach thus can contribute to enhanced CO2sequestration for storage owing to the oxidation of sulfide at minimized costs.

[0062] The critical metals including copper and nickel can be directly recovered from the leach solution. Sulfide precipitation is one of the recovery methods. The suitable sulfide reagents can be H2S, NaHS, Na2S or gas mixture of H2S and CO2. The concentration of sulfide ions is important for selective precipitation of copper and nickel over iron.

[0063] The leached copper from complexation heap leaching can be recovered by solvent extraction with the following reactions, followed by electrowinning to produce high-purity copper cathode. CuL- + H2A2(o) = CuA2(o) + H2L- NiL- + H2A2(o) = NiA2(o) + H2L-

[0064] The following reactions can happen during the sulfide precipitation for copper and nickel recovery. CuL- + HS- = CuS + HL2-NiL- + HS- = NiS + HL2-FeL- + HS- = FeS + HL2-

[0065] The copper and nickel depleted solution can be regenerated to remove iron and magnesium as stable metal carbonates at elevated CO2pressure. CO2storage can be achieved as in-direct CO2mineralization during the regeneration step. The in-direct CO2mineralization is optional and dependent on the surrounding CO2sources.

[0066] The following reactions can happen during the solution regeneration and CO2storage. CO2(g) + H2O = HCO3- + H+FeL- + HCO3- = FeCO3+ HL2-MgL- + HCO3- = MgCO3+ EXAMPLE I Atmospheric complexation leaching copper from pure chalcopyrite

[0067] An example of atmospheric complexation leaching copper from pure chalcopyrite as a fundamental study with comparison to the conventional acid leaching by sulfuric acid and ferric is shown in Figs.2 and 3. The leaching conditions provided were: atmospheric pressure, room temperature (~25°C), 0.02~0.3 M Na3NTA (a complexing ligand), 53~63 um chalcopyrite, 0.4wt% pulp density. As shown in Fig.2, the copper leaching efficiency increased proportionally with increase in reaction time throughout all dosages of NTA. In contrast, the conventional acid leaching by 1.0 M sulphuric acid and 5 g / L ferric ions kept at the lowest level and the leaching kinetics has been significantly slowed down after 12 days. In 14 days of reaction time, the Cu leaching efficiency was 18%, 25%, 28%, and 30% for leaching by 0.02 M, 0.05, 0.15, and 0.3 M NTA while it was only 11% for leaching by 1.0 M sulphuric acid and 5 g / L ferric ions. In 21 days, the Cu leaching efficiency increased to 23%, 32%, 36%, and 41% for leaching by 0.02 M, 0.05, 0.15, and 0.3 M, respectively. The Cu leaching continued to increase to 35%, 50%, 72%, and 79% at 58 days for leaching by 0.02 M, 0.05 M, 0.15 M, and 0.3 M, respectively. It was also noticed that there was white substance generated and floating on the slurry. The generated white substance was believed as elemental sulfur.

[0068] The effect of sodium bicarbonate (1.0 M) adding to the leaching system by 0.15 M NTA was shown in Fig.3. Although there were differences during the leaching, the difference of leaching efficiency after 50 days with / without using sodium bicarbonate became insignificant. At 58 days, the Cu leaching efficiency reached 72% and 75% for 0.15 M NTA only and 0.15 NTA with 1.0 M NaHCO3, respectively. In addition, the Cu leaching efficiency was general higher than Fe leaching efficiency, and the difference became larger with increase in reaction days, where the pH values of the leach solution also gradually increased (pH>9.5).

[0069] The effect of types of complexing ligand at 0.1 M ligand concentration and 1.0 M sodium bicarbonate was shown in Fig.4. The type NTA generally presented the best leaching behaviour, followed by GLDA and citrate. Glycine may not be suitable for the simultaneous chalcopyrite leaching and carbon sequestration. After 51 days, the leaching with NTA reached 67% and the pH value of the leach solution also gradually increased to 10.3. The leaching efficiency at 51 days was 38% and 22% for using GLDA and citrate, respectively. In contrast, the leaching with glycine was only 3% after 51 days.II Atmospheric complexation neutral leaching copper from pure chalcopyrite

[0070] An example of atmospheric complexation neutral leaching copper from pure chalcopyrite as a fundamental study is shown in Fig.5. The leaching conditions provided were: atmospheric pressure, room temperature (~25°C), 0.1 Na2HNTA (a complexing ligand) at pH=7.0, 53~63 um chalcopyrite, 0.4wt% pulp density. As shown in Fig.4, the copper leaching efficiency increased proportionally with increase in reaction time. In 57 days, the copper leaching efficiency has reached 77%. The aqueous pH value also gradually increased from 7.0 to 7.5 in the first 10 days, followed by slowly increasing to 7.7. The increased pH value can correspond to the potential of direct CO2capture from air. Roughly around 4.4 g CO2per tonne chalcopyrite can thus be captured. EXAMPLE III Atmospheric complexation weakly acidic leaching copper from pure chalcopyrite

[0071] An example of atmospheric complexation weakly acidic leaching copper from pure chalcopyrite as a fundamental study is shown in Fig. 6. The leaching conditions provided were: atmospheric pressure, room temperature (~25°C), 0.1 Na2HNTA (a complexing ligand) at pH=4.0, 53~63 um chalcopyrite, 0.4wt% pulp density. As shown in Fig.5, the copper leaching efficiency increased proportionally with increase in reaction time. The copper leaching efficiency has reached 43% at 51 days and further increased to 52% at 71 days. The aqueous pH value also gradually increased from 4.0 to 7.5. The increased pH value can correspond to the potential of direct CO2 capture from air. Roughly around 3.5 g CO2per tonne chalcopyrite can thus be captured. In another word, the removal of potential acid mine drainage is also possible by this approach. EXAMPLE IV Atmospheric complexation leaching copper and zinc from low-grade sulfide raw ore

[0072] An example of atmospheric complexation leaching copper and zinc from a low-grade sulfide raw ore as a case study is shown in Fig.7. The leaching conditions provided were: atmospheric pressure, room temperature (~25°C), 0.1 M GLDA (a complexing ligand at molar ratio of GLDA / TNi=2.7) and 1.0 M NaHCO3, P80=30 um raw ore containing 0.37% Cu, 0.17% Zn, 17% Fe, and 18.8% S, 30wt% pulp density. As shown in Fig. 5, the copper and zinc leaching efficiency increased proportionally with increase in reaction time to 82% and 63%, respectively, in 26 days. In addition, theleaching efficiency on impurities iron, and calcium maintained at around 2%, 2%, and 10%, respectively. It is highly selective for the copper and zinc extraction over all impurities from low-grade sulfide raw ores. The molar ratio of leached copper and zinc over iron reached approximately 1.0, indicating that a subsequent recovery can potentially obtain high-value products. Furthermore, the aqueous pH value also gradually increased from 8.5 to around 10. The increased pH value can correspond to the direct CO2capture from air, i.e., roughly around 1.2 kg CO2sequestered per tonne chalcopyrite. The total inorganic carbon (TIC) in the leach residue was also analyzed with an increase from originally 0.01% to 0.14%. In another words, around 5t CO2 / kt raw ore can be permanently sequestered extraction and mineralized as stable mineral carbonates during the selective copper and zinc. Considering that the iron and sulfide contents were so high in the feed raw ores, 17% and 18.8% respectively, this case study also confirms that this novel approach can be suitable for high iron sulfide containing resources without the concern of potential acid mine drainage. EXAMPLE V Atmospheric complexation leaching copper and nickel from copper and nickel sulfide raw ore

[0073] An example of atmospheric complexation leaching copper and nickel from a sulfide raw ore as case studies is shown in Fig.8-9. The sulfide raw ore contains 1.9% Cu, 2.5% Ni, 23% Fe, 8.9% Mg, 1.5% Ca, and 9.9% S. The complexation weakly alkaline leaching of coarse sulfide raw ore is shown in Fig. 8 under the leaching conditions: atmospheric pressure, room temperature (~25°C), NTA (a complexing ligand) at increasing molar ratio of NTA / (TCu+TNi), 1.0 M NaHCO3, P80=1 mm raw ore, and 30wt% pulp density. The leaching of copper and nickel was highly selective over all impurities Fe, Mg, and Ca. With increase in NTA concentration, the leaching efficiency of copper and nickel reached 85% and 78%, respectively at NTA / (TCu+TNi) =1.7, while the leaching efficiency of all impurities remained lower than 1%. It was a highly selective leaching process. The copper and nickel contents of this sulfide raw ores were quite high and thus needed relatively high concentration of NTA. When the supply of NTA was not sufficient to complex all copper and nickel from the raw ores, the leaching efficiency of copper and nickel increased firstly but then cannot further increase with time. For instance, at NTA / (TCu+TNi) =0.3, i.e., 0.1 M NTA, The copper and nickel leaching efficiency increased rapidly to 10% and 24% in the first 18 days. The further increase in time did not benefit the critical metal leaching anymore. In contrast, the increase in NTA from 0.1 M to 0.5 M (i.e., NTA / (TCu+TNi) from 0.3 to 1.7) improved the copper and nickelquickly while all impurities remained non-leached. In addition, the total inorganic carbon (TIC) content in residues gradually increased from 0.11% to around 0.51%. In another words, around 15t CO2 / kt raw ore were sequestered and mineralized to stable mineral carbonates during the selective copper and nickel leaching process. The pH value in leach solution firstly increased from 8.5 to around 10 in first 10 days. Although there was some decrease subsequently, the pH still maintained at around 8.0.

[0074] The complexation neutral leaching of this sulfide raw ore is shown in Fig.9 under the leaching conditions: atmospheric pressure, room temperature (~25°C), NTA (a complexing ligand) at increasing molar ratio of NTA / (TCu+TNi), P80=30 um raw ore, and 30wt% pulp density. With the increase in NTA concentration, the copper and nickel leaching efficiency also gradually increased while the leaching of impurities remained at low levels. Each time when NTA was introduced to increase its concentration, the leaching impurities was increased, followed by a subsequent decrease. It was still a selective process of copper and nickel extraction over impurities. The total inorganic carbon (TIC) content in residues also increased from 0.11% to 0.25%. It means that around 5t CO2 / kt raw ore was sequestered from air and mineralized to stable mineral carbonates during the neutral leaching process although no initial sodium bicarbonate was introduced. EXAMPLE VI Atmospheric complexation leaching nickel from pure nickel sulfide

[0075] An example of atmospheric complexation leaching nickel from pure nickel sulfide as a fundamental study is shown in Fig. 10. The leaching conditions provided were: atmospheric pressure, room temperature (~25°C), 0.1 M Na3NTA (a complexing ligand) and 1.0 M NaHCO3, 0.4wt% pulp density. As shown in Fig.10, the nickel leaching efficiency rapidly increased to completion within only 10 days. The aqueous pH value also gradually increased from 8.5 to around 9.7. EXAMPLE VII Atmospheric complexation leaching copper and nickel from flotation tailings

[0076] An example of application to leaching of copper and cobalt from sulfide flotation tailings is shown in Figs. 11-14. The leaching conditions provided were: atmospheric pressure, room temperature (~25°C), 0.1 M Na3NTA (a complexing ligand) with / without 1.0 M NaHCO3, flotation tailings with particle size at P80=53 um, 33wt% pulp density. The sulfide flotation tailings contained 0.03% copper, 0.09% nickel, 11% iron,and 8% magnesium. As shown in using the complexing ligand NTA together with sodium bicarbonate, copper, nickel, and magnesium leaching efficiency gradually increased to 39%,13%, and 0.6% at 60 days while iron leaching efficiency gradually decreased from 2% at the first day to 0.6% at 60 days. The change in concentration of leach solution as shown in Fig.12 can further confirm the selectivity for leaching copper and nickel. Iron concentration in aqueous solution reached the maximum 1033 mg / L at 1stday followed by the gradual decrease to 325 mg / L at 60 days. The copper, nickel and magnesium gradually increased to 55 mg / L, 57 mg / L, and 215 mg / L, respectively. Compared to the original molar ratio of Fe / Cu>410 (due to the very low copper and nickel content in tailings), the Fe / Cu molar ratio in leach solution has decreased to around 6 only. The decrease in iron leaching from tailings was due to the precipitation of iron as iron hydroxides with red colour. The copper and nickel leached from mainly residual chalcopyrite and pentlandite in tailings can be remained in aqueous solution by the complexing ligand. It was a very selective process.

[0077] As shown in Fig.13, with using the complexing NTA only, both copper and nickel together with iron and magnesium gradually increase with reaction time but the copper and nickel leaching efficiency (39% and 12% at 60 days, respectively) were much higher than iron and magnesium leaching efficiency (1.4% and 0.7% at 60 days, respectively). The metal concentration of leach solution is shown in Fig.14. Although the copper and nickel leaching efficiency much higher than the iron and magnesium leaching, the concentrations of iron and magnesium in leach solution were much higher than the concentrations of copper and nickel because of the originally residual low-level copper and nickel content. The maximum iron and magnesium concentrations were 784 mg / L and 287 mg / L at 55 days, followed by slight decrease to 737 mg / L and 268 mg / L at 60 days, respectively. The final Fe / Cu molar ratio in leach solution was at 14 decreased from the original 413 but much lower than 6 for leaching by NTA and NaHCO3together. It indicates that the addition of sodium bicarbonate can substantially increase the selectivity of copper and nickel over iron probably due to the increased pH values in solution for iron precipitation during the atmospheric leaching process. EXAMPLE VII Recovery of copper and nickel from leach solution through sulfide precipitation

[0078] An example for copper and nickel recovery from leach solution is through sulfide precipitation as high-value copper and nickel sulfides as shown in Fig.15. The leach solution from the sulfide flotation tailings leached by 0.1 M Na3NTA (a complexingligand) with / without 1.0 M NaHCO3temperature and pressure. The sulfide precipitation was at 120 °C and 1.6 bar H2S over pressure within 1 hour for precipitation. It indicated that all the copper, nickel and iron (>98%) were coprecipitated as sulfides where the Fe / (Cu+Ni) molar ratio was 3. No magnesium was precipitated by hydrogen sulfide. The residual magnesium in the aqueous solution can go through the optional CO2mineralization process at elevated CO2over pressure. Alternatively, the magnesium in the aqueous solution can be also remained in the barren solution and be potentially precipitated as carbonates during the atmospheric complexation leaching process. EXAMPLE VIII CO2mineralization of iron from chalcopyrite complexation leaching

[0079] An example for indirect CO2mineralization of iron from chalcopyrite complexation leaching is shown in Fig. 16. The leach solution was obtained from chalcopyrite complexation leaching under 0.2 M NTA only at room temperature and open atmosphere and contained 842 mg / L iron. The CO2mineralization was carried out at 120°C, CO2pressure=41 bar, and for 1 hour. After CO2mineralization, the residual iron concentration was 766 mg / L and the corresponding CO2mineralization reached 13 g CO2 / kg chalcopyrite. In this case, although there was no sodium bicarbonate originally added to the leaching matrix, the indirect CO2mineralization can still be reached. Since the increase in sodium bicarbonate concentration can facilitate the CO2mineralization precipitation based on our previously published work, it is believed that addition of sodium bicarbonate cannot only enhanced chalcopyrite leaching but also increase the CO2mineralization. EXAMPLE IX Recovery of copper from leach solution through solvent extraction

[0080] An example for copper recovery from leach solution is through solvent extraction as shown in Fig. 17. The leach solution contained 1 g / L copper that was complexed with 0.1 M NTA at pH=7.0, 8.5, and 10.2, respectively. The solvent extraction conditions were: 20v / v% LIX 984N in matrix SX12, O / A=1 / 2, room temperature, 5-10 min mixing. As shown in Fig.17, with an increase in pH of the leach solution, the Cu recovery increased significantly to reached 99% at pH=10.2 that can be reached by weakly alkaline leaching. The blue color in the leach solution disappeared since all copper transferred from leach solution to the organic phase as Cu-loaded extractant. Thetitration of the complexing ligand and after solvent extraction shows that there was no loss throughout the complete solvent extraction process. In contrast, the complexing ligand NTA was regenerated by solvent extraction and thus can recycled back to leaching and atmospheric carbon sequestration. EXAMPLE X Atmospheric complexation leaching lead from pure lead sulfide

[0081] An example of atmospheric complexation leaching lead from pure lead sulfide is shown in Fig.18. The leaching conditions provided were: atmospheric pressure, room temperature (~25°C), 0.1 M Na3NTA (a complexing ligand) and 1.0 M NaHCO3, 0.4wt% pulp density. As shown in Fig.18, the lead leaching efficiency increased proportionally to around 80% after 65 days with increase in pH values from 8.5 to around 10.3 after 20 days. The mineral composition analysis of the leach residue after the complexation leaching shows that there was obvious elemental sulfur generated from the leaching process. The elemental sulfur may be further recovered as a valuable by-product. EXAMPLE XI Atmospheric complexation leaching critical metals from metal oxide residues

[0082] An example of atmospheric complexation leaching critical metals from metal oxide (alloy) residues as a case study is shown in Fig.19. The critical metals include nickel (1.9%), cobalt (3.5%), cadmium (17%), copper (12%), zinc (17%), and lead (12%). The leaching conditions provided were: atmospheric pressure, elevated temperature (85°C), 0.33 M Na3NTA (a complexing ligand), 2.0wt% pulp density, initial pH=8.8. As shown in Fig.19, the complexation leaching process of the oxide residues was rapid and has been almost completed within 30 minutes for the majority of critical metals including nickel, cobalt, cadmium, zinc, and lead, except for copper. Within the first 30 minutes, the leaching efficiency of the critical metals reached around 90% followed by a slight increase while copper leaching efficiency reached only 20% followed by a gradual increase with time. In addition, the pH value of the leach solution increased from initially 8.8 to 11 at the end of the test.

[0083] While the present description has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations and including such departures from the present disclosure as come within known or customary practicewithin the art and as may be applied to features hereinbefore set forth, and as follows in the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A process for recovering metals from a sulfide containing feedstock comprising the steps of: a) leaching the feedstock comprising at least one of chalcopyrite, pentlandite and gangue minerals in a leach solution producing a metals-containing leach solution, wherein the sulfide from the chalcopyrite sequester CO2as bicarbonate ions and the iron from chalcopyrite and pentlandite or the magnesium from the gangue minerals sequester CO2into iron and magnesium carbonates into the leach residue as stable CO2storage; b) recovering copper and nickel from the metals-containing leach solution producing high-value copper and nickel products and a copper and nickel depleted solution; c) optionally regenerating the copper and nickel depleted solution by removing iron and magnesium as stable metal carbonates at elevated CO2 pressure producing a regenerated solution; and d) recycling the regenerated solution to the leaching step.

2. The process of claim 1, wherein the feedstock is a low-grade sulfide resource.

3. The process of claim 1 or 2, wherein the feedstock is raw ores, waste rocks, or tailings.

4. The process of claim 3, wherein the feedstock is low-grade copper, nickel, zinc, and lead sulfide waste rocks or tailings.

5. The process of any one of claims 1-4, further comprising a step b’) of recovering cobalt, cadmium, zinc, and lead.

6. The process of any one of claims 1-5, wherein the copper and nickel are recovered by precipitation, or by solvent extraction followed by electrowinning to produce high- purity copper cathode.

7. The process of any one of claims 1-6, further comprising the step of further regenerating the copper and nickel depleted solution to remove iron and magnesium by CO2 mineralization precipitation at elevated CO2 pressure.

8. The process of claim 4, wherein grade copper, nickel, zinc, and lead sulfide resource is selectively leached at weakly alkaline, neutral, or weakly acidic leaching by applying a suitable complexing ligand.

9. The process of claim 8, further comprising applying the suitable complexing ligand with or without sodium bicarbonate.

10. The process of any one of claims 1-9, the heap leaching is carried out at a temperature of less than 90 C.

11. The process of any one of claims 1-10, the heap leaching is carried out at a pH between 2.5-11.

12. The process of any one of claims 1-11, wherein the copper and nickel are recovered from the leach solution by sulfide precipitation.

13. The process of claim 12, wherein a sulfide reagent is used to precipitate the copper and nickel.

14. The process of claim 13, wherein sulfide reagent is H2S, NaHS, Na2S or a gas mixture of H2S and CO2.

15. The process of any one of claims 1-11, wherein the copper is recovered by solvent extraction followed by electrowinning to produce a high-purity copper cathode.

16. The process of claim 1, wherein the feedstock is chalcopyrite and pentlandite concentrate.

17. The process of claim 1, wherein the feedstock is metal oxide resources or residues.

18. The process of claim 8, where an elemental sulfur is produced as by-product during leaching of sulfide metals.

19. The process of any one of claims 1-18, wherein CO2gas from air or flue gas is directly captured as bicarbonate ions into the leach solution followed by precipitation as mineral carbonates.

20. The process of any one of claims 1-19, wherein a potential of acid mine drainage from sulfides is removed.

21. The process of any one of claims 1-20, further comprising using the iron from sulfide minerals and magnesium from waste minerals to store CO2as stable carbonates.

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