Acid leaching of deposits for carbon mineralization and nickel recovery and in the presence of aqueous fe(II)

Abstract

A method for extracting metals from metal-bearing deposits includes preparing a sample from the laterite deposit; exposing the sample to a Fe-enriched aqueous Fe(II) solution in an oxygen depleted environment for a period of time to induce mineral recrystallisation; and collecting at least one metal from the solution in at least one of an aqueous phase, an extract phase, and a solid phase. The method enhances metal release and offers a sustainable alternative over current metal extraction processes. The method produces less deleterious carbon emissions and acidic waste than traditional mining techniques.

Description

ACID LEACHING OF DEPOSITS FOR CARBON MINERALIZATION AND NICKEL RECOVERY AND IN THE PRESENCE OF AQUEOUS FE(II)RELATED APPLICATIONS

[0001] This application claims priority benefit of U.S. Provisional Application Serial Number 63 / 690,957 filed September 5, 2024, the contents of which are hereby incorporated by reference.FIELD OF THE INVENTION

[0002] The present invention generally relates to methods of extracting metals from deposits such as serpentinites, kimberlites and nickel laterites, and more particularly to leaching nickel and cobalt from these deposits using iron enriched aqueous solutions with reduced deleterious carbon emissions and acidic waste.BACKGROUND

[0003] More mining is required to build the renewable energy infrastructure needed to achieve carbon neutrality (Vidal et al., 2013). For instance, a doubling in nickel mining is anticipated within the 21stcentury (Renforth, 2019). There is also a need to remove 100-1000 Gt of carbon dioxide (CO2) from the atmosphere by 2100 to limit climate warming below 2 °C (IPCC, 2018, 2021). Critical metals are needed to build the infrastructure of the green economy and they are typically mined from ultramafic rocks. These magnesium-rich rocks are mined for nickel, cobalt, chromium, diamonds and platinum group elements. They are also amongst the best feedstocks for CO2 mineralization — a CO2 removal technology that turns this greenhouse gas into carbonate rock.

[0004] In 2016 alone, the minerals industry generated 8.9 Gt of finely pulverized mineral wastes (‘tailings’) that were disposed of in onsite waste storage facilities (Baker et al., 2020).These facilities typically occupy 1-40 km2for a single mine, and they include (1) dry-stacked, subaerial piles and (2) subaqueous storage ponds. Approximately 420 Mt of the tailings produced in any given year (-5 % of total production) are from ultramafic ore deposits, which means they can be used to bind and store an estimated 175 Mt / year of CO2 in minerals (Power et al., 2013a). Almost all of this carbonation potential is related to nickel mining (Sandalow et al., 2021). The necessary doubling of nickel mining, and tailings production at nickel mines (Renforth, 2019), offers an opportunity to expand the scale of CO2 mineralization (i.e., -350 Mt / year of CO2) while refraining it as an ore processing technology (Hamilton et al., 2018, 2020). With more research and development, it may be possible to extend tailings carbonation to less favorable rock types. For instance, if more calcium- and silica-rich mafic and intermediate tailings can be carbonated, the global annual CO2 removal potential of the mining sector increases to 1-5 GtCCh / year (Bullock et al., 2021).

[0005] Most of the world’s land-based nickel resources (-60 %) are found in nickel laterites, which are nickel-rich soils formed by weathering of ultramafic rock, and the remaining -40 % are hosted by sulfide deposits in unweathered ultramafic rock (USGS, 2021). Nickel alloy deposits represent a third, new class of ore deposit that is anticipated to supply nickel in the future (Britten, 2017). Although alloy deposits have not yet been mined for nickel, some have been mined for chrysotile asbestos, and it is expected that they will soon become a major resource in the coming decades owing to their extraordinarily high tonnages and the declining grades and scarcity of new sulfide deposits.

[0006] The scale of the nickel resource found in historical mine tailings is currently unknown. Geological surveys and natural resources and energy ministries in some countries (e.g., Natural Resources Canada, United States Department of Energy) are only just beginning to develop the programs needed take stock of critical metal inventories in mineral wastes. However, it is anticipated that the stockpiled tailings resource will be on the scale of 10s of Gt,with > 2 Gt alone associated with a few chrysotile asbestos mines in Quebec, Canada (Power et al., 2013a).

[0007] In some instances, 30-40 % of the nickel from sulfide ore is disposed of as waste in mine tailings (e.g., Grguric et al., 2006). Thus, there is a vast amount of nickel that could be recovered from mine tailings. It is also likely that mining from alloy deposits will be relatively inefficient because approximately half the nickel in these deposits is found in magnesium silicate minerals (Hamilton et al., 2018), which are typically remitted to tailings. Nickel laterites host nickel and other critical metals within iron-(oxy)hydroxide minerals, which are the components of everyday rust. The benefit of mining laterites is that the weathering process by which they form extracts critical metals from all nickel-containing minerals — silicates, sulfides and alloys — concentrating them to a much higher grade than was present in the original, unweathered rock. On the flip side, the carbonation potential of laterites is lower because they have already been leached of magnesium during weathering and soil formation.

[0008] While nickel laterite deposits host the majority of the world’s Ni resources within the crystal structure of goethite, traditional mining techniques for these deposits require energy intensive processing that creates deleterious carbon emissions and acidic wastewater. Existing mining techniques are expensive and require an extensive infrastructure.

[0009] Thus, there exists a need for a more sustainable, environmentally friendly method for extracting metals from metal-bearing deposits that results in reduced carbon emissions and acidic wastewater, as compared to current metal extraction processes.SUMMARY OF THE INVENTION

[0010] The present invention provides a method for extracting metals from metal-bearing deposits via the recry stallisati on of iron oxides catalyzed by aqueous Fe(II) at ambientconditions (i.e., 22 °C, atmospheric pressure, pH 7.5) in order to enhance metal release and offer a sustainable alternative over current metal extraction processes. The present invention also provides a method for turning unweathered ultramafic rocks into artificial metal-bearing deposits that can then be processed using this new metal extraction method while producing a magnesium-rich leachate that can be used to turn CO2 into solid magnesium carbonate. According to embodiments, the method produces less deleterious carbon emissions and acidic waste than traditional mining techniques. The method includes acid leaching ultramafic rocks to generate a magnesium-rich solution and an artificial metal-bearing deposit. Then exposing the resulting solid material (or a naturally occurring laterite) to an Fe-enriched aqueous Fe(II) solution in an oxygen depleted environment, which in some instance is at ambient conditions, for a period of time to induce mineral recrystallisation; and collecting at least one metal from the solution in at least one of an aqueous phase, an extract phase, and a solid phase. A number of methods can be used to carbonate the magnesium-rich solution including but not limited to: electrolytic acid recycling with carbon mineralization (Lammers et al., 2023) or microbially mediated precipitation of carbonate minerals (McCutcheon et al., 2019).BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention is further detailed with respect to the following drawings that are intended to show certain aspects of the present of invention, but should not be construed as limit on the practice of the invention, wherein:

[0012] FIG. 1A is a graph showing Mn release from batch reactions of the different Ni- laterite samples from Brazil (red circles), New Caledonia (blue triangles), and Western Australia (green squares);

[0013] FIG. IB is a graph showing Co release from batch reactions of the different Ni- laterite samples from Brazil (red circles), New Caledonia (blue triangles), and Western Australia (green squares);

[0014] FIG. 1C is a graph showing Ni release from batch reactions of the different Ni- laterite samples from Brazil (red circles), New Caledonia (blue triangles), and Western Australia (green squares);

[0015] FIG. 2 shows a flow chart describing the artificial metal-bearing deposits process, including the leaching reactor (Reactor 1), nickel recovery reactor (Reactor 2), carbonation reactor (Reactor 3), and one of the scenarios for acid recycling;

[0016] FIG. 3 A is a photograph showing an experimental set up for artificial metal-bearing deposits production;

[0017] FIG. 3B is a photograph showing development of a rust (ferrihydrite) layer within two weeks of acid treatments (Hamilton et al., 2021);

[0018] FIG. 3C shows synchrotron X-ray fluorescence maps showing upgrading of nickel and other critical metals to -2 wt% (from an original ~0.2 wt.%) following dilute acid leaching (Hamilton et al., 2020);

[0019] FIG. 3D shows reactive transport model results predicting the location and concentration of the rust layer in experiments (Hamilton et al., 2020); and

[0020] FIG. 3E shows one implementation of critical metal recovery and CO2 mineralization using artificial nickel laterites.DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention has utility as a more sustainable, environmentally friendly method for extracting metals from a variety of deposits including but not limited toserpentinite-hosted deposits and metal-bearing deposits with reduced deleterious carbon emissions and acidic wastewater as compared to current metal extraction processes.

[0022] The tailings produced by ultramafic-hosted mines naturally remove CO2 from the atmosphere, storing it within the crystal structures of newly formed magnesium carbonate minerals (Wilson et al., 2006, 2009). In one instance, the tailings from the Mount Keith nickel mine, in Western Australia, have been removing enough atmospheric CO2 to offset 11 % of the mine’s CChe emissions since the mine began operation in the 1990s (Wilson et al., 2014). This type of ‘passive’ or unintentional CO2 removal can be accelerated dramatically by (1) enhancing the dissolution rate of magnesium-bearing silicate and hydroxide minerals in mine tailings and (2) increasing the supply of CO2 available to make carbonate minerals using either higher-concentration CO2 streams or simple bioreactors (e.g., McCutcheon et al., 2019; Hamilton et al., 2020). The Measurement, Monitoring and Verification (MMV) protocols for CO2 removal in mine tailings already exist and many of them were developed by our team and collaborators (e.g., Wilson et al., 2006, 2009a,b, 2011, 2014; Turvey et al., 2017, 2018a, b; Hamilton et al., 2020, 2021).

[0023] Nickel, cobalt and other valuable first row transition metals are incorporated into the structures of magnesium carbonate minerals, where they replace magnesium, and they are also sorbed to iron-(oxy)hydroxide minerals during passive carbonation of mine tailings (Hamilton et al., 2016, 2018). Thus, when magnesium is both (1) leached from waste silicate and hydroxide minerals and (2) carbonated within the same tailings storage facility, CO2 and critical metals are sequestered by the same carbonate minerals. In this scenario, there is no way to recover the critical metals without dissolving the carbonate minerals and releasing the CO2.

[0024] The present invention turns ultramafic mine tailings into artificial metal-bearing deposits. This process concentrates critical metals in a layer of rust within the tailings (i.e., an artificial nickel laterite) while producing a separate high-magnesium leachate for carbonation.The present invention couples enhanced weathering of ores and mine tailings to critical metal recovery (Hamilton et al., 2018, 2020, 2021). More recently, this method has been applied to using traditional ex situ carbon mineralization (i.e., using high temperatures and pressures) as part of a nickel ore processing circuit (Khan et al., 2021; Wang et al., 2021a, b).

[0025] An acid heap-leaching technique works on rocks from nickel sulfide and alloy deposits. It dissolves abundant magnesium silicate and hydroxide minerals that contain nickel and iron while liberating grains of nickel-rich alloys and sulfides. Equations 1 and 2 describe the dissolution of serpentine (Eq. 1) and brucite (Eq. 2) using hydrochloric acid as an example. The nickel and other critical metals are trapped by the formation of the iron-(oxy)hydroxide mineral, ferrihydrite, which is a component of rust (Eq. 3). This mineral concentrates nickel, cobalt and other critical metals ~10x within a layer of rust — the artificial metal-bearing deposit. The magnesium-rich leachate produced in Equations 1 and 2 is then carbonated in a separate step (Hamilton et al., 2020). It is appreciated that other acids, such as sulfuric acid are operative herein. In particular, sulfuric acid affords certain advantages as to reactions with calcium-poor rock.

[0026] Unlike the highly crystalline rust minerals in naturally-occurring nickel laterites (e.g., goethite and hematite), the poorly crystalline iron-(oxy)hydroxide mineral, ferrihydrite, produced in the inventive process is a more labile host of critical metals. This means that, rather than using high-temperature and pressure acid leaching typical of laterite processing, nickel and other metals can be recovered from artificial metal-bearing deposits at ambient conditions (i.e., standard temperature and pressure) using a reductive dissolution process (e.g., Frierdich et al., 2012; 2019). This process uses aqueous iron(II) to trigger recrystallization of iron- (oxy)hydroxide minerals, releasing nickel and other valuable metals into solution where they can be precipitated and recovered (Eq. 4).

[0027] A supply of base (hydroxyl groups) and CO2 gas are then added to the magnesium- rich solution to drive precipitation of carbonate minerals (Eqs. 5-7).

[0028] In previous field trials, cyanobacteria-dominated microbial consortia were used to supply CO2 from air and catalyze precipitation of carbonate minerals in bioreactors. This is typically done by cultivating chlorine- or sulfate-adapted microbes from mine sites or nearby alkaline lakes. This style of photosynthetic bioreactor provides a low-energy, low-maintenance approach to concentrating atmospheric CO2 into solution using the metalloenzyme carbonic anhydrase (E Zn in Eqs. 5-7; after Mirjafari et al., 2007). Photosynthesis (Eq. 8) maintains the elevated pH needed to form aqueous carbonate (Eq. 9) and precipitate magnesium carbonate minerals such as hydromagnesite (Eq. 10). Finally, negatively charged functional groups on microbial cell walls and extracellular polymeric substances serve as nucleation sites that immobilize positively-charged magnesium ions, thereby accelerating mineral precipitation. The abiological alternative is to continuously titrate a basic reagent while sparging low purity CO2 (e.g., of the kind produced by Direct Air Capture) into solution to precipitate magnesium carbonate minerals (Zhu et al., 2022a, b).Reactor 1: Magnesium leaching and formation of an artificial metal -bearing depositReactor 2: Nickel recovery (+ other critical metals) from the artificial metal-bearing deposit

[0029] The formation of artificial metal-bearing deposits (Reactor 1) and the magnesium carbonation (Reactor 3) have been demonstrated in the laboratory (FIG. 3C; Hamilton et al., 2020) and at the 1-10-m3scale in the field (FIGS. 3A and 3B; Hamilton et al., 2021). The process works best when dilute acid treatments are used to leach critical metals and magnesium from brucite-bearing ultramafic rock. The laboratory and field trials have generally employed daily to weekly treatments of one pore volume of dilute sulfuric acid (0.08 M). The results show that for every 1 mol of sulfuric acid used, it is typically possible to extract 1.23 mol of magnesium (Hamilton et al., 2020) with the capacity to sequester up to 1.23 mol of CO2, depending on the MgT'Ch ratio of the mineral precipitated. Twice the number of moles of hydrochloric acid would likely be needed to obtain the same result. Some of the inefficiency observed is attributable to dissolution of non-magnesium minerals.

[0030] It has been shown that this process enhances magnesium supply for carbonation 14- 25 x relative to what can be achieved using brucite carbonation via flue gas injection (Hamilton et al., 2020). Preliminary results indicate that, once the process is optimized, separating the magnesium extraction and carbonation steps will greatly simplify MMV, making it possible to measure CO2 mineralization using inexpensive and straightforward mineral identification, total carbon analyses and weighing the amount of carbonate minerals produced.

[0031] Accurate reactive transport models have been built using the MIN3P code (Mayer et al., 2002). Having validated these models using laboratory data, one is able to predict the effectiveness and efficiency of the leaching process on rocks with differing mineralogical compositions (FIG. 3D). Additional lab-based leaching trials and modelling have been done using ultramafic rocks with different proportions of olivine (a slow reacting mineral) and serpentine + brucite (fast reacting minerals) and dilute hydrochloric acid (0.04 M, 0.08 M, 0.12 M and 0.16 M) to begin optimizing treatment conditions as a function of mineralogy (i.e., crystal chemistry and crystal structures), surface area, porosity, permeability, and particle size (Wang et al., 2024; Wang, 2024). Cl-rich brine carbonation (Zhu et al., 2022a, b) experiments suggest carbonation reactions are more efficient using hydrochloric acid than sulfuric acid, which produces some magnesium sulfate minerals owing to the strength of MgSCfy' complexation in solution (Hamilton et al., 2020).

[0032] According to certain inventive embodiments, the inventive process requires a large amount of low-cost, dilute acid, creating a synergy with the Ebb Carbon (SEA MATE) process or the Travertine Tech process. The Ebb Carbon electrochemical process creates dilute hydrochloric acid from seawater while leaving sodium hydroxide behind, thereby mitigating ocean acidification while increasing the capacity of the ocean to remove CO2 from the atmosphere (reviewed by NASEM, 2021). Implemented at scale, the SEA MATE process would produce much more hydrochloric acid than is needed by current global demand, and atan uncommercially low concentration that would require further refinement. A large nickel sulfide mine will produce on the order of 10 Mt of tailings per year, containing approximately 40 wt.% magnesium. It would require -3.30 x 1011mol of hydrochloric acid to extract all of the magnesium (-1.65 x 1011mol) from these tailings. The Travertine Tech process, which uses sulfuric acid, would require half as many moles of sulfuric acid to extract as much magnesium from the same tailings. Recycling of acids, as implemented in the Travertine process can reduce the overall amount of acid required. FIG. 3E shows one implementation of critical metal recovery and CO2 mineralization using artificial nickel laterites.

[0033] It is to be understood that in instances where a range of values are provided that the range is intended to encompass not only the end point values of the range but also intermediate values of the range as explicitly being included within the range and varying by the last significant figure of the range. By way of example, a recited range of from 1 to 4 is intended to include 1-2, 1-3, 2-4, 3-4, and 1-4.

[0034] According to embodiments, a method for extracting metals from metal-bearing deposits and artificial metal-bearing deposits includes the recrystallisation of goethite, ferrihydrite or other Fe(III) minerals catalyzed by aqueous Fe(II) at ambient conditions (i.e., 22 °C, atmospheric pressure, pH 7.5) in order to enhance metal release and offer a sustainable alternative over current metal extraction processes. According to embodiments, the method produces less deleterious carbon emissions and acidic waste than traditional mining techniques.

[0035] According to embodiments, a method for extracting metals from metal-bearing deposits and artificial metal-bearing deposits produced from ultramafic rocks includes first preparing a sample from the deposit. Preparing a sample from the deposit includes collecting a portion of a deposit from the Earth. According to embodiments, this collection is accomplished by drilling into a deposit contained in the Earth. Such drilling may be carried out using anyknown method for drilling. According to some embodiments, the samples are extracted from the deposit at a depth of between 3 to 33 m below the Earth’s surface.

[0036] According to certain inventive embodiments, the laterite deposit is a metal-bearing deposit. According to embodiments, the samples come from the oxide zone within the laterite deposit. According to some embodiments, the laterite deposit has a Ni grade of less than 0.5 wt % to 2 wt %. According to some embodiments, the laterite deposit has a Ni grade of 1.78 % at 49 Mt. According to some embodiments, the laterite deposit has aNi grade of 1.48 % Ni at 120 Mt.

[0037] According to embodiment, preparing the sample additionally includes characterizing the sample. According to embodiments, characterizing the sample is accomplished by dry sieving the sample collected from a metal-bearing deposit, which according to some embodiments, the dry sieving uses a 150 pm, 100 mesh. The dry sieving may be carried out by hand or by a machine operation. According to embodiments, the sample is further prepared and characterized by using powder X-ray diffraction patterns to identify a crystalline mineral phase of the sample. According to embodiments, characterizing the sample additionally includes determining an initial elemental composition in a HCl soluble fraction by dissolving 20 ± 0.5 mg of the sample in 2 mL of 5 M HC1 at 70 °C for 24 hours and subsequently conducting ICP- MS analysis thereon.

[0038] According to certain inventive embodiments, a method for extracting metals from metal-bearing deposits additionally includes exposing the sample to an aqueous Fe(II) solution in a reaction chamber at ambient conditions for a period of time to induce mineral recrystallisation. According to still other inventive embodiments, the aqueous Fe(II) solution comprises water, a pH buffer solution, and an isotope tracer to monitor the extent of recrystallization. According to embodiments, the reaction chamber is oxygen depleted and contains a controlled atmosphere of inert gas. It is appreciated that inert gases are operativeherein illustratively include dinitrogen, argon, helium, neon, or a combination thereof.According to some inventive embodiments, the ambient conditions include temperature of between 10 and 35 °C, while is still other embodiments the temperature is 22 ± 2 °C, a pressure of atmospheric pressure of 720 to 790 torr, and / or a pH of 7 to 8, while in other inventive embodiments, the pH is 7.5 ± 0.1. According to embodiments, the period of time is 1 to 60 days. According to some inventive embodiments, the method additionally includes replenishing the aqueous Fe(II) solution from 1 to 30 days thereafter, and in some embodiments, after 14 days.

[0039] According to embodiments, a method for extracting metals from metal-bearing deposits additionally includes collecting at least one metal from the solution in at least one of an aqueous phase, an extract phase, and a solid phase. According to embodiments, at least one metal collected from the solution includes at least one of Ni, Co, and Mn. In the aqueous phase, any metals present are contained in the solution. In the aqueous phase, metals are separated by centrifugation, then filtered into a clean tube containing HC1. In the extract phase, any metals sorbed to the mineral surfaces are extracted and collected after adding more HC1, reacting for at least 10 minutes, centrifuged and filtered into a clean tube. In the solid phase, which is the residual, reacted solid laterite sample, the reacted solid used has already been separated by centrifuge during collection of the aqueous phase. The residual, reacted solid remaining in the original reactor is taken outside of the anaerobic chamber and dissolved in HC1 at 70 °C for 24 hours and subsequently collected.

[0040] The critical metals in artificial metal-bearing deposits are bound to poorly crystalline iron-(oxy)hydroxide minerals. The inventive method uses a novel pathway to recover nickel, cobalt and other critical metals. Critical metals can be recovered at room temperature and pressure using Fe(II)-catalyzed recrystallization of iron-oxide and hydroxide minerals (Eq. 4; Frierdich et al., 2012, 2019). Artificial metal-bearing samples are reacted with syntheticprocess waters with the addition of aqueous Fe(II) under anoxic conditions to determine rates, extraction efficiencies and optimal conditions for metal recovery.

[0041] According to embodiments, artificial metal-bearing deposits are produced at a situs of mining, in laboratory experiments and in larger, on-campus field experiments. These are used in benchtop tests of the prototype reductive dissolution reactor and in on-campus field experiments using the scaled-up reactor.

[0042] Sensors, attached to data loggers, are built into these anoxic reactors to monitor pH, electrical conductivity, temperature and dissolved oxygen levels. A sampling port is used so that aqueous concentrations of iron and nickel can be monitored over time. Both solids and fluids are analyzed using inductively coupled plasma - optical emission spectrometry (ICP- OES) and inductively coupled plasma - mass spectrometry (ICP-MS) to measure the amount of nickel and other valuable metals extracted. Stable metal isotope analyses of fluids and solids are used to monitor reaction kinetics and to elucidate mechanisms of extraction. Solids are also analyzed using (1) synchrotron X-ray absorption spectroscopy (XAS) to measure the oxidation state and co-ordination environment in which nickel and other metals are found in iron- (oxy)hydroxides and (2) powder X-ray diffraction to monitor mineral phase transitions and changes in microstructure, particularly changes in crystallite size that can lock in valuable metals.

[0043] Ore deposits are mineralogically heterogeneous. It is common practice (1) to tailor conditions within processing plants to the mineralogy of the ore that is being processed at any given time and (2) to mix ores with different metallurgical properties to optimize recovery of metals and process water.).

[0044] The inventive process is suitable for use with samples having a variety of mineralogical compositions, elemental compositions and physical properties of ore and / or tailings. This will enable models for optimizing key parameters such as acid concentration,treatment frequency, porosity and particle size to maximize magnesium and critical metal extraction and CO2 mineralization.

[0045] Mineralogy before and after leaching is characterized using quantitative powder X- ray diffraction (XRD), bulk X-ray fluorescence (XRF) spectroscopy, ICP-MS, total carbon analyses, synchrotron XAS, synchrotron X-ray fluorescence mapping (XFM), scanning electron microscopy (SEM), electron microprobe analysis (EPMA) and Fourier Transform Infrared spectroscopy (FTIR). This combination of analyses allows the determination of precisely how mineral stoichiometry and mineral abundances affect results.

[0046] Laser particle size analysis, Brunauer-Emmett-Teller surface area analysis and X- ray computed tomography (X-ray CT) are done to characterize physical properties of pulverized rock. Hydrological tests are done to determine parameters required for reactive transport modelling. Leachate chemistry is characterized using ICP-OES, ICP-MS and total carbon analyses.

[0047] Yields of carbonate minerals from carbonation reactors are measured for all parallel laboratory treatments.

[0048] The present invention also provides for integrated and optimized leaching, metal recovery and carbonation process. This integrated system uses at least 1-10 m3of pulverized rock. According to embodiments, an artificial metal-bearing deposit (Reactor 1) is produced, the scaled-up reductive dissolution reactor is used to recover critical metals (Reactor 2) and the magnesium-rich leachate (Reactor 3) is carbonated under environmentally and operationally relevant conditions.

[0049] Samples of solids and solutions are collected at hourly to daily intervals. Limited field-based monitoring of mineralogy, elemental compositions of solids, as well as aqueous concentrations of carbonate, bicarbonate, iron, nickel and silica may be done using a portableX-ray diffractometer, portable X-ray fluorescence spectrometer, and portable spectrophotometer.

[0050] A weather station may be set up to collect temperature and relative humidity data to support reactive transport modelling and water mass balance. Data loggers for pH, soil moisture, electrical conductivity and temperature probes are buried at three depths within the tailings to monitor changes in these parameters in real time. Data loggers are also be used to monitor pH, electrical conductivity and temperature of leachates emerging from the acidleaching reactor (Reactor 1). These leachates are continuously delivered to the carbonation reactor (Reactor 3) where pH, electrical conductivity, redox, temperature and dissolved oxygen are logged in bulk solution. Data are also logged continuously from the pH, electrical conductivity, temperature and dissolved oxygen sensors built into the reductive dissolution reactor (Reactor 2).

[0051] Embodiments also provide for the recycling of acid. Concentrated acids are relatively expensive ($100s per ton) and are consumed on a similar mass to the CO2 that is removed. However, the creation and use of dilute acid produced through the Travertine Tech process, Ebb Carbon (SEA MATE) process or similar processes may be notably cheaper. For a scaled industry it is also necessary to have relatively high recycling rates to limit environmental impact. Furthermore, accumulation of chlorine at high concentrations can be deleterious to microbes in bioreactors and to remediation efforts following mine closure; as such, recovery of chlorine or hydrochloric acid is particularly important. The inventive process provides for acid and metal recovery (e.g., electrolysis, thermal brine / precipitate decomposition, carbonation, ion exchange) for atmospheric CO2 removal. Designs of the large- scale combined leaching, collection, concentration, and acid recycling systems are produced; the reactive transport models are used to constrain reactor volume, and the techno economics and life-cycle impacts are assessed. Data from the field-based demonstration are integrated intothis model to determine the most suitable process for obtaining and recycling acid. The present invention is further illustrated with respect to the following non-limiting example:

[0052] MATERIALS AND METHODS

[0053] Ni-laterite samples used in this study are collected from three locations: Brazil, Australia, and New Caledonia. The Ni-laterite from Brazil comes from the Morro Sem Bone deposit in Mato Grosso. Samples are taken at four depths from a selected drill hole at 3.0-3.2 m, 6.0-6.2 m, 8.5-8.7 m and 10.0-10.2 m. Preliminary reports from Anglo American pic estimate the orebody to be 6 km x 1.5 km with a Ni grade of 1.78 % at 49 Mt. Morro Sem Bone is situated in the Guapore Belt, on the southwestern part of the Amazonian Craton.

[0054] The New Caledonia Ni-laterite samples are from the Goro deposit (19 km2, 1.48 % Ni at 120 Mt) in the South Province of New Caledonia. Ni-laterite samples are collected under the New Caledonia National Technological Research Centre (Centre National de Recherche Technologique (CNRT)) project: Nickel and its Environment, from which three yellow-laterite samples are selected for this study. Samples named C148-22 and C148-32 are from the same drill hole, at average depths of 32.1 m and 21.12 m, respectively, and sample C77-11 is from another drill hole at 30.7 m depth, all of which come from the oxide zone within the laterite profde.

[0055] The two Australian Ni-laterite samples come from undisclosed sites near Kalgoorlie in the Yilgam Craton, Western Australia. Both are limonite-type laterites containing low-grade Ni (<0.5 wt%), named Al 5 and Bl 1, and have been used in previously published studies (Wang et al., 2013, Wang et al., 2014). Specific details of the mine sites remain confidential and cannot be disclosed. Generally, Ni-laterite deposits in the Yilgam Craton formed during the during the Early Tertiary and are associated with the Archean granite-greenstone belts (Elias et al., 1981). In all three localities, the laterites were formed from ultramafic parent rocks of dunite and peridotite, with varying degrees of serpentinization.

[0056] Sample Characterization

[0057] The laterite samples are dry sieved, for example by hand (150 pm, 100 mesh). Powder X-ray diffraction (XRD) (Br ker D8 Advance ECO: Co source) patterns are used to identify the crystalline mineral phases in the Brazil samples (DiffracEvav5.1.06, Bruker AXS). The New Caledonia and Australia laterite samples have been previously characterized with XRD by external sources (referred to in the text). To determine the initial elemental compositions in the HC1 soluble fraction, triplicate samples of 20 ±0.5 mg of each powdered Ni-laterite sample are dissolved in 2 mL of 5 M HC1 at 70 °C for 24 hours, then diluted for analysis by ICP-MS (see section 2.5. Isotopic and Elemental Measurements below).

[0058] Reactor Preparation

[0059] To ensure no oxidation of aqueous Fe(II) occurs by air (i.e., atmospheric oxygen), reactions are conducted within an anaerobic chamber that contains a controlled atmosphere of H2-N2, where H2 levels are maintained between 1.5 - 3.5 %. Powder samples, labware, or other items brought into the chamber are subject to a vacuum-gas cycle to remove O2, then left to equilibrate with the chamber atmosphere for >48 hours before use. Liquids containing dissolved O2 are sparged with N2 outside the chamber (30 min), and again with the chamber atmosphere once inside (30 min, pumped through a pyrogallol and KOH trap). Trace amounts of O2 (<1 ppm) that inadvertently enter the chamber are removed with continuous Pd scrubbers.

[0060] Fe-exchange batch reactors follow methods consistent with previous work (Frierdich et al., 2019), with minor adjustments. Briefly, duplicate reactors are set up in 15 mL tubes (polypropylene) by combining 20 ±0.5 mg of Ni-laterite sample; 8.9 mL H2O (>18.2 M.Q cm, simply referred to as water unless otherwise stated); 1 mL of the pH buffer solution, 100 mM ‘3-(N-Morpholino) propanesulfonic acid’ (MOPS) in 0.1 M NaCl; and 0.05 mL of the isotope tracer solution (57Fe-enriched >96%), 0.1 M57Fe(II)aqin 1 M HC1, the addition of which marks the start of the reaction. The final pH is adjusted to 7.5 ± 0.07 using a small volume (-0.05 mL)of 1 M NaOH. To avoid any interference with light, reactors are wrapped in Al foil, then rotated to allow mixing for the duration of the reactions.

[0061] Control reactors are prepared in a similar manner, but with the major exception that these controls do not contain any added57Fe(II)aq, and contain 9 mL of water to make up the volume to 10 mL, and a small volume (<0.05 mL) of 0.1 M HC1 to adjust it to the same pH. These Fe(II)-free control reactors are used to distinguish any changes in the laterite samples in either the presence of the buffer solution or reaction conditions from the expected reactions with Fe(II)aq.

[0062] Sampling involves collecting (z) the aqueous phase, which contains any metals in solution; (zz) the extract phase, in which any metals sorbed to the mineral surfaces are extracted and collected; and (Hi) the solid phase, which is the residual, reacted solid laterite sample. The aqueous phase is separated by centrifugation, then filtered into a clean tube containing 1 mL of 1 M HC1, resulting in a total sample volume of 10 mL in a matrix of 0.1 M HC1. The extract phase is prepared by adding 9.8 mL of 0.1 M HC1 to the reacted solid for 10 min, then this is centrifuged and filtered into a clean tube. The reacted solid used has already been separated by centrifuge during collection of the aqueous phase. The residual, reacted solid remaining in the original reactor is taken outside of the anaerobic chamber and dissolved in 2 mL of 5 M HC1 at 70 °C for 24 hours.

[0063] Additional series of reactions on are conducted on the Brazil laterite sample that simulate a flow-through system by reacting the same batch reactor multiple times. The motivation is to investigate a potential method for negating the effect of Ni redistributing on the goethite surface and blocking sites of Fe(II) interaction (Frierdich et al., 2019a), which can impact goethite recrystallisation. Named here as the cycle reactors, the experiments are similar to the non-cycle reactors except they are sampled every 14 days. The aqueous and extract phases are collected; however, the residual solid is re-suspended in a fresh57Fe-enrichedFe(II)aqsolution to initiate another reaction cycle. These reactions are run in duplicate for a total of four, 14-day cycles (i.e., 56 days total reaction). Two reactors are sacrificed at the end of each cycle for compositional analysis of the solid by ICPMS. Fe(II)-free controls are also conducted in duplicate for the full duration of the four cycles and undergo sampling of the aqueous and extract phases, as well as solution replenishment at each cycle, but this solid is only collected at the completion of the final cycle.

[0064] The concentrations of Ni, Co and Mn in the aqueous, extract and residual solid phases are measured using standard-based ICPMS at specific time points during batch reactions between samples from the three laterite deposits (located in Brazil, New Caledonia and Western Australia) and spiked Fe(II)aqsolutions. The concentration of Ni in solution generally increases with ongoing reactions of the Brazil 10 m sample. The concentration of Ni in the extract phases is -3 times greater than that of the aqueous phase for these samples. Co concentration is also higher in the extract phases than the aqueous by ~1.6 times, for the 10m sample. Co concentration shows a slight increase in solution with time, but the values are almost within error of each other. In all depths of the Brazil laterite, the concentration of Ni is higher in the extracts than the aqueous phases. Contrastingly, the concentration of Mn is higher in the aqueous phases than the extracts for all depths. The overall concentrations seem low (pm scale) but this is due to the reaction conditions using 20 mg of sample in 10 mL reactors. When converting the amount of release relative to the starting composition, these values equate to a total metal release %.

[0065] The Brazil 10m sample shows an increase from 3.0 ± 0. 1 % Ni at 1 d to 4.2 ± 0.2 % Ni at 14 d. All samples exhibit the greatest increase in metal release for Ni, Co and Mn between 1 d and 14 d of reaction. Then, the relative increase in metal release between time points becomes smaller. The 10m sample increases to 5.0 ±0.2 % Ni release at 30 d, before reaching a maximum of 5.1 ± 0.1% total Ni release, 54.8 ± 0.9% Co, and 70 ± 2% Mn release after 60d of batch reactions. All samples show a general trend of increasing metal release with time forNi, Co and Mn, where most 60 d reactions are within error of their respective 30 d values. Except 3m where Co and Mn reach the maximum release at 14 d, however these values are nearly within error (0.4 % difference) of the 60 d values. The Brazil laterite (10m) exhibits the most Ni, Co, Mn release out of the three deposits used in this study.

[0066] Samples from New Caledonia (represented by sample C148-22) show similar, yet slightly lower total metal release (%) than the Brazil laterite. However, the New Caledonia samples have a higher concentrations of metal release than the Brazil laterite by an order of magnitude. For example, New Caledonia reaches ~38 pM Ni in solution (aqueous + extract) at 30 d, and Brazil reaches ~4 pM Ni in solution in the same amount of time. Recall that the overall low absolute concentrations are also a result of the experimental conditions. The concentration of Ni and Co is higher in the extract phase than the aqueous for all New Caledonia samples, by ~10, ~20, and ~25 times for C148-22, C148-32, and C77-11. The concentration of Mn in the aqueous phases are similar to that of the extract phases (<1.6 times difference). Ni and Co concentrations appear to be slightly higher at earlier reaction times (1 d) but are mostly stable throughout the 30 d reactions. Mn concentration increases from 1 d to 30 d for all samples, in both the aqueous and extract phases, by 12 ±5 pm. This results in the total metal release of the New Caledonia laterite samples appearing to plateau for Ni, with minimal change throughout reactions, and a slight decrease in the amount of Co released with time, e.g., C148-22 exhibits 52.8 ±0.9 % total Co release at 1 d, which decreases to 39 ±1 % by 30 d. Yet Mn release shows an increase with time, e.g., 52.8 ±0.9 % Mn at 1 d, increasing to 39 ±1 % total Mn release at 30 d for the same sample. These trends occur for all three New Caledonia samples.

[0067] Contrastingly, both samples from Western Australia provide minimal metal release. Similar to the other laterite deposits, sample Bl 1 shows that Ni and Co concentration is greaterin the extract phases than the aqueous phases, by ~7 and ~2 times, respectively, and Mn concentration is greater in the aqueous phase rather than extract phases, by ~3 times. The other sample from Western Australia, A15, follows the same trend for Mn with ~8 times higher concentration in the aqueous than the extract phase. However, Co concentration is nearly equal in both phases, but slightly higher in the aqueous, and Ni shows no clear trend for either phase throughout the reaction time points between 1 and 30 d. In both samples from Western Australia, the Ni concentration in solution is an order of magnitude lower than the Brazil 10m samples, and nearly two orders of magnitude lower than the New Caledonia samples. The total amount of Ni release is low, with Al 5 reaching a maximum of 0.5 ±0.4 % Ni at 7 d and maintains this until 14 d, but then decreases to 0.3 ±0.03 % Ni at 30 d. Bl l is similarly low, but shows a slight increase throughout 30 d reaction period, reaching a maximum of 0.42 ±0.06 % Ni release. Co release increases over the 30 d period as well, reaching 6.4 ±0.2 % Co and 4.4 ±0.4 % Co for A15 and Bl 1 respectively. Mn release similarly increases slightly over 30 d for Bl 1 to 3.7 ±0.2 % Mn, yet sample Al 5 shows all values for Mn release from 1 d to 30 d are within error of one another at 6.9 ±0.5 % Mn release.

[0068] Ni-laterite samples from Brazil, New Caledonia and Australia are reacted in aqueous Fe(II) solutions in order to induce and measure goethite recrystalhsation as a potential process for extracting Ni and Co from laterite deposits under ambient conditions and circumneutral pH. Batch reactions of the Brazil laterite reached ~5 % Ni release and ~55 % Co release after 60 days. Simulated flow-through (cycle) reactors improve extraction, reaching ~10 % Ni release and ~70 % Co release. This indicates that an in-situ open system may be a better application than a closed system. Laterites rich in goethite and poor in clay content appear to be the most suitable candidates for this process. According to embodiments, yields are increased by running a series of the cycle experiments on thermally treated laterite. Although the initial Ni yields in this study are modest, successful metal release shown here demonstrates a greener future formetal extraction from laterite ore. Since Ni-laterites comprise an estimated 178.1 Mt Ni worldwide, the maximum in-ground value that could be extracted by the techniques described here would equate to $284 billion (USD) with much reduced infrastructure and environmental costs compared to conventional techniques (based on the estimated Ni price of $ 16k USD per tonne, current at mid 2024).

[0069] While at least one exemplary embodiment has been presented in the foregoing description and attached appendix, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the described embodiments in any way. Rather, the foregoing description and incorporated references will provide those skilled in the art with a convenient roadmap for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes may be made in the function and arrangement of elements without departing from the scope as set forth in the appended claims and the legal equivalents thereof.

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Claims

CLAIMS1. A method for extracting metal from a metal -bearing deposit, the method comprising: preparing a sample from an artificial metal-bearing deposit; exposing the sample to an aqueous Fe(II) solution in an oxygen depleted environment for a period of time to induce mineral recrystallisation or reductive dissolution to create a product; and collecting at least one metal in at least one of an aqueous phase, an extract phase, and a solid phase derived from the product.

2. The method of claim 1 wherein the artificial metal-bearing deposit is a nickel-bearing deposit.

3. The method of claim 1 wherein the sample is extracted from a metal-bearing deposit at a depth of between 3 to 33 m.

4. The method of claim 1 wherein the metal-bearing deposit has a Ni grade of less than 0.5 wt %.

5. The method of claim 1 wherein the metal-bearing deposit has a Ni grade of 1.78 % at 49 Mt.

6. The method of claim 1 wherein the metal-bearing deposit has a Ni grade of 1.48 % Ni at 120 Mt.

7. The method of claim 1 wherein preparing the sample includes dry sieving the sample.

8. The method of claim 7 wherein the dry sieving uses a 150 pm, 100 mesh.

9. The method of any one of claims 1 to 8 wherein preparing the sample includes using powder X-ray diffraction patterns to identify a crystalline mineral phase of the sample.

10. The method of any one of claims 1 to 8 further comprising determining an initial elemental composition in aHCl soluble fraction and subsequently conducting ICP-MS analysis thereon.

11. The method of any one of claims 1 to 8 wherein the Fe-enriched aqueous Fe(II) solution comprises water, a pH buffer solution, and an isotope tracer solution.

12. The method of any one of claims 1 to 8 wherein the oxygen depleted environment comprises H2 levels from 1.5 to 3.5 % in an inert gas.

13. The method of any one of claims 1 to 8 wherein the oxygen depleted environment is at ambient conditions of temperature of pressure, where the temperature is optionally between 10 and 35 °C.

14. The method of any one of claims 1 to 8 wherein environment has a pressure of from 720 to 790 torr.

15. The method of any one of claims 1 to 8 wherein the environment has a pH of 7 to 8, and optionally 7.5.

16. The method of any one of claims 1 to 8 wherein the method produces less deleterious carbon emissions and acidic waste than traditional mining techniques.

17. The method of any one of claims 1 to 8 wherein the period of time is 1 to 60 days.

18. The method of any one of claims 1 to 8 wherein the at least one metal collected from the solution includes at least one of Ni, Co, and Mn.

19. The method of any one of claims 1 to 8 further comprising replenishing the Fe-enriched aqueous Fe(II) solution after 1 to 30 days.

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