WO2023002460A1 - Procédés d'accélération de séquestration de carbone - Google Patents

Procédés d'accélération de séquestration de carbone Download PDF

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Publication number
WO2023002460A1
WO2023002460A1 PCT/IB2022/056833 IB2022056833W WO2023002460A1 WO 2023002460 A1 WO2023002460 A1 WO 2023002460A1 IB 2022056833 W IB2022056833 W IB 2022056833W WO 2023002460 A1 WO2023002460 A1 WO 2023002460A1
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heap
sequestration
agglomerated
less
rock
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PCT/IB2022/056833
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English (en)
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Anthony Owen FILMER
Christopher Alan BILEY
Luke Mark KEENEY
Philip Duncan Newman
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Anglo American Technical & Sustainability Services Ltd
Anglo Corporate Services South Africa (Pty) Ltd
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Publication of WO2023002460A1 publication Critical patent/WO2023002460A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/62—Carbon oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/81—Solid phase processes
    • B01D53/82—Solid phase processes with stationary reactants
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/20—Reductants
    • B01D2251/206—Ammonium compounds
    • B01D2251/2062—Ammonia
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/40—Alkaline earth metal or magnesium compounds
    • B01D2251/402—Alkaline earth metal or magnesium compounds of magnesium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/40—Alkaline earth metal or magnesium compounds
    • B01D2251/404—Alkaline earth metal or magnesium compounds of calcium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/60—Inorganic bases or salts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/60—Inorganic bases or salts
    • B01D2251/608—Sulfates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/70—Organic acids
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/80—Organic bases or salts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/90—Chelants
    • B01D2251/902—EDTA
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/40—Capture or disposal of greenhouse gases of CO2

Definitions

  • ex-situ sequestration does not rely on finding geological options for pressurized injection of the concentrated gas into underlying basic rock structures, with all the uncertainties around regional permeability and the impact of CO2 sequestration rate on this rock permeability.
  • Suitable rock for sequestration is often already exposed to the atmosphere by mining for the purpose of mineral recovery and metal production. Sequestration has been studied to illustrate the potential for using these mine residues as a sequestration agent. Examples are the use of residues from asbestos mining such as studies at Thetford in Canada – Lecht et. al.
  • CO2 from the gas phase is absorbed into the water coating the rock particle to form carbonic acid.
  • the acid protons
  • the protons migrate from the CO2 absorption site they convert the carbonic acid into carbonate and the protons ultimately reach the surface of the rock where they dissolve some magnesium or calcium ions.
  • this dissolution causes the magnesium or calcium content of the water to exceed the solubility of the associated carbonate, causing its precipitation.
  • the precipitation might occur as a hydrated form of magnesium carbonate.
  • the pH difference between surface of the water and surface of the mineral is muted, and the reaction is slow. High CO2 concentrations increase the pH difference.
  • the reaction rate is also very temperature dependent.
  • the minimum rock crush size that can be used in heap leaching is typically around 50 mm, too coarse for acceptable sequestration rates. Any finer crush and the fines cause macro-permeability issues in the heap, again restricting sequestration.
  • Some acidic heap leach operations for copper ores utilise an agglomeration approach to get the fines to adhere to the coarse particles in the heap. But even if one extended the Walder concept to agglomerate the ore prior to being stacked for a heap leach, the smallest agglomerated heap operation has a p80 of around 12mm. The average size is too coarse to sequester CO2 at an acceptable rate within the heap. This phenomena explains why Walder favoured acid heap leaching to dissolve the magnesium, then CO2 addition external to the heap.
  • heap leaching of the valuable metals may be successful, but at the pH required to recover these metals from the base of the heap, the strong acids will consume the most acid soluble gangue, which is also the most reactive rock for sequestration. Furthermore, in trying to combine the heap leaching and sequestration, at the pH required for metal recovery from the base of the heap, any magnesium or calcium carbonate which may have sequestered in the lower parts of the heap will be redissolved. Walder does not disclose the extent of CO2 capture from the exhaust gas as it passes through his heap. Nor does he disclose how partial sequestration reaction of the fines in the heap affects the subsequent and ongoing extent of CO2 capture.
  • the Walder concept provides for a 3-dimensional structure that will achieve the desired heap leaching objectives, but at best an incremental level of sequestration. And even if the leachants were identified which were consistent with both heap leaching and sequestration, the heap leaching structure claimed by Walder would be too coarse and hence very slow to meaningfully sequester the CO2 from an exhaust gas. Whilst a wide array of laboratory studies has identified mechanisms to accelerate the dissolution of basic rocks such as olivine, no-one has found a way to include this information into a working system to achieve this ex-situ sequestration in an economically acceptable way. It has also been proposed by Walder and others that acidification, for example by strong acids like sulphuric acid, will dissolve magnesium from the rock.
  • a supplementary problem for those ultramafic orebodies that also contain other valuable metals, is how to combine the sequestration with the co- extraction of the valuable metals contained in the ore, such that both sequestration and metal recovery can be achieved from the same mined rock.
  • This invention relates to a method of sequestering CO2 containing gas with the preparation of a high surface area of rock suited for sequestration in a 3- dimensional permeable heap, including the steps of: • obtaining, or obtaining and comminuting, a material which is suitable for CO2 sequestration to generate a feed stock with a p80 less than 5mm and preferably less than 1mm; • agglomerating the feedstock to form an agglomerated particle with an apparent p80 of less than 10mm diameter, typically from about 1 to 5mm; and with a p10 > 0.15mm, or separating the feedstock into a coarse fraction and a fine fraction, and agglomerating the fine fraction to form an agglomerated particle with an apparent p80 of less than 10mm diameter, typically from about 1 to 5mm; and with a p10 > 0.15mm • stacking the agglomerated particles in a permeable heap or heaps; and then passing the CO2
  • Suitable materials are those containing calcium or magnesium with sufficient basicity that they will sequester CO2, and include natural rocks such as ultramafic rocks, or man-made basic materials such as smelter slags, or byproducts from other processes such a fly-ash from combustion. Typically, these materials contain high proportions of calcium or magnesium, which dissolves slowly and reacts with carbonate ions in the solution to precipitate the respective calcium or magnesium carbonates.
  • agglomeration is meant the aggregation of fine particles into composite structures of coarser diameter, typically having a large internal porosity in excess of 20% and up to 35%, whilst still retaining much of the effective surface area of the original fines. Agglomeration terminology includes such techniques as pelletisation, granulation and briquetting.
  • the agglomerates may be bound by physical attractive forces typical of those resulting from binding and ‘rolling’ with controlled water additions, typically in the range of 5-15% moisture, or by the addition of a binding agent such as lime or cement, which cause chemical bonds to form between adjacent particles.
  • An aqueous binder solution used for agglomeration of the fines preferably contains one or more of a soluble magnesium salt, for example the sulphate or chloride salt, and a readily protonated/deprotonated acid which has a pKa of greater than 6 to 9, typically 7 to 9, such as ammonia, citrate or EDTA.
  • the aqueous binder solution will typically contain the additives at concentrations close to saturation limits of the selected additive salt.
  • the agglomerated particles have an internal porosity of >20% and preferably greater than 25% and even more preferably greater than 30% and up to 35%.
  • the material is crushed to less than 5mm and preferably around 1mm then classified, with a coarser fraction from classification being separated from fines for direct stacking.
  • the p80 of the coarser fraction is less than 5mm, and typically around 1.0 mm, and can be as low as 0.5mm.
  • the fine fraction from the classification is separately agglomerated and stacked in either the sand heap or a separate heap.
  • the material may be milled to a much finer size prior to agglomeration, to generate a fines stream of typically p80 ⁇ 150 micron, and preferably less than 100 micron, and even as low as 15 micron, for agglomeration and stacking.
  • the agglomerates with the requisite size characteristics may be formed from either all, or only from the fines fraction, of the comminuted ore.
  • fines can be removed from a more coarsely crushed rock and separately agglomerated.
  • fines may be agglomerated using all the crushed rock, wherein the coarser particles form a substrate to bind the fines.
  • all the rock may be finely ground then agglomerated.
  • These examples form three broad categories of agglomeration through which the fine fraction is reduced prior to stacking, and are such that the heap permeability after stacking is suitable for 3- dimnsional gas flow.
  • the agglomerates are less than 10mm in diameter and typically around 1- 5mm, such that the space between the roughly spherical agglomerates can provide both additional porosity within the heap to accommodate gas flow and increase in molar volume during sequestration, and to limit the migration distance for CO2 through the agglomerate to the inner surfaces of reactive rock.
  • stacking is meant the placement of the agglomerates in a 3-dimensional structure with high porosity.
  • the porosity is made up of the microporosity within the individual agglomerates, and the macro-porosity in the spaces between the individual agglomerates.
  • overall stacked porosity of the heap is greater than 40% and preferably about 50-60%, and up to 65%.
  • the heap or heaps contain/s less than 20% by weight ⁇ 100 micron particle size, and preferably less than 15% ⁇ 100 micron and even more preferably less than 10% ⁇ 100 micron.
  • Irrigation rates are selected to maintain the heap in a partially saturated state, such that the agglomerates are physically stable, and gas permeability of the heap is mostly retained, providing for a thin film of moisture covering the finely crushed rock to be sequestered.
  • the irrigation does not need to wash dissolved species through the heap, rather simply ensure that the unreacted rock remains wetted.
  • irrigation rates can be much slower than the typical 1-10 l/m2/hr used in heap leaching, enabling lower liquid permeability than is required for heap leaching.
  • the irrigation rates may be adjusted to less than 1l/m2/h and preferably around 0.1 l/m2/hr or even lower.
  • the irrigant typically initially water, may also be an aqueous solution which contains chemical additives.
  • the aqueous solution builds up in soluble species, as it resides in and flows through the heap of rock being sequestered, and is recovered from the base of the heap and can be recirculated.
  • the mineral species present in the rock react with dissolved CO2, which forms a weak carbonic acid, to form calcium or magnesium solution carbonate species according to reactions like MgO.SiO2 + CO2 >>> MgCO3 + SiO2 Whilst the reaction will occur naturally, additives to the system may be employed to accelerate the sequestration reaction. These additives can be added to the system through either or both the irrigant or the binder in agglomeration. In one embodiment, magnesium containing solutions are used as the additive.
  • the 3-dimensional structure of finely crushed and agglomerated rock is used to provide the basicity to neutralise the acid generated by CO2 which is transferring from the gas phase to the moisture in the heap.
  • the dissolving rock raises the pH to precipitate an external source of soluble magnesium in the irrigant solution.
  • This may contain a soluble magnesium salt, for example the sulphate, or chloride, which precipitates the magnesium as it contacts the basic rock.
  • the pH is buffered by dissolution of additional CO2 gas.
  • the dissolution of the finely divided rock liberates additional calcium or magnesium.
  • the rate of rock dissolution is increased by adding to the irrigant a readily protonated/deprotonated acid which has a pKa of around 6-9. Examples are citrate or EDTA or ammonia.
  • the buffering agent together with any complexing action with magnesium ions, increases the effective proton transfer between the gas solution interface and the surface of the dissolving rock.
  • the irrigant may contain a magnesium salt, at a magnesium concentration of greater than 1gpl, and preferably greater than 10 gpl magnesium and even more preferably around 50gpl magnesium.
  • the irrigant may contain a salt of ammonium, or citrate or EDTA in an amount at a concentration greater than 1gpl, and preferably around 10gpl.
  • the stacked heap is constructed to provide for adequate gas permeability and operated to maximise gas distribution through the heap. Flow is distributed by installing piping near the surface of the heap and gas distribution near the base.
  • the irrigant may comprise an aqueous solution generated from liquor recovered from the base of the heap.
  • the heap designed for sequestration may also be used for heap leaching of contained metals in the rock.
  • the heap may be constructed such that thermal energy can be injected into the heap through externally heating either the CO2 containing gas or the irrigant prior to their addition to the heap, thus raising the rock temperature within the heap.
  • the CO2 containing gas passed through the heap may be natural atmosphere, typically containing about 400ppm CO2.
  • the CO2 containing gas passed through the heap may contain elevated levels of CO2 such as those generated by a variety of industrial processes i.e.
  • the CO2 containing gas may also be upgraded by a variety of well known techniques to generate a gas source close to 100% CO2 prior to introduction to the heap.
  • At least part of the rock suitable for sequestration may be formed from historical residues arising from mining, or smelting, or power generation operations. These historical residues can be crushing if necessary or agglomerated directly, and may be bound to a substrate to provide greater structural strength to the agglomerate heap.
  • the agglomeration substrate may be formed from ultramafic rock and is partially sequestered along with the agglomerated fines.
  • the agglomerated rock may be reclaimed after sequestration, deagglomerated and screened, with the coarse fraction re-used as substrate.
  • the agglomerated rock may be reclaimed after sequestration, deagglomerated and screened, with the fine fraction recovered for subsequent use in a separate process.
  • the invention also relates to a permeable heap constructed with the agglomerated fines, the coarser sand, or a blend thereof, as described above.
  • the essence of the current invention is to provide a large surface area of reactive rock within a highly porous 3-dimensional structure. This reaction system is not agitated, and hence can accommodate solids reaction times measured in months or years.
  • the high surface areas of particles, and large dimensions of the reactor enables sufficient residence time for most of the CO2 to be extracted from the feed gas as it passes through the structure. And the system arranges this high surface area in a structural form that enables steady and uniform distribution of the reactants through the structure, for the duration of the reaction.
  • Figure 1 is a schematic diagram of the CO2 sequestration process
  • Figure 2A is a graph showing particle carbonation kinetics of olivine rocks with 1 ⁇ m particle size with varying temperature
  • Figure 2B is a graph showing particle carbonation kinetics of olivine rocks with 100 ⁇ m particle size with varying temperature
  • Figure 2C is a graph showing particle carbonation kinetics of olivine rocks with 10mm particle size with varying temperature
  • Figure 3 is a flow diagram of 3 alternative methods of forming a permeable 3-dimensional structure suitable for CO2 sequestration
  • Figure 4 is a schematic illustration of air gaps and wetted fines in an agglomerated heap
  • Figure 5 is an experimental curve illustrating the rate of sequestration of finely crushed ultramafic rock types in an atmosphere of CO2 at 70oC.
  • the invention provides for accelerated sequestration of suitable material through preparation, stacking of the prepared material in a high porosity, permeable 3-dimensional structure through which gas, typically air or an exhaust gas from another process or enriched CO2 is passed, to remove the CO2 from the gaseous phase.
  • suitable materials include rocks with sufficient basicity that they will sequester CO2, and may include natural rocks such as ultramafic rocks, or man-made basic materials such as smelter slags or byproducts from other processes such a fly-ash from combustion processes.
  • the materials may have previously been processed for recovery of metals, such as flotation tailings from a nickel mine, or diamond residues, or wastes from asbestos production.
  • the rate of sequestration is dependent on both surface area of the material and temperature.
  • laboratory data obtained from the literature has been normalized to approximate the sequestration rate for wetted particles of olivine rocks, at various sizes expected, and at different temperatures, when exposed to current levels of atmospheric CO2.
  • the normalization is shown in Figures 2A to 2C.
  • the rate of sequestration is also proportional to the CO2 content of the surrounding gas. It is evident from this modelled data that if a CO2 containing gas were exposed to suitable rock particles sized at a p50 well below say 1mm, in the presence of water, sequestration would occur at an acceptable rate within a static heap.
  • the apparent particle comminution crush size of the material is typically greater than a p80 of 1mm and typically around 2- 5mm.
  • apparent particles can be made up mostly from solid rock, or from agglomerated fines, or from a mix of both. The macro-porosity between the apparent particles provides for even flow of gas through the heap.
  • the individual particles making up each accessible rock sequestration surface within the apparent particle should be less than 5mm, and preferably less than 1mm, and even more preferably less than 0.1mm.
  • suitable rock 10 is crushed to a size of ⁇ 5mm.
  • the rock is crushed 10 to less than 5mm, preferably between 1-5mm, and classified 12 to separate the rock into a finer fraction 14 with a p80 size ⁇ 1mm, and preferably between 0.15 – 1mm, with a remaining coarser fraction 16 having a p10 > 0.1mm and preferably greater than 0.15 mm.
  • the coarser fraction of rock 16 can be directly stacked in a permeable heap 18, designed to facilitate air flow through the heap
  • the finer fraction of rock 14 is agglomerated 20 to form agglomerated apparent particles 22 with a p80 of 1-5mm and a p10 of > 0.15mm.
  • these apparent particles may be cured to further enhance their structural integrity, prior to stacking.
  • the rock is crushed 10 to less than 5mm, and preferably between 1-5mm, and agglomerated 20 to bind the fines to the coarser particles and form agglomerated apparent particles 22 with a p80 of 1-5mm and a p10 of > 0.15mm.
  • these apparent particles may be cured to further enhance their structural integrity, prior to stacking.
  • the rock is crushed 10 to a p80 less than 0.5mm, and preferably to between 0.05- 0.2mm, and agglomerated 20 to bind the fines and form agglomerated apparent particles 22 with a p80 of 1-5mm and a p10 of > 0.15mm.
  • these apparent particles may be cured to further enhance their structural integrity, prior to stacking.
  • the particle size of the rock that forms the agglomerated fraction of the apparent particles can be adjusted according to the required sequestration rate. This is achieved whilst creating sufficiently a large surface area of rock, and large enough apparent particles to enhance heap porosity and gas distribution, and also creating a short flow length for CO2 to migrate in and react with the interior of the individual particles making up the apparent particle.
  • the coarser fraction of rock 16 and the agglomerated fraction 22 may be combined into a single heap or in separate heaps.
  • the stacked heap 18 is sequestered 24 by irrigation with an aqueous solution 26 to maintain the heap as a whole in an unsaturated condition to ensure adequate gas flow but with effective wetting of the heap of coarse sand from classification and wetting of the fine coating on the surface of the substrate.
  • the irrigation rate can be slower than that typically used for heap leaching, maintaining greater porosity for gas transfer.
  • the irrigation rate is typically less than 1 litre per m2 per hr.
  • the agglomerated rock can be reclaimed, deagglomerated, and if desired the coarser substrate recycled for further sequestration.
  • the rock in this form is suitably sized and presented in the heap such that any valuable metals can also be leached and recovered either prior to, concurrent with, or subsequent to the sequestration.
  • the individual components of the system which make up the various embodiments of the invention, are: •
  • the particle sizes are selected, prepared and stacked to provide for a high 3-dimensional surface area of a rock type that is suited to carbon sequestration, that also provides for a high overall porosity, and permeability of gas through the wetted rock structure •
  • the aqueous solution is selected and irrigated to distribute water, or solutions containing one or more of the additives to accelerate sequestration, to increase the reactivity of rock particles in the heap •
  • the gas flow is selected and managed to maintain an adequate CO2 content in the gas as it passes through the heap
  • the invention presents a 3-dimensional structure with high surface area, porosity and permeability, through the use of agglomeration and rock sizing suited to sequestration rates.
  • the binders that can be utilised for such agglomeration will be specific to each rock type. Examples are lime and or cement, added to the rock with controlled quantities of water. As has been demonstrated in the gold heap leaching industry, such binders create significant crush strength in the apparent particles such that they can be stacked in heaps several metres high. The binding does not substantively reduce the surface area of the agglomerated fines and is resistant to addition of water at the pH required for sequestration. Only minor degradation of the agglomerates occurs during subsequent stacking. And the different irrigation rates required for sequestration relative to heap leaching enable a lower crush size without loss of macro-permeability.
  • the binder also can be water, or other mixes of other organics which retain their structural integrity in aqueous solutions, or other fine pozzolanic materials, preferably containing soluble magnesium and/or salts of other sequestration accelerants such as ammonia or citrate.
  • the agglomeration strength of the apparent particles can be further enhanced by partial sequestration by addition of CO2 to the green agglomerates prior to stacking in large heaps.
  • Figure 4 shows a substrate 28 made from rock or other material suitable for sequestration coated with a fine material 30 suitable for sequestration and agglomeration (typically containing 10 to 200 micron fines in a coating of around 1mm thick) which during irrigation will become saturated, and large gaps 32 between the agglomerated particles through which air can flow past the wetted fines, enabling absorption of CO2.
  • This agglomeration process enables large air gaps 32 between adjoining apparent particles to enable a CO2 containing gas to circulate through the heap.
  • This high porosity typically 20 to 35% within the agglomerates and typically an additional 20 to 30% between agglomerates, is important to accommodate the increased molar volume that occurs during sequestration.
  • High permeability is also required such that gas can pass through the heap, gradually reducing the CO2 content in the gaseous phase.
  • the design is such that individual agglomerates are of a limited thickness of fines, as these can become saturated or close thereto, without substantively impeding CO2 transfer through to the reactive rock surfaces.
  • the agglomerated rock is stacked such as to avoid significant decrepitation of the agglomerates.
  • the agglomerates enable effective gas flow through the heap, and irrigation to maintain sufficient solution in the agglomerates and wetting the surface of the coarser sand, to maintain conditions suitable for sequestration of CO2 from the gas. Once sufficient sequestration has occurred, the agglomerated heap can be reclaimed.
  • the fines can be separated from any substrate, typically by washing, thus enabling recycling of the substrate for further agglomeration.
  • the fine sequestered rock can be stored in perpetuity, or further refined to produce other products.
  • a second set of embodiments making up the invention is the use of additives to further increase the rate of sequestration.
  • One preferred accelerant is a magnesium salt, which could typically be the sulphate or chloride salt.
  • An example could be the seawater or more concentrated brines.
  • the magnesium salt will be added to increase the magnesium concentration in the water film adhering to the rock, to avoid the delay in sequestration which would occur if all the magnesium to precipitate as MgCO 3 must be built up from the acidic dissolution of the rock.
  • a second preferred chemical accelerant for natural sequestration is a readily protonated/deprotonated acid which has a pKa of around 6-7. At this pKa, the accelerant can act as a buffer in the system accelerating both acid dissolution and CO2 absorption. Both citrate and EDTA have a pKa in the ideal range.
  • the third component making up the system that is this invention is provision of CO2 containing gas to the surface of the wetted particles that are stacked in the heaps. This gas can be added such as to pass through the apparently evenly sized 3-dimensional heap structure, with CO2 being removed during this permeation.
  • Sufficient CO2 flow into the heap is required to maintain an acceptable concentration of CO2 within the heap, even as it is being removed by sequestration as the gas flows through the heap.
  • the 3-dimensional structure can be utilised to enable natural sequestration with air, but rates will be slow as, even with the high permeability of the heaps, natural air flow through the heap will be rate limiting.
  • the system will sequester much faster than natural waste rock or tailings dams, but using air reactions will take many years for the solids to reach almost full sequestration capacity.
  • the system can also be utilised for sequestration of exhaust gasses that have a CO2 concentration much higher than natural air.
  • exhaust gasses that have a CO2 concentration much higher than natural air.
  • Examples might be exhaust gasses produced by thermal power generation or iron production or at a more localized level by various chemical processes.
  • gasses can be further enriched prior to addition to the heap.
  • the sequestration system can be located at the source, or the exhaust gas transferred to the rock location. These exhaust gasses can also be further concentrated up to close to 100% CO2.
  • the heap will be aerated from the base, using the exothermic nature of the sequestration rate to warm the heap. This natural heating of the heap can be supplemented by solar or other forms of heating of the gas as it is being directed into the base of the heap, or of the irrigant being supplied to the top of the heap.
  • the preferred alternative is to use a warm gas with elevated levels of CO2, even up to 100% CO2, such as that which is produced as part of thermal power generation or smelting; or generated by a direct air capture device.
  • This enables CO2 to be introduced to the heap at a much higher concentration resulting in a rate where the reactions will reach completion in a shorter duration, and heat retention in the heap can be enhanced.
  • the CO2 can be added in part to the irrigant externally, by contacting the CO2 source with irrigant recovered from the base of the heap. The increased CO2 solution activity achieved in the external contact vessel will enable partial precipitation and recovery of MgCO3 external to the heap.
  • the first ancillary benefit is the prior, simultaneous, or subsequent use of the crushed sand or the agglomerated heap structure to extract metals contained in the ultramafic ore. This recovery can be through coarse beneficiation or by heap leaching.
  • heap leaching requires similar high surface areas to expose the valuable metal minerals, and particularly where the values are in the form of sulphide minerals, well aerated conditions.
  • a complexant such as ammonia or citrate
  • nickel recovery at a basic pH is satisfactory.
  • subsequent sequestration capacity is retained.
  • the second ancillary benefit is that the accelerated rate of sequestration offered by the invention which extends the range of mineral types in which the sequestration can be achieved at a reasonable rate.
  • the agglomeration component of the invention can be utilised to sequester carbon in reclaimed historical residues.
  • these can be tailings and waste rock from historical nickel, diamonds, asbestos, PGMs and chrome mining. These fine tailings are often highly reactive for sequestration but have been stored such that access to air has been limited. Agglomerating the historical tailings, enables their stacking with high permeability, thus enhancing ongoing sequestration.
  • this preparation for sequestration can even be integrated with additional recovery of the leachable values contained in the tailings.
  • slags from smelters, fly-ash from coal combustion, and other historical wastes can be utilised for sequestration.
  • the fourth ancillary benefit is the impact of the coarser crush size on energy consumption. The increase in the mean size of rock at which sequestration can take place at a meaningful rate, reduces both the cost of crushing.
  • the fifth ancillary benefit of the much faster reaction rate is the low footprint and the consequential ability to collocate a sequestration heap at the site of a high concentration of CO2 emissions, such as directly from a combustion source such as a blast furnace, power plant, or cement kiln.
  • the CO2 source can be generated from separation of natural gas or the production of hydrogen from various organic feedstocks.
  • the faster sequestration rate enables not only a smaller footprint but also a much more extensive capture of CO2 as the emissions gas flows through the heap.
  • efficient ex-situ capture of CO2 from these large carbon sources becomes practically achievable in the residence times within a heap, whether the rock is transferred to the carbon source, or the CO2 gas is transferred to the heap.
  • the carbonate that is sequestered either in the heap or in external carbonation reactions can be recovered after the sequestration for subsequent sale.
  • the hydrated magnesium carbonate precipitated during sequestration could be recovered for use as a fire retardant, or a soil additive.
  • one or more of the agglomerated fines or the sand prepared for sequestration can be transported and utilised at smaller and more localized sites.
  • the sequestration could be undertaken in a suitable reactor located in a suburban environment, with subsequent disposal of the sequestered rock, and replacement with a fresh charge at appropriate intervals.
  • the invention could be utilised for bioremediation of sewerage with sequestration of the carbon dioxide formed by the oxidation of the organic matter.
  • the prepared rock could be used to strip CO2 from recirculating air within a confined space.
  • the preparation of rock in permeable aerated heaps at a particle size and apparent particle size that enables effective sequestration, and with potential addition of accelerants through the liquid phase of the system, and with effectively distributed gas flow through the permeable heap, creates optionality for not only effective natural sequestration of carbon dioxide, but also for configuring the system for wider applications.
  • Example 1 To illustrate the potential for sequestration of ultramafic rock, samples were selected from two different nickel resources, one Canadian and the second Finnish. Also compared were a South African PGM ore, and a ferronickel slag from Brazil. In each case, the rock was ground to 80% ⁇ 75 micron, mixed with 30% moisture and placed in a container with a depth of a few centimetres to measure the uptake from a CO2 enriched atmosphere (cycling between 50% and as low as a few %) at 70oC. Sequestration rates, measured in kg CO2/tonne rock, are illustrated in figure 5. These rates demonstrate that with a high surface area achieved by fine crushing, sequestration can be achieved in a 3-dimensional heap.
  • Example 2 A sample of a South African PGM ore was ground to ⁇ 106 micron, and then pelletised using a small pelletising disc, using 8% moisture content with various binders. Cement added in various levels in the range from 3-10% by weight, or lime at around 5% by weight, all formed competent pellets that were capable of stacking, and were also resistant to subsequent water flow. The agglomerates were sized at between 1-3mm. Details of the pellets are provided in Table 1 below. Table 1

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Abstract

La présente invention concerne un procédé de séquestration d'un gaz contenant du CO2 à l'aide de la préparation d'une zone à haute surface d'une roche adaptée à la séquestration dans un tas perméable tridimensionnel. Le procédé comprend les étapes consistant à obtenir, ou à obtenir et à pulvériser, un matériau (10) adaptée à la séquestration de CO2, afin de produire une charge d'alimentation présentant une valeur p80 inférieure à 5 mm. La charge d'alimentation est séparée en une fraction grossière (16) et une fraction fine (16), et la fraction fine est agglomérée (20) afin de former des particules agglomérées (22) présentant une valeur p80 apparente inférieure à 10 mm et une valeur p10 > 0,15 mm. Les particules agglomérées sont empilées en un tas (18), et un gaz contenant du CO2, et un agent d'irrigation (26), sont passés à travers le tas perméable et insaturé, afin de séquestrer (24) le CO2 contenu dans le gaz.
PCT/IB2022/056833 2021-07-23 2022-07-25 Procédés d'accélération de séquestration de carbone WO2023002460A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090139234A1 (en) * 2006-01-16 2009-06-04 Gurin Michael H Carbon dioxide as fuel for power generation and sequestration system
US20110313218A1 (en) * 2010-03-23 2011-12-22 Dana Todd C Systems, Apparatus and Methods of a Dome Retort
US20120213688A1 (en) * 2007-12-28 2012-08-23 Constantz Brent R Methods of sequestering co2
US20140127094A1 (en) * 2012-11-02 2014-05-08 Strategic Metals Ltd. Processing of sulfate and/or sulfide-rich waste using co2-enriched gases to sequester co2, reduce environmental impacts including acid rock drainage and produce reaction products
US20160121298A1 (en) * 2014-10-09 2016-05-05 Blue Planet, Ltd. Continuous carbon sequestration material production methods and systems for practicing the same

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090139234A1 (en) * 2006-01-16 2009-06-04 Gurin Michael H Carbon dioxide as fuel for power generation and sequestration system
US20120213688A1 (en) * 2007-12-28 2012-08-23 Constantz Brent R Methods of sequestering co2
US20110313218A1 (en) * 2010-03-23 2011-12-22 Dana Todd C Systems, Apparatus and Methods of a Dome Retort
US20140127094A1 (en) * 2012-11-02 2014-05-08 Strategic Metals Ltd. Processing of sulfate and/or sulfide-rich waste using co2-enriched gases to sequester co2, reduce environmental impacts including acid rock drainage and produce reaction products
US20160121298A1 (en) * 2014-10-09 2016-05-05 Blue Planet, Ltd. Continuous carbon sequestration material production methods and systems for practicing the same

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