METHODS FOR OBTAINING CARBON NEUTRAL OR CARBON NEGATIVE METALS FROM PLANTS, AND RELATED COMPOSITIONS
20260002233 ยท 2026-01-01
Assignee
Inventors
Cpc classification
C22B23/0453
CHEMISTRY; METALLURGY
C22B3/08
CHEMISTRY; METALLURGY
C22B1/14
CHEMISTRY; METALLURGY
International classification
C22B3/00
CHEMISTRY; METALLURGY
C22B1/14
CHEMISTRY; METALLURGY
C22B3/08
CHEMISTRY; METALLURGY
Abstract
Provided are methods of extracting metals from rocks and sequestering carbon dioxide. In some embodiments, provided are methods of using phytomining to extract metals from ultramafic rocks while sequestering carbon dioxide. Provided are also compositions, including metal compositions produced by the methods herein.
Claims
1. A method, comprising: mechanically grinding a weatherable rock comprising at least 20% by weight of magnesium, and at least 0.1% each by weight of one or more metal to provide a particulate weatherable rock composition; combining the particulate weatherable rock composition with a soil to provide a weatherable rock-enriched soil; subjecting the weatherable rock-enriched soil to conditions sufficient to cause the weatherable rock to undergo a chemical weathering process, wherein the chemical weathering process releases the one or more metals; and growing one or more metal hyperaccumulator plant in the weatherable rock-enriched soil, wherein each of the metal hyperaccumulator plants is a hyperaccumulator of at least one of the one or more metals released from the weatherable rock.
2. The method of claim 1, further comprising: harvesting the one or more metal hyperaccumulator plant; and processing the one or more harvested metal hyperaccumulator plant to provide one or more substantially pure metal.
3. The method of claim 1, wherein the at least one metal comprises nickel, cobalt, chromium, or a combination thereof.
4. The method of claim 2, wherein the processing of the harvested metal hyperaccumulator plants comprises: ashing the harvested metal hyperaccumulator plant to provide a metal-enriched ash comprising at least 5% of the one or more metal by weight; and refining the metal-enriched ash composition to provide one or more substantially pure metal.
5. The method of claim 1, wherein Mg.sup.2+ is leached at a rate of at least 1% by weight of the total Mg.sup.2+ in the weatherable rock per year from the weatherable rock-enriched soil while the metal hyperaccumulator plant is growing.
6. The method of claim 1, wherein at least 10 tonnes of carbon dioxide are sequestered for every tonne of metal that is produced.
7. The method of claim 1, wherein the weatherable rock comprises ultramafic or mafic rock containing trace levels of the metal.
8. The method of claim 1, wherein the weatherable rock comprises serpentine or serpentinite, or a combination thereof.
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. The method of claim 1, wherein the particulate weatherable rock composition has a particle size between 1 m and 10 cm.
14. The method of claim 1, wherein the weatherable rock-enriched soil comprises between 10% and 100% particulate weatherable rock composition by weight.
15. The method of claim 1, wherein the metal hyperaccumulator plant is a plant belonging to the genus Odontarrhena.
16. (canceled)
17. The method of claim 1, wherein growing a metal hyperaccumulator plant in the weatherable rock-enriched soil further comprises continuously irrigating the weatherable rock-enriched soil.
18. The method of claim 1, wherein the pH of the weatherable rock-enriched soil is at least 7.
19. (canceled)
20. The method of claim 2, wherein the processing of the harvested metal hyperaccumulator plant comprises: directly leaching the harvested metal hyperaccumulator plant using sulfuric acid to provide an acid leachate; purifying the acid leachate using column chromatography to provide a Ni-enriched acid leachate; and processing the Ni-enhanced acid leachate to provide a substantially pure nickel.
21. The method of claim 3, wherein the at least one metal is nickel, and wherein refining the metal-enriched ash composition comprises: leaching the metal-enriched ash composition to provide a leachate; recovering nickel from the leachate using solvent extraction or an ion exchange resin to obtain a recovered nickel composition; and purifying the recovered nickel composition using electrowinning to obtain a substantially pure nickel.
22. The method of claim 3, wherein the at least one metal is nickel, and wherein refining the metal-enriched ash composition comprises: acid leaching the metal-enriched ash composition to provide an acid leachate; neutralizing the acid leachate with Ca(OH).sub.2 to provide a first treated leachate; adding NaF to the neutralized leachate to provide a second treated leachate; adding ammonium sulfate to the second treated leachate to provide a third treated leachate; drying the third treated leachate to provide ammonium Ni sulfate hexahydrate (ANSH); and processing the ANSH to obtain a substantially pure nickel.
23. (canceled)
24. (canceled)
25. A processed nickel composition comprising substantially pure nickel, and one or more of the following (i)-(v): (i) precipitated gypsum; (ii) one or more low weight carboxylic acids; (iii) one or more Ni-containing compounds selected from the group consisting of NiO, Ni(OH).sub.2, nickel sulfides, nickel hydroxides, nickel oxalate, and nickel sulfate; or (iv) one or more carbonates selected from the group consisting of K.sub.2CO.sub.3, CaCO.sub.3, K.sub.2Ca(CO.sub.3).sub.2.
26. A nickel-enriched ash comprising at least 5% nickel by weight, and one or more of the following (i)-(v): (i) one or more elements selected from the group consisting of Ca, Fe, K, Mg, P, C, H, N, and O; (ii) one or more carbonates selected from the group consisting of K.sub.2CO.sub.3, CaCO.sub.3, K.sub.2Ca(CO.sub.3).sub.2; (iii) plant cells; (iv) hydroxyapatite or oxy-hydroxyapatite; or (v) one or more oxides selected from the group consisting of NiO, CaO, MgO, and MgNiO.sub.2.
27. A method for sequestering carbon dioxide, comprising: providing a weatherable rock comprising a metal; subjecting the weatherable rock to conditions sufficient to cause the weatherable rock to undergo a chemical weathering process at an accelerated rate relative to natural chemical weathering, wherein the chemical weathering process generates alkalinity and releases the metal, and wherein the alkalinity facilitates the sequestration of carbon dioxide by converting carbon dioxide to bicarbonate or carbonate; and extracting and processing the released metal to provide a metal-enriched composition.
28. The method of claim 27, wherein: the subjecting of the weatherable rock comprises growing a metal hyperaccumulator plant in the weatherable rock; and the extracting and the processing of the released metal comprises growing a metal hyperaccumulator plant in the weatherable rock.
Description
DESCRIPTION OF THE FIGURES
[0032] The present application can be understood by reference to the following description taken in conjunction with the accompanying figures.
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DETAILED DESCRIPTION
[0050] The following description sets forth exemplary compositions, methods, systems, parameters and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure but is instead provided as a description of exemplary embodiments.
[0051] In one aspect, provided herein is a method of sequestering carbon dioxide comprising providing a weatherable rock comprising one or more metals, subjecting the weatherable rock to conditions sufficient to cause the rock to undergo a chemical weathering process at an accelerated rate relative to natural chemical weathering, wherein the chemical weathering process generates alkalinity and releases the one or more metals, and wherein the alkalinity facilitates the sequestration of carbon dioxide through the conversion of carbon dioxide to bicarbonate or carbonate, and extracting and processing the released metals to provide a metal-enriched composition. In some embodiments, the conditions cited above comprise growing one or more metal hyperaccumulator plants in a medium comprising the weatherable rock. In some embodiments, the conditions comprise growing one or more metal hyperaccumulator plants in a medium comprising the weatherable rock and continuously irrigating the one or more metal hyperaccumulator plants using a drip irrigation system. In some embodiments, the extracting and processing the released one or more metals comprises growing one or more metal hyperaccumulator plants in a medium comprising the weatherable rock, wherein the one or more metal hyperaccumulator plants accumulate the released one or more metals. In some embodiments the extracting and processing the released one or more metals further comprises processing the metal hyperaccumulator biomass using any suitable technique known in the art to prepare a metal-enriched composition. In some embodiments, the one or more metals comprise a heavy metal. In some embodiments, the one or more metals comprise a toxic metal. In some embodiments, the one or more metals comprise a metal selected from the group consisting of Ni, Cr, Co, Al, Ag, Cu, Mn, Mo, Hg, Mo, Pb, or Zn, or any combination thereof. In some embodiments, the one or more metals comprise cobalt. In some embodiments, the one or more metals comprise chromium. In some embodiments, the one or more metals comprise nickel. In some embodiment the one or more metals comprise any metal that can be hyperaccumulated by a hyperaccumulator plant. In some embodiments, providing the weatherable rock comprises mining the weatherable rock. In some embodiments, providing the weatherable rock further comprises mechanically processing the weatherable rock to reduce the particle size of the weatherable rock to between about 1 m and about 10 cm. In some embodiments, providing the weatherable rock further comprises admixing the weatherable rock with one or more additional growing media including, for example, soil.
[0052] In one aspect, provided herein is a method of sequestering carbon dioxide comprising providing a weatherable rock comprising a metal, subjecting the weatherable rock to conditions sufficient to cause the rock to undergo a chemical weathering process at an accelerated rate relative to natural chemical weathering, wherein the chemical weathering process generates alkalinity and releases the metal, and wherein the alkalinity facilitates the sequestration of carbon dioxide through the conversion of carbon dioxide to bicarbonate or carbonate, and extracting and processing the released metal to provide a metal-enriched composition. In some embodiments, the conditions cited above comprise growing a metal hyperaccumulator plant in a medium comprising the weatherable rock. In some embodiments, the conditions comprise growing a metal hyperaccumulator plant in a medium comprising the weatherable rock and continuously irrigating the metal hyperaccumulator plant using a drip irrigation system. In some embodiments, the extracting and processing the released metal comprises growing a metal hyperaccumulator plant in a medium comprising the weatherable rock, wherein the metal hyperaccumulator plant accumulates the released metal. In some embodiments the extracting and processing the released metal further comprises processing the metal hyperaccumulator biomass using any suitable technique known in the art to prepare a metal-enriched composition. In some embodiments, the metal is a heavy metal. In some embodiments, the metal is a toxic metal. In some embodiments, the metal is selected from the group consisting of Ni, Cr, Co, Al, Ag, Cu, Mn, Mo, Hg, Mo, Pb, or Zn, or any combination thereof. In some embodiments, the metal comprises cobalt. In some embodiments, the metal comprises chromium. In some embodiments, the metal comprises nickel. In some embodiment the metal is any metal that can be hyperaccumulated by a hyperaccumulator plant.
[0053] In some embodiments, the weatherable rock comprises a magnesium-bearing silicate mineral. In certain embodiments, the magnesium-bearing silicate mineral is in the olivine mineral group. In certain embodiments, the magnesium-bearing silicate mineral is in the serpentinite mineral group. In other variations, any combination of suitable weatherable rocks described herein may be used.
[0054] In some embodiments, providing the weatherable rock comprises mining the weatherable rock. In some embodiments, providing the weatherable rock further comprises mechanically processing the weatherable rock to reduce the particle size of the weatherable rock to between about 1 m and about 10 cm. In some embodiments, providing the weatherable rock further comprises admixing the weatherable rock with one or more additional growing media including, for example, soil.
[0055] In another aspect, provided herein is a method that utilizes plants that are not only tolerant to serpentine, but that evolved especially to live in high alkalinity (e.g., high pH) soils, composed of high percentages of low nutrient and metal heavy soils. These plants that typically take up nickel as a means of protection can be utilized to produce commercial yields of nickel. In certain aspects, provided is a method to bring fresh serpentine-containing rock from nearby quarries, utilizing mechanical activation to grind them to particles, for example micron-sized particles, to increase the reactive surface area, then transported to fields where nickel hyperaccumulating plants have been planted to capture the nickel release from the soil, and also accelerate the release of magnesium ions from the crystal lattice of the serpentine in order to increase the amount of carbon sequestered when those ions run off to the ocean. The methods provided herein overcome the previous blockers that prevented the deployment of terrestrial enhanced weathering for the purposes of carbon removal, and by increasing the revenue streams available to the process are able to make direct and intentional phytomining possible. The methods provided make phytomining a primary mining technique. In some variations, the methods can also use tailings, waste, or overburden from traditional nickel mines. In certain variations, the methods involve actively grinding minerals to below a certain size in order to specifically increase the reactive surface area. Further, in some variations, direct irrigation can be utilized to both enhance the weathering rate, and increase the plant growth, the plant then releases acids that further break down the rocks, releasing magnesium that leads to carbon removal and drawing nickel into the plants, preventing its release into the environment.
[0056] In some variations of the foregoing, the chemical weathering process results in the formation of new soil minerals. In certain variations of the foregoing, the chemical weathering process results in fully weathered rock. In some embodiments, the weathering process results in fully weathered rock within about 20 years; or between 1 year and 20 years; or within about 1 year, about 2 years, about 3 years, about 4 years, about 5 years, about 6 years, about 7 years, about 8 years, about 9 years, about 10 years, about 11 years, about 12 years, about 13 years, about 14 years, about 15 years, about 16 years, about 17 years, about 18 years, about 19 years, or about 20 years.
[0057] With reference to
[0058] Thus, in some embodiments, provided is a method for preparing a metal comprising mechanically grinding a weatherable rock comprising magnesium, and a metal to provide a particulate weatherable rock composition; combining the particulate weatherable rock composition with a soil to provide a weatherable rock-enriched soil; growing a plant that is a hyperaccumulator of the metal in the weatherable rock-enriched soil; harvesting the metal hyperaccumulator plant; and processing the harvested metal hyperaccumulator plant to provide a substantially pure metal. In some embodiments, processing the harvested metal hyperaccumulator plant comprises ashing the harvested metal hyperaccumulator plant to provide a metal-enriched ash and refining the metal-enriched composition to provide a substantially pure metal by weight. In some embodiments, processing the harvested metal hyperaccumulator plant to provide a substantially pure metal may be accomplished using any suitable techniques known in the art. In some embodiments, the weatherable rock comprises at least 20% by weight of magnesium and 0.1% by weight of the metal. In some embodiments, the metal-enriched ash comprises at least 5% of the metal by weight.
[0059] In some embodiments, provided is a method for preparing one or more metals comprising mechanically grinding a weatherable rock comprising magnesium, and one or more metals to provide a particulate weatherable rock composition; either combining the particulate weatherable rock composition with a soil to provide a weatherable rock-enriched soil or using the particulate weatherable rock composition directly as a weatherable rock-enriched soil without combining it with any additional media; growing one or more metal hyperaccumulator plants in the weatherable rock-enriched soil, wherein each of the one or more plants is a hyperaccumulator of at least one of the one or more metals; harvesting the one or more metal hyperaccumulator plants; and processing the one or more harvested metal hyperaccumulator plants to provide one or more substantially pure metals. In some embodiments, processing the one or more harvested metal hyperaccumulator plants comprises ashing the harvested metal hyperaccumulator plant to provide a metal-enriched ash and refining the metal-enriched composition to provide one or more substantially pure metals by weight. In some embodiments, processing the harvested metal hyperaccumulator plant to provide one or more substantially pure metals may be accomplished using any suitable techniques known in the art. In some embodiments, the weatherable rock comprises at least 20% by weight of magnesium and 0.1% by weight of each of the one or more metals. In some embodiments, the metal-enriched ash comprises at least 5% of each of the one or more metals by weight.
[0060] In some embodiments, provided is a method for obtaining one or more substantially pure metals comprising mechanically grinding a weatherable rock comprising at least 20% by weight of magnesium and at least 0.1% by weight of each of the one or more metals to provide a particulate weatherable rock composition; combining the particulate weatherable rock composition with a soil to provide a weatherable rock-enriched soil; growing one or more metal hyperaccumulator plants in the weatherable rock-enriched soil, wherein each of the one or more plants is a hyperaccumulator of at least one of the one or more metals; harvesting the one or more metal hyperaccumulator plants; and processing the one or more harvested metal hyperaccumulator plants to provide one or more substantially pure metals.
[0061] In some variations, substantially pure metal refers to a metal that is at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.9%, at least 99.99%. at least 99.999%, or at least 99.9999% pure by weight.
[0062] In some embodiments, Mg.sup.2+ is leached at a rate of at least 1% by weight of the total Mg.sup.2+ in the weatherable rock per year from the weatherable rock-enriched soil while the metal hyperaccumulator plant is growing. In some embodiments, about 10% of the Mg by weight is weathered per year. In some embodiments, about 90% of the Mg by weight is weathered per month. In some embodiments, at least about 90% of the weatherable Mg.sup.2+ ions by weight are liberated. In some embodiments, at least about 90% of the weatherable Mg.sup.2+ ions by weight are liberated over a period of about 20 years. In some embodiments, at least about 90% of the weatherable Mg.sup.2+ ions by weight are liberated over a period of less than about 20 years. In any of the foregoing embodiments, the weight of Mg.sup.2+ refers to the weight of the magnesium component alone, and does not include, for example, the weight of any ligands or counter ions in any complexes or salts that the Mg.sup.2+ is a part of.
[0063] In some embodiments, provided is a method for preparing a metal comprising mechanically grinding a weatherable rock comprising calcium and a metal to provide a particulate weatherable rock composition; combining the particulate weatherable rock composition with a soil to provide a weatherable rock-enriched soil; growing a plant that is a hyperaccumulator of the metal in the weatherable rock-enriched soil; harvesting the metal hyperaccumulator plant; and processing the harvested metal hyperaccumulator plant to provide a substantially pure metal. In some embodiments, processing the harvested metal hyperaccumulator plant comprises ashing the harvested metal hyperaccumulator plant to provide a metal-enriched ash and refining the metal-enriched composition to provide a substantially pure metal by weight. In some embodiments, processing the harvested metal hyperaccumulator plant to provide a substantially pure metal may be accomplished using any suitable techniques known in the art. In some embodiments, the weatherable rock comprises at least 10% by weight of calcium and at least 0.1% by weight of the metal. In some embodiments, the metal-enriched ash comprises at least 5% of the metal by weight.
[0064] In some embodiments, Ca.sup.2+ is leached at a rate of at least 1% by weight of the total Ca.sup.2+ in the weatherable rock per year from the weatherable rock-enriched soil while the metal hyperaccumulator plant is growing. In some embodiments, about 10% of the Ca by weight is weathered per year. In some embodiments, about 90% of the Ca by weight is weathered per month. In some embodiments, at least about 90% of the weatherable Ca.sup.2+ ions by weight are liberated. In some embodiments, at least about 90% of the weatherable Ca.sup.2+ ions by weight are liberated over a period of about 20 years. In some embodiments, at least about 90% of the weatherable Ca.sup.2+ ions by weight are liberated over a period of less than about 20 years. In any of the foregoing embodiments, the weight of Ca.sup.2+ refers to the weight of the calcium component alone, and does not include, for example, the weight of any ligands or counter ions in any complexes or salts that the Ca.sup.2+ is a part of.
[0065] In some embodiments, the rate at which Mg.sup.2+ is leached is measured by measuring the concentration of the Mg.sup.2+ in the water used to irrigate the hyperaccumulator plant. In some embodiments, the rate at which Ca.sup.2+ is leached is measured by measuring the concentration of Ca.sup.2+ in the water used to irrigate the hyperaccumulator plant.
[0066] In some variations of the foregoing, the weatherable rock comprises between 0.01% and 20% of the metal by weight. In some embodiments, the weatherable rock comprises between 0.2% and 0.4% of the metal by weight. In some embodiments, the weatherable rock comprises at least about 0.2% metal by weight. In some embodiments, the weatherable rock comprises about 0.01%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1%, about 2%, about 3%, about 4%, about 5%, about 10%, about 15%, about 20%, or about 25% by weight of the metal.
[0067] In some embodiments, the metal comprises Ni, Cr, Co, Al, Ag, Cu, Mn, Mo, Hg, Mo, Pb, or Zn, or any combination thereof. In some embodiments, the metal comprises a rare earth metal. In some embodiments, the metal comprises nickel. In some embodiments, the metal comprises cobalt. In some embodiments, the metal comprises chromium. In some embodiments, the metal is a metal that can be hyperaccumulated by a hyperaccumulator plant. In some embodiments, the metal is a metal found in a weatherable rock. In some embodiments, the metal is a metal found in a weatherable rock that can be hyperaccumulated by a hyperaccumulator plant.
[0068] In some embodiments, provided is a method for preparing a metal comprising mechanically grinding a weatherable rock comprising magnesium and nickel to provide a particulate weatherable rock composition; combining the particulate weatherable rock composition with a soil to provide a weatherable rock-enriched soil; liberating nickel from the weatherable rock by subjecting the weatherable rock-enriched soil to conditions sufficient to cause the weatherable rock to undergo a chemical weathering process at an accelerated rate relative to natural chemical weathering, wherein acid is not added to the weatherable rock-enriched soil; growing a plant that is a hyperaccumulator of nickel in the weatherable rock-enriched soil; harvesting the nickel hyperaccumulator plant; and processing the harvested nickel hyperaccumulator plant to provide substantially pure nickel.
[0069] In some embodiments, the amount of carbon dioxide emitted from the weathering of the weatherable rock is less than amount of carbon dioxide sequestered from the weathering of the weatherable rock. In some embodiments, the amount of carbon dioxide emitted from the weathering of the weatherable rock, harvesting the nickel hyperaccumulator plant, and processing the harvested nickel hyperaccumulator plant is less than amount of carbon dioxide sequestered from the weathering of the weatherable rock.
[0070] In some embodiments, provided is a method for preparing nickel metal comprising mechanically grinding a weatherable rock comprising magnesium, and nickel to provide a particulate weatherable rock composition; combining the particulate weatherable rock composition with a soil to provide a weatherable rock-enriched soil; growing a nickel hyperaccumulator plant in the weatherable rock-enriched soil; harvesting the nickel hyperaccumulator plant; and processing the harvested nickel hyperaccumulator plant to provide a substantially pure nickel. In some embodiments, processing the harvested nickel hyperaccumulator plant comprises ashing the harvested nickel hyperaccumulator plant to provide a nickel-enriched ash and refining the nickel-enriched composition to provide a substantially pure nickel by weight. In some embodiments, processing the harvested nickel hyperaccumulator plant to provide a substantially pure nickel may be accomplished using any suitable techniques known in the art. In some embodiments, the weatherable rock comprises at least 10% by weight of magnesium and at least 0.1% by weight of nickel. In some embodiments, the nickel-enriched ash comprises at least 5% nickel by weight.
[0071] In some variations of the foregoing, Mg.sup.2+ is leached at a rate of at least 1% by weight of the total Mg.sup.2+ in the weatherable rock per year from the weatherable rock-enriched soil while the nickel hyperaccumulator plant is growing.
[0072] In some variations of the foregoing, the weatherable rock comprises between 5% and 60% Mg by weight. In some embodiments, the weatherable rock comprises between 25% and 50% Mg by weight. In some embodiments, the weatherable rock comprises about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, or about 70% Mg by weight.
[0073] In some variations of the foregoing, the weatherable rock comprises between 5% and 60% Ca by weight. In some embodiments, the weatherable rock comprises between 25% and 50% Ca by weight. In some embodiments, the weatherable rock comprises about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, or about 70% Ca by weight.
[0074] In some variations of the foregoing, the weatherable rock comprises between 0.01% and 20% of nickel by weight. In some embodiments, the weatherable rock comprises between 0.2% and 0.4% of nickel by weight. In some embodiments, the weatherable rock comprises at least about 0.2% metal by weight. In some embodiments, the weatherable rock comprises about 0.01%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1%, about 2%, about 3%, about 4%, about 5%, about 10%, about 15%, about 20%, or about 25% by weight of nickel.
[0075] In some variations of the foregoing, the weatherable rock comprises nickel and Mg. In some embodiments, the weatherable rock comprises between 0.01% and 25% of nickel by weight and between 5% and 60% of Mg by weight. In some embodiments, the weatherable rock comprises between 0.01% and 25% of nickel by weight and between 25% and 50% of Mg by weight.
[0076] In some embodiments, the weatherable rock comprises between 0.2% and 0.4% of nickel by weight. In some embodiments, the weatherable rock comprises at least about 0.2% metal by weight. In some embodiments, the weatherable rock comprises about 0.01%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1%, about 2%, about 3%, about 4%, about 5%, about 10%, about 15%, about 20%, or about 25% by weight of nickel.
[0077] In some variations of the foregoing, the nickel-enriched ash composition comprises between 1% and 99.8% nickel by weight. In some embodiments, the nickel-enriched ash composition comprises between 1% and 35% nickel by weight. In some embodiments, the nickel-enriched ash composition comprises between 1% and 30% nickel by weight. In some embodiments, the nickel-enriched ash composition comprises between 0.1% and 30% nickel by weight. In some embodiments, the nickel-enriched ash composition comprises between 0.1% and 20% nickel by weight. In some embodiments, the nickel-enriched ash composition comprises between 0.1% and 15% nickel by weight. In some embodiments, the nickel-enriched ash composition comprises about 0.1%, about 0.5%, about 1%, about 1.5%, about 2%, about 2.5%, about 3%, about 4%, about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, or about 40% nickel by weight.
[0078] In some variations of the foregoing, refining the nickel-enriched composition provides a nickel that is at least 15%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98%, at least 99%, at least 99.9%, at least 99.9%, at least 99.99%, at least 99.999%, or at least 99.9999% pure by weight. In some embodiments, refining the nickel-enriched composition provides a nickel that is between 15% and 100% pure by weight.
[0079] In some embodiments, ashing the harvested nickel hyperaccumulator plant comprises drying the nickel hyperaccumulator plant to provide a dried biomass composition, crushing the dried biomass composition to provide a crushed biomass composition; and burning the crushed biomass composition to provide a nickel-enriched ash composition. In some embodiments, the ashing is performed at a temperature of about 500 C.
[0080] In some embodiments, processing the harvested nickel hyperaccumulator plant comprises directly leaching the harvested nickel hyperaccumulator plant to provide a leachate; purifying the leachate to provide a Ni-enriched leachate; and further processing the Ni-enhanced leachate to provide a substantially pure nickel. In some embodiments, the direct leaching is performed using a hydrothermal process. In some embodiments, the direct leaching is performed in acid. In some embodiments, the acid is sulfuric acid. In some embodiments, the acid is hydrochloric acid. In some embodiments purifying the leachate comprises purifying the leachate using column chromatography. In some embodiments purifying the leachate comprises purifying the leachate using solvent extraction. In some embodiments purifying the leachate comprises purifying the leachate using ion exchange chromatography. In some embodiments, further processing the Ni-enhanced leachate comprises electrowinning the nickel.
[0081] In some embodiments, processing the harvested nickel hyperaccumulator plant comprises ashing the harvested nickel hyperaccumulator plant to provide a nickel-enriched ash, leaching the nickel-enriched ash composition to provide a leachate, treating the leachate to provide ammonium Ni sulfate hexahydrate (ANSH), and processing the ANSH to obtain a substantially pure nickel. In some embodiments, the leaching is performed in acid. In some embodiments treating the leachate comprises neutralizing the leachate using a base to provide a first treated leachate, adding a fluoride source to the first treated leachate to provide a second treated leachate, adding ammonium sulfate to the second treated leachate to provide a third treated leachate, and drying the third treated leachate to provide ANSH. In some embodiments, the base is Ca(OH).sub.2. In some embodiments, the fluoride source is NaF. In some embodiments, treating the leachate comprises purifying the ANSH via recrystallization.
[0082] In some embodiments, provided is a method for preparing nickel catalysts comprising mechanically grinding a weatherable rock comprising magnesium, and nickel to provide a particulate weatherable rock composition; combining the particulate weatherable rock composition with a soil to provide a weatherable rock-enriched soil; growing a nickel hyperaccumulator plant in the weatherable rock-enriched soil; harvesting the nickel hyperaccumulator plant; and processing the harvested nickel hyperaccumulator plant to provide nickel catalysts. In some embodiments, processing the harvested nickel hyperaccumulator plant comprises ashing the harvested nickel hyperaccumulator plant to provide a nickel-enriched ash, leaching the nickel-enriched ash to provide a leachate, and further processing the leachate to provide nickel catalysts. In some embodiments, the ashing is performed at a temperature of 500 C. In some embodiments, the leaching is performed in acid. In some embodiments, the acid is hydrochloric acid. In some embodiments, further processing the leachate to provide nickel catalysts comprises dispersing the leachate onto montromorillonite K10. In some embodiments, the weatherable rock comprises at least 10% by weight of magnesium and at least 0.1% by weight of nickel.
[0083] In some embodiments, the amount of carbon dioxide sequestered is on the tonne scale for every tonne of nickel metal that is produced. In some embodiments, at least 1 tonne, at least 5 tonnes, at least 10 tonnes, at least 20 tonnes, at least 30 tonnes, or at least 40 tonnes of carbon dioxide are sequestered for every tonne of nickel metal that is produced. In some embodiments, between 1 tonne and 100 tonnes, or between 10 tonnes and 100 tonnes of carbon dioxide are sequestered for every tonne of nickel metal that is produced. In some embodiments, between 100 tonnes and 500 tonnes, or between 300 tonnes and 500 tonnes of carbon dioxide are sequestered for every tonne of nickel metal that is produced.
[0084] In some embodiments, the weatherable rock comprises an ultramafic rock. In some embodiments, the weatherable rock comprises serpentine. In some embodiments, the weatherable rock comprises serpentinite. In some embodiments, the weatherable rock comprises olivine. In some embodiments, the weatherable rock contains less than 1% by weight of nickel. In some embodiments, the weatherable rock contains a metal that can be hyperaccumulated by a hyperaccumulator plant.
[0085] In some embodiments, the method further comprises mining the weatherable rock. In other embodiments, the method further comprises transporting the mined weatherable rock from a mining location to a grinding location.
[0086] In some embodiments, mechanically grinding the weatherable rock comprises crushing and/or milling the weatherable rock. In some embodiments, the energy used to mechanically grind the rock comes from renewable sources.
[0087] In some embodiments, the particulate weatherable rock composition has an average particle size between about 1 m and about 10 mm, between about 1 m and about 10 cm, between about 1 m and about 20 cm, between about 1 m to about 5 mm, between about 1 m to about 3 mm, or between about 100 m to about 3 mm.
[0088] In some embodiments, the weatherable rock-enriched soil comprises between 10% and 100%, between 70% and 100%, between 70% and 90%, between 70% and 80%, or between 80% and 90% particulate weatherable rock composition by weight. In certain embodiments, the weatherable rock-enriched soil comprises about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, or about 100% particulate weatherable rock composition by weight.
[0089] In some embodiments, the weatherable rock-enriched soil is formed by natural weathering of silicate rocks. In some embodiments, the weatherable rock-enriched soil is formed by natural weathering of serpentinite rocks. In some embodiments, the weatherable rock-enriched soil is formed by natural weathering of olivine rocks. In some embodiments, natural weathering of serpentinite rocks results in weatherable rock-enriched soil with high nickel concentrations.
[0090] In some embodiments, the nickel hyperaccumulator plant is a plant belonging to the genus Odontarrhena. In some embodiments the plant belongs to the genus Alyssum. In some embodiments the plant belongs to the family Brassicacaea. In some embodiments the plant belongs to the genus Bornmuellera. In some embodiments the plant belongs to the genus Thlaspi. In some embodiments, the plant is Alyssum Murale. In some embodiments, the plant is of the genus Odontarrhena. In some embodiments, the plant is Odontarrhena chalcidica. In some embodiments, the plant is Odontarrhena decipiens. In some embodiments, the plant is Berkheya coddii. In some embodiments, the plant is B. emarginata. In some embodiments, the plant is Stackhousia tryonii. In some embodiments, the plant is Phyllanthus balgooyi. In some embodiments, the plant is Rinorea bengalensis. In some embodiments, the plant may be a tree, bush, or vine. In some embodiments, the plant is a genetically modified plant. In some embodiments, the plant is any plant capable of hyperaccumulating a metal found in a weatherable rock. In some embodiments, the plant is any plant capable of hyperaccumulating nickel. In some embodiments, the plant is any hyperaccumulator plant species of the class known as a hypernickelophores, containing more than 1,000 g Ni g.sup.1.
[0091] In some embodiments, the nickel hyperaccumulator plant is grown inside of a greenhouse. In some embodiments, the nickel hyperaccumulator plant is grown inside of a vertical farm. In some embodiments, the nickel hyperaccumulator plant is grown hydroponically. In some embodiments, the nickel hyperaccumulator plant is grown under a polyethylene film (e.g., a polytunnel).
[0092] In some embodiments, the environmental conditions under which the nickel hyperaccumulator plant is grown are optimized to maximize the weathering rate of the weatherable rock. In some embodiments, the environmental conditions under which the nickel hyperaccumulator plant is grown are optimized to maximize the efficiency of nickel uptake by the plant. In some embodiments, the environmental conditions under which the nickel hyperaccumulator plant is grown are optimized to maximize the weathering rate of the weatherable rock and the efficiency of nickel uptake by the plant.
[0093] In some embodiments, the environmental conditions of the weatherable rock-enriched soil are controlled to cause the weatherable rock to undergo a chemical weather process at an accelerated rate relative to natural chemical weathering environmental conditions. In some embodiments, the conditions cited above comprise growing one or more metal hyperaccumulator plants in the weatherable rock-enriched soil. In some embodiments, the conditions comprise growing one or more metal hyperaccumulator plants in a weatherable rock-enriched soil and continuously irrigating the one or more metal hyperaccumulator plants using a drip irrigation system. In some embodiments, the temperature, pH, irrigation, or bioactivity of the weatherable rock-enriched is controlled.
[0094] In some embodiments, the rate of weathering of the weatherable rock is between about 0% and about 40% by mass of the weatherable rock between about 12 months and about 72 months from the date of combining the particulate weatherable rock composition with a soil to provide a weatherable rock-enriched soil and planting the hyperaccumulator plant in the weatherable rock-enriched soil. Any suitable methods known in the art may be used to determine the rate of weathering of the weatherable rock. For example, in one variation, the foregoing rates of weathering may be calculated using the Arrhenius equation.
[0095] In some embodiments, the weathering rate is calculated by measuring the accumulation of rock-derived cations (e.g., Ca, Mg, Na, and K) in plant, soil, and/or aqueous effluent associated within a certain plot of land and subtracting the baseline amount of the corresponding cation measured in a corresponding control plot. For example, the net accumulation of Ca-cations due to mineral dissolution of weatherable rock can be calculated by subtracting the amount of Ca-cations measured in a control plot from the total amount of Ca-cations calculated by totaling the amount of Ca-cations in the water and/or effluent, the Ca-cations in plant tissues, and Ca-cations in the soil cation exchange pool. The amount of Ca-cations attributable to the weathering of weatherable rock can then be converted into spatially-averaged cation weathering rates (per unit of land area) or rates related to mineral surface area. In some embodiments, the weatherable rock is calculated in the number of moles of calcium, magnesium, sodium, and/or potassium released from the weatherable rock material into the soil per hectare of treated land per annum.
[0096] In some embodiments, the weathering rate of the weatherable rock increases when the average particle size of the weatherable rock decreases.
[0097] In some embodiments, the environmental conditions under which the nickel hyperaccumulator plant is grown are optimized to increase the weathering rate of the weatherable rock. In some embodiments, the environmental parameter that is optimized to increase the weathering rate of the weatherable rock is temperature. In some embodiments, the temperature of the surrounding air (e.g., climate) is increased to increase the weathering rate of the weatherable rock. In some embodiments, the temperature of the topsoil (e.g., where the weatherable rock is admixed into the soil) is increased to increase the weathering rate of the weatherable rock. In some embodiments, the amount of irrigation of the soil admixed with the weatherable rock is increased to increase the weathering rate of the weatherable rock. In some embodiments, the pH of the soil admixed with the weatherable rock is increased to decrease the weathering rate of the weatherable rock. In some embodiments, the pH of the soil admixed with the weatherable rock is decreased to increase the weathering rate of the weatherable rock.
[0098] In some embodiments, the weathering rate of the weatherable rock is increased by increasing the amount of biological activity of the soil admixed with the weatherable rock. In certain embodiments, the increased biological activity of the soil is measured by the amount of carbon dioxide produced by the microbes per a given amount of the soil. In certain embodiments, the increased biological activity of the soil is measured by the amount of nitrogen-cycling and secretion of organic acids by plant roots and mycorrhizal fungi present in the soil.
[0099] In some embodiments, increasing the concentration of Mg.sup.2+ ions in the soil admixed with the weatherable rock increases the weathering rate of the weatherable rock. In some embodiments, increasing the concentration of Ca.sup.2+ ions in the soil admixed with the weatherable rock increases the weathering rate of the weatherable rock. In certain variations, higher soil Ca and Mg content may decrease the weathering rate of rock material added to the soil, because chemical conditions in the groundwater may approach saturation for certain Ca (and Mg) bearing minerals.
[0100] In some embodiments, the environmental conditions under which the nickel hyperaccumulator plant is grown are optimized to maximize the accumulation of nickel by the plant. In some embodiments, the environmental conditions under which the nickel hyperaccumulator plant is grown are optimized to maximize the growth rate of the plant. In some embodiments, the humidity, temperature, or lighting of the environment in which the nickel hyperaccumulator plant is grown are controlled. In some embodiments, the nickel hyperaccumulator plant is grown in an outdoor field.
[0101] In some embodiments, the amount of weatherable rock mixed into the soil for every hectare on which the hyperaccumulator plant is grown is optimized to maximize the accumulation of nickel by the hyperaccumulator plant. In some embodiments, the amount of weatherable rock mixed into the soil to maximize the accumulation of nickel by the hyperaccumulator plant is between about 5 tonnes and 300 tonnes. In some embodiments, the amount of weatherable rock mixed into the soil to maximize the accumulation of nickel by the hyperaccumulator plant is between about 10 tonnes and 50 tonnes. In some embodiments, the amount of weatherable rock mixed into the soil to maximize the accumulation of nickel by the hyperaccumulator plant is about 37 tonnes.
[0102] In some embodiments, the amount of nickel accumulated by a nickel hyperaccumulator plant increases proportionally with the amount of weatherable rock mixed into the soil in which the plant is grown. In some embodiments, increasing the amount of weatherable rock mixed in the soil does not result in an increase in the amount of nickel accumulated by a hyperaccumulator plant growing in the soil. In certain embodiments, high amounts of weatherable rock mixed into the soil result in high alkaline (e.g., high pH) soils which can negatively impact the mobility of the one or more metals released from the weatherable rock during the weathering process.
[0103] In some embodiments, the amount of weatherable rock mixed into the soil for every hectare on which the hyperaccumulator plant is grown and the environmental conditions under which the hyperaccumulator plant is grown are optimized to control the pH of the soil. In some embodiments, the amount of weatherable rock mixed into the soil for every hectare on which the hyperaccumulator plant is grown is optimized to control the pH of the soil. In some embodiments, an increase in the pH of the soil decreases the mobility of the one or metals released by the weatherable rock mixed in the soil. In some embodiments, decreased mobility of the one or more metals in the soil results in lower accumulation of the metals by a hyperaccumulator plant of the same metal growing in the soil. In some embodiments, an increase of the pH of the soil decreases the amount of metal accumulated by the hyperaccumulator plant growing in the soil, the mobility of the one or metals released by the weatherable rock, or both.
[0104] In some embodiments the amount of weatherable rock mixed into the soil for every hectare on which the hyperaccumulator plant is grown is optimized to maximize the growth rate of the hyperaccumulator plant.
[0105] In some embodiments, at least 5 tonnes of weatherable rock are mixed into the soil for every hectare on which the nickel hyperaccumulator plant is grown. In some embodiments, at least 10 tonnes of weatherable rock are mixed into the soil for every hectare on which the nickel hyperaccumulator plant is grown. In some embodiments, between 10 tonnes and 100 tonnes of weatherable rock are mixed into the soil for every hectare on which the nickel hyperaccumulator plant is grown. In some embodiments, between 5 tonnes and 10 tonnes of weatherable rock are mixed into the soil for every hectare on which the nickel hyperaccumulator plant is grown. In some embodiments, between 25 tonnes and 50 tonnes of weatherable rock are mixed into the soil for every hectare on which the nickel hyperaccumulator plant is grown. In some embodiments, between 35 tonnes and 40 tonnes of weatherable rock are mixed into the soil for every hectare on which the nickel hyperaccumulator plant is grown. In some embodiments, between 100 tonnes and 200 tonnes of weatherable rock are mixed into the soil for every hectare on which the nickel hyperaccumulator plant is grown. In some embodiments, about 150 tonnes of weatherable rock are mixed into the soil for every hectare on which the nickel hyperaccumulator plant is grown. In some embodiments, between 400 tonnes and 800 tonnes of weatherable rock are mixed into the soil for every hectare on which the nickel hyperaccumulator plant is grown. In some embodiments, about 600 tonnes of weatherable rock are mixed into the soil for every hectare on which the nickel hyperaccumulator plant is grown.
[0106] In some embodiments, at least about 20 tonnes of nickel hyperaccumulator biomass is grown per hectare. In some embodiments, at least about 400 kg, at least about 500 kg of nickel, at least about 600 kg, at least about 700 kg, at least about 800 kg, at least about 900 kg, or at least about 1,000 kg of nickel is produced per hectare. In other variations, between about 100 kg and 5000 kg, or between 250 kg and 1000 kg, or between 400 kg and 1000 kg of nickel is produced per hectare.
[0107] In some embodiments, between about 5 tonnes and about 50 tonnes, between about 100 tonnes and about 700 tonnes, between about 500 tonnes and about 700 tonnes, between about 100 tonnes and about 600 tonnes, between about 200 tonnes and about 600 tonnes, between about 300 tonnes and about 600 tonnes, between about 400 tonnes and about 600 tonnes, between about 500 tonnes and about 600 tonnes, between about 100 tonnes and about 500 tonnes, between about 200 tonnes and about 500 tonnes, between about 300 tonnes and about 500 tonnes, between about 400 tonnes and about 500 tonnes, between about 100 tonnes and about 400 tonnes, between about 200 tonnes and about 400 tonnes, between about 300 tonnes and about 400 tonnes, between about 100 tonnes and about 300 tonnes, between about 200 tonnes and about 300 tonnes, or between about 100 tonnes and about 200 tonnes of weatherable rock are mixed into the soil for every hectare on which the hyperaccumulator plant is grown. In some embodiments, about 500 tonnes about 600 tonnes, or about 700 tonnes of weatherable rock are mixed into the soil for every hectare on which the hyperaccumulator plant is grown.
[0108] In some embodiments, the amount of carbon dioxide sequestered is proportional to the number of Mg.sup.2+ ions liberated from the weathering of the weatherable rock. In some embodiments, the amount of carbon dioxide sequestered per hectare is proportional to the number of Mg.sup.2+ ions liberated from the weathering of the weatherable rock mixed into the soil for every hectare.
[0109] In some embodiments, the amount of carbon dioxide sequestered is proportional to the number of Ca.sup.2+ ions liberated from the weathering of the weatherable rock. In some embodiments, the amount of carbon dioxide sequestered per hectare is proportional to the number of Ca.sup.2+ ions liberated from the weathering of the weatherable rock mixed into the soil for every hectare.
[0110] In some embodiments, the nickel hyperaccumulator plant is harvested mechanically. In some embodiments, the nickel hyperaccumulator plant is harvested manually. In some embodiments, the nickel hyperaccumulator plant is harvested by an automated process.
[0111] In some embodiments, growing a nickel hyperaccumulator plant in the weatherable rock-enriched soil further comprises continuously irrigating the weatherable rock-enriched soil. In some embodiments, the plant is irrigated using a drip irrigation system. In some embodiments, the plant is irrigated using sprinkler systems. In some embodiments, growing a nickel hyperaccumulator plant in the weatherable rock-enriched soil further comprises intermittently irrigating the weatherable rock-enriched soil. In some embodiments, the plant is irrigated using a flood irrigation approach. In some embodiments, the plant is irrigated using traditional irrigation.
[0112] In some embodiments, the pH of the weatherable rock-enriched soil is above 7. In some embodiments, the pH of the weatherable rock-enriched soil is between 7 and 14. In some embodiments, the pH of the weatherable rock-enriched soil is between 5 and 14. In some embodiments, increasing the content of the weatherable rock of the weatherable rock-enriched soil increases the pH of the soil.
[0113] In some embodiments, ashing the harvested nickel hyperaccumulator plant comprise drying the nickel hyperaccumulator plant to provide a dried biomass composition; crushing the dried biomass composition to provide a crushed biomass composition; and burning the crushed biomass composition to provide a nickel-enriched composition.
[0114] In some embodiments, the method further comprises quantifying the amount of carbon dioxide that is released or sequestered in one or more steps of any of the methods described herein. In some embodiments, the amount of carbon dioxide released or sequestered by a process is measured directly. In some embodiments, the amount of carbon dioxide released or sequestered by a process is measured using a proxy. In some embodiments, the quantity of Mg.sup.2+ is used as a proxy to quantify the amount of carbon dioxide sequestered by chemical weathering of the weatherable rock.
[0115] In another aspect, provided herein is nickel metal prepared according to any of the methods described above.
[0116] In another aspect, provided herein is a processed nickel composition comprising a substantially pure nickel, and one or more of the following: Nickel rich ashes also containing K, Ca, oxides (e.g., NiO, MgO), carbonates (e.g., K.sub.2CO.sub.3, CaCO.sub.3, K.sub.2Ca(CO.sub.3).sub.2), K.sub.2SO.sub.4, precipitated gypsum, low-mass carboxylic acids, Ni-bearing organic and inorganic compounds. Ni-based compounds such as NiO, Ni(OH).sub.2, nickel sulfides, nickel hydroxides, Ni oxalate, and Ni sulfate. In some variations of the foregoing, the processed nickel composition is at least 15%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98%, at least 99%, at least 99.8%, at least 99.9%, at least 99.99%, at least 99.999%, or at least 99.9999% pure by weight. In some embodiments, the processed nickel composition is between 15% and 100% pure by weight.
[0117] In another aspect, provided herein is a nickel-enriched ash comprising at least 5% nickel by weight, and one or more of the following: Nickel rich ashes also containing K, Ca, oxides (e.g., NiO, MgO) and carbonates (e.g., K.sub.2CO.sub.3, CaCO.sub.3, K.sub.2Ca(CO.sub.3).sub.2), K.sub.2SO.sub.4, precipitated gypsum, low-mass carboxylic acids, Ni-bearing organic and inorganic compounds. Ni-based compounds such as NiO, Ni(OH).sub.2, nickel sulfides, nickel hydroxides, Ni oxalate, and Ni sulfate. In some embodiments, provided herein is a nickel-enriched ash comprising at least 5% nickel by weight, and one or more of the following: Ca, Fe, K, Mg, carbonates (e.g., K.sub.2CO.sub.3, CaCO.sub.3, or K.sub.2Ca(CO.sub.3).sub.2), P, plant cells, C, H, N, O, hydroxyapatite, oxy-hydroxyapatite, or oxides (e.g., NiO, CaO, MgO, or MgNiO.sub.2). In some embodiments, the nickel-enriched ash comprises between 5% and 100% nickel by weight.
[0118] In any of the foregoing embodiments, the weight of nickel refers to the weight of the nickel component alone, and does not include, for example, the weight of any ligands or counter ions in any complexes or salts, respectively, that the nickel is a part of.
EXAMPLES
[0119] The presently disclosed subject matter will be better understood by reference to the following Examples, which are provided as exemplary of the invention, and not by way of limitation.
Example 1: Assessment of Weathering Rates for Different Soil and Plant Configurations
[0120] Samples of O. decipiens (a close relative to the hyperaccumulator known in the art as O. chalcidica or A. murale) were shipped to a testing facility. There, the seeds were separated from the remainder of the plant biomass, soaked in water to prepare them for germination, and germinated. The germinated seeds were observed to have root systems. Separately, a sample of serpentinite rock was obtained, and was ground into a fine powder, herein referred to as serpentine soil.
[0121] Nine sample planters were prepared, with each planter containing a specific ratio of serpentine soil to potting soil (including both pure potting soil and pure serpentine soil). Seeds of the hyperaccumulator plants were planted in eight of the nine planters, and one planter was left with no seeds, as a control. Additionally, NPK hydroponic fertilizer was added in different concentrations to the continuous, closed-loop irrigation systems of two of the planters. The experimental conditions for each planter are illustrated in
[0122] Because Mg.sup.2+ is released in the weathering reaction of serpentine, the quantity of Mg.sup.2+ leached from the soils in each planter was used as a proxy for the rate of weathering that occurred under each condition. Over the course of 4 months, the total concentration of Mg.sup.2+ leached into the closed-loop irrigation system was measured for each of the nine planter conditions shown in
Example 2: Field-Scale Enhanced Rock Weathering Experiment
[0123] A field-scale trial was employed to investigate the synergistic combination of nickel phytomining and enhanced weathering. The principal aim of this experiment was to evaluate the scope for nickel extraction by the hyperaccumulator plant Odontarrhena decipiens and to quantify the carbon capture potential of crushed serpentinite rock added to the naturally occurring serpentine agricultural soil.
[0124] A 112 m168 m field site was selected for this trial based on aerial photography and ground observations. Four permanent reference points for determining precise locations were established by cementing steel posts into the ground at the corners of the field site. The area was then partitioned into four equally-sized rectangular blocks, each measuring 56 m84 m. A scale diagram of the randomized complete block design used in the trial is shown in
[0125] The entire field site was tilled prior to the trial. Crushed serpentinite rock was sourced from a nearby quarry and applied by hand to the soil surface of each plot at rates ranging from 9.375 to 600 tonnes per hectare, whereby the next higher rate was set to be double the previous as illustrated in FIG. 4. Each block also contains a control treatment where no serpentinite rock is added (i.e. 0 tonnes per hectare), against which all other treatments were compared statistically. The applied rock material was incorporated into the soil to an approximate depth of 150 mm using a rotavator. One-year-old Odontarrhena decipiens specimens were then transplanted into each plot, in thirteen rows with 1 m row-spacing and 0.5 m spacing between the individual plants. Organic fertilizers, pesticides, and fungicides were added to the experimental plots to ensure baseline crop performance and mitigate pest/pathogen interference in all treatments.
[0126] At the beginning of the experiment, over a hundred mesh bags were filled with 0.4 g of crushed serpentinite and buried in the plots at soil depths between 50-200 mm. Retrieval of the grains from these bags at the end of the trial permits the direct assessment of mineral weathering through X-ray analysis.
Soil Sample Collection and Measurements
[0127] Before applying the serpentinite rock material, fifteen baseline soil samples were collected from each block using a steel auger and following a W-shaped sampling pattern. These initial (pre-planting, pre-rock application) soil samples are taken from three depths: 0-0.3 m, 0.3-0.6 m, and 0.6-0.9 m. Soils are then passed through a 2 mm mesh size sieve, air dried, and tested for the following physical and chemical parameters: pH (in H.sub.2O and 1M KCl); organic matter and humus %; plant-available nitrogen, phosphorus and potassium; soil texture (sand/silt/clay %); cation exchange capacity; and, total and plant-available Ca, Mg, K, Na, Fe, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn. Further soil samples were collected monthly from each of the thirty-two experimental plots and tested for pH, electrical conductivity, cation exchange capacity, and plant-available cations. These data were used to monitor changes in the concentrations of plant-available nutrients and nickel over time, and to estimate rock weathering and carbon dioxide capture rates via a conventional mass balance approach, in combination with novel quantification methods.
Plant Sample Collection and Measurements
[0128] Aboveground plant tissues are harvested from all plots after a suitable time (e.g., approximately 6-8 months) after the trial began. Plant materials are dried and weighed to determine crop yields, and ground for analysis of nutrients and metals. These data are used to measure the efficiency of nickel uptake by the hyperaccumulator plants, and to evaluate the correlation between rock application and nickel uptake rates. Moreover, values for total uptake of calcium, magnesium, potassium and sodium are fed into mass budget calculations for carbon capture quantification.
[0129] Aboveground plant tissues were harvested from five different mature hyperaccumulator plant specimens randomly selected from all plots after a suitable time (e.g., approximately 6-8 months) after the trial began. Plant samples were washed with distilled water, dried in a forced-air oven at 60 C. for 48 hours, and powdered separately using a laboratory grinding mill. These plant samples were used to determine total heavy metal concentrations in the plant tissues.
Soil pH and Electrical Conductivity Measurements
[0130] The pH and the electrical conductivity (EC) of the soil samples determined using a Combined Conductivity/pH Meter equipped with a temperature input, which internally corrects for the effect of temperature on measured values. pH and EC were standardized using a 3-point calibration protocol with certified reference solutions (buffers at pH 4.00, 7.00, and 14.00; EC standards at 12.88 mS, 1413 S, and 84 S). To streamline the measurements, pH and EC were tested sequentially from the same sample. For each soil sample, 15.00000.0005 g of soil was weighed into a 50 mL polypropylene centrifuge tube and combined with 30.00000.0150 mL of ultrapure water (resistivity of 18.2 M.Math.cm at 25 C.). The tubes were stoppered, agitated on a rotary shaker for 3 minutes, unstoppered and then left to equilibrate with the atmosphere for 30 minutes. An additional three replicates of control soil (initial/baseline soil containing no additives) were prepared and used to precondition the pH and conductivity electrodes prior to analysis of the experimental samples. This preconditioning process shortens the timescales for stable measurements and mitigates measurement error in the first few experimental samples (e.g. due to contamination with trace amounts of buffer solution). To obtain pH measurements, the pH electrode was swirled into the soil-water mixture's supernatant for 10 seconds, and then gently released into the slurry until the instrument identified that a stable pH reading was achieved (or 3 minutes after initial insertion, where stabilization was not achieved). pH measurements were recorded to 0.001 pH units, and the electrode was rinsed thoroughly with ultrapure water between samples. To obtain EC measurements, the conductivity electrode was inserted into the soil-water mixture's supernatant and held until the instrument indicated that a stable EC reading was achieved (or 1 minute after initial insertion, where stabilization was not achieved). EC measurements were recorded to four significant figures, and the electrode was rinsed thoroughly with ultrapure water between samples.
Soil Analysis Methods for Total Heavy Metals
[0131] The soil samples were tested for total heavy metals by first drying a test portion of the soil and reducing the grain size of the soil to below a particle size of 250 microns. Each test portion of the soil was then weighed (0.5 g to 1.0 g based on dry mass) and transferred to a microwave extraction vessel. A few drops of water were then added to the extraction vessel before adding a HCl and nitric acid solution and mixing well. The temperature of the extraction mixture was increased at a rate of approximately 10 C./min to 1755 C. using a microwave digestion system. The amount of total Ni in the soil samples was then determined using ICP-OES.
Availability of Ni with Mehlich-1 Digestion
[0132] The soil samples were prepared by mixing 5 g of the soil samples with 20 mL of a Mehlich-1 extraction solution consisting of a mixture of HCl and H.sub.2SO.sub.4. The mixture was then stirred for 5 min at 180 cycles/min after which the suspension was allowed to rest for 16 h before decanting off the supernatant The total amount of Ni in the soil samples was then determined by testing an aliquot of the supernatant using ICP-OES.
Other Analytical Methods
[0133] It should be understood that one or more additional techniques may be used to determine the amount of Ni in the soil, the amount of rock-derivable cations in the tissue of the hyperaccumulator plants or the soil, the amount of heavy metals in the tissue of the hyperaccumulator plants or the soi, the pH of the soil, the electrical conductivity of the soil, and other aspects of the weatherable rock, soil, and hyperaccumulator plants, including quantification of the weathering rate. For example, X-ray fluorescence analysis of weathered rock material (retrieved from mesh bags buried in the plots) is used to quantify changes in grain surface chemistry. These data provide an independent method for mineral weathering rate quantification. The loss of cations from the added rocks may serve as a proxy for the accumulation of cations released from this process in the plant and soil.
Determination of Total Heavy Metal and Ca, Mg, K Concentrations in Plants with Digestion
[0134] Aboveground plant tissues were digested in an acid solution (HNO.sub.3 65% and H.sub.2O.sub.2 30%) using a microwave digestion system to determine total heavy metal concentrations in plants. A sample of the plant matter (300 mg) was mixed with 2 mL of HNO.sub.3 and 2 mL of H.sub.2O.sub.2, stirred for at least 20 min, and then digested using a microwave digestion system. Plant tissue samples calibration curves were plotted from Ni concentrations of 2, 4 and 6 mg/L. The solution was diluted 20 times. The amount of Ni in the plant tissue samples was then determined using ICP-OES.
Results and Analysis
[0135] Approximately 8 months after the trial began, representative soil samples were collected from the plots for analysis. As shown in
[0136] Amendment of soils with serpentinite rock also resulted in higher nickel uptake into the tissues of the hyperaccumulator plants as compared to the hyperaccumulator plants grown in the control soils, with the highest nickel yields observed in soils amended with 3.75 to 15 kg m.sup.2 of serpentinite rock as shown in
[0137] Timeseries data for soil-extractable Ni was determined by a Mehlich 1 extraction procedure and confirms that soil concentrations increased in all plots treated with serpentinite rock between when the trial began (0 m) and the following spring (5 m), when the hyperaccumulators would have exhibited low primary production as shown in
Statistical Analyses
[0138] Statistical analysis was also performed to determine the significance of the relationships between rock application, plant nickel uptake, and (potential) carbon capture rates. Statistical analysis of the soil data was performed using a linear mixed model with fixed model Treatment*Time and random model of Block/Plot. Where appropriate, variables were first transformed to ensure homogeneity of variance. F statistics were obtained using the Kenward-Roger approximation. Statistical analysis of the plant data was performed using a linear model accounting for differences between blocks. A third order polynomial was fitted over application rate with highest order terms successively dropped if found to be non-significant.
[0139] Regarding soil pH, statistically significant differences were observed both between treatments (F4,12=21.54, p<0.0001) and over time (F3,45=7.18, p=0.0005). Predicted means and standard errors for each significant main effect is shown in
[0140] The above preliminary data was collected over the first 8 months of the field trial experiment. Additional data will be gathered until 12 months after the start of the field trial experiment to further elucidate the relationship between the application rate of the weatherable rock and the accumulation of metal by the hyperaccumulator plant, the soil pH, the soil electrical conductivity, the weatherable rock-derivable cations in the soils and plants, and the heavy metals in the soils and the plants, as well as determining the weathering rate of the weatherable rock, the amount of nickel ore extractable from the plants, and quantifying the amount of carbon dioxide sequestered.
Example 3: Field-Scale Enhanced Rock Weathering Experiment with Two Controls
[0141] In this example, a field-scale trial is employed to further investigate the synergistic combination of nickel phytomining and enhanced weathering. A scale diagram of the randomized complete block design used in the trial is shown in
[0142] Two control treatments are included in this study: a rock-free control (i.e. 0 tonnes of rock added per hectare) where hyperaccumulator plants are grown, and a second control where no plants, rock amendments, or management practices are employed, as denoted by XX in
[0143] Soil Sample Collection and Measurements
[0144] Following a W-shaped sampling pattern, multiple baseline soil samples are collected and aggregated from each of the forty plots at three discrete depths (0-0.3, 0.3-0.6 and 0.6-0.9 m) using a steel auger. These initial soil samples are separately homogenized, passed through a 2-mm mesh size sieve, and air-dried. Soils are then tested for pH (in H.sub.2O and 1M KCI) and electrical conductivity (in H.sub.2O); inorganic/organic carbon and nitrogen %; plant-available nitrogen, phosphorus and potassium; soil texture (sand/silt/clay %), bulk density and water holding capacity; cation exchange capacity and exchangeable acidity; major oxide and soil mineralogy %; and, total and plant-available Ca, Mg, K, Na, Fe, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn. Further soil samples are taken at bi-monthly intervals and tested to determine changes in fundamental soil parameters (pH, electrical conductivity, organic/inorganic carbon) and the concentration of exchangeable (plant-available) metals. These data are critical for monitoring changes in nickel availability and carbon dioxide capture rates in the plots.
Plant Sample Collection and Measurements
[0145] Approximately 1-year after the start of the field trial, shoot tissues are harvested from all plots, and the shoot tissues are dried and weighed to quantify crop performance. In addition, plant materials are powdered, digested, and tested to determine metal content and analyze the correlation between rock application rate and nickel uptake efficiency. Total plant calcium, magnesium, potassium, and sodium values are added to the respective values from the soil analyses of exchangeable elements, which together enable the quantification of rock weathering and carbon capture rates.
Aqueous Sample Collection and Measurements
[0146] Pore water samples are extracted from the soil using lysimeters installed in the plots. These aqueous samples are analyzed for changes in the following parameters: pH, electrical conductivity, and alkalinity; and dissolved cations (e.g. nickel, magnesium) and anions (e.g. chloride, nitrate). These data are essential for accurate monitoring of rock dissolution, nickel release, and carbon capture rates.
Soil-Atmosphere Greenhouse Gas Sample Collection and Measurements
[0147] Gaseous samples are collected during the trial using static chambers installed in the plots and are analyzed using gas analysis mass spectrometry to determine soil-atmosphere fluxes of major greenhouse gasses, such as carbon dioxide, methane, and nitrous oxide. This example seeks to determine the effects of the addition of alkaline rocks to the soil on overall emissions of potent non-CO.sub.2 greenhouse gasses, and thus impact on climate change. These gas measurements are performed in serpentine soils, and also provide evidence that the soil amendments and agricultural management practices associated with the trial result in the conversion of existing soil organic carbon into atmospheric carbon dioxide.
Example 4: Life Cycle Assessment at Kilotonne and Megatonne Scales Per Year
[0148] A Life Cycle Assessment (LCA) was employed to ensure that the enhanced rock weathering/hyperaccumulator plant operation is sufficiently CO.sub.2 negative at the necessary scale. The aim was to model the net sequestration of 1 kilotonne and 1 megatonne of CO.sub.2 per year. The LCA was conducted using SimaPro software which draws data from various databases. The study adopted a cradle-to-gate approach, which includes all the major processes in the life cycle from the mining operation to the production of nickel ore, however the environmental impact of waste treatment was excluded from the LCA due to the ambiguity of its relevance. The two products of the operation are CO.sub.2 uptake (carbon dioxide removal through enhanced rock weathering) and the production of nickel ore through phytomining. The major processes within the established system boundaries include the mining, crushing, and milling of serpentine, the transportation of the serpentine rock to the site of placement, the fertilizer used, and harvesting, drying, and combustion of the hyperaccumulator plants. A unit area of land was used as the functional unit for the LCA to account for both the CO.sub.2 extraction and the nickel ore production. For example, per every m.sup.2 of area of serpentine soil used for the cultivation of A. Murale (or a similar hyperaccumulator plant), a certain amount of nickel will be produced and a certain amount of CO.sub.2 will be sequestered. This functional unit ensures that neither of the two products of the system (i.e. CO.sub.2 uptake and the production of nickel ore) are neglected from the LCA analysis and that their amounts are calculated independently of each other.
[0149] The data used for the LCA was collected from several sources and the model was built on the basis of existing models. The data related to standard transportation, machinery, energy, and materials were kept as they were in the models, apart from several necessary adjustments to bring the model closer in line with the operation. For example, during the whole process, the electricity comes from the grid, where it is mostly produced using hydropower. This feature was reflected in the model. It is not required that hydropower be utilized in the process, though it will lower the net negative efficiency. A range of parameters, such as the weathering rate and serpentine content in soil, was introduced into the model. The information used to determine the parameter values was sourced from a combination of existing literature on similar experiments with hyperaccumulators and mineral weathering. The firm relied on rates of natural weathering processes which resulted in calculations that predict significant CO.sub.2 uptake and nickel production.
[0150] The models for 1 kilotonne-scale production yearly can be seen in