Methods for obtaining carbon neutral or carbon negative metals from plants, and related compositions

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.

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 2+  is leached at a rate of at least 1% by weight of the total Mg 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 μm 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) 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) 2 , nickel sulfides, nickel hydroxides, nickel oxalate, and nickel sulfate; or   (iv) one or more carbonates selected from the group consisting of K 2 CO 3 , CaCO 3 , K 2 Ca(CO 3 ) 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 2 CO 3 , CaCO 3 , K 2 Ca(CO 3 ) 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 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.