Systems and methods for generating hydrogen and magnetite from rock

Abstract

Systems and methods for sequestering carbon, evolving hydrogen gas, producing iron oxide as magnetite, and producing magnesium carbonate as magnesite through sequential carbonation and serpentinization/hydration reactions involving processed olivine- and/or pyroxene-rich ores, as typically found in mafic and ultramafic igneous rock. Precious or scarce metals, such nickel, cobalt, chromium, rare earth elements, and others, may be concentrated in the remaining ore to facilitate their recovery from any gangue material.

What is claimed is: 
     
         1 . A method for sequestering carbon and generating hydrogen and magnetite from rock, the method comprising:
 obtaining an ore containing olivine or pyroxene;   introducing the ore into a reactor that is operable at temperatures above ambient temperature and pressures above atmospheric pressure;   introducing carbon dioxide into the reactor at a first temperature for a first residence time to react with the ore to generate magnesium carbonate;   introducing water into the reactor at a second temperature for a second residence time to react with the ore to generate magnetite and hydrogen gas;   removing the hydrogen gas from the reactor; and   removing any remaining ore from the reactor.   
     
     
         2 . The method of  claim 1 , further comprising comminuting the ore into smaller size fractions prior to introducing the carbon dioxide into the reactor. 
     
     
         3 . The method of  claim 2 , further comprising washing the ore with either water or an acidic solution prior to comminuting the ore into the smaller size fractions. 
     
     
         4 . The method of  claim 1 , further comprising removing at least a portion of the magnesium carbonate from the reactor prior to introducing the water into the reactor. 
     
     
         5 . The method of  claim 1 ,
 wherein the water has a pH of between about 8.3 and about 11.1;   wherein the carbon dioxide that is introduced into the reactor is gaseous or supercritical carbon dioxide; or   wherein at least one of the first temperature and the second temperature is no greater than 300° C.   
     
     
         6 . The method of  claim 1 , further comprising:
 passing the water through a heated bed of copper filings to reduce an oxygen fugacity of the water prior to introducing the water into the reactor;   applying, prior to introducing the carbon dioxide into the reactor, an acidic solution to the ore that is introduced into the reactor; or   removing oxygen from the reactor prior to introducing the carbon dioxide into the reactor.   
     
     
         7 . The method of  claim 1 , further comprising separating at least one of nickel, cobalt, lithium, chromium, or rare earth elements from the remaining ore. 
     
     
         8 . A method for sequestering carbon and generating hydrogen and magnetite from rock, the method comprising:
 obtaining an ore containing olivine or pyroxene;   introducing the ore into a first reactor that is operable at temperatures above ambient temperature and pressures above atmospheric pressure;   introducing carbon dioxide into the first reactor at a first temperature for a first residence time to react with the ore to generate magnesium carbonate;   passing any remaining ore to a second reactor;   introducing water into the second reactor at a second temperature for a second residence time to react with the remaining ore to generate magnetite and hydrogen gas;   removing the hydrogen gas from the second reactor; and   removing any remaining ore from the second reactor.   
     
     
         9 . The method of  claim 8 , further comprising:
 sieving the ore prior to introducing the ore into the first reactor to allow ore particles up to a pre-selected size to pass into the first reactor,   wherein introducing the ore into the first reactor comprises introducing, into the first reactor, only a subset of the ore having particles up to the pre-selected size.   
     
     
         10 . The method of  claim 9 , wherein the pre-selected size comprises a size of between about 25 microns and about 150 microns. 
     
     
         11 . The method of  claim 8 , wherein the water has a pH between about 8.3 and about 11.1. 
     
     
         12 . The method of  claim 8 , further comprising passing the water through a heated bed of copper filings to reduce an oxygen fugacity of the water prior to introducing the water into the second reactor. 
     
     
         13 . The method of  claim 8 , wherein at least one of the first temperature and the second temperature is no greater than 400° C. 
     
     
         14 . The method of  claim 8 , wherein a pressure inside the first reactor during the first residence time is at or above about 5 bars of carbon dioxide. 
     
     
         15 . The method of  claim 8 , wherein a pressure inside the second reactor during the second residence time is at or above about 1 bar of carbon dioxide. 
     
     
         16 . The method of  claim 8 , further comprising:
 washing the ore with either water or an acidic solution prior to introducing the carbon dioxide into the first reactor; and   sieving the ore prior to introducing the ore into the first reactor to allow ore particles up to a pre-selected size to pass into the first reactor,   wherein introducing the ore into the first reactor comprises introducing, into the first reactor, only a subset of the ore having particles up to the pre-selected size,   wherein the pre-selected size comprises a size of between about 25 microns and about 150 microns.   
     
     
         17 . The method of  claim 16 , wherein the water has a pH of between about 8.3 and about 11.1. 
     
     
         18 . A system for sequestering carbon and producing hydrogen and magnetite from rock, the system comprising:
 a source of ore containing olivine or pyroxene;   a reactor having an inlet that receives ore particles and at least one outlet, the reactor also having at least one additional inlet through which one or more of carbon dioxide or water is introduced, the reactor operable at a first temperature for a first residence time to react carbon dioxide that enters the reactor through the at least one additional inlet with the ore to generate magnesium carbonate, the reactor also operable at a second temperature for a second residence time to react water that enters the reactor through the at least one additional inlet with the ore to generate magnetite and hydrogen gas; and   a gas separator that is connected to and in fluid communication with the at least one outlet of the reactor, the gas separator configured to separate hydrogen gas from gases that exit the reactor through the at least one outlet.   
     
     
         19 . The system of  claim 18 , further comprising a crusher that physically reduces a particle size of the ore introduced therein from the source. 
     
     
         20 . The system of  claim 19 , further comprising:
 a sieve that receives ore from the crusher and that allows ore particles up to a pre-selected size to pass into the reactor, wherein the inlet that receives ore particles is configurable to only receive, from the sieve, ore particles having a size at or below to the pre-selected size; and   a magnetic separator that receives any remaining ore from the at least one outlet of the reactor, the magnetic separator having a magnet that attracts the magnetite and thereby separates the magnetite from other components of the remaining ore.