Processing of sulfur containing compounds and mixtures

Abstract

A method that includes reacting a solid sulfur-containing compound of a first metal with hydrogen to reduce at least a portion of the solid sulfur-containing compound with at least a portion of the hydrogen to form hydrogen sulfide and elemental first metal.

Description

[0001]Attorney Docket No. 07114-2408878 PROCESSING OF SULFUR CONTAINING COMPOUNDS AND MIXTURES CROSS REFERENCE TO RELATED APPLICATION This application claims priority to United States Provisional Application No. 63 / 608,934, filed December 12, 2023, the disclosure of which is hereby incorporated by reference in its entirety. FIELD This invention generally relates to hydrogen reduction processes, methods, process control and systems for sulfur containing compounds and mixtures. BACKGROUND Increased awareness of climate change and the Paris Agreement’s goals to limit the global temperature rise measured against pre-industrial levels have motivated the metals industry to seek solutions to improve process sustainability. For metal production, total greenhouse gas emissions from direct and indirect sources are significant across every step of the supply chain1, from mining and beneficiation to smelting and refining to casting and rolling. A variety of technical solutions have been considered, including but not limited to expanded electrification, exploration of new process chemistries, increased recycling, improved scrap utilization, and the adoption of new reductants2,3. Significant work has been directed toward the use of hydrogen as a replacement for fossil fuel and carbon reductants in metal production from oxides. However, the widespread use of hydrogen has so far been limited due to challenges with its supply, consumption, and inadequate synergies with new process chemistries. A variety of approaches have been considered to move away from fossil fuel and carbon reductants during metal production. For oxide feedstocks, conventional processes rely on coal or metallurgical coke to conduct carbothermic reduction to produce metals, with carbon dioxide emitted from the process. One approach to improve process sustainability while continuing to leverage existing technologies and facilities is the adoption of biobased, carbon-neutral sources carbon in place of fossil carbon4. These biobased reductants are increasingly popular, yet metals producers must compete with other industries seeking to utilize biomass sources for fuel. Hydrogen is another promising reductant to support decarbonization of metal production. When hydrogen reacts with a metal oxide to produce a metal, water or steam is 1 60E5644.DOC Attorney Docket No. 07114-2408878 generated instead of the direct greenhouse gasses formed in the conventional carbothermic process5. A variety of approaches have been considered to utilize hydrogen as a reductant in conventional blast furnace and solid gas reactors, as well as in emerging plasma reduction processes6. Commercially available hydrogen can be grouped into three main categories corresponding to increasing greenhouse gas emissions in production: “green” from electrolysis of water powered by renewable sources of electricity, “blue” from steam methane reforming or gasification with carbon capture, and “gray” from steam methane reforming or gasification without carbon capture. The supply of low carbon “green” and “blue” hydrogen is currently limited and geographically isolated, constituting less than 2% of the 94 million tonnes of global hydrogen demand in 20217. The massive scale of global commodity metals production – nearly 2 billion tonnes of raw steel products alone in 2022 – complicates efforts to decarbonize metals manufacturing using processes that only consume low carbon hydrogen. Other novel processing approaches include the direct reduction of oxide feedstocks to metal via molten oxide electrolysis. While molten oxide electrolysis potentially enables direct electrification of metals production, sustainable implementation of the technology requires the use of inert anodes that enable the direct evolution of oxygen as a byproduct in place of carbon dioxide or steam, as well as low carbon electricity. Inert anodes are at various stages of deployment for aluminum8and niche ferroalloy applications such as ferroniobium9yet have not yet seen broader deployment across ferroalloy markets and supply chains. An alternative approach to metal decarbonization is the adoption of new processing chemistries, in particular the development of sulfide-based production pathways. Many metals, such as nickel, copper, molybdenum, lead, and zinc are already produced from sulfide minerals10. Oxides and other oxygen containing compounds, including but not limited to peroxides, super oxides, sulfates, carbonates, nitrates, and phosphates, can also be readily converted to sulfides or other sulfur containing compounds, including but not limited to sulfates, oxysulfides, and thiophosphates without direct greenhouse gas emissions11,12. These sulfide and / or sulfur-containing compound intermediates enable improved decarbonization strategies. Selective sulfidation processes have also been developed to facilitate separation of target elements from mixed and multimetal compound feedstocks13. Typical processing routes for naturally occurring sulfide ores have relied on two main approaches14–16: 2 60E5644.DOC Attorney Docket No. 07114-2408878 1. Hydrometallurgical processing and leaching of sulfides into aqueous or organic solutions, followed by solvent extraction or ion exchange to separate impurities, followed by hydrogen reduction or electrowinning to produce metals; or 2. Roasting of sulfides to form oxides, followed by carbothermic reduction or metallothermic reduction to produce metals. Electrolytic pathways have been considered to produce metal products from native sulfides or those produced by compound sulfidation without direct carbon dioxide emissions. The use of halide supporting electrolytes have been extensively explored17; the sustainability of this approach may be complicated due to the potential production of sulfur-halide species at the anode which can exhibit higher global warming potentials than carbon dioxide. Alternatively, molten sulfide electrolysis using barium-lanthanum sulfide supporting electrolytes has enabled the electrolytic production of a range of metals and elemental sulfur at the laboratory scale18,19. However, barium-lanthanum sulfide electrolytes create challenges in refractory development due to the potential for thermodynamically spontaneous anion exchange between lanthanum sulfide and refractory oxides11. Furthermore, thermophysical properties and kinetic behaviors in molten sulfide electrolytes remain underdeveloped. FFC- Cambridge type electrolysis processes have also been considered20. It remains undetermined if mass transport challenges21in the FFC-Cambridge process may be overcome by shifting from oxide to sulfide-based processing chemistries. Metallothermic reduction of sulfides is another avenue that has been considered to produce metals from sulfides without direct greenhouse gas emissions. Aluminothermic reduction of sulfides via reactive vacuum distillation has been conducted at the laboratory scale for a range of metal products, including ferronickel, ferrochromium, aluminum- manganese, aluminum-scandium, and aluminum-lanthanum22–25. However, the approach has not yet been proven for pure metal product production. Direct vacuum thermal decomposition of iron and trace rare earth sulfides to produce gaseous elemental sulfur has also been demonstrated at the laboratory scale11,25; this approach has so far required elevated temperatures and reduced pressures to achieve reduction, conditions at which many metals themselves exhibit appreciable volatility. Hydrogen reduction of sulfides is a promising approach to enable metal production without direct greenhouse gas emissions. In conventional hydrogen reduction of oxides, hydrogen is lost to the formation of water or steam. In the direct hydrogen reduction of sulfides, hydrogen sulfide is formed, which can then potentially serve as a useful reactant in other processes. Decomposition of hydrogen sulfide to recover hydrogen for reuse also 3 60E5644.DOC Attorney Docket No. 07114-2408878 exhibits a substantially lower thermodynamic barrier than water splitting. However, thermodynamic and operational challenges have previously hindered the deployment of direct hydrogen reduction of sulfides for metals production. Under conditions where solid sulfides may be reduced with hydrogen to form sulfide products and hydrogen sulfide, the stoichiometric reaction is generally thermodynamically unfavorable26–29. To achieve thermodynamic spontaneity, a substantial excess of hydrogen or deficit of hydrogen sulfide must be maintained in the reduction reactor30,31. Kinetic studies for the direct hydrogen reduction of some solid sulfides, including those of nickel, cobalt, and molybdenum have been conducted under excess hydrogen to study the scientific aspects of interactions between hydrogen and metal sulfides32–34. Hydrogen reduction of molten sulfides has also been explored35. However, operational challenges with process control remain. More generally, oxides or carbonates with a high affinity for sulfidation, such as calcium oxide or sodium carbonate, have been blended with sulfide feedstocks to aid in the hydrogen reduction of sulfides. These oxide / carbonate additions serve as in situ solid state collectors for sulfur species, generally attributed to operate through the either reaction with product hydrogen sulfide or through the direct anion exchange reaction between the oxide / carbonate and sulfide feedstocks to form an oxide intermediate of the target metal product36–48. This oxide intermediate may then be the species that is subsequently reduced via hydrogen. Another strategy to improve the thermodynamics of hydrogen reduction is the utilization of hydrogen as a plasma. Hydrogen plasmas have been considered for reduction of a range of metal oxides. During reduction of a metal oxide, atomic and ionic hydrogen species generated in the hydrogen plasma have been observed to improve the reduction of metal oxides over gaseous molecular hydrogen alone49. However, this approach has seen limited application to sulfur containing compound reduction, except for with the above mentioned sulfur collector methods37. The use of hydrogen plasma to refine liquid metals and remove impurities, such as sulfur, has been previously explored. During removal of sulfur from liquid metals under hydrogen plasma, evolved sulfur species have been observed to react with molecular, atomic, or ionic hydrogen to form hydrogen sulfide50–52. Alternatively, when metals are present that can form volatile sulfides, such as silicon and germanium, sulfur may be expunged from liquid metals during hydrogen plasma processing via gaseous metal sulfide formation53. Reaction of sulfides with hydrogen plasma has been employed to control vacancy and defect chemistry in sulfur-containing catalyst production and to produce metal / metal sulfide heterostructures54,55. Phosphosulfides have also been reduced via hydrogen reduction to control sulfide catalyst morphology56. This prior art in the hydrogen 4 60E5644.DOC Attorney Docket No. 07114-2408878 plasma processing of sulfides has largely been geared towards liquid metal refining and catalyst synthesis and generally does not pertain to hydrogen reduction of sulfur containing compounds to form metals or metal sulfide intermediates for metals production. To our knowledge, operational methods and systems have not previously been described to facilitate the practical, direct hydrogen (molecular, atomic, or ionic) reduction of sulfides for metal production without in situ condensed phase sulfur collectors. Our invention centers on the integration of direct hydrogen reduction for sulfides with gas utilization, separation, and treatment systems for management, control, and recycling of hydrogen rich gas streams flowing into and out of hydrogen reduction reactors for sulfur containing metal compounds. Processing and treatment of sulfur containing streams of hydrogen and hydrogen sulfide have been considered in other areas, including but not limited to petrochemical, coal, and power generation industries. A variety of approaches for separation of hydrogen from hydrogen sulfide in those sectors have been conceived, including but not limited to pressure swing adsorption and membrane separation57–60. Decomposition of hydrogen sulfide into one or more of its elemental constituents have been conducted in other applications via a variety of methods, including but not limited to thermal decomposition, oxidation, catalytic cracking, plasma cracking, the Claus process, or reaction with transition metals57,61–71. To our knowledge, methods and systems for hydrogen separation from hydrogen sulfide and decomposition of hydrogen sulfide into elemental constituents have not been previously employed to enable hydrogen reduction of sulfides or hydrogen sulfide decomposition and / or hydrogen recycling within the sulfur containing compound reduction process. Below is a list of references potentially relevant to this disclosure or cited using numbered superscripts herein. 1. Nuss, P. & Eckelman, M. J. Life Cycle Assessment of Metals: A Scientific Synthesis. PLoS One 9, e101298 (2014). 2. Raabe, D., Tasan, C. C. & Olivetti, E. A. Strategies for improving the sustainability of structural metals. Nature 575, 64–74 (2019). 3. Raabe, D. The materials science behind sustainable metals and alloys. Chem Rev 123, 2436–2608 (2023). 4. Franke, S. Outokumpu sources biocoke from Sweden for stainless steel production. Heat Processing (2023). 5 60E5644.DOC Attorney Docket No. 07114-2408878 5. El‐Zoka, A. A., Stephenson, L. T., Kim, S., Gault, B. & Raabe, D. The fate of water in hydrogen‐based iron oxide reduction. Advanced Science 10, (2023). 6. Rukini, A., Rhamdhani, M. A., Brooks, G. A. & Van den Bulck, A. Metals Production and Metal Oxides Reduction Using Hydrogen: A Review. Journal of Sustainable Metallurgy 8, 1–24 (2022). 7. International Energy Agency. Global hydrogen review 2022. (2022). 8. Svendsen, A. Elysis moves toward commercialization of inert anodes. Light Metals Age 32–33 (2022). 9. Gleeson, D. Boston Metal looks to disrupt and decarbonise steel and iron ore industries. International Mining (2022). 10. U.S. Geological Survey. Mineral commodity summaries 2023. (2023) doi:10.3133 / mcs2023. 11. Stinn, C. Pyrometallurgical oxide-sulfide anion exchange for improved material separation and metal production. (Massachusetts Institute of Technology, 2023). 12. Allanore, A. & Stinn, C. Selective sulfidation and desulfidation. (2020). 13. Stinn, C. & Allanore, A. Selective sulfidation of metal compounds. Nature 602, 78–83 (2022). 14. Gasik, M. Handbook of Ferroalloys. (Elsevier, 2013). doi:10.1016 / C2011-0- 04204-7. 15. Crundwell, F. K., Ramachandran, V. & Davenport, W. G. Extractive Metallurgy of Nickel, Cobalt and Platinum Group Metals. (Elsevier, 2011). doi:10.1016 / C2009-0-63541-8. 16. Schlesinger, M. E., King, M. J., Sole, K. C. & Davenport, W. G. Extractive Metallurgy of Copper. (Elsevier, 2011). doi:10.1016 / C2010-0-64841-3. 17. Qu, J. et al. Anode electrolysis of sulfides. Proceedings of the National Academy of Sciences 119, (2022). 18. Stinn, C. & Allanore, A. Selective sulfidation and electrowinning of nickel and cobalt for lithium ion battery recycling. in 99–110 (2021). doi:10.1007 / 978-3-030-65647- 8_7. 19. Daehn, K. E. et al. Liquid Copper and Iron Production from Chalcopyrite, in the Absence of Oxygen. Metals (Basel) 12, 1440 (2022). 20. Ahmadi, E., Suzuki, R. o., Kaneko, T. & Kikuchi, T. A sustainable approach for producing Ti and TiS2 from TiC. Metallurgical and Materials Transactions B 52, 77–87 (2021). 6 60E5644.DOC Attorney Docket No. 07114-2408878 21. Hu, D. et al. Development of the Fray-Farthing-Chen Cambridge process: Towards the sustainable production of titanium and its alloys. JOM 70, 129–137 (2018). 22. Stinn, C. & Allanore, A. Ferronickel production from nickel laterite via sulfide chemistry. in 281–297 (2023). doi:10.1007 / 978-3-031-22634-2_25. 23. Stinn, C., Benderly-Kremen, E. & Allanore, A. Scandium master alloy production via sulfidation and vacuum aluminothermic reduction. in 1195–1203 (2023). doi:10.1007 / 978-3-031-22532-1_160. 24. Stinn, C., Toll, S. & Allanore, A. Aluminothermic reduction of sulfides via reactive vacuum distillation. in 681–688 (2022). doi:10.1007 / 978-3-030-92529-1_89. 25. Allanore, A. & Stinn, C. Sulfide reactive vacuum distillation, absorption, stripping, and extraction for metal and alloy production. (2022). 26. Jha, A. Carbothermic reduction of sulphide minerals. (1984). 27. Igiehon, U. O. Carbothermic reduction of complex sulphides. (Imperial College London, 1989). 28. Sintim-Damoa, K. Lime enhanced reduction of chalcocite by hydrogen. (The Ohio State University, 1979). 29. Najafabadi, S. G., Abbasi, M. H. & Saidi, A. Thermodynamic investigation of lime-enhanced molybdenite reduction using methane-containing gases. Thermochim Acta 503–504, 46–54 (2010). 30. Goode, C. L. Kinetics of hydrogen reduction of molybdenite. (Colorado School of Mines, 1960). 31. Udupa, A. R., Smith, K. A. & Moore, J. J. Lime-enhanced reduction of sulfide concentrates: A thermodynamic discussion. Metallurgical Transactions B 17, 185–196 (1986). 32. Fahim, M. A. & Ford, J. D. Kinetics of hydrogen reduction of cobalt sulfide. Can J Chem Eng 54, 578–583 (1976). 33. Chida, T. & Ford, J. D. Kinetics of hydrogen reduction of nickel sulfide. Can J Chem Eng 55, 313–316 (1977). 34. Mehdi Afsahi, M., Sohrabi, M., Vasant Kumar, R. & Ale Ebrahim, H. A study on the kinetics of hydrogen reduction of molybdenum disulphide powders. Thermochim Acta 473, 61–67 (2008). 35. Byerley, J. J., Rempel, G. L., Takebe, N. & Teo, W. K. Reactions of molten Fe, Co, Cu, and Pb sulfides with hydrogen. Metallurgical Transactions 4, 1507–1511 (1973). 7 60E5644.DOC Attorney Docket No. 07114-2408878 36. Habashi, F., Dugdale, R. & Nagamori, M. The recovery of copper, iron, and sulfur from chalcopyrite concentrate by reduction. Metall (Berlin) 28, 1051–1054 (1974). 37. Lelievre, C., Stedman, M. & Pickles, C. A. Plasma production of ferromolybdenum from molybdenite in the presence of sodium carbonate. in Ferrous and Non-Ferrous Alloy Processes 64–74 (Elsevier, 1990). doi:10.1016 / B978-0-08-040411- 0.50009-2. 38. Abolpour, B., Afsahi, M. M. & Abolpour, M. Fuzzy logic model of lime enhanced hydrogen reduction of cuprous sulphide. Canadian Metallurgical Quarterly 53, 190–198 (2014). 39. Amini, A., Ohno, K., Maeda, T. & Kunitomo, K. A kinetic comparison between microwave heating and conventional heating of FeS-CaO mixture during hydrogen- reduction. Chemical Engineering Journal 374, 648–657 (2019). 40. Afsahi, M. M., Abolpour, B., Kumar, R. V. & Sohrabi, M. Modelling of noncatalytic hydrogen reduction of molybdenum disulfide in the presence of lime, by complex multistep gas–solid reactions. Mineral Processing and Extractive Metallurgy Review 34, 151–175 (2013). 41. Afsahi, M. M., Kumar, R. V., Sohrabi, M. & Park, Y. J. Reaction kinetics of direct hydrogen reduction of molybdenum disulfide in the presence of lime: A single pellet experimental investigation. Chemical Engineering and Processing: Process Intensification 75, 1–7 (2014). 42. Mankhand, T. R. & Prasad, P. M. Lime-enhanced hydrogen reduction of molybdenite. Metallurgical Transactions B 13, 275–282 (1982). 43. Tan, T. C. & Ford, J. D. Reduction of cobalt sulphide in the presence of calcium oxide. The Chemical Engineering Journal 34, 73–80 (1987). 44. Pathnak, R., Mankhand, T. R., Kachhawaha, J. S. & Prasad, P. M. Kinetics of lime-enhanced hydrogen reduction of solid nickel sulphide. Mineral Processing and Extractive Metallurgy Review 10, 109–120 (1992). 45. Shah, I. D. & Ruzzi, P. L. Pentlandite: Preparation, hydrogen reduction in the presence of lime to yield an iron-nickel alloy. Metallurgical Transactions B 9, 247–253 (1978). 46. Kiuchi, H., Funaki, K., Nakai, Y. & Tanaka, T. Thermochemical decomposition cycle of H2S with nickel sulfide. Int J Hydrogen Energy 9, 701–705 (1984). 47. Tan, T. C. & Ford, J. D. Hydrogen reduction kinetics of nickel sulfide in the presence of calcium oxide. Metallurgical Transactions B 15, 719–723 (1984). 8 60E5644.DOC Attorney Docket No. 07114-2408878 48. Prasad, P. M., Mankhand, T. R. & Rao, P. S. Lime-scavenged reduction of molybdenite. Miner Eng 6, 857–871 (1993). 49. Sabat, K. C., Rajput, P., Paramguru, R. K., Bhoi, B. & Mishra, B. K. Reduction of oxide minerals by hydrogen plasma: An overview. Plasma Chemistry and Plasma Processing 34, 1–23 (2014). 50. Kumar, R., Saha, A. K. & Mandal, A. K. Removal of metallic and non- metallic impurities by hydrogen plasma-arc melting. Canadian Metallurgical Quarterly 62, 383–395 (2023). 51. Guo, X. et al. Mechanism of desulfurization from liquid iron by hydrogen plasma arc melting. Metallurgical and Materials Transactions B 49, 2951–2955 (2018). 52. Kumar, R., Saha, A. K., Malik, K. N. & Mandal, A. K. Removal of C, Si, Mn, S and P in iron melt under hydrogen plasma. JOM 75, 5667–5675 (2023). 53. Elanski, D., Lim, J.-W., Mimura, K. & Isshiki, M. Impurity removal from Fe, Cr, Ti, and V metals by hydrogen plasma arc melting and thermodynamic estimation of hydride and sulfide formation. J Alloys Compd 421, 209–216 (2006). 54. Li, J. et al. Plasma-assisted rhodium incorporation in nickel–iron sulfide nanosheets: enhanced catalytic activity and the Janus mechanism for overall water splitting. Inorg Chem Front 9, 6237–6247 (2022). 55. Cheng, C.-C. et al. Activating basal-plane catalytic activity of two- dimensional MoS2 monolayer with remote hydrogen plasma. Nano Energy 30, 846–852 (2016). 56. He, M. et al. Controllable synthesis of nanostructured nickel phosphosulfide by reduction of mixtures of Na4P2S6 and NiCl2 with low P / Ni ratios in hydrogen plasma. Catal Today 423, 113999 (2023). 57. Bandermann, F. & Harder, K. Production of H2 via thermal decomposition of H2S and separation of H2 and H2S by pressure swing adsorption. Int J Hydrogen Energy 7, 471–475 (1982). 58. Full-temperature-range pressure swing adsorption gas separation, purification and purification method. (2016). 59. Hufton, J. R. et al. Gas purification by adsorption of hydrogen sulfide. (2008). 60. Izumi, J., Morimoto, T., Tsutaya, H. & Araki, K. Hydrogen sulfide removal with pressure swing adsorption from process off-gas. in 293–299 (1993). doi:10.1016 / S0167- 2991(08)63527-2. 9 60E5644.DOC Attorney Docket No. 07114-2408878 61. Eow, J. S. Recovery of sulfur from sour acid gas: A review of the technology. Environmental Progress 21, 143–162 (2002). 62. Pujare, N. U., Tsai, K. J. & Sammells, A. F. An electrochemical Claus process for sulfur Recovery. J Electrochem Soc 136, 3662–3678 (1989). 63. Zhang, Q.-Z., Wang, W., Thille, C. & Bogaerts, A. H2S decomposition into H2 and S2 by plasma technology: Comparison of gliding arc and microwave plasma. Plasma Chemistry and Plasma Processing 40, 1163–1187 (2020). 64. Karakaya, C. System and method for decomposing gaseous hydrogen sulfide into hydrogen gas and elementary sulfur. (2017). 65. Startsev, A. The reaction mechanisms of H2S decomposition into hydrogen and sulfur: Application of classical and biological thermodynamics. Journal of Thermodynamics & Catalysis 08, (2017). 66. Palma, V. et al. H2S oxidative decomposition for the simultaneous production of sulphur and hydrogen. Chem Eng Trans 52, 1201–1206 (2016). 67. Palma, V. et al. H2 production by thermal decomposition of H2S in the presence of oxygen. Int J Hydrogen Energy 40, 106–113 (2015). 68. Startsev, A. N. et al. Low temperature catalytic decomposition of hydrogen sulfide into hydrogen and diatomic gaseous sulfur. Top Catal 56, 969–980 (2013). 69. Karan, K., Mehrotra, A. K. & Behie, L. A. On reaction kinetics for the thermal decomposition of hydrogen sulfide. AIChE Journal 45, 383–389 (1999). 70. Traus, I., Suhr, H., Harry, J. E. & Evans, D. R. Application of a rotating high- pressure glow discharge for the dissociation of hydrogen sulfide. Plasma Chemistry and Plasma Processing 13, 77–91 (1993). 71. Chivers, T., Hyne, J. & Lau, C. The thermal decomposition of hydrogen sulfide over transition metal sulfides. Int J Hydrogen Energy 5, 499–506 (1980). 72. United States National Institute of Standards and Technology. NIST chemistry webbook. https: / / webbook.nist.gov / chemistry. 73. Barin, I., Knacke, O. & Kubaschewski, O. Thermochemical properties of inorganic substances. (Springer Berlin Heidelberg, 1977). doi:10.1007 / 978-3-662-02293-1. 74. Zhong, Y., Wang, Z., Guo, Z. & Tang, Q. Defluidization behavior of iron powders at elevated temperature: Influence of fluidizing gas and particle adhesion. Powder Technol 230, 225–231 (2012). 75. Siegell, J. H. High-temperature de fluidization. Powder Technol 38, 13–22 (1984). 10 60E5644.DOC Attorney Docket No. 07114-2408878 SUMMARY In accordance with one embodiment, a method comprising reacting a solid sulfur- containing compound, including but not limited to a sulfide, oxysulfide, or sulfate, of a first metal with hydrogen to reduce at least a portion of the solid sulfur-containing compound with at least a portion of the hydrogen to form hydrogen sulfide and elemental first metal, and at least one of (a) separating at least a portion of the hydrogen sulfide from hydrogen; (b) thermally decomposing at least a portion of the hydrogen sulfide to regenerate hydrogen and produce elemental sulfur; (c) catalytically decomposing at least a portion of the hydrogen sulfide to regenerate hydrogen and produce elemental sulfur; (d) decomposing at least a portion of the hydrogen sulfide with a plasma to regenerate hydrogen and produce elemental sulfur; (e) reacting at least a portion of the hydrogen sulfide with a second metal to produce a sulfide of the second metal and regenerate hydrogen; (f) recovering at least a portion of the elemental first metal; (g) recovering at least a portion of the hydrogen sulfide; and / or (h) recovering at least a portion of the elemental first metal in an alloy of third metal. In accordance with one embodiment, a method comprising reacting a solid sulfur- containing compound, including but not limited to a sulfide, oxysulfide, or sulfate, of a first metal with hydrogen to reduce at least a portion of the solid sulfur-containing compound with at least a portion of the hydrogen to form hydrogen sulfide and a sulfide of first metal; and at least one of (a) separating at least a portion of the hydrogen sulfide from hydrogen; (b) thermally decomposing at least a portion of the hydrogen sulfide to regenerate hydrogen and produce elemental sulfur; (c) catalytically decomposing at least a portion of the hydrogen sulfide to regenerate hydrogen and produce elemental sulfur; (d) decomposing at least a portion of the hydrogen sulfide with a plasma to regenerate hydrogen and produce elemental sulfur; (e) reacting at least a portion of the hydrogen sulfide with a second metal to produce a sulfide of the second metal and regenerate hydrogen; (f) reacting at least a portion of the hydrogen sulfide with a sulfide of the second metal forming a sulfide with a different cation valency than the feedstock of the second metal sulfide; (g) recovering at least a portion of the sulfide of the first metal; (h) recovering at least a portion of the hydrogen sulfide; and / or (i) forming a sulfide of the first metal with a different cation valency than the sulfur-containing feedstock compound of a first metal. In an alternative embodiment, a method in which following hydrogen reduction of a sulfur-containing compound, at least one of (a) a portion of hydrogen sulfide and hydrogen are separated via pressure swing adsorption; (b) a portion of hydrogen sulfide and hydrogen 11 60E5644.DOC Attorney Docket No. 07114-2408878 are separated via a membrane; (c) a portion of hydrogen sulfide and hydrogen are separated via cryogenic distillation; (d) a portion of hydrogen sulfide and hydrogen are separated via pressure increase and condensation; (e) a portion of hydrogen sulfide and hydrogen are separated via centrifuge; (f) a portion of hydrogen sulfide and hydrogen are contacted with an aqueous phase; (g) a portion of hydrogen sulfide and hydrogen are contacted with an organic liquid; (h) a portion of hydrogen sulfide and hydrogen are contacted with an ionic liquid; (i) a portion of hydrogen sulfide and hydrogen are contacted with a melt containing some portion of sulfur species. In accordance with various embodiments, a method in which at least a portion of the separated hydrogen, or hydrogen sulfide, and / or regenerated hydrogen is mixed with at least a portion of the hydrogen reductant. In accordance with one embodiment, a method in which the solid sulfur-containing compound of a first metal is mixed with a compound including but not limited to an oxide, a carbonate, a phosphate, a hydroxide, a sulfide, a sulfate, an oxysulfide, alloy, and / or elemental form of a third metal. This compound of the third metal may or may not also inhibit sintering of the sulfur-containing compound of the first metal. In accordance with one embodiment, a method in which elemental first metal is liberated from at least one of (a) a solid sulfur-containing compound of a first metal; or (b) a compound of a second metal. In accordance with various embodiments, a method in which at least a portion of the sulfur-containing compound of the first, second, or third metal is at least partially molten during the reaction or reduction. In accordance with various embodiments, a method wherein at least one of (a) a portion of the hydrogen is molecular; (b) a portion of the hydrogen is atomic; (c) a portion of the hydrogen is ionic; or (d) a portion of the hydrogen is a plasma. In accordance with one embodiment, a method wherein the hydrogen reactant is mixed with an inert, carbon containing, and / or oxygen containing gas or plasma. In accordance with one embodiment, a system wherein at least one of (a) a reactor or vessel that contains a fluidized bed; (b) a reactor or vessel that contains a packed bed; (c) a reactor or vessel that contains multiple hearths; (d) a reactor or vessel that is rotated during operation; (e) a reactor or vessel contains an electric arc; (f) a reactor or vessel contains a plasma source; or (g) a reactor or vessel is a kiln. Additional embodiments may be disclosed and claimed. 12 60E5644.DOC Attorney Docket No. 07114-2408878 BRIEF DESCRIPTION OF THE DRAWINGS Those skilled in the art of hydrogen reduction processes and systems for sulfur containing compounds should more fully appreciate the advantages of the invention, discussed in “DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS” and the figures summarized below. FIG. 1 illustrates the critical thermodynamic ratio of hydrogen to hydrogen sulfide( ) for several metal sulfide feedstocks and metal products, in accordance withone or more embodiments. FIG. 2 illustrates the critical thermodynamic ratio of hydrogen to hydrogen sulfide for chromium sulfide reduction for different thermodynamic activities of thesulfide ( ) and the metal ( ), in accordance with one or more embodiments.FIG. 3 is a simplified flowsheet for gas / plasma roasting or reduction reactor(s) employed for hydrogen reduction of sulfides and / or mixtures of sulfur containing metal compounds with hydrogen recovery and recycling, in accordance with one or more embodiments. FIG. 4 is a simplified flowsheet for gas / plasma roasting or reduction reactor(s) and subsequent gas separation and gas treatment employed for hydrogen reduction of sulfides and / or mixtures of sulfur containing metal compounds with hydrogen recovery and recycling, in accordance with one or more embodiments. FIG. 5 illustrates a simplified flowsheet for gas / plasma roasting or reduction reactor(s) and subsequent gas treatment employed for hydrogen reduction of sulfides and / or mixtures of sulfur containing metal compounds with hydrogen recovery and recycling, in accordance with one or more embodiments. These figures and drawings are included primarily for illustrative purposes and are not intended to limit the scope of the invention described herein. The figures and drawings depicted herein are not necessarily drawn to any scale or a consistent scale. Like elements are depicted by like numerals unless the context suggests otherwise. 13 60E5644.DOC Attorney Docket No. 07114-2408878 DETAILED DESCRIPTION Notable industrial precedence exists for the use of hydrogen as a reductant for metals, yet this approach has seen limited deployment for the roasting of non-oxide feedstocks. To our knowledge, practical processing conditions and operational parameters have not previously been invented for the hydrogen reduction of metal sulfides via solid-gas or liquid gas roasting reactions with hydrogen recycling, recovery, and / or reuse by the same and / or other processes after reduction hydrogen recovery in order to set and control the hydrogen gas atmosphere in the reactor. Significant attention has been focused elsewhere toward the direct reduction of oxides via roasting with hydrogen, either gaseous or plasma. Hydrogen reduction of sulfides has long been conducted industrially in aqueous systems following hydrometallurgical processing circuits for nickel, cobalt, and other metals. Some studies have explored the chemistry and physics of interactions between hydrogen and metal sulfides at relevant operating temperatures; yet, these fundamental scientific developments have so far failed to yield predictive insight into useful methods and processing systems for industrially scalable metal production via hydrogen reduction of metal sulfides. We have invented an integrated plasma roasting / hydrogen reduction / gas separation process to produce metals from metal sulfide containing precursors. Hydrogen may be molecular, atomic, or ionic in a gaseous or plasma form. Our approach is applicable to a wide range of metal and alloy production challenges, including pure metal and alloy manufacturing, metal separations, metal powder production, and recycling. Our technique lowers direct greenhouse gas emissions by partially or fully replacing or supplementing carbon based reductants, including but not limited to coal, coke, and biomass. Through integrating gas separation and recovery with hydrogen reduction, lower hydrogen consumption is achievable with our technology versus alternative oxide reduction or aqueous approaches. Progress in process sustainability and hydrogen consumption are expected to yield useful improvements to process cost and flexibility, while mitigating bottlenecks in metal feedstock procurement and impurity management. The methods and systems described herein constitute a new platform technology that is applicable to a wide range of metals processing challenges, including but not limited to pure metal and alloy production, targeted materials production and recovery from multielement primary or secondary feedstocks, and control of metal powder morphology. Key advancements achievable with our technology, include, but are not limited to: 14 60E5644.DOC Attorney Docket No. 07114-2408878 • Production of metals from their respective sulfur containing compounds or mixtures via hydrogen reduction • Selective reduction of a target metal from mixed sulfur containing compound or mixture via hydrogen reduction • Spontaneous liberation of a target metal from a mixed metal compound matrix following selective reduction of a sulfur containing compound or mixture • Separation of unreacted hydrogen and byproduct hydrogen sulfide via membrane separation following sulfur containing compound or mixture reduction, enabling hydrogen recirculation into the reduction reactor • Separation of unreacted hydrogen and byproduct hydrogen sulfide via pressure swing adsorption following sulfur containing compound or mixture reduction, enabling hydrogen recirculation into the reduction reactor • Separation of unreacted hydrogen and byproduct hydrogen sulfide via absorption following sulfur containing compound or mixture reduction, enabling hydrogen recirculation into the reduction reactor • Separation of unreacted hydrogen and byproduct hydrogen sulfide via stripping following sulfur containing compound or mixture reduction, enabling hydrogen recirculation into the reduction reactor • Separation of unreacted hydrogen and byproduct hydrogen sulfide via cryogenic air separation following sulfur containing compound or mixture reduction, enabling hydrogen recirculation into the reduction reactor • Separation of unreacted hydrogen and byproduct hydrogen sulfide via pressure increase and condensation following sulfur containing compound or mixture reduction, enabling hydrogen recirculation into the reduction reactor • Separation of unreacted hydrogen and byproduct hydrogen sulfide via centrifuge following sulfur containing compound or mixture reduction, enabling hydrogen recirculation into the reduction reactor • Regeneration of hydrogen from separated hydrogen sulfide for reintroduction into the reduction reactor via thermal decomposition under near ambient or vacuum pressures • Regeneration of hydrogen from separated hydrogen sulfide for reintroduction into the reduction reactor via catalyzed decomposition • Indirect metallothermic reduction of a sulfur containing compound or mixture via first reacting hydrogen with a sulfur containing compound or mixture of a first metal, then 15 E5644.DOC Attorney Docket No. 07114-2408878 decomposing product hydrogen sulfide via sulfidation of a second metal to regenerate hydrogen for use in reduction of sulfur containing compound or mixture of the first metal • Gas flowrates, particle sizes, gas compositions, operating temperatures, and mass transport conditions for hydrogen reduction of a sulfur containing compound or mixture in a fluidized bed reactor, packed bed reactor, multi-hearth furnace, rotary kiln, shaft furnace, arc furnace, or plasma furnace • Chemical or mechanical additives to inhibit sintering of metal sulfur containing compound or mixture feedstocks or metal powder products during hydrogen reduction Hydrogen reduction of sulfur containing compounds or mixtures via our technology is critical to accessing new technological avenues including, but not limited to those listed above. The production of a condensed metal product from a solid sulfide feedstock via solid-gas roasting with molecular hydrogen ( ) is described by the following net reaction (Eq. 1),where is a metal, is a metal sulfide, is a hydrogen sulfide byproduct, and , , and are material-specific stoichiometric coefficients: 1) While Eq. 1 depicts the net hydrogen reduction reaction, the reaction may or may not be conducted stoichiometrically in our invention; any species may or may not be at an excess or deficit in the system. Assuming an ideal gas phase, at thermodynamic equilibrium a criticalratio of to partial pressures ( must be present locally within the reactorat the site of the reaction in Eq. 1 to proceed thermodynamically spontaneously. For a given metal, at thermodynamic equilibrium is related to the standard Gibbs energyof reaction of Eq. 1 ( ), the ideal gas constant ( ), the absolute temperature ( ), and theactivities of and ( and respectively): 2) 16 60E5644.DOC Attorney Docket No. 07114-2408878 In some embodiments of our invention, the sulfide feedstock for hydrogen reduction may or may not be a component of a chemical, physical, or mechanic mixture of different chemical compounds, including but not limited to sulfides, oxides, sulfates, oxysulfides, oxysulfates, carbonates, phosphates, and hydroxides. Eqs. 1-2 may be redefined for mixed feedstocks, either by adjusting and accordingly for the given chemical environment or by considering complex anions containing sulfur and other components. For example, thehydrogen reduction of a sulfate ( ) or an oxysulfide ( is described by thefollowing reactions, where is water and , , , , , and are material-specific stoichiometric coefficients: (Eq. 4) (Eq. may be derived for Eqs. 4-5 following a similar approach as in Eqs. 1-3. Relations like Eqs. 1-5 may be determined for any single or combination of metals or alloys for which our technology is relevant, including but not limited to feedstocks and / or products containing one or more of lithium, magnesium, aluminum, silicon, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, arsenic, zirconium, niobium, silver, molybdenum, rhodium, palladium, cadmium, indium, tin, antimony, tantalum, tungsten, rhenium, platinum, mercury, lead, and bismuth. Similar relations to Eqs. 1-5 may also be derived for other forms of hydrogen in our technology,including but not limited to atomic ( ) and ionic species (ex: , , etc.). Similar relationsto Eqs. 1-5 may also be used for feedstock sulfur containing compounds that are at least partially molten during reduction. Similarly, for other forms of hydrogen, hydrogen to hydrogen sulfide ratios similar to may be defined for our technology, 17 60E5644.DOC Attorney Docket No. 07114-2408878 including but not limited to . The hydrogen may be contained in a gas, plasma, or some combination of gas and plasma. Calculated for some pure immiscible sulfide reactants reacted with pure molecular hydrogen to produce pure immiscible metal products as a function of temperature between 400 °C and 2000 °C are reported in FIG. 1. Calculated for some pure immiscible sulfide reactants reacted with pure molecular hydrogen to produce pure immiscible metal products at 1000 °C are also reported in Table 1. Calculated for some pure immiscible sulfide reactants reacted with pure atomic hydrogen to produce pure immiscible metal products at 1000 °C are also reported in Table 1. Thermodynamic data from the United States National Institute of Standards and Technology (NIST)72and from other tabulated sources are utilized13,73. or similar ratios for other hydrogen species may also be derived using the above methodology of Eqs. 1-3 for other sulfur-containing feedstocks (including but not limited to sulfides, sulfates, oxysulfides, etc.) and pure or alloyed metal products not depicted in FIG. 1 or reported in Table 1. The relative spacing between in FIG. 1 and Table 1 is correlated with the selectivity achievable in reduction of pure immiscible sulfide reactants to pure immiscible metal products. Wider spacing between or for two metal compound species indicating that reduction is more selective for one metal compound versus the other. Thereby, our technology to control and modulate the composition of hydrogen and in a reduction reactor in principle also enables improved selectivity in metal reduction. is generally lower than , indicating that atomic hydrogen is a stronger reductant than molecular hydrogen. Atomic hydrogen may be generated through the decomposition of molecular hydrogen, such as in a hydrogen containing plasma. Ionic species of hydrogen are also stronger reductants than molecular hydrogen. Embodiments of our technology may or may not leverage a hydrogen plasma to improve reduction versus molecular hydrogen alone. Table 1, below, provides calculated for hydrogen reduction of some sulfides to their respective elements at 1000 °C. Abbreviations correspond to those utilized in the periodic table of elements. Similar relations may be defined for other elements, metal valences, and sulfur containing feedstock compounds (including but not limited to sulfides, sulfates, oxysulfides, etc.). and can vary 18 60E5644.DOC Attorney Docket No. 07114-2408878 up or down by orders of magnitude based on interactions with other species in the system and temperature, as demonstrated in FIG. 1 and FIG. 2. Table 1 Metal Metal Valency in Sulfide 1 13.1 2.8 2 6.3 0.4 3 0.7 -5.2 1 9.2 3.3 2 10.1 4.2 3 5.0 -0.9 4 1.3 -4.5 1 7.9 2.1 2 15.2 9.4 3 12.0 6.2 4 4.8 -1.1 3 3.5 -2.4 3 1.7 -4.2 2 6.3 0.4 2 1.8 -4.1 2 0.2 -5.6 3 -0.4 -6.3 1 2.2 -3.7 2 3.8 -2.1 3 2.7 -3.1 2 0.2 -5.7 1 5.9 0.0 2 15.0 9.1 3 13.2 7.4 4 8.0 2.2 4 3.3 -2.5 4 1.7 -4.2 4 0.1 -5.8 19 60E5644.DOC Attorney Docket No. 07114-2408878 3 -0.2 -6.0 1 0.1 -5.8 2 0.8 -5.0 3 0.7 -5.1 4 -0.8 -6.7 1 5.3 -0.6 2 14.7 8.8 3 12.7 6.9 3 12.1 6.3 3 11.7 5.8 3 12.1 6.2 3 12.3 6.5 3 9.4 3.5 3 12.6 6.8 3 12.7 6.8 3 12.8 6.9 3 12.9 7.0 3 13.0 7.2 4 8.2 2.4 4 3.4 -2.5 4 1.4 -4.5 4 -0.5 -6.4 3 -1.1 -6.9 1 0.4 -5.4 2 0.4 -5.5 3 -1.5 -7.4 4 9.1 3.3 4 7.5 1.6 For real systems where the sulfide reactant and metal products are miscible or impure, the thermodynamically calculated or other hydrogen / hydrogen sulfide ratios will deviate with the thermodynamic activities of species in the 20 60E5644.DOC Attorney Docket No. 07114-2408878 system. In FIG. 2, calculated shown as a function of temperature and hypothetical ratios for chromium metal and sulfide with a cation valency of 2( ). Similar relations may be derived for other metals, alloys, sulfides, and sulfurcontaining compounds without limitation, including but not limited to metals, alloys, sulfides, sulfates, and oxysulfides containing one or more of lithium, magnesium, aluminum, silicon, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, arsenic, zirconium, niobium, silver, molybdenum, rhodium, palladium, cadmium, indium, tin, antimony, tantalum, tungsten, rhenium, platinum, mercury, lead, and bismuth. Similarly, for other forms of hydrogen, as a function hydrogen to hydrogen sulfide ratios similar to may be defined for our technology, including but not limited Calculated at 1000 °C for chromium sulfide with a chromium valency in Table 1 and a valency of 2 ( , ) in FIG. 2 are different, withthe lower valency exhibiting higher . This demonstrates that thermodynamically, hydrogen reduction of sulfides using our invention may be conducted selectively for not only different feedstock and product elements / metals, but also for feedstock and intermediate sulfur-containing product valences. Likewise, hydrogen reduction of sulfide and sulfur-containing compounds using our technology may also be leveraged to produce sulfide products of a target valency from other sulfur containing compounds. As shown in FIG. 2, calculated for the thermodynamically spontaneous reduction of a given sulfide may in principle vary by over 10 orders of magnitude depending on the specific operating temperature and the extent of solution interactions within the system. Such solution interactions in both metallic and sulfur containing systems at elevated temperatures remain impossible to accurately derive fully mathematically. Roasting of metal compounds in the presence of sulfur containing species in the gas atmosphere often accentuates non ideal solution interactions in mathematically unquantified ways. Therefore, the actual ratio employed at a given point in our invention to achieve hydrogen reduction of a sulfide and / or sulfur containing compound is termed The value of may be numerically similar to however is a value that may be calculated from thermodynamics while is a key operational parameter for the reactor that also includes uncharacterized contributions from mass 21 60E5644.DOC Attorney Docket No. 07114-2408878 transport, kinetic, unquantified solution thermodynamics in the system, and operational factors for specific reactor or hydrogen sulfide treatment and recirculation systems. Due to differences in kinetic, transport, and reactor specific behaviors between species, the relative order of for different species with increasing may differ from the relative order of such as depicted in FIG. 1. For example, in some embodiments, may be lower for the reduction of nickel than iron or ferronickel, as shown in FIG. 1. Yet operationally, the actual may be higher to produce nickel than ferronickel or other iron alloys due to a combination of thermodynamic, kinetic, transport, reactor, and method specific factors. Operational differences between are impossible to predict through scientific theory alone. Two hydrogen reduction trials were conducted in a laboratory scale fluidized bed reactor with fine particle sized nickel sulfide feedstock. The composition of feed material was 58.8 wt% nickel, 35 wt% sulfur, 3.7 wt% iron, 1.7 wt% zinc, 3.7 wt% iron, 0.8 wt% cobalt, 0.3 wt% calcium, 0.2 wt% aluminum and 0.1 wt% silicon. The first and second trials were performed at 680 °C and 700 °C respectively. gas was used to fluidize the material bed and to act as reducing agent, with no other gasses fed into the reactor. The duration of reaction time was 60 minutes for both trials. Pressure of around 1 atm was used. Inert sand was used to reduce sintering of the bed. The product from Trial 1 contained 3.5 wt% nickel metal and 6.2 wt% metal. The product from Trial 2 contained 6.5 wt% nickel metal and 7.2 wt% metal. Nickel yield to metal in the first trial was 14% and 20% in the second trial. Different temperatures and atmospheres or reduction times could have been used to reduce or increase nickel yield to metal phase. Nickel to iron ratio in feed material was 15.9. Trial 1 metal product had nickel to iron ratio of 1.5 and trial 2 had 1.7 which indicates that iron was preferentially reduced in contrary to the thermodynamic assumption in which nickel should reduce more easily than iron. This demonstrates that the thermodynamics alone are not enough to predict the results of the invention. These results in indicate that hydrogen reduction can be utilized in a variety of approaches, including as a pre- reduction step for subsequent metallurgical treatments. Depending on the modelling assumptions employed and the thermodynamic databases utilized, slightly different relative values of or in FIGS. 1-2 and Table 1 may be calculated for our technology. These variations in the 22 60E5644.DOC Attorney Docket No. 07114-2408878 thermodynamic and from different data sources and modelling assumptions are generally negligible with respect to actual relevant operational ranges for or other ratios of hydrogen to hydrogen sulfide when uncertainties in solution effects, mass transport considerations, and kinetic effects are also considered. This further motivates the use of real operational ratios of hydrogen to hydrogen sulfide, such as may vary spatially through the reduction reactor, informed by the interactions of hydrogen and with both condensed and other gaseous species in the system. Gas phase species may either flow counter-current, co- current, or some mixture of counter-current and co-current with solid species within the reactor, or be bubbled through mush or at least partially molten regions. For Eq. 1, one potential rate equation for the generation of from molecular hydrogen is described below, where denotes the rate of hydrogen sulfide production from reduction, denotes the reaction rate constant, denotes the concentration of molecular in thesystem, [ ] denotes the concentration of in the system, denotes the observedreaction order with respect to , denotes the observed reaction order with respect to and denotes a kinetic effectiveness factor: 6) The actual form and functional dependencies of Eq.6 are materials specific and may be redefined using these and / or other relevant operating parameters within the scope of our invention, including but not limited to particle surface areas, packing densities, the concentration of other species, particle sizes, or rate constants attributed to reverse or side reactions. Different models for rate limiting steps and mechanisms may also be adopted in our invention for equations similar to Eq. 6. Eq. 6 may also be modified to describe the hydrogen reduction of other sulfur containing feedstocks, such as those included in Eqs. 2-3. may be defined on a concentration basis, mass basis, surface area basis, or based on other relevant operational quantities for a particular material system. All parameters in Eq. 6 may also exhibit temperature dependence. Similar relations to Eq. 6, with potentially 23 60E5644.DOC Attorney Docket No. 07114-2408878 different rate dependencies, may also be defined for other forms of hydrogen, includingatomic ( ) and ionic species (ex: , , etc.) in gaseous or plasma forms.The kinetic effectiveness factor describes limitations to the reaction rate constant due to mass transport or other kinetic effects, including but not limited to intergrain, intragrain, surface tension, viscosity, and external mass transport limitations. Sintering effects can also greatly modulate mass transport and kinetic effects in the reactor. Loss of surface area or densification can lower due to reductions in porosity, void fraction and / or increase other intergrain, intragrain, or external mass transport limitations in a feedstock powder bed during solid / gas operation. Furthermore, changing a feedstock powder bed morphology, porosity, and or particle size can also influence and / or whether rate expressions are defined based on including but not limited to concentration, mass, or surface area. In embodiments where a fluidized bed reactor is utilized, sintering or partial melting can further lead to changes in the necessary operation criteria for bed fluidization, including but not limited to gas velocity, gas viscosity, gas density, gas residence time, feedstock compound residence time, and . Additional condensed species may be introduced to the system that inhibit reactant or product particle adhesion. These may be condensed compounds that provide a higher melting coating on feedstock particles, inhibiting diffusion, adhesion, and sintering between the particles. Inert particles may also or instead be added that aid to break apart particles that tend to agglomerate in the system at elevated temperature. Potential examples of condensed species added in our invention to inhibit sintering and / or agglomeration include but are not limited to oxides, sulfides, phosphates, halides, carbon, or metals. Gas phase options for minimizing sintering are also applicable to our invention. Through dilution of hydrogen with another gas species, a higher gas velocity may be maintained to mitigate defluidization at higher operating temperatures. Inert and other gasses including but not limited to argon, nitrogen, and / or carbon monoxide also exhibit higher densities and viscosities than hydrogen74,75, aiding in fluidization in some embodiments. Gaseous species in the system may also inhibit agglomeration via chemical adsorption to and the coating of feedstock or product particles in the system. When some or all of the hydrogen is utilized as a plasma, other gas species may also serve to form or stabilize the plasma, including but not limited to argon or helium. The use of faster gas flowrates helps mitigate the effects of sintering in fluidized beds in some embodiments. Increasing the gas flowrate can also modulate within 24 60E5644.DOC Attorney Docket No. 07114-2408878 the reactor due to decreasing the residence times of and . When these added gas species are not inert, their presence may also modulate in some embodiments. Based on reactions that enrich or deplete the system in and / or , embodiments of our invention may have increase, decrease, or remain fairly constant as condensed or gaseous species move through the reduction reactor. From Eqs. 4-5, the oxidation, sulfidation, or reduction of other species within the reactor may also help enrich and / or deplete the gas phase in and / or to help control . The presence of oxygen or water containing species in the gas phase may further enrich and / or deplete and / or , with an example depicted below in Eq. 7, where , , , and are material-specific stoichiometric coefficients: 7) Similarly, species in the gas phase containing carbon may also modulate the amount of and / or in the gas phase as it flows through the reactor. An example reaction is depicted below in Eq. 8, where , , , , , , , and are material-specific stoichiometric coefficients: 8) Supplemental carbon may also be delivered to the reactor via condensed sources, including but not limited to carbonates, carbides, graphite, carbon black, coal, biomass, biochar, biocoke, and fossil coke. An example reaction is depicted below in Eq. 9 for interactions with a condensed carbon source, where , , , , , , , and are material-specific stoichiometric coefficients: 9) Supplemental oxygen may also be delivered to the reactor via condensed sources, including but not limited to carbonates, sulfates, nitrates, phosphates, oxides, peroxides, super oxides, 25 60E5644.DOC Attorney Docket No. 07114-2408878 hydroxides, and hydrates. Addition of these compounds and / or others can enable oxygen and carbon species to be shuttled in and out of the gas phase as a function of the spatial distribution of operating conditions within the reactor. An example reaction is depicted belowin Eq. 10 for interactions with a thermally unstable metal carbonate ( ), where , , ,, , , , and are material-specific stoichiometric coefficients: (Eq. 10) In Eqs. 7-10, additional carbon, oxygen, sulfur, and hydrogen containing species may be added, generated, and / or reacting beyond those shown. Furthermore, Eqs. 7-10 may also be conducted together in the reactor at the same time. A combination of Eqs. 1, 4-5, and 7-10 may be used to enrich or deplete the system in and / or and modulate and control . Similar relations to Eqs. 1-10, may also be defined for the enrichment ordepletion other forms of hydrogen in the system, including atomic ( ) and ionic species (ex:, , etc.) in gaseous or plasma states. Relations including but not limited to those similar to shown in Eqs. 1-10 for molecular, atomic, or ionic hydrogen may inform the design of an internal model controller for reduction process design. This model may also inform the identification of proportional, integral, and derivative terms in a PID or similar process controller. Condensed or gaseous species containing oxygen, carbon, and / or other elements that bond with and / or sequester sulfur containing species to regenerate hydrogen in situ may be employed as dedicated “collector species” to increase or similar relations foratomic ( ) or ionic species (ex: , , etc.) of hydrogen in the system. The use of“collector” species in our invention differs from “collector” species employed in prior art28,29,31,37–45,47,48where oxidic and / or carbonate species become sulfidized and hydrogen is liberated as mainly as water or steam. Our collector species liberate hydrogen in elemental form or as instead, potentially for recirculation through the reduction process. In our technology, as material flows through the reduction reactor and the reaction progresses, is produced at some rate described by an appropriate rate law for , including but not limited to that defined in Eq. 6. Therefore, the value of orsimilar relations for atomic ( ) or ionic species (ex: , , etc.) of hydrogen can vary26 60E5644.DOC Attorney Docket No. 07114-2408878 spatially within the reactor as is produced and hydrogen is consumed by the reduction reaction and side reactions with collector species. Likewise, if some portion of molecular hydrogen is disassociated into atomic or ionic species within the reactor, the thermodynamic affinity for reduction may differ in regions with varying amounts of molecular, atomic, or ionic hydrogen. Operationally for our invention, this establishes two key locations of interestfor or similar relations for atomic ( ) or ionic species (ex: , , etc.) ofhydrogen in the reactor: at the reactor inlet ( ) and at the reactor outlet may also bedefined for atomic ( ) or ionic species (ex: , etc.) for embodiments of our inventionwhere plasma, disassociated, or ionized forms of hydrogen are fed into the reactor, instead of being generated within the reactor. When some degree of hydrogen-containing plasma is utilized in reduction, or corollaries for atomic or ionic hydrogen species may vary distinctly from and or corollaries for atomic or ionic hydrogen species due to the differing reduction thermodynamics of atomic and ionic versus molecular hydrogen. When hydrogen plasma (including molecular, atomic, and / or ionic species) is utilized as a reductant for sulfur containing compounds, it is generated in the reactor from the inlet gas stream with composition informed by Identified operating temperature, feed particle size, and gas residence time, and metal compound residence time in our invention are identified in Table 2 for some relevant metal sulfide compounds. Operational values in our invention may vary from those in Table 2 due to the inclusion of other sulfur containing feedstock compounds, sulfur-free feedstock compounds / additives, gangue impurities, metal product impurities, and metal product alloying additions, not captured in Table 2. Likewise, the degree in which molecular, atomic, ionic, gaseous, or plasma species of hydrogen are generated and / or utilized in the reactor may shift and temperature. Similar operating conditions may be defined for any single or combination of metals, alloys, and / or impurities for which our technology is relevant, including but not limited to feedstocks and / or products containing one or more of lithium, magnesium, aluminum, silicon, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, arsenic, zirconium, niobium, silver, molybdenum, rhodium, palladium, cadmium, indium, tin, antimony, tantalum, tungsten, rhenium, platinum, mercury, lead, and bismuth. 27 60E5644.DOC Attorney Docket No. 07114-2408878 Table 2, below, provides operating conditions for hydrogen reduction of some pure sulfides to pure metals. Operating condition ranges in our invention will vary with the inclusion of other sulfur containing feedstock compounds, sulfur free feedstock compounds / additives, gangue impurities, metal product impurities, and metal product alloying additions. 5 There is no upper limit for the plasma temperature in our invention, so when a hydrogen containing plasma is utilized the reaction temperature in the plasma or the surface of the feedstock can be extremely high and above that which is shown here. Table 2 Pure feed Temperature, P80 Gas Metal compound °C feed residence compound Size time, s residence time, s 100 – 2000 -5 – 8 -6 – 9 1 µm - 10-6– 10-6– 106200 106mm 400 – 2000 -4 – 9 -5 – 10 1 µm - 10-6– 10-6– 106200 106mm 400 – 2000 -5 – 10 -6 – 11 1 µm - 10-6– 10-6 – 106200 106mm 400 – 2000 -3 – 13 -4 – 14 1 µm - 10-6– 10-6– 106200 106mm 400 – 2000 -5 – 8 -6 – 9 1 µm - 10-6– 10-6– 106200 106mm 400 – 2000 -1 – 13 -2 – 14 1 µm - 10-6– 10-6– 106200 106mm 350 – 2000 -4 – 9 -5 – 10 1 µm - 10-6– 10-6– 106200 106mm 28 60E5644.DOC Attorney Docket No. 07114-2408878 400 – 2000 -2 – 12 -3 – 13 1 µm - 10-6– 10-6– 106200 106mm 400 – 2000 -5 – 8 -6 – 9 1 µm - 10-6– 10-6 – 106200 106mm 0 – 2000 -5 – 8 -6 – 9 1 µm - 10-6– 10-6– 106200 106mm Molecular, atomic, or ionic hydrogen as a reductant in our process may take the form of a gas and / or plasma. Plasma in the system may or may not be at equilibrium with itself or other species in the reactor. Nonthermal, cold, anisothermal, weakly ionized, or thermal plasmas may be employed in our invention, and may include other inert or non-inert components in addition to hydrogen species. In various embodiments of our invention leveraging hydrogen species in gaseous and / or plasma forms, there may or may not be a significant difference in the temperatures of the gas phase, plasma phase, feedstock particle surface, feedstock particle core, and electrons. Depending on where and how temperature is measured or defined, values in our invention may fall outside the range shown in Table 2. The temperature of a plasma in our invention may simultaneously differ depending on the degree of freedom of the plasma considered and may or may not be distinct for electrons, ions, atoms, and molecules. There is no upper limit for hydrogen plasma temperature in our invention, so the reaction temperature at the surface of a feedstock particle can be extremely high and above that which is shown in Table 2. Molecular, atomic, or ionic hydrogen as a reductant in our process may take the form of a gas and / or plasma. Gaseous hydrogen may be regenerated from unreacted hydrogen plasma. A range of pressures may be employed in our invention as motivated by a range of chemical and operational factors, including compound stability, plasma stability, volatility, and vapor pressure. Pressures may range from medium vacuum (10-6atm) up to 1000 atm depending on the degree in which molecular, atomic, ionic species of hydrogen are leveraged in gaseous or plasma forms. Pressures above ambient may be employed to suppress compound volatility or decomposition. A single reduction reactor may be employed, or multiple reactors may be utilized. Multiple reduction reactors may or may not be arranged in series and / or parallel to facilitate 29 60E5644.DOC Attorney Docket No. 07114-2408878 including, but not limited to pre-reduction, post-reduction, calcination, sintering, sulfidation, dead roasting, preheating, and / or heat recovery. Supporting infrastructure may be included to generate plasma within a reduction reactor or to feed it into a reduction reactor. In embodiments with multiple reactors in series or parallel, corresponding values of may be defined for each reactor. Generally, defines the composition of gas flowing into a reduction reactor(s), and is a key value to measure, model, and / or control during operation of our invention. Some examples of simplified process flowsheets for hydrogen reduction of sulfur containing compounds are included in FIG. 3, FIG. 4, and FIG. 5. Simplified flowsheets in FIGS. 3-5 are included for illustrative purposes only and are not intended to limit the scope of the present invention. Additional and / or supporting unit operations beyond those shown in FIGS. 3-5 may also be employed in our invention. In some embodiments summarized by the simplified flowsheet in FIG. 3, a gas stream containing some portion of at a given may be utilized to reduce a feedstock containing a sulfur containing compound, including but not limited to a sulfide, sulfate, or oxysulfide, to form a metal or sulfide compound. Product gasses at a given or a similar ratio considering atomic or ionic hydrogen may then be sent to other processing operations, including, but not limited to combustion, fuel cells, or chemical synthesis. In one embodiment, the flowsheet in FIG. 3 describes one example of a hydrogen reduction process for sulfur containing feed material (stream 1). Product off gas stream 4 is connected to a subsequent process. Reactor(s) in block 3 is / are solid-gas / plasma or liquid- gas / plasma reactor(s) that can be fluidized bed, rotary kiln, multi hearth, packed bed, electric arc, plasma, and / or shaft furnace types. The system can consist of single or multiple of those units in different combinations and arrangements. Feed gas stream 2 to the reactor(s) consists mainly of hydrogen gas and may also include other gases that are used to control the conditions for reactions in reactor(s). Reactors may also include a settling chamber, cyclones, or other unit operations not shown to remove solid particles from the produced off gas as integrated part of the reactors. Unit operations to support plasma generation and management may also be present. Possible subsequent processes (consuming stream 4) include but not limited to thermal energy production and / or heat recovery to produce electricity, fuel cells, ammonia production, fertilizer production, and / or petrochemical and refinery processes. 30 60E5644.DOC Attorney Docket No. 07114-2408878 In one alternative embodiment, in the flowsheet described in FIG. 3, feed material stream 1 to hydrogen reduction reactor step 3 contains mainly metal sulfate(s). Product gas stream 4 has high concentrations of and gases and the stream can be connected in sulfuric acid production plant. Other embodiments may employ different variations of stream and reactor components versus those described here. In embodiments summarized by the simplified flowsheet in FIG. 4, in the inlet gas stream is set via control of the introduction of fresh gas into the system along with recycled , , and / or other gas species recovered following reduction and subsequent gas separation and / or gas treatment. Following reduction, through the use of gas separation and gas treatment operations, a portion of in the reactor(s) outlet gas stream(s) at given may be separated from other gas species, enabling some portion of unreacted , , and other gas species, including but not limited to inert, carbon containing, oxygen containing, phosphorous containing, nitrogen containing, and / or sulfur containing gasses, to be recycled back into the reduction reactor(s). Gas separation options that our technology may utilize include, but are not limited to, pressure swing adsorption, membrane separation, cryogenic separation, pressure increase to induce selective condensation, centrifuge, contacting with an aqueous phase, contacting with a liquid metal, contacting with an organic liquid, contacting with an ionic liquid, and / or contacting with a melt containing some portion of elemental sulfur or sulfur-containing compounds. Other embodiments may employ different variations of stream and reactor components versus those described here. Separated may then be abated via scrubbing and / or decomposed or react to recover some portion of hydrogen and sulfur containing species as other products, includingbut not limited to , elemental sulfur, , sulfuric acid ( ), or . Methods fordecomposition include, but are not limited to thermal decomposition under ambient or partial vacuum pressures, catalyzed decomposition, the Claus process, and / or plasma decomposition. Following decomposition, some portion of , and / or other gas species, may be recirculated into the reduction process and / or utilized in other applications, including, but not limited to, combustion, chemical synthesis, or fuel cells. In one embodiment, the simplified flowsheet in FIG. 4 can be used to describe different deployments of the invention that have a possibility to recirculate and recover hydrogen back to the reactor(s). Gas separation step 6 can include membrane filter, cryogenic air separation process or pressure swing adsorption process with the intention of recovering 31 60E5644.DOC Attorney Docket No. 07114-2408878 and separating the unreacted hydrogen to recirculate it back to the first reactor(s) in step 3. Gas separation can be connected to gas treatment step 9 to purify hydrogen and separate or decompose remaining hydrogen sulfide gas prior recirculating back to reactor(s) in stream 2 for step 3. Upstream, downstream, and in gas separation and treatment steps 6 and 9 there is a possibility to include heat recovery solutions which can be used to cool down or heat up gas streams to required temperatures prior the different processing steps. Other embodiments may employ different variations of stream and reactor components versus those described here. In one alternative embodiment also represented by the simplified flowsheet in FIG. 4, single or multiple solid-gas / plasma reactors in step 3 are used for hydrogen reduction of feed stream 1 consisting of metal sulfide or a mixture containing metal sulfide producing metal as product. Produced gas stream 4 is separated in step 6 and / or 9 with molecular sieve(s) / membrane filter(s), cryogenic air separation, pressure swing adsorption and / or catalyzed or thermal decomposition. Recovered hydrogen streams 7 and 10 are recirculated back in the reducing reactor(s) in stream 2 for step 3. Other embodiments may employ different variations of stream and reactor components versus those described here. In one alternative embodiment also represented by the simplified flowsheet in FIG. 4, the fluidized bed reactor in step 3 is used for hydrogen reduction of nickel sulfide or a nickel sulfide containing feed stream 1 mixture. Product gas is separated with membrane filter in step 6 to separate hydrogen sulfide and hydrogen gas. Hydrogen gas is recirculated back to the fluidized bed reactor in step 3. Hydrogen sulfide is thermally decomposed in gas treatment step 9 to elemental sulfur and hydrogen gas. Elemental sulfur is removed as byproduct stream 12 and hydrogen is recirculated back to fluidized bed reactor in step 3. Other embodiments may employ different variations of stream and reactor components versus those described here. In one alternative embodiment also represented by the simplified flowsheet in FIG. 4, separated hydrogen sulfide gas stream 8 is connected to a Claus process in step 9 where elemental sulfur and water is recovered as products in stream 12. Water steam can be also fed through stream 10 as inert gas for step 3 reactor. Other embodiments may employ different variations of stream and reactor components versus those described here. In one alternative embodiment also represented by the simplified flowsheet in FIG. 4, separated hydrogen sulfide gas steam 8 is connected to thermal decomposition step 9 where elemental sulfur stream 12 and hydrogen gas stream 10 are recovered with the use of plasma heating / decomposition. Other embodiments may employ different variations of stream and reactor components versus those described here. 32 60E5644.DOC Attorney Docket No. 07114-2408878 In one alternative embodiment also represented by the simplified flowsheet in FIG. 4, hydrogen gas streams 7 and / or 10 are chemically scrubbed in steps 6 and / or 9 as part of the process to remove hydrogen sulfide from hydrogen prior reusing it in reactor(s) in step 3. Other embodiments may employ different variations of stream and reactor components versus those described here. In other embodiments summarized by the simplified flowsheet in FIG. 5, additional processing steps or combinations of processing steps may be employed for product gas treatment and utilization. In one embodiment represented by the simplified flowsheet in FIG. 5, describes simplified the product gas stream 4 from 1st reactor step 3 is reacted with other solid or liquid metal or compound in stream 15 in second reactor step 13 to decompose hydrogen sulfide and recover hydrogen back to 1st reactor step 3. Other embodiments may employ different variations of stream and reactor components versus those described here. In one alternative embodiment also represented by the simplified flowsheet in FIG. 5, single or multiple solid-gas / plasma or liquid-gas / plasma reactors in step 3 are used for hydrogen reduction of feed stream 1 consisting of sulfur containing compound or mixture of the first metal. Produced gas stream 4 is flowed through second gas treatment reactor step 13, where hydrogen sulfide is decomposed via sulfidation of a second metal or metal compound in stream 15 to regenerate hydrogen stream 14 for use in reduction of sulfur containing compound or mixture of the first metal. This embodiment effectively serves as an indirect metallothermic reduction process of the first metal by the third metal with hydrogen and hydrogen sulfide serving as a bridge between the two metals. This allows the third metal to effectively aid in the reduction of the first metal without being in direct contact with it. Other embodiments may employ different variations of stream and reactor components versus those described here. In one alternative embodiment also represented by the simplified flowsheet in FIG. 5, a fluidized bed reactor is used for hydrogen reduction of sulfur containing feed stream 1 of the first metal. Produced gas stream 4 is flowed through second gas treatment reactor step 13, where hydrogen sulfide is decomposed via sulfidation of a sulfur containing second metal compound stream 15 to produce targeted valency sulfide of second metal to stream 16. Regenerated hydrogen stream 14 is recirculated back to the reduction reactor step 3. Other embodiments may employ different variations of stream and reactor components versus those described here. 33 60E5644.DOC Attorney Docket No. 07114-2408878 In any of the embodiments described above for simplified flowsheets in FIG. 3, FIG. 4, and / or FIG. 5, some portion of the hydrogen from stream 2 may or may not be dissociated or ionized in a plasma in the reactor(s) within unit operation(s) and / or reactor(s) depicted by block 3. Molecular hydrogen may be regenerated from unreacted plasma. In any of the embodiments described above for simplified flowsheets in FIG. 3, FIG. 4, and / or FIG. 5, some portion of the condensed metal or sulfide production stream 5 may or may not be separated, purified, or recovered through a range of unit operations, including but not limited to comminution, physical separation (including but not limited to froth flotation, gravimetric separation, electrostatic separation, density separation, sieving, dense media separation, and / or magnetic separation), leaching, distillation, dissolution, precipitation, melting, filtering, decanting, roasting, stripping, absorption, adsorption, and / or electrolysis. In any of the embodiments described above for simplified flowsheets in FIG. 3, FIG. 4, and / or FIG. 5, at least some portion of the sulfur containing feed stream 1 may be at least partially molten during reduction. Additional embodiments may be disclosed and claimed. It should be noted that headings are used above for convenience and are not to be construed as limiting the present invention in any way. While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the function and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the inventive teachings is / are used. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described to and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and / or method 34 60E5644.DOC Attorney Docket No. 07114-2408878 described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure. Various inventive concepts may be embodied as one or more methods, of which examples have been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments. All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms. The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one." The phrase "and / or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and / or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and / or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and / or B", when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional 35 60E5644.DOC Attorney Docket No. 07114-2408878 unlisted items. Only terms clearly indicated to the contrary, such as "only one of" or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e., "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law. As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and / or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "composed of," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03. Although the above discussion discloses various exemplary embodiments of the invention, it should be apparent that those skilled in the art can make various modifications that will achieve some of the advantages of the invention without departing from the true scope of the 36 60E5644.DOC Attorney Docket No. 07114-2408878 invention. Any references to the "invention" are intended to refer to exemplary embodiments of the invention and should not be construed to refer to all embodiments of the invention unless the context otherwise requires. The described embodiments are to be considered in all respects only as illustrative and not restrictive. Example claims directed to the subject matter described above for the present invention are included below and are not intended to limit the scope of the present invention. Applicant reserves the right to pursue claims to any of the disclosed subject matter. 37 60E5644.DOC

Claims

Attorney Docket No. 07114-2408878 CLAIMS 1. A method comprising: reacting a sulfur-containing compound of a first metal with hydrogen to reduce at least a portion of the sulfur-containing compound with at least a portion of the hydrogen to form hydrogen sulfide and elemental first metal; and at least one of: (a) separating at least a portion of the hydrogen sulfide from hydrogen; or (b) thermally decomposing at least a portion of the hydrogen sulfide to regenerate hydrogen and produce elemental sulfur; or (c) catalytically decomposing at least a portion of the hydrogen sulfide to regenerate hydrogen and produce elemental sulfur; or (d) decomposing at least a portion of the hydrogen sulfide with a plasma to regenerate hydrogen and produce elemental sulfur; or (e) reacting at least a portion of the hydrogen sulfide with a second metal to produce a sulfide of the second metal and regenerate hydrogen; or (f) recovering at least a portion of the elemental first metal; or (g) recovering at least a portion of the hydrogen sulfide; or (h) recovering at least a portion of the elemental first metal in an alloy of third metal.

2. A method comprising: reacting a sulfur-containing compound of a first metal with hydrogen to reduce at least a portion of the sulfur-containing compound with at least a portion of the hydrogen to form hydrogen sulfide and a sulfide of first metal; and at least one of: (a) separating at least a portion of the hydrogen sulfide from hydrogen; or (b) thermally decomposing at least a portion of the hydrogen sulfide to regenerate hydrogen and produce elemental sulfur; or (c) catalytically decomposing at least a portion of the hydrogen sulfide to regenerate hydrogen and produce elemental sulfur; or (d) decomposing at least a portion of the hydrogen sulfide with a plasma to regenerate hydrogen and produce elemental sulfur; or 38 60E5644.DOCAttorney Docket No. 07114-2408878 (e) reacting at least a portion of the hydrogen sulfide with a second metal to produce a sulfide of the second metal and regenerate hydrogen; or (f) recovering at least a portion of the sulfide of the first metal; or (g) recovering at least a portion of the hydrogen sulfide; or (h) forming a sulfide of the first metal with a different cation valency than the sulfur-containing feedstock compound of a first metal.

3. The method according to claim 1 or 2, in which at least one of: (a) a portion of hydrogen sulfide and hydrogen are separated via pressure swing adsorption; or (b) a portion of hydrogen sulfide and hydrogen are separated via a membrane; or (c) a portion of hydrogen sulfide and hydrogen are separated via cryogenic distillation; or (d) a portion of hydrogen sulfide and hydrogen are separated via pressure increase to induce selective condensation; or (e) a portion of hydrogen sulfide and hydrogen are separated via centrifuge; or (f) a portion of hydrogen sulfide and hydrogen are contacted with an aqueous phase; or (g) a portion of hydrogen sulfide and hydrogen are contacted with an organic liquid; or (h) a portion of hydrogen sulfide and hydrogen are contacted with an ionic liquid; or (i) a portion of hydrogen sulfide and hydrogen are contacted with a melt containing some portion of sulfur species.

4. The method according to claim 1 or 2, wherein at least a portion of the separated hydrogen is mixed with at least a portion of the hydrogen reactant.

5. The method according to claim 1 or 2, wherein at least a portion of the separated hydrogen sulfide is mixed with at least a portion of the hydrogen reactant. 39 E5644.DOCAttorney Docket No. 07114-2408878 6. The method according to claim 1 or 2, wherein at least a portion of the regenerated hydrogen is mixed with at least a portion of the hydrogen reactant.

7. The method according to claim 1 or 2, wherein the sulfur-containing compound of a first metal is a sulfide.

8. The method according to claim 1 or 2, wherein the sulfur-containing compound of a first metal is a sulfate.

9. The method according to claim 1, wherein the sulfur-containing compound of a first metal is an oxysulfide.

10. The method according to any of the above claims, wherein the sulfur-containing compound of a first metal is mixed with a compound of a fourth metal.

11. The method according to any of the above claims, where the elemental first metal is liberated from at least one of: (a) a sulfur-containing compound of a first metal; or (b) a compound.

12. The method according to claim 11, wherein the compound of the fourth metal is at least one of: (a) an oxide of a fourth metal; or (b) a carbonate of a fourth metal; or (c) a phosphate of a fourth metal; or (d) a hydroxide of a fourth metal; or (e) a sulfide of a fourth metal; or (f) a sulfate of a fourth metal; or (g) an oxysulfide of a fourth metal; or (h) a fourth elemental metal.

13. The method according to claim 12, where the compound of a fourth metal inhibits sintering of the sulfur-containing compound of a first metal or elemental first metal. 40 E5644.DOCAttorney Docket No. 07114-2408878 14. The method according to any of the above claims, wherein hydrogen reactant is mixed with an inert gas.

15. The method according to any of the above claims, wherein the reduction reaction is conducted in which at least one of: (a) the sulfur containing feedstock compound of the first metal is at a temperature range of 0 °C to 2000 °C; or (b) the surface of the sulfur containing feedstock compound of the first metal is at a temperature greater than 0 °C; or (c) molecular hydrogen is at a temperature greater than 0 °C; or (d) atomic hydrogen is at a temperature greater than 0 °C; or (e) ionic hydrogen is at a temperature greater than 0 °C; or (d) electrons in a hydrogen containing plasma are at a temperature greater than 0 °C.

16. The method according to any of the above claims wherein the reduction reaction is conducted with a ratio of hydrogen to hydrogen sulfide between 10-6and 1021.

17. The method according to any of the above claims in which at least one of: (a) a portion of the hydrogen reactant is gaseous; or (b) a portion of the hydrogen reactant is a plasma; or (c) a portion of the hydrogen reactant is molecular; or (d) a portion of the hydrogen reactant is atomic; or (e) a portion of the hydrogen reactant is ionic.

18. A reactor according to any of the above claims for reacting a sulfur-containing compound of a first metal compound consisting of a metal oxide, oxysulfide, sulfate, or sulfide.

19. A system comprising one or more reactors or vessels in which any of the above methods are performed.

20. The system according to claims 18-19, wherein at least one of: (a) a reactor or vessel contains a fluidized bed; or 41 E5644.DOCAttorney Docket No. 07114-2408878 (b) a reactor or vessel contains a packed bed; or (c) a reactor or vessel contains multiple hearths; or (d) a reactor or vessel is rotated during operation; or (e) a reactor or vessel contains an electric arc; or (f) a reactor or vessel contains a plasma source; or (g) a reactor or vessel is a kiln.

21. The method according to any of claims 1-17, wherein hydrogen reduction is conducted at a total reactor gas pressure of 10-6atm to 1000 atm.

22. The method according to any of claims 1-17 and 21, wherein a reactor inlet hydrogen to hydrogen sulfide partial pressure ratio of 10-6to 1021is employed.

23. The method according to any of claims 1-17 and 21-22, wherein a reactor outlet hydrogen to hydrogen sulfide partial pressure ratio of 10-6to 1021is employed.

24. The method according to any of claims 1-17 and 21-23, wherein a reactor gas residence time of 10-6to 106seconds is employed.

25. The method according to any of claims 1-17 and 21-24, wherein a solid residence time of 10-6to 106seconds is employed in the reactor.

26. The method according to any of claims 1-17 and 21-25, wherein a P80 solid particle size of 1 micron to 10 mm is employed in the reactor.

27. A method for the reduction of sulfur-containing compound with at least a portion of the hydrogen to form hydrogen sulfide and elemental first metal from oxides of one or more of hydrogen sulfide from hydrogen contained in a feed, comprising the steps of: (a) introducing a feedstock material into a reactor, said feedstock material containing a target metal compound consisting of a metal oxide, oxysulfide, sulfate, or sulfide; (b) introducing a gas into a reactor, said feedstock material containing a portion of molecular hydrogen; (c) converting a portion of the molecular hydrogen into a plasma; (d) regenerating a portion of the molecular hydrogen from unreacted plasma. 42 E5644.DOCAttorney Docket No. 07114-2408878 28. A method for the reduction and processing of solid sulfur-containing compounds comprising: (a) reacting a sulfur-containing compound of a first metal, selected from the group consisting of sulfide, oxysulfide, or sulfate, of a first metal with gaseous hydrogen, thereby reducing at least a portion of the solid sulfur-containing compound and forming hydrogen sulfide and elemental first metal; (b) selecting at least one of the following options: (i): mixing a compound of a fourth metal with the compound of the first metal; or (ii): separating a compound of a fourth metal from elemental first metal via comminution and physical separation; or (iii): separating a compound of a fourth metal from elemental first metal via melting; or (iv): separating a compound of a fourth metal from elemental first metal via distillation; or (v): separating a compound of a fourth metal from elemental first metal via electrolysis.

29. The method of Claim 28, wherein the sulfur-containing compound is selected from the group consisting of a sulfide, oxysulfide, or sulfate.

30. The method of Claim 28, wherein the elemental first metal is recovered through a process selected from the group consisting of comminution, physical separation, melting, precipitation, electrolysis, melting, and / or distillation.

31. The method of Claim 28, wherein the hydrogen sulfide is separated from hydrogen through a process selected from the group consisting of absorption, adsorption, distillation, and membrane separation.

32. A comprehensive method for the production and utilization of metal compounds, comprising: 43 E5644.DOCAttorney Docket No. 07114-2408878 a. introducing a feedstock material into a reactor, said feedstock material containing a target metal compound consisting of a metal oxide, oxysulfide, sulfate, or sulfide; b. Producing a flow of sulfur-containing gas within the reactor; c. Passing the flow of sulfur-containing gas through the feedstock material, while controlling a roasting atmosphere in the reactor about the feedstock material, wherein the roasting atmosphere is controlled based on at least a process temperature and a ratio of hydrogen to hydrogen sulfide; d. Reacting a solid sulfur-containing compound of a first metal and a metal compound with hydrogen to facilitate the reduction of at least a portion of the solid sulfur-containing compound and metal compound, resulting in the production of hydrogen sulfide, elemental first metal, and elemental metal from the metal compound; e. Employing at least one of the following processes: (i) Separating at least a portion of the hydrogen sulfide from hydrogen and at least a portion of the elemental metal for subsequent use; (ii) Thermally decomposing at least a portion of the hydrogen sulfide to regenerate hydrogen and produce elemental sulfur, and at least a portion of the elemental metal for downstream applications; (iii) Catalytically decomposing at least a portion of the hydrogen sulfide to regenerate hydrogen and produce elemental sulfur, wherein the regenerated gaseous hydrogen, elemental sulfur, and elemental metal are utilized in various industrial processes; (iv) Decomposing at least a portion of the hydrogen sulfide with a plasma to regenerate hydrogen and produce elemental sulfur, with the regenerated gaseous hydrogen, elemental sulfur, and elemental metal finding utility in diverse applications; (v) Reacting at least a portion of the hydrogen sulfide with a second metal to produce a sulfide of the second metal and regenerate gaseous hydrogen, and at least a portion of the elemental metal for subsequent use; (vi) Recovering at least a portion of the elemental first metal for incorporation into various alloys or manufacturing processes; 44 E5644.DOCAttorney Docket No. 07114-2408878 (vii) Recovering at least a portion of the elemental first metal in an alloy with a third metal for incorporation into various alloys or manufacturing processes; (viii) Separation at least a portion of the elemental first metal from a compound of a fourth metal; (ix) Recovering at least a portion of the hydrogen sulfide and elemental metal for utilization in chemical synthesis or other industrial applications.

33. A process controller for any of the above claims.

34. The method according to Claim 33, in which the process controller utilizes an internal model that relates the ratio of hydrogen to hydrogen sulfide with the rate of hydrogen sulfide generation during reduction.

35. The method according to Claim 34, in which a proportional term in a PID controller is derived from a model that relates the ratio of hydrogen to hydrogen sulfide with the rate of hydrogen sulfide generation during reduction.

36. The method according to Claim 34, in which an integral term in a PID controller is derived from a model that relates the ratio of hydrogen to hydrogen sulfide with the rate of hydrogen sulfide generation during reduction.

37. The method according to Claim 34, in which a derivative term in a PID controller is derived from a model that relates the ratio of hydrogen to hydrogen sulfide with the rate of hydrogen sulfide generation during reduction. 45 E5644.DOC