Silicon Reduction of Iron Oxide

The present application claims priority to U.S. patent application No. 63/662,920.

This invention was made with government support under HR0011-24-3-0312 awarded by DARPA. The government has certain rights in the invention.

The present disclosure relates to systems and methods for producing metallic iron with silicon metal.

Lunar ore is of great interest for future human settlement of the moon. Without in situ resource utilization of Lunar resources, human settlement will require all resources to be provided from Earth, potentially pushing the cost of human utilization of space out of the realm of reality.

In some examples, the disclosure provides a method for producing metallic iron. The method involves mixing a slag, the slag comprising metallic silicon, with a first ore, the first ore comprising iron oxide, to produce a first mixture. The method further involves reducing the iron oxide by oxidation of the metallic silicon, producing metallic iron and silicon oxides.

In some examples, the disclosure provides a system for producing metallic iron. A crucible is provided to mix a slag and a first ore to form a first mixture, the slag including metallic silicon and the first ore including iron oxide. The system either provides a heater to heat the crucible to a temperature to initiate the iron oxide reduction by the metallic silicon, producing metallic iron and silicon oxides, or provides a heater to heat the slag to a molten temperature such that mixing the slag and the first ore initiates iron oxide reduction by the metallic silicon, producing metallic iron and silicon oxides.

In some examples, the disclosure provides a system for producing metallic iron. A crucible is provided to mix metallic silicon and a first ore, the first ore including iron oxide. A heater is provided to heat the crucible to a temperature to initiate the iron oxide reduction by the metallic silicon, producing metallic iron and silicon oxides.

In some examples, the disclosure provides a system for producing metallic iron. A separator is provided to separate a slag into an oxide residue and a metal product. A crucible is provided to mix the metal product and a first ore, the metal product including metallic silicon and the first ore including iron oxide. The system either provides a heater to heat the crucible to a temperature to initiate the iron oxide reduction by the metallic silicon, producing metallic iron and silicon oxides, or provides a heater to molten the metal product, the first ore, or both before mixing. In this manner, mixing the slag and the first ore initiates iron oxide reduction by the metallic silicon, producing metallic iron and silicon oxides.

In some examples, the disclosure provides a system for producing metallic iron. A mixer is provided to mix a silicon metal with a first ore, the ore including iron oxide. The system further provides either a heater to heat the mixer to initiate reduction of the iron oxide by the silicon metal, producing metallic iron and silicon dioxide, or a comminution device to reduce particle size of the silicon metal and the ore to initiate the reduction of the iron oxide by the silicon metal by frictional heating, producing the metallic iron and the silicon dioxide.

Further examples are provided in the drawings, detailed description, and claims.

The following description recites various example systems and methods disclosed herein. No particular example is intended to define the scope of the present systems and methods. Rather, the examples provide non-limiting examples of various systems, and methods, that are included within the scope of the present disclosure and the present claims. The description is to be read from the perspective of one of ordinary skill in the art. Therefore, information that is well known to the ordinarily skilled artisan is not necessarily included.

The following terms and phrases have the meanings indicated below, unless otherwise provided herein. This disclosure may employ other terms and phrases not expressly defined herein. Such other terms and phrases shall have the meanings that they would possess within the context of this disclosure to those of ordinary skill in the art. In some instances, a term or phrase may be defined in the singular or plural. In such instances, it is understood that any term in the singular may include its plural counterpart and vice versa, unless expressly indicated to the contrary.

As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. For example, reference to “a substituent” encompasses a single substituent as well as two or more substituents, and the like.

As used herein, “for example,” “for instance,” “such as,” “illustratively,” or “including” are meant to introduce examples that further clarify more general subject matter. Unless otherwise expressly indicated, such examples are provided only as an aid for understanding embodiments illustrated in the present disclosure and are not meant to be limiting in any fashion. Nor do these phrases indicate any kind of preference for the disclosed example.

As used herein, “oxides” are oxide containing chemicals that may occur in the form of multi-element oxides, silicates, and aluminates, and often as distinct mineral types. All oxides, silicates, and aluminates are referred to as oxides herein.

As used herein, “slag” refers to any of the following terms. Slag, dross, waste ore, mineral processing byproducts, or any mix of the results of oxides and metals from a molten unit operation.

In some examples, the metallic silicon can be sourced from scrap man-made resources such as solar panels, computer chips, and similar silicon containing materials. In some examples, slag and man-made silicon sources are blended.

The examples, drawings, and descriptions herein disclose utilization systems and methods for carbothermal reduction residue (or any other silicon-metal containing material) to produce metallic iron from relatively low-grade iron oxide feeds.

A carbothermal reduction module carries out carbothermal reduction. Much of the description herein is directed towards a Lunar application, but the disclosure should not be construed to be limited to Lunar applications. The disclosure can be utilized terrestrially, on Mars, asteroids, comets, or any rocky body, as well as in orbit. The most immediate applications are envisioned on the Moon as a high-yielding oxygen production process. The process generates a “deoxygenated residue” (DOR) that consists of a metallic phase (mostly silicon containing iron and manganese) and an oxide phase containing oxides of silicon, aluminum, and calcium along with smaller amounts of other oxides present in lunar regolith. The oxide phase of the residue has some potential use as feed to more-advanced oxygen and metal generation processes (such as Molten Regolith Electrolysis). The metallic phase of the DOR has been identified as a potential feed for refinement to produce silicon metal for various applications following significant refining to achieve purities required for solar or electronic applications.

Given the relatively low demand for silicon metal on the Moon (at least during early phases of exploration and settlement), alternative uses of the metallic phase have been identified that provide a valuable near-term benefit to the lunar economy and infrastructure. This involves the use of the metallic silicon-containing residue as a reducing agent to produce metallic iron from relatively low-grade feeds such as lunar regolith.

Carbothermal reduction is expected to be carried out by organizations that have tailored the process to the lunar application. In initial implementation, the combined metallic and oxide portions of DOR are expected to be discharged from the reactor system for disposal or potential additional use.

The silicothermic reduction process recovers the metallic fraction of DOR for use as a silicothermic reducing agent for production of metallic iron. Because carbothermal reduction is carried out at high temperature (in excess of 1600 C), the metallic and oxide components are entirely molten. The metallic phase coalesces and separates from the oxide phase due to differences in surface tension. Upon discharge from the reactor, and as the residue cools and solidifies, coalesced metal and oxides exist as separate phases. Recovery of the cooled DOR (from a lunar-derived ceramic pad, for example) with application of soft crushing can then release the brittle, glassy, oxide phase from the metal phase. This crushing action to break the oxide component from the metal phase can be conducted by various means as follows.

Tumbling in a rotary drum with baffles to break the oxides from the metal phase followed by discharge and feed to physical separation based on differences in particle size, shape, or density. Magnetic separation of the metal phase when the iron concentration is high enough, and if the ferrosilicon structure is correct. Each of these steps can be conducted in the low-pressure lunar environment in hardware delivered from Earth or produced via in-situ resources (such as iron/steel) produced from the proposed methods and system.

After recovery of the metal phase from the DOR, some additional crushing may be required to achieve a particle size distribution (likely less than about 1 mm) that has sufficient surface area to provide interparticle contact with fresh ore or regolith as described later. If additional crushing of the metallic phase is required, this might be achieved after allowing the metal to be cooled to lunar night time temperatures to boost the brittleness. Under this environment, additional tumbling with hard grinding media or potentially autogenously with coarser silicon metal containing feed could produce the desired size reduction.

Alternatively, the metallic fraction could be heated, melted, and sprayed to create particles of controlled size as feed to the silicothermic reduction step.

In one example, separation has no integration with carbothermal reduction. In other examples, integration with carbothermal reduction allows for recovery of the silicon containing metal in a molten state separately from the oxides in DOR. This allows a tailoring of the particle size of the metallic fraction to minimize physical processing needs.

The oxide portion of DOR is stored for other processing while the metallic portion is advanced to the iron oxide reduction module or maintained in inventory until use.

In this example, the iron oxide reduction module utilizes a crucible for the molten temperatures and corrosion characteristics of the silicon-containing metal and fresh ore or regolith. In this example, this step is conducted in the low-pressure lunar environment. Because no significant emissions are produced due to the transfer of oxygen from the ore or regolith constituents to the silicon metal, gas handling hardware is not required. However, with appropriate selection of temperatures for the process, some vaporization of contaminants or metals or silicon monoxide will occur. In some examples, condensers will be installed to selectively recover these fumes based on their condensation temperatures.

The silicothermic reduction process can be initiated in several ways. In one example, the mixture of the silicon metal phase plus fresh ore or regolith is heated (via induction or resistive heating, for example) until the exothermic reaction begins (likely below the melting temperature). In this case, the reaction would generate more heat that would melt the entire contents with no further heat input. As an alternative example, a small localized flow of hot oxygen is provided in proximity to the metallic silicon to generate enough heat initiate a metallothermic reduction reaction that spreads through the entire reaction crucible. In other examples, igniters or small pyrotechnic devices are used to initiate the reaction.

Because the silicothermic reduction reaction can generate significant excess energy, provisions to recover heat from the reaction system may be installed. In some examples, the heat is removed from the reactor and recovered for heat exchange via a variety of gas- or liquid-based systems for use in preheating additional feed, providing lunar night-survival heat for other hardware and systems, and generating electricity via thermoelectric devices.

Although many metallothermic reduction systems are operated in batch mode, options to operate in a semi-continuous manner are provided herein to significantly boost the efficiency of heat recovery methods described above. In one example, the metallic and/or regolith constituents can be added incrementally to spread the rate of heat release during reaction. This provides a more-steady heat flow to facilitate heat recovery and transfer. The metallic iron and oxide phases are tapped periodically in a manner similar to that employed in blast furnaces to provide sufficient reaction time while controlling the inventory in the reactor.

In one example, upon completion of the silicothermic reduction reaction, the molten iron product is tapped separately from the oxide phase as part of metal-oxide slag separation. In one example, the oxide phase is cooled and stored for potential future recycle to carbothermal reduction or for other purposes. In other examples, the metal phase is maintained in the molten phase while transferring to the next step, as in the transfer of iron from blast furnaces to nearby steelmaking facilities. At this point in the example, the metal phase will consist of iron along with manganese, chromium, and small amounts of nickel, depending on the compositions of the feeds to carbothermal reduction and silicothermic reduction.

In this example, further impurity removal, alloying, and manufacturing are conducted. In this Lunar example, operations occur in a low-pressure lunar environment. Some purification will be achieved in a manner analogous to terrestrial vacuum metallurgy. In one example, the low-pressure environment facilitates the release of dissolved gases (such as oxygen) and more-volatile impurities that can affect steel properties. This reduces the requirements for steel making additives that would otherwise be added to move these constituents to a slag phase. In some examples, additional impurity removal is provided. Contaminants for possible removal include sulfur and phosphorus. Conventional steelmaking methods may be adapted to remove these and other contaminants to the desired levels in a Lunar environment. In one example, the hardening effect of phosphorus is exploited to the benefit of the final steel product by keeping concentrations below required levels. In some examples, the calcium-oxide rich slag components that aid impurity removal are derived from Lunar regolith, or in particular from slags that have elevated concentration of calcium oxide after carbothermal reduction and/or molten regolith electrolysis.

These examples provide significant flexibility for control of the amount of residual silicon metal in the alloy.

For lunar applications requiring service temperatures far lower than those designed for on Earth, additional alloying may be required. For example, increasing nickel additions (up to about 10 percent) can increase steel microstructure stability at increasingly lower temperatures. Several other alloying options applied for cryogenic application on Earth are well known. These can be adapted for lunar use under reduced gravity and lack of atmospheric corrosion agents.

Many lunar regolith compositions contain manganese in concentrations relative to iron that constitute favorable alloying compositions. Therefore, the proposed system and methods carry a built-in advantage for manufacture of low-alloy steel.

After tapping the molten steel from the refining vessel, the steel can be handled in a manner similar to terrestrial use for the fabrication of components via casting or extrusion. In a lunar application, the recovery of heat as material solidifies and cools is a valuable additional step. A continuous or semi-continuous approach aids the efficiency of heat recovery and exchange.

An additional benefit of the proposed approach is that a silicothermic reduction based welding approach is provided. This is applied in a manner analogous to terrestrial thermite rail welding, which uses an aluminum metal/iron oxide mix. With appropriate molds and ignition, the thermite reaction creates sufficient heat to reduce the iron oxide to metal, which sinks below the oxides and pours into the weld area. A silicon metal-iron oxide mix thermite mix can be tailored to achieve similar results for field fabrication on the Moon.

The Lunar ore, provided both in the initial carbothermal reaction or in the metallothermic reaction, may be used as-is or after beneficiation. Beneficiation can include particle size adjustment and separations to alter the concentrations of iron oxide. On the moon, the two ores can be the same or different. They can be of a highlands-type composition (with a relatively high calcium-aluminum-silicate composition and relatively low iron oxide concentration that is more typical near the south pole and over wide regions at lower latitudes) or of a mare-type composition (with a relatively higher iron oxide concentration in basalt and with iron oxide also existing as ilmenite, iron titanate, typically in lower latitude and equatorial regions). In some regions, mare and highlands soils may exist in relatively close proximity, allowing for their separate selection as the carbothermal or metallothermic feed ores. This flexibility allows for the silicon-producing process to create a higher-purity silicon metal product while the iron oxide producing process creates a higher-purity iron oxide feed that can reduce the total mass subjected to silicothermic reduction. With consideration of the presences of the more minor elements (including manganese, an important alloying agent) the final iron metal product composition can be controlled.

Silicon metal in small amounts can be considered to be a beneficial alloying agent in steel. By reducing the ratio of silicon metal to feed ore to a sub-stoichiometric ratio, the residual silicon concentration in the metal can be controlled to near zero. Conversely, a higher silicon-metal-containing iron product can be obtained by using a slight excess of silicon metal to feed ore ratio. A thermodynamic equilibrium evaluation shows that near complete reaction between iron oxide, manganese oxide, and silicon metal takes place up to at least 1600 C. Above 1600 C, the extent of reduction of FeO to Fe gradually drops. In vacuum conditions, iron metal, manganese metal, and silicon monoxide (SiO) would be partially vaporized above about 1600 C. This may be leveraged to perform at least some product refinement, or allow for recovery of a relatively pure SiO product that is reoxidized to SiO2 as a glass component or further reduced as a first step in manufacture of solar or electronic grade silicon.

In some examples, as an initial step toward the silicothermic reduction of metal oxides contained in fresh regolith, the metallic constituent of the carbothermal reduction residue is separated from the remaining oxidized portion of the residue. The carbothermal reduction residue containing both the metallic and oxide fractions may be used for silicothermic reduction of oxides in fresh regolith without separation but with reduced thermal efficiency. The metallic phase of the carbothermal reduction residue may be separated from the oxide phase while molten. The metallic fraction of the carbothermal reduction residue may be separated from solidified residue by crushing to release coalesced metal from the oxide phase followed by physical separation.

The reaction of metallic silicon with Lunar ore may be carried out by mixing the components. The reaction may be initiated as a solid-solid reaction when sufficient interparticle contact is present between the metal and oxide phases. Beneficiation to optimize particle packing and/or physical compression may be used to boost interparticle contact. The reaction may be initiated by gradually heating until the exothermic silicothermic reaction starts, at which time it will self sustain. The reaction may be initiated at relatively low temperature by a small, concentrated heat source, like a pyrotechnic discharge or localized oxidation of an initiating agent such as the already-present silicon metal or a small addition of a reactive metal such as magnesium. The reactants may be charged with the full target mass of each constituent prior to initiating reaction. Alternatively, one reactant may be metered into the other reactant to control temperature and rate of reaction. Heat removal may be utilized to control temperature while providing a high-quality (high-temperature) heat source. The process may be conducted as a typical batch thermite reaction. Alternatively, the reactants may be introduced in a semi-continuous fashion while periodically removing the resulting metal and slag constituents.

The reaction of silicon metal with Lunar ore may be used as a welding method (similar to the aluminothermic reduction of iron oxide for terrestrial rail welding) as part of a manufacturing process (and for remote/field fabrication).

Lunar iron oxides are generally less oxidized that those on earth. Most iron on the moon exists as ferrous iron (+2) with small amounts of metallic iron (from micrometeorites or from reduction of iron oxide upon high-temperature impact of micrometeorites). Iron on Earth is more typically in the form of ferrous or ferric (+3). The effect of this is that less silicon metal is required on the moon than on earth to produce metallic iron.

Now referring to,is a block flow diagram showing an example systemfor producing iron that may be used in some examples provided herein. This example is purely illustrative, and multiple other examples are envisioned or may be readily envisioned without undue experimentation.

The example inis based on Lunar mining, but terrestrial, Martian, asteroid, comet, or other planetary body ores could be used. In examples where the mining occurs on a planetary body with an atmosphere, any steps involving vacuum would require the appropriate equipment to produce vacuum, whereas vacuum is made on the moon and other no-atmosphere planetary bodies by simply opening a valve or similar to the vacuum of space. Examples on any planetary body are readily understood using the examples herein.

Lunar regolith is as complex an ore body as any Earth ore. There are metal oxides, metal sulfides, and in some locations, volatiles and other contaminants. For this example, iron oxide is the primary ore of interest, while other ores, listed elsewhere, are of secondary concern.

At, raw Lunar regolith stream, containing iron oxide, is passed into a carbothermal reduction modulewhere heat is used to melt streamand evolve an oxygen product streamand produce a carbothermal reduction residue stream. Streamcontains reduced iron, also referred to as metallic iron or iron metal, reduced silicon, also referred to as metallic silicon or silicon metal, other reduced metals, as well as any remaining oxides, sulfides, and contaminants as slag. The molten streamis passed into a carbothermal reduction residue separation unit. Streamis cooled below molten temperatures and the slag and metals separated in unitinto carbothermal reduction residue oxide byproduct streamand carbothermal reduction residue metal product. In this example, the metal productstill contains a small amount of slag. As is known in mineral processing, complete separation can be accomplished by increasingly complex unit operations. Therefore, the metal product streamcontains as much slag as the process design allows for. Streamis combined with more raw Lunar regolith streamin iron oxide reduction module. Streamcan be from the same source as stream, or can be from a different Lunar regolith source. The goal of reduction moduleis to reduce iron oxide with silicon metal. The reduction moduleof this example can include multiple sub-unit operations. In this example, a beneficiation unit, such as a grinder, reduces particle size of the metal product streamand the ore streamto reduce the heat requirement for initiation of the reduction reaction. The grinder may even produce enough heat to initiate the reaction, at which point the mixture is moved into a crucible for the reduction reaction. The beneficiation of this example brings the mixture near the temperature to initiate reaction, but the final heat is provided by inductive heating in the crucible. The metallic silicon in the mixture reduces the iron oxide in the mixture, and the heat of reaction causes the mixture to molten and self-propagate. In some examples, the heat from this reaction is sufficient that removal of the heat is required, and can even be beneficial. These examples will be shown in greater detail in.

The molten slagproduced by the reaction, which includes metallic iron and silicon oxides, is passed to a metal-oxide slag separation unit. The silicon oxides include both silicon dioxide and silicon monoxide. The separation unitof this example includes multiple sub-unit operations. First, vacuum, which is free and omnipresent on the Lunar surface, can be utilized to boil off silicon monoxide and any other volatile contaminants. The list of potential contaminants is the list of naturally-occurring elements on the periodic table, minus iron, as Lunar ore is just as complex as terrestrial ore. These are discussed in greater detail herein. Unitwould further include units to cool and physically separate the slag from the metal product. The reduction oxide byproduct stream(slag) is removed while the metallic iron product streamis passed on to impurity removal, alloying, and manufacturing units.

Unitis actually several unit operations. Impurity removal agentsare made available to the system and impurities such as sulfur, phosphorus, and other contaminants that made it through to this stage are removed as impurities stream. Alloying agentsare added to the purified metal and the steel productis either shipped as a raw material or manufacturing is completed in unitbefore the steel productis shipped.