Systems and methods for silicon purification

Abstract

Systems and methods for purification of silicon are provided herein. In one embodiment, a method of purifying an aluminum silicon melt is provided. The method can include forming a molten liquid that includes an impure aluminum silicon melt and at least one metal additive, cooling the molten liquid to form a precipitate that contains an impurity, a derivative of the impurity, or a reaction product. The method can further include separating the precipitate from the cooled molten liquid to create a purified aluminum silicon melt having a reduced amount of the impurity as compared to the amount of the impurity in the molten liquid. Aspects further include a method of purifying silicon using an aluminum silicon melt.

Description

SYSTEMS AND METHODS FOR SILICON PURIFICATION

[0001] A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This international application claims the benefit of priority to U.S. Provisional Application No. 63 / 561,538, filed on March 5, 2024, entitled “SYSTEMS AND METHODS FOR SILICON PURIFICATION.”STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0003] Not applicable.THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

[0004] Not applicable.FIELD OF THE DISCLOSURE

[0005] The present disclosure relates, in general, to apparatuses, systems, and methods for purifying silicon, and more particularly, to apparatuses, systems, and methods for purifying silicon with al Al-Si melt.BACKGROUND

[0006] This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.

[0007] Solar cells are currently utilized as an energy source by using their ability to convert sunlight to electrical energy. Silicon is used almost exclusively as the semiconductor material in such photovoltaic cells. A significant limitation currently on the use of solar cells has to do with the cost of purifying metallurgical grade silicon to solar grade (SG). In view of current energy demands and supply limitations, there is an enormous need for a more cost-efficient way of purifying metallurgical grade (MG) silicon (or any other silicon having greater impurities than solar grade) to solar grade silicon.

[0008] Companies and research groups have been working on making upgraded metallurgical (UMG) silicon. Many of these processes are limited in that they have difficulty reducing the amount of boron or phosphorus. For example, the process of purifying silicon via an aluminum solvent is ultimately limited by the purity of the aluminum used. The amount of naturally occurring boron in aluminum is relatively low and can be screened from the population of castings at the primary producer’s site. This can generally provide aluminum with boron content in the range of 0.6 ppmwt. While this is sufficient to produce silicon crystals in the range of 0.4 ppmwt, this level of boron is still considered too high to produce solar cells which do not suffer from degraded conversion efficiencies.BRIEF SUMMARY

[0009] The present disclosure addresses and / or provides advantages over the problems identified above, amongst others. Implementations consistent with the present disclosure provide systems, methods, and apparatuses for purifying silicon. Embodiments include apparatuses, systems, and methods for purifying silicon with al Al-Si melt. Additional aspects of the present disclosure include apparatuses, systems, and methods for purifying an aluminum silicon melt.

[0010] The present disclosure provides a method of purifying an aluminum silicon melt. In embodiments, the method comprises forming an initial molten liquid, the molten liquid comprising a starting aluminum silicon melt and at least one metal additive; cooling the molten liquid to a precipitation end temperature to form a precipitate and a cooled molten liquid, wherein the precipitate comprises: an impurity, a derivative of the impurity, or a reaction product; and separating the precipitate from the cooled molten liquid to create a purified aluminum silicon melt, wherein the amount of the impurity in the purified aluminum silicon melt is less than the amount of the impurity in the initial molten liquid.

[0011] In certain embodiments, the starting aluminum silicon melt comprises about 12% to about 14% wt of silicon.

[0012] The step of forming the initial molten liquid can comprise combining the metal additive with aluminum and silicon, wherein, after the time of combining, the metal additive, the aluminum, the silicon, or a combination thereof are in a liquid state.

[0013] In certain embodiments, the step of forming the molten liquid comprises melting an alloy with silicon to form the starting aluminum silicon melt, wherein the alloy comprises aluminum and the metal additive.

[0014] In various embodiments, the molten liquid is held at a temperature of at least about 800' C prior to the step of cooling the molten liquid.

[0015] The precipitation end temperature can comprise any temperature between about 577°C and about 950°C. In embodiments, the precipitation end temperature is around 577°C. The precipitation end temperature can be about the same as a eutectic point of the purified aluminum silicon melt. In embodiments, the step of cooling the molten liquid to the precipitation end temperature occurs over a cooling time period of at least about four hours. The cooling time period can be up to about fifty hours.

[0016] In certain embodiments, the at least one metal additive comprises titanium, strontium, vanadium, niobium, tantalum, calcium, barium, zirconium, chromium, magnesium, or a combination thereof. The at least one metal additive can comprise titanium, strontium, vanadium, or a combination thereof. In embodiments, the molten liquid comprises at least about 1,000 ppmwt titanium, up to about 5,000 ppmwt strontium, or a combination thereof.

[0017] The impurity can comprise boron, phosphorus, a derivative thereof, or any combination of the foregoing. In embodiments, the precipitate comprises the reaction product between the metal additive and at least one of boron and phosphorus. The reaction product can comprise a boride, a phosphide, or a combination thereof.

[0018] In various embodiments, the step of separating the precipitate from the cooled molten liquid comprises: removing a top skin from the cooled molten liquid; centrifuging the cooled molten liquid, decanting the cooled molten liquid; filtering the precipitate from the cooled molten liquid; solidification of the cooled molten liquid into an ingot and cutting a solidified precipitate from the ingot; impelling a liquid salt flux into the cooled molten liquid followed by removal of a resultant flux; or a combination thereof.

[0019] In embodiments, the method of purifying an Al-Si melt further comprises adding at least about 50 ppmwt vanadium to the molten liquid.

[0020] Tn another aspect, the present disclosure provides for a method of purifying silicon, the method comprising: forming a first melt that comprises an initial aluminum silicon melt and an input silicon; holding the first melt at a melting temperature until the initial aluminum silicon melt and the input silicon are substantially co-molten to form a resulting aluminum-silicon melt; cooling the resulting aluminum-silicon melt to a crystallization end temperature that is below a crystallization temperature, wherein the crystallization temperature is a temperature that depends upon a composition of the resulting aluminum-silicon melt and permits the formation of a plurality of silicon crystals and a mother liquor; and separating the silicon crystals from the mother liquor. The crystallization end temperature can be above 577°C. In embodiments, the melting temperature is any temperature higher than a liquidus temperature given by the Al-Si binary phase diagram of Figure 9 for the first melt composition.

[0021] In certain embodiments, the first melt comprises a total silicon content of up to about 60% wt. In embodiments, the initial aluminum silicon melt comprises a near eutectic aluminum silicon melt. The initial aluminum silicon melt can comprise the purified aluminum silicon melt obtained according to the Al-Si purification process disclosed herein.

[0022] In various embodiments, the input silicon comprises a relatively pure silicon, wherein the relatively pure silicon comprises about 15 ppmwt boron or less. In one embodiment, the input silicon comprises a moderately pure or impure silicon, wherein: the moderately pure silicon comprises a boron concentration that is above about 15 ppmwt boron and up to about 70 ppmwt; and the impure silicon comprises a boron concentration that is above about 70 ppmwt.

[0023] In embodiments, the step of cooling the impure aluminum-silicon melt to the crystallization end temperature occurs over a crystallization cooling time period of at least about five hours. The crystallization cooling time period can be up to about fifty hours.

[0024] Tn various embodiments, the method of purifying silicon can be repeated for n passes until a desired silicon purity is achieved, wherein the input silicon of each pass comprises the plurality of silicon crystals obtained in the immediately preceding pass.

[0025] In one embodiment, the step of forming the first aluminum-silicon melt comprises adding the input silicon to the aluminum silicon melt.

[0026] The step of separating the plurality of silicon crystals from the mother liquor comprises pouring off the mother liquor from the silicon crystals, filtering the silicon crystals from the mother liquor, centrifugation, or a combination thereof.

[0027] In yet another aspect, the present disclosure provides a method of purifying silicon, the method comprising: forming an initial molten liquid, the initial molten liquid comprising a starting aluminum silicon melt and at least one metal additive; cooling the initial molten liquid to a precipitation temperature to form a precipitate and a cooled molten liquid, wherein the precipitate comprises an impurity, a derivative of the impurity, or a reaction product; separating the precipitate from the cooled molten liquid to create a purified aluminum silicon melt, wherein the amount of the impurity in the purified aluminum silicon melt is less than the amount of the impurity in the initial molten liquid; forming a first melt that comprises the purified aluminum silicon melt and an input silicon; holding the first melt at a melting temperature until the initial aluminum silicon melt and the input silicon are substantially co-molten to form a resulting aluminum-silicon melt; cooling the resulting aluminum-silicon melt to a crystallization end temperature that is below a crystallization temperature, wherein the crystallization temperature is a temperature that permits the formation of a plurality of silicon crystals and a mother liquor; and separating the plurality of silicon crystals from the mother liquor.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Hereinafter, various exemplary embodiments of the disclosure are illustrated in more detail with reference to the drawings.

[0029] Figure 1 illustrates a block flow diagram of a method of purifying an aluminum silicon alloy under one embodiment of the present disclosure.

[0030] Figure 2 provides a schematic representation of a method of purifying an aluminum silicon melt under an embodiment.

[0031] Figure 3A provides data showing the boron concentration (in ppmwt) in a purified Al-Si melt obtained following treatment of an initial molten liquid (Dev4 in Table 1) with an Al-Si purification process according to one embodiment of the present disclosure.

[0032] Figure 3B provides data showing the phosphorus concentration (in ppmwt) in a purified Al-Si melt obtained following treatment of an initial molten liquid (Dev4 in Table 1) with an Al- Si purification process according to one embodiment of the present disclosure.

[0033] Figure 4 provides box and whisker plots showing a time-dependent reduction of boron concentration during treatment of an initial molten liquid with the Al-Si purification process disclosed herein. Boron concentration was measured at each of the following times: prior to beginning the purification treatment and 4-, 8-, and 17-hours following initiation of the purification treatment. Treatments were performed on an initial molten liquid comprising (a) a starting Al-Si melt that was about 88% Al and about 12% Si and (b) a metal additive in an amount sufficient to bring the initial molten liquid to about 1400 ppmwt Ti, about 100 ppmwt V, and about 5000 ppmwt Sr.

[0034] Figure 5 shows a histogram distribution fit function of boron in raw mix (blue) and after 17 hours of the purification procedure as described herein (red), wherein the initial molten liquid comprises 1400 ppmwt Ti, 100 ppmwt V, and 5000 ppmwt Sr. As can be seen, even with a highlyvariable degree of boron input in the raw mixture, the purification Al-Si purification process described herein results in a narrow distribution of low B -concentrations in the purified Al-Si alloy. Thus, consistent purification results can be obtained in the purified Si-Al alloy following exposure to the Al-Si purification process disclosed herein, even with variable boron content in the starting Al-Si alloy.

[0035] Figure 6 shows a log scale of boron concentration in ppmwt in the raw mix (prior to purification) and after purification treatment. As can be seen, extreme inputs (100 ppmwt B) can be purified to comparatively low levels (around 0.1 ppmwt B) because the equilibrium of the purification doesn’t depend on input B as long as Ti is in excess.

[0036] Figure 7 illustrates a block flow diagram of a method of purifying silicon with exposure to an aluminum silicon melt under one embodiment of the present disclosure.

[0037] Figure 8 illustrates a block flow diagram of a method of purifying silicon wherein the input silicon is a moderately pure or impure silicon. The block diagram provides an embodiment that combines use of an optimized silicon purification process with a high purity silicon process to obtain a highly purified silicon product.

[0038] Figure 9 shows a phase diagram of Al and Si under one embodiment. The mass % of Si in an Al / Si composition is represented on the x-axis, whereas the temperature in °C is represented on the y-axis. The eutectic point of an Al / Si composition is found at 577°C for a composition of 12% (w / w) Si.

[0039] Figure 10 shows three curves to visualize an optimization problem under one embodiment. Each curve represents a variety of mixes between an MG-Si and different input Al-Si melts with all mixes resulting in 40% silicon (referred to herein as a “resulting melt” or an “obtained melt”). While the MG-Si is of the same source for an individual curve the mixing partner (input Al-Simelt) varies in composition and following this the amounts of both mixing partners are chosen to obtain 40% silicon in the mix. The input Al-Si melt for every mix comes from an Al-Si purification process which had an individual end temperature (described elsewhere) and therefore resulted in an individual B- and Si-concentration for this input melt. The plot in Figure 10 shows the resulting B-concentration of the mixes versus the individual end temperature of the Al-Si purification process mentioned before. As can be seen there is an optimum (lowest B) for each series of mixtures marked with a black dot which is different for each of the three curves (input MG-Si with 50 ppmwt B (red); input MG-Si with 40 ppmwt B (blue); and input MG-Si with 30 ppmwt B (grey)).DETAILED DESCRIPTION

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The present disclosure may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the embodiments of the disclosure be considered in all aspects as illustrative and not restrictive. Any headings utilized in the description are for convenience only and no legal or limiting effect. Numerous objects, features, and advantages of the embodiments set forth herein will be readily apparent to those skilled in the art upon reading of the following disclosure when taken in conjunction with the accompanying drawings.

[0041] The singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise. The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and / or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”

[0042] Wherever any of the phrases “for example,” “such as,” “including” and the like are used herein, the phrase “and without limitation” is understood to follow unless explicitly stated otherwise. Similarly, “an example,” “exemplary,” and the like are understood to be non-limiting.

[0043] The term “substantially” allows for deviations from the descriptor that do not negatively impact the intended purpose. Descriptive terms are understood to be modified by the term “substantially” even if the word “substantially” is not explicitly recited. Therefore, for example, the phrase “wherein the lever extends vertically” means “wherein the lever extends substantially vertically” so long as a precise vertical arrangement is not necessary for the lever to perform its function.

[0044] The terms “comprising” and “including” and “having” and “involving” (and similarly “comprises,” “includes,” “has,” and “involves”) and the like are used interchangeably and have the same meaning. Specifically, each of the terms is defined consistent with the common United States patent law definition of “comprising” and is therefore interpreted to be an open term meaning “at least the following,” and is also interpreted not to exclude additional features, limitations, aspects, etc. Thus, for example, “a process involving steps a, b, and c” means that the process includes at least steps a, b, and c. Wherever the terms “a” or “an” are used, “one or more” is understood, unless such interpretation is nonsensical in context.

[0045] As used herein the term “about” is used to mean approximately, roughly, around, or in the region of. When the term “about” is used in conjunction with a numerical range, it modifies that range by extending the boundaries above and below the numerical values set forth. Tn general, the term “about” is used herein to modify a numerical value above and below the stated value by a variance of 20 percent up or down (higher or lower).

[0046] References in the specification to “one embodiment,” “an embodiment,” “an exemplary embodiment,” etc., indicates that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include such feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0047] As used herein, “purifying” can mean the physical separation of a substance of interest from one or more foreign or contaminating substances. By contrast, “impurities” or “impurity” can mean one or more foreign or contaminating substances that are undesirable. In embodiments, “impurity” refers to boron, phosphorus, or both.

[0048] As used herein, “molten” or “molten liquid” refers to one or more substances, together, that are melted.

[0049] As used herein, “melting” refers to the process of heating one or more solid substances to at least the temperature wherein such solid substances become a liquid (also referred to as the “melting point”). As such, the “melting” can refer to the process by which a substance changes from a solid to a liquid when exposed to sufficient heat. Melting can refer to heating a solid substance to any temperature at or above the melting point for such substance.

[0050] As used herein, “aluminum” refers to the chemical element that has the symbol Al and atomic number 13. The term includes metal aluminum, elemental aluminum, or an alloy thereof.In embodiments, aluminum is used as a solvent metal.

[0051] As used herein, “solvent metal” can mean one or more metals, or an alloy thereof, which upon heating, dissolves silicon, resulting in a molten liquid. Suitable exemplary solvent metals include but are not limited to aluminum or an alloy thereof, copper, tin, zinc, antimony, silver, bismuth, cadmium, gallium, indium, magnesium, lead, alloys of any of the foregoing, and any combinations thereof.

[0052] As used herein, an “alloy” can mean a homogeneous mixture of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. In embodiments, the resulting metallic substance in an alloy can have different properties (sometimes significantly different) from those of its individual components. Unless context clearly dictates otherwise, any mention of an alloy is not limited to existing in a particular state of matter for such alloy. For instance, the referenced alloy can be present in a liquid state (such as a melt) or a solid state (such as an ingot, sow, billet, slab, bar, plate sheet, etc.).

[0053] The phrase “metal additive” as used herein can refer to a composition comprising a metal that can be added to an original molten liquid resulting in the formation of a new molten liquid that comprises the original molten liquid and the metal additive. In embodiments, the metal additive can be used to remove an impurity from the original molten liquid or a solvent metal such as by complexing or reacting with the impurity. In embodiments, the metal additive comprises a transition metal, an alkaline earth metal, or a combination thereof. The metal additive can comprise any one or more of titanium, strontium, vanadium, niobium, tantalum, calcium, barium, zirconium, chromium, magnesium, and the like.

[0054] As used herein, “chromium” refers to the chemical element refers to the chemical element that has the symbol Cr and atomic number 24. The term includes metal chromium or elemental chromium, as well as an alloy thereof.

[0055] As used herein, “titanium” refers to the chemical element that has the symbol Ti and atomic number 22. The term includes metal titanium or elemental titanium, as well as an alloy thereof.

[0056] As used herein, “vanadium” refers to the chemical element that has the symbol V and atomic number 23. The term includes metal vanadium or elemental vanadium, as well as an alloy thereof.

[0057] As used herein, “zirconium” refers to the chemical element refers to the chemical element that has the symbol Zr and atomic number 40. The term includes metal zirconium, elemental zirconium, as well as an alloy thereof.

[0058] As used herein, “strontium” refers to the chemical element refers to the chemical element that has the symbol Sr and atomic number 38. The term includes metal strontium, elemental strontium, as well as an alloy thereof.

[0059] As used herein, “niobium” refers to the chemical element refers to the chemical element that has the symbol Nb and atomic number 41. The term includes metal niobium, elemental niobium, as well as an alloy thereof.

[0060] As used herein, “tantalum” refers to the chemical element refers to the chemical element that has the symbol Ta and atomic number 73. The term includes metal tantalum, elemental tantalum, as well as an alloy thereof.

[0061] As used herein, “calcium” refers to the chemical element refers to the chemical element that has the symbol Ca and atomic number 20. The term includes metal calcium, elemental calcium, as well as an alloy thereof.

[0062] As used herein, “barium” refers to the chemical element refers to the chemical element that has the symbol Ba and atomic number 56. The term includes metal barium, elemental barium, as well as an alloy thereof.

[0063] As used herein, “magnesium” refers to the chemical element refers to the chemical element that has the symbol Mg and atomic number 12. The term includes metal magnesium, elemental magnesium, as well as an alloy thereof.

[0064] As used herein, a “reaction product” refers to a compound formed by the chemical reaction of two or more substances. By way of example, a reaction product of titanium and boron includes titanium diboride (TiB2).

[0065] As used herein, “coordination complex,” “metal complex” or “complex” refers to an atom or ion (usually metallic, such as metal additive), bonded to a surrounding array of molecules or anions (including, e.g., boron, phosphorus, or a combination thereof), that are in turn known as ligands or complexing agents.

[0066] As used herein, “solidifying” refers to the process of cooling one or more liquid substances (e.g., molten liquid) to at least a temperature, where such substances turn into a solid. As such, the term “solidifying” can refer to a substance changing from a liquid to a solid, upon cooling.

[0067] As used herein, “separating” or “removing” refers to the process of separating a substance from another substance (e.g., removing a solid or a liquid from a mixture) or separating a portion of a substance from another portion (e.g., removing a part of a solid from another part of the solid). The process can employ any technique known to those of skill in the art. By way of non-limiting example, the process of “separating” or “removing” one substance from another substance can include decanting the mixture (such as, e.g., after one or more solids have settled along or adhered to at least one surface of a container), skimming one or more liquids or solids from the mixture, centrifuging the mixture, filtering one or more solids from the mixture, cutting a solid to remove a portion thereof, or a combination thereof. Certain embodiments can include separating or removing a precipitate from a mixture.

[0068] As used herein, “skimming” can refer to the process of removing one or more liquids, solids, or combination thereof from a mixture, wherein the one or more liquids or solids are floating on top of the mixture.

[0069] As used herein, “boron” refers to the chemical element that has the symbol B and atomic number 5. The term includes compounds that include boron (i.e., boron-containing compounds that include B3+, B2+, or B+), and combinations thereof.

[0070] As used herein, “silicon” refers to the chemical element that has the symbol Si and atomic number 14. The term includes metal, elemental silicon, or an alloy thereof.

[0071] As used herein, “crystalline” includes the regular, geometric arrangement of atoms in a solid. As such, “silicon crystals” refers to silicon having regular, geometric arrangement of the silicon atoms in a solid state.

[0072] The term “eutectic,” as used herein, can refer to a specific composition of a mixture of substances, typically an alloy (such as a binary alloy), which has a melting point that is lower than the melting points of the individual components within the mixture. The phrase “eutectic composition” can refer to the specific ratio or proportion of components in an alloy where the lowest melting point occurs. Likewise, the phrase “eutectic point” can mean the specific temperature at which the eutectic reaction occurs for a given composition in a binary alloy. Thus, the eutectic point can be the temperature at which a specific composition transforms directly from a liquid phase to a solid phase (and vice versa). In a phase diagram, the eutectic point can be represented as the intersection of the liquidus and solidus lines, corresponding to the conditions where the lowest possible melting point for that combination of substances occurs. By way of example, the phase diagram of FIG. 9 shows that eutectic point for an ALSi alloy occurs at about 577°C, and the eutectic composition comprises about 12.6% silicon.

[0073] As used herein, the phrase “near eutectic” when referring to an Al-Si alloy can refer to an Al-Si alloy that comprises an Si concentration of between about 12%-15% Si. In specific embodiments, a near eutectic Al-Si alloy comprises a silicon concentration of about 12.6%, about 12.7%, about 12.8%, about 12.9%, about 13.0%, about 13.1%, about 13.2%, about 13.4%, about 13.5%, about 13.6%, about 13.8%, about 13.9%, about 14.0%, about 14.1%, about 14.2%, about 14.3%, about 14.4%, about 14.5%, about 14.6%, about 14.7%, about 14.8%, about 14.9%, or 15.0%.

[0074] As used herein, “contacting” refers to the act of touching, making contact, or of bringing substances into immediate proximity.

[0075] As used herein, “decanting” or “decantation” includes pouring off a fluid, leaving a sediment or precipitate, thereby separating the fluid from the sediment or precipitate.

[0076] As used herein, “filtering” or “filtration” refers to a mechanical method to separate solids from liquids by passing the feed stream through a porous sheet such as a ceramic or metal membrane, which retains the solids and allows the liquid to pass therethrough. This can be accomplished by gravity, pressure, vacuum (suction), or a combination thereof.

[0077] The abbreviations “ppmwt,” “ppm,” and “ppmw” are used interchangeably to mean the “parts per million by weight” of a recited substance.

[0078] As used herein, “precipitating” can refer to the process of causing a solid substance (e.g., crystals) to be separated from a solution. The precipitating can include crystallizing.

[0079] The phrase “metallurgical grade silicon” (“MG-Si”), as used in the present disclosure, can refer to a silicon composition with a purity of at least about 95.0 wt.% silicon. In embodiments, MG-Si can refer to a silicon composition that comprises boron. By way of example, MG-Si has a boron content of up to about 100 ppmwt boron. MG-Si can have a boron content of up to any ofthe following: about 90 ppmwt, about 85 ppmwt, about 80 ppmwt, about 75 ppmwt, about 70 ppmwt, about 65 ppmwt, about 60 ppmwt, about 55 ppmwt, about 50 ppmwt, about 45 ppmwt, about 40 ppmwt, about 35 ppmwt, about 30 ppmwt, about 25 ppmwt, about 20 ppmwt, and about15 ppmwt.

[0080] In the methods of manufacturing described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Recitation in a claim to the effect that first a step is performed, then several other steps are subsequently performed, shall be taken to mean that the first step is performed before any of the other steps, but the other steps can be performed in any suitable sequence, unless a sequence is further recited within the other steps. For example, claim elements that recite “Step A, Step B, Step C, Step D, and Step E” shall be construed to mean step A is carried out first, step E is carried out last, and steps B, C, and D can be carried out in any sequence between steps A and E, and that the sequence still falls within the literal scope of the claimed process. A given step or sub-set of steps may also be repeated.

[0081] Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed step of doing X and a claimed step of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

[0082] Reference will now be made in detail to embodiments of the present disclosure, one or more drawings of which are set forth herein. Each drawing is provided by way of explanation of the present disclosure and is not a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the teachings of the present disclosure without departing from the scope of the disclosure. For instance, features illustrated or describedas part of one embodiment can be used with another embodiment to yield a still further embodiment.

[0083] While the inventive subject matter is susceptible of various modifications and alternative embodiments, certain illustrated embodiments thereof are shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the disclosure to any specific form disclosed, but on the contrary, the inventive subject matter is to cover all modifications, alternative embodiments, and equivalents falling within the scope of any appended claims. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the disclosure.

[0084] Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present disclosure are disclosed in, or are obvious from, the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present disclosure. Referring generally to Figs. 1-11, various exemplary embodiments of a system for purification of silicon and a method associated therewith are described in detail. Where the various figures may describe embodiments sharing various common elements and features with other embodiments, similar elements and features are given the same reference numerals and redundant description thereof may be omitted below.

[0085] In various exemplary embodiments, the process described herein employs a combination of reactive chemistry and control of melting temperatures to achieve a reduction in impurities that are otherwise present in an aluminum silicon (“Al-Si”) alloy, such as an Al-Si melt. By way of non-limiting example, such impurities can comprise boron (B), phosphorus (P), or a combinationthereof. When provided in excess a metal additive can be added to an Al-Si alloy to form a molten liquid. In embodiments, the metal additive therein interacts with the impurity to form an impuritycontaining reaction product. By way of example, when titanium (Ti) is present in the metal additive and the impurity comprises boron, such an impurity-containing reaction product can comprise TiB2 particles. The molten liquid can then be cooled to a precipitation temperature which permits the formation of solid precipitates. Such impure reaction products can form a solid precipitate in the molten liquid during cooling, which can be physically separated therefrom. This can effectively reduce the level of impurities in the Al-Si alloy, to form a purified Al-Si melt or purified Al-Si alloy. By way of example, such purified Al-Si melt can comprise a boron level that is below about 0.2 ppmwt, a phosphorus level that is below about 0.3 ppmwt, or a combination thereof. The purified Al-Si alloy can, advantageously, be utilized in a subsequent process to purify silicon, resulting in a highly pure silicon product. Without being bound by theory, such resulting silicon product, characterized by its high purity, represents a practical choice for the use in solar cells. A metal additive (e g., titanium) can be introduced during the process to purify an Al-Si melt, wherein such a metal additive does not have any significant or appreciable adverse effects on performance of the final product (e.g., solar cells) for their intended purpose.

[0086] Aspects of the present disclosure further relate to methods of purifying silicon. For instance, as discussed herein, such methods can permit the formation of a highly pure silicon, having relatively low amounts of boron, phosphorus, or a combination thereof and any other elements or substances that would prevent of inhibit the function of a solar cell . The production of such highly purified silicon crystals can be used to generate higher quality products, such as solar panels. Without wishing to be bound by theory, the highly purified silicon crystals obtained from the methods disclosed herein can be used in the production of batteries or electronic devices.. Themethods can be carried out in a relatively cost-effective manner, while utilizing materials that are relatively cost- effective. In various embodiments, the systems and method disclosed herein permit the use of a moderately pure or impure input silicon, a moderately pure or impure (e.g., noneutectic) input Al-Si alloy, or a combination thereof. The ability to use less pure input materials can lower cost and access to a greater supply of raw material, such as scrap aluminum and silicon scrap from the solar industry. The production of purified silicon crystals in accordance with the embodiments disclosed herein can, therefore, be accomplished, in a relatively cost-effective manner.

[0087] Referring to FIG. 1, an example of a block flow diagram 100 of a method for purifying an aluminum silicon alloy 101 is shown, according to some embodiments. Similarly, FIG. 2 provides a protocol under one embodiment 100 for removing impurities 107 from a molten liquid 104. A molten liquid 104 can be formed by heating 103 a starting Al-Si alloy 101 and metal additive 102. After the starting Al-Si alloy 101 and the metal additive 102 are substantially dissolved within the molten liquid 104, the molten liquid 104 can then be cooled to a precipitation temperature 106, which permits the formation of solid precipitates 107, wherein such solid precipitates comprise one or more impurities that were present in the starting Al-Si alloy 101. Such solid precipitates 107 can be removed from the molten liquid to provide a purified melt 110.

[0088] In various embodiments, the starting Al-Si alloy 101 is a close to a eutectic composition (see, e.g., the phase diagram of FIG. 9). In embodiments, the silicon content in the starting Al-Si alloy 101 is at least about 12%. In certain embodiments, the starting Al-Si alloy 101 comprises up to 30%. Silicon. The silicon content in the starting Al-Si alloy 101 can be up to 20%. In embodiments the silicon content in the starting Al-Si alloy 101 is up to about 14%. In one embodiment, the starting Al-Si 101 alloy comprises an aluminum content of between about 86-88%, inclusive, a silicon content of between about 12-14%, inclusive, or a combination thereof. In certain embodiments, there can be a measurable amount of coprecipitation of TiE and silicon, and in such embodiments, silicon may enhance the removal of TiEh. Thus, in these embodiments, it may be preferable if the starting Al-Si alloy 101 comprises a silicon content that is higher than that found in a eutectic composition.

[0089] The heating of the starting Al-Si alloy 101 and metal additive 102 can be carried out for a given time and temperature that is efficient to effectively form a substantially molten liquid 104. For example, the temperature can be at least about 650°C. In embodiments, the heating temperate can be as low as about 660°C. A minimum of 660°C for the heating or holding temperature can be particularly useful when substantially pure aluminum is melted prior to adding silicon to create the Al-Si alloy 101. The metal additive 102 and the starting Al-Si alloy 101 can be held at a temperature of at least 800°C until each of the metal additive 102 and the Al-Si alloy 101 are substantially dissolved to form a molten liquid 104 that comprises the Al-Si alloy and metal additive in molten form. In embodiments, the starting Al-Si alloy 101 and metal additive 102 are held at a temperature of up to about 2000°C. The starting Al-Si alloy 101 and metal additive 102 can be held at a temperature of up to about 1000°C. In embodiments, starting Al-Si alloy 101 and metal additive 102 are held at temperature of between about 800°C and about 900°C, inclusive, until a molten liquid 104 is formed.

[0090] Any suitable amount of a metal additive 102 can be employed, provided the amount of metal additive 102 is sufficient to form at least one reaction product with an impurity that is present within the molten liquid 104 to permit formation of a solid precipitate 107 with the impurity and subsequent removal of the same. In certain embodiments, the metal additive 102 is added in an amount that is sufficient to permit the molten liquid 104 to contain at least about 300 ppmwttitanium, at least about 300 ppmwt strontium, or a combination thereof. In certain embodiments, the metal additive 102 can be added in an amount sufficient to permit the molten liquid 104 to comprise at least about 30 ppmwt vanadium. In embodiments the metal additive 102 is added in an amount such that the molten liquid 104 contains between about 500 and about 2000 ppmwt titanium, between about 500 and 10000 or 1% ppmwt strontium, about 50 to about 500 ppmwt vanadium, or a combination thereof. The molten liquid 104 can comprise about 1400 ppmwt Ti, about 100 ppmwt V, and about 5000 ppmwt Sr.

[0091] Table 1 provides exemplary metal additives 102 and exemplary concentrations of the same within a given melt for use in various embodiments of the Al-Si purification process 100 described herein.

[0092] Each of Devl-Dev4 in Table 1 comprise an exemplary Al-Si melt that is between about 12 to 14% wt of silicon. Devi contains 1400 ppmwt Ti as a metal additive. The metal additive for Dev2 comprises 1400 ppmwt Ti and 100 ppmwt v, and the metal additive for Dev4 contains 1400 ppmwt Ti, 100 ppmwt V, and 5000 ppmwt Sr.

[0093] The metal additive 102 can be included in the molten liquid 104 with the intent to assist with removal of impurities (e.g., boron-containing impurities, phosphorus-containing impurities, or a combination thereof) from the Al-Si alloy 101. As such, the Al-Si alloy 101 can be purifiedfrom boron, phosphorus, or both, such that at least some of the boron, phosphorus, or both are removed therefrom.

[0094] The solid precipitates 107 which form during the Al-Si alloy purification process 100 comprise a reaction product of the metal additive 102 and the impurity being removed from the starting Al-Si alloy 101. For instance, when boron is an impurity present in the starting Al-Si alloy 101 and titanium is present in the metal additive 102, the reaction product, which forms a solid precipitate during cooling, comprises titanium diboride (TiB2). In another embodiment, when vanadium is present in the metal additive 102, the reaction product comprises vanadium diboride (VB2). In embodiments where both titanium and vanadium are present in the metal additive, the reaction product can comprise TiB2, VB2, or a combination thereof. Additional impurities include those impurities formed from the reaction product of metal additive, boron, phosphorus, and an additional substance present in the molten liquid 104 or which contacts the molten liquid 104, wherein generation of the reaction product is catalyzed by, or coordinated with, the metal additive 102. An exemplary substance present in the molten liquid, or which contacts the molten liquid, includes, e.g., oxygen.

[0095] In embodiments, the metal additive 102 comprises at least one transition metal, at least one alkaline earth metal, or a combination thereof. In embodiments wherein the metal additive 102 comprises both a transition metal and an alkaline earth metal, such transition metal and alkaline earth metal react with different impurities in the starting Al-Si alloy 101 to form reaction products that are separate and independent form one another. The at least one transition metal can be the primary component in the metal additive 102 that contributes to formation of the solid precipitate 107, such as by forming a reaction product with boron or other impurities that were present in the starting Al-Si alloy 101. The at least one alkaline earth metal can form a reaction product withphosphorus that may be present within the starting Al-Si alloy 101, thereby reducing the amount of phosphorus in the purified Al-Si alloy 110 following treatment via the Al-Si purification process 100. In certain embodiments wherein alkaline earth metal comprises strontium, the strontium interacts with at least a portion of the phosphorus present in the starting Al-Si alloy 101 to form Sr3P2.

[0096] In embodiments, the metal additive 102 can be added to the starting Al-Si alloy 101 as shown in FIG. 1, be present together with the aluminum that is within the starting Al-Si alloy 101, or a combination thereof. In embodiments wherein at least a portion of the metal additive 102 is present in the aluminum of the starting Al-Si alloy 101, such aluminum can include a significant and appreciable amount of metal additive 102. In embodiments, the aluminum and silicon, which form the starting Al-Si alloy 101, and the metal additive 102 can be combined either concurrently or consecutively. For instance, each of aluminum, silicon, and the metal additive can be added in a solid form and then heated 103 to create the molten liquid 104. Alternatively, the Al-Si alloy 101 can be melted and the metal additive 102 subsequently added (or vice versa) to form the molten liquid 104. In alternative embodiments, the molten liquid 104 can be formed by placing the starting Al-Si alloy 101 and metal additive 102 together then heating 103 until both the starting Al-Si alloy 101 and the metal additive 102 are substantially in liquid form. In yet another embodiment, the Al- Si alloy 101 and the metal additive 102 are each provided in a substantially liquid (pre-heated) form, combined, and held a temperature 103 sufficient to maintain such liquid form to create the molten liquid 104. In any suitable manner as described above, the molten liquid 104 can be formed by holding the starting Al-Si alloy 101 and the metal additive 102 at any temperature 103 at or above the melting temperature of the metal additive 102.

[0097] As can be seen in FIG. 1 , after achieving a molten liquid 104, the Al-Si purification process 100 can comprise cooling 105 the molten liquid 104 to a precipitation temperature 106. The precipitation temperature 106 can be a temperature that is sufficient to permit formation of solid precipitates 107 within the cooled molten liquid, wherein such solid precipitates comprise a reaction product formed between the metal additive 102 and impurities that were originally present in the starting Al-Si alloy 101. The precipitation temperature 106 can be below about 665°C. The precipitation temperature 106 can be about 600°C. In embodiments, the precipitation temperature 106 can be between about 578°C and about 660°C. In certain embodiments, the precipitation temperature 106 can be sufficiently low to permit formation of the solid precipitates 107 while also being warm enough to ensure that that the Al-Si alloy remains in a molten state. Thus, when the Al-Si alloy comprises about 12-14% silicon, the precipitation temperate 106 can be any temperature that is above the eutectic point of an Al-Si alloy but below the melting point of the solid precipitates 107.

[0098] In certain embodiments, cooling the molten liquid 104 can occur over a given period of time, which can be referred to herein as a “precipitation cooling ramp.” Utilizing a precipitation cooling ramp can increase the yield of solid precipitates 107 formed as a reaction product between the metal additive 102 and the impurities within the starting Al-Si alloy 101. Thus, in various embodiments, a precipitation cooling ramp can result in improved separation of the cooled molten liquid and the solid precipitates 107 and, ultimately a purified Al-Si alloy with a substantially reduced level of impurities as compared to the starting Al-Si alloy. For instance, the temperature can be cooled from the holding temperature (that which is sufficient to create the molten liquid 104) to the precipitation temperature over a period of at least 1 hour. The precipitation cooling ramp can be longer than at least about 3 hours. In certain embodiments, the precipitation coolingramp can be a period of up to 100 hours. In embodiments, the precipitation cooling ramp occurs over a period of between about 2 hours and 75 hours. In specific embodiments, the precipitation cooling ramp is between about 5 hours and about 50 hours. The precipitation cooling ramp can be about 5 hours, about 10 hours, about 15 hours, about 20 hours, about 25 hours, about 30 hours, about 35 hours, about 40 hours, about 45 hours, or about 50 hours. In various embodiments, the precipitation cooling ramp period comprises a duration of time that is sufficient to permit completion of the reaction kinetics to create a reaction product between the metal additive 102 and the one or more impurities (e.g., TiB2). The precipitation cooling ramp period can comprise a duration of time that is sufficient to permit nucleation of the reaction product (e.g., TiB2), the sufficient growth of reaction-product precipitates that can be filtered from the purified Al-Si alloy 110 (e.g., TiB2), the settling rate of the reaction product (e.g., TiB2), or a combination thereof.

[0099] Following formation during cooling of the molten liquid 104 over the precipitation cooling ramp period, the solid precipitates 107 can be separated from the cooled and still liquid Al-Si melt. As understood from the description provided herein, since the solid precipitates 107 comprise the impurities that were present in the starting Al-Si alloy, following removal of the solid precipitates 107, a purified Al-Si alloy 110 is obtained.

[0100] In specific embodiments, after cooling of the molten liquid 104 over the precipitation cooling ramp period, the solid precipitates 107 can be separated from the cooled and still liquid Al-Si melt 108 via any method known in the art.

[0101] As shown in the exemplary embodiment of FIG. 2, following cooling, solid precipitates 107 can form within the partially cooled molten liquid 108. A skin 109 of oxides, precipitates, or both can also form on the top of the cooled molten liquid 108. Without wishing to be bound by theory, the skin can comprise swimming phosphates, which can be removed from thecooled molted liquid 108 (such as via skimming). In addition, the solid precipitates 107 comprising the impurities can form along the sides or bottom of a vessel containing the partially cooled molten liquid 108. In such embodiments, the impurity-containing solid precipitates can be separated from the partially cooled molten liquid 108 such as by decanting or filtering to form a purified Al-Si melt 110.

[0102] In alternate embodiments, after the impurity-containing solid precipitates 107 form they can be permitted to settle to the bottom of the mold (or can nucleate and grow on the sides or bottom of the mold) and the cooled molten liquid 108 can be further cooled to form a solidified Al-Si alloy. Such cooling can be carried out in any suitable manner, provided the solidified Al-Si alloy is obtained. For example, the cooling can be carried out at about room temperature (about 20°C), for an extended period of time. Upon cooling, a portion of the solidified Al-Si alloy that comprises the previously settled impurities can be removed. Such a portion of the solidified Al-Si alloy can be removed by any suitable means. For example, that portion of the solidified Al-Si alloy can be mechanically removed, such as by cutting the impurities from the alloy.

[0103] In certain embodiments, impurity-containing solid precipitates 107 can move toward the top of the mold containing the partially cooled molten liquid 108, and, after further cooling and solidification of the Al-Si alloy, the top portions of the solidified alloy can be removed (i.e., the portion of the solidified Al-Si alloy comprising a significant amount of the impurities). Moving the impurities toward the top of the mold containing the partially cooled molten liquid 108 can be accomplished, e.g., by introducing substances to the partially cooled molten liquid 108 that will result in the impurities floating or rising to the surface thereof.

[0104] In embodiments, the purified Al-Si alloy 110 comprises a very low concentration of boron, a very low concentration of phosphorus, or both. In certain embodiments, the purifiedAl-Si alloy 1 10 can be substantially free of boron, phosphorus, or both. For example, following treatment with the purification process 100 of FIG. 1, the purified Al-Si alloy 110 can include less than about 5 ppmwt boron. In embodiments, the purified Al-Si alloy 110 comprises as little as 0.001 ppmwt boron. In certain embodiments, the purified Al-Si alloy 110 comprises less than 0.001 ppmwt boron. In various embodiments, the purified Al-Si alloy 110 comprises as little as 0.01 ppmwt boron. The purified Al-Si alloy 110 can comprise between about 0.05 ppmwt boron and about 3 ppmwt boron. In certain embodiments, the purified Al-Si alloy 110 comprises less than about 2 ppmwt boron. The purified Al-Si alloy 110 can comprise less than about 1 ppmwt boron. In certain embodiments, the purified Al-Si alloy 110 comprises up to about 0.30 ppmwt boron.

[0105] In embodiments, following treatment with the purification process 100 of FIG. 1, the purified Al-Si alloy 110 can include less than about 5 ppmwt phosphorus. In embodiments, the purified Al-Si alloy 110 comprises as little as 0.001 ppmwt phosphorus. In certain embodiments, the purified Al-Si alloy 110 comprises less than 0.001 ppmwt phosphorus. In various embodiments, the purified Al-Si alloy 110 comprises as little as 0.01 ppmwt phosphorus. The purified Al-Si alloy 110 can comprise between about 0.05 ppmwt phosphorus and about 3 ppmwt phosphorus. In certain embodiments, the purified Al-Si alloy 110 comprises less than about 2 ppmwt phosphorus. The purified Al-Si alloy 110 can comprise less than about 1 ppmwt phosphorus.

[0106] The purified Al-Si melt 110 can be solidified (such as to form sows or ingots), stored further used or can be directly further used (such as for silicon purification as described herein) in liquid form without intermediate solidification.

[0107] In specific embodiments, the method for purifying an Al-Si alloy 100 can be carried out once. In alternative specific embodiments, the method for purifying an Al-Si alloy 100 can be carried out two or more (e.g., 2, 3 or 4) times.

[0108] As discussed above, the method for purifying an Al-Si alloy 100 provides a purified Al-Si alloy 110 that is relatively pure, compared to the starting Al-Si alloy 101. This purified Al- Si alloy 110 can then be used, e.g., for the purification of silicon (see, FIGS. 7 & 8). For example, the method for purifying an Al-Si alloy 100 provides purified Al-Si alloy 110 that is purified from boron, phosphorus, or both, such that at least some of the boron, phosphorus, or both are removed from the starting Al-Si alloy 101. As such, a significant and appreciable amount of boron, phosphorus, or both present in the starting Al-Si alloy 101 can be removed to provide the purified Al-Si alloy 110.

[0109] Figure 3-6 provide data showing that the Al-Si purification process 100 can effectively and reproducibly remove impurities (such as boron and phosphorus) from a starting Al-Si. Briefly, the Al-Si purification process 100 can produce a purified Al-Si alloy (such as a purified Al-Si melt) having boron concentrations at or below 0.1 ppmwt, phosphorus concentrations at or below 0.1 ppmwt, or a combination thereof.

[0110] Figure 7 illustrates another aspect of the present disclosure. Briefly, a block flow diagram provides of a method of purifying silicon 200 through exposure of an input silicon 202 to an initial Al-Si alloy or melt 201 under one embodiment. The initial Al-Si alloy 201 can be combined with an input silicon 202 to be purified and heated 203 to at least a melting temperature. The Al-Si alloy 201 and the input silicon 202 can be held at the melting temperature until the substances are co-molten to form a resulting Al-Si melt 204. The resulting Al-Si melt 204 can then be cooled to a crystallization temperature 206, which permits the formation of one or more siliconcrystals 210. The one or more silicon crystals 210 can be removed from the resulting Al-Si melt 204 such that a resultant mother liquor 207 remains. The silicon crystals 210 have a reduced amount of impurities as compared to the original input silicon 202.

[0111] In embodiments, the initial Al-Si melt 201 can be combined with an input silicon 202 in amounts sufficient to create a resulting Al-Si melt 204 with a silicon concentration of between about 30% to about 60 % by weight. The resulting Al-Si melt 204 can have a silicon concentration of about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, or to about 60 % by weight.

[0112] Input silicon 202 for processing may be generated or obtained from a number of sources. The input silicon 202 may be scrap or discarded silicon from manufacturing solar cell panels, semiconductor wafers or shaping ingots, for example. Specifically, the input silicon 202 can include metallurgical grade silicon (MG-Si). Employing less pure silicon can provide costsavings, as well as allowing for the use of silicon that would otherwise not be feasible or practical.

[0113] Alternatively, in specific embodiments, the input silicon 202 to be purified can be the silicon crystals 210 obtained in a previous purification process. Specifically, the method for purifying silicon 200 can provide silicon crystals 210. These silicon crystals 210 can then be employed (as input silicon 202) in a subsequent method for purifying silicon 200. This can be carried out one or more (e.g., two, three or four) times.

[0114] In embodiments, the input silicon 202 can have a boron content of up to any one or more of the following: about 100 ppmwt, about 90 ppmwt, about 80 ppmwt, about 70 ppmwt, about 60 ppmwt, about 50 ppmwt, about 40 ppmwt, about 30 ppmwt, and about 20 ppmwt, about 10 ppmwt. In certain embodiments, input silicon 202 has a boron content of between about 1 ppmwt and 10 ppmwt. Input silicon 202 can have a boron content of about 1 ppmwt, about 2ppmwt, about 3 ppmwt, about 4 ppmwt, about 5 ppmwt, about 6 ppmwt, about 7 ppmwt, about 8 ppmwt, about 9 ppmwt, or about 10 ppmwt. In certain embodiments, the input silicon 202 can have a boron content of less than about 1 ppmwt.

[0115] In embodiments, the input silicon 202 comprises a relatively pure silicon, a moderately pure silicon, or an impure silicon. By way of example, a relatively pure silicon can comprise a boron content of about 10 ppmwt or less. An impure silicon can comprise a boron content of between about 30 ppmwt and 100 ppmwt boron. A moderately pure silicon can comprise a silicon content of between about 10 ppmwt and 30 ppmwt.

[0116] In embodiments, the initial Al-Si melt 201 (also referred to herein as the “input Al- Si”) used in the silicon purification process 200 can comprise a purified Al-Si alloy, such as that which can be obtained via the Al-Si purification process 100 described herein. The initial Al-Si melt can comprise an alloy with a silicon concentration of about 12% to about 15%. In embodiments, the initial Al-Si melt 201 comprises an Al-Si alloy with a composition that is at or near the eutectic composition for an Al-Si binary alloy. The initial Al-Si melt can comprise a silicon concentration of about 12.6%, about 12.7%, about 12.8%, about 12.9%, about 13.0%, about 13.1%, about 13.2%, about 13.4%, about 13.5%, about 13.6%, about 13.8%, about 13.9%, about 14.0%, about 14.1%, about 14.2%, about 14.3%, about 14.4%, about 14.5%, about 14.6%, about 14.7%, about 14.8%, about 14.9%, or 15.0%. When using a purified Al-Si alloy or near eutectic Al-Si alloy as the initial Al-Si melt 201, the end product can be highly purified silicon crystals 210 as more particularly described herein.

[0117] Alternatively, the initial Al-Si melt 201 can comprise a moderately pure or impure, non-eutectic Al-Si alloy, wherein the concentration of silicon within the non-eutectic Al-Si alloy is greater than that found in an Al-Si eutectic or near eutectic composition. In embodiments, a non-eutectic Al-Si alloy comprises a silicon concentration that is greater than about 15%. In certain embodiments, a non-eutectic Al-Si alloy comprises a silicon concentration that is up to about 60% silicon. In specific embodiments, a non-eutectic Al-Si alloy comprises a silicon concentration that is between about 17% to about 40%, inclusive. In embodiments, the non-eutectic Al-Si alloy has a silicon concentration of about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, or about 60%. The non-eutectic Al-Si alloy can have a silicon concentration of about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about29%, about 30%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about49%, or about 50%.

[0118] In embodiments, such an impure or moderately pure Al-Si alloy will have a lower purity and a higher silicon concentration than a purified Al-Si alloy 110 (such as that obtained from the Al-Si purification process 100). In embodiments, an impure or moderately pure Al-Si melt as initial Al-Si melt 201 can comprise a purity that is less than the starting Al-Si alloy 101 used in the Al-Si purification process. Although the term Al-Si “melt” is used, it is to be understood that the Al-Si can be an alloy that is initially in a solid form and later melted, such as when being combined with an input silicon 202 to form a resulting Al-Si melt 204.

[0119] In the silicon purification process 200, the resulting Al-Si melt 204 can be formed from combining the initial Al-Si alloy 201 and the input silicon 202 and heating 203 the combined initial Al-Si alloy 201 and the input silicon 202 at a melting temperature that is effective to create a substantially molten resulting Al-Si melt 204. Heating 203 of the initial Al-Si alloy 201 and the input silicon 202 can be carried out, to achieve a melting temperature that is higher the liquidustemperature given by the Al-Si binary phase diagram of FIG. 9 for the specific silicon concentration in the resulting melt composition. For example, the melting temperature for a resulting Al-Si melt with 40% Silicon (SI) is at least about ~930°C, and a melt with -28% silicon (S2) is liquid at temperatures of ~800°C and higher.

[0120] As can be seen in FIG. 7, after achieving a molten resulting Al-Si Melt 204, the silicon purification process 200 can comprise cooling 205 the resulting Al-Si melt 204 to a crystallization temperature 206. The crystallization temperature 206 can be a temperature that is sufficient to permit formation of solid silicon crystals 210 within the resulting Al-Si melt 204. The crystallization temperature 206 can be any temperature that is between the melting temperature and the eutectic point of an Al-Si binary alloy. In embodiments, the crystallization temperature 206 can be above about 577°C. In certain embodiments, the crystallization temperature 206 can be sufficiently low to permit formation of the silicon crystals 210 while also being warm enough to ensure that that the resultant mother liquor 207 remains in a molten state.

[0121] In certain embodiments, cooling the resulting Al-Si melt 204 can occur over a given period of time, which can be referred to herein as a “crystallization cooling ramp.” Utilizing a crystallization cooling ramp can increase the yield or size of the silicon crystals 210 formed during the silicon purification process 200. Thus, in various embodiments, a crystallization cooling ramp can result in improved silicon crystal 210 formation and, ultimately a purified silicon with a substantially reduced level of impurities as compared to the input silicon 202. For instance, the temperature can be cooled from the melting temperature (that which is sufficient to create the molten resulting Al-Si melt 204) to the crystallization temperature over a period of at least 3 hours. The crystallization cooling ramp can be longer than at least about 3 hours. In certain embodiments, the crystallization cooling ramp can be a period of up to about 200 hours. The crystallizationcooling ramp can be a period of up to 100 hours. In embodiments, the crystallization cooling ramp occurs over a period of between about 2 hours and 75 hours. In specific embodiments, the crystallization cooling ramp is between about 5 hours and about 50 hours. The crystallization cooling ramp can be about 5 hours, about 10 hours, about 15 hours, about 20 hours, about 25 hours, about 30 hours, about 35 hours, about 40 hours, about 45 hours, or about 50 hours. In various embodiments, the crystallization cooling ramp comprises a time period that is sufficient to permit completion of the reaction kinetics to permit the formation of purified silicon crystals 201 within the resulting Al-Si melt 204.

[0122] Following formation during cooling of the resulting Al-Si melt 204 over the crystallization cooling ramp period, the silicon crystals 210 can be separated from the cooled and still liquid resulting Al-Si melt 204 to form a resultant mother liquor 207.

[0123] In specific embodiments, after cooling of the resulting Al-Si melt 204 over the crystallization cooling ramp period, the silicon crystals 210 can be separated from the cooled and still liquid resultant mother liquor 207 via any method known in the art.

[0124] In certain embodiments, the resultant mother liquor 207 can be treated with the Al- Si purification process 100 disclosed herein, wherein the resultant mother liquor 207 is added as the starting Al-Si alloy 101.

[0125] In embodiments, and as further shown in the flow diagram of FIG. 8, the composition of the initial Al-Si melt 301 (such as the relative percent weight of silicon in the starting melt), the purity of the input silicon 202 (such as the ppmwt boron present within the input silicon), and the crystallization temperature 206 can be interdependent as further described in Example 3. Briefly, in embodiments, when a relatively pure input silicon 202 is provided, a high purity silicon purification process 400 can be used, wherein the initial Al-Si melt 201 comprises apurified Al-Si alloy, such as the purified Al-Si alloy 110 obtained following the Al-Si purification process 100. In alternate embodiments, when the input silicon 202 comprises a boron content of between about 15 ppmwt and 100 ppmwt, the optimized silicon purification process 300 can be utilized, wherein the composition of the optimized initial Al-Si melt 301 is determined according to the optimized melt curves discussed in Example 3.

[0126] FIG. 8 illustrates a block flow diagram 500 of a method of purifying silicon wherein the input silicon is a moderately pure or impure silicon 302. The block diagram provides an embodiment 500 that combines use of an optimized silicon purification process 300 with a high purity silicon process 400 to obtain a highly purified silicon product 410 when starting with a moderately pure or impure silicon 302. As can be seen, when the input silicon comprises a moderately pure or impure silicon 302, the input silicon can be subject to the optimized Si purification process 300 as discussed in Example 3 to create at least one moderately pure silicon crystal 315, at least one relatively pure silicon crystal 310, or a combination thereof. In embodiments, when one or more moderately pure silicon crystals 315 are precipitated, such moderately pure silicon crystals 315 can be used as the input silicon to undergo another pass 350 through the optimized silicon purification process 300. Such process can be repeated any number of times until relative pure silicon crystals 310 are precipitated from the optimized purification process 300.

[0127] As can be seen, the relatively pure silicon crystals 310 can then be passed 450 through the high purity silicon purification process 400, wherein the initial Al-Si melt comprises a purified Al-Si alloy 110, to produce a highly purified silicon 410. The highly purified silicon 410 can then be used, such as in the formation of solar panels or passed through another round of high purity silicon purification process 400. Such repeated passing through the high purity siliconprocess 400 can be repeated one or more times until the desired silicon purity is achieved. As can be seen, in forming the highly purified silicon 410, a remaining Al-Si melt 407 can be produced, wherein the remaining Al-Si melt 407 comprises more impurities than the purified Al-Si melt used as the initial Al-Si melt in the high purity Si purification process 400. In such embodiments, the remaining Al-Si melt 407 can be subject to the Al-Si purification process 100 described herein to produce a purified Al-Si alloy 110 for further use in the high purity Si purification process 400. Alternatively, the remaining Al-Si melt 407 can be used as the initial Al-Si melt for the optimized silicon purification process 300.

[0128] In specific embodiments, the silicon crystals 210 precipitated from the silicon purification process 200, 300, 400 can include less than about 0.50 ppmwt boron. In additional specific embodiments, the silicon crystals 210 can include less than about 0.45 ppmwt boron. In additional specific embodiments, the silicon crystals 210 can include less than about 0.40 ppmwt boron. In additional specific embodiments, the silicon crystals 210 can include less than about 0.35 ppmwt boron. In additional specific embodiments, the silicon crystals 210 can include less than about 0.30 ppmwt boron. In additional specific embodiments, the silicon crystals 210 can include less than about 0.25 ppmwt boron. In additional specific embodiments, the silicon crystals 210 can include less than about 0.20 ppmwt boron. In certain embodiments, the silicon crystals 210 can include less than about 0.15 ppmwt boron. In additional specific embodiments, the silicon crystals 210 can include less than about 0.10 ppmwt boron. The silicon crystals 210 can include about 0.09 ppmwt boron, about 0.08 ppmwt boron, about 0.07 ppmwt boron, about 0.06 ppmwt boron, about 0.05 ppmwt boron, about 0.04 ppmwt boron, about 0.03 ppmwt boron, about 0.02 ppmwt boron, or about 0.01 ppmwt boron. In certain embodiments, the silicon crystals 210 comprise about 0.001 ppmwt boron. The silicon crystals 210 comprise less than about 0.001 ppmwt boron.

[0129] In specific embodiments, at least about 25 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 30 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 35 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 40 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 45 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 50 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 55 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 60 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 65 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 70 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 75 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 80 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 85 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 90 wt.% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 95 wt.% ofboron present in the input silicon 202 can be removed to provide the silicon crystals 210. In additional specific embodiments, at least about 96 wt.%, 97 wt.%, 98 wt.%, or 99wt% of boron present in the input silicon 202 can be removed to provide the silicon crystals 210.

[0130] In specific embodiments, the silicon crystals 210 can include silicon in at least about 70 wt.%. In additional specific embodiments, the silicon crystals 210 can include silicon in at least about 75 wt.%. In additional specific embodiments, the silicon crystals 210 can include silicon in at least about 80 wt.%. In additional specific embodiments, the silicon crystals 210 can include silicon in at least about 85 wt.%. In additional specific embodiments, the silicon crystals 210 can include silicon in at least about 90 wt.%. In additional specific embodiments, the silicon crystals 210 can include silicon in at least about 95 wt.%. In additional specific embodiments, the silicon crystals 210 can include silicon in at least about 96 wt.%. In additional specific embodiments, the silicon crystals 210 can include silicon in at least about 97 wt.%. In additional specific embodiments, the silicon crystals 210 can include silicon in at least about 98 wt.%. In additional specific embodiments, the silicon crystals 210 can include silicon in at least about 99 wt.%.EXAMPLES

[0131] Examples are provided below to facilitate a more complete understanding of the invention. The following examples illustrate the exemplary modes of practicing the invention. However, the scope of the invention is not limited to specific embodiments disclosed in these Examples, which are for purposes of illustration only, since alternative methods can be utilized to obtain similar results.EXAMPLE 1

[0132] Exemplary “eutectic treatment” process description: Purification of an Al-Si melt with the goal to reduce its Boron and Phosphorus can be accomplished via the following steps: a. Melting the (B- and P- containing) Al-Si alloy or form an Al-Si- melt by heating and holding a mix of about 86-88%wt aluminum and about 12%- 14% wt silicon at a temperature ranging from about 800 to about 900°C, inclusive.-OR- adjusting the silicon content of an existing (B- and P- containing) Al- or Al-Si- melt to about 12 to about 14%wt of silicon (such as by adding metallurgical grade silicon, aluminum or other sources of silicon or aluminum) at a holding temperature of about 800 to about 900°C. This creates a primary Al-Si melt or a starting Al-Si melt. b. At a holding temperature of 800 to 900°C, adding titanium, strontium, or both to the Al-Si starting melt in an amount sufficient to achieve between about 500 and about 2000 ppmwt titanium, between about 500 and about 5000 ppmwt strontium, or a combination thereof. In certain embodiments, about 50 to about 500 ppmwt vanadium can be added into the starting melt. To ensure adequate contribution to the purification process and because unmolten or solidified material does not substantially contribute to purification, any materials or additives can be fully or substantially dissolved. c. Slowly cooling the obtained melt to temperatures below about 660°C with a ramping time between 5 and 50 hours, whereby precipitates are formed. In embodiments, the obtained melt is cooled to temperatures of at least 600°C. Theformed solid precipitates can comprise at least some of the Boron, Phosphorus, or both that were present in the starting melt. d. Separating the solid precipitates from the cooled yet still liquid aluminum-silicon melt, whereby an aluminum-silicon melt is obtained, which is low in concentration of boron and phosphorous. In embodiments, the purified melt is at or near a eutectic point. The purified melt can be solidified (such as to form sows or ingots), stored. Alternatively, the purified melt can be used in liquid form without intermediate solidification. e. In various embodiments, the purified melt can be used to purify silicon (e.g., metallurgical grade silicon, or similar). For example, the purified melt can be used in the process referred to in Example 2 as the “silicon purification using Al-Si melt.”

[0133] In various embodiments, the content of silicon in the primary or initial aluminumsilicon melt can be determined initially and adjusted to achieve about 12.6%wt Si with respect to the Al content. At such a concentration, the Al-Si comprises a low or reduced melting point which is close to the minimal melting point (e.g., the eutectic point, which occurs at about 577 °C, see FIG. 9). The melt can be cooled after addition of titanium, strontium, alternatives thereof (including any combination of the foregoing) to precipitate any compounds formed between impurities and the added Ti / Sr (for example, TiB2). Such compounds formed from impurities have a lower residual solubility (as compared to Al and Si) at such lower temperatures. Subsequently, the impurities can form precipitates, which can be removed from the melt, yielding a substantially pure Al-Si melt.

[0134] In embodiments, titanium, strontium, or both are added to the primary aluminumsilicon melt. Alternatively, the presence of titanium, strontium, or both in the melt can result from titanium and / or strontium being present in the aluminum source used to provide the primary aluminum-silicon melt. In the various embodiments disclosed herein titanium, strontium, or both promote the formation of impurity precipitates that can otherwise be difficult to remove from the silicon.

[0135] Certain embodiments utilize only one of either Ti or Sr for silicon purification. In addition, further elements, such as further transition metals or alkali earth metals, can be added to improve the precipitation or purification process. Non-limiting, exemplary additional elements include any one or more of V, Zr, Cr, Ba, Mg, and Ca. Each of the exemplary elements can be added solely or in combination with Sr, Ti, or both to assist with precipitation of impurities from the primary aluminum-silicon melt.

[0136] The separation of precipitates and cooled melt can be one part of the process of purifying the eutectic. If the precipitates were to remain in the melt, such precipitates would redissolve during the next temperature elevation (e.g., during the silicon purification process), which would release the previously precipitated impurities back into the melt.

[0137] The sequence of (a) providing the primary melt and (b) adjusting of the Ti / Sr and Si content can be interchangeable. Such steps can be performed in parallel or interchanged, as long as the target of joint melting of Al, Si and a quantity of Ti / Sr is reached at a temperature between about 800-900° C. Ti, Sr, or both can be dissolved at high temperature in the Al melt, and, following dissolution, the Ti, Sr, or both can form precipitates with certain impurities (e.g. as TiB2) during subsequent cooling. As can be seen, solid Ti, Sr, or both, which floats in the melt at lowertemperature, could not bind with impurities to form precipitates and, thus, would be ineffective asSi purification tools.

[0138] Additional Non-Limiting, Exemplary Protocol:

[0139] • Melt Al with about 8-14%wt Si at about 800 - about 900°C

[0140] • Dissolve about 800 to aboutl400 ppmwt Ti and about 1000 to about 5000 ppmwt Sr into the above melt.

[0141] • Optional additives include, but are not limited to: Ca, Mg, Ba, Cr, V, Zr,

[0142] • Slowly cool the obtained melt to about 580 - about 620°C over about 8 to about 48h to precipitate out impurities.

[0143] • Separate solids from the liquid. Exemplary methods for separating such solid precipitates from the liquid melt include, but are not limited to decanting, solidification and cutting, filtration, impelling of liquid salt flux and removing flux from melt.EXAMPLE 2

[0144] Exemplary process for “Silicon purification using Al-Si melt” under one embodiment:1. Obtain an Al-Si melt. Such an Al-Si melt can comprise an Al-Si alloy that was obtained according to the process described herein for removal of boron and phosphorus from the melt. The Al-Si melt can comprise an Al-Si melt that is substantially fee of boron, phosphorus, or both. In alternate embodiments (as described in more detail with reference to Example 3), the Al-Si melt can have a boron concentration that is greater than that of a purified Al-Si melt that was obtained from the boron and phosphorus purification process disclosed herein.2. Add input silicon that is to be purified (e.g., “input silicon” can include metallurgical grade silicon, a partially purified silicon which has already undergone a purification process, or a similar or known source of silicon) to the Al-Si alloy melt up to a total silicon content between about 30%wt and about 60%wt while increasing the melt temperature to values between about 900°C and about 1200°C respectively. Hold until everything is completely molten.3. Then the obtained melt can be cooled slowly to temperatures below about 800°C with a ramping time between about 5 and about 50 hrs. In embodiments, the obtained melt is cooled to temperatures of about 600°C or below. Such cooling of the obtained melt permits the formation of at least partially purified silicon crystals. In various embodiments, these at least partially purified silicon crystals are of higher purity than the input silicon. In certain embodiments, the at least partially purified crystals form and any previously associated impurities remain in the still liquid and residual Al-Si-melt.4. The solid silicon crystals can then be separated from the cooled and still liquid aluminum-silicon melt according to any of the various methods discussed within the present disclosure or otherwise apparent to one of skill in the art. Both separate portions (i.e., the partially purified crystals and the residual melt) can be further processed (as described below).5. In one embodiment, the separated partially purified silicon crystals can be re-melted and re-crystallized as described in steps 1 .) to 4.) until a desired purity grade is reached.6. The separated cooled and still liquid melt can be re-used in steps such as those described in 1.) to 4.) if its purity is still sufficient to have a desired purification effect, or it can be purified from boron and phosphorous as described under “Eutectic treatment”. Inembodiments, the separated, cooled, and still liquid melt can be re-used to purify any input silicon that comprises a boron or phosphorus content that is higher than the separated, cooled, and still liquid melt.EXAMPLE 3

[0145] As determined by model calculations, under certain circumstances, such as when the input silicon to be purified in the purification process comprises a comparatively high boron content (e. g., metallurgical grade silicon (“MG-Si”) which can be about 30ppmwt boron) it can be preferable to employ an initial or input Al-Si melt that is not highly purified. Briefly, in embodiments, a highly purified Al-Si melt (as generated in Example 1) can have a silicon content of about 12%; however, the silicon purification process (as discussed in more detail in Step 2 of Example 2, above) can require adding silicon to reach a total silicon content in the obtained or resulting melt of between about 30%wt and about 60%wt. Thus, when the input silicon comprises an MG-Si, if the initial Al-Si melt is highly purified with only about 12% silicon, a large amount of input MG-Si must be added to bring total concentration of silicon in the resulting melt to a value of between about 30%wt and about 60%wt (e.g., up to about 40%). Addition of such a large amount of MG-Si may overly contaminate the obtained melt, which could reduce the efficiency of the silicon purification process.

[0146] As such, it may be preferable to utilize an optimized input Al-Si melt 301 that comprises a silicon content greater than 12-14%, even if such an optimized input Al-Si melt 301 has a higher boron content as compared to a highly pure Al-Si melt. The following table shows one example when the input MG-Si contains 30 ppmwt B:

[0147] As used above, “optimum” refers to the conditions that will provide effective purification of silicon for a given input silicon. As can be seen, the optimum result depends on several factors at the same time. For instance, the optimum result can depend upon one or more of the following: the B-content of MG-Silicon, the B-content of the input Al-Si melt, and the Si- content of the input Al-Si-melt.

[0148] Similarly, with regard to the Al-Si melt, since the input Al-Si melt in certain embodiments results form an equilibrium achieved in the Al-Si-purification step, the B- and Si- contents of the melt cannot be independently chosen. Both can depend on temperature and the relative concentrations of one or more of Ti, Sr, and V that were added to the mixture of Al and Si.

[0149] The equilibrium concentration of silicon in such Al-Si melt is described by the Al- Si phase diagram in dependence of temperature (see FIG. 9).

[0150] For instance, an Al-Si melt with about 40% silicon (SI) is molten liquid at about 930°C and higher while a melt with about 28% silicon (S2) is liquid at about 800°C. If SI has a temperature of ~930°C and then is cooled to about 800°C it changes composition by crystallizing out a certain amount of pure silicon until the molten liquid is only about 28% silicon. Following the so called liquidus-curve, every temperature is linked to a certain silicon concentration.

[0151] Likewise, the boron concentration of an Al-Si melt with a given concentration of any one or more of Ti, V, and Sr can vary with temperature in a predictable manner. By way of non-limiting example, the boron concentration of an Al-Si melt comprising about 1400ppmwtTi, about lOOppmwt V, and about 5000ppmwt Sr will be about 12.7ppmwt at about 930°C, about2.95ppmwt at about 800°C, and as low as about 0.05ppmwt at temperatures close to 577°C (near eutectic point). In embodiments, boron can crystallize during cooling of an Al-Si melt in the form of TiB2 (in the presence of excess Ti), VB2 (in the presence of excess V) or both (in the presence of both Ti and V).

[0152] In certain embodiments, vanadium (V) can be employed to increase precipitation of boron. For instance, without being bound by theory the addition of vanadium can increase the speed or efficiency of boron precipitation from the Al-Si melt. Vanadium can be used in combination with Ti to increase precipitation or settling of TiB2. In certain embodiments, vanadium exhibits a stronger bond with boron as compared to Ti, which can result in faster precipitation. Without being bound by theory, vanadium can be added to a later point of the Al-Si purification process (such as after precipitation of TiB2 has begun) to promote agglomeration of formed TiB2 reaction products.

[0153] In various embodiments, it is possible to adjust the silicon and boron concentrations of an Al-Si melt by placing an initial Al-Si alloy composition to a specific end temperature (referred to herein as the “breakout temperature”) which gives fixed concentration values for boron and silicon linked to this temperature.

[0154] FIG. 10 shows curves of three different Al-Si melts that are 40% silicon (referred to herein as a “resulting melt” 204 of a silicon purification process step 200). The graph shows the effective B-concentration of the mix (“resulting melt” 204) using a given MG-Si as a function of the end temperature (or breakout temperature) of a preceding Al-Si purification step similar to 100 but with an individual, higher end temperature of the cooling ramp for the purified Al-Si in the mix. Each Al-Si melt curve was created with an input MG-Si with individual boron concentrations(input MG-Si with 50 ppmwt B (red); input MG-Si with 40 ppmwt B (blue); and input MG-Si with30 ppmwt B (grey)).

[0155] A black dot denotes the point along each curve that is associated with both (1) the lowest effective boron concentration in the mix being used as a “starting melt”, 204, and (2) the end temperature (or breakout temperature) of a preceding Al-Si purification step similar to 100 but with an individual, higher end temperature of the cooling ramp for the purified Al-Si which is used in the mix being used as a “starting melt”, 204. This point can represent the “optimum” or “best” condition for achieving an Al-Si resulting melt that contains 40% silicon.

[0156] The amounts of MG-Si and Al-Si melt to be combined must be calculated accordingly in a separate part of the same calculation and are not shown in the graph.

[0157] In various embodiments, the melt optimization by customized Al-Si inputs as described immediately above may only be useful for input silicon of certain ranges in boron content. For instance, an input silicon having lOOppmwt B can only be added to achieve a resulting Al-Si melt with 40% silicon by mixing 5kg of such input silicon into 95kg treated Al-Si melt which had a breakout temp of 931°C. This is practically almost the same as treating an Al-Si melt with 40% Silicon and then directly crystallizing silicon from it in one step. Furthermore, such impure input silicon would require an uneconomically high number of purification-passes while MG- Silicon with 30 to 50ppmwt Boron is readily available on the market.

[0158] On the other hand, for an input silicon with less than 15ppmwt boron the difference between “best possible eutectic” and optimized alloy is only ~0.5ppmwt. Such “optimization” seems unnecessary.

[0159] In embodiments wherein the input silicon for a given pass has more than about lOOppmwt B, an optimization as described before has lost its advantage and therefore an inputsilicon with less boron should be utilized. By contrast, in embodiments wherein the input silicon for a given pass is less than about 15ppmwt B, then the purest possible Al-Si meltl 10 from the Al- Si purification process, 100, can be utilized as the initial Al-Si melt 201. For embodiments with an input silicon therebetween, a melt optimization as described immediately above can be employed.

Claims

CLAIMSWhat is claimed is:

1. A method of purifying an aluminum silicon melt, the method comprising: forming an initial molten liquid, the molten liquid comprising a starting aluminum silicon melt and at least one metal additive; cooling the molten liquid to a precipitation end temperature to form a precipitate and a cooled molten liquid, wherein the precipitate comprises: an impurity, a derivative of the impurity, or a reaction product; and separating the precipitate from the cooled molten liquid to create a purified aluminum silicon melt, wherein the amount of the impurity in the purified aluminum silicon melt is less than the amount of the impurity in the initial molten liquid.

2. The method of claim 1, wherein the starting aluminum silicon melt comprises about 12% to about 14% wt of silicon.

3. The method of claim 1, wherein the step of forming the initial molten liquid comprises combining the metal additive with aluminum and silicon, wherein, after the time of combining, the metal additive, the aluminum, the silicon, or a combination thereof are in a liquid state.

4. The method of claim 1, wherein the step of forming the molten liquid comprises melting an alloy with silicon to form the starting aluminum silicon melt, wherein the alloy comprises aluminum and the metal additive.

5. The method of claim 1, wherein the molten liquid is held at a temperature of at least about 800° C prior to the step of cooling the molten liquid.

6. The method of claim 1, wherein the precipitation end temperature comprises any temperature between about 577°C and about 950°C.

7. The method of claim 6, wherein the precipitation end temperature is around 577°C.

8. The method of claim 1, wherein the precipitation end temperature is about the same as a eutectic point of the purified aluminum silicon melt.

9. The method of claim 1, wherein the step of cooling the molten liquid to the precipitation end temperature occurs over a cooling time period of at least about four hours.

10. The method of claim 9, wherein the cooling time period is up to about fifty hours.

11. The method of claim 1, wherein the at least one metal additive comprises titanium, strontium, vanadium, niobium, tantalum, calcium, barium, zirconium, chromium, magnesium or a combination thereof.

12. The method of claim 1, wherein the at least one metal additive comprises titanium, strontium, vanadium, or a combination thereof.

13. The method of claim 1, wherein the molten liquid comprises at least about 1,000 ppmwt titanium, up to about 5,000 ppmwt strontium, or a combination thereof.

14. The method of claim 1, wherein the impurity comprises boron, phosphorus, a derivative thereof, or any combination of the foregoing.

15. The method of claim 1 wherein the precipitate comprises the reaction product between the metal additive and at least one of boron and phosphorus.

16. The method of claim 1 wherein the reaction product comprises a boride, a phosphide, or a combination thereof.

17. The method of claim 1 wherein the step of separating the precipitate from the cooled molten liquid comprises: removing a top skin from the cooled molten liquid; centrifuging the cooled molten liquid, decanting the cooled molten liquid;filtering the precipitate from the cooled molten liquid; solidification of the cooled molten liquid into an ingot and cutting a solidified precipitate from the ingot; impelling a liquid salt flux into the cooled molten liquid followed by removal of a resultant flux; or a combination thereof.

18. The method of claim 1, further comprising adding at least about 50 ppmwt vanadium to the molten liquid.

19. A method of purifying silicon, the method comprising: forming a first melt that comprises an initial aluminum silicon melt and an input silicon; holding the first melt at a melting temperature until the initial aluminum silicon melt and the input silicon are substantially co-molten to form a resulting aluminum-silicon melt; cooling the resulting aluminum-silicon melt to a crystallization end temperature that is below a crystallization temperature, wherein the crystallization temperature is a temperature that depends upon a composition of the resulting aluminum-silicon melt and permits the formation of a plurality of silicon crystals and a mother liquor; and separating the silicon crystals from the mother liquor.

20. The method of claim 19, wherein the crystallization end temperature is above 577°C.

21. The method of claim 19, wherein the melting temperature is any temperature higher than a liquidus temperature given by the following Al-Si binary phase diagram for the first melt composition:

22. The method of claim 19, wherein the first melt comprises a total silicon content of up to about 60% wt.

23. The method of claim 19, wherein the initial aluminum silicon melt comprises a near eutectic aluminum silicon melt.

24. The method of claim 23, wherein the initial aluminum silicon melt comprises the purified aluminum silicon melt of claim 1.

25. The method of claim 23, wherein the input silicon comprises a relatively pure silicon, wherein the relatively pure silicon comprises about 15 ppmwt boron or less.

26. The method of claim 19, wherein the input silicon comprises a moderately pure or impure silicon, wherein:the moderately pure silicon comprises a boron concentration that is above about 1 ppmwt boron and up to about 70 ppmwt; and the impure silicon comprises a boron concentration that is above about 70 ppmwt.

27. The method of claim 19, wherein the step of cooling the impure aluminum-silicon melt to the crystallization end temperature occurs over a crystallization cooling time period of at least about five hours.

28. The method of claim 19, wherein the crystallization cooling time period is up to about fifty hours.

29. The method of claim 19, further comprising repeating the method of purifying silicon for n passes until a desired silicon purity is achieved, wherein the input silicon of each pass comprises the plurality of silicon crystals obtained in the immediately preceding pass.

30. The method of claim 19, wherein the step of forming the first aluminum-silicon melt comprises adding the input silicon to the aluminum silicon melt.

31. The method claim 19 wherein the step of separating the plurality of silicon crystals from the mother liquor comprises pouring off the mother liquor from the silicon crystals, filtering the silicon crystals from the mother liquor, centrifugation, or a combination thereof.

32. A method of purifying silicon, the method comprising: forming an initial molten liquid, the initial molten liquid comprising a starting aluminum silicon melt and at least one metal additive; cooling the initial molten liquid to a precipitation temperature to form a precipitate and a cooled molten liquid, wherein the precipitate comprises an impurity, a derivative of the impurity, or a reaction product;separating the precipitate from the cooled molten liquid to create a purified aluminum silicon melt, wherein the amount of the impurity in the purified aluminum silicon melt is less than the amount of the impurity in the initial molten liquid; forming a first melt that comprises the purified aluminum silicon melt and an input silicon; holding the first melt at a melting temperature until the initial aluminum silicon melt and the input silicon are substantially co-molten to form a resulting aluminum-silicon melt; cooling the resulting aluminum-silicon melt to a crystallization end temperature that is below a crystallization temperature, wherein the crystallization temperature is a temperature that permits the formation of a plurality of silicon crystals and a mother liquor; and separating the plurality of silicon crystals from the mother liquor.

33. The method of 32, wherein the step of separating the plurality of silicon crystals from the mother liquor comprises pouring off the mother liquor from the silicon crystals, filtering the silicon crystals from the mother liquor, centrifugation, or a combination thereof.

34. The method of claim 32, wherein the crystallization end temperature is above about577°C.

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