Method for removing interfering metals such as iron from glass

Abstract

The present invention relates to a method for producing glass by removing coloring ions by reduction, as well as to the products obtained by this method.

Description

[Technical field]

[0001] The present invention relates to a method for producing glass by removing coloring ions by reduction, as well as to the products obtained by this method. [Background technology]

[0002] Glass is made of sand (mostly SiO 2 ), and soda (Na 2 CO 3 ), lime (CaO / CaCO 3 ), magnesium oxide, magnesium carbonate, aluminum oxide, boron trioxide (B 2 O 3 ), potassium carbonate, potassium oxide, lead oxide, germanium oxide (GeO 2 ), phosphate, sodium oxide (Na 2 O), sodium hydroxide (NaOH), titanium dioxide (TiO 2 ), and other additives such as manganese, magnesium, mercury, and tungsten. Metals such as iron, chromium, manganese, and others tend to result in coloration of the glass. Iron oxide and chromium (II) oxide generally result in green glass, while sulfur, together with iron, can result in yellow to almost black glass. For some applications, such as bottles, coloration is desirable, but in other cases, clear glass is desired, for example, flat glass (windows, window shields, fireproof glass, Gorilla Glass), low iron glass (e.g., for aquariums, display cases, windows, and other applications where transparency is desired), high tech materials (e.g., optical components such as fiber optics, lenses), and chemicals such as sodium metasilicate.

[0003] Commonly encountered coloring ions are iron, chromium, manganese, copper, uranium, nickel, and cobalt. Often the raw materials already contain coloring ions, and therefore many methods have been developed to reduce the ion content, for example washing the raw materials with sequestering agents to remove iron and other ions, but this only removes ions present on the surface of the raw materials. It is understood that simply removing these ions from the surface may not be sufficient. Another technique is to use reducing conditions to convert Fe(III) to Fe(II), which can reduce coloration to some extent, but does not eliminate the iron, as it is not actually removed from the glass melt.

[0004] General information on glass production can be found in Wolfgang Trier: Glasschmelzofen-Konstruktion und Betriebsverhalten, Springer, Berlin 1984. It is known that there are two types of processes for producing glass, which generally use either a continuous glass melting tank or a pot furnace. The processes are described in https: / / www.schott.com / advanced_optics / english / capabilities / melting.html and can be summarized as follows:

[0005] Prior to melting, the raw materials (or batch) are prepared. The first step in this process involves weighing out the ingredients of the so-called batch recipe. Historically, crucible ovens or pot furnaces have been used for this melting process, where the individual steps in the glass melting process are performed in sequential order.

[0006] More recently, tank melting has been introduced, where the process steps are carried out continuously, which may offer advantages when processing glass for mass production, however, both melting processes are still used for glass melting today.

[0007] The process for making glass typically involves the following steps. (i) Melting / Smelting: A batch containing raw materials placed inside a furnace is heated to form a molten mass, which is then reacted with the raw materials to produce gaseous by-products (e.g. CO) 2 ) often results in the formation of bubbles.

[0008] (ii) Refining: Removal of air bubbles from the molten mixture. (iii) Homogenization: Stirring the molten mixture to be free of air bubbles. (iv) Casting & Hot Forming: The liquid glass is discharged from the feeder and formed into bars, rods, or blocks. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] Wolfgang Trier: Glasschmelzofen-Konstruktion und Betriebsverhalten, Springer, Berlin 1984 Summary of the Invention

[0010] The present invention relates to a method for producing glass by removing coloring ions by reduction, as well as to the products obtained by this method. Commonly used sand may contain up to 15% by weight of iron ions. To produce clear glass, usually only raw materials containing small amounts (<0.1%) of iron are used, which are expensive and may not always be available. Thus, the object of the present invention is to remove such impurities, which not only reduces the discoloration of the glass, but also allows a wider range of raw materials to be used in the production of clear glass.

[0011] In contrast to previously known methods for removing discoloration, the method of the present invention does not require costly removal of impurities from the raw materials, but allows the removal of undesirable metal ions after the components of the glass have been mixed and melted. As a result, the removal of undesirable metal ions is not only more thorough, but also less expensive, since the agents used as reducing agents in the present invention are generally readily and inexpensively available. Furthermore, the method of the present invention can be practiced with a wide range of currently used glass melting equipment and therefore can be practiced without costly capital investments in adapted hardware.

[0012] To achieve these objectives, the invention proposes treating the raw glass composition with one or more reducing agents, which can be added before, during or after melting of the raw glass composition or its components.

[0013] definition The terms "gas", "liquid" and "solid" as used herein generally refer to the respective aggregated states of the compounds at a temperature of 25°C and a pressure of 1 atmosphere, except for the "gaseous by-products" referred to herein, which refer to any compounds having a boiling point below the temperature of the molten glass composition, preferably between 400°C and 1720°C. To facilitate understanding of the term "gaseous by-products" referred to herein, it may be more preferably defined to refer to any compounds having a boiling point below 600°C, more preferably below 400°C. In the above, the boiling points are based on a pressure of 1 atmosphere.

[0014] Unless clearly indicated to the contrary, amounts specified herein as "%" refer to "% by weight" amounts. The terms "weight", "wt", and "mass" are used interchangeably herein.

[0015] In the present invention, specific compounds or components are referred to in the singular or plural form thereof. Unless expressly indicated otherwise, a reference in the singular form should be understood as a reference to one or more of the respective compound or component. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention relates to a method for producing glass by removing coloring ions by reduction, as well as to the products obtained by this method.

[0017] Method steps The method of the invention preferably comprises step (i) of preparing a molten raw glass composition by heating the raw glass composition or components of the raw glass composition.

[0018] It should be understood that any known method for preparing the raw glass composition can be used. The components of the raw glass composition can be melted separately and then the molten components can be mixed to form the raw glass composition. Alternatively, the components can be mixed at ambient temperature, such as 0° C. to 50° C., to form the raw glass composition, and the components are heated after mixing. Suitable components of the raw glass composition are described below.

[0019] The temperature and heating rate in step (i) are not particularly limited. However, from an economical point of view, the heating rate is preferably as fast as technically possible, more preferably in the range of 1°C / min to 50°C / min, even more preferably in the range of 2°C / min to 45°C / min, even more preferably in the range of 5°C / min to 40°C / min, and most preferably in the range of 10°C / min to 30°C / min. The temperature at which the raw material glass composition is heated is usually determined by the chemical composition of the raw material glass composition. This temperature is preferably in the range of 400°C to 1720°C, more preferably in the range of 800°C to 1700°C, even more preferably in the range of 1100°C to 1650°C, and even more preferably in the range of 1400°C to 160°C.

[0020] The method of the present invention further comprises the step (ii) of adding one or more reducing agents to the raw glass composition before, during or after melting in step (i). The one or more reducing agents can be added to the raw glass composition in any way. In particular, they can be added before, during or after melting in step (i). Preferably, they are added when the raw glass composition is in a molten state. However, the invention is not limited thereto. The temperature of the raw glass composition is not particularly limited, but the raw glass composition is preferably in a molten state at this temperature, preferably within the range indicated as the heating temperature in step (i).

[0021] Solid reducing agents (i.e. solid at 25° C. and 1 atm) can be added as solids or in the molten state (when heated above their melting point). Liquid reducing agents can be injected into the raw glass composition. A gaseous reducing agent, such as a gas mixture containing hydrogen and / or carbon monoxide, e.g., syngas, is preferably added to be bubbled through the molten raw glass composition. This approach has the added advantage that undesirable gaseous impurities of the raw glass composition, e.g., carbon dioxide, can be more easily and completely removed. As a result of the partial pressure difference, the carbon dioxide diffuses into the bubbles, e.g., air, hydrogen, or hydrogen / CO, and is removed from the melt by the growth and rise of the bubbles. This process is also used to homogenize the molten glass to prevent streaking and the resulting optical impairment. Furthermore, conventional vessels for forming molten glass compositions may already be equipped with suitable means for bubbling gas into the molten raw glass composition to remove gaseous impurities. In this case, the step of introducing the gaseous reducing agent into the molten raw glass composition does not require any modification to the already available vessels and does not require any additional steps, since only the type of gas used for bubbling needs to be changed, e.g., from air to hydrogen and carbon monoxide, or a gas mixture containing hydrogen and / or carbon monoxide.

[0022] Preferably, in step (ii), a precipitate is formed which comprises one or more selected from iron, chromium, manganese, copper, nickel, cobalt and / or uranium metals in an amount of preferably 20% by weight or more (preferably 35% by weight or more, more preferably 50% by weight or more, even more preferably 65% ​​by weight or more, most preferably 80% by weight or more) based on the total mass of the precipitate.

[0023] The process according to the invention optionally comprises a step (iii) of removing precipitates formed after steps (i) and (ii) from the molten glass composition. Depending on the selection of the reducing agent(s) and the metal ions to be removed, the addition of a reducing agent in the process of the present invention typically results in the formation of either a gaseous or solid by-product.

[0024] In the case of gaseous by-products, they can be removed from the molten glass composition without any specific means or can be accelerated by bubbling a gas, which may or may not be the same as the gaseous reducing agent, into the molten glass composition. Gaseous by-products are usually formed when using gaseous reducing agents such as hydrogen or carbon monoxide or mixtures thereof. Products formed by adding one or more reducing agents, which may be gaseous at the temperature of the molten glass composition, include Mn 2 (CO) 10 , Fe(CO) 5 , Co(CO) 4 , Ni(CO) 4 , and Ru(CO) 5 Thus, when a gaseous reducing agent such as hydrogen or carbon monoxide or a mixture thereof is used, the method can be used to obtain Mn 2 (CO) 10 , Fe(CO) 5 , Co(CO) 4 , Ni(CO) 4 , and Ru(CO) 5 and mixtures thereof, are allowed to desorb from the molten glass composition.

[0025] On the other hand, the use of reducing agents may result in the formation of reduction products of metal ions, which do not dissolve or dissolve only to a limited extent in the molten glass composition. Such reduction products usually precipitate from the molten glass composition and can be collected at the bottom of the vessel holding the molten glass composition. Examples of such reduction products include, but are not limited to, Fe, Cr, Mn, Cu, Ni, Co, and / or U. Thus, when using one or more reducing agents selected from aluminum, magnesium, sodium, silicon, hydrogen, carbon monoxide, potassium, lithium, calcium, strontium, barium, gallium, germanium, boron, or any combination thereof, preferably including hydrogen, and optionally also electricity, the method preferably includes removing the precipitates formed after steps (i) and (ii) from the molten glass composition.

[0026] It should be understood that any gaseous and non-gaseous by-products, such as reduction products of metal ions that are not soluble or are only soluble to a limited extent in the molten glass composition, are removed in the present method, particularly while the glass composition is in a molten state. Thus, in accordance with the subject matter of the present invention, it is not necessary to cool the molten glass composition to remove the by-products, such as by separating a solidified glass phase and a solidified by-product phase. Rather, the method can be carried out in a continuous manner without the need to solidify the glass composition to remove the by-products. As a result, the present method is not only more cost-effective, but also consumes less energy and is more environmentally friendly.

[0027] It should further be appreciated that the use of reducing agents other than CO, and optionally other than hydrogen, preferably results in the formation of non-gaseous by-products, more preferably solid by-products (also referred to herein as precipitates), even more preferably in the form of particles. The solid by-products preferably have a density higher than that of the molten glass composition to enable precipitation of the solid by-products.

[0028] The removal of metals by precipitation can result in the formation of particles, preferably iron particles, on the bottom of the vessel. The precipitates can be removed during maintenance or by a second feeder. In the case of pot furnaces, usually only the top glass mold is used and the bottom glass mold containing the precipitate is discarded.

[0029] The precipitate or precipitates removed in step (iii) usually comprise one or more selected from iron, chromium, manganese, copper, nickel, cobalt and / or uranium metals, preferably at least 20% by weight (preferably at least 35% by weight, more preferably at least 50% by weight, even more preferably at least 65% by weight, most preferably at least 80% by weight), based on the total mass of the precipitate. The precipitate or precipitates removed in step (iii) are preferably not related to potential precipitates of the glass that would be formed even without the use of the reducing agents mentioned herein. Such precipitates may be present, for example, because one or more of the components of the glass are not dissolved during the preparation of the glass or because two or more compounds used in the glass preparation react with each other to form a precipitate. Such precipitates may also be removed in step (iii) essentially when removing precipitates containing reduced metals, but the gist of the present invention is the removal of precipitates containing these metals formed by the reduction of metal ions and, optionally, the reduction of metals by the addition of one or more reducing agents. Thus, the precipitate or precipitates removed in step (iii) preferably refer only to precipitates formed in the method of the invention compared to a similar method which differs only in that no reducing agent or agents are added to the raw glass composition. In other words, the precipitate or precipitates removed in step (iii) preferably refer only to precipitates formed in the method of the invention by carrying out step (ii). However, this does not exclude the possibility that other solid substances may be removed (intentionally or unintentionally) together with (or simultaneously with) these precipitates.

[0030] Thus, in a preferred embodiment, step (iii) may also be referred to as "removing one or more metals from the molten glass composition". It should be understood that such metals are metals that are formed by using one or more reducing agents (in step (ii)). Furthermore, it should be understood that this term also does not exclude the simultaneous removal of other solid materials from the molten glass composition.

[0031] It is therefore a gist of the present application that depending on the selection of the reducing agent(s) and the metal ions to be removed, the addition of a reducing agent in the process of the present invention preferably results in the formation of gaseous and / or solid by-products.

[0032] In a further preferred embodiment, the present invention provides a method for producing a pharmaceutical composition comprising the steps of: (i) preparing a molten raw glass composition, preferably by heating the raw glass composition or components of the raw glass composition; (ii) adding one or more reducing agents to the raw glass composition before, during, or after melting in step (i), where the reducing agents are one or more selected from aluminum, magnesium, sodium, silicon, hydrogen, carbon monoxide, potassium, lithium, calcium, strontium, barium, gallium, germanium, and boron, or any combination thereof, and where adding the one or more reducing agents results in the formation of gaseous and / or solid by-products; and (iii) optionally removing from the molten glass composition any precipitates formed after steps (i) and (ii), wherein the content of one or more ions selected from iron ions, chromium ions, manganese ions, copper ions, nickel ions, cobalt ions, and uranium ions in the glass composition is reduced by 50% by weight or more compared to their content in the raw glass composition, and wherein the one or more reducing agents can be added before, during, or after melting of the raw glass composition or components thereof; The present invention relates to a method for producing a glass composition comprising the steps of:

[0033] The method may include any additional steps commonly used in the manufacture of glass compositions, for example, the method may further include a step (iv) of producing one or more selected from flat glass, window glass, container glass, and optical glass from the molten glass composition.

[0034] In one embodiment of the method of the present invention, post-consumer glass, such as recycled glass, can be used as the glass composition in step (i). This embodiment provides a wide range of potential starting materials. Moreover, even when using glasses containing different types of metal ions resulting in different colors, the method of the present invention is still suitable for providing transparent glass as the final product. Thus, it can provide a means for recycling mixtures of different types of glasses that would otherwise be very difficult to separate and / or recycle.

[0035] The present invention further allows the recycling of glass fiber-containing materials such as printed circuit boards. Circuit boards usually contain large amounts of glass fibers and certain amounts of metals such as Fe, Cr, Mn, Cu, Ni, and Co in spatial arrangements and ratios that make their recycling economically and technically very difficult. In the present invention, such circuit boards can be used as glass sources, and the metals to be separated can be separately recovered and then recycled for use in other industries. Any organic components such as any plastics (e.g., carbon-containing components) of the circuit boards are preferably removed by incinerating the circuit boards before use in the present invention. Alternatively, such circuit boards can be used in combination with an oxidation process to burn off any plastic parts.

[0036] Thus, especially when using more non-traditional raw materials such as circuit boards, the metal ions removed by the method of the present invention can also include precious metals such as rhodium, ruthenium, osmium, iridium, platinum, rhenium, palladium, mercury, silver, and gold.

[0037] In addition to the above, it is contemplated to use different reducing agents sequentially to achieve sequential removal of specific metal ions. This sequential removal can be achieved by first introducing a weaker reducing agent to reduce the precious metal ions, removing these precious metals from the glass composition, and then introducing a stronger reducing agent to reduce the base metals. This aspect of the invention can be implemented, for example, by using a circuit board (e.g., the original board or the incinerated board) as the first reducing agent, and then introducing a stronger reducing agent, preferably aluminum, to reduce the base metals. In this way, aluminum-silicate glass could be produced with the Si and Al added thereby.

[0038] Raw Glass Composition As known to those skilled in the art, a wide range of different chemical compositions can be made into glasses. Different formulations affect the mechanical, electrical, chemical, optical, and thermal properties of the resulting glass. Since there is no single chemical composition that characterizes all glass types, the definition of the chemical composition of the raw glass compositions used in the present invention (and the resulting glass compositions according to the present invention) is not particularly limited.

[0039] A typical glass comprises a former, a flux, and a stabilizer. The former constitutes the largest proportion of the components to be melted. In a typical soda-lime-silica glass, the former is silica, which is often introduced in the form of sand. The flux lowers the temperature at which the former melts. Commonly used fluxes are sodium carbonate and potassium carbonate. The density of potash glass is usually slightly higher than that of soda-lime glass. The stabilizer is preferably added to increase the strength and water resistance of the glass. An example of a stabilizer for glass compositions is calcium carbonate.

[0040] It should be understood that some components of the glass compositions are used as starting materials in the form of carbonates. When glass compositions prepared from such carbonates are heated, the glass compositions are typically heated to a temperature sufficient to convert the carbonates to their respective oxides, during which carbon dioxide gas is formed in the process and is then typically removed from the molten glass composition. The glass compositions identified herein are referred to by the amount (calculated or measured) of each metal oxide contained therein.

[0041] Typical soda-lime-silica glass, commonly used for bottles and windows, typically contains 70-75% by weight silica, 10-15% by weight sodium oxide, 4-12% by weight calcium oxide, 0.05-2% by weight aluminum oxide, 0.01-1% by weight potassium oxide, 0.1-5% by weight MgO, and up to 0.5% by weight iron oxide.

[0042] In contrast, glasses commonly used in laboratory or heating equipment generally contain higher amounts of silica, as well as boron oxide, and lower amounts of sodium oxide and calcium oxide.

[0043] The chemical composition of the raw material glass composition used in step (i) is not particularly limited, but from the viewpoint of improving properties such as transparency, thermal conductivity, thermal expansion coefficient, tensile strength, compressive strength, or refractive index, it preferably contains, in weight % based on the total weight of the glass composition, 30 to 100% silica, 15% or less sodium oxide, 15% or less calcium oxide, 10% or less aluminum oxide, 15% or less potassium oxide, 5% or less MgO, 20% or less iron oxide, 70% or less lead oxide, 15% or less boron oxide, 15% or less rare earth metals, 15% or less germanium oxide, and 5% or less phosphorus pentoxide. Optionally, the chemical composition of the raw glass composition used in step (i) may contain up to 15% in total of oxides of Li, Rb, Cs, Be, Sr, Ba, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cf, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Ga, As, In, Sn, Sb, Te, Tl, Bi, Ac, Th, Pa, U, and / or Pu.

[0044] Pure silica glass typically has a melting point of about 1720° C., but glasses containing other components may have melting points as low as 400° C. Therefore, the melting point of the raw material glass composition used in step (i) of the present invention is preferably in the range of 400° C. to about 1720° C.

[0045] The raw glass composition in step (i) can be obtained by mixing and melting the respective components of the raw glass composition separately or together, or by simply melting a raw glass composition that has been pre-prepared or is derived from an already used glass, such as a post-consumer glass.

[0046] One or more reducing agents The type of reducing agent or agents is not particularly limited and includes any material suitable for reducing the metal ions to be removed from the raw glass composition. Examples of reducing agents include aluminum, magnesium, sodium, silicon, hydrogen, carbon monoxide, potassium, lithium, calcium, strontium, barium, gallium, germanium, boron, or any combination thereof, and electrolysis. Preferred examples of reducing agents include aluminum, magnesium, sodium, silicon, hydrogen, carbon monoxide, potassium, lithium, calcium, strontium, barium, gallium, germanium, boron, or any combination thereof. It should be understood that any of these may be used alone or in any combination with one or more other reducing agents. For example, an alloy of one or more of the above compounds may be used. Preferred reducing agents are carbon monoxide (CO), hydrogen (H 2 ), aluminum (Al), silicon (Si), magnesium (Mg), sodium (Na), or any combination thereof. Additionally, precursors of any of the above reducing agents can be used, provided that they are capable of forming one or more of the above reducing agents.

[0047] The reducing agent is preferably added after heating the raw glass composition to form the molten raw glass composition. As used herein, the term "reducing agent" preferably does not include carbon. Furthermore, as used herein, the term "reducing agent" preferably includes any CO and / or H that may be formed in the molten glass composition due to the presence of a carbon source and moisture in the molten glass composition. 2 Therefore, CO and / or H 2 When any mixture containing these gases is given as an example of a "reducing agent", these are preferably CO and / or H 2 It should be understood that the term refers only to CO and / or H, or any mixture containing these gases that is introduced into the molten glass composition after the raw glass composition has been heated to the temperatures disclosed herein. 2Any reducing agent other than, or any mixture containing these gases, may be added prior to melting the raw glass composition in step (i) and / or may be added in step (ii).

[0048] Without wishing to be bound by theory, it is assumed that the use of the reducing agents described above usually results in the reduction of the metal ions to be removed, typically to the metal or respective metal carbonyl. Preferably, the reducing agent reduces at least one of the metal ions to be removed to the metallic state, i.e., to an oxidation state of 0.

[0049] Electrolysis can also be used alone or in combination with one or more of the reducing agents disclosed herein. Electrolysis is typically performed by applying a voltage of about 0.5 to 50 V between two electrodes that are placed in the molten glass composition. The molten glass can be circulated between the electrodes. To aid in this circulation, the distance between the electrodes is preferably greater than the electrochemically standard 1 cm, for example anywhere in the range of 20 cm to 2 m, preferably 50 cm to 1.5 m, more preferably 80 to 100 cm, even more preferably 90 to 110 cm, and even more preferably about 1.0 m. As a result of the greater distance between the electrodes, the absence of water as a solvent, and operating at high temperatures, the voltage between the electrodes is high compared to standard electrode potentials. When using electrolysis, the reduced metal ions typically precipitate on one or more cathodes. Additionally, the voltage can be adjusted to remove certain types of metal ions. A similar process is the Hall-Erut process, which produces aluminum from a melt of cryolite and aluminum oxide at 2072 °C. Additionally, the sequential removal of metal ions can be achieved by electrolysis, for example by varying the voltage.

[0050] The amount of reducing agent is determined by the amount of metal that must be removed. After determining the total molar concentration of the metal to be removed (e.g., preferably using energy dispersive X-ray spectroscopy (EDX) as shown in the experimental examples), the minimum amount of reducing agent required can be calculated. In such cases, an excess of reducing agent is often used, especially when it can be easily removed from the product, as in the case of gaseous reducing agents. However, when quantitative removal of disturbing metals is not required, it is also possible to use slightly less reducing agent than is necessary to completely remove the metal to be removed.

[0051] The solid reducing agent can be added as a powder, granules, or rod-shaped members. Rod-shaped members are preferred from the viewpoint of avoiding oxidation of the reducing agent during addition. On the other hand, powders may be preferred if a higher reaction rate is desired. Such powders usually have a volume average particle size, as determined by laser diffraction, in the range of 10 nm to 1 mm, preferably 50 nm to 0.5 mm, more preferably 100 nm to 0.2 mm, and even more preferably 500 nm to 100 μm. Granules provide a good balance of both effects. Such granules usually have a particle size, as determined by image analysis, of more than 1 mm and up to 50 mm.

[0052] Metal ion or ions removed by the method of the present invention The metal ion or ions removed by the method of the present invention include, but are not limited to, one or more selected from iron, chromium, manganese, copper, nickel, cobalt, and uranium ions. It should be understood that these ions can be in any oxidation state typically encountered in molten glass compositions. For example, iron can be Fe 2+ and / or Fe 3+ The reducing agent used in the process of the invention is usually selected so that the metal ion or ions to be removed are reduced to their respective oxidation state of 0. The oxidation state of 0 can be represented by the respective metal(s) and / or metal carbonyl(s).

[0053] As will be appreciated by those skilled in the art, some of the metal ions to be removed, after reduction to oxidation state 0, may form carbonyl compounds that have a boiling point lower than the temperature at which the molten glass composition of the present invention is held. Thus, carbonyl compounds may be formed that evaporate from the molten glass composition, especially when the reducing agent or agents include CO. The removal of these carbonyl compounds can be facilitated and increased by introducing one or more gases into the molten glass composition, usually by bubbling through the bottom or sidewall of the vessel in which the molten glass composition is held. The one or more gases may or may not include CO and optionally hydrogen.

[0054] When using a reducing agent or agents other than CO, the metal ion or ions to be removed are preferably reduced to their metallic form.

[0055] [ka]

[0056] Due to their low solubility, these metals usually precipitate in the molten glass composition. As a result, preferably metal particles are formed. These metal particles usually have a volume average particle size, determined by laser diffraction, between 1 μm and 100 μm. They are usually spherical, possibly with a polycrystalline structure. Iron (7.9 g / cm 3 ) of the metal to be removed, such as a glass melt (e.g. 2.5 g / cm 3 ), the particles settle out of the molten glass composition. The precipitate formed after introduction of the one or more reducing agents preferably comprises one or more selected from iron, chromium, manganese, copper, nickel, cobalt, and / or uranium metals, preferably at least 20 wt. % (preferably at least 35 wt. %, more preferably at least 50 wt. %, even more preferably at least 65 wt. %, and most preferably at least 80 wt. %), based on the total mass of the precipitate.

[0057] Glass composition obtained by the method of the present invention As a result of using the methods of the present invention, not only can product glass compositions be obtained at lower costs than previously possible, but the products are also believed to be superior in transparency, thermal conductivity, coefficient of thermal expansion, tensile strength, compressive strength, and / or refractive index to glass products obtained by state of the art methods.

[0058] The chemical composition of the glass composition obtained by the method of the present invention may be the same as that of the raw material glass composition, except that the concentration of one or more ions selected from iron ions, chromium ions, manganese ions, copper ions, nickel ions, cobalt ions, and uranium ions is reduced. Preferably, in the glass composition obtained by the method of the present invention, the concentration of at least one of iron ions, chromium ions, manganese ions, copper ions, nickel ions, cobalt ions, and uranium ions is less than 1.0% by weight, preferably less than 0.5% by weight, more preferably less than 0.2% by weight, even more preferably less than 0.1% by weight, even more preferably less than 0.5% by weight, and most preferably less than 0.2% by weight. More preferably, the total concentration of iron ions, chromium ions, manganese ions, copper ions, nickel ions, cobalt ions, and uranium ions is less than 1.0% by weight, preferably less than 0.5% by weight, more preferably less than 0.2% by weight, even more preferably less than 0.1% by weight, even more preferably less than 0.5% by weight, and most preferably less than 0.2% by weight.

[0059] By maintaining the concentration of one or more ions selected from iron ions, chromium ions, manganese ions, copper ions, nickel ions, cobalt ions, and uranium ions within these ranges, properties such as transparency, thermal conductivity, thermal expansion coefficient, tensile strength, compressive strength, or a specific refractive index can be improved.

[0060] Use according to the invention The present invention also relates to the use of one or more reducing agents to reduce the concentration of one or more ions selected from iron ions, chromium ions, manganese ions, copper ions, nickel ions, cobalt ions, and uranium ions in a molten glass composition.

[0061] The present invention further relates to the use of one or more reducing agents to increase the transparency and / or reduce the coloration of a glass composition. In these aspects of the invention, the reducing agent is preferably one or more selected from aluminum, magnesium, sodium, silicon, hydrogen, carbon monoxide, potassium, lithium, calcium, strontium, barium, gallium, germanium, boron, or any combination thereof, and electrolysis, preferably one or more selected from aluminum, magnesium, sodium, silicon, hydrogen, carbon monoxide, and electrolysis, or any combination thereof, more preferably one or both selected from hydrogen and carbon monoxide.

[0062] More preferably, the reducing agent is silicon. Even more preferably, the reducing agent is electrolysis, and the voltage applied to the molten glass composition is preferably 50V or less, more preferably 10V or less.

[0063] It should be understood that the (preferred) features of the method of the invention are also applicable to the use according to the invention, in particular the features indicating the type of reducing agent, the temperature at which the reduction is carried out and the type of glass composition. EXAMPLES

[0064] The present invention may be better understood by reference to the following examples, which represent specific embodiments of the invention and are not intended to limit the scope of the invention.

[0065] Working Example method: Batches were prepared from reagent-grade chemicals, all of which are assumed to convert to equal amounts of oxides after decomposition. Batches (100 g) were mixed in a ball mill (Retsch Planeten-Kugelmuhle PM 100) for 1 h, placed in crucibles (Pt / Ir-90 / 10-200 mL) and heated to 1450 °C for 2-3 h in an electric resistance furnace (Nabertherm LHTCT 01 / 16). Bulk glasses were prepared by pouring the homogeneous melt into preheated steel molds and immediately transferring it into a muffle furnace (Nabertherm Muffelofen L 5 / 11) preheated to 650 °C and annealing at 650 °C for 2 h.

[0066] Glass transparency The transparency of the glass is defined as the absorbance at 380 nm. The absorbance at 380 nm was determined by UV / Vis / NIR spectroscopy. A glass plate with a thickness of 1 cm (d=1 cm) was placed in a spectrometer and the absorbance was measured (Lambda 950 UV / Vis / NIR spectrometer PerkinElmer).

[0067] Glass composition The composition of the glasses was determined by EDX (energy dispersive X-ray spectroscopy). Samples were placed in an EVO 50 XVP (Zeiss) with an EDX-Unit XFlash detector 4010 (Bruker axs). Unless otherwise indicated, the respective substance contents / amounts are given in weight % based on the total mass of the respective components.

[0068] Example 1

[0069] [Table 1]

[0070] Example 2

[0071] [Table 2]

[0072] Example 3

[0073] [Table 3]

[0074] Example 4

[0075] [Table 4]

[0076] Example 5

[0077] [Table 5]

[0078] Example 6

[0079] [Table 6]

[0080] Example 7

[0081] [Table 7]

[0082] Example 8

[0083] [Table 8]

[0084] Example 9

[0085] [Table 9]

[0086] Example 10

[0087] [Table 10]

[0088] Example 11

[0089] [Table 11]

Claims

1. A method for producing a glass composition comprising the steps of: (i) preparing a molten raw glass composition by heating a raw glass composition or components of the raw glass composition; (ii) adding one or more reducing agents to the raw glass composition or components of the raw glass composition before melting in step (i), to the raw glass composition or components of the raw glass composition during melting in step (i), or to the molten raw glass composition after melting in step (i), the reducing agents being one or more selected from aluminum, magnesium, sodium, silicon, hydrogen, carbon monoxide, potassium, lithium, calcium, strontium, barium, gallium, germanium, boron, or any combination thereof, whereby the addition of the reducing agents reduces metal ions to be removed to an oxidation state of zero and results in the formation of gaseous by-products that are gaseous at a temperature of the molten raw glass composition and / or solid by-products that have a density higher than the density of the molten raw glass composition and that precipitate from the molten raw glass composition; (iii) removing gaseous and / or solid by-products formed after steps (i) and (ii) from the molten raw glass composition, wherein the content of one or more ions selected from iron ions, chromium ions, manganese ions, copper ions, nickel ions, cobalt ions, and uranium ions in the glass composition is reduced by 50 wt. % or more relative to their content in the raw glass composition; The above method comprising the steps of:

2. 2. The method of claim 1, wherein the reducing agent is one or both selected from hydrogen and carbon monoxide.

3. The method of claim 2 , wherein the reducing agent is silicon.

4. 4. The method according to claim 1 , wherein the content of one or more ions selected from iron ions, chromium ions, manganese ions, copper ions, nickel ions, cobalt ions and uranium ions in the glass composition is reduced by at least 70 wt.-%, preferably at least 90 wt.-%, relative to their content in the raw glass composition after step (iii).

5. 5. The method according to claim 1 , wherein the content of iron ions in the glass composition is reduced by at least 50 wt.-%, preferably 70 wt.-%, even more preferably 90 wt.-% relative to the content of iron ions in the raw glass composition after step (iii).

6. The method according to any of the preceding claims, wherein the "raw glass composition components" used in step (i) are one or more types of glass, preferably including recycled glass.

7. The method of any of claims 1 to 6, further comprising the step (iv) of producing one or more selected from glass sheets, window glass, container glass, and optical glass from the molten raw glass composition.

8. The method of any of claims 1 to 6, wherein one or more gases are introduced into the molten raw glass composition.

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