Glass production method with alternative raw materials

Abstract

The present invention relates to a method for producing silicate glass from natural silicate rocks. The natural silicate rocks comprise alkalis and earth-alkalis at a level of equal to or greater 5wt%, preferably 10wt%, preferably 15wt%, more preferably 20wt%, even more preferably 25% by weight of the total composition of the natural silicate rocks and comprise at least one metal and / or metalloid elements (M) selected from the group consisting of Fe, Co, Cr, Ni, V, Sb, Zn, Mn, Sn, Bi, Pb, Ag, Cu, W, Nb, Mo and mixtures thereof. The amount of at least one metal and / or metalloid elements (M), is lowered by the method comprising the steps of : a) melting the natural silicate rocks to obtain a silicate melt; b) performing a chemical reaction to reduce the silicate melt to precipitate a metal phase enriched in the metal and / or metalloid elements; c) separating at least a part of the metal phase from the silicate melt to obtain a purified silicate melt; d) preferably, performing an oxidation treatment on the purified silicate melt to obtain a highly purified silicate material; and e) using the purified silicate melt and / or preferably the highly purified silicate material, as component for silicate glass.

Description

Glass production method with alternative raw materialsTechnical field

[0001] The present invention relates to a method for producing silicate glass from natural silicate rocks as alternative raw materials.Background art

[0002] As for the entire industry, the glass industry is faced with the obligation of drastically reducing its CO2 emissions. Hence, use of raw materials, resource recycling and greenhouse gas reduction, are becoming increasingly important topics to be addressed.

[0003] Glass is usually prepared by melting in a furnace, raw materials including silica and at least one silica flux such as sodium carbonate, and at least one alkaline earth (to give the glass resistance to hydrolysis) such as limestone (CaCO3) and dolomite (CaMg(CO3)2). During fusion, the carbonates release carbon dioxide, the bubbles of which contribute to the mixing of the mass being fused. In a conventional process for manufacturing soda-lime glass, the CO2 emission from the raw materials is generally around 20% of the total mass of the raw materials used. Carbon dioxide being a greenhouse gas, it is desirable to develop glass manufacturing processes that generate as little CO2as possible for environmental reasons, while leading to good quality glass and at an acceptable cost.

[0004] In addition to the release of CO2directly during the melting process of the batch of raw materials, it is therefore important to consider the glass manufacturing process as a whole, taking into account other factors such as the cost of raw materials, their transport or the energy cost of making said raw materials available.

[0005] One solution is therefore to address the quality and quantity of the glass manufacturing material. One route would be to increase the amount of glass cullet recycled into the glass production process. Another route would be to find sources of alternative raw materials.

[0006] At present, most of available natural or industrial waste materials including glass cullets, are discarded without being recycled. Indeed, such materials typically contain external foreign matter, a coloring component and / or an unnecessary component. It is difficult to use such materials as glass raw material, since the obtained glass may have manufacturing drawbacks or undesired properties such as coloring, opacity,...

[0007] When looking for alternative sources of raw materials, it is possible to find other silicate materials in nature, that contain suitable oxide components (e.g. CaO, MgO and alkalis) and that could replace the traditional carbonated raw materials dedicated to glass production. However, other alternative materials usually contain unacceptable impurities and / or excessive levels of certain elements that make it not possible to include at all and / or in high quantities into the glass manufacturing process.

[0008] The object of the present invention is therefore to contribute to solving such a technical problem by proposing a silicate glass manufacturing process for which the CO2emissions are effectively reduced based on all the glass forming steps leading to the formation of silicate glass. Hence, there is still a need to find a method to use or to increase the amount of uncarbonated materials in glass industry that are currently not appropriate because of their high contents in unnecessary components and / or coloring elements (mainly transition elements like iron, chromium and cobalt).

[0009] A further object of the present invention is have the glass manufacturing industry to participate to the European Union ambitious goal to transition from linear to circular economy, in the implementation of an industrial side stream, traditionally branded as waste, being the raw material for the formation of the next product.Summary of the present invention

[0010] The present invention relates to a method for producing silicate glass from natural silicate rocks. The natural silicate rocks comprise alkalis and earth-alkalis at a level of equal to or greater 5wt%, preferably 10wt%, preferably 15wt%, more preferably 20wt%, even more preferably 25% by weight of the total composition of the natural silicate rocks and comprise at least one metal and / or metalloid elements (M) selected from the group consisting of Fe, Co, Cr, Ni, V, Sb, Zn, Mn, Sn, Bi, Pb, Ag, Cu, W, Nb, Mo and mixtures thereof.

[0011] The method to lower the amount of at least one metal and / or metalloid elements (M), comprising the following steps in the following order : a) melting the natural silicate rocks to obtain a silicate melt; b) performing a chemical reaction to reduce the silicate melt to precipitate a metal phase enriched in the metal and / or metalloid elements; c) separating at least a part of the metal phase from the silicate melt to obtain a purified silicate melt;d) preferably, performing an oxidation treatment on the purified silicate melt to obtain a highly purified silicate material; and e) using the purified silicate melt and / or preferably the highly purified silicate material, as component for silicate glass.

[0012] Natural silicate rocks typically comprise from 30% to 99% by weight of SiO2. Preferably, the natural silicate rock is a magmatic rock comprising from 30% to 90% by weight of SiO2; more preferably the natural silicate rock is a basalt rock comprising from 41 % to 57% by weight of SiO2.

[0013] Natural silicate rocks have a concentration of at least one metal and / or metalloid element in oxide-based mass% or mass ppm equivalent being [MO]before and the purified silicate melt, and / or preferably the highly purified silicate material, has a concentration of the at least one metal and / or metalloid element in oxide-based mass% or mass ppm equivalent being [MO]after. For at least one metal and / or metalloid element, it is preferred that the ratio of [MO]after / [MO]before is equal to or lower than 0.850, preferably equal to or lower than 0.700, preferably equal to or lower than 0.500, preferably equal to or lower than 0.250; preferably equal to or lower than 0.100 preferably equal to or lower than 0.010, more preferably equal to or lower than 0.001 . Preferably the metal and / or metalloid element is selected from Fe oxide, Co oxide, Cr oxide, Ni oxide and mixtures thereof.

[0014] The reduction treatment of step (b) uses preferably one or more reducing agent(s) comprising one or more of elements selected from the group consisting of C, Al, Si, Ca, Ti, N, Fe and H2and mixtures thereof; and is preferably selected from C, Al, Si, SiC, Ca, Ca-Si, Ti, H2JCO, Fe — Si alloy, Ca — Si alloy, CH4, NH3, and mixtures thereof; more preferably the reducing agent is one or more selected from C, Ca-Si, SiC, CO and mixtures thereof. Typical treatment temperature in the reduction treatment of step (b) is from 1300°C to 1800°C.

[0015] The oxidation treatment of step (d) uses preferably an oxidizing gas as an oxidizing agent, preferably a gas containing O2.

[0016] When the silicate glass produced is a clear silicate glass composition, the iron expressed as total Fe2O3, is typically comprised at a level of 300ppm and 1500ppm; preferably, at a level equal to or greater than 400ppm, 450ppm, 500ppm, 550ppm, 600ppm, 650ppm, and even, 700ppm by weight of total glass composition. Preferably iron is comprised at a level equal to or lower than 1300ppm, 1200ppm, 1100ppm, OOppm, 900ppm, 850ppm, 800ppm, andeven, 750ppm by weight of total glass composition.

[0017] The silicate glass composition produced by the method of the present invention, has preferably a visible light transmittance LTD4 equal to or greater than 80.0%, preferably equal to or greater than 85.0%, preferably equal to or greater than 86.5%, preferably equal to or greater than 88.0%, preferably equal to or greater than 89.0%, preferably equal to or greater than 90.0%, more preferably equal to or greater than 91.0%.

[0018] The present invention further relates to the use of a purified silicate melt and / or highly purified silicate material obtained by the method of the present invention, as a glass raw material for producing a silicate glass composition comprising iron expressed as total Fe2O3based on the total weight of the glass composition, at a level of 20ppm to 1500ppm. The present invention also relates to the use of a purified silicate melt and / or highly purified silicate material obtained by the method of the present invention, as a glass raw material for producing a silicate glass composition having a LTD4 equal to or greater than 85.0%, preferably equal to or greater than 86.5%, preferably equal to or greater than 88.0%, preferably equal to or greater than 89.0%, preferably equal to or greater than 90.0%, more preferably equal to or greater than 91.0%.Detailed description of the present invention

[0019] The present invention relates to a method for producing silicate glass from alternative glass raw materials. ‘Alternative’ is used herein to mean unconventional raw materials currently not used, or not used in significant quantities in the glass industry, to produce in particular soda-lime glass.

[0020] Main glass raw materials to produce Soda-Lime-Silicate glass (herein after referred to as SLS glass or silicate glass) are silica sand (quartz) and carbonates (limestone, mainly composed of the crystal calcite CaCO3; dolostone, mainly composed of the crystal dolomite CaMgCO3; and soda-ash consisting mainly of Na2CO3). These sources of alkalis and earth- alkalis are necessary components to produce glass sheets and container glass at relatively low temperatures (freezing point depression of silica minerals by soda) and to improve glass durability (Ca and Mg). However, they generate more or less 0,2 ton of CO2per ton of produced glass. During the melting step, the carbonate minerals reacts with sand to form a glass melt and release CO2into the atmosphere.

[0021] Natural silicate rocks rich in alkalis and earth alkalis, in particular magmatic and metamorphic rocks, are abundant in continental crust and are already mined as marble stones, basalt, or minerals... Among them, basaltic rocks are very abundant and homogeneous in composition, and contain significant amount of alkalis and earth-alkalis to be interesting to partly replace the carbonates in the SLS raw material batch composition.

[0022] However, the presence of high amounts of iron and other transition elements make the use of natural silicate rocks rich in alkalis and earth alkalis almost anecdotal, if not impossible. The present invention aims to use high quantity of natural silicate rocks rich in alkalis and earth alkalis in SLS glass raw materials (SLS glass batch) by performing a preliminary high- temperature reduction reaction to obtain an iron-rich metal phase mechanically separable from a residual molten silicate which gives a “purified” natural silicate rock (i.e. lean in transition elements like Fe, Cr, Co, Ni...). This purified natural silicate rock can be used as an alternative glass raw material to make SLS glass, especially clear glass or colored glass.

[0023] A first objective of the present invention is to prepare (highly) purified natural silicate materials as alternative glass raw materials that are suitable to be used in high quantities in a glass furnace and therefore to decrease substantially the release of CO2 directly during the glass forming process.

[0024] Another objective of the present invention is to prepare (highly) purified natural silicate materials as alternative glass raw material that are suitable to be used in medium quantities in a glass furnace to produce clear and even extra clear glasses while still significantly decrease the release of CO2directly during the melting process.

[0025] The method used in the present invention can appropriately remove unnecessary substances and unnecessary components from natural silicate rocks to allow their introduction in glass batch material in medium I high quantities and therefore greatly reduce the CO2release during the glass making process.

[0026] Hence, the present invention teaches a process whereby the amount of iron and other transition elements are significantly reduced within the natural silicate rocks. The present invention proposes to perform a reduction reaction at high temperature to concentrate the coloring elements into a metal phase and then mechanically separate this metal phase. The silicate melt, after the removal of the metal phase, is transformed in a silicate material rich in the suitable oxide components CaO, MgO, Na2O, K2O but contains a low amount of transitionelements like iron, chromium, nickel, cobalt, etc... These components being concentrated in the separated metal phase.

[0027] Hereinafter, the present invention will be described in details, but the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented within the range that does not deviate from the gist of the present invention. In addition, the numerical range is used in the sense of including the numerical values described before and after as lower limit values and upper limit values.METHOD FOR PRODUCING SILICATE GLASS

[0028] The present invention relates to method for producing purified silicate melt and / or highly purified silicate materials from natural silicate rocks, rich in alkaline and alkaline earth elements, wherein the amount of metal and / or metalloid elements (M) selected from the group consisting of Fe, Co, Cr, Ni, V, Sb, Zn, Mn, Sn, Bi, Pb, Ag, Cu, W, Nb, Mo and mixtures thereof has been lowered within the natural silicate rocks.

[0029] By ‘rich in alkaline and alkaline earth elements’, it is herein understood that the natural silicate rock comprises alkalis and earth-alkalis at a level of equal to or greater 5wt%, preferably 10wt%, preferably 15wt%, more preferably 20wt%, even more preferably 25% by weight of the total composition of the natural silicate rock. Since the method of the present invention aims at replacing as much as possible the carbonated raw material in the glass making production to avoid the release of CO2, the more alkaline and alkaline earth elements in the natural silicate rock, the better.

[0030] As commonly understood by persons skilled in the art, ‘lowered’ means that the amount expressed in % by weight of the metal and / or metalloid elements within the purified silicate melt and / or highly purified silicate material is lower than the amount of the metal and / or metalloid elements within the original natural silicate rock. The purified natural silicate rocks become suitable glass raw materials that can be used to produce regular silicate glass.

[0031] The method comprises the following steps in the following order : a) melting the natural silicate rocks to obtain a silicate melt; b) performing a chemical reaction to reduce the silicate melt to precipitate a metal phase enriched in the metal and / or metalloid elements; c) separating at least a part of the metal phase from the silicate melt to obtain a purifiedsilicate melt; d) preferably, performing an oxidation treatment on the purified silicate melt to obtain a highly purified silicate material; and e) using the purified silicate melt and / or preferably the highly purified silicate material, as component for silicate glass.

[0032] The following embodiment illustrates a particular the method of the present invention based on Pyroxenites, being one example of natural silicate rocks. Pyroxenites are mainly constituted by silicate minerals called pyroxenes (ortho and clinopyroxenes). These minerals have a general formula Cax(Fe, Mg)(1-x)SiO3(x ranges from 0 to 1 ). Iron and magnesium have similar chemical behaviors and form a solid solution in the pyroxene lattices. Their valence are Fe2+and Mg2+and form ionic bonds with the oxygens from the silicate chains. Calcium, magnesium and silicium are components of interest to produce silicate glass. However, if iron can be used in colored glass, this element is considered has an impurity in most of the glass productions as it imparts a greenish tint to the glass which is detrimental for the aesthetic of the product.

[0033] By melting the pyroxenite rock at high temperature (step (a)) with a reducing agent such as calcium silicide or graphite, Fe2+can be reduced into its metallic form while the elements of interest, mainly calcium and magnesium being difficult to reduce, stay bonded to oxygen in the silicate melt (step (b)). By separating physically the metal phase from the melt lean in iron, a purified silicate melt is obtained (step (c)).

[0034] Since it is highly difficult to reach a yield of metal removal of 100%, some small metal particles can remain in the purified silicate melt. It is well known by the skilled person in that art that metal can be a risk for glass quality (redox control, defect generation) or the refractory wear (downward drilling). An oxidation step of the purified silicate melt is therefore preferred to oxidize the metal, such in the present case: Fe°. The oxidation step dissolves the remaining metal elements back into the purified silicate melt to obtain the highly purified silicate material (step (d)). This highly purified silicate material is now a suitable, uncarbonated and lean in iron (or other elements M) material for glass forming process, either by direct injection in a glass furnace with other glass raw materials, either after cooling and processed like any other glass batch materials.

[0035] The solution provided by the present invention is to perform a chemical reaction at high temperature to reduce the (coloring) elements into a metal phase and then mechanicallyseparate this metal phase. The purified silicate melt, after the removal of the metal phase, is transformed in a highly purified silicate material rich in the suitable oxide components CaO, MgO, Na2O, K2O but contains a low amount of transition elements like iron, chromium, nickel, cobalt, etc...

[0036] The method of the present invention aims indeed at decreasing the amount of metal elements (M) selected from the group consisting of Fe, Co, Cr, Ni, V, Sb, Zn, Mn, Sn, Bi, Pb, Ag, Cu, W, Nb, Mo and mixtures thereof from natural silicate rocks so that they can used as carbonate free or carbon-reduced glass raw material.GLASS RAW MATERIAL

[0037] The purified silicate melt and / or the highly purified silicate material are added to other glass raw materials, to form the glass raw material mixture called also glass batch material.

[0038] Silica is usually introduced into the glass raw material mixture in the form of sand. If necessary, the mixture of raw materials can also advantageously include an Al carrier, a precursor of alumina in glass, such as a feldspar.

[0039] According to the invention, as little carbonate as possible, or even no carbonate, is introduced into the mixture of glass raw materials. Preferably, the sum of the weight of alkali carbonate and earth alkali carbonate is less than 40%, preferably less than 25%, preferably less than 10%, preferably less than 5%, and preferably less than 1 % in weight, or even zero in the mixture of glass raw materials. It is indeed advantageous not to release any carbon oxide from the materials during their glass forming process.

[0040] The mixture of glass raw materials may comprise between 5% and 25% by weight of alkali hydroxide (sum of all alkali hydroxides), in particular sodium hydroxide or between 5% and 25% by weight of alkaline earth hydroxide (sum of all alkaline earth hydroxides), in particular magnesium hydroxide, notably in the form of brucite.

[0041] To make the silicate glass, the Si carrier is introduced into the mixture of glass raw materials in the form of sand, the alkaline carriers are advantageously introduced into the mixture of glass raw materials in the form of hydroxides such as NaOH, KOH and the possible Al carrier can be introduced into the glass raw material mixture in the form of feldspar powder.

[0042] Each glass raw material is introduced into the glass raw material mixture in such quantitythat the percentage of its cation (such as Si, Na, Al, Fe, etc.) relative to the sum of all cations, is the same as in the final glass.

[0043] In one embodiment of the present invention, it can be contemplated - for example, for colored silicate glass compositions, that the mixture of glass raw materials could also include in very small proportions a dye such as iron oxide, cobalt oxide, chromium oxide; depending on the color target required by the customer. However, such amounts are very limited versus the concentration of those components typically found in natural silicate rocks. Adding such components in a small amount is easier than adapting the purification steps of the method of the present invention to obtain the required concentration and proportions of those dye components. Furthermore, it allows to maintain the technical benefit of greatly reducing the CO2release.

[0044] The raw materials are chosen so to lead to a glass whose target composition falls within the framework (the percentage ranges of the different oxides) described later in the text.NATURAL SILICATE ROCKS

[0045] Some natural silicate rocks or minerals are already used in glass industry: Sand or crushed quartzite as a source of SiO2and feldspar, nepheline or phonolite as source of alumina. These silicate raw materials for glass industry are carefully selected so that their iron content is low, typically with a total Fe2O3content below 0.2 wt% for the sand used in large quantities and below 2 wt% for the source of alumina (e.g. phonolite). Many natural silicate rocks are rich in calcium and / or magnesium and therefore interesting for the production of glass to replace carbonates (limestones and dolostones). However, most of them cannot be incorporated into the raw glass composition in significant quantities without an additional treatment to remove unnecessary element(s) and / or unnecessary compound(s), typically, coloring elements. Iron being usually the most important among these coloring elements.

[0046] Natural silicate rocks are naturally present in continental crust and are by definition mostly composed by silicate minerals, even if small amount of other mineral groups can be present like oxides, carbonates, sulfides. Typically, the proportion of non-silicate minerals in silicate rocks is less than 10 % by volume. Typically, they comprise from 30wt% to 99wt% of SiO2, preferably from 35wt% to 75wt%, more preferably from 40wt% to 65wt% of SiO2by weight of the total natural silicate rock composition.

[0047] Preferably, natural silicate rocks are magmatic rocks that comprises from 30% to 90% by weight of SiO2and their metamorphic equivalents. Many of them contain significant quantities of alkalis and earth-alkalis, their sum exceeding 10.0wt%, preferably 15.0wt% and more preferably 20.0wt%. AI2O3 content is typically lower than 25.0 wt%, preferably lower than 20.0wt% and preferably lower than 15.0wt%, more preferably lower than 7.5wt%.

[0048] More preferably magmatic rocks are basalt. Basalts are dark-colored, fine-grained, extrusive igneous rocks that are formed from the rapid cooling of low-viscosity magma rich in magnesium, calcium and iron. Basalts can be classified into different types based on their chemical and mineralogical composition, such as basanite, tholeiite, alkali basalt, basaltic andesites and so on. Based on the IUGS classification of volcanic rocks, the definition of basalt lato sensu includes magmatic rocks with a range in SiO2between 41% and 57 wt%, i.e. from picro-basalts to basaltic andesite. In this extended definition, also included are alkaline volcanic rocks within this range of silica content, and therefore include basanite, tephrite, latite, shoshonite and others. During slow cooling inside the crust, the magma rich in magnesium, calcium and iron crystallizes into a coarse grains rock called gabbro. No distinction is made here between intrusive and volcanic rocks, and the general name of the volcanic rock is used here to refer to both intrusive and extrusive rocks, independently of the microstructures.

[0049] Typically, natural magmatic rocks comprise more than 2 wt% of the metal and / or metalloid element. Please refer for example to the basalt rock which comprises typically 5% to 15% by weight iron oxide, from 0.1 to 0.4% by weight of chromium oxide and 0.005 to 0.02% by weight of nickel oxide. Another example of interesting magmatic rock with high amount of earth- alkaline (MgO) is peridotite which contains about 10 wt% of Fe2O3(total iron), 0.4 wt% Cr2O3and 0.25 wt% NiO. Another example are andesites which contains more than 10 wt% of alkalis and earth alkalis but also about 7 wt% of total iron. These examples illustrates that if natural silicate rock are a potential source to replace carbonates material in glass industry, their high contents in elements with high impact in the optical properties of glass (iron, chromium, nickel) make them of little practical use without further treatment described in this invention.

[0050] Examples of unnecessary (coloring) element(s) include Fe, Co, Cr, Ni, V, Zn, Mn, Sn, Bi, Pb, Sb Ag, Cu, W, Nb, Mo and the like. These elements tend to be reduced more easily than the main components of glass. According to the present production method, since these impurity elements contained in the silicate melt can be suitably removed, the coloring of theobtained glass can be suppressed, and a glass having excellent transparency can be obtained.

[0051] Hereinafter, Fe, Co, Cr, Ni, V, Sb, Zn, Mn, Sn, Bi, Pb, Ag, Cu, W, Nb and Mo are referred to indistinctively as "impurity element, impurity, element, metal and / or metalloid element, metal element, element M". Impurity element means one or more elements selected from the group consisting of. Their content is expressed by the oxide-based total composition weight% or weight ppm representation. The method of the present invention typically focuses on one or more of the elements selected from the group consisting of Fe, Co, Cr and / or Ni.

[0052] When processed by the method of the present invention, the natural silicate rocks having previously exceeding levels of impurity elements are now purified and then suitable to be used in high quantities within a glass forming process at industrial scale or in a more limited amount but still very significant, for clear or even extra-clear glass production.The melting step (a) of the method for producing silicate glass

[0053] In step (a), the natural silicate rocks is melted to obtain the silicate melt.

[0054] In this first step (a) of melting, most of the organic matter is gasified and removed. Some of the organic matter remains in the melt as a residual coal component and acts as a reducing agent to reduce glass. It is considered that such residual coal components will lead to the occurrence of disadvantages. However, the degree of reduction by the residual coal component is small compared to the subsequent reduction treatment step (b), and the influence can be completely eliminated by the oxidation treatment in step (d). Therefore, according to this manufacturing method, the defect derived from organic matter can also be suppressed.

[0055] The specific method of melting natural silicate rocks is not particularly limited. For example, the raw material can be melted by injecting it into a known heat-resistant container, heating furnace, or the like, and raising the temperature to the temperature at which the reduction treatment in the process (step(b)) is performed, and the first melt can be obtained.

[0056] The production method may further include the step of adjusting the viscosity of the first melt. The viscosity of the first melt is preferably comprised between 0.1 dPa. s to 100000 dPa.s at the temperature of step (b), being the temperature during the reduction treatment. Theviscosity is preferably equal to or lower than 100000 dPa.s, more preferably equal to or lower than 10000 dPa s, and further preferably equal to or lower than 1000 dPa.s. For viscosities lower than or equal to the upper limit value, it becomes easier to perform the reduction treatment in the step (b). The lower limit value of viscosity is not particularly limited, but is preferably equal to or greater than 0.1 dPa s from the viewpoint of suppressing erosion of refractory products, for example. The viscosity of the first melt can be measured by a rotating cylindrical method, a sphere pulling method, or the like.

[0057] The method for adjusting the viscosity of the silicate melt is not particularly limited, and examples thereof include adding a natural silicate rock or a substance whose viscosity can be adjusted to the silicate melt. Substances that can be added to the natural silicate rock or the silicate melt are not particularly limited, but when the viscosity is relatively small, carbonates, silicates, hydroxides, oxides, fluorides, chlorides, etc. containing alkali metal elements and alkaline earth metal elements are mentioned, and when the viscosity is to be relatively large, oxides containing silicon, aluminum, boron, phosphorus, and the like can be mentioned.The chemical reducing step (b) of the method for producing silicate glass

[0058] In step (b), the silicate melt is reduced to precipitate a metal phase enriched in the metal and / or metalloid elements M.

[0059] The method of the reduction treatment is not particularly limited, and examples thereof include a method using a reducing agent, a method of electrolyzing the silicate melt, and the like. From the viewpoint of ease of equipment maintenance and power consumption, a reducing agent is preferred.

[0060] The reducing agent can be a simple substance or a compound comprising several substance. Substances can be selected from one or more of C, Al, Si, Ca, Ti, N, Fe and H, and mixtures thereof. Specific examples of the reducing agents include C, Al, Si, Ca, Ca-Si, SiC, Ti, H2, CO, Fe — Si alloy, Ca — Si alloy, CH4, NH3, and mixtures thereof. Preferably, the reducing agent is one or more selected from C, Ca-Si, SiC and / or CO.

[0061] The state of the reducing agent is not particularly limited, and may be a gas at room temperature or a solid. Further, when the reducing agent is solid, the shape and the like are not particularly limited, but may be, for example, granular, powdery, lumpy, plate-shaped, or the like.

[0062] In the method of reduction treatment using a reducing agent, the reducing agent and the silicate melt are put in contact. For example, by adding a solid reducing agent to the silicate melt; by blowing a gas reducing agent, and / or by melting the natural silicate rock I in a container in which the reducing agent is arranged in advance. The container in which the reducing agent is added, can include a part to include the reducing agent, and / or a part or all of the container itself acts as a reducing agent. Further, when the natural silicate rock is melted in a container in which the reducing agent is arranged in advance, the step (a) and the step (b) are typically performed in parallel. Therefore, for simplicity of operation, a method of melting natural silicate rocks in a container in which a reducing agent is arranged in advance, is preferred.

[0063] When the reducing agent is a granular or lumpy solid and especially, the natural silicate rock is melted in a container in which the reducing agent is arranged in advance, the size of the reducing agent particle, which accounts for 80% or more of the total based on mass, is preferably comprised between 0.1 mm and 200 mm (0.1 mm < particle size < 200mm). Preferably, the size of the reducing agent, is comprised between 1 .0 mm and 150 mm (1 .0mm < particle size < 150mm), and further preferably 2.0 and 100 mm (2.0mm < particle size < 100mm). Smaller particle size of the reducing agents are preferred to increase its reactivity with the natural silicate rock. The size and ratio of the reducing agent can be evaluated by measuring the mass with a balance through a sieve having a predetermined eye opening. The preferred range does not include minute reducing agents generated by collisions between reducing agents at the time of addition or conveyance or reactions with the melt.

[0064] When the reducing agent is a solid, the mass ratio of the reducing agent to the silicate melt is preferably comprised from 0.001 to 100. For efficient reduction, the mass ratio is preferably equal to or greater than 0.001 , more preferably equal to or greater than 0.005, and further preferably equal to or greater than 0.01. On the other hand, for space-saving processing, the mass ratio is preferably equal to or lower than 100, more preferably equal to or lower than 50, and further preferably equal to or lower than 30. The mass ratio of the reducing agent to the silicate melt is obtained by calculating from the average composition and input amount of the melt and the average composition and input amount of the reducing agent. When the natural silicate rock is melted in a container in which the reducing agent is arranged in advance, the reducing agent can be lowered as long as it does not disappear due to a reaction with an oxidizing gas such as oxygen contained in a small amount in the melt or atmosphere.

[0065] The method of reduction treatment may be a method of electrolyzing the silicate melt, and may be used in combination with a method using a reducing agent. When electrolyzing the silicate melt, for example, electrolysis can be performed by arranging two electrodes in the silicate melt and applying a voltage between them.

[0066] The treatment temperature in the reduction treatment is preferably from 1300°C to 1800°C. For ensuring sufficient reduction reaction rate and reducing power, the treatment temperature is preferably equal to or greater than 1300°C, more preferably equal to or greater than 1400°C, and further preferably equal to or greater than 1450°C. For suppressing erosion of refractory products and limiting energy consumption, the treatment temperature is preferably equal to or lower than 1800°C, more preferably equal to or greater than 1700°C, and further preferably equal to or greater than 1650°C.

[0067] The reduction treatment time is not particularly limited by the type of reducing agent, the composition of the silicate melt, and the like, but is preferably, from 10 minutes to 48 hours. To ensure the sufficient reduction reaction, the processing time is preferably equal to or greater than 10 minutes, more preferably equal to or greater than 30 minutes, and further preferably equal to or greater than 60 minutes. For suppressing erosion of refractory products and for limiting energy consumption, the treatment time is preferably equal to or lower than 48 hours, more preferably equal to or lower than 24 hours, and further preferably equal to or lower than 12 hours.

[0068] In order to selectively precipitate the impurity element as a metal phase, it is preferable to appropriately adjust conditions such as the type of reducing agent and the processing temperature in the reduction treatment. For example, by making these the above-described preferred conditions, the impurity element in the silicate melt tends to be selectively precipitated as a metal phase. In addition, it has been found that the purification process of the present invention, has no significant impact on the other components such as SiO2, Na2O, K2O, CaO, MgO and K2O, of the original natural silicate rocks and therefore neither on the purified silicate melt and / or preferably on the purified silicate material.Metal phase

[0069] Part or all of the metal elements contained in the silicate melt are precipitated as a metal phase by reduction treatment. The metal phase contains at least one element contained in a natural silicate rock before reduction treatment, and preferably contains the above-describedimpurity element. More preferably, it can be said that the larger the ratio of impurity elements in the metal phase, the more the impurity elements are selectively precipitated as the metal phase.The separation step (c) of the method for producing silicate glass

[0070] In step (c), at least a part of the metal phase is separated from the reduced silicate melt to obtain the purified silicate melt. Here, separating at least a part of the metal phase from the silicate melt means physically removing at least a part of the metal phase from the silicate melt, and the purified silicate melt means that at least a part of the metal phase has been removed from the silicate melt.

[0071] The method for separating the metal phase is not particularly limited, and can be for example, a method of precipitating the metal phase from the silicate melt and settling e.g. gravity; converting the metal phase into a highly volatile substance by halogenation or the like and separating it as a gas. In a more preferable method of separating the metal phase, the metal phase is coarsened by bubbling to a size sufficient to settle the metal particles.

[0072] Another method is to intentionally add an alloying component such as silicon which combines with the precipitated metal fine particles to a size sufficient to settle. Yet, another method consists of separating the metal phase by capturing it on the surface of the reducing agent. In such method wherein the metal phase is precipitated on the surface of the reducing agent, a reducing agent is filled in a container in advance and the purified silicate material is melted in the container. Step (b) and step (c) may be performed in parallel.

[0073] Another suitable method comprises a crushing step after the chemical reduction step followed by a separation step via a magnet on a conveyor belt.

[0074] By separating the metal phase by these more preferred methods, the metal phase can be more suitably separated, and the amount of metal phase remaining in the purified silicate melt is likely to be limited.The oxidation step (d) of the method for producing silicate glass

[0075] The method of the present invention preferably further comprise an oxidation step (d). The oxidation treatment is performed on the purified silicate melt to obtain a highly purified silicate material.

[0076] As described above, even if the metal phase is separated from the purified silicate melt in step (c), a metal phase in the fine particle state having a relatively small particle size could remain in the melt. Therefore, by performing an oxidation treatment on the purified silicate melt in step (d) to obtain a highly purified silicate material, the defect derived from metal fine particles is suppressed when using the highly purified silicate material as an alternative glass raw material within glass forming process.

[0077] The method of oxidation treatment is not particularly limited, and examples thereof include a method using an oxidizing gas and a method of adding an oxidizing agent. Since the composition change of the melt is not desired, a method of using an oxidizing gas is preferable.

[0078] Specific examples of the oxidizing gas include a gas containing O2, a gas containing H2O, a gas containing CO2, and the like. From the viewpoint of oxidizing efficiency and ease of obtainability, a gas containing O2is preferable as the oxidizing gas. Examples of the gas containing O2include air (atmosphere), O2gas, mixed gas of O2gas and inert gas and the like, and air (atmosphere) and O2gas are preferable since easily obtainable.

[0079] Specific methods for performing oxidation treatment using an oxidizing gas include, for example, a method of bubbling the purified silicate melt with an oxidizing gas. If necessary, an inert gas may be mixed with an oxidizing gas. Examples of the inert gas include nitrogen gas, argon gas, and helium gas.

[0080] Specific examples of the oxidizing agent include nitrates such as sodium nitrate, sulfates such as sodium sulfate, cerium oxide, antimony (V) oxide, tin (IV) oxide and the like. For oxidizing efficiency, ease of obtainability, and environmental impact, nitrate, cerium oxide, and tin (IV) oxide are preferable.

[0081] Another method for performing oxidation treatment includes the addition of an oxidizing agent to the purified silicate melt. The oxidizing agent is preferably in powder form in order to react efficiently. A powder injection method is preferable because it reacts efficiently.

[0082] The treatment temperature in the oxidation treatment is preferably comprised between 1300°C and 1800°C. For ensuring a sufficient oxidation reaction rate, the treatment temperature is preferably equal to or greater than 1300°C, more preferably equal to or greater than 1400°C, and further preferably equal to or greater than 1450°C. For suppressing erosionof refractory products and limiting energy consumption, the treatment temperature is preferably equal to or lower than 1800°C, more preferably equal to or lower than 1700°C, and further preferably equal to or lower than 1650°C.

[0083] The time of the oxidation treatment is not particularly limited, but when bubbling with oxidizing gas, for example, 1 minute ~ 24 hours is preferable. For sufficient elimination of the metal fine particles, the processing time is preferably equal to or greater than 1 minute, more preferably equal to or greater than 5 minutes, and further preferably equal to or greater than 15 minutes. On the other hand, for suppressing erosion of refractory products and limiting energy consumption, the treatment time is preferably equal to or lower than 24 hours, more preferably equal to or lower than 12 hours, and further preferably equal to or lower than 8 hours.The purified silicate melt and highly purified silicate material

[0084] Before and after being processed by steps (a) to (c) and preferably by the additional step (d), the natural silicate rock has a concentration of element M in the oxide-based mass% or mass ppm equivalent is [MO]before and the purified silicate melt and / or the purified silicate material has a concentration of element M in the oxide-based mass% or mass ppm equivalent is [MO]after-

[0085] In a preferred embodiment, for at least one element M, the ratio of [MO]after / [MO]before is equal to or lower than 0.850 ([MO]after / [MO]before s 0.850), preferably equal to or lower than 0.700 ([MO]after / [MO]before 0.700); preferably equal to or lower than 0.500 ([MO]after / [MO]before < 0.500); preferably equal to or lower than 0.250 ([MO]after / [MO]before 0.250); more preferably equal to or lower than 0.100 ([MO]after / [MO]before 0.100). The smaller the ratio value of [MO]after / [MO]before, the preferable, and the lower limit value of this ratio is not particularly limited, but may be, for example, equal to or lower than 0.010 or even more equal to or lower than 0.001 . Preferably the metal and / or metalloid element is selected from Fe oxide, Co oxide, Cr oxide, Ni oxide and mixtures thereof.

[0086] In another embodiment, the concentration of the elements M in the natural silicate rock [MO]before, and in the purified silicate melt and / or in the highly purified silicate material [MO]after, satisfies the following equation :0,001 < [(sum of ([MO]aftei7[MO]before) / n] < 0.850wherein n is the number of metal and / or metalloid element(s) and preferably wherein the metal and / or metalloid element is selected from Fe oxide, Co oxide, Cr oxide, Ni oxide and mixtures thereof.

[0087] Such equation is preferably satisfied wherein MO is selected from Fe oxide, Co oxide, Cr oxide, Ni oxide and mixtures thereof.

[0088] The values of 0.001 to 0.850 means that the impurity element is appropriately removed in the obtained silicate glass. From this point of view, the value is preferably equal to or lower than 0.850, more preferably equal to or lower than 0.800, more preferably equal to or lower than 0.750, more preferably equal to or lower than 0.700 more preferably equal to or lower than 0.600 and particularly preferably equal to or lower than 0.500. The smaller the value, the better. The lower limit is not particularly limited, but may be, for example, equal to or lower than 0.01 , more preferably equal to or lower than 0.001 .

[0089] For example, for a natural silicate rock comprising as elements M, Fe3O3in 5 % by mass in the oxide standard mass % equivalent and CoO in 500 ppm by mass, with no other element M, the "number of types of element M contained in natural silicate rock" is 2. The ratios [Fe203]after / [Fe203]before and [CoO]after / [CoO]before, are respectively calculated, and their sum is divided by n=2. For example, if after the chemical reduction step followed by the metal separation step to obtain a purified silicate melt with 0,2 % Fe2O3and 10 ppm CoO, the calculated sum of [MO]after / [MO]before is 0.06, which divided by n = 2 gives (sum of ([MO]after / [MO]before) ) / n=0.03.

[0090] If the [MO] element is under the limit of detection by conventional analytical methods, then those are not considered within the above calculation.STEP (e) of the method for producing silicate glass

[0091] By a method including the above steps (a) to (c) and preferably (d), a purified silicate melt and preferably a highly purified silicate material, in which impurity elements are removed from the natural silicate rocks can be produced.

[0092] This manufacturing method may include a known glass manufacturing process step (e) in addition to steps (a) to (d). For example, step (e) will typically comprise sub-steps of (i) known glass batch adjustment step in the melting zone or in the melting and the fining zones, (ii) amelting step, (iii) a fining step (iv) cooling step flowing the refined melt from the fining zone to a working zone.Silicate Glass

[0093] The composition of the silicate glass obtained by this production method is not particularly limited, and may be selected from the group consisting of, for example, soda-lime glass, aluminosilicate glass, alkali-free glass, and alkali borosilicate glass. Soda-lime glass is preferable from the viewpoint of having the largest production in the world and making a significant contribution to resource recycling and greenhouse gas reduction. The composition of the silicate glass obtained by this production method using a purified silicate melt and / or preferably a highly purified silicate material as alternative glass raw material is not particularly limited, and may be the same as the composition of the silicate glass obtained by the glass forming process using glass raw material known in the art except for the content of the impurity element.

[0094] When the silicate glass obtained by this production method is soda-lime glass, the composition is expressed as a weight% based on oxide, and typically the total of SiO2and AI2O3 is 50 to 85%, the alkaline earth metal oxide (RO) is 5 to 30%, and the alkali metal oxide (R2O) is 0.1 ~ 25%. More preferably, it contains 60 to 80% SiO2, 5 to 20% Na2O, 0 to 15% MgO, 5 to 20% CaO, 0 to 10% AI2O3. It may also contain less than 5% K2O.

[0095] Hereinafter, an example of a preferred composition when the silicate glass obtained by the present production method is soda-lime glass will be described more specifically. When % or ppm is described for the glass composition, it means the oxide-based mass% or oxidebased mass ppm unless otherwise specified.

[0096] The total content of SiO2and AI2O3is preferably 50 to 85%. If the total content of SiO2and AI2O3is 50% or more, it can exist stably as a glass and has high weather resistance, which is preferable. The total content of SiO2and AI2O3is more preferably 55% or more, and even more preferably 60% or more. The total content of SiO2and AhO3is more preferably 80% or less, and further preferably 78% or less.

[0097] SiO2is the main component of soda-lime glass. The SiO2content is preferably 50~80%. If the content of SiO2is 50% or more, the weather resistance is good and preferable. The content of SiO2is more preferably 60% or more, and even more preferably 65% or more. Ifthe content of SiO2is 80% or less, it is preferable because it is difficult to devitrify. The content of SiO2is more preferably 75% or less, and further preferably 73% or less.

[0098] AI2O3is a component that improves weather resistance. The content of AI2O3is preferably 0 to 20%. When containing AI2O3, weather resistance is good. The content of AI2O3is preferably 0% or more, more preferably 0.1% or more, more preferably 0.5% or more, and particularly preferably 1 % or more. The content of AI2O3is preferably 15% or less and preferably 10% or less, more preferably less 7.5% or less.

[0099] The total content of alkaline earth metal oxides (RO) is preferably 5% to 30%. It is preferred that the total content of alkaline earth metal oxides (RO) is 5% or more. The total content of alkaline earth metal oxides (RO) is more preferably 7% or more, and further preferably 10% or more. If the total content of alkaline earth metal oxides (RO) is 30% or less, it is preferable because it is difficult to devitrify. The total content of alkaline earth metal oxides (RO) is more preferably 25% or less, and further preferably 20% or less. Here, the total content of alkaline earth metal oxides (RO) means the total content of MgO, CaO, SrO and BaO.

[0100] MgO is a component that promotes the melting of glass raw materials and improves weather resistance. The content of MgO is preferably 0 to 15%. When MgO is contained, meltability and weather resistance are good. The content of MgO is preferably 0% or more, more preferably 1 % or more, further preferably 2% or more, and particularly preferably 4% or more. If the MgO content is more than 15%, devitrification can occur. The content of MgO is more preferably 10% or less, and further preferably 5% or less.

[0101] CaO is a component that promotes the melting of glass raw materials and improves weather resistance. The CaO content is preferably 5% to 20%. If the CaO content is 5% or more, meltability and weather resistance are good, which is preferable. The content of CaO is more preferably 6% or more, and further preferably 7% or more. If the CaO content is more than 20%, devitrification can occur. The CaO content is more preferably 15% or less, and further preferably 12% or less.

[0102] The total content of alkali metal oxides (R2O) is preferably from 0.1 % to 25%. If the total content of alkali metal oxides (R2O) is 0.1 % or more, the meltability is good and preferable. The total content of alkali metal oxides (R2O) is more preferably 1 % or more, more preferably 3% or more, and particularly preferably 5% or more. If the total content of alkali metal oxides (R2O) is 25% or less, weather resistance is good and preferable. The total content of alkalimetal oxides (R2O) is more preferably 20% or less and even more preferably 15% or less. Here, the total content of alkali metal oxides (R2O) means the total content of Li2O, Na2O and K2O.

[0103] Na2O is a component that promotes the melting of glass raw materials. The Na2O content is preferably from 0.1 to 25%. If the content of Na2O is 0.1 % or more, the meltability is good and preferable. The content of Na2O is more preferably 1 % or more, more preferably 3% or more, and particularly preferably 5% or more. If the content of Na2O is 25% or less, the weather resistance is good and preferable. The content of Na2O is more preferably 20% or less, and further preferably 15% or less.

[0104] K2O is a component that promotes the melting of glass raw materials. K2O is not required, but may contain less than 5%. That is, the content of K2O may be less than 0 to 5%. When K2O is contained, meltability is good. The content when containing K2O is preferably 0.01 % or more, more preferably 0.5% or more. If the content of K2O is less than 5%, the weather resistance is good and preferable. The content of K2O is more preferably 3% or less, and even more preferably 2% or less.

[0105] The composition of the silicate glass obtained by this production method can be measured by performing composition analysis by fluorescent X-ray analysis. In addition, components having a content of less than 1 % and light element components such as Li2O and B2O3may be difficult to quantify by fluorescent X-ray analysis, and electron beam probe microanalyzer (EPMA), ICP emission spectroscopy, or ICP mass spectrometry may be performed for composition analysis.

[0106] The shape of the silicate glass obtained by this production method is not particularly limited, and may be various shapes such as a block, a crushed piece, a container shape, a fiber shape, a bead shape, and a sheet. When the glass is a sheet, it may be flat or may be formed or bent to include a curved surface. When the glass is a sheet, the plate thickness is not particularly limited, but for example, 0.1 to 20 mm is conventional.

[0107] The silicate glass obtained by this production method can be used for various purposes, but is preferably used as building material glass, automobile glass, container glass, glass wool, glass beads, and the like.

[0108] Advantageously, the expression soda-lime-silicate glass in the present invention is usedin a broad sense and relates to any silicate glass which comprises the following components in weight percentage, expressed with respect to the total weight of glass (Comp. A). More preferably, the silicate glass composition (Comp. B) is a soda-lime-silicate-type glass with a base glass matrix of the composition comprising the following components in weight percentage, expressed with respect to the total weight of glass.

[0109] As conventionally understood by persons skilled in the art, glass compositions are classified as ‘colored’, ‘clear’ and ‘extra-clear’ compositions based on the content of total iron expressed in total Fe2O3and the light transmission LTD4, according to the criteria described herein below.Ill Content of total jron expressed jnjpta FeaOs

[0110] In colored glass compositions, the content of total iron expressed in total Fe2O3, is typically greater than 1500ppm up to 2.0% by weight of total glass composition. Preferably, it is comprised at a level equal to or greater than 2000ppm, equal to or greater than 2500ppm and more preferably equal to or greater than 3000ppm. Preferably, the total iron expressed in total Fe2O3, is comprised at a level equal to or lower than 1 ,7wt%.

[0111] For non-colored glass compositions, it is preferred that the content of Fe2O3is 1500 ppm or less to suppress coloring.

[0112] For clear glass compositions, the content of total iron expressed in total Fe2O3, is typically comprised between 300ppm and 1500ppm (300ppm < Fe2O3< 1500ppm). Preferably, it iscomprised at a level equal to or greater than 400ppm, preferably equal to or greater than 450ppm, equal to or greater than 500ppm, equal to or greater than 550ppm, equal to or greater than 600ppm, equal to or greater than 650ppm, and even more preferably, equal to or greater than 700ppm by weight of total glass composition. Preferably, the content of total iron expressed in total Fe2O3, is comprised at a level equal to or lower than 1300ppm, preferably equal to or lower than 1200ppm, equal to or lower than 1100ppm, equal to or lower than 1000ppm, equal to or lower than 900ppm, equal to or lower than 850ppm, equal to or lower than 800ppm, and even more preferably, equal to or lower than 750ppm by weight of total glass composition.

[0113] For extra-clear glass compositions, the content of total iron expressed in total Fe2O3, is typically comprised between 20ppm and less than 300ppm (20ppm < Fe2O3< 300ppm). Preferably, it is comprised at a level equal to or greater than 50ppm, preferably equal to or greater than 60ppm, equal to or greater than 70ppm, equal to or greater than 80ppm, equal to or greater than 90ppm, equal to or greater than 100ppm, equal to or greater than 120ppm, equal to or greater than 150ppm and even more preferably equal to or greater than 170ppm by weight of total glass composition. Preferably, total iron expressed in total Fe2O3, is comprised at a level equal to or lower than 280ppm, preferably equal to or lower than 250ppm and even more preferably equal to or lower than 200ppm by weight of total glass composition.

[0114] In a preferred embodiment, the iron redox expressed in Fe2+ / Fetot, is equal to or lower than 30% (Fe2+ / Fetot 30%), preferably equal to or lower than 28% (Fe2+ / Fetot 28%), preferably equal to or lower than 25% (Fe2+ / Fetot 25%), more preferably equal to or lower than 23% (Fe2+ / Fetot 23%). Preferably, the iron redox expressed in Fe2+ / Fetot, is equal to or greater than 15% (Fe2+ / Fetot 15%), is equal to or greater than 20% (Fe2+ / Fetot s 20%).(2)_ Li2.ht_transmissio_n_ LTD4

[0115] Colored silicate glasses typically have a LTD4 equal to or greater than 7.0% and less than 85.0%.

[0116] Clear glass silicate glasses preferably have a visible light transmittance LTD4 equal to or greater than 85.0%, preferably equal to or greater than 86.5%, preferably equal to or greater than 88.0%, preferably equal to or greater than 89.0%, preferably equal to or greater than 90.0%, more preferably equal to or greater than 91.0%.

[0117] Extra clear glass compositions, preferably have a LTD4 is equal to or greater than 90.0%, preferably equal to or greater than 91 .0%, preferably equal to or greater than 91 .5%.

[0118] In present description, examples and claims, to quantify the visible transmission (also called luminous transmission / transmittance or LT) of a glass sheet, one considers the visible transmission with illuminant D65 for a sheet thickness of 4 mm (LTD4) at a solid angle of observation of 2° (according to standard IS09050). The visible transmission (LT) represents the percentage of radiation flux emitted between wavelengths 380 nm and 780 nm which is transmitted through the glass sheet.

[0119] Color is another factor that is relevant for consumers. Colors L*a*b* are defined by the International Commission on Illumination CIELAB color space (1976). In general, clear glass and extra-clear silicate glasses have a color characterized by a* ranging between 0,1 to -1 ,7; typically between -0,19 to -1 ,20 and b* ranging from -0,5 to 1 ; typically between 0,1 to 0,65. Clear glass compositions typically have a* ranging between -0.6 to -1 ,7 and b* ranging from 0.2 to 1. Extra clear glass compositions typically have a* ranging between -0.8 to 0.2 and b* ranging from -0.2 to 0.5.

[0120] It is well recognized in the art, that the color of the glass is not only impacted by the amount of iron but as well by the presence and quantities of other coloring elements such as chromium, selenium, etc. and other glass characteristics such as redox, etc.USE

[0121] The present invention further relates to the use of a purified silicate melt and / or highly purified silicate material obtained by the method of the present invention, as a glass raw material for producing a silicate glass composition comprising iron expressed as totalFe2O3 based on the total weight of the glass composition, at a level of 20ppm to 1500ppm.

[0122] The present invention also relates to the use of a purified silicate melt and / or highly purified silicate material obtained by the method of the present invention, as a glass raw material for producing a silicate glass composition having a LTD4 equal to or greater than 85.0%, preferably equal to or greater than 86.5%, preferably equal to or greater than 88.0%, preferably equal to or greater than 89.0%, preferably equal to or greater than 90.0%, more preferably equal to or greater than 91 .0%.

[0123] Preferably, the present invention further relates to the use of a purified silicate melt and / or highly purified silicate material obtained by the method of the present invention, as a glass raw material for producing a silicate glass composition comprising iron expressed as total Fe2O3based on the total weight of the silicate glass composition, at a level of 20ppm to1500ppm combined with a LTD4 equal to or greater than 85.0%, preferably equal to or greater than 86.5%, preferably equal to or greater than 88.0%, preferably equal to or greater than 89.0%, preferably equal to or greater than 90.0%, more preferably equal to or greater than 91.0%.

[0124] The method of the present invention provides indeed purified silicate melt and / or highly purified silicate material as alternative glass raw material and offers a large flexibility to the glass formulator to balance the advantage of CO2 reduction and the technical benefits of iron content and LTD4, to match the clients’ needs. One can focus on a drastic reduction of the CO2emission and accept a slight increase in iron content and a slight decrease in LTD4. Another can focus on a medium CO2reduction while provide a silicate glass with low and even very low iron content and high even super high LTD4. All variations between these 2 options are contemplated within the invention.

[0125] In a preferred embodiment of the present invention, the production of the silicate glass by the method of the present invention, provide a reduction of CO2calculated in kg / Tgiassand expressed in percentage equal to or greater than 5%, preferably equal to or greater than 10%, preferably equal to or greater than 15%, preferably equal to or greater than 25% and more preferably equal to or greater than 50%.PRODUCTION OF SILICATE GLASS

[0126] In the state of the art, vitrifiable materials or glass raw materials are melted in a glass furnace that commonly comprises :- a melting zone containing a melt when the furnace is in use;- inlet means located upstream of the furnace, for charging it with the glass raw materials / batch to be heated / melted;- heating means located in the melting zone for (i) melting the glass raw materials and (ii) downstream, for fining the melt, and finally,- an outlet for the melt to reach a processing zone or a working end.

[0127] As commonly adopted in the glass art, by “melting zone”, it is meant a zone / tank where the glass batch are charged / fed and melted by heating, and which comprises, when the furnace is in operation, a melt and a “blanket” of unmelted glass batch that floats on the melt and is progressively melted. It is equipped with heating means, for example said heatingmeans in the melting zone are comprised of a plurality of electrodes and / or burners and / or thermal plasma torches.

[0128] As commonly adopted in the glass art, by “fining zone”, it is meant a zone / tank where the glass melt is heated at temperatures higher than melting zone temperatures (generally above 1400°C or even above 1450°C), in order to refine the glass (mainly by eliminating major part of bubbles). This fining zone is also commonly called “clarification zone” in the art. It is equipped with heating means, for example said heating means in the fining zone are comprised of a plurality of electrodes and / or burners and / or thermal plasma torches.

[0129] Within the glass forming process, the glass raw material mixture is heated to form a molten glass, at more or less high in temperature and for more or less time depending on the quality of the glass, in particular depending on the degree of tolerance in unmelted particles and in bubbles. Generally, the maximum heating temperature of molten glass is between 1200°C and 1700°C. For the transformation of the mixture of raw materials into glass, glass furnaces techniques well known to those skilled in the art can be used. This transformation can be carried out in any type of furnace designs such as electric furnace, combustion conventional furnace as well as furnaces combining combustion and electric heating means called hybrid furnace and revamping of conventional combustion furnace. Whatever the glass furnace design, the melting and fining steps are commonly operated by heating through combustion (thanks to burners) and / or through electricity (thanks to electrodes and / or thermal plasma torches).

[0130] In a combustion-type heating, a fuel source reacts with oxidizer (air or oxygen) in order to generate a flame above the surface of the molten glass. Fuel may be, for example, fossil fuel, natural gas, biogas or hydrogen. Flames coming from combustion / burners are provided above the bath of molten glass / raw materials and heat it from the top, while generally electrodes are generally immersed in said bath. In particular, the use of oxy-combustion technology (oxygen as comburant and fuel as combustible) is known to reduce energy consumption and also to reduce exhaust gas emissions.

[0131] In an electrical heating, electrodes are commonly immersed (partially / totally) and often located at the bottom of the tank, and allow an electric current / power to pass through and heat the bath from its bulk. In the glass art, it is known to call a full-electrical melter as a “cold-top melter”, by opposition to classical combustion melter called “hot-top furnaces” (or “warm-top”).A lot of configurations and designs of glass furnaces with a cold-top melter have been proposed these last years in order to reduce energy consumption and CO2fingerprint of glass manufacturing.

[0132] In the invention, the glass furnace comprises at least one glass batch charger located at the melting zone. In particular, the glass furnace comprises further at least one batch charger located at the fining zone with a second glass batch. By “glass batch” in the invention, it is meant the common and known sense given in the glass art, namely a mixture of starting materials including glass raw materials and / or cullet. For example, when glass to manufacture is a soda-lime glass, a glass batch comprises silica source(s) (commonly sand) and source(s) of alkalis and alkaline earths (often sodium carbonate / soda ash, limestone and dolomite and / or their decarbonated products), but it may also comprise other materials like cullet, potash, salt cake (or sodium sulfate), feldspar, coloring agents (cobalt oxide, chromium oxide,...), clarifying agents (cerium oxide,..), oxidizers (sodium nitrate,...), reducing agents (graphite, coke, pyrite,...), decolorizing agents (selenium, cobalt,...), etc. Preferably, the glass batch comprises glass raw materials and cullet. Use of cullet is advantageous as it allows (i) raw materials sustainability and (ii) reducing of the CO2production / emission of the furnace when operating (due to a reducing of the emission occurring from the decarbonization of the carbonate raw materials used otherwise). Preferably, the total glass batch in the invention comprises more than 20% in weight, or preferably more than 30% and even up to 95% in weight of cullet.

[0133] The mixture of raw materials, particularly powdery, can optionally be humidified before introduction into a glass furnace in order to reduce the flight of raw materials into the glass furnace due to combustion gas currents.

[0134] For heating glass raw materials within the glass forming process, the mixture of raw materials, if necessary moistened, can be introduced into a furnace in a powder state, which implies that each raw material it contains is in a powder state. Alternatively, the mixture of raw materials, if necessary humidified, can be introduced into a furnace in the state of composition comprising cullet and the mixture of raw materials, the latter being if necessary powdery.

[0135] The person skilled in the art realizes that the present invention is by no means limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. It is further noted that the invention relates to all possible combinations of features, and preferred features, described herein and recited in the claims or in the described embodiments.

[0136] It is well understood by persons skilled in the art that, as used herein the terms “a”, “an” or “the” means at least “one” and should not be limited to “only one” unless explicitly stated otherwise. However, it is to be understood that the invention can assume various alternative orientations and, accordingly, such terms are not to be considered as limiting. Further, all numbers expressing dimensions, physical characteristics, processing parameters, quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical values set forth in the following specification and claims are approximations that can vary depending upon the desired properties sought to be obtained by the present invention. In the following description, unless otherwise specified, expression “substantially” mean to within 10%, preferably to within 5%.

[0137] Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. When it is described that a constituent element (e.g., a first constituent element) is "(functionally or communicatively) coupled to" or is "connected to" another constituent element (e.g., a second constituent element), it should be understood that the constituent element may be directly connected to the another constituent element or may be connected to the another constituent element through another constituent element (e.g., a third constituent element).Example1. Purified silicate melt

[0138] The steps (a) and (b) are the melting stage of the natural silicate rock with a reducer component added to precipitate the metal phase.

[0139] In these examples, basalt VR11880 (Germany source) is the selected natural silicate rock. Melting temperature is 1500°C for 3 hours. The reducing agent is coke comprising about 85 wt% of carbon. Quantity of coke per 100g of basalt is 3 to 12g (Table 1). The furnace is flushed with N2gas during the melting stage.

[0140] The step (c) at the lab scale is realized by crushing the content of the crucible into powder and separate the metal particles with a magnet. XRF measurements confirmed the removal of iron, chromium and nickel which are enriched in the metal (see Table 2).No oxidation step (d) was realized at the laboratory scale and the results are presented in the table 1.

[0141] Tableau 1 . X-ray fluorescence analyses (XRF) of natural basalts (VR11880) and purified basalts after the reduction reaction and mechanical separation of the metal phase formed during the melting step with coke.

[0142] The composition of the precipitated metal phase is described for test 2 in Table 2.

[0143] Table 2 : Electron microprobe analyses (EPMA) of metal particles produced during the reduction reaction of natural basalt VR11880.2. Silicate glass composition

[0144] Different examples of silica glass compositions are provided below (Table 3 and Table 4) comprising basalt as natural silicate rock that has been processed or not, though the purification steps at high temperature. Four batches were melted in crucibles in a laboratory electric furnace:

[0145] Example 1 is a comparative example. It represents the reference glass batch typically used to produce a SLS glass.

[0146] Example 2 is also a comparative batch of glass material similar to batch 1 but wherein basalt has been introduced to replace partly dolostone and the proportion of the other raw materials are adjusted. No purification of the basalt method is performed.

[0147] Example 3 is an example of the present invention. It is a batch identical to Example 2 but wherein the method of the present invention has been performed to use purified basalt material instead of natural basalt rock. The purified basalt material is obtained via melting, reduction reaction and metal separation. Purified basalt material used in batch 3 is from tests 1 to 3 in Table 1 , used in equal quantities.

[0148] Example 4 is an example of the present invention. It is a batch identical to Example 3 wherein a much higher amount of purified basalt material is used.

[0149] Sulfate and coke have been included in the crucible tests to achieve a glass of good quality in term of homogeneity and bubble number as it is well known by the skill man.

[0150] Table 3 : Glass batch compositions

[0151] Table 4 : glass element compositions and glass properties

[0152] Comparative silicate glass from Example 2 wherein Feldspar conventional glass raw material is replaced by unpurified basalt, allows a substantial reduction in CO2emissions: 172 kg / TgiaSSinstead of 207kg / Tgiass(16.4%). However, this glass composition has a very significantdrop of light transmission LTD4 of 65.8% and has an iron content above 1wt%. It is therefore classified as ‘colored’. Its color is dark green. Industrial glass having a content of total iron oxide above 1 % do exist - however are sold in very limited quantities. Typical architectural colored glass have a total iron oxide content of 0.3wt% and typical automotive colored glass have an iron oxide content of 0.5wt%.

[0153] Silicate glass of example 3 of the present invention comprising the same amount of basalt rock but in its purified silicate form (up to step (c)). Such silicate glass maintains the same CO2emissions reduction but provide a much higher LTD4 of 90.5% and an amount of iron oxide of 530ppm. It is therefore classified as ‘clear’. Clear glass represents the main stream glass production and much higher volume, about 50% of the current glass market. The glass composition of example 3 could also be used for low iron automotive glass.

[0154] Silicate glass of example 4 represents another embodiment of the present invention wherein a substantial amount of purified basalt is used (about 3.3 times more than example 3) and therefore, a substantial decrease of 54% of the CO2emissions is achieved while still being classified as clear glass with 650ppm of iron and a slight loss in light transmission (89.7%).

Claims

1. CLAIMS1. A method for producing silicate glass from natural silicate rocks comprising alkalis and earth-alkalis at a level of equal to or greater 5wt%, preferably 10wt%, preferably 15wt%, more preferably 20wt%, even more preferably 25% by weight of the total composition of the natural silicate rocks and comprising at least one metal and / or metalloid elements (M) selected from the group consisting of Fe, Co, Cr, Ni, V, Sb, Zn, Mn, Sn, Bi, Pb, Ag, Cu, W, Nb, Mo and mixtures thereof; wherein the amount of at least one metal and / or metalloid elements (M), has been lowered; the method comprising the following steps in the following order: a) melting the natural silicate rocks to obtain a silicate melt; b) performing a chemical reaction to reduce the silicate melt to precipitate a metal phase enriched in the metal and / or metalloid elements; c) separating at least a part of the metal phase from the silicate melt to obtain a purified silicate melt; d) preferably, performing an oxidation treatment on the purified silicate melt to obtain a highly purified silicate material; and e) using the purified silicate melt and / or preferably the highly purified silicate material, as component for silicate glass.

2. The method according to claim 1 wherein the natural silicate rock comprises from 30% to 99% by weight of SiO2.

3. The method according to any one of the preceding claims wherein the natural silicate rock is a magmatic rock comprising from 30% to 90% by weight of SiO2.

4. The method according to any one of the preceding claims wherein the natural silicate rock is a basalt rock comprising from 41 % to 57% by weight of SiO2.

5. The method according to any one of the preceding claims a. wherein the natural silicate rock has a concentration of at least one metal and / or metalloid element in oxide-based mass% or mass ppm equivalent being [MO]before and the purified silicate melt, and / or the highly purified silicate material, has aconcentration of the at least one metal and / or metalloid element in oxide-based mass% or mass ppm equivalent being [MO]after; and wherein, b. for at least one metal and / or metalloid element, the ratio of [MO]after / [MO]before is equal to or lower than 0.850, preferably equal to or lower than 0.700, preferably equal to or lower than 0.500, preferably equal to or lower than 0.250; preferably equal to or lower than 0.100 preferably equal to or lower than 0.010, more preferably equal to or lower than 0.001.

6. The method according to any one of the preceding claims wherein the reduction treatment of step (b) uses one or more reducing agent(s) comprising one or more of elements selected from the group consisting of C, Al, Si, Ca, Ti, N, Fe and H and mixtures thereof; and is preferably selected from C, Al, Si, SiC, Ca, Ca-Si, Ti, H2, CO, Fe — Si alloy, Ca — Si alloy, CH4, NH3, and mixtures thereof.

7. The method according to any one of the preceding claims wherein the reducing agent is one or more selected from C, Ca-Si, SiC, CO and mixtures thereof.

8. The method according to any one of the preceding claims wherein the treatment temperature in the reduction treatment of step (b) is from 1300 °C to 1800 °C.

9. The method according to any one of the preceding claims wherein the oxidation treatment of step (d) uses an oxidizing gas as an oxidizing agent, preferably a gas containing O2.

10. The method according to any one of the preceding claims wherein the viscosity of the first melt during the reduction treatment step (b) at the temperature of the reduction treatment is adjusted to 0.1 dPa s to 100000 dPa s.11 . The silicate glass produced by the method according to any one of the preceding claims 1 to 10, is a clear silicate glass comprising iron expressed as total Fe2O3, at a level of equal to or greater than 300ppm; preferably at a level equal to or greater than 400ppm, preferably at a level equal to or greater than 450ppm, preferably at a level equal to or greater than 500ppm, preferably at a level equal to or greater than 550ppm, preferably at a level equal to or greater than 600ppm, preferably at a level equal to or greater than 650ppm, and even more preferably at a level equal to or greater than 700ppm by weight of total glass composition and at a level equal to or lower than 1500ppm, preferably at a level equal to or lower than 1300ppm, preferably at a level equal to or lower than 1200ppm,preferably at a level equal to or lower than 1100ppm, preferably at a level equal to or lower than 1000ppm, preferably at a level equal to or lower than 900ppm, preferably at a level equal to or lower than 850ppm, preferably at a level equal to or lower than 800ppm, and even more preferably at a level equal to or lower than 750ppm by weight of total glass composition.

12. The silicate glass according to claim 10, having a visible light transmittance LTD4 equal to or greater than 85.0%, preferably equal to or greater than 86.5%, preferably equal to or greater than 88.0%, preferably equal to or greater than 89.0%, preferably equal to or greater than 90.0%, more preferably equal to or greater than 91.0%.

13. Use of a purified silicate melt and / or highly purified silicate material obtained by the method according to any one of the preceding claims 1 to 10, as a glass raw material for producing a silicate glass composition comprising iron expressed as total Fe2O3based on the total weight of the glass composition, at a level of 20ppm to 1500ppm.

14. Use of a purified silicate melt and / or highly purified silicate material obtained by the method according to any one of the preceding claims 1 to 8, as a glass raw material for producing a silicate glass composition having a LTD4 equal to or greater than 85.0%, preferably equal to or greater than 86.5%, preferably equal to or greater than 88.0%, preferably equal to or greater than 89.0%, preferably equal to or greater than 90.0%, more preferably equal to or greater than 91 .0%.

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