Glass manufacturing method with alternative raw materials

Abstract

The present invention relates to a method for producing silicate glass from oxide-based waste 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 oxide-based waste; 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. The amount of at least one metal and / or metalloid elements (M), has been lowered by the following steps : a) melting the oxide-based waste to obtain a oxide melt; b) performing a chemical reaction to reduce the oxide 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 oxide melt to obtain a purified oxide melt; d) preferably, performing an oxidation treatment on the purified oxide melt to obtain a highly purified oxide material; and e) using the purified oxide melt and / or preferably the highly purified oxide material, as component for silicate glass.

Description

Glass manufacturing method with alternative raw materialsTechnical field

[0001] The present invention relates to a method for producing silicate glass from oxide-based waste 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] A 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] One part of the solution to reach the glass industry decarbonization 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 for low carbon glass manufacture.

[0005] 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,...

[0006] When looking for alternative sources of raw materials, it is possible to find industrial waste 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 ofcertain elements that make it not possible to include at all and / or in large quantities into the glass manufacturing process.

[0007] The object of the present invention is therefore to contribute to solving such a technical problem by proposing a glass manufacturing process for which the CO2emissions are effectively reduced, based on all the stages leading to the formation of glass. Hence, there is still a need to find a method to use or to increase the amount of low-carbon 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).

[0008] 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

[0009] The present invention relates to a method for producing silicate glass from oxidebased waste. The oxide-based waste 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 oxidebased waste and comprises 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), has been lowered by the method comprising the following steps in the following order: a) melting the oxide-based waste to obtain a oxide melt; b) performing a chemical reaction to reduce the oxide 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 oxide melt to obtain a purified oxide melt; d) preferably, performing an oxidation treatment on the purified oxide melt to obtain ahighly purified oxide material; and e) using the purified oxide melt and / or preferably the highly purified oxide material, as component for silicate glass.

[0010] The oxide-based waste to be used in the method of the present invention ca be selected from the group consisting of : Analcime sand, Biomass ashes, Concrete, Cofalit®, Basic oxygen furnace slag, Electric arc furnace slag and / or municipal waste.

[0011] The oxide-based waste 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 oxide melt, and / or the highly purified oxide 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. In one preferred embodiment, 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.

[0012] The reduction treatment of step (b) uses one or more reducing agent(s) comprising one or more of elements typically selected from the group consisting of C, Al, Si, Ca, Ti, N, Fe and H2and mixtures thereof; and preferably selected from C, Al, Si, SiC, Ca, Ca-Si, Ti, H2, CO, Fe — Si alloy, Ca — Si alloy, CH4, NH3, and mixtures thereof, more preferably selected from C, Ca-Si, SiC, CO and mixtures thereof.

[0013] The treatment temperature in the reduction treatment of step (b) is generally from 1300°C to 1800°C.

[0014] The oxidation treatment of step (d) uses preferably an oxidizing gas as an oxidizing agent, preferably a gas containing O2

[0015] The viscosity of the oxide melt during the reduction treatment step (b) at the temperature of the reduction treatment is typically adjusted to 0.1 dPa s to 100000 dPa s.

[0016] For clear silicate glass, iron expressed as total Fe2O3, is typically comprised 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, morepreferably at a level equal to or greater than 700ppm by weight of total glass composition and at a level equal to or lower than and 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 110Oppm, preferably at a level equal to or lower than 10OOppm, 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.

[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 oxide melt and / or highly purified oxide 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 oxide melt and / or highly purified oxide 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 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 sodalime 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 dolomiteCaMgCO3; 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] The present invention is based on the use of oxide-based and / or hydroxide-based waste or by-product that contain significant amount of alkalis and earth-alkalis to partly replace the carbonates in the SLS raw material batch composition. The waste and / or by-product can come from any source such as industrial, domestic and / or agricultural source, typically from industrial source. These are herein referred to as ‘oxide-based waste’.

[0022] However, the presence of high amounts of iron and other transition elements make the use of oxide-based waste rich in alkalis and earth alkalis almost anecdotal, if not impossible. The present invention aims to use high quantity of oxide-based waste rich in alkalis and earth alkalis in SLS 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” oxide-based waste (i.e. lean in transition elements like Fe, Cr, Co, Ni...). This purified oxide-based waste can be used as a raw materials to make SLS glass, especially with low amount of coloring agents, like clear or colored glass.

[0023] A first objective of the present invention is to prepare the oxide-based waste to be suitable to be used in float glass production process in high quantities and therefore to decrease substantially the release of CO2directly during the melting process.

[0024] Another objective of the present invention is to prepare the oxide-based waste to be suitable to be used in float glass production process in medium quantities 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 the oxide-based waste to allow their introduction in glass batch material in high quantities and therefore greatly reduce the CO2release of the glass making process.

[0026] Hence, the present invention teaches a process whereby the amount of iron and othertransition elements are significantly reduced within the oxide-based waste. 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 oxide melt, after the removal of the metal phase, is transformed in a 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... 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 oxide melt and / or highly purified oxide material from oxide-based waste, 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 oxide-based waste.

[0029] By ‘rich in alkaline and alkaline earth elements’, it is herein understood that the oxidebased waste 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 oxide-based waste. 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 are present in the oxide-based waste, 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 oxide melt and / or highly purified oxide material is lower than the amount of the metal and / or metalloid elements within the original oxide-based waste. The purified oxide melt and / or highly purified oxide material become suitable 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 oxide-based waste to obtain an oxide melt; b) performing a chemical reaction to reduce the oxide 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 oxide melt to obtain a purified oxide melt; d) preferably, performing an oxidation treatment on the purified oxide melt to obtain a highly purified oxide material ; and e) using the purified oxide melt and / or preferably the highly purified oxide material, as component for a silicate glass.

[0032] The following embodiment illustrates a particular method of the present invention based on wood ashes, representing one example of oxide-based waste. Wood ashes are coming from the combustion of biomass and they are mainly constituted by Calcium and Silicium oxides. By melting the biomass ashes at high temperature (step (a)) with a reducing agent such as calcium silicide or graphite, the oxidized iron cation can be reduced into its metallic form while the elements of interest, mainly calcium being difficult to reduce, stay bonded to oxygen in the oxide melt (step (b)). By separating physically the metal phase from the melt lean in iron, a purified oxide melt is obtained (step (c)).

[0033] Since it is highly difficult to reach a yield of metal removal of 100 %, some small metal particles can remain in the purified oxide 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 oxide 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 oxide melt to obtain the highly purified oxide material (step (d)). This highly purified oxide material is now a suitable, uncarbonated and lean in iron (or other elements M) material for glass production, either by direct injection in a glass furnace with other raw materials, either after cooling and processed like any other batch materials.

[0034] 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 mechanically separate this metal phase. The purified oxide melt, after the removal of the metal phase, is transformed in a highly purified oxide 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...

[0035] 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 oxide-based waste so that they can used as carbonate free or carbon-reduced glass raw material.GLASS RAW MATERIAL

[0036] The purified oxide melt and / or the highly purified oxide material are added to other glass raw materials, to form the raw material mixture.

[0037] Silica is usually introduced into the 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.

[0038] According to the invention, as little carbonate as possible, or even no carbonate, is introduced into the mixture of 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 raw materials. It is indeed advantageous not to release any carbon oxide from the materials during their glass forming process.

[0039] The mixture of 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.

[0040] To make the glass, the Si carrier is introduced into the mixture of raw materials in the form of sand, the alkaline carriers are advantageously introduced into the mixture of raw materials in the form of hydroxides such as NaOH, KOH and the possible Al carrier can be introduced into the raw material mixture in the form of feldspar powder.

[0041] Each raw material is introduced into the raw material mixture in such quantity that 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.

[0042] In one embodiment of the present invention, it can be contemplated - for example, for colored glass compositions, that the mixture of 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 oxide-based waste. 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.

[0043] 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.OXIDE-BASED WASTE

[0044] Some The oxide-based waste cannot be incorporated into the raw glass composition in significant quantities without an additional treatment to remove impurity element(s) and / or unnecessary compound(s), typically, coloring elements. 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”.

[0045] Because of its effect on the glass viscosity, AI2O3content in the oxide-based waste is typically lower than 25wt%, preferably lower than 20wt% and preferably lower than 15wt% and more preferably lower than 7.5wt% of the total composition of the oxide-based waste.

[0046] When processed by the method of the present invention, the oxide-based waste having previously exceeding levels of impurity elements is now suitable to be used in high quantities within a glass production method at industrial scale or in a more limited amount but still very significant, for clear glass.

[0047] It has been found that the following oxide-based wastes are of particular interest to the glass manufacturing industry : Analcime by-product / waste, Biomass ashes, Concrete waste, Cofalit®, Basic oxygen furnace slag and Electric arc furnace slag, and / or municipal waste.

[0048] It Today the use of Lithium is on the increase mainly for the production of batteries but also for the ceramic and glass industry. Lithium could be extracted from salar or from someminerals which are enriched in Lithium such as Spodumene, Amblygonite, Eucryptite,...

[0049] There are several ways to extract lithium from mineral enriched in lithium such as the / 3- spodumene. The conventional method involves calcination of the mineral at high temperature and then digestion with sulfuric acid at 250°C. The by-product of this method is Na2SO4. An other method is called the Analcime method and consist to add small amount of NaOH to the solution of NaCI and results in the dissolution of / 3-spodumene and precipitation of in particular analcime (NaAISi2O6H2O) as a by-product / waste. The analcime method is the one having the best balance between high lithium extraction effectiveness and the protection of the workers and the environment. Today, the by-product / waste of the analcime method are mainly deposit as waste in landfill and are then not valued.

[0050] Nevertheless, this by-product / waste could be used as a decarbonated raw material for the soda-lime glass industry. Indeed, the analcime is a zeolite (and feldspathoid) characterized by hydrated aluminosilicate framework and Na, Al and Si are the base element of soda-lime glasses. Nevertheless, other component than Analcime, which remains the main component, such as quartz, feldspar, muscovite,... could also be present in the waste from the lithium extraction.

[0051] The usage of this by-product / waste as a raw material for glass forming process has two benefits. Firstly, it decreases the quantity of waste produced by the lithium extraction industry and secondly, it reduces the footprint for glass forming process by using a decarbonated raw material instead of carbonated sources such as sodium carbonate and limestone. However, the main drawback of the analcime is its high Fe2O3content which is usually higher than 1wt% of the total composition of the by-product / waste. Such a high Fe2O3content limits significantly the quantity of analcime which could be used to produce clear soda-lime silicate glass. Therefore the treatment of the analcime with the present invention would allow to use this raw material with lower impact on the optical properties of the glass.

[0052] Another suitable oxide-based waste for the method of the present invention are biomass ashes. Indeed, biomass ashes could be a low carbon raw material of interest for glass forming process due to their high network modifiers content such as potassium oxide, calcium oxide and magnesium oxide. Biomass ashes can come frompaper combustion herein after referred to as ‘paper ashes’ or from wood combustion - herein after referred to as ‘wood ashes’. Both paper and wood ashes being mainly composed of CaO-SiO2-Al2O3-SO3-TiO2-Fe2O3 are interesting alternative glass raw materials. Wood ashes have typically the following composition (Table 1 ):

[0053] Table 1 : Typical composition of wood ashes

[0054] The Carbon content is measured with the Leco (infrared spectrometry after combustion) indicates that despite the combustion process, some carbonate materials or reduced carbon are still present in the samples. The other elements are measured by XRF.

[0055] However, the main drawback of the ashes is their high Fe2O3content which is in the above illustrative composition about 6.3% of the total composition of the wood ashes. Such a high Fe2O3content limits significantly the quantity of biomass ashes which could be used to produce clear soda-lime silicate glass. Cr and Ni elements might also be problematic. Therefore, the treatment of the biomass ashes with the present invention would allow to use this raw material with lower impact on the optical properties of the silicate glass.

[0056] Attention should be paid to the chlorine content of the wood ashes. Indeed, the presence of chlorine should preferably be avoided for its corrosive effect on the refractories of the glass production furnace. A specific treatment to remove the chlorine salt can be applied. Furthermore, the significant presence of coloring elements in those ashes such as the Fe2O3, Cr2O3and NiO is limiting the usage of this raw material for the production of clear silicate glass. The treatment of the ashes with the present invention would allow to use higher quantities of those ashes in clear silicate glass composition.

[0057] Approximately ten billion tons of concrete are manufactured each year for the building industry. When structures reach the end of their useful life or are to be removed for new construction, the concrete is typically demolished and considered a waste material. The demand for recycled concrete is still very low and therefore, concrete is routinely trucked to landfills for disposal. Available are recycled and / or waste concrete. Recycled concrete being any concrete that has been taken out of service. Waste concrete may be excess concrete or concrete that does not meet strength or other required properties for the application and washout concrete from ready mix concrete trucks and mixers, for example.

[0058] Concrete is mainly composed of SiO2, CaO, AI2O3and Fe2O3and could then be another alternative raw material effective for glass forming process. Concrete contains generally the following approximate oxides: silicon oxides in a range from 75 wt.% to 85 wt.%, iron oxide in a range of from 0.1 wt.% to 2.0 wt.%, aluminum oxides in the range from 0.5 wt% to 3.0 wt.%, magnesium oxides from 0.1 wt.% to 2.0 wt.%, calcium oxides in a range of from 10 wt.% to 20 wt.%, sodium oxides in a range from 0 wt.% to 1 wt.%, potassium oxides in a range from 0 wt.% to 1 wt.%, sulfate in the range of 0 wt.% to 1 wt.%, and other minor constituents. A typical concrete may comprise silicon oxides in a concentration of about 80 wt.%, iron oxides in a concentration of about 0.9 wt.%, aluminum oxides in a concentration of about 2.0 wt.%,magnesium oxides in a concentration of about 0.7 wt.%, calcium oxides in a concentration of about 15.5 wt.%, sodium oxides in a concentration of about 0.2 wt.%, potassium oxides in a concentration of about 0.1 wt.%, sulfates in a concentration of about 0.5 wt.%, and other minor constituents.

[0059] Again the main drawback of the concrete waste is its high Fe2O3content which is usually in a range of from 0.1 wt.% to 2.0 wt.%, of the total composition of concrete waste.

[0060] An illustration is provided in example 16 of WO2021 / 035204 that shows in table 2 below a glass batch composition and a silicate glass composition in which concrete has been used as a raw material. Comparison is made with a typical soda lime glass composition shown in the table 2 below.

[0061] Table 2 : Glass batch and silicate glass composition, example 16 of WO2021 / 035204Theoretical Glass Composition

[0062] Table 2 illustrates the advantages of the method of the present invention. First, the fusion loss (CO2) is lower when concrete is used in the glass composition (compared to a typical composition). This means that using waste / recycled concrete allows to reduce the global footprint of the glass production. Secondly, the Fe3O3content of the ‘concrete glass’ is more than doubled when compared than the typical soda-lime glass. This highlights the necessity of applying the purification steps of the method of the present invention to reduce the Fe2O3content of the produced silicate glass and then being able to produce clear silicate glass composition with significant amount of concrete or colored silicate glass compositions with even higher amount of concrete waste.

[0063] Asbestos has been used in the building industry for many years as an insulating material but is now banned in most countries because asbestos is responsible for very serious respiratory diseases in its dust form. Currently, asbestos waste is sorted and then stored in suitable landfill sites, at a cost of between €200 and €500 per ton, payable by the owner of the waste under the ‘polluter pays’ principle. With 500 000 tons of asbestos waste extracted every year, there is the question of what to do with this waste. Vitrification of asbestos by plasma torch technology has been developed as a reprocessing solution to transform this material in an harmless form. Cofalit® is the tradename for vitrified asbestos and is available in the form solid blocks that can be further crushed.

[0064] The Cofalit® produced by the INERTAM company has a typical composition as shown in the Table 3 below. Cofalit® is mainly composed of SiO2and CaO and comprises as well high quantity of Fe2O3which indeed limits its usage in silicate glass production

[0065] Table 3 - Typical composition of Cofalit® produced with the INERTAM process

[0066] Slag is a by-product of the steel industry. Slag mainly consists of silicates, aluminosilicates, and calcium aluminosilicates. Three main categories of slag exist: blast furnace slag, basic oxygen furnace slag and electric arc furnace slag.

[0067] Blast furnace slag is already used as a raw material in glass forming process. Blast furnace slag have the following advantages : it is an environmentally beneficial alumina source, it allows to reduce the energy consumption of the furnace, it reduces the CO2emissions. However, the other categories of slag are not easily used in the soda-lime glass industry because of their high content in Fe2O3and in other polluting elements such as for examples Chromium and Manganese. The present invention would a good way to remove those impurities elements (Fe, Cr, Mn) and allow the usage of other kind of slag that the blast furnace slag. This would allow to increase the proportion of slag which is used for SLS glass production and it will help to decarbonated the glass industry.

[0068] The main basic oxygen furnace slag components and the variation range are 34-55% of CaO, 8-20% of SiO2, 1-7% of AI2O3, 14-32% of Fe2O3, and 1-10% of MgO by weight of the total composition.

[0069] As shown in the Table 4 below, the main elements in the electric arc furnace slag (EAF) are iron (Fe), calcium (Ca), silicon (Si), and aluminum (Al) oxides, while the minor elements are magnesium (Mg) and manganese (Mn) oxides, with trace elements (wt.% of <1.0%) such as lead (Pb), phosphorus (P), and fluoride (F). The compositions of electric arc furnace slag from different sources would vary often, based on the composition of the scrap steel materials used for the steel production, the grade of steel produced, and the condition of the EAF refractory lining. Hence a proper sampling method and analysis of the electric arc furnace slag composition have to be performed prior to its recycling as well as a careful choice of the source to avoid slag with too high metal and / or metalloid elements.

[0070] Table 4 : typical examples of electric arc furnace (EAF) slag sources and their main elements.

[0071] Every year, the world generates over 2 billion tons of municipal solid waste, of which, at the very least, 33% is not handled at all and disposed of in landfills or finds its way to open fields or the oceans. Until this day, no comprehensive solution for municipal waste has been present. US2024 / 0191122 proposes an integrating advanced vitrification technology for material conversion can allow 100% recycling in municipal waste treatment. Typical recycled non sorted municipal waste composition comprises 30-40% w / w SiO2, 30-40% w / w CaO, 5- 10% w / w MgO, 3-5% w / w Fe2Os, 0-5% w / w ZnO, 0-5% w / w AI2Os, 0-5% w / w Na2O, 0-5% w / w TiO2, 0-5% w / w ZrO2and 0-5% w / w K2O and therefore could be used as an alternative glass raw material.The melting step (a) of the method for producing silicate glass

[0072] In step (a), the oxide-based waste is melted to obtain the oxide melt.

[0073] 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 coalcomponent 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.

[0074] The specific method of melting oxide-based waste 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 oxide melt can be obtained.

[0075] The production method may further include the step of adjusting the viscosity of the oxide melt. The viscosity of the oxide 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. The viscosity 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 oxide melt can be measured by a rotating cylindrical method, a sphere pulling method, or the like.

[0076] The method for adjusting the viscosity of the oxide melt is not particularly limited, and examples thereof include adding oxide-based waste or a substance whose viscosity can be adjusted to the oxide melt. Substances that can be added to the oxide-based waste or the oxide 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 mentionedThe chemical reducing step (b) of the method for producing silicate glass

[0077] In step (b), the oxide melt is reduced to precipitate a metal phase enriched in the metal and / or metalloid elements M.

[0078] 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 oxide melt, and the like. From the viewpoint of ease of equipment maintenance and power consumption, areducing agent is preferred.

[0079] 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, Si-C, 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.

[0080] 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.

[0081] In the method of reduction treatment using a reducing agent, the reducing agent and the oxide melt are put in contact. For example, by adding a solid reducing agent to the oxide melt; by blowing a gas reducing agent, and / or by melting the glass-containing raw material 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 oxide-based waste 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 oxide-based waste in a container in which a reducing agent is arranged in advance, is preferred.

[0082] When the reducing agent is a granular or lumpy solid and especially, the oxide-based waste 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 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 oxide-based waste. 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.

[0083] When the reducing agent is a solid, the mass ratio of the reducing agent to the oxide meltis 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 oxide 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 oxidebased waste 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.

[0084] The method of reduction treatment may be a method of electrolyzing the oxide melt, and may be used in combination with a method using a reducing agent. When electrolyzing the oxide melt, for example, electrolysis can be performed by arranging two electrodes in the oxide melt and applying a voltage between them.

[0085] 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.

[0086] The reduction treatment time is not particularly limited by the type of reducing agent, the composition of the oxide 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.

[0087] 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 oxide melt tends to be selectively precipitatedas 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 initial oxide-based waste and therefore neither on the purified oxide melt and / or the highly purified oxide materialMetal phase

[0088] Part or all of the metal elements contained in the oxide melt are precipitated as a metal phase by reduction treatment. The metal phase contains at least one element contained in an oxide-based waste of the oxide melt before reduction treatment, and preferably contains the above-described impurity 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

[0089] In step (c), at least a part of the metal phase is separated from the reduced oxide melt to obtain the purified oxide melt. Here, separating at least a part of the metal phase from the oxide melt means physically removing at least a part of the metal phase from the oxide melt, and the purified oxide melt means that at least a part of the metal phase has been removed from the oxide melt.

[0090] 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 oxide 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.

[0091] 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 a glass-containing raw material is melted in the container. Step (b) and step (c) may be performed in parallel.

[0092] Another suitable method comprises a crushing step after the chemical reduction step followed by a separation step via a magnet on a conveyor belt.

[0093] By separating the metal phase by these more preferred methods, the metal phase can bemore suitably separated, and the amount of metal phase remaining in the purified oxide melt is likely to be limited.The oxidation step (d) of the method for producing silicate glass

[0094] The method of the present invention preferably further comprise an oxidation step (d). The oxidation treatment is performed on the purified oxide melt to obtain a highly purified oxide material.

[0095] As described above, even if the metal phase is separated from the purified oxide 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 oxide melt in step (d), the defect derived from metal fine particles in the obtained glass is suppressed.

[0096] 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.

[0097] 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.

[0098] Specific methods for performing oxidation treatment using an oxidizing gas include, for example, a method of bubbling the purified oxide 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.

[0099] 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.

[0100] Another method for performing oxidation treatment includes the addition of an oxidizing agent to the purified oxide melt. The oxidizing agent is preferably in powder form in order to react efficiently. A powder injection method is preferable because it reacts efficiently.

[0101] 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 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 lower than 1700°C, and further preferably equal to or lower than 1650°C.

[0102] 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 oxide melt and highly purified oxide material

[0103] Before and after being processed by steps (a) to (c) and preferably by the additional step (d), the oxide-based waste has a concentration of element M in the oxide-based mass% or mass ppm equivalent is [MO]before and the purified oxide melt and / or the highly purified oxide material has a concentration of element M in the oxide-based mass% or mass ppm equivalent is [MO]after-

[0104] 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 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 s 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.

[0105] In another embodiment, the concentration of the elements M in the oxide-based waste [MO]before, and in the purified oxide melt and / or in the highly purified oxide material [MO]after, satisfies the following equation :0,001 < [(sum of ([MO]after / [MO]before) I n] < 0.850 wherein 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.

[0106] Such equation is preferably satisfied wherein MO is selected from Fe oxide, Co oxide, Cr oxide, Ni oxide and mixtures thereof.

[0107] 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 .

[0108] For example, for an oxide-based waste comprising as elements M, Fe2O3in 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 oxide-based waste 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 oxide 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.

[0109] 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

[0110] By a method including the above steps (a) to (c) and preferably (d), a purified oxide melt and preferably a highly purified oxide material, in which impurity elements are removed from the oxide-base waste can be produced.

[0111] 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) a melting step, (iii) a fining step (iv) cooling step flowing the refined melt from the fining zone to a working zone.Silicate Glass

[0112] 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 glass in the glass-containing raw material used in the production method is not particularly limited, and may be the same as the composition of the glass obtained by the production method except for the content of the impurity element.

[0113] 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 AI2O3is 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.

[0114] 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.

[0115] 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 AI2O3is more preferably 80% or less, and further preferably 78% or less.

[0116] 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.

[0117] 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 1.0% or more. The content of AI2O3is preferably 15.0% or less; more preferably 10.0% or less; and even more preferably 7.5% or less.

[0118] The total content of alkaline earth metal oxides (RO) is preferably 5% to 30%. If the total content of alkaline earth metal oxides (RO) is 5% or more, the meltability is good and preferable. 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] The composition of the silicate glass obtained by this manufacturing 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 B2O3 may 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.

[0125] The shape of the silicate glass obtained by this manufacturing 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 preferable.

[0126] 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.

[0127] Advantageously, the expression soda-lime-silicate glass in the present invention is used in 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). Morepreferably, 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.

[0128] 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 FejOs

[0129] 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%.

[0130] For non-colored glass compositions, it is preferred that the content of Fe2O3is 1500 ppm or less to suppress coloring.

[0131] 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 is comprised 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 totaliron 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.

[0132] 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.

[0133] 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)_ Lifl.ht .transmission. LTD4

[0134] Colored silicate glasses typically have a LTD4 equal to or greater than 7.0% and less than 85.0%.

[0135] 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%.

[0136] 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%.

[0137] 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) representsthe percentage of radiation flux emitted between wavelengths 380 nm and 780 nm which is transmitted through the glass sheet.

[0138] 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.

[0139] 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

[0140] The present invention further relates to the use of a purified oxide melt and / or highly purified oxide 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 to 1500ppm.

[0141] The present invention also relates to the use of a purified oxide melt and / or highly purified oxide 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%.

[0142] Preferably, the present invention further relates to the use of a purified oxide melt and / or highly purified oxide 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 Fe2Os based on the total weight of the silicate glass composition, at a level of 20ppm to 1500ppm 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%.

[0143] The method of the present invention provides indeed purified oxide melt and / or highlypurified oxide material as alternative glass raw material and offers a large flexibility to the glass formulator to balance the advantage of CO2reduction and the technical benefits of iron content and LTD4, to match the clients’ needs. One can focus on a drastic reduction of the CO2 emission 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.

[0144] 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

[0145] 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.

[0146] 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 heating means in the melting zone are comprised of a plurality of electrodes and / or burners and / or thermal plasma torches.

[0147] 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 above1400°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.

[0148] 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 conventional 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).

[0149] 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.

[0150] 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.

[0151] 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 ismeant 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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, allnumbers 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%.

[0156] 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).Example

[0157] Example 1 of the present invention - Cofalit®

[0158] The Cofalit® produced by the INERTAM process has a typical composition as shown in the Table 1 above. Cofalit® is mainly composed of SiO2and CaO and comprises as well high quantity of Fe2O3which indeed limit its usage in silicate glass production.

[0159] Therefore to reduce the content of impurities in this recycled product, the steps (a) and (b) of the present invention has been applied with a reducer component added to precipitate the metal phase. In these examples, the Cofalit® has been melted at 1500°C for 3 hours. The reducing agent is coke comprising about 85wt% of carbon. Quantity of coke per 100 g of Cofalit® is 3g. The furnace is flushed with N2gas during the melting stage.

[0160] 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. No oxidation step (d) was realized at the laboratory scale and the results are presented below.

[0161] After those treatment, the Fe2O3content in the purified Cofalit® has been reduced by a factor of 22 since the purification method of the present invention allows to reduce the original Fe2O3content from 5wt% to 0.23wt%. The treatment has also succeed to reduce the Cr2O3content by a factor 9.

[0162] Composition 1 is a comparative example. It represents the glass batch and glass composition typically used to produce a conventional SLS glass.

[0163] Composition 2 is also a comparative example of the glass batch and glass composition similar to example 1 but wherein untreated Cofalit® has been introduced to replace partly limestone. The proportion of the other raw materials are adjusted.

[0164] Composition 3 is an example of the present invention. It is a the glass batch and glass composition similar to example 2 but wherein the method of the present invention has been performed to use purified Cofalit® material instead of untreated Cofalit®. The purified Cofalit® material is obtained via melting, reduction reaction and metal separation.

[0165] Composition 4 is an example of the present invention. It is a batch identical to composition 3 wherein a much higher amount of purified Cofalit® material is used.

[0166] Table 5: glass batch compositions

[0167] Table 6: glass element compositions

[0168] Table 7: glass properties

[0169] Versus comparative example 1 , comparative silicate glass from example 2 wherein conventional glass raw materials are replaced by untreated Cofalit®, allows a reduction inCO2emissions: 200 kg / Tgiassinstead of 211 kg / Tgiass. However, this glass composition has a very significant drop of light transmission LTD4 of from 89.9% to 83.1% and has a green color. Comparative example 2 is classified as a colored glass composition. 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%.

[0170] Silicate glass of example 3 of the present invention comprising the same amount of Cofalit® but in its purified form. Such silicate maintains the same CO2emissions reduction but provide a much higher LTD4 and significantly reduced of total iron of 670ppm. This glass is therefore classified as a clear glass. It has a neutral color. Clear glass represents the main stream glass production and much higher volume, about 50% of the current glass market.

[0171] Silicate glass of example 4 represents another embodiment of the present invention wherein a substantial amount of purified Cofalit® is used (about 5 times more than example 3) and therefore, a substantial decrease of the CO2emissions is achieved : 144 kg / Tgiassversus example 1 having 211 kg / Tgiass. The silicate glass of example 4 is still classified as clear glass with an amount of 682ppm of total iron despite a slight loss in light transmission. Its color is however slight green because of the remaining presence of chromium.

Claims

CLAIMS1. A method for producing silicate glass from oxide-based waste 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 oxide-based waste 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 oxide-based waste to obtain an oxide melt; b) performing a chemical reaction to reduce the oxide 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 oxide melt to obtain a purified oxide melt; d) preferably, performing an oxidation treatment on the purified oxide melt to obtain a highly purified oxide material; and e) using the purified oxide melt and / or preferably the highly purified oxide material, as component for silicate glass2. The method according to claim 1 wherein the oxide-based waste is selected from the group consisting of : Analcime sand, Biomass ashes, Concrete, Cofalit®, Basic oxygen furnace slag, Electric arc furnace slag and / or municipal waste.

3. The method according to any one of the preceding claims a. wherein the oxide-based waste 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 oxide melt and / or the highly purified oxide 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; and wherein, b. for at least one metal and / or metalloid element, the ratio of [MO]after / [MO]before isequal 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.

4. 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 H2and 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.

5. 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.

6. 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.

7. 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.

8. The method according to any one of the preceding claims wherein the viscosity of the oxide 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.

9. The silicate glass produced by the method according to any one of the preceding claims 1 to 8, 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 110Oppm, preferably at a level equal to or lower than 10OOppm, 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 preferablyat a level equal to or lower than 750ppm by weight of total glass composition.

10. The silicate glass according to claim 9, 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%.

11. Use of a purified oxide melt and / or highly purified oxide 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 comprising iron expressed as total Fe2O3based on the total weight of the glass composition, at a level of 20ppm to 1500ppm.

12. Use of a purified oxide melt and / or highly oxide 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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