Use for the production of glass of a granular material in a substantially spheroidal shape comprising hydrated air lime, method for the production of glass and method for the production of the granular material

Abstract

The present invention relates to the use for the production of glass of a granular material of substantially spheroidal shape comprising hydrated air lime, to a method for the production of glass using said granular material and to the method of producing the granular material.

Description

[0001] " USE FOR THE PRODUCTION OF GLASS OF A GRANULAR MATERIAL OF SUBSTANTIALLY SPHEROIDAL SHAPE COMPRISING HYDRATED AIR LIME, METHOD OF PRODUCING GLASS AND METHOD FOR THE PRODUCTION OF THE GRANULAR MATERIAL"

[0002] Cross-Reference to Related Applications This Patent Application claims priority from Italian Patent Application No. 102025000004864 filed on March 10, 2025, the entire disclosure of which is incorporated herein by reference.

[0003] Technical Sector of the Invention

[0004] The present invention relates to the use for the production of glass of a granular material of substantially spheroidal shape comprising hydrated air lime. The present invention also refers to a method for the production of glass comprising mixing at least a vitrifying material forming a glass network and a granular material of substantially spheroidal shape comprising hydrated air lime as defined above. The present invention further refers to a method of producing said granular material.

[0005] State of the Art

[0006] The use of raw materials supplying calcium and magnesium elements is essential in the production of glass as these elements fulfil the fundamental role of glass network modifiers by acting as stabilisers.

[0007] In general, glass is a material obtained through solidification of a liquid, not accompanied by crystallization: it is therefore an amorphous solid, comparable to a supercooled liquid at very high viscosity, obtained by melting crystalline minerals.

[0008] Glass is composed of a homogeneous mixture of oxides, in varying proportions, distinguished into glass network formers and glass network modifiers.

[0009] The main network formers (also called vitrifyingagents) are silica (SiO2) and boric anhydride (B2O3), but also some other tri- or tetra-valent oxides (of phosphorus, germanium, arsenic, etc. ) have these characteristics. The most commonly used vitrifying agent, constituting the basic structure of glass (network in which silicon and oxygen atoms are bonded together by strong covalent chemical bonds), is silica (SiO2) normally deriving from silicate or quartzbearing stone materials as well as from natural sands (silica sand or quartz sand).

[0010] The network modifiers are distinguished into fluxes (alkaline oxides, mainly of Na and K) and stabilizers (alkaline-earth oxides of Ca, Mg, Ba, etc. ): said elements interrupt the continuity of the network ( for this reason they are called modifiers) creating ionic bonds.

[0011] Among the fluxes, whose function is to facilitate the passage of the vitrifying agent into the liquid state during melting by lowering its own melting temperature, are soda (sodium carbonate, Na2CO3) and potash (potassium carbonate, K2CO3): said compounds also have the property of lengthening the temperature range within which the glass solidifies, thus bringing benefits regarding the workability of the glass in the processing steps for the manufacture of finished products.

[0012] With regard to the glass stabilizers, their function is to improve meltability and fining and to enhance workability (by exerting a beneficial influence on viscosity at high temperatures), as well as to impart the desired physical properties and reduce the possibility of alterations of the glass surface by improving its chemical properties, such as, for example, through the replacement of part of the soda with other compounds, to operate a reinforcement of the network (improvement of the mechanical and thermal shock resistance, reduction of the tendency to devitrification), to limit the effects of surface corrosion of humidity(increase in hydrolytic resistance) and chemical attack by gaseous substances, as well as to contribute to conferring a longer-lasting shine to the appearance of the finished product. In this regard, bivalent oxides of calcium (CaO) and magnesium (MgO) are widely used, whose supply is generally provided through raw materials deriving from carbonate rocks (limestone and dolomite). Barium (BaO), lead (PbO) and zinc (ZnO) oxides can also be used, as well as alumina (Al2O3) and boric anhydride (B2O3): for example, alumina, generally added in the form of alkaline feldspars, serves to improve the chemical resistance of the glass and to control the viscosity of the melt, whereas lead, added in the form of oxide (Pb3O4or PbO), increases the shine of the glass.

[0013] Further raw materials that make up the vitrifiable mixture are given by the so-called refining compounds, such as for example sulfates (e. g. sodium sulfate, Na2SO4) optionally associated with reducing agents such as carbon, which, by releasing oxygen due to the effect of thermal decomposition, favour by coalescence the elimination of the bubbles of the gases produced by decomposition of the raw materials (mostly CO2mainly attributable to the decomposition of the carbonates ) and contribute to the homogenization process of the molten glass.

[0014] Decolouring components (e. g. manganese dioxide, nickel oxide, selenium, cobalt, etc. ) can also be added to the vitrifiable mixture, which, especially in the production of glass with a high degree of transparency ("white" glass), are designed to eliminate the effects induced by the presence of some particularly colouring elements even in traces (e. g. iron, chromium, etc. ) contained as an impurity in the raw materials. Further additives may include the addition of opacifying components or colouring components.

[0015] A further component of the vitrifiable mixture can berepresented by glass cullet: since glass is a totally recyclable material, it can be remelted and shaped countless times, without losing or modifying its properties. Glass cullet can be either of "internal" origin, i. e. deriving from the production process (having the same composition as the glass produced) or of "external" origin deriving from post-consumer selection and recycling operations (greater variability in composition and colour homogeneity). The presence of glass cullet in the vitrifiable mixture accelerates melting and saves energy and raw materials.

[0016] Normally, the preparation of the vitrifiable mixture fed to the glass furnace is carried out in "batch" mode inside the so-called composition and preparation station (batch house). The process takes place by dosing and weighing the various virgin raw materials, having a calibrated particle size distribution, being fed to a mixing apparatus in which a predetermined water quantity in liquid or steam form is generally additivated (batch moistening generally up to maximum values by weight not higher than 4-5%) in order to optimise the homogeneity of the mixture itself, maintaining the various components with a certain degree of adhesion to each other so as to prevent segregation phenomena as well as the development of fugitive dust emissions in the various handling steps up to the loading section of the vitrifiable mixture to the melting furnace and losses of material attributable to entrainment phenomena in the flow of the exhaust gases inside the furnace ( carryover).

[0017] The addition of any glass cullet is carried out at a time subsequent to the preparation of the vitrifiable mixture itself and in some cases immediately upstream of the entrance into the furnace.

[0018] Normally, the raw materials that make up the vitrifiable mixture are stored in dedicated silos, arranged in a battery, each provided with a special extractor provided with aweighing scale that discharges the material onto a conveyor, usually a belt one, which runs along the entire battery of the storage volumes until the vitrifiable mixture is supplied, which is then made up with layers of the various raw materials, to the mixing apparatus; alternatively the discharge of the various raw materials can take place by means of screw dosing systems or by means of vibrating channel systems, inside an intermediate containment volume, optionally weighed, and from here in turn transferred to the mixing system.

[0019] The glass furnaces for the production of hollow glass and flat glass on an industrial scale have characteristics and design geometries that are completely peculiar to the two categories of glass, although they still fall within the category of so-called "tank" type furnaces in which the melting process develops in continuous mode within a large rectangular tank (surface area ranging from a few tens up to over a hundred m2) provided with a refractory-lined crownin which the vitrifiable mixture, brought to temperature values of the order of 1300-1600°C, melts until a molten glass bath is formed with a depth of 80-150 cm, is homogenised and refined. The input of thermal energy to the melting process is conventionally and commonly provided by a flame fuelled by natural gas or fuel oil that laps above the melting bath and produces its heating mainly by irradiation, or through a mixed system or, especially in smaller furnaces, completely electric, in which a portion (electric boosting generally between 5-20% and in some cases even up to 30%) or the entire energy requirement ( 100%) is given, by Joule effect, by a series of electrodes immersed in the molten bath itself. The most modern glass furnaces are however designed to optimise melting, for example, by adopting oxy-fuel combustion systems, i. e. to maximise heat recovery from flue gases (e. g. pre-heating of the comburent air, pre-heating of the glasscullet, etc. ) and the heat input is organised and controlled in such a way as to generate temperature gradients in melting of the glass and induce recirculating natural convection flows within the molten mass which are adapted to guarantee a constant homogeneity of the molten glass introduced in the subsequent forming processes.

[0020] In the furnaces with a flame heating system, in order to increase the thermal efficiency of the melting process, the combustion air is preheated by recovering heat from the flue gases generated by the combustion. The preheating systems of the combustion air can be of a recuperative type, i. e. with heat recovery by means of metal or ceramic heat exchangers (" Unit Melter" furnace) or of a regenerative type, in furnaces equipped with chambers consisting of checkerwork of refractory material (regenerators) for heat recovery. The regenerative furnaces are of two types: furnaces with longitudinal flame (parallel to the glass flow) and rear regenerative chambers (" End-Port" furnace) which, as they involve a periodic reversal of the gas flow, are also called " U-shaped flame" furnaces and the furnaces with "transverse flame" (perpendicular to the glass flow) and lateral regenerative chambers (" Side-Port" furnace).

[0021] In the case of preheating with metal heat recuperators (" Unit Melter" furnace) the system provides continuous heating of the combustion air up to temperature values of 800°C, whereas with the regenerative system (" End-Port" furnace, " Side-Port" furnace) the heat recovery process is intermittent, since the furnace is equipped with two chambers that operate alternately, in a first step by receiving the hot flue gases and discharging them at about 400-450°C and in a second step by receiving the cold combustion air and preheating it up to a temperature of about 1350°C. In the case of using pure oxygen in place of the combustion air (oxy-fuel combustion), the preheating step is not carriedout. Generally, for the production of hollow glass, the type of " End-Port" furnace is the most commonly employed, whereas for the production of flat glass, the most widely used type of furnace is the " Side-Port" furnace.

[0022] Once the melting in the designated zone of the tank furnace is completed, the molten glass passes, by flowing through a submerged throat, to a subsequent refining and conditioning zone in order to eliminate the trapped gas bubbles and make the glass mass comply with the production specifications for subsequent processing.

[0023] The industrial production of the hollow glass includes the manufacture of products intended to contain liquids or foodstuffs, both products for home use and glassware with a higher value, as well as products that can be related to the chemical-pharmaceutical industry, perfumes and cosmetics: drinking glasses, bottles, vases, j ars, ampoules, etc.

[0024] The industrial production of flat glass involves the manufacture of products intended mainly for the construction and interior design sectors as well as the automotive industry and also in other sectors such as, for example, the manufacture of household appliances and electronic equipment, medical devices, products in the field of renewable energies, etc.

[0025] With regard to the production of hollow glass, the molten glass exiting the tank furnace undergoes the following processing:

[0026] forming step: the molten liquid enters the so-called thermal conditioning channels ( 1050-1250 °C) and, having reached the appropriate viscosity that allows it to be formed, is cut into "gobs" of appropriate weight and size and therefore, by guided vertical fall, reaches the moulding sections (blanking and finishing) of the forming machine at the outlet of which the articles are cooled by convection by forced-air and made to rapidly solidify in order to preventcollapse or deformation thereof; - annealing step: the formed articles undergo a hot surface treatment (500-600°C) and a subsequent gradual cooling under controlled conditions down to room temperature that allows the internal stresses introduced during the forming process to be eliminated. In this step the glass retains its shape and undergoes no change in chemical composition. At the same time as the annealing step, a series of hot-end and cold-end surface treatments are usually carried out in order to make the glass surface water-repellent and prevent the formation of abrasions and microcracks caused by direct glass-to-glass contact;

[0027] further possible secondary processing of the hollow glass may include decorative treatments such as screen printing, engraving, painting, sandblasting, satin finishing, etc.

[0028] As regards instead the production of flat glass, the molten glass exiting the tank furnace undergoes the following processing:

[0029] forming step: it takes place through the so-called " Float" process which provides that the molten glass exiting the melting furnace ( 1000-1100 °C) is poured and passes in a second furnace floating on top of a molten tin bath, 4-8 metres wide and up to 60 metres long, kept in a reducing atmosphere in order to prevent oxidation thereof. The glass, by floating and expanding on the liquid and flat surface of the tin bath, is pulled until it becomes a ribbon with perfectly flat and parallel faces; since the balance between gravitational forces and surface tension produces a layer of uniform thickness, appropriate devices act on the edge of the ribbon to slow down or accelerate its spreading so that the width and thickness of the resulting ribbon is adjusted up to the desired value, generally between 1.1 mm and 19 mm;

[0030] annealing step: the glass ribbon exiting the tin bath, sufficiently solidified, is deposited on the rollersof an annealing lehr where it undergoes a slow and controlled cooling from temperature values of 500-600°C down to room temperature;

[0031] cutting and squaring step: once cooled, the glass strip is cut into sheets with the elimination of the longitudinal edges;

[0032] further possible secondary processing of the flat glass may include surface and edge treatments of the formed sheets (e. g. cutting, drilling, bending, grinding of the edges), processes aimed at improving mechanical strength (e. g. tempering, hardening, lamination), processing for the modification of the optical properties (e. g. coating, silvering) as well as decorative processes (e. g. engraving, sandblasting, acid etching, painting, frosting, etc. ).

[0033] Given the extent of both the hollow and flat glass manufacturing industry, the need is felt to provide new calcium and magnesium element-supplying materials that effectively act as glass network stabilisers and are energy and environmental beneficial.

[0034] In view of the aforementioned state of the art, the Applicant has set itself the primary obj ective of replacing carbonate-based raw materials supplying calcium and magnesium to the vitrifiable mixture, such as the "raw" products deriving from the processing of limestone (CaCO3) or dolomite (CaCO3.MgCO3) rocks, which are commonly used in the glass sector, with a product that entails advantages from the melting point of view (increase in melting kinetics), from the energy point of view (reduction in specific consumption) and from the environmental point of view (lower CO2emissions).

[0035] It has already been partially demonstrated that the use of hydrated air lime (hereinafter, also referred to as "hydrated lime" ) in place of carbonate raw materials in vitrifiable mixtures can bring a series of benefits. In fact,hydrated lime, by decomposing by dehydration and dissociating itself, originates, already at lower temperatures (T= 420-580°C) than a homologous carbonate (T= 700-898 °C), a calcium oxide particularly active towards soda and therefore more reactive towards silica that can lead to the increase in the kinetics of glass formation (increase in the solubilization rate with increase in the dissolution rate of silica following a faster formation of eutectic compounds by reaction with soda until completing the melting of the sodium-calcium pre-silicates formed still in the solid phase) and to a better final refining of the molten glass. The melting process of the vitrifiable mixture basically takes place according to 3 fundamental steps:

[0036] 1 ) initial reactions between the raw materials that produce a pre-melt: this reaction is extremely important since the amount of pre-melt formed affects the rate with which the subsequent steps of the melting process proceed;

[0037] 2 ) dissolution of the sand granules (silica) in the pre-melt (the more abundant the amount of pre-melt, the more accelerated the process of dissolution of the sand granules);

[0038] 3) homogenization and refining of the molten glass. Step ( 1 ) is the one most affected by the characteristics of the raw materials, which, by coming into contact with each other, react and form low-melting silicates (pre-melt); since said reactions take place in the solid phase, the reactivity of the raw materials and the rate of the reactions between them are extremely important. The decomposition of hydrated lime generates a very active air quicklime (hereinafter also referred to as "quicklime" ) which, by combining with sodium carbonate, is particularly reactive towards silica; the reaction compounds of calcium and sodium with silica are rapidly formed still in the solid phase immediately after the structural transformation of the quartz which, at a temperature of about 600°C, passes fromthe alpha to the beta allotropic form.

[0039] The formation of a liquid phase therefore occurs at relatively low temperatures as a result of the melting of the eutectic which reacts significantly with the silica.

[0040] In the molten glass with hydrated lime, the silica segregation phenomenon is less marked, and the rate at which the residual silica disappears is higher.

[0041] The above results in potential energy benefits ( less energy required for the melting process and therefore less consumption of electricity and fuels) and environmental benefits (reduction of CO2emissions deriving from combustion and from the process). The use of already decarbonated and hydrated products allows in fact to increase the melting rate of the raw materials and, consequently, to improve the melting capacity of a glass furnace or, with the same production output, to reduce the specific consumption of fuel with lower CO2emissions.

[0042] Further benefits in the use of raw materials based on hydrated lime lie in the fact that, with the raw materials supplying calcium and magnesium being of the same origin, the use of a material in hydrated form and already decarbonated compared with the homologous carbonate product of derivation, precisely because raw materials of lower molecular weight are used, is able to increase the yield of the vitrifiable mixture so that relative to the raw material used it is possible, with the same thermal cycle adopted, to produce, in mass terms, a greater quantity of glass (increase in the so-called "pull rate" of the furnace). Other benefits in the use of raw materials based on hydrated lime can be found in an optimization of the viscosity of the glass that leads to better workability conditions. Additional advantages may also derive from the fact that raw materials based on hydrated lime are, in general, able to give the glass greater brilliance and transparency in relation to apossible lower content of organic matter and, especially in the case of the production of "semi-white" or "white" glasses, reduce in certain cases the demand for decolouring additives since the oxides that give greater colouring problems such as, for example, in the case of iron oxides, are more present in the ferrous form (FeO) rather than in the ferric form (Fe2O3), it being known that the latter form turns out to have a more significant negative influence.

[0043] Although the use of hydrated lime in substitution of the corresponding carbonate raw materials has already been tested, the large-scale adoption of this type of raw material has never actually become widespread due to the inherent nature of hydrated lime, which presents as a powder characterised by extreme fineness which, if not properly managed, can give rise to several problems of extraction from storage silos: for example, if in a highly aerated state, hydrated lime can exhibit the risk of erratic flow and uncontrolled discharge, whereas in the presence of moisture and electrostatic charges or of prolonged conditions of rest, the hydrated lime, following an increase in cohesive forces, may exhibit outflow difficulties. In addition to this, its micronized powdered nature makes the material extremely volatile, an unfavourable condition as regards the risk of accidental dust dispersions into the surrounding space during material handling ( fugitive dust emissions).

[0044] Further problems related to the use of micronized powdered hydrated lime can arise due to the high reactivity of the fine particles of hydrated lime with the other components of the vitrifiable mixture batch (e. g. sodium carbonate, silica sand, feldspathic sand, etc. ) which, in the presence of water and of modest temperature increases starting from values as low as 35–40°C, can give rise to the formation of concretions on the conveying and processequipment.

[0045] In addition to the problems that can be encountered in the handling operations upstream of the vitrifiable mixture composition and preparation station (batch house) and downstream thereof up to the furnace, given the high fineness of the micronized powdered hydrated lime, especially in furnaces with a flame heating system where there is significant gas circulation, undesirable phenomena of material loss attributable to entrainment effects in the exhaust gas flow inside the furnace (carryover) could occur; in such a case, in addition to the loss of raw material and the alteration in the glass composition, the risk of fouling of the surfaces of the regenerative or recuperative type heat exchange systems may materialise, with a consequent loss of energy efficiency or even worse, in the most extreme cases, the occurrence of chemical attack phenomena on the same.

[0046] The possible use of quicklime in the production of glass in place of calcium carbonate and calcium-magnesium carbonate is also known.

[0047] US 2020 / 0156980 Al, for example, considers the use of calcium oxide in the preparation of the mixture of the vitrifiable raw materials in place of calcium carbonate by admixing the batch with a certain time delay with respect to the mixing of the other raw materials, sand, sodium carbonate and water.

[0048] Document US 2007 / 0098610 Al describes a method for delaying the reactivity with water of the quicklime, to be used in the field of glass production, by means of a chemical modifying agent that involves contacting the quicklime with an aqueous solution containing boron-based compounds (e. g., a saturated borax solution); the contact with the borax (2-5% by weight with respect to the total weight of the quicklime) is promoted by spraying or dripping onto thequicklime in lumps or granules while in transit on a conveyor belt before the material reaches a grinding step or can be applied on the material directly inside a grinding apparatus.

[0049] However, the possible use of quicklime in substitution of carbonate raw materials (limestone and dolomite) in glass production raises certain concerns. In fact, in the case of using quicklime in the preparation of the vitrifiable mixture, it is absolutely useful to provide that the free water constituting the moisture of the batch is brought more into contact with the sodium carbonate rather than with the quicklime in order to prevent hydration effects of the latter with consequent problems, even in the case of using granular materials which compared to those in powdered form have smaller contact surfaces with water, nevertheless linked to the increased generation of fine powdered particles of calcium hydroxide and of the potential emission of dusts. The dehydrating nature of quicklime, combined with the exothermic hydration reaction of calcium oxide, can also lead to a more marked and undesired drying of the batch, which is a condition under which potential negative effects of demixing of the raw materials may occur, as well as problems of material loss upon introduction into the melting furnace due to gas entrainment phenomena (carryover).

[0050] Further problems may be encountered with regard to operator safety since quicklime, being particularly reactive with water (exothermic behaviour associated with the hydration reaction of the respective calcium or calcium / magnesium oxides) and exhibiting strong alkalinity and causticity as well as intense desiccating properties, on contact with the skin, mucous membranes, eyes and respiratory tract, can cause hypersensitisation, irritation and inflammation reactions which in the most severe cases may cause burns and injuries.

[0051] Even when it is in granular form, i. e. intrinsicallyhaving a lower reactivity with water than a homologous product in powdered form (e. g. smaller contact surfaces), although surface treated in order to maintain some delay in reactivity, quicklime still retains a certain activity once inserted into the glass production process following any comminution effects that may occur in the normal handling and use (storage, extraction, mixing and preparation of the vitrifiable mixture batch, conveying to the glass furnace) and which may result in exfoliation of the particles by abrasion or cause them to break, thus exposing the core and renewing the active part of the substance.

[0052] Various agglomeration solutions for the entire batch of vitrifiable mixture by means of granulation techniques known in the state of the art have also been proposed.

[0053] Document US 4, 028, 131 describes a method for the generation of a batch mixture of glass raw materials, capable of increasing the melting rate and having an optimized refining, obtained by mixing sand with calcium and / or dolomitic quicklime and a caustic alkali in the presence or absence of an alkali metal salt; the batch thus formulated can be produced in the form of dry granules.

[0054] Document US 2017 / 0174545 Al describes the production process of composite granules, having an average size between 412 pm and 2 mm, containing homogeneously and in due proportions the various raw materials that give rise to a specific glass composition; the production process of the granules is a wet granulation process that includes water ( 6-20 parts by weight) as the working fluid and may also comprise specific binding agents (e. g. boric acid, sodium hydroxide, calcium chloride) and a subsequent drying step of the granules produced.

[0055] Document US 2016 / 0168011 Al deals with a method for the production of the granules of glass raw materials through a wet granulation process which includes mixing the glass rawmaterials (a silicon source, an aluminium source and a calcium source in the form of calcium oxide and / or calcium hydroxide) with water ( 15-25% by weight) by using a high shear mixer and providing downstream of said wet granulation step a drying step of the produced granules (having a median particle size (D50) in the range of 1-15 mm).

[0056] In any case, the granulation of the entire batch of vitrifiable raw materials raises concerns about the flexibility of plant productivity management with regard to any adjustment of the composition of the batch itself or of the glass recipe change. Another aspect concerns the need to have a substantial plant equipment as well as to have a management of raw materials entirely different from the one that is usually adopted in the glass industry.

[0057] Intermediate solutions have still been proposed which are adapted to obtain granular products as precursor materials of the glass matrix as, for example, described in document US 6, 271, 159 Bl in which a method of manufacturing cylindrical pellets based on synthetic calcium and magnesium silicates is reported, which are obtained by mixing a source of calcium and / or magnesium (in the form of quicklime or hydrated lime, or hydraulic lime, etc. ), water and a source of silicon dioxide (silica sand, soluble silicates, sodium silicates, etc. ) which, however, often have the drawback of having to implement medium- to high-temperature thermal processes to stabilize and impart mechanical strength to the granulate products generated.

[0058] In the state of the art, it is known to produce granular hydrated lime by granulation or pelletizing processes in which quicklime or hydrated lime in powdered form is used as the starting material.

[0059] EP 2 039 655 Al, for example, describes the preparation of spherically shaped porous granules based on calcium hydroxide (Ca(OH)2), to be used as fixed-bed packing materialfor the absorption of hydrohalogen gases, characterized by a high specific surface area (BET > 20 m2 / g), a high pore volume of sizes 2-100 nm (BJH = 0.25-0.40 ml / g) and having dimensions equal to or less than 1 mm in an amount not exceeding 5% by weight and dimensions equal to or greater than 10 mm in an amount less than 5% by weight. The porous granules based on calcium hydroxide (Ca(OH)2) are generated starting from calcium hydroxide having a specific surface area BET > 30 m2 / g which is mixed with amounts of water on the order of 35-55% and then subj ected to a wet granulation process inside a rotating cylinder and to a subsequent drying step; alternatively the starting material may consist of calcium oxide and the process may provide for a preliminary hydration step.

[0060] Summary of the Invention

[0061] An aim of the present invention is to provide the use for the production of glass of a granular material of substantially spheroidal shape comprising hydrated air lime capable of overcoming the drawbacks highlighted by the raw materials supplying calcium and magnesium elements of the prior art.

[0062] In particular, the use of this granular material is aimed at overcoming the problems related to the handling (dustiness), interaction with the other raw materials making up the vitrifiable mixture ( formation of concretions) and use in the furnace (entrainment in the flow of the exhaust gases) and is able to bring benefits in terms of melting kinetics and the quality of the glass produced, as well as from an energy and environmental point of view.

[0063] The product in granules of substantially spheroidal shape based on hydrated air lime is also able to guarantee adequate flexibility during use in the glass process as it does not interfere with any need to be able to implement a rapid change of recipe during the production of the glass.A second aim of the present invention is to provide a method for the production of glass that is simpler, more efficient and more advantageous from an energy and environmental standpoint.

[0064] These and other aims, which will be better explained below, can be achieved by means of the use for the production of glass of a granular material as defined in claim 1. The present invention further concerns a method for the production of glass as defined in claim 8.

[0065] Further features and advantages of the present invention will be more apparent from the following detailed description.

[0066] Detailed Description of the Invention According to the present invention, a granular material of substantially spheroidal shape comprising hydrated air lime is used for the production of glass, the material having:

[0067] - a total concentration of CaO and MgO equal to or greater than 80% with respect to the weight of the granular material after subtraction of its free water and chemically bound water content;

[0068] - a compressive load until rupture equal to or greater than 40 N / granule, preferably equal to or greater than 50 N / granule;

[0069] wherein said hydrated air lime (hereinafter, also referred to only as "hydrated lime" ) is selected from the group consisting of:

[0070] - calcium hydrated air lime having an MgO content equal to or less than 5% by weight with respect to the weight of the hydrated air lime after subtraction of its free water and chemically bound water content;

[0071] - magnesium hydrated air lime having an MgO content greater than 5% by weight and less than 30% by weight with respect to the weight of the hydrated air lime aftersubtraction of its free water and chemically bound water content;

[0072] - dolomitic hydrated air lime having an MgO content equal or greater than 30% by weight and, preferably, equal to or less than 42% by weight with respect to the weight of the hydrated air lime after subtraction of its free water and chemically bound water content; and

[0073] - mixtures thereof.

[0074] The hydrated lime usable for the purposes of the present invention is in fact selected from: calcium hydrated lime, magnesium hydrated lime, dolomitic hydrated lime and mixtures thereof. Hydrated lime is represented by the chemical formula Ca (OH) 2 (calcium hydrated lime), or the formula Ca (OH) 2. MgO (magnesium hydrated lime, dolomitic hydrated lime), where magnesium is only partially in hydrated form.

[0075] As mentioned, the hydrated lime usable for the purposes of the present invention comprises calcium and magnesium, expressed as CaO and MgO, in a total amount CaO+MgO equal to or greater than 80% by weight, said percentage being referred to the weight of the calcined hydrated lime, that is after subtraction of the free water and bound water content, where the free water is the film water, combined by surface absorption and retained by only physical forces, removable by a drying heat treatment at 105°C until constant in weight and the bound water is the water chemically combined with the calcium oxide and with the magnesium oxide with which it forms the corresponding hydroxides, removable, for example, by a calcination heat treatment at 600°C until constant in weight.

[0076] In a preferred embodiment, the hydrated lime usable for the purposes of the present invention is selected from calcium hydrated lime of type CL90-S (having, with respect to the weight of the hydrated lime devoid of free water andchemically bound water, calcium and magnesium content in terms of the summation CaO+MgO > 90%, magnesium content expressed as MgO < 5% and residual CO2 content < 4% and sulfur content reported in terms of SO3≤ 2%), magnesium hydrated lime of type DL90-5-S1 (having, with respect to the weight of the hydrated lime devoid of free water and chemically bound water, calcium and magnesium content in terms of the summation CaO+MgO > 90%, magnesium content expressed as MgO > 5% and residual CO2 content < 6% and sulfur content reported in terms of SO3≤ 2%) and dolomitic hydrated lime of type DL90-30-S1 (having, with respect to the weight of hydrated lime devoid of water free and chemically bound water, calcium and magnesium content in terms of the summation CaO+MgO > 90%, magnesium content expressed as MgO > 30% and residual CO2 content < 6% and sulfur content reported in terms of SO3≤ 2%), the above types of lime being defined in standard EN 459-1: 2015.

[0077] The chemical composition of the hydrated lime usable for the purposes of the present invention, in particular the CaO, MgO, CO2and SO3content, is intended to be determined in accordance with standard EN 459-2: 2021.

[0078] The granular product based on hydrated lime used in the invention has chemical composition, density, mechanical strength compatible with the formulation of the glass recipe, as well as with the preparation steps of the vitrifiable mixture and has a high chemical activity under the conditions of use in the melting process for the manufacture of glass.

[0079] The particular characteristics of mechanical strength of the granules, as well as the spheroidal geometric shape of the granules ( substantially free of sharp edges), reduce the formation of fine powders following the handling of the material, thus limiting the degradation of the particle size curve of the product and the generation of fugitive dust emissions.The substantially spheroidal shape of the granules makes the granular material extremely free-flowing and prevents undesirable agglomeration phenomena, thus improving the problems typically associated with the storage of powdered and granular products with a low degree of sphericity and irregular shape, such as the cohesive phenomena with the formation of compact agglomerates (caking) or the mechanical interlocking phenomena with consequent difficulties in extracting of the material from the storage silos and in dosing it.

[0080] The granular product based on hydrated lime used in the present invention is obtained through a wet granulation process that provides for the use, as starting materials of the corresponding hydrated products in agglomerated form, of calcium hydrated lime ( identified by the main substance calcium hydroxide - Ca(OH)2), dolomitic hydrated lime, so-called "type N" (i. e. also referred to as dolomitic semihydrated lime and identified by the main substance calcium hydroxide-magnesium oxide - Ca(OH)2.MgO, although a percentage portion of the magnesium oxide is actually also hydrated whereby the substance de facto comprises calcium hydroxide - Ca(OH)2, magnesium oxide – MgO and magnesium hydroxide - Mg(OH)2) and magnesium hydrated lime (comprising calcium hydroxide, magnesium hydroxide and magnesium oxide and identified, similarly to dolomitic hydrated lime, by the main substance calcium hydroxide-magnesium oxide -Ca(OH)2.MgO).

[0081] The starting hydrated lime to be used in the wet granulation process derives from the hydration of air quicklime, in particular of calcium air quicklime having a MgO content equal to or lower than 5% by weight, of magnesium air quicklime having a MgO content greater than 5% by weight and lower than 30% by weight and of dolomitic air quicklime having a MgO content equal to or greater than 30% by weightand, preferably, equal to or lower than 42% by weight.

[0082] In particular, the present invention also relates to a method of producing a granular material of substantially spheroidal shape comprising hydrated air lime having:

[0083] - a total concentration of CaO and MgO equal to or greater than 80% with respect to the weight of the granular material after subtraction of its free water and chemically bound water content;

[0084] - a compressive load until rupture equal to or greater than 40 N / granule and preferably equal to or greater than 50 N / granule;

[0085] wherein said hydrated air lime is selected from the group consisting of:

[0086] - calcium hydrated air lime having an MgO content equal to or less than 5% by weight with respect to the weight of the hydrated air lime after subtraction of its free water and chemically bound water content;

[0087] - magnesium hydrated air lime having an MgO content greater than 5% by weight and less than 30% by weight with respect to the weight of the hydrated air lime after subtraction of its free water and chemically bound water content;

[0088] - dolomitic hydrated air lime having an MgO content equal or greater than 30% by weight and, preferably, equal to or less than 42% by weight with respect to the weight of the hydrated air lime after subtraction of its free water and chemically bound water content; and

[0089] - mixtures thereof;

[0090] including at least:

[0091] a. preparing a mixture comprising:

[0092] 1 ) hydrated lime with a total concentration of CaO and MgO equal to or greater than 80% with respect to the weight of the hydrated lime after subtraction of its free water and chemically bound water content;2 ) a granulation fluid comprising water;

[0093] b. mixing this mixture until wet granules are obtained comprising particles of said hydrated lime;

[0094] c. drying said wet granules to obtain granules comprising hydrated lime with a residual content of free water of less than 1.5% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight, and even more preferably less than 0.2% with respect to the weight of the dried granules, said granules having a substantially spheroidal shape.

[0095] It should be noted that the hydration of quicklime, i. e. the reaction between calcium oxide - CaO (calcium quicklime) or mixed calcium / magnesium oxide - CaO. MgO (magnesium quicklime, dolomitic quicklime) and water in stoichiometric amounts sufficient to satisfy its chemical affinity, leads to the disintegration of the original lattice structure (cubic) and the formation of a new crystal lattice (ditrigonal scalenohedral in the form of a bipyramid or hexagonal prism) with an increase in volume that precisely results in the formation of a hydrated product.

[0096] In the industrial field, the process of hydration of quicklime for the production of hydrated lime in solid powder form is also defined as "dry" as opposed to the so-called "wet" processes which, implemented by means of water quantities in large excess with respect to the stoichiometric ratio, lead to obtaining hydrated lime-based products in paste or liquid form such as, for example, lime putty (a dense dispersion of hydrated lime in water) and milk of lime (a fluid suspension of hydrated lime in water).

[0097] The "dry" hydration process of quicklime for the production of hydrated lime in solid powder form is carried out in dedicated reactors by adding an amount of hydration water strictly necessary to obtain a dry powdery product with a small percentage of residual moisture content of theorder of a few percent and usually less than 1%; in practice, to ensure the complete conversion of the quicklime into hydrated lime, a moderately overstoichiometric water dosage is required in order to compensate for the fraction of water lost through evaporation (exothermic reaction) and / or dispersion to the surroundings of the plant.

[0098] Regardless of the dimensional and structural form of the starting quicklime of standard industrial production (lumps, granules or powder) fed to the hydration process, the hydrated lime in solid form is by its nature a solid material (ionic solid with a crystalline structure) in a subdivided form, consisting of a discrete set of particles having sizes ranging from nanometric to micrometric scale, whose upper extreme is generally less than 200 micrometres and typically less than 90 micrometres. The powdery nature of the hydrated lime results from the separation of the mineralogical associations of the crystalline forms of its elementary components along the contact planes. The hydrated lime in solid form having a finely subdivided particle nature exhibits an absolute density between 2.25-2.70 g / cm3, an apparent density between 1.10-2.45 g / cm3and bulk density values between 0.30-0. 65 g / cm3.

[0099] In general terms, the density (or volumetric mass) of a substance is the ratio of its mass to the volume it occupies.

[0100] For a solid particle material, there are essentially three different types of density, as described below.

[0101] Absolute density (true density or solid density): it is the ratio of the mass to the volume (solid) excluding any voids optionally present between granules (intergranular) and the voids (open and closed) within each granule ( intragranular ). Absolute density depends on the packing of atoms in the crystal lattice and therefore represents the so-called "solid density".Apparent density: is the ratio of the mass to the volume of the material in its existing state, in which any voids contained in each granule ( intragranular ) are considered. Apparent density therefore represents the average volumetric mass of the granules comprising a given material, defined as the ratio of mass to the unit volume of material excluding only the voids between granules (intergranular); for granular materials, whether they are in granular or powder form, this property therefore represents the so-called "particle density" (i. e. the "granule density" ).

[0102] Bulk density: it is the ratio of the mass to the volume occupied by a loose material in bulk not vibrated or compacted in any way. It is therefore defined as the mass of the solid fraction of the entire set of particles constituting the bulk, divided by the total volume, which occupies the entire set of particles constituting the bulk including the volume of any intragranular voids (open and closed) and the volume of all intergranular voids. Bulk density is correlated to the average apparent density of the particles as well as their sizedistribution and shape.

[0103] The specific surface area BET of hydrated lime is generally between 11-18 m2 / g (on average of the order of 12-16 m2 / g), although there are products, physically improved, so-called "high specific surface area", having values of said parameter greater than 20 m2 / g (typically between 25-35 m2 / g) and up to values greater than 45 m2 / g, obtained by adopting particular conditions during the hydration step of quicklime and the use of appropriate additives. In general, hydrated lime has a value of the total volume of the pores BJH between 0.04-0.08 cm3 / g, while for physically improved products ( for example in the case of "high specific surface area" hydrated lime) it is usually greater than 0.10 cm3 / g also up to 0.20 cm3 / g or even greater; reasoning in terms of pore size distribution, hydrated lime is typically amesoporous product whose pore width falls in the range of 20-500 A (2-50 nanometres), the average pore diameter usually being between 50-60 A at the lower end and between 200-250 A at the upper end, although it can be up to 400-650 A.

[0104] The above-mentioned product of substantially spheroidal shaped granules based on hydrated lime used in the present invention shows chemical characteristics generally depending on the starting raw material which, however, can present a further increase in the MgO hydration rate, in addition to peculiar physical properties (shape, structure, specific surface area and porosity, mechanical strength) which make it extremely interesting when compared to the powder products from which it originates (degree of dustiness, ease of use and handling, optimized physical characteristics such as, for example, specific surface area and porosity).

[0105] Further benefits with respect to the hydrated limebased materials of common industrial production arise from the optimized handling, processing and end use in that the hydrated lime-based products in granules with substantially spheroidal shape generated artificially as described herein are able to overcome, for example, phenomena of poor flowability or undesired particle agglomerations with all the related problems (poor silo discharge, difficulties in dosing, etc. ) as may happen in the case of powder products especially with a high degree of fineness, as well as the release of unintended powder fractions ( fugitive dust emissions, etc. ).

[0106] Another advantage arising from the production of a hydrated lime-based product in granules of substantially spheroidal shape starting from the homologous materials in powder form is the possibility of being able to formulate a new product also using fine fractions resulting from the processes that are routinely performed in the lime production cycle ( for example, powders generated during lime kilnoperation or powders captured by the environmental control systems such as, specifically, those generated during comminution and particle-size separation operations, or at silo discharge and vehicle loading points, etc. ). In some cases, due to their heterogeneity, these fine fractions can pose challenges for the reuse and for operational balance of lime production plants.

[0107] The hydrated lime usable for the purposes of the present invention, in addition to Ca, Mg, 0 and H may also comprise impurities of other elements (e. g. sulfur, silicon, iron, aluminium), preferably in a total amount (expressed in terms of the sum of the amounts of the corresponding oxides SO3, SiO2, Fe2O3and Al2O3) not greater than 1.0%, preferably less than 0.5%, more preferably less than 0.2% by weight and even more preferably less than 0.1%.

[0108] The hydrated lime usable for the purposes of the present invention may comprise a residual fraction of inorganic carbon expressed as CO2 not greater than 6%, preferably less than 4%, more preferably less than 2% and even more preferably less than 1%.

[0109] In a preferred embodiment, the hydrated lime usable for the purposes of the present invention is a dolomitic hydrated lime in which the Mg / Ca weight ratio is between 0.36 and 0. 62, more preferably between 0.52 and 0. 62, and / or the Mg / (Ca+Mg) ratio is in the range of 0.27-0.38, more preferably in the range of 0.34-0.38.

[0110] In another preferred embodiment, the hydrated lime usable for the purposes of the present invention is a calcium hydrated lime in which the Mg / Ca weight ratio is between 0.002 and 0.04, preferably between 0.01 and 0.02, and / or the Mg / (Ca+Mg) ratio is in the range of 0.002-0.04, more preferably in the range of 0.01-0.02.

[0111] In a further preferred embodiment, the hydrated lime usable for the purposes of the present invention is amagnesium hydrated lime in which the Mg / Ca weight ratio is between 0.05 and 0.35, more preferably between 0.06 and 0.25, and / or the Mg / (Ca+Mg) ratio is in the range of 0.05-0.26, preferably in the range of 0.06-0.20.

[0112] Preferably, the Particle Size Distribution (or PSD) of the particles of the starting hydrated lime used for the preparation of the product in granules based on hydrated lime according to the present invention, determined by particle size analysis by laser diffraction, is characterized in that at least 90% by weight of the particle mass, preferably at least 95% by weight, even more preferably at least 98% by weight, is formed by particles having size in the range of 0.5-200 micrometres, more preferably in the range of 1-100 micrometres and even more preferably in the range of 1.5-80 micrometres.

[0113] Preferably the particle size distribution of the particles of the starting hydrated lime usable for the purposes of the present invention is characterized by one or more of the following indices: D10index between 1.5-3.5 micrometres; D50index between 5-30 micrometres; D90index between 10-70 micrometres; average diameter (Dave) in the range of 6-45 micrometres.

[0114] Preferably the starting hydrated lime usable for the purposes of the present invention has a specific surface area, determined by multi-layer physical adsorption of nitrogen on the surface of the material in accordance with the BET method, greater than 9 m2 / g, preferably greater than 12 m2 / g, more preferably greater than 14 m2 / g and even more preferably greater than 16 m2 / g. Preferably, the starting hydrated lime usable for the purposes of the present invention has a total pore volume, determined by nitrogen desorption isotherms and calculated on the assumption of pores having cylindrical geometry in accordance with the BJH method, greater than 0.04 cm3 / g, more preferably between 0.06cm3 / g and 0.15 cm3 / g and even more preferably between 0.07 cm3 / g and 0.10 cm3 / g.

[0115] In a preferred embodiment, the product in granules of substantially spheroidal shape based on hydrated air lime used according to the present invention comprises at least hydrated air lime and one or more substances functional to the production of glass, containing glass precursor phases (e. g. amorphous glass phases, silicate phases comprising one or more of calcium and / or magnesium and / or aluminium, etc. ) such as secondary metallurgical slag (SMS), white cement, natural hydraulic lime (NHL), blast furnace slag, fly ash derived from thermoelectric processes, as well as fine undersized fractions of silica sand or feldspathic sand or even finer fractions of glass cullet. Advantageously, the substances containing glass precursor phases preferably have a low iron content, particularly for use in the production of "white" glass. The formulation of the product in granules used according to the present invention preferably comprises at least hydrated air lime and one or more substances containing glass precursor phases in a weight percentage ratio respectively equal to 50%-50%, preferably equal to 60%-40%, more preferably equal to 70%-30%, even more preferably equal to 80%-20% and even better equal to 90%-10%, which allows to modulate the calcium and magnesium input to the batch of the vitrifiable raw materials and allows to supply at the same time glass precursor phases with consequent savings of virgin raw materials and relative benefits in accordance with circularity and sustainability principles.

[0116] The granular material of substantially spheroidal shape based on hydrated air lime used in the present invention can be obtained by a wet granulation process according to the methods known to the person skilled in the art, in particular a wet granulation process that is based on the agglomerationof particles of hydrated lime powder by means of a granulation fluid comprising water and, optionally, binding additives.

[0117] The process of preparing the granular material used in the present invention comprises preparing a mixture comprising at least powdered hydrated lime and a granulation fluid comprising water. The mixture is prepared by mixing the two components. The granulation fluid may be added to the solid mass of powdered hydrated lime by spraying (atomisation, nebulisation) or pouring. Preferably, the granulation fluid is gradually added to the powder while it is kept in a mixing regime.

[0118] The granulation fluid may optionally contain one or more binding agents to improve the compactness and mechanical strength of the final granular material.

[0119] The binding agents may conveniently be chosen from compounds based on alkali metal silicates (e. g. sodium alkali silicates, lithium alkali silicates, potassium alkali silicates, etc. ) or alkali metal hydroxides (e. g. sodium hydroxide, lithium hydroxide, potassium hydroxide, etc. ) or a mixture thereof. Preferably, the concentration of the binding agent is in the range of 0.1% to 15% by weight with respect to the weight of the hydrated lime, more preferably between 0.3% and 10% by weight with respect to the weight of the hydrated lime and even more preferably in the range of 0.5% to 5% by weight with respect to the weight of the hydrated lime.

[0120] In a preferred embodiment, the granulation fluid does not comprise any binding agents.

[0121] For the formation of the mixture (wetting step of the hydrated lime powder), the amount of granulation fluid employed is preferably in the range of 0.27-0.39 kg / kg of hydrated lime, more preferably in the range of 0.30- 0.36 kg / kg of hydrated lime and even more preferably in the rangeof 0.32-0.35 kg / kg of hydrated lime.

[0122] The mixture comprising the wetted hydrated lime powder is subjected to mixing under granulation conditions to form wet granules. During mixing, the wetted powder particles aggregate with each other to form nuclei or "seeds" of hydrated lime, which progressively grow in size (nucleation step) and finally agglomerate with each other (coalescence step) until complete consolidation to form wet granules comprising hydrated lime particles (also referred to as "green" granules).

[0123] The "green" granules are then subjected to a thermal drying treatment to remove free water. Drying is preferably conducted at a temperature in the range of 90-300°C, more preferably conducted at a temperature in the range of 100-250°C and even more preferably conducted at a temperature in the range of 120-230°C, optionally using a stream of predried air and preferably a CO2-depleted air stream. Preferably, drying is conducted until obtaining a dried granular material having a residual free water content of less than 2.5% by weight, preferably less than 2% by weight, preferably less than 1.5% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight, and even more preferably less than 0.2% with respect to the weight of the dried granules.

[0124] At the end of drying, the granular material can be subjected to a screening process.

[0125] The preparation of the granules can be carried out with granulation devices of the type known in the art for the wet preparation of granular materials, such as high-shear or low-shear mixing, or fluid bed, or rotating drum granulators.

[0126] The formation of the granular material used in the present invention is favoured by the use of high-shear mixing systems.

[0127] In accordance with one aspect of the present invention,a high-shear granulator is preferably used. Typically, a high-shear granulator comprises a mixing chamber ( vessel) inside which there is a mixing tool (*impeller*) for kneading the powder together with the granulation fluid.

[0128] The mixing chamber may include a wall scraper and / or a chopper which promotes the cleaning of the wall of the mixing chamber and the breakdown of larger aggregates and thus the formation of the granules of the desired size. The granulation fluid is introduced into the mixing chamber generally through one or more openings, which may for example be provided with nebulising nozzles.

[0129] The granulation fluid can be added to the solid mass of powdered hydrated lime by spraying (atomisation, nebulisation) or pouring; in cases where the liquid is not sprayed, the mechanical forces inside the granulator (e. g. imparted by the motion of the mixing tool and by the movement of the solid material itself inside the mixing chamber, as well as optionally by the chopper) are used to distribute the granulation fluid over the mass of solid particles. The mixture comprising powdered hydrated lime and the granulation fluid is prepared by mixing the two components. Preferably the granulation fluid is gradually added to the powder while it is kept under mixing inside the granulator.

[0130] In a preferred embodiment, the granular material of substantially spheroidal shape has granules having an apparent density from 1.2 g / cm3to 3 g / cm3, preferably from 1.3 g / cm3to 2.9 g / cm3, more preferably from 1.4 g / cm3to 2.8 g / cm3and even more preferably from 1.5 g / cm3to 2.7 g / cm3and a bulk density from 0.7 g / cm3to 1.2 g / cm3, preferably from 0.8 g / cm3to 1.15 g / cm3, more preferably from 0.9 g / cm3to 1.1 g / cm3.

[0131] The Particle Size Distribution (or PSD) of the granules is to be determined by dry-sieving through shaking in accordance with the standard EN 459-2: 2021, using thestandard method EN 933-1: 2012, in control sieves with squareshaped aperture as reported in the standard EN 933-2: 2020.

[0132] Preferably, the particle size distribution is characterized in that 100% by weight of the granules passes through the sieve with aperture of 12.5 mm. In a preferred embodiment, the particle size distribution is characterized in that at least 90% by weight of the granular mass, more preferably at least 95% by weight, even more preferably at least 98% by weight, is formed by granules having a size in the range of 1-10 mm (i. e. it passes through the sieve with aperture of 10 mm and does not pass through the sieve with aperture of 1 mm, even more preferably in the range of 1.4-9 mm and even more preferably in the range of 2-8 mm.

[0133] Preferably, the particle size distribution is characterized by a value of the D10index equal to or greater than 1.5 mm, more preferably in the range of 2-3 mm.

[0134] Preferably, the D50index has a value equal to or greater than 2.5 mm, more preferably in the range of 3-6 mm.

[0135] Preferably, the D90 index has a value equal to or greater than 4.5 mm, more preferably in the range of 5-8 mm.

[0136] Preferably, the amplitude of the particle size distribution curve has a ratio between the D90and D10indices in the range of 1.5-4, preferably in the range of 1.05-1.50.

[0137] Preferably, the distance between the points relative to 10% and 90% of the particle size distribution and normalized with respect to the median (50% of the particle size distribution) that determines the so-called span index value – (D90– D10) / D50– is a value between 0.75 and 1.50, preferably between 0.95 and 1.40 and more preferably between 1.10 and 1.35.

[0138] The values of the D10, D50and D90indices are calculated from the cumulative particle size distribution curve and correspond, respectively, to the sizes of the granules for which 10%, 50% and 90% by weight of the granular materialhas a size smaller than the D10, D50and D90values. Other " Dx" indices, where x is a number between 0 and 100, can be determined in the same way, so that for a given Dxvalue, x% by weight of the material has a size equal to or less than the Dx value.

[0139] The granules of the granular material used in the present invention have a substantially spheroidal shape; that is, they have a substantially spherical or ellipsoidal shape, and are substantially free of sharp edges. The granules have a circularity value, defined as the circumference of a circle identical to the projected surface, i. e. referred to the circumference of the circle having the same area as the actual projection of the granule, greater than 0.80, preferably greater than 0.85, more preferably greater than 0.90 and even more preferably greater than 0.95.

[0140] The granular material used in the present invention has specific surface area BET and BJH porosity relatively high compared to those of the homologous granular quicklime and derived carbonate rock.

[0141] Preferably, the specific surface area BET of the granules is in the range of 12–40 m2 / g, preferably in the range of 14–35 m2 / g and even more preferably in the range of 16–32 m2 / g.

[0142] In particular, in the case of calcium hydrated lime, the specific surface area BET of the granules is more preferably in the range of 15–30 m2 / g; in the case of dolomitic hydrated lime, the specific surface area BET is more preferably in the range of 16–32 m2 / g.

[0143] With regard to porosity, preferably the granules have a total pore volume (BJH), in the range of 0.05–0.25 cm3 / g. In particular, in the case of calcium hydrated lime, the aforesaid BJH volume is more preferably in the range of 0.07–0.15 cm3 / g; in the case of dolomitic hydrated lime, the aforesaid BJH volume is more preferably in the range of 0.08-0.20 cm3 / g.

[0144] For the purposes of the present invention, the specific surface area (BET) of the granules is intended to be determined by multi-layer physical adsorption of nitrogen on the surface of the granular material in accordance with the BET method; the total pore volume (BJH) is intended instead to be determined by nitrogen desorption isotherms and calculated on the assumption of pores having a cylindrical geometry in accordance with the BJH method.

[0145] The granular material of substantially spheroidal shape used in the present invention has high mechanical strength. The mechanical strength can be determined by measuring the compressive load until rupture of the granules or the resistance of the granules to abrasion and to breakage following dynamic stresses.

[0146] For the purposes of the present description and of the appended claims, the compressive load until rupture of the granular hydrated lime and the resistance to abrasion and to breakage following dynamic stresses are understood to be determined according to the methods described in the examples.

[0147] As specified above, the granular material of substantially spheroidal shape used in the present invention has a compressive load until rupture equal to or greater than 40 N / granule, preferably equal to or greater than 50 N / granule.

[0148] The granules of the granular material of substantially spheroidal shape used in the present invention have a high resistance to abrasion and to breakage following dynamic stresses. This property of the granules can be evaluated through a shatter test conducted according to the methods described in the examples. During the shatter test, the granular material is subjected to a series of controlled impacts, inside a test chamber consisting of a cylindricalsteel container kept rotating, which generate a fraction of fine particles that modifies the original particle size distribution of the material. The extent of the change in the particle size curve determined at the end of the shatter test provides an indication on the resistance to abrasion and to breakage of the granular material. Quantitatively, the aforesaid change in the particle size curve is indicated in the present description by means of the so-called "shatter test index" ( ISTX)

[0149] ISTx= FPf– FPi

[0150] where:

[0151] FPi is the percentage fraction by weight of the granular material passing through the sieve having square aperture with side x mm before the test;

[0152] FPf is the percentage fraction by weight of the granular material passing through the same sieve after the test;

[0153] x is the net opening of the aforesaid sieve, i. e. the length in mm of the side of the square aperture of the sieve.

[0154] The shatter test index is expressed in percentage points (pp) •

[0155] The granular material of substantially spheroidal shape used in the present invention preferably has an ISTi value (arithmetic difference, expressed in terms of percentage points pp, of the percentage fraction by weight passing through the square aperture sieve with side 1 mm before and after the execution of the shatter test) of less than 1.5 pp, preferably less than 1.2 pp, more preferably less than 0.7 pp, even more preferably less than 0.5 pp. The granular material preferably has an IST0.5value (arithmetic difference, expressed in terms of percentage points pp, of the percentage fraction by weight passing through the square aperture sieve with side 0.5 mm before and after theexecution of the shatter test) of less than 0.5 pp, more preferably less than 0.3 pp, even more preferably less than 0. 2 pp.

[0156] The particular characteristics of mechanical strength to compression and resistance to abrasion and to breakage following dynamic stresses of the granules of the granular material used in the present invention, as well as their substantially spheroidal geometric shape (substantially free of sharp edges), reduce the formation of fine powders following the handling of the material, thus limiting the degradation of the particle size curve of the product and the generation of fugitive dust emissions in the handling steps as well as the lower tendency to generate fine fractions that may be more subject to entrainment phenomena in the flow of the exhaust gases inside a glass furnace ( carryover).

[0157] The method for the production of glass according to the present invention comprises:

[0158] a. mixing at least:

[0159] 1 ) a vitrifying material forming a glass network; 2 ) a granular material of substantially spheroidal shape comprising hydrated air lime having:

[0160] - a total concentration of CaO and MgO equal to or greater than 80% with respect to the weight of the granular material after subtraction of its free water and chemically bound water content;

[0161] - a compressive load until rupture equal to or greater than 40 N / granule, preferably equal to or greater than 50 N / granule;

[0162] wherein said hydrated air lime is selected from the group consisting of:

[0163] - calcium hydrated air lime having an MgO content equal to or less than 5% by weight with respect to the weight of the hydrated air lime after subtraction of its free waterand chemically bound water content;

[0164] - magnesium hydrated air lime having an MgO content greater than 5% by weight and less than 30% by weight with respect to the weight of the hydrated air lime after subtraction of its free water and chemically bound water content;

[0165] - dolomitic hydrated air lime having an MgO content equal or greater than 30% by weight and, preferably, equal to or less than 42% by weight with respect to the weight of the hydrated air lime after subtraction of its free water and chemically bound water content; and

[0166] - mixtures thereof,

[0167] in a weight ratio between 3: 1 and 6: 1 to obtain a mixture;

[0168] b. adding water to the mixture in an amount of 1% to 5% by weight of the mixture obtained in step (a);

[0169] c. heating the mixture of step (b) to a temperature between 1300°C and 1600°C to obtain a molten mixture;

[0170] d. forming the molten mixture of step (c); and

[0171] e. annealing the product obtained in step (d).

[0172] Preferably, at least a fluxing compound, a refining compound, a decolouring compound, an opacifying compound, a colouring compound or a reducing compound is also added in the mixing step.

[0173] Preferably, glass cullet is also added to the vitrifiable mixture after the mixing step. The glass cullet is generally added to the batch of vitrifiable mixture at a time after preparation and in some cases immediately upstream of the entrance into the furnace.

[0174] The product obtained in step (d) may be hollow glass. In case the product obtained in step (d) is flat glass, the method includes a further step ( f ) of cutting and squaring the product.

[0175] The following embodiment examples are provided merelyto illustrate the present invention and should not be construed in a sense that would limit the scope of protection defined by the appended claims.

[0176] EXAMPLES EXAMPLE 1

[0177] Preparation of the granular material based on hydrated lime - Samples A-H

[0178] Eight series (Samples A-H) of five samples each of granular material of substantially spheroidal shape according to the present invention were prepared in the laboratory starting from calcium hydrated air lime and dolomitic hydrated air lime in powder form of normal industrial production, respectively classified, according to the designation reported in the standard EN 459-1: 2015, as CL90-S (calcium hydrated lime, Ca(OH)2) and DL90-30-S1, the latter also referred to as " N-type" dolomitic hydrated lime (i. e., dolomitic semi-hydrated lime, Ca(OH)2.MgO).

[0179] Based on this classification, the compositions, expressed as a percentage weight fraction with reference to the weight of the starting material after subtraction of the free water and chemically bound water content, of the starting powdered hydrated limes were as follows:

[0180] • CL90-S (calcium hydrated lime - Ca(OH)2):

[0181] - calcium and magnesium content in terms of the summation CaO+MgO > 90%;

[0182] - magnesium content in terms of MgO < 5%;

[0183] - sulfur content in terms of SO3≤ 2%;

[0184] - residual CO2content ≤ 4%.

[0185] • DL90-30-S1 (dolomitic hydrated lime, Ca(OH)2.MgO):

[0186] - calcium and magnesium content in terms of the summation CaO+MgO > 90%;

[0187] - magnesium content in terms of MgO > 30%;

[0188] - sulfur content in terms of SO3 2%;

[0189] - residual CO2 content < 6%.The powdered starting material was characterized by the following particle size distribution determined by laser diffraction technique:

[0190] • CL90-S (calcium hydrated lime, Ca(OH)2): D10= 2.94 μm, D50= 5.70 μm, D90= 12.15 μm, Dave= 6.75 μm;

[0191] • DL90-30-S1 (dolomitic hydrated lime, Ca(OH)2.MgO): Dio= 3.02 pm, Dso= 21.48 pm, Dgo= 55.71 pm, Dave= 25.58 pm.

[0192] The starting calcium hydrated air lime also had a specific surface area BET equal to 14.9 m2 / g, a total pore volume BJH equal to 0.07 cm3 / g, said pores having an average diameter of 12. 6 nm.

[0193] The starting dolomitic hydrated air lime also had a specific surface area BET equal to 16.0 m2 / g, a total pore volume BJH equal to 0.08 cm3 / g, said pores having an average diameter of 17.5 nm.

[0194] The granular hydrated lime as defined in the present invention was prepared by a wet granulation process of the aforementioned calcium and dolomitic hydrated limes in powder form, followed by a thermal drying treatment, as reported below.

[0195] The wet granulation process was conducted, according to a process in "batch" mode with a total duration equal to 10 minutes, with the aid of an intensive high-shear laboratory mixer. The mixer comprised a tilted rotating vessel having a capacity of 5 litres and a high-speed rotating eccentric mixing tool. The vessel and the mixing tool were configured to rotate in opposite rotation directions.

[0196] For each batch, about 2650 g of powdered hydrated air lime and about 900 g of granulation liquid consisting of water and optionally a binding agent (binding agent concentration equal to 2% by weight with respect to the weight of the hydrated lime) were overall loaded into the vessel by successive additions.

[0197] In a first step, into the vessel it was loaded hydratedair lime in an amount equal to 75% of the total mass amount used and water (granulation liquid) in an amount equal to about 78% of the mass amount used (corresponding to 26% with respect to the mass of hydrated air lime used in the process). The mixture of hydrated lime and granulation liquid was obtained by setting a rotation speed of 350 rpm for the vessel and 3000 rpm (counter-current rotation) for the mixing tool. This mixing regime was maintained for a period of time equal to 4 minutes and, at regular intervals of 1 minute starting from the second minute and for the subsequent 3 minutes, amounts of hydrated air lime and of granulation liquid were added at a rate respectively of 17% of the total mass of hydrated air lime and 17% of the total wetting agent (corresponding to 6% in relation to hydrated air lime) used in the entire wet granulation process ( first and second steps).

[0198] During the first step of the granulation process, the wetting and saturation stage of the starting powder and the nucleation stage of the primary particles of hydrated air lime take place with formation of of particle nuclei (seeds) that agglomerate forming agglomerates with progressively increasing size.

[0199] The second step of the process, lasting 6 minutes, involved a different mixing regime, characterised by a rotation speed of the vessel of 750 rpm and a rotation speed of the mixing tool of 1500 rpm. During the second step, starting from the second minute and for the subsequent 3 minutes at regular intervals, amounts of hydrated air lime and of wetting agent were added in the mixing vessel at rates respectively of 8% of the total mass of hydrated air lime and 5% of the total mass of granulation liquid (corresponding to 2% by mass in relation to the hydrated air lime) used in the entire wet granulation process ( first and second steps).

[0200] During the second step of the process the coalescenceof the agglomerates formed in the first step with formation of granular nuclei of increasing size and their consolidation (green granular cores) take place; the second step is also characterized by competing phenomena of breakage of the granules formed and of coalescence of smaller granules and of agglomerates with the formation of new granules.

[0201] At the end of the wet granulation process, the green granules were dried in a laboratory oven at a temperature of 115°C for a time at least equal to 6 hours to remove free water until dried granules of calcium hydrated air lime and dried granules of dolomitic hydrated lime with a final residual free water content of less than 0.2% by weight were obtained. The results of the determination of the free water content of the green granules of calcium hydrated air lime and of the green granules of dolomitic hydrated air lime produced by the wet granulation process are reported in Table 1.

[0202] After the drying step, the granular material of substantially spheroidal shape based on calcium hydrated air lime and the granular material of substantially spheroidal shape based on dolomitic hydrated air lime were cooled in a laboratory desiccator before being subj ected to characterization analyses.

[0203] Granular hydrated lime - Samples A-H

[0204] Samples A-D consist respectively of calcium hydrated lime (Samples A-B) and dolomitic hydrated lime (Samples C-D) and were prepared according to the process described above, using the following granulation liquids and optionally a binding agent:

[0205] - Sample A: calcium hydrated lime + water;

[0206] - Sample B: calcium hydrated lime + water + sodium silicate;

[0207] - Sample C: dolomitic hydrated lime + water;

[0208] - Sample D: dolomitic hydrated lime + water + sodiumsilicate.

[0209] In Sample B and Sample D, the amount of binding agent added was equal to 2% by weight on a dry basis relative to the total weight of the calcium hydrated air lime and of the dolomitic hydrated lime fed to the process. As the binding agent, a sodium salt of silicic acid in aqueous solution was used, having a sodium silicate content equal to 45.25% and composition equal to 29.09% in terms of SiO2and 16.16% in terms of Na2<9, relative density equal to 1.56 g / ml at 20°C and dynamic viscosity equal to 530 mPa. s at 20°C.

[0210] Samples E-H were prepared in accordance with the method described above using the following mixing regime of overall duration of 15 minutes. In the first step (wetting and nucleation; duration 6 minutes) a rotation speed of 350 rpm for the vessel and 1800 rpm (counter-current rotation) for the mixing tool were set. This mixing regime was maintained for a time equal to 6 minutes and, at regular intervals of 1 minute starting from 2 minutes and for the subsequent 4 minutes, additional amounts of hydrated air lime and of wetting agent were added at rates respectively of 17% of the total mass of hydrated air lime and 17% of the total wetting agent (corresponding to 6% in relation to the hydrated air lime) used in the entire wet granulation process ( first and second steps).

[0211] The second step of the process, lasting 9 minutes, involved a mixing regime characterized by an increase in the rotation speed of the vessel up to 750 rpm and a decrease in the speed of the mixing tool up to 900 rpm, and theaddition, starting from 2 minutes and for the subsequent 3 minutes at regular intervals, of additional amounts of hydrated air lime and of wetting agent at rates, respectively, of 8% of the total mass of hydrated air lime and 5% of the total wetting agent (corresponding to 2% in relation to hydrated air lime) used in the entire wet granulation process.Samples E-H consist respectively of calcium hydrated lime (Samples E-F) and dolomitic hydrated lime (Samples G-H) and were prepared according to the process described above, using the following granulation liquids and optionally a binding agent:

[0212] - Sample E: calcium hydrated lime + water;

[0213] - Sample F: calcium hydrated lime + water + sodium silicate;

[0214] - Sample G: dolomitic hydrated lime + water;

[0215] - Sample H: dolomitic hydrated lime + water + sodium silicate.

[0216] In Sample F and Sample H, the amount of binding agent added was equal to 2% by weight on a dry basis with respect to the total weight of the calcium hydrated air lime and of the dolomitic hydrated air lime fed to the process. As the binding agent, a sodium salt of silicic acid in aqueous solution was used, having a sodium silicate content equal to 45.25% and composition equal to 29.09% in terms of SiO2and 16.16% in terms of Na2<9, relative density equal to 1.56 g / ml at 20°C and dynamic viscosity equal to 530 mPa. s at 20°C.

[0217] Chemical composition of the granular hydrated lime - Samples A-H

[0218] Based on its chemical composition, the granular material of Samples A-H can be classified, according to the designation reported in standard EN 459-1: 2015 and in relation to the characteristics of the starting hydrated lime in powder form, as calcium hydrated lime CL90-S (Samples A-B and Samples E-F) and DL90-30-S1 (Samples C-D and Samples G-H) having, in relation to the finished product respectively:

[0219] • CL90-S (calcium hydrated lime - Ca(OH)2):

[0220] calcium and magnesium content in terms of the summation CaO+MgO > 90%;

[0221] - magnesium content in terms of MgO < 5%;- sulfur content in terms of SO3≤ 2%;

[0222] - residual CO2content ≤ 4%;

[0223] where said percentages by weight are referred to the weight of the product without free water and chemically bound water;

[0224] • DL90-30-S1 (dolomitic hydrated lime, Ca(OH)2.MgO):

[0225] calcium and magnesium content in terms of the summation CaO+MgO > 90%;

[0226] - magnesium content in terms of MgO > 30%;

[0227] - sulfur content in terms of S

[0228]

[0229] O3 2%;

[0230] - residual CO2 content < 6%;

[0231] where said percentages by weight are referred to the weight of the product without free water and chemically bound water.

[0232] Particle size analysis of the granular hydrated lime - Samples A-H

[0233] The particle size analysis of the granular hydrated lime samples was carried out by dry-sieving by shaking in accordance with standards EN 459-2: 2021, EN 932-2: 2000 and EN 933-1: 2012 in control sieves with square-shaped aperture as reported in standard EN 933-2: 2020: the test was conducted with a series of ISO 3310 sieves stacked in a column in order of (square) aperture size decreasing from top to bottom ( 16 mm, 14 mm, 12.5 mm, 10 mm, 9 mm, 8 mm, 7.1 mm, 6.3 mm, 5. 6 mm, 4 mm, 3.15 mm, 2 mm, 1 mm, 0.5 mm) so as to have an opening area of the apertures in geometric progression.

[0234] From the cumulative curve of the particle size distribution determined for each sample, the characteristic diameters D10, D50and D90, indicating respectively the particle size corresponding to 10%, 50% (median) and 90% by weight of the cumulative curve, as well as the average diameter (Dave), the width of the particle size distribution (D90 / D10ratio) and the span index (correlation of the D10, D50and D90indices through the formula (D90- D10) / D50) wereobtained.

[0235] The characteristic values of the particle size distribution of the analysed samples are reported in Table 1.

[0236] Determination of the mechanical durability of the granular hydrated lime - Samples A-H

[0237] Mechanical strength: the compressive load until rupture of the granular hydrated lime was determined by means of a structure analyser consisting of a high-precision dynamometer operating in compression, provided with a piston that imparts to the hydrated lime granule, placed on a test support, an increasing compressive load until rupture thereof. The dynamometer records the maximum force applied, i. e. the peak stress until the granule breaks. The compressive load until rupture is expressed as the average value of thirty measurements performed on thirty granules of the same material sample having a diameter in the range D50 ± 15%, where D50 is the median value of the particle size distribution of the analysed granular hydrated lime.

[0238] The results of the determination of the compressive mechanical strength are reported in Table 1.

[0239] Wear resistance deriving from dynamic stresses: the abrasion and impact breakage resistance deriving from dynamic stresses of the granular hydrated lime was determined by shatter test (determination of the shatter test index, ISTx) according to the methods described below.

[0240] A sample of about 150 grams of granular hydrated lime was subj ected to a shatter test consisting in a series of controlled impacts by collision of the particles inside a test chamber consisting of a cylindrical steel container (internal diameter equal to 78 mm and length equal to 690 mm), provided with closures at both ends. The test chamber containing the granular material to be tested was kept rotating around a pin fixed on the outer lateral surface ofthe chamber, at the median cross-section of the chamber itself. The chamber was kept rotating at a rotation speed equal to 15 rpm for a total number of complete rotations equal to 75. Before and after the shatter test, the percentage fraction by weight of granular material passing through the 0.5 mm and / or 1 mm square aperture sieve was determined. The ISTX(expressed in percentage points, pp) is calculated according to the formula:

[0241] ISTx= FPf− FPi

[0242] where:

[0243] FPi is the percentage fraction by weight of the granular material passing through the sieve having square aperture with side x mm before the test;

[0244] FPf is the percentage fraction by weight of the granular material passing through the same sieve having square aperture with side x after the test;

[0245] x is the net opening of the aforesaid sieve, i. e. the length in mm of the side of the square aperture of the sieve.

[0246] The extent of the ISTXshatter test index provides an indication on the abrasion resistance and impact breakage resistance deriving from dynamic stresses of the hydrated lime granules.

[0247] The results of the determination of the ISTi and ISTo.s shatter test indices, expressed in percentage points (pp), are reported in Table 1.

[0248] Physical characteristics of the granular hydrated lime - Samples A-H

[0249] For each sample constituting the specific series of granular materials of substantially spheroidal shape based on calcium hydrated air lime and dolomitic hydrated air lime, the specific surface area (BET) of the granules was determined by multi-layer physical adsorption of nitrogen onthe surface of the granular material in accordance with the BET method; the total pore volume (BJH) and the average pore diameter (Dp-ave) were instead determined by means of the nitrogen desorption isotherms and calculated on the assumption of pores having cylindrical geometry in accordance with the BJH method.

[0250] The results of the measurements are reported in Table 1.TABLE 1 Characteri zation of the hydrated lime granules

[0251] A B C D EbFcGdHe

[0252] D10[mm]f1. 98 1. 87 2. 91 2. 33 2. 02 2. 23 2. 63 2. 57 D50[mm]f3. 28 3. 07 4. 26 4. 17 3. 31 3. 54 4. 24 4. 01 D90[mm]f5. 61 5. 23 8. 02 7. 96 5. 73 5. 98 8. 09 8. 11 Dave[mm]f3. 55 3. 29 5. 31 4. 24 3. 64 3. 79 4. 75 5. 44 D90 / D10 [ - ]f2. 83 2. 80 2. 76 3. 42 2. 84 2. 68 3. 08 3. 16 ( D90-D10 ) / D50 [ - ]f1. 11 1. 10 1. 20 1. 35 1. 12 1. 06 1. 29 1. 38 Compressive stength

[0253] 52. 85 56. 42 85. 75 89. 47 49. 90 51. 39 82. 14 85. 62 [N / granule ]f

[0254] ISTi [pp]f0. 65 0. 46 0. 52 0. 49 0. 84 0. 71 0. 63 0. 52 IST0.5 [pp]f0. 33 0. 34 0. 29 0. 26 0. 56 0. 42 0. 41 0. 37 BET [m2 / g ]f15. 63 15. 27 17. 17 16. 22 16. 60 15. 77 16. 46 15. 91 B JH [ cm3 / g]f0. 13 0. 12 0. 14 0. 13 0. 14 0. 13 0. 13 0. 12 Dp-ave [A ]f145. 01 147. 95 230. 90 232. 32 142. 5 137. 60 216. 07 215. 84 Free water [ % ]g23. 77 25. 01 22. 59 22. 99 24. 62 24. 46 22. 93 23. 07

[0255]

[0256] aresults expressed as the average value of the values determined on the five samples that make up each of the eight series A-H;

[0257] bas Sample A, but granulated with different mixing regime;

[0258] cas Sample B, but granulated with different mixing regime;

[0259] das Sample C, but granulated with different mixing regime;

[0260] eas Sample D, but granulated with different mixing regime;

[0261] fparameter determined by analysis of the granular material after the drying step;

[0262] g% value referred to the weight of the granular material before drying.The results of the characterization show that the granular hydrated lime according to the present invention has a high mechanical strength, with values equal to or greater than 40 N / granule and of the order of 50 N / granule with regard to the calcium hydrated lime and greater than 60 N / granule and of the order of 80 N / granule for the dolomitic hydrated lime when only water is used as granulation liquid and slightly higher when the granulation liquid also includes a binding agent.

[0263] The ISTx shatter test index, moreover, highlights the high wear and abrasion resistance of the granular hydrated lime according to the invention and therefore the limited tendency to generate fine powders during handling and transport.

[0264] EXAMPLE 2

[0265] A comparative laboratory study was conducted to evaluate the tendency of the granular hydrated lime of substantially spheroidal shape used in the present invention to generate fine powder fractions and therefore, in the case of use in the production of glass, to be able to give rise to fugitive dust emissions in the handling operations upstream of the composition and preparation station of the vitrifiable mixture (batch house) and downstream thereof until reaching the melting furnace for the production of glass as well as inside the furnace itself ( carryover).

[0266] Comparative tests of wear resistance deriving from dynamic stresses through shatter test were conducted on a series (Sample J) of three samples of granular dolomitic hydrated air lime (Ca(OH)2.MgO) of substantially spheroidal shape according to the present invention, on a series (Sample K) of three samples of natural granular dolomitic air quicklime (CaO. MgO) of normal industrial production and on a series (Sample L) of three samples of natural granular dolomitic rock (CaCOs. MgCOs) also of normal industrialproduction from which the previous materials are derived. The different samples of the series of granular materials mentioned above (Samples J-L) were suitably sieved in order to obtain a "calibrated" particle size distribution, reconstructed by maintaining appropriate weight ratios between the different particle size frequency classes (2-3.15 mm, 3.15-4 mm, 4-5. 6 mm, 5. 6-6.3 mm, 7.1-8 mm, 8-9 mm, 9-10 mm) as reported below.

[0267] The abrasion and impact breakage resistance deriving from dynamic stresses of the granular materials described above (Samples J-L) was determined by shatter test (determination of the shatter test index, ISTX) according to the methods described below.

[0268] A test sample of about 150 grams of the granular materials described above, characterized by having a "calibrated" particle size distribution being composed for each of the particle size frequency classes 3.15-4 mm; 4-5. 6 mm; 5. 6-6.3 mm; 7.1-8 mm, 8-9 mm of a weight quantity equal to 20 grams and for each particle size frequency class 2-3.15 mm and 9-10 mm, representative of the "tails" of the particle size distribution, of a weight quantity equal to 15 grams, was subj ected to a shatter test consisting in a series of controlled impacts by collision of the particles inside a test chamber consisting of a cylindrical steel container (internal diameter equal to 78 mm and length equal to 690 mm), provided with closures at both ends. The test chamber containing the granular material to be tested was kept rotating around a pin fixed on the outer lateral surface of the chamber, at the median cross-section of the chamber itself. The chamber was kept rotating at a rotation speed equal to 15 rpm for a total number of complete rotations equal to 75. Before and after the shatter test, the percentage fraction by weight of granular material passing through the 2 mm, 1 mm, 0.5 mm, 0.25 mm and 0.125 mm squareaperture sieve was determined. The ISTX(expressed in percentage points, pp) is calculated according to the formula:

[0269] ISTX= FPf - FPi

[0270] where:

[0271] FP± is the percentage fraction by weight of the granular material passing through the sieve having square aperture with side x mm before the test;

[0272] FPf is the percentage fraction by weight of the granular material passing through the same sieve having square aperture with side x after the test;

[0273] x is the net opening of the aforesaid sieve, i. e. the length in mm of the side of the square aperture of the sieve.

[0274] The extent of the ISTXshatter test index provides an indication on the abrasion and impact breakage resistance deriving from dynamic stresses of the granular materials.

[0275] The results of the determination of the IST2, ISTi, IST0.5, ISTO.25, and IST0.125 shatter test indices, expressed in percentage points (pp), are reported in Table 2.

[0276] Table 2 also reports the characteristic values of the particle size distribution (Dio, D50, D90; Dave, D90 / D10, (D90-D10) / D50) of the granular materials described above (Samples J-L) before ("calibrated" particle size distribution) and after the shatter test.TABLE 2 - Comparative evaluation of abrasion and impact breakage resistance deriving from dynamic stresses of granular materialsa

[0277] J K L

[0278] 2.82b-- 2.83b-- 2.82b-- Dio [mm]

[0279] 2. 36c1. 38c2. 34c5. 64b-- 5. 65b-- 5.73b-- D50 [mm]

[0280] 5. 63c5. 05c5. 64c9.13b-- 9.13b-- 9.15b-- D90 [mm]

[0281] 9. 13c9. 01c9. 13c5.82b-- 5.83b-- 5.84b-- Dave [mm]

[0282] 5. 62c5. 15c5. 67c3.24b-- 3.23b-- 3.24b-- D90 / D10 [-]

[0283] 3. 87c6.53c3. 90c1.12b-- 1.12b-- 1.10b-- ( D90-D10 ) / D50 [_]

[0284] 1.20c1. 51c1.20cIST2[pp] 5.44 11. 44 5.81 ISTi [pp] 2. 64 9.13 2.31 IST0.5 [pp] 1. 62 8. 62 1. 66 ISTO.25 [pp] 1. 09 8.29 1. 33

[0285]

[0286] ISTO.125 [pp] 0.75 8. 04 1. 13

[0287] results expressed as the average value of the values determined on the three samples that make up each of the three J-L series;

[0288] characteristic values of the "calibrated" particle size distribution before the shatter test;

[0289] characteristic values of the particle size distribution after the shatter test.The product in granules of substantially spheroidal shape based on dolomitic hydrated lime according to the present invention when subj ected to shatter test trials highlighted a lower tendency to generate fine powder fractions than a homologous material based on natural granular dolomitic quicklime, as well as lower than a homologous natural granular dolomitic rock. This effect is attributable to the fact that the granules making up the granular product based on hydrated air lime according to the present invention have a substantially spheroidal shape characterised by the absence of sharp edges and greater regularity than the natural granular products. In any case, it could be noted that even when the granular product based on hydrated air lime is subj ected to dynamic stresses, any breakage phenomena occur mainly through the breakdown into smaller particles rather than through the generation of fine powder fractions.

[0290] EXAMPLE 3

[0291] A comparative laboratory study was conducted with the dual purpose of:

[0292] evaluating the tendency of the granular hydrated lime of substantially spheroidal shape used in the present invention to generate fine powder fractions and therefore, in the case of use in the production of glass, to be able to give rise to fugitive dust emissions in the handling operations upstream of the composition and preparation station of the vitrifiable mixture (batch house) and downstream thereof until reaching the melting furnace for the production of glass as well as inside the furnace itself ( carryover);

[0293] evaluating the ability of the product in granules of substantially spheroidal shape based on hydrated lime according to the present invention to meet specificreactivity requirements when used in the glass production process (e. g. formation of sodium-calcium pre-silicates).

[0294] The comparative tests of wear resistance deriving from dynamic stresses through shatter tests were conducted on a series of three samples of granular calcium hydrated air lime (Ca(OH)2) of substantially spheroidal shape according to the present invention (Sample M), on a series of three samples of granular dolomitic hydrated air lime (Ca(OH)2.MgO) of substantially spheroidal shape according to the present invention (Sample N) and for comparison on two series of three samples each of carbonate products normally used in the glass industry available on the market such as limestone (CaCO3) and dolomite (CaCOs. MgCOs) referred to as Sample 0 and Sample P, respectively.

[0295] The abrasion and impact breakage resistance deriving from dynamic stresses of the granular materials based on calcium and dolomitic hydrated lime described above (Samples M-N) and of the carbonate materials, limestone and dolomite, reported above (Samples 0-P) was determined by shatter test (determination of the shatter test index, ISTX) according to the methods described below.

[0296] A test sample of about 150 grams of the materials described above was subj ected to a shatter test consisting in a series of controlled impacts by collision of the particles inside a test chamber consisting of a cylindrical steel container (internal diameter equal to 78 mm and length equal to 690 mm), provided with closures at both ends. The test chamber containing the granular material to be tested was kept rotating around a pin fixed on the outer lateral surface of the chamber, at the median cross-section of the chamber itself. The chamber was kept rotating at a rotation speed equal to 15 rpm for a total number of complete rotations equal to 75. Before and after the shatter test, the percentage fraction by weight of granular materialpassing through the 0.25 mm and 0.125 mm square aperture sieve was determined. The ISTX(expressed in percentage points, pp) is calculated according to the formula:

[0297] ISTx= FPf– FPi

[0298] where:

[0299] FPi is the percentage fraction by weight of the granular material passing through the sieve having square aperture with side x mm before the test;

[0300] FPf is the percentage fraction by weight of the granular material passing through the same sieve having square aperture with side x after the test;

[0301] x is the net opening of the aforesaid sieve, i. e. the length in mm of the side of the square aperture of the sieve.

[0302] The extent of the ISTXshatter test index provides an indication on the abrasion and impact breakage resistance deriving from dynamic stresses of the particles of the granular materials and their propensity to generate fine powder fractions.

[0303] The results of the determination of the IST0.25, and IST0.125 shatter test indices, expressed in percentage points (pp), are reported in Table 3.

[0304] The particle size analysis of the samples of the granular materials described above (Samples M-P) was carried out by dry-sieving by shaking in accordance with standards EN 459-2: 2021, EN 932-2: 2000 and EN 933-1: 2012 in control sieves with square-shaped aperture as reported in standard EN 933-2: 2020: the test was conducted with a series of ISO 3310 sieves stacked in a column in order of (square) aperture size decreasing from top to bottom ( 12.5 mm, 10 mm, 9 mm, 8 mm, 7.1 mm, 6.3 mm, 5. 6 mm, 4 mm, 3.15 mm, 2 mm, 1 mm, 0.5 mm, 0.25 mm, 0.125 mm) so as to have an opening area of the apertures in geometric progression.From the cumulative curve of the particle size distribution determined for each sample, the characteristic diameters Dio, D50 and D90, the average diameter Dave, the width of the particle size distribution D90 / D10 and the span index (D90 - Dio) / D50) were obtained: the characteristic values of the particle size distribution of the analysed granular samples (Samples M-P), before and after the shatter test are reported in Table 3.

[0305] The comparative tests to evaluate the reactivity of the granular materials described above (Samples M-P) under the conditions of use at the time of introduction into the glass furnace, provided for a calcination heat treatment according to the methods described below and the wet slaking test for the determination of the reactivity in water of the resulting materials according to the method described below.

[0306] In glassmaking practice, the reactivity of the raw materials supplying calcium and magnesium to the glass melting process can be considered as the rate of generation of the corresponding reactive calcium oxides (CaO) and calcium and magnesium oxides (CaO. MgO) capable of interacting with the oxides deriving from the dissolution of sodiun carbonate (Na20) and sand (SiO2).

[0307] Calcination was conducted in a laboratory TGA muffle furnace, provided with a precision electronic balance and software for recording both the temperature curve and weight loss over time. The calcination was carried out under atmospheric pressure, according to a heating program from room temperature to a predefined maximum temperature with a heating rate of 5°C / minute and a holding time at said temperature equal to 1 hour. Three predefined maximum temperature levels were considered, 600°C, 800°C and 1000°C. The samples of the granular materials resulting from calcination, according to the correspondences with the starting samples of the granular materials of substantiallyspheroidal shape based on calcium and dolomitic hydrated lime described above (Samples M-N) and of the carbonate materials, limestone and dolomite, reported above (Samples 0-P), are referred to as:

[0308] Samples Ml-Pl: calcination at T = 600°C; Samples M2-P2: calcination at T = 800°C; Samples M3-P3: calcination at T = 1000°C.

[0309] Table 4 reports the values of free water, residual CO2 content and loss on ignition (LOI ) determined on the starting granular materials (Samples M-P) and on the granular materials obtained from calcination (Samples Ml-Pl, Samples M2-P2, Samples M3-P3) as prescribed by standard EN 459-2: 2021.

[0310] In the case of complete calcination of the starting granular materials (Samples M-P), a calcium air quicklime (CaO) is obtained from Sample M and Sample 0 and a dolomitic air quicklime (CaO. MgO) is obtained from Sample N and Sample P, respectively classified, according to the designation reported in standard EN 459-1: 2015, as CL90-Q (CaO+MgO > 90%, MgO < 5%, CO24%, SO32%) e DL90-30-Q (CaO+MgO > 9

[0311]

[0312] 0%, MgO > 30%, CO26%, SO3 2%).

[0313] The wet slaking test for the determination of the water reactivity of the granular materials obtained from calcination was carried out as prescribed by standard EN 459-2: 2021. The reactivity test is performed on the calcined granular material as such, i. e. without reducing the particle size thereof to values < 5 mm (as required instead by the standard for the fractions of materials not passing 100% through a 5 mm sieve).

[0314] The reactivity test, normally explained in a timetemperature graph in which the so-called reactivity curve is plotted, involves the slaking of the quicklime ( 150 g) in distilled water in a water / lime mass ratio equal to 4: 1, under adiabatic conditions inside a Dewar vessel in whichthe water / lime system is kept under stirring (300 rpm), recording the evolution over time of the temperature starting from the initial value of 20°C and until completion of the reaction (the reaction is considered completed when the temperature of the water / lime system during the performance of the test reaches the maximum value T'max and it stabilizes on it, without further increasing and in any case after 50 minutes in the event that the temperature does not stabilize on a maximum value).

[0315] The temperature (in °C) and time measurements therefore allow to define a reactivity curve from which it is possible to obtain the tso and teo indices, corresponding to the time necessary to reach the temperature of, respectively, 50°C and 60°C. For the purposes of the present invention, the value tso is used to characterize the reactivity of the dolomitic quicklime having an MgO content greater than 5% by weight, while the value teo is used to characterize the reactivity of the calcium quicklime having an MgO content of less than or equal to 5% by weight.

[0316] Another index that is used to outline the rapidity of the slaking reaction of the quicklime in water is represented by the time required to complete the reaction at 80% (tu) corresponding to the temperature value (Tu), expressed in degrees Celsius, at which the reaction is 80% completed calculable according to the relationship Tu= [ ( 0.8 x T'max) + ( 0.2 x To) ], being To the initial temperature (in degrees Celsius) and T'max the maximum temperature (in degrees Celsius) reached by the water / lime system.

[0317] The results of the water reactivity tests of the calcined granular material samples (Samples Ml-Pl, Samples M2-P2, Samples M3-P3) are reported in Table 4.TABLE 3 - Comparative evaluation of abrasion and impact breakage resistance deriving from dynamic stresses of granular materialsa

[0318] M N 0 P 2.24b-- 2.74b-- 1.03b-- 0. 62b-- Dio [mm]

[0319] 2.23c2.46c1. 00c0. 61c3.32b-- 4.21b-- 1.57b-- 1.15b-- D50 [mm]

[0320] 3. 30c4. 05c1. 53c1. 14c4.70b-- 8. 02b-- 2.49b-- 1.83b-- D90 [mm]

[0321] 4. 66C7.76c2. 34c1. 83c3.49b-- 4.49b-- 1. 63b-- 1.19b-- Dave [mm]

[0322] 3. 46c4.47c1. 57c1. 18c2.10b-- 2. 93b-- 2.41b-- 2.96b-- D90 / D10 [-]

[0323] 2. 09c3. 15c2. 34c2. 97c0.74b-- 1.25b-- 0.93b-- 1.05b-- ( D90-D10 ) / D50 [_]

[0324] 0. 74c1.31c0. 88c1. 06cIST0.25 [pp] 0.10 0.33 0. 62 0.30

[0325]

[0326] ISTO.125 [pp] 0.10 0.26 0. 33 0.23 results expressed as the average value of the values determined on the three samples that make up each of the four M-P series;

[0327] bcharacteristic values of the particle size distribution before the shatter test;

[0328] ccharacteristic values of the particle size distribution after the shatter test.TABLE 4 - Characterization of the granular material s be fore and after calcination

[0329] M MlbM2CM3dN NlbN2CN3d0 Olb02c03dP PlbP2CP3dFree H2O

[0330] 0. 21 - - - 0. 15 - - - - - - - - - - - [ % ]

[0331] C02[ % ] 1. 29 - - - 3. 87 - - - - - - - - - - - 24. 8 16. 4 23. 7 24. 9 23. 0 18. 8 21. 7 23. 0 43. 9 42. 9 47. 9 18. 6 47. 2 LOI [ % ] 0. 10 6. 66 6. 53

[0332] 9 3 3 7 4 7 9 1 4 9 0 8 3

[0333] T ' ma T ' ma T ' ma T ' ma time tso 00: 1 00: 1 00: 4 49: 1 01: 2 00: 2 X X 00: 1 00: 1

[0334] - - - - [min: sec ] 7 7 0 3 1 1 <50 <50 5 <50 <50 8

[0335] ° C ° C ° C ° C

[0336] T ' ma T ' ma T ' ma T ' ma T ' ma T ' ma T ' ma time teo 00: 2 00: 1 00: 5 X X X X 00: 1 X X 34: 1

[0337] - - - - [min: sec ] 0 9 3 < 60 < 60 < 60 < 60 < 60 7 < 60 < 60 0

[0338] ° C ° C ° C ° C ° C ° C ° C time tu00: 1 00: 2 01: 0 00: 4 00: 5 00: 2 39: 4 18: 2 00: 1 45: 3 33: 1 12: 5

[0339] - - - -

[0340]

[0341] ( 80 % 7 0 5 7 4 2 0 8 9 4 0 6eaction)

[0342] min: sec]

[0343] emperatur

[0344] Tu(80%

[0345] - 55.3 65. 6 68. 5 - 41.2 47. 7 50. 6 - 21.2 23. 9 67. 5 - 20. 1 20. 9 5 eaction)

[0346] °C]

[0347] emperatur

[0348] T ' max - 64.2 77. 0 80. 7 - 50. 3 54. 6 58. 3 - 2. 4 24. 8 79.5 - 20. 3 21. 1 6

[0349]

[0350] °C]

[0351] aresults expressed as the average value of the values determined on the three samples that make up each of the M-P series and the Ml-Pl series, the M2-P2 series and the M3-P3 series;

[0352] bSamples Ml-Pl obtained by calcining Samples M-P up to the predefined maximum temperature T = 600°C for a time t = 1 h;

[0353] cSamples M2-P2 obtained by calcining the Samples M-P up to the predefined maximum temperature T = 800°C for a time t = 1 h;

[0354] dM3-P3 samples obtained by calcining the M-P samples up to the predefined maximum temperature T = 1000°C for a time t = 1 h.The data of Table 3 show that the granular hydrated lime of substantially spheroidal shape according to the present invention has a low tendency to generate fine powder fractions following dynamic stresses during handling and transport ( ISTXshatter test index) which were also found to be lower than those of carbonate products normally used in the glass industry available on the market which are normally characterised by smaller particle sizes.

[0355] The data reported in Table 4 show that the granular hydrated lime of substantially spheroidal shape according to the present invention when subj ected to a thermal calcination process at T = 600°C, T = 800°C and T = 1000°C, such as the one that can undergo under the conditions of use in the melting process of glass manufacture, leads to the generation of corresponding calcium oxides (CaO) and calcium and magnesium oxides (CaO. MgO) characterized by a greater reactivity than the same oxides generated starting from the homologous carbonate raw materials, limestone and dolomite, normally used in the glass industry.

[0356] The results of the calcination heat treatment tests at various temperature levels have also highlighted, for the granular hydrated lime of substantially spheroidal shape according to the present invention compared to the carbonate materials normally used in the glass industry, the need for a lower input of thermal energy for the transformation into the corresponding readily reactive quicklime for the subsequent chemical reactions inside the melting bath of the glass manufacturing process (acceleration of the of the overall melting kinetics).

[0357] EXAMPLE 4

[0358] A comparative laboratory study was conducted in order to evaluate the effect of the complete replacement of the carbonate raw materials (limestone, dolomite) conventionally used in the batch formulation of the vitrifiable mixture,with raw materials based on quicklime (calcium quicklime, dolomitic quicklime) or with raw materials based on hydrated lime (calcium hydrated lime, dolomitic hydrated lime) as substances supplying calcium and magnesium.

[0359] The complete replacement of the carbonate raw materials was nevertheless intended to guarantee the same equivalent content of CaO and MgO in the composition of the resulting glass.

[0360] In this comparative experimental study, a composition of the batch of the "simplified" vitrifiable mixture was considered, which involved the use of the following raw materials:

[0361] silica sand commonly used in the glass sector, feldspathic sand commonly used in the glass industry,

[0362] sodium carbonate commonly used in the glass sector,

[0363] sodium sulfate commonly used in the glass sector, raw materials supplying calcium and magnesium, such as limestone and dolomite commonly used in the glass sector, or calcium quicklime and dolomitic quicklime (both in powder form and in natural granular form, of normal industrial production), or calcium hydrated lime and dolomitic hydrated lime (both in powder form of normal industrial production and in granular form of substantially spheroidal shape according to the present invention). According to the designation reported in standard EN 459-1: 2015, calcium quicklime and dolomitic quicklime are respectively classified as CL90-Q (CaO+MgO > 90%, MgO < 5%, C

[0364]

[0365] O24%, SO32%) and DL90-30-Q (CaO+MgO > 90%, MgO > 30%, CO2

[0366]

[0367] 6%, SO3 2%), while calcium hydrated lime and dolomitic hydrated lime are designated as CL90-S (CaO+MgO > 90%, MgO < 5%, CO2

[0368]

[0369] 4%, SO3 2%, net of free water and chemically bound water content) and DL90-30-S1 (CaO+MgO > 90%, MgO >30%, CO2

[0370]

[0371] 6%, SO3 2%, net of free water and chemically bound water content).

[0372] Table 5 reports the characteristic values of the particle size distribution of the aforementioned raw materials making up the vitrifiable mixture obtained from the particle size analysis carried out by dry-sieving by shaking in accordance with standards EN 459-2: 2021, EN 932-2: 2000 and EN 933-1: 2012 in control sieves with square-shaped aperture as reported in standard EN 933-2: 2020.

[0373] The raw materials used for the formulation of the various batches of vitrifiable mixture were previously dried in a laboratory oven at a temperature of 115°C for a time at least equal to 12 hours to remove free water with the only exceptions for the materials based on quicklime and based on calcium and dolomitic hydrated lime which were not subj ected to said treatment in order to prevent undesired effects of re- carbonation.

[0374] Five comparative series (Samples Q-U) of three samples each of batches of vitrifiable mixture whose percentage composition referred to dry weight is reported below were prepared in the laboratory, according to the process reported below:

[0375] Sample Q: 31.1% silica sand + 32.2% feldspathic sand + 17.3% sodium carbonate + 0.3% sodium sulfate + 12.0% limestone + 7.1% dolomite;

[0376] Sample R: 34.2% silica sand + 34.8% feldspathic sand + 18.9% sodium carbonate + 0.3% sodium sulfate + 7.8% powdered calcium quicklime + 4.0% powdered dolomitic quicklime;

[0377] Sample S: 34.2% silica sand + 34.8% feldspathic sand + 18.9% sodium carbonate + 0.3% sodium sulfate + 7.8% granular calcium quicklime + 4.0% granular dolomitic quicklime;Sample T: 32.9% silica sand + 33.9% feldspathic sand + 18.2% sodium carbonate + 0.3% sodium sulfate + 9. 6% powdered calcium hydrated lime + 5.1% powdered dolomitic hydrated lime;

[0378] Sample U: 32.9% silica sand + 33.9% feldspathic sand + 18.2% sodium carbonate + 0.3% sodium sulfate + 9. 6% granular calcium hydrated lime of substantially spheroidal shape according to the present invention + 5.1% granular dolomitic hydrated lime of substantially spheroidal shape according to the present invention.

[0379] In all cases, the composition of the resulting glass, expressed in terms of oxides, considered in this study was practically the same and is reported in Table 6.

[0380] The comparative tests of the effects of replacing the carbonate raw materials supplying calcium and magnesium with homologous raw materials based on quicklime and hydrated lime aimed to evaluate what could be, under the conditions of use in a full-scale glass process, the possible impacts on the batch in terms of temperature variation, moisture level and particle size distribution, both in relation to any hydration phenomena of the components and their modification over time during a maturation and resting step prior to use, and as a result of the mechanical action due to the mixing step.

[0381] Three specific steps of the batch preparation process of the vitrifiable mixture were considered:

[0382] a) batch formulation: dosing of raw materials and moistening of the mixture by adding liquid water;

[0383] b) batch mixing: mixing of the moistened raw materials;

[0384] c) batch maturation: keeping the batch of vitrifiable mixture at rest prior to use in a melting process for the production of glass.

[0385] The mixing of the batch of vitrifiable mixture, suitablymoistened until having a free water content of 3.50% and a total weight equal to about 2500 grams, took place in a bench-top planetary mixer for a mixing time of 5 minutes according to a mixing regime characterized by a planetary rotation speed of 62 rpm and a rotation speed of the mixing blade of 140 rpm.

[0386] At the end of each of the three specific steps of the preparation process of the batch of the vitrifiable mixture described above, the particle size analysis of the samples of the batches of vitrifiable mixture (Samples Q-U) was conducted and, starting from the end of the mixing step, the free water content and the temperature were monitored, with a frequency of 15 minutes and for a total time of 60 minutes coinciding with the end of the maturation step of the batch considered in the context of this study.

[0387] Table 7 reports the characteristic values of the particle size distribution (Dio, D50, D90, Dave, D90 / D10, (D90-D10) / D50) for the three specific steps of the process of preparation of the batch of vitrifiable mixture (batch formulation, batch mixing and batch maturation) as well as the values of the percentage by weight of particles passing through the 0.125 mm sieve (representative of the finest part of the particle size distribution of the batch of vitrifiable mixture) and the values of the percentage by weight of the cumulative residue of the particles retained on the 3.15 mm sieve (representative of the coarsest part of the particle size distribution of the batch of vitrifiable mixture) indicative, respectively, of the tendency to generate fine fractions that may be more subject to entrainment phenomena in the flow of the exhaust gases inside a glass furnace ( carryover) or of the tendency to have extremely coarse particles with difficulty in melting once they are introduced into the melting bath.

[0388] Table 7 also reports the values of the temperature andfree water content (moisture) of the batch of vitrifiable mixture monitored starting from the end of the mixing step every 15 minutes and up to 60 minutes, which is the time taken as coinciding with the end of the maturation step of the batch considered in the context of this experimental study.TABLE 5 — C haracteristi c values of the particle size distribution of the raw materials constituting the batch of "simplified" vitrifiable mixture

[0389] ( D9 Dio D50 D90 Dave D90 / D10

[0390] D10) / [mm] [mm] [mm] [mm]

[0391] Silica sand 0. 14 0.22 0. 42 0.24 3. 00 1.2 Feldspathic sand 0. 14 0. 37 0.80 0.41 5.71 1.7 Sodium carbonate 0.18 0. 35 0.49 0. 37 2.77 0.8 Sodium sulfate 0. 13 0. 34 0.49 0. 34 3.77 1.0 Limestone 0. 51 0.86 1.71 0. 96 3. 35 1.4 Dolomite 1. 05 1.71 2.80 1.77 1.75 1. 0 Powdered calcium quicklime

[0392] 0. 02 0. 09 0.23 0.11 11. 50 2. 3 a

[0393] Powdered dolomitic quicklime30. 01 0. 07 0.16 0. 08 16.00 2. 1 Granular calcium quicklime

[0394] 2. 64 4.70 8. 90 5.30 3. 37 1. 3 a

[0395] Granular dolomitic quicklime32. 63 3. 97 7. 52 4.44 2.86 1.2 Powdered calcium hydrated

[0396] 0. 01 0. 07 0.16 0. 08 16.00 2. 1 lime3

[0397]

[0398] Powdered dolomitic hydrated

[0399] 0. 01 0. 07 0.16 0. 08 16.00 2. 1 limea

[0400] ranular calcium hydrated lime

[0401] of substantially spheroidal

[0402] shape 2.29 3. 69 7.24 4. 14 3. 17 1. 3 according to the present

[0403] inventionb

[0404] Granular dolomitic hydrated

[0405] lime of substantially

[0406] spheroidal shape

[0407] 2. 91 4.26 8. 02 4.74 2.76 1.2 according to the present

[0408] invention13

[0409]

[0410] raw materials supplying calcium and magnesium of normal industrial production;

[0411] raw materials supplying calcium and magnesium produced according to the present

[0412] invention.TABLE 6 Composition of the glass resulting from the batch of " simplified" vitrifiable mixture

[0413] Glass composition % by weight

[0414] SiO271.89

[0415] Al2O31.44

[0416] Na2O 12.29

[0417] K2O 1. 08

[0418] CaO 11. 02

[0419] MgO 1. 93

[0420] BaO 0. 02

[0421] SO30.22

[0422] Fe2O30. 03

[0423] Cr2O30. 01

[0424] TiO20. 02

[0425] ZrO20. 01

[0426] PbO 0. 00

[0427] P2O50. 01

[0428] MnO 0. 00

[0429]

[0430] SrO 0. 01TABLE 7 Characteri zation of the batches o f vitri f iable mixture

[0431] Q R S T U

[0432] 0. 26b-- 0. 25c- - 0. 15b-- 0. 12c0. 30b-- 0. 23c0. 26b-- 0. 21c0. 26b-- 0. 25 D10[mm]

[0433] 0. 22d-- 0. 11d— 0. 19d— 0. 19d- - 0. 23d0. 47b-- 0. 45c- - 0. 39b-- 0. 37c0. 64b-- 0. 42c0. 44b-- 0. 41c0. 46b-- 0. 44 D50 [mm]

[0434] 0. 45d— 0. 37d— 0. 41d— 0. 40d— 0. 44d1. 35b-- 1. 31c- - 0. 84b-- 0. 79c4. 33b-- 1. 17c0. 96b-- 0. 90c2. 92b-- 1. 84 D90[mm]

[0435] 1. 31d-- 0. 78d- - 1. 00d-- 0. 88d- - 1. 80d0. 65b-- 0. 61c- - 0. 46b-- 0. 41c1. 32b-- 0. 73c0. 60b-- 0. 50c0. 96b-- 0. 74 Dave[mm]

[0436] 0. 61d-- 0. 41d- - 0. 70d-- 0. 48d- - 0. 73d5. 19b-- 5. 24c- - 5. 60b-- 6. 58c14. 43b-- 5. 09c3. 69b-- 4. 29c11. 23b-- 7. 3 6 D90 / D10 [ - ]

[0437] 5. 95d— 7. 09d— 5. 26d— 4. 63d— 7. 83d2. 32b-- 2. 36c- - 1. 77b-- 1. 81c6. 30b-- 2. 24c1. 59b-- 1. 68c5. 78b-- 3. 61 ( D90-D10) / D50[ - ]

[0438] 2. 42d-- 1. 81d- - 1. 98d-- 1. 73d- - 3. 57dPas sing-through fraction - 0. 125 0. 61b-- 1. 14c- - 7. 48b- - 10. 21c0. 15b-- 1. 74c0. 57b-- 1. 77c0. 81b-- 1. 94 mm sieve [ % ] 3. 42d-- 11. 25d- - 3. 88d-- 2. 45d- - 1. 75dResidual fraction - 3. 15 mm sieve 0. 01b-- 0. 01c- - 0. 01b-- 0. 01c10, 42b-- 2, 39° 0, 23b- 0, 01c- 4. 15b-- 0. 81

[0439]

[0440] [ % ] 0. 00d-- 0. 00d- 2, 34d- 0, 00d- - 0. 84dBatch temperature - To ( t= 0

[0441] 32. 8 42. 0 37. 0 30. 0 30. 3 minutes ) [ ° C ]e

[0442] Batch temperature - Ti ( t= 15

[0443] 31. 9 55. 2 41. 2 30. 9 30. 5 minutes ) [ ° C ]

[0444] Batch temperature - T2 ( t= 30

[0445] 29. 6 55. 1 47. 6 27. 9 27. 5 minutes ) [ ° C ]

[0446] Batch temperature - T3 ( t= 45

[0447] 27. 7 50. 9 39. 7 28. 3 26. 6 minutes ) [ ° C ]

[0448] Batch temperature - T4 ( t= 60

[0449] 26. 2 46. 0 38. 1 25. 7 25. 0 minutes ) [ ° C ]f

[0450] Batch free water - Initial

[0451] 3. 50 3. 50 3. 50 3. 50 3. 50 moistening - Uinitial[ % ]g

[0452] Batch free water - Uo ( t= 0

[0453] 3. 12 2. 24 2. 41 3. 19 3. 18 minutes ) [ % ]h

[0454] Batch free water - Ui ( t= 15

[0455] 3. 11 1. 61 2. 20 3. 15 3. 16 minutes ) [ % ]

[0456] Batch free water - U2 ( t= 30

[0457] 3. 06 1. 51 1. 96 3. 09 3. 10

[0458]

[0459] minutes ) [ % ]Batch free water - U3 (t= 45

[0460] 3. 05 1.37 1. 91 3. 02 3. 03 minutes ) [% ]

[0461] Batch free water - U4 (t= 60

[0462] 3. 05 1. 17 1.88 3.01 3.04

[0463]

[0464] minutes ) [%]i

[0465] aresults expressed as the average value of the values determined on the three samples that make up each of the Q-U series;

[0466] bafter the batch formulation step: dosing of the raw materials and moistening of the mixture by adding liquid water;

[0467] cafter the batch mixing step: mixing of the moistened raw materials;

[0468] dafter batch maturation step: keeping the batch of vitrifiable mixture at rest prior to use in a melting process for glass production;

[0469] emeasurement of the batch temperature at the end of the mixing step of the previously moistened batch of vitrifiable mixture (addition of liquid water to the dosed raw materials until a moisture content equal to 3.50% with respect to the total mass of the batch is obtained). Starting from this moment (t= 0 minutes) the batch temperature is detected every 15 minutes;

[0470] fmeasurement of batch temperature at the end of the maturation step (keeping the batch at rest for 1 hour);

[0471] g initial moisture content of the batch of vitrifiable mixture (addition of liquid water to the dosed raw materials until a moisture content equal to 3.50% with respect to the total mass of the batch is obtained) before the batch mixing step;

[0472] hmeasurement of the moisture content at the end of the mixing step of the batch of previously moistened vitrifiable mixture (addition of liquid water to the dosed raw materials until a moisture content equal to 3.50% with respect to the total mass of the batch is obtained). Starting from this moment (t= 0 minutes) the monitoring of the degree of moistening ( freewater content) of the batch takes place every 15 minutes;

[0473] measurement of the degree of moistening ( free water content) of the batch at the end of the maturation step (keeping the batch at rest for 1 hour).The data of Table 7 show that in the case of the batch of vitrifiable mixture prepared with the granular hydrated lime of substantially spheroidal shape according to the present invention in place of the carbonate raw materials usually used in the glass industry, despite any initial differences in particle size with respect to the other raw materials making up the batch, these are mitigated following the mixing process for the preparation of the batch, however, the generation of fine powder fractions being absolutely contained.

[0474] The replacement of limestone and dolomite with calcium quicklime and dolomitic quicklime involves a general rise in the temperature of the batch of vitrifiable mixture due to the establishment of exothermic hydration reactions. The replacement of limestone and dolomite with calcium quicklime and dolomitic quicklime entails further negative variations in the moisture content of the batch of vitrifiable mixture, which are more significant in the case of powdered quicklime than not in the case of natural granular quicklime; by contrast, the depletion of the moisture of the batch is almost zero in the case of use of hydrated lime in place of the carbonate raw materials typically used in glass production.

[0475] EXAMPLE 5

[0476] A comparative laboratory study was conducted to evaluate the dissolution kinetics under controlled melting conditions of a typical glass composition obtained by using carbonate raw materials, limestone and dolomite, typycally used in the industrial formulation of the batch of the vitrifiable mixture and, for comparison, by melting an analogous glass composition obtained using, as calcium and magnesium-supplying substances, raw materials based on granular calcium hydrated lime and granular dolomitic hydrated lime of substantially spheroidal shape according tothe present invention.

[0477] In this comparative experimental study, a composition of the batch of the "simplified" vitrifiable mixture was considered, which involved the use of the following virgin and recycled (glass cullet) raw materials:

[0478] silica sand commonly used in the glass sector, feldspathic sand commonly used in the glass industry,

[0479] sodium carbonate commonly used in the glass sector,

[0480] sodium sulfate commonly used in the glass sector, raw materials supplying calcium and magnesium, such as limestone and dolomite commonly used in the glass sector, or granular calcium hydrated lime and granular dolomitic hydrated lime of substantially spheroidal shape according to the present invention respectively classified, based on standard EN 459-1: 2015, as CL90-S (CaO+MgO > 90%, MgO < 5%, CO2

[0481]

[0482] 4%, SO3 2% net of free water and chemically bound water content) and DL90-30-S1 (CaO+MgO > 90%, MgO > 30%, CO2

[0483]

[0484] 6%, SO3 2% net of free water and chemically bound water content);

[0485] glass cullet commonly used in the glass industry for the production of "white" glass.

[0486] The virgin raw materials used for the formulation of the various batches of vitrifiable mixture were previously dried in a laboratory oven at a temperature of 115°C for a time at least equal to 12 hours to remove free water with the only exceptions for the materials based on granular calcium hydrated lime and granular dolomitic hydrated lime of substantially spheroidal shape according to the present invention which were not subj ected to said treatment in order to prevent undesired effects of re-carbonation. The glass cullet was washed and dried and was reduced to a particle size of less than 10 mm, having commonly, in industrialglassmaking practice, particle sizes of the order of 1 - 3 cm or larger. The virgin raw materials were used while maintaining the sizes according to which they are usually used in industrial glassmaking.

[0487] Table 8 reports the characteristic values of the particle size distribution of the aforementioned raw materials making up the vitrifiable mixture obtained from the particle size analysis carried out by dry-sieving by shaking in accordance with standards EN 459-2: 2021, EN 932-2: 2000 and EN 933-1: 2012 in control sieves with square-shaped aperture as reported in standard EN 933-2: 2020.

[0488] Four batches of comparative vitrifiable mixtures (Samples V-Y) were prepared in the laboratory according to the process described below whose composition, expressed as a percentage by dry weight, is reported hereinafter:

[0489] Sample V: 31.1% silica sand + 32.2% feldspathic sand + 17.3% sodium carbonate + 0.3% sodium sulfate + 12.0% limestone + 7.1% dolomite;

[0490] Sample W: 32.9% silica sand + 33.9% feldspathic sand + 18.2% sodium carbonate + 0.3% sodium sulfate + 9. 6% granular calcium hydrated lime of substantially spheroidal shape according to the present invention + 5.1% granular dolomitic hydrated lime of substantially spheroidal shape according to the present invention;

[0491] Sample X: 15.5% silica sand + 16.1% feldspathic sand + 8.7% sodium carbonate + 0.1% sodium sulfate + 6.0% limestone + 3. 6% dolomite + 50% glass cullet;

[0492] Sample Y: 16.5% silica sand + 16.9% feldspathic sand + 9.1% sodium carbonate + 0.1% sodium sulfate + 4.8% granular calcium hydrated lime of substantially spheroidal shape according to the present invention + 2. 6% granular dolomitic hydrated lime of substantially spheroidal shape according to the present invention + 50% glass cullet.

[0493] In the four formulations, the same equivalent contentof CaO and MgO was maintained in the resulting glass composition reported in Table 9.

[0494] The preparation of the various batches of vitrifiable mixture (Samples V-Y), each weighing 2500 grams, was carried out in a bench-top planetary mixer for a mixing time of 5 minutes according to a mixing regime characterized by a planetary rotation speed of 62 rpm and a rotation speed of the mixing blade of 140 rpm. The preparation of the batches of vitrifiable mixture (Samples V-Y) was carried out under completely dry conditions in order to free the results of the melting tests from any effects of the moisture in the mixture.

[0495] Each batch of vitrifiable mixture (Samples V-Y) was then subj ected to kinetic dissolution test aimed at describing the dissolution rate of the sand particles (silica) in a glass batch under controlled melting conditions. The experimental melts were carried out in five times ( from 1 hour to 5 hours), after each test time, measuring the number of undissolved silica particles per 100 grams of glass compared to the residence time in the crucible inside an indirect heating laboratory furnace at the melting temperature of 1450°C.

[0496] For each batch of vitrifiable mixture (Samples V-Y) the tests were repeated three times according to the procedure indicated below.

[0497] A series of five silica-alumina crucibles, preheated to a temperature of 1250°C were charged with about 400 grams of vitrifiable mixture and then brought, in a time equal to 2 hours, to the designated melting temperature (T = 1450°C) at which the crucibles were kept inside the furnace for a maximum of 5 hours (the melting time at 3 hours can be considered a significant residence time in the furnace for this type of test) and being gradually extracted according to time intervals of 1 hour. At the end of each meltinginterval, the glass was cast, annealed at the temperature of 550°C for a time equal to 3 hours, inertially cooled in a laboratory desiccator, sectioned and prepared for counting undissolved silica particles under a stereoscopic microscope with magnifications up to 160x.

[0498] Table 10 reports the data of the counts of the undissolved sand particles in the glass produced.TABLE 8 - C haracteristi c values o f the particle s i ze di stribution o f the raw material s constituting the batch of " simpli fied" vitri f iable mixture (virgin raw material s and glas s cullet )

[0499] ( D90- D10 D50 D90 Dave D90 / D10

[0500] D10 ) / D5 [mm] [mm] [mm] [mm] [ - ]

[0501] [ - ] S il ica sanda0. 14 0. 22 0. 42 0. 24 3. 00 1. 28 Feldspathic sanda0. 14 0. 37 0. 80 0. 41 5. 71 1. 78 Sodium carbonatea0. 18 0. 35 0. 49 0. 37 2. 77 0. 89 Sodium sul fatea0. 13 0. 34 0. 49 0. 34 3. 77 1. 06 Limestonea0. 51 0. 86 1. 71 0. 96 3. 35 1. 40 Dolomitea1. 05 1. 71 2. 80 1. 77 1. 75 1. 02 Granular calcium hydrated lime

[0502] o f substantially spheroidal shape 2. 29 3. 69 7. 24 4. 14 3. 17 1. 34 according to the present invention5

[0503] Granular dolomitic hydrated l ime of

[0504] substantially spheroidal shape 2. 91 4. 26 8. 02 4. 74 2. 7 6 1. 20 according to the present invention5

[0505] Glas s culletc4. 93 7. 27 9. 54 7. 31 1. 94 0. 63

[0506]

[0507] raw materials commonly used in the glass industry;

[0508] b raw materials supplying calcium and magnesium produced according to the present invention;

[0509] recycled raw material (white glass cullet) commonly used in glassmaking practice subj ected to a comminution process.TABLE 9 - Composition of the glass resulting from the batch of "simplified" vitrifiable mixture

[0510] Glass composition % by weight

[0511] SiO271.89

[0512] Al2O31.44

[0513] Na2O 12.29

[0514] K2O 1. 08

[0515] CaO 11. 02

[0516] MgO 1. 93

[0517] BaO 0. 02

[0518] SO30.22

[0519] Fe2O30. 03

[0520] Cr2O30. 01

[0521] TiO20. 02

[0522] ZrO20. 01

[0523] PbO 0. 00

[0524] P2O50. 01

[0525] MnO 0. 00

[0526]

[0527] SrO 0. 01

[0528] TABLE 10 - Count of the undissolved sand particles deriving from the kinetic dissolution test of the batches of vitrifiable mixture3

[0529] V W X Y

[0530] Melting time [# [# [# [# at T = 1450°C undissolved undissolved undissolved undissolved

[0531]

[0532] silica silica silica silicaparticles per particles per particles per particles per 100 grams 100 grams 100 grams 100 grams glass ] glass ] glass ] glass ] Melting time - 10. 7 12. 8 7.2 8. 4 1 h

[0533] Melting time - 6. 6 7. 5 2.3 1. 5 2 h

[0534] Melting time - 2. 7 1. 8 n. d. * n. d. *3 h

[0535] Melting time - n. d. * n. d. * n. d. * n. d. * 4 h

[0536] Melting time - n. d. * n. d. * n. d. * n. d. *

[0537]

[0538] 5 h

[0539] results expressed as the average value of three repetitions of the melting tests for each of the batches of vitrifiable mixture (Samples V-Y) tested;

[0540] n. d. = no particles of undissolved silica detected in the glass.

[0541] The data of Table 10 show that in the case of the batch of vitrifiable mixture prepared with the granular hydrated lime of substantially spheroidal shape according to the present invention in place of the carbonate raw materials usually used in the glass industry, a glass free of solid inclusions is produced at the level of laboratory tests whose quality is also higher than that obtainable with the use of the carbonate raw materials usually used in the glass industry.

Claims

1. CLAIMS1. Use for the production of glass of a granular material in a substantially spheroidal shape comprising hydrated air lime having:- a total concentration of CaO and MgO equal to or greater than 80% with respect to the granular material after subtraction of its free water and chemically bound water content;- a compressive load until rupture equal to or greater than 40 N / granule, preferably equal to or greater than 50 N / granule;wherein said hydrated air lime is selected from the group consisting of:- calcium hydrated air lime having an MgO content equal to or less than 5% by weight with respect to the weight of the hydrated air lime after subtraction of its free water and chemically bound water content;- magnesium hydrated air lime having an MgO content greater than 5% and less than 30% by weight with respect to the weight of the hydrated air lime after subtraction of its free water and chemically bound water content;- dolomitic hydrated air lime having an MgO content equal or greater than 30% by weight and, preferably, equal to or less than 42% by weight with respect to the weight of the hydrated air lime after subtraction of its free water and chemically bound water content; and- mixtures thereof.

2. Use according to claim 1, wherein the hydrated air lime is a calcium hydrated air lime in which the Mg / Ca weight ratio is between 0.002 and 0.04, preferably between 0.01 and 0.02, and / or the Mg / (Ca+Mg) ratio is in the range from 0.002 to 0.04, more preferably in the range from 0.01 to 0.02.

3. Use according to claim 1, wherein the hydrated airlime is a magnesium hydrated air lime in which the Mg / Ca weight ratio is between 0.05 and 0.35, more preferably between 0.06 and 0.25, and / or the Mg / (Ca+Mg) ratio is in the range from 0.05 to 0.26, preferably in the range from 0.06 to 0.20.

4. Use according to claim 1, wherein the hydrated air lime is a dolomitic hydrated air lime in which the Mg / Ca weight ratio is between 0.36 and 0. 62, more preferably between 0.52 and 0. 62, and / or the Mg / (Ca+Mg) ratio is in the range from 0.27 to 0.38, more preferably in the range from 0.34 to 0.38.

5. Use according to any of claims 1 to 4, wherein the particle size distribution of the granular material is characterised in that at least 90% by weight of the mass of the granular material, preferably at least 95% by weight, more preferably at least 98% by weight, is formed by granules having size in the range from 1 to 10 mm, preferably in the range from 1.4 to 9 mm and more preferably in the range from 2 to 8 mm.

6. Use according to any of claims 1 to 5, wherein the apparent density of the granular material is between 1.2 g / cm3and 3 g / cm3, preferably between 1.3 g / cm3and 2.9 g / cm3, more preferably between 1.4 g / cm3and 2.8 g / cm3and even more preferably between 1.5 g / cm3and 2.7 g / cm3and / or the bulk density is between 0.7 g / cm3and 1.2 g / cm3, preferably between 0.8 g / cm3and 1.15 g / cm3, more preferably between 0.9 g / cm3and 1.1 g / cm3.

7. Use according to any of claims 1 to 6, wherein the IST1shatter test index value of the granular material is less than 1.5 percentage points (pp), preferably less than 1.2 pp, more preferably less than 0.7 pp, even more preferably less than 0.5 pp and wherein the value of the IST0.5shatter test index is less than 0.5 pp, preferably less than 0.3 pp and even more preferably less than 0.2 pp.

8. A method for the production of glass comprising: a. mixing at least:1 ) a vitrifying material forming a glass network; 2 ) a granular material of substantially spheroidal shape comprising hydrated air lime having:- a total concentration of CaO and MgO equal to or greater than 80% by weight with respect to the weight of the granular material after subtraction of its free water and chemically bound water content;- a compressive load until rupture equal to or greater than 40 N / granule, preferably equal to or greater than 50 N / granule;wherein said hydrated air lime is selected from the group consisting of:- calcium hydrated air lime having an MgO content equal to or less than 5% by weight with respect to the weight of the hydrated air lime after subtracting its free water and chemically bound water content;- magnesium hydrated air lime having an MgO content greater than 5% by weight and less than 30% by weight with respect to the weight of the hydrated air lime after subtracting its free water and chemically bound water content;- dolomitic hydrated air lime having an MgO content equal to or greater than 30% by weight and, preferably, equal to or less than 42% by weight with respect to the weight of the hydrated air lime after subtracting its free water and chemically bound water content; and- mixtures thereof,in a weight ratio between 3: 1 and 6: 1 to obtain a mixture;b. adding water to the mixture in an amount of 1 to 5% by weight of the mixture obtained in step (a);c. heating the mixture of step (b) to between 1300°Cand 1600°C to obtain a molten mixture;d. forming the molten mixture of step (c); ande. annealing the product obtained in step (d).

9. The method according to claim 8, wherein at least one fluxing compound, refining compound, decolouring compound, opacifying compound, colouring compound or reducing compound is also added in the mixing step.

10. The method according to claim 8 or 9, wherein glass cullet is also added to the vitrifiable mixture after the mixing step (a).

11. The method according to any of claims 7 to 9, wherein the product obtained in step (d) is hollow glass.

12. The method according to any of claims 8 to 10, wherein the product obtained in step (d) is flat glass and the method includes a further step ( f ) of cutting and squaring the product.

13. A method of producing a granular material in a substantially spheroidal shape comprising hydrated air lime having:- a total concentration of CaO and MgO equal to or greater than 80% by weight with respect to the weight of the granular material after subtraction of its free water and chemically bound water content;- a compressive load until rupture equal to or greater than 40 N / granule and preferably equal to or greater than 50 N / granule;wherein said hydrated air lime is selected from the group consisting of:- calcium hydrated air lime having an MgO content equal to or less than 5% by weight with respect to the weight of the hydrated air lime after subtracting its free water and chemically bound water content;- magnesium hydrated air lime having an MgO content greater than 5% by weight and less than 30% by weight withrespect to the weight of the hydrated air lime after subtracting its free water and chemically bound water content;- dolomitic hydrated air lime having an MgO content equal to or greater than 30% by weight and, preferably, equal to or less than 42% by weight with respect to the weight of the hydrated air lime after subtracting its free water and chemically bound water content; and- mixtures thereof;including at least:a. preparing a mixture comprising:1 ) hydrated air lime with a total concentration of CaO and MgO equal to or greater than 80% by weight with respect to the weight of the material after subtraction of its free water and chemically bound water content;2 ) a granulation fluid comprising water;b. mixing this mixture until wet granules are obtained comprising particles of said hydrated lime;c. drying said wet granules to obtain granules comprising hydrated lime with a residual content of free water of less than 2.5% by weight, preferably less than 2% by weight, preferably less than 1.5% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight, and even more preferably less than 0.2% by weight with respect to the weight of the dried granules, said granules having a substantially spheroidal shape.

Images