Furnace process for the preparation of silicate and precipitated silica from spent foundry sand, and silicate and precipitated silica obtainable thereby

Abstract

The invention relates to a silicate and to a precipitated silica that have a high iron content and to processes especially well-suited for their preparation, starting from a spent foundry sand using a furnace route that comprises the step of melting the spent foundry sand in a furnace at high temperature in the presence of a base.

Description

[0001] FURNACE PROCESS FOR THE PREPARATION OF SILICATE AND PRECIPITATED SILICA FROM SPENT FOUNDRY SAND, AND SILICATE AND PRECIPITATED SILICA OBTAINABLE THEREBY

[0002] TECHNICAL FIELD

[0003] The present invention relates to a process for the preparation of silicate, preferably alkali metal silicate, from spent foundry sand (SFS) and to a process for the preparation of precipitated silica from this silicate. The present invention also relates to a silicate and to a precipitated silica that can be obtained by the aforesaid processes.

[0004] TECHNICAL BACKGROUND

[0005] Silicon dioxide (SiO?), also known as silica, is a silicon compound that is commonly found in nature. Naturally-occurring silica exists both in amorphous and crystalline forms such as cristobalite, tridymite, and quartz, the latter being the major constituent of sand. Natural quartz sand, such as Fontainebleau sand, is frequently employed for the preparation of silicate, in particular sodium silicate, which can be obtained, for example, by hydrothermal treatment of said sand with strong bases, such as sodium hydroxide, or via a furnace route, namely by fusion of said sand with alkali metal carbonates, hydrogen carbonates or hydroxides, at high temperatures in the range of 1000 °C to 1600 °C as described, for example, in DE3012073A1.

[0006] Silicates and, particularly, sodium silicates are commonly employed as raw materials for the precipitation of precipitated silica, which is a form of synthetic silica in amorphous form. Both silicates and precipitated silica are highly versatile materials with a variety of applications in the most diverse technological fields, from constructions to detergents, tire, adhesives, food, and pharmaceutical industries, and their global demand is constantly increasing.

[0007] However, the above-mentioned processes for producing silicates and precipitated silica have the major disadvantages that natural quartz sand, used as raw material, is not a renewable resource over human timescales as its replenishment happens through rocks erosion or weathering processes over geological time.

[0008] It appears thus clear that there is the need to identify and valorize new sustainable circular source of SiCE that can be employed to produce silicates and precipitated silica in a more environmentally friendly way while at the same time assuring good quality and yields of the final product. A possible alternative for this purpose can be envisaged in spent foundry sand (SFS), a SiCh-rich waste which is produced in large amounts by the foundry industries. Spent foundry sand (SFSs) or waste foundry sand (WFSs) is in fact the most common waste from foundries which use new, virgin natural quartz sand to make casting molds to design metal parts of various sizes. Although such sand can be reused multiple times within the foundry, heat and mechanical abrasion eventually render the sand unsuitable for use in casting molds, and a portion of the sand is continuously removed and replaced with new virgin sand.

[0009] SFS thus represents a large amount of the waste produced by the foundry industries and its management and disposal (mainly in landfill) not only is an increasing environmental issue but also involves high costs.

[0010] In this context, the recovery and reuse of SFS plays a fundamental role as its recycling can save energy, costs, as well as reduce the need to mine virgin materials and exploit natural resources. Hence, from a circular economy perspective, there is a rising need towards the development of new environmentally friendly approaches for the conversion of SFS into value added products, such as silicates and precipitated silica.

[0011] However, one of the criticalities related to the use of spent foundry sand as starting material for producing silicate and precipitated silica is connected to the high variability of its chemical nature, morphology, and elemental composition which can be substantially different depending on the type of SFS, type of foundry processes, and on how the waste is managed locally by the various foundries. Moreover, different impurities may be present which, if not properly handled, can be detrimental for the production of silicates of high quality (i.e., having high Rp values) and with satisfactory yields.

[0012] IN201941016001 discloses a process for obtaining sodium silicate though a catalytic hydrothermal reaction route using spent foundry sand.

[0013] This process involves a hydrothermal treatment of spent foundry sand using a solution of concentrated caustic soda over a period of 6 to 36 hours over a temperature range between 150 °C and 350 °C in a closed pressure vessel. According to this document, before being subjected to said hydrothermal treatment, the spent foundry sand is subjected to a thermal pre-treatment at a temperature of about 400 °C to 600 °C for about 5 to 6 hours in order to remove the residual carbon present in the sand, which yields light brown coarse sand. The color removed sample is then treated with a solution of acidic catalyst to remove any volatile soluble impurities and to modify the surface of the spent foundry sand. The sample is then further washed to remove any acidic residues.

[0014] A similar approach is disclosed in IN202041002565 and IN201941026558 which all use similar thermal pre-treatments of the SFS before hydrothermal treatments.

[0015] None of these documents discloses a process involving a furnace route to produce silicate and precipitated silica from SFS.

[0016] Moreover, in the above documents, a thermal pre-treatment of the SFS is necessary to purify the sand and be able to obtain a silicate having the desired properties for further applications, such as for the production of precipitated silica. Such a thermal pre-treatment, however, increases the CO2 production of the method and the overall process steps and time.

[0017] In this context, it remains the need to develop a novel process for producing circular silicate and precipitate silica from a spent foundry sand which is easy, environmentally friendly, cost-efficient, and at the same time assures that the desired properties of the final product are obtained.

[0018] SUMMARY OF THE INVENTION

[0019] The present invention relates to a process for the preparation of a silicate from a spent foundry sand via a furnace route, wherein said silicate can in turn be used for the preparation of silica, in particular, precipitated silica.

[0020] A first objective of the present invention is to provide a process for the preparation of a solid silicate from a spent foundry sand.

[0021] Said process comprises the steps of:

[0022] (i) melting the spent foundry sand and, optionally in addition a sand other than a spent foundry sand, in a furnace in the presence of a base, preferably an alkali metal base, by heating at a temperature of at least 850 °C so as to obtain a molten vitreous silicate, followed by

[0023] (ii) cooling down, from the temperature of step (i) to a temperature below 550 °C, the molten vitreous silicate in a period of time of less than 30 minutes so as to obtain solidification of the molten vitreous silicate into a solid silicate, wherein said solid silicate is an amorphous solid silicate.

[0024] The process according to the present invention can further comprise a step (i’), before step (i), of purifying the spent foundry sand. The process according to the present invention can further comprise a step (ii’) of milling said amorphous solid silicate.

[0025] The amorphous solid silicate according to the present invention can be advantageously and easily dissolved in a liquid medium, preferably an aqueous medium, to produce a solution of silicate, preferably an aqueous solution of silicate.

[0026] A further objective of the present invention is thus to provide a process for the preparation of a solution of silicate, wherein the process of the invention further comprises the steps of:

[0027] (iii) dissolving the solid silicate in a liquid medium, preferably an aqueous medium, to obtain a liquid mixture comprising silicate and, if any, solid by-products,

[0028] (iv) if any solid by-products are comprised in said liquid mixture, separating said solid by-products from the liquid mixture to obtain a solution of silicate, preferably an aqueous solution of silicate, and

[0029] (v) optionally adding to said solution of silicate, at least one of a secondary silica source, an alkali metal hydroxide, preferably NaOH, a silicate other than the silicate obtained in step (iv), or a mixture thereof.

[0030] According to an embodiment of the present invention, the liquid mixture obtained in step (iii) or the solution of silicate obtained in step (iv) or (v) can be dried (step (vi)) so as to obtain a solid silicate.

[0031] The sand other than a spent foundry sand, when present, is advantageously natural sand. An example of such sand is Fontainebleau sand. The purity (SiCh content) of the sand other than a spent foundry sand, possibly natural sand, is preferably of at least 95.0 wt%, more preferably at least 97.0 wt%, still more preferably at least 99.0 wt%. between 99 wt% and 100 wt%.

[0032] This being said, the sand other than a spent foundry sand, when present, is advantageously natural sand. An example of such sand is Fontainebleau sand. The purity (SiCh content) of the sand other than a spent foundry sand, possibly natural sand, is preferably of at least 95.0 wt%, more preferably at least 97.0 wt%, still more preferably at least 99.0 wt%. between 99 wt% and 100 wt%.

[0033] The weight of the sand other than a spent foundry sand can range from 0 up to 85% by weight, preferably from 0 up to 75%, possibly from 0 up to 60%, 50%, from 0 to 40%, from 0 to 30%, from 0 to 20%, from 0 to 10%, from 0 to 5.0%, from 0 to 2.0% or from 0 to 1.0% by weight, based on the total weight of sand (that is to say based on the combined weight of the spent foundry sand and of the sand other than a spent foundry sand); it can also be zero (that is to say that no sand other than a spent foundry sand is then used). Besides, the weight of the sand other than a spent foundry sand can be of at least, at least 0.1%, at least 0.2%, at least 0.5%, at least 1.0%, at least 2.0%, at least 5.0%, at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60% or at least 70% by weight based on the total weight of sand.

[0034] According to an embodiment, the process of the invention comprises step (i’), before step (i), of purifying the spent foundry by applying thereto a pretreatment. By doing so, impurities possibly contained in the spent foundry sand are advantageously removed. Said impurities are often impurities selected from the group consisting of: metals, carbon-rich impurities, clays, metallic silicates, and other insoluble impurities, or a combination thereof.

[0035] Preferably, said pre-treatment step (i’), when present, is not a thermal treatment and, preferably too, the process according to the invention is free of any thermal treatment of the spent foundry sand before step (i).

[0036] The silicate obtained by the process according to the present invention (steps (ii), (ii’), (iii), (iv), (v) or (vi)) is preferably an alkali metal silicate and can be advantageously used as raw material for the preparation of silica, in particular precipitated silica.

[0037] Said silicate is indeed preferably characterized by a high SiCh / MxO weight ratio (Rp) of at least 2, preferably of at least 2.5, more preferably comprised between 2 and 4, even more preferably comprised between 3 and 4, most preferably of about 3.5, wherein M is a metal, preferably wherein M is an alkali metal and x is 2.

[0038] Said silicate is also preferably characterized by an amount of SiCh (i.e., SiCh final) of up to 100% of the amount of silica contained in the sand used in step (i) of the process (i.e., SiCh initial). Preferably, SiCh final is between 70% and 100% of SiCh initial. This corresponds to the yield of the process according to the present invention (i.e., the yield of SiCh recovered from the sand).

[0039] A further objective of the invention is therefore a silicate obtained or obtainable by the process according to the present invention and the use of said silicate for the preparation of silica, in particular, precipitated silica. Accordingly, an objective of the invention is also the provision of a process for the preparation of precipitated silica, wherein said process comprises the steps of:

[0040] (I) preparing a silicate by the process according to the present invention,

[0041] (II) reacting the silicate obtained in step (I) and, optionally in addition a silicate other than said silicate obtained in step (I), with at least one acidifying agent in a liquid medium, preferably an aqueous liquid medium, to obtain a suspension of precipitated silica,

[0042] (III) separating the precipitated silica from the liquid medium to provide wet precipitated silica, and

[0043] (IV) drying said wet precipitated silica to obtain precipitated silica.

[0044] Preferably, according to an embodiment, said process for the preparation of precipitated silica comprises, after step (I) and before step (II) a step (I’) of adding to the silicate obtained in step (I) at least one of a secondary silica source, an alkali metal hydroxide, preferably NaOH, a silicate other than the silicate obtained in step (I), or a mixture thereof, so as to obtain a new silicate. Accordingly, step (II) comprises reacting the new silicate obtained in step (I’) and, optionally in addition a silicate other than the new silicate obtained in step (I’), with at the one acidifying agent in a liquid medium, preferably an aqueous liquid medium to obtain a suspension of precipitated silica.

[0045] The present invention solves the aforementioned problems of the prior art by providing a process for the preparation of silicate from a spent foundry sand via a direct furnace route without the need of thermally pre-treating said sand.

[0046] The process of the present invention advantageously allows obtaining silicate and precipitated silica having the desired quality and yield as those obtainable by the conventional approach starting from natural quartz sand (i.e., pure sand, such as Fontainebleau sand).

[0047] The process of the present invention is thus particularly advantageous not only from an environmental but also from an economic point of view as it allows to recycle a waste material such as the spent foundry sand and at the same time produce high quality silicate and precipitated silica, without affecting the overall yield of the final products. DETAILED DESCRIPTION OF THE INVENTION

[0048] Before the issues of the invention are described in detail, the following should be considered:

[0049] It is to be understood that this invention is not limited to particular embodiments described, since such embodiments may, of course, vary. It is also to be understood that the terminology used herein is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

[0050] As used herein, the singular forms “a”, “an”, and “the” include both singular and plural referents unless the context clearly dictates otherwise. By way of example, “a compound” means on compound or more than one compound.

[0051] The terms “comprising”, “comprises”, and “comprised of’ as used herein are synonymous with “including”, “includes” or “containing”, “contains”, and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms “comprising”, “comprises” and “comprised of’ as used herein comprise the terms “consisting of’, “consists”, and “consists of’.

[0052] Throughout this application, the term “about” is used to indicate that a value includes the standard deviation of error for the device or method being employed to determine the value.

[0053] As used herein, the terms “% by weight”, “wt.-%”, “wt%”, “weight percentage”, or “percentage by weight”, are used interchangeably.

[0054] The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75, and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

[0055] The term “furnace” is used as a synonym of “oven” or of any other vessel or container suitable to bear elevated temperatures and melting process as those described herein.

[0056] The term “spent foundry sand” abbreviated SFS is used herein to refer to the waste sand deriving from foundry processes, such as the sand used for casting metal parts. The expressions “spent foundry sand” and “waste foundry sand” abbreviated WFS are used herein interchangeably.

[0057] The terms “natural quartz sand” or “natural sand” are used herein to refer to “pure sand” or “high purity sand”. An example of such sand is Fontainebleau sand.

[0058] The terms “natural quartz sand”, “natural sand”, “pure sand” or “high purity sand” may be used interchangeably and are used to distinguish such sand from a spent foundry sand (SFS).

[0059] As used herein, the term “room temperature” is used as a synonym of “ambient temperature” and refers to a temperature comprised between 15 °C and 25 °C.

[0060] The expression SiCh / MxO indicates the SiCh / MxO weight ratio: [%weight (SiCh) / %weight (MXO)], also defined as “Rp” or “Rp value”, which is a parameter which describes the quality of the silicate (and the corresponding silica obtained therefrom). M is a metal, preferably selected from the group consisting of alkaline metals and, accordingly, x is preferably 2. For the avoidance of any doubts, alkaline metals correspond to the group 1 elements according to IUPAC nomenclature. Where the silicate is a sodium silicate, the Rp value is represented by the SiCh / lSfeO weight ratio [%weight (SiCh) / %weight (Na20)].

[0061] The expression “(hydrogen)carbonate” is used herein to refer, in a compact way, independently, to “carbonate” and “hydrogen carbonate” (also defined as “bicarbonate”). For example, the sentence “said base is an alkali metal (hydrogen)carbonate” corresponds to the sentence “said base is selected from the group consisting of an alkali metal carbonate and an alkali metal hydrogen carbonate”. The same applies to similar expressions and sentences.

[0062] The terms “vitreous” and “amorphous” are used herein interchangeably. In particular, the expressions “vitreous silicate” and “amorphous silicate” are used herein as synonyms. Analogously, the expressions “amorphous solid silicate” or “solid amorphous silicate” are used as synonyms of a “vitreous solid silicate” or “solid vitreous silicate”.

[0063] According to the present invention, the expression “aqueous liquid medium” indicates an “aqueous medium” comprising, or essentially consisting of, or consisting of water, preferably deionized water.

[0064] According to the embodiment where the “aqueous liquid medium” indicates an “aqueous medium” comprising water, preferably deionized water, said aqueous liquid medium can further comprise one or more liquids / solvents other than said water, preferably other than said deionized water, such as, C1-C4 alcohols preferably selected from the group consisting of: ethanol, isopropanol, n-butanol, iso-butanol, butanol, or combinations thereof.

[0065] Similar considerations apply to the expression “aqueous liquid mixture”.

[0066] All references cited in the present specification are hereby incorporated by reference in their entirety. In particular, the teachings of all references herein specifically referred to are incorporated by reference.

[0067] Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

[0068] In the following passages, different alternatives, embodiments, and variants of the invention are defined in more detail. Each alternative and embodiment so defined may be combined with any other alternative and embodiment, and this for each variant unless clearly indicated to the contrary or clearly incompatible when the value range of a same parameter is disjoined. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0069] Furthermore, the particular features, structures, or characteristics described in the present description may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are mean to be within the scope of the invention, and form different embodiments, as would be understood by those in the art.

[0070] The present invention refers to a process for the preparation of a silicate from a spent foundry sand comprising the steps of:

[0071] (i) melting the spent foundry sand and, optionally in addition a sand other than a spent foundry sand, in a furnace in the presence of a base by heating at a temperature of at least 850 °C so as to obtain a molten vitreous silicate, followed by (ii) cooling down, from the temperature of step (i) to a temperature below 550 °C, the molten vitreous silicate in a period of time of less than 30 minutes so as to obtain solidification of the molten vitreous silicate into a solid silicate, wherein said solid silicate is an amorphous solid silicate.

[0072] The base used in step (i) is preferably used in an amount of up to 50% by weight based on the total weight of the spent foundry sand, the sand other than a spent foundry sand if any, and the base in the furnace. Preferably said amount is of at least 30% by weight, more preferably comprised between 34% and 36% by weight.

[0073] The base can be a strong or a weak base, preferably a weak base.

[0074] According to a preferred embodiment, said base is an alkali metal base, wherein said alkali metal is preferably selected from the group consisting of sodium and potassium. More preferably said base is selected from the group consisting of: alkali metal hydroxide, alkali metal (hydrogen)carbonate, alkali metal sulphate, or a combination thereof, even more preferably said base is an alkali metal carbonate.

[0075] In an embodiment of the invention, said base is an alkali metal hydroxide, more preferably selected from the group consisting of sodium and potassium hydroxide, most preferably sodium hydroxide (NaOH).

[0076] In a particularly preferred embodiment of the invention, said base is an alkali metal (hydrogen)carbonate, more preferably selected from the group consisting of sodium and potassium (hydrogen)carbonate, most preferably sodium carbonate (ISfeCCh).

[0077] Among the possible counterions, carbonate is particularly preferred because, during the melting reaction of step (i), CO2 is produced as gaseous byproduct (i.e., fuel gas) instead of other possibly hazardous fuel gases which can instead be formed if different counterions are employed. During the melting step (i), the base is indeed decomposed. For example, in case of the preferred base, Na2CC>3, this base is decomposed into Na2O (which forms part of the solid sodium silicate thus produced) and CO2 (which, as mentioned above, is released as flue gas in the furnace).

[0078] According to a particularly preferred embodiment of the invention, when the base is an alkali metal base as described above, said silicate is an alkali metal silicate; the alkali metal silicate is typically of formula A2O.nSiO2 wherein A is the alkali metal and n is a real number ranging from 1.0 to 5.0, preferably from 2.0 to 4.5 and more preferably from 3.0 to 4.0. More preferably, said silicate is selected from the group consisting of sodium silicate and potassium silicate, most preferably sodium silicate; the sodium silicate is typically of formula Na2O.nSiO2 wherein n is a real number ranging from 1.0 to 5.0, preferably from 2.0 to 4.5 and more preferably from 3.0 to 4.0.

[0079] According to a particularly preferred embodiment of the invention, the silicate is sodium silicate and the base is sodium carbonate.

[0080] Preferably, the reaction of step (i), i.e., the melting of the sand in the furnace in the presence of the base, is carried out at a temperature of at least 1000 °C, preferably at a temperature of up to 1600 °C, more preferably at a temperature of between 1000 °C and 1600 °C, even more preferably between 1200 °C and 1500 °C, most preferably between 1400 °C and 1500 °C.

[0081] The timing of the reaction of step (i), i.e., the residence time in the furnace, may vary to a large extent. This one may be of at least 10 minutes, preferably of at least 30 minutes, more preferably of from 30 minutes to 3 hours, possibly of from 1 hour to 2.5 hours. Good results can be obtained with a timing of about 2.5 hours.

[0082] Without wishing to be bound to a specific theory, it has been found that the addition of the base to the spent foundry sand and, the sand other than the spent foundry sand if any, in the furnace in combination with the temperature employed in step (i), not only allows the effective melting of the sand but at, the same time, contributes to the achievement of a silicate having the desired quality for further applications, in particular, a silicate having the desired quality in terms of Rp value for the preparation of precipitated silica.

[0083] Particularly, it has been found that the use of the base in combination with the temperature of step (i) contributes increasing the dissolution yield of the SiCh contained in the sand (i.e., %SiO2 initial) during the melting step (i) and thus the amount of SiCh contained in the silicate thus produced (i.e., %SiO2 final). In other words, this allows increasing the yield of SiCh recovered from the sand.

[0084] Additionally, the temperature used in step (i) also allows obtaining a solid silicate with the desired solubility. It is indeed an object of the present invention to produce an amorphous solid silicate which can also by easily dissolved in a liquid medium, in particular in an aqueous liquid medium, without the need to use special dissolution conditions such as solvents, salts, basic conditions, high pressures, or a combination thereof.

[0085] In fact, on the one hand, it has been found that a too high temperature (i.e., higher than 1600 °C) would lead to at least a partial crystallization of the silicate which would in turn render the silicate less soluble and more difficult to dissolve in a liquid medium, in particular, in an aqueous medium.

[0086] On the other hand, a too low temperature (e.g., lower than 850 °C) would not allow obtaining a silicate with the desired Rp values as it would typically prevent the complete melting of the sand in the furnace, thus lowering the dissolution yield of SiO? and the yield of SiO? recovered from the sand.

[0087] Similarly, it has been found that a too low residence time (e.g., below 30 minutes) would also lead to a limited melting of the sand (and limited dissolution yield of SiCh) while a longer time (e.g., more than 3 hours) is not expected to bring any benefits.

[0088] According to a particularly preferred embodiment of the invention, the cooling down (according to step (ii)) of the molten vitreous silicate, is carried out immediately after step (i) and as quick as possible. In other words, as soon as step (i) is concluded, the so-produced molten vitreous silicate is cooled down according to step (ii).

[0089] According to the present invention, step (i) begins once a temperature of at least 850 °C is reached in the furnace and the spent foundry sand, the sand other than a spent foundry sand if any, and the base start to melt.

[0090] Step (i) ends once complete melting of the sand is achieved.

[0091] According to the process of the present invention, the cooling down of the molten vitreous silicate is carried out in a period of time of less than 30 minutes, preferably in a period of time of less than 20 minutes, more preferably of less than 10 minutes.

[0092] For the purposes of the present invention such a cooling down, to be carried out as quick as possible (i.e., in a period of time of less than 30 minutes), is to be distinguished by a slow cooling down, for example, by letting the molten vitreous silicate cooling down by inertia.

[0093] Preferably, in step (ii) the molten vitreous silicate is cooled down from the temperature of step (i) to a temperature below 300 °C, more preferably below 25 °C (room temperature).

[0094] According to a preferred embodiment of the invention, step (ii) is carried by casting the molten vitreous silicate on a plate, preferably a metallic plate, preferably wherein said plate is at room temperature. Alternatively, the cooling down by casting of the molten vitreous silicate can be done on any other suitable vessel or surface that can allow the desired solidification of the silicate in the amorphous form. Without wishing to be bound to a specific theory, it has been found that the fast cooling down of the molten vitreous silicate advantageously assure its solidification into an amorphous solid, which, as mentioned above, can easily be dissolved in a liquid medium, in particular in an aqueous liquid medium. In contrast, a slower cooling down would result in a slower solidification of the molten silicate which would internally re-organize and at least partially crystallize (resulting in a reduced solubility of the solid silicate).

[0095] In conclusion of step (ii), i.e., when the silicate is completely solidified, a solid silicate is obtained. Said solid silicate is an amorphous solid silicate or, in other words, a solid silicate in amorphous form.

[0096] According to an embodiment of the invention, the process further comprises a step (ii’), after step (ii), of milling the solid silicate thus obtained.

[0097] The solid silicate obtained by the process according to the present invention is a soluble silicate, preferably a water-soluble silicate. In other words, said solid silicate can be dissolved in a liquid medium, preferably an aqueous liquid medium. As indicated above, it has been found that the dissolution of the solid silicate obtained according to the process of the present invention is particularly advantageous as it can be easily carried out in “mild” conditions without the need to use additional solvents, salts, basic condition, elevated pressure, or a combination thereof.

[0098] According to an embodiment, the process of the present invention further comprises the steps of

[0099] (iii) dissolving the solid silicate in a liquid medium so as to obtain a liquid mixture comprising silicate and, if any, solid byproducts,

[0100] (iv) if any solid by-products are comprised in said liquid mixture, separating said solid by-products from the liquid mixture to obtain a solution of silicate, and

[0101] (v) optionally adding to said solution of silicate at least one of a secondary silica source, an alkali metal hydroxide, preferably NaOH, a silicate other than the silicate obtained in step (iv), or a mixture thereof.

[0102] Preferably, said liquid mixture is an aqueous liquid mixture, more preferably water, even more preferably deionized water. The solid silicate dissolved in step (iii)is preferably the solid silicate obtained in step (ii) or step (ii’) of the process according to the present invention.

[0103] For the purposes of the present invention, said liquid medium is also referred to, interchangeably, as “dissolving medium” or “dispersing medium” (in this latter case, step (iii) is a step of “dispersing” the solid silicate in the dispersing medium).

[0104] According to an embodiment, step (iii) comprises:

[0105] (iii. a) heating up the liquid mixture to a temperature of up to 180 °C, preferably with a rate of from 0.5 to 5 °C / min, preferably maintaining the liquid mixture at said temperature for at least 0.4 hours, and

[0106] (iii.b) cooling down said liquid mixture by inertia until room temperature is reached.

[0107] Preferably, in step (iii. a) the liquid mixture is heated up to a temperature of up to 170 °C. According to an embodiment, in step (iii. a) the liquid mixture is heated up to a temperature of between 140 °C and 180 °C, preferably between 140 °C and 170 °C.

[0108] Preferably, the liquid mixture is maintained at said temperature for at least 0.5 hours, more preferably for at least 2.5 hours, even more preferably from 0.5 to 2.5 hours.

[0109] According to an embodiment of the present invention, the liquid mixture obtained in step (iii) or (iii.b) can also comprise solid by-products and can be thus also defined as a solid-liquid mixture comprising liquid silicate (in the form of a silicate solution) and said solid by-products.

[0110] Said solid by-products are also defined for the purposes of the present invention as “residual solids”. The content of such solid by-products, if any, in the liquid mixture obtained in step (iii) may be between 0.1% and 30% by weight based on the total weight of the liquid mixture.

[0111] Said solid by-products can typically comprise carbon-rich impurities (i.e., carbon-rich solids), metal impurities, such as aluminum or iron impurities, and / or any other insoluble materials typically originally contained in the spent foundry sand.

[0112] Said carbon-rich solids are generally by-products deriving from the carbon originally present in the SFS and / or from the combustion of carbon-containing compounds possibly contained in the SFS (such as, for example, the chemical binders contained in chemically bonded sand as disclosed below) which occurs in the furnace during the melting of sand in step (i).

[0113] Aluminum or iron impurities are generally due to the type of the SFS (green sand and / or chemically bonded sand as disclosed below) and / or to the foundry processes, where said SFS was employed (such as, for example, ferrous metal casting).

[0114] According to the embodiment of the present invention where solid byproducts are comprised in the liquid mixture obtained in step (iii) or (iii.b), these solid by-products are separated from the liquid silicate according to step (iv) which is carried out in order to eliminate the above-mentioned possible residual impurities and to recovery (i.e., purify) the silicate in the form of a solution of silicate. The separation of the residual solid by-products from the liquid phase of the solid-liquid mixture, which liquid phase comprises the liquid silicate (in the form of a solution of silicate), can be carried out using any separation technique and equipment that are commonly used by a skilled person to separate a solid phase from a liquid phase.

[0115] As suitable techniques well known to the skilled person to achieve such a solid / liquid separation, are: decantation, filtration, centrifugation, and combinations thereof.

[0116] Decantation is advantageously achieved using a blanket settling tank, a circular settling tank, a rectangular settling tank, a lamellar settling tank or a combination thereof. Filtration is advantageously achieved using a vacuum-drum filter, a rotary filter, a filter press, belt filter or a combination thereof. It is also possible to use a carbon bed to eliminate, for example, aluminum or iron present in the SFS. Centrifugation is advantageously achieved using a two-phase decanter centrifuge, a three-phase decanter centrifuge, a hollow bowl centrifuge, a disk stack centrifuge, a hermetic bowl centrifuge, a multi-chamber centrifuge (i.e. a centrifuge with an inner centrifuge chamber and exterior mounted) or a combination thereof.

[0117] According to a preferred embodiment, the separation step (iv) is carried out by filtration, more preferably carried out with a vacuum filter.

[0118] In conclusion of step (iv), i.e., when the silicate has been separated from the residual solid by-products, a recovered solution of silicate is obtained.

[0119] Preferably, following step (iv), the process according to the present invention can comprise a step (v) of adding to the solution of silicate at least one of a secondary silica source, an alkali metal hydroxide, preferably NaOH, a silicate other than the silicate obtained in step (iv), or a mixture thereof.

[0120] According to the invention, after step (v) a new solution of silicate, preferably a new aqueous solution of silicate, is obtained.

[0121] Without wishing to be bound to a specific theory, it has been found that this may be advantageous to adjust the characteristic of the silicate obtained in step (iv), in particular, to achieve the desired Rp values.

[0122] According to the invention, the silicate other than the silicate obtained in step (iv), is a silicate produced by any conventional process other than the process of the present invention.

[0123] Preferably said silicate other than the silicate obtained in step (iv) is an alkali metal silicate, more preferably sodium or potassium silicate, even more preferably sodium silicate.

[0124] According to the invention, said secondary silica source is a silica produced by any conventional process other than the process of the present invention and / or naturally occurring silica. Preferably, said secondary silica source is amorphous silica.

[0125] According to an embodiment, it may be desirable, following either step (iii), (iii.b), (iv), or (v), to dry the liquid mixture obtained in step (iii) or (iii.b) or the solution of silicate obtained in step (iv) or (v) to obtain a solid silicate (according to step (vi)). Said solid silicate, is a solid silicate in amorphous form.

[0126] The dying step (vi) can be carried out using any known means. Preferably, the drying step (vi) is carried out by atomization. To this end, use may be made of any type of suitable atomizer, in particular a rotary, nozzle, oven, furnace, liquid pressure or two-fluid atomizer.

[0127] Without wishing to be bound to a specific theory it has been found that an advantage of the present invention is that the silicate obtained via the furnace route according to the process of the present invention has a high SiCh / MxO ratio (Rp) and can thus be directly used as raw material for the preparation of precipitated silica without the necessity to add further sources of silica to correct the Rp.

[0128] Preferably the silicate obtained according to the process of the present invention (i.e, the solid silicate obtained after step (ii), (ii’), and / or (vi), as well as the liquid silicate obtained after step (iii), (iii.b), (iv), and / or (v)) has a SiCh / MxO ratio (Rp) of at least 2, preferably of at least 2.5, more preferably comprised between 2 and 4, even more preferably comprised between 3 and 4, most preferably of about 3.5. M and x are as defined above.

[0129] Preferably, the amount of SiCh (i.e., %SiO2 final) contained in the silicate obtained after step (ii), (ii’), and / or (vi), as well as the liquid silicate obtained after step (iii), (iii.b), (iv) and / or (v) of the process of the invention, is of up to 100% of the amount of silica initially contained in the sand used in step (i) of the process (i.e., %SiO2 initial). Preferably, %SiO2 final is between 70 and 100 % of %SiO2 initial.

[0130] According to an embodiment, the spent foundry sand used in the process of the invention is selected from the group consisting of: green sand (GS), chemically bonded sand (CBS), or a combination thereof. Typically, green sand is a type of SFS which, in addition to SiCh, further comprises clay, in particular bentonite, coal, and water. Chemically bonded sand, instead, is a type of SFS which, in addition to SiCh, typically comprises chemical binders.

[0131] Preferably, the spent foundry sand used in the process according to the present invention comprises from 85 wt% to 99 wt% of SiCh (%SiO2 initial), generally between 92 wt% and 97 wt%. The SiCh in the spent foundry sand is typically only crystalline silica.

[0132] Typically, green sand comprises from 85 wt% to 95 wt% SiCh, while chemically bonded sand comprises from 93 wt% to 99 wt% SiCh. For comparison, the silica content in pure sand, such as Fontainebleau sand is generally between 97.0 wt% and 100.0 wt%, often between 98.0 wt% and 100.0 wt%, sometimes between 99.0 wt% and 100.0 wt%. According to the present invention, the SiCh content in the spent foundry sand is measured by X-ray fluorescence.

[0133] The carbon content in a spent foundry sand is generally between 0.1 wt% and 5 wt%. For comparison, the carbon content in high purity sand is 0 wt%.

[0134] According to the present invention, the carbon content in the spent foundry sand is measured by carbon / sulfur analysis.

[0135] According to an embodiment of the present invention, green sand has preferably the following composition: 85-95 wt% SiCh, 8-10 wt% bentonite, 4-7 wt% coal, and 3-4 wt% water.

[0136] Green sand typically comprises metal impurities such as iron, likely deriving from foundry processes such as ferrous metal casting, and aluminum, likely deriving from the clays, particularly from the bentonite which is an aluminosilicate clay. In fact, clays correspond to metallic silicates and thus could bring a many different metal impurities to the final silicate depending to the nature of the clay, such as metals, earth-alkaline metals, and the like.

[0137] According to an embodiment of the present invention, green sand comprises from 3 wt% to 5.5 wt% AI2O3 (Al impurity) measured by X-ray fluorescence and / or from 0.5 wt% to 3 wt% Fe2Os (Fe impurity) measured by X- ray fluorescence.

[0138] According to an embodiment of the present invention, chemically bonded sand has preferably the following composition: 93-99 wt% SiCh and 1-3 wt% chemical binder.

[0139] Typically, the chemical binders of the chemically bonded SFS are organic or inorganic binders. The organic binders are generally selected from the group consisting of: alkyl, phenolic acid, phenolic urethane, phenolic ester, furan acid, furan resin, phenolic resin, or a combination thereof. Chemically bonded sand typically comprises organic impurities (mainly carbon-rich impurities) deriving from the chemical binder as well as metal impurities (such as aluminum and iron impurities) in this case likely deriving from the metal casting of the foundry processes.

[0140] According to an embodiment of the present invention, chemically bonded sand comprises from 0.5 w% to 1.8 wt% AI2O3 (Al impurity) measured by X-ray fluorescence and / or from 0.1 wt% to 1.5 wt% Fe2C>3 (Fe impurity) measured by X-ray fluorescence.

[0141] Possibly, the invented process can be free of any pre-treatment step to purify the spent foundry sand before step (i). Sometimes, a purification of the SFS is indeed unnecessary, in particular, when the SFS contains a low amount of metal impurities or when preparing a silicate containing a high amount of impurities is acceptable in view of a certain intended use of the silicate.

[0142] This being said, there might be situations where a purification of the SFS is particularly advantageous, in particular, when the SFS contains a high amount of metal impurities.

[0143] Accordingly, in a particularly preferred embodiment, the process of the invention comprises step (i’), before step (i), of purifying the spent foundry by applying thereto a pre-treatment. By doing so, impurities possibly contained in the spent foundry sand are advantageously removed.

[0144] Preferably said pre-treatment step (i’) is a step of purifying the spent foundry sand from carbon impurities and / or metal impurities and / or from particles having a size less than 100 pm so to provide a purified spent foundry sand mainly comprising or consisting of quartz (crystalline silica).

[0145] Said pre-treatment is selected from the group consisting of sieving, mechanical attrition, density selection, granulometry selection, magnetic removal of magnetic elements, impurity dilution by addition of pure sand, or a combination thereof.

[0146] Particularly preferred are the pre-treatments selected from the group consisting of sieving, mechanical attrition, the treatment comprising adding pure sand to the SFS, or a combination thereof.

[0147] The sieving is generally carried out to select the preferred silica-rich phase (i.e., quartz) of the SFS, which is instead generally composed of different phases depending on the type of the SFS as disclosed above (such as: clays, quartz, carbon, and / or chemical binders forming polymeric resin). Preferably, said sieving is carried out to select particles having a size bigger than 60 pm, preferably a size bigger than 100 pm. These particles of the SFS are the preferred selected particles to be used in the melting process of the invention as they mainly correspond to quartz (crystalline silica) particles.

[0148] Said sieving is also advantageous to purify the SFS (prior to step (i)) from clays particles and the corresponding metal impurities (in particular aluminum). Said clays particles generally have a size comprised between 6 pm and 100 pm, preferably between 20 pm and 100 pm.

[0149] Said sieving is also advantageous to remove from the SFS (prior to step (i)), particles having a size below 10 pm, preferably below 1 pm, (i.e. fine particles) in order to prevent exposure to harmful products, such as STOT RE products (i.e., Specific Target Organ Toxicity- Repeated Exposure, referring to adverse, non-lethal, organ-specific health effects of a toxic substance that manifest after multiple exposures).

[0150] Preferably, the mechanical attrition is carried out when the SFS is composed of different phases with a strong link between them.

[0151] According to a particularly preferred embodiment, the mechanical attrition is carried out when the SFS is a green sand (GS).

[0152] Advantageously, mechanical attrition removes clays, polymeric resins, and / or carbon at the quartz surface without modifying (particularly, without reducing) the quartz particle size.

[0153] Preferably the dilution of the SFS with pure sand is carried out by adding pure sand to the SFS in an amount of up to 85% by weight, preferably up to 75%, possibly up to 60%, 50%, 40%, 30%, 20% or 10% or 5.0% or 2.0% or 1.0% by weight, by weight based on the total weight of the sand (comprising SFS and pure sand).

[0154] Without wishing to be bound to a specific theory, it has been found that using a purified SFS in the process of the present invention is particularly advantageous because, when said purified SFS is melted in the furnace, a vitreous silicate having a particularly low concentration of impurities is obtained. This in turn results in a silicate which is easily dissolvable in a liquid medium, preferably an aqueous medium.

[0155] In fact, it has been found that if a too high number of impurities, in particular metal impurities, are present during the melting step, these impurities enter the silicate lattice and stabilize it. This would result in at least a partial crystallization of the silicate and thus in a less soluble silicate. Moreover, a too high number of impurities would not allow achieving a silicate having the desired high Rp value.

[0156] Particularly preferred is the combination of a pre-treatment (i’) as described above with the quick cooling down of step (ii) which allows obtaining, in a particularly efficient way, a solid silicate in the desired soluble amorphous form and with the desired high Rp values.

[0157] Without wishing to be bound to a specific theory, it has been found that the desired properties in terms of easy dissolution and high quality (high Rp) are advantageously achieved by the process of the present invention without the need of a thermal pre-treatment but in a single step (i.e., melting step (i)). In fact, the elevated temperatures of the melting step (i) allow avoiding a thermal pretreatment of the sand which is instead typically required in the art to remove volatile impurities before the subsequent processing of the spent foundry sand.

[0158] The present invention thus relates to a process which does not comprise any thermal treatment of the spent foundry sand before step (i). This has the further advantage of reducing CO2 emissions which are instead present if a thermal pre-treatment is carried out.

[0159] The present invention also relates to the use of the silicate as obtained or obtainable according to the process of the invention for the preparation of silica, in particular precipitated silica. Said silicate is preferably the silicate obtained after step (ii), (ii’), (iii), (iii.b), (iv), (v) and / or (vi) of the process of the present invention. The invention relates also to a process for the preparation of a precipitated silica comprising the steps of:

[0160] (I) preparing a silicate by the process according to the present invention as disclosed according to any of the above embodiments,

[0161] (II) reacting the silicate obtained in step (I) and, optionally in addition a silicate other than said silicate obtained in step (I), with at least one acidifying agent in an aqueous liquid medium, preferably an aqueous liquid medium, to obtain a suspension of precipitated silica,

[0162] (III) separating the precipitated silica from the liquid medium, preferably an aqueous liquid medium, to provide a wet precipitated silica, and

[0163] (IV) drying said wet precipitate silica to obtain precipitates silica.

[0164] Said silicate of step (I) is preferably the silicate obtained after step (ii), (ii’), (iii), (iii.b), (iv), (v) and / or (v) of the process of the present invention and is as disclosed according to any one of the above embodiments.

[0165] The silicate used in the process for the preparation of precipitated silica may consist of the silicate obtained or obtainable by the process according to the present invention.

[0166] Alternatively, the silicate used in the process for the preparation of precipitated silica may represent only a portion of the overall silicate employed in step (II). According to this embodiment, step (II) comprises reacting the silicate obtained in step (I) (i.e., the silicate obtained by the process according to the present invention) and, in addition thereto, a different silicate. Said different silicate is preferably an alkali metal silicate, more preferably sodium or potassium silicate, even more preferably sodium silicate.

[0167] According to the invention said silicate other than the silicate obtained in step (I), is preferably a silicate produced by any conventional process other than the process of the present invention.

[0168] According to another embodiment, the process of the present invention is a process for the preparation of precipitated silica comprising:

[0169] (I) preparing a silicate by the process according to the present invention as disclosed according to any of the above embodiments,

[0170] (T) adding to the silicate obtained in step (I) at least one of a secondary silica source, an alkali metal hydroxide, preferably NaOH, a silicate other than the silicate obtained in step (I), or a mixture thereof, so as to obtain a new silicate, (II) reacting the new silicate obtained in step (I’) and, optionally in addition a silicate other than the new silicate obtained in step (I’), with at least one acidifying agent in a liquid medium, preferably an aqueous liquid medium, to obtain a suspension of precipitated silica,

[0171] (III) separating the precipitated silica from the liquid medium to provide wet precipitated silica, and

[0172] (IV) drying said wet precipitated silica to obtain precipitated silica.

[0173] Said silicate of step (I) is preferably the silicate obtained after step (ii), (ii’), (iii), (iii.b), (iv), (v) and / or (v) of the process of the present invention and is as disclosed according to any one of the above embodiments.

[0174] According to the present invention, the silicate other than the silicate obtained in step (I) is as defined above.

[0175] According to the invention, said secondary silica source is a silica produced by any conventional process other than the process of the present invention and / or naturally occurring silica. Preferably, said secondary silica source is amorphous silica.

[0176] Preferably, the new silicate obtained in step (I’) is an alkali metal silicate, more preferably sodium or potassium silicate, even more preferably sodium silicate.

[0177] According to the present invention, the silicate other than the new silicate obtained in step (I’) is preferably an alkali metal silicate, more preferably sodium or potassium silicate, even more preferably sodium silicate. According to the invention said silicate other than the new silicate obtained in step (F), is preferably a silicate produced by any conventional process other than the process of the present invention.

[0178] The choice of the acidifying agent is made in a way well known in the art.

[0179] The acidifying agent is preferably selected from the group consisting of: a mineral acid, preferably selected from the group consisting of: sulfuric acid (H2SO4), hydrochloric acid (HC1), nitric acid (HNO3), phosphoric acid (H3PO4), and combinations thereof, and an organic acid, preferably selected from the group consisting of: acetic acid, formic acid, carbonic acid, and combinations thereof.

[0180] The acidifying agent can be dilute or concentrated; its normality can be between 0.4 and 36N, for example, between 0.6 and 2.5N. In particular, in the case where the acidifying agent is sulfuric acid, its concentration can be between 40 and 180 g / 1, for example between 60 and 130 g / 1.

[0181] Preferably, step (II) is carried out at a temperature of at least 40 °C, preferably of at least 60 °C, even more preferably of at least 75°C, most preferably of at least 80°C.

[0182] The process for the preparation of precipitated silica can be carried out according to conditions well-known in the art, preferably by the processes disclosed in US11241370, WO23118281, US10011495, FR2985993, US5547502, US9938154, US2009214449, US10259715, US9369215, US11208331, or US11279623, all incorporated by reference herein.

[0183] Particularly, the preparation of precipitated silica by reaction of a silicate, preferably sodium silicate, with an acidifying agent, can be carried out according to any known method of preparation, in particular by addition of an acidifying agent to a feedstock of silicate, preferably sodium silicate, or else by simultaneous addition, total or partial, of acidifying agent and of silicate, preferably sodium silicate, to a feedstock of water, or of silicate, or of acidifying agent.

[0184] In the process according to the invention, on conclusion of the step of the reaction of precipitation between silicate and acidifying agent (step (II)), a suspension of precipitated silica is obtained.

[0185] The precipitated silica is subsequently separated (step (III)).

[0186] The separation carried out in the preparation process according to the invention, usually comprises a filtration, followed by a washing operation, if necessary. The filtration is carried out according to any suitable method, for example using a filter press, a belt filter or a vacuum filter.

[0187] The silica suspension thus recovered (filtration cake) is subsequently dried.

[0188] Drying (step (IV)) can be carried out according to any means known in the art as described above for step (vi).

[0189] The process for the preparation of a silicate according to the present invention generally results in a silicate having a high iron content. This is so because spent foundry sands used for the silicate preparation process have a high iron content that is not otherwise evacuated during or after the silicate synthesis.

[0190] Then, the present invention also relates to a silicate having an iron content, expressed as iron metal, of at least 100 ppm, based on the amount of SiCh contained in the silicate. The iron content of the invented silicate and the amount of SiCE contained in the invented silicate are both determined by ICP OES (inductively coupled plasma optical emission spectrometry), as detailed in the examples. The invented silicate may be one that is obtained or that is obtainable by the process of the present invention.

[0191] The iron content, expressed as iron metal, of the invented silicate is preferably of at least 250 ppm, more preferably of at least 400 ppm and still more preferably of at least 500 ppm, based on the amount of SiCE contained in the silicate. Said iron content can sometimes be even higher, e.g. of at least 600 ppm, at least 750 ppm or at least 900 ppm, based on the amount of SiCE contained in the silicate.

[0192] Besides, the iron content, expressed as iron metal, of the invented silicate is advantageously of at most 2000 ppm, preferably of at most 1500 ppm, more preferably of at most 1250 ppm and still more preferably of at most 1000 ppm, based on the amount of SiCE contained in the silicate. Said iron content can sometimes be even lower, e.g. of at most 900 ppm, at most 750 ppm or at most 600 ppm, based on the amount of SiCE contained in the silicate.

[0193] The aluminum content of the invented silicate, like its iron and its SiCE content, is also determined by ICP OES (inductively coupled plasma optical emission spectrometry), as detailed in the examples. The aluminum content, expressed as aluminum metal, of the invented silicate is generally of at least 50 ppm, very often of at least 100 ppm and often of at least 150 ppm, based on the amount of SiO? contained in the silicate. Said aluminum content can sometimes be even higher, e.g. of at least 200 ppm, at least 250 ppm or at least 300 ppm, based on the amount of SiCE contained in the silicate.

[0194] Besides, the aluminum content, expressed as iron metal, of the invented silicate is generally of at most 450 ppm, very often of at most 400 ppm and often of at most 350 ppm, based on the amount of SiCE contained in the silicate. Said aluminum content can sometimes be even lower, e.g. of at most 300 ppm, at most 250 ppm or at most 200 ppm, based on the amount of SiCE contained in the silicate.

[0195] Many invented silicates that can be prepared by the process of the present invention have an aluminum content, expressed as aluminum metal, in a range from 50 ppm to 250 ppm, especially from 100 ppm to 200 ppm, based on the amount of SiCE contained in the silicate.

[0196] Silicates in accordance with the present invention include ammonium silicates, lithium silicates, sodium silicates, potassium silicates, rubidium silicates and mixtures thereof. The invented silicate is advantageously an alkali metal silicate, preferably a sodium silicate or a mixed sodium-potassium silicate, more preferably a sodium silicate.

[0197] The invented silicate is preferably characterized by a high SiCh / MxO weight ratio (Rp), which is advantageously of at least 2.0, preferably of at least 2.5, more preferably in a range from to 2.0 to 4.0, even more preferably in a range from 3.0 to 4.0, and the most preferably of about 3.5, wherein M is a metal, preferably wherein M is ammonium or an alkali metal (especially sodium) and x is 2.

[0198] The invented silicate is advantageously available as an aqueous solution. When it has to be transported, the aqueous silicate solution can be dried using conventional drying means, resulting in a solid silicate, e.g. a silicate powder.

[0199] Likewise, the process for the preparation of a precipitated silica according to the present invention generally results in a precipitated silica having a high iron content. This is so because silicates prepared from spent foundry sands that are used in the precipitated silica preparation process have a high iron content that is not otherwise evacuated during or after the precipitated silica synthesis.

[0200] Then, the present invention also relates to a precipitated silica having an iron content, expressed as iron metal, of at least 100 ppm, based on the amount of SiCh contained in the precipitated silica. The iron content of the invented precipitated silica and the amount of SiCh contained in the invented precipitated silica are both determined by ICP OES (inductively coupled plasma optical emission spectrometry), as detailed in the examples. The precipitated silica may be one that is obtained or that is obtainable by the process of the present invention.

[0201] The iron content, expressed as iron metal, of the invented precipitated silica is preferably of at least 250 ppm, more preferably of at least 400 ppm and still more preferably of at least 500 ppm, based on the amount of SiCh contained in the precipitated silica. Said iron content can sometimes be even higher, e.g. of at least 600 ppm, at least 750 ppm or at least 900 ppm, based on the amount of SiCh contained in the precipitated silica.

[0202] Besides, the iron content, expressed as iron metal, of the invented precipitated silica is advantageously of at most 2000 ppm, preferably of at most 1500 ppm, more preferably of at most 1250 ppm and still more preferably of at most 1000 ppm, based on the amount of SiCh contained in the precipitated silica. Said iron content can sometimes be even lower, e.g. of at most 900 ppm, at most 750 ppm or at most 600 ppm, based on the amount of SiCh contained in the precipitated silica.

[0203] The aluminum content of the precipitated silica, like its iron and its SiCh content, is also determined by ICP OES (inductively coupled plasma optical emission spectrometry).

[0204] In certain first embodiments, the aluminum contained in the invented precipitated silica results exclusively or essentially from the aluminum contained in the silicate that is used for the preparation of the precipitated silica. Then, the aluminum content, expressed as aluminum metal, of the invented precipitated silica is generally of at least 50 ppm, very often of at least 100 ppm and often of at least 150 ppm, based on the amount of SiCh contained in the precipitated silica; said aluminum content can sometimes be even higher, e.g. of at least 200 ppm, at least 250 ppm or at least 300 ppm, based on the amount of SiCh contained in the precipitated silica. Besides, the aluminum content, expressed as iron metal, of the invented precipitated silica is then generally of at most 450 ppm, very often of at most 400 ppm and often of at most 350 ppm, based on the amount of SiCh contained in the precipitated silica; said aluminum content can sometimes be even lower, e.g. of at most 300 ppm, at most 250 ppm or at most 200 ppm, based on the amount of SiCh contained in the precipitated silica. Many invented precipitated silicas prepared in accordance with said first embodiments have an aluminum content, expressed as aluminum metal, in a range from 50 ppm to 250 ppm, especially from 100 ppm to 200 ppm, based on the amount of SiCh contained in the precipitated silica.

[0205] In certain other embodiments, the aluminum contained in the invented precipitated silica results from the aluminum contained in the silicate that is used for the preparation of the precipitated silica and from the subsequent addition of an aluminum compound, such as sodium aluminate, to the wet precipitated silica obtained after the separation step (III). This subsequent addition typically increases the fluidity of the wet precipitated silica before it is dried in accordance with the step (IV) and facilitates its drying in accordance with the step (IV); this addition, commonly referred to as “liquefaction”, and its benefits are well known to the skilled person. Then, the aluminum content, expressed as aluminum metal, of the invented precipitated silica is advantageously above 200 ppm, preferably of at least 250 ppm and more preferably of at least 300 ppm, based on the amount of SiCh contained in the precipitated silica. Besides, the aluminum content, expressed as aluminum metal, of the invented precipitated silica is then advantageously of at most 450 ppm and preferably of at most 400 ppm, based on the amount of SiCh contained in the precipitated silica. Many invented precipitated silicas prepared in accordance with said other embodiments have an aluminum content, expressed as aluminum metal, in a range from 250 ppm to 450 ppm, especially from 300 ppm to 400 ppm, based on the amount of SiCh contained in the precipitated silica.

[0206] The BET surface area of the invented precipitated silica is advantageously in a range of from 10 to 400 m2 / g, preferably of from 25 to 350 m2 / g and more preferably of from 50 to 300 m2 / g. The BET surface area of the invented precipitated silica may be in a range selected from the group consisting of from 80 m2 / g up to less than 140 m2 / g, from 140 m2 / g up to less than 190 m2 / g, from 190 m2 / g up to less than 240 m2 / g and from 240 m2 / g up to 300 m2 / g, depending typically on the particular application for which it is intended to be used. The BET surface area can be determined according to the method that is described in the examples.

[0207] Besides, the invented precipitated silica has a CTAB surface area ranging advantageously from 10 to 400 m2 / g, preferably from 25 to 350 m2 / g and more preferably from 40 to 280 m2 / g. The CTAB surface area of the invented precipitated silica may be in a range selected from the group consisting of from 60 m2 / g up to less than 130 m2 / g, from 130 m2 / g up to less than 180 m2 / g, from 180 m2 / g up to less than 230 m2 / g and from 230 m2 / g up to 280 m2 / g, depending typically on the particular application for which it is intended to be used. The CTAB surface area can also be determined according to the method that is described in the examples.

[0208] The invented precipitated silica can be in any form, including in the form of a powder, in the form of pearls or in the form of granules.

[0209] The invented precipitated silica can be used in a number of applications, such as catalyst, catalyst support, absorbent for active materials (in particular support for liquids, especially used in food, such as vitamins, e.g. vitamin E or choline chloride), as viscosity modifier, texturizing or anticaking agent, or as additive for toothpaste, concrete or paper. The invented precipitated silica may also conveniently be used in the manufacture of thermally insulating materials or in the preparation of resorcinol -formaldehyde / silica composites.

[0210] The invented precipitated silica finds a particularly advantageous application as filler in polymeric compositions. Accordingly, further objects of the present invention are: - a use of a filler for the manufacture of a filled polymeric composition, wherein the filler is the invented precipitated silica as above defined, and

[0211] - a composition comprising the invented precipitated silica as above defined and at least one polymer.

[0212] The phrase “at least one” when referring to the polymer in the composition is used herein to indicate that one or more than one polymer of each type can be present in the composition. The expression “copolymer” is used herein to refer to polymers comprising recurring units deriving from at least two monomeric units of different nature.

[0213] The at least one polymer can be selected among the thermosetting polymers and the thermoplastic polymers, the latter being preferred. Notable, non-limiting examples of suitable thermoplastic polymers include styrene-based polymers such as polystyrene, (meth)acrylic acid ester / styrene copolymers, acrylonitrile / styrene copolymers, styrene / maleic anhydride copolymers, ABS; acrylic polymers such as polymethylmethacrylate; polycarbonates; polyamides; polyesters, such as polyethylene terephthalate and polybutylene terephthalate; polyphenylene ethers; polysulfones; polyaryletherketones; polyphenylene sulfides; thermoplastic polyurethanes; polyolefins such as polyethylene, polypropylene, polybutene, poly-4-methylpentene, ethyl ene / propylene copolymers, ethylene / a-olefins copolymers; copolymers of a-olefins and various monomers, such as ethylene / vinyl acetate copolymers, ethylene / (meth)acrylic acid ester copolymers, ethylene / maleic anhydride copolymers, ethylene / acrylic acid copolymers; aliphatic polyesters such as polylactic acid, polycaprolactone, and aliphatic glycol / aliphatic dicarboxylic acid copolymers.

[0214] The invented precipitated silica may advantageously be employed as reinforcing filler in elastomeric compositions. Accordingly, an object of the invention is an elastomeric composition comprising the invented precipitated silica and one or more elastomer(s), preferably exhibiting at least one glass transition temperature between -150 °C and +300 °C, for example between -150 °C and +20 °C.

[0215] Notable non-limiting examples of suitable elastomers comprised in the elastomeric compositions are diene elastomers. For example, use may be made of elastomers deriving from aliphatic or aromatic monomers, comprising at least one unsaturation such as, in particular, ethylene, propylene, butadiene, isoprene, styrene, acrylonitrile, isobutylene or vinyl acetate, polybutyl acrylate, or their mixtures. Mention may also be made of functionalized elastomers, that is elastomers functionalized by chemical groups positioned along the macromolecular chain and / or at one or more of its ends (for example by functional groups capable of reacting with the surface of the silica), and halogenated polymers. Mention may be made of polyamides, ethylene homo- and copolymer, propylene homo-and copolymer. Other suitable elastomers are those including chloro- or bromo- butyl monomers. Among diene elastomers mention may be made, for example, of polybutadienes (BRs), polyisoprenes (IRs), butadiene copolymers, isoprene copolymers, or their mixtures, and in particular styrene / butadiene copolymers (SBRs, in particular ESBRs (emulsion) or SSBRs (solution)), isoprene / butadiene copolymers (BIRs), isoprene / styrene copolymers (SIRs), isoprene / butadiene / styrene copolymers (SBIRs), ethyl ene / propylene / diene terpolymers (EPDMs), and also the associated functionalized polymers (exhibiting, for example, pendant polar or reactive groups or polar groups at the chain end, which can interact or react with the silica). Mention may also be made of natural rubber (NR) and epoxidized natural rubber (ENR).

[0216] The elastomeric polymer compositions can be vulcanized with sulfur or crosslinked, in particular with peroxides or other crosslinking systems (for example diamines or phenolic resins).

[0217] In some embodiments, the elastomeric polymer compositions additionally comprise at least one (silica / polymer) coupling agent and / or at least one covering agent; they can also comprise other additives, for instance an antioxidant. Nonlimiting examples of suitable coupling agents are for instance "symmetrical" or "unsymmetrical" silane poly sulfides; mention may more particularly be made of bis((Cl-C4)alkoxyl(Cl-C4)alkylsilyl(Cl-C4)alkyl) polysulfides (in particular disulfides, trisulfides or tetrasulfides), such as, for example, bis(3- (trimethoxysilyl)propyl) polysulfides or bis(3-(triethoxysilyl)propyl) polysulfides, such as triethoxysilylpropyl tetrasulfide. Mention may also be made of monoethoxy dimethyl silylpropyl tetrasulfide. Mention may also be made of silanes comprising masked or free thiol functional groups (like NXT™ or NXT™ Z45 silanes), of mercaptopropyltriethoxy silane, and of a mixture mercaptopropyltriethoxysilane+octyltriethoxysilane (like SI 363® from Evonik). As to the coupling agent, it can be grafted beforehand to the polymer. It can also be employed in the free state (that is to say, not grafted beforehand) or grafted at the surface of the silica. It is the same for the optional covering agent. In case a coupling agent is added to the silica after drying (i.e. grafted on it), it generally is an ethoxy- or a chloro- silane. The coupling agent can optionally be combined with an appropriate "coupling activator", that is to say a compound which, mixed with this coupling agent, increases the effectiveness of the latter.

[0218] The proportion by weight of the invented precipitated silica in the elastomeric polymer composition can vary within a fairly wide range. It normally represents from 1% to 250%, in particular from 5% to 200%, especially from 10% to 170%, for example from 20% to 140% or even from 25% to 130%, or alternatively from 10% to 40%, with relation to the amount of the polymer(s). Hence, the % are sometimes referred to as phr or Per Hundred Rubber in case of elastomeric compositions.

[0219] The invented precipitated silica can advantageously constitute all of the reinforcing inorganic filler and even all of the reinforcing filler of the elastomeric polymer composition.

[0220] In the elastomeric polymer composition, the invented precipitated silica can optionally be combined with at least one other reinforcing filler, for instance with a conventional or a highly dispersible silica, such as Zeosil® Premium SW, Zeosil® Premium 200MP, Zeosil® 1165MP, Zeosil® 1115MP or Zeosil® 1085 GR (commercially available from Solvay), or another reinforcing inorganic filler, such as nanoclays, alumina. Alternatively, the invented precipitated silica may be combined with an organic reinforcing filler, such as carbon black nanotubes, graphene, starch, cellulose and the like. The invented precipitated silica then preferably constitutes at least 30% by weight, preferably at least 60%, indeed even at least 80% by weight, of the total amount of the reinforcing filler that is comprised in the elastomeric polymer composition.

[0221] Still other optional elements of the elastomeric polymer composition include accelerators (such as CBS, MBTS, TBzTD and DPG), crosslinking agents (such as peroxide or sulfur), processing oils, resins (terpenes and C> resins, notably commercialized as Wingtack™ or as Dercolyte™), oligomers of SBR, BR or IR, activators (such as stearic acid and / or zinc oxide), processing aids (such as fatty acids, zinc soaps and PEG), waxes (e.g. PE wax) acting as protectors, antioxidants, UV protectors and antiozonants (such as 6PPD and TMQ).

[0222] Polymer compositions comprising the invented precipitated silica as above defined and at least one polymer, in particular one or more elastomer(s), may be used for the manufacture of a number of shaped articles. Non-limiting examples of shaped articles comprising a polymer composition as described above, are for instance footwear soles, floor coverings, gas barriers, flame-retardant materials and also engineering components, such as rollers for cableways, seals for domestic electrical appliances, seals for liquid or gas pipes, braking system seals, pipes (flexible), sheathings (in particular cable sheathings), cables, engine supports, battery separators, conveyor belts, transmission belts. They also include parts of tires, e.g. tire treads, the latter being preferred.

[0223] Accordingly, a preferred object of the present invention is a part of a tire comprising a composition comprising (i) an invented precipitated silica and (ii) at least one polymer, especially a part of a tire comprising a composition comprising (i) an invented precipitated silica and (ii) one or more elastomer(s), and a much preferred object of the present invention is a tire tread comprising a composition comprising (i) an invented precipitated silica and (ii) at least one polymer, especially a tire tread comprising a composition comprising (i) an invented precipitated silica and (ii) one or more elastomer(s).

[0224] A related object of the present invention is a tire comprising this part, in particular a tire comprising this tread.

[0225] Another related object of the present invention is an article comprising a tire comprising this part, generally a vehicle, especially an automotive vehicle (e.g. a car, a van, a mobile home, a bus, a coach, a truck, or a construction machine such as a backhoe-loader or a dumper), possibly also a non-automotive vehicle (such as a trailer or a cart).

[0226] The present invention will now be illustrated by the following examples, which are not intended to be limiting.

[0227] EXAMPLES

[0228] Materials and methods

[0229] All starting materials used in the examples are commercially available.

[0230] Potentiometry method to determine Rp of a silicate

[0231] A Titrando 808 was used in order to determine the weight ratio (Rp) [%weight (SiCh) / %weight (Na2O)]. The device was equipped with a reference electrode Ag / AgCl in KC1 3M and a working electrode in tungsten. Each Rp was measured in duplicate and the Rp values presented were the average between the two measurements. 0.5 g of sample was weighed and completed with 30 mL of demineralized water. The titration solution was a 0. IN HC1 solution. The volume Vi (mL) was determined as the equivalence of the titration. After the equivalence, 0.5 mL of titration solution was added.

[0232] Afterward, 50 mL of KF solution (50 g / 1 of KF in a water / ethanol (50 / 50) solution) was added and allowed to react for 3 minutes. Then, 15 mL of 0. IN HC1 solution were added. The excess of HC1 was titrated by a NaOH IN solution and the volume V2(mL) was the equivalent point of the titration.

[0233] The Rp was then calculated following the formula below:

[0234] Rp = (0.31 *VI) / (1.5(15* 1-V2* 1) +(0.5*0.1))

[0235] X-Ray Fluorescence method used to determine elemental composition of a spent foundry sand, notably its iron, aluminum and silicium content

[0236] The elemental analysis was done by XRF (X-Ray Fluorescence). Glass disks were prepared using commercial fusion instrument (LeNeo from Malvern Panalytical, X-300 from Katanax or other equivalent system).

[0237] For the preparation of the glass disk, the sample was mixed with lithium metaborate, lithium tetraborate and non-wetting agent (LiBr). The fusion was carried out in platinum crucibles at 1050 °C for 20 minutes before pouring into the platinum mould to obtain a glass disk.

[0238] The measurement was realized thanks to a XRF instrument (Epsilon 3XL from Malvern-Panalytical).

[0239] Standard geological samples (ACE, ANG, BEN, or other equivalent) and 3 blanks were used to determine the calibration of the desired elements.

[0240] Different measurement conditions allowed an optimization of the signal for the following elements:

[0241] - for Al, Mg, Na, Si: 5kV, 6pA, under Helium sweep.

[0242] - for P: 10 kV, 30pA under Helium scan.

[0243] - for Ca, K, Ti: 12 kV, 25 pA, under Helium scan.

[0244] - for Fe and Mn: 20 kV, 15 pA in air.

[0245] Laser granulometry to determine the Particle Size Distribution (PSD) of a precipitated silica

[0246] The particle size of the precipitated silica was determined by means of a laser granulometer (Malvern Mastersizer 3000). The Fraunhofer optical model was used for the measurement. This measurement allows to determine the following parameter (based on the volume distribution):

[0247] - Dio: particle size below which 10 % of the distribution lies (from cumulative curve);

[0248] - D50 [median]: particle size at 50% of the cumulative curve;

[0249] - D90: particle size below which 90 % of the distribution lies (from cumulative curve)..

[0250] Carbon sulfur analysis (C / S method) to determine the carbon content of a material, especially a spent foundry sand

[0251] A 200 mg sample was analyzed in Horiba EMIA 320-V2. Lecocel®, iron and tin balls were used as combustion accelerators. CS26 - 3.19 % was used to calibrate the sensor.

[0252] Determination of CTAB surface area SCTAB of a precipitated silica

[0253] CTAB surface area (SCTAB) values were determined according to an internal method derived from standard NF ISO 5794-1, Appendix G. The method was based on the adsorption of CTAB (N hexadecyl-N,N,N-trimethylammonium bromide) on the "external" surface of the silica.

[0254] In the method, CTAB was allowed to adsorb on silica under magnetic stirring. Silica and residual CTAB solution were then separated. Excess, unadsorbed CTAB, was determined by back-titration with bis(2- ethylhexyl)sulfosuccinate sodium salt (hereinafter " AOT") using a titroprocessor, the endpoint being given by the turbidity maximum of the solution and determined using an optrode.

[0255] Equipment

[0256] Metrohm Optrode ( Wavelength : 520 nm) connected to photometer 662 Metrohm; Metrohm Titrator: Titrino DMS 716; Metrohm titration software: Tiamo.

[0257] Glass beaker (2000 mL); volumetric flasks (2000 mL); sealed glass bottles (1000 and 2000 mL); disposable beakers (100 mL); micropipette (500 - 5000 pL); magnetic stirring bars with 25 mm discs ends (Ref VWR 442-9431) for adsorption; magnetic stirring bars (straight) for titration; polycarbonate centrifugation tubes (at least 20 mL), centrifuge (allowing a 10000 rpm speed); glass vials (30 mL); thermobalance.

[0258] Preparation of the solutions Preparation of CTAB solution at 5.5 g / L (buffered at about pH 9.6): in a 2000 mL beaker containing about 1000 mL of distilled water at 25 °C were added: 54.25 g of boric acid solution ([c]= 4%); 2.60 g of KC1, 25.8 mL (±0.1 mL) of sodium hydroxide. The so-obtained solution was stirred for 15 min before adding 11.00 g ± 0.01 g of CTAB powder (99.9% purity, purchased from Merck). After stirring, the solution was transferred to a 2000 mL volumetric flask kept at 25°C and the volume brought at 2000 mL with distilled water. The solution was transferred in a 2000 mL glass bottle. The solution was kept at a temperature not lower than 22°C to avoid CTAB crystallization (occurring at 20 °C).

[0259] Preparation of AOT solution: about 1200 mL of distilled water in a 2000 mL beaker were heated to 35 °C under magnetic stirring. 3.7038 g of AOT (98% purity, purchased from Aldrich) were added. The solution was transferred to a 2000 mL volumetric flask and allowed to cool back to 25 °C. The volume was brought to 2000 mL with distilled water and the solution was transferred in two glass bottles of 1000 mL which were stored at 25 °C in a dark place.

[0260] All equipment and solutions were kept at 25 °C during analysis. Procedure at the beginning and at the end of each experiment

[0261] Experiment beginning: solutions were agitated before use. The dosing device was purged before use. At least 40 mL of AOT were passed through the device to ensure that the device is clean and that all the air bubbles were removed.

[0262] Experiment end: purge the dosing device in order to remove the AOT solution. Clean the optrode. Soak the optrode in distilled water. Blank factor determination

[0263] The variation of AOT and CTAB solutions concentrations, over time, are corrected through the determination of a daily ‘blank factor’ called ratio Ri = Vi / mi.

[0264] In a 100 mL disposable beaker: 4.9000 g ± 0.0100 g of the 5.5 g / L CTAB solution (mi) were accurately weighed. The tare was set and 23.0000 g ± 1.0000 g of distilled water (MWATER) were accurately added. The solution was placed under stirring using a magnetic stirrer at 500 rpm on the dosing device and the titration was started. Stirring speed must strictly be steady throughout the titration without generating too much air bubbles.

[0265] Vi is the end point volume of AOT solution required to titrate the CTAB solution mi. The Ri determination is performed at least in duplicate. If the standard deviation of Ri = Vi / mi exceeds 0.010, the titration is repeated until the standard deviation is lower or equal to 0.010. The daily ratio Ri is calculated as the average of the 2 or 3 measurements. Note: the optrode must be washed with distilled water after every measurement and dried with absorbent paper.

[0266] CTAB adsorption on silica

[0267] The moisture content (%H2O) for each silica sample was determined with a thermobalance (temperature : 160°C) before the adsorption step as follows: tare the balance with an aluminum cup; weigh about 2 g of silica and distribute equally the powder on the cup, close the balance; note the percentage of moisture.

[0268] In a 100 mL disposable beaker: 0.0100 g of silica (mo) were accurately weighed. 50.0000 mL + 1.0000 mL of the CTAB stock solution (Vo) were added. The total mass was recorded. The suspension was stirred for 40 minutes ±1 minute on the stirring plate at 450 rpm using magnetic stirring bars with disc ends. After 40 minutes the sample was removed from the stirring plate.

[0269] 25 to 50 mL of the suspension were transferred in a centrifuge tube (volume depends on centrifuge tube size) and they were centrifuged for 35 minutes at a 10000 rpm speed at 25 °C. After centrifugation, the tube was gently removed from the centrifuge not to unsettle the silica. 10 to 20 mL of CTAB solution were transferred in a glass vial which was then stoppered and kept at 25°C.

[0270] Titration of the CTAB solution

[0271] In a 100 mL disposable beaker = 4.0000 g ± 0.0100 g of the CTAB solution at unknown concentration (m2) were accurately weighed.

[0272] Tare was set and 19.4000 g ± 1.0000 g of distilled water (Mwater) were added. The solution was placed under stirring at 500 rpm on the dosing device and the titration with the AOT solution was started.

[0273] V2 is the end point volume of AOT required to titrate an amount m2 of CTAB solution.

[0274] The CTAB surface area SCTAB is calculated as follows: V 578.435 x - M ES wherein: SCTAB = surface area of silica (including the moisture content correction) [m2 / g] Ri = Vi / mi; mi = mass of the CTAB stock solution titrated as the blank (kg);

[0275] Vi = end point volume of AOT required to titrate mi of the CTAB stock solution as the blank (L)

[0276] R2 = ¥2 / 1112; m2 = mass of the CTAB solution titrated after adsorption and centrifugation (kg); V2 = end point volume of AOT required to titrate m2 of the CTAB stock solution after adsorption and centrifugation (L)

[0277] [CTAB]i = Concentration of the CTAB stock solution (g / L)

[0278] Vo = Volume of the CTAB stock solution used for the adsorption on silica (L) MBS = Solid content of silica used for the adsorption (g) corrected for the moisture content as follows:

[0279] MBS = mo x (100 - %H2O) / 100 wherein mo = initial mass of silica (g).

[0280] Determination of specific surface area SBET of a precipitated silica

[0281] BET surface area SBET was determined according to the Brunauer - Emmett - Teller method as detailed in standard NF ISO 5794-1, Appendix E (June 2010) with the following adjustments: the sample was pre-dried at 160°C ± 10°C; the partial pressure used for the measurement P / Po was between 0.05 and 0.2.

[0282] Determination of particle size distribution of a precipitated silica by centrifugal sedimentation in a disc centrifuge using a centrifugal photosedimentometer - CPS method (dip, dso, dgo and mode)

[0283] Values of dso, die, ds4, FWHM and La were determined centrifugal sedimentation in a disc centrifuge using a centrifugal photosedimentometer type “CPS DC 24000UHR”, marketed by CPS Instruments company. This instrument is equipped with operating software supplied with the device (operating software version 11g).

[0284] Instruments used: for the measurement requirement, the following materials and products were used: Ultrasound system: 1500W generator type Sonics Vibracell VC 1500 / VCXI 500 equipped with 19 mm probe (Converters: CV154+ Boosters (Part No: BHNVC21) + 19 mm Probe (Part No: 630-0208)).

[0285] Analytical balance with a precision of 0.1 mg (e.g. Mettler AE260);

[0286] Syringes: 1.0 ml and 2.0 ml with 20ga needles; high shape glass beaker of 50 mL (SCHOTT DURAN: 38 mm diameter, 78 mm high); magnetic stirrer with a stir bar of 2 cm; vessel for ice bath during sonication.

[0287] Chemicals: deionized water; ethanol 96%; sucrose 99%; dodecane, all from Merck; PVC reference standard from CPS Instrument Inc.; the peak maximum of the reference standard used should be between 200 and 600 nm (e.g. 237nm).

[0288] Preparation of the disc centrifuge

[0289] For the measurements, the following parameters were established. For the calibration standard parameters, the information of the PVC reference communicated by the supplier were used. xcps=centipoise

[0290] System configuration

[0291] The measurement wavelength was set to 405 nm. The following runtime options parameters were established:

[0292] All the others options of the software are left as set by the manufacturer of the instrument.

[0293] Preparation of the disc centrifuge

[0294] The centrifugal disc is rotated at 24000 rpm during 30min. The density gradient of sucrose (CAS n°57-50-l) is prepared as follows:

[0295] In a 50mL beaker, a 24% in weight aqueous solution of sucrose is prepared. In a 50mL beaker, a 8% in weight aqueous solution of sucrose is prepared. Once these two solutions are homogenized separately, samples are taken from each solution using a 2 mL syringe which is injected into the rotating disc in the following order:

[0296] Sample 1 : 1.8 mL of the 24 wt% solution

[0297] Sample 2: 1.6 mL of the 24 wt% solution + 0.2 mL of the 8 wt% solution

[0298] Sample 3: 1.4 mL of the 24 wt% solution + 0.4 mL of the 8 wt% solution

[0299] Sample 4: 1.2 mL of the 24 wt% solution + 0.6 mL of the 8 wt% solution

[0300] Sample 5: 1.0 mL of the 24 wt% solution + 0.8 mL of the 8 wt% solution

[0301] Sample 6: 0.8 mL of the 24 wt% solution + 1.0 mL of the 8 wt% solution

[0302] Sample 7: 0.6 mL of the 24 wt% solution + 1.2 mL of the 8 wt% solution

[0303] Sample 8: 0.4 mL of the 24 wt% solution + 1.4 mL of the 8 wt% solution

[0304] Sample 9: 0.2 mL of the 24 wt% solution + 1.6 mL of the 8 wt% solution

[0305] Sample 10: 1.8 mL of the 8 wt% solution

[0306] Before each injection into the disk, the two solutions are homogenized in the syringe by aspiring about 0.2 mL of air followed by brief manual agitation for a few seconds, making sure not to lose any liquid.

[0307] These injections, the total volume of which is 18 mL, aim to create a density gradient useful for eliminating certain instabilities which may appear during the injection of the sample to be measured. To protect the density gradient from evaporation, we add 1 mL of dodecane in the rotating disc using a 2 mL syringe. The disc is then left in rotation at 24000 rpm for 60 min before any first measurement.

[0308] Sample preparation

[0309] 3.2 g of silica in a 50mL high shape glass beaker (SCHOTT DURAN: diameter 38 mm, height 78 mm) were weighed and 40 mL of deionized water were added to obtain a 8 wt% suspension of silica. The suspension was stirred with a magnetic stirrer (minimum 20 s) before placing the beaker into a crystallizing dish filled with ice and cold water. The magnetic stirrer was removed and the crystallizing dish was placed under the ultrasonic probe placed at 1 cm from the bottom of the beaker. The ultrasonic probe was set to 56% of its maximum amplitude and was activated for 8 min. At the end of the sonication the beaker was placed again on the magnetic stirrer with a 2 cm magnetic stir bar stirring at minimum 500 rpm until after the sampling.

[0310] The ultrasonic probe should be in proper working conditions. The following checks have to be carried out and in case of negative results a new probe should be used: visual check of the physical integrity of the end of the probe (depth of roughness less than 2 mm measured with a fine caliper); the measured dso of commercial silica Zeosil® 1165MP should be 93 nm ± 3 nm.

[0311] Analysis

[0312] Before each sample was analysed, a calibration standard was recorded. In each case 0.1 mL of the PVC standard provided by CPS Instruments and whose characteristics were previously entered into the software was injected. It is important to start the measurement in the software simultaneously with this first injection of the PVC standard. The confirmation of the device has to be received before injecting 100 pL of the previously sonicated sample by making sure that the measurement is started simultaneously at the injection.

[0313] These injections were done with 2 clean syringes of 1 mL.

[0314] At the end of the measurement, which is reached at the end of the time necessary to sediment all the particles of smaller diameter (configured in the software at 0.02 pm), the ratio for each diameter class was obtained. The curve obtained is called aggregate size distribution.

[0315] Results

[0316] The values dso, die, ds4 and La are on the basis of distributions drawn in a linear scale. The integration of the particle size distribution function of the diameter allows obtaining a “cumulative” distribution, that is to say the total mass of particles between the minimum diameter and the diameter of interest. dso: is the diameter below and above which 50% of the population by mass is found. The dso is called median size, that is diameter, of the silica particle. ds4: is the diameter below which 84% of the total mass of particles is measured. die: is the diameter below which 16% of the total mass of particles is measured.

[0317] La: is calculated according to equation: Ld=(d84-di6) / dso Determination of the dry extract of liquid or solid silicates and of precipitated silicas

[0318] The dry extract of liquid or solid silicate samples and the dry extract of precipitated silica samples were determined by means of a Mettler TOLEDO HC103 moisture analyzer thermobalance. The samples were heated from room temperature up to 160 °C, then maintained at 160 °C until their weight was stabilized (no more weight loss), resulting in the automatic stop of the measurement by the thermobalance.

[0319] ICP method to be used for the determination of the iron content of a silicate or of a precipitated silica

[0320] The iron content of liquid or solid silicates and of precipitated silica samples was determined by means of ICP OES (inductively coupled plasma optical emission spectrometry).

[0321] Silicate and precipitated silica samples available in solid form were preliminary digested in fluorhydric acid (e.g. 0.2-0.3 g of SiCE with 1 mL of fluorhydric acid 40%) to obtain a limpid solution. Silicates in liquid form did not require such a preliminary digestion.

[0322] The digested limpid solution or the liquid silicate as such, as the case may be, was diluted in a 5% nitric acid aqueous solution according to the expected Fe concentration. The intensity measured at a Fe specific wavelength, namely 259.4 nm, was compared to a calibration curve in the range of 0.05 to 2 mg / L obtained using iron standards (4 standards at 0.10, 0.20, 1.00 and 2.00 mg / L) in similar analytical conditions. The Fe amount in the samples was obtained by calculation using the dilution factor and the dry extract of the samples.

[0323] ICP method to be used for the determination of the aluminum content of a silicate or of a precipitated silica

[0324] The aluminum content of liquid or solid silicates and of precipitated silica samples was determined by means of ICP OES (inductively coupled plasma optical emission spectrometry).

[0325] Silicate and precipitated silica samples available in solid form were preliminary digested in fluorhydric acid (e.g. 0.2-0.3 g of SiO? with 1 mL of fluorhydric acid 40%) to obtain a limpid solution. Silicates in liquid form did not require such a preliminary digestion. The digested limpid solution or the liquid silicate as such, as the case may be, was diluted in a 5% nitric acid aqueous solution according to the expected Al concentration. The intensity measured at an Al specific wavelength, namely 396.152 nm, was compared to a calibration curve in the range of 0.05 to 2.00 mg / L obtained using aluminum standards (4 standards at 0.10, 0.20, 1.00 and 2.00 mg / L) in similar analytical conditions. The Al amount in the samples was obtained by calculation using the dilution factor and the dry extract of the samples.

[0326] ICP method to be used for the determination of the Si content (expressed as SiCh) of a silicate or of a precipitated silica

[0327] The silicium content of liquid or solid silicates and of precipitated silica samples was determined by means of ICP OES (inductively coupled plasma optical emission spectrometry).

[0328] Silicate and precipitated silica samples in solid form were preliminary digested in fluorhydric acid (e.g. 0.2-0.3 g of SiCL with 1 mL of fluorhydric acid 40%) to obtain a limpid solution. Silicates in liquid form did not require such a preliminary digestion.

[0329] The digested limpid solution or the liquid silicate as such, as the case may be, was diluted in a 5% nitric acid aqueous solution according to the expected Si concentration. The intensity measured at a Si specific wavelength, namely 251.6 nm, was compared to a calibration curve in the range of 0.05 to 1 mg / L obtained using silicium standards (4 standards at 0.05, 0.10, 0.50 and 1.00 mg / L) in similar analytical conditions. The Si amount in the samples was obtained by calculation using the dilution factor and the dry extract of the samples, then expressed as SiCL amount.

[0330] Determination of the pore size distribution curve of a precipitated silica by mercury porosimetry

[0331] Pore volume and pore size distribution were determined using a Micromeritics AutoPore® IV 9520 porosimeter; they were calculated by the Washburn relationship with a contact angle theta equal to 140° and a surface tension gamma equal to 485 dynes / cm. Each sample was dried before the measure in an oven at 200°C for 2 hours at atmospheric pressure. The starting weight of silica placed in the type 10 penetrometer, having an accuracy of 0.001 g, was selected for good reproducibility of the measurement, in such a way that the "stem volume used", i.e. the percentage mercury (Hg) volume consumed for filling of the penetrometer was from 40% to 80%. The penetrometer was then slowly evacuated to 50 pm of Hg and kept at this pressure for 5 min.

[0332] The AutoPore® equipment was operated using Software Version IV 1.09. No corrections were performed on the raw data. The measurement range was from 3.59 kPa (0.52 psi) to 413685 kPa (60000 psi), and at least 100 measurement points were used (19 measurement points from 3.59 kPa (0.52 psi) to 193 kPa (28 psi) with 10 seconds of equilibrium time and then 81 points from 193 kPa (28 psi) to 413685 kPa (60000 psi) with a 20 seconds equilibrium time). If appropriate, the software introduced further measurement points if the incremental intrusion volume was >0.5 mL / g. This corresponds to the first intrusion analysis. The intrusion curve was smoothed by means of the "smooth differentials" function of the equipment software.

[0333] After the first intrusion analysis, additional points were measured with decreasing pressures down to 226 kPa (32.8 psi). Then, a second intrusion analysis was carried out with 88 points from 226 kPa (32.8 psi) to 413685 kPa (60000 psi) with a 20 seconds equilibrium time. If appropriate, the software introduced further measurement points if the incremental intrusion volume was >0.5 mL / g.

[0334] The Log Differential Intrusion (mL / g) versus pore size data was analysed in the pore diameter range from 3.5 nm to 405 pm.

[0335] The values of the mode of the distribution, the breadth of the pore size distribution as well as of the volume of the pores having a diameter of less than 1 pm (VD<1 pm) was determined on the 2ndintrusion curve.

[0336] The breadth of the pore size distribution, Ldp, is obtained from the pore distribution curve (2ndintrusion) which provides the pore volume (mL / g) as a function of the pore diameter (nm). The coordinates of point S corresponding to the maximum in the curve are determined, wherein Xs is the value of the diameter (nm) and Ys is value of the pore volume (mL / g). A straight line of equation Y = Ys / 2 is plotted on the pore distribution curve. The intercepts of line Y = Ys / 2 with the pore distribution curve define points A and B having the x- axis values (nm) XA and XB, respectively, on either side of Xs; the breadth of the pore distribution curve, Ldp, is equal to the ratio (XA - XB) / XS. Ldp is an adimensional number. Example 0 - Sand characterization

[0337] Different samples of spent foundry sand and high purity sand (for comparison) have been analyzed as following.

[0338] Example 0.1 - Spent Foundry Sand 1 (SFS1)

[0339] Spent foundry sand 1 (SFS1) presents the following characteristics:

[0340] Particle size distribution by laser granulometry

[0341] The granulometric distribution of SFS1 presents the following main values:

[0342] Carbon / Sulfur analysis

[0343] SFS1 presents a carbon content of 3.9 wt.% according to the carbon / sulfur analysis.

[0344] X-Ray Fluorescence (elemental analysis)

[0345] Example 0.2 - Spent Foundry Sand 2 (SFS2)

[0346] Spent foundry sand 2 (SFS2) corresponds to SFS1 of Example 0.1 after a purification step, described as follows:

[0347] Purification of the sand SFS1: Purification of the first spent foundry sand (SFS1) was realized by granulometry selection (sieving), using a sieve having a cut-off threshold = 100 pm.

[0348] The purified spent foundry sand (SFS2) thus only contains particles having a particle size bigger than 100 pm which are the selected particles for the purpose of the present invention (to be employed for the production of silicate as disclosed in the following examples) as they are rich in silica.

[0349] Spent foundry sand 2 (SFS2) presents the following characteristics:

[0350] Particle size distribution by laser granulometry.

[0351] The granulometric distribution of SFS2 presents the following main values:

[0352] Carbon / Sulfur analysis:

[0353] SFS2 presents a carbon content of 3.2 wt.% according to the carbon / sulfur analysis.

[0354] X-Ray Fluorescence (elemental analysis) Example 0.3 - Spent Foundry Sand 3 (SFS3)

[0355] Spent foundry sand 3 (SFS3) presents the following characteristics:

[0356] Particle size distribution by laser granulometry

[0357] The granulometric distribution of SFS3 presents the following main values:

[0358] Carbon / Sulfur analysis

[0359] SFS3 presents a carbon content of 1.1 wt.% according to the carbon / sulfur analysis.

[0360] X-Ray Fluorescence (elemental analysis)

[0361] Example 0.4 - Spent Foundry Sand 4 (SFS4)

[0362] Spent foundry sand 4 (SFS4) presents the following characteristics:

[0363] Particle size distribution by laser granulometry

[0364] The granulometric distribution of SFS4 presents the following main values: Carbon / Sulfur analysis

[0365] SFS4 presents a carbon content of 4.3 wt.% according to the carbon / sulfur analysis.

[0366] X-Ray Fluorescence (elemental analysis)

[0367] Example 0.5 - Spent Foundry Sand 5 (SFS5)

[0368] Spent foundry sand 5 (SFS5) presents the following characteristics:

[0369] Particle size distribution by laser granulometry

[0370] The granulometric distribution of SFS5 presents the following main values:

[0371] Carbon / Sulfur analysis

[0372] SFS5 presents a carbon content of 2.4 wt.% according to the carbon / sulfur analysis.

[0373] X-Ray Fluorescence (elemental analysis)

[0374] Example 0.6 - High Purity Sand (comparative)

[0375] The high purity sand presents the following characteristics:

[0376] Particle size distribution by laser granulometry

[0377] The granulometric distribution of said high purity sand presents the following main values:

[0378] Carbon / Sulfur analysis

[0379] The high purity sand presents a carbon content of 0 wt.% according to the carbon / sulfur analysis.

[0380] X-Ray Fluorescence (elemental analysis) Example 0.7 - Spent Foundry Sand 6 (SFS6)

[0381] Spent foundry sand 6 (SFS6) presents the following characteristics:

[0382] Particle size distribution by laser granulometry

[0383] The granulometric distribution of SFS6 presents the following main values:

[0384] Carbon / Sulfur analysis

[0385] SFS6 presents a carbon content of 5.3 wt.% according to the carbon / sulfur analysis.

[0386] X-Ray Fluorescence (elemental analysis)

[0387] Example 0.8 - Spent Foundry Sand 7 (SFS7)

[0388] Spent foundry sand 7 (SFS7) presents the following characteristics:

[0389] Particle size distribution by laser granulometry

[0390] The granulometric distribution of SFS7 presents the following main values: Carbon / Sulfur analysis

[0391] SFS7 presents a carbon content of 4.5 wt.% according to the carbon / sulfur analysis.

[0392] X-Ray Fluorescence (elemental analysis)

[0393] Example 1 - Silicate preparation

[0394] The spent foundry sand described in Example 0 was employed to produce silicate according to the process of the present invention as disclosed in the following Examples 1.1 to 1.15.

[0395] Example 1.1

[0396] In an alumina crucible, the following reagents were introduced and mixed together: 206.2 g of spent foundry sand 2 (SFS2) and 108.7 g of Na2CO3. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia). The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 1” (SI).

[0397] Example 1.2

[0398] In an alumina crucible, the following reagents were introduced and mixed together: 30.9 g of spent foundry sand 2 (SFS2), 169.6 g of high purity sand and 108.5 g of Na2COs. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.9 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0399] The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 2” (S2).

[0400] Example 1.3

[0401] In an alumina crucible, the following reagents were introduced and mixed together: 51.6 g of purified spent foundry sand 2 (SFS2), 148.9 g of high purity sand and 108.2 g of ISfeCCE. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.9 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia). The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 3” (S3).

[0402] Example 1.4

[0403] In an alumina crucible, the following reagents were introduced and mixed together: 103.1 g of purified spent foundry sand 2, 97.2 g of high purity sand and 107.2 g of Na2COs. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.7 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0404] The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 4” (S4).

[0405] Example 1.5

[0406] In an alumina crucible, the following reagents were introduced and mixed together: 30.9 g of raw spent foundry sand 1 (SFS1), 169.6 g of high purity sand and 107.9 g of ISfeCCE. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.8 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia). The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 5” (S5).

[0407] Example 1.6

[0408] In an alumina crucible, the following reagents were introduced and mixed together: 51.6 g of raw spent foundry sand 1 (SFS1), 148.9 g of high purity sand and 107 g of ISfeCCh. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.6 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0409] The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 6” (S6).

[0410] Example 1.7

[0411] In an alumina crucible, the following reagents were introduced and mixed together: 103.1 g of raw spent foundry sand 1 (SFS1), 97.2 g of high purity sand and 104.9 g of ISfeCCE. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.1 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia). The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 7” (S7).

[0412] Example 1.8

[0413] In an alumina crucible, the following reagents were introduced and mixed together: 206.2 g of spent foundry sand 3 (SFS3) and 108.7 g of ISfeCCh. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.1 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0414] The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 8” (S8).

[0415] Example 1.9

[0416] In an alumina crucible, the following reagents were introduced and mixed together: 30.9 g of spent foundry sand 3 (SFS3), 169.6 g of high purity sand and 108.5 g of Na2COs. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.6 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia). The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 9” (S9).

[0417] Example 1.10

[0418] In an alumina crucible, the following reagents were introduced and mixed together: 51.5 g of spent foundry sand 3 (SFS3), 148.9 g of high purity sand and

[0419] 108.2 g of Na2COs. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.5 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0420] The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 10” (S10).

[0421] Example 1.11

[0422] In an alumina crucible, the following reagents were introduced and mixed together: 103.1 g of spent foundry sand 3 (SFS3), 97.2 g of high purity sand and

[0423] 107.2 g of Na2COs. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia). The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 11” (Si l).

[0424] Example 1.12

[0425] In an alumina crucible, the following reagents were introduced and mixed together: 100 g of spent foundry sand 4 (SFS4) and 35.2 g of ISfeCCh. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 6 g of the previous vitreous sodium silicate and 8.37 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0426] The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 12” (S12).

[0427] Example 1.13

[0428] In an alumina crucible, the following reagents were introduced and mixed together: 100 g of spent foundry sand 5 (SFS5) and 45.3 g of ISfeCCE. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 6 g of the previous vitreous sodium silicate and 20.69 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia). The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 13” (S13).

[0429] Example 1.14 (comparative)

[0430] In an alumina crucible, the following reagents were introduced and mixed together: 100 g of high purity sand and 49.8 g of ISfeCCh. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 6 g of the previous vitreous sodium silicate and 12.98 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0431] The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 14” (S14).

[0432] Example 1.15

[0433] In an alumina crucible, the following reagents were introduced and mixed together: 30.9 g of purified spent foundry sand 2 (SFS2), 169.6 g of high purity sand and 108.5 g of ISfeCCE. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1400°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of the previous vitreous sodium silicate and 21.9 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170°C with a ramp of l°C / min. Once the temperature was reached, the mixture was left for 7 hours at 170°C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia). The solution obtained was centrifuged at 4500 tr / min for 35 min to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 15” (SI 5).

[0434] Results

[0435] For each of the liquid sodium silicates obtained according to Examples 1.1 to 1.15 above, the experimental Rp (Rp exp or Rp) was measured by infrared spectroscopy technique (IR-ATR) and compared to the target one (Rp target).

[0436] The results are shown in Table 1 below.

[0437] Rp target is the theoretical ratio Rp = %wt SiO? / %wt Na?O (concentrations in weight) based on the quantity of SiCh (from the Spent Foundry Sands), Na?O (from the ISfeCCE) and water introduced. The Rp targeted is so called Rp(theo). Parallely, the Rp actually obtained is the Rp(exp) or Rp.

[0438] Table 1

[0439] If the targeted Rp(theo) is too high (typically above 3.5), that is the silica content is really much more important than the ISfeCCh amount, the melting process could also lead to the formation of crystalline silica in the sodium silicate. Such a reaction has to be avoided because crystalline silica cannot be easily dissolved to make the liquid sodium silicate.

[0440] Example 2 - Preparation of precipitated silica

[0441] Example 2.1

[0442] In a 2 L glass reactor, 969 g of water and 28.5 g of sodium silicate are introduced. The suspension so obtained is heated to 72 °C and kept at this temperature for 5 minutes before being re-heated to 82 °C. Simultaneously to this temperature profile, 80 g / L of sulfuric acid is introduced under stirring (350 rpm) at a flow rate of 5.9 g / min until the pH reaches 8.7. A sodium silicate solution with a ratio %wtSiO2 / %wtNa2O (Rp) equal to 3.5 and a concentration of 230 g / L and sulfuric acid with a concentration equal to 80 g / L are simultaneously introduced into the reactor over a period of 58 minutes, wherein the sodium silicate solution is introduced at a flow rate of 12 g / min and the sulfuric acid is introduced at a flow rate regulated in such a way as to maintain the pH of the reaction medium at a value of 8.7. At the end of the 58 minutes, the sodium silicate flow rate is stopped. The flow rate of the 80 g / L sulfuric acid is put at 5.4 g / min that allows to maintain the pH of the solution above 5.2.

[0443] The slurry thus obtained is filtered and washed through a filter (20 wt% dry cake extract). The resulting cake is then mechanically broken down and the resulting slurry dried using a spray dryer.

[0444] Example 2.2

[0445] In a 2 L glass reactor, 969 g of water and 28.5 g of sodium silicate are introduced. The suspension so obtained is heated to 72 °C and kept at this temperature for 5 minutes before being re-heated to 82 °C. Simultaneously to this temperature profile, 80 g / L of sulfuric acid is introduced under stirring (350 rpm) at a flow rate of 5.9 g / min until the pH reaches 9.1. A sodium silicate solution with a ratio %wtSiO2 / %wtNa2O (Rp) equal to 2.5 and a concentration of 230 g / L and sulfuric acid with a concentration equal to 80 g / L are simultaneously introduced into the reactor over a period of 60 minutes, wherein the sodium silicate solution is introduced at a flow rate of 12 g / min and the sulfuric acid is introduced at a flow rate regulated in such a way as to maintain the pH of the reaction medium at a value of 9.1. At the end of the 60 minutes, the sodium silicate flow rate is stopped. The flow rate of the 80 g / L sulfuric acid is put at 5.4 g / min that allows to maintain the pH of the solution above 5.2.

[0446] The slurry thus obtained is filtered and washed through a filter (20 wt% dry cake extract). The resulting cake is then mechanically broken down and the resulting slurry dried using a spray dryer.

[0447] Example 3 - Preparation of precipitated silica

[0448] Example 3.1 (for comparison purposes)

[0449] This example describes the preparation of a precipitated silica from a silicate of the prior art prepared conventionally by thermally treating a Fontainebleau sand in a furnace in the presence of sodium carbonate.

[0450] In a 25 L stainless steel reactor were introduced 13 kg of water, 7.6 kg of a sodium silicate solution (SiCh / Na?!) ratio = 3.49; SiCh concentration = 19.98 wt%) and 250 g of ISfeSCU (solid). The same sodium silicate solution was used throughout the process. After starting the agitation (250rpm), the tank feed thus constituted was heated to 79.2 °C. A 7.7 wt% sulfuric acid solution was introduced into the reactor at a flowrate of 164 g / min during 20 min. Next, a 96 wt% sulfuric acid solution was simultaneously introduced over 15.47 min period at a flowrate of 22.5 g / min to reach pH 8. In the same time, the temperature was increased from room temperature up to reach 92°C.

[0451] Sodium silicate at a flowrate of 90 g / min and a 96 wt% sulfuric acid solution were then introduced simultaneously over a period of 20.1 min. The flowrate of the 96 wt% sulfuric acid solution was regulated so that the pH of the reaction medium was maintained at a value of 8.00.

[0452] At the end of this simultaneous addition, the pH of the reaction medium was brought to a value of 4.1 with 96 wt% sulfuric acid, and the reaction mixture was matured for 2 minutes. A slurry was obtained.

[0453] The reaction slurry was filtered and washed on a filter press to obtain a cake. The cake obtained was disintegrated mechanically. The resulting slurry was dried by means of a nozzle spray dryer to obtain a precipitated silica for comparison purposes.

[0454] This one (hereinafter, comparative silica CS1) had an iron content well below 100 ppm and an aluminum content well below 400 ppm. Example 3.2 (according to the invention)

[0455] This example describes the preparation of a precipitated silica under conditions mimicking those effective when using as silicate reagent that is prepared by the process according to the invention. Silicates obtainable by the process according to the invention can be characterized by a high iron content; to mimic such conditions, sulfuric acid, which was caused to react with the silicate reagent, was doped with ferrous sulfate as detailed hereinafter.

[0456] In a 25 L stainless steel reactor were introduced 13 kg of water, 7.6 kg of a sodium silicate solution (SiCh / Na?!) ratio = 3.49; SiCh concentration = 19.98 wt%) and 248g of ISfeSCU (solid). The same sodium silicate solution was used throughout the process. After starting the agitation (250rpm), the tank feed thus constituted was heated to 79.2 °C. A 7.7 wt% sulfuric acid solution was doped by ferrous sulfate at a concentration, expressed as Fe2+, of 500 ppm, based on the total amount of silicate, expressed as SiCh, that is used for the preparation of the precipitated silica. The doped solution sulfuric acid solution was introduced into the reactor at a flowrate of 163.7 g / min during 20 min. Next an undoped 96 wt% sulfuric acid solution was simultaneously introduced over 15.85 min period at a flowrate of 22.8 g / min to reach pH 8. In the same time, the temperature was increased from room temperature up to 92°C.

[0457] Sodium silicate at a flowrate of 90.7 g / min and an undoped 96 wt% sulfuric acid solution were then introduced simultaneously over a period of 20.1 min. The flowrate of the undoped 96 wt% sulfuric acid solution was regulated so that the pH of the reaction medium was maintained at a value of 8.00.

[0458] At the end of this simultaneous addition, the pH of the reaction medium was brought to a value of 4.1 with undoped 96 wt% sulfuric acid, and the reaction mixture was matured for 2 minutes. A slurry was obtained.

[0459] The reaction slurry was filtered and washed on a filter press to obtain a cake. The cake obtained was disintegrated mechanically. The resulting slurry was dried by means of a nozzle spray dryer to obtain a precipitated silica SI in accordance with the invention.

[0460] Example 3.3 (according to the invention)

[0461] This example describes also the preparation of a precipitated silica under conditions mimicking those effective when using as silicate reagent that is prepared by the process according to the invention. As in example 3.2, to mimic such conditions, sulfuric acid, which is caused to react with the silicate reagent, was doped with ferrous sulfate, as detailed hereinafter.

[0462] In a 25 L stainless steel reactor were introduced 13 kg of water, 7.6 kg of a sodium silicate solution (SiCh / Na?!) ratio = 3.49; SiCh concentration = 19.98 wt%) and 250 g of ISfeSCU (solid). The same sodium silicate solution was used throughout the process. After starting the agitation (250rpm), the tank feed thus constituted was heated to 79.2 °C. A 7.7 wt% sulfuric acid solution was doped by ferrous sulfate at a concentration, expressed as Fe2+, of 1000 ppm, based on the total amount of silicate, expressed as SiCh, that is used for the preparation of the precipitated silica The doped solution sulfuric acid solution was introduced into the reactor at a flowrate of 169.6 g / min during 20 min. Next an undoped 96 wt% sulfuric acid solution was simultaneously introduced over 15.11 min period at a flowrate of 22.5 g / min to reach pH 8. In the same time, the temperature was increased from room temperature up to 92°C.

[0463] Sodium silicate at a flowrate of 91 g / min and an undoped 96 wt% sulfuric acid solution were then introduced simultaneously over a period of 20 min. The flowrate of the undoped 96 wt% sulfuric acid solution was regulated so that the pH of the reaction medium was maintained at a value of 8.00.

[0464] At the end of this simultaneous addition, the pH of the reaction medium was brought to a value of 4.1 with undoped 96 wt% sulfuric acid, and the reaction mixture was matured for 2 minutes. A slurry was obtained.

[0465] The reaction slurry was filtered and washed on a filter press to obtain a cake. The cake obtained was disintegrated mechanically. The resulting slurry was dried by means of a nozzle spray dryer to obtain a precipitated silica S2 in accordance with the invention.

[0466] Results obtained for examples 3.1, 3.2 and 3.3

[0467] Physico-chemical characteristics of the precipitated silicas prepared according to the above examples 3.1 to 3.3 were determined. The results are reported in Table 2. Table 2

[0468] Multivalent metal ions are generally known to modify particle size and pore size distributions of precipitated silicas, with possibly detrimental effects on end use properties, for example on mechanical properties of shaped parts made of silica-filled rubber compositions such as wear and / or rolling resistance of tire treads. Surprisingly, silicas SI and S2, despite their very high iron content exhibit the same or substantially the same particle size distribution and the same or substantially the same pore size distribution as reference silica CS1. Thus, advantageously, no effort needs to be undertaken to remove the iron that is generally present in a silicate prepared by the process according to the present invention for allegedly make it suitable for use in the preparation of a precipitated silica having desirable particle size and pore size distributions.

[0469] Example 4 - Attrition mechanical regeneration

[0470] Example 4.1 - Purification of the Spent Foundry Sand 1 (SFS1)

[0471] Purification of the spent foundry sand (SFS1 - Example 0.1) was realized by a regeneration process, which is a mechanical attrition treatment comprising the following steps.

[0472] A preliminary sieving correlated with a screener was used to remove block sand with a size more than 3 mm. Then, the spent foundry sand was dried at a temperature of more than 100 °C by using a fluidized bed to obtain a moisture of less than 1%. The dried sand was then introduced into a hopper before passing into a first attrition chamber through a screw. The sand flow rate was 6 kg / min.

[0473] The attrition process involved two millstones rotating in the opposite direction in a rotating drum. The pressure of the two millstones on the rotating drum was set using the pressure of a hydraulic cylinder allowing the breaking of the shell around the sand particles.

[0474] After this step in a first attrition chamber, the sand was evacuated in a second attrition chamber wherein the same conditions as in the first chamber were used. In total, four steps in attrition chambers were performed for the present experiment.

[0475] To evacuate the fine particles so obtained and mainly composed by coal and clay, an aspirator was installed above the attrition chamber with a flow rate of 5000 m3 / h. By this methodology it was possible to purify 360 kg spent foundry sand per hour.

[0476] At the end of the mechanical attrition process, a regenerated spent foundry sand was obtained.

[0477] The regenerated spent foundry sand presented the following characteristics:

[0478] Particle size distribution by laser granulometry

[0479] The granulometric distribution of the SFS1 presents the following main values before and after the mechanical attrition treatment:

[0480] Carbon / Sulfur analysis

[0481] SFS1 presents the following carbon content according to the carbon / sulfur analysis before and after the mechanical attrition treatment:

[0482] X-Ray Fluorescence (elemental analysis)

[0483] The profile of the impurities before and after the mechanical attrition treatment was measured by X-ray fluorescence and is reported below:

[0484]

[0485] Example 4.2 - Purification of the Spent Foundry Sand 6 (SFS6)

[0486] Purification of the spent foundry sand (SFS6 - Example 0.7) was realized by a regeneration process, which is a mechanical attrition treatment comprising the following steps.

[0487] A preliminary sieving correlated with a screener was used to remove block sand with a size more than 3 mm. Then, the spent foundry sand was dried at a temperature of more than 100 °C by using a fluidized bed to obtain a moisture of less than 1%. The dried sand was then introduced into a hopper before passing into a first attrition chamber through a screw. The sand flow rate was 6 kg / min.

[0488] The attrition process involved two millstones rotating in the opposite direction in a rotating drum. The pressure of the two millstones on the rotating drum was set using the pressure of a hydraulic cylinder allowing the breaking of the shell around the sand particles.

[0489] After this step in a first attrition chamber, the sand was evacuated in a second attrition chamber wherein the same conditions as in the first chamber were used. In total, four steps in attrition chambers were performed for the present experiment.

[0490] To evacuate the fine particles so obtained and mainly composed by coal and clay, an aspirator was installed above the attrition chamber with a flow rate of 5000 m3 / h. By this methodology it was possible to purify 360 kg spent foundry sand per hour. At the end of the mechanical attrition process, a regenerated spent foundry sand was obtained.

[0491] The regenerated spent foundry sand presented the following characteristics:

[0492] Particle size distribution by laser granulometry

[0493] The granulometric distribution of the SFS6 presents the following main values before and after the mechanical attrition treatment:

[0494] Carbon / Sulfur analysis

[0495] SFS6 presents the following carbon content according to the carbon / sulfur analysis before and after the mechanical attrition treatment:

[0496] X-Ray Fluorescence (elemental analysis)

[0497] The profile of the impurities before and after the mechanical attrition treatment was measured by X-ray fluorescence and is reported below:

[0498] Example 4.3 - Purification of the Spent Foundry Sand 7 (SFS7)

[0499] Purification of the spent foundry sand (SFS7 - Example 0.8) was realized by a regeneration process, which is a mechanical attrition treatment comprising the following steps.

[0500] A preliminary sieving correlated with a screener was used to remove block sand with a size more than 3 mm. Then, the spent foundry sand was dried at a temperature of more than 100 °C by using a fluidized bed to obtain a moisture of less than 1%. The dried sand was then introduced into a hopper before passing into a first attrition chamber through a screw. The sand flow rate was 6 kg / min.

[0501] The attrition process involved two millstones rotating in the opposite direction in a rotating drum. The pressure of the two millstones on the rotating drum was set using the pressure of a hydraulic cylinder allowing the breaking of the shell around the sand particles.

[0502] After this step in a first attrition chamber, the sand was evacuated in a second attrition chamber wherein the same conditions as in the first chamber were used. In total, four steps in attrition chambers were performed for the present experiment.

[0503] To evacuate the fine particles so obtained and mainly composed by coal and clay, an aspirator was installed above the attrition chamber with a flow rate of 5000 m3 / h. By this methodology it was possible to purify 360 kg spent foundry sand per hour.

[0504] At the end of the mechanical attrition process, a regenerated spent foundry sand was obtained.

[0505] The regenerated spent foundry sand presented the following characteristics:

[0506] Particle size distribution by laser granulometry

[0507] The granulometric distribution of the SFS7 presents the following main values before and after the mechanical attrition treatment:

[0508] Carbon / Sulfur analysis

[0509] SFS7 presents the following carbon content according to the carbon / sulfur analysis before and after the mechanical attrition treatment:

[0510] X-Ray Fluorescence (elemental analysis)

[0511] The profile of the impurities before and after the mechanical attrition treatment was measured by X-ray fluorescence and is reported below:

[0512] Example 5 - Silicate preparation

[0513] The regenerated spent foundry sand described in Example 4 was employed to produce silicate according to the process of the present invention as disclosed in the following Examples 5.1 to 5.4

[0514] Example 5.1

[0515] In a crucible, the following reagents were introduced and mixed together: 22.5g of regenerated spent foundry sand (SFS6 - according to Example 4.2), 127.5 g of high purity sand, and 74.3 g of Na2C0s. The crucible was then introduced in a muffle furnace glass, pre-heated at 1450 °C. The mixture was left for 2 hours and 30 minutes at 1450 °C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). This operation is carried out four times to obtain at the end 800 kg of silicate.

[0516] In a PARR combustion bomb, 10 g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the colling is by inertia).

[0517] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 5.1” (S5.1).

[0518] Example 5.2

[0519] In an alumina crucible, the following reagents were introduced and mixed together: 37 g of regenerated spent foundry sand 6 (SFS6 - according to Example 4.2), 112 g of high purity sand, and 74.3 g of Na2COs. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450 °C. The mixture was left for 2 hours and 30 minutes at 1450 °C. Then, the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the colling is by inertia).

[0520] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 5.2” (S5.2).

[0521] Example 5.3

[0522] In an alumina crucible, the following reagents were introduced and mixed together: 75 g of regenerated spent foundry sand 6 (SFS6 - according to Example 4.2), 75 g of high purity sand, and 74.1 g of Na2COs. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450 °C. The mixture was left for 2 hours and 30 minutes at 1450 °C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C with a ramp of 1 °C / min. Once the temperature was reached, the mixture was left for 7 hours at 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0523] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 5.3” (S5.3).

[0524] Example 5.4

[0525] In an alumina crucible, the following reagents were introduced and mixed together: 150 g of regenerated spent foundry sand 6 (SFS6 - according to Example 4.2), and 74.34 g of ISfeCCh. The crucible was then introduced in a NABERTHERM muffle furnace, pre-heated at 1450 °C. The mixture was left for 2 hours and 30 minutes at 1450 °C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 10 g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C with a ramp of 1 °C / min. Once the temperature was reached, the mixture was left for 7 hours at 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0526] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 5.4” (S5.4).

[0527] Results

[0528] For each of the liquid sodium silicates obtained according to Examples 5.1 to 5.4 above, the experimental Rp (Rp exp or Rp) was measured by potentiometric method as described below: Table 3

[0529] The profile of the impurities was measured by X-ray fluorescence and is reported in Table 4 below:

[0530] Table 4 Example 6 - Silicate preparation

[0531] The regenerated spent foundry sand described in Example 4 was employed to produce silicate according to the process of the present invention as disclosed in the following Examples 6.1

[0532] Example 6.1

[0533] In a crucible, the following reagents were introduced and mixed together: 60 kg of regenerated spent foundry sand (SFS6 - according to Example 4.2), 90 kg of high purity sand, and 74.3 g of ISfeCCE. The crucible was then introduced in a muffle furnace glass, pre-heated at 1450 °C. The mixture was left for 2 hours and 30 minutes at 1450 °C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). This operation is carried out four times to obtain at the end 800 kg of silicate.

[0534] In a reactor under agitation of 1 m3, 190 kg of vitreous sodium silicate so obtained, and 655 kg of water were introduced. Temperature was raised up to 95°C with a ramp of 5°C / min. Once the temperature was reached, the mixture was left for 4 hours at 95 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0535] The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 6.1” (S6.1).

[0536] Results

[0537] For the liquid sodium silicates obtained according to Example 6.1 above, the experimental Rp (Rp exp or Rp) was measured by potentiometric method as described below:

[0538] Table 5

[0539] The profile of the impurities was measured by X-ray fluorescence and is reported in Table 6 below:

[0540] Table 6

[0541] Example 7 - Preparation of precipitated silica

[0542] Example 7.1

[0543] This example describes the preparation of a precipitated silica from a silicate with a regenerated spent foundry sand SFS6 (silicate produced according to Example 6.1 - “Silicate S6.1”).

[0544] In a 25 L stainless steel reactor were introduced 10.98 kg of water, 9.2 kg of a sodium silicate solution (SiCh / Na?!) ratio = 3.64; SiCh concentration = 16.14 wt%) and 243 g of ISfeSCU (solid). The same sodium silicate solution was used throughout the process. After starting the agitation (250rpm), the tank feed thus constituted was heated to 81.1 °C. 7.7 wt% sulfuric acid solution was introduced into the reactor at a flowrate of 164 g / min during 20 min. Next, a 96 wt% sulfuric acid solution was simultaneously introduced over 14.24 min period at a flowrate of 24.3 g / min to reach pH 8. At the same time, the temperature was increased from room temperature up to reach 92°C. Sodium silicate at a flowrate of 90 g / min and a 96 wt% sulfuric acid solution were then introduced simultaneously over a period of 20.1 min. The flowrate of the 96 wt% sulfuric acid solution was regulated so that the pH of the reaction medium was maintained at a value of 8.00.

[0545] At the end of this simultaneous addition, the pH of the reaction medium was brought to a value of 4.1 with 96 wt% sulfuric acid, and the reaction mixture was matured for 2 minutes. A slurry was obtained.

[0546] The reaction slurry was filtered and washed on a filter press to obtain a cake. The cake obtained was disintegrated by a mechanical action and by a chemical action with alumina additive 0.3%wt. The resulting slurry was dried by means of a nozzle spray dryer to obtain a precipitated silica The resulting slurry was dried by means of a nozzle spray dryer to obtain a precipitated silica SI in accordance with the invention

[0547] Example 7.2

[0548] This example describes the preparation of a precipitated silica from a silicate with a regenerated spent foundry sand SFS6 (silicate produced according to Example 6.1 - “Silicate S6.1”).

[0549] In a 25 L stainless steel reactor were introduced 13 kg of water, 7.57 kg of a sodium silicate solution (SiCh / Na?!) ratio = 3.64; SiCh concentration = 16.14 wt%) and 248 g of ISfeSCU (solid). The same sodium silicate solution was used throughout the process. After starting the agitation (250rpm), the tank feed thus constituted was heated to 79.4 °C. A 7.7 wt% sulfuric acid solution was introduced into the reactor at a flowrate of 163 g / min during 20 min. Next, a 96 wt% sulfuric acid solution was simultaneously introduced over 13.80 min period at a flowrate of 25.1 g / min to reach pH 8. At the same time, the temperature was increased from room temperature up to reach 92°C.

[0550] Sodium silicate at a flowrate of 91 g / min and a 96 wt% sulfuric acid solution were then introduced simultaneously over a period of 20.2 min. The flowrate of the 96 wt% sulfuric acid solution was regulated so that the pH of the reaction medium was maintained at a value of 8.00.

[0551] At the end of this simultaneous addition, the pH of the reaction medium was brought to a value of 4.1 with 96 wt% sulfuric acid, and the reaction mixture was matured for 2 minutes. A slurry was obtained.

[0552] The reaction slurry was filtered and washed on a filter press to obtain a cake. The cake obtained was disintegrated by a mechanical action and by a chemical action with alumina additive 0.3%wt. The resulting slurry was dried by means of a nozzle spray dryer to obtain a precipitated silica S2 in accordance with the invention.

[0553] Example 7.3

[0554] This example describes the preparation of a precipitated silica from a silicate with a regenerated spent foundry sand (silicate produced according to Example 6.1 - “Silicate S6.1”).

[0555] In a 170 L stainless steel reactor were introduced 10.98 kg of water, 9.24 kg of a sodium silicate solution (SiCh / Na?!) ratio = 3.64; SiCh concentration = 16.14 wt%) and 243 g of ISfeSCU (solid). The same sodium silicate solution was used throughout the process After starting the agitation (250rpm), the tank feed thus constituted was heated to 79.2 °C. A 7.7 wt% sulfuric acid solution was introduced into the reactor at a flowrate of 159.6 g / min during 20 min. Next, a 96 wt% sulfuric acid solution was simultaneously introduced over 15.60 min period at a flowrate of 22.4 g / min to reach pH 8. At the same time, the temperature was increased from room temperature up to reach 92°C.

[0556] Sodium silicate at a flowrate of 111 g / min and a 96 wt% sulfuric acid solution were then introduced simultaneously over a period of 20.1 min. The flowrate of the 96 wt% sulfuric acid solution was regulated so that the pH of the reaction medium was maintained at a value of 8.00.

[0557] At the end of this simultaneous addition, the pH of the reaction medium was brought to a value of 4.1 with 96 wt% sulfuric acid, and the reaction mixture was matured for 2 minutes. A slurry was obtained.

[0558] The reaction slurry was filtered and washed on a filter press to obtain a cake. The cake obtained was disintegrated by a mechanical action and by a chemical action with alumina additive 0.3%wt. The resulting slurry was dried by means of a nozzle spray dryer to obtain a precipitated silica S3 in accordance with the invention.

[0559] Results obtained for examples 7.1, 7.2 and 7.3

[0560] Physico-chemical characteristics of the precipitated silicas prepared according to the above examples 7.1 to 7.3 were determined. The results are reported in Table 7. Table 7

[0561] Multivalent metal ions are generally known to modify particle size and pore size distributions of precipitated silicas, with possibly detrimental effects on end use properties, for example on mechanical properties of shaped parts made of silica-filled rubber compositions such as wear and / or rolling resistance of tire treads. Surprisingly, silicas SI S2 and S3, despite their very high iron content exhibit the same or substantially the same particle size distribution and the same or substantially the same pore size distribution as reference silica CS1. Thus, advantageously, no effort needs to be undertaken to remove the iron that is generally present in a silicate prepared by the process according to the present invention for allegedly make it suitable for use in the preparation of a precipitated silica having desirable particle size and pore size distributions.

[0562] Example 8 - Silicate preparation

[0563] The unpurified or regenerated spent foundry sand was employed to produce silicate according to the process of the present invention as disclosed in the following Examples 8.1 to 8.8

[0564] Example 8.1

[0565] In a platinum / gold crucible, the following reagents were introduced and mixed together: 18.75 g of regenerated spent foundry sand 7 (SFS7 - according to Example 4.3), 56.25 g of high purity sand, and 37.22 g of ISfeCCE. The crucible was then introduced in an electric furnace high temperature, Model ELV 160 / 08 with a bell oven with lifting hearth, pre-heated at 1150°C. The mixture was left for 2 hours and 30 minutes at 1150°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 7.75 g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C with a ramp of 1 °C / min. Once the temperature was reached, the mixture was left for 7 hours at 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0566] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 8.1” (S8.1).

[0567] Example 8.2

[0568] In a platinum / gold crucible, the following reagents were introduced and mixed together: 37.5 g of regenerated spent foundry sand 7 (SFS7 - according to Example 4.3), 37.5 g of high purity sand, and 37.22 g of ISfeCCh. The crucible was then introduced in an electric furnace high temperature, Model ELV 160 / 08 with a bell oven with lifting hearth, pre-heated at 1150°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 7.75g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C with a ramp of 1 °C / min. Once the temperature was reached, the mixture was left for 7 hours at 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0569] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 8.2” (S8.2).

[0570] Example 8.3

[0571] In an alumina crucible, the following reagents were introduced and mixed together: 56.25 g of regenerated spent foundry sand 7 (SFS7 - according to Example 4.3), 18.75 g of high purity sand, and 37.22 g of ISfeCCE. The crucible was then introduced in an electric furnace high temperature, Model ELV 160 / 08 with a bell oven with lifting hearth, pre-heated at 1150°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 7.75 g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C with a ramp of 1 °C / min. Once the temperature was reached, the mixture was left for 7 hours at 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0572] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 8.3” (S8.3).

[0573] Example 8.4

[0574] In an alumina crucible, the following reagents were introduced and mixed together: 37.5 g of regenerated spent foundry sand 7 (SFS7 - according to Example 4.3), 37.5 g of high purity sand, and 37.22 g of ISfeCCh. The crucible was then introduced in an electric furnace high temperature, Model ELV 160 / 08 with a bell oven with lifting hearth, pre-heated at 1150°C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 7.75 g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C with a ramp of 1 °C / min. Once the temperature was reached, the mixture was left for 7 hours at 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0575] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 8.4” (S8.4).

[0576] Example 8.5

[0577] In an alumina crucible, the following reagents were introduced and mixed together: 75 g of regenerated spent foundry sand 7 (SFS7 - according to Example 4.3) and 37.22 g of ISfeCCE. The crucible was then introduced in an electric furnace high temperature, Model ELV 160 / 08 with a bell oven with lifting hearth, pre-heated at 1450°C. The mixture was left for 2 hours and 30 minutes at 1450 °C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 7.75 g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C with a ramp of 1 °C / min. Once the temperature was reached, the mixture was left for 7 hours at 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0578] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 8.5” (S8.5).

[0579] Example 8.6

[0580] In an alumina crucible, the following reagents were introduced and mixed together: 18.75 g of unpurified spent foundry sand 7 (SFS7 - according to Example 0.8), 56.2 g of high purity sand and 37.01 g of ISfeCCh. The crucible was then introduced in an electric furnace high temperature, Model ELV 160 / 08 with a bell oven with lifting hearth, pre-heated at 1150°C. The mixture was left for 2 hours and 30 minutes at 1150 °C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 7.75 g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C with a ramp of 1 °C / min. Once the temperature was reached, the mixture was left for 7 hours at 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0581] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 8.6” (S8.6).

[0582] Example 8.7

[0583] In an alumina crucible, the following reagents were introduced and mixed together: 37.5 g of unpurified spent foundry sand 7 (SFS7 - according to Example 0.8), 37.5 g of high purity sand and 36.94 g of ISfeCCE. The crucible was then introduced in an electric furnace high temperature, Model ELV 160 / 08 with a bell oven with lifting hearth, pre-heated at 1150°C. The mixture was left for 2 hours and 30 minutes at 1150 °C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 7.75 g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C with a ramp of 1 °C / min. Once the temperature was reached, the mixture was left for 7 hours at 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0584] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 8.7” (S8.7).

[0585] Example 8.8

[0586] In an alumina crucible, the following reagents were introduced and mixed together: 56.25 g of unpurified spent foundry sand 7 (SFS7 - according to Example 0.8) 18.75 g of high purity sand and 36.8 g of ISfeCCh. The crucible was then introduced in an electric furnace high temperature, Model ELV 160 / 08 with a bell oven with lifting hearth, pre-heated at 1150°C. The mixture was left for 2 hours and 30 minutes at 1150 °C. Then the crucible was taken out of the furnace and the silicate was immediately cast on a metallic plate (to quickly cool it down). In a PARR combustion bomb, 7.75 g of vitreous sodium silicate so obtained, and 22.3 g of deionized water were introduced. The PARR combustion bomb was then introduced in an oven. The temperature was raised up to 170 °C with a ramp of 1 °C / min. Once the temperature was reached, the mixture was left for 7 hours at 170 °C and then cooled down until room temperature was reached (there was no ramp for the temperature decrease, the cooling is by inertia).

[0587] The solution obtained was centrifuged at 4500 tr / min for 35 minutes to separate the residual solid and the solution. The sumatant (liquid phase) is a solution of sodium silicate, also called “Silicate 8.8” (S8.8).

[0588] Results

[0589] For each of the liquid sodium silicates obtained according to Examples 8.1 to 8.8 above, the experimental Rp (Rp exp or Rp) was measured by potentiometric method as described below: Table 8

[0590] The profile of the impurities was measured by X-ray fluorescence and is reported in Table 9 below:

[0591] Table 9

[0592]

Claims

C L A I M S1. An alkali metal silicate having an iron content, expressed as iron metal, of at least 100 ppm, based on the amount of SiCh contained in the silicate, wherein the iron content of the silicate and the amount of SiCh contained in the silicate are determined by inductively coupled plasma optical emission spectrometry.

2. The silicate according to claim 1, which is a sodium silicate.

3. The silicate according to claim 2, which has a SiCh / Na?!) ratio Rpof at least 2.5, more preferably in a range from 3.0 to 4.0.

4. The silicate according to any one of the preceding claims, which has an iron content, expressed as iron metal, of at least 250 ppm, based on the amount of SiCh contained in the silicate.

5. The silicate according to claim 4, which has an iron content of at least 400 ppm, possibly of at least 750 ppm, based on the amount of SiCh contained in the silicate.

6. The silicate according to any one of the preceding claims, which has an iron content of at most 2000 ppm, preferably of at most 1500 ppm, more preferably of at most 1250 ppm and still more preferably of at most 1000 ppm, based on the amount of SiCh contained in the silicate.

7. The silicate according to any one of the preceding claims, which has an aluminum content, expressed as aluminum metal, of at least 100 ppm, in particular from 100 ppm to 200 ppm, based on the amount of SiCh contained in the silicate, wherein the aluminum content of the silicate and the amount of SiCh contained in the silicate are determined by inductively coupled plasma optical emission spectrometry.

8. An alkali metal silicate characterized in that it has: an iron content, expressed as iron metal, of at least 400 ppm, based on the amount of SiCh contained in the silicate, wherein the iron content of the silicate and the amount of SiCh contained in the silicate are determined by inductively coupled plasma optical emission spectrometry, an aluminum content, expressed as aluminum metal, of at least 100 ppm, based on the amount of SiCh contained in the silicate, wherein the aluminum content of the silicate and the amount of SiCh containedin the silicate are determined by inductively coupled plasma optical emission spectrometry, and a SiO2 / Na2O ratio Rpin a range from 3.0 to 4.0.

9. A process for the preparation of a silicate from a spent foundry sand comprising the steps of:(i’) optionally, purifying the spent foundry sand,(i) melting the spent foundry sand and, optionally in addition a sand other than a spent foundry sand, in a furnace in the presence of a base by heating at a temperature of at least 850 °C so as to obtain a molten vitreous silicate, followed by(ii) cooling down from the temperature of step (i) to a temperature below 550 °C the molten vitreous silicate in a period of time of less than 30 minutes so as to obtain solidification of the molten vitreous silicate into a solid silicate, wherein said solid silicate is an amorphous solid silicate; and(ii’) optionally milling said solid silicate.

10. The process according to claim 9, wherein the base is used in an amount of up to 50% by weight, preferably of at least 30% by weight, more preferably comprised between 34% and 36% by weight, based on the total weight of the spent foundry sand, the sand other than a spent foundry sand if any, and the base in the furnace.

11. The process according to claim 9 or 10, wherein the silicate is an alkali metal silicate, preferably sodium silicate, and wherein the base is an alkali metal base, preferably selected from the group consisting of an alkali metal hydroxide, an alkali metal (hydrogen)carbonate, an alkali metal sulphate, or a combination thereof, more preferably an alkali metal carbonate, even more preferably ISfeCCh.

12. The process according to any of claims 9 to 11 wherein step (i) is carried out by heating at a temperature of at least 1000 °C, preferably at a temperature of up to 1600 °C, more preferably between 1000 °C and 1600 °C, even more preferably between 1200 °C and 1500 °C, most preferably between 1400 °C and 1500 °C.

13. The process according to any of claims 9 to 12, wherein step (i) carried out for a period of time of at least 10 minutes, preferably of at least 30 minutes, more preferably of between 30 minutes and 3 hours.

14. The process according to any of claims 9 to 13 wherein step (ii) is carried out in a period of less than 20 minutes, more preferably of less than 10 minutes, preferably by casting the molten vitreous silicate on a plate, preferably a metallic plate, wherein said plate is at room temperature.

15. The process according to any of claims 9 to 14, further comprising the steps of:(iii) dissolving the solid vitreous silicate in a liquid medium, preferably an aqueous liquid medium, so as to obtain a liquid mixture comprising silicate and, if any, solid by-products,(iv) if any solid by-products are comprised in said liquid mixture, separating said solid by-products from the liquid mixture to obtain a solution of silicate, preferably an aqueous solution of silicate, and(v) optionally adding to said solution of silicate, at least one of a secondary silica source, an alkali metal hydroxide, preferably NaOH, a silicate other than the silicate obtained in step (iv), or a mixture thereof.

16. The process according to claim 15, wherein step (iii) comprises: (iii. a) heating up the liquid mixture to a temperature of up to 180 °C, preferably with a rate of from 0.5 to 5 °C / min, preferably maintaining the liquid mixture at said temperature for at least 0.4 hours, and(iii.b) cooling down said liquid mixture by inertia until room temperature is reached.

17. The process according to claim 15 or 16 further comprising a step of:(vi) drying the liquid mixture obtained in step (iii) or (iii.b) or the solution of silicate obtained in step (iv) or (v) so as to obtain a solid silicate.

18. The process according to any of claims 9 to 17, wherein the silicate obtained in any of steps (ii), (ii’), (iii), (iii.b), (iv), (v), and / or (vi) is characterized by a SiCh / MxO molar ratio of at least 2, preferably of at least 2.5, more preferably comprised between 2 and 4, even more preferably comprised between 3 and 4, most preferably of about 3.5, wherein M is a metal, preferably wherein M is an alkali metal and x is 2, and preferably wherein said silicate is characterized by an amount ofSiC>2 of up to 100% of the amount of silica contained in the sand used in step (i), preferably by an amount of between 70 % and 100%.

19. The process according to any one of claims 9 to 18 comprising step (i’), before step (i), of purifying the spent foundry sand by applying thereto a pre-treatment, wherein said pre-treatment is preferably selected from the group consisting of: sieving, mechanical attrition, density selection, granulometry selection, magnetic removal of magnetic elements, impurity dilution by addition of pure sand, or a combination thereof.

20. The process according to any of claims 9 to 19, wherein said process is free of any thermal treatment of the spent foundry sand before step (i).

21. The process according to any of claims 9 to 20 wherein the prepared alkali metal silicate is the alkali metal silicate according to any of claims 1 to 7 or the alkali metal silicate according to claim 8.

22. A process for the preparation of a silicate from a spent foundry sand comprising the steps of:(i’) purifying the spent foundry sand, by applying thereto a pretreatment, wherein said pre-treatment is preferably selected from the group consisting of: sieving, mechanical attrition, density selection, granulometry selection, magnetic removal of magnetic elements, impurity dilution by addition of pure sand, or a combination thereof,(i) melting the spent foundry sand and, optionally in addition a sand other than a spent foundry sand, in a furnace in the presence of a base by heating at a temperature of at least 850 °C so as to obtain a molten vitreous silicate, followed by(ii) cooling down from the temperature of step (i) to a temperature below 550 °C the molten vitreous silicate in a period of time of less than 30 minutes so as to obtain solidification of the molten vitreous silicate into a solid silicate, wherein said solid silicate is an amorphous solid silicate; and(ii’) optionally milling said solid silicate.

23. An alkali metal silicate obtained by the process according to any one of claims 9 to 20 or the process according to claim 22, having an iron content, expressed as iron metal, of at least 100 ppm, based on the amount of SiCh contained in the silicate, wherein the iron content of thesilicate and the amount of SiCh contained in the silicate are determined by inductively coupled plasma optical emission spectrometry.

24. An alkali metal silicate obtained by the process according to any one of claims 9 to 20 or the process according to claim 22, characterized in that it has: an iron content, expressed as iron metal, of at least 400 ppm, based on the amount of SiCh contained in the silicate, wherein the iron content of the silicate and the amount of SiCh contained in the silicate are determined by inductively coupled plasma optical emission spectrometry, an aluminum content, expressed as aluminum metal, of at least 100 ppm, based on the amount of SiCh contained in the silicate, wherein the aluminum content of the silicate and the amount of SiCh contained in the silicate are determined by inductively coupled plasma optical emission spectrometry, and a SiO2 / Na2O ratio Rpin a range from 3 to 4.

25. A precipitated silica having an iron content, expressed as iron metal, of at least 100 ppm, based on the amount of SiCh contained in the precipitated silica, wherein the iron content of the precipitated silica and the amount of SiCh contained in the precipitated silica are determined by inductively coupled plasma optical emission spectrometry.

26. The precipitated silica according to claim 25, which has an iron content, expressed as iron metal, of at least 250 ppm, based on the amount of SiCh contained in the precipitated silica.

27. The precipitated silica according to claim 26, which has an iron content of at least 400 ppm, possibly of at least 750 ppm, based on the amount of SiCh contained in the precipitated silica.

28. The precipitated silica according to any one of claims 25 to 27, which has an iron content of at most 2000 ppm, preferably of at most 1500 ppm, more preferably of at most 1250 ppm and still more preferably of at most 1000 ppm, based on the amount of SiCh contained in the precipitated silica.

29. The precipitated silica according to any one of claims 25 to 28, which has an aluminum content, expressed as aluminum metal, in a range from 50 to 250 ppm, in particular from 100 ppm to 200 ppm, based on the amount of SiCh contained in the precipitated silica, wherein the aluminumcontent of the precipitated silica and the amount of SiCh contained in the precipitated silica are determined by inductively coupled plasma optical emission spectrometry.

30. The precipitated silica according to any one of claims 25 to 28, which has an aluminum content, expressed as aluminum metal, in a range from 250 to 400 ppm, in particular from 300 ppm to 400 ppm, based on the amount of SiCh contained in the precipitated silica, wherein the aluminum content of the precipitated silica and the amount of SiCh contained in the precipitated silica are determined by inductively coupled plasma optical emission spectrometry.

31. A precipitated silica characterized in that it has:- an iron content, expressed as iron metal, of at least 400 ppm, based on the amount of SiCh contained in the precipitated silica, wherein the iron content of the precipitated silica and the amount of SiCh contained in the precipitated silica are determined by inductively coupled plasma optical emission spectrometry, and- an aluminum content, expressed as aluminum metal, in a range from 50 to 250 ppm or in a range from 250 to 400 ppm, based on the amount of SiCh contained in the precipitated silica, wherein the aluminum content of the precipitated silica and the amount of SiCh contained in the precipitated silica are determined by inductively coupled plasma optical emission spectrometry.

32. Use of the silicate according to anyone of claims 1-7, the silicate according to claim 8, the silicate according to claim 23, or the silicate according to claim 24 for the preparation of silica, in particular, precipitated silica.

33. A process for the preparation of precipitated silica comprising the steps of:(I) preparing a silicate by the process according to any one of claims 9 to 21 or the process according to claim 22,(II) reacting the silicate obtained in step (I) and, optionally in addition a silicate other than said silicate obtained in step (I), with at least one acidifying agent in a liquid medium, preferably an aqueous liquid medium, to obtain a suspension of precipitated silica,(III) separating the precipitated silica from the liquid medium to provide wet precipitated silica, and(IV) drying said wet precipitated silica to obtain precipitated silica.

34. A process for the preparation of precipitated silica comprising the steps of:(I) preparing a silicate by the process according to any one of claims 9 to 21 or the process according to claim 22,(I’) adding to the silicate obtained in step (I) at least one of a secondary silica source, an alkali metal hydroxide, preferably NaOH, a silicate other than the silicate obtained in step (I), or a mixture thereof, so as to obtain a new silicate(II) reacting the new silicate obtained in step (I’) and, optionally in addition a silicate other than the new silicate obtained in step (I’), with at least one acidifying agent in a liquid medium, preferably an aqueous liquid medium, to obtain a suspension of precipitated silica,(III) separating the precipitated silica from the liquid medium to provide wet precipitated silica, and(IV) drying said wet precipitated silica to obtain precipitated silica.

35. The process according to claim 33 or claim 34 wherein the prepared silicate is the alkali metal silicate according to any of claims 1 to 7 or the alkali metal silicate according to claim 8.

36. The process according to any one of claims 33 to 35 wherein the prepared precipitated silica is the precipitated silica according to any one of claims 25 to 30 or the precipitated silica according to claim 31.

37. A precipitated silica obtained by the process according to any one of claims 33 to 35 characterized in that it has an iron content, expressed as iron metal, of at least 100 ppm, based on the amount of SiCh contained in the precipitated silica, wherein the iron content of the precipitated silica and the amount of SiCh contained in the precipitated silica are determined by inductively coupled plasma optical emission spectrometry.

38. A precipitated silica obtained by the process according to any one of claims 33 to 35 characterized in that it has:- an iron content, expressed as iron metal, of at least 400 ppm, based on the amount of SiCh contained in the precipitated silica, wherein the iron content of the precipitated silica and the amount of SiCh contained in theprecipitated silica are determined by inductively coupled plasma optical emission spectrometry, and- an aluminum content, expressed as aluminum metal, in a range from 50 to 250 ppm or in a range from 250 to 400 ppm, based on the amount of SiCh contained in the precipitated silica, wherein the aluminum content of the precipitated silica and the amount of SiCh contained in the precipitated silica are determined by inductively coupled plasma optical emission spectrometry.

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