HK1094572A - Method of producing synthetic silicates and use thereof in glass production - Google Patents

Description

Synthetic silicates and their use in glass production

The application is a divisional application of Chinese patent application with the application number of 98812725.3, the application date of 30.12.1998 and the invention name of "artificial silicate and application thereof in glass production".

Technical Field

The invention relates to a composition for preparing glass and a production method thereof. More particularly, the present invention relates to an alkali metal precursor material prepared from calcium and magnesium oxides, water and sodium silicate and silica sand. The material is particularly useful in glass production and results in reduced energy consumption, while the volatile matter associated with the glass production materials is reduced.

Background

The glass may be formed from a glass former defined by glass disordered network theory as a material having a heavy cation-oxygen bond strength greater than about 335 kilojoules/mole. Typical formers are oxides such as B₂O₃、SiO₂、GeO₂、P₂O₅、As₂O₅、P₂O₃、As₂O₃、Sb₂O₃、V₂O₅、Sb₂O₅、Nb₂O₅And Ta₂O₅. Fluoride BeF₂Can also be used as a formed body. Other ingredients may be mixed with the glass former to provide a variety of different effects. These compositions include glassThe glass intermediate and glass modifier, the intermediate having a bond strength of about 250-350 kJ/mol, and which may or may not become part of the network; while the modifier bond strength is less than about 250 kilojoules/mole and it does not become part of the network. Typical modifiers are oxides of gallium, magnesium, lithium, zinc, calcium, sodium and potassium. Other formers, intermediates and modifiers are also well known and are described in "glass", Kirk-Othmer encyclopedia of chemical technology, volume 12, page 555 (1994).

One form of glass is a silicate system containing modifiers and intermediates. Such silicates have a network of silicon and oxygen formed by bonding. These silicon-oxygen bonds can be cleaved to form sodium terminated chains using a modifier such as sodium oxide. Other modifiers may also be used. Such modifiers may result in better glass flow, lower electrical resistance, increased thermal expansion, lower chemical stability or increased flow.

Soda lime glass is probably the most common glass article. Such soda-lime glasses contain a mixture of alkali and alkaline earth metals. These glasses can be produced with oxides of sodium, calcium, silicon, magnesium, aluminum, barium, and potassium.

Most glasses are produced by a process in which the raw materials are brought to a high temperature to form a homogeneous melt. The starting material used is typically sand, as the silicon source; limestone or dolomitic lime as a source of calcium and/or magnesium; and soda ash or caustic as a sodium source. Limestone is typically high calcium limestone (95% calcite, CaCO)₃) Aragonite, or dolomitic limestone (dolomite CaMg (CO)₃)₂And mixtures of calcites). Soda ash (sodium carbonate Na)₂CO₃) But the mineral deposit is the product of the Solvay process. A typical production process involves the quantitative mixing of sand, soda ash, limestone and other materials at temperatures above 1000 ℃.

There is therefore a continuing need to develop new processes and materials that facilitate the production of glass while saving energy and increasing the yield.

Us.5004706 discloses a process for producing molten glass in which silica is heated with other components of the batch, including sodium alkaline earth silicates, which in turn include a major portion of the sodium in the final molten glass. The patent also discloses a composition of matter for use in the production of glass that includes a soda-lime silicate and optionally a soda-magnesium silicate. Also disclosed is a method of producing a composition of matter comprising a sodium calcium silicate, comprising heating a source of sodium oxide, a source of silica, and a source of calcium silicate or calcium oxide at a temperature greater than 800 ℃, wherein Na is₂O∶CaO∶SiO₂The molar ratio is 1: 1. The final feed components can be preheated without the necessity of melting prior to mixing and feeding into the furnace.

US4920080 discloses a method for the production of glass, wherein silica is reacted with sodium carbonate to form sodium silicate as an initial step. The final sodium silicate is mixed with a calcium carbonate containing material (which is preferably a calcined material, thereby evolving carbon dioxide prior to contact with the sodium silicate). The patent suggests that: the process maximizes the recovery of waste heat from the glass melting process and minimizes the gaseous inclusions in the glass by making the final material substantially free of carbon dioxide.

US4023976 discloses an improved process for making glass in which a glass mass is mixed with a binder, aged, kneaded, and pressed into a green mass, which is heated to partially react the contents of the mass in a preheating stage. The method minimizes segregation and non-homogeneity in the glass material and reduces the operating temperature of the glass melting furnace.

US3883364 discloses a dust-free alkaline earth carbonate particulate material which is particularly suitable as a raw material for glass melting furnaces. The process for preparing the particulate material comprises: the as-prepared aqueous slurry of alkaline earth carbonate is mixed with a solution of alkali silicate, the slurry is dried and sintered at a temperature of about 700-900 c, thereby converting the solids of the aqueous slurry into a dense material that can be ground to a dust-free, free-flowing form suitable for use as raw material in a glass furnace.

Us.3967934 discloses a method of modifying a molten glass batch by using an aqueous sodium silicate solution as a batch ingredient to provide about 1-10% Na₂Total content of O, while conventional sodium-containing materials provide significant amounts of Na₂And (4) the content of O. The patent suggests that: the addition of the aqueous sodium silicate solution may result in a reduction in melting temperature and/or fuel used during melting. As a result, dusting is also reduced and the incidence of glass inhomogeneity or defects is also reduced.

Disclosure of Invention

The invention relates to a method for producing a molten silicate product by using an artificial silicate, wherein the artificial silicate can be produced by mixing a source of digested calcium and/or magnesium and a source of silica. Preferably, the artificial silicate may be prepared by a water-soluble silicate technical route or a silica sand technical route. Advantageously, the synthetic silicate may form cylindrical particles.

In accordance with one or more aspects of the present invention, the present invention provides the advantages of energy savings and other benefits, including (but not limited to) reduced carbon dioxide emissions, reduced bubble formation, reduced impurities in the formed glass, increased furnace output, more quantitative ratios of the elements in the produced glass, and improved material homogeneity.

One embodiment of the present invention is a method of producing a molten silicate article, the method comprising: the digested calcium source and/or magnesium source is admixed with a silica source to form a silicate material (hereinafter referred to as an artificial silicate) comprising one or more compounds selected from the group consisting of calcium silicate, magnesium silicate and magnesium calcium silicate, which artificial silicate may be a precursor material for the production of glass or other silicate articles. The synthetic silicate optionally contains free water as residual water resulting from the digestion process producing the digested calcium and/or magnesium source. The method further includes blending the artificial silicate with a second silica source under suitable production conditions to produce a molten silicate article. The second silica source may be the same silica source used to produce the synthetic silicate or a different silica source.

The molten silicate product produced depends on the choice of raw materials and the corresponding conditions of production of the silicate product. The molten silicate is preferably a glass precursor suitable for producing glass articles including, but not limited to, glass containers, glass bottles, glass windows (e.g., buildings, vehicles, etc.), glass fibers, optical glasses, optical fibers, and the like, and other glass articles such as those produced with the addition of aluminum, boron, gallium, and the like.

The calcium source and/or magnesium source may be any natural or man-made material capable of being digested with water, such as calcium oxide and/or magnesium oxide which is reactive with water. Such calcium and/or magnesium sources may be natural types of calcium and/or magnesium oxide, or may be ground, calcined, or otherwise processed. A non-limiting example thereof is wollastonite (CaO. SiO)₂) Diopside (CaO. MgO. multidot.2SiO)₂) Akermanite (2 CaO. MgO. 2 SiO)₂) Calcium silicate (CaO. SiO)₂) Dolomites (i.e., dolomitic lime, CaO · MgO), and various forms of lime such as quicklime, hydrated lime, slaked lime, and high calcium lime (i.e., 95% or more active).

Preferred calcium and/or magnesium sources include dolomitic lime and high calcium lime. The calcium source and/or magnesium source may be digested with water at ambient temperature or pressure. High temperatures and pressures may also be used. When more than one calcium and/or magnesium source is used, mixing may be performed before, during, or after digestion. The amount of water is preferably at least the stoichiometric amount at complete digestion, but may also be an amount that is in excess such that the digested calcium and/or magnesium source contains an amount of free water.

The silica source may be any convenient silica source that can be blended with the specific source of slaked calcium and/or magnesium to form the artificial silicate. For example, the silica source may be silica in which silica is not combined with other compounds, and silica as a natural material, exemplified by sand, quartz, and the like. The silica source may be silica combined with other compounds, and as such silica, sodium silicate is exemplified.

In addition to the silica source, one or more of a calcium source, a magnesium source, and a sodium source may also be required in order to complete the production of the glass or other silicate material. For example, one or more of limestone, dolomite, and soda ash materials may be used. Depending on the desired composition. The use of such materials can result in the evolution of volatile gases, such as carbon dioxide, in the process. Therefore, it is desirable to minimize the use of such materials.

The digested calcium source and/or magnesium source may be admixed with a silica source at the same time as or after digestion to form a digested source. The proportions of the calcium source and/or magnesium source, the digestion water, and the silica source may be varied to produce a variety of different artificial silicates. The preferred weight ratio of water to calcium and/or magnesium sources during digestion will also vary with the desired product, and the water temperature at the time of digestion.

The blending of water with the calcium source and/or magnesium source may be fed sequentially or simultaneously. The blending time of the silica with the digested calcium source and/or magnesium source is about 5 seconds to 2 hours, preferably about 10 seconds to 30 seconds.

The blending and continuous stirring of the silica and calcium and/or magnesium sources, if necessary, is effected to form an artificial silicate suitable for the production of glass or other silicate articles. When excess water (free water) is present, the material is in a slurry state. Additional materials may be added to the slurry during or after blending or stirring, depending on the composition and type of glass or other silicate product formed with the synthetic silicate. For example, if additional silica is desired, a silica source, such as silica powder, may be added. Also, the slurry may be treated, such as by filtration, evaporation or heating, to remove at least a portion of the free water before such synthetic silicates are used in the production of glass. For example, the slurry may be dried at a temperature of about 110 ℃.

The slurry may also be further heat treated at higher temperatures, such as at about 110-1100 deg.C or higher. The heating time and speed may vary depending on the ultimate desired synthetic silicate, as such heating may further result in a reaction or a continuous reaction.

The artificial silicates produced by the present invention can have a wide variety of one or more of calcium silicate, magnesium silicate, and/or magnesium calcium silicate components. Such variations in silicate composition are related to variations in the amounts of calcium source, magnesium source, water and silica source, as well as operating conditions such as temperature, pressure, time, stirring, and the like.

Detailed Description

Water soluble silicate technology route

One embodiment of the present invention is a method of producing molten glass comprising the steps of: blending the digested calcium source and/or magnesium source with a water-soluble silicate to form an artificial silicate. The artificial silicate optionally contains free water, which may be residual water formed by the digestion process. The method further comprises the following steps: the synthetic silicate and a silica source, preferably silica, are mixed to form a glass article.

Preferred calcium and/or magnesium sources include dolomitic lime and high calcium lime. The calcium source and/or magnesium source may be digested with water at ambient temperature or pressure. High temperatures and pressures may also be used. When more than one calcium and/or magnesium source is used, mixing may be performed before, during, or after digestion. The amount of water is preferably at least the stoichiometric amount at complete digestion, but may also be an amount that is in excess so that the digested calcium and/or magnesium source contains an amount of free water (unreacted).

A water-soluble silicate is a silicate that has sufficient solubility in water to be able to react with the source of calcium being digested. The preferred water-soluble silicate is sodium silicate. The sodium silicate may be dry or liquid and anhydrous or aqueous, preferably sodium silicate pentahydrate.

In addition to the silica source, one or more of a calcium source, a magnesium source, and a sodium source may be required in order to complete the production of the glass. For example, one or more of limestone, dolomite, and soda ash materials may be used. Depending on the desired composition. The use of such materials can result in the evolution of volatile gases, such as carbon dioxide, in the production of glass. Therefore, it is desirable to minimize the use of such materials.

In a preferred embodiment, the sodium silicate is of the formula Na₂O·XSiO₂Wherein X is 0.5 to 3.75, preferably Na₂O·SiO₂、Na₂O·SiO₂·5H₂O and Na₂O·10/3SiO₂. When the sodium silicate is anhydrous, it is preferably admixed with the source of digested calcium after digestion is complete.

The digested calcium source and/or magnesium source may be admixed with the water-soluble silicate at the same time as or after digestion to form a digested source. The proportions of the calcium source and/or magnesium source, the digested water and the water-soluble silicate may be varied to form a variety of different silicates. In a preferred embodiment, the calcium source and/or magnesium source is a mixture of dolomitic lime and high calcium lime, the mixing ratio of which may also vary, the weight ratio of dolomitic lime to high calcium lime being preferably from about 100: 1 to about 1: 100, more preferably from about 4: 1 to about 2: 1. The preferred weight ratio of water to lime during digestion is from about 10: 1 to about 0.35: 1, more preferably from about 2.5: 1 to about 1: 1. The water temperature for digesting the calcium source is preferably about 10 to 90 c, more preferably about 20 to 30 c.

The blending of water with the calcium source and/or magnesium source may be fed sequentially or simultaneously. Preferably, water is added to the digested calcium source and/or magnesium source over a period of about 5 seconds to 2 hours, preferably about 10 seconds to 30 seconds. Digestion times are preferably from about 1 to about 60 minutes, more preferably from about 2.5 to about 10 minutes.

The amount of water-soluble silicate blended with the digested calcium source and/or magnesium source is preferably: the weight ratio of water-soluble silicate to digested calcium source and/or magnesium source (dry) is about 0.044-2.2, more preferably about 0.048-1.2. The time for blending the water-soluble silicate with the digestion source may preferably be about 5 seconds to 2 hours, more preferably 10 seconds to 30 seconds. The blend of water-soluble silicate and calcium and/or magnesium source is preferably subjected to continuous stirring for a period of about 5 minutes to about 2 hours, more preferably about 30 minutes to about 1 hour.

The blending and continuous stirring (if necessary) of the water-soluble silicate and the digested calcium and/or magnesium source is effected to form an artificial silicate suitable for glass production. When excess water (free water) is present, the material is in a slurry state. Additional materials may be added to the slurry during or after blending or stirring, depending on the composition and type of glass formed with the synthetic silicate. For example, if additional silica is desired, a silica source, such as silica powder, may be added. Also, the slurry may be treated, such as by filtration, evaporation or heating, to remove at least a portion of the free water before such synthetic silicates are used in the production of glass. For example, the slurry may be dried at a temperature of about 110 ℃.

The slurry may also be further heat treated at higher temperatures, such as at about 110-. The heating time and speed may vary depending on the ultimate desired synthetic silicate, as such heating may further result in a reaction or a continuous reaction.

The artificial silicates produced using water-soluble silicates can have a wide variety of one or more of calcium silicate, magnesium silicate, and/or magnesium calcium silicate components. The change in silicate composition is related to changes in the amounts of calcium source, magnesium source, water and water-soluble silicate, as well as operating conditions such as temperature, pressure, time, agitation, and the like. In a preferred embodimentIn an embodiment of (1), the artificial silicate has Na_ACa_BMg_C(O)_D(OH)_ESi_FO_G·XH₂Formula O, wherein one of D and E is zero and the other labeled parameters vary with the above conditions. Table 1 discloses in a non-limiting manner the possible relationship between the amount of work and the resulting artificial silicate.

TABLE 1

Weight ratio of

Lime	Water (W)	Water-soluble silicon dioxide	Product of
				1	1	0.5	Ca5(OH)2Si6O16·4H2O
1	1	0.7	Ca5(OH)2Si6O16·4H2O
				1	3.3	1.2	Ca5(OH)2Si6O16·4H2O
1	3.3	0.7	(CaO)1.5·SiO2·H2O
				1	3.3	1.2	(CaO)1.5·SiO2·H2O
1	7	1.1	(CaO)·SiO2·H2O

In a preferred embodiment, the artificial silicate produced from the water-soluble silicate comprises one or more components selected from the group consisting of those represented by the general formula (CaO)_x·SiO₂·Y(H₂O) is represented by formula (I), wherein X is 5/6-3/2 and Y is not zero. More preferably, X is 1.5 and Y is 1.

In another preferred embodiment, the artificial silicate produced from the water-soluble silicate comprises one or more components selected from the group consisting of those represented by the general formula X (Na)₂O)·Y(CaO)·SiO₂And optionally also comprises a compound represented by the general formula W (Na)₂O)·V(MgO)·SiO₂Compounds of formula (I) wherein X and W are each independently 1/6-1/1 and W and V are each independently 1/3-1/1. Preferably, the artificial silicate precursor material comprises 0.5 (Na)₂O)·1(CaO)·SiO₂. More preferably, the artificial silicate precursor material further comprises: na (Na)₂O·MgO·SiO₂。

In another aspect, the present invention fixes the disclosed reaction process parameters within a novel set of process parameters that yield satisfactory results. Thus, the present invention may be the above-described invention in which the quantitative ratio between the artificial silicate and the silica source is effectively controlled to thereby lower the temperature required to produce molten glass in a fixed time. Alternatively, the quantitative ratio between the synthetic silicate and the silica source is effectively controlled to reduce the time required to produce molten glass at a fixed temperature. On the other hand, the temperature and the time can be reduced at the same time by effectively controlling the above ratio. Various parameters constituting the above parameters can also be controlled. For example, molten glass is produced by fixing a set of parameters including the number of calcium and/or magnesium sources after digestion, the number of water-soluble silicates, the amount of free water, the number of silica sources, the time and temperature at which the molten glass is produced. Once a certain number of parameters are determined, the remaining parameters will depend on their degrees of freedom. The amount of other calcium, magnesium or sodium sources such as limestone, dolomite and soda ash can vary with these parameters, and will depend on the desired glass composition.

The following examples are intended to illustrate, but not limit, the scope of the invention when water-soluble silicates are used.

Example 1

The following process is a process for producing a blend of sodium calcium silicate and sodium magnesium silicate, the reaction being carried out in a paddle mixer. A calcium oxide source and a magnesium oxide source comprising 37.2 grams of dolomitic lime (55.1% CaO, 42.5% MgO) and 13.2 grams of high calcium lime (96% active) were premixed in a blender. To the mixed oxide, 210 grams of dried sodium silicate pentahydrate was added, thus providing sufficient silica to react with all of the calcium oxide and magnesium oxide in a 1: 1 molar ratio. To this dry mixture was added 50 grams of water. The slurry was stirred for 30 minutes. After the reaction was complete, the free water was removed in a kiln at 110 ℃. Subsequently, the dried material was heated to 400 ℃ in a kiln. X-ray diffraction (XRD) was used to confirm that: the phase formed in this reaction is Na₂MgSiO₄And Na₂Ca₂Si₂O₇。

Example 2

An example of this process is the reaction of Na₂MgSiO₄And Na₂Ca₂Si₂O₇Precursor materials are used in glass production. The glass comprises the following ingredients: 74.1% SiO₂、13.3％Na₂O, 8.6% CaO, and 4.1% MgO. The precursor material is composed of 100% of the required Na₂O, CaO and MgO and 21% SiO required₂And (4) forming. Thereafter, 67.9 grams of SiO were added to 50 grams of the precursor material₂And (4) sand. Preparing calcium carbonate as CaO source, magnesium carbonate as MgO source and sodium carbonate as Na₂The O source formed a control of the glass batch composition described above. Subsequently, both sets of mixtures were heated to 1300 ℃ and 1400 ℃ for 1, 3, 6 and 12 hours, respectively. Grinding and feeding glass sampleAnd performing XRD test. The percentage of amorphous glass for these samples was as follows:

1300℃	test of	Comparison of	1400℃	Test of	Comparison of
						1 hour	90	80		98	85
3 hours	98	90		98	85
						6 hours	-	-		98	95
12 hours	-	-		99	99

At this time and this temperature, the percentage of the control is greater at low temperatures (i.e., 90 to 85) due to thermodynamic effects in the formation of cristobalite.

Example 3

The following procedure is a method for synthesizing calcium silicate hydrate, the reaction being carried out in a paddle stirrer. 300 grams of dolomitic lime consisting of 55.1% CaO and 42.5% MgO was digested with 500 grams of water in a paddle mixer for 10 minutes. In addition, 100 grams of high calcium lime was digested with 500 grams of water. Both samples were passed through a 60 mesh screen. 400 ml of dolomitic digestate and 500 ml of calcium digestate were placed in the blender. 945 g of liquid sodium N-type silicate was added to the mixed digests. The addition of sodium silicate took 5 minutes. Sodium silicate provides sufficient water soluble silica to react with MgO and CaO in a 1: 1 molar ratio. The slurry was stirred for 60 minutes. After the reaction was complete, the free water was removed in a kiln at 110 ℃. The dried material was then heated to 400 ℃ in a kiln. X-ray diffraction (XRD) was used to confirm that: the phase formed in this reaction is (CaO)_1.5SiO₂·H₂O, together with unreacted MgO and excess sodium silicate.

Example 4

An example of a list of the process is (CaO)_1.5SiO₂·H₂The O precursor material is used in glass. The glass comprises the following ingredients: 74.1% SiO₂、13.3Na₂O, 8.6% CaO, and 4.1% MgO. The precursor material consists of 100% of required CaO and MgO and 21% of required Si₂O and 35% of required Na₂And (C) O. Thereafter, 36.1 grams of SiO were added to 20 grams of the precursor material₂And 9 g of soda ash. Preparing calcium carbonate as CaO source, magnesium carbonate as MgO source and sodium carbonate as Na₂The O source formed a control of the glass batch composition described above. Subsequently, both sets of mixtures were heated to 1300 ℃ and 1400 ℃ for 1, 3, 6 and 12 hours, respectively. Glass samples were ground and subjected to XRD testing. The percentage of amorphous glass for these samples was as follows:

1300℃	test of	Comparison of	1400℃	Test of	Comparison of
						1 hour	95	80		98	85
3 hours	98	90		99	85
						6 hours	-	-		99	95
12 hours	-	-		99	99

At this time and this temperature, the percentage of the control is greater at low temperatures due to the thermodynamic effect of cristobalite formation.

Path of silica sand technology

Another preferred embodiment of the present invention is a method of producing molten glass comprising the steps of: the calcium source and/or magnesium source digested and sieved to remove impurities (e.g., a size control step) is blended with a silica source, preferably silica, and the blend is subsequently heated at elevated temperatures to form an artificial silicate (e.g., calcium magnesium silicate, and/or calcium silicate). The method still further comprises: the synthetic silicate and a second silica source and a second sodium source, preferably soda ash, are mixed to form a glass article. The second silica source may be the same or different from the silica sand.

The calcium source and/or magnesium source may be any natural or man-made material capable of being digested with water, such as calcium oxide and/or magnesium oxide which is reactive with water. Such calcium and/or magnesium sources may be natural types of calcium and/or magnesium oxide, or may be ground, calcined, or otherwise processed. A non-limiting example thereof is wollastonite (CaO. SiO)₂) Diopside (CaO. MgO. multidot.2SiO)₂) Akermanite (2 CaO. MgO. 2 SiO)₂) Calcium silicate (CaO. SiO)₂) Dolomites (i.e. dolomites)Lime, CaO · MgO) and various forms of lime such as quicklime, hydrated lime, slaked lime, and high calcium lime (i.e., 95% or more active).

Preferred calcium and/or magnesium sources are dolomitic lime and high calcium lime. The calcium source and/or magnesium source may be digested with water at ambient temperature or pressure. High temperatures and pressures may also be used. When more than one calcium and/or magnesium source is used, mixing may be performed before, during, or after digestion. Moreover, a portion of the calcium and magnesium may be derived from calcite and dolomite sources. Calcite and dolomite may be blended with lime prior to or during digestion. The percentage of calcite or dolomite substitution of calcium and magnesium may be 0-100%. The preferred range is about 25-50%. The use of calcium carbonate and magnesium carbonate has the advantage of reducing raw material costs. The amount of water is preferably at least the stoichiometric amount at complete digestion, but may also be an amount that is in excess so that the digested calcium and/or magnesium source contains an amount of free water (unreacted).

The digested calcium and/or magnesium source may then be sieved to remove impurities. The size of the screen may vary from about 10 mesh to about 325 mesh. More preferably, the size of the screen may be approximately 30 mesh to 60 mesh. Non-limiting examples of impurities are iron particles, gravel, refractory residues, inclusions and other particles that do not melt in the glass batch.

The silica source may be any natural or man-made silica source of varying size, examples of which include, but are not limited to, silica sand, silica fume, precipitated silica, and the like.

In addition to the silica source, one or more of a calcium source, a magnesium source, and a sodium source may be required in order to complete the production of the glass. For example, one or more of limestone, dolomite, and soda ash materials may be used. Depending on the desired glass composition. The use of such materials can lead to the emission of volatile gases, such as carbonates, in the production of glass. Therefore, it is desirable to minimize the use of such materials.

The digested calcium and/or magnesium sources may be blended with silica sand simultaneously with or after digestion to form a digested source. Preferably, the lime, carbonate and silica sand are ground together prior to digestion. The proportions of the calcium and/or magnesium source, the digestion water and the silica sand may be varied to form a variety of different silicates. In a preferred embodiment, the calcium source and/or magnesium source is a mixture of dolomitic lime and/or high calcium lime, the mixing ratio of which may also vary, the weight ratio of dolomitic lime to high calcium lime preferably being from about 100: 1 to about 1: 100, more preferably from about 4: 1 to about 2: 1. The preferred weight ratio of water to lime during digestion is from about 10: 1 to about 0.35: 1, more preferably from about 2.5: 1 to about 1: 1. The water temperature for digesting the calcium source and/or magnesium source is preferably about 10 to 90 c, more preferably about 20 to 30 c.

The blending of water with the calcium source and/or magnesium source may be fed sequentially or simultaneously. Preferably, the water is added to the calcium source and/or the magnesium source over a period of about 5 seconds to 2 hours, preferably about 30 seconds. Digestion times are preferably from about 1 to about 60 minutes, more preferably from about 2.5 to about 15 minutes.

The amount of silica sand blended with the digested calcium source and/or magnesium source is preferably: the weight ratio of silica sand to digested calcium and/or magnesium source (dry) is about 0.044-2.2, more preferably about 0.048-1.2. The blending time of the silica sand with the digested calcium and/or magnesium source may preferably be from about 5 seconds to about 2 hours, more preferably from about 10 seconds to about 30 seconds. The blend of silica sand and digested calcium and/or magnesium source is preferably subjected to continuous stirring for a period of about 1 minute to 2 hours, more preferably about 5 minutes to 30 minutes.

The blending and continuous stirring (if necessary) of silica sand and digested calcium and/or magnesium sources is effectively carried out to form an artificial silicate suitable for glass production. When excess water (free water) is present, the material is in a slurry state. Additional materials may be added to the slurry during or after blending or stirring, depending on the composition and type of glass formed with the synthetic silicate. For example, if additional silica is desired, a silica source, such as silica powder, may be added. Also, the slurry may be treated, such as by filtration, evaporation or heating, to remove at least a portion of the free water before such synthetic silicates are used in the production of glass. For example, the slurry may be dried at a temperature of about 110 ℃.

The slurry may also be further heat treated at higher temperatures, such as at about 1000-1800 c, more preferably about 1300-1400 c. The heating time and speed may vary depending on the final desired synthetic silicate.

In another embodiment of the invention, silica sand and dolomitic lime and high calcium lime are ground and premixed. Subsequently, the dry mixture is added to the water in the above proportions over a few minutes. The dough-like mixture is then extruded and dried to remove free water.

The artificial silicate produced from silica sand may have a wide variety of one or more magnesium silicate, magnesium calcium silicate, and/or calcium silicate components. The variation in the composition of the artificial silicate is related to the variation in the amounts of calcium and/or magnesium source, water and silica sand, as well as the operating conditions such as temperature, pressure, time, stirring, etc. Forms of magnesium calcium silicate and/or calcium silicate produced by the present invention include, but are not limited to, diopside (CaMgSi)₂O₆) Wollastonite (CaSiO)₃) Akermanite (Ca)₂MgSi₂O₇) Magadiite (Ca)₃MgSi₂O₈) Calcium forsterite (CaMgSiO)₄) Forsterite (Mg)₂SiO₄) And so on. In a preferred embodiment, the magnesium calcium silicate and/or calcium silicate glass precursor material comprises diopside and/or wollastonite.

Diopside and wollastonite formed in the solid phase reaction are different from other artificial and natural sources of diopside and wollastonite in that scanning electron microscopy reveals their unique morphology.

In another aspect, the present invention fixes the process parameters within a new set of process parameters that yield satisfactory results. Thus, the present invention may be the above-described invention wherein the quantitative ratio between the artificial silicate and the silica source, preferably silica, is effectively controlled to reduce the temperature required to produce molten glass in a fixed time. Alternatively, the quantitative ratio between the calcium silicate precursor material and the silica source is effectively controlled to reduce the time required to produce molten glass at a fixed temperature. The various parameters making up the above may also be controlled. For example, molten glass is produced by fixing a set of parameters including the number of calcium and/or magnesium sources after digestion, the number of water-soluble silicates, the amount of free water, the number of silica sources, the time and temperature at which the molten glass is produced. Once a certain number of parameters are determined, the remaining parameters will depend on their degrees of freedom. The amount of other calcium, magnesium or sodium sources such as limestone, dolomite and soda ash can vary with these parameters, and will depend on the desired glass composition.

Advantages in glass have been shown to include fewer bubbles, better heat transfer, reduced fining time due to 30-40% less gas, shorter melting time due to better eutectic properties, and possibly lower soda ash usage due to better melting properties.

In addition, by using the residual heat of the glass melting furnace, glass can be produced more efficiently from the cost viewpoint. The production equipment for the synthetic silicate can be located at the production site of the glass plant, which makes it possible to make full use of the residual heat and energy of the glass melting furnace. The synthetic silicate glass batch composition can then be more easily delivered to the glass batch plant without the need for truck or truck shipment.

The following examples are presented to illustrate, but not to limit, the process of producing synthetic silicates using silica sand.

Example 5

The following process is a method for producing calcium magnesium silicate, more specifically diopside. The reaction was carried out in a Hobart mixer. A magnesium oxide source and a calcium oxide source consisting of 600 grams of dolomitic lime (56.06% CaO and 38.31% MgO) and 960 grams of water were simultaneously placed in the mixer. The oxide was allowed to digest for 15 minutesIn this way, a maximum viscosity is achieved. Subsequently, the digested calcium source and magnesium source were passed through a 30 mesh sieve to remove impurities. 702 grams of dried 30 mesh silica sand was added to the mixed oxide. This provided sufficient silica to react with all of the magnesia and calcia in a 1: 1 molar ratio. The slurry was stirred for 10 minutes. After the reaction was complete, the free water was removed in a kiln at 110 ℃. The dried material was then heated to 1375 ℃ for 15 minutes in a kiln. X-ray diffraction (XRD) confirmed that: diopside (CaMgSi) in the phase formed by this reaction₂O₆)＞98％。

Example 6

An illustrative example of this approach is the use of diopside precursors in glass production. The glass comprises the following ingredients: 74.1% SiO₂、13.3Na₂O, 8.6% CaO, and 4.1% MgO. The precursor material consists of 77.2% of the required CaO and MgO and 16.5% of the required Si₂And (C) O. Thereafter, 61.9 grams of SiO in 30 mesh sand was added to 22.4 grams of the precursor material₂5.43 g of calcium carbonate with 53.04% CaO and 22.6 g of soda ash with 58.5% NaO. Preparing calcium carbonate as CaO source, dolomite as MgO/CaO source, 30-mesh sand as silicon dioxide source and sodium carbonate as Na₂The O source formed a control of the glass batch composition described above. Subsequently, both sets of mixtures were heated to different temperatures and left for a period of time. In each case, the control glasses were placed side by side. Glass samples were ground and subjected to XRD testing. The percentage of amorphous glass for these samples was as follows:

temperature/time	Amorphous glass% (comparison sample)	Amorphous glass% (test sample)
			783 deg.C/30 min	5	7
817 ℃ for 30 minutes	7	10
			875 ℃/30 minutes	25	30
1000 deg.C/30 min	45	50
			1100 deg.C/30 min	65	70
1300 ℃ for 1 hour	95	98
			1400 ℃ for 1 hour	96	100

In addition, thermogravimetric/differential thermal analysis (TGA/DTA) showed that: glasses with diopside materials require less energy consumption and have less heat absorption than the control glass. On a theoretical basis, the glass using diopside-type synthetic silicate consumed 13.8% less energy than the control glass. This is mainly due to the fact that less energy is required for decarboxylation in the use of diopside artificial silicate glasses.

Artificial silicate granules

In another embodiment, the invention is a process for producing synthetic silicate granules, wherein the synthetic silicate granules can be further processed into synthetic silicate particles. The synthetic silicate is produced by a water-soluble silicate technical route or a silica sand technical route. A preferred method of producing such particles comprises the steps of:

1) forming a mixture by blending (a) silica, preferably sand, (b) calcium oxide and/or magnesium oxide, preferably dolomitic lime or high calcium lime, and (c) water;

2) forming an undried mass from the mixture, such as extruding into an undried pellet;

3) drying the non-dried mass, i.e. the pellets, in order to dehydrate, preferably to obtain sufficient structural strength for handling and/or controlling disintegration during the reaction;

4) reacting the unreacted mass to form the desired artificial silicate, preferably diopside pellets, preferably in a kiln or microwave apparatus under controlled conditions to form the desired article; and

5) the particle size of the artificial silicate product is reduced to a particle size suitable for use as a glass production component.

Step 1 is effectively carried out in order to control the respective material proportions, which is crucial for the "green strength" of the pre-reacted granulate and the desired composition of the granulate of the artificial silicate product. When magnesium oxide alone is used in step (1) without the presence of calcium oxide, pellets may be produced by other optional methods, such as the use of pressure or cement.

The step (2) of forming the blocks can be effectively controlled to increase the green strength and control the reactions that produce the desired granules of the synthetic silicate product. Such controls may include the pressure at which the impression is formed and the molding pressure. Other considerations include, but are not limited to, the density and moisture content of the pellets after molding. Preferably by extrusion or by balling. Preferably, undried pellets are formed from the digested mixture of calcium oxide and/or magnesium oxide, more preferably lime, and sand and extruded into cylindrical shapes having a particle size of about 1/4 inches to several inches, with a preferred aspect ratio (diameter to central axis) of less than about 1. The cylindrical shape provides a better reaction in the rotary kiln and reduces dust. The possibility that uniform pellet sizes result in uniform reactions and thus no glass formation in the kiln is also reduced. The prefired pellets were dense white cylinders. Upon heating, the pellets become porous as water in the hydrate is released and reacts with the diopside. The porous structure of the calcined pellets makes grinding easier, so that the particle size is selected, preferably between about-30 mesh and +100 mesh.

These unreacted pellets had an analytical composition (% by weight): about 3-18% magnesium oxide; about 6-34% calcium hydroxide; about 0-27% calcium carbonate; about 0-22% magnesium carbonate; about 48-60% silica sand. More preferably, the composition consists of about 16-17.5% magnesium oxide, about 30-34% calcium hydroxide, about 50-54% silica sand. Compositions in which the weight percent of calcium hydroxide is less than about 6% no longer have the green strength necessary to prevent binding and dusting in the calciner. These "green" pellets, which are unique in composition, transfer heat very well and can therefore be calcined in larger production facilities.

Thus, another embodiment of the present invention is an unreacted pellet of the above composition wherein it can be reacted to form an artificial silicate, such as a cylindrical pellet having a particle size of at least about 1/4 inches and an aspect ratio (diameter to central axis) of less than about 1. The artificial silicate may be magnesium calcium silicate, magnesium silicate and/or calcium silicate.

Step (3) dries the formed undried pellets into unreacted pellets. Initially, the drying conditions controlled were mainly the drying rate of the unreacted pellets and the final water content. The drying conditions can be effectively controlled to obtain greater green strength.

The reaction in step (4) is effectively controlled to form the desired synthetic silicate, such as diopside or wollastonite (although this is not necessarily limiting). The time and the temperature of the reaction are effectively controlled. The green pellet strength is sufficiently high to prevent undesirable pellet breakage leading to dusting, refractory adhesion such as sticking to the refractory surface, reaction run-away, non-uniformity of reaction such as differences in reaction rates, and negative reaction conditions when high temperature processing of powdered raw materials is performed. The reaction temperature is preferably about 700 deg.C, more preferably about 1000 deg.C, and still more preferably about 1350 deg.C to 1400 deg.C. Higher temperatures are also possible. But the temperature is selected so that the material melts without breakage of other structures.

Step (5) reduces the particle size of the calcined synthetic silicate pellets to a desired particle size suitable for use in a glass-producing component. Such reduction may be achieved by grinding/crushing or other known methods of reducing particle size, with appropriate screening if desired.

One preferred embodiment is the formation of shaped pellets by the above steps (1) to (3).

Another preferred embodiment is the formation of the synthetic silicate granules by the above-described steps (1) to (4).

A further preferred embodiment is a glass produced from the material formed in the above-mentioned steps (1) to (3).

Yet another preferred embodiment is a glass produced from the material formed in the above-described steps (1) to (4).

Yet another preferred embodiment is a glass produced from the material formed in the above-described steps (1) to (5).

The following examples are intended to illustrate, but not to limit, the synthetic silicate granules of the invention.

Example 7

Dolomitic lime and calcium oxide (i.e., quicklime) are placed in the reactor along with water and silica sand. The digested reactants were charged to a drier at about 200 ℃ and pellets which were shaped into dry pellets in an extruder were thus obtained. The dried pellets were then calcined at about 1350 c after which they were crushed and sieved prior to use in a glass production facility.

Claims (2)

1. A pellet produced by a process comprising the steps of:

(1) forming a mixture by blending (a) silica, (b) calcium oxide and/or magnesium oxide and water;

(2) forming a pellet from the mixture, the pellet comprising from about 3% to about 18% magnesium oxide, from about 6% to about 34% calcium hydroxide, from about 0% to about 27% calcium carbonate, from about 0% to about 22% magnesium carbonate, and from about 48% to about 60% silica sand; and

(3) the pellets are dried to drive off moisture to achieve sufficient structural strength for handling and/or controlling breakage during the chemical reaction.

2. A pellet made by a process comprising reacting the pellet by the heating produced in claim 1 to produce an artificial silicate product.