ES2361265T3 - SILICATE PREPARATION IN AN OVEN OF SUBMERGED BURNERS IN REDUCING MEDIA. - Google Patents

Abstract

Method of preparing silicate of an element chosen from alkaline, alkaline earth or rare earth, comprising a reaction between silica and a sulfate of said element in a reactor provided with at least one burner submerged in a melting table, said submerged burner being fed by a gas comprising oxygen, an excess of reducing fuel being introduced into the reactor with respect to the oxygen consumed effectively.

Description

Preparation of silicate in an oven burners submerged in reducing medium.

The invention relates to a method of silicate preparation, such as sodium silicate, which can be used to make glass or silica in the form of particles (silica precipitate).

In the context of the present invention, "raw materials" means all materials, materials vitrifiable, natural minerals or synthesized products, materials resulting from the recycling of powdered glass type, etc., which may enter the composition that comes to feed a glass oven "Glass" means any material of vitreous, ceramic or ceramic matrix, whose silica is the main component The term "manufacturing" includes the indispensable fusion stage of raw materials and eventually all subsequent / complementary stages that try to fine-tune / condition the melting glass with a view to putting it into definitive form, particularly in the form of flat glass (glazing), concave glass, (bottles, bottles), glass in form of mineral wool (glass or rock) used for its properties of thermal or sound insulation or even glass in form of threads called textiles used in reinforcement.

The invention is particularly interested in the raw materials necessary to manufacture the glasses that have a significant proportion of alkalines, in particular sodium, for example type glasses silico-sodo-calcium used to manufacture flat glass. The raw material currently used with more often to provide sodium or potassium is sodium carbonate Na 2 CO 3 or potassium carbonate K 2 CO 3, choice that It is not devoid of inconveniences. Indeed, on the one hand that compound does not contribute more than sodium as constitutive element of glass, decomposing the entire carbonated part in the form of CO2 evolution during fusion. On the other hand, it it is an expensive raw material compared to others, because it is a synthesis product obtained by the Solvay procedure a starting from sodium chloride and limestone, a procedure that imposes a certain number of manufacturing stages and it consumes a lot Energy.

This is the reason why it has been proposed use as a source of sodium, not a carbonate, but a silicate, possibly in the form of a mixed alkali metal silicate (Na) and of alkaline earth (Ca) that is prepared previously. The use of This type of intermediate product has the advantage of providing jointly several constituents of glass, suppress the phase of decarbonation, and reduce CO2 emissions from the furnace fusion. It also allows accelerating the merger of raw materials in as a whole and favor its homogenization during the merger, as it is indicated, for example, in patents FR 1211098 and FR 1469109. Without However, this route poses the problem of manufacturing that silicate.

A first mode of synthesis has been described in the WO 0046161: it is about converting a halide, for example NaCl, and silicate silicate at high temperature, being supplied the thermal contribution by submerged burners. It was already known combustion by submerged burners, for example in US 3627504, US3260587 or US4539034, to guarantee the fusion of vitrifiable materials to make glass. Use this technology in the different context of the synthesis of silicates, therefore before the actual manufacture of the glass, in fact, brings many advantages: this mode of combustion causes strong materials during the reaction turbulence, strong convection movements around the flames or jets of gas from submerged burners, which It favors a very effective mixture of reagents. In addition, the submerged burners directly provide heat where it is necessary, in the mass of the products in reaction. This is also an environmentally friendly combustion mode. The Direct conversion of NaCl and silica performed in this way is, Therefore, very attractive for several reasons. However, it turns out that this direct conversion was difficult to use at great scale.

WO 03031357 teaches manufacturing silicate in two different stages, causing the reaction to intervene global a halide (such as NaCl) and silica to produce a silicate, passing this global reaction by the manufacture of a sulfate. That document teaches that sulfur or coal can serve as solid fuel.

The invention aims firstly the development of a silicate manufacturing process particularly productive and easy to use on an industrial scale. In addition, this new type of manufacturing can also be environmentally friendly to the extent that all reaction products involved can be valued or recycled

It is understood by "submerged burners" burners configured so that the "flames" they generate or the flue gases from these flames develop in the reactor where the conversion takes place, within the same mass of materials in the process of transformation (mass of reaction). They are generally arranged so that they are flush or slightly exceed the side walls or the bottom of the reactor used.

The invention firstly aims at a process for manufacturing silicate-based compounds (s)
of alkalines, such as Na, K, and / or alkaline earth metals, such as Ca, Mg, and / or rare earths such as Ce, possibly in the form of mixed silicates that associate at least two of those elements. This process involves a conversion reaction of said sulfates with silica in the corresponding silicates, the thermal contribution necessary for this conversion being provided, at least in part, by a combustion reaction using one or a plurality of submerged burner (s) (s) In the furnace of submerged burners sufficient thermal energy is provided to form the silicate and that it remains liquid and of a sufficiently weak viscosity to flow fast enough out of the oven. The interest of submerged burners is to provide the necessary calories directly in the liquid reaction mass, also causing this to provide an effective mixture of the different materials in the oven due to turbulence caused by the gases that remove them. According to the invention, it is preferable to provide the essential energy for submerged burners, but it is also not excluded to provide a part of it by other means such as electrical resistors, although the coexistence of electrical resistances and submerged burners is not recommended ( resistance corrosion). Generally a caloric intake between 500 and 2500 KWh per ton of silicate produced is appropriate.

Combustion by submerged burners you need an oxygen supply, either in the form of pure oxygen or in form of a mixture of oxygen and at least one other gas, as is the air case. This oxygen is intended to react with the fuel to provide the necessary heat. According to nature of the fuel and how to introduce it, the Fuel can react more or less quickly with oxygen. Thus, if the fuel is a gas (a hydrocarbon such as methane, propane or butane or a sulfurized gas such as H2S) that feeds directly to the submerged burner already fed with oxygen, the combustion is fast and is considered to be complete (of course it is convenient here that the fuel and oxygen reach the same point of the submerged burner, for example by a premix cell). That means that if the submerged burner is powered by oxygen and fuel gas stoichiometrically, all gas Fuel and all oxygen react at once. Yes for him on the contrary the oxygen is in excess with respect to this stoichiometry, oxygen will escape from the fumes, which is measurable. If you are excess fuel gas with respect to this stoichiometry, that fuel will also have a tendency to escape, but there will be a risk of post-combustion more or less explosive and that scenario is not recommended.

Solid fuel can also be introduced such as solid sulfur or solid carbon (carbon). In that In case the solid fuel is generally introduced into the tank reaction as vitrifiable material, that is, regardless of submerged burners, but nevertheless as close as possible to said burners if desired to react effectively with the oxygen that passes through these burners. However, even if it introduce that solid fuel very close to the burners submerged it is difficult to have perfect combustion performance, which means that oxygen can generally pass through the mass reaction without fully reacting with the fuel and found in the fumes (measurable amount), and even if the fuel was in stoichiometry or even in excess with Regarding oxygen.

According to the invention, a excess fuel (or reducer) with respect to oxygen effectively consumed (and not with respect to the oxygen introduced only). Indeed, the requesting party has discovered that if the reaction medium is with excess fuel, the reaction of silicate formation was activated and could even be performed at lower temperature than in the absence of this excess, which also it means that the silicate formation reaction is activated at lower temperatures than in the absence of this excess. It seems that the excess fuel, not consumed by the oxygen of the burners submerged, in fact plays in that case a direct role in the silicate formation reaction, a reducing type paper. Without that the present explanation may have a limiting effect, may that at least one of the following reactions is then put in game:

one

the reaction intervening (1) in presence of carbon fuel or that generates carbon as coal, coke coal, a carbon-containing plastic material (a polymer such as poly (ethylene), poly (propylene) or other), the reaction (2) intervening in the presence of fuel that Contains or generates sulfur. You can also use a fuel which contains both carbon and sulfur, such as rubber vulcanized (as vehicle tires cars).

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Therefore, according to the invention it is possible to be particularly in one of the following cases:

to)

submerged oxygen-fed burners (which includes air) and combustible gas, the combustible gas being in insufficient amount with respect to oxygen and being consumed completely by oxygen, adding on the other hand in the mass reaction a solid or liquid fuel that reacts partially with oxygen, but being present in quantity important enough not to be completely consumed by oxygen and to play a reducing role in the sense of invention to favor the formation of silicate, being able to eventually escaping oxygen with the fumes;

b)

submerged oxygen-fed burners (which includes air) and combustible gas, the combustible gas being in stoichiometry with respect to oxygen, reacting oxygen and fuel gas completely at once, adding for another part a solid or liquid or gaseous fuel (such as H2S) in the reaction mass and playing a reducing role in the sense of invention to favor the formation of silicate;

C)

submerged oxygen-fed burners (which includes air) without combustible gas, being added on the other hand in the reaction mass a solid or liquid fuel that reacts with at least part of the oxygen, but being present in amount important enough to also play a role reducer in the sense of the invention to favor the formation silicate, generally escaping part of the oxygen with the smoke

d)

submerged oxygen-fed burners (which includes air) and fuel gas H 2 S, the gas being excess fuel with respect to oxygen and playing a role reducer with respect to sulfate favoring the formation of silicate.

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It is seen that in all these scenarios there is a excess fuel in the reaction mass with respect to oxygen It reacts effectively. You can easily evaluate oxygen that reacts effectively by measuring the oxygen that escapes in the smoke Therefore, the professional can by routine tests, knowing the amounts of oxygen that do not react, evaluate the necessary quantities of fuel to be introduced to be in excess fuel in the sense of the invention.

We point out that the materials called "fuels" or "reducers" are really the same and You can play those two roles. Being played the role of fuel by reaction with oxygen, and the role of reducer being played in the silicate manufacturing reaction. Excess fuel in the sense of the invention allows this combustible material to have a most important reducing paper.

Thus, the invention aims at first place a silicate preparation process of an element chosen among alkaline, alkaline earth or rare earths, which comprises a reaction between silica and a sulfate of said element in a reactor equipped with at least one burner submerged in a mass in fusion, said submerged burner being fed by a gas comprising oxygen, and an excess being introduced into the reactor of reducing fuel with respect to the oxygen consumed effectively.

Excess fuel in the direction of The present invention plays a reducing role thanks to carbon or sulfur that contains and that is combined with sodium sulfate. For each fuel it is possible to define a carbon equivalent or a sulfur equivalent corresponding to the mass of carbon or of pure sulfur that actually provides fuel as reducer. Indeed, by way of example, a hydrocarbon polymer it has a more important mass than the carbon it contains and that It effectively plays a reducing role. Excess fuel in the meaning of the present invention preferably represents 0.1 to 2 moles and still preferably 0.3 to 1 moles of equivalent of carbon or sulfur per mole of sulfate. Therefore the excess of reducing fuel can be a solid or liquid source of carbon or source of sulfur or at the same time source of carbon and sulfur. We cite as solid or liquid fuel that provides sulfur and / or Carbon the following materials: vulcanized rubbers, tires, wood, cardboard, paper, animal flours, sand contaminated by oil (being at the same time this last source material of fuel / reducer and silica), fuel. The fuel that can being in excess can also be a gaseous source of sulfur as H2_S.

A silica / sulfate molar ratio corresponding to the silicate to be obtained is used. That silicate may be represented by the formula M_ {O} {y} .n (SiO2) in which M represents an alkali metal or alkaline earth metal or a rare earth, x e y represent whole or non-integer positive numbers and n represents a positive integer or non-integer. M_ {x} O_ {y} may in particular be Na 2 O, K 2 O, CeO 2. In general, n (SiO2 / M_ {x} O_ {molar ratio) is between 1 and 4 and more particularly between 1, 3 and 4, especially when M represents an alkali or alkaline earth metal. In the case where M is Na, n is more particularly between 1.5 and 3.8. For the case where M is a rare earth like Ce, n can generally be greater than 5 and generally less than 1000.

In the reaction mass are at least The following distinct phases:

-

silica solid

-

liquid sulfate,

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liquid silicate,

-

gas from submerged burners and the reaction of formation of the silicate (which may contain according to the case SO2, SO 3, CO 2, H 2, H 2 O, O 2, etc).

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The reaction medium therefore contains numerous different phases and burner technology submerged is particularly effective for mixing them vigorously and Move the reaction forward.

Liquid sulfate and liquid silicate form Two different phases. Reaction conditions are investigated (temperature, agitation by submerged burners, time of residence, excess reducer) such that the sulfate phase liquid disappear before the reactor exit and anyway be in the weakest amount possible during manufacturing. This amount of residual sulfate is usually expressed in amount of SO_ {3}. The absence of sulfate at the outlet of the reactor It shows that he has reacted well. Otherwise, it observe undesirable inclusions with the naked eye sulfate In addition, hot, there may be sulfate projections more or less explosive liquid in manufacturing outlet. Usually This defect can be remedied by increasing the excess reducer. By both the minimum amount of excess reducer can be determined by the disappearance of the sulfate phase in the final silicate. Is useless to introduce too much excess of reducer because that it can lead to a final silicate coloration yellow-brown visible to the naked eye (due to Sulfide ion formation S 2-), coloration that may not be desired. Generally the excess reducer is between once and twice the amount of excess necessary for the disappearance of the sulfate phase. Therefore, preferably a excess fuel in sufficient quantity so that the silicate does not Contains sulfate inclusion.

Sufficient temperature is chosen to make advance the reaction and that results in an adapted viscosity of the reaction medium Indeed, if the viscosity is too strong, The reaction mass solidifies and the reaction does not proceed. If the viscosity is too weak, projections are too important and this tends to corrode the walls and the vault and by both drag unwanted foreign particles into the product of manufacturing. Also, what goes to the walls and the vault is no longer available to react with what is introduced. In fact those two extremes lead both to too weak agitation of the reagents, which decreases performance. Proper agitation of the medium also leads to a homogeneity of temperature in the reaction mass It is investigated that the silicate phase has a viscosity between 50 and 3000 poises and more particularly between 100 and 1000 poises at the temperature of the reaction medium. Generally a temperature between 1000 and 1500 ° C and more particularly between 1200 and 1400 ° C.

The final silicate is a solid translucent to the room temperature. Preferably it does not contain particles without melt, i.e. initial silica particles that have not participated in the reaction The presence of unmelted particles increasing residence time in the reactor.

Preferably, the reactor for preparing the silicate is followed by a refining tank. This Cuba is separated from the reactor to avoid silicate returns from the tank to the reactor as well as ongoing silicate contamination of refining by the crude silicate of the reactor. This refined provides the following advantages:

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remove the last particles without melt (silica particles),

-

remove maximum sulfur from final silicate (the sulfur released in the form of H2S by the Final silicate is toxic and produces unwanted odors)

-

reduce redox, in practice it intends to leave a redox in Cuba (equal to the mass ratio Total FeO / Fe 2 O 3 in the final silicate) less than 0.5, even less than 0.4,

-

consume the excess reducer that is still found in silicate, which is equivalent to improving the yield of the silicate formation reaction (the reducer that has not reacted with sulfate in the reactor).

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The refining tank is generally equipped with heating means, such as at least one submerged burner. That (those) burner (s) has one more flame or less oxidizing according to the intended redox in output. Those burners can be fueled with fuel gas and air or of oxygen with an excess of oxygen with respect to the combustible gas. In the course of this refining operation, the crude silicate will Clarea to become even colorless and translucent. Temperature of the silicate in the refining tank is generally comprised between the same temperature as in the reactor and 150ºC below the temperature in the reactor, and preferably between 50 ° C per below the temperature in the reactor and 150 ° C below the reactor temperature

The separation between the fusion reactor and the refining tank can be a throat or a drain or compartments on the sides.

The "silica" can be taken to the medium of reaction for any compound that contains mostly silica (silicon oxide) SiO2, even if it can contain also other elements, other minority compounds, which is very particularly the case when natural materials are used Like the sand

The effectiveness of burners at all levels (mix quality, excellent thermal transfer) makes that the conversion according to the reaction is greatly favored, and this without necessarily needing to reach temperatures extremely high

Another advantage of submerged burners is the following: they allow the introduction of liquid / solid fuels
two in the same way as vitrifiable raw materials. In fact, this leads to obtaining varied redox of the melt silicate in the reactor, which can vary from 0.1 to 0.9 depending on the residence time (a higher residence time generates a weaker redox). In fact, it is convenient that at the reactor inlet, at the site where the different raw materials are baked, the redox is relatively high (between 0.35 and 0.9) because this is favorable to the sulfate decomposition reaction. After the tuning tank, the redox is generally in the 0.1 to 0.9 domain.

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The oxidizer chosen to feed the submerged burner (s) (reactor and tuning tank) can simply be air. But nevertheless, preference is given to a combustion in the form of air enriched in oxygen, and even in the form of oxygen substantially alone. A large concentration of oxygen for different reasons: the volume of the fumes is reduced of combustion, which is favorable under the energy point of view and avoid any risk of excessive fluidization of materials in the process of reaction that can cause projections on superstructures, in particular the reactor vault where It produces the conversion. In addition, the "flames" obtained are more short, more emissive, allowing faster transfer of its energy to materials in the process of fusion / conversion. Further, where appropriate, the concentration of sulfur oxide in the fumes is major, which facilitates further acid transformation sulfuric.

Regarding the choice of fuel for the burner (s), three ways are possible, alternatives or cumulative: you can choose a liquid fuel, gas or solid form.

If it is at least partially in solid form, Can directly feed submerged burners. Yes it's in liquid form, solid, can be brought near the burners submerged.

Gas can be cited as gas natural (mostly methane), propane, hydrogen, and any another hydrocarbon and / or sulfur compound, in particular H 2 S (advantage of H 2 S: no discharge of CO 2 at atmosphere).

As solid or liquid fuel can be cited any compound mostly in carbon form and / or hydrocarbon and / or sulfur (which includes sulfur and carbon): as in In the previous case, it can be industry by-products oil (heavy fuel, asphalts). You can also try polymer-based materials that can be recycled like this (any material called plastic, tire, rubbers vulcanized ...), and even stained hydrocarbon sand, which it will also supply both silica and fuel, which is an ingenious way to deal with the problem of decontamination of the beaches after the black tides for example.

According to the invention, they can be used in particular fuels containing sulfur as compounds sulfur, such as used tires (which may contain for example 0.5 to 4% sulfur) and still pure sulfur. Traces of sulfur in all vulcanized polymers (pneumatic), it found also in by-products of the oil industry, and the invention makes it possible to value them in an interesting way: in fact, the sulfur contained in the fuel supplied to perform the combustion reaction will oxidize. Now you can transform those sulfur oxides (SO2 and / or SO3) into acid sulfuric, recovering them in the fumes and treating them so appropriate. There are two options (alternative or cumulative) in fact, particularly depending on the amount of H_ {2} SO_ {4} manufactured, which depends closely on the proportion of S chosen in the fuel): or is valued H 2 SO 4 as reagent widely used in industry chemistry, regardless of the procedure according to the invention, or it is reused according to a variant of the process of the invention. Indeed, according to a procedure "in loop ", the combustion product of the formation reaction of the silicate is used as a reagent to attack the silicate and lead to precipitated silica. Therefore the invention relates also to a procedure for preparing precipitated silica that it comprises a step a) of preparing a silicate according to any one of the preceding claims, the reactor equipped with a chimney, which is equipped with a system of recovery of sulfur oxides leading to sulfuric acid, a step b) of acid attack of the silicate produced in a) by the sulfuric acid produced in a), conducive to silica precipitated by one part and sulfate of said element on the other, this being last recycled in a).

There is another way, alternative or cumulative with the previous one, to manufacture H 2 SO 4 from Process according to the invention: the conversion reaction of silicate sulfate also produces sulfur oxides SO2 and / or SO_ {3}. Therefore, those oxides of sulfur and subject them to a sulfuric acid conversion reaction. As in the previous case, this sulfuric acid can be reused as a reagent against silicate and / or value it as a reagent for chemical industry.

In fact, if the fuel contains a significant amount of sulfur, the reactions at stake by the invention they can produce more, and even significantly more, sulfuric acid than what is necessary for the reaction of conversion of halides into sulfates, which increases the value of the process according to the invention as a whole.

A first outlet for manufactured silicates according to the invention it refers to the glass industry: they can replace, at least in part, the raw materials traditional alkaline or rare earth suppliers, very particularly as regards sodium, with a substitution at least partial Na2CO3 and silica sand. So silicates manufactured in accordance with the invention to feed a glass oven. Before the further processing, for example in a glass oven, the silicate can be transformed into granules to be stored momentarily. The glass oven can be of conception traditional (for example, electrode electric melting furnace submerged, air burner furnace running with regenerators side, loop oven, and any type of oven known in the glass industry thus including burner ovens submerged), eventually with a conception and mode of operation slightly adapted to a fusion process without carbonate or less carbonate than for standard fusions.

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It should be noted that some silicates apart of sodium silicate are also very interesting to manufacture from according to the invention. Therefore, the invention allows manufacturing potassium silicate from K 2 SO 4, which is at least economically, very convenient as a raw material carrying Si and of K to make glasses called "mixed alkalis", is that is, they contain both Na and K. Those glasses are used particularly for manufacturing touch screens, glass TV screen, plasma screen glasses visualization ("Plasma Display Panel" in English).

Likewise, the invention allows manufacturing of most economical way special glasses containing additives individuals such as rare earths, for example cerium: the presence of cerium oxide that confers anti-U.V properties. to the glasses, and the rare earths of that type also enter the composition of special glasses with high elastic module for disc Lasted. The invention thus allows to have a carrier raw material of Si and Ce, cerium silicate, of a moderate cost.

A second outlet for manufactured silicates according to the invention (apart from being used as materials glass oven premiums), more particularly soda silicate, refers to the detergent industry; soda silicate which frequently enters into the composition of bleach / detergents.

A third outlet for silicates formed according to the invention refers to the preparation of silicates individuals, commonly designated by the expression "silicas precipitates "that enter, for example, the composition of concrete or as cargo in rubbers, in particular tires for vehicles, or food products. In fact it can be done an acid attack of silicates formed according to the invention, conveniently by sulfuric acid, so that precipitate silica in the form of particles that have a particular granulometry: the intended particle size it is generally nanometric (0.5 to 300 nm and more particularly 1 to 100 nm for example).

To use the conversion reaction of silicate sulfates can be used, as described in the patent WO-00/46161, a reactor equipped with submerged burner (s) and at least one means of introduction of silica and / or sulfates below the level of fusion materials, particularly in the form of one or more worm loaders. The same happens, preferably, for solid or liquid fuels, if used, such as carbon and / or hydrocarbon and / or sulfur compounds (which include solid sulfur and solid carbon) mentioned previously. It can thus be introduced directly into the mass of products in the process of melting / reacting at least those of the starting reagents capable of vaporizing before having The time to react.

The process according to the invention It therefore includes many advantages, including:

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a decrease in CO2 emissions in glass furnaces that replace all or part of sodium carbonate by sodium silicate, lower consumption energy of these furnaces because they reduce or suppress the decarbonation reactions,

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a possibility of doing rotate the procedure in loop, with by-product reuse H 2 SO 4 manufactured,

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a possibility to value as fuel sulfur derivatives.

Figure 1 represents a device of silicate manufacturing comprising a reactor followed by a Cuba of refining.

Figure 2 is a schematic of a variant Preferred method according to the invention, which It works in a loop and leads to a precipitated silica.

Figure 1 represents a reactor 1 provided with submerged burners 2 and comprising an introduction system 3 of solid materials (sand, sulfate, coal, sulfur, etc.) under the reaction mass level 4, the fumes escaping through the chimney 5. The crude silicate passes through the throat 6 to the tank tuned 7 also equipped with at least one submerged flame burner more oxidizing than those in the reactor. The fumes generated in the tank of Refined escape through chimney 8. Refined silicate 9 is recover by landfill 10.

Figure 2 shows how the silicate manufactured according to the invention it can be reatacado by sulfuric acid produced in the fusion reactor to prepare precipitated silica of calibrated particle size. The silicate on the one hand and the Sulfate on the other turn in loop in this procedure. Acid sulfuric also turns in a loop, being able to create the case surplus according to the nature of the fuel and / or reducer used.

Example 1

A melting furnace equipped with a submerged burner followed by a refining tank equipped with a submerged burner The oven and the tank are both cylindrical (shaft vertical) and both have a floor area of 0.07 m2. The submerged burners (oven and tank) both work in stoichiometry with methane and pure oxygen (therefore oxygen is consumes completely in each burner flame). It is introduced in the sand oven and sodium sulfate in a relationship that allows obtaining a sodium silicate that has a molar ratio SiO 2 / Na 2 O of 3.5. Coke is also introduced, which serves as excess fuel / reducer, at the level of 0.5 moles of carbon per mol sulfate introduced. The production is 3 tons per day and per m2. The oven and the tank both work at 1300ºC. The redox at oven output it is 0.7 (weight ratio FeO / Fe2 O3) total) and residual SO3 (SO3 dissolved by silicate) is 0.42% by weight (measurable by fluorescence X or by carbon / sulfur analyzer), which indicates that the performance of the reaction in the oven is of the order of 98%. In the refining tank, The residual sulfate will react with the residual reducer. In the out of the tank a silicate of formula is obtained Na 2 O.3,5 (SiO 2) translucent and colorless whose SO 3 residual (release of SO3 from residual sulfate) It is less than 0.05%. The redox is here 0.20.

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Example 2

Proceed as for the previous example, except that the submerged burner of the refining tank works with oxygen insufficiency (reducing flame of -15% flow rate of oxygen with respect to stoichiometry). At the exit of the Cuba a silicate of formula Na2O.3.5 (SiO2) is obtained Translucent and colorless whose residual SO3 is less than 0.05%. The redox is here 0.55.

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Example 3 (comparative)

Proceed as in Example 1, unless it is not add excess in the form of coke. They are found in the final silicate inclusions visible to the naked eye of sodium sulfate. The SO_ {3} residual is greater than 1%. This indicates a reaction yield much lower than in example 1. The sulfate introduced has not been decomposed sufficiently. The enrichment in silica is too strong, the reaction mass quickly becomes too viscous and is due to the reactor.

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Example 4

Proceed as for example 1, unless replace the excess coke reducer with an excess of reducer in the form of used tires whose composition is practically: 2% by weight of sulfur, 80% by weight of carbon, 18% by weight hydrogen weight That reducer is introduced in an amount that It represents 5% of the mass of sodium sulfate introduced. Is obtained a silicate containing 0.1% residual SO3 and whose redox is 0.5 The presence of sulfur in the reducer allows acid to be produced supplemental sulfuric acid

Claims (20)

1. Preparation procedure of silicate an element chosen among alkaline, alkaline earth or earth rare, comprising a reaction between silica and a sulfate of said element in a reactor equipped with at least one burner submerged in a table in fusion, said burner being fed submerged by a gas comprising oxygen, being introduced into the reactor a excess reducing fuel with respect to the oxygen consumed effectively. 2. Method according to the preceding claim, characterized in that the excess reducing fuel is a solid or liquid source of carbon. 3. Method according to any one of the preceding claims, characterized in that the excess reducing fuel is a solid or liquid source of sulfur. Method according to any one of the preceding claims, characterized in that the excess reducing fuel is a sulfur source gas. 5. Method according to any one of the preceding claims, characterized in that the silicate phase in the reaction mass has a viscosity between 50 and 3000 poises. Method according to the preceding claim, characterized in that the silicate phase in the reaction mass has a viscosity between 100 and 1000 poises. 7. Method according to any one of the preceding claims, characterized in that the reaction mass has a temperature between 1000 and 1500 ° C. Method according to the preceding claim, characterized in that the reaction mass has a temperature between 1200 and 1400 ° C. 9. Method according to any one of the preceding claims, characterized in that the excess fuel is sufficient so that the silicate does not contain sulfate inclusion. Method according to any one of the preceding claims, characterized in that the excess fuel represents 0.1 to 2 moles of carbon equivalent and / or sulfur per mole of sulfate. Method according to the preceding claim, characterized in that the excess fuel represents 0.3 to 1 moles of carbon equivalent and / or sulfur per mole of sulfate. 12. Method according to any one of the preceding claims, characterized in that the reactor is followed by a refining tank of the silicate leaving the reactor. 13. Method according to the preceding claim, characterized in that the temperature of the silicate in the refining tank is between the same temperature as in the reactor and 150 ° C below the temperature in the reactor. 14. Method according to the preceding claim, characterized in that the temperature of the silicate in the refining tank is between 50 ° C below the temperature in the reactor and 150 ° C below the temperature in the reactor. 15. Method according to any one of claims 12 to 14, characterized in that the tank is provided with at least one submerged burner. 16. Method according to any one of claims 12 to 15, characterized in that the redox of iron in the silicate leaving the tank is less than 0.5. 17. Method according to any one of the preceding claims, characterized in that the silicate is of the formula M_ {O} {y} .n (SiO2) in which M_ {x} O_ {is} Na_ { 2} O or K 2 O and n represents a number of moles between 1 and 4. 18. Method according to the preceding claim, characterized in that n is between 1.3 and 4. 19. Silica preparation procedure precipitate comprising

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a step a) of preparing a silicate according to any one of the preceding claims, the reactor being provided with a chimney, which is equipped with a recovery system for sulfur oxides conducive to sulfuric acid.

-

a step b) of acid attack of silicate produced in a) by acid sulfuric acid produced in a), which leads to silica precipitated by a part and sulfate of said element on the other hand, this being last recycled in a).

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20. Method according to the preceding claim, characterized in that the precipitated silica has a size between 0.5 and 300 nm.