PROCESS FOR PREPARING A METALLIC SILICATE, SILICATE THUS OBTAINED AND APPLICATION IN GLASSWARE

Abstract

The process for preparing according to the invention a metallic silicate of an alkali metal and at least one other metal is of the type by contacting and continuously reacting an alkali metal silicate, a solution of a salt of the other metal and an organic liquid, and it is characterized in that in a first step the alkali metal silicate and the organic liquid are brought together and mixed, and then in a second step the mixture obtained previously is brought together with the solution of the salt of the other metal, at least one of said steps being carried out continuously.

Description

METHOD FOR PREPARING A METALLIC SILICATE, SILICATE THUS OBTAINED AND APPLICATION IN GLASSWORKS The present invention relates to a process for preparing a metallic silicate, the silicate thus obtained and its application in the glass industry. The present application is an addition to patent application No. 89 02758. In the latter, a process for preparing a metallic silicate of an alkali metal and another metal was described in which an alkali metal silicate and a solution of a salt of the other metal were continuously reacted in an organic liquid. Such a process makes it possible to obtain a product with good chemical homogeneity and a fine and compact particle size. However, efforts were made to further improve this process. To this end, the process according to the invention of preparing a metallic silicate of an alkali metal and at least one other metal according to claim 1 of the main patent by bringing into contact and continuously reacting a silicate of the alkali metal, a solution of a salt of the other metal and an organic liquid is characterized in that in a first step, the silicate of the alkali metal and the organic liquid are brought together and mixed, and then in a second step, the mixture obtained previously is brought together with the solution of the salt of the other metal, at least one of said steps being carried out continuously. It appears that the process of the invention makes it possible to obtain a precipitate which has a particularly high dry extract value. Other features and details of the invention will become clearer upon reading the description and concrete examples that follow. It should first be noted that the general principles of the main vocational diploma apply here. Specifically, regarding the starting materials, or reagents, an alkali metal silicate is used first, generally potassium or sodium silicate. The salt of the other metal must be a soluble salt. This can be an organic salt, such as an acetate, but a mineral salt is preferred, and in this case, more specifically a nitrate. The choice of the other metal depends of course on the intended use of the resulting product. When the aim is to prepare precursor compositions of glass compositions using the process of the invention, this metal is chosen from the group comprising metals whose oxides are glass-modifying oxides. Examples include lead, barium, calcium, zinc, and magnesium. In particular, especially in the context of the preparation of glass compositions, it may be advantageous to work also under conditions such that the molar ratio Rm: SiO2 / alkali metal oxide of the starting alkali metal silicate is equal to the molar ratio SiO2 / sum of the molar concentrations of alkali oxides and metal oxides of other metals in the final composition of the metal silicate obtained. Of course, it is quite possible to use salts of several metals at the same time, depending again on the type of product one wants to obtain. The organic liquid should preferably be miscible with the other reactants. It should generally be chosen from among those likely to decrease the solubility of the reaction products in the reaction medium. It is chosen in particular from among alcohols and more specifically saturated alcohols. Examples include methanol, ethanol, propanol, isopropanol, butanol, and isobutanol. Finally, as in the main patent, continuous means a reaction taking place without interruption of the flow of incoming raw materials and the finished products formed, in particular a reaction with simultaneous introduction of reactants into the reactor and maintenance at a constant volume of the reaction medium in the reactor. According to the main feature of the invention, the first step of the process consists of bringing the alkali silicate into contact and mixing it with the organic liquid. A mixture is obtained, to which, in a second step, the solution of the salt of the other metal(s) is added. It should be noted that one of the steps can be carried out batchwise. Here, batchwise means a reaction in which, in particular, the volume of the reaction medium is not maintained constant. Once the reaction has taken place, the reaction mixture is filtered. The resulting precipitate is filtered, washed, and dried by any known method. Filtration and washing can also be carried out continuously. The precipitated metallic silicate obtained can, depending on the nature of the reactants, constitute or serve as a basis for a precursor composition of glass composition. This same precursor composition, through a heat treatment of melting and refining, will lead to a glass composition. Concrete examples will now be given. EXAMPLE 1 1051 g of potassium silicate (silo2 = 18k - Rm = 3.5) and 687 g of pure methanol are added continuously over 45 minutes. 485 g of a 30% lead nitrate solution is added to this suspension discontinuously over 4 minutes. The precipitate is allowed to mature for 1 hour under stirring. It is then filtered. The dry extract of the precipitate obtained, determined after heating to 1000°C (in 10 hours), is 65%. COMPARATIVE EXAMPLE 2 We start with the same reagents as in the previous example, but in the first step we continuously mix lead nitrate and methanol at a flow rate of 0.84 l / h and 2.06 l / h respectively. Then, we introduce this mixture into a continuous reactor at the same time as the silicate solution at a flow rate of 2.1 l / h. The resulting precipitate has a dry extract of 45%.

Claims

DEMANDS 1 - A process for preparing a metallic silicate of an alkali metal and at least one other metal according to claim 1 of the main patent by contacting and continuously reacting an alkali metal silicate, a solution of a salt of the other metal and an organic liquid, characterized in that in a first step the alkali metal silicate and the organic liquid are brought together and mixed, and then in a second step the mixture obtained previously is brought together with the solution of the salt of the other metal, at least one of said steps being carried out continuously. 2 - Process according to claim i, characterized in that the aforementioned organic liquid is an alcohol, in particular a saturated alcohol, especially methanol. 3 - Method according to claim 1 or 2 for the preparation in particular of precursor compositions of glass compositions, characterized in that the other metal mentioned above is chosen from the group comprising metals whose oxides are glass-modifying oxides. 4 - Method according to claim 3, characterized in that the other metal mentioned above is lead. 5 - A process according to any one of the preceding claims, characterized in that the molar ratio SiO2 / alkali metal oxide of the starting alkali metal silicate is determined so as to be equal to the molar ratio SiO2 / sum of the molar concentrations of alkali and metallic oxides of other metals in the final composition of the metallic silicate obtained. 6 - Precursor composition in particular of glass composition characterized in that it is based on a metallic silicate obtained by the process according to any one of the preceding claims. 7 - Glass composition, characterized in that it is obtained by a heat treatment of melting and refining of the precursor composition according to claim 6.