Method and apparatus for producing a silicon based binding composition and product prepared therefrom

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FIELD OF THE INVENTION

This invention relates to the manufacture of silicon based binding compositions from silica. In particular, the invention relates to binding compositions which are prepared by the wet grinding of silica in an alkaline medium and products which may be prepared from the binding composition. In addition, this invention relates to the apparatus which may be used to prepare the binding composition.

BACKGROUND OF THE INVENTION

Ceramics may generally be defined as products manufactured by the action of heat on earthy raw materials in which silicon with its oxide and silicates occupy a predominant position. Various types of products are made from ceramics including structural clay products (such as brick, tile, terra cotta and glazed architectural brick); whitewares (such as dinnerware, chemical and electrical porcelain, sanitary ware and floor tile); glass products of all types; porcelain enamels; refractories; Portland cement, lime, plaster and gypsum products; abrasive materials such as fused alumina, silicon carbide and related products; and, aluminum silicate fibres.

Clay based ceramic products have become a staple in many areas of industry including the construction industry. In particular, structural clay products are used extensively in the construction of buildings.

Accordingly, one disadvantage of structural clay products is that an extensive amount of time is required to produce a single product. Further, large amounts of energy must be utilized during the baking process in the kiln. Typically, in order for a manufacturing plant to be economically efficient, kilns having a capacity to simultaneously bake a large quantity of bricks are required. In addition, manufacturing plants tend to be located near the source of the clay, thus increasing the cost of transporting the bricks to the construction site where they will be used.

More recently, silicate based material has been utilized to produce bricks. For example, calcium silicate bricks may be prepared by grinding lime together with sand to produce a lime-silica bonding adhesive, mixing this adhesive with sand, pressing the mixture of sand and bonding adhesive into a mold and baking the mixture in an autoclave. Calcium silicate bricks may be utilized in place of more conventional clay bricks in the construction industry.

One disadvantage with calcium silicate bricks is the amount of time required to produce a single brick. In addition, a large amount of processing equipment and power input is required to produce calcium silicate bricks.

Binding compositions have also been prepared by the wet grinding of sand in an alkaline medium. According to the method disclosed in U.S.S.R. Author's Priority Certificate No. 992487, sand is ground in a ball mill in an alkaline medium (pH 9.0-10.5) to produce a silica based binding composition. The feedstock is divided into three portions. The first portion, which comprises 50% of the feedstock of sand, is milled for 6 hours. In the presence of a waterglass having a pH of 10.5. The second portion, which comprises 25% of the initial feedstock, is then combined with the milled feedstock and the mixture is milled for 7 hours. The third portion, which comprises 25% of the initial feedstock, is added to this milled product and this mixture is then milled for an additional 12 hours. One disadvantage of this method is that each batch requires 24 hours of milling time. This reduces the potential throughput of the process. In addition, the lengthy grinding time increase the wear of the components of the ball mill and substantially decrease the lifetime of the ball mill. In addition, the product produced by this method may not have sufficient compressive strength for use in some applications.

SUMMARY OF THE INVENTION

According to the instant invention, a binding composition comprising silica is prepared by fractionating a silicon feedstock in the presence of an alkaline medium to produce fines that are substantially spherical in shape. The fines are surrounded by a layer of orthosilicic acid sol. Preferably, the binding solution has no or substantially no iron therein. The binding solution may contain from about 25 to about 0 ppm iron, more preferably from about 15 to about 0 and, most preferably, from about 10 to about 0 ppm iron.

The binding solution may be prepared by passing the silica through one or more grinders. Preferably, at least two grinders are utilized. In the first grinder, preliminary grinding of the silica feed material is undertaken and a dispersed mass of silica in an alkaline medium is formed. This dispersed mass is continuously fed into a second grinder where the silica particles are ground to the required level of fineness and the binding solution in produced. The grinding is conducted so as to shear the silicon dioxide and to achieve a high degree of fractionation of the silica particles so as to produce a highly uniform binding solution.

In accordance with the instant invention, the binding solution may be prepared in a grinder having first and second frusto conical sections. The second frusto conical section is coaxially mounted within the first frusto conical section. The second frusto conical section rotates relative to first frusto conical section. The binding solution is passed through the work zone between the first and second frusto conical sections. During its passage through this work zone, the silica is ground to the desired size. As will be appreciated by those skilled in the art, each grinder has an optimum size reduction of particles which may be achieved. Accordingly, depending upon the feed size of the feed material, one, two or more grinders may be required.

If more than one grinder is required, then the final grinder may have a plurality of conical spindles positioned in the working zone of the grinder. The apex of the conical spindles is positioned adjacent the discharge end of the grinder. The work zone of the grinder narrows from the entrance to the work zone to the discharge end of the work zone. The work zone narrows at a greater rate than the conical spindles. Accordingly, the apex of the conical spindles is in contact with the grinding surfaces of the first and second conical sections while the end of the conical spindles distal to the apex of the spindles will not be in contact with both of these surfaces. The conical spindles act as additional grinding surfaces to fracture the silica particles as they pass through the work zone.

One advantage of the instant invention is that a binding solution is prepared in a substantially shorter amount of time than has been achieved using a ball mill. In particular, a binding solution may be prepared in about one to two hours whereas approximately twenty-four hours have been required utilizing ball mills.

The binding solution of the instant invention may also be utilized to produce a finished product such as a brick. According to the process, the binding solution is intimately mixed with a filler. Preferably, the filler is sheared in the presence of the binding solution such as by passing the filler and binding solution through a grinder similar to the final grinder described above wherein the spindles have been removed. The prepared mixture is then compacted into a mould and cured. By varying the filler or mixture of fillers, a variety of products having a wide range of performance characteristics including high compressive strength, high yield strength, good acid r