Sodium carbonate silicate production

The product of the fusion of silica with sodium carbonate, sodium silicate (strictly called sodium poly trioxosilicate but usually metasilicate), dissolves in water to give a clear, viscous solution known as waterglass . It hydrolyses slowly and silica is precipitated. Besides the metasilicate, other silicates of sodium are known, e.g. the poly-tetroxosilicate (orthosilicate), Na4Si04. Only the silicates of the alkali metals are soluble in water. Other silicates, many of which occur naturally, are insoluble, and in these substances the polysilicate anions can have highly complicated structures, all of which are constructed from a unit of one silicon and four oxygen atoms arranged tetrahedrally (cf. the structure of silica). Some of these contain aluminium (the aluminatesilicates) and some have import ant properties and uses. 

The next major raw material for which we discuss the derived chemicals is calcium carbonate, common limestone. It is the source of some carbon dioxide, but, more importantly, it is used to make lime (calcium oxide) and slaked lime (calcium hydroxide). Limestone, together with salt and ammonia, are the ingredients for the Solvay manufacture of sodium carbonate, soda ash. Soda ash is also mined directly from trona ore. The Solvay process manufactures calcium chloride as an important by-product. Soda ash in turn is combined with sand to produce sodium silicates to complete the chemicals in the top 50 that are derived from limestone. Since lime is the highest-ranking derivative of limestone in terms of total amount produced, we discuss it first. Refer to Fig. 2.1, Chapter 2, Section 1, for a diagram of limestone derivatives. 

As sodium carbonate may be mined directly, its use may be preferred over a manufactured product. It is used mainly in the glass industry. Sodium silicates may be derived from sodium carbonate and in their finely divided form, silica gel, may be used in detergents and soaps. 

Fusion of silica with sodium carbonate yields a mixture of silicates, excess of silica producing the so-called water-glass, a thick, syrup-like liquid employed as a cement and in the preservation of eggs. The commercial product contains 3 or 4 molecules of silica to each molecule of sodium oxide.10... 

A large part of the sodium carbonate consumed (e.g. 50% in the USA) is utilized in the glass industry, of which ca. 40% is used in the manufacture of bottle glass. Sodium carbonate serves both as a raw material and as a flux for the glass melt to dissolve the sand (see Section 5.1.2.2). A further 19% is utilized in the manufacture of chemicals, of which ca. 10% is for the production of sodium phosphates, mainly pentasodium triphosphate, in addition to silicates (sodium metasilicate pentahydrate and sodium orthosilicate), sodium chromate, sodium dichromate, sodium hydrogen carbonate, sodium nitrate etc. About 13.5% is utilized in the soap and detergent industry and 2.5% in the paper and pulp industry. Small quantities of sodium carbonate are necessary in almost all industry... 

Sodium silicates are made by fusing (melting) sand (silicon dioxide) and soda ash (sodium carbonate) or sodium hydroxide in a gas-fired open hearth furnace, somewhat similar to the furnaces used in the manufacture of steel. The products of this reaction are lumps of sodium silicate that are broken apart and dissolved in a stream of hot steam. The proportions of sand and soda ash used, the temperature of the reaction, and the amount of water that remains in the final product all determine the physical properties of the final product. 

The cooled product is ground and extracted with water. The soluble sodium aluminate is removed as a filtrate from the dicalcium silicate and insoluble matter. Injection of carbon dioxide into the filtrate produces a precipitate of aluminium hydroxide and sodium carbonate liquor (11.10), which is recycled to the initial stage. The aluminium hydroxide is heated to above 300 °C to produce pure alumina which is dissolved in fused cryolite (NaAIp4) at about 900 °C and electrolysed between carbon electrodes to produce molten aluminium. 

In general a module of 3.2-3.5 — that indicates the ratio between disodium monoxide and Si02-content in the sodium silicate — is used in order to reduce by-products. In all cases a corresponding by-product is produced that can be sodium sulfate, sodium chloride or sodium carbonate depending on the acid component used. In case of the use of potassium silicate the corresponding potassium salts develop. These by-products must be removed in the downstream process. 

The ore is first treated with caustic soda under pressure. The aluminium largely dissolves as the aluminate, the iron oxide is insoluble and the silica also remains in the form of a sodium aluminium silicate, which leads to a loss of aluminium. Hence the best bauxites are those low in silica. After filtration, the hydrated aluminium oxide is reprecipitated by seeding and the caustic soda solution may be re-used. The alumina is washed and then heated at 1200°C to remove water. The final step in the production of aluminium metal has to be electrolytic since the reduction of alumina with carbon is only possible at very high temperatures and the reverse reaction occurs on cooling. Moreover, because of the chemistry of aluminium, the electrolysis medium cannot be water in fact almost all commercial production of aluminium during the last ninety years has used an electrolysis in molten cryolite (Na3AlF5). 

To achieve full bleach performance, nonactivated formulations often contain sodium carbonate or layered silicates to increase the application pH, as the perhydroxyl anion is the bleach active species. Eormulations containing bleach catalysts also work best at high pH. In contrast, TAED-based products often contain a certain amount of acidification agent, such as citric acid or sodium bicarbonate for optimum performance of peroxyacetic acid. 

The original product sold in the United States contains -30% lithium hypochlorite (35% available chlorine), 34% sodium chloride, 20% of potassium and sodium sulfates, 3% lithium chloride, 3% lithium chlorate, 2% lithium hydroxide, 1% lithium carbonate, and the balance is water. It is made from lithium sulfate that is extracted into water from a lithium aluminum silicate ore after it is treated with sulfuric acid. The resulting solution also contains sodium and potassium sulfates. It is neutralized with calcium carbonate to pH 6, treated to remove calcium and magnesium, filtered, and concentrated. Sodium hydroxide is added to convert lithium carbonate to lithium hydroxide. The solution is cooled to 0°C and the resulting sodium carbonate decahydrate crystals are removed by filtration. Slightly more sodium hydroxide than the molar equivalent of lithium hydroxide is then... 

The Bayer process results in a waste stream known as red mud , which contains considerable amounts of sodium aluminium silicates. These can be converted into ATH if the red mud is mixed with limestone and sodium carbonate and calcined, to form sodium aluminate. This is extracted into water and gibbsite then precipitated as in the Bayer process. These products are known as sinter hydrates. They are whiter than the Bayer products as the calcination destroys the organics, but they still contain similar levels of sodium. 

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