Manufacture of Alkali Silicates

Si02/metal oxide 1.5 from quartz sand and alkali carbonates or hydroxides 

Anhydrous alkali silicates with Si02/alkali oxide 1.5 (solid glasses) are manufactured by reacting fine particulate quartz sand, which is as pure as possible, is clay-free and has a low iron content, with alkali carbonates or hydroxides at 1300 to 1500°C in tank furnaces lined with refractory bricks or in rotary tube 

The alkali silicate melt flows into casting molds in which it solidifies to transparent more or less colored lumps. 

Aqueous solutions of alkali silicates can also be produced in an energetically favorable reaction by reacting sand with sodium hydroxide e.g. in autoclaves with stirrers under pressure and high temperatures. 

Of the alkali silicates with Na20 nSi02. only sodium metasilicate, Na2Si03, with n = 1, has industrial and commercial importance. It is either produced by melting sand with sodium carbonate in a 1 1 molar ratio or by reaction of sand with solid sodium carbonate in rotary or drum furnaces. 

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