Abstract: A process is disclosed for the hydrothermal production of potassium silicate solutions with high SiO.sub.2 :K.sub.2 O molar ratios, by the hydrothermal reaction of quartz sand with aqueous potassium hydroxide solutions at temperatures in the range of 150.degree. to 300.degree. C. at the pressures of saturated water vapor corresponding to these temperatures in a pressure reactor, which is characterized in that the potassium silicate solutions obtained thereby, which have SiO.sub.2 :K.sub.2 O molar ratios of less than 2.75:1, are then reacted with a quartz tempered at temperatures in the range of over 1100.degree. C. up to melting point, the temperatures and pressures also being maintained in the ranges named.

Abstract: Method for producing alkali metal silicates from crystalline siliceous material and aqueous alkali metal hydroxide solution at high temperature and normal pressure, characterized in that cristobalite and/or tempered quartz sand are used as the siliceous material, and this material is reacted with aqueous, 20 to 50 wt. % sodium or potassium hydroxide solution at temperatures of 100.degree. to 150.degree. C. and normal pressure, the molar ratio of SiO.sub.2 to Na.sub.2 O or K.sub.2 O in the reaction mixture being between 2:1 and 1:7.

Abstract: The direct hydrothermal production of high purity potassium silicate solutions having a high SiO.sub.2 : K.sub.2 O molar ratio by reaction of a silicon dioxide source with aqueous potassium hydroxide solutions is made possible by using a silicon dioxide source that contains a sufficient fraction of cristobalite phase, or by conditioning other crystalline forms of silicon dioxide by heating at or above 1100.degree. C., but below the melting point of silica, before the hydrothermal treatment. Preferably the potassium hydroxide solution has a concentration range of 10 to 40% by weight, and the reaction is carried out in a closed pressure reactor at temperatures of 150.degree. to 300.degree. C. and under saturated steam pressures corresponding to those temperatures.

Abstract: The direct hydrothermal production of high purity sodium silicate solutions having a high SiO.sub.2 : Na.sub.2 O molar ratio by reaction of a silicon dioxide source with aqueous sodium hydroxide solutions, or with aqueous sodium silicate solutions having a lower SiO.sub.2 : Na.sub.2 O molar ratio, is made possible by using a silicon dioxide source that contains a sufficient fraction of cristobalite phase, or by conditioning other crystalline forms of silicon dioxide by heating at or above 1100.degree. C., but below the melting point of silica, before the hydrothermal treatment. Preferably the sodium hydroxide solution has a concentration range of 10 to 50% by weight, and the reaction is carried out in a closed pressure reactor at temperatures of 150.degree. to 300.degree. C. and under saturated steam pressures corresponding to those temperatures.

Abstract: A process for the hydrothermal production of clear sodium silicate solutions by reacting sand and aqueous NaOH solution wherein an excess of 5 to 10% by weight of sand is used and the reaction is conducted in a rotating pressure vessel until 90 to 95% complete, after which it is transferred and completes in a blow-off vessel.

Abstract: An apparatus for the continuous production of clear sodium silicate solution with an SiO.sub.2 :Na.sub.2 O weight ratio of 1-2.8:1 by fusing sand in aqueous sodium hydroxide using a pressure-sealed circulating suspension reactor having an upper portion comprising a partially tapered gravity thickener and a lower portion comprising a cylindrical jet loop mixer. The jet loop mixer has a concentric cylindrical insertion tube suspended therein, and a recirculating power jet nozzle is upwardly directed through the bottom of the jet loop mixer so that its stream is directed into the lower end of the insertion tube, causing a continuous circulation flow.

Abstract: Methods for removing deposits formed in the heat exchange tube of waste heat recovery boilers for glass furnaces in which sodium aluminum silicate fine particles are introduced into the waste gases before they enter the heat exchange tubes.

Abstract: A process for hydrothermally disintegrating wastes or residues having a high content of calcined aluminum oxides by reacting said wastes or residues with an aqueous sodium hydroxide solution having a concentration of sodium hydroxide of from about 20 to about 50% by weight at a temperature in the range of from about 180.degree. to about 250.degree. C. under a saturated steam pressure corresponding to said temperature. The sodium aluminate solution obtained is separated off and optionally filtered.

Abstract: A process for the hydrothermal fusion of aluminum silicate and alkali aluminum silicates with aqueous sodium hydroxide solution under pressure and at elevated temperatures in the presence of soluble silicates, in which an aqueous solution containing from about 20 to about 50% by weight of NaOH is mixed with aluminum silicates and/or alkali aluminum silicates, and with a hydrothermally fusible silicate component, wherein the ratio by weight of SiO.sub.2 to Al.sub.2 O.sub.3 in the mixture amounts to at least 30:1 and the ratio by weight of SiO.sub.2 to Na.sub.2 O amounts to at least 1.5:1, and the mixtures are reacted at temperatures of from about 180.degree. to about 250.degree. C. and under the saturated steam pressures corresponding to those temperatures. The resulting sodium silicate solution, which contains the dissolved aluminum, is then separated off.