Patent GB-367407-A (GB)
Title: Process for preparing bleaching materials and products thereof
IPC: B01J20/12
Filed: 1930-10-06
Abstract: A magnesium silicate for use as a bleaching earth is obtained by treating siliceous material, preferably hydrated and of organic origin, such as diatomaceous earth, in the presence of water, with either normal or basic magnesium carbonate.  Crude magnesite is calcined in a rotary kiln at a temperature of 700-900 DEG  C., ground and mixed with water to form a slurry containing magnesium hydroxide. This slurry is treated with carbon dioxide, obtained for example from flue gases from the boiler supplying steam for later use in the process, to form a hydrated magnesium carbonate which is then mixed with finely ground diatomaceous earth.  In the presence of excess magnesium hydroxide and carbon dioxide, the hydrated magnesium carbonate tends to crystallize on the surface of the diatomaceous earth particles.  The mixture is then separated from heavy impurities and passed to a final carbonator where it is treated with carbon dioxide at a low temperature until practically all the magnesia is converted into carbonate. The slurry is then treated in autoclaves to effect the final reaction.  Preferably a magnesium carbonate is used which retains its water of crystallization at a temperature above 212 DEG  F.  The slurry is treated for about 1 hour with steam at a pressure of 200 lbs. per sq. in. and a corresponding temperature, the autoclave being provided with a regulator steam valve operating at 150 lbs. pressure.  At a temperature of about 390 DEG  F., the hydrated magnesium carbonate reacts with the silicic acids present to give a magnesium silicate which appears to be adsorbed on the particles of diatomaceous earth remaining.  The carbon dioxide evolved, together with steam, passes through the regulator valve, through a heat exchanger, and to a cooling and drying tower, and the carbon dioxide thus obtained may be used for the final carbonation step. The reaction product may be passed to a water separator, where the coarser material is separated and then filtered, to obtain a coarse product of higher filtration rate and lower decolourizing power than the fine material, or the mass may be filtered directly. If necessary, the product may be treated with dilute acid to remove unreacted magnesium compounds.  The filtered product is then dried to a moisture content of 5-10 per cent. Several autoclaves may be arranged in a battery for continuous working.  In the final product, the ratio of silica to magnesia may vary from 5 or 6 : 1 to 1\ba1/2\be : 1.  The product is preferentially wetted by oil, and is used in the preparation of oil and asphalt emulsions, insecticide emulsions, in the dehydration of petroleum emulsions &c.  As a bleaching and filtering material, it is used for purifying and decolourizing oils, both of mineral and organic origin, carbohydrates such as sugars, and food products.ALSO:A material for use as a filtering medium, for example in decolourizing oils, carbohydrates, &c., is obtained by treating siliceous material, preferably hydrated and of organic origin, such as diatomaceous earth, in the presence of water, with a magnesium carbonate.  The reaction is carried out under pressure at a temperature of about 390 DEG  F., and the product is stated to be a basic magnesium silicate, in which the ratio of silica to magnesia may vary from 5 or 6 : 1 to 1 1/2 : 1, and is preferentially wetted by oil.ALSO:A material for use as a bleaching agent in decolourizing carbohydrate solutions and for use in the preparation of insecticide emulsions is obtained by treating siliceous material, preferably hydrated and of organic origin, such as diatomaceous earth, in the presence of water, with a magnesium carbonate.  The reaction is carried out under pressure at a temperature of about 390 DEG  F., and the product is stated to be a basic magnesium silicate, in which the ratio of silica to magnesia may vary from 5 or 6 : 1 to 1 1/2 : 1, and is preferentially wetted by oil.