Carbon dioxide-silica process

Carbon dioxide-silica process. Sand is mixed with sodium silicate (3.0 to 3.5% of sand volume), and the mixture is blown or hand-rammed into a core box or around a pattern. Carbon dioxide gas is passed through the compacted sand to harden the binder. The bonding strength eliminates the need for drying or baking the mold and metal can be poured into the mold immediately. Over-gassing should be avoided because it makes the mixture friable. 

The sulfur dioxide is recovered as sulfuric acid and reconverted to sodium sulfate. Alumina hydrate is precipitated from the sodium aluminate by carbon dioxide. The process has not become widely accepted because the product is contaminated by silica, but it was used in Belgium before and after World War I and in Germany in the 1920s and 1940s. 

In the course of mixture separation, the composition and properties of both mobile phase (MP) and stationary phase (SP) are purposefully altered by means of introduction of some active components into the MP, which are absorbed by it and then sorbed by the SP (e.g. on a silica gel layer). This procedure enables a new principle of control over chromatographic process to be implemented, which enhances the selectivity of separation. As a possible way of controlling the chromatographic system s properties in TLC, the pH of the mobile phase and sorbent surface may be changed by means of partial air replacement by ammonia (a basic gaseous component) or carbon dioxide (an acidic one). 

Both hot and cold processes are employed, although the hot process, which takes place at or above 212 °F (100 °C), is usually preferred for boiler FW applications, because it produces water of lower hardness levels and usually a lower silica content as well. Also, less lime is needed because the carbon dioxide with which it would normally react is driven off at the higher temperatures. Sometimes caustic soda (sodium hydroxide) is used in place of soda, depending on the alkalinity of the water and the chemical costs however, irrespective of the process or chemicals used, the major precipitants are always calcium carbonate and magnesium hydroxide. 

Demineralization by SAC(H)/Degassing/WBA(OH) Removes virtually all ionic TDS and carbon dioxide, but not silica. It is a cost-effective process. 

Demineralization by SAC(H)/Degassing/SBA(OH)/MB Removes all TDS, including carbon dioxide and silica. This is a standard process where the RW is high in alkalinity and silica. The MB acts as a polisher with infrequent regeneration. Silica and sodium are both reduced to below 0.02 ppm as CaC03. Conductivity is below 0.1 pS/cm. A schematic layout of this type of plant is shown in Figure 9.3c. 

Volatile silicones are broken down by oxidative chemical processes on entering the atmosphere. The partially oxidised degradation products are less volatile and these are scrubbed out of the atmosphere by rain or deposited on the ground to be further diluted and degraded, the final products being natural silica, carbon dioxide and water. 

All the silica present in the bauxite was converted to insoluble sodium aluminosilicate, which represented a loss of sodium and aluminum. The aluminum hydroxide was calcined to the oxide, and the sodium carbonate solution was concentrated for re-use. The process was developed by H. E. St-Claire Deville in the 1860s the carbon dioxide stage had been invented earlier by H. L. Le Chatelier. It was superseded by the Bayer process. 

Seailles-Dyckerhoff A process for extracting aluminum from clays and other aluminous minerals rich in silica. The ore is calcined with limestone in a rotary kiln. The product is leached with aqueous sodium carbonate, yielding sodium aluminate solution, from which alumina is precipitated by carbon dioxide. Invented by J. C. Seailles and W. R. G. Dyckerhoff in 1938 piloted in Tennessee in 1942, South Carolina in 1945, and Germany during World War II. See also Pedersen. 

The sodium chloride and sulphate regularly found in Leblanc soda ash are not usually injurious the insoluble matter should not exceed 1 to 1J per cent. It consists principally of calcium carbonate, alumina, silica, and ferric oxide. The sulphides should not be detectable by lead paper thiosulphates are destroyed in calcining the ash sulphites are usually present and can be detected by iodine soln. and sodium hydroxide, except in the so-called caustic ash, does not usually exceed 1 per cent. The moisture in fresh ash ranges below one per cent. Owing to the mode of preparation, ash by Solvay s process is more pure than that prepared by Leblanc s process. It does not contain sodium hydroxide, sulphides, sulphites, or thiosulphates it may contain a slight excess of carbon dioxide a little sodium sulphate is always present iron, alumina, and silica are present in minute traces sodium chloride is perhaps the only... 

The fundamental reason for using lime-soda softening processes is to reduce the temporary hardness (carbonate hardness) content of the raw water in order to minimize risks of carbonate scaling in the user s cooling systems. Often some of the permanent hardness (noncarbonate hardness) is also removed, as is some silica. The principal temporary hardness salt is calcium bicarbonate, formed by dissolution of limestone (calcium carbonate) by water containing dissolved carbon dioxide. 

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