Modern Gasworks Practice

574 MODERN GASWORKS PRACTICE Another sensitive material is “ Lux.” This material is prepared from the xesidues left after the extraction of alumina from bauxite (ferric aluminate), these residues containing a high proportion of iron. The material is powdered, mixed with a definite proportion of sodium carbonate, and raised to a red heat, resulting in the formation of sodium aluminate and sodium ferrate. The mass consisting of these two compoimds is then treated with. water, wheu the sodium aluminate dissolves out, and the ferrate is decomposed with the formation of a colloidal ferric Hydrate. The English caustic soda process of extracticn leaves the iron oxide in its original condition in the bauxite ore. In the condition as delivered for use “ Lux ” contains about 55 per cent, of ferric oxide and 20 per cent, of alkaline salts. In many cases it is desirable to mix a certain proportion of sawdust with the material as it is received, the usual ratio being 3 parts of “ Lux ” to 1 part of sawdust. It is said by some that with. “ Lux ” the absorption of H2S takes place more rapidly than with bog-ore, owing to the faet that the ferric hydrate is separated out in a finely divided state during the manufacture of the material. In addition, it is claimed that a greater percentage of sulphur may be obtained before the material is finally spent; but some trouble may be experienced from firing. The Chemical Waste Products Committee of the Munitions Inventions Department 1 has studied various processes for the conversion of residues containing oxide of iron into material suitable for gas purification. Among the substances examined and found effeetive was a residue resulting from the manufacture of cyanide. This contained a high percentage of ferric hydrate, and was prepared for use by a special ■drying process which produced the correct pliysical texture. Iron was also recovered from the waste hydrochloric acid liquors, obtained in the pickling of iron, by the addition of lime, a suitable purification material being yielded. The artificial preparations made up from bumt spent oxide are sold under a number of trade names (e.g. “ Ferrox,” “ Brownox,” “ Metroxide,” etc.), and contain in general a higher proportion of ferric hydrate than is the case with natural bog-ore. This accounts for their somewhat vigorous action, although in their prepara-tion the addition of otter ingredients adds to their efficiency. Broadly speaking, they may be said to result from bumt spent oxide, which is obtained from sulphuric acid works, rendered active by special treatment. This treabment varies witlithe type of material, but in one instance it consists almost solely of grinding the burnt product in a disintegrator with the addition of a definite proportion of soda ash and sawdust. A product known as Laming’s mass was at one time a great favourite in France, Spain, Italy and the East. This consists of sawdust mixed with lime and wetted with a solution of snipha.te of iron. A. H. Scott,2 dealing with the sources and methods of production of some of the better known forms of gas purification oxides, says that, so far as the mineral bauxite is concerned, European methods are more efficient than American, and leave less than 6 per cent, of alumina in the residue. In America as mueh as 11 per cent. 2 Special Report, Ministry of Munitions, 1919. 3 New England Assoen. Gas Eng. Ann. Meeting, 1917.