Patent GB-369244-A (GB)
Title: Improvements in or relating to the production of alumina
IPC: C01F7/38
Filed: 1930-11-11
Abstract: <PICT:0369244/III/1> Alumina is obtained from materials containing aluminium, iron, calcium, &c. by treating them with reducing agents at a temperature sufficiently high to render the alumina insoluble but below the melting point of the material, removing the reduced iron and other impurities by means of an acid or a gas such as chlorine, and repeating the reducing and iron removing steps alternately until the residue comprises alumina, with or without carbon.  Reducing gases such as hydrogen or carbon monoxide may be used instead of carbon or in addition thereto in these subsequent reducing steps.  The carbon may be added in the form of a carbohydrate solution as described in Specification 358,000 or the ground material may be mixed with carbon in the solid form as sugar, fire-soot, lampblack, starch or colloidal graphite, provided that no silica is present in these bodies.  In the treatment of clays containing silica, such as common refractory clay and the so-called ancylus clay, the silica is rendered insoluble by calcination at a temperature of 700-800 DEG  C. and the remaining components are dissolved in an acid, such as hydrochloric acid, which can easily be regenerated.  The solution is preferably effected on the counter-current principle and, if desired, under pressure to obtain a saturated solution of alumina in the acid.  In the case of ancylus clay, the potassium may be recovered as chloride by crystallization from the solution, and if the iron content is high, a reducing agent is added during the calcination step and any iron or ferroso-ferric oxide produced removed magnetically.  Hydrogen is obtained as a bye-product in the dissolving stage after the main reduction step if acid is used, or the iron may be removed by precipitation, hydrolysis, &c., and the remaining components which have been removed from the alumina-carbon mixture recovered.  The primary chloride solution is heated at high temperatures and in such a manner as to permit of ready evaporation, for example, the solution is atomized in a heated tower or spread on a heated moving surface.  The acid vapours are collected and may act on wood to form an acid wood-sugar solution which may be used to treat the raw material or the acid may act first on the clay &c. and the chloride solution formed may act on wood.  The coating of oxides and carbon is removed and heated in the absence of air until the iron is reduced and the alumina converted into an insoluble form, after which all soluble components are removed, again in the absence of air.  A suitable arrangement for carrying out the process is shown in the Figure.  The chloride solution is sprayed through a nozzle 3 on to a rotating drum 1 heated by burners 7, or the drum may dip into the liquid introduced at the bottom of the shaft, to form a thin coating which is evaporated and removed by a knife 12.  The temperature at the surface of the drum is 500-600 DEG  C. and the products of combustion led off through pipes 9 may be used to concentrate the acid evolved, which passes off through pipe 10, or to concentrate the chloride solution to be evaporated.  The dry mixture is compressed by pistons 14 into tubular retorts 15 heated to a temperature of about 1000 DEG  C.  Outlets, e.g. tube 23, are provided for the gases evolved which may be used to form a non-oxidizing atmoshpere for the drum 1.  After reduction of the iron oxide, the mass is passed into a tube 21, provided with supply means 22 for a liquid hydrocarbon or reducing gas to prevent oxidation.  The tube 21, with its open end covered, is transported to a cooler 25 and the mass passed therethrough to the acid vessel 24, definite portions being fed in by valves 27, 28. The soluble components are dissolved, and the hydrogen evolved passes off through pipe 29.  When beryllium is present in the raw clay, the final product contains beryllium oxide, and aluminium produced therefrom will be alloyed with beryllium.