PART IX. MANUFACTURE OF ALUMINIUM AT Salindres (Gard). We will now give the actual preparation at Salindres,* with the latest improvements which it has received in practice. Aluminium is there regularly prepared at the works of the Chemical Manufacturing Company of Alais and Camargue, the old firm of Henry Merle & Co., new firm A. R. Pechiney & Co. The principal chemical reactions on which this process rests are the following: Formation of aluminate of soda by calcining beauxite with Na2CO3— (AlFe)203.2H2O+3Na2CO3= Al2O3.3Na2O+Fe203 +2H2O+3CO2. Formation of alumina by precipitating the aluminate of soda with a current of carbon dioxide Al2O3.3Na 0+3CO2+ 3H20= Al203.3H20+ Formation of Al2C16.2NaCl by the action of * Fremy's Ency. Chem., M. Margottet. chlorine on a mixture of alumina, carbon, and sodium chloride Al2O3+3C+2NaCl +6Cl=Al2C16.2NaCl +3CO. Reduction of this double chloride by sodium. Al2C16.2NaCl +6Na=2A1+8NaCl. The primary material then to furnish the aluminium is beauxite. It will be seen that to obtain the metal it is necessary to proceed successively through the following operations: I. Preparation of the aluminate of soda and solution of this salt to separate it from the ferric oxide contained in the beauxite. II. Precipitation of hydrated alumina from the aluminate of soda by a current of carbon dioxide; washing the precipitate. III. Preparation of a mixture of alumina, carbon, and salt, drying it, and then treating with gaseous chlorine to obtain the double chloride of aluminium and sodium. IV. Lastly, treatment of this chloride by sodium to obtain aluminium. We will now review these operations as practically carried out in detail. We will not consider the preparation of the crude materials as chlorine, sodium, etc., which is spoken of elsewhere. I. Preparation of the Aluminate of Soda. The aluminate to serve for the preparation of AP2C16.2NaCl was first obtained by the calcination of ammonia alum. At Salindres this was withdrawn and beauxite used, a material consisting of sesqui-oxide of iron and aluminium in varying proportions, with two molecules of water and a little silica. It is redder the more iron it contains. Beauxite is plentiful enough in the south of France, principally in the departments of Herault, Bouchesdu-Rhone, and Var. That used at Salindres comes from Var. It contains at least seventy-five per cent. alumina. To separate the alumina from Fe2O3, it is treated with carbonate of soda, under the influence of a sufficiently high temperature, the Al303 displacing the CO2 and forming aluminate of soda, Al2O3.3Na2O, while the Fe2O3 remains unattacked. A simple washing with water then permits the separation of the Al2O3.3Na2O from the insoluble Fe2O3. The beauxite is first finely pulverized by means of a vertical mill-stone, then intimately mixed with some Na2CO3. The mixture is made for one operation, of— This mixture is introduced into a reverberatory furnace, resembling in form a soda furnace, and which will bear heating strongly. The mass is stirred from time to time, and it is kept heated until all the carbonate has been attacked, which is recognized by a test being taken which does not effervesce with acids. The operation lasts from five to six hours. The aluminate thus obtained is separated from Fe2O3 by a washing with warm water. This washing is made at first with a feeble solution which has served for the complete exhaustion of the preceding charge, which was last washed with pure water, forming thus this feeble solution. This gives, on the first leaching, solutions of aluminate concentrated enough to be called strong liquor, which are next treated by the current of CO2 to precipitate the hydrated alumina. The charge is next washed with pure water, which completely removes the aluminate; this solution is the weak liquor, which is put aside in a special tank, and used as the first leaching liquor on the next charge treated. This treatment takes place in the following apparatus (see Fig. 8): B is a sheet-iron vessel, in the middle of which is a metallic grating, F, on which is held all round its edges, by pins, a cloth, serving as a filter. The upper part of this vessel is called simply the filter. A ought to be closed by a metallic lid held on firmly by bolts. To work the apparatus, about 500 kilos of the charge to be washed is placed on the filter cloth, the lid is closed, then the steam-cock ƒ of the reservoir A is opened. In A is the weak solution from the last washing of the preceding charge. The pressure of the steam makes it rise by the tube T'into the filter; another jet of steam, admitted by the cock b, rapidly warms the feeble liquor as it soaks into the charge. After filtering through, the strong liquor is drawn off by turning the stopcock G. The weak solution of the reservoir A is put into the filter in successive portions, and not all at once; and after each addition of solution has filtered through, its strength in B. is taken, before any more solution is run in; then, when the solution marks 3 to 4°, it is placed in the special tank for weak liquor, with all that comes through afterwards. Just |