Page:The American Cyclopædia (1879) Volume V.djvu/330

 326 COPPER SMELTING tained by either of these processes is still somewhat impure, from the presence of small quantities of sulphur and foreign metals, chiefly arsenic, tin, iron, and sometimes nickel. To remove these it is fused in contact with the air, by which these are oxidized and the fixed oxides combine with the silicious matters of the hearth. In this process, however, the copper absorbs a portion of oxygen and holds in solu- tion a quantity of suboxide, which impairs its malleability. This is removed by covering the surface of the melted metal with anthracite or charcoal, and stirring it with wooden poles, which by giving off reducing gases deoxidize the metal and give it the toughness of pure copper, after which it is cast into ingots. The details of these processes vary considerably with different ores and in different localities. The consumption of fuel in the treatment of copper ores is very great. Thus in the old Welsh process it is said that as much as 15 tons of coal is used in extracting one ton of copper from the low-grade ores of Cornwall. In Chili, however, owing to the great improve- ments introduced there, a ton of ingot copper is now made from ores of 13 per cent, with the aid of five tons of coal. The extraction of copper from its ores by solution has been long known. The spontaneous oxidation of the sulphuretted ores in certain mines gives rise to solutions of sulphate of copper, which when brought in contact with metallic iron yield their copper in a metallic state, while the iron is dissolved. The copper thus obtained is in a granular, more or less crystalline form, and is known as cement copper. By the artificial oxidation, by roasting in furnaces or in heaps with burning wood, of sulphuretted ores, a large proportion of the metal is converted into sulphate, and may then be dissolved out by water. From the solutions thus obtained the copper is either thrown down by iron in the metallic state, or in some cases by lime as an oxide, or by sulphuretted hydrogen gas as a sulphide, to be subjected to further treatment. Other methods of rendering the copper soluble have been devised. Thus, in some cases, the naturally or artificially oxidized ores are di- rectly treated with sulphuric or hydrochloric acid, by which the copper is dissolved as sul- phate or chloride, and then precipitated by metallic iron. Another plan consists in cal- cining the ores with a portion of common salt, by which, with the aid of the oxidized sulphur, sulphate of soda and chloride of copper are formed. This is known as Longmaid's process, and has been extensively applied by Henderson in England to the treatment of the pyritous ores from Spain, of which several hundred thousand tons are annually imported into Eng- land and calcined in proper kilns for the ex- traction of the large amount of sulphur which they contain, which is used for the manufacture of sulphuric acid. The residues, still contain- ing a little sulphur and from one to four per cent, of copper, are calcined with salt as above described, and give up to water, with the help of a little hydrochloric acid, the whole of their copper. The consumption of iron by these processes is considerable, amounting to from one and a quarter to two tons for each ton of copper produced. When the copper is present as sulphate, the resulting sulphate of iron is a valuable by-product. The protochloride of iron obtained when the copper is precipitated from its chloride has been converted by ex- posure to air or by chlorine gas into perchloride, and used to dissolve oxide of copper from oxid- ized ores. The occurrence of large quantities of low-grade copper ores in localities remote from cheap supplies of fuel has caused increased attention to be given to wet processes for the extraction of copper from its ores, and two newly devised methods have been brought forward and patented. The one, known as Monnier's, differs from that of Longmaid in substituting sulphate of soda for chloride of sodium hi the calcining furnace. By* this means it is possible to convert the whole of the copper in a sulphuretted ore into sulphate, which is then decomposed by metallic iron, or, as has been lately proposed, is partially separated by a process of concentration from the sulphate of soda, and then decomposed by calcination with charcoal. The other, known as the Hunt and Douglas process, is based on a new principle, and applied either to native oxides and carbonates or to the artificially pre- pared oxides resulting from the roasting of sul- phuretted ores. Protoxide of copper reacts with protochloride of iron to form peroxide of iron and a mixture of protochloride and di- chloride of copper: 3CuO + 2FeCl=Fe 2 O 3 + Cu 2 Cl + CuCl. The dichloride is insoluble in water, but readily soluble in hot and concen- trated brine; and from the solution holding the two chlorides of copper, the metal is readily thrown down by metallic iron, regener- ating the protochloride of iron, with a con- sumption of about two thirds of a ton of iron for a ton of metallic copper. In practice the ores (oxidized if necessary by roasting) are digested with a hot brine mixed with proto- chloride of iron ; and the resulting solution, being brought in contact with metallic iron, gives up its copper, and is then ready for the treatment of a fresh portion of ore. The ce- ment copper thus obtained is very pure, and is readily melted down into ingot copper. The small quantities of silver very often present in copper ores are dissolved in the form of chlo- rides in the Hunt and Douglas and Longmaid processes, and may be economically separated therefrom by the ingenious process of Claudet, which consists in precipitating the silver in com- bination with iodine. Swansea in Wales, which is in a coal district, has been for a long time one of the great copper-smelting centres, and re- ceives the ores and regulus not only of Corn- wall, but from many other parts of the globe. In former years much of the copper ore from Chili was carried to England for smelting, but