COP′PER

Cu. Syn. Cu′′prum , L.; Cuivre , Fr.; Kupfer , Ger. Sources. Metallic copper (native copper) is found in many parts of the globe, diffused in isolated particles in the form of thin lam inæ, in loose grains intermixed with quartz (copper sand, copper barilla), in dendritic pieces, and in solid blocks, occasionally of many tons weight. The richest deposits of native copper are those of Lake Superior, in North America. More frequently and more abundantly it occurs as an ore, e.g. red oxide, black oxide, green carbonate of copper or mal′achite, blue carbonate of copper, vitreous sulphide of copper, purple copper, copper pyrites, or yellow copper ore, with sulphur, antimony, or arsenic, and other metals (true grey copper ore or fah′lerz), as an impure hydrated silicate (chrys′ocolla), and as an impure hydrated oxy chloride (atac′amite). The most abundant and important ore is copper pyrites. It is principally obtained from the mines of Cornwall, Devons hire, and Cuba. The carbonates smelting them is generally of the best quality. Prep. We will not attempt to give a minute description of the various complex proce es by which the reduction of copper from its ores is effected, but will merely give an outline of the common or Welsh proce . This proce includes six distinct operations, as follows:—1. The ore (copper and iron pyrites), containing from 8 to 10% of copper, is roasted in a reverberatory furnace, called a ‘calciner,’ by which much of the sulphide of iron is converted into oxide. 2. The calcined ore is melted with ‘metal slag’ (a product of a subsequent operation—No. 3), in a melting furnace called the ‘ore furnace.’ The products are a regulus, termed ‘coarse metal,’ containing about 35% of copper, and ‘ore-furnace slag,’ which is thrown away. Much of the iron, and the whole of the so-called earthy matter of the ore, are thus separated as slag. 3. The coarse metal, having been granulated by causing it to flow from the furnace into water, is calcined with free acce of air in a calciner, and a considerable amount of sulphur is expelled. 4. The calcined granulated, coarse metal is melted with the addition of matters rich in oxides of copper, namely, ‘roaster’ and ‘refinery slags’ (from the two remaining operations, Nos. 5 and 6, respectively), and native carbonates of copper, or ores containing oxide of copper. The products are a regulus, termed ‘metal,’ which contains about 75% of copper, and metal slag (see No. 2). The metal should be in the state of ‘white metal,’ compact and brittle, with a feeble metallic lustre and a dark, bluish-grey colour. It is tapped off into sand moulds. 5. The pigs of regulus obtained by the last operation are roasted in a furnace through which air pa es. The temperature is so regulated that the regulus may be melted in from 6 to 8 hours. The slag is skimmed off, and after a time the heat is lowered, to allow the regulus to solidify. It is again melted and tapped into sand moulds, the product being called ‘blister copper.’ 6. This, the last operation, is termed ‘refining.’ From 6 to 8 tons of blister copper, in pigs, are melted in a furnace, and kept exposed for about 15 hours to the oxidising influence of the air. The slag is skimmed off through the end opening. When the oxidation has been sufficiently prolonged, anthracite or free-burning coal, as pure as po ible, is thrown upon the surface of the metal, and after a short time the thick end of a long birch or oak pole is plunged into the molten ma . This part of the operation is termed ‘poling.’ The wood in contact with the copper is rapidly decomposed; much gas is evolved, which causes the metal to be splashed about, and every part of it to be exposed to the reducing action of the coal. When the refiner finds the metal to be at the state of ‘tough pitch,’ the pole is taken out, and the coal pushed back from the end opening, through which the copper is then ladled out as quickly as po ible, and cast into suitable moulds. For full details of this and other proce es, the reader is referred to Dr Percy’s work on ‘Metallurgy,’ and Ure’s ‘Dictionary of Arts, Manufactures, and Mines.’ In the laboratory copper is commonly employed under the following forms: — refining furnace into hot water. In small lumps like peas and beans; hence its name. Used to make alloys, solutions, . 2. Electrotype copper. A very pure form, obtained by decomposing sulphate of copper in an electrotype apparatus. It does not contain lead, whereas most varieties of commercial copper do contain that metal. copper from the furnace into cold water. In small pieces, with a feathered edge. Used to make calamine, bra , solution of copper, . 4. Copper in plates or foil. Those of commerce (best, annealed) are generally employed. 5. Copper in powder. — a. A solution of sulphate of copper is heated to the boiling-point, and precipitated with distilled zinc; the precipitated copper is then separated from the adherent zinc by dilute sulphuric acid, washed with water, and dried by exposure to a moderate temperature. 6. Copper prepared by the hydrometallurgical method. —One of the oldest proce es of this kind, is that known as the ‘cementation’ method, and consists in precipitating copper from a solution of the sulphate of the metal, by means of metallic iron. In some mines solutions of the sulphate are met with occurring naturally, in others they are prepared artificially by treating poor ores containing oxide of copper, with sulphurous acid or diluted sulphuric acid, and sometimes by roasting copper pyrites and afterwards washing them with water to extract the resulting sulphate. The copper obtained by any of the above proce es is called ‘cementation copper.’ In the Isle of Angle sea the cementation liquid containing the di olved sulphate of copper, is first run into large ve els where the suspended matters are allowed to subside; from these it is conveyed to tanks containing old scrap-iron, which serves as the precipitating agent. The scrap-iron is occasionally stirred up so as to renew the metallic surface presented to the solution. The muddy liquor which contains metallic copper as a spongy ma , besides impurities, is run into ve els where it deposits the copper, which after the removal of the supernatant fluid, is removed and dried in a furnace. 7. Wet Proce . (Henderson’s proce .) The ores (Spanish and Portuguese pyrites) treated by this method vary very slightly in composition, rarely containing much more than 3 per cent. of copper, nearly 50 per cent. of sulphur, from 43 to 44 per cent. of iron, with small quantities of lead, arsenic, zinc, lime, . The ores are first employed by the vitriol manufacturers, as a source of sulphuric acid. In the proce of burning they lose about 30 per cent. of their sulphur. The copper is extracted from the residue by subjecting this latter to the following proce es, which are thus described in the ‘Encyclopædia Brittanica.’ I. Grinding. The burnt ore, as received from the acid burners, is first mixed with about 15 per cent. of common salt, and ground to a fine powder by pa ing it between a pair of heavy cast-iron rolls. As the amount of sulphur left in the burnt ore is apt to vary, it is nece ary to ascertain its proportion in each parcel of burnt pyrites. When the sulphur falls short of the proportion nece ary for effecting the decomposition which follows, a sufficient quantity of ‘green’ or unburned pyrites is added to produce a proper balance. If, on the other hand, the sulphur has been sufficiently extracted, dead roasted ore is added. II. Calcination. This operation is accomplished in several kinds of furnaces, that used by the Tharsis Sulphur and Copper Company, being a large muffle or close furnace. By others a patent furnace with a revolving hearth and mechanical stirring arrangement has been adopted with good results; and some use open reverb a tory furnaces heated by gas from Siemens’s generators. During the roasting the mixture is frequently stirred, and in the case of hard-worked furnaces, turned with long rabbles, and the completion of the operation is ascertained by test a ays. When the copper has been brought into a soluble condition, the charge is raked out of the furnace and permitted to cool under a screen at its mouth. By the calcination the sulphur in the compound is first oxidised, sulphate of sodium is formed, and at the same time the chlorine from the sodium chloride unites with the copper to form cupric chloride. A small proportion of cuprous chloride is also formed, and special precautions have to be taken to prevent the extensive formation of this compound which is di olved only with difficulty. The hydrochloric acid and other gaseous products evolved during the calcination are condensed as ‘tower liquor’ in ordinary condensing towers, and the product is used in the subsequent proce of lixiviation. III. Lixiviation. The calcined ore is conveyed to tightly caulked wooden tanks, in which it receives repeated washings with hot water, tower liquor, and dilute hydrochloric acid till all the soluble copper is thereby extracted. The product of the latter washings is pumped or drawn up by a modification of Gilford’s injector, to serve as a first liquor for subsequent charges of the lixiviating tanks, and no solution under a definite strength is permitted to pa on to the next stage in the proce . The insoluble residue in the tanks consist of “purple ore,” an almost pure ferric oxide, largely used in “settling” blast furnaces, and for smelting purposes; besides which it is available as jewellers’ rouge. IV. Precipitation. The precipitation of metallic copper from the solution of its chloride is accomplished in large tanks by means of metallic iron in the same way that cementation copper is obtained from solutions of the sulphate. The solution is run into the tanks in which there are miscellaneous heaps of old malleable iron; the chlorine combined with the copper unites with the iron, and metallic copper in the state or fine division is thrown down. The completion of the precipitation is ascertained by dipping a bright steel knife into the solution in the tank, and when no deposit of copper covers the steel, the liquor is run off and a new charge conveyed into the tank. The tanks are drained periodically for removing the precipitate, which is first roughly separated from the small pieces of iron, after which it is more thoroughly freed from iron, ., by washing in water in a rocking sieve apparatus. The precipitate so obtained should contain 80 per cent. of metallic copper, which is either smelted directly for blister copper, or may be fused with the white metal of the ordinary smelting proce , and subsequently roasted. It has been found po ible to extract in this proce with profit the small proportions of lead, silver and gold, which Spanish pyrites is known to contain. Two proce es are in operation for this purpose—one devised by Mr P. Claudet, and the other by Mr W. Henderson, the original patentee of the wet proce . The liquors from the first three washings contain practically, all these metals, and they alone are treated. Mr Claudet precipitates them from the solution by means of iodide of pota ium. Mr Henderson dilutes his solution from 20° to 25° Twaddell, and adds a very weak solution of lead salt, such as the acetate by which he obtains a cream-coloured precipitate containing 5 or 6 per cent. of silver, and 3 oz. of gold to each ton of the precipitate. The importance of the wet proce may be estimated from the fact, that although it originated only