158 ECONOMIC GEOLOGY 



the ore in the presence of carbon. The following equations 

 indicate the process as applied to cuprite and tenorite: 



Cu 2 0+C = CO+2Cu 

 2CuO+2C = 2CO+2Cu. 



The two carbonates, malachite and azurite, when roasted lose 

 both water and carbon dioxide. The resulting product is the 

 black oxide of copper, which in the presence of carbon yields 

 metallic copper and carbon monoxide according to the equation 

 given under tenorite. 



(2) The Oxidation Process. The sulphides of copper are roasted 

 in large beds in the open air to volatilize the sulphur con- 

 tent as sulphur dioxide. These beds at the Ely mine at Copper- 

 field in Vershire, Vermont, in the days when 1700 miners were em- 

 ployed at one time, were approximately 50 rods in length and 

 about 4 ft. high. The copper by the open-air roasting was 

 largely converted into the oxide. In the later years at the same 

 camp the ore was roasted in a blast-furnace and the sulphur 

 passed out of the chimney flues as sulphur dioxide. The con- 

 centrated and oxidized ore is then roasted with carbon or coke 

 and copper matte is obtained. From the matte by further 

 treatment blister copper is obtained, from which arsenic and 

 antimony are removed by volatilization, if present, then the lead, 

 then the iron, and the copper is finally obtained in a compara- 

 tively pure state and cast into blocks weighing about 200 Ib. 



(3) The Chlorination Process. When copper ores contain about 

 3 per cent, of copper, too poor for the extraction of copper by 

 roasting alone, they are sometimes calcined with about 15 per 

 cent, of common salt. This converts all the copper into the 

 chloride which is readily soluble in water. The fused mass is 

 then leached with water and the resulting solution of the chloride 

 of copper is drawn off into precipitating tanks. Scrap iron is 

 often used to reduce the copper to the elemental state. 



(4) The Electrolytic Process. This process consists in bringing 

 the copper into solution and reducing the metal by electroly- 

 sis. The process is applicable to the forsaken residues around 

 many old copper mines. The cost of reduction is said to be 

 about one-half cent per ton of solution. 



(5) The Scrap-iron Process. The Rio Tinto mines in Spain 

 furnish many pounds of copper by simple reduction with scrap 

 iron. At Wicklow, Ireland, at one time about 500 tons of scrap 



