Extractive Metallurgy of Copper

Beneficiation and extractive metallurgy of copper ores comprises several steps that have for objectives concentrate and extract the copper present in the ore. The methods to be used vary with the mining operation and depend on the ore characteristics and economical aspects. Thus, initially is common to have the sizing and classification stage which employs crushing, screening, grinding, and sorting operations. In a second step can be required a concentration which can be done by froth flotation, ion exchange, solvent extraction, and precipitation. The next step usually involves pyrometallurgical processes, and finally an electrolytical process that let to obtain metallic copper.

The minerals employed in the copper extraction are usually sulphides that content iron and other impurities with economical interest or not such as arsenic, antimony, lead, bismuth, gold, silver, and nickel. The gangue is usually quartz. Two fundamental methods are used: dry and wet route. The first is the most important and treats concentrates with not less than 24% copper. The second route is the hydrometallurgical option and usually treats ores with less than 2% copper.

With the first route, the copper is concentrate from 0.5 to 1 %Cu until 24 to 30% Cu. In this part is very important to eliminate no useful material. Once the concentrate is obtained, will be sent to a pyrometallurgical process where the concentrate is partially roasted in order to eliminate sulphur, and later is smelted to produce a mate that contains all the material in liquid state. In this part, there is an unproductive material called slag. The latter one is formed from the gangue and iron oxide formed during the roasting, and left a product, the mate (Cu2S, nFeS). This product needs to be oxidized in order to obtain an impure copper. For this operation is used the remanent iron and for several reaction will be obtained a copper no pure.

The copper obtained in the last step needs to be improved in grade and quality. The improving can be done in two steps, the first steps involves a pyrometallurgical process where the metal is introduced into a furnace at the temperature of 1100 ^oC, then is produced an oxidant reaction which forms cuprous oxide and some impurities are liberated by air addition. Once the impurities are eliminated as a slag, is required to reduce the copper to the called blister copper (99% Cu). The second step is to purify electrolytically the impure metal by an acid solution of copper sulphate. Thus, the final product is obtained in cathodes which has a purity of 99.999% Cu. The remanent impurities go to the electrolytic sludge.

The second route is a hydrometallurgical option that is done by acid leaching and metal precipitation. The leaching process can be done in tanks, heaps, vats, or dumps. The election depends strongly of the type of copper mineral present in the ore body. The leaching agent is usually sulfuric acid. The solution obtained is always low in copper (approximately 1 g/l). The metallic copper can be precipitated from the solution by scrap iron. Other possibility is to improve the copper content in the solution by solvent extraction. In this case, the solution is treated electrolytically in an acid bath, and the copper is recovered as cathodes of high purity which are called copper electrowon.