Extractive Metallurgy Non Ferrous

According to their chemical composition, the minerals can be classified in five categories: natives, oxides and carbonates, sulphides, silicates and chlorides. As most of metals can be found in native state (excepting copper and gold), is necessary to extract one metal from a mixture. Native copper can be treated by a simple process where the gangue is separated in form of slag. In the case of native gold, the process is not simple many times and some concentration operations can be necessary. These operations are usually gravimetric and are practiced with special equipment.

Most the time is indispensable to concentrate valuable minerals because its direct treatment is not economical. In this case, initially the ore is crushed and ground in order to liberate the valuable minerals. The second stage involves process like flotation which is probably the most concentration process used around the world. Normally sulphides of copper, lead and zinc are treated by this way. Other specimens like tungsten minerals and tin mineral require special processes. In all cases the main idea is to obtain a concentrate which can be sent to the next the step of the extractive process.

Considering concentrates of sulphides, these are treated by steps of roasting and smelting which have for objective, improve the grade and eliminated impurities which could affect the final product. Many times is possible to separate selectively some metals which can be upgraded separately. Once the pyrometallurgical process is finished, the next step is related to hydrometallurgical processes which employ a solvent to dissolve the valuable metal. The final solution is sent to electrolytical processes that give a metal of high purity. The base metals follow this procedure and its practice in carry out in many countries.

Some times, concentrate is not an economical route and the treatment can involve hydrometallurgical and electrometallurgical operations. For example, copper oxides are leached by using sulfuric acid and the metallic copper is obtaining by electrowinning, and the cathodes are smelted. Other case is the uranium mineral because its treatment is direct leaching by alkaline or acid solvents. The rich solution is treated by ion exchange resins or solvent extraction, and the final solution is treated with ammonium to produce the called yellow cake which is used in nuclear reactors. Perhaps, the most common metals treated by this route belong to the platinum group. Of course, gold and silver are recovered around the world by cyanidation.

There are special methods to the treatment of certain metals such as titanium and magnesium. In the first case, the ore is treated by magnetic concentration and the concentrate is treated with chlorine to form a titanium chloride which reacts with magnesium under inert atmosphere to obtain metallic titanium.  In the case of magnesium, the processes involve electrolytical and thermic steps. As can be seen, some metals only respond to specific and special extractive procedures.