. Occurrence of metals In general, pure metals are shiny and malleable, however, most of them are found in nature as compounds with different properties. Metals having least chemical reactivity such as copper, silver, gold and platinum occur in significant amounts as native elements. Reactive metals such as alkali metals usually occurs in their combined state and are extracted using suitable metallurgical process.
. . Mineral and ore A naturally occurring substance obtained by mining which contains the metal in free state or in the form of compounds like oxides, sulphides etc... is called a mineral .
In most of the minerals, the metal of interest is present only in small amounts and some of them contains a reasonable percentage of metal. For example iron is present in around minerals. However, some of them such as hematite magnetite etc., containing high percentage of iron are commonly used for the extraction of iron. Such minerals that contains a high percentage of metal, from which it can be extracted conveniently and economically are called ores .
Hence all ores are minerals but all minerals are not ores. Let us consider another example, bauxite and china clay (Al O .2SiO .2H O). Both are minerals of aluminium. However, aluminium can be commercially extracted from bauxite while extraction from china clay is not a profitable one.
Hence the mineral, bauxite is an ore of aluminium while china clay is not. The extraction of a metal of interest from its ore consists of the following metallurgical processes. (i) concentration of the ore (ii) extraction of crude metal (iii) refining of crude metal Malachite – copper mineral XII U1 Metallurgy - XII U1 Metallurgy - - - - - Table . List of some metals and their common ores with their chemical formula Metal Ore Composition Metal Ore Composition Aluminum Bauxite Al O .
nH O Zinc Zinc blende or Sphalerite ZnS Diaspore Al O .H O Calamine ZnCO Kaolinite Al Si O (OH) Zincite ZnO Iron Haematite Fe O Lead Galena PbS Magnetite Fe O Anglesite PbSO Siderite FeCO Cerrusite PbCO Iron pyrite FeS Tin Cassiterite (Tin stone) SnO Limonite Fe O .3H O Silver Silver glance (Argentite) Ag S Copper Copper pyrite CuFeS Pyrargyrite (Ruby silver) Ag SbS Copper glance Cu S Chlorargyrite (Horn Silver) AgCl Cuprite Cu O Stefinite Ag SbS Malachite CuCO .Cu(OH) Proustite Ag AsS Azurite 2CuCO .Cu(OH)