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Intro to Purification of Metals

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Intro to Purification of Metals

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  • Feb. 2012
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Introduction
• The Earth's crust contains many different rocks. Rocks are a mixture of minerals and from some we can make useful substances. • A mineral can be a solid metallic or non-metallic element or a compound found naturally in the Earth's crust. • A metal ore is a mineral or mixture of minerals from which economically viable amounts of metal can be extracted, i.e. its got to have enough of the metal, or one of its compounds, in it to be worth digging out! Ores are often oxides, carbonates or sulphides. They are all finite resources so we should use them wisely! • In order to extract a metal, the ore or compound of the metal must undergo a process called reduction to free the metal (i.e. the positive metal ion gains negative electrons to form the neutral metal atom, or the oxide loses oxygen, to form the free metallic atoms). o Detailed REDOX notes on the metal reactivity page, and on this page where appropriate.  • Generally speaking the method of extraction depends on the metals position in the reactivity series • The reactivity series of metals can be presented to include two non-metals, carbon and hydrogen, to help predict which method could be used to extract the metal. o lower Pt Au Ag Cu (H) Pb Sn Fe Zn (C) Al Mg Ca Na K higher in series o RULE: Any element higher in the series can displace any other lower element • Metals above zinc and carbon in the reactivity series cannot usually be extracted with carbon or carbon monoxide. They are usually extracted by electrolysis of the purified molten ore or other suitable compound o e.g. aluminium from molten aluminium oxide or sodium from molten sodium chloride. o The ore or compound must be molten or dissolved in a solution in an electrolysis cell to allow free movement of ions (electrical current). Theory given in the appropriate sections. • Metals below carbon can be extracted by heating the oxide with carbon or carbon...

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