Metals and metallurgy Notes - METALS AND METALLURGY CHAPTER...

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METALS AND  METALS AND  METALLURGY METALLURGY CHAPTER 23 CHAPTER 23
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Metallurgy Metallurgy Science and technology of extracting metals from  their ores and of compounding alloys. Most metals are found in nature in solid inorganic  compounds (minerals)                                                                                          except Au and PGM’s (Pt, Pd,  Rh, Ru, Ir, Os) NB source of minerals    oxides (O 2- ),  sulphides (S 2- ) and  carbonates  (CO 3 2- ) Silicates are abundant, BUT they are generally  difficult to treat (not economically viable)
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What is involved? Mining (then crushing and grinding) Concentrating  the ore   remove the gangue    e.g. magnetic separation, flotation, amalgamation Reducing  the concentrate to obtain free metal Refining /purifying the metal Alloying    mixing metal with other elements to  modify properties 1 2 4 3 5
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PYROMETALLURGY PYROMETALLURGY Use  high temperatures  to alter  the mineral chemically and  reduce it to the free metal. Requires large amounts of energy  + often the source of atmospheric pollution. Used in concentration reduction and refining  processes
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Some pyrometallugical processes Some pyrometallugical processes Calcination:   Heat ore to decompose and eliminate volatile  products Carbonates often calcined to drive off CO 2  and form  metal oxide e.g. PbCO 3 (s)   PbO(s) +CO 2 (g) Require temps ~400-500 o C (1000 o C for CaCO 3 ) Hydrated minerals lose H 2 O at ~100-300 o C
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Roasting:   Themal treatment causes chemical reaction  between ore an furnace atmosphere. Leads to reduction or oxidation (depending on  atm) and may be accompanied by calcination. e.g. Roasting of sulphides to produce oxides 2ZnS(s) + 3O 2 (g)   2ZnO(s) + 2SO 2 (g) e.g. Sulphides of less active metals can be roasted to  the free metal HgS(s) + 3O 2 (g)   Hg(g) + SO 2 (g) e.g. Free metal also obtained by using reducing atm PbO(s) + CO(g)   Pb(l) + CO 2 (g)
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