Production of Pb
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Transcript of Production of Pb
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Production of Pb
- bluish-white color when freshly cut- 11,34g/cm3, melting point 327°C (10,69g/cm3)- boiling point 1740°C (vaporizes at 550°C)- bad heat and electrical conductor- very soft, highly malleable
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- výroba plášťů zemních kabelů- radiation shields - bullets and shot- lead-acid batteries- alloys: PbSb, solder - PbSn,antifriction
alloy - PbSnSb- compounds: carbonate, oxides
Usage
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only in compounds
Occurance
galena - PbS cerussite - PbCO3 anglesite– PbSO4
- galena is the most important and widely used - the main impurities: Cu, Zn, Sb, Fe, As, Sn, Ag, Bi a big amount of gangue
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only in compounds
Occurance
- selective&collective (PbZn) concentrate: 40-70% Pb- other source(40%): waste batteries etc.
galena - PbS cerussite - PbCO3 anglesite– PbSO4
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Pb is produced mainly by pyro. way
Production
- Reduction smelting: 90%- ISP: 5 %- Others: 5%
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Production of PbRoasting:removal of S, conversion of sulphide into oxide
Sintering: coarsening agllomerate
Reduction smelting
Purification of lead bullion
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Roasting and sintering
- Done together on a (Dwight-Lloyd)sintering machine
- providing Pb content under 2% (mixing raw concentrate with returned agglomerate)
- partial removal of Sn and Sb as As2O3 a Sb2O3
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Reduction smelting in lead blast furnace
Obtain as much as possible lead bullion
Dissolve as much as possible noble metals in Pb
Move all gangue and Zn into slag
Separate Cu off Pb in form of matte
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1. zone: under 400°C, drying and warming of charge .2. zone (reduction): 400-900°C, removal of water, decomposition of carbonate & sulfate, reduction of oxides, sulfidization of Cu3. zone (melting): above 900°C, streaming down liquid Pb to crucible, dissolution of Au, Ag, Cu, As, Sb, Sn etc. into lead bullion
Reduction smelting in lead blast furnace
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- charge: coke, air, sinter, CaO
Main reactionsPbO + CO = Pb + CO2PbO.SiO2 + CaO = PbO + CaO.SiO2PbO.Fe2O3 = PbO + Fe2O3PbSO4 = PbO + SO3PbS +2PbO = 3Pb + SO2PbSO4 + 4 CO = PbS + 4 CO2PbSO4 + Pb = 2PbO + SO2PbSO4 + SiO2 = PbO.SiO2 + SO3
Reduction smelting in lead blast furnace
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Reduction smelting in lead blast furnace
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Reduction smelting in lead blast furnace
Construction of the furnace
continuous taping, the principle of connected vessels
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Products of reduction smelting
- lead bullion90-96% Pb, 0,2-2,5% Cu, 0,5-5% Sb, 0,1-0,8% As, 0,1-1,5% Sn, 0,06-0,5% Ag
- slag25 - 32% SiO2, 34 - 40% FeO, 10 - 16% CaO, 5 - 8% Al2O3 + MgO, Pb, ZnO ( 30%)
- BF gasCO, CO2, SO2, vapor, N2, dust (3-50 g/m3, 40-80% Pb, toxic)
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Refining of lead bullion
- removal of dross and Cu- removal of As, Sn, Sb,- removal (recovery) of noble metals- removal of Bi
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removal of dross: - stirring at 500°C - physical impurities ascending to the surface of lead melt (difference in specific gravity) - withdrawing as dross
Refining of lead bullion
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removal of Cu: - limited dissolution of Cu v Pb at low temp., higher affinity of Cu to S than that of Pb - 1. step: lowering or increasing temperature of the melt just above of melting point of Pb - 2. step (350°C): adding elemental S to form Cu2S (under 0,002%)
Refining of lead bullion
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removal of Sn, As, a Sb - higher affinity with oxygen, comparing to Pb - oxidation with air or with sodium nitrate- oxidation with air: 500°C to remove Sn, 700°C-800°C to remove As, Sb
Refining of lead bullion
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removal of Sn, As, a Sb - oxidation with sodium nitrate (Harris’ refining) + fused sodium hydroxide, 500°C + oxides As, Sb, Sn have acidic character, reaction with oxides of alkli metals to form arsenate, antimonate (V), stannate
Refining of lead bullion
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removal of Sn, As, a Sb - oxidation with sodium nitrate (Harris refining) 2NaNO3 = Na2O +2.5 O2 + N2 2As + 2.5 O2 =AsO5 Sn + O2 = SnO2 2Sb + 2.5 O2 = Sb2O5 As2O5 + 3Na2O = 2Na3AsO4 Sb2O5 + 3Na2O = 2Na3SbO4 SnO2 + Na2O = Na2SnO3
Refining of lead bullion
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recovery of noble metals (Parkes’ method) - de-silvering lead by adding metal Zn to form inter- metallic compound (higher melting point, lower specific gravity)
- 500C, stirring, cooling almost to consolidation, formation of foam containing noble metals (Ag, Au..) - removal of Zn by vacuum
Refining of lead bullion
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removal of Bi atd1.) Kroll-Betterr’s method (under1%Bi) - adding Pb-Ca (3- 4% Ca) and Mg metal - slow cooling from 400°C to 360°C, foam forming atd2.) electrolytic refining (Bi >1%) - electrolyte : PbSiF6 + H2SiF6
(fluorosilicate and fluorosilic acid) - Pb cathodes - Bi and noble metals report into do anode slugde
Refining of lead bullion
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