removal of Sn, As, a Sb

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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
Usage
- výroba plášťů zemních kabelů
- radiation shields
- bullets and shot
- lead-acid batteries
- alloys: PbSb, solder
alloy
-
carbonate, oxides
- PbSn,antifriction
PbSnSb-
compounds:
Occurance
only in compounds
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
Occurance
only in compounds
galena - PbS
cerussite - PbCO3
anglesite– PbSO4
- selective&collective (PbZn) concentrate: 40-70% Pb
- other source(40%): waste batteries etc.
Production
Pb is produced mainly by pyro. way
- Reduction smelting: 90%
- ISP: 5 %
- Others: 5%
Production of Pb
Roasting:removal of S, conversion of sulphide into
oxide
Sintering: coarsening agllomerate
Reduction smelting
Purification of lead bullion
Roasting and sintering
- Done together on a (Dwight-Lloyd)sintering machine
-
providing
Pb
content
under
(mixing raw concentrate with returned agglomerate)
- partial removal of Sn and Sb as As2O3 a Sb2O3
2%
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
Reduction smelting in lead blast furnace
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
- charge: coke, air, sinter, CaO
Main reactions
PbO + CO = Pb + CO2PbO.SiO2 + C
Reduction smelting in lead blast furnace
Reduction smelting in lead blast furnace
continuous
taping,
the
principle
of
connected vessels
Construction of the furnace
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 gas
CO, CO2, SO2, vapor, N2, dust (3-50 g/m3, 40-80% Pb, toxic)
Refining of lead bullion
- removal of dross and Cu- removal of As, Sn, Sb,- removal
(recovery) of noble metals- removal of Bi
Refining of lead bullion
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
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):
(under
adding elemental S to form Cu2S
0,002%)
Refining of lead bullion
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
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
antimonate (V), stannate
arsenate,
Refining of lead bullion
removal of Sn, As, a Sb
- oxidation with sodium nitrate (Harris refining)
2NaNO3 =
Na2O +2.5 O2 + N2
Sn + O2 =
SnO2
2Na3AsO4
= Na2SnO3
2As + 2.5 O2 =AsO5
2Sb + 2.5 O2 = Sb2O5
Sb2O5 + 3Na2O = 2Na3SbO4
As2O5 + 3Na2O =
SnO2 + Na2O
Refining of lead bullion
recovery of noble metals (Parkes’ method)
- de-silvering lead by adding metal Zn to form intermetallic
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
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
+
(fluorosilicate and fluorosilic acid)
- Pb cathodes
- Bi and noble metals report into do anode slugde
H2SiF6
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