Secondary lead refining phase

1. 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

2. - výroba plášťů zemních kabelů
- radiation shields
- bullets and shot
- lead-acid batteries
- alloys: PbSb, solder - PbSn,antifriction
alloy - PbSnSb- compounds:
carbonate, oxides
Usage

3. 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

4. only in compounds
Occurance
- selective&collective (PbZn) concentrate: 40-70% Pb
- other source(40%): waste batteries etc.
galena - PbS cerussite - PbCO3 anglesite– PbSO4

5. Pb is produced mainly by pyro. way
Production
- Reduction smelting: 90%
- ISP: 5 %
- Others: 5%

6. Production of Pb
Roasting:removal of S, conversion of sulphide into
oxide
Sintering: coarsening agllomerate
Reduction smelting
Purification of lead bullion

7. 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

8. 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

9. 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

10. - charge: coke, air, sinter, CaO
Main reactions
PbO + CO = Pb + CO2PbO.SiO2 + C
Reduction smelting in lead blast furnace

11. Reduction smelting in lead blast furnace

12. Reduction smelting in lead blast furnace
Construction of the furnace
continuous taping,
the principle of
connected vessels

13. 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)

14. Refining of lead bullion
- removal of dross and Cu- removal of As, Sn, Sb,- removal
(recovery) of noble metals- removal of Bi

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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