Electrolytic separation of Pb and PbO2 from ore residuum

1. IndianJournal of ChemicalTechnology
Vol.2, November 1995,pp. 343-344
Short Communication
Electrolytic separation of lead and its
dioxide from carbonate ore residiuum
Loutfy H Madkour
Chemistry Department, Faculty of Science,Tanta University,
Tanta, Egypt
Received 2 November 1994;accepted 11August 1995
Electrowinning work is carried out on the roasted
Eastern Desert complex carbonate ore residuum. Lead and
its dioxide are electrodeposited from various electrolyte ore
baths and the results showed a wide variety of ore electrolyte
solutions, either in the form of soluble simple ore salts, or
those containing complex ore anions. The optimum
conditions and the efficiency of the electrolytic extraction
are determined experimentally on the ore leach solutions.
The acid-leach residue resulting after controlled
sulphate roasting of the complex carbonate Zn-Pb
ore, contains 5.6% Pb, 2.0% Zn, 14.2% Fe and 4.6%
SiO~. Theelectrodepositionoflead and lead.dioxide
is of very much commercial and technical Importance
and is discussed in much detaiF - 9. In the present
investigation a variety of both acid and alkaline baths
as well as fairly complex solutions have been
investigated for Pb and Pb02 deposition from the
pre-roasted carbonate ore residuum.
Experimental procedure-The lead silicofluoride
electrolyte PbSiF6 was prepared by the action of
silicofluoric acid with the mother Pb(CH3COOh ore
liquor after dryness. The solution contains 70 g dm - 3
ofPb2 + ions and 110g dm - 3 ofH2SiF 6. The solution
[Pb(BF 4hl was prepared from lead ore ions resulting
from the dryness of the mother CH3C002 - ore liquor
and fluoboric acid and the bath contain 100 g dm - 3
Pb2 + and 40 g dm - 3 free HBF 4 acid,. with
approximately 109 dm - 3 boric acid as a buffer. The
sulphamate bath contained 100 g dm - 3 of lead as
[Pb(H2NS03hl and the pH was adjusted with addition
of H2S04 in the range 1.5-2.5. A lead gluconate
[(HOCH2{CH(OH)}4C02hPb] bath contained 80 g
dm - 3 Pb2 + ions, 40 g dm - 3 sodium gluconate and 40 g
dm - 3 sodium hydroxide. Alkaline lead baths or
sodium plumbite solutions were prepared by
saturating sodium hydroxide solution with Pb2 + ions
resulting from the dryness oflead acetate ore mother
liquor. The solution has a high pH (9-10).
The cell design and general experimental
procedure have been described earlier4·s.1o.11. All
chemicals and organic additives such asgelatin and
glue were of Analar quality and usedwithout further
purification. For each experiment 500 cm3 of the ore
mother liquor containing lead ions either in the form
of soluble simple salts or complex anions were used for
the electrodeposition process of Pb and Pb02•
Results and discussion
Electrodeposition of Pb and Pb02from ore simple
salt baths-Lead and lead dioxide may be
cathodically and anodically electrodeposited,
respectively, from the ore liquor after the conversion
process into acetate and or nitrate electrolyte
solutions. The optimum conditions necessary for the
cathodic deposition ofPb were 10-15 mA cm - 2. The
bath was usually operated at 30-40·C has a pH 5 and
the current efficiency being reported to be 96-97%.
Lead dioxide was deposited anodically at 55-60°C
with a currrcnt density of 45-50 mA cm-2 and the
current efficiency being reported to be 95-96%. The
resultant lead electrodeposits from this ore liquor
containing lead soluble simple salts either in the case
of acetate or nitrate have no commercial or technical
usefulness.
Electrodeposition of lead from ore complex salt
solutions-The optimum current density for cathodic
deposition of metallic lead from the ore silicofluoride
solution [Sif 6]2 - was 40-60 mAcm - 2. The bath was
operated at 40°C, and the cathode current efficiency
was found to be 92%. In order to achieve dense
electrodeposits, additions of 0.015% glue were
made.
The ore lead fluoborate (Pb(BF 4h bath may be
operated over the temperature range of25-40·C and
at cathode current densities of 10-30 mAcm -2. The
cathode current efficiency was close to 98%. 0.2
gdm - 3 of glue or hydroquinone was added to refine
the grain structure of the electrodeposit and prevent
"treeting" .
The ore sulphamate bath was operated at a
temperature of 30-50·C and current densities of
10-30 mAcm - 2. The solution has a pH 1.5-2.5. The
bath yields dense, fine-grain lead deposits at cathode
current efficiencies close to 98%.
The ore leadgluconate bath
[(HOCH2{ CH(OH) }4C02)2Pb] was operated at 60°C
with a current density of 50 mAcm - 2 and the current
efficiency being reported to be 98%. It was found that,
addition of 0.2 g dm - 3 glue increases the throwing

2. 344 INDIAN 1. CHEM. TECHNOL., NOVEMBER 1995
power, which in case of gluconate is greater than that
of the fluoborate and silicofluoride electrolytes.
Alkaline lead ore baths were based on sodium
plum bite solutions. The bath was operated at a
temperature of25-30°C and cathodic current density
of 20 mAcm - 2 for the cathodic deposition of metallic
lead. The current efficiency being reported to be 97%.
Lead dioxide was deposited anodically at a
temperature of 60T and anodic current density of 40
mAcm - 2 and the anodic current efficiency was found
to be 98%. It was observed in alkaline solutions, that
the cathodic polarization exhibited a linear
dependence on the logarithm of the current density.
Effect of current density, temperature and metal ion
concentration on the Faradic current eJticiency~ The
optimum current density ranges from 10 to 60 mA
cm - 2 depending on the bath used. At low current
density ( < 20 mA cm - 2) only a thin layer oflead was
deposited whereas at higher values (> 60 mA cm - 2) a
non adherent and randomly oriented deposit of lead
over the surface of the platinum cathode was
obtained. In general, increasing the temperature of
the bath from 25 to 60°C favoured the deposition of
the metal and its dioxide. This is due to the improved
mass transport of complex species towards the
cathode and the acceleration of both the ionic
migration ofthe complex species and the oxidation of
ions at the anode12. Although commercially, baths
are operated at 60°C or higher, it was found that
cracking is ·observed when deposition takes place
above 70°C. The efficiency of the deposition process
or the current yieldisnearly ~ 95%. A marked decrease
in current efficiency was obtained with rise of
temperature due to enhanced discharge of oxygen at
higher temperatures.
References
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