Lead Alloys For Permanent Anodes in
Lead Alloys For Permanent Anodes in
Lead Alloys For Permanent Anodes in
This paper reviews the common lead used in electrolytic solutions. During use, To prevent this type of creep failure, the
alloys associated with insoluble anodes the lead surface is oxidized to its highest lead is normally alloyed to increase the
in different metal deposition operations. valence state, coating the anode surface mechanical properties during operation.
Metallographic techniques were used to with a smooth, adherent layer of PbO2. A more rigid anode maintains the uni-
evaluate microstructures as they relate The layer inhibits further oxidation and form corrosion-resistant layer. Table I
to physical and mechanical properties. corrosion and remains highly conduc- shows typical alloys used throughout the
Alloy additions and manufacturing tive, thus passing the electrowinning industry and corresponding mechanical
processes are examined as appropriate current. properties.2
methods to meet the performance needs Oxygen evolved at the anode during
of a lead anode. operation is released at the surface as a
The Pb-Ca anodes gas. The oxygen can oxidize materials
INTRODUCTION
were developed to in the electrolyte, corrode the anode, or
Electrowinning anodes continue to form peroxides at the anode surface. The
employ lead alloys as the major materials reduce corrosion and major consequence of oxygen evolution
suitable for use in electrometallurgical spalling rates of the is the corrosion of the lead anode. The
plant practice. Lead alloys are used as oxygen corrodes the anode directly by
permanent anodes for electrowinning PbO2 corrosion the formation of PbO, PbSO4, complex
and plating of metals such as copper, product compared sulfates, PbO2, and PbO2 on the sur-
zinc, nickel, cobalt, chromium, and face. The PbSO4 compound is especially
manganese. Different alloys are utilized with conventional undesirable because it acts as an insulator
throughout these nonferrous industries. Pb-Sb alloys, thus and passivating the anode surface. The
The desired properties of the anode can morphology of the PbO2 layer is impor-
help achieve less contamination of the reducing the lead tant in inhibiting the spalling effect which
cathode, longer anode life, lower anode contributes to cathode contamination.
potential, and consequently, reduced
contamination of Alloy additions and anode fabrication
oxygen overpotential. the cathode. techniques can promote a more continu-
The primary objective of an electro- ous, adherent layer. Once formed, the
winning or plating practice is to produce a Pure lead, however, is not strong PbO2 layer serves to evolve oxygen as a
high-purity cathode or metal deposit with enough to support its own weight. A pure gas instead of corroding the underlying
good physical appearance at the lowest lead anode will creep during use. As the lead surface.
possible consumption of energy.1 Lead lead elongates and deforms, the adherent
COPPER ELECTROWINNING
anodes are preferred because of their high PbO2 layer cracks and exposes fresh lead
resistance to corrosion in the sulfuric acid surface to oxidation and rapid corrosion. Rolled Pb-Ca-Sn alloys are the pre-
ferred anode materials in copper solvent
Table I. Mechanical Properties of Various Lead Alloy Anode Sheets* extraction-electrowinning (SX-EW)
Alloy UTS 0.2% YS Elongation Hardness facilities. The rolled anodes replaced
(wt.%) (MPa) (MPa) (%) (RR30) cast anodes, which have lower strength.
Pb-3Sb Cast 65.5 55.2 10 85 The Pb-Ca anodes were developed to
Pb-3Sb Rolled 24.6 16.3 40 64 reduce corrosion and spalling rates of
Pb-6Sb Cast 73.8 71.0 8 87 the PbO2 corrosion product compared
Pb-6Sb Rolled 30.6 19.5 35 65 with conventional Pb-Sb alloys, thus
Pb-0.07Ca-1.35Sn Cast 46.4 35.3 29 71
reducing the lead contamination of
Pb-0.07Ca-1.35Sn Rolled 71.0 65.3 14 85
Pb-0.07Ca-1.35Sn-0.05Ag Rolled 80.0 76.8 10 88 the cathode. The calcium strengthens
Pb-0.07Ca-0.35Ag Rolled 37.8 35.5 42 68 the lead via a precipitation-hardening
Pb-0.75Ag Rolled 18.8 9.0 54 26** process. The calcium particles are very
*UTS = ultimate tensile strength, YS = yield strength; **extrapolated value. small and are formed after solidification