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  • Lead Anode Failure MechanismsAbbas Mirza, RSR Technologies, Inc., Dallas, TXRicardo Cabrejas, Quemetco Metals Limited, Casa Grande, AZLarry Webb, Quemetco Metals Limited, Casa Grande, AZ

  • Lead Anode Corrosion in Sulfuric Acid-PbO2

    -PbO2

    Lead

    CONFIDENTIAL

  • Protective -PbO2

    Brownish, Hard, Dense, AdherentCONFIDENTIAL

  • Lead Corrosion Films-PbO2 / -PbO2

    1.77

    1.69

    1.18

    0.25

    0.00

    -0.30

    Electrode Potential(Volts, SHE) Metal Interface

    Electrolyte/AnodeInterface

    Pb

    Pb(OH)2

    PbO / PbSO4

    PbSO4

    PbSO4

    PbSO4 / -PbO2-PbO2 / t-PbO

    -PbO2 / -PbO2

    t-PbO

    -PbO2

    Lead corrosion films; adapted from BurbankBurbank, J., Anodization of Lead in Sulfuric Acid, J. Electrochemical Society,Volume 103, Issue 2, 87-91, 1956.

    CONFIDENTIAL

  • Uniform Corrosion

    CONFIDENTIAL

  • Penetrating Corrosion

    Penetration Corrosion Uniform Corrosion

    CONFIDENTIAL

  • Penetrating Corrosion

    Sulfate deposits enhance penetration corrosion

    CONFIDENTIAL

  • Manganese attacks PbO2 layer and causes MnO2to build up in the layer.MnSO4 + PbO2 -> PbSO4 +MnO2The PbSO4 is converted back to PbO2, but it isnow deposited in loose layers.These layers are easily spalled off causingcontamination of the copper cathode.

    Must control Mn at SX

    Manganese Problem

    CONFIDENTIAL

  • MnO2 Disruption of PbO2

    CONFIDENTIAL

  • MnO2 Corrosion

    Formation of large, soft, loosely adherent layers of PbO2

    CONFIDENTIAL

  • Reduction Potential ElectrodepositionCu2++2e- Cu E0 = 0.34 VPbSO4 + 2e- Pb + SO42- E0 = -0.36 VPb2++2e- Pb E0 = -0.13 VNo co-reduction of Pb ionsOnly physical occlusion of particulate Pb species

    PbO2 reduction to PbSO4 or PbO possiblePbO2 + SO42- + 4H+ 2e- PbSO4 + 2H2O E0 = 1.69 VPbO2 + H2O + 2e- PbO + 2OH- E0 = 0.25 V

    No further reduction of PbOPbO + H2O + 2e- PbO + 2OH- E0 = -0.58 V

    Lead Contamination in Copper Deposit

    CONFIDENTIAL

  • PbO2 Particle Encapsulated

    Contamination of cathode metal Particle are mechanically

    entrapped Issues

    Excessive organics Cell mud accumulation Uneven anode side wall

    spacing, non-uniform faceflow patterns

    Flow eddys around isolators

    CONFIDENTIAL

  • Organics are Not my Friend

    CONFIDENTIAL

  • Solution Line Corrosion

    Corrosion at Solution Line by Organics

    CONFIDENTIAL

  • Hoods

    CONFIDENTIAL

  • Corrosion of Lead over Hanger Bar

    Corrosion of Lead by CuSO4:5H2O

    2CuSO4:5H2O (Blue) + Pb Cu2SO4 (Green) + PbSO4 (White) + 10 H2OGrkn @ 40 C = -21.72 kcal/mole

    CONFIDENTIAL

  • Hanger Bar Design

    Corrosion of Hanger Bar due to immersion or seepageProgressive evolution in hanger bar design

    CONFIDENTIAL

  • Uneven Electrode Spacing

    Risk of shorts due to dendrites at narrow electrode spacing

    CONFIDENTIAL

  • Housekeeping

    Risk of shorts due to housekeeping

    CONFIDENTIAL

  • Why Lead Anodes? Lead anodes are the preferred material for EWAnodes from Acidic Sulfate Solution

    Insoluble Ability to form a protective PbO2 layer Corrosion resistant Robust in tankhouse environment Economical Acceptable Operating Voltage

    CONFIDENTIAL

  • Oxygen evolution reaction at anodes is necessary to protectthe anodes from corrosion.

    Establish and maintain adequate cobalt content in electrolyte Clean anodes and cells regularly. Do not expose anode to baremetal during washing

    Anodes must be straightened before inserting into cell Suspended solids /Precipitates can lead to concentration cellcorrosion

    Organics in cells will lead to solution line corrosion Temperature fluctuations could result in shedding

    CONFIDENTIAL