Corrosion Assessment of Lead Anodes in Nickel Electrowinning

Abstract

Due to their insolubility, lead and its alloys have always been candidates for anodes in electrowinning plants. However, corrosion problems associated with lead anodes cost millions of dollars for industries annually. Cast and rolled lead-silver and lead-calcium anodes were tested under typical nickel electrowinning conditions. Effects of sulfuric acid and chloride concentrations on overall corrosion performance of the anode materials were investigated. Moreover, oxygen evolution reaction rate and overpotential were determined for specific electrode material/solution conditions. Galvanostatic experiments were performed so the actual conditions that the electrodes are exposed to were simulated. Corrosion rates of the electrodes were calculated using the discharge plateau recorded during OCP measurements following the galvanostatic experiments. SEM and XRD were used to study the correlation between the surface morphology of the electrodes, their phase composition and their corrosion rates.

Electrochemical Reactions on Metal-Matrix Composite Anodes for Metal Electrowinning

“…The majority of the current density is due to the OER, while a small contribution is made by PbO 2 formation. 48 The current densities of the samples were higher in the reverse scan direction compared to those of the forward scan direction. This difference can be attributed to the higher anode surface coverage with PbO 2 in the reverse scan direction.…”

“…The second linear region represents mostly the Tafel line for the OER on the surface of the samples since the rate of the other reactions is negligible compared to that of the OER. 48 The exchange current density for the OER on the surface of the Pb-Sn-Ca and Pb anodes, which was calculated based on the second linear region, was approximately 7.4 × 10 −10 A/cm 2 . The obtained Tafel slope (120 mV/decade) and the calculated OER exchange current density of these samples are in agreement with the data reported for the β-PbO 2 .…”

Corrosion Assessment of a Lead-Based Composite in Sulfuric Acid Electrolytes

“…Lead-based alloys are the preferred material for this application because of special properties of lead such as low solubility in H 2 SO 4 solutions, low cost, and high conductivity in both metallic and oxidized states. [1][2][3] Lead-based composites are the new generation of the electrowinning anodes that have been developed in order to address the problems associated with conventional lead-based alloys such as PbSnCa, PbAg, and PbCa. [4][5][6][7] These issues include low corrosion resistance, short lifetime, high oxygen evolution overpotential, significant energy consumption during the electrowinning process, and considerable cost of alloying with alloying elements, especially silver.…”

The Role of Electrolyte Hydrodynamic Properties on the Performance of Lead-Based Anodes in Electrometallurgical Processes

“…Using insoluble materials as an anode in electrowinning leads to the higher purity of the deposited metal on the cathode. 10 Lead (Pb) is usually the preferred material for anode electrodes due to its special properties such as insolubility in solutions containing sulphuric acid, relatively low cost, low melting point, as well as high conductivity in both metallic and oxidized states. 7,11 Since a high rate of OER on the anode is required in the electrowinning process, significant cell potential should be applied to reach high current densities, which is 40-60 mA/cm 2 in the case of zinc electrowinning, contributing to higher corrosion rates of anodes.…”

“…Therefore, improvement of corrosion performance of lead-based anodes has been the subject of many researches in the past years. 10 Furthermore, the anodes in electrowinning should have a high enough mechanical strength in order to prevent failure due to creep during service time. 13 Pure lead, however, is not strong enough to resist against creep and guarantee a safe and long service life.…”