Characterization of anodized titanium for hydrometallurgical applications - Evidence for the reduction of cupric on titanium dioxide

Anodic oxide films (AOFs) were potentiostatically formed on commercially pure titanium in 0.5 M sulfuric acid solutions at various anodizing voltages (up to 80 V) at room temperature. The subject of this study was the corrosion resistance of the AOFs in synthetic copper sulfide leaching solutions containing 30 g L ^-1 sulfuric acid as well as 12 g L ^-1 Cl ^- , 15 g L ^-1 Cu ²⁺ and 1 g L ^-1 Fe ³⁺ . Open circuit potential (OCP) measurement, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) were used to study the corrosion response of the AOFs in copper sulfide leaching solutions up to 85 C. Scanning electron microscopy (SEM) was used to investigate the morphology of the AOFs before and after 12 h of immersion at 85 C. X-ray photoelectron spectroscopy (XPS) was used to examine the surface chemistry of the AOFs after immersion. OCP measurements showed that the final failure of the AOFs occurred in 2 h in de-aerated 30 g L ^-1 H ₂ SO ₄ and 12 g L ^-1 Cl ^- solutions at 85 C. Both LPR and EIS results showed a significant increase in the corrosion resistance of the anodized titanium versus that of freshly polished titanium. Electrochemical results were confirmed by SEM analysis, where the AOF formed at 80 V lead to the best improvement in corrosion resistance. XPS measurements revealed that Cu ²⁺ was reduced to Cu or Cu ⁺ within the titanium oxide film. It was further confirmed that the presence of leaching oxidants would inhibit the reduction of Cu ²⁺ on titanium dioxide in chloride containing copper sulfide leaching solutions.