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Titanium corrosion in simulated hydrometallurgical leaching solutions in the presence of solids Liu, Yu

Abstract

This work comprehensively investigated the corrosion behaviour of titanium in the presence of the solids in simulated copper sulfide leaching solutions. The effect of inert solid deposits on the corrosion behaviour of titanium grade 2 (Ti-2) was investigated. The solid deposits effectively slowed the mass transfer of the corrosion process, thus resulted in a decreased corrosion rate of the underlying Ti-2 in sulfuric acid-chloride solution. This effect, however, resulted in an increased corrosion rate of Ti-2 in simulated leaching solution (acid plus dissolved metals) since its barrier effect slowed the formation and repair of the protective oxide film by passivating species from the bulk solution. The deposit-covered Ti-2 showed a significant increase in corrosion rate at high temperatures compared with the bare Ti-2. The barrier effect of the four deposits for the investigated condition was in the sequence of gypsum > S3 (d₀.₅: 20.4 μm) > S2 (d₀.₅: 193 μm) > S1 (d₀.₅: 425 μm). Titanium hydrides—important titanium acid corrosion products—were investigated due to their close relationship to titanium substrate cracking. Titanium hydrides generated by electrolysis catalysed the hydrogen evolution reaction and facilitated subsequent passivation of Ti-2. X-ray diffraction analysis revealed that these hydrides were primarily composed of TiH₁.₅, with small amounts of TiH₁.₇ and TiH₂. The effect was investigated of Fe(III) and Cu(II) species in leaching solutions on Ti-2 passivation. The critical concentrations of Fe (III) and Cu(II) species required to induce passivation increased linearly with temperature from 30 to 80°C. The mechanism associated with the passivation was acceleration of cathodic reactions due to the introduction of Ti-2 oxidants. Cu(II) was more effective than Fe(III) at passivating Ti-2 under experimental conditions. Erosion-corrosion of Ti-2, which pertains to mineral slurries in acidic leaching conditions, was investigated using electrochemical techniques. Erosion-corrosion of Ti-2 was caused by solid particle impingement. Electrochemical noise revealed that solid particle impacts resulted in localised fracture of the passive film, and erosion-corrosion proceeded in the form of current transients. The investigation based on the current transients revealed that erosion-corrosion is a threat to titanium equipment exposed to acidic slurries.

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