technical case study
greater than 3 mm. This practical limitation is overcome by duplex stainless steels, which combine ferritic and austenitic crystal structures. In duplex alloys, austenitic grains may crack, but the surrounding ferritic structure impedes crack propagation. Duplex grades can experience this type of cracking, but typically only at temperatures above 100°C and under high chloride concentrations. Commonly Extracted Metals Hydrometallurgical processes are used to extract and refine various metals, including: • Zinc (Zn) • Copper (Cu) • Nickel (Ni) • Platinum (Pt) • Cobalt (Co) These plants use aqueous solutions to recover metals from ores, which means corrosion mechanisms are classified as wet corrosion. In wet corrosion, both temperature and solution concentration are crucial. A general rule is that corrosion rates double with every 10°C increase in temperature. Process Stages and Material Use Hydrometallurgical processes often involve the use of hot, pressurised sulphuric acid. Stainless steels are commonly used in process tanks, reactors, and cathode plates for electrowinning. The leaching stage is typically the most corrosive, due to the combination of high temperatures, pressures, and acid concentrations. In copper production, ores are oxidised in heaps or reactors during leaching. This is followed by solvent extraction and electrowinning, which deposits copper on stainless steel cathodes. Poor material selection may cause pitting on cathode plates, making copper removal difficult.
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Issue 3 – 2025
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