Evaluation of the Corrosion Behavior of Various Metallic Materials for Material Selection of Citric Acid Hydrothermal Leaching Apparatus for Lithium-Ion Battery Recycling

Hydrothermal leaching with citric acid has proven to be an efficient and environmentally friendly technology for complete leaching of various spent lithium-ion battery (LIB) cathode materials. However, the corrosion behavior of citric acid under hydrothermal conditions has not yet been thoroughly investigated, limiting the further development of a leaching apparatus. In this work, we conduct experiments to study the corrosion behavior of three different metallic materials, carbon steel (SA516–70), austenitic stainless steel (316L), and Ni–Mo–Cr alloy (Hastelloy, C276), under hydrothermal leaching conditions at 200 °C in the presence of 1 mol/L citric acid solution. The surface morphology changes of samples during the corrosion process are observed, and the corrosion rates at different exposure times are calculated. When the exposure time reaches 144 h, the corrosion rates tend to be stable, at 24.26, 0.73, and 0.04 mm/year, for SA516–70, 316L, and C276, respectively. The corrosion rates of 316L and C276 at 200 °C are much lower than that of SA516–70, comparable to those measured on carbon steels at temperatures lower than 100 °C. The chemical compositions of liquid solutions after corrosion tests are analyzed, and the crystal structures and elemental compositions of the corrosion products formed on the metal surface are characterized. Based on these results, a mechanism is proposed to explain the corrosion reactions of three metallic materials in citric acid solution, which indicates that Cr and Mo elements play a critical role in inhibiting the acid corrosion of citric acid under hydrothermal conditions. By utilizing the corrosion rate data obtained, high-pressure vessels made from different metallic materials serving as hydrothermal leaching reactors are designed as well as the estimation of wall thickness and material cost. Given the technical and cost advantages, carbon steel and Hastelloy cladding plate materials become suitable options when selecting metallic materials for the facilities used for citric acid hydrothermal leaching of LIB cathode materials.

This study investigates the corrosion behavior of three metallic materials used in constructing facilities for citric acid hydrothermal leaching of LIB cathode materials.