A decomposition method for nickel-based superalloys by sulfurization: Recycling valuable metals

Since nickel-based superalloys contain many valuable metals, the recycling of which is of great meaningfulness. However, the high strength and oxidation resistance of nickel-based superalloys makes it difficult to decompose them. Considering that nickel-based superalloy exhibits low resistance to sulfur corrosion, this study proposes a novel method of decomposing alloys by sulfurization. The main process was to exploit the sulfurization reaction of metal elements in the alloy to obtain metal sulfides, and then further exploited the differences of metal sulfides to achieve the separation of metal elements. In this study, the sulfidation process of nickel-based superalloys and the existing forms of metal elements in the alloy after sulfurization were investigated. The results of SEM-EDS surface scanning and line scanning of the sulfurized alloys cross-section showed that, except for part of the Fe and Ni existed in the form of γ-phase (Ni-Fe phase), the other main alloy elements existed in the form of sulfide, achieving the sulfurization of nickel-based superalloys. After that, the sulfurized alloys were crushed and decomposed by hydrochloric acid, the results showed that the recycling rate of Fe, Ni were 97.6 % and 98.1 % after acid leaching. Furthermore, the majority of Mo can also be recycled by roasting-alkaline leaching with a large amount of Cr and Nb retained in the form of oxides in the leaching slag. Thus, the sulfurization decomposition method is an effective approach for recycling nickel-based superalloys.