Recovery and regeneration of waste liquid from stainless steel etching process

FeCl₃ solution is commonly used in the etching process of stainless steel. The typical etching waste liquid contains a significant amount of Fe³⁺, Fe²⁺, Cr³⁺, and Ni²⁺, making it difficult to reuse and posing pollution issues. The FeCl₃ etching waste liquid was the present subject, which aimed to extract Cr³⁺ and Ni²⁺ by selectively adjusting process parameters. Additionally, it investigates the migration behavior and phase transition mechanisms of the iron, chromium, and nickel in different solution systems during treatment, systematically elucidating the regeneration mechanisms of FeCl₃ etching waste liquid. The results indicate that Cr and Ni can be recycled by controlling parameters such as pH value, temperature, and the valence states of the ions. Following a selective reduction of Fe³⁺ to Fe²⁺ using Fe powder, 98.3% of Cr³⁺ was recovered by adjusting the solution’s pH. Subsequently, 93.3% of Ni²⁺ was extracted from the Cr-depleted solution through further adjustments to the process parameters. The recovered Cr and Ni can be used to prepare Fe–Cr and Fe–Ni alloy powders. Furthermore, the FeCl₃ etching solution was regenerated by oxidizing Fe²⁺ and recovering impurities. The theoretical support for the development of new processes for treating FeCl₃ etching waste liquid is provided.