Recovery and regeneration of waste liquid from stainless steel etching process

FeCl ₃ solution is commonly used in the etching process of stainless steel. The typical etching waste liquid contains a significant amount of Fe ³⁺, Fe ²⁺, Cr ³⁺, and Ni ²⁺, making it difficult to reuse and posing pollution issues. The FeCl ₃ etching waste liquid was the present subject, which aimed to extract Cr ³⁺ and Ni ²⁺ 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 FeCl ₃ 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 Fe ³⁺ to Fe ²⁺ using Fe powder, 98.3% of Cr ³⁺ was recovered by adjusting the solution’s pH. Subsequently, 93.3% of Ni ²⁺ 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 FeCl ₃ etching solution was regenerated by oxidizing Fe ²⁺ and recovering impurities. The theoretical support for the development of new processes for treating FeCl ₃ etching waste liquid is provided.