Extraction and Recovery of Zinc from Spent Pickling Solution: Experimental Design and Mechanism Analysis

Solvent extraction of zinc with N, N-di(1-methylheptyl) acetamide (N503) from hot-dip galvanizing spent pickling solution is studied. The interaction between N503 concentration, extraction time, and phase ratio (O/A) is investigated using response surface methodology (RSM), and the experimental parameters are optimized as follows: the concentration of N503 is 50 % (v/v), the extraction time is 12 min, and the O/A is 16:5. The extraction efficiency of zinc is 82.12 %, and the separation coefficient (βZn/Fe) is 278.92 under the condition of single stage extraction. After four stages of countercurrent extraction, zinc is almost completely extracted from the aqueous phase. Additionally, it is found that zinc can be stripped effectively under the conditions of 0.4 mol/L HCl, stripping time of 10 min and O/A of 4:1. Also, the extraction mechanism of N503 is determined by electrostatic potential, FT-IR, and 1H NMR spectroscopy, and the extraction complex is [CH3CONR2H]ZnCl3. In summary, a method for separating zinc from spent pickling solution has been developed, and it has a certain industrial application prospect.