Extraction and Separation of Scandium from Titanium White Waste Acid Using Long-Chain Monoalkyl Phosphates: Mechanism

Titanium white waste acid contains economically recoverable concentrations of scandium (25 mg/L); however, the high acid content and presence of multiple impurity ions present significant challenges for scandium separation. In this study, a novel monoalkyl phosphate extractant, PC68, consisting of 1-hexadecyl phosphate and 1-octadecyl phosphate, was synthesized. The effects of extraction time, sulfuric acid concentration, and temperature on scandium extraction were systematically investigated using a simulated titanium white waste acid solution. The results demonstrated that equilibrium was reached within 50 min at 298 K, and that the extraction efficiency of scandium with 0.1 mol/L PC68 was 99%. Analytical techniques, including the Equimolar Series Method, FT-IR, and XPS, confirmed that PC68 extracts scandium through coordination with P-O − and P=O groups. The separation performance of scandium from titanium white waste acid was evaluated, yielding high separation factors of 1093 for Sc/Fe and 733 for Sc/Mn, which demonstrates excellent separation efficiency. The addition of 1% H 2 O 2 followed by three-stage countercurrent extraction enabled effective separation of scandium and titanium. These results provide new insights and practical approaches for scandium separation from titanium white waste acid.