Review: Research Progress on Liquid–Liquid Extraction of Chromium

The wide application of chromium will definitely increase the probability of impact of chromium-containing effluents on the surrounding environment and human health. Prior to reviewing the research progress on the liquid–liquid extraction of chromium, the common methods for treating chromium-containing wastewater and chromium species in solution are first introduced. Liquid–liquid extraction processes of Cr(VI) and Cr(III) are respectively investigated in detail in subsequent sections. The typical oxidization effect of Cr(VI) and aging effect of Cr(III) are analyzed. Most of the mechanisms involved in chromium extraction processes are also reviewed. This literature review provides not only a theoretical basis for choosing an appropriate ion host, but also an important reference for optimization of chromium removal processes by solvent extraction. In the industrial production of nickel, cobalt, and scandium, it can also be used to predict the effects of Cr(III) aging and Cr(VI) oxidation on chromium-containing solvent extraction systems and further avoid these negative effects in advance.