Separation of Cr3+ and Fe3+ in high sulfate systems using P507. Part I: A new extraction mechanism involving sulfate coordination

Solvent extraction is an effective method for addressing the difficult separation of Cr 3+ and Fe 3+ in sulfuric acid media. Bis(2-ethylhexyl)phosphate (P204) has been shown to extract Fe 3+ from systems where Cr 3+ and Fe 3+ coexist. However, the issue of co-extraction of chromium remains. Considering that 2-ethylhexyl 2-ethylhexylphosphate (P507) and P204 are the same class of extractants, this study proposes the use of P507 to separate Cr 3+ and Fe 3+ . Under optimal conditions, the primary extraction efficiency for Fe 3+ reached 99.65%, with Cr 3+ being co-extracted at only 5.93%, and Al being co-extracted by 8.66%. The co-extracted Al 3+ was removed by a three-stage cross-current scrubbing process. After three-stage counter-current stripping, selective stripping of iron was achieved, leading to the effective separation of Cr 3+ and Fe 3+ . To date, no studies have reported on the role of sulfate ions in the extraction of Fe 3+ by P507. This study for the first time, reveals a new extraction mechanism in which sulfate ions (SO 4 2− ) play a role in the formation of complexes during the extraction process. It also provides a technological foundation for the further recovery of high-purity Cr 3+ and offers valuable insights into the behavior of sulfate ions during the extraction process.