Recovery of zinc from spent pickling solutions by liquid–liquid extraction using TBP

In this paper, recovery of zinc from real spent pickling solutions by liquid–liquid extraction with tributyl phosphate (TBP) was studied. In particular, the effects of some parameters were investigated, such as the volume ratio between the organic phase and real spent pickling liquor (O/A) (1:2, 1:1, 2:1, 4:1), the stirring time (5–20–30 min) and the TBP concentration (10%–55%–100%), in order to determine the conditions leading to higher zinc extraction efficiency, as well as selectivity in relationships to other metals such as iron. After zinc extraction, TBP was successfully regenerated. Among several tested solutions, water allows zinc recovery higher than 90%, especially at 10% diluted TBP solution. In addition, a double stripping step with water led to a near complete regeneration of TBP. In the present work, a process flowsheet is also proposed, where TBP at 10% concentration is used for zinc extraction from a spent pickling solution and then regenerated in a double-step stripping stage with water.