Application of a Novel Phosphonium-Based Ionic Liquid to the Separation of Platinum Group Metals from Automobile Catalyst Leach Liquor

Abstract

The recovery of platinum group metals (PGMs) from automotive exhaust catalysts is important, and hydrometallurgical extraction is an effective approach. In the present study, a newly designed phosphonium-based ionic liquid (IL) was applied to the separation and recovery of PGMs from an automobile catalyst leach liquor in conjunction with varying pH levels. This IL, trioctyldodecyl phosphonium chloride (P 8,8,8,12 Cl), allows quantitative extraction of Pd(II) at any HCl concentration, with almost 80% removal of Rh(III) at 1 mol L −1 HCl after two extractions. Significant amounts of Fe(III) were extracted into the IL phase, but could be removed using 1 mol L −1 Na 2 SO 3 . The Pd(II) and Rh(III) were selectively recovered from the IL using 1 mol L −1 CS(NH 2 ) 2 and 5 mol L −1 HCl, respectively. This work therefore demonstrated the selective recovery of PGMs through optimization of various parameters and shows the significant potential of this IL with regard to recycling PGMs from leach liquor.

Selective Recovery of Platinum Group Metals from Spent Automotive Catalysts by Leaching and Solvent Extraction

“…The metal-chloro complex species, which depends on the HCl concentration, determines the extraction mechanism. As reported in our previous study, extraction of FeCl 3 , which is the dominant Fe species in the aqueous feed solution, occurs by ion association of the IL cation with [FeCl 4 ] − (Firmansyah et al, 2019).…”

“…In our previous study, we found that Fe(III) can be stripped from the P 8,8,8,12 Cl phase by reducing Fe(III) to Fe(II) using Na 2 SO 3 (Firmansyah et al, 2019). About 90% of Fe can be removed from the metal-loaded IL phase by contact with 1.2 mol L −1 Na 2 SO 3 at 303 K, while Pt and Pd remain in the IL phase (Table 3).…”

“…Among the PGMs in the leachate, Pt and Pd are readily separated from Rh using P 8,8,8,12 Cl by changing the HCl concentration in the aqueous feed phase, as described in a previous paper (Firmansyah et al, 2018). It has also been reported that quantitative extraction of Pd is achieved in a short time (Firmansyah et al, 2019). Automotive waste catalysts contain a variety of metals depending on the type, model, and year of the car.…”

“…3 mol L −1 HCl, where [RhCl 5 ] 2− is the dominant Rh species in aqueous solution (Firmansyah et al, 2019). Formation of the 1 : 2 complex of [RhCl 5 ] 2− with P 8,8,8,12 Cl is preferable under such conditions.…”

“…Regeneration and reuse of P 8,8,8,12 Cl are also possible with a slight decrease in performance. P 8,8,8,12 Cl has also been applied to selective recovery of Pd(II) and Rh(II) from the leachate of an unused automotive catalyst containing Pd(II) and Rh(II) as PGMs and various other metals (Firmansyah et al, 2019).…”