Precious Metal Separations

Abstract

Separation of precious metals (PMs) is becoming increasingly important because of their growing application in industrial products, such as electronics and catalysts. Most PM separation and purification processes are performed using acidic chloride solutions; therefore, a thorough understanding of the chemical properties and separation mechanisms of PM chloridometalates in solution is of key importance for improving these processes. This article focuses on the solvent extraction of PM ions from acidic chloride solutions as the main technology for the mutual separation of PMs. In addition, leaching methods, dominant species in acidic chloride solutions, and non‐solvent‐extraction separation methods are discussed.

Urea-Introduced Ionic Liquid for the Effective Extraction of Pt(IV) and Pd(II) Ions

“…The difference in the time to reach equilibrium between Pt­(IV) and Pd­(II) was attributed to the difference in the extraction mechanism. Pt­(IV) is inert to ligand exchange, while Pd­(II) is relatively ligand-exchangeable. , The extraction equilibrium time suggests that Pt­(IV) extraction by L 1 in [C 2 mim]­[Tf 2 N] and L 2 in isooctane proceeds through an outer-sphere extraction (ion-pair or anion-exchange) rather than an inner-sphere coordination (ligand-exchange). Here, the kinetic constant ( k ) and equilibrium half-time ( t 1/2 ) were determined to clearly compare the difference in Pd­(II) extraction equilibrium between the IL and organic solvent extraction systems.…”

“…This result suggests that the stoichiometry with Tf 2 N – for Pt­(IV) extraction is 1:2 (Pt­(IV):Tf 2 N – ) and those for Pd­(II) extraction are 1:1 and 1:0 (Pd­(II):Tf 2 N – ). Pt­(IV) and Pd­(II) exist mainly as [PtCl 6 ] 2– and [PdCl 4 ] 2– , respectively, at high Cl – concentrations before extraction, − and spectroscopic verification of the chemical species of Pt­(IV) and Pd­(II) in the IL phase after extraction will be discussed later in Section . Based on these results, the extraction equilibrium reaction equations for Pt­(IV) and Pd­(II) by L 1 are …”

“…In the practical production of PGM, the separation and purification of PGM are currently carried out using hydrometallurgical processes based mainly on a solvent extraction method. , In the practical hydrometallurgical process of PGMs, primary and secondary resources containing PGMs are leached by chlorine-containing HCl solutions to form various chloro-anionic species. , The extraction properties related to PGM chloro-anionic complexes and PGM cations in aqueous solution depend on the type of chloro-complex and elements. For example, the tendency of chloro-anionic complexes to form ion-pair with cationic extractants is [MCl 4 ] − ≫ [MCl 6 ] 2– > [MCl 4 ] 2– ≫ [MCl 6 ] 3– > [MCl n – x (H 2 O) x ] m − .…”

“…Here, M is the PGM cation. On the other hand, the ligand exchange for each PGM is Pd­(II) > Pt­(II) > Ru­(III) ≫ Rh­(III) > Ir­(III) > Os­(III) ≫ Ir­(IV), Pt­(IV). , Hence, in a conventional organic–aqueous biphasic system, Pt­(IV) and Pd­(II) are often extracted by an ion-pair reaction with tri- n -octylamine and a ligand-exchange extraction reaction with di- n -octyl sulfide. , However, the use of large quantities of volatile organic solvents in hydrometallurgy is harmful to human health and the environment. Hence, their use should be reduced and alternative methods found.…”

Novel Mechanically Assisted Dissolution of Platinum Using Cerium(IV) Oxide

“…Other recent studies including pretreatment, leaching media, and mutual separation processes are summarized in a literature. 11 In order to avoid the use of Cl 2 , we previously reported novel methods for dissolving PGMs via the formation of complex oxides, such as Li 2 PtO 3 , Li 2 PdO 2 , and Li 2 RhO 3 . 12−18 The most reactive alkali metal salt for forming a complex oxide is Li 2 CO 3 .…”