Unique Anion-exchange Properties of 3,3′-Diaminobenzidine Resulting in High Selectivity for Rhodium(III) over Palladium(II) and Platinum(IV) in a Concentrated Hydrochloric Acid Solution

Abstract

The effective recovery of Rh(III) from mixtures also containing Pd(II) and Pt(IV) is one of the most difficult tasks in platinum group metal refining. Adding 3,3′-diaminobenzidine (DAB) to 7 and 10 M HCl aqueous solutions containing Rh(III), Pd(II), and Pt(IV) chlorido species affords the effective separation of Rh(III) from Pd(II) and Pt(IV) through a process where Rh(III) becomes sequestered into solid phases composed of DAB. The stoichiometry and inner coordination sphere of the metal in Rh-DAB complexes were determined by estimating the Rh(III), H + , and Clconcentrations in the solid phase and X-ray absorption fine structure measurements to clarify the mechanism of DAB selectivity for Rh(III). These results indicate that the Rh-DAB reaction in a concentrated HCl solution occurs in two steps: (1) the precipitation of DAB trihydrochloride salts, where DAB's amino groups are protonated and (2) anion exchange of the trihydrochloride salts for chloride ions with [RhCl6] 3-, which is the predominant species in a concentrated HCl solution. By contrast, ion-pair complexes with [PdCl4] 2and [PtCl6] 2were not observed in DAB phases. The significantly lower affinity of the DAB trihydro cation for [PtCl6] 2and [PdCl4] 2than for [RhCl6] 3in 7 and 10 M HCl solutions accounts for the effective separation of Rh(III) from Pd(II) and Pt(IV).

Adsorption Behavior of Pu(IV), Am(III), Cm(III), and U(VI) on Desferrioxamine B-immobilized Micropolymer and Its Applications in the Separation of Pu(IV)

“…To increase the efficiency of separation, it is desirable to develop effective separation resins for Pu(IV), as well as other resins for metal ions. [8][9][10][11][12] Microbial metabolite desferrioxamine B (DFB), a trihydroxamate-based siderophore produced by the actinobacteria Streptomyces pilosus, has a very strong chelating ability for many high-valence ions under certain conditions. [13][14][15] For instance, it has been reported that DFB chelates with Pu(IV), 13,14 Am(III), 16 Cm(III), 17 and U(VI) 15 in aqueous solution.…”

Application of Ion Exchange for Recovery of Noble Metals

“…The noble metals complexes have a specific tendency to create ion pairs with ion exchangers, according to: [MCl 6 ] 2− > [MCl 4 ] 2− >> [MCl 6 ] 3− > aquacomplexes. In accordance with this series, rhodium is the last one to undergo the ion exchange process, hence its low sorption yields in the experiments [21,22].…”

Amide-functionalised phosphonium-based ionic liquids as ligands for rhodium(iii) extraction

“…At relatively high HCl concentrations (>1 mol dm À3 ), anionic Rh chloride complexes [RhCl x (H 2 O) 6Àx ] 3Àx (x ¼ 4-6) are the major species present and some binuclear complex [Rh 2 Cl 9 ] 3À has been also reported. [6][7][8][9] Recovery of anionic Rh complexes from acidic leachates has been investigated by separation methods including cementation, 10 calcination, 11 precipitation, [12][13][14] adsorption, [15][16][17] solid-liquid extraction, 18 liquid-liquid extraction, 19,20 and membrane transport. 21 Among these methods, liquid-liquid extraction (also called solvent extraction) has been widely used as an analytical separation method in laboratories and as a rening methods in industries owing to advantages, such as ease of scale-up and the possibility of continuous operation.…”