Rhodium separation from iridium

Iridium can be separated from Rh and Pt owing to the fact that the anionic Ir chloride complex is precipitated with Ag [7]. Precipitation methods have been proposed also for separation of Rh from Ir and Pt [28]. Rhodium(III) may be separated from iridium(IV) by reduction to the metal [iridium being reduced only to Ir(III)] with Cu powder in 1 M HCl or sodium borohydride (NaBH4)] [29,30]. Iridium can also be separated from Rh and Ru by flotation of the ion-associate formed by the chloride complex of Ir(IV) with a cationic... 

In the commercial flow sheets, these elements are left in the aqueous raffinate after platinum and palladium extraction. Indium can be extracted in the -l-IV oxidation state by amines (see Fig. 11.11), or TBP (see Figs. 11.10 and 11.12). However, although the separation from rhodium is easy, the recovery of iridium may not be quantitative because of the presence of nonextractable iridium halocomplexes in the feed solution. Dhara [37] has proposed coextraction of iridium, platinum, and palladium by a tertiary amine and the selective recovery of the iridium by reduction to Ir(III). Iridium can also be separated from rhodium by substituted amides [S(Ir/ Rh) 5 X 10 ). 

Vinylidene-mediated reactions involving rhodium and iridium are discussed separately from those involving Groups 10 and 11 transition metals. The reactions of Group 9 metal vinylidenes are more numerous and have more in common with one another. Extensive stoichiometric organometallic literature aids in the understanding of these processes. In contrast, reactions of Groups 10 and 11 metal vinylidenes are more scattered and often controversial. 

Rhodium is insoluble in acids, even in aqua regia, although when its alloys are attacked by this latter mixture a portion of the rhodium passes into solution. When fused -with potassium hydrogen sulphate, rhodium dissolves, yielding the sulphate. This reaction is interesting as affording a convenient method of separating the metal from iridium and platinum (see p. 34-1). 

This alum is of interest inasmuch as its formation renders it easy to separate rhodium from iridium. The sulphates of the metals, dissolved in acidulated water, are treated with caesium sulphate and evaporated. The rhodium alum crystallises out in a pure state, entirely free from iridium.1... 

When boiled with concentrated acetic acid, rhodium cyanide is precipitated, hydrogen cyanide escaping. Since the corresponding iridicyanide is not affected by similar treatment, this affords a useful method of separating rhodium from iridium. 

All sol-gel derived catalysts were stable under reaction conditions, except the rhodium and iridium catalysts, whose colour changed significantly during reaction. The catalysts could easily be separated from the reaction mixture by simple filtration. The filtrated liquid product, that flew out colourless, exhibited no further catalytic activity. GC analysis of the liquid phase indicated the production of dmf with 100% selectivity in all cases, except for the platinum containing catalyst (Table 1). 

With modem instrumentation it is often possible to make determinations of individual elements without the necessity for any chemical separations, but while mutual interferences for AAS and ICP emission spectrometry are often small the sensitivity, for example, for iridium, may be unacceptably low and chemical separations are required. The separation of rhodium from iridium is one of the most challenging analytical tasks. Ruthenium and osmium are most commonly separated from other PGMs and matrix elements by distillation of their tefroxides. ... 

Other examples of selective electrodeposition are given in books by Lingane, Diehl, and Sand. As examples may be cited the separation of silver from copper, bismuth from copper, antimony from tin, cadmium from zinc, and rhodium from iridium. 

Tertipis G.G., Beamish F.E. Separation of rhodium from iridium by copper powder. Analytical Chemistry 1960 32 486-489. 

In contrast to cobalt, simple alkene complexes of rhodium and iridium have been the subjects of prolific research, much of it ultimately directed toward the development of catalysts for hydrogenation and C—H bond activation processes. In view of the expansive literature on these materials, it would seem appropriate to consider their synthesis and structural facets separately from their reactivity. 

Fire assay describes a group of separation methods in which precious metals (PMs) are separated from other species by dissolution in other molten metals, usually lead, nickel, or tin. Fire assay has been and continues to be fundamental to the determination of PMs. These are defined as gold (Au), silver (Ag), and the platinum group metals (PGMs) platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os). In the context of fire assaying other elements are referred to as base elements or metals. 

The platinum group metals occur jointly as alloys and as mineral compounds in placer deposits of varying compositions. Ru and Os are separated from the PGM mix by distillation of their volatile oxides, whereas platinum, iridium, palladium, and rhodium are separated by repeated solution and precipitation as complex PGM chlorides, or by solvent extraction and thermal decomposition to sponge or powder. PGM scrap is recycled by melting with collector metals (lead, iron, or copper) followed by element-specific extraction. 

Hexachloro Species and the Separation of Rhodium from Iridium... 

The first step in the refining of the platinum group metals (PGMs) is the dissolution of the sulfide matte residue from the base metals refinery. This is done by reaction at high temperature with concentrated HCl and CI2 gas under pressure. Under these conditions the PGMs are oxidized and form stable chloro species. Iridium achieves the oxidation state Ir(IV), while rhodium attains only the 3+ state. The chloro species in solution are thus [AuCy, [PdCy, [PtCy -, [RhCy, and [IrCy -. Gold, palladium, and platinum are easily removed. The separation of rhodium from iridium can be achieved by solvent extraction with tributylphosphate from the acidic HCl... 

Anionic metal cyanide extraction Iridium separation from rhodium Gold extraction from cyanide media... 

Piccini was obsessed with studying the limiting form of the elements as placed in the periodic table. With this in mind, he took up a new field of research, the synthesis of double sulfates (or alums), a work that enormously stimulated his creativity and enthusiasm [58]. In rapid succession, he prepared the alums of vanadium [59], titanium [60, 61], rhodium [62], manganese [63], iridium, and, finally, of thallium [64] with ammonium and then with the following alkaline metals cesium, mbidium, and potassium. Piccini ably used his method of synthesizing the rhodium sulfates virtually to quantitatively separate rhodium from iridium in solution. Through successive fractional crystallizations, Piccini obtained the alums of rhodium and cesium free of iridium, and through electrolysis of the alums he was able to obtain pure rhodium. 

Recognizing the difficulty of separating rhodium from iridium by... 

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