Platinum group metals chlorides

Anion Retention. Transition metal chlorides are often favored as catalyst precursors because of their ready availability, high solubility, and their ease of reduction. However, residual chloride anions (from incomplete catalyst reduction) can have a very marked effect on the properties of the catalysts. While the platinum group metal chlorides are, from a thermodynamic standpoint, very easy to reduce (Pt > Ru > Ir > Rh), residual chloride ions on the metal surface can be tenaciously bonded. The severity necessary to remove all the surface chloride reflects the surface energy of the metal (Ru, Mo, Ir > Rh > Pt > Pd). In the case of ruthenium, although bulk reduction apparently occurs at around 470 K, extended reduction above 700 K can be necessary to remove all chloride anions. The presence... 

Treatment of impure gold is largely via the Miller process (30) in which chlorine is bubbled through the molten metal and converts the base metals to chlorides, which volatilise. Silver is converted to the chloride, which is molten and can be poured. The remaining gold is less pure (99.6%) than that produced by the WohlwiU process and may require additional treatment such as electrolysis. If platinum-group metals (qv) are present, the chlorine process is unsuitable. 

Platinum-group metals (qv) form complexes with chelating polymers with various 8-mercaptoquinoline [491-33-8] derivatives (83) (see Chelating agents). Hydroxy-substituted quinolines have been incorporated in phenol—formaldehyde resins (84). Stannic chloride catalyzes the condensation of bis(chloromethyl)benzene with quinoline (85). 

All metals, except those belonging to the platinum group, form chlorides and the free energy change for the reaction (referred to as reaction (1))... 

Alam, M. S. Inoue, K. Extraction of rhodium from other platinum group metals with Kelex 100 from chloride media containing tin. Hydrometallurgy 1997, 46, 373-382. 

Vest, P. Schuster, M. Konig, K. H. Influence of tin(II) chloride on the solvent-extraction of platinum group metals with N,N-di-normal-hexyl-N -benzoylthiourea. Fresenius J. Anal. Chem. 1991, 339, 142-144. 

The use of amine salts in the commercial solvent extraction of the platinum-group metals from chloride solutions is described in Section 63.3.2.5. 

The use of solvating extractants in the recovery of gold and platinum-group metals (PGM) was described in the previous section. These extractants have also found some specialized applications in the extractive metallurgy of base metals. For example, they have been used in the recovery of uranium, the separation of zirconium and hafnium, the separation of niobium and tantalum, the removal of iron from solutions of cobalt and nickel chlorides, and in the separation of the rare-earth metals from one another. 

FIGURE 21.2 Primary mineral sources of metals. The s-block metals occur as chlorides, silicates, and carbonates. The d- and p-block metals are found as oxides and sulfides, except for the group 3B metals, which occur as phosphates, and the platinum-group metals and gold, which occur in uncombined form. There is no mineral source of technetium (Tc in group 7B), a radioactive element that is made in nuclear reactors. 

We might also expect to find oxide ores for the s-block metals and sulfide ores for the more electronegative p-block metals. In fact, sulfide ores are common for the p-block metals, except for A1 and Sn, but oxides of the s-block metals are strongly basic and far too reactive to exist in an environment that contains acidic oxides such as CO2 and SiC>2. Consequently, s-block metals are found in nature as carbonates, as silicates, and, in the case of Na and K, as chlorides (Sections 6.7 and 6.8). Only gold and the platinum-group metals (Ru, Os, Rh, Ir, Pd, and Pt) are sufficiently unreactive to occur commonly in uncombined form as the free metals. 

The most usual synthetic routes to the derivatives of platinum group metals are the exchange reactions of the complexes containing halide ligands with alkali metal alkoxides (method 5), alcoholysis of the same kind derivatives (usually by phenols, method 4), alcoholysis of hydroxide complexes (method 3), and redox reactions — reduction of chlorides or 0s04 in alcohol media (method 7) (Table 12.25). 

Chlorinated hydrocarbons (CHCs) are widely used in industry but bring both environmental and health risks 5,120 catalytic oxidation is a low cost method for their destruction. The most active catalysts are the platinum group metals supported on alumina, but high temperature is needed to obtain a satisfactory rate and to overcome chloride poisoning,121 but hydrogen chloride attacks the alumina support, so the use of other supports that... 

To obtain vinylsilanes from alkynes, transition metal complexes of Group VIII combined with a main group metal chloride are particularly effective." In the presence of a heterogeneous catalyst like Pd/y-alumina, Rh/carbon and polymer bound Pt, trichlorosilane gives trichlorovinylsilane with atmospheric pressure of acetylene." Platinum supported on sulfur-containing silica gel is a practical catalyst for 1,2-dihydrosilylation, as exemplified in equation (10). ... 

Palladium (Pd, at. mass 106.42) is a platinum-group metal, and occurs in the II and IV oxidation states. Palladium(II) compounds are the more stable. Unlike the other platinum metals, palladium is soluble in cone. HNO3. Brown-red Pd(OH)2 precipitates at pH 4, but dissolves in excess of an alkali-metal hydroxide. Palladium(ll) gives stable nitrite, ammine, cyanide, chloride, bromide, and iodide complexes. Palladium(ll)- and (IV) are reduced to the metal by SO2, Fe(II), and ethanol. 

The addition of platinum group metals to the Co-catalyzed carbonylation significantly lowers reaction requirements. A catalyst mixture of 2.7 parts cobalt acetate, 3 parts iodine, 1.2 parts bis(triphenylphosphine)-palladium(II) chloride and 2.4 parts adi-ponitrile converts methanol to acetic acid at 120 C and 25 MPa. 

The chloride is obtainable also as a water-sol hydrate with variable amounts of water. Prepn of trihydrate Anderson, Basolo, Inorg. Syn. 7, 214 (1963). Similar to the chlorides of other platinum group metals, rhodium chloride readily forms double salts with alkali chlorides. 

Platinum and also some platinum group metals can be deposited by decomposition or, better, reduction with hydrogen of their carbonyl chlorides [186,187] ... 

Warshawski A., Fieberg M.M.B., Mihalik P., Murphy T.G., Ras Y.B. The separation of Platinum group metals (PGM) in chloride media by isothiouronium resins. Separation and Purification Methods 1980 9 209-265. 

A. Wardiawsky, Hydrometallurgical Processes for the Separation of Platinum Group Metals (PGM) in Chloride Media, in D. Naden and M. Streat (Eds.), /on Exchange Tedmology, Ellis Horwood, London, 1984. 

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. 

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