Platinum-group metals precipitation

The effect of Bi promotion for the selective oxidation of 1-octanol using H202 as oxidant is reported in Table 2. Since decomposition of H202 by Platinum Group Metals is rapid, H202 is fed continuously into the reactor over 2 hours. The results obtained demonstrate that the presence of Bi203 as an additive within the reaction mixture displays no significant influence on catalyst activity. However, Bi promoted Pt/C catalysts, prepared by co-precipitation of... 

The traditional route for industrial separation of the platinum-group metals (PGM) comprises a complicated series of operations based largely on selective precipitations, often of low efficiency.219-221 A multitude of solid—liquid separations and recycle operations are required. The... 

Kondo, Y and Kuboto, M., Precipitation Behavior of Platinum Group Metals from Simulated High Level Liquid Waste in Sequential Denitration Process, J. Nucl. Sci. Technol., 29(2), (1992), ppl40-l48. 

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. 

All the platinum group metals are isolated from platinum concentrates which are commonly obtained either from anode slimes in the electrolytic refining of nickel and copper, or as converter matte from the smelting of sulfide ores. The details of the procedure used differ from location to location and depend on the composition of the concentrate. Classical methods of separation, relying on selective precipitation, are still widely employed but solvent extraction and ion exchange techniques are increasingly being introduced to effect the primary separations (p. i 147). 

In the systematic macroanalysis of the platinum group metals. Os and Ru are first separated by volatilization of the tetraoxides, and Pd, Rh, and Ir are then precipitated as hydrous oxides in the... 

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. 

The strong catalytic activity of platinum group metals has a significant impact on the properties of the solid products obtained in above described precipitation systems after longer hydrothermal treatment (9-72 h) at I60°C. In the course of hydrothermal treatment, the products of TMAH decomposition (methanol and trimethylamine) affect the reduction of metal cations and the formation of platinum group metal nanoparticles. These nanoparticles act as the catalyst for the reduction of Fe(lll) to Fe(ll) by the products of TMAH decomposition and the formation of characteristic Fe304 octahedra, which is followed by Mossbauer spectroscopy and FE-SEM (Fig. 23.19). 

Metals and Metallic Ions. Under appropriate conditions, ozone oxidizes most metals with the exception of gold and the platinum group. When oxidized by ozone, heavy metal ions, such as Fe and Mn , result in the precipitation of insoluble hydroxides or oxides upon hydrolysis (48—50). Excess ozone oxidizes ferric hydroxide in alkaline media to ferrate, and Mn02 to MnO. ... 

The halides of the palladium and platinum groups of metals closely resemble in character those of gold, which have already been described. The dihalides of the palladium group are all soluble, save Pdl2, which is prepared by precipitation with potassium iodide. Nitro-hydro-chloric acid yields the higher chloride it remains on evapo-... 

The plan for the quantitative separation of the metals of the platinum group, given in Table XLVIII, must be considered as an approximation. It may be necessary to repeat the fusion with Na202 in dissolving the melt in HC1. Heating the solution must be avoided to prevent loss of OsO<. It is probable that the chlorine distillation will have to be repeated several times in order to remove all of the ruthenium. Precipitation of platinum and iridium by means of ammonium chloride is never complete and the precipitate is always contaminated with rhodium and palladium. 

The following procedure, modified from Gilchrist s method, is intended for the recovery of platinum from residues containing base metals and noble metals (other than those of the platinum group) as well as strong com-plexing agents. A preliminary separation of base metals as hydrated oxides considerably reduces the time required to obtain pme platinum by the precipitation of ammonium hexachloroplatinate(IV). The authors have tested the procedure both with actual laboratory residues and with syn-... 

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