Platinum group metals sulfides

Catalytic Reductive Alkylation of Aromatic and Alkyl Amines and Diamines over Sulfided and Unsulfided Platinum Group Metals... 

Palladium occurs in combination with platinum and is the second most abundant platinum group metal (pgm), accounting for 38% of pgm reserves. The USSR produces over 50% of the world s palladium, which is more than double that produced in South Africa. Two major sources of the metal are braggite, a mixed sulfide of platinum, palladium and nickel, which contains 16-20% palladium, and michenerite (PdBi3). 

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. 

Platinum group metals Mixtures of anionic or neutral chlorocomplexes Extractants either anion exchangers (e.g., long-chain amino acids) or ligands (e.g., alkyl sulfides)... 

The platinum-group metals consist of ruthenium, rhodium, palladium, osmium, iridium, and platinum. Each of the metals occurs naturally in its native form, and in economically exploitable deposits the elements occur overwhelmingly as individual platinum-group mineral (PGM) species. Mutual substitution of the various PGE is common, but substitutions in other minerals, such as base-metal sulfides, typically occur to only a limited extent. A comprehensive review of PGM and PGE geochemistry is given by Cabri (2002). 

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). 

The platinum-group metals (Ru, Os, Rh, Ir, Pd and Pt) are rare (Figure 23.1) and expensive, and occur together either native or in sulfide ores of Cu and Ni. Three sites of mineral deposits in the former Soviet Union, Canada and South Africa hold the world s reserves. The main source of ruthenium is from wastes from Ni refining, e.g. from pentlandite, (Fe,Ni)S. Osmium and iridium occur in osmiridium, a native alloy with variable composition 15-40% osmium and 80-50% iridium. Rhodium occurs in native platinum and in pyrrhotite ores (Fei S, n = 0-0.2, often with <5% Ni). Native platinum is of variable composition but may contain as much as 86% Pt, other... 

Natural occurrence. Rhodium is one of the rarest element in the Earth s crust with an abundance of 1 pg/kg (i.e., ppb wt.). Rhodium occurs in nature as a native metal along with other platinum-group metals in the native mineral iridosmine or in sulfide ores such as rhodite, sperrylite, and some copper-nickel ores. 

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... 

The platinum group metals are usually found as sulfides, arsenides or as the native metal, usually in conjunction with base metals. The concentration is almost always too low to justify mining for the precious metals alone, and the worldwide availability of the precious metal component tends to be determined by the demand for the other metal. For example, platinum is most commonly associated with nickel and copper sulfide deposits, and it is the extraction of the base metals from their ores that provides an economic route to the precious metal. In a typical operation in the US, 10 lbs copper can be extracted from a ton of ore, but the content of palladium is 0.000029 tr.oz and the platinum content is only 0.0000029 tr.oz. Significant quantities are only available in South Africa, Canada, Russia and the United States. 

The magnetic criterion is particularly valuable because it provides a basis for differentiating sharply between essentially ionic and essentially electron-pair bonds Experimental data have as yet been obtained for only a few of the interesting compounds, but these indicate that oxides and fluorides of most metals are ionic. Electron-pair bonds are formed by most of the transition elements with sulfur, selenium, tellurium, phosphorus, arsenic and antimony, as in the sulfide minerals (pyrite, molybdenite, skutterudite, etc.). The halogens other than fluorine form electron-pair bonds with metals of the palladium and platinum groups and sometimes, but not always, with iron-group metals. 

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