Platinum separation

MRR) to recover platinum. The extraction of palladium by the sulfide is slow with 2-3 hr to achieve equilibrium, which inhibits flow sheet design. However, it has been shown that tertiary amines can act as a kinetic accelerator, reducing equilibrium times to minutes, but no information has been published on the effect of these amines on palladium-platinum separation. High loading of the sulfides is possible, and stripping is easy with aqueous ammonia. The overall extraction and stripping equations are as follows ... 

The phosphine sulfide CYANEX 471X has been proposed as an alternative to the foregoing reagents for palladium platinum separation. Here, the faster extraction of palladium affords separation factors of 10 1, with a 10 min contact time. The chemistry of the process is similar to that of the alkyl sulfides. Various other separations have been published for example, TBP will extract platinum(IV) chloroanions preferentially to pal-ladium(II). 

Figure 22. The tunneling current, I, measured between two metal electrodes (tungsten en platinum) separated by a vacuum barrier as a function of the difference in electrochemical potential (here denoted as C/emitter-anode) the distance between the two electrodes (12, 20, 17 A) is indicated in the figure. Reprinted from Scanning Probe Microscopy and Spectroscopy , R. Wiesendanger, Cambridge University Press 1994...

Some results in the literature show that nitrogen monoxide (NO) is bound N-down and is normal to the platinum surface at hollow sites with an increase in the N-O bond length by 0.046 A over the gas phase. The GGA-calculated adsorption energies in [54] at the 1/16 and 1/4 monolayer are 2.00 and 1.93 eV, respectively. Previously reported values at the 1/4 monolayer are from 1.75 to 2.10 eV [64,67]. These differences arise from the difference in the number of atoms simulating the cluster surface that affect the absolute value of adsorption energies. The adsorption of NO causes the platinum atoms local to the adsorbate to relax laterally or parallel to the surface and away from the adsorbate, as well as vertically, or normal to, and upward from the surface. These relaxations can result in substantial changes in the platinum-platinum separations near the adsorbates. In the case of... 

Where the products are water, chlorine, and hyponitrous acid. While neither nitric nor hydrochloric acid, if pure, can dissolve gold or platinum separately, this mixture does so readily. It is certain, that free chlorine can dissolve those metals, and that their solution in aqua regia yields chlorides on evaporauon but there is reason also to believe, that the nitrons, or hyponitrous acids, contribute powerfully to the solvent power of the aqua regia, possibly by yielding oxygen to the metals, as these acids are more easily decomposed than nitric acid. 

One-dimensional stacks of equivalent neutral molecules comprise the second type of divalent haloamine complexes of platinum. The best characterized are theethylenediaminedihaloplatinum(ll) (PtenX2, X = Cl, Br) complexes with 3.39 (290,514,529,530) and 3.50 A (514,529) platinum-platinum separations in the solid state, respectively. In the chain alternate molecules are rotated 180 such that all of the donor atoms eclipse each other (290). The eclipsed donor atoms as well as the nonplanarity of the bidentate ethylenediamine ligand are... 

On a large scale, hydrogen peroxide is produced by the electrolysis of ammonium hydrogensulphate, using a platinum anode and a lead cathode separated by a diaphragm. The essential process occurring is ... 

It U better to employ the special palladium catalyst which is incorporated in the Deoxo catalytic gas purifier (obtainable from Baker Platinum Limited, 52 High Holbom. London, W.C. 1). 1 his functions at the laboratory tamperature and will remove up to 1 per cent of oxygen. The water vapour formed is carried away in the gas stream and is separated by any of the common desiccants. 

Discovered in 1803 by Wollaston, Palladium is found with platinum and other metals of the platinum group in placer deposits of Russia, South America, North America, Ethiopia, and Australia. It is also found associated with the nickel-copper deposits of South Africa and Ontario. Palladium s separation from the platinum metals depends upon the type of ore in which it is found. 

Pemoval of Other Impurities. After softening, the impurities that may stiU remain in the lead are silver, gold, copper, tellurium, platinum metals, and bismuth. Whereas concentrations may be tolerable for some lead appHcations, the market values encourage separation and recovery. The Parkes process is used for removing noble metals and any residual copper, and the KroU-Betterton process for debismuthizing. 

Platinum—Iridium. There are two distinct forms of 70/30 wt % platinum—iridium coatings. The first, prepared as prescribed in British patents (3—5), consists of platinum and iridium metal. X-ray diffraction shows shifted Pt peaks and no oxide species. The iridium [7439-88-5] is thus present in its metallic form, either as a separate phase or as a platinum—iridium intermetallic. The surface morphology of a platinum—iridium metal coating shown in Figure 2 is cracked, but not in the regular networked pattern typical of the DSA oxide materials. 

The anode and cathode chambers are separated by a cation-permeable fluoropolymer-based membrane (see Membrane technology). Platinum-electroplated high surface area electrodes sold under the trade name of TySAR (Olin) (85,86) were used as the anode the cathode was formed from a two-layer HasteUoy (Cabot Corp.) C-22-mesh stmcture having a fine outer 60-mesh stmcture supported on a coarse inner mesh layer welded to a backplate. The cell voltage was 3.3 V at 8 kA/m, resulting ia a 40% current efficiency. The steady-state perchloric acid concentration was about 21% by weight. 

PGM Concentration. The ore mined from the Merensky Reef in South Africa has a maximum PGM content of 8.1 g/1, of which 50—60% is platinum, and 20—25% palladium. The PGMs are in the form of a ferroplatinum alloy, or as their sulfides, arsenides, or teUurides. The aim of the concentration process is to separate from the ore a cmde metal concentrate, having a PGM content of 60%. The majority of other metals, such as nickel and copper, are separated out at this stage for further refining. 

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