Gold complexes thiocyanates

Ni4N2Oi2C2(iH24, Nickelate(2-), hexa-p.-car-bonyl-hexacarabonylhexa-bis(tetramethylammonium, 26 312 NSC, Thiocyanate, gold complex, 26 90... 

NSC, Thiocyanate, gold complex, 26 90 NS2C5H11, Dithiocarbamic acid, diethyl-, molybdenum complex, 28 145 NSiC,H , Ethanamine, 1,1-dimethyl-A -(trimethylsilyl)-, 27 327 NSi2C4H , Silanamine, 1,1,1-trimethyl- -(trimethylsilyl)-, ytterbium complex, 27 148... 

NSC, Thiocyanate, gold complex, 26 90 NSbCsHii, Dithiocarbamk acid,... 

SNC, Thiocyanate, gold complex, 26.-90 SNO3C7HJ, l,2-Benzisotbiazol-3(2H)-one 1,1-dioxide, chromium and vanadium complex, 27 307, 309 SOOsPCsgHgs, Osmium, carbonyl-(tbiocarbonyl)tris(tripbenyl-pbospbine)-, 26 187... 

The details of the mechanism(s) of gold adsorption remain uncertain, mainly because of the many variables involved with the carbon itself. There is a need to characterize fully porosity and PSD. There is the question of extents of surface oxygen complex formation, the chemistry of these complexes and their location in porosities, some of which may not be accessible to gold complex species. At the same time, the pH and the ionic strengths of the solutions have to be controlled. Such a series of diagnostic experiments would be expensive to carry out and may not now be necessary if the use of cyanide solution is replaced by less toxic materials, such as thiocyanates. Already, there is experience with this lixiviant, as it is easily available, it is of low toxicity, stable in acid solutions, carbons can be easily regenerated and solutions can be used repeatedly. 

Determination. To an aliquot of the silver(I) solution containing between 10 and 50 pg of silver, add sufficient EDTA to complex all those cations present which form an EDTA complex. If gold is present (>250 xg) it is masked by adding sufficient bromide ion to form the AuBr4 complex. Cyanide, thiocyanate or iodide ions are masked by adding sufficient mercury(II) ions to complex these anions followed by sufficient EDTA to complex any excess mercury(II). Add 1 mL of 20 per cent ammonium acetate solution, etc., and proceed as described under Calibration. 

The solution should be free from the following, which either interfere or lead to an unsatisfactory deposit silver, mercury, bismuth, selenium, tellurium, arsenic, antimony, tin, molybdenum, gold and the platinum metals, thiocyanate, chloride, oxidising agents such as oxides of nitrogen, or excessive amounts of iron(III), nitrate or nitric acid. Chloride ion is avoided because Cu( I) is stabilised as a chloro-complex and remains in solution to be re-oxidised at the anode unless hydrazinium chloride is added as depolariser. 

The development of more benign alternatives to cyanide for gold-leaching (see Section 9.17.3.1) such as thiourea, thiocyanate, or thiosulfate, which form stable complexes in water has prompted research to identify suitable solvent extractants from these media. Cyanex 301, 302, 272, Ionquest 801, LIX 26, MEHPA, DEHPA, Alamine 300 (Table 5) have been evaluated as extractants for gold or silver from acidic thiourea solutions.347 Whilst the efficacy of Cyanex 301 and 302 was unaffected by the presence of thiourea in the aqueous feed, the loading of the other extractants is severely depressed. Formation of solvated complexes of gold and of an inner-sphere complex of silver has been proposed.347... 

Most Intensification treatments accelerate development as well as increase the effective speed of the photographic material. The gold Intensification is especially notable in this respect, and is of interest in relation to the mechanism of development. A simple motion picture positive film responds well to the gold treatment, which consists simply in bathing the exposed film for a few minutes in a solution containing the aurous thiocyanate complex in the presence of excess thiocyanate and bromide ions. Figure 7 shows the developed densities for several... 

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