Gold thiocyanates

Another hydrometaHurgical use of Caro s acid is for destroying cyanide effluents from gold-leaching. It is more useful than catalyzed hydrogen peroxide for this duty because it also destroys thiocyanate ion. This appHcation has been demonstrated ia the laboratory (66) and at two gold mines (66,67). 

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... 

Thiocyanates are present in water primarily because of discharges from coal processing, extraction of gold and silver, and mining industries. Thiocyanates in soil result from direct application of weed killers and disposal of by-products from industrial processes. Less important sources include release from damaged or decaying tissues of certain plants such as mustard, kale, and cabbage. 

No information could be found in the available literature on the levels of thiocyanate in ground, surface, or drinking water. Thiocyanate is found in concentrations ranging from 100 to 1,500 mg/L in coal plant waste waters (Ganczarczyk 1979 Jensen and Tuan 1993), and from 300 to 450 mg/L in mining (gold extraction) waste waters (Boucabeille et al. 1994b). 

Bashong, W., Lucocq, J. M., and Roth, J. (1985) Thiocyanate-Gold small (2-3 nm) colloidal gold for affinity cytochemical labeling in electron microscopy. Histochem. 83,409 11. 

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... 

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

If the ratio be unity, the concentrations of the solute in each solvent will be the same if the ratio be far removed from unity, a correspondingly large proportion of the solute will be found in the one solvent which can be utilized to extract the Soln. from the other solvent. E.g. ether will remove ferric chloride from its aq. soln., and since many other chlorides are almost insoluble in ether, the process is utilized in analysis for the separation of iron from the other elements the solubility of cobalt thiocyanate in ether is utilized for the separation of cobalt perchromic acid is similarly separated from its aq. soln. by ether molten zinc extracts silver and gold from molten lead the extraction of organic compounds from aq. soln. by shaking out with ether or other solvent is much used in organic laboratories. 

Gold, a mixt of aureus azidodithiocarbonate azidocarbondisulfide bulky wh fibrous ppt which changes to om on standing Lead, Pb(SCSN3)a, It grn-yel crysts, fairly stable but may det under si mechanical shock Mercuric, Hg(SCSNj)a silky ppt which undergoes spontaneous thermal decompn at RT, yielding mercuric thiocyanate. This salt may det violently under si mechanical shock... 

All are based on a centred icosahedron of gold atoms with two atoms missing, and each peripheral gold is bound to either a phosphine or a halide or thiocyanate ligand.693-696 A typical skeletal structure for the [AU11X3L7] structure is (111). Some closely related derivatives of formula [AunX2L8]+ are also known.692... 

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