Gold complexes thiourea

The best eluant found for the strong base resin A-500 was a mixture of thiourea and sulphuric acid. This eluant reacts chemically with the anionic gold complex on the resin (AuBr4+) and converts it to a cationic gold thiourea complex (AuTLH4). Since the cationic gold thiourea complex has absolutely no affinity for an anionic resin, gold elution is very fast and efficient ( 98%). This elution process has... 

In this chapter, a review of our recent SFE work is provided, covering the design and application of new fluorinated macrocyclic calixarenes and the discovery of the effectiveness of linear flourinated thiourea reagents for gold complexation and extraction in unmodified SC-CO2. 

THE CONSTANTS OF REPLACEMENT AND THE CONSTANT OF STABILITE MIXED BROMID-THIOUREA COMPLEXES OF GOLD (HI)... 

A number of thiourea complexes of silver have shown the tendency to bind up to four ligands, in contrast to gold. Thus Agtu2X (X = Cl, NCS) have essentially 3-coordinate silver (one distant fourth atom) Agtu3C104 is a 4-coordinate dimer (Figure 4.12) [58]. 

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... 

Thiourea gives a very stable water-soluble gold(I) complex [Au S=C(NH2)2 2]+> which is useful in the extraction of gold from its ores. 6 There is no tendency to add a third thiourea ligand or for gold to interact with the counter ion in solid complexes.207,208 Derivatives such as... 

An example of chemical destruction of an anionic species is the elution of aurocyanide from an anion-exchange resin with thiourea, a neutral ligand that reacts with gold cyanide in the presence of acid to form a cationic complex. The elution reaction can be described by the following equation ... 

Thiocyanate can be recovered and recycled from this solution by the precipitation of iron as iron(III) hydroxide.366 Aurocyanide can also be eluted from a strong-base resin by chemical conversion of the gold to a cationic complex with the thiourea ligand, as shown above (equation 98). This method of gold elution is favoured in the Soviet Union, but suffers from the drawback that elution of the other metal cyanide complexes is generally poor, and multi-elution procedures are necessary. 

The water-soluble gold-thiourea complex cation [Au S= C(NH2)2 ]+ is usefiil in the extraction of gold from its ore. 

When the dissolution and recovery are done using acidic thiourea solutions, the cathodic reaction is the reduction of gold-thiourea complex (34)... 

The type of analysis discussed in the preceding paragraph with particular respect to c/ iron(ii) complexes has also been attempted for c/ palladium(ii) and gold(iii) substitutions. In the case of the reactions of [Pd(fo)L], where Hgfo is the formazan (5) and L=ammonia or pyridine, with thiocyanate, thiourea, or triphenylphosphine, a kinetic-thermodynamic analysis shows Gibbs free... 

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