Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9632580 | Hydrometallurgy | 2005 | 7 Pages |
Abstract
Literature data is re-interpreted to show that the anodic oxidation of gold in ammoniacal thiosulfate solutions is dependent upon the concentration product [M2S2O3][NH3] to the order 0.8 (M=Na or NH4). Analysis of chemical speciation in solution shows that the concentration of NH4S2O3â ion-pair is equal or larger than that of the unassociated S2O32â ion. A species distribution diagram for the gold(I)-ammonia-thiosulfate-hydroxide system in solutions of 1 M ammonium thiosulfate solutions containing 0.5-2 M ammonia at pH 10-11 shows that although Au(S2O3)23â is the predominant complex (>99%), a small fraction of Au(S2O3)(NH3)â is present. It is proposed that ammonia facilitates gold dissolution via oxidation of the surface adsorbed species Au(S2O3)(NH3)2â(ads). This oxidation corresponds to a rate constant of kAu=2.8Ã10â4 mol mâ2 sâ1 to produce Au(S2O3)(NH3)â(ads/aq) followed by desorption and re-equilibration in solution to Au(S2O3)23â.
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Physical Sciences and Engineering
Chemical Engineering
Chemical Engineering (General)
Authors
Gamini Senanayake,