The Anodic Dissolution of Gold in Cyanide Solutions

Abstract

higher than given by the equation above, say nl ----2.18 + 0.296 (k/103A --2.305)-1-2. No information is available on what effect surface imperfections may have on the ellipsometric method.The ellipsometric method could detect the small dependence of n, on formation conditions, such as was found to exist to at least statistical significance by the modification of the Abel,s method, only by working at the most sensitive 4o and D. Since data based on thicknesses of anodic oxide films derived from the density of Ta205 8.735g cm -~ of unknown origin given by the Handbook of Physics and Chemistry are still being published (11), it is perhaps worth noting that the thickness obtained from this density will be about 10% too small on the basis of the values of nl here confirmed. The fact that a good fit is obtained for 4o ----70 ~ and for 4o ~ 50 ~ confirms that the optical constants do not depend on the angle of incidence. The fit immersed as well as dry confirms the accuracy of nl and also shows that pores into which electrolyte may enter are absent. A further test is that when points of equal thickness are compared at different angles of incidence (Fig. 6, 7) experimental and theoretical results agree. The increases in thickness for one cycle of the ellipsometer plot ~/2nl cos 41 are consistent when the thickness is obtained from spectrophotometric data with adjustment of nl. ConclusionsThe chief value of the ellipsometric technique in the determination of the thickness of films would seem to lie in its application to films to which the more precise and speedy spectrophotometric location of wavelengths of minimum reflectivity (1, 6) cannot be applied either because the films are too thin (<150A or so for tantalum) or because they must be measured still immersed in the electrolyte or because the optical constants of oxide and substrate are poorly "matched" for sharp interference minima. The method is very sensitive to the film thickness at certain thicknesses and quite insensitive at others, as may be seen by examining the figures. The measurement of intensity of reflection of p-light ( 7) is more precise for the determination of the optical constants of the oxide and metal.

Electron Stoichiometry of Anodic Dissolution of Gold in Aqueous Alkaline Cyanide

“…These peaks were shown to correspond to three potential regions of enhanced gold dissolution rates. These current peaks also had been observed by other workers (2,3,4,5); but, no attempts had been made to determine electron stoichiometry, which was assumed to be 1 or 2, depending on the peak.…”

“…The chemical process may occur as a result of trace oxygen contamination (6): 2Au + 4CN-+ 2!O2 + H20 + 2Au(CN)2 + 2OH- [2] Alternatively, an oxygen-free process such as the following_(1) may be involved:…”

Multi-electron transfer mechanism of dimethylamine borane in electroless gold deposition

“…Peaks 2 and 3 occur in the region of gold oxide formation. Previous work by other groups [13][14][15] attributed the appearance of these two anodic peaks to surface reactions that are subsequently passivated due to the formation of Au(I) and Au(III) oxides during the anodic scan in this potential region. Peak 2 exhibits a shift of À0.0597, which is in excellent agreement with theory and therefore describes a reversible process [12,13], as shown in Fig.…”

“…Dimethylamine would adsorb to the gold surface in a similar manner as the dissolution of gold by cyanide, the latter process of which has been studied in detail by several workers [13][14][15][16][17]. Then, an increase in pH would favor the right side of the reaction and the electrons provided by dimethylamine are available for interaction with the electropositive gold.…”

Electrochemical dissolution of roasted gold ore in cyanide solutions

“…Principally agitation does not promote the peak formation since the presence of intermediates at the interface becomes more limited. Second peak, known as a less anodic gold dissolution peak, could be passivated due to the oxygen adsorption (Dorin and Woods, 1991), gold oxide formation (Nicol, 1980), and by the formation of gold (I) hydroxide according to Au + OH − → AuOH ads + e − (Kirk et al, 1978), or by the conversion of Au(I) to Au (III) was 2CN − + [Au(I)OHCN − ] ads → [Au(III)OH(CN 3 ) − ] ads + 2e − (Cathro and Koch, 1964). Moreover, the adsorption of cyanide ions was found to initiate the passivation of second peak (Poskus and Agafonovas, 1995).…”