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The rate of dissolution of gold in aqueous alkaline cyanide solutions was studied as a function of potential within the range --0.9 to +0.4V vs. SCE. The dissolution rate was found to exhibit three maxima at --0.66, +0.04, and +0.38V vs. SCE. These maxima corresponded to three current peaks found in anodic potential sweep measurements. Data from weight loss measurements were used for the determination of the stoichiometry of the electrochemical dissolution reaction and showed that for the region --0.9 to +0.6V vs. SCE, n ~ 0.85 ~ 0.01; for the region --0'.1 to +0.15V vs. SCE, n ~ 0.95 0.01; for the region +0.2 to +0.38V 'vs. SCE, n = 1.05 • 0.06. The dependence of the dissolution rate on the concentration of potassium hydroxide and potassium cyanide was determined in the two more anodic regions. At +0.38V vs. SCE the dissolution was directly proportional to the cyanide concentration and independent of hydroxide concentration. At +0,04~ r vs. SCE the dissolution rate was approximately linear with cyanide for low concentrations (<0.1M) and decreased with increased hydroxide concentration. At moderate hydroxide concentrations (0.1M) the dissolution rate decreased for cyanide concentrations greater than 0.2M. Several of the mechanisms suggested in the literature to account for the reactions in these two reglons were shown to be incorrect in some way; instead, the following sequence was proposed Au

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The behavior of gold in aqueous potassium hydroxide was studied using potentiodynamic methods. Three peaks found at potentials more negative than the gold (III) oxide formation region were identified as adsorption reactions. These reactions were shown to depend on the hydroxyl ion in solution. The following reaction was proposednormalAu+OH−→AuOHnormalads+e−Each of the peaks was found to correspond to the formation of only a monolayer of adsorbed species, with each peak being restricted to a particular type of surface site. By means of the work function values and the ease of oxidation of the three most common crystal planes, the peaks at −1.2 to −0.7V vs. SCE, −0.7 to −0.3V vs. SCE, and −0.3 to +0.3V vs. SCE were identified with monolayer hydroxide adsorption on the (110), (100), and (111) crystal faces, respectively.