Kinetic Analysis of Dissolution of Gold and Silver by Thiourea

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Glennawa et al. have studied the kinetics of thiourea dissolved gold . It is more consistently believed that the rate of gold dissolved in thiourea acidic solution in the presence of oxidant is controlled by the diffusion process and the thiourea is determined. Diffusion coefficient. The galvanic corrosion process of gold dissolved in thiourea acidic solution is shown in Figure 1.

Since the standard oxidation potential difference of gold dissolution is large when dissolved oxygen is used as the oxidant, the speed is mainly controlled by the diffusion process, and the main factor affecting the diffusion is the concentration difference, which obeys Fick's law. Therefore, the diffusion rate of thiourea to the surface of the gold particles in the anode region is: [next]

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The concentration of oxygen should be kept at a certain ratio, and the ratio is 10-20 at room temperature. Because it can dissolve 8.2mg/L volumetric oxygen in water at room temperature and pressure, which corresponds to ordinary oxygen with a molar concentration of 0.26×10 -3 mol/L, the corresponding thiourea concentration is 5.2×10 -3 moUL. , about the equivalent of a mass fraction of 0.04%.
According to the above equilibrium concentration of thiourea, and the lower limit of the potential value of thiourea is 0.38V, the pH can be determined to be 1.68. If the concentration of thiourea in the solution is increased, the concentration of dissolved oxygen should be increased correspondingly. When the pH of the medium, such as a thiourea concentration of 0.03 mol, the pH of the medium should be less than 1.29.
Under the optimal conditions, more than 90% of gold can be dissolved in 30 minutes, and 95% of gold can be dissolved in 60 minutes.

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