关键词: 金, 碱性硫脲溶液, 溶解, 电化学行为, 电化学动力学

Abstract: Electrochemical behavior and kinetics of gold dissolution in alkaline thiourea solution have been investigated by electrochemical techniques. The results indicate that open circuit potential moves negatively from -130 mV to -280 mV and the time for reaching stable state changes from 400 s to 800 s when the concentration of thiourea increases from 0 to 0.2 mol/L. The anodic current peak at cyclic voltammetric curves represents oxidation of gold, current increasing rapidly after 850 mV results from the evolution of oxygen when scanning positively, while the cathodic reduction peak at 220 mV is the reduction of gold-thiourea complex ion when scanning negatively. The peak potential of anodic oxidation moves negatively for 30 mV with the addition of thiourea, and peak current is raised 15.5 times. Anodic peak potential and current change from 655 mV down to 480 mV and from 1.985 mA down to 0.09528 mA, respectively when the concentration of thiourea increases from 0.05 mol/L to 0.20 mol/L. Anodic dissolution of gold becomes easier when improving pH value of solution. The peak current increases from 0.761 mA to 4.387 mA sharply and peak potential decreases from 655 mV to 596 mV when temperature rises from 25℃ to 35℃. However, too high temperature will result in the decomposition of thiourea, so room temperature is optimal. Theoretical analysis illustrates that anodic dissolution of gold is an irreversible electron transfer reaction.

Key words: gold, alkaline thiourea solution, dissolution, electrochemical behavior, electrochemical kinetics