金在碱性硫脲溶液中溶解的电化学动力学

Electrochemical Kinetics of Gold Dissolution in Alkaline Thiourea Solution

研究了金在碱性硫脲溶液中阳极溶解的电化学行为及动力学.结果表明,硫脲浓度由0增加至0.2mol/L时,开路电势由-130mV移至-280mV,达到稳态的时间由400s延长至800s.循环伏安曲线上正向扫描时700mV的电流峰为金的阳极氧化峰,850mV之后阳极电流急速上升为氧气的大量析出,反扫时220mV处为溶液中金离子的还原峰.溶液中加入硫脲使金的阳极氧化峰电势负移了30mV,峰电流则提高了15.5倍.由于硫脲的分解及其产物对金电极表面的钝化,硫脲浓度由0.05mol/L增加至0.20mol/L时,阳极峰电势由655mV负移至480mV,峰电流则由1.985mA降至0.09528mA.pH值升高有利于金在碱性硫脲溶液中的阳极溶解.温度由25℃升高至35℃时,峰电流由0.761mA迅速增加至4.387mA,峰电势由655mV负移至596mV,有利于金的溶解;但温度太高会增加硫脲自身的氧化分解.金的阳极溶解为不可逆电荷转移反应.

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 0.095 28 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 thiottrea, so room temperature is optimal. Theoretical analysis illustrates that anodic dissolution of gold is an irreversible electron transfer reaction.