engleski

Electrochemical Deposition of Gold in Cizrate Solution Containing Thalium

The process of electrochemical deposition of gold in citrate solution containing thalium ions is studied on the rotating disc electrode using cyclic voltametry method of polarization. The results obtained by the cyclic voltametry method show that limiting current density is not achieved in citrate solution. The rotation speed of the electrode has no significant influence on gold deposition process. The mechanism of gold deposition is predominantly dependent on the electrolyte composition. In the citrate solution free from thalium the adsorption of Au(CN)- and CN- on the electrode surface is presumed resulting in the formation of Au(CN)_ad species which afterwards reduced are to Auo. In the citrate solution containing thalium an adsorption of Tl+ ion on the surface is presumed at the potential of -750 mV (SCE) including its catalytic effect as an adatom. Simultaneously the presence of thalium in citrate solution shifts the deposition potential to the positive values diminishing the activation energy as well. The values of the activation energy indicate that an adsorption mechanism of gold deposition is predominating. Tafel line slopes have confirmed that the electrochemical reaction occurs in two steps. The reaction kinetics is changed in the presence of thalium. The reduced reaction of hydrogen has also a significant influence on the electrochemical deposition of gold.

electrochemical deposition; gold; citrate solution; thalium

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