Fariba Safizadeh

Active and passive behaviors of gold in cyanide solutions

Abstract Active and passive behaviors of pure gold (Au) and roasted gold ore (RGO) electrodes were investigated at 25 °C in de-aerated agitated cyanide media. Cyclic voltammetry and potentiodynamic polarization with agitation at 100 r/min in 0.04 mol/L NaCN solution showed different peak positions and current densities. Potentiodynamic tests illustrate that the peak current densities increase greatly with increasing the cyanide concentration. Increasing the pH value from 10 to 11 resultes in a great decrease of current density, while it increases noticeably by decreasing the agitation from 100 to 60 r/min. In the presence of oxygen, Au and RGO electrodes show different characteristics of peak positions and corrosion rates. The potentiostatic studies show that increasing the potential from 1 to 1.4 V at pH value of 11 results in an 80% decrease of current density while decreasing the pH value from 11 to 10 at 1 V gives a 1.7 fold increase of current density, possibly due to more effective passive layer. Following polarization, electrochemical noise measurements (ENM) during decay periods show that Au results in more passive states at high potentials, showing pitting corrosion. The ENM results show that this technique can be a promising tool for a better understanding of gold leaching. The XPS studies prove the presence of passive oxides.

Electrochemical noise of copper anode behaviour in industrial electrolyte using wavelet analysis

Electrochemical noise (EN) data were measured during the dissolution and passivation of an Cu-Pb anode at 65 °C in 1 L industrial electrolyte containing 2 mg of gelatine and 4 mg of thiourea. The EN data corresponding to three stages or regions of active, pre-passive and passive on chronopotentiogram curve were analyzed by wavelet transform technique. The results reveal the pitting type of localized corrosion form during both active and pre-passive stages under a constant current density of 215 mA/cm2. During the passive stage, a general corrosion form accompanied by oxygen evolution was observed.

Monitoring the Influence of Gelatin and Thiourea on Copper Electrodeposition Employing Electrochemical Noise Technique

Abstract The copper electrodeposition from sulphuric acid electrolytes in the presence of thiourea and gelatin as additives was investigated using Electrochemical Noise (EN) and Linear Sweep Voltammetry (LSV) in conjunction with the scanning electron microscopy technique. This study was oriented to examine the utility of using EN technique to characterize the electrowinning process and the deposit structure morphology was compared to LSV, an electrochemical method generally used industrially. Both EN and LSV techniques were successful in revealing the effect of different concentrations of thiourea and gelatin on the copper electrodeposition process. In this study, LSV detected an excess of thiourea leading to porous deposit; while the EN analysis in the time domain (skewness and kurtosis parameters) detected the presence of nodules and has provided useful information concerning the morphology of the deposit closely related to the macroscopic and microscopic studies.

Detection and Identification of Cobalt Cyanide Complexes using Capillary Electrophoresis

Capillary electrophoresis (CE) technique was used to separate and identify different cobalt-cyanide complexes from solutions containing various molar ratios of cyanide to cobalt (II). The formation of target complexes was confirmed using UV spectrophotometry. Raman spectroscopy was employed to study the general composition of each synthetized solution. Various new peaks found on CE electropherograms were assigned to appropriate complexes present in the solution. These assignments were made on the basis of a thorough survey of the cobalt-cyanide chemistry at work under cyanidation conditions. According to CE results, [Co(CN) 5 H 2 O] 2− and [Co(CN) 4 (H 2 O) 2 ] − were identified as the most important complexes to be potentially produced under simulated gold leaching conditions where [Co(CN) 5 H 2 O] 2− was distinctly the dominant complex.