Abstract
The present work investigated the comparison of the effects of Na2SO3 and Na2SiO3 on thiourea stabilization, and a systematic study was undertaken to establish the effects of these stabilizers on the stability of alkaline thiourea, both qualitatively and quantitatively. The effects of these stabilizers on the activation energy of alkaline thiourea gold leaching was also studied. The results showed that sodium silicate was more suitable as a stabilizer in this system than sodium sulfite because the peak current of gold dissolution with sodium sulfite was higher than that with sodium silicate, but the inhibition of thiourea decomposition by the former was less obvious than that of sodium silicate in the cyclic voltammetry curve. The quartz crystal microbalance results showed that the quality decreased to about 100 ng cm2 in the presence of a stabilizer, while it increased to 300 ng cm2 in the absence of the stabilizer. It is inferred that gold can be dissolved by alkaline thiourea in the presence of a stabilizer, while it cannot without a stabilizer because of the decomposition of thiourea. This assumption was confirmed by atomic force microscopy measurements. The surface activation energy of Au dissolution decreased from 183.76 to 98.07 kJ/moL with the addition of sodium silicate, indicating that Au dissolution was promoted with the chemical.
Highlights
Thiourea leaching of gold has attracted much attention because of its environmentally friendliness
There are no reports on the kinetic study of alkaline thiourea gold leaching systems by quartz crystal microbalance electrochemical workstations
In this study, along with the presentation of electrochemical measurements that can be used to select the Na2 SO3 or Na2 SiO3 stabilizer, quartz-crystal microbalance (QCM-D), which is a new method for gold leaching, and atomic force microscopy were used to study the effects of the stabilizers on thiourea stabilization
Summary
Thiourea leaching of gold has attracted much attention because of its environmentally friendliness. Based on a molecular-field analysis, and with the application of HYCHEM technology software, Chai et al studied the mechanism of molecular thiourea stability in terms of the molecular field, by comparing the highest occupation molecule orbit (HOMO) of a thiourea molecule in related media [11,12,13,14], the result of which helped to establish the structure–activity correlation between the stabilizer and the construction/stabilization of thiourea. There are no reports on the kinetic study of alkaline thiourea gold leaching systems by quartz crystal microbalance electrochemical workstations. In this study, along with the presentation of electrochemical measurements (including cyclic voltammetry curves, and the steady state polarization method) that can be used to select the Na2 SO3 or Na2 SiO3 stabilizer, quartz-crystal microbalance (QCM-D), which is a new method for gold leaching, and atomic force microscopy were used to study the effects of the stabilizers on thiourea stabilization. The Tafel curve method and activation energy calculations were used to establish the effects of the stabilizers on the system
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