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UBC Theses and Dissertations

Fundamental study of the chemical stability and oxidation of thiourea in acidic ferric media Zuniga Sanchez, Pablo Andres


Thiourea (Tu) has been widely studied and claimed to be used in many applications in medicine, industry, and analytical chemistry. Although, the significant discrepancies in the results reported have rendered a lack of consensus with regards to the mechanism and reaction pathway for the oxidation of Tu. Therefore, the main goal of the study was to improve the understanding of the chemical stability and oxidation of Tu in acidic ferric media. Using experimental data from both batch reactor and electrochemical tests, the sub-processes involved, their mechanism and kinetics were thoroughly examined to identify the rate-limiting sub-processes and the overall Tu oxidation rate. Of the four factors tested (pH, temperature, Tu concentration, and ferric concentration), the effects of the temperature and the pH were the most significant. Increasing the temperature over 35°C, in acidic ferric media, results in an average of 75% Tu consumption during the first 48 h. A direct dependence between the Tu and the ORP measurements was observed in the tests with 10 mM Fe³⁺ and under various [Tu]₀. These results confirm the assumption that in the presence of Tu, the ORP is not solely controlled by the Fe³⁺/Fe²⁺ and the Tu/FDS couple may play an important role. This investigation into the chemical stability and oxidation of Tu in ferric media demonstrated that Tu presents a rich and dynamic behavior. In this highly complex system, the oxidation reactions occurring in both series/parallel manner seem to play a key role in the formation of intermediate species, which influences the final concentrations. The proposed rate expressions are the first serious attempt at integrating the two main processes occurring in solution, oxidation of Tu in the presence of ferric ions and the hydrolysis of FDSH₂²⁺, into a single expression. Therefore, the findings of this study just begin to unravel the influence that different factors present in solution exert on Tu stability, besides establishing general guidelines for future research.

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