Study of xanthate decomposition in aqueous solutions

• A new method using headspace GC–MS is proposed to evaluate xanthate decomposition.
• Xanthate decomposition kinetics follows first-order law.
• Decomposition is affected by the interactions parallel or sequential to decomposition.
• Decomposition in aqueous solutions serves as control to that under other conditions.

Xanthate is one of the commonly used collectors in froth flotation beneficiation of sulfide ores. It decomposes and generates toxic compounds such as carbon disulfide (CS2) which is a concern in the mining industry. A vast body of literature exists for studies on xanthate/mineral interactions, but xanthate decomposition under various conditions (e.g., in solutions or flotation pulps) is not fully understood. We have undertaken detailed studies to fill this knowledge gap, and this paper shows our study of the xanthate decomposition in aqueous solutions in the absence of minerals. This condition has not been appropriately examined by past researchers, while decomposition under this condition is used as control to other complicated ones (e.g., in flotation pulps). A GC–MS based method was developed to directly measure the decomposition products in the gas phase. Decomposition kinetics was then established based on the generation of CS2. Decomposition followed the first order kinetics, and the rate constant for Sodium iso-Butyl Xanthate (SIBX) at neutral pH level was determined to be 9.3 × 10−4 h−1 at 25 °C, 1.7 × 10−2 h−1 at 50 °C and 1.3 × 10−1 h−1 at 70 °C. The effect of pH on decomposition behavior was examined in the pH range of 1.5–12.5. We determined experimentally a maximum in the extent of decomposition as a function of pH, which was predicted theoretically in literature. A mechanism involving multiple reactions that occurred in parallel or sequentially along with the decomposition was proposed to explain the observed change of xanthate decomposition over the entire pH range. These results offer valuable insights and can serve as the basis to mitigate the detrimental effects of xanthate decomposition in plant operations, for example, by modifying plant parameters to reduce xanthate decomposition without sacrificing its performance.