Kinetic study on extraction of metal-cyanide complex ions by the N263-TBP system

Abstract

In this study, the extraction of metal-cyanide complex ions in gold-leaching, cyanide-containing wastewater by a trioctylmethylammonium chloride (N263)-tributyl phosphate (TBP)-n-octanol-sulfonated kerosene system was investigated. The effects of N263 and TBP concentrations, the aqueous phase pH, and phase ratio (O/A) on the extraction were investigated by adopting the response surface methodology, and the operating parameters were optimized. The optimal solution was obtained by solving the model optimally. A Cu ion concentration of 3,000 mg/L, an N263 concentration of 0.459 mol/L, a TBP concentration of 0.214 mol/L, an initial pH of the aqueous phase of 10.064, and O/A of 0.900 were determined to be optimal for realizing an extraction yield of 99%. The effects of column height, oil droplet volume, metal ion concentration, N263 and TBP concentrations, and temperature on the mass transfer rate were investigated using the single droplet method. Kinetic studies showed that the kinetic equation for the extraction system was Rf (Mass transfer rate) = 1.57 × 10-4·CCu·CTBP·CN263. The apparent activation energy of Cu(I) was 15.186 kJ/mol. The extraction process was controlled by the diffusion process. Furthermore, the chemical reaction occurred at the two-phase interface, where the copper cyanide complex ions preferentially bound to TBP at the interface between the two phases, and the bound anion cluster then reacted with the N263 cation to form the extractive complex, which then entered the organic phase from the interface.