Study of Cadmium Extraction with Aliquat 336 from Highly Saline Solutions

A large number of model solutions with high ionic strength were synthesised to mimic industrial conditions and were used as a first approach to study Cd extraction in the presence of chloride at high salinity, as experienced in real industrial solutions. The extractant used throughout in this work was Aliquat 336, a quaternary ammonium salt well known to the hydrometallurgical industry. The effects of some selected anions in addition to chloride (i.e., perchlorate, nitrate, and sulfate) were studied. The distribution of cadmium was measured using 109Cd as a tracer. Liquid-scintillation spectroscopy quantified the concentration of 109Cd in both phases. Raman and NMR spectroscopy were employed to gain further insight into the extraction chemistry. A careful analysis of all Cd extraction data showed that within specific windows of the reactant concentrations the chemical reactions could be represented by simplified equations, as discussed thoroughly in the text. Equilibrium constants for the extraction of \({\text{CdCl}}_{3}^{ - }\) from chloride and chloride/sulfate media were determined to be log10Kext = 4.9 ± 0.8 and log10Kext = 5.7 ± 0.5, respectively. For the nitrate environment, an exchange reaction involving a LiNO3 ion pair is proposed and agrees with the experimental data, but was not proven. 14N-NMR and Raman spectroscopy confirmed that the relative affinity of Aliquat 336 for the relevant anions followed the order: perchlorate > nitrate > chloride > sulfate. Finally, 14N-NMR enabled the equilibrium constant of the exchange reaction between nitrate and chloride for Aliquat 336 to be determined.