Solvent Extraction of Cadmium by Di (2-ethylhexyl) Phosphoric Acid

Abstract

Studies were conducted on the equilibrium and reaction kinetics for the extraction of cadmium from aqueous chloride solutions by di (2-ethylhexyl) phosphoric acid (D2EHPA) in n-heptane, kerosene, toluene and m-xylene as diluents. Distribution ratios for the paraffinic hydrocarbon solvents are considerably higher than those for the aromatic ones; it was found that the extractable species is CdR₂.3HR for n-heptane and CdR₂.4HR for the aromatics. The equilibrium constants for the respective extraction reactions were also determined by taking into account the overall stability constants of cadmium chloride complex in aqueous solution.
The extraction rates of cadmium by D2EHPA in n-heptane as the diluent were obtained using a stirred vessel with a plane interface. The initial extraction rate is proportional to the total concentrations of cadmium in the aqueous phase and of D2EHPA in the organic phase, and inversely proportional to hydrogen ion concentration. The reaction mechanism is also discussed.