MPhil Thesis Presentation - Palladium Recovery from Electroplating Wastewater by a Binary Separation Process

A binary separation method was proposed to recover palladium from wastewater and to deliver pure metallic palladium as a final product. Wastewater samples from electroplating plants contained ppb level of palladium and metal impurities, including Copper, Nickel, Zinc, Iron, etc. Palladium was first selectively recovered from the wastewater via precipitation by iodide ions, and the palladium precipitated was then reduced by L-ascorbic acid. The conditions for palladium recovery were optimised by adjusting the pH, temperature and reagent dosage. Palladium could be separated from the wastewater few minutes after the addition of iodide ion. By adding a slight excess amount of iodide ion, 100% palladium recovery was achievable from a solution of pH below 2, while no coprecipitation of metal impurities was observed within a pH range of 1-3. At least 96% palladium was recovered in a 2hr reduction reaction at 80℃, with twice the molarity of Lascorbic acid compared to that of palladium. The recovered products from precipitation and reduction were analysed, by X-ray photoelectron spectroscopy, X-ray Powder Diffraction, Scanning electron microscopy, and Fourier-transform infrared spectroscopy. These characterisation methods confirmed that the palladium iodide was obtained from precipitation, and pure metallic palladium was obtained from reduction. Based on the obtained results, this method guaranteed a high recovery of pure palladium. Considering the minimal time and reagent amount required, this binary separation method is safe, straightforward, and practical for industrial application.