Synthesis of magnetite–gold nanoshells by means of the secondary gold resource

Methods for refining gold from copper anode slime, as the richest secondary source (approximately 1000 ppm), have been used for decades. But by production of magnetite–gold nanoshell we have managed to make a product with higher added value by applying a novel method. Magnetite nanoparticles (NPs) were prepared using co-precipitation method. Magnetite nanoparticles are used as cores and gold shell obtained directly from copper anode slime by hydrometallurgical process. The electrostatic interaction between negatively charged magnetite nanoparticles and positively charged cationic gold solution leads to formation of nanoshell structures. In this method, Thiourea acts as both selective leachant for gold solution and ligand for formation of gold shell on magnetite nanoparticles. The principles of inter-phase synthesis and properties of prepared nanoparticles have been investigated by high resolution transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and vibrating sample magnetometer. Based on the X-ray diffraction results, three main peaks of Au (1 1 1), (2 0 0) and (2 2 0) were identified. The formation of gold shell is also demonstrated by Fourier transform infrared results. The High resolution transmission electron microscopy, measurements show that the category of nanoshell with mean diameters of 20 nm for the core and mean diameters of 5 nm for gold shell is formed.