Chemical synthesis of gold nanoparticles with different morphology from a secondary source

Nowadays, the conversion of waste materials into advanced material is taken into much consideration. The present paper attempts to investigate the chemical synthesis of gold nanoparticles from copper anode slime (containing 0.1 % Au) that is an insoluble product deposited at the bottom of the electrorefining tank during electrorefining of copper. First, the anode slime was washed by nitric acid. To separate gold from anode slime, it was dissolved by thiourea solution as a selective extraction of gold; a cationic complex of gold-thiourea was then obtained and used as the gold solution. The gold nanoparticles were synthesized directly from gold-thiourea solution by two different reducing agents sodium citrate and VenMet solution, the latter being a mixture of sodium borohydride and sodium hydroxide. These reductants play the role of both a reducing and capping agent for synthesis at different temperatures (25–65 °C) and different agitation rates (400, 800, 1200 rpm). X-ray fluorescence and atomic absorption spectroscopy showed the chemical composition of the anode slime and gold-thiourea solution. The scanning electron microscopy and transmission electron microscopy images showed various shapes, including spherical and cubic nanoparticles of an average size of about 190–500 nm for sodium citrate reduction, and 15–190 nm for reduction by VenMet solution at different temperatures and agitation rates. Furthermore, energy-dispersive X-ray and X-ray diffraction pattern illustrated that gold crystal was formed. Dynamic light scattering measurements were performed to investigate the average particle size and particle size distribution.