Recovery of Nanoparticles of Metal Values from Spent Metallized Graphite Brushes and Slip Rings

Abstract

This work provides a method to recover monolayer metal values having nanoparticle in size from spent metalized graphite brushes. The recovered metals are supported on porous glassy carbon substrate by chemical or electro deposition process. The chemical method involves crushing and grinding of the spent brushes to pass 200 mesh. Magnetic separation removed magnetic susceptible metals such as iron. Nonferrous metals were leached using 3N nitric acid in hot conditions. Hydroxide gel of the dissolved metals generated with 1N ammonium hydroxide. The carbon substrate was multi-impregnated with metals hydroxide 3-4 times. In each time, the loaded carbon was dried. Free metals on the carbon substrate are obtained by reducing the hydroxide with hydrazine hydrate or by thermal reduction using hydrogen gas at 900°C. In the electro deposition process, ground spent brushes were packed in a polyethylene cloth used as anode. The electrolyte is 3M of sulfate salt of the metal of concern. Pulse current cyclic voltmetric technique was applied to control the particle diameter and thickness of the deposited metal. Results revealed that monolayer silver and copper of nanoparticles has been successfully prepared from spent metalized graphite brushes. Electro deposition is more friendly environment procedure and more convenient, less cost and more precise.