Selective removal of the cobalt binder in WC/Co based hardmetal scraps by acetic acid leaching

Abstract

Scraps of hardmetal tools and pieces of original size were contacted with aqueous solutions of acetic acid under simultaneous introduction of pure oxygen or air to dissolve selectively the cobalt binder and recover the tungsten carbide. The influences of nominal composition of the scrap on the necessary time for a complete removal of the binder, as well as temperature, concentration and pressure were evaluated. Increasing the pressure during leach operation, as well as the temperature and the oxygen potential in the solution, significantly improves the rates of dissolution. Increasing the concentration of acetic acid does not necessarily increase the rates, also a decrease can be observed mainly depending on the tungsten concentration in the binder. The time for a complete binder removal also strongly depends on the nominal composition, respectively the grain size providing a mean free path for the penetration of the solvent and the oxygen into the scrap pieces. Altogether it was shown that it is possible to work up hardmetal scraps without any preceding comminution by a very selectively removal of the binder within reasonable times by applying a simple and very effective process, as the rates of dissolution are surprisingly high. The proposed process uses ecologically friendly educts and gives high-quality tungsten carbide raw materials as well as cobalt acetate solutions from which the cobalt can be easily recovered.