First evaluation of semidirect recycling methods for the reclamation of cemented carbides based on a literature survey

Resumo

At the moment the industrially applied techniques for cemented carbide reclamation feature several
deficiencies. Depending on the process route, obstacles consist in high energy and chemical consumption
(indirect recycling methods) or a deterioration of the recycled product in comparison with the primary
material (direct recycling approach). Therefore, an alternative middle course provided by semidirect
recycling processes seems promising. Accordingly, the coating materials as well as the binder metals are
leached off the substrate keeping the hard phase unaffected and ready for reuse. However, the literature
reports various difficulties like the slow dissolution of the binder, particularly if the scrap consists of larger
pieces, contains a low binder metal perecentage or a small grain size. Furthermore, oxidation of the cemented
tungsten occurs as an undesired reaction, causing even slower lixiviation and a contamination of the recycled
product.
Due the fact of an inexistent comparable systematic analysis of the semidirect recycling procedures, this
article deals with a primary screening of potential combinations of acids, additives and oxidizing agents
found in a literature survey. All experiments took place under the same conditions in a temperature controlled
double-walled reaction vessel, varying only the molar concentrations of the different species as used in
literature. A crucial point comprised of the development of an appropriate sample preparation, which allowed
a simplification of the analysis along with its applicability in future kinetic investigations of selected
solutions. As a result, promising combinations of chemicals are ready for further investigations determined
by penetration depth and abrasion of the hard metal substrate. Successfully applied mixtures incorporate
acids such as HNO3 and HCl followed by some organic acids, all combined with H2O2 as oxidant.
Keywords: semidirect hard metal recycling, reclamation of cemented carbides, leaching of cobalt