ECO-FRIENDLY LEACHING PROCESSES FOR HARD-METAL WASTES VALORISATION

Hard Metal (HM) is a composite material consisting, in most cases, of tungsten carbide (WC) particles embedded in cobalt metal binder, widely used for highly wear-resistant tools production. Since 2011, W and Co are listed among the critical raw materials by the European Union due to their high economic importance and the risk related to their supply. The demand of W and Co in HM production and in other applications affects heavily their criticality and price. For these reasons, the use of secondary resources seems a more sustainable approach following a circular economy model encouraged by European Directives. In this work, hydro- solvo-metallurgical processes with organic acids (OA) are applied to three different powders deriving from the three main steps of carbothermal regeneration, a direct recycling process performed by FILMS SpA. This process allows to recover a WC-Co powder with the same composition of the starting HM end-of-life tools, limiting its re-employment in the HM production process. The leaching method aims to obtain a product more versatile in its reuse in HM manufacturing. Leaching process is conducted on powders (oxidized, reduced and carburized) with OA in aqueous and non-aqueous solution by varying operative conditions such as temperature, pH solution and liquid-to solid ratio. Leaching solution is analysed trough an ICP-OES to determine leaching efficiency and treated powders are characterised by XRD, FT-IR and elemental analyses. OA can be obtained from agro-industrial wastes with low-cost biological process (Patent Submission Number: 102022000007502). They proved to be efficient leaching agents in metal dissolution in all powders. In the case of reduced and carburized ones, OA show greater affinity in complexing Co binder, making the reaction of leaching selective. However, in oxidized form both W and Co are dissolved at high rates. These results are noteworthy because: -OA selectivity allows to tune Co content without powder oxidation, especially in non-aqueous solution, against to what happens using inorganic acids. -OA leaching could be used as an alternative to alkaline methods in recycling W from HM wastes. Microstructure and quality assessments of recycled material are ongoing.