Circular economy and urban mining for the sustainable development of the production of hardmetals based on tungsten carbide-cobalt (WC-Co)

Abstract

One of the most complex issues nowadays is the disposal of waste, particularly industrial ones. Recycling has been shown to be the most appropriate and economically viable way to avoid aggressions to the environment. The hardmetals (cemented carbides) belongs to a class of material, resistant to wear, in which the refractory metals, such as tungsten (W), in the form of carbide (WC), agglutinated with metallic binders, such as cobalt and nickel, to form a structure that combines hardness with toughness. Although the term "Cemented Carbide" has been widely used in the United States, these materials are best known internationally, and also in Brazil, such as hardmetals. The carbide is obtained by a process generically called powder Metallurgy (M/P), through a sequence of carefully controlled operations. Carbide powder is prepared and mixed with the metal binder, also in the form of very fine powder, mainly cobalt or nickel. The main carbide used is tungsten, which together with cobalt, the most used form of hard metals, WC-Co. Nickel is used as binder for applications requiring high corrosion resistance. The metal carbide and transition metal powders (Co or Ni) are sintered with paraffin to facilitate their compaction. The process of production hardmetals involves, therefore: mixture of raw material, compaction; Pre-sintering for paraffin removal; Machining to obtain details not possible by compaction; High temperature sintering (high shrinkage); and finishing, carried out mainly by grinding. In each of these steps there is waste generation. In addition, it should be considered mainly the scrap generated by the parts that had their life cycle exhausted. Between waste and scrap it is estimated that Brazil manages annually about 200 tonnes of recyclable product, which can be evaluated in up to 25 USD per kilo. We are therefore talking about a market up to USD 5 million per year. This market has been exploited outside the country, since much of the residue is collected and exported for recycling. The recycling of the carbide is of great importance for its high added value and large global consumption, mainly in applications such as machining inserts, cutting, mining (oil and gas), transport and construction, mechanical conformation and special tools. There are few who know the product, manufacturing process, structure and properties, and that can give the best destination to the various residues. The main objective of this project is to work in the process of recycling the carbide, considering residues of different origins, such as: inserts (cutting tools), grinding slurries, sintered parts, powder machining of green parts, and coated inserts. The objective is to give the most suitable destination for each of them, which can be returned to the production chain of the hard metal to produce sintered parts, or recovery to obtain powder for thermal spraying (metallization). A complete characterization of each of these residues and the products obtained from them will be carried out. (AU)