Assessing impacts of tungsten carbide: A substance and particle flow analysis

Paper in proceeding, 2015

Tungsten carbide (WC) is an extremely hard material used in industrial machinery, abrasives, missiles, tire studs and jewelry. Produced by reacting tungsten metal, produced from ammonium paratungstate with carbon at high temperature, WC carry a number of potential environmental and resource problems. First, tungsten is a critical material since resources are very unevenly distributed and it is sometimes produced from so-called conflict minerals. Second, although being a hard material, WC is torn into small, nano-sized particles which are emitted to the environment during various uses due to dissipative applications. Third, WC has high life cycle energy use due to high production temperatures, in a production chain with many steps. The aim of an ongoing project is to assess all these three impacts. As a first step, particle emissions are assessed. By applying substance flow analysis (SFA), along with a related method developed by Arvidsson et al. (2011, 2012) called particle flow analysis (PFA), global extraction rates, flows, stocks, and emissions of WC were estimated. By combining SFA and PFA, estimations were conducted both in terms of mass and in terms of particle number. From an environmental fate and ecotoxicological point of view, particle number has been suggested to be more relevant than mass for subsequent assessment of nanoparticle risks. Particle emissions are compared to previously estimated emissions of engineered nanoparticles made from silver, titanium dioxide, zinc oxide, and carbon. Preliminary results indicate that the emissions of WC are in the same order of magnitude as some of the most emitted engineered nanoparticles globally. Life cycle energy use assessment and resource criticality assessment will be persued later in the project in order to also assess other impacts of WC.