Environmental, Resource and Health Assessments of Hard Materials and Material Substitution: The Cases of Cemented Carbide and Polycrystalline Diamond

Doctoral thesis, 2019

The conventional hard material used in manufacturing industry, cemented carbide (WC-Co), mainly consists of the geochemically scarce elements tungsten and cobalt. This use of scarce resources could potentially be avoided by a material substitution to the more abundant and largely carbon-based material polycrystalline diamond (PCD). The aims of this thesis are to (i) assess environmental, resource and health impacts of WC-Co, (ii) assess environmental and resource impacts of PCD and (iii) assess the environmental and resource potential of substituting WC-Co with PCD. For fulfilling these aims, life cycle assessment (LCA) and material flow analysis (MFA) are applied.

Papers I-III show that WC-Co has notable environmental, resource and health impacts. LCA results for non-Chinese WC-Co production show that most environmental impacts are dominated by a limited number of inputs and outputs (e.g. kerosene, sulfidic tailings and electricity) (Paper I). MFA results for flows of tungsten in the specific product of passenger car tire studs made from WC-Co show that the recycling of tungsten in this product is non-existing (0%) and thus considerably lower than the global average (10- 25%) (Paper II). Net health impact results for tire studs in a studded Scandinavian passenger car show that the purpose of tire studs – to prevent injuries – is not justified since the negative health impacts, mainly due to emissions of road particles during use, outweigh the positive health impacts from accident reduction (Paper III).

Paper IV provides LCA results for PCD production and compares WC-Co and PCD tools regarding environmental and resource impacts in the specific applications of wood working and titanium machining. The results show that PCD is preferable in wood working but not in titanium machining. In Paper V, a framework for defining functional units in comparative LCAs of materials is presented. The framework outlines three functional unit types: the reference flow, material property and product performance types. The selected functional unit greatly affects the result when comparing WC-Co to PCD. The main methodological contributions of this thesis are the inclusion of negative health impacts associated with conflict minerals in Paper III and the framework for comparative LCAs of materials in Paper V.