Systematic life cycle assessment of cobalt-based blue ceramic pigments: evaluating CoAl2O4 and lower-cobalt alternatives

Abstract

To enable a sustainable transition of the ceramic industry towards digital decoration via inkjet printing, it is imperative to promote the production of more environmentally friendly pigments. Despite its widespread use as a blue pigment, the environmental profile of cobalt–aluminium spinel (CoAl₂O₄) has never been assessed by Life Cycle Assessment (LCA), therefore potentially overlooking opportunities for less impactful alternatives. This work presents the first comparative environmental LCA of four distinct synthetic strategies for producing CoAl₂O₄ and several lower-cobalt alternatives. The study also accounts for two hybrid pigments, three M²⁺-doped spinels (M_1−xCo_xAl₂O₄, M = Zn²⁺, Mg²⁺), cobalt olivine (Co₂SiO₄) and its lower-cobalt variants, including Co²⁺-doped willemite (Zn₂SiO₄). The results throw light on the main substances and processes contributing to the environmental burdens of cobalt-based blue ceramic pigments and identify strategies to reduce their potential impacts. The study revealed that hybrid pigments are promising candidates with intense blue hues and lower environmental impacts than the traditional CoAl₂O₄, with Co_0.05Zn_1.95SiO₄ delivering the lowest environmental impacts among all the analysed pigments. The reliability of these findings was validated through Monte Carlo (MC) simulations. Potential environmental impacts were plotted against CIELAB colour parameters to identify pigments that exhibit desirable blue hues while being environmentally sustainable, thereby supporting their practical application.