Industrial Symbiosis for the ceramic sector: recycling of thermal spray waste in sintered products

Glazed ceramic tiles are the most common building material for floor and wall covering. Glazes are produced from frits. Among the available commercial frits, those containing zircon (ZrSiO4) and zirconia (ZrO2) are of great interest. The cost of pure zircon and zirconia, in the last few years has greatly increased. Therefore, finding alternatives or replacements to these raw materials is an economic advantage.
An opportunity derives from industrial gas turbines applications which are protected by a so called Thermal Barrier Coating (TBC) system, containing zirconia. TBC are commonly applied via an Atmospheric Plasma Spraying deposition process, during which a high amount (70- 90%) of thermally sprayed zirconia does not stick to the growing coating, becoming “overspray”. That is a waste material which can either stick, instead, to the walls of the deposition chamber, or, mainly, fall on the ground or be sucked in by the air filter.
This demonstration project, with EU LIFE funding, has demonstrated the possibility of absorbing 100% of the waste produced by the thermal spraying plants as secondary raw material for frits. The material reuse is possible thanks to separating waste generation at the source, and immobilization of harmful contaminants of spent thermal spray powders (mainly heavy metals) in matrices (glass-ceramics, pigments, ceramic mixtures, glazes).