Incineration of a commercial coating with nano CeO2
Résumé
The potential environmental risk arising from the incineration of waste containing nanomaterials is a new field which deserves further attention. Some recent studies have begun to focus on this topic (e.g. Walser 2012, Le Bihan 2014, Ounoughene 2015) but the data are incomplete. In addition, there is a need to consider real life waste. The present study gives some insight into the fate and behavior of a commercial coating containing a commercial additive (7%) based on nano-CeO2 (aggregates of 10 to 40 nm, with elemental particles of 2-3 nm). The tests have been conducted with a system developed in the frame of the NanoFlueGas project (Le Bihan 2014). It involves the combustion parameters of incineration (temperature around 850°C, highly ventilated combustion, at least 2 s residence time for the combustion gas in a postcombustion chamber at 850°C, and high oxygen/fuel contact). Time tracking by electric low pressure impaction (ELPI) shows that the incineration produces aerosol with number concentration dominated by sub-100 nm particles. Cerium is observed by TEM and EDX analysis but as a minority in the frame of heterogeneous particles (Figure 1). ICP-MS analysis indicates that the residual material consists mainly of CeO2 (60% of the mass). Observation by TEM establishes that is in the form of 40-200 nm aggregates and suggests that sintering occurred during incineration (Figure 2). As a conclusion, incineration led mainly to the release of nano-CeO2 in the residual material, as the major component. This is consistent with a scale 1 experiment conducted by spraying nano-CeO2 onto waste in the furnace entrance (Walser 2012). Aggregates are larger compared to the initial waste, and sintering is observed. So, the incineration did not destroy the nano-structure of the waste but transformed it (and probably decreased the specific surface).