Feasibility of using organosilane dry-coated detoxified quartzes as raw material in different industrial sectors

Abstract

Respirable crystalline silica (RCS), in the form of quartz and cristobalite from occupational sources, was classified by the International Agency for Research on Cancer (IARC) as carcinogenic to humans (category 1). In addition, RCS has recently been included in the Directive (EU) 2017/2398 about carcinogens and mutagens at work. Numerous studies suggest that the toxicity of quartz is conditioned by density and distribution of surface silanol groups, and it has been widely demonstrated at lab scale that masking these silanol groups significantly reduces silica toxicity. Based on these findings, a detoxifying, wet-coating method, using organosilanes as coating agent for reactive surface silanols, was previously developed and tested at industrial scale. In the present work, a new dry-coating process (patent pending) also using organosilanes was developed and applied to detoxify quartzes from different industrial branches. Dry-coating efficiency and stability were assessed and confirmed by both in-vitro tests (lactate dehydrogenase release and alkaline comet assay) and an intratracheal instillation study in rats. Finally, industrial trials were performed by different quartz end users (elastomers, foundry, adhesives, pigments and glazes) to evaluate the technical and economic feasibility of implementing this dry-coating process at industrial scale. From the obtained results, it can be drawn that the proposed methodology seems to represent a promising strategy to significantly reduce the risk associated with the handling of RCS-bearing materials. This RCS coating approach shows enough flexibility to be adapted to different industrial processes without significantly interfering with product quality.