Ash properties relevance to beneficial uses

Despite being a wood-derived biomaterial, wood ash generated by Canadian pulp paper mills (PPM) is generally landfilled. This is mainly because of the heterogeneous nature of ash, variations in ash quality and differences in the requirement of ash applications. Unlike limited past work on ash analysis for environmental compliance purposes for specific mills, a comprehensive database of ash quality for the PPM has been developed. Samples of three ash streams, bottom ash (BA), multiclone ash and electrostatic precipitator (ESP) ash, were collected. They were analyzed for physical, chemical and engineering properties of relevance to potential ash uses in areas such as the construction industry, compost production, soil amendment and waste stabilization/ solidification. Results show that the ash quality varied widely from one mill to another. Even within a mill individual ash streams varied substantially in properties. For example, the unburned carbon, a unique parameter for wood ash, in multiclone ash could be over twice the amount in the ESP ash. It is suggested that the traditional definition of fly ash (FA) could be refined to multiclone ash and ESP (or baghouse) ash thereby promoting the source segregation concept for the various ash streams produced at a mill. It is believed that the ash segregation approach, whereby ash sub-streams are kept separate to preserve their quality for specific uses, will minimize heterogeneity and quality variations of ash. This study will not only help divert wood ash away from landfills in favour of beneficial applications but also reduce carbon footprint of a mill.