(368b) Leaching Behavior of Hazardous Heavy Metals From Lime Fly Ash Cements

Disposal of fly ash in landfills in large amounts results in sacrificing precious land space and potentially endangering neighboring communities and water resources. Productive utilization of fly ash is one approach to reduce the impact of this disposal problem.  A major use for fly ash is in portland cement-based materials such as concrete.  Unfortunately, not all fly ash is suitable for use as a partial cement substitute.  One concern among concrete producers is the high residual content of carbon of some ashes, which interferes with other additives used to make modern concrete. Therefore, other large volume application for off-specification ash are sought.  One possibility is to use high carbon bearing ash in combination with lime to provide cement for low strength non-structural applications such as in road base mix formulations. Incorporating such materials in road base formulations however, presents several environmental challenges. The main concern with this application is the possibility that the fly ash will come into contact with water and hence contaminate drinking resources or wildlife waters.  Fly ashes, by virtue of their origin, can contain trace toxins and hazardous heavy metals. The goal of this research is to investigate the efficacy of hydrated ash to sequester heavy metal ions and discern if ash chemistry is a factor in the ability of the associated hydrates to bind the metals.  Two ashes were investigated, one that is suitable for use as a cement substitute and the other having a high carbon content.