Evaluation of leaching of trace metals from concrete amended with cement kiln baghouse filter dust

Abstract

The production of Portland cement (PC) can result in the release of trace amounts of mercury (Hg) in stack emissions. As a means of controlling Hg stack emissions at Portland cement kiln operations, some facilities have instituted a process known as dust shuttling, where baghouse filter dust (BFD), a partially calcined byproduct, is collected and blended with PC as an inorganic process addition, instead of returning the material to the kiln pyro-process. In response to questions raised regarding environmental impacts of recycling BFD into concrete products, research was performed to investigate the chemical composition of BFD and to assess the potential for leaching of trace metals from concrete products amended with BFD. Leaching of monolithic concrete under submerged conditions was examined as a function of time; concentrations of detected elements were found to be below applicable risk thresholds. Despite elevated Hg in the BFD relative to the PC, no elevated Hg risk was observed. Leachates from raw BFD did exceed risk-based thresholds for Se and V. However, leaching of size-reduced BFD-amended concrete did not show concentrations of these elements above applicable risk based thresholds. The results of this study suggest that the use of BFD as an inorganic process addition, within the percentages currently allowed by US industry standards, does not pose any additional risk with respect to direct human hazard or leaching of trace metals to water supplies.