Sludge-Amended Brick Production: Applicability for Metal-Laden Residues

Abstract

This paper will examine the general concept of using sludge during brick manufacture, and will specifically address the fate of metals contained within the employed sludge relative to the vitrification process. Overall, it appears that most metals will be trapped within sludge-adulterated brick, both during firing and weathering. This behavior appears related to a silicate-based physico-chemical containment mechanism. Volatilization of metal during firing was observed in the case of selenium, and in this instance only for specimens spiked with elevated metals levels (i.e. 1000 ppm Se). Simulated weathering in pH=2.5 and pH=5.0 acetic acid resulted in nominal leachate losses beyond the U.S. EPA extraction procedure limits for arsenic, selenium, and cadmium. Here again, though, these marginally elevated losses were only observed for those bricksspiked with extremely high metals levels (i.e. 1000 ppm, or higher). Overall, the research findings presented by this paper suggest that standard municipal sludges laden with “normal” metal levels could be satisfactorily incorporated within a brick manufacturing process with little concern regarding metal release. As for hazardous metal-laden sludges, brick manufacture may comprise a similarly acceptable sludge management option; however, this latter strategy would likely warrant additional site-specific investigation prior to implementation (i.e. relative to the given metal species, concentrations, metal release characteristics, etc).