Leachability of Lead and Cadmium from Cementitious Wastes

Abstract

AbstractIn this paper, the leachability of lead and cadmium from cementitious waste was investigated to determine the leaching mechanism of these heavy metals from a cement matrix so that a more appropriate leaching test can be designed. The leaching studies were carried out using a modified Toxicity Characteristic Leaching Procedure (TCLP), and variations in leaching parameters such as leachate pH, the duration of agitation, the particle size, and the liquid to solid ratio were investigated. The main finding of these studies was that the leachability of Pb and Cd in cementitious waste was highly dependent on the pH of the leachate. Other findings included: (i) the leachability of metals initially decreased with increasing leaching duration but increased after the leachate pH reached equilibrium; (ii) the particle size of the cementitious waste affected the rate of leaching of alkalinity from cement and hence the leachability of the heavy metal ions; and (iii) the total metals in the leachate, increased with increasing liquid to solid ratio. Overall, the TCLP was found to be inappropriate for assessing the leachability of heavy metals from cementitious waste due to the high buffering capacity of the calcium ions in the cement. This maintained the pH of the leachate at a value where heavy metals are insoluble. The test was found to underestimate the concentration of heavy metal ions leached from cementitious waste relative to the concentration in the actual landfill environment.