The limitation of the toxicity characteristic leaching procedure for evaluating cement-based stabilised/solidified waste forms

The United States Environmental Protection Agencyʹs Toxicity Characteristic Leaching Procedure (TCLP) is commonly used as a regulatory tool to determine whether or not a waste can be classified as a hazardous waste. The validity of the test procedure for assessing cement-based stabilized/solidified heavy metal wastes is examined in this paper. Synthetic cement-based heavy metal waste forms with different ANC were prepared and subjected to TCLP to study the effect of waste acid neutralizing capacity (ANC) on metal leaching. A “real” waste was also obtained from a local commercial treatment facility and tested to verify the findings. The results showed that as long as the stabilized/solidified waste forms have sufficient ANC to neutralize the acidity of the leachant, the leaching of metals will be small and the performance of the different waste forms cannot be differentiated. The test therefore has limited use in comparing the performance of different cement-based waste forms. A modified test procedure is proposed.