Stabilization/solidification of hazardous metallic wastes: prediction of leach test performance to optimize S/S mixtures

Abstract

The main tool available for ascertaining the effectiveness attained by a hazardous waste stabilization/solidification (S/S) process is the chemical analysis of the leachate of the solid product obtained. Moreover, it is a well-known fact that the pH of the leachate is the most significant factor in con trolling the leachability of solidified metal bearing wastes, so the lowest concentrations in the leachate of many important metals appear within an optimum range of this pH. In this paper, a methodology is proposed for predicting the final pH of the leachate of different formulations used in the treatment of metallic industrial wastes. This methodology allows us to adjust the proportion of agents used in the S/S processes. In this method, the neutralization curves must first be obtained by acetic acid titration (GANC) of the mixture components. Based on the GANC curves of the components, the alkaline buffer capacity of the S/S solid can be defined and the final pH of the leachate can be predicted. Excellent concordance has been seen between predicted values and test results. How ever, we have also noticed discrepancies for some wastes and S/S agents. These discrepancies can be attributed to internal alkali-consuming reactions that produce lower final leachate pHs than predicted. The methodology proposed helps iden tify the reactions responsible for this process and helps study the evolution over time of the solids obtained.