Determining the leaching characteristics of solidified/stabilized wastes using constant pH leaching tests

Abstract

Solidification/Stabilization treatment using Portland cement is an established procedure in the management of hazardous wastes. The technology is relatively simple, cheap, and highly reliable in prohibiting the migration of hazardous contaminants into groundwater. The success of this technology is measured by the amount of contaminants retained in the solidified matrix system. The most widely-used procedure to determine the amount that can leach out of the solidified waste is the Toxicity Characteristics Leaching Procedure (TCLP), which was developed by the EPA. The TCLP, however, lacks control on the shape and dimensions of the samples, as well as the pH at which the test takes place. Thus, it does not provide a true leaching characteristic of the contaminants through the solidified matrix. By keeping the pH at a constant value and using samples with fixed dimensions, the TCLP can be vastly improved. These conditions allow most of the contaminants to leach out of the matrix at controlled conditions. Consequently, the characteristics of the leaching process can be measured more accurately. The procedure developed in this research, the Constant pH Leaching Test (CPLT), is a modification of the TCLP. It is designed to measure the leaching rates of a fixed-dimension sample at a constant pH. In addition to measuring the leaching rates, the research also investigated the effects of different water-to-cement ratios, pH of the acid baths, and concentrations of the acid baths.