Characterization of solid matrices for solidification/stabilization of hazardous wastes using solid state nuclear magnetic resonance spectroscopy and other analytical techniques.

摘要

Solidification/stabilization (S/S) is a valuable technology for the treatment of certain waste streams, e.g., metal plating wastes, incinerator ashes, etc., and has great potential for use in treatment of contaminated soils. Although this technology is relatively cheap, significant questions remain about the range of its applicability. Cement chemistry is very complex and poorly understood, and the possibility that contaminants could adversely affect the durability and permeability of the matrix is very real. The broad aims of the present studies are to survey S/S binding agents and additives with respect to their abilities to immobilize As, Cr, Pb, and phenols, the wastes which are known to give problems in S/S practice. A basic piece of information obtained in this study is the waste concentration in leachates using the Toxicity Characteristic Leaching Procedure carried out on solidified samples prepared with cementitious and pozzolanic binders and a variety of additives. These data show the general effectiveness of cement in binding certain metals, and also that certain deficiencies of cement can be corrected using additives. The second goal of the present study was to understand the interactions between waste and matrix with the eventual intention of predicting performance and designing effective mixes. Solid-state NMR has been extensively used to follow the profound changes in both the aluminate and silicate components of the cement matrix brought about by the addition of waste to cement. These matrix effects are correlated with leachability.;The wastes exhibit a variety of influences upon cement hydration and the leaching behavior depending upon their chemical nature. Similarly the same waste shows marked differences toward the hydration of different cements.;Addition of fly ash to OPC causes reversal of aluminate hydration, and silicate depolymerization occurs after initial polymerization. NMR studies of samples cured at least 1 year showed that the nature of added waste becomes almost irrelevant with respect to percent hydration over very longer periods of time.;Solid residues after leaching were also investigated by NMR. The cement matrices show marked differences in their characteristics depending upon pH of the leachate.