Environmental assessment of a cement-based solidified soil contaminated with lead

The use of equilibrium-based and mass transfer rate extraction tests has be en proposed to provide an integrated assessment of leaching processes from stabilized/solidified wastes. The objectives of the research presented here are to validate this assessment approach and to evaluate the applicability of (i) using models assuming diffusive controlled release or coupled disso lution and diffusion for estimating rates of constituent release from cemen t solidified matrices, and (ii) using results from batch equilibrium leachi ng tests and physical characterization to obtain parameters for release rat e models. The test matrix consisted of soil fines contaminated with lead du ring manufacturing operations that were subsequently treated by two methods of Portland cement solidification/stabilization. Fundamental leaching para meters (i.e., acid neutralization capacity of the waste, constituent solubi lity as a function of pH, pore water properties and, release rates fi:om mo nolithic leach tests) were measured. Results were interpreted according to behavioral models based on mechanistic understanding of leaching processes. Results showed that (i) a good assessment of the release of contaminants f rom cement-based S/S treated wastes can be obtained by integrated use of eq uilibrium-leaching tests and mass transfer leaching tests, (ii) equilibrium -leaching tests are sensitive to the extent of particle size reduction and contact time and need therefore to be adapted according to waste properties co ensure equilibrium, (iii) mass transfer leaching tests need to be defin ed according to the specified scenario, (iv) estimation of the activity coe fficient within the waste pore water is necessary for accurate prediction o f constituent release rates, (v) results need to be interpreted according t o the considered scenario and the relevant behavioral model,(vi) the releas e of lead was governed by solubilization phenomenon at the solid-liquid int erface (i.e., at the interface between the matrix and the leaching solution ), and(vii) when release of lead is controlled by solubilization at the lea chant-monolith interface, the release flux of lead can be directly calculat ed from the release flux of hydroxide and consequently from pH data measure d in the leachate. (C) 1999 Elsevier Science Ltd. All rights reserved.