Evaluation of the leachability of heavy metals from cement-based materials

A new leaching test on comminuted (0.125-2.0 mm gradation) cementitious matrices, designated as Modified-Pore Water (M-PW) test, was developed to evaluate the effect of varying leachate pH (4-12.8) and/or liquid-to-solid, LIS, ratio (0.6-50 dm(3)/kg) on the availability factor, F-AV, of heavy metals. The M-PW test was applied to leaching of lead and zinc ions from ground Portland cement mortar incorporating Municipal Solid Waste Incinerator (MSWI) fly ash. Correlation of M-PW test results (F-AV-L/S data) allowed the determination of the pore-liquid availability factor. F-AVP, at different leachate pHs. These F-AVP values were utilized, in conjunction with a kinetic pseudo-diffusional model, to evaluate the leaching behavior of monolithic mortar specimens subjected to dynamic leaching tests (constant leachant pH 4 or 6). A good agreement was found between the effective diffusion coefficients, D-e, of lead and zinc ions calculated by such a methodological approach and those obtained from recognized microstructural models. In contrast, no satisfactory agreement was found when these D-e values were compared with the ones calculated from the results of other availability tests on granular solid samples (MEN 7341 and AAT tests). (C) 2012 Elsevier B.V. All rights reserved.