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

► The availability factor (FAV) for contaminant leaching varies with leachate pH. ► FAV changes with liquid/solid ratio (L/S) when release is controlled by solubility. ► FAV is taken equal to FAVP (pore-liquid availability factor) when L/S=bulk porosity. ► FAVP is used in calculation of effective diffusion coefficients in porous monoliths. A new leaching test on comminuted (0.125–2.0mm 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, L/S, ratio (0.6–50dm3/kg) on the availability factor, FAV, 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 (FAV–L/S data) allowed the determination of the pore-liquid availability factor, FAVP, at different leachate pHs. These FAVP 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, De, 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 De values were compared with the ones calculated from the results of other availability tests on granular solid samples (NEN 7341 and AAT tests).