ABSTRACT: This study was carried out to investigate the effects of nano-sized zero-valent iron (nZVI) particles (coated with carboxymethyl cellulose) and cow manure on the speciation of Pb in a calcareous soil. The experiment was conducted in a completely randomized design with two levels of cow manure (0 and 1.5% w/w) and in two time intervals (3- and 21-day) with three replications. The sequential extraction method used in current work fractionated soil lead into: sol+exch.-, organic-, carbonate-, Fe/Mn oxides-, and residual-Pb forms. Results from the fractionation study showed that nZVI significantly decreased carbonate-bound Pb by 22% and concomitantly increased Fe/Mn oxides-bound Pb and residual forms by 6% and 75%, respectively. Application of cow manure in soil treated with nZVI significantly decreased carbonate-bound Pb and increased Fe/Mn oxides-bound Pb and residual forms, while no change in Pb speciation of untreated (without nZVI) soil was recorded. Moreover, in untreated soil, the distribution of Pb in different fractions changed significantly with time, while in the case of treated soil, it was not significant. In general, from the data obtained in this research, it may be concluded that, although the use of cow manure increased the nZVI efficiency on Pb stabilization in soil, its effect on the remediation of Pb contaminated soil may not be appreciable.

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