Dissolved and colloidal transport of Cd, Pb, and Zn in a silt loam soil affected by atmospheric industrial deposition.

As a result of processing of metal ores, trace metals have contaminated large areas of northern France. Metal migration from the soil to groundwater presents an environmental risk that depends on the physico-chemical properties of each contaminated soil. Soil water samples were obtained over the course of 1 year with zero-tension lysimeters from an acidic, loamy, metal contaminated soil. The average trace metal concentrations in the soil water were high (e.g. for Zn 11 mg l-1 under the surface horizon), but they varied during the sampling period. Zn concentrations were not correlated with pH or total organic carbon in the solutions but were correlated with Cd concentrations. On average, 95% of the Zn and Cd but only 50% of Pb was present in a dissolved form. Analytical transmission electron microscopy was used to identify the Zn or Pb carriers. Colloids containing Pb and Zn were biocolloids, whereas colloids containing only Zn were smectites.     

Efficient use of Fe metal as an electron transfer agent in a heterogeneous Fenton system based on Fe0/Fe3O4 composites

In this work a novel heterogeneous Fenton system based on Fe(0)/Fe3O4 composites is described. The composites with several Fe(0)/Fe3O4 ratios were prepared by two different methods, i.e. mechanical alloying of Fe(0) and Fe3O4 powders and controlled reduction of Fe3O4 with H2. Reaction studies and detailed Conversion Electron M?ssbauer surface characterization of the composites Fe(0)/Fe3O4, Fe(0), Fe3O4, alpha-Fe2O3 and gamma-Fe2O3 suggested that Fe2+surf species are essential to produce an active Fenton system. Kinetic studies for the oxidation of the dye methylene blue, used as an organic model molecule, and for the peroxide decomposition suggest that the reactions proceed via HO* radicals generated from Fe2+surf species and H2O2 in a Fenton like mechanism. The increase in activity caused by the addition of Fe(0) is discussed in terms of a creation of Fe2+surf species during the preparation of the composite and by an electron transfer mechanism from Fe(0) to Fe3+surf during the Fenton reaction to regenerate the Fe2+surf active species.