Transport of radionuclides and heavy metals during the cleanup of a polluted cinnamonic soil

Abstract

A fresh sample of cinnamonic soil heavily polluted with radionuclides (U, Ra) and toxic heavy metals (Cu, Pb, Zn) was subjected to clean-up in lysimeters containing 70 kg of soil each. The clean-up was connected with solubilization of the pollutants located mainly in the horizon A, their transportation through the soil profile in soluble forms, and their precipitation in the rich-in-clay subhorizon B3. The solubilization was studied by means of different variants and it was due to the joint action of natural soil microflora and leach waters containing ammonium and phosphate ions, and in some cases-hydrocarbonate ions. Additionally, the microbial activity in some lysimeters was enhanced by mulching the top soil horizon A with finely-cut hay and maintaining optimal soil humidity by controlling the irrigation rate. After 18 months of treatment, each of the soil profiles in different lysimeters was divided into five sections reflecting the different soil layers (horizon A, and the subhorizons B1, B2, B3, B4). The soil in these sections was subjected to a detailed chemical analysis and the data obtained were compared with the relevant data obtained before the start of the treatment. It was found that considerable fractions of the pollutants were removed from the horizon A and were transported to different zones in the soil profile, mainly in the subhorizons B3 and B4. In these subhorizons the non-ferrous metals were precipitated mainly as the relevant sulphides, uranium was precipitated mainly as uraninite (UO2), and radium-mainly as adsorbed ions and complexes. The transport and precipitation of pollutants depended strongly on the pH, the content of dissolved organic compounds in the soil solutions, and the prevailing anaerobic conditions maintained into deeper soil horizons.