S, Zn, Cr, Cu and Fe changes during fluvial sediments oxidation

M. DI NANNO, G. CURUTCHET AND RATTO, S.

Ciencia del Suelo

ASOCIACIÓN ARGENTINA DE LA CIENCIA DEL SUELO

Año: 2009 vol. 27

0326-3169

To assess the risks associated to dredged sediments superficial disposal it is important to understand the changes caused by redox shifts. The aim of the present work is to assess changes in sulphur, metal speciation and acidity caused by a polluted sediment oxidation during controlled desiccation. Sulphide compounds (acid volatile sulphides-AVS- and sulphate), pH and neutralization potential were measured through time during 36 days. Zn, Cu, Cr and Fe speciation (BCR metal sequential extraction procedure) were measured at the beginning of the experiment and at day 22. An acid base account method based on the BCR procedure was employed to assess the sediment acidification risk. Some of the re-suspension experiments were inoculated with an Acidithiobacillus ferrooxidans strain to assess biological catalysis on sulphide oxidation. Acid-base account results indicate the sediment sample has a significant acidification potential. Oxidation increased sulphate levels (56 to 2300 mg S kg-1 in the desiccation experiment with a temporal evolution adjusted by a logistic model, and 2100 to 3000 mg SO4-2 L-1 increase for the re-suspension experiments). Sulphide oxidation rates varied between 0 to 3.1.10-9 mg O2 kg-1 s-1 for the drying sediment. Zn changes could be explained partially by ZnS conversion to ZnSO4 during oxidation. Fe reduction could be attributed to an increase in Fe oxides crystallinity. Acid base account for the sample indicates it is a potentially acid generating material. Zn increased its bioavailability during drying and was the only metal that appeared in significant amounts in solution during re-suspension. Land-filling with dredged sediments could present increased metals bioavailability problems despite having an important and effective neutralization potential.