Textural changes and heavy metal distribution in sediments after decontamination treatment by soil washing and attrition scrubber

Purpose: The study was aimed to provide information on the decontamination of sediments polluted with heavy metals by soil washing and attrition scrubber techniques, assessing the efficiency of a prototype machinery for the improvement of sediment quality dredged in the Ravenna Harbor (Italy). An additional purpose was to compare the heavy metal distribution in sediment fractions collected after these treatments. Materials and methods: Textural and geochemical characteristics were determined in bulk sediments and after the treatments of soil washing and attrition scrubbing by a smaller scale prototype. Statistical analyses were carried out to verify the heavy metal correlations at each step of the treatments. Results and discussion: Textural features after treatments showed moderate separation of sand and silt/clay fractions after soil washing and an increase of the fine fractions after attrition scrubbing. Bulk sediments polluted by arsenic (As) were decontaminated after treatments. Concerning heavy metals, mercury was concentrated in the sand while aluminum, As, cadmium, chrome, iron, manganese, zinc, and vanadium were concentrated in the silt/clay fraction. Bivariate plots showed a significant correlation of heavy metals with sand percentage after soil washing and attrition scrubbing. Conclusions: The results suggest that heavy metal concentrations were significantly affected by grain size distribution. Soil washing resulted in the complete decontamination of As in the sediments. The heavy metal concentration was altered in each step of the treatments according to three different trends.