Quantifying the environmental impact of As and Cr in stabilized/solidified materials.

The assessment of the quality of sediment from the Great Backi Canal (Serbia) based on the pseudo-total As and Cr content according to the corresponding Dutch standards and Canadian guidelines showed its severe contamination with these two elements. Microwave assisted BCR sequential extraction procedure was employed to assess their potential mobility and risk to the aquatic environment. Comparison of the results of sequential extraction and different criteria for sediment quality assessment has led to somewhat contradictory conclusions. While the results of sequential extraction showed that Cr comes under the medium risk category, As shows no risk to the environment, despite of its high pseudo-total content. The contaminated sediment, irrespective of the different distribution of As and Cr, was subjected to the same immobilization, stabilization/solidification (S/S) treatment. Semi-dynamic leaching test was conducted for As and Cr contaminated sediment in order to assess the long-term leaching behavior of these elements. In order to simulate "worst case" leaching conditions, the test was modified using acetic acid and humic acid solution as leachants instead of deionized water. The effectiveness of S/S treatment was evaluated by determining diffusion coefficients. Four different single-step leaching tests were applied to evaluate the extraction potential of As and Cr. A diffusion-based model was used to elucidate the controlling leaching mechanisms. The test results indicated that all applied S/S treatments were effective in immobilizing As and Cr, irrespective of their different availabilities in the untreated samples. In most treated samples, the controlling leaching mechanism appeared to be diffusion, which indicates that a slow leaching of As and Cr could be expected.