Capping of marine sediments with valuable industrial by-products: Evaluation of inorganic pollutants immobilization.

In-situ capping of polluted sediment is considered as an inexpensive and effective treatment technology to immobilize contaminants in a short time. In this remediation technique sediments are capped by placing a layer of sand, clean sediment or other materials over sediments in order to mitigate risk. In this study, low cost industrial by products (bauxaline, steel slag, and mixture of the two products) were applied as capping agents. A bench scale laboratory experiment in aquariums was performed to evaluate their effects on Cd, Zn, As, and Cr mobility from an artificially contaminated marine sediment. Without capping, all the contaminants are constantly released with various kinetic depending of mineral oxidation or dissolution or leaching. Nevertheless, release did not exceed 31% of the initial amount of pollutant. Capping sediment with steel slag, bauxaline and their mixture totally captured Cd, Zn, and As. In the case of Cr, only steel slag actively blocked its release. A kinetic model was developed to model As and Cr release, with and without capping. The release times for Cr and As from the sediment were close to 6 days. In the presence of capping agents, the capture time for Cr was found to be 57 days for steel slag, and 7 days for bauxaline. Despite a high capture time, steel slag was the best capping agent since bauxaline matrix was a source of Cr and rapidly released it (release time = 1 day). The results indicated that steel slag and its mixture additive can be used as potential capping materials for the remediation of contaminated sites due to their significant entrapping of Cd, Zn, As, and Cr.
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