Use of neutralized industrial residue to stabilize trace elements (Cu, Cd, Zn, As, Mo, and Cr) in marine dredged sediment from South-East of France

- Bauxite residue (bauxaline®) was neutralized with gypsum to lower its pH.
- Neutralized bauxaline® was used as amendment at 5% and 20% for trace elements stabilization in marine dredge sediment.
- 20% neutralized bauxaline® immobilized significantly cationic pollutants.
- Leachates toxicity towards rotifers (Brachionus plicatilis) was sufficiently decreased with 20% amendment application.

Management of marine dredged sediments polluted with trace elements is prime issue in the French Mediterranean coast. The polluted sediments possess ecological threats to surrounding environment on land disposal. Therefore, stabilization of contaminants in multi-contaminated marine dredged sediment is a promising technique. Present study aimed to assess the effect of gypsum neutralized bauxaline® (bauxite residue) to decrease the availability of pollutants and inherent toxicity of marine dredged sediment. Bauxaline®, (alumia industry waste) contains high content of iron oxide but its high alkalinity makes it not suitable for the stabilization of all trace elements from multi-contaminated dredged sediments. In this study, neutralized bauxaline® was prepared by mixing bauxaline® with 5% of plaster. Experiments were carried out for 3 months to study the effect of 5% and 20% amendment rate on the availability of Cu, Cd, Zn, As, Mo, and Cr. Trace elements concentration, pH, EC and dissolved organic carbon were measured in all leachates. Toxicity of leachates was assessed against marine rotifers Brachionus plicatilis. The Results showed that both treatments have immobilization capacity against different pollutants. Significant stabilization of contaminants (Cu, Cd, Zn) was achieved with 20% application rate whereas As, Mo, and Cr were slightly stabilized. Toxicity results revealed that leachates collected from treated sediment were less toxic than the control sediment. These results suggest that application of neutralized bauxaline® to dredged sediment is an effective approach to manage large quantities of dredged sediments as well as bauxite residue itself.