Comparison of monometal and multimetal adsorption in Mississippi River alluvial wetland sediment: Batch and column experiments

Monometal and multimetal adsorption of selected heavy metals in a sediment from a coastal Louisiana forested swamp used for wastewater treatment was studied. Results from the batch experiments show that the maximum adsorption capacities of the metals by the sediment were in the order of Pb ≫ Hg > Cr > Cd ⩾ Cu ⩾ Zn ≫ As based on monometal adsorption isotherm, and Hg > Cr > Cu ⩾ Cd ≈ Pb ≫ As ≈ Zn based on multimetal adsorption isotherm, respectively. Batch experimental data best fit the Langmuir model rather than the Freundlich isotherms. In the column experiments, the maximum adsorption capacities of the metals were in the order of Pb ≫ Hg > Cr > Cd > Cu > Zn ≫ As in monometal conditions, and Hg ≫ Cr ≫ Pb > Cu ⩾ Zn ≈ Cd > As in multimetal conditions. The metals became more mobile in multimetal than in monometal conditions. Results from both the batch and column experiments show that competitive adsorption among metals increases the mobility of these metals. Particularly, in this study, Pb in multimetal conditions lost it adsorption capacity most significantly. In both monometal and multimetal conditions, the maximum adsorption capacity of the metals in the column experiments was higher than that in the batch experiment indicating other metal retention mechanisms rather than adsorption may be involved. Therefore, both column and batch experiments are needed for estimating retention capacities and removal efficiencies of metals in sediments.