Investigation of bio-removing metal ions from wastewater-a viewpoint of micro forces

Biosorption is one of the effective methods to treat the wastewater containing heavy metal ions, especially the biosorption using magnetotactic biosorbents (MTB). The interaction between metal ions and MTB was investigated using molecular dynamics simulations. A model of a bacterial cell consisting of functional groups and Fe3O4 was created. The principal functional groups on the MTB surface included -COOH, -PO3H2, and -OH, and physical adsorption was deduced as the primary adsorption mechanism. Free energy profiles for ions approaching the bacterial cell were computed using the adaptive biasing force method. The adsorption of ions occurred at a distance of 5 angstrom from the MTB surficial groups. Repulsive force had to be overcome when ions approached the functional groups in the simulation. The electrostatic attraction between ions and the adsorbent promotes adsorption, while the van der Waals force hinders adsorption. The -PO3H2 and -COOH groups were found to contribute to the adsorption selectivity in the binary aqueous solutions.