Deposition Kinetics of Colloidal Manganese Dioxide onto Representative Surfaces in Aquatic Environments: The Role of Humic Acid and Biomacromolecules

The initial deposition kinetics of colloidal MnO ₂ on three representative surfaces in aquatic systems (i.e., silica, magnetite, and alumina) in NaNO ₃ solution were investigated in the presence of model constituents, including humic acid (HA), a polysaccharide (alginate), and a protein (bovine serum albumin (BSA), using laboratory quartz crystal microbalance with dissipation monitoring equipment (QCM-D). The results indicated that the deposition behaviors of MnO ₂ colloids on three surfaces were in good agreement with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Critical deposition concentrations (CDC) were determined to be 15.5 mM NaNO ₃ and 9.0 mM NaNO ₃ when colloidal MnO ₂ was deposited onto silica and magnetite, respectively. Both HA and alginate could largely retard the deposition of MnO ₂ colloids onto three selected surfaces due to steric repulsion, and HA was more effective in decreasing the deposition rate relative to alginate. However, the presence of BSA can provide more attractive deposition site and thus lead to greater deposition behavior of MnO ₂ colloids onto surfaces. The dissipative properties of the deposited layer were also influenced by surface type, electrolyte concentration, and organic matter characteristics. Overall, these results provide insights into the deposition behavior of MnO ₂ colloids on environmental surfaces and have significant implications for predicting the transport potential of common MnO ₂ colloids in natural environments and engineered systems.