Adsorption Behavior of Manganese Dioxide Towards Heavy Metal Ions: Surface Zeta Potential Effect
2018
He, Chunxiang | Xie, Fencun
The zeta potential of hydrous manganese dioxide (HMO) may significantly influence its adsorption towards heavy metals. The effect of zeta potential of HMO on adsorption efficiency of three heavy metal ions, Pb(II), Cd(II), and Ni(II), was investigated. The zeta potential values decreased with decreasing Mn²⁺/MnO ₄ ⁻ ratio in the HMO synthesis. The larger adsorption capacity was observed for HMO with more negative zeta potentials, and its zeta potential values increased after the adsorption of Pb(II), Cd(II), and Ni(II). The adsorption equilibrium of HMO at 303.15 K could be well described by Langmuir isotherm equation with qₘₐₓ value of 502.85 mg/g for Pb(II), 155.11 mg/g for Cd(II), and 87.52 mg/g for Ni(II), respectively. Higher initial heavy metal concentration and solution pH both favored the enhancement of adsorption capacity. The pseudo-second-order equation could best fit the adsorption process. Furthermore, the Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that Pb(II), Cd(II), and Ni(II) may form inner-sphere complex on HMO surface. In addition, HMO adsorbent can be regenerated readily by treating with 50% KMnO₄ solutions. After five rounds, the zeta potential value decreased to − 50.6 mV and the Pb(II) removal efficiency is 91% as compared to previous HMO removal efficiency of 93%. These findings revealed that the surface zeta potential of HMO adsorbent might be used as a parameter to determine its performance for the removal of heavy metals from contaminated water.
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