Removal of Cu(II) from an Aqueous Solution Using Manganese Dioxide-Loaded Volcanic Rocks

In this study, the preparation of a new adsorbent, manganese dioxide-loaded volcanic rock (termed 3VRM), to improve the copper adsorption capacity of volcanic rocks (VRs) is reported. The effects of the loading ratio, 3VRM dosage, pH, and ionic strength on the Cu(II) adsorption capacity of 3VRM were determined. The samples were characterized by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). SEM analysis revealed that spherical nanoscale manganese dioxide with a plum pattern was attached to the surface of VR, effectively increasing the specific surface area and number of reactive sites on the adsorbent. The main components of volcanic rocks are schistose and foshagite; manganese dioxide also exists in an amorphous form. Manganese dioxide is stable in the form of Mn⁴⁺ before and after adsorption. The results revealed that 3VRM had the greatest effect on Cu(II) adsorption at a loading ratio of 3 : 1, dosage of 2.5 g/L, and pH of 4–6. The Cu(II) adsorption capacity of 3VRM was shown to fit well with the pseudo-first-order kinetic model and the Freundlich model. The reaction equilibrium time was 10 min, and the theoretical maximum adsorption amount reached 434.7 mg/g. The acidity of the solution had less effect on the 3VRM, so it could be used in a wide pH range of 3–6. Studies of ion exchange and surface complexation have shown that the material demonstrated high efficiency in removing copper ions. Owing to its good adsorption performance and high efficiency, it is expected to be used for copper-containing wastewater treatment in the future.