Catalytic assistance of ultrasound for manganese removal by waste oyster shells

The catalytic assistance of ultrasound (designated as US) for the removal of Mn(II) by oyster shells (designated as OS) was investigated with respect to major parameters such as pH, initial Mn(II) concentration, and US power density. The kinetic data of Mn(II) removal by the combination of oyster shells and ultrasound (OS/US) was fitted by the first-order kinetic model. Results show that the rate constant of the OS/US system was in the range 3.1–54.5 × 10−2 min−1, which is about 130 times higher than that of the homogeneous oxidation of Mn(II) by O2, and was about two times higher than that of commercial surrogate materials (CaO and CaCO3) associated with US under the same operational condition. The US power densities for the OS/US system and the log-scale of the first-order rate constants showed a linear positive correlation with a slope of 0.042. X-ray diffraction, and Fourier transform infrared analyses revealed that the dissolved Mn(II) was oxidized into Mn2O3 or MnO2, as well as precipitated in the form of MnCO3 by OS/US.

► The catalytic effect of ultrasound on the heterogeneous oxidation of Mn(II) by waste oyster shells were studied.
► The kinetic constants increased logarithmically as the ultrasound power density increased.
► Spectroscopic analyses revealed that the dissolved Mn(II) was oxidized into Mn2O3 and MnO2, and it was also precipitated as a form of MnCO3.
► The reuse of waste oyster shells can not only protect the marine environment, but also achieve the environmentally-friendly application of a waste for water treatment.