Removal of strontium ions from nuclear waste using synthesized MnO₂-ZrO₂ nano-composite by hydrothermal method in supercritical condition

This study focuses mainly on the synthesis of MnO₂-ZrO₂ nano-composite as a new inorganic adsorbent. Supercritical water was used as a preparation medium for particle deposited materials. MnO₂-ZrO₂ was prepared from metal nitrate solutions in supercritical region. The resulting sample was characterized by Fourier transform infrared (FTIR), X-ray fluorescence (XRF), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and transmission electron microscope (TEM). Analyses of the TEM images show the possibility for crystallizing nano-sized particles. The synthesized adsorbent was then used for the removal of strontium(Ⅱ) from the nuclear waste. Moreover, a number of factors such as aqueous phase pH, contact time and initial metal ions concentration in the adsorption process were investigated. Comparison of the adsorption efficiency of the MnO₂-ZrO₂ nano-particles with those of the non-nano particles shows a shift of uptake of the metal ions vs. pH curves towards lower pH values and a significant improvement in adsorption of strontium ions was observed by using the nano-adsorbent. The kinetic data corresponds well to the pseudo-second-order equation. The adsorption data for strontium(Ⅱ) were well fitted by the Langmuir isotherm. The synthesized nano-composite also showed a strong affinity toward the removal of Y(Ⅲ), Ni(Ⅱ), Pb(Ⅱ) and Co(Ⅱ) from the nuclear radioactive waste