2020同步年報

Environmental and Earth Science 067 P bZrO 3 is a Pb zirconate titanate (PZT) ceramic of the perovskite family. The site of the Pb−O bond can be easily broken with an acidic attack because the bond Pb−O (2.5 Å) is longer than that of Zr−O (1.9 Å), giving rise to substantial free Pb(II) ions found in an acidic condition of landfill. An insufficient management of PZT-containing ceramic waste disposed of in landfill sites hence promotes a release of Pb(II) ions and poses a severe threat to the landfill operation and the surrounding environment. Herein, Kaimin Shih (The University of Hong Kong, China) focused on the treatment of waste PZT-based ceramics using a novel treatment and synchrotron X-rays to investigate the struc- tural stabilization of PZT, in an effort to find more effective treatment techniques to remediate Pb-laden waste. PbZr(PO 4 ) 2 can be obtained through sintering at 1000 °C for 96 h and a HNO 3 wash (2% v/v) to remove poorly crystallized materials on the surface to decrease any interference. Based on the Fourier-transform infrared spectral analysis, the wavenumbers for the phosphate normal mode were identified to assure the orthophosphate group in the de- signed structure. The diffraction signals were also matched with the X-ray Diffraction (XRD) patterns, indicating that crystalline PbZr(PO 4 ) 2 was obtained in the process of heat and acid treatment. According to the extinction rule, the space group for crystal PbZr(PO 4 ) 2 was assigned to P3c1, which is consistent with the indices ( a = 8.7455 Å and c = 32.4963 Å) confirmed with synchrotron X-ray diffraction (SXRD) using TPS 09A at the NSRRC. The atomic structure (short-range order) around the target ions was further demonstrated for the local bonding envi- ronment of PbZr(PO 4 ) 2 based on the X-ray absorption spec- tral measurements at the Zr K-edge and Pb LIII-edge. The Zr Fig. 1 : Normalized Zr K-edge XANES spectra; (a) two main features of BaZrO 3 and ZrSiO 4 were labeled as a and b with different relative intensities, show- ing octahedral and dodecahedral arrangements of oxygen neighbors around Zr; the spectrum of m-ZrO 2 exhibits a broad feature at c and Fourier transform k 2 -weighted EXAFS spectra in the R space of Pb; (b) the intensity of the first shell was in accordance with the signal from PbO, indicating that the Pb atom was tetra-coordinated to oxygen in the target structure. [Reproduced from Ref. 1] Using Synchrotron X-rays to Investigate the Pb Stabilization for PZT Ceramic Materials PZT has become popular in the field of industrial applications worldwide, triggered to create a voltage on introducing a mechanical stress on a poled piezoelectric ceramic material so as to in- duce a change of dipole moment. PZT contains Pb up to 60% of total mass. Because Pb is proved to be accumulated in the food chain and its toxicity causes chronic disease for life, Pb zero-emis- sion and Pb-free piezo-material systems are the next generations of piezo-material because of increasing environmental awareness and more restrictive regulations being made for environ- mental protection. Kaimin Shih et al. have recently developed a novel chemical Pb-stabilization to incorporate Pb into PbZr(PO 4 ) 2 to enhance the Pb stabilization effect through the formation of PbZr x Ti (1−x) (PO 4 ) 2 solid solutions. Synchrotron X-ray experiments demonstrated that the newly robust crystalline structure, developed through a well designed thermal treatment, provides an effective strategy to treat Pb frequently encountered in electronic wastes.