Paper Journal of the Ceramic Society of Japan 111mAAn806810iB@@Cj Recovery of Lead in Lead Zirconate Titanate Ceramics by Wet Ball Mill with Acidic Solution Masahiro KAMIYA, Ryo SASAI and Hideaki ITOH Research Center for Advanced Waste and Emission Management (ResCWE), Nagoya University, Furo­cho, Chikusa­ku, Nagoya­shi 4648603 _«n}pC^ØôçÛçj PZT ·åÛ¿ªµJmmñû _JsGEùä ºEÉ¡GÍ ¼Ã®åwïlH¨¤Z^[C4648603 ¼Ã®sçíæsV¬ The possibility of preferential recovery of lead from lead zirconate titanate (PZT) ceramics by wet ball mill­ ing with aqueous H2SO4 solution was investigated. The wet ball milling was performed using a pot mill ap­ paratus in air for 096 h at room temperature with the rotational speed xed at 300 rpm. Untreated PZT was dipped in aqueous H2SO4 solution for comparison with the wet­ball­milled specimen. The diraction lines of the PZT crystallites disappeared completely from the XRD results, and only the diraction lines of PbSO4 were conrmed by the wet ball milling for more than 48 h. For all the dipped specimens, the diraction lines 3 of PZT were identied even when the specimens were treated in 4.5 mol/dm H2SO4 solution for 96 h. Ac­ cording to ICP analysis of the dissolved components into the H2SO4 ltrate, the amounts of zirconium and titanium dissolved in the solution were found to increase with increasing treatment time, and the leaching behavior of both ions conformed closely to the collapsing behavior of the PZT crystal structure. As for lead ioninthesolution,thedissolutionamountwasbelow0.1÷ compared with the initial lead content in PZT ceramics under all the ball milling conditions. These results indicated that more than 99.9 mass÷ of lead in PZT can be recovered as PbSO4 by wet ball milling for more than 48 h. The purity of the recovered PbSO4 cal­ culated from the ICP results was approximately 98 mass÷. [Received March 28, 2003;Accepted August 29, 2003 ] Key­words : Ball mill, PZT, Lead recovery, PbSO4 1. Introduction crystal system: tetragonal) having a morphotropic phase Lead is a heavy metal whose discharge into the environ­ boundary neighborhood composition was used as a speci­ ment has been strictly regulated because it is hazardous men. A PZT sintered compact was roughly precrushed in when contained in the human body. However, a large agate mortar by hand. The wet ball milling of the amount of lead­containing products, such as lead accumula­ precrushed PZT was performed using a pot mill apparatus tor, lead glass and lead­based dielectric devices, still con­ in air for 096 h at room temperature, and the rotational tinue to be produced and consumed. Some of the wastes speed was xed at 300 rpm. About 2.5 g of precrushed PZT containing lead from industries and households have been (7.7 mmol) was placed in a polypropylene container of inner disposed by land lling without any eort exerted to volume 50 ml together with ZrO2 balls (diameter: 5 mm, recovering lead in the products and/or recycling it as weight ratio of PZT/ZrO21/50), and then 4 ml of aqueous 3 resources. Lead­based piezoelectric materials such as lead H2SO4 solution (4.5 mol/dm ) was added into the container. zirconate titanate (PZT) and lead­free piezoelectric materi­ On the other hand, a dipped specimen was prepared by als, which are expected to replace lead­based piezoelectric exposing the precrushed PZT into 4 ml of aqueous H2SO4 materials, have been extensively investigated by many solution (4.5 mol/dm3) for 096 h at room temperature to researchers.1)5) However, it is anticipated that a large compare it with the milled specimens. The wet­ball­milled amount of lead­based dielectric materials will still be and dipped specimens were sonicated in 100 ml of aqueous 3 produced and discharged even in the future because lead­ H2SO4 solution (0.5 mol/dm ) for 15 min, after which solid based materials have superior properties.6)8) constituents in the solution were separated by ltration, and The mechanochemical (MC) processisavailablenotonly they were washed by the ltrate again. Finally, solid for the fabrication of engineering materials9)14) but also for constituents on the lter were dried at 323 K in an oven for extracting precious and rare metals from wastes.15),16) 24 h. Moreover, detoxication and decomposition processes of 2.2 Characterization hazardous organic compounds, such as dioxins, have been The precrushed PZT and the specimens treated by ball recently developed using the MC process.17),18) However, milling and dipping were identied by XRD (Rigaku; the recovery of heavy metals in electronic materials has not RINT2500H). The surface morphology and texture of the been reported. In the present study, PZT ceramics were specimens were observed by scanning electron microscopy treated by wet ball milling at room temperature with aque­ (SEM;JEOL, JSM6330F ). The distribution of elements ous H2SO4 solution, and the possibility of preferential recov­ included in the recovered powder was analyzed by energy eryofleadinitssulfateformbyreactingPZTceramicswith dispersive X­ray spectroscopy (EDS;JEOL, JFC2140 ). H2SO4 solution during milling was investigated. Quantitative and qualitative analyses of lead, zirconium and titanium ions dissolved in the H2SO4 ltrate were performed 2. Experimental procedure by inductively­coupled­plasma atomic­emission spectro­ 2.1 Specimen and wet ball mill scopy (ICPAES;Perkin Elmer Japan, 3300DV ). Commercially available PZT sintered compact (Kojundo Chemical Lab. Co., Ltd., composition: Pb(Zr0.52Ti0.48)O3, 806 Masahiro KAMIYA et al. Journal of the Ceramic Society of Japan 111mAAnB@@C 807 3. Results and discussions the number of formed ne particles was found to increase 3.1 Dipped specimen with treatment time, and the large particles were fully co­ Figure 1 shows the XRD proles of (a) the precrushed vered with ne particles. This SEM observation leads to the PZT powder and the specimens obtained after dipping conclusion that the contact areas of PZT particles with in aqueous H2SO4 solution for (b) 4, (c) 12, (d) 48and H2SO4 solution decrease with increasing treatment time, be­ (e) 96 h. In all the XRD proles of the dipped specimens, cause the PbSO4 ne particles precipitated on the surface of new peaks corresponding to PbSO4 appeared. The intensi­ the larger PZT particles. Therefore, it takes a very long ties of the PZT peaks decreased gradually with increasing time to transform PZT into PbSO4 under the present condi­ treatment time. In contrast, the intensities of the peaks of tions. PbSO4 increased with increasing treatment time. However, Figure 3 shows the EDS images of (a) the secondary­ the peaks of PZT were still conrmed even after dipping for electron image (SEI) and the element maps for (b) Pb, 96 h. This is because the reaction of PZT with H2SO4 solu­ (c) Zr and (d) Ti in the recovered powder after dipping for tion occurs only on the coarse particle surface of the 48 h. The gray part in the element map indicates the exist­ precrushed PZT. ing area of each element. EDS images show that the parti­ Figure 2 showstheSEMimagesof(a) the precrushed cles with a relatively large grain size (34 mm) are basically PZT powder, and the specimen obtained after dipping for composed of Pb, Zr and Ti atoms. In contrast, ne particles (b) 4and (c) 12 h. The particle sizes of precrushed PZT are seen in the SEI (Fig. 3(a)) which overlaps only with the ceramics were approximately 210 mm, as seen in Fig. 2(a). Pb image. This result also indicates that the large particles The recovered powder after dipping in H2SO4 solution main­ are PZT particles and ne particles correspond to the ly consisted of ne particles with diameters less than 500 precipitated PbSO4. This conclusion is supported by the nm which adhered on particles as large as those of the results of the XRD analysis shown in Fig. 1. precrushed PZT, as seen in Figs. 2(b) and (c).Moreover, Fig. 1. XRD proles of (a) the precrushed PZT powder and the specimens obtained after dipping in aqueous H2SO4 solutions for Fig. 3. EDS images of (a) the secondary­electron image and the (b) 4, (c) 12, (d) 48and(e) 96 h. Symbols show PZT (¥) and element maps for (b) Pb, (c) Zr and (d) Ti in the recovered powder PbSO4 (). after dipping for 48 h. Fig. 2. SEM images of (a) the precrushed PZT powder and the specimens obtained after wet ball milling for (b) 4and (c) 12 h. 808 Recovery of Lead in Lead Zirconate Titanate Ceramics by Wet Ball Mill with Acidic Solution Fig. 4. XRD proles of the specimens obtained after wet ball mill­ ing for (a) 4, (b) 12, (c) 48 and (d) 96 h. Symbols show PZT (¥) and PbSO4 (). Fig. 6. SEM images of the specimens obtained after wet ball mill­ ing for (a) 12 and (b) 48 h. only because the PZT particles are nely ground, but also because PbSO4 particles precipitated on the PZT surface are detached and well dispersed during the milling process. Preliminary experiments revealed that the perfect conver­ sion of lead in the PZT sintered compact to PbSO4 was not attained by hydrothermal treatment with aqueous H2SO4 so­ lution. Thus, milling of the PZT plays a signicant role in accelerating the reaction rate by enlarging the fresh surface area of the PZT particles. A few milligrams (13 mg) of weight loss of ZrO2 balls were observed after wet ball mill­ ingwithaqueousH2SO4 solution. Figure 6 shows the SEM images of the specimens ob­ Fig. 5. Treatment time dependence of the XRD intensity ratio tained after wet ball milling for (a) 12 and (b) 48 h. In the [PbSO4/(PZT{PbSO4)] for wet ball­milled specimens (¡) and dipped specimens ( ).