Effective Self-Purification of Polynary.pdfVIP

Effective Self-Purification of Polynary Metal Electroplating Wastewaters through Formation of Layered Double Hydroxides J I Z H I Z H O U , ? Y U E Y I N G W U , ? C H O N G L I U , ? A J A Y O R P E , ? Q I A N G L I U , ? Z H I P I N G X U , ? G U A N G R E N Q I A N , * , ? A N D S H I Z H A N G Q I A O * , ? School of Environmental and Chemical Engineering, Shanghai University, No. 333, Nanchen Road, Shanghai 200444, P. R. China, and ARC Centre of Excellence for Functional Nanomaterials, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Queensland 4072, Australia Received February 2, 2010. Revised manuscript received October 22, 2010. Accepted October 27, 2010. Heavy metal ions (Ni2+, Zn2+, and Cr3+) can be effectively removed from real polynary metal ions-bearing electroplating wastewaters by a carbonation process, with～99% of metal ions removed in most cases. The synchronous formation of layered double hydroxide (LDH) precipitates containing these metal ionswasresponsiblefor theself-purificationofwastewaters. The constituents of formed polynary metals-LDHs mainly depended on the Ni2+:Zn2+:Cr3+ molar ratio in wastewaters. LDH was formed at pH of 6.0-8.0 when the Ni2+/Zn2+ molar ratio g 1 where molar fraction of trivalent metal in the wastewaters was 0.2-0.4, otherwise ZnO, hydrozincite, or amorphous precipitate was observed. In the case of LDH formation, the residual concentration of Ni2+, Zn2+, and Cr3+ in the treated wastewaters was very low, about 2-3, ～2, and ～1 mg/L, respectively, at 20-80 °C and pH of 6.0-8.0, indicating the effective incorporation of heavy metal ions into the LDH matrix. Furthermore, the obtained LDH materials were used to adsorb azoic dye GR, with the maximum adsorption amount of 129-134 mg/g. We also found that the obtained LDHs catalyzed more than 65% toluene to decompose at 350 °C under ambient pressure. Thus the current research has not only shown effective recovery of heavy metal io