| Heavy metals in wastewater treatment has become a topic of common concern toscientists from various countries, people come to realize the seriousness of heavymetal waste on human health threats. Conventional processing methods (e.g.chemicalreduction、ion exchange,adsorption、membrane separation) is mainly applied to heavymetal ions at a higher concentration, but a low heavy metal ion concentration, notonly the processing efficiency is low, and high operating costs, complicated operation,easy to cause secondary pollution. For agricultural and forestry waste, its widespreadutilization is low, and because of the open agricultural and forestry wastes piling andburning, not only caused a huge waste of energy but also cause environmentalpollution. However, agricultural and forestry waste with regeneration cycle is short、production、biodegradable、inexpensive and easy to get, etc. The main component ofcellulose、hemicellulose、lignin and other rich carboxyl、hydroxyl、amino reactivegroups and having larger surface area, can be used as an efficient adsorbent of heavymetal ions. Biosorption of heavy metals as a new wastewater treatment technology, itis not only environmentally friendly but also very strong adsorption capacity.Therefore, research on agricultural and forestry wastes removal of heavy metal ionsis necessary.The paper selected for the study Paulownia leaves,paulownia leaves powderwere modified with three treatments methods of NaOH-ethanol、 H2SO4-formaldehyde、and butylene oxide-thioglycollic acid, and the surface and structure ofPaulownia powder adsorbents were characterized using Fourier transform infraredspectroscopy (FTIR) and scanning electron microscope (SEM). The adsorptioncharacterstics of adsorbents for Pb2+and Cd2+were investigated. And the adsorptioncharacterstics of Pb2+and Cd2+from single and their binary onto modified Paulownialeaves were investigate though equilibrium adsorption method.The results showed that three modified paulownia leaves powder adsorbentsreached an adsorption equilibrium within4h, and the adsorption process of Pb2+andCd2+can be expressed by pseudo-second-order kinetics model at pH5, temperature of25℃and adsorbent dose of3g·L-1in solution. Adsorption ability of NaOH-ethanolmodified paulownia leaves powder adsorbent (MPPA NO.1) was improved significantly compared with unmodified paulownia leaves powder adsorbent(UMPPA), and equilibrium adsorption capacity of Pb2+and Cd2+were15.38mg·g-1and14.71mg·g-1, respectively. In addition, adsorption speed for Cd2+was fasterthan that for Pb2+. UMPPA revealed flat and smooth surface, while MPPA NO.1exhibited rough and the honeycomb-patterned surface. Its specific surface area was3.124m2·g-1, which was increased by150%compared with UMPPA. Paulownialeaves contain active functional groups such as hydroxyl, carboxyl and amides belt,which is conducive to the adsorption of Pb2+and Cd2+. In conclusion, NaOH-ethanolmodified paulownia leaves exhibited excellent adsorption properties for Pb2+and Cd2+in wastewater. The saturated adsorption capacity of Pb2+and Cd2+were found to be33.33mg·g-1and45.45mg·g-1for MPPA in single solution, respectively. Theadsorption process of Pb2+can be described well by Freundlich model, and theequilibrium adsorption data of Cd2+fitted well with the Freundlich and Langmuirisotherm models in the single solution. In addition, competitive adsorption ofPb2+and Cd2+on MPPA adsorbent was found in binary solution. Comparing with thesole ion adsorption results, the competitive adsorption had made adsorption capacityof Cd2+and Pb2+fall about55.69%and19.62%, respectively. The results showed theadsorption capacity of Pb2+and Cd2+was markedly restrained with the coexisting ionsin the aqueous solution. In conclusion, chemically modified Paulownia leaves inpresent study have great potential to be used as a cost-effective adsorbent for theremoval of Pb2+and Cd2+from the wastewater. |
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