Removal Of Heavy Metals From Wastewater By Nanoscale Zero-valent Iron Supported On Modified Clay

Zero valent iron （ZVI） technology show a good application prospect for remediation ofsoluble, high mobility and toxic radionuclie heavy metal uranium （U（VI）） contaminated sites.Compared to micron iron, nanoscale zero valent iron （NZVI） has much higher removel efficiencydue to the large specific surface area. However, the poor stability, easy oxidation and easyagglomeration of NZVI limit its application in large scale. Therefore, an appropriate carrier andeasy operation immobilization method should be selected to synthetize some stabilityperformance and high reactivity NZVI, which is proposed as a critical step in practical applicationabout NZVI.In this paper, Na-bentonite （Na-bent） and pillared bentonite （OH-Al-bent） with variousfunctional groups and surface charge were successfully syntheticed by adjusting the type andcomposition of modified agents according to the natural clay bentonite with the specific propertiesof adjustable structure-funtion apart from other carriers, subsequently, two novel composites, i.e.,NZVI/Na-bent and NZVI/OH-Al-bent were prepared and used for radioactive UO₂²⁺remediation.The NZVI, NZVI/OH-Al-bent and NZVI/Na-bent were characterized by X-ray diffraction （XRD）,transmission electron microscopy （TEM） and BET specifce surface area. The removal rate andreaction rate constant of UO₂²⁺by NZVI and the two supported NZVI （NZVI/OH-Al-bent,NZVI/Na-bent） treatment were investigated by bath experiments. The reinforcement regularly ofUO₂²⁺removal by NZVI using modified bentonite as the carrier was evaluated by the combinationof the adsorption of the two carriers to UO₂²⁺and the X-ray photoelectron spectroscopy （XPS）analysis on the reaction product surface. The major research results were as follows:⑴The two modifided bentonites （Na-bent and OH-Al-bent） could effectively prevent NZVIfrom aggregation.⑵The removal of UO₂²⁺by NZVI supported on such modified bentonite was positivelyrelated to the adsorption capability of the corresponding modified bentonite to UO₂²⁺. Under thesame experimental conditions, the removal rate of cationic UO₂²⁺by NZVI supported on Na-bent,the zeta potential of which was negative reached to99.2%. It was not only higher than those ofNZVI （48.3%） and NZVI supported on OH-Al-bent （63.8%），the zeta potential of which waspositive, but also superior to the sum （65.2%） of removal by NZVI with the same dosage of ironand adsorption by Na-bent（16.9%） with the same amount bentonite. ⑶The kinetic studies suggested that the removal of UO₂²⁺by NZVI, NZVI/OH-Al-bent andNZVI/Na-bent can be fitted well to the Langmuir-Hinshlwood model, and the reaction rate waspositively related to the adsorption capability of （supported） NZVI on UO₂²⁺.⑷The XPS analysis results conformed that using Na-bent as acarrier was not only obviouslyenhanced removal rate of UO₂²⁺by NZVI, but also effectively prompt the reduction ability ofNZVI on U（VI） into the insoluble UO2，than fixed U（VI） for a long time.