| With the increasingly widespread application of ozonation technology in drinking water treatment, bromate is recognized as a disinfection byproduct in drinking water from the ozonation of bromide-containing source waters and has been classified by the International Ageney for Researeh on Cancer(IARC) as a possible human carcinogen. In China, the maximum contaminant level(MCL) of bromate in drinking water sanitary standard (GB5749-2006) and drinking natural mineral water (GB8537-2008) is10μg/L, thereby the research of control and the removal of bromate is urgent. As the present technologies for bromate control or removal have some deficiencies, it is urgent to develop new bromate removal technologies. In this paper, bromate removal by Zn-Fe (Ⅱ)-Al layered double hydroxides was proposed on the basis of previous studies.In this study, the Zn-Fe(Ⅱ)-Al LDHs sample with different molar ratios of metal ions were prepared by co-precipitation under a nitrogen flow and a subsequent hydrothermal treatment method after ultrasonic oscillation. The freshly synthesized Zn-Fe(Ⅱ)-Al LDHs samples were applied to remove the bromate in the aqueous solution. The effects of parameters such as reaction time, solid-to-solution ratio, initial bromate concentration, initial pH and coexisting anions on the bromate removal were also investigated in the paper. Meanwhile, the potential reaction mechanisms involved in the bromate removal process were proposed. The properties of stability and reuse of the sample were also investigated.Batch experiments were performed, and the influence of various experimental parameters were discussed. It also showed that Zn-Fe(Ⅱ)-Al(2:2:1) LDHs had the highest ability for reducing the bromate in the aqueous solution and inorganic metal ions were not released into the aqueous solution after the reaction. The bromate was reduced to the bromide by Zn-Fe(Ⅱ)-Al LDHs and the fraction of bromide ions were adsorbed to the interlayer to compensate for the net positive charge. Therefore, the layered structure of the samples still maintained after the reaction with bromate in aqueous solution. Zn-Fe(Ⅱ)-Al LDHs showed a good performance on the bromate removal at the pH range of7.0to11.0. Compared to previous studies, the performance of Zn-Fe(Ⅱ)-Al LDHs samples on the removal of bromate in drinking water already has been dramaticlly improved. The coexisting anions showed no significant effect at lower concentration (<78μmol/L) except PO43-, which had remarkable effect on the removal of bromate. However, the bromate removal rate decreased as the concentration of coexisting anions in solution increased further, The effect of coexisting anions on bromate removal related to the ionic potential and decreased in the following order: PO43-> SO42->CO32->NO3->ClO3-.The mechanisms of the removal of bromate by the Zn-Fe(Ⅱ)-Al LDHs can be described as follows:the first stage, the bromate were reduced to the bromide by the Fe2+in the brucite-like layer of the samples, with the generation of net positive charge on the octahedral unit; The second stage, the bromide anions or hydroxyl groups from the aqueous solution were adsorbed to the interlayer region to compensate net positive charge. The ionic potential of bromate was weak, the particle diffusion was investigated to, be the rate-controlling step and the whole removal process fitted well with the pseudo-second-order reaction kinetics model. The Zn-Fe(Ⅱ)-Al LDHs samples showed an excellent stability and could be recycled without significant loss of activity, indicating its excellent prospects for bromate removal.The crystallinity, BET surface areas, particle sizes, morphologies and chemical constitution of samples were conducted to investigate by the X-ray diffraction (XRD), BET surface area, Scanning Electronic Microscopy (SEM) and Inductively Coupled Plasma-mass Spectrometry (ICP-MS). The results showed that the Zn-Fe(Ⅱ)-Al(2:2:1) LDHs sample had single phase with fine crystallinity. Meanwhile, the particle size and morphologies of the recycled Zn-Fe(Ⅱ)-Al(2:2:1) LDHs remained unchanged. It indicated that the layered structures remained in the Zn-Fe(Ⅱ)-Al(2:2:1) LDHs samples collected after the reaction with bromate in the aqueous solution. |
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