Adsroption Of Cr(?) And Mn(?) By Different Modified Layered Double Hydroxides(LDHs)

With the enormous development of urbanization and industrialization, heavy metal pollution has threated human health and damaged the environment seriously, it is necessary to develop effectivemethods to remove heavy matel contamination.In this paper, the preparation of LDO and LDH-DTPA and the adsorptive behavior of two materials for Cr(VI) and Mn(II) were investigated respectively. The relationships between the structureand the adsorptive property of adsorbentswere measured. The mechanisms of LDO and LDH-DTPA to uptakemetal ions were discussed.LDH were synthysised by co-precipitation method, two modified materials(LDOand LDH-DTPA) were obtained by thermal modification and calcination-rehydration, respectively. The LDO and LDH-DTPA were characterized by XRD, SEM, FT-IR, TG and XPSevidenced that the surface properties of two adsorbentscould be successfully varied using modification.Comparative study in adsorption isotherms and kinetics for LDH and LDO in Cr(VI) adsorption was carried out. It indicated that the maximum uptake capacity of LDO for Cr(VI) was 105.3 mg·g-1, much higher than that of LDH(20.7 mg·g-1). The adsorption kinetics could be by either the pseudo-second-order model or the intra-particle diffusion equation could be successfully used to fit the process of Cr(VI) adsorption process with LDO. It suggested that the Cr(VI) removed by LDO should be controlled by the rate of reaction of Cr(VI) with the LDO and the rate of diffusion. In addition, several parameter affecting the Cr(VI) adsorption by LDO was also investigated. The adsorption process was temperature-independent and performed best at the solution p H of 5. The main adsorption mechanism was “memory effect”, the LDO adsorbed a large number of Cr(VI) as interlayer anion during the rehydration process.The maximum uptake capacity of LDH-DTPA for Mn(II) was 80-90mg/g. The adsorption kinetics could be fitted to the pseudo-second-order model and equilibrium experimental data were well represented by Langmuir isotherm. It indicated that the process of adsorption dominated by chemical adsorption. The adsorption process was spontaneous and endothermic according to the thermodynamic study, and the optimal p H was 6.5-7.0. The adsorptive saturated LDH-DTPA could desorbed by 0.1M Na CO3 / Na2HPO4 / Na H2PO4, the adsorption capacity was decreased after desorption. LDH-DTPA could effectively adsorbed a variety of cations such as Co2+, Cd2+, Ni2+, it indicated that the chelation was one of the important mechanisms.LDHs were applied to remove heavy matels in aqueous solution, such as obvious adsorptive capacity, convenient to operate, easy to solid-liquid separation and so on. It shows the good application potential as a new treatment agent for heavy metal in waste water.