Adsorption Of Orange ? By Magnesium-Iron Layered Double Hydroxides And Its Utilization

Layered double hydroxides was an anionic clay with layered controllability,exchangeable interlayer anions and memory effect,which was widely used as adsorbents to treat dye wastewater.Meanwhile,a large number of spent LDHs adsorbents was also produced,and its toxicity and harmfulness were likely to cause secondary pollution.Therefore,this article focused on how to correctly handle and dispose of these spent absorbents that was resource-recycled,the differences in the adsorption performance of MgFe-LDH and its calcined products?CLDH?on Orange II acid dyes were examined and the mechanism of nitrogen adsorption by MgxFe1-xOy/C composites was studied.The main original conclusions of this work were shown as follows:?1?MgFe-LDH was prepared by the traditional coprecipitation method.The effect of different calcination temperatures on the adsorption of Orange II by MgFe-LDH was investigated.The adsorption capacity of MgFe-CLDH-450 at 450 ?for Orange II was as high as 1403.5 mg/g,which was higher than that of uncalcined MgFe-LDH 15%.The crystal structure of MgFe-CLDH-450 was changed by XRD,FT-IR and BET characterization.,which the characteristic diffraction peak of MgO was formed.The stretching vibration of the hydroxyl of the plate and the bending vibration peak of the interlaminar water molecules were weakened.The specific surface area increased to 30.726 mz/g.The adsorption isotherm was in accordance with the Freundlich adsorption isotherm equation,and the adsorption process conformed to the pseudo-second-order kinetics model.The correlation coefficient was greater than 0.98.Because of the ""memory effect",the MgFe-CLDH-450 sample was recombined with Orange II as anion in the solution to form an interlayer structure of hydrotalcite.And the adsorption of the anionic dye was enhanced by the enhanced surface adsorption.On the other hand,the MgxFe1-xOy/C composites which was produced after the spent sorbent of MgFe-CLDH-450 adsorbed the dyestuff Orange II still had a large adsorption capacity for the Orange ??792.22 mg/g?,indicating that the material can be recycled and used,but the adsorption equilibrium time greatly was increased and it took about 6 hours.And its adsorption process of Orange II was more consistent with the Elovich kinetic model,indicating that the material had an intragranular diffusion effect on the absorption of Orange ?.?2?Based on the resource recovery and utilization of the spent sorbent MgFe-CLDH-O?,a heat treatment process was adopted to develop MgxFe1-xOy/C composites with high-efficiency nitrogen adsorption at high temperature and atmospheric pressure.The structures and morphologies of MgxFe1-xOy/C composites were investigated by XRD,Raman,BET,XPS,FT-IR and SEM characterization.The results showed that MgFe²⁺3O4 composites appeared oxide characteristic diffraction peaks in the heat-treated MgFe-CLDH-OII materials,containing graphene-like structure,which IG/ID ratio was 4.4 nm indicating that the graphene structure of the composite crystal size was about 4.4 nm and its structural composition contained sp2 and sp3 hybrid carbon,than the surface area was 56.799 m2/g.Through heat treatment,the redox reaction occured between the interlayer cations and interlayer anions in MgFe-CLDH-O?,and Fe³⁺ was reduced to Fe²⁺ and Orange II was formed to graphene-like structures.At 400 ? and ambient pressure,the MgxFe1-xOy/C composites reached adsorption equilibrium after adsorption of nitrogen for 3 h,and the adsorption amount was 2.8%.With the adsorption temperature be increased to 600 ?,the adsorption equilibrium was quickly reached at 100 min,and the adsorption amount was 2.7%.Nitrogen cycling experiments showed that the adsorption of nitrogen increased gradually from 396 ? to 738 ? and then nitrogen desorption occurred,while the temperature rose to 800 ?.During the cooling process,the rapid desorption began at 396 ?,and the nitrogen was desorbed completely when the temperature dropped to 45 ?.The results of FT-IR spectra before and after nitrogen adsorption has no change,indicating that the adsorption-desorption of MgxFe1-xOy/C composites occurred.