| The chloride ions in wastewater often cause corrosion of processing equipment,shorten the life of equipment,increasing the indirect production costs.With the development of wastewater recycling technology,it is required to reduce the high salinity,which decreases excessive concentration of chloride ions in wastewater has become one of the important issues in the field of environmental protection.The existing process has a big investment,high energy consumption,poor performance of chloride ions removal.Layered double hydroxides(LDHs)having a large specific surface area,special layered structure,the interlayer anion exchangeability,memory effect,has been widely used in the field of wastewater treatment.In this paper,in order to obtain the relationship between the properties of LDHs and adsorption performance,the structure and properties of LDHs were controlled by changing metal cations and its ratios in the layer,grain size,calcined product metal cations,guest anions in the interlayer galleries,and the effects of properties and structure of LDHs on their chloride removal performance was investigated,which is expected to contribute to designing adsorbent with high performance.The physical and chemical properties of LDHs were characterized by XRD,FT-IR,N2-BET and TG-DSC.Finally,the adsorption kinetics of chloride on hydrotalcite,adsorption equilibrium isotherms and reproducibility were studied.The results are as follows:1.To investigate the effects of adsorption conditions on dechlorination performance of MgAI-LDHs.The results show that the maximum chloride ion removal rate can reach under the conditions of the solution of the initial pH of 7,adsorbent dosage of 0.3 g,temperature of 30 ?,time of 6 h.2.To investigate the dechlorination performance of LDHs,a series of hydrotalcite and hydrocalumite including MgFe-NO3,MgAl-NO3,NiAl-NO3,ZnAI-NO3,and CaAl-NO3 LDHs were synthesized with different M2+/M3+molar ratios.The results show that ZnAl-NO3 LDHs has the biggest gallery height,the higher the gallery height,the smaller diffusion resistance of chloride ions,leading to the highest chloride removal;the molar ratio of zinc and aluminum of 2 is the best,with adsorption amount reaching 28.97 mg/g.3.To study the effect of grain size on chloride removal,four kinds of zinc-aluminum LDHs with different grain size were synthesized by changing the crystallization temperature in the process of synthesis.The results shows that the lower the crystallization temperature,the smaller the synthetic zinc-aluminum hydrotalcite grain size,leading to the higher chloride ions removal.When the crystallization temperature is 80?,the grain size of ZnAl-LDHs is the minimum,with adsorption amount reaching 59.4 mg/g.4.To investigate the influence of calcined LDHs(LDO)on chloride removal,MgFe-NO3,MgAl-NO3,NiAl-NO3,ZnAl-NO3,and CaAl-NO3 LDHs were calcined under 400?.The results shows that at 30?,the concentration of 100 mg/L NaCl solution in stirring 6 h,these LDOs were partial reconstructed except NiAlO;the chloride removal of LDOs were related to the precursors;but not as well as the dechlorination of the precursors.5.To investigate the influence of guest anions in the interlayer of LDHs on chloride removal,various anions were intercalated into the interlayer of ZnAl-LDHs,including L-glutamic acid,L-aspartic acid,L-tryptophan and dodecyl sulfonate and carbonate,compared with nitrate.It is found that five hydrotalcites are inferior to the N03-LDHs;the performance of chloride ion removal of different anion intercalated LDHs is:ZnAl-NO3>ZnAl-Td>ZnAl-Gu>ZnAl-Se>ZnAl-Sw>ZnAl-CO3;the higher anionic charge,the better the performance of chloride ion removal;the more the hydrophilic group of organic anion,the more hydrophily,leading to exchange of chloride ion in the water easily and the dechlorination is stronger;the properties of anions in the interlayer of LDHs are more important than gallery height of LDHs to chloride ion removal.ZnAl-LDHs have a certain buffering capacity and relatively stable adsorption capacity in the range of the pH of 5-8.6.The adsorption kinetics and isotherm of chloride on ZnAl-LDHs were investigated.The results shows that adsorption kinetics can be well described by the pseudo second-order kinetic equation,with the theoretical equilibrium adsorption quantity of 71.43 mg/g;the adsorption isotherm could be well fitted by the Langmuir equation,with the theoretical maximum adsorption capacity of 175.4 mg/g,higher than theory of chloride ion exchange capacity(91.20 mg/g),suggesting the surface adsorption and ion exchange. |
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