| Panzhihua area,Hunan,Hebei and other places in our city are rich in vanadium and titanium magnetite resources.After years of mining and smelting produced a large number of vanadium-bearing slag.Under the long-term weathering leaching,the vanadate migrate into soil and water with the highest bio-toxic pentavalent vanadium forms.A large number of studies have shown that the content of vanadium in the vicinity of large dregs is much higher than that of Chinese soil background,and even rich in severe pollution,which causes serious harm to animals and plants in the area.People can easily lead to sore throat,emphysema,conjunctivitis,kidney damage,cardiovascular disease and other diseases when they intake superfluous vanadium;Plant will cause withers,limiting plant growth,reduce crop yields when ingesting vanadium overdose,so governance is imperative the vanadium pollution.In view of LDHs and its roasting products LDO is a type of new and highly efficient adsorbent in the field of pollution control.With the adsorption method,the vanadium pollution has the advantages of simple operation,low cost and difficult to cause secondary pollution.In this paper,the use of self-synthesized LDHs and their calcined products LDO adsorption vanadate for the vanadium pollution control to provide technical support,has important significance.Mg Al-CO3-LDHs and MgAlFe-CO3-LDHs were synthesized by urea hydrothermal method and steady-state coprecipitation method.The effects of synthesis time,synthesis temperature,synthetic pH value,n(Mg2+)/n(Al3+)or n(Mg2+)/(n(Al3+)+n(Fe3+))on the properties of the composites were investigated.The composites were characterised by XRD phase analysis,FT-IR infrared spectroscopy,XRF composition analysis,SEM / EDS morphology and energy spectrum analysis,ICP-OES micro-component analysis and thermogravimetric analysis.The effects of different preparation methods on the phase,morphology,composition and adsorption properties of MgAl-CO3-LDHs or MgAlFe-CO3-LDHs were investigated.The adsorption conditions of MgAl-CO3-LDHs or MgAlFe-CO3-LDHs were investigated by adsorption conditions such as adsorption time,initial concentration of vanadate and initial pH value of vanadate.The adsorption equation was characterized by isothermal adsorption equation and adsorption kinetic equation and the adsorption mechanism and adsorption mechanism were discussed.The results are as follows:?1?MgAl-CO3-LDHs and MgAlFe-CO3-LDHs were synthesized by urea hydrothermal method.The synthesis time should be greater than 48 h,it helps to the synthesis of the target product.The crystal is thick?greater than about 2 ?m?,n(Mg2+)/n(Al3+)is 3:1,MgAl-CO3-LDHs is self-assembled flowers.MgAlFe-CO3-LDHs crystallization is weak,in addition to hexagonal chip.There are spherical particles.However,adsorption stability of MgAlFe-CO3-LDHs is preferable to that of MgAl-CO3-LDHs.It is an important influence on the phase,morphology and adsorption properties of the composites when Fe3+ is substituted for Al3+.?2?MgAl-CO3-LDHs was synthesized by the steady-state coprecipitation method under different n(Mg2+)/n(Al3+)?1:1,2:1,3:1,4:1?.The adsorption capacity and removal rate of vanadate of MgAl-CO3-LDHs increased gradually with the n(Mg2+)/n(Al3+)increasing,and the adsorption capacity of MgAl-CO3-LDHs increased from 15.27 mg/ g to 30.19 mg/g.The results of XRF test show that the n(Mg2+)/n(Al3+)of the lattice is 0.97:1,1.58:1,2.13:1,2.33:1 with the order of n(Mg2+)/n(Al3+)increasing.However,the n(Mg2+)/n(Al3+)is 2:1 in the crystal formula of MgAl-CO3-LDHs.It is indicating that the proper excess of Mg2 + is beneficial to improve the adsorption performance of the composites.With the increase of n(Mg2+)/n(Al3+),the absorption peaks of CO32-,-OH and Al-O in FT-IR are gradually weakened.When the concentration of n(Mg2+)/n(Al3+)is 4: 1,the flake crystal is larger than that of n(Mg2+)/n(Al3+)is 2: 1.?3?MgAl-CO3-LDHs were synthesized by steady-state coprecipitation method with different synthetic pH values?8 ± 0.1,9 ± 0.1,10 ± 0.1,11 ± 0.1,12 ± 0.1?,but the pH was 11 ± 0.1,12 ± 0.1,there is a heterogeneous phase.With the increase of pH,the crystallinity of MgAl-CO3-LDHs was enhanced,and the development of lamellar crystals was more complete and the particle size was larger.Compared with other pH compounds,when the pH value was 8 ± 0.1,CO32-and Al-O bond infrared absorption peak was stronger.?4?MgAlFe-CO3-LDHs was synthesized by the steady-state coprecipitation method under different n(Mg2+)/(n(Al3+)+n(Fe3+))?1: 1,2: 1,3: 1,4:1?,There is a heterogeneous phase when n(Mg2+)/(n(Al3+)+n(Fe3+))is 4:1.The sheet-like wafer layer of the MgAlFe-CO3-LDHs increased and the adsorption capacity and removal rate of vanadate ion decreased with the increase of n(Mg2+)/(n(Al3+)+n(Fe3+)),the unit adsorption capacity decreased from 37.53mg/g to 17.51 mg/g.When n(Mg2+)/(n(Al3+)+n(Fe3+))is 1:1,3:2,the absorption peak intensity of CO32-is obviously weaker than that of n(Mg2+)/(n(Al3+)+n(Fe3+))is 2:1,3:1,4:1.?5?MgAlFe-CO3-LDHs were synthesized by steady-state coprecipitation method at different synthetic pH values?8 ± 0.1,9 ± 0.1,10 ± 0.1,11 ± 0.1,12 ± 0.1?.The sheet-like wafer layer of the composition is increased with the pH increasing.The adsorption capacity and removal rate of vanadate ion showed a decreasing trend,and the unit adsorption capacity decreased from 34.05 mg/ g to 28.24 mg/ g.?6?MgAl-CO3-LDHs and MgAlFe-CO3-LDHs were calcined at different temperatures.The adsorption effect of calcined products on vanadate showed that the adsorption of vanadate didn't change significantly when the LDHs calcined in the low temperature.The product on the vanadate adsorption effect increased sharply when MgAl-CO3-LDHs calcination temperature of 517 ? and MgAlFe-CO3-LDHs calcination temperature of 646 ?.The unit adsorption capacity at the time of non-calcination was 25.05 mg/g and 38.62 mg/g increased to 67.21 mg/g and 66.35 mg/g respectively.?7?MgAl-CO3-LDHs and MgAlFe-CO3-LDHs were 0.2g adsorbed with 100 mL of vanadate solution.With the initial concentration of pollutants from 49.53 mg/L,102.70 mg/L,128.00 mg/L,225.40 mg/L,280.00 mg/L,the unit adsorption of vanadate increased?MgAl-CO3-LDHs increased from 21.11 mg/g to 50.80 mg/g,MgAlFe-CO3-LDHs increased from 21.64 mg/g to 54.65 mg /g?.The removal rate of MgAl-CO3-LDHs decreased from 85.24% to 36.29%.The results of isothermal adsorption model shown that the adsorption thermodynamics of the LDHs is more consistent with the Langmuir equation.The saturated adsorption capacity was 53.73mg/g and 58.82 mg /g respectively.Only the amount of pollutants close to the amount of saturated adsorption,it is most conducive to play the adsorbent adsorption efficiency.?8?In different pH value of the pollution solution?pH value of about 1 to 13?,the adsorption effect of MgAl-CO3-LDHs and MgAlFe-CO3-LDHs on acid condition was better than that of the alkaline condition.When the pH value is about 3,the adsorption effect is the best,unit adsorption capacity is 47.62 mg/g and 50.94mg/g respectively.?9?The adsorption thermodynamics and the kinetic equation of MgAl-CO3-LDHs and MgAlFe-CO3-LDHs were fitted.The results showed that the adsorption of vanadate is more consistent with the Langmuir equation and quasi-second order kinetic equation.It is indicating that the adsorption characteristics of more inclined to single molecular layer adsorption and chemical adsorption. |
PDF Full Text Request