Preparation Of Nano-sized Illite-smectite Clay-based Nanocomposites For Removal Of Heavy Metal Ions In Aqueous Solution

Non-biodegradable heavy metal ions in aqueous solution would threat eco-environment and health of humanbeing through food chains.It is thus necessary to remove heavy metal ions in aqueous solution by various methods,particularly the use of clay-based adsorbents.Illite/smectite mixed-layer clay mineral is abundant and widespread in nature.However,little work on the preparation of nano-sized illite/smectite clay(denoted as NI/S)and NI/S clay-based nanocomposites for removal of heavy metal ions have been reported yet.In this dissertation,NI/S clay-based nanocomposites were prepared by compounding NI/S clay,inorganic nanoparticles(i.e.,Fe₃O₄)and/or organic compounds(i.e.,3-aminopropyltriethoxysilane or polyethyleneimine)for removal of heavy metal ions leached from municipal solid waste incineration fly ash in simulated landfill leachate and/or in aqueous solution,respectively.The main research aspects and obtained results are given as follows:(1)NI/S clay(fineness:70%<100 nm,and cationic exchange capacity:40.35 cmol(+)/kg)was used for adsorption of heavy metal ions leached from municipal solid waste incineration(MSWI)fly ash.The leaching rates of heavy metal ions(i.e.,Cr(?),Mn(?),Co(?),Ni(?),Cu(?),Zn(?),Cd(?),and Pb(?))significantly decrease,and the leaching concentration of heavy meatal ions can reach the effluent standard of landfill after adding NI/S in Na₂S or cement for solidification of MSWI fly ash.In addition,the effects of factors(i.e.,NI/S amount,pH value,adsorption time,initial heavy metal ions concentration)on the adsorption performance of Ni(?),Cu(?),Cd(?),and Pb(?)ions onto NI/S were investigated,respectively.The maximum adsorption amounts of Ni(?),Cu(?),Cd(?),and Pb(?)ions are 7.704 mg/g,8.813mg/g,17.16 mg/g,and 36.20 mg/g,respectively.The adsorption mechanisms were analyzed by energy disperse spectroscopy(EDS),X-ray photoelectron spectroscopy(XPS),and Fourier transform infrared spectroscopy(FTIR),respectively.The results show that the dominant mechanism in the adsorption of heavy metal cation onto NI/S is due to the ion-exchange reaction.(2)Amino-functionalized NI/S clay-based nanocomposite(denoted as NH₂-NI/S)was prepared by grafting 3-aminopropyltrithoxysilane(APTES)onto NI/S nanoflakes via a silanization reaction for removal of Pb(?)cations and Cr(?)anions in aqueous solution,respectively.The results obtained from ²⁹Si nuclear magnetic resonance spectroscopy show that APTES molecules are chemically on the surface and fractured edges of NI/S nanoflakes.Compared to NI/S clay,NH₂-NI/S nanocomposite can adsorb the more amounts of Pb(?)cations and Cr(?)anions,and the maximum adsorption amounts for Pb(?)and Cr(?)ions are131.23 mg/g and 36.91 mg/g,respectively.The effects of parameters(i.e.,NH₂-NI/S amount,pH value,adsorption time,and initial concentration of Pb(?)or Cr(?)ion)on the adsorption performance of Pb(?)cations or Cr(?)anions onto NH₂-NI/S nanocomposite were investigated.Also,the adsorption kinetic,isotherm and mechanism were discussed.(3)Magnetic NI/S clay-based nanocomposites were prepared by a mechanochemical method and a chemical co-precipitation method(denoted as MNI/S-m and MNI/S-c),respectively,for removal of Pb(?)ions in aqueous solution.The results obtained from X-Ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),specific surface area analysis(SSA)and scanning electron microscopy(SEM)show that mechanical stresses(i.e.,compression and shear stresses)occurred in grinding facilitate the dispersion and attachment of Fe₃O₄ nanoparticles on NI/S nanoflakes.Compared to MNI/S-c nanocomposite(i.e.,38.77mg/g),MNI/S-m nanocomposite can adsorb the more amounts of Pb(?)ions(i.e.,68.34 mg/g)in aqueous solution due to the broken bonds generated in mechanical grinding.The effects of factors,i.e.,pH value,adsorption time,and initial Pb(?)ions concentration,on the adsorption amounts of Pb(?)ions onto MNI/S-m nanocomposite were investigated.The adsorption kinetic,isotherm and mechanism were also discussed.In addition,a quasi-superparamagnetic MNI/S-m nanocomposite can be magnetically separated and regenerated.After 4-cycle adsorption/desorption processes,the regenerated MNI/S-m nanocomposite still remains 89.01%of initial adsorption efficiency for Pb(?)ions in aqueous solution..(4)An amino-functionalized magnetic NI/S-based nanocomposite(denoted as AMNI/S)was prepared by grafting 3-aminopropyltrithoxysilane(APTES)on magnetic NI/S based-nanocomposite prepared in a chemical co-precipitation route.AMNI/S nanocomposite was analyzed by Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy(SEM),respectively.The results show that the well-dispersion/attachment of Fe₃O₄ nanoparticles on NI/S nanoflakes facilitates the grafting of APTES molecules due to the synergetic effect between Fe₃O₄ nanoparticles and NI/S nanoflakes.Also,a quasi-superparamagnetic AMNI/S nanocomposite was used for removal of Pb(?)ions in aqueous solution.The effects of initial concentration of Pb(?)ions,pH value,adsorption time on the adsorption amounts of Pb(?)ions onto AMNI/S nanocomposite were investigated.The adsorption kinetic,isotherm,thermodynamics and mechanism were also discussed.AMNI/S nanocomposite can be magnetically separated and regenerated.The regenerated AMNI/S nanocomposite remains 82.91%of initial adsorption capacity for Pb(?)ions in aqueous solution after 6-cycle adsorption/desorption processes.(5)A ternary magnetic NI/S clay-based nanocomposite(denoted as PEI-MI/S)integrating polyethyleneimine(PEI),magnetite(Fe₃O₄)nanoparticles and NI/S clay,was prepared in a mechanochemical route.PEI-MI/S nanocomposite was characterized by thermal gravimetric analysis(TGA),X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy(SEM),respectively.The results show that PEI-MI/S nanocomposite prepared in the presence of mechanical grinding can graft the more amounts of PEI(i.e.,12.49%)rather than PEI-MI/S-0(i.e.,3.40%)prepared in the absence of mechanical grinding.The compressive and shear stresses in grinding processes can disperse and attach Fe₃O₄ nanoparticles on exfoliated NI/S nanoflakes,facilitating hydrogen bond and electrostatic interactions among PEI,Fe₃O₄nanoparticles and NI/S nanoflakes.Also,the mechanochemical effect in grinding facilitates a crosslink reaction between PEI and glutaraldehyde,resulting in a more grafting amounts of PEI.The effects of parameters(i.e.,pH value,adsorption time,and initial concentration of Cr(?))on the adsorption amounts of Cr(?)onto PEI-MI/S nanocomposite were investigated.The adsorption kinetic,isotherm,thermodynamics and mechanism were also discussed.In addition,a quasi-superparamagnetic PEI-MI/S nanocomposite can be magnetically separated and subsequently regenerated.The regenerated PEI-MI/S nanocomposite can maintain 71.43%of initial activity for adsorption of Cr(?)after 6-cycle adsorption/desorption processes.