| Heavy metals was one of main environmental pollutants for its characteristics of non-biodegradable,toxic and persistent.It has received extensive attention all over the world due to its destructive effect on environment and health.Adsorption was widely used as a feasible and environmental-friendly technology.However,the cost of adsorbent was considered as one of the key factors in the treatment of wastewater.Clay minerals were widely applied as adsorbents because of its large surface area,low cost,and certain cation exchange capacity.Sepiolite is one of clay minerals,which has certain heavy metal adsorption ability.Accordingly,the Xiangtan sepiolite was chosen as modified object,the morphology,properties and adsorption mechanism was discussed in this study.The main results are as follows:(1)By using hydrothermal synthesis method,the polymeric hydroxyl iron,hexadecyldimethyl(3-sulphonatopropyl)ammonium(Z16)and the two mixed reagents were used to modify sepiolite,inorganic modified sepiolite(ISP),organic modified sepiolite(OSP)and organic-inorganic compound modified sepiolite(IOSP)were obtained.The modified sepiolite and raw sepiolite were characterized by Fourier transform infrared spectra(FTIR),X-ray diffraction(XRD),Scanning electron microscopy(SEM),X-ray photoelectron spectroscopy,Zeta potential and so on.Results showed that isp’s crystal structures was changed,the polymeric hydroxyl iron entered into the interlayer structure of sepiolite,thus the pore volume and surface area of sepiolite were increased;Meanwhile,Z16 were mainly coated in surface of sepiolite,the potential adsorption point of the metal cation could be increased by the reduction of the isoelectric point of the sepiolite after Z16 modification;And the organic inorganic modification has two characteristics above.(2)The single adsorption properties of Cu2+,Cd2+ and Cr3+ in water were studied by using the above modified sepiolite and raw sepiolite,and the effects of factors on the adsorption behavior were investigated.The results showed that the adsorption capacity of the three heavy metals on modified sepiolite was greater than that of raw sepiolite,the order of adsorption capacity was:IOSP>ISP>OSP>SP.The single factor effect on adsorption showed that the adsorption efficiency for the three heavy metal was increased with the increase of initial pH,adsorption time and amount of adsorbents,while decreased with the increase of the initial concentration.Under the optimal conditions determined by the experiment,the maximum adsorption capacity of iosp for Cue+,Cd2+ and Cr3+ was 45.32 mg/g,37.76 mg/g and 36.90 mg/g,respectively.At the same time,the adsorption mechanism of Cu2+,Cd2+ and Cr3+ over iosp might be the combination of electrostatic adsorption,ion exchange and coordination complexation.(3)The competitive adsorption properties of sepiolite and modified sepiolite were studied.The results showed that the affinity was different for different metals on sepiolite and modified sepiolite,and the selective adsorption order was consistent,which was Cu2+>Cr3+>Cd2+.The reason was due to that the hydration energy of Cu2+ was smallest in three heavy metals,it was easiest to lost the surface bonding water and turn into the free ion,thus it obtained the strongest binding ability with sepiolite.Besides,the combining capacity of Cr3+ with sepiolite whose surface was negatively charged was greater than Cd2+,it was because that Cr3+ had higher charge density compared with Cd2+. |
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