Adsorption Of Cr(Ⅵ) And Cu(Ⅱ) On Hydrotalcite-like Compounds And Bentonite

When untreated heavy metal emitted into the environments,they may cause serious harm to ecological safety and human health.So the problem is to be urgently resolved. The adsorption/desorption behavior of heavy metal at the solid liquid interface is the fundamental problem which determines the geochemistry process of heavy metal and environmental ecological effect.The scientific knowing of the basic phenomenon is the basis of understanding the speciation distribution,transport and fate of heavy metal pollutants and technology on remediation of contaminated soil and waste water treatment.Based on previous studies,we chose structurally negative charged bentonite and structurally positive charged hydrotalcite-like compounds(HTlc)as model adsorbents and study the adsorption behavior of Cu²⁺which positively charged on them,as well as the behavior of Cr⁶⁺which negatively charged on HTlc.Using batch methods,we studied the adsorption/desorption behavior of heavy metal on clay. The influence of various factors such as pH,ionic strength,additives etc.were investigated.We hope to obtain the influence law of structural charge on heavy metal adsorption and deepen the cognition to the adsorption mechanism.In the summary part,firstly,we introduced the knowledge of heavy metal such as properties,damage,sources and treating methods.Secondly,we reviewed the development of adsorption of heavy metal on bentonite,kaolinite and other adsorbents.Experimental section 1.Study on adsorption behavior and adsorption mechanism of Cr(â…¥)on MgAl-Cl HTlc.Sorption properties of Cr(â…¥)on MgAl-Cl HTlc were studied,the influence of temperature,initial pH,ion strength and additives on the sorption of Cr(â…¥)were investigated,and the sorption mechanism was discussed in combination with the results of XRD and FTIR experiments.The sorption kinetics can be well described by the pseudo-second-order kinetics and the sorption isotherms can be described by Langmuir isotherm.The additives may decrease q_e of Cr(â…¥)on MgAl-Cl LDHs.The adsorption layer of Cr(â…¥)on the external surface may be divided into two layers;the inner-sphere surface complexes arising from the chemical binding and the outer-sphere surface complexes arising from the electrostatic interaction.The performance of desorbing agents were also investigated,it is found that the valence of anions is higher,the more Cr(â…¥)desorbed.The interaction of Cr(â…¥)and MgAl-Cl HTlc is strong and the desorption amount of Cr(â…¥)is lower,so MgAl-Cl HTlc can be used to absorbents which could not bring second pollution.Experimental section 2.Adsorption/desorption of CuSO₄ on MgAl-Cl HTlc.Hydrotalcite-like compounds with an Mg/Al molar ratio of 2;1(Mg₂Al- HTlc)were synthesized by using a co-precipitation method.The sorption removal of CuSO₄ by them was investigated.It was found that Mg-Al-HTlc show good sorption ability and they could be a new type of environmental sorbent for the removal of CuSO₄.The sorption kinetics and the sorption isotherms of CuSO₄ on the Mg-Al-HTlc can be described by the pseudo-second order kinetics and Langrnuir isotherm,respectively. The percent removal of CuSO₄ by the HTlc was strongly dependent of the initial pH of bulk solution,The presence of AlCl₃ might obviously low the q_e of CuSO₄ on the HTlc;however,the presences of NaCl and MgCl₂ might increase the q_e of CuSO₄ on the HTlc.The presences of ligands(citric acid and EDTA)in the studied concentration range may obviously decrease the q_e values of CuSO₄ on the HTlc.The removal mechanism of CuSO₄ by HTlc in the presence of SO₄^{2_</sup>anions may be attributed into the surface-induced precipitation of Cu(â…¡)hydroxides and the surface complex adsorption by the linking effect of SO₄2_</sup>between the HTlc and Cu(â…¡) cations,Experimental section 3.Adsorption of CuCl₂ on Mg₂Al-Cl HTlc was studied.The sorption removal of CuCl₂ on Mg₂Al-HTlc were investigated.The influence of sequences of agents added on the adsorption was investigated.The results showed that CuCl₂ could be adsorbed on Mg₂Al- HTlc and the sequence could affect the adsorption behavior.In the system of HTlc-EDTA-CuCl₂ and HTlc-CuCl₂-EDTA,the presence of EDTA may decrease q_e of Cu2+obviously.In the system of EDTA-CuCl₂-HTlc,the q_e of Cu2+was not varied by EDTA added almostly. Adsorption isotherms could be fitted with the Langmuir equation,the sorption kinetics of CuCl₂ on Mg₂Al-HTlc could be well described by pseudo-second-order kinetics equation.Experimental section 4.Adsorption of CuSO₄ and CuCl₂ on bentonite were studied.The sorption removal of CuSO₄ and CuCl₂ on bentonite were investigated.The sorption kinetics and the sorption isotherms of CuSO₄ and CuCl₂ on bentonite can be described by the pseudo-second order kinetics and Langmuir isotherm,respectively. In most case,the adsorption amount of CuCl₂ is more than that of CuSO₄.The additives of inorganic and organic matters may inhibited the adsorption.The extent of depression by inorganic electrolytes towards CuSO₄ and CuCl₂ is different.With pH increased,the amount of adsorption enlarged.The mechnism of resorption of CuSO₄ and CuCl₂ on bentonite were surface complexation.The adsorption layer of CuSO₄ and CuCl₂ on the external surface may be divided into two layers;the inner-sphere surface complexes arising from the chemical binding and the outer-sphere surface complexes arising from the electrostatic interaction.}