Experimental Research On The Adsorption Of Cd (â…¡) By EDTA Intercalated Hydrotalcite

Heavy metal waste water pollution is more serious in our country.Wastewatercontaining cadmium is one of the most serious heavy metal waste water, enrichmentof cadmium in water by a variety of biological chain, pose a serious threat to theecological environment and human health. At present, three treatment methods ofwastewater containing cadmium (physical and chemical method, plants andmicroorganisms) has its own disadvantages. Thus, to research a simple and efficientremoval method, this paper insert hydrotalcite material layer after assembly asadsorbent, used in the treatment of wastewater containing cadmium.This paper studies the synthesis of ethylenediamine tetraacetic acid intercalatedhydrotalcite and the properties of adsorption of Cd2+in the solution, compared andanalyzed EDTA intercalated hydrotalcite and magnesium aluminum hydrotalcite onthe adsorption of Cd2+effect and influence factors, studied the adsorption kinetics andadsorption thermodynamics, preliminary analysis of the EDTA intercalatedhydrotalcite adsorption mechanism of the adsorption of Cd2+in the solution.(1) The study adopts the method of coprecipitation synthesis magnesiumaluminum hydrotalcite and EDTA intercalated hydrotalcite, obtain the best synthesisconditions the effect of EDTA intercalated hydrotalcite adsorption Cd2+by means oforthogonal experiment. The intercalated hydrotalcite synthesized under the bestconditions, XRD, SEM analysis confirm Y4-success insert hydrotalcite layers, is tohave a combination of hydrotalcite and EDTA characteristics of EDTA intercalatedhydrotalcite.(2) In the study of single factor experiment, compared the magnesium aluminumhydrotalcite and EDTA intercalated hydrotalcite adsorption of Cd2+in the solution.Results show that under the condition of same, magnesium aluminum hydrotalcitewere far lower than on the adsorption of Cd2+adsorption quantity of EDTAintercalated hydrotalcite. Was investigated by orthogonal test, the single factor (dosingquantity, time, initial pH value and temperature) on the adsorption effect of theinteraction, finally get the best adsorption conditions: adsorbent additive amount:1.0g/L; time:50min; pH:6; temperature:50℃. (3) Examines the three competitive anions (NO3-, CO32-, Cl-) and three kinds ofcompetitive cations (Cu2+, Fe2+, Zn2+) effect on the adsorption effect. Test resultsshowed that due to the structure memory effect of hydrotalcite materials, CO32-biggerinfluence on the adsorption effect, With the increase of concentration of CO32-,adsorption capacity from48.24mg/g to40.37mg/g; Competitive cations, Cu2+havebigger influence on the adsorption effect, its result with EDTA chelation conditionalstability constant of metal cations.(4) With different concentration of hydrochloric acid and nitric acid solution afterreaching adsorption saturation of EDTA intercalated hydrotalcite desorption, andregeneration experiment was carried out. The results showed that both solutions canachieve the saturated adsorption desorption recycling of intercalated hydrotalcite,nitric acid solution of desorption rate is higher. After desorption regeneration ofEDTA intercalated hydrotalcite still have higher adsorption capacity of Cd2+insolution, but with the increase of times of regeneration, intercalated hydrotalcitestructure was damaged, its adsorption capacity decreases.(5) In the optimum adsorption conditions, use the method of linear regressionmethod on the adsorption kinetics and adsorption thermodynamic datas, are linearfitting and discussed. Studies have shown that EDTA intercalated hydrotalciteregularity in the adsorption of Cd2+in the solution can better conform to thesecondary dynamics model and the Langmuir isotherm equation model, thecorrelation coefficient of0.99. Combine with secondary kinetic parameters andArrhenius experience, calculated adsorption activation energy of17.651KJ·mol-1,showed that the adsorption process for the chemical adsorption process. Results of thecalculation of thermodynamics parameters, G＜0、 H＞0、 S＞0, can beconcluded that the adsorption of approximation in monolayer adsorption, spontaneousand endothermic chemical adsorption.(6) Through the surface structure analysis and adsorption properties study canspeculate that EDTA intercalated hydrotalcite for the adsorption of Cd2+in thesolution is mainly surface adsorption and chelating mechanism synthesis. In theprocess of adsorption, adsorption quantity greatly influenced by the solution pH value.When the pH value is small, due to the large number of H+existence, and Y4-willcombine with H+, decrease and the equilibrium concentration of Y4-and affected thechelating main reaction, thus the materials for the adsorption of Cd2+is not high, thisis consistent with the effect of EDTA acid. When the pH value after the rise to thelevel, as a result of hydrolysis inhibited the EDTA chelation with Cd2+, adsorption capacity has a certain degree of reduced. However the adsorption quantity at this time,though still high, but the mechanism of adsorption is no longer the chelation, but OH-on the surface of the material increased, surface subsidence induced predominates.EDTA intercalated hydrotalcite for the adsorption of Cd2+in the solution showedgood adsorption, desorption regeneration performance is good. The theoretical basis isprovided for the application of this material to the wastewater of heavy metal cationsby the research of this paper.