Analysis The Metallic Elements Of Red Mud And CTAB/STAB Modified Red Mud Adsorption Cr (Ⅵ) Research

In this arcital, the Bayer red mud and sintering red mud were used as the experimental materials. Thedetermination of the metal element content in the two kinds of red mud are got using AES,AAS andtitration analysis method, characterized analysis to determine the internal structure using infraredspectroscopy, differential thermal analyzer and X-ray diffraction. Then we use CTAB and STAB to modifythe Sintering red mud which was neutralized by hydrochloric acid and the obtained adsorbents were namedas CARM and SARM.Then we use CARM and SARM to study the adsorption capability of Cr（Ⅵ） insolution, during this process, we investigate the optimum adsorption conditions and discuss the mechanismof adsorption in reference of the adsorption isotherms, adsorption kinetics and adsorption thermodynamics.The main research contents in this paper are as follows:（1） Treat the red mud samples by acid digestion after their pretreatment,then use ICP-AES qualitativeanalysis to make a full scanning of the digestion solution so as to determine whether a certain metalelement exist and its content by ICP-AES quantitative analysis, while Fe, Al, Ca, Mg, K and Na by AASwith titrimetry analysis method for comparison and standard recovery test for verification. We finally theaccurate contents of47kinds of metal elements of sintering red mud contains and46kinds of metalelements of the Bayer red mud in this study. In addition,silicon content in red mud is determined bygravimetric method.（2） According to the determination result and application of building materials as well as metalelements extracting statuses of red mud, we made a analysis of the potential utilization of the metalelements in red mud and it proves that many metal elements of the red have their certain amounts of extractvalue, but limited to the industrialized technical factors, there is little economic value. In short, there arevarious comprehensive utilization methods of red mud,but the current application ways and extractingtechnology still need to be improved.（3） The characterization of red mud was made by infrared spectroscopy, differential thermal analyzer andX-ray diffraction. It was found that the red mud contains about8%of the hydroxyl water which exists asthe form of crystal water, combined with the shape of the water and structural water present in the complexmineral structure of the red mud. Red mud contains the minerals which are rich in CaCO3, and these minerals break down at580℃⁶80℃and release CO2,which leads Bayer red mud about5%weight lossand sintering red mud about10%weight loss. The mineral composition of red mud are rathercomplicated,including mainly calcite, declaim silicate, perovskite, calcium nepheline, water calciumgarnet,etc.（4） The surface of Sintering red mud is rich in exchangeable cations, so the surface of Sintering redmud was combined with the cationic group C16H33（CH3）3N+from the cationic surfactant CTAB and thecationic group C18H37（CH3）3N+from the cationic surfactant STAB to the sintering of red mud surface byion exchange principle, this,as a result, achieves the purpose of expanding the aperture of the sintering redmud and increasing its surface area. CTAB and STAB are best modified when their concentration aredetermined as0.5%and0.6%. From the infrared spectra of CARM and Warmth peaks of CH3-（N+） and-CH2-were found and it is proved the modification was successful.（5） We got the best adsorption conditions of Cr（Ⅵ） by CARM and SARM through adsorptionexperimental conditions selection. With CARM for example, the highest adsorption rate can be obtainedwhen the initial acid condition is pH2; Adsorption equilibrium time is30minutes; the best adsorbentdosage is0.2g;Adsorption rate increases at lower temperature; with the same other conditions, adsorptioncapacity will increase with the concentration of Cr （Ⅵ）. All the mentioned conditions are same to theCARM except that the adsorption equilibrium time is45minutes.（6） Under the optimal experimental conditions, Cr（Ⅵ） adsorption rate by CARM and SARM canreach over95%and97%when the initial concentration is100mg/L,while this value can be up to more than99%when the initial concentration of Cr（Ⅵ） is20mg/L. The maximum adsorption capacity of original redmud,CARM and SARM are4.658mg/g,22.03mg/g and25.16mg/g and it shows that red mud adsorptionquantity increases considerably after its modifition, while STAB better.（7） Adsorption isotherm was analyzed using Langmuir and Freundlich two adsorption isotherm modelanalysis, and the results show that the Langmuir isothermal adsorption model fitted qmaxvalue for theadsorption of Cr （Ⅵ） of CARM is22.20mg/g and it is very close to the experimental value of22.03mg/g,with linear relationship0.9997. Moreover, this value for SARM adsorption of Cr（Ⅵ） is25.21mg/g andvery close to its experimental value of25.16mg/g,too, with linear relationship value0.9990. In a word, it can be supposed that the adsorption processes of Cr（Ⅵ） of CARM and STAB from aqueous solution are inline with the Langmuir isotherm model based on single-molecule adsorption.（8） As for the analysis of adsorption kinetics,both of the pseudo first-order kinetics and dynamicsmodel of quasi two levels were discussed. The values of qefitted out from the pseudo-first order kineticwere0.2165mg/g and0.9531mg/g during the adsorption processes, with a vast deviation from theexperimental ones. However, for the adsorption of Cr （Ⅵ） by CARM,the value of R2in the quasi twolevels dynamic model fitting equation is0.9999, and theoretical calculation value of qeis11.87mg/g whichis very close to the experiment value of qe11.86mg/g. While for the adsorption of Cr （Ⅵ） by SARM，thevalue of R2in the quasi two level dynamic model fitting equation is also0.9999, and theoretical calculationvalue of qeis11.87mg/g which is very close to the experiment value of qe11.86mg/g,too. The resultsshow that, the adsorption processes of Cr （Ⅵ） by CARM and STAB meet quasi two level dynamic modelsand two adsorption processes is a joint action of both physical adsorption and chemical adsorption.（9） For adsorption thermodynamics, we calculated the Gibbs free energy△G0, adsorption enthalpyvalue△H0and entropy variable value△S0of CARM and STAB during the process of Cr（Ⅵ） adsorption.The△G0of the two processes are both less than zero and it can be determined the adsorption can bespontaneous. Delta△H0of two adsorption reaction are21.75kJ/mol and16.48kJ/mol accounting foradsorption reaction are-66.86J·mol^-1·K^-1and-48.76J·mol^-1·K^-1which prove that the two adsorptionreaction are both entropy reduction processes.