Equilibrium Adsorption Characteristics Of Amphoteric Modified Bentonites To Cd(Ⅱ) And Phenol

Oganic-heavy metal complex contamination has became the main form of environmentalpollution in soil and water environment. Because of the hydrophobicities of organiccontaminatants and the hydrophilcities of heavy metal ions, the conventional adsorptiontechnique is hard to remove simultaneously the organic pollutants and heavy metalions in theenvironment. Therefore, the treatment for oganic-heavy metal complex contamination hasbecame the focus in the study of environment branch field.A series of new bentonite-based amphiphilic adsorbing materials were synthesized bymodifying bentonite with long-chain amphoteric surfactants dodecyldimethylbetaine（BS-12） and octadecyldimethylbetaine（BS-18）. The structure of amphoteric modifiedbentonite were characterized by the organic carbon contents, X-ray diffraction and FTIRanalysis, the adsorption regularity of phenol and Cd²⁺on amphoteric-bentonite and itsaffecting factors, i.e. modified ratio, temperature, pH and ionic strength, were studied, and theadsorption mechanism was also discussed according to its adsorption isotherms andthermodynamics. This master’s thesis aimed to provide a theoretical basis for exploiting newamphiphilic adsorbents and its application in the environmental pollution treatment. The mainconclusion of this work are as follows:（1） The organic carbon contents and interlamellar spacing of amphoteric-bentoniteshowed a positive correlation with modified ratio. XRD analysis indicated that the bentonitewas modified by amphoteric surfactants which included two adsorption mechanism, theamphoteric surfactants entered into the layers by means of intercalation in the region of0～100%CEC ratio, which was instead by hydrophobic bond in higher than100%CEC.（2） The equilibrium sorption amount of phenol on the amphoteric-bentonite samplesshowed a positive correlation with amphoteric surfactants modified ratio, the adsorptioncapacity increased in the order:150BS-12>100BS-12>50BS-12>25BS-12>CK with theBS-12bentonite treatments,150BS-18>100BS-18>50BS-18>25BS-18>CK with the BS-18bentonite treatments, indicated that the phenol adsorption on amphoteric-bentonites could beenhanced significantly. In the same modified ratio of the BS-12bentonite treatments and BS-18bentonite treatments, the adsorption of phenol increased with an increase of the carbonchain of amphoteric surfactants. The adsorption isotherms can be described with Henryequation. The adsorption of phenol on the amphoteric-bentonite depended mainly on partitioneffect, the equilibrium sorption amount decreaseed with an increase of temperature and pH,but increaseed with ionic strength rise. The coexistence of Cd²⁺could promote the adsorptionof phenol on BS-18modified bentonite and BS-12modified bentonite except150BS-12treatment （20℃and40℃） and50BS-12treatment （40℃）. The phenol adsorptionthermodynamics demonstrated that the phenol adsorption on the amphoteric-bentonite was aphysical adsprption, which was a spontaneous process with the exothermic character.（3） Compared with the unmodified bentonite, the equilibrium sorption amount of Cd²⁺onthe amphoteric-bentonite decreased. The adsorption capacity of Cd²⁺showed a negativecorrelation with modified ratio in the region of0～100%CEC ratio, while an opposite change,i.e. a positive correlation with modified ratio, appeared when the modified ratio was higherthan100%CEC. In the same modified ratio of the BS-12bentonite treatments and BS-18bentonite treatments, the adsorption of Cd²⁺increased with the increase of carbon chainlength when the modified ratio was higher than100%CEC, but in the region of0～100%CEC ratio, the result was faint. The adsorption isotherms can be described with Langmuirequation. The main adsorption mechanism of Cd²⁺on the amphoteric-bentonite was the resultof the interaction between ionic exchanging adsorption and hydrophobic bond. Thecoexistence of phenol was not favorable for the adsorption of Cd²⁺in low modified ratio,while an opposite change, i.e. favorable for the adsorption of Cd²⁺in higher modified ratio.The adsorption of Cd²⁺on the amphoteric-bentonite was not sensitive to temperature, and theequilibrium sorption amount increaseed with an increase of pH, but decreaseed with ionicstrength rise. The Cd²⁺adsorption thermodynamics indicated that the Cd²⁺adsorption on theamphoteric-bentonite was a spontaneous process which regulated by enthalpy increasing.