Adsorption Mechanism And Characteristic Of CTAB/SDS Complex Modification On BS-12 Modified Bentonite And Kaolin

In this paper, kaolin and bentonite were chosed as matrix material, dodecyl dimethyl betaine(BS-12) was the single modifier, prepared BS-12 modified bentonite with proportion of 25%, 50%, 100% CEC and BS-12 modified kaolin with proportion of 15%, 30%, 60% CEC. Adsorption mechanism and characteristic of Cetyl trimethyl ammonium bromide(CTAB), sodium dodecyl sulfate(SDS) modification on bs-12 modified bentonite and kaolin was studied.Surface characteristics of BS-12 modified bentonite and BS-12 modified kaolin was measured by a series of methods such as XRD, organic carbon, specific surface area, infrared spectroscopy and so on. Combined with changes of surface feature and SCC, SCS value change with the modifier mole fraction on clay minerals, complex mechanism of CTAB, SDS and the turning point for adsorption mode was find out. At the same time, complex adsorption characteristics of modifier on BS-12 modified clay minerals under 20℃ and 40℃ was studied. Discussing changes in the adsorption mechanism according to the changes in adsorption quantity under the effect of temperature. Research goal is to find out complex mechanism for CTAB, SDS adsorption on BS-12 bentonite, kaolin and the key parameters for the conversion of different mechanisms. It provides a theory basis for amphoteric compound clay minerals to adsorb metal and organic contaminants simultaneously. The results of the study have good value in water pollution control and soil pollution control.Following conclusions was obtained in the thesis:1. On the surface of bentonite and kaolin, with the increase of BS-12, organic carbon content increased and specific surface area decreased. Increase or decrease magnitude was more significant on bentonite. FTIR and XRD results showed, BS-12 intercalated into the interlayer structure of bentonite and adsorbed on kaolin surface; Masking effect of the alkyl chain for charge became obviously with the BS-12 modification ratio increased, the CEC and AEC were reduced;2. Complex mechanism for CTAB was ion exchange and hydrophobic adsorption. When CTAB added amount was less than the critical ratio of hydrophobic, on exchange occured only. Add an amount above the critical ratio of hydrophobic, ion exchange and hydrophobic patterns coexist. The lower the proportion of BS-12 modification, the higher the critical ratio of hydrophobic adsorption. Critical point for ion exchange turning to hydrophobic bonding on 25 BS, 50 BS and 100 BS bentonite was 20.30%, 11.56% and 2.00%; Hydrophobic adsorption mode occupied absolute advantage in the modified proportion of 200%, 150% and 100% nearby. Critical point for the appearance of hydrophobic bond on 15 BS, 30 BS and 60 BS kaolin was 12.00%, 5.75% and 1.00%, and its dominant adsorption absolutely was at the proportion of 250% nearby;3. Turning point of hydrophobic adsorption appearance at about 50% and 30% was sum proportion of BS-12 and CTAB, which was closed to the single critical ratio of BS-12; sum of the proportion was about 200% when hydrophobic adsorption occupied absolute advantage on BS-12 modified bentonite, while it was affected by CTAB only on BS-12 modified kaolin, the low proportion of BS-12 had nothing to do with it;4. The AEC of bentonite and kaolin was small, so the exchangeable anion content was poor. Certain proportion of Ion exchange reaction existed on 25 BS bentonite with SDS modification, and hydrophobic binding adsorption mode happened at modification proportion of 14.78%, While it happened early on 50 BS, 100 BS bentonite and 15 BS, 30 BS, 60 BS kaolin at 0.38%, 0.86%, 0.70%, 0.03% and 0.35%;5. The adsorption isotherms of CTAB on BS-12 modified bentonite and kaolin fitted Langmuir model, and CTAB adsorption capacity decreased with the increase of BS-12. The adsorption isotherms of SDS on BS-12 modified clay minerals was consistent with Freundlich model. SDS adsorption capacity increased with BS-12. Adsorption capacity of CTAB was jointly controlled by the ion exchange and hydrophobic carbon chain reaction, while the adsorption of SDS depended mainly on the sorption of hydrophobic bond. Modification of SDS on BS-12 modified bentonite and kaolin were spontaneous adsorption process. The modification process was endothermic reaction and Entropy was increased on 25 BS bentonite,while it’s a exothermic reaction and entropy decrease process on 50 BS, 100 BS bentonite, 15 BS, 30 BS and 60 BS kaolin.