Stability Of Amphoteric-cationic And Amphoteric-anionic Modified Clays

The stability of organic-modified clay not only affect their adsorption capacity to pollutants,but also the desorption of surfactant may lead to two pollution problems.therefore,research on the stability of clay minerals has important significance for the practical application of modified clays.In order to explore the stability of the amphoteric-cationic and amphotericanionic modified clays,this study used amphoteric modifier dodecyldimethyl betaine(BS-12),cationic modifier hexadecyl-trimethyl ammonium bromide(CTMAB)and anionic modifier sodium dodecyl sulfate(SDS)to modify bentonite(2:1 type clay)and kaolin(1:1 type clay)clay matrixes.we investigated the stability of the modifiers in NaCl desorption solution with batch method and compared the influence of temperature,pH and concentration of salt solution on desorption.The surface characteristics such as total organic carbon(TOC),specific surface area(SBET),X-ray diffraction(XRD),fourier transformed infrared spectrum(FTIR)and thermogravimetry(TG)were investigated in a part of modified clays.The change law of modified clays before and after desorption was described in various ways.The stability mechanism of amphoteric-composite modified clays was revealed from microcosmic angle,which provided basis for practical application of amphoteric-composite modified clays.The main conclusions of this study were as follows:1 BS-12 modified bentonite had a better desorption stability than BS-12 modified kaolin.Stability of the desorption of amphoteric-cationic and amphoteric-anionic modified bentonite was higher than that of kaolin.Amphoteric-cationic modified clays had better stability than amphoteric-anionic ones.2 BS-12 modified bentonite had a better desorption stability without considering the influence of other factors.The desorption rate of BS-12 is less than 5%.The stability of BS-12 modified kaolin was less than that of BS-12 modified bentonite,and the desorption rate of BS-12 is less than 18%.3 The desorption stability of BS-12 modified bentonite and kaolin decreased with the increase of BS-12 modified ratio,that is,the BS-12 combined with soil sample in a cation exchange mode was more stable than that in hydrophobic mode.The stability of soil samples was enhanced by increasing pH value,the concentration of NaCl,and decreasing temperature of desorption solution.In the range of test conditions,BS-12 modified bentonite and kaolin were the most stable when NaCl concentration was 2mol/L,pH condition was 2 and temperature was 20?.4 BS+CT complex modified bentonite had a better desorption stability than BS+CT complex modified kaolin.The desorption stability of BS-12 and CTMAB decreased with the increase of CTMAB modified ratio in BS+CT complex modified clays.100BS+CT bentonite and 60BS+CT kaolin had a better stability when CTMAB had the same proportion of modification.5 The desorption stability of various modifiers in BS+CT complex modified bentonite and kaolin enhanced with increasing pH value and solution concentration,and decreased with increasing temperature.Within the range of test conditions,the stability of BS+CT complex modified clays were the most stable when NaCl concentration was 2mol/L,pH condition was 10 and temperature was 20?.6 BS-12 complex modified bentonite had a better desorption stability than BS-12 complex modified kaolin.When the BS-12 modified ratio were the same,the desorption stability of various modifiers in BS+SDS bentonite decreased with the increasing of SDS modified ratio.The higher the modified ratio of BS-12,the better the stability of SDS,the worser the stability of BS-12 when the SDS modified ratio were the same.Generally,the stability of BS+SDS bentonite were from high to low in order: 100BS+SDS>50BS+SDS>25BS+SDS bentonite.The desorption stability of different modifiers in BS+SDS complex modified kaolin decreased with increasing SDS and BS-12 modified ratio.7 The desorption rate of SDS had the greatest influence on the stability of BS+SDS modified clays.The BS+SDS modified clays were most stable,When the desorption concentration was 2mol/L,the pH value was 2 and the temperature was 20?.8 The TOC content was decreased after desorption by NaCl solution of each soil sample.After desorption,the specific surface area of BS bentonite and BS+CT bentonite decreased while the specific surface area of BS kaolin,BS+CT kaolin,BS+SDS bentonite and BS+SDS kaolin increased.After desorption by NaCl solution,the interlayer spacing of BS bentonite and BS+CT bentonite decreased,and the interlayer spacing in BS+SDS bentonite and modified kaolin did not change significantly.The change in results of FTIR analysis and TG curve analysis showed that the absorption process reduced the organic modifier in soil samples.