Effect Of Clay Mineral Composition On The Adsorption Of Phenol In Amphoteric Complex Modified Red Soil

To explore the response of red soil as substrate,after modifying with a mixture of amphoteric modifier such as dodecyl dimethyl betaine?BS-12?,and cationic modifier,dodecyl trimethyl ammonium bromide?DTAB?was investigated.The structure of amphoteric-cationic modified red soil was characterized by the carbon contents,SEM,FTIR and specific surface area analysis.A batch experiment was performed to understand the adsorption mechanism underlying isotherms and thermodynamic characteristics of phenol by complex modified red soil with total modification ratio?TMR?,temperature,ionic strength,and pH.On this basis,by adding bentonite?BN?and kaolinite?KN?to change the mineral composition of red soil,the effects of changes in mineral composition on the adsorption of phenol by complex modified red soil were studied and discussed.The main purpose was to elucidate the effect of mineral composition on the adsorption of organics by complex modified red soil,and to provide a theoretical basis for the restoration of polluted soil.The main conclusions of this present study are as follows:?1?The carbon concentration in amphoteric modified red soil was evidently increased with increasing proportion of BS-12.After DTAB was modified,the carbon contents of complex modified red soil were increased with increasing rate of DT,when the TMR was within 200%of the CEC.The specific surface area of soil samples showed a decreasing trend with modification of BS-12.Consequently,after DTAB complexed,the specific surface area further decreased,and both were smaller than BS-12 modified soil.Indeed,the FTIR results showed that BS-12 and DTAB considerably modified the structure of red soil.Meanwhile,SEM results revealed that the different structural features of BS-12 and DTAB on the surface of red soil were observed at different modification ratios.?2?The equilibrium adsorption experimental results showed that the adsorption amount of phenol on single phenol treatment and phenol+Cd²⁺complexed treatment was higher in BS-12+DTAB complex modified soils than that of un-modified and BS-12 modified red soils..The phenol adsorption dramatically increased with an increase of modifier ratio in phenol single treatment,when the TMR was within 150%of the CEC,and the 100BS+50DT modified soil sample had the best adsorption effect.Henry equation is the best model to describe the phenol isotherms.The phenol adsorption decreased with increases in temperature,pH,and ionic strength,The results of thermodynamic parameters explore that the adsorption of phenol on amphoteric-complex-modified red soils was a spontaneous control process of enthalpy decrement,mainly based on physical adsorption.The CEC determined by the composition of clay minerals was the determining factor in controlling phenol adsorption onto the amphoteric-complex-modified red soil.?3?The changes in mineral composition of red soil were observed which may probably enhanced the CEC concentration with increasing dose of BN.Besides,with the same BS+DT modification ratio,the adsorption amount of phenol increased significantly.It is documented that 100BS+50DT was the best modification ratio of phenol adsorption of bentonite-added red soil.The adsorption isotherms were suitable to be described by Henry equation.The adsorption amount of phenol decreased with an increase of temperature and pH,and the adsorption amount increased first and then decreased with an increase of ionic strength.Thermodynamic parameters indicated that the adsorption process of phenol considered a spontaneous exothermic process,and the adsorption of phenol on bentonite-added red soil was generally controlled by enthalpy decrement.?4?The CEC concentration in red soil was significantly decreased with addition of KN.Similarly,BS-12+DTAB modification ratio,the adsorption of phenol on kaolinite-added red soil was decreased compared with red soil.The mixture of 100BS+50DT was also considered the best modification ratio for phenol adsorption of kaolinite-added red soil.The adsorption of phenol on soil sample had a negative effect because of an increase of temperature,and the phenol adsorption drastically decreased with an increase of pH.The phenol adsorption increased first and then decreased with an increase of ionic strength.Thermodynamic parameters showed that the adsorption process of phenol was controlled by enthalpy decrement.It is assumed that the Phenol adsorption depended on the TOC in soil,and CEC was considered as a primary cause of changes in adsorption.?5?The content of organic carbon determined by the CEC of substrate is the main factor affecting the phenol adsorption of soil.Over all,the variation in clay mineral composition after incorporation to soil which can increase the CEC concentration in soil system,considered an effective way to improve the adsorption of phenol on the amphoteric complex modified soil.