Enhancing Effect Of Gemini Complex Modification On Adsorption Of Cr(Ⅵ) And Phenol By Amphoteric Bentonite

The combined pollution of organic matter and heavy metals in the hydrosphere has become an important environmental problem.The exploration and development of new adsorption materials with excellent adsorption performance and high feasibility can effectively inhibit the mobility of heavy metals and organic pollutants in the hydrosphere,reduce their biological effectiveness,and have practical significance for the treatment of water and soil pollution.In this paper,the gemini cationic surfactant ethylene ditetradecyl dimethyl ammonium chloride（EB）and the amphoteric surfactant dodecyl dimethyl betaine（BS）were used to prepare amphoteric-gemini complex modified bentonite.Through X-ray diffraction（XRD）,specific surface area(S_BET),scanning electron microscope（SEM）,infrared spectroscopy（FTIR）,carbon and nitrogen content（TC,TN,C/N）,cation exchange capacity（CEC）and anion exchange capacity（AEC）characterized the structural characteristics and changes of bentonite.Combined with adsorption kinetics and equilibrium adsorption,the adsorption characteristics of BS+EB modified bentonite on Cr（Ⅵ）and phenol were studied,then studyed the influence of modification ratio,temperature,p H value,ionic strength and other factors on the Cr（Ⅵ）and phenol adsorption by BS+EB complex modified soil samples.Further explored the enhanced effect and mechanism of gemini-cation complex modification on the adsorption of heavy metals and organic pollutants,and it provided a theoretical basis for the research and application of amphoteric complex modification to enhance the simultaneous adsorption of organic and heavy metals.The main results obtained in this paper were as follows:（1）FTIR spectroscopy and SEM image characteristics showed that BS and EB were successfully modified to bentonite.Both BS single modification and BS+EB complex modification increased the TC,TN,AEC content and interlayer spacing of bentonite,and raised with the increase of the modification ratio.But the CEC and specific surface area decreased with the increase of the modification ratio.The modification mechanism of BS and EB modifiers for bentonite varied with the modification ratio.When the modification ratio was low,ion exchange modification was the main one,and when the modification ratio was high,the hydrophobic distribution binding mode was the main one.（2）For the Cr（Ⅵ）adsorption in a single system,both BS single modification and BS+EB complex modification improved the Cr（Ⅵ）adsorption capacity of bentonite,and the Sips model had a better fitting effect on Cr（Ⅵ）equilibrium adsorption.Compared with CK,the saturated adsorption capacity of BS single modified and BS+EB complex modified bentonite increased by 2.92～6.38 and 8.32～87.47 times respectively.Among them,the saturated adsorption capacity of 50BS+EB,100BS+EB modified soil was 2.84～27.25 times and2.02～13.71 times of 50BS,100BS modified soil.It showed the order of BS+150EB>BS+100EB>BS+50EB>BS+25EB>BS>CK.The experimental results of adsorption kinetics showed that the Cr（Ⅵ）adsorption on the tested soil samples reached equilibrium in about 15 min,and the pseudo-second-order kinetic model could better describe the Cr（Ⅵ）adsorption on the tested soil samples.The Cr（Ⅵ）adsorption by BS+EB complex modified soil was mainly physical adsorption,and it was a process of exothermic spontaneous.However,the increase of temperature,initial p H value and ionic strength of the solution were not conducive to the Cr（Ⅵ）adsorption on the tested soil samples.The Cr（Ⅵ）adsorption mechanism of BS single modification and BS+EB complex modified bentonite was mainly based on the charge attraction,and the adsorption of Cr（Ⅵ）depended on the anion exchange amount on the modified soil sample.（3）For the phenol adsorption in a single system,the Sips model was the best model to describe the adsorption of each test soil sample.Compared with CK,the saturated adsorption capacity of BS single modified and BS+EB complex modified bentonite for phenol increased by 3.36～9.17 times and 9.98～15.96 times,respectively.Moreover,the adsorption effect of bentonite modified by BS+EB complex modification was more significant,and the adsorption capacity of 100BS+50EB modified clay was the largest,which was 1280.76 mmol·kg^-1.The phenol adsorption capacity of BS+EB complex modified bentonite was related to the modification ratio used during modification,and the specific performance was BS+50EB>BS+100EB>BS+150EB>BS+25EB>BS>CK.The results of kinetic experiments showed that the phenol adsorption on the tested soil samples reached equilibrium in about 20minutes,and the pseudo-second-order kinetic model could better describe the adsorption of phenol on the tested soil samples.The results of condition influencing factors showed that the phenol adsorption on the tested soil samples was mainly physical adsorption,and it was an exothermic spontaneous process.Among them,the BS+EB complex modification could enhance the spontaneous adsorption of phenol on bentonite.However,the increase of the initial p H value was not conducive to the phenol adsorption by the modified soil samples,and the ionic strength was in the range of 0.01～0.1 mol·L^-1,and the salting-out effect promoted the phenol adsorption by the modified soil.The adsorption mechanism of BS single modification and BS+EB complex modified bentonite on phenol was mainly hydrophobic partition adsorption at low equilibrium concentration,and the coexistence of partitioning and surface adsorption at high equilibrium concentration.（4）For the phenol and Cr（Ⅵ）adsorption in the composite system,the Cr（Ⅵ）adsorption characteristics of BS amphoteric modification and BS+EB complex modification were consistent with the single Cr（Ⅵ）system,but the phenol adsorption characteristics were different from that of single system.Under complex pollution conditions,the coexistence of phenol promoted the Cr（Ⅵ）adsorption on each test soil sample by forming a complex with Cr（Ⅵ）or reducing it.The coexistence of Cr（Ⅵ）inhibited the phenol adsorption on each test soil sample by enhancing the hydrophilicity of the modified soil surface,but the high modification ratio of BS+EB complex modified bentonite would be less affected.In summary,after comparison and screening of surface properties,adsorption characteristics and environmental factors,the modified soil sample with 100BS+50EB showed the best adsorption performance for Cr（Ⅵ）and phenol in the BS+EB complex modified bentonite series.