Comparison Of Phenol And Cr(VI) Adsorption Onto Different Cationic Modified Magnetic Bentonite

Recently,problems of heavy metals and organic pollution in water have become seriously with economic growth.For protecting human health and the ecological environment,It is essential to study how to remove heavy metals and organic pollutants from water.In this paper,four different cationic surfactants,octadecyl trimethy lammonium chloride(OT-8),dodecyl trimethy lammonium bromide(DT),Octadecyl trimethy lammonium chloride(OT-18)and ethylenete trimethy leneammonium chloride(ET),were used to modify the magnetic bentonite.The surface structure of each cationic modified bentonite was characterized by TOC and FTIR.The adsorption kinetics,adsorption thermodynamics and adsorption isotherm characteristics of organic pollutant phenol and anionic heavy metal pollutant Cr(VI)were investegated.The effects of experimental condition(temperature,pH,ionic strength,dosage)on the adsorption of phenol and Cr(VI)and the adsorption and regeneration experiments of these two pollutants were studied also.The experiment that investigating and comparing the difference of adsorption capacity of cationic modified magnetic bentonites between phenol and Cr(VI)was also done.This study might provide valuable information for the research and application of cationic modified bentonite to adsorption anionic heavy metals and organic pollutants in wastewater.The results obtained by this paper are as follows:(1)Modidied by various cationic surfactants,magnetic bentonite had significant improvements in TOC content,and the content of each cationic modified magnetic bentonite was ordered by ET > OT-18 > DT > OT-8.The results of FTIR indicated the successful loading of each cationic surface modifier on magnetic bentonite.The modification rate of each cationic surface modifier on magnetic bentonite showed the order of OT-18 > ET > DT > OT-8.The carbon chain length is the critical factor affecting the surface modification rate of the cationic surfactants on the magnetic bentonite.The longer the carbon chain of the surfactants,the higher the modification rate on the surface of the magnetic bentonite.(2)The pseudo second-order model exhibited a much better fitting for the adsorption of phenol and Cr(VI)on each modified cationic magnetic bentonite.It was observed that the removal of phenol and Cr(VI)increased quickly and reached equilibrium almost in 10 min.(3)The Sips model fitted well to the adsorption of phenol on modified magnetic bentonites.The maximum adsorption capacity of the magnetic bentonite for phenol all had marked increase after modification and exhibited the law of ET > OT-18 ? DT >> OT-8.Moreover,the double carbon chain type cationic modified magnetic bentonite had a significantly higher adsorption capacity for phenol than single carbon chain type cationic modified magnetic bentonite.The longer the carbon chain of the single carbon chain type cationic modifier,the larger the maximum adsorption capacity of the modified magnetic bentonite to phenol.The maximum adsorption capacity of each cationic modified magnetic bentonite showed an up ward trend with the increase of the modification ratio.(4)The Sips model is the best isotherm adsorption model for describing the adsorption of Cr(VI)on various cationic modified magnetic bentonites.The modification of the cationic modifier enhances the adsorption capacity of magnetic bentonite for Cr(VI).The maxium adsorption capacity of Cr(VI)on three kinds of single-carbon chain cationic modified bentonite was ordered by OT-18 > DT > OT-8.The longer the carbon chain of the cationic modifier,the higher the maximum adsorption amount of the modified magnetic bentonite to Cr(VI).The maximum adsorption capacity of Cr(VI)by double carbon chain type cationic modified bentonite is higher than that of three single carbon chain type cationic modified magnetic bentonite at the modification ratio of 50%and 100%,but lower than OT-18 cationic modified magnetic bentonite at 150% modification ratio.The maximum adsorption capacity of Cr(VI)by cationic modified magnetic bentonite increased with the increase of the modification ratio.(5)The adsorptions of phenol and Cr(VI)by magnetic bentonite were mainly physical processes,and the adsorption capacities decreased with the increase of temperature.The adsorptions were spontaneous and exothermic processes.The increase of pH had negative impact on the adsorption of phenol and Cr(VI),and the increasing ionic strength benefitted the removal of phenol,but impeded the adsorption of Cr(VI).(6)The increasing removal rates of phenol and Cr(VI)in tested magnetic bentonites attributed to the increase of dosage,while the adsorption amount decreased with the increase of dosage.Reasonable regeneration performance present to 100 ET modified magnetic bentonite and 100OT-18 cationic modified magnetic bentonite After three regenerations,100 ET modified magnetic bentonite still possessed 89.9% of maximum adsorption capacity for phenol,while 100OT-18 maintain 79.7% of maximum adsorption capacity for Cr(VI).The modified of cationic surfactants improve the adsorption capacity of magnetic bentonite for phenol and Cr(VI),the carbon chain length and the modification ratio of the cationic surfactants is the key factor affecting the capacity of phenol and Cr(VI).