Study On The Adsorption Characteristics And Mechanism Of Typical Benzene Series Compounds By Soil Organic Matter

Benzene series are hazardous to the ecological environment and human health,which could be transferred into the soil by water migration and atmospheric deposition.At present,it is urgent for highly efficient remediation technologies to control the benzene series contained in soil.Adsorption technology takes the advantages in low operation cost and environmental friendliness.Therefore,it is of great support to promote the research and development of soil adsorption technology and process mechanism by exploring the occurrence and migration characteristics and mechanism of benzene series in soil.Unfortunately,rare investigations in the occurrence and migration of benzene series in soil have been performed,which would have a great contribution to the application of adsorption technology in soil remediation.Therefore,in this study,toluene was selected as the target benzene series,and explored the adsorption capacity of soil.The results indicated organic matters in soil were the major adsorption materials.Moreover,the adsorption characteristics the mechanism of typical organic matters to toluene were further investigated.The specific results were illustrated as follows:1)Three types soil（including sand,clay,and loam）were used to adsorb toluene.The results showed that clay could be treated as the typical soil adsorbent,due to its higher adsorption capacity than sand and loam.Besides,the organic matters were found as the major adsorption materials compared with the mineral substances.The adsorption capacity of black carbon,humic acid,humin,and fulvic acid were further explored.The saturated adsorption capacity of black carbon,humic acid,humin,and fulvic acid were 37.182mg·g^-1、30.453 mg·g^-1、28.059 mg·g^-1and 6.155 mg·g^-1,respectively.Therefore,the adsorption capacity of organic matters rank from top to bottom was black carbon,humic acid,humin,and fulvic acid.Moreover,fulvic acid was much lower compared with the other three organic matters.2)The effects of temperature,pH and ionic strength on the adsorption capacity of black carbon,humic acid,and humin were investigated.It was found that the adsorption capacity of the three organic matters decreased with the increasing temperature and Ca Cl₂concentration.However,as the pH increasing,the adsorption capacity of humin presented no obvious variation,because humin was stable and undissolved in various pH solutions.The response surface analysis results showed that effects of different operation conditions on adsorption capacity of the organic matters were significant difference（P<0.05）.Kinetic and thermodynamic analysis results fitted the pseudo-second-order kinetic model（R²≥0.967）,Langmuir model（R²≥0.953）,Freundlich model（R²≥0.978）and Dubinin-Ashtakhov model（R²≥0.963）,suggesting physical and chemical adsorption were both existed,and physical adsorption was more important.It also should be noted the adsorption process was nonlinearity.3)The black carbon,humic acid and humin were characterized by SEM.It was found that the black carbon surface had rich pore structure.Besides,the BET analysis results showed the specific surface area and pore volume of black carbon were larger than the other two,which were helpful for its physical adsorption process.The surface of the three organic matters contained functional groups,which could produce hydrogen bonds.This result proved that the organic matters could perform chemical adsorption.The characteristic parameter（K_L）of Langmuir model during toluene adsorption by three organic matters could be obtained,which could be used for the further calculation of thermodynamic parameters.The analysis of thermodynamic parameters demonstrated that the toluene adsorption by the organic matters was spontaneous process,due to the increasing degree of freedom and exothermic.