The Experimental Study On Sorption Of Benzene And MTBE To Maize-straw Derived Biochars

Biochar, as an important part of soil organic matter, has significant influence onmigration and transformation of organic contaminants in soil. The characterizations ofman-made biochars, influenced by the different preparation processes, showedvarious sorption mechanisms to organic contaminant. In this study, biochars derivedfrom maize straws at different temperatures (200to800°C, referred as MB200,MB300, MB400, MB500, MB600, MB700, and MB800, respectively) weresystematically characterized. Batch experiments are used to study the sorptionbehavior of benzene and methyl tert-butyl ether (MTBE) on biochars. The sorptionmechanisms were discussed combined with surface characterizations of biochars andexperimental results. The main conclusions are as follows:(1) The yields of biochars descended with the increasing pyrolysis temperatures,while the ash content of biochars increased. The extent of biochar carbonizationenhanced, along with the increased amount of aromatic functional groups anddecreased of aliphatic functional groups. At the pyrolysis temperature lower than400℃, biochars’ aromaticity increased and polarity reduced rapidly. The changescope of aromaticity and polarity of biochars flatten out when the pyrolysistemperature was higher than400℃. Pore structure of maize-straw transferred frommacopore to micropore in the carbonization process. It resulted in the surface area andmicropore volume of biochars raised with pyrolysis temperature.(2) Sorption data of MTBE and benzene on biochars generated from200℃and300℃, showed well linearity. This suggested that the sorption mechanisms ofMTBE and benzene were mainly partition to noncarbonized organic matters (NOM).Partition and adsorption acted together on the sorption of MTBE and benzene tobiochars produced at400-600℃. At low organics concentration, benzene and MTBEsorption on the biochars surface adsorption sites firstly. And then the sites becamesaturation quickly with the increased benzene and MTBE. When the pyrolysis temperature was higher than700℃, surface adsorption was dominant on sorption ofbiochars on benzene and MTBE.(3) Removal efficiency of benzene or MTBE in the binary solution was betterthan that in the single-solute solution. The pyrolysis temperature of biochars leaded tothe increase of monolayer surface sorption sites to benzene and MTBE. Competitivesorption, aiming at the surface adsorption sites of biochars, happened in the binarysolution. However, it made little effects on partition and pore-filling.(4) The sorption of organic contaminants to biochars was not only affected bythe characterizations of biochars, but also influenced on the properties of organicmatters. Biochars’ sorption affinity to benzene and MTBE enhanced with increasingpyrolysis temperatures, meanwhile polarity decreased and aromaticity, surface areaand micropore volume increased. Moreover, sorption affinity of benzene to biocharswas better than that of MTBE. The interaction between MTBE and biochars includedthe intermolecular hydrogen-bond of sorbent and MTBE, and heterogeneous diffusionin multimoclecular layer. In the meantime, sorption of benzene to biochars wascontrolled by chemisorption (π-π joint between benzene ring and aromatic ring ofbiochars) and pore-filling.