Study On Sorption Characterristics Of Typical S-triazine And Carbamate Pesticides To Biochars

The residual and transport of pesticides in soils pose potential risks to groundwater.Biochar,as a kind of cost-effective and environmental-friendly sorbent,can be employed to amend the soil to retard the organic pollutants transport to groundwater.In present study,wheat straw biochars were produced under pyrolysis temperatures at 300,500 and 700 ?(referred to WB300,WB500 and WB700,respectively).Carbaryl(CAR,a kind of carbamate insecticide)and atrazine(ATZ,a kind of s-triazine herbicide),two commonly used pesticides,were used as model sorbates.The sorption mechanisms of two pesticides to biochars were investigated via batch experiments.Meanwhile,sorption behaviors of pesticides to biochar-kaolinite mixtures were also studied.The main conclusions are as follows:(1)Sorption of CAR and ATZ to biochars followed the order: WB700>WB500>WB300.The main reasons were that WB700 has a higher degree of carbonization,with higher specific surface areas and more developed micropores.From WB300 to WB700,the dominant sorption mechanism changed from H-bonding interaction to ?-? EDA interaction.Partition and pore-filling process were also involved in the sorption of WB300 and WB500 or WB700.(2)In bi-solute systems,strong competitive sorption occurred between CAR and ATZ,in which CAR manifested higher sorption ability for sorption sites than ATZ,because the ester group and naphthalene ring of CAR had a stronger bonding ability with biochars than N-heterocycle and NH-groups of ATZ.Biochars,produced at higher temperatures had higher aromaticity,making it more easily interact with naphthalene ring of CAR,so the competitive sorption ability of CAR increased with pyrolysis temperatures of biochars.(3)The sorption abilities of CAR and ATZ to biochars were weak,H-bonding interaction and hydrophobicity were the main sorption mechanisms.The sorption capacities of CAR and ATZ to kaolinite amended with biochars were significant enhanced at mass ratios of 5% WB300,1% WB500 and 0.1% WB700.When the added ratio of WB700 was 0.1%,it can also make biochar-kaolinite obtain the strongest sorption effects,so WB700 showed the best amendment ability.(4)In biochar-kaolinite mixtures,the sorption capacities of which were weaker than that of pure biochars.Kaolinite mainly competed with pesticides for sorption sites by covering the surface of biochars.Therefore,when biochars were applied to soils,the interactions between biochars and soil constitutions must be taken into consideration to avoid overestimating the amendment ability of biochar.