Study On The Sorption Behavior Of Typical Imidazolium-based Ionic Liquids On Soils

Ionic liquids?ILs?,a kind of emerging“green”solvents,have gained widespread public attention at present.Sorption is an important process affecting the transport of ILs from soil to groundwater.In this study,the effects of alkyl chain length of ILs,coexisting inorganic cations,dissolved organic matter?DOM?and soil components on sorption/desorption of typical imidazolium-based ILs?i.e.,1-methyl-3-octyl imidazolium chloride,[OMIM]Cl?to soils were studied.Sorption characteristics of[OMIM]Cl on rice straw-based biochars with different carbonization degrees were also investigated in order to provide the bases for controlling the ILs transport in soils by adding biochars.The main conclusions were as follows:?1?Based on the experiments data,a prediction model for the relationship between sorption coefficient?K_d?and cation exchange capacity from soil components(CEC_SOM and CEC_CMs)as well as solution concentration?C_e?was established:LogK_d=Log(1.67*CEC_SOM+3.22*CEC_CMs)-0.58LogC_e.This model can provide a good prediction for sorption coefficients within 0.48 log unit.Sorption of[OMIM]Cl was inhibited by coexisting inorganic cations and the competitive sorption affinity was in the order of Ca²⁺?Mg²⁺>K⁺>Na⁺.?2?Coexisting DOM in solution can promote[OMIM]Cl sorption on soil mainly by cosorption.DOM with small molecular weight contains more polar functional groups while DOM with high molecular weight has abundant aromatic structures.Electrostatic attraction occurred between[OMIM]Cl and the polar functional groups of DOM,and?-?EDA interaction was mainly controlled by the aromatic structure of DOM.?-?EDA interaction was stronger than electrostatic attraction.The adding DOM would cover the soil surfaces and inhibit[OMIM]Cl previously-sorbed desorbing from the soils.?3?The prepared biochars produced at 400,500 and 700°C were referred to as RB400,RB500,and RB700,respectively.Electrostatic attraction and hydrogen bonding controlled the sorption of[OMIM]Cl on RB400,while?-?EDA interaction between[OMIM]Cl and the aromatic rings of biochar dominated the sorption of[OMIM]Cl on RB500 and RB700.With increasing solution pH,carboxyl and hydroxyl groups on biochar became deprotonated,and sorption mechanism changed from hydrogen bond to electrostatic attraction.Sorption process of[OMIM]Cl on biochar was spontaneous and endothermic.The sorption capacity of[OMIM]Cl by RB700 with high carbonization were about 3¹0 times of that by soils.Thus,RB700could be an ideal soil modifier.