Effcets Of Low Molecular Weight Organic Acids On Adsorption Of Chorsulfuron In Soils

Chlorsulfuron can cause phytotoxicity to the following crops resulted from its long residue in soil and unscientific application. In this study, batch expiriments were carried out to study the effects of four low molecular weight organic acids (LMWOAs) included citric acid, oxalic acid, malic acid, acetic acid and their mixed acids on the adsorption of chlorsulfuron in two typical soils (variable charge soil, red soil and permanent charge soil, brown soil) and its colloids. Further study was done to assess impacts of LMWOAs on the adsorption of chlorsulfuron in geothite (G), hematite (H) and their complex with humic acid (geothite-humic acid, G+HA and hematite-humic acid, H+HA).1. The aosorption data of chlorsulfuron in tested sorbents with or without5mmol/L LMWOAs were fitted by Langmiur and Freundlich isothem equation, in which Freundlich equation was more suitable than that of Langmiur equation.2. The adsorption process of chlorsulfuron in soil involves two phases including a fast adsorption period in0-9h and a slow adsorption period in9-18h, and the adsorption equilibrium time was about18h. The adsorption dynamic of chlorsulfuron in soil consisted with the pseudo-second-order and Evolich equation in which the pseudo-second-order was the better one.3. The adsorption free energy (â–³G) of chlorsulfuron in soils was negative values, which indecated that the adsorption was spontaneous. The absolute value ofâ–³G was less than40kJ/mol, which was suggested that the adsorption be physicosorption. The adsorption enthalpy changes (â–³H) of chlorsulfuron in soils were positive, indecated that the adsorption of chlorsulfuron in soils was endothermic, and the amount of chlorsulfuron adsorption increased with temperature increasing, which was consisted with the influence of temperature on the adsorption.4. The results showed that, in different tested sorbents, LMWOAs could enhance the adsorption of chlorsulfuron and amount of chlorsulfuron increased with the concentration of LMWOAs increasing. While added the LMWOAs, the KF values of Freundlich equation cofficient was more than that of without LMWOAs, which indecated that adhesion force was strengthen. Overall, the order of the LMWOAs to enhance the chlorsulfuron amount of adsorption in sorbents was:oxalic acid, citric acid> malic acid> acetic acid. When mixed acids were added into the sorbents, the adsorption of chlorsulfuron had less difference between different mixed acids than single acids. 5. The adsorption capacity of chlorsufuron in red soil was more than brown soil under same conditions, which because red one had more free iron oxide content and less cation exchange capacity.6. The adsorption capacity of chlorsulfuron on G+HA and H+HA surface had less than geothite and hematite, respectively, as the presence of adsorbed HA might block some pores of the solid and increased surface polarity or hydrophilicity.7. According to XRD and FT-IR, HA interacted with geothite or hematite surface through hydrogen bonds and surface complexation.