Study On Adsorption-desorption Characteristic Of Ciprofloxacin In Soda Saline Soil

In recent years,the number of the production and use of antibiotics in China increased quickly.Quinolones has been clinically used the second kinds of antimicrobial agents,is widely used in livestock and poultry breeding industry because of the strong antimicrobial activity,adverse reaction is lighter and other characteristics.Add antibiotics in the livestock feed cannot be completely absorbed by organisms,most of the antibiotics with livestock and poultry manure education body to outside,and along with the manure into the soil pollution caused by piled up at random and direct application.With the decrease of cultivated land in China,saline-alkali has become a huge development potential of reserve cultivated land resources.And the addition of organic fertilizers to the saline soil during the remediation process,can lead to antibiotics contaminated soil.This study use the saline-alkali soil in Changhcun Jianbala village as the research samples,the commonly used quinolones: ciprofloxacin is selected as the object of the study.The adsorption-desorption isotherms,adsorption-desorption kinetics and adsorption-desorption thermodynamics of ciprofloxacin adsorption-desorption in the saline-alkali soil were investigated by batch equilibrium studies according to DECD Guideline 106,and the effects of pH,Ca2 +,cation type and organic matter concentration on adsorption-desorption process were also discussed in this study.The results are summarized as follows:The adsorption-desorption of ciprofloxacin in saline-alkali soil with different initial concentrations was in accordance with the pseudo-second order kinetics equation,the whole adsorption-desorption process can be divided into two stages: the fast adsorption and the slow equilibrium.The adsorption-desorption equilibrium time of ciprofloxacin in different initial concentrations with 80 mg·L^-1、100 mg·L^-1and 120 mg·L^-1 was 24 h.The equilibrium adsorption ratios were 89.9%,92.2% and 92.7%,and equilibrium desorption ratios were 97.1%、97.8%、96.9%,respectively.The adsorption isotherm of ciprofloxacin was well fitted with the Freundlich equation,and the correlation constant r was 0.9905.Adsorption isotherm is S type,the adsorption ratios increased with the initial concentrations.Results with less than 0.7 of HI revealed that the desorption of ciprofloxacin in the saline-alkali soil has distinct hysteresis.With the increase of temperature,the adsorption capacity of saline-alkali soil on the ciprofloxacin showed a trend of decrease.Results with-3.58 5 KJ·mol^-1 of ΔH and less than 0 of ΔG revealed that the adsorption of ciprofloxacin in the saline-alkali soil was a spontaneous exothermic process;With the increase of temperature,the desorption capacity of saline-alkali soil on the ciprofloxacin showed a trend of increase.With the increase of pH,the capacity of ciprofloxacin adsorption diminished constantly and the desorption capacity increased constantly.The maximum adsorption capacity was 6649.379 mg·kg^-1 when pH was 3.The adsorption capacity decreased rapidly and the desorption capacity increased rapidly when pH was above 9.The maximum desorption capacity was 1711.872 mg·kg^-1 when pH was 11.The higher ion valence state,the weaker adsorption capacity of saline-alkali soil on the ciprofloxacin: lgKf（K+）>lgKf（Na+）>lgKf(CaCl_<sup>2+)>lgKf(Mg²⁺),The higher ion valence state,the stronger desorption capacity of saline-alkali soil on the ciprofloxacin: HI（K+）<HI（Na+）<HI(Ca²⁺)<HI(Mg²⁺).The maximum adsorption capacity was 6281.227 mg·kg^-1 when the K+ was used as background solution,and the maximum desorption capacity was 583.420 mg·kg^-1 when the Mg²⁺ was used as background solution.Different concentrations of CaCl₂ were used as the background solution,with the increase of CaCl₂ concentration,the capacity of ciprofloxacin adsorption diminished constantly and the desorption capacity increased constantly.The maximum adsorption capacity was 6213.641 mg·kg^-1 when the concentration of CaCl₂ was 0.01 mol/L.Results with more than 1 of HI revealed that the desorption of ciprofloxacin in the saline-alkali soil had negative hysteresis effect.When the concentration of CaCl₂ was in the range of 0.15mol·L^-10.2mol·L^-1and the maximum desorption capacity was 2381.199 mg·kg^-1when the concentration of CaCl₂ was 0.01 mol/L.The decrease of organic content will lead to the capacity of ciprofloxacin adsorption decrease,and the capacity of ciprofloxacin desorption increase.Compared with the original soil,the adsorption capacity of ciprofloxacin decreased by 73.440¹55.073mg·kg^-1,and the desorption capacity increased by 54.607²25.485mg·kg^-1.