环丙沙星在盐碱土中吸附特性的研究

采用OECD guideline 106批平衡吸附法研究环丙沙星在碱土中的等温吸附特性、吸附动力学、吸附热力学以及pH值和Ca~(2+)浓度对其吸附的影响。结果表明环丙沙星在盐碱土中的吸附较好地符合Freundlich方程(拟合系数R~2=0.981),不同初始浓度的环丙沙星在盐碱土中的吸附过程符合准二级动力学方程,吸附常数为1.17×10~(-3)~5.67×10~(-3)kg·min~(-1)·m L~(-1)。吸附过程可分为快速吸附和慢速平衡两个阶段,初始浓度分别为80、100、120 mg·L~(-1)的环丙沙星吸附平衡时间为24 h,平衡吸附比例分别为89.9%、92.2%、92.7%。吸附热力学参数ΔG0且ΔH=-3.58 5 k J·mol~(-1),表明环丙沙星在盐碱土上的吸附为自发的放热反应。随着溶液pH值的升高,盐碱土对环丙沙星的吸附能力不断减弱,当pH9后吸附能力快速减少。以不同浓度CaCl_2作为背景液,环丙沙星在盐碱土中的等温吸附曲线用Freundlich方程拟合效果较好,lgKf值随着CaCl_2背景溶液浓度的增加而减小,且环丙沙星初始浓度较小时其所受离子强度的影响相对较小。

Adsorption characteristics of ciprofloxacin on saline-alkali soil

Adsorption isotherms, adsorption kinetics and adsorption thermodynamics of ciprofloxacin on a saline-alkali soil were investigated by batch equilibrium studies according to DECD Guideline 106. The effects of pH and Ca2+concentration on adsorption process were also examined. Results indicated that the adsorption isotherm of ciprofloxacin was well fitted to the Freundlich equation, with correlation constant R2 of 0.981. The kinetics of ciprofloxacin adsorption by saline-alkali soil at different initial concentrations was in accordance with the pseu-do-second order kinetic equation, with adsorption constant of 1.17í10-3~5.67í10-3 kg·min-1·mL-1. The whole process of ciprofloxacin ad-sorption by soil can be divided into two stages:the fast adsorption and the slow equilibrium. The adsorption equilibrium time of ciprofloxacin at initial concentrations of 80 mg·L-1, 100 mg·L-1 and 120 mg·L-1 was 24 h. The equilibrium adsorption ratios were 89.9%, 92.2% and 92.7%, respectively. The△H values of-3.585 kJ·mol-1 and negative△G values revealed that the adsorption of ciprofloxacin on the saline-alkali soil was a spontaneous exothermic process. The capacity of ciprofloxacin adsorption decreased constantly with increasing pH, and re-duced drastically when pH was above 9. At different concentrations of CaCl2 as background solution, the isothermal adsorption curves of ciprofloxacin by saline-alkali soil were well described by the Freundlich equation. The lgKf values decreased with the increase of CaCl2 concentration. The impact of ionic strength on ciprofloxacin adsorption was less when its initial concentrations were lower.