可溶性腐殖酸和溶液pH对高岭土吸附诺氟沙星的影响

以DHA(可溶性腐殖酸)作为DOM(可溶性有机质)的替代目标物,研究高岭土对诺氟沙星的吸附机理以及不同ρ(DHA)下高岭土对不同存在形式的诺氟沙星吸附作用的影响. 结果表明:无论是否添加DHA,高岭土对诺氟沙星的吸附过程均符合二级反应动力学方程(R2>0.999),DHA的加入会影响吸附平衡时间,使其由24 h增至48 h; 高岭土对诺氟沙星的吸附等温线均可由Langmuir方程较好的描述. 不添加DHA时,当溶液pH在诺氟沙星的2个酸碱解离常数附近时,高岭土对诺氟沙星的吸附效果最好. 吸附模型拟合的结果表明,在试验pH范围内,诺氟沙星兼性离子(NOR±)对整体吸附的贡献最大. DHA与诺氟沙星在高岭土上的共吸附和累积吸附可促进高岭土对诺氟沙星的吸附,而DHA对诺氟沙星的增溶作用则抑制吸附. 累积吸附和增溶作用的贡献随着ρ(DHA)和pH的变化而改变,同时也与溶液中ρ(诺氟沙星)有关. 

Effects of pH and Dissolved Humic Acid on Norfloxacin Sorption to Kaolin

Studying the effects of environmental factors on norfloxacin sorption to kaolin is helpful for understanding sorption and transport of norfloxacin in soils. The static sorption experiment results showed that the sorption process of norfloxacin follows a pseudo-second-order kinetic equation (R2>0.999), regardless of the existence of dissolved humic acid (DHA). The existence of DHA reduced the sorption rate of norfloxacin, which prolonged the adsorption equilibrium time from 24 to 48 hours. The isotherms of norfloxacin sorption to kaolin were well described by the Langmuir equation. The maximum sorption of norfloxacin to kaolin can be obtained, when the solution pH values were around pK_a1 and pK_a2 of norfloxacin. The modeling sorption results indicated that the zwitterionic form of norfloxacin (NOR±) contributes most to the overall sorption in the experimental pH range. Co-sorption and cumulative sorption resulted from DHA can promote norfloxacin sorption to kaolin. Solubility enhancement of norfloxacin caused by DHA can inhibit sorption of norfloxacin. The promotion and inhibition of sorption resulted from DHA are related to the solution pH and concentrations of DHA and norfloxacin.