不溶性腐殖酸对环丙沙星吸附的研究

Study on adsorption of ciprofloxacin to insoluble humic acids

制备了两类不溶性腐殖酸(IHA),采用批平衡吸附试验方法探讨了水体中环丙沙星在IHA上的吸附特性。结果表明,两类IHA对环丙沙星的吸附行为均可用Freudlich等温方程描述,但钙型IHA对环丙沙星的吸附能力远强于铝型IHA。同时考察了IHA投加量、吸附时间、离子强度以及pH值对吸附的影响。在pH=5.5,环丙沙星质量浓度为15 mg/L时,钙型IHA对环丙沙星的吸附率可达95.3%,比铝型IHA吸附率高2.13倍;吸附进行24h后基本达到平衡;随着溶液中离子强度的增加,环丙沙星在钙型IHA表面的吸附量逐渐减小,吸附以阳离子交换作用为主;在pH=5.0～9.0的范围内,钙型IHA对环丙沙星的吸附系数逐渐减小,但并非呈线性下降关系。

The present paper has investigated the removal of ciprofloxacin from the aqueous solutions via its adsorption to insoluble humic acid （IHA） at different pH values and ionic strength. As is known, insoluble humic acid enjoys an excellent adsorptive ability, which can be cultivated by heating the highly soluble humic acid at 330℃ and then treated with 2 mol/L CaCl2 solution or 2 mol/L AlCl3. Batch equilibrium experiments were used to reveal ciprofloxacin adsorption on two insoluble humic acids. The results show that the adsorption of isotherms can be well defined by using the Freundlich model and ciprofloxacin, for it tends to be adsorbed more strongly on the insoluble humic acid of calcium type than on the acid of aluminum type. At the same time, we have also investigated the effects of adding volume, time, pH value and ionic strength on the adsorptive behavior of ciprofloxacin. It can thus be said that the adsorptive capacity tends to decrease in a nonlinear relation with the increase of the ionic strength and pH value. The greatest removal efficiency of ciprofloxacin by insoluble humic acid of calcium type turns out to be as high as 95.3% in aqueous solutions at pH=5.5, 2.13 times as high as that done by the insoluble humic acid of aluminum type, with the adsorption equilibrium gained within 24 hours. However, it was found that the adsorption of ciprofloxacin on insoluble humic acid of calcium type tends to decrease gradually with the increase of natural cation concentrations in solution in a nonlinear manner, which suggests that the absorptive process is mainly dominated by the cation exchange. In addition, it has been found that the adsorption coefficient of the ciprofloxacin tends to decrease with the increase of pH value in a range between 5.0 and 9.0. At the same time, we have gained quite a high and stable removing rate of ciprofloxacin on insoluble humic acid under nearly the same acid or faintly acid conditions. The above results reveal that insoluble humic acid of calcium type can be used as a potentially efficient absorbent for purifying water from the ciprofloxacin contaminants.