A mechanistic study of ciprofloxacin removal by kaolinite

• Published in: Colloids and surfaces, B, Biointerfaces B, Biointerfaces, 2011-11, Vol.88 (1), p.339-344
• Main Authors: Li, Zhaohui, Hong, Hanlie, Liao, Libing, Ackley, Caren J., Schulz, Laura A., MacDonald, Roberta A., Mihelich, Amanda L., Emard, Shannon M.
• Format: Article
• Language: English
• Subjects: Adsorption; Anti-Bacterial Agents - chemistry; antibiotics; aqueous solutions; Cation exchange; Cation exchanging; Ciprofloxacin; Ciprofloxacin - chemistry; climate; Colloids; exchangeable cations; Fourier transform infrared spectroscopy; FTIR; Hydrogen-Ion Concentration; Kaolin - chemistry; Kaolinite; Mechanism; soil; Soil (material); solubility; Spectroscopy, Fourier Transform Infrared; Surface chemistry; Transport; X-ray diffraction
• ISSN: 0927-7765; 1873-4367
• DOI: 10.1016/j.colsurfb.2011.07.011

[Display omitted] ► Kaolinite is a good adsorbent for ciprofloxacin (Cip) in aqueous solution. ► Cation exchange is the dominant mechanism for Cip adsorption. ► Cip adsorption is on the external surfaces of kaolinite. ► Solution pH had strong influence on Cip adsorption. As one of the most important soil components, kaolinite plays a vital role in transport and retention of ionizable contaminants in soils of warm and wet climate. Ciprofloxacin (Cip) is a second generation fluoroquinolone (FQ) antibiotic of high use. It has high aqueous solubility under high and low pH conditions and higher stability in soil system. In this study, the interactions between Cip and kaolinite in aqueous solution were investigated by batch experiments, XRD and FTIR analyses. Quantitative correlation between the exchangeable cations desorbed and Cip adsorbed confirmed experimentally that cation exchange was the dominant mechanism of Cip adsorption on kaolinite. Fitting of experimental data to the cation exchange model resulted in a selectivity coefficient of 27, suggesting a strong affinity of Cip on negatively charged kaolinite surfaces. At the adsorption maximum 190–200 Å 2 was available per Cip molecule, much larger than the Cip molecule area, confirming charge-limited instead of surface-limited Cip adsorption. The invariable d-spacing after uptake of different amounts of Cip suggested that the adsorption of Cip was on the external surfaces of kaolinite. As solution pH increased beyond 8, the amount of Cip adsorption decreased significantly and reached close to zero at pH 11. The high adsorption rate constant due to surface adsorption instead of intercalation and the wide distribution of kaolinite in different soils suggest that the fate and transport of Cip may be governed by the transport of colloidal sized clays.