The Study Of Adsorption Behavior Of Three Typical Antibiotics On Attapulgite

In resent years, there have been many researches about the adsorption of antibiotics on soil, sediment and other adsorption materials, which has made a lot of meaningful achievements. But studies about the adsorption of antibiotics and coadsorption of heavy mental and antibiotics on attapulgite have not been reported. Due to the possible ecological and toxical impact of antibiotics, this paper mainly focused on the adsorption behavior of antibiotics on attapulgate-one of the most important processes in environment effecting the migration and transformation of antibiotics. Works in details:three antibiotics with different structural properties were selected as target pollutants, after exploring the adsorption dynamics and thermodynamics of antibiotics on attapulgtie and the effect of pH and foreign ions on the adsorption of three antibiotics, adsorption mechanisms of selected antibiotics were proposed on the basis of the analysis result of FTIR、XRD. Meantime, Cu2+and Mg2+were chosen as the coexistent ions, the mechanism and influence of ions on different properties of antibiotics were discussed.The main results and conclusion were as follows:(1)The adsorption pattern of doxycycline and norfloxacin could be described with Langmuir isotherm equation, while isotherm data of sulfadizine was fitted well with Freundlich isotherm equation. Adsorption capacity of doxycycline was very much pH-dependent and had a maximum value of292.3μmol·g-1at pH8.5, the solution pH increased after the equilibrium of doxycycline, for most of H*were absorbed through the protonation of doxycycline as well as exchanged with interlayer ions in attapulgite. As the increase of pH, the adsorbed norfloxacin firstly increased slowly and then decreased rapidly, but there was no obviously change for sulfadizine.The affinity of norfloxacin and doxycycline to attapulgite was much higher than that of sulfadizine.(2)The adsorption dynamics of doxycycline, norfloxacin and sulfadizine were all better fitted with pseudo-second-order kinetic model with a relatively high adsorption rate in the initial2hours. In12hours three antibiotics all basically reached equilibrium. Intra-particle diffusion might be the main rate limiting process for norfloxacin while film diffusion for sulfadizine.(3)Iron strength basically had no effect on the adsorption of doxycycline, but Mg2+could deeply decrease the adsorption of doxycycline, while K+and Na+slightly increased doxycycline’s adsorption. For norfloxacin, Cu2+could compete with norfloxacin to suppress the adsorption of norfloxacin at pH=3, while increase the adsorption of norfloxacin at pH=7and9though complexion with norfloxacin; the competition effect of Mg2+on norfloxacin would be much greater with the increase of Mg2+concentration. As in the case of sulfadizine, the introduction of Cu2+could also increase the adsorption of sulfadizine at alkaline condition and had no influence on the adsorption of norfloxacin, but Mg2+basically had no influence on the adsorption of sulfadizine.(5)The adsorption mechanism of doxycycline and norfloxacin was chemical interaction, while the adsorption mechanism of sulfadizine was physical patrition. At acid condition, cationic exchange, electrostatic interaction and hydrogen bonding might be the dominate adsorption mechanism of doxycycline. At weak alkali condition, doxycycline could be interacted with attapulgite through water bridging, coordinating with the interlayer cationic ions of attapulgite and bonding with adsorption sites of the edge of attapulgite. Ion exchange, electrostatic interaction, hydrogen bonding plus with cationic bridge and surface complex with foreign ion was the main adsorption mechanism of norfloxacin, In natural environment condition, the carboxyl and hydroxyl group of Nor can complex with Cu2+and both norfloxacin and Cu2+can also complex or bond with functional group of ATP, and finally were adsorbed in the form of Nor-Cu2+-ATP or Cu2+-Nor-ATP.