天然及CaCl_2改性沸石对四环素的吸附

Adsorption of tetracycline on natural and CaCl_2-modified zeolites

通过静态吸附实验研究了水中四环素在天然和CaCl2改性沸石上的吸附行为及机制。实验表明,天然沸石对四环素具有吸附能力,CaCl2改性可以提高沸石对四环素的吸附能力。天然和改性沸石对四环素的吸附符合拟二级动力学模型,颗粒内扩散不是吸附过程的主要控制步骤。Freundlich和Dubinin-Radushkevich(D-R)等温吸附模型可以较好地描述实验所用2种沸石对四环素的吸附行为,D-R等温方程拟合结果显示吸附过程包含离子交换作用。通过对天然和改性沸石吸附四环素前后溶液中主要阳离子浓度变化分析证实了该吸附过程包含离子交换作用。实验研究了pH值变化对沸石吸附四环素的影响,当pH=3～5时,天然和改性沸石对四环素的吸附量均随pH值的增加而急剧下降,而pH=5～10时,天然和改性沸石对四环素的吸附量变化均不明显,推测可能是离子交换作用和化学沉淀吸附作用所致。另外,实验还初步探索了溶液离子强度对沸石吸附四环素的影响情况,随着溶液中Na+和Ca2+离子强度的增加,吸附量先急剧降低随后趋向平稳,进一步说明了沸石对四环素的吸附过程不是由单一机制控制的。

The adsorption of tetracycline（TC）on natural and CaC12-modified zeolites was conducted under varied pH and ionic strength conditions. Adsorption kinetics and adsorption equilibrium isotherms were investiga- ted by conducting series of batch experiments. The results showed that CaC12-modified zeolite exhibited higher adsorption capacity than natural zeolite. The kinetic studies indicated that the pseudo-second-order kinetic model well described the adsorption of tetracycline onto natural and CaC12-modified zeolites, and intraparticle diffusion was not the only limiting mechanism in the adsorption process. The results from adsorption equilibrium studies indicated that the Freundlich and Dubinin-Radushkevich（D-R） isotherm models were well fitted to experimental data, the D-R model suggested that the process was mainly dominated by the ion exchange. The analysis results of the major cations in solution before and after the adsorption of tetracycline on nature and CaC12-modified zeo- lites confirmed that the adsorption process involves ion exchange. The adsorption capacity decreased rapidly when pH increased from 3 to 5 and basically constant when pH increased further, we speculated that it may be caused by ion exchange function combined with chemical precipitation adsorption. Tetracycline adsorption quantity first reduced and then remained stable along with Na ＋ and Ca2 ＋ ionic strength increased, which further confirmed that the adsorption was not only a single mechanism controlled.