阳离子交换树脂对NH_4^+的吸附热力学与动力学研究

Investigation on kinetics and thermodynamics of removal of NH_4^+ adsorption on cation exchange resin

采用静态吸附法,研究了NH4+在阳离子交换树脂上的吸附行为,并从热力学和动力学两方面对吸附过程进行了分析。结果表明,NH4+为200～1 000mg/L时,强酸性阳离子交换树脂001×7的NH4+吸附容量大于D001、D113树脂;在实验温度下,采用Langmuir吸咐等温模式能够更好地描述NH4+在001×7树脂上的静态吸附行为,001×7树脂对NH4+的交换吸附属于单分子层吸附;常温(25℃)时,001×7树脂吸附NH4+过程的焓变(ΔH)大于零,说明NH4+进入树脂后与H+的交换反应为吸热反应,升温有利于反应的进行,此吸附过程的熵变(ΔS)也大于零,说明该离子交换过程属于熵增的过程,此吸附过程的吉布斯自由能变(ΔG)小于零,说明该离子交换过程能够自发进行;吸附动力学研究表明,液膜扩散是001×7树脂对NH4+吸附的限速步骤,吸附交换过程符合Lagergren准一级动力学方程;4%(质量分数)NaOH溶液较适合作为001×7树脂的再生液,经过5次再生后,001×7树脂的吸附量只下降了8.8%。

The static adsorption experiments were conducted to study the behavior of NH4^＋ adsorption on cation exchange resin from thermodynamics and kinetics aspect. The experimental results showed that, when NH4^＋ ranged 200-1 000 mg/L, the NH＋ adsorption capacity of strong-acid cation exchange resin 001 ×7 was larger than that of D001, D113 resin. The experiment data of NH4^＋ adsorption on 001 ×7 resin could be well fitted by Langmuir iso- therm; the adsorption process belonged to monolayer adsorption reaction; the positive enthalpy change （AH） consist with the endothermic ion-exchange process, so increasing the temperature could enhance NH4^＋ adsorption on 001 ×7 resin. The thermodynamics parameter （△S〉 0, △G〈0） showed that the adsorption was spontaneous running in which entropy was increased. Kinetic analysis showed that the adsorption rate was mainly governed by liquid film diffusion. The ion-exchange kinetics was tested with the Lagergren （pseudo） first-order and （pseudo） second-order reaction models. The （pseudo） first-order kinetic model provided the best correlation of the experimental data compared to the （pseudo） second-order model; 4% （mass ratio） NaOH was a appropriate solution for 001×7 resin regeneration, the adsorption capability of 001 ×7 resin reduced 8.8% after five times of regeneration.