Chatterjee Sudipta, Woo Seung Han
Department of Chemical Engineering, Hanbat National University, Yuseong-Gu, Daejeon, Republic of Korea.
J Hazard Mater. 2009 May 30;164(2-3):1012-8. doi: 10.1016/j.jhazmat.2008.09.001. Epub 2008 Sep 5.
A physico-chemical investigation of the adsorption of nitrate by chitosan hydrobeads was conducted. The adsorption of nitrate by chitosan hydrobeads was increased with a decrease in the pH of the solution. The adsorption process was found to be temperature dependant with an optimum activity at 30 degrees C. Adsorption capacity was found to decrease with increases in temperature after 30 degrees C, indicating the exothermic nature of this process. Theoretical correlation of the experimental equilibrium adsorption data for the nitrate-chitosan hydrobeads system was properly explained by the Langmuir isotherm model. This was supported by the fact that homogeneity index was close to unity (0.98-1.08) from Langmuir-Freundlich isotherm model. The maximum adsorption capacity was 92.1mg/g at 30 degrees C. The kinetic results corresponded well with the pseudo-second-order rate equation. Intra-particle diffusion also played a significant role at the initial stage of the adsorption process. Thermodynamic parameters such as the Gibbs free energy (DeltaG(0)), enthalpy (DeltaH(0)), and entropy (DeltaS(0)) for the nitrate adsorption were estimated. Results suggest that the adsorption process is a spontaneous, exothermic process that has positive entropy. Desorption of nitrate from the loaded beads was accomplished by increasing the pH of the solution to the alkaline range, and a desorption ratio of 87% was achieved around pH 12.0.
对壳聚糖水凝胶珠吸附硝酸盐进行了物理化学研究。壳聚糖水凝胶珠对硝酸盐的吸附随着溶液pH值的降低而增加。发现吸附过程与温度有关，在30℃时活性最佳。30℃后，吸附容量随温度升高而降低，表明该过程具有放热性质。Langmuir等温线模型很好地解释了硝酸盐 - 壳聚糖水凝胶珠体系实验平衡吸附数据的理论相关性。Langmuir - Freundlich等温线模型的均一性指数接近1（0.98 - 1.08）支持了这一点。30℃时最大吸附容量为92.1mg/g。动力学结果与伪二级速率方程吻合良好。颗粒内扩散在吸附过程的初始阶段也起重要作用。估算了硝酸盐吸附的热力学参数，如吉布斯自由能（ΔG(0)）、焓（ΔH(0)）和熵（ΔS(0)）。结果表明吸附过程是一个自发的、放热的且具有正熵的过程。通过将溶液pH值提高到碱性范围实现了负载珠上硝酸盐的解吸，在pH 12.0左右实现了解吸率87%。
