改性稻草对Cr(Ⅵ)的吸附动力学

Adsorption kinetics of Cr(Ⅵ) onto modified rice straw

以氢氧化钠作为预处理剂,以环氧氯丙烷作为醚化交联剂,以三甲胺作为季铵化反应剂,对原稻草进行改性;比较改性前后稻草的吸附效果,探究pH对吸附效果的影响以及不同初始浓度、温度条件下改性稻草吸附Cr(Ⅵ)的动力学特性.结果表明,改性稻草对Cr(Ⅵ)的吸附量得到很大提高;pH值在2.0—6.4之间时,Cr(Ⅵ)的吸附量达到最大值,本实验选择pH=6.4;不同Cr(Ⅵ)初始浓度和不同温度下,准二级速率方程相关系数R2的范围为0.9562—0.9982,证明准二级速率方程能够很好地描述改性稻草对Cr(Ⅵ)的吸附过程,准二级速率方程的吸附速率常数k2随温度的升高而增大;准一级速率方程只适合描述Cr(Ⅵ)吸附过程的初始阶段,吸附过程受颗粒内扩散的控制;稻草秸秆通过化学改性制成表面有季铵基的氯型吸附剂,Cr(Ⅵ)的阴离子与改性稻草上的氯离子交换从而得以去除.

In this paper,rice straws were modified using sodium hydroxide as a pretreatment agent,oxygen-chloropropane for etherification,trimethylamine as a quaternary ammonium reagent.A comparison of the adsorption ability between raw and modified rice straw was also made.The effect of pH on the adsorption rate and adsorption kinetics of Cr（Ⅵ） onto modified rice straw were investigated under different intial Cr（Ⅵ） concentrations and different temperatures.The results showed that,compared with the raw rice straw,adsorption capacity of the modified straw adsorbent for Cr（Ⅵ） was greatly improved.At pH between 2.0 to 6.4,the amount of adsorbed Cr（Ⅵ） reached maximum.At pH 6.4,correlation coefficient R2 of pseudo-second-order rate equation was 0.9562—0.9982 under different intial Cr（Ⅵ） concentrations and different temperatures.The pseudo-second-order equation provided the best correlation to the experimental data and correlation coefficient R2 increased with increasing temperature.The pseudo-first-order equation was only suitable for the description of Cr（Ⅵ） sorption process in the initial stage.The adsorption was controlled of the intra-particle diffusion model.Amino groups and chloride ions were introduced to the rice straw structure after chemical convertion.In addition,the positive relationship between adsorbed Cr（Ⅵ） and desorbed Cl-suggested that Cr（Ⅵ） was mostly removed by ion exchange with chloride.