改性荞麦壳对水溶液中Cu^(2+)离子吸附效果及机理

Adsorption of Cu^(2+) from aqueous solution by modified buckkwheat shell and study on its mechanism

以柠檬酸对荞麦壳进行化学改性,改性后荞麦壳吸附剂对Cu2+的吸附量增加。研究了不同pH、吸附剂投入量、浓度和时间对吸附效果的影响。在pH值为5.5,Cu2+初始浓度50 mg/L,吸附剂投入量为1 g,吸附时间为120 min的条件下,Cu2+的吸附量达到较大值。通过用改性荞麦壳吸附剂对Cu2+的热力学吸附过程的分析,结果表明,改性荞麦壳吸附剂符合Langmuir吸附等温模式,改性荞麦壳吸附剂对Cu2+的吸附存在化学吸附,改性荞麦壳的最大吸附量可以达2.26 mg/g。研究改性荞麦壳吸附剂吸附Cu2+的动力学特性,吸附动力学行为可用准二级速率方程进行很好的描述,准二级吸附速率常数随温度升高而增大。准一级速率方程和颗粒扩散模型可以较好地描述吸附初始阶段,Cu2+浓度较高,颗粒内扩散;吸附后期,Cu2+浓度较低,受到颗粒外扩散的控制。总之,整个吸附过程可能是多种动力学机理共同作用的结果。

In this study,the buckwheat shell was chemically modified by using citric acid,which compared with the raw buckwheat shell,increased its Cu2 +absorption. Effects of various parameters,including the pH, the initial Cu2 +concentration,and the absorption duration were also evaluated to determine the optimal conditions for Cu2 +removal. The results showed that the Cu2 +absorption reached the maximum under the conditions of pH of 5. 5,an initial Cu2 +concentration of 50 mg/L,1 g of the adsorbent,and 120 min for absorption duration. Sorption isotherms were also studied,which revealed that equilibrium sorption data were well represented by Langmuir model and the maximum sorption capacity of the modified buckwheat shell was found to be 2. 26 mg/g. Furthermore,results of the effect of adsorption kinetics of Cu2 +onto modified buckwheat shell existed good correlations with the experimental data in pseudo-second-order equation. The rate constant of pseudo-second-order equation increased with increasing temperature. The pseudo-first-order model and the particle diffusion model can well describe the initial stage of adsorption; the particle diffusion,occurred with relative high concentration of Cu2 +,which would be restricted when the Cu2 +concentration was relatively low. Taken together,these results demonstrated that the whole absorption process is probably a result of the combination of various dynamic mechanisms.