Aksu Z, Kabasakal E
Department of Chemical Engineering, Hacettepe University, Ankara, Turkey.
J Environ Sci Health B. 2005;40(4):545-70. doi: 10.1081/PFC-200061533.
The removal of 2,4-dichlorophenoxyacetic acid (2,4-D), one of the most commonly used phenoxy acid herbicides, from aqueous solution was studied by using acid-washed powdered activated carbon (PAC) as an adsorbent in a batch system. Adsorption equilibrium, kinetics, and thermodynamics were investigated as a function of initial pH, temperature, and initial 2,4-D concentration. Powdered activated carbon exhibited the highest 2,4-D uptake capacity of 333.3 mg g(-1) at 25 degrees C and an initial pH value of 2.0. Freundlich, Langmuir, and Redlich-Peterson isotherm models were used to express the equilibrium data of 2,4-D depending on temperature. Equilibrium data fitted very well to the Freundlich equilibrium model in the studied concentration range of 2,4-D at all the temperatures studied. Three simplified models including pseudo-first-order, pseudo-second-order, and saturation-type kinetic models were used to test the adsorption kinetics. It was shown that the adsorption of 2,4-D on PAC at 25, 35, and 45 degrees C could be best fitted by the saturation-type kinetic model with film and intraparticle diffusions being the essential rate-controlling steps. The activation energy of adsorption (EA) was determined as--1.69 kJ mole(-1). Using the thermodynamic equilibrium coefficients obtained at different temperatures, the thermodynamic constants of adsorption (deltaG degrees, deltaH degrees, and deltaS degrees) were also evaluated.
采用酸洗粉末活性炭（PAC）作为吸附剂，在间歇系统中研究了从水溶液中去除2,4-二氯苯氧乙酸（2,4-D）（一种最常用的苯氧羧酸类除草剂）的过程。研究了吸附平衡、动力学和热力学与初始pH值、温度和初始2,4-D浓度的关系。在25℃和初始pH值为2.0时，粉末活性炭对2,4-D的吸附容量最高，为333.3 mg g(-1)。采用Freundlich、Langmuir和Redlich-Peterson等温线模型来表达2,4-D在不同温度下的平衡数据。在所有研究温度下，在所研究的2,4-D浓度范围内，平衡数据与Freundlich平衡模型拟合得非常好。采用包括准一级、准二级和饱和型动力学模型在内的三种简化模型来测试吸附动力学。结果表明，在25、35和45℃下，2,4-D在PAC上的吸附最适合用饱和型动力学模型，膜扩散和颗粒内扩散是主要的速率控制步骤。吸附活化能（EA）测定为-1.69 kJ mole(-1)。利用不同温度下获得的热力学平衡系数，还评估了吸附的热力学常数（ΔG°、ΔH°和ΔS°）。
