纳米γ-Fe2O3对汞离子的吸附行为研究

为了研究用于含汞离子废水处理的新型高效材料,研究了纳米γ-Fe₂O₃对汞离子的吸附行为。探讨pH值(3、8和12)、温度(288 K、298 K、308 K、318 K)和离子强度(Ca²⁺,0.001 mol/L、0.01 mol/L、0.1 mol/L)对该吸附的影响。使用吸附动力学方程(拉格朗日准一级、准二级)和等温吸附方程(Langmuir和Freundlich)分别对吸附数据进行拟合,并讨论吸附机理。结果表明:pH值为3、8、12时,纳米γ-Fe₂O₃对汞离子的吸附动力学方程符合准二级动力学模型(R2=0.997~0.999);288 K、298 K、308 K、318 K时,纳米γ-Fe₂O₃对汞离子的吸附过程更符合Langmuir吸附模型(R²=0.970~0.995),并且随温度升高,吸附量增加;在不同pH值下,纳米γ-Fe₂O₃对汞离子的吸附等温式可使用Langmuir模式(R²=0.983~0.996)进行表征,随p H值降低,吸附量减少,中性环境有利于吸附;在不同Ca²⁺浓度下,可用Langmuir等温吸附式拟合(R²=0.990~0.996)。通过Langmuir等温吸附式推算出最大吸附量随Ca²⁺浓度增加而减少。

Investigation on the adsorption behav-ior of nano-γ-Fe2O3 for mercury

In order to introduce an efficient absorbent for removing mercury from the aqueous solution,the given paper has made an investigation of the adsorption of mercury on the nano-γ-Fe₂O₃ by doing a batch of experiments on the effects of the contact time on the adsorption.The data we have gained tend to be regressive with the pseudo-1-st-order kinetic equation,and the pseudo-2-nd-order kinetic equation.What is more,we have also investigated the impacts of pH values of 3,8 and 12,as well as the temperatures involved (say,288 K,298 K,308 K and 318 K),in addition to the ionic strength (Ca²⁺,0.001 mol/L,0.01mol/L and 0.1 mol/L),for the isotherm adsorption.The investigation results in the data form can then be regressed with the Langmuir and Freundlich equations,which also indicate that,when the pH values turn to be from 3,8 to 12,it would be easy to describe the adsorption kinetics of the nano-γ-Fe₂O₃ on the mercury in accordance with the pseudo second order kinetic equation (R²=0.997-0.999.This may suggest that the adsorption process of Hg²⁺ on the nano-Fe₂O₃ should be attributed to the chemical adsorption.And,then,with the decrease of the pH value,the amount of the adsorptive matter would become decreased.This may suggest that,in the acidic solution,there may exist somewhat quick diffusions of Hg²⁺ due to the repulsion between H+ and Hg²⁺.And,when the pH os equal to 8,the quick adsorption has been accomplished in 5 minutes due to the high temperature of the pH value of the solution,the iron oxide surface may then tend to be charged negatively due to the disprotonality,which can help to promote the adsorptive power of the positively charged Hg²⁺.At the same time,with the increase of pH value,negative charge on the surface of the iron oxide may tend to drop down,and,consequently,to result in the decrease of the adsorption capacity of Hg²⁺s.And,then,at the temperatures of 288 K,298 K,308 K and 318 K,it would be possible for the adsorption process of mercury to be made consistent with the Langmuir adsorption model (R²=0.970-0.995) under the impact of nano-γ-Fe₂O₃.And,then,with the increase of the temperature,the amount of the adsorption may tend to rise up,too.And,then,furthermore,the process can be speeded up for the process to be dominated by the chemisorption and the increase of the temperature.Nevertheless,with the increase of the temperature,the adsorption to the outer surface and the inner surface of nano-Fe₂O₃ can be made up approximately saturated,so that the amount of the adsorption may remain unchanged.And,consequently,at the different Ca²⁺ concentration rates,the isothermal adsorption (R²=0.990-0.996) may turn to be promoted with the help of Langmuir formula.In such a situation,it would be possible to work out the maximum adsorption amount by the reduction of the Langmuir isotherm adsorption due to the increase of the Ca²⁺ concentration,for,the high concentrations of Ca²⁺ can help to compete with Hg²⁺ for the adsorptive site on the nano-γ-Fe₂O₃.