花生壳吸附Cr(Ⅵ)动力学方程研究

On the kinetic equation of peanut shell adsorp tion chromium (Ⅵ)

通过试验对粒径介于0.25～0.50 mm的花生壳颗粒吸附Cr(VI)的动力学行为进行探讨,从吸附时间、pH值、吸附剂投加量、温度、Cr(VI)的初始质量浓度方面对吸附性能的影响进行研究。结果表明,最佳吸附条件为:Cr(VI)初始质量浓度100 mg/L,pH=2.0,振荡速度140 r/min,温度30℃。此时Cr(VI)的吸附率可达到90%以上。用Lagergren一级吸附速率方程、二级吸附速率方程及平均绝对偏离率对以上因素对吸附性能的影响数据进行处理,发现二级吸附动力学模型可以更好地描述各种影响因素条件下的吸附过程。二级吸附速率常数随着溶液pH值和Cr(VI)初始质量浓度的减小而增大。在低浓度和低pH值的条件下,Cr(VI)主要以HCrO_4^-形式存在,并且HCrO_4^+是花生壳主要吸附的Cr(VI)。二级吸附速率常数随着溶液温度的升高而快速的增加。温度对反应速率的影响可以通过Arrhenius方程来描述,所得曲线近似为直线方程,决定系数R^2=0.986 2,反应的活化能E_a为8.67kJ/mol,该反应活化能在物理吸附反应活化能范围(0～40 kJ/mol)内。

This paper takes it as its aim to present our experimental study findings on how to improve the treated peanut shell for removing heavy metals from the sewage with using Cr6＋ in the modified peanut shell. It comes from this need that we have also investigated the effects of pH value, the initial Cr6＋ concentration, adsorption time, temperature and peanut shell dosage on its adsorption effect.Under the condition of 30 ℃, it proves enough to use 1.0 g modified peanut shell, 100 mL/L Cr6＋ solution, the initial pH value 2.0, contact time 360 min, concussion speed 140 r/min to make the adsorption rate to Cr6＋ reach 98.4%. We have also found that there is a bit higher mean absolute deviation from the equilibrium adsorption by using the Lagergren first order rate equation whereas the use of the Lagergren second order tends to be kept well in accord with the equilibrium adsorption by using the rate equation. And, therefore, it can be said that the first order adsorption rate equation is improper to be used to obtain the equilibrium adsorption qe,exp and the adsorption rate constant k／-1 in the experimental process whereas its linear equation can be used very conveniently to get the second adsorption rate constant k／-2 and the equilibrium adsorption qe, which is found to increase with the decrease of pH value and Cr（VI） initial concentration. At lower concentrations of Cr（VI） and lower pH value, Cr（VI） ions tend to get adsorbed by the peanut shell mainly in the form of HCrO-／-4 in the solution. In addition, we have also found the second adsorption rate constant k／-2 increase fast with the increase of temperature, which can be described in an approximately linear form by means of the Arrhenius equation and the curve obtained. In addition, the curve correlation coefficient R2 proves to be equal to 0.986 2 with the reaction activation energy being 8.67 kJ/mol, which is within the range of the physical adsorption reaction （0-40 kJ/mol）.