Investigation of various isotherm equations for mercury removal from aqueous solutions by walnut shell activated carbons

In the present investigation, the experimental data acheivied from our previous published paper were analyzed and modeled by, Sips, Toth, Unilan, Jovanovich and modified langmuir isotherms. To the best of our knowledge, Langmuir isotherm was modified and compared with various isotherm theories. Activated carbon was also prepared from walnut shell by phsical method using water vapor as the activation agent for comparison with our other carbonaceous adsorbents. The adsorption was studied by three types of activated carbon derived from walnut shell (carbon A: 1:0.5 ZnCl2 wt/wt, carbon B: 1:1 ZnCl2 wt/wt and Carbon C: Physical method). It was shown that Hg (II) adsorption follows the modified form better than the Langmuir isotherm. Langmuir assumed that each site accommodates one and only one adsorbed entity. However, it is not a precise assumption and instead the mean number of entities should be defined. The obtained equilibrium data for carbon A, B and C were modeled with Langmuir and Modified Langmuir isotherm equations. The monolayer sorption capacity of this optimum adsorbent was obtained by Langmuir isotherm as 151.5, 100.9 and 87.97 mg/g for carbon A, B and C, respectively. However, these results were determined as 174.97, 104.02 and 88.65 mg/g by modified Langmuir for carbon A, B and C, respectively.

Keywords:

Adsorption , Modeling , Isotherm , Modified Langmuir , Activated Carbon , Mercury