In my experiment, I used activated carbon as adsorbents, Cu (II) and Pb (II) as adsorbates, contact time 1 hr, stirring speed 120 rpm, optimum pH 5, concentration 25 ppm, adsorbent dose 0.1g/200 ml, and in room temperature (it varied from 20.3-22 deg. celsius).
I have followed up a question where the effect of temperature has been questioned with respect to adsorption efficiency. And the provided answer was very well-explained and the issue of endothermic or exothermic nature of reaction was brought up.
Now I'm interested to know about my adsorption system. How do I know that my adsorption system was endothermic or exothermic?
Hi
You should do the experiments at different temperatures (25, 35, 45,45, 55) and calculate the K value at each T, then draw lnK with 1/T and get from the figure DeltaS/R as intrcept and DeltaH/R as intercept and get the values, if DeltaH is negative it is exothermic. Calculate DeltaG= -RT lnK. Send me you email I will send you a paper for me to do similar.
Hello Sirajus,
To determine whether the adsorption system id endothermic or exothermic, perform the adsorption experiments at different concentrations and at different temperatures. by looking at the results - if the adsorption increases as a function of temperature, then the system is endothermic. Vice versa is true. You can also get thermodynamic parameters from a graph of Kd versus 1/T (T in Kelvin). Check out my papers:
1. Zaynab Aly, Adrien Graulet, Nicholas Scales, Tracey Hanley, “Removal of aluminium from aqueous solutions using PAN-based adsorbents: characterisation, kinetics, equilibrium and thermodynamic studies, Journal of Environmental Science and Pollution Research (2014) 21: 3972-3986. DOI 10.1007/s11356-013-2305-6.
2. Z. Aly and V. Luca, “Uranium extraction from aqueous solution using dried and pyrolyzed tea and coffee wastes”, J. Radioanaly. Nucl. Chem., Volume 295, issue 2, (2013) pages 889-900. DOI: 10.1007/s10967-012-1851-6.
In my opinion, the adsorption process is always exothermic because we create a new liaison. I think your question should be: how to determine if your adsorption process is physisorption or chemisorption. And you can use Freundlich and Langmuir isotherms to study your system.
BR,
Thank you for your reply Mr. Le Phuc. But why do people study the thermodynamics in adsorption process of different pollutants?
