Hello, so I'm doing some research on clinoptilolite, a naturally made zeolite. I'm testing on its ability to treat hard water (water with high levels of magnesium/calcium), and how temperature can impact its ability to extract cations.
From my results, I can observe that as temperature increases, its ability to adsorb/extract cations decrease, and I would like some understanding as to why this could be.
Along with this, I have read that its selectivity in cations range from charge densities, where it would be Ca2+ > Mg2+, but my results don't reflect that. Could there be a reason why?
Thank you.
Dear Dr. Victoria Nguyen,
regarding the effect of temperature on adsorption by zeolite, two cases may be considerd: physiosorption or chemisorption.
Like any other equilibrium, adsorption is a process involving a true equilibrium where the two opposing processes: condensation (adsorption) and evaporation (desorption) operate. The condensation being exothermic, increasing the temperature a decreasing adsorption (and vice versa) is obtained.
Chemisorption, is a tendency of the formation a compound between the gas and the zeolite. This requires some actvation energy (analogous to every chemical reaction) which means that chemisorption, first increase with te increase in temperature, till the activated complexe between the gas and zeolite is formed.
For more details, please see the following, intersting papers:
Natural Zeolites in Water Treatment – How Effective is Their Use
Karmen Margeta, Nataša Zabukovec Logar, Mario Šiljeg and Anamarija Farkaš
Available at: https://www.google.it/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwiBzsHNnIbpAhWZ7aYKHUg2DuUQFjAAegQIAhAB&url=https%3A%2F%2Fwww.researchgate.net%2Fprofile%2FRafik_Karaman%2Fpost%2FIs_Zeolite_can_increase_the_value_of_pH_in_wastewater%2Fattachment%2F59d6319279197b807798f5d4%2FAS%253A366416336310272%25401464371870616%2Fdownload%2FZeolites.pdf&usg=AOvVaw2bKjtrEdWqe-Et79jn4aVb
Best regards, Pierluigi Traverso
A large number of parameters can influence the process of ion sorption/removal from water treatment.
1. Conductivity
2. pH value,
3. initial concentrations
4. temperature and
5. contact time
6. Zeolite mass
7. Zeolite particle size
Natural zeolites have advantages over other cation exchange materials such as commonly used organic resins, because they are cheap, they exhibit excellent selectivity for different cations at low temperatures, which is accompanied with a release of non-toxic exchangeable cations (K+, Na+, Ca2+ and Mg2+) to the environment, they are compact in size and they allow simple and cheap maintenance in the full-scale applications. The efficiency of water treatment by using natural and modified zeolites depends on the type and quantity of the used zeolite, the size distribution of zeolite particles, the initial concentration of contaminants (cation/anion), pH value of solution, ionic strength of solution, temperature, pressure, contact time of system zeolite/solution and the presence of other organic compounds and anions. For water treatment with natural zeolites, standard procedures are used, usually a procedure in column or batch process.Thermal treatment at high temperature, depending on the solid sample and temperature used can enhance pore volume by removing water molecules and organics from pore channels.
Dear Victoria,
Adsorption process mainly occurs through physisorption (through weak electrostatic forces such as van der Waal forces) or chemisorption (through chemical bonding) between the adsorbate and the surface of the adsorbent. These processes release heat when formed, and therefore are exothermic processes.
When the temperature of these adsorption process (which are exothermic) is increased, the process sees this (temperature increase) as a constraint and therefore shifts towards the backward reaction (of physisorption or chemisorption) to bring the system to equilibrium, leading to a decrease in adsorption. This is according to the Le Chatelier's principle.
Also, the extent of decrease in the adsorption ability will depend on the heat of adsorption; higher the heat of adsorption of an adsorbate-adsorbent system higher the temperature needed to decrease adsorption to a certain value.
Hope this helps!
The answer of Imranul Laskar is the most relevant and best to understand. Physisorption is an equilibrium depending of temperature.
Certainly it will be physical adsorption, which decreases with increase in temp. At higher temp London dispersion forces decreases.
Another chance may also arise in the case of zeolites "during adsorption cations may fit ito the cavities of the crystal. As temp increases cavity size increases cation may be loosely held.
Zeolites pore shape commonly referred as Honey comb or truncated octahedron.
If you apply Langmuir's adsorption isotherm model and consider that an adsorption process is thermodynamically exothermic, you can find the answer to your query.
Cordially
The motive of mass transfer between solid and liquid phases is the difference in saturation and solubility of Ions in those phases. The solubility of cations in water is a function of temperature, but the variation rate of them are different. For example it is for Na+ very low and for Ca2+ and Mg2+ is high and moderate, also not constant. Please see thermochemistry references.
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