In my experiments of heavy metal removal from wastewater, i have obtained less value of qm (adsorption capacity, mg/g); how we can increase adsorption capacity. As it is the indicator of a good adsorbent although my adsorbent is working efficiently for higher PPM.
Dear Renu,
There are few factors which affecting the adsorption capacity of an adsorbent towards adsorbates such as heavy metal:
1-The pH of the medium
2-The particle size of the adsorbent
3-The presence of compounds which compete with the heavy metals on the adsorbent's sites.
4-The ratio of adsorbent/adsorbate
And others.
The following links contain publications which illustrate some of the factors I have mentioned above:
http://scialert.net/fulltext/?doi=rjes.2008.13.22&org=10
http://publications.lib.chalmers.se/records/fulltext/21678.pdf
http://www.ncbi.nlm.nih.gov/pubmed/16080329
Hoping this will be helpful,
Rafik
@Michael: generally, there is an optimal ratio of adsorbate/adsorbent.
Rafik
Michael is correct!
The question also requires clarity. The candidate should mention about the adsorbent. In any case, the adsorbent surface can be modified: treated suitably for surface area, functionality, etc.
Dear Renu,
For increasing the adsorption capacity, along with the factors discussed above few others also needs to be considered viz.
1. Agitation speed, as, if the adsorption is physiosorption then there may be possibilieties of leaching of the adsorbate in the reaction mixture again leading to the decrease in adsorption capacity as it is basically the weight ratio of adsorbate to the adsorbent.
2. Contact time, it also plays an important role in adsorption process, because it is necessary to estimate the equlibrium contact time, may be adsorption capacity can increase with increase in contact time if you have not performed the process until it reaches its equilibrium.
3. Reaction temperature. as mostly the adsorption phenonmenon is exothermic in nature and at some point temperature can play important role in increasing the adsorption capacity.
4. Adsorbent dose, It is the most influential parameter if you calculate the adsorption capacity, as increase in amount of adsorbent with fixed volume reaction mixture leads to increase in number of active sites available for the adsorption to takes place but simultaneously it decrease the adsorption capacity as they are inversely propotional. while removal percentage will increase.
5. As you have mentioned that the adsorbent is effective for higher PPM, I want to suggest you that Initial concentration also plays an important role, if the initial concentration is higher then there is availability of the more substrate to get adsorbed and basically provides the larger driving force for diffusion to takes place from the solution to thesurface as it is totally a mass transfer phenomenon. While if we decrease the initial concentration suppose for lower concentrations adsorption capacity will surely decrease as again the sufficient adsorbate is not able to get adsorbed on the active sites and there is also the interefence of the other ions and also the wall effects needs to be considered in adsorption process.
For further refrence you can go through my papers.
Regards
Sumit
Dear Michael,
I am not trying to obfuscate Renu, Instead, let me tell you that the above-mentioned points are very important by chemical engineering point of view and if you follow the literature it is well explained in the papers published in reputed journals. I have personally performed the experiments on adsorption for fluoride and chromium (VI) so I don't think I am confusing her. Rather it seems that you are trying to insist her to focus on the hints that you have given and I didn't found any of them more relevant excluding analysis of chromium.
@Renu, I think it is always better to consider all the factors because chemical processes like adsorption are greatly influenced by the parameters mentioned above and I suggesting you these issues from my personal experience and as a chemical engineer.
Thank you
Dear Renu,
You can increase the adsorption capacity by treatment of your adsorbent. For example if your adsorbent is an agricultural waste, you can try acid treatment or base treatment. You can also try both of them as a consecutive treatment.
You have to take into consideration that some agricultural wastes will not adsorb certain pollutants. That means you have to try different agricultural wastes.
If your adsorbent is AC you can try activating using water vapor at high temperature.
Dear Hossam Sir,
Please let me know the logic of consecutive acid and base treatment of the material. And activated carbon is already activated. Id AC shows a poor capacity, it means that we have to select another adsorbent material.
Dear Sir,
I am attaching some articles that deal with acid-base treatment. Thanks a lot for your question.
file:///C:/Users/Hossam/Downloads/208087.pdf
http://staff.ui.ac.id/system/files/users/ykrisna/publication/382-909-1-pb-atom_indonesia_-_th.pdf
http://www.tandfonline.com/doi/abs/10.1080/19443994.2012.719467?journalCode=tdwt20
http://connection.ebscohost.com/c/articles/79567868/effect-organic-inorganic-acid-pretreatment-structural-properties-rice-husk-adsorption-mechanism-phenol
https://www.hindawi.com/journals/isrn/2013/208087/
https://www.jstage.jst.go.jp/article/jswmepac/18/0/18_0_347/_pdf
By the way, I appreciate and approve the response of Prof Michael. The term 'Adsorption capacity' literally means how much of the quantity (mg) of adsorbate/contaminant can adhere to per g of the adsorbent material. By modification, we are basically changing the material also.If a cellulosic material is modified by any treatment, its surface becomes a different. If you want to test, please determine some of the surface parameters, they will have to be different.
Where is Renu who started this discussion?
Research on the Adsorption Behavior of Heavy Metal Ions by Porous Material Prepared with Silicate Tailings
By changing either the adsorbent or the process conditions (pH, T).