Sorption of Fluoride Ions from Aqueous Solutions Using Kenyan Kisii Soapstone and Calcium Bentonite Clay
| dc.contributor.author | Omolo, Ted David | |
| dc.date.accessioned | 2025-08-28T12:41:54Z | |
| dc.date.available | 2025-08-28T12:41:54Z | |
| dc.date.issued | 2025-06 | |
| dc.description | A Thesis Submitted in Partial Fulfilment of the Requirements for the Award of the Degree of Master of Science in Applied Analytical Chemistry in the School of Pure and Applied Science of Kenyatta University, June 2025. Supervisors 1. Ruth Wanjau 2. Damaris Mbui | |
| dc.description.abstract | Safe drinking water is scarce and has been established to be the leading source of dietary fluoride intake by humans. The amount of fluoride absorbed by humans can either be beneficial or detrimental and for that reason there is a need to control its level in water. Various methods have been applied to remove excess fluorides from water including the use of adsorption techniques, electrocoagulation and membrane filtration but they have been proved to be neither cost effective nor sustainable for low-income communities. It has also been established that the adsorption method offers the comparatively cheaper and most effective method for the defluoridation of water. Some of the adsorbents that have been used in the removal of fluorides include bone char and alum. In this study soapstone and calcium bentonite capability of offering a cheap and effective method for removal of fluorides from aqueous solutions was explored. The study was anchored on borrowed conceptual theory of structure activity relationship given the presence of hydroxides and aluminum in both minerals. The soapstone was obtained from Tabaka, Sub County in Kisii County while the bentonite clay origin was Mount Kenya National Park. The composition, heat pre-treatment and adsorption capacities of Kisii soapstone and calcium bentonite for removal of excess fluoride in water was determined. Synthetic samples tested with the adsorbents had pH values held at 5.8. Varying the temperature of heat treatment from 100 oC to 500 oC resulted in a decline in adsorption capacity of both adsorbents from 34% to 25.5% and 31.0% to 15.3% for soapstone and calcium bentonite respectively, soapstone exhibiting better heat stability. Addition of 2.5 mgL-1 , 5.0 mgL-1 and 7.5 mgL-1 chlorides into the fluoridated water resulted in reduced percentage adsorption of fluorides steadily from 32% to 16 % and 28% to 16% for soapstone and calcium bentonite respectively. However, adjusting the pH downwards improved the adsorption capacity of both adsorbents where both reached their peaks at pH of 3.6 while increasing the pH upwards to 11.6 reduced the adsorption ability of both adsorbents quite significantly from 29.41% to levels below the instruments limit of detection for calcium bentonite and 27.46% to 4.55% for soapstone. The water samples used were drawn from Kiamunyeki area, a suburb of Nakuru town and they were found to have fluorides values of between 2.9 mgL-1 to 6.2 mgL-1 which is high with respect to the WHO and (KS EAS 12, 2018) maximum allowed limit for drinking water of 1.5 mgL-1 . The test performed on these water samples indicated that the adsorbents under investigation had the capacity to remove fluorides from the water. The highest removal rate of soapstone was found to be 0.02 mgg-1 while that of calcium bentonite was found to be 0.05 mg/g both at room temperature and at the samples pH values which varied from 7.3 to 8.5. Calcium bentonite also displayed a higher fluoride adsorption capability in laboratory model water samples with 0.21 mgg-1 while soapstone had adsorption capacity was established as 0.08 mgg -1 . The results obtained from adsorption of fluorides from ground water sample indicated a fluoride level of 3.0 mgL-1 was reduced to 1.3 mgL-1 and 1.5 mgL-1 using 8 g and 1.5 g of soapstone and calcium bentonite respectively in 50 mL of the water sample. The ability to adsorb fluorides was confirmed by Fourier Transform Infrared Spectroscopy spectrum that revealed abundance of hydroxyl groups in bentonite as compared to soapstone and SEM images also depicted higher porosity of the bentonite mineral allowing more absorption of the fluoride ions in its matrix. This study therefore concludes that, Kisii soapstone and calcium bentonite can reduce fluorides from water. | |
| dc.identifier.uri | https://ir-library.ku.ac.ke/handle/123456789/31301 | |
| dc.language.iso | en | |
| dc.publisher | Kenyatta University | |
| dc.title | Sorption of Fluoride Ions from Aqueous Solutions Using Kenyan Kisii Soapstone and Calcium Bentonite Clay | |
| dc.type | Thesis |