Date of Award
5-1-2026
Document Type
Thesis
Degree Name
M.S. in Engineering Science
First Advisor
Inoka Hasanthi Widanagamage
Second Advisor
Brian Platt
Third Advisor
Andrew O'Reilly
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Bauxite, which is the main ore for aluminum, has shown promise as a cost-effective material for removing toxic ions from contaminated water. This study evaluated the effectiveness of bauxite sourced from Pontotoc County, Mississippi, in eliminating fluoride, arsenic, and nitrate from polluted water. It also examined the factors such as the type of bauxite, surface modifications, amount of adsorbent used, initial concentrations of the contaminants, and duration of contact are influenced ion removal efficiency. Two different varieties of bauxite, one rich in kaolinite clay and the other rich in iron, were collected and tested in both their raw state and modified state; acid activation, calcination, and a combination of acid and calcination methods. Batch adsorption experiments were conducted using solutions containing fluoride, arsenic, and nitrate, and the resulting filtered solutions were analyzed through Ion Chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS).
The mineralogical composition and surface features of the bauxite were examined through X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). The XRD analysis revealed that the clay-rich bauxite primarily consisted of kaolinite (65 ± 5 wt%) and gibbsite (33 ± 5 wt%). In contrast, the iron-rich bauxite was predominantly composed of hematite (80.2 wt%), with minor quantities of phlogopite (16.2 wt%) and anatase (3.3 wt%). After undergoing acid treatment, the clay-rich bauxite exhibited an increased kaolinite concentration of 84.2 ± 1.2 wt% and a decrease in gibbsite to 10.5 ± 1.0 wt%, which is a notable change in its mineralogical composition.
Among the tested materials, acid-activated bauxite was the most effective at removing fluoride, while both raw and modified bauxite were successful in reducing arsenic levels. The fluoride removal rate increased with higher doses of the adsorbent: about 5% at a concentration of 1 g/L, roughly 25% at 5 g/L, around 45% at 10 g/L, and nearly 70% at 20 g/L, based on an initial fluoride concentration of 4 mg/L over a period of 24 hours. At a 10 g/L dosage, fluoride removal reached about 70% after 48 hours for 4 ppm, but it dropped to approximately 56% for 12 ppm. Conversely, with 20 g/L dosage, removal efficiency improved to around 95% for 4 ppm and about 60% for 12 ppm. Arsenic removal remained consistently high, exceeding 95% at 21.5 ppb and above 90% even at 353.4 ppb, with most removal occurring within the first 3 to 6 hours. In comparison, nitrate adsorption was very low across all materials and treatments, achieving a maximum removal of just 7.3% at the highest dosage tested.
The acid-treated clay-rich bauxite showed the greatest effectiveness in fluoride removal, while both the raw and modified bauxite demonstrated high efficiency in eliminating arsenic. Isotherm and kinetic studies revealed that the adsorption of fluoride and arsenic was best represented by Langmuir-type isotherms and pseudo-second-order kinetics. This indicates that the adsorption process takes place on reactive surface sites through mechanisms controlled by chemisorption. These results highlight the significant potential of Mississippi bauxite, particularly after acid activation, as an efficient and economical adsorbent for fluoride and arsenic removal.
Recommended Citation
Hewahetawaththa, Hasini Upendra Bandara, "Study of The Application of Bauxite and Optimization of Modified Bauxite for Efficient Removal of Toxic Ions from Contaminated Water" (2026). Electronic Theses and Dissertations. 8831.
https://egrove.olemiss.edu/etd/8831