Synthesis of Ce/Al/Fe Tri-Metal Oxide Modified Diatomaceous Earth /Chitosan Composite Films for Fluoride Removal from Groundwater

MENVSC

Department of Geography and Environmental Sciences

Sustainable Development Goal 6.1 calls for developing technologies to improve water quality for human consumption to ensure clean drinking water for everyone by 2030. This study aims to contribute to the goal by synthesizing Ce/Al/Fe metal oxides modified diatomaceous earth and the fabrication of Ce/Al/Fe tri-metal oxide modified DE/chitosan composite films for the adsorption of fluoride from drinking water. The results were presented in two chapters i.e. Enhancing the fluoride adsorption efficiency of diatomaceous earth through modification by Ce/Al/Fe metal oxides and Synthesis of Ce/Al/Fe tri-metal oxide modified DE/chitosan composite films for fluoride removal from groundwater. The first chapter of results focused on enhancing the fluoride adsorption efficiency of diatomaceous earth through modification by Ce/Al/Fe metal oxides. Adsorption experiments were performed to determine the efficiency of the Ce/Al/Fe metal oxides modified diatomaceous earth in fluoride removal. About 98% fluoride removal efficiency was obtained from an initial fluoride concentration of 5 mg/L using 0.6 g/100 mL adsorbent dosage at an initial pH range of 7 after 50 mins’ agitation time. The adsorption kinetics models revealed that fluoride adsorption occurred via chemisorption, while the isotherm models confirmed both monolayer and multi-layer adsorption. Thermodynamic studies showed that the adsorption process was spontaneous, endothermic, and random, as denoted by the negative ΔG˚, positive ΔH˚, and positive ΔS˚, respectively. Regeneration studies showed that Ce/Al/Fe metal oxides modified diatomaceous earth can be reused for 8 successive regeneration-reuse cycles. This study revealed that modification of diatomaceous earth with Ce/Al/Fe metal oxides enhances the adsorption of fluoride and the material has the potential for use in defluoridation of groundwater. The synthesized adsorbent in the first chapter had low permeability due to its fine particle size which limits its applicability in a column set-up. Therefore, there was a need to further modify the synthesized adsorbent. The second chapter of results aimed to synthesize the Ce/Al/Fe tri-metal oxide modified diatomaceous earth-chitosan composite films for removal of fluoride from drinking water. The modified DE/chitosan films were developed using the casting method. The functional groups, elemental composition and morphology of the synthesized material were characterized using Fourier Transform Infrared (FTIR) and scanning electron microscopy-energy dispersion X-ray (SEM-EDX), respectively. Batch experiments were conducted to evaluate the effectiveness of the material in fluoride removal. The results showed 7.89 mg/g adsorption capacity towards fluoride from 5 mg/L initial fluoride concentration, when adsorbent dosage of 0.3 g/100 mL was used at initial pH range of 7 after 50 mins agitation time at shaking speed of 200 rpm. The data for adsorption kinetics showed a better fit to pseudo-second order which indicates that the adsorption mechanism was chemisorption. The adsorption isotherm model data best fitted to Langmuir isotherm model which suggests that the adsorption took place on a monolayer surface. The presence of co-existing anions such as Cl-, SO42-, CO32- and NO32- reduces the fluoride removal efficiency of the material. The Ce/Al/Fe tri-metal oxide modified DE/chitosan composite films showed lower adsorption capacity relative to Ce/Al/Fe tri-metal oxide modified DE. Based on the results obtained, the synthesized Ce/Al/Fe tri-metal oxide modified DE/chitosan composite films can be used for Groundwater defluoridation. It is therefore recommended that future studies further modify Ce/Al/Fe tri-metal oxide modified DE/chitosan composite films to enhance their fluoride affinity. Furthermore, future studies should evaluate Ce/Al/Fe tri-metal oxide modified DE/chitosan composite films performance in a column set-up and further evaluate their anti-microbial potency.