Uptake studies of fluoride ions from an aqueous media using triethylamine modified watermelon rind biowastes

The current study utilized triethylamine modified watermelon rind biowastes in defluoridation of water. The raw adsorbent was chemically modified using thionyl chloride and triethylamine. Both raw and modified adsorbent were characterized using Thermogravimetric Analyzer (TGA), Fourier Transform Infrared (FT-IR) and Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX). The FT-IR results showed functional groups of hydroxyl (-OH), carbonyl (-C = O), carboxylate (-COO-) (raw adsorbent) and additional anchored amine (-+N(CH2CH3)3) groups (modified adsorbent) as important adsorption sites for fluoride ions removal. The presence of nitrogen (N) element (EDX results) confirmed the modification process. The SEM results showed a more porous adsorbent which also took part in the adsorption process. Thermal stability of the modified adsorbent was up to a temperature of 400 °C. Maximum efficiency of 85.97% was obtained at optimal values of pH (1), 50 min, 70 mg and 50 mg/L. The optimal conditions were confirmed by 3D surface plots. Adsorption of the F− ions fitted Langmuir isotherm model and pseudo-second-order (R2 > 0.9) which was more suitable in explaining the chemisorption process. Water samples from Lake Baringo water reported fluoride ion concentration of 3.59 mg/L (above WHO levels) which was reduced to 0.76 mg/L. The regeneration showed a good reusability of the adsorbent with > 50% desorption efficiency. The research findings report a potential adsorbent that can be applied in defluoridation of water to safe levels both at household and industrial scale.