Defluoridation Of Water By Adsorption With Triethylamine Modified Maize Tassels

ABSTRACT 

Lack of access to safe drinking water is a major concern due to negative health effects experienced by people in many parts of the world. The quality of such waters is mainly affected by pollutants from natural and anthropogenic sources when they get incorporated in the water sources. These pollutants are either organic or inorganic species. Among the inorganic pollutants are fluorides. Continuous consumption of high concentrations of fluoride ions leads to their accumulation in the body tissues which causes dental fluorosis, skeletal fluorosis and other non-skeletal disorders. These health effects are irreversible and the only way to overcome them is by removing fluoride from water. Several methods for the removal of fluorides in water have been proposed, most of which rely on the use of biomaterials and bone char. In such processes, the adsorbents become loaded with the pre-concentrated pollutants leading to disposal problems. This study reports on the modification of the maize tassels with triethylamine followed by its subsequent application on the removal of fluoride ions from water. The maize tassels were collected, washed, dried, ground and then modified with triethylamine. Modification was carried out in two steps which included chlorination of maize tassels using thionyl chloride followed by amination using triethylamine. The modified and unmodified biomaterial were characterised using FTIR (Fourier transform infrared) spectrophotometer and then used in the removal experiments on both model solutions and water sample from Lake Baringo. The effects of pH, contact time, initial fluoride concentration and modified biomaterial resin dosage on removal of fluoride were investigated. The experimental data were analysed using Langmuir and Freundlich isotherms. FTIR spectrophotometer results confirmed the presence of the anchored functional group on the maize tassels. The removal of fluoride by the modified biomaterial increased with increase in concentration up to an optimum of 60 mg/L. The optimum pH and time were found to be 4.0 and 20 min, respectively. The biomaterial was very effective in fluoride removal as 86% was removed within the first 20 min in model solution containing 20 mg/L of fluoride. The amount adsorbed on the modified biomaterial increased with increase in the modified biomaterial dosage. The uptake of fluoride however, in real water sample from Lake Baringo was found to be slightly lower compared to the experimental water. The experimental data fitted best in the Langmuir isotherm with an adsorption capacity of 5.26 mg/g. This implied a monolayer chemisorption process. It was also found that when the adsorbent was packed in a SPE column, it could be regenerated by stripping the attached fluoride ions with dilute hydrochloric acid. The theory underlying the removal method was based on the interaction of the permanently charged quaternized material with the highly electronegative fluoride ion. This is a regeneratable, eco-friendly and sustainable water remediation method of this toxic water pollutant.