Abstract
In this study the fluoride removal potential of nanoscale aluminium oxide hydroxide (nano-AlOOH) has been investigated. The material was produced using aluminium nitrate (Al(NO3)3.9H2O, 95%), and ammonium bicarbonate (NH4HCO3, 98%) and its density and mineralogy were investigated. A series of batch adsorption experiments were carried out to assess parameters that influence the adsorption process. The parameters considered were contact time and adsorbent dose, initial fluoride concentration, and pH. Results showed that most of the adsorption took place during the first 30 min; and equilibrium was reached at one hour contact time with an optimum adsorbent dose of 1.6 g L-1 for initial fluorideconcentration of 20 mg L-1. The removal efficiency of fluorideincreased with increase in adsorbent dosage. The fluoride removal efficiency was increased as the pH of the solution increases from pH 3 to 8, but any further increase in pH led to a decrease in fluoride removal efficiency. Maximum adsorption occurred at around pH 7 with initial fluoride concentration of 20 mg L-1. The adsorption data were well fitted to the Langmuir isotherm model with a maximum adsorption capacity of 62.5 mg F- g-1. The kinetic studies showed that the adsorption of fluoride by nano-AlOOH obeys a pseudo-second order rate equation. The intraparticle diffusion was not a rate-controlling step for the adsorption process. Thus, the overall study indicates that nano-AlOOH is an efficient defluoridating material. KEY WORDS: Nanoscale AlOOH, Defluoridation, Fluoride removal efficiency, Adsorption capacity, Adsorption kinetics, Adsorption mechanism Bull. Chem. Soc. Ethiop. 2014, 28(2), 215-227.DOI: http://dx.doi.org/10.4314/bcse.v28i2.6
Highlights
Water can be contaminated by natural or anthropogenic activities such contaminant is fluoride [1]
The X-ray diffraction (XRD) pattern (Figure 1) of nano-AlOOH shows a broad peak in the reflection angle range for two theta values between (10-15, 25-30, 35-40, 45-50 and 60-70), which indicates high crystalline order of the synthesized compound
For a given initial fluoride concentration, the removal efficiency of the adsorbent increased with increasing adsorbent dose
Summary
Water can be contaminated by natural or anthropogenic activities such contaminant is fluoride [1]. Fluoride has a narrow range between intakes that cause beneficial and detrimental health effects [3] At low concentrations, it has beneficial effects on teeth; excessive exposure to fluoride causes adverse health effects [4]. The concentrations of fluoride in the Rift Valley communities, which are supplied from boreholes, are reported between 1 and 33 mg L-1 [8]. This high fluoride content in the rift system has been related to volcanoes, high temperature, high subsurface carbon dioxide pressure and low calcium content [9]
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