Fluoride ion removal from water for human supply by adsorption on activated alumina

Fluoride is an essential element in the water for human consumption, but at concentrations higher than 1.5 mg L- 1 , becomes harmful to human health. Fluoride contamination in groundwater has been recognized as a global problem. In small quantities fluoride present in the water is beneficial to human health by reducing the rate of occurrence of dental caries, particularly in children. However, excess fluoride intake can lead to several diseases such as osteoporosis, arthritis , cancer , infertility in women, brain damage , Alzheimer's syndrome, and disorders of the thyroid. For these reasons, the removal of excess fluoride from water is important in terms of public health protection. Among the various processes that may be used for removal of fluoride from water, adsorption has been extensively studied because of its low cost, simplicity of design and operation . In this context, this work aims to evaluate the removal of fluoride ions from water by adsorption on activated alumina. Significant  fluoride ion reduction, about 60%, was achieved in 30 minutes and approximately 95% when equilibrium was reached. It was observed that the greater fluoride removal capacity was obtained for the solution at pH 3. The kinetic model of pseudo-second order was what got the most satisfactory fit to the experimental data. In the interpretation of the experimental data of equilibrium, both isotherms evaluated were satisfactory. However, based on the values of the correlation coefficient (r² = 0.9966), the Langmuir isotherm showed the best fit.