Abstract
A magnesia-pullulan composite (MgOP) was previously shown to effectively remove fluoride from water. In the present study, a continuous fixed-bed column was used to examine the application of the composite at an industrial scale. The influencing parameters included bed mass (4.0, 6.0 and 8.0 g), influent flow rate (8, 16 and 32 mL/min), inlet fluoride concentration (5, 10 and 20 mg/L), reaction temperature (20, 30 and 40 °C), influent pH (4, 7 and 10) and other existing anions (HCO3−, SO42−, Cl− and NO3−), through which the breakthrough curves could be depicted for the experimental data analysis. The results indicated that MgOP is promising for fluoride removal with a defluoridation capacity of 16.6 mg/g at the bed mass of 6.0 g, influent flow rate of 16 mL/min and inlet fluoride concentration of 10 mg/L. The dynamics of the fluoride adsorption process were modeled using the Thomas and Yan models, in which the Yan model presented better predictions for the breakthrough curves than the Thomas model. Moreover, the concentration of magnesium in the effluent was monitored to determine Mg stability in the MgOP composite. Results indicated the effluent concentration of Mg2+ ions could be kept at a safe level. Calcination of fluoride-loaded MgOP effectively regenerated the material.
Highlights
Fluoride is an essential micronutrient because a trace intake of fluoride (0.4–0.6 mg/L)is helpful for normal mineralization of bones and formation of dental enamel
Volumetric flow rate and inlet adsorbate concentration are crucial for efficient column design and operation, and these factors affect the breakthrough, or discharge, of fluoride
The defluoridation capacity of magnesia-pullulan composite (MgOP) increased in acid and alkaline environments compared to the capacity at neutral pH
Summary
Fluoride is an essential micronutrient because a trace intake of fluoride (0.4–0.6 mg/L). Is helpful for normal mineralization of bones and formation of dental enamel. Excessive concentrations of fluoride in drinking water may result in a progressive crippling disease known as fluorosis. The optimum fluoride level in drinking water set by the World. Fluoride in the aquatic environment is derived mainly from natural weathering of fluorine-containing minerals such as fluorapatite and fluorite, industrial activities such as the production of glass and semiconductors, and mineral processing (Wang et al, 2017). More than 200 million people globally are exposed to drinking water containing > 1.5 mg fluoride/L (Chai et al, 2013). Fluoride contamination has serious effects on the geo-environment in many countries, and especially in developing countries (Mohan et al, 2017)
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