Treatment of fluoride-contaminated water. A review

International audienceDelivering the right amount of fluoride to drinking water protects the teeth from decay and reduces the risk of cavities. Nonetheless, fluorosis has been diagnosed as the result of excessive exposure of fluoride, which induces brain impairment, muscle disorders and hyperactivity. Fluoride ingestion during the formation of the tooth enamel is the main reason for fluo-rosis, which is characterized by hypomineralization. Dissolution of fluoride-containing rock minerals contributes to naturally occurring fluoride contamination in water. The intentional addition of fluoride to water in dental care is alarming in growing countries such as India. This article reviews the origin of fluoride, the analysis of fluoride derivatives and the technologies to remove fluoride from water. The manuscript presents adsorption techniques for fluoride removal, using different types of adsorbents. The adsorption capacities of adsorbents under various conditions, such as contaminant concentration, adsorbent dosage, time, pH and temperature, are presented. Adsorbent types include alumina, zeolites, organic waste, shell-based and carbon-based including graphite and carbon nanotubes. Defluoridation of water using clays and muds, modified activated alumina, chitosan derivatives and composites are also discussed

Ultrasonic Functionalized Egg Shell Powder for the Adsorption of Cationic Dye: Equilibrium and Kinetic Studies

The present research focuses on synthesizing surface-modified egg shell powders using ultrasonic modification method for the effective adsorption of malachite green dye (MG). The presence of functional groups and surface morphology of ultrasonic-assisted egg shell powder (UAESP) was characterized using Fourier transform infrared spectrophotometer (FTIR) and scanning electron microscopy (SEM) analysis, respectively. A batch adsorption study was performed to predict the optimum conditions, and the results showed that maximum adsorption rate at the solution pH of 8.0 within the interaction time of 90 min, dosage of 1.5 g/L for MG dye concentration of 25 mg/L, and temperature 30°C. The isotherm and kinetics modeling of the present adsorption system can be well described by Freundlich and pseudosecond-order kinetics, respectively. The monolayer adsorption capacity of UAESP for MG dye was originated to be 64.58 mg/g. The results of the thermodynamic study reported that adsorption removal of MG dye onto UAESP was exothermic and spontaneous. This study accredited that UAESP has higher efficiency, cost-effective, and sustainable adsorbent for the removal of hazardous dyes on an industrial level

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