Adsorption of fluoride by Fe-Mg-La triple-metal composite: Adsorbent preparation, illustration of performance and study of mechanisms

Consumption of drinking water containing excess fluoride can cause a series of health problems. A novel iron-magnesium-lanthanum trimetallic composite was synthesized by a co-precipitation approach for efficient treatment of fluoride in water solutions. The field emission scanning electron microscopic study showed the adsorbent was of amorphous structure and composed of the aggregated smaller particles with different sizes. The adsorption process was highly pH-dependent, and the optimal adsorption was obtained at pH 4.0. The adsorption isotherm could be well described by Langmuir equation; the maximum adsorption capacity was as high as 270.3 mg/g, much higher than most reported adsorbents. The adsorption rapidly occurred in the initial 1 h and adsorption equilibrium was established within 5 h. The presence of natural organic matters, chloride and bicarbonate had almost no effect on the fluoride adsorption. The Fourier transform infrared spectroscopy, the X-ray photoelectron spectroscopy analysis and the ion exchange experiment revealed that the uptake of fluoride was due to a complicated process including an ion exchange between the sulfate ion on the surfaces of adsorbent and the fluoride in the solution.