The emerging interest in fluoride-removal from wastewater has attracted attention to zeolite since it has been considered as a natural adsorbent. However, the fluoride-removal efficiency of natural zeolite is generally low. As part of the effort to improve the zeolite adsorption efficiency, we have produced and tested the Mn-Ti modified zeolite. In the current work, the material preparation is discussed, and prepared materials were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy, and Fourier transform infrared (FTIR) spectra. Both static and dynamic experiments were conducted to examine the effects of independent variables. In the static adsorption section, sensitivity analysis experiments were conducted for independent variables, such as adsorbent dosage, pH, temperature, and competitive ions. The maximum adsorption capacity is 2.175 mg/g, which was obtained at PH = 7, temperature = 25 °C, and initial fluoride concentration = 10 mg/L. For adsorption kinetics, both Lagergren and Pseudo-second order models predict the experiments very well, which probably demonstrates that the current process is a combination of physical sorption and chemisorption. For adsorption isotherms, the Freundlich model performs better than the Langmuir model since it is usually applied to illustrate adsorption on inhomogeneous surfaces. In the dynamic adsorption section, sensitivity analysis experiments were also conducted for independent variables, such as adsorbent thickness, flow velocity, initial fluoride concentration, and PH. Additionally, the adsorption mechanism is also discussed. The main reason is the hydrated metal fluoride precipitate formation. As we know, the current work provides the first quantified comparison of the natural zeolite and the Mn-Ti modified zeolite regarding fluoride-removal efficiency.

Excessive fluoride in mine water has become a major concern because it can cause detrimental effects to human health. Nevertheless, the removal efficiency of traditional adsorbents is far from satisfactory. Herein, La and Fe bimetallic supported zeolite was synthesized by co-precipitation method, for efficient defluoridation. The defluoridation performance of La-Fe zeolite was studied by a batch adsorption experiment and dynamic adsorption column test. Results indicated that the removal efficiency of F− was 99.04% under the optimal conditions (4 h, adsorbent dosage 8.0 g/L, agitation rate 200 rpm/min, temperature 298K and pH = 6 ± 1) that were determined through the batch adsorption experiments. CO32− and HCO3− can inhibit the defluorination effect of La-Fe zeolite. The adsorption of fluoride ions on La-Fe zeolite can be well described by the Langmuir adsorption model, and the maximum fluoride ion adsorption capacity is 2.64 mg/g. The test of dynamic adsorption column shows that the adsorption efficiency of F− by La-Fe zeolite on was higher than 85% for continuous adsorption of 9 h, indicating that La-Fe zeolite has good practical applications. The mechanism analysis indicated that the adsorption of fluoride ion by La-Fe modified zeolite involves both ion exchange and complexation, which belongs to the physicochemical process.

This study presented an original study on the F- removal by Fe and Zr doped Gismondine-dominated Zeolite. Various modified zeolites are prepared by systematically adjusting the synthesis variables, namely pH, mass ratio of zeolite to modify agent (mZeolite:m(Fe+Zr)), mass ratio of Fe to Zr (Fe:Zr) to investigate their effects on the F- adsorption. The performance of prepared Fe-Zr-Zeolite on F- removal was examined through both statistic adsorption and dynamic adsorption. Results indicated that when the modified pH was 7, the Fe:Zr ratio was 1:1 and mZeolite:m(Fe+Zr) was 1:2, the modified natural zeolites which was named Fe-Zr-Zeolite showed the best removal efficiency on F-. Fe-Zr-Zeolite could remove over 80% when the initial concentration was less than 20 mg/L and F- adsorption followed pseudo-second-order adsorption kinetic and Langmuir adsorption isotherm, indicating that F- adsorption by Fe-Zr-Zeolite was chemically dominated. Besides, Fe-Zr-Zeolite had better removal efficiency of F- under acidic conditions than that under alkaline conditions, and the competing anions, typically, Cl-, NO3- and SO42- had negligible effect on F- removal by Fe-Zr-Zeolite. The dynamic adsorption test demonstrated that in order to maintain the high removal efficiency of F-, the filling thickness of Fe-Zr-Zeolite should be at least 30 cm and the small the flow rate is, the higher the F- removal efficiency will be.

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