Adsorption studies of fluoride by activated carbon prepared from Mucuna prurines plant

Defluoridation of drinking water by magnesium and aluminum electrocoagulation in continuous flow-rate: a response surface design

The goal of this research is to apply an electrocoagulation process in continuous flow for the defluoridation of drinking water. Two sampling sites were studied, Temascalcingo (T), Mexico state and Jerecuaro (J), Guanajuato, with fluoride (F^-) concentrations above the norms (2.3 mg L^-1 and 4.5 mg L^-1, respectively). In addition, a second Temascalcingo sample was enriched (T_E) to 9.2 mg L^-1 F^- to study the effect of the F^- concentration. A response surface design was proposed through a Box-Behnken model, and the variables studied were electrode system, flow-rate and current intensity. 51 experiments were performed with T-site to determine the best operating conditions for the system. These conditions were applied to the J-site. The experiments for T, Al/Al system achieves an F^- concentration within permissible limits (0.72 mg L^-1 F^-) at 10 min of treatment, 0.2 A (Current density j 48.78 A m^-2) and 10 mL min^-1 with a removal efficiency of 68.69%, and after 160 min, the removal increased to 99.56%. AlMg/AlMg needs 10 min to achieve a concentration of 0.75 mg L^-1 F^- at 0.2 A (j 25 A m^-2), 16 mL min^-1 with a removal efficiency of 67.39%, and after 100 min, the removal is increased to 92.17%. An important and novel advantage is the use of AlMg allows an acceptable removal of F^- (<1.5 mg L^-1) at high and low concentrations in short periods of time; this also allows save energy costs and the effluent is free of residual aluminum, avoiding side effects.

Functional activated carbon: from synthesis to groundwater fluoride removal

Developing green and functional adsorbents for the removal of inorganic pollutants from industrial wastewater is still a great challenge. Activated carbons (ACs) are promising eco-friendly materials for adsorption applications. This study reports on the preparation and functionalization of AC and its application for fluoride removal from water. Activated carbon was prepared from date stems, and the material was employed as a support for different modifications such as incorporation of Al(OH)₃, in situ dispersion of aluminum particles (Al⁰) and grafting of 3-(aminopropyl)triethoxysilane (APTES). The resulting functional adsorbents were fully characterized by Fourier transform infrared spectroscopy, scanning electronic microscopy, energy dispersive X-ray fluorescence, X-ray diffraction, differential scanning calorimetry and zeta potential analysis. The results evidenced successful surface modifications. All adsorbents had affinity for the removal of fluoride ions (F⁻). The highest F⁻ removal rate was up to 20 mg g⁻¹ for AC-Al(OH)₃. Removal of fluoride ions obeyed Langmuir isotherms and a second-order kinetic model, and reached 99% uptake. The AC-Al(OH)₃ adsorbent was successfully used to treat a groundwater solution contaminated by fluoride ions. These results open an interesting avenue for developing eco-friendly functionalized AC for adsorption applications.

Conversion and surface modification of date stems to obtain a relevant adsorbent to remove fluoride contamination.

Enhanced Adsorption Performance of Oxytetracycline by Desugared Reed Residues

The performance of oxytetracycline adsorption by untreated reed roots, stems and leaves, as well as the desugared reed roots, stems and leaves, was investigated with scanning electron microscopy, Fourier-transform infrared spectroscopy, elemental analysis and surface area analysis to understand the adsorption mechanism. The results showed that the adsorption capacities of untreated reed were 416.35 mg/kg for roots, 341.92 mg/kg for stems and 280.21 mg/kg for leaves, and can be increased significantly by a factor of 8–12 after desugarization. The pseudo-first-order kinetic model was more suitable for describing the adsorption kinetics of reed residues, and the isothermal adsorption process was fitted well by both the Langmuir and Freundlich models. The thermodynamic process suggested that the adsorption was a spontaneous endothermic reaction, and mainly physical adsorption-dominated. The desugared reed tissues had a larger surface area and smaller pore area, and the aromaticity of reed residues increased; on the other hand, the polarity and hydrophilicity decreased after desugarization, thus revealing the mechanism of enhanced OTC(oxytetracycline) adsorption by desugared reed residues. This study suggests that the reed residues contribute the complex adsorption ability for both inorganic and organic contaminates. Corruption of the reed can enhance the adsorption; thus, protecting the natural reed residue and letting it naturally corrupt, rather than artificially cleaning it up, can effectively promote the adsorption of pollutants in the environment and protect environmental and public health.