Papers by Keyword: Fluoride

Abstract: Magnetic biochar derived from various residual agricultural wastes have been widely studied due to their abundance, low cost, and minimal environmental impact. Pecan nutshell (Carya illinoinensis) residuals were incorporated with γ-Fe₂O₃, transforming them into magnetic adsorbents. The effect of particle size (granular: 0.38-0.7 mm; powder: 0.15-0.38 mm) and pyrolysis temperature (500 °C and 650 °C) were investigated for their influence on adsorption capacity of arsenic and fluoride in aqueous solutions. Our findings showed that finely powdered magnetic biochar produced at 650 °C (PMPH-650) exhibited the highest removal efficiency (99.09%) and adsorption capacity (4.925 mg/g) for arsenic compared to other materials. The arsenic adsorption isotherm followed both Langmuir and Freundlich models well. The kinetics of fluoride adsorption fit the Elovich equation, suggesting chemisorption and chemical bond formation. XRD and FTIR analyses confirmed the presence of the γ-Fe₂O₃ phase. SEM/EDX and FTIR analyses confirmed the presence of arsenic on the biochar surface after the adsorption. This research paves the way for using magnetic biochar derived from pecan nutshell as a cost-effective and eco-friendly approach for arsenic and fluoride remediation in water.

Abstract: In this study, LiTi₂(PO₄)₃ (LTP) was synthesized by the addition of lithium fluoride (LiF) of 0 %, 5 %, and 10 wt.%. A wet solid-state reaction method is applied by mixing Li₂CO₃, TiO_2, and NH₄H₂PO₄ into a ball mill, then calcined at 900^o C for 12 hr. XRD pattern of Fluoride-doped LTP is indexed and found in two phases. First is the Nasicon phase (LiTi₂(PO₄)₃) with rhombohedral structure, and second, the Olivine phase (LiTiPO5) with orthorhombic structure at the addition of 5 % and 10 wt. % of LiF. The higher LiF decreases the cell volume while the crystallite size, particle size, and material density increase. The morphology of the Fluoride-doped LTP is increasingly homogeneous and more rectangle-shape. LTP 2, adding 10 wt. % of LiF, has high ionic conductivity at 4.77 10^-4 S cm^-1 as a promising candidate material for solid-electrolyte of lithium-ion battery.

Abstract: Mesoporous boehmite (γ-AlOOH) was synthesized from naturally occurring coal-bearing kaolinite (CBK) by direct sulfuric acid leaching and hydrothermal method to explore a new possible route to the synthesis of product with high value added using the CBK. The Brunauner-Emmett-Teller (BET) surface area and the average crystallite size of the γ-AlOOH powder could be controlled in the range from 6.3 to 192.5 m² g^-1 and from 5.5 to 14.4 nm, respectively, by varying the reaction temperature and reaction time. Owing to its porous structure and high surface area, the synthesized mesoporous γ-AlOOH powder exhibited better adsorption abilities for CR and fluoride in contrast to commercial boehmite, and it only took 20 min to reach removal efficiency of 99.6% for CR and 90.5% for fluoride, when the initial concentration of CR and fluoride was 100 and 10 mg L^-1, respectively.

Abstract: In addition to conventionally casting, dental metallic framework can be manufactured using different CAD/CAM technologies (selective laser melting, milling). The milling of porous CoCr blanks followed by sintering under protective gas is a new 2012 introduced dental technology called Ceramill Sintron. For this new material so far, there exist few studies on the corrosion behavior. The aim of this study was to investigate the influence of different pH values as well as fluoride additions on the corrosion behavior of the sintered CoCr alloy compared to the cast condition by electrochemical corrosion measurements according to ISO 10271.

Abstract: This paper describes both aqueous and solvent-based formulations aimed at etching silicon oxide (SiO_x) with etching rates (E/R) of the order of 10-20 A/min with selectivity greater than 5 with respect to silicon nitride (SiN_x) . Diluted hydrofluoric acid (dHF) with very low pH was tried first but the selectivity was found to increase only with higher SiO_x E/R. Solvent-based formulations derived from previous work also behaved in a similar way, however its SiO_x E/R could be reduced by modifying the total fluoride concentration inside formulation. Finally, we found that low SiO_x E/R could also be implemented in the diluted buffer-oxide etch (BOE) solution and the selectivity could be adjusted by addition of a specific surfactant at a very low concentration level.

Abstract: The use of biohydrometallurgical processes may be restricted by microbial inhibition due to inhibiting fluoride originating from the feed material. In this work, phosphorus bioleaching experiments on fluorapatite ore were conducted in a reactor using Fe-and S-oxidizing bacteria, resulting in 56 % leaching yield for P, despite abundant (800 mg l^-1) F in the pregnant leach solution. In further F toxicity experiments it was observed that aluminum had a significant role in decreasing the inhibition caused by F, by producing stable complexes with Al. The bioleached ore contained plenty of Al, explaining why bioleaching was not strongly inhibited.

Abstract: F-doped hydroxyapatite (FHAp, Ca₁₀(PO₄)₆OH_2-xF_2x) was synthesized by two step technology – wet-chemical precipitation and pH-cycling. Obtained powders were dried and calcined for further characterization. FHAp were analyzed by Fourier transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM) and UV-VIS spectrophotometry. FT-IR analysis approved fluoride incorporation into HAp structure, confirmed by OH...F bonding at 3546 and 745 cm^-1. SEM microphotographs showed, that as-synthesized FHAp precipitates consist of needle-like crystallites. UV-VIS spectroscopy results were used for the determination of actual F^- substitution level. After evaluation of results it was concluded, that fluoride substitution level in FHAp structure reached only x≤0.6. To perform higher substitution level, the technological parameters of the process need to be optimized.

Abstract: The chemical quality of several water samples comprised groundwater from various aquifers and water dam, in Biskra area of South Algeria was investigated. Water samples were collected to monitor water chemistry of major ions and minor ions comprising inorganic pollutants such as fluoride, phosphates, nitrates and trace element as cadmium. The results showed a high salinity associated with an excessive hardness. The concentrations of many inorganic compounds are above the permissible limits for standard drinking water in almost water sources. The pollution is mainly attributed to a geological origin and an extensive use of fertilizers. Some water need adequate treatment to overcome inorganic pollution problem for drinking purpose. The adsorption of fluoride, nitrate, phosphate and cadmium ions onto Algerian bentonitic clay was studied in batch system. The results showed that sulphuric acid activated bentonite was more efficient than raw clay for fluoride, nitrate and phosphate removal. The results also revealed that cadmium adsorption was better with raw bentonite. The equilibrium data were confirmed using Langmuir isotherm model.

Abstract: Monazite is a light rare earth phosphate which is difficult to process when using conventional chemical processes. It is considered to be one of the most important commercial sources of thorium and lanthanides. Using conventional chemicals to process monazite have caused severe environmental damage as has been demonstrated in the Baotou region, China. Monazite is found in combination with other minerals in nature such as bastnaesite and xenotime. The conventional techniques and chemicals used for the processing of monazite are expensive. In order to address this issue, South Africa would like to beneficiate monazite as part of its mineral beneficiation strategy. Doing so competitively would require a new cheaper and more environmentally friendlier process. A new method for the processing of monazite is currently being investigated. It is proposed to feed the monazite is fed into a plasma reactor to crack it. Potentially the cracking will allow the monazite to be more reactive and susceptible to react with less harsh chemicals. The plasma treated monazite is reacted with a fluorinating compound such as ammonium bifluoride. Ammonium bifluoride is used rather than fluorine or hydrogen fluoride as it is less dangerous to handle. The fluorinated rare earth mixture can now be separated using various methods.

Abstract: There are many people who are dental decay in He-Jia-Ping, Chang Yang, HuBei Province, China. The fluoride content of water samples was measured by fluoride ion-selective electrode method. The main drinking water source for these villages, ranged from 0.11 to 0.21 mg/L, with the average of 0.16 mg/L, was much lower than the appropriate content. People should drink tea to replenish the supply of fluoride.