Fluorides removal

The fluoride removal efficiency of the control equipment at primary aluminum reduction plants is shown in Table 30-6. The removal efficiency for total fluorides is a matter of great concern. 

Fluoride Removal Efficiencies Selected Aluminum Industry Primary and Secondary Control Systems... 

Control system Total fluoride removal efficiency (%)... 

Noncorrosive medium Complete regeneration of the catalyst Fewer demands on the plant material Omission of neutralization streams Omission of fluoride removal Smaller technical safety costs Smaller apparatus costs... 

In a quite different approach, shown in Scheme 204, cycloaddition of nitrile 1232 to trimethylsilyldiazomethane provides silylated triazole 1233, isolated in 75% yield. Treatment with tetrabutylammonium fluoride removes the trimethylsilyl group and simultaneously the silyl protection of the carboxylic group to afford 4-substituted triazole derivative 1234 in 81% yield <2003PEN699>. 

Characterization and identification of fluoride removal methods for use when processing nerve agent GB. 

In addition to the preceding fluoride transport tests, laboratory-scale tests were conducted to investigate the possibility of containing or removing fluoride from the system to allow more economical materials of construction to be used in the design of the full-scale plant (AEA, 20011). A series of nine tests was to be conducted to obtain kinetic data on the use of calcium as an agent for fluoride removal from the GB simulant, fluorophosphoric acid. Data were to be obtained for the hydrolysis reaction under acidic, neutral, and alkaline conditions. 

AEA. 20011. Fluoride Removal System, Report Number 20/3034/13/009 (draft), November 14. Pittsburgh, Pa. AEA Technology Engineering Services, Inc. 

Fig. 2. Anion exchange separation of trace anions in HF following fluoride removal using ion exclusion. See text for details. Peaks 1, fluoride 2, chloride, 7.9 (Xg/1 3, carbonate 4, nitrate, 0.89 mg/1 5, unidentified 6, sulfate 10.1 mg/1 7, phosphate, 2.4 jxg/1.

The loaded reactor is heated for 24 hours, then removed from the furnace, and cooled to room temperature. The system is depressurized and the silicon tetrafluoride expelled into a hood, or bled into a water scrubber. The system is purged several times with helium and the heating procedure repeated for an additional 4 hours, after which the silicon(IV) fluoride removal procedure is repeated as well. The solid black product is niobium(IV) fluoride, 3.752 g. or 90% of theoretical yield. Anal. Calcd. for NbF4 Nb, 55.0 F, 45.0. Found Nb, 55.1 F, 44.3. 

Fluoride Removal from Water Using Adsorption Technique... 

Considering the above screening strategies as well as the summary in Table 1, it is observed that adsorption technique for fluoride removal from water is an established, low-cost, environmentally benign technique that has public acceptance. Thus, our discussion will henceforth concentrate on adsorptive removal of fluoride from drinking water. 

Table 1. Summary of fluoride removal technology screening... 

Adsorption technology is frequently used as a robust technique to remove water-soluble ions that are detrimental to human health from aqueous solutions, especially when these ions exist in low concentrations. Thus, a lot of studies have been reported in literature on the use of various adsorbents for fluoride removal from drinking water. The studies have mainly been motivated by the need to have alternative adsorbents that are low in cost, have local availability, require little processing and are superior in performance. Synthetic adsorbents have good capacities for fluoride but are always expensive, while natural materials that are available in large quantities or certain wastes from agricultural or industrial concerns may potentially be low-cost materials. An overview of some of the adsorbents that have been reported in literature over the last two decades are given below. 

The authors further explored the optimum heating temperature and found that heating the tertiary soil at 400-500°C enhanced the adsorbent s fluoride removal capacity. Moreover, a preliminary column experiment showed that 4.0 kg of 400°C heat-treated soil could treat more than 300 L of 5 mg/L fluoride feed water before the effluent fluoride concentration of 1.0 mg/L was reached. To minimize environmental impact of the used material, a cost-effective regeneration technique was devised and it involved rinsing the soil with sodium carbonate solution, followed with dilute HCI and finally twice with distilled water. 

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