Alumina Fluoride

Aluminum fluoride is a white, crystalline substance soluble in water that may cause eye, nose, throat and lung irritation in those exposed to it. Long term exposure may aggravate asthma symptoms.

Activated alumina is an effective defluoridation agent. It should be combined with other treatment techniques and maintained between pH range 5.5-6.5 to maximize fluoride adsorption onto its surface.

Chemical Structure

Aluminum Fluoride (AlF3) is an inorganic compound composed of one aluminum atom and three fluorine atoms. It’s white in color, denser than water, odorless, soluble in both alkalis and acids and resistant to oxidation; its molecular symmetry has D3h symmetry with 163 pm bond length between Al-F bonds; upon evaporation it forms molecular dimers which eventually evaporate away completely.

Aluminium fluoride has an ionic structure due to the donation of three of aluminium’s valence electrons to fluoride atoms by means of aluminium donating its three valence electrons; as a result, positively charged aluminum ions and negatively charged fluoride ions form, respectively. Furthermore, its highest-occupied molecular orbital is called the p orbital which requires eight electrons fill it and therefore forms covalent bonds between aluminium and fluoride atoms.

As soon as water enters alumina fluoride is exposed to it, a hydrate with the formula Al(F2)3 forms, possessing a tetragonal crystal structure. This form serves as an important source of alumina used in metal aluminum production as a raw material; additionally it is widely utilized as a sputtering target to prepare low index films and as an inhibitor against fermentation and catalyst for organic reactions in ceramic and glass production as well.

Activated alumina can be used to remove excess fluoride from drinking water. For optimal performance, the treatment system must operate between the pH levels 5.5 and 6.5; otherwise it could leach out impurities exceeding those set forth by Commission Directive 2003/40/EEC or national applicable regulations.

Aluminum fluoride has been observed to interact with numerous proteins. It can effectively inhibit the activity of PLD, an enzyme involved in Golgi vesicle transport that also plays an integral role in metabolism, cell growth and differentiation as it transfers phosphate via GTP/ATP exchange reactions mediated by these energy sources for biochemical reactions.


AlF3 (aluminum fluoride) is produced when aluminium hydroxide reacts with fluorine in water, yielding a colorless solid with a melting point of 900 degC and molecular structure consisting of three fluorine atoms bonded to two aluminum atoms forming a tetrahedron shaped structure. AlF3 can be found naturally as the rare mineral rosenbergite.

Alumina fluoride is highly soluble in acidic pH waters; however, its effect is undetectable in hard water with pH 7; while highly soluble in alkaline solutions. At high concentrations it inhibits protein synthesis as well as interfering with energy metabolism in cells and inducing apoptosis in them; additionally it can irritate and poisonous when inhaled; it has also been known to cause stomach upset as well as aggravating respiratory ailments like asthma and chronic bronchitis.

Alumina fluoride also inhibits phospholipase D, an enzyme involved in cell signaling processes and cell communication pathways. Phospholipase D serves as a crucial regulator of multiple important biological reactions involved with growth and differentiation processes, acting as a competitive inhibitor of phosphoryl transfer reactions as well as possessing allosteric properties; its inhibition by alumina fluoride results in its Hill-type kinetics that characterize allosteric proteins.

Activated alumina is an efficient sorbent for defluoridating drinking water, capable of removing up to 76% of fluoride when saturated with moisture. European standards regulate its usage and mandate that its quality meet these requirements in order to ensure safe consumption. Alumina must be replaced periodically depending on both volume treated and initial fluoride concentration levels; replacement intervals vary according to these factors.

Silica may be used in place of alumina as an inert sorbent, though its fluoride removal capacity is much lower and its pore size distribution less uniform; similarly, it does not reversible. Alum has higher fluoride-removal capabilities but forms unstable complexes with other ions in solution and therefore lacks stability; in addition it has low solubility in water which increases corrosion risk in aquatic systems.


Adsorption of fluoride by alumina is one of the most widely-used treatments for water with high concentrations of the ion, often used by municipalities to remove excessive fluoride that could potentially be toxic if consumed at high levels, but home users also utilize this method. Adsorption occurs due to chemical affinity between fluoride ions and the surface alumina particles; strong covalent bonds bind them tightly together making fluoride more easily adsorbable than sulfate, chloride and bromide adsorption methods.

Alumina fluoride is highly soluble in aqueous solutions, making it an ideal candidate for purifying drinking water. Due to its strong adsorption capacity and use in large quantities for fluoride reduction in drinking water, Alumina fluoride’s use may be limited only by your initial fluoride concentration, pH level, adsorbent dose and contact time – it’s therefore crucial to optimize this process for maximum efficiency at minimal costs.

This study’s primary aim is to investigate the effect of natural organic matters (NOMs) and pH on fluoride adsorption by an alumina impregnated with alum impregnation, specifically its fluoride adsorption properties. Physical-chemical properties were determined through scanning electron microscopy, Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy, Fourier transform infrared spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Simulation was achieved by modelling with PHREEQC geochemical modelling software using input scripts taken from various sources found online and from multiple sources published within literature.

Results indicated that fluoride adsorption onto an alumina surface was heavily influenced by NOMs and pH values, with fluoride being rapidly taken up at higher pH values due to replacement of surface OH- with fluoride ions. Adsorption also depended on crystal phase with th-Al2O3(010) being particularly reactive due to high unsaturation level Al atoms present within its crystal lattice structure.

Excess Fluoride

Fluoride is an essential element in human diets, particularly at levels between 1-1.5 mg*L-1 as it strengthens teeth and promotes bone formation. However, higher concentrations can cause demineralization of bones and teeth which leads to dental and skeletal fluorosis1.

Fluoride needs to be carefully controlled in drinking water supplies around the world to remain below its maximum permitted level of 1.5 parts per million (ppm). In many countries it has already been added as part of public water systems so as to comply with applicable standards and laws regarding its presence.

Still, due to their geographical source, certain natural mineral waters contain high levels of fluoride. Furthermore, some ground and surface water sources also have elevated concentrations of fluoride.

Adsorption is one of the most efficient and economical technologies for reducing fluoride concentration in drinking water, featuring an extremely large surface area-to-weight ratio and high capacity for adsorption. Activated alumina (AA) is used as the medium due to its microporous structure which enables regeneration following use in dilute caustic solutions.

Alumina was initially utilized for defluoridating drinking water, however over the years numerous materials have been tested and proven effective, including low-cost materials like calcite, clay charcoal, saw dust, rice husk and groundnut husk as well as rare earth oxides such as thallium(VI) and ytterbium(VI). Unfortunately all these can only reduce fluoride at very high pH values which is why alumina remains the media of choice.

Aluminum fluoride is an irritant chemical which, if inhaled, may cause respiratory irritation, nose irritation and bleeding. Furthermore, this substance has also been recognized by the US Department of Transportation’s Hazardous Chemical Data Base as toxic and listed as poison for potential liver and kidney damage. For more information on ALUMINUM FLUORIDE visit the CAMEO Chemicals record page dedicated to this substance.

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